MEMOIRES DU MUSEUM NATIONAL D'HISTOIRE NATURELLE

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3 3001 00099870 7

Source ; MNHN, Paris

Cover photograph / Photographic de couverture :

Aggradational internal platform beds (marls and limestones, mudstone and floatstone) in the Bathonian infilling of the Atlas Trough (Tana

Plateau. Central High Atlas. Morocco) photograph Ch. DURLET.

Agradation des depots de plate-forme interne (/names el calcaires, mudstone a floatstone) dans le remplissage hathonien du Si/Ion Atlasique

(Plateau de Tana. Haul Atlas Central. Maroc) cliche Ch. DURLET.

The Peri-Tethys Program, sponsored by international industries (AGIP. ARCO, BRGM. CHEVRON. CONOCO.

EAP(ELF). EXXON, SHELL, SONATRACH. TOTAL), research centres (CNRS. IFP). and a university (UPMC), stoned

in 1993. It examines the influence of Tethyan evolution on the bordering cratons since its birth (through the break-up of

Pangea), its life (by the extension and formation of oceanic seaways) and finally its death (by collision between the main

bordering plates which led to inversion within the epicratonic basins).

Volumes deja parus I Previously published volumes :

Peri-Tethys Memoir 1 (1994): Peri-Tethyan platforms. Proceedings of the IFP/Peri-Tethys Research Conference. Technip,

Paris: 1-275. ISBN: 2-7108-0679-7.

Peri-Tethys Memoir 2 (1996): Structure and Prospects of Alpine Basins and Forelands. Mem. Mas. natn. Hist, not ., 170:

1-550 (+ Atlas). ISBN: 2-85653-507-0.

Peri-Tethys Memoir 3 (1998): Stratigraphy and Evolution of Peri-Tethyan Platforms. Mem. Mas. natn. Hist, nat ., 177:

1-262. ISBN: 2-85653-512-7.

Peri-Tethys Memoir 4 (1998): Epicratonic Basins of Peri-Tethyan Platforms. Mem. Mas. natn. Hist. nat.. 179: 1-294.

ISBN: 2-85653-518-4.

Peri-Tethys Memoir 5 (2000): New Data on Peri-Tethyan Sedimentary Basins. M4m. Mus. natn. Hist. nat.. 182: 1-266.

ISBN: 2-85653-524-0.

Aussi /Also:

Peri-Tethys: stratigraphic correlations 1 (1997). 330 pp. Geodiversitas , 19 (2): 169-499. ISSN

Peri-Tethys: stratigraphic correlations 2 (1998). 224 pp. Geodiversitas. 20 (4): 515-738. ISSN

Peri-Tethys: stratigraphic correlations 3 (1999). 211 pp. Geodiversitas , 21 (3): 285-496. ISSN

1280-9659.

Source: MNHN, Paris

Peri-Tethys Memoir 5

New Data on Peri-Tethyan

Sedimentary Basins

BIBL. DU

.MUSfUMi

\ PARIS/

ISBN : 2-85653-524-0

ISSN : 1243-4442

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MEMOIRES DU MUSEUM NATIONAL D HISTOIRE NATURELLE

TOME 182

GEOLOG IE

Peri-Tethys Memoir 5

New Data on Peri-Tethyan

Sedimentary Basins

edited by

Sylvie Crasquin-Solf.au'" & Eric Barrier 12 ’

i,! Universite Pierre et Marie Curie / CNRS

Departement de Geologie Sedimentaire

T15-25, E.4. case 104

4, Place Jussieu

F-75252 Paris Cedex 05

121 Universite Pierre el Marie Curie / CNRS

Departement dc Geotectonique

T25-26, E. 1, case 129

4. Place Jussieu

F-75252 Paris Cedex 05

PUBLICATIONS SCIENTIFIQUES

DU MUSEUM

PARIS

2000

Source: MNHN, Paris

Nous dedions ce volume a la memoire de A. Boudjema (Sonatrac)

assassine a Alger en 1994 et du Professeur P. Hancock (Bristol

University) decede en 1998.

This volume is dedicated in the memory of A. Boudjema (Sonatrac)

murdered in Alger in 1994 and Professor P. Hancock (Bristol

University) died in 1998.

CONTENTS

SOMMAIRE

Pages

1. The Westphalian Basin of Sidi-Kassem (Central Massif, Morocco).

Continental sedimentation and Late Variscian deformations. 11

Christian Hoepffner. Mohamed EL Wartiti, Abdesslam BENSAHAL

& Karima GHAZALI

2. Triassic series of Morocco: stratigraphy, palaeogeography and structuring

of the Southwestern Peri-Tethyan Platform. An overview. 23

Mostafa OUJ1DI, Louis COUREL, Nai'ma BF.NAOUISS, Mohamed EL MOSTAINE,

Mohamed El YOUSSI. Mohamed EtTOUHAMI, Driss OUARHACHE, Abdellah SABAOUl

& Abdel-Illah Tourani

3. The Liassic carbonate platform on the western part of the Central

High Atlas (Morocco): stratigraphic and palaeogeographic patterns. 39

Abdellatif Souhel, Joseph Canerot, Fatma El BCHARI. Driss Chafiki,

Abdelhak Gharib, Khadija El Hariri & Aziz Bouchouata

4. The Jurassic events and their sedimentary and stratigraphic records

on the Southern Tethyan margin in Central Tunisia. 57

Mohamed SOUSSI. Raymond ENAY. Charles MANGOLD & Moncef TURKI

5. The Tethys southern margin in Morocco; Mesozoic and Cainozoic

evolution of the Atlas domain. 93

Alain PIQUE, Mohamed CHARROUD, Edgard LAVILLE, Lahcen A IT BRAHIM

& Mustafa AMRHAR

6. The Southern Tethyan margin in Northeastern Morocco; sedimentary

characteristics and tectonic control. 107

Pierre CHOTIN, Lahcen A IT BRAHIM & Hassan TABYAOUl

7. Subsidence history of the Essaouira Basin (Morocco). 129

Kamal Labbassi, Fida Medina. Abdelkrim Rimi. Hosna Mustaphi

& Rkia BOUATMANI

Source: MNHN, Paris

8 .

10 .

11.

12 .

Index

PERI-TETHYS 5: NEW DATA ON PER1-TETHYAN SEDIMENTARY BASINS

Hydrocarbon systems of Morocco.

Haddou JABOUR, A1 Moundir Morabet & Rabah BOUCHTA

fhc Jurassic in Syria: an overview. Lithostratigraphic and

biostratigraphic correlations with adjacent areas.

Mikhail MOUTY

Basin development and tectonic history of the Euphrates graben

(Eastern Syria): a stratigraphic and seismic approach.

Cecile Caron. Maher Jamal. Hassan Zeinab & Francis Cerda.

Palaeogeography and palaeotectonic of the jointing area between

the Eastern European Basin and the Tethys Basin during Late

Carboniferous (Moscovian) and Early Permian (Asselian and Artinskian)

Boris I. Chuvashov & Sylvie CRASQUIN-SOLEAU

Palaeotectonic conditions of Cretaceous basin development

m the southeastern segment of the Mid-Polish Trough.

Jolania Swidrowska & Maciej Hakenberg

159

169

203

239

257

Source: MNHN, Paris

The Westphalian Basin of Sidi-Kassem (Central

Massif, Morocco). Continental sedimentation

and Late Variscan deformations

Christian HOEPFFNER, Mohamed El WARTITI,

Ahdesslam BENSAHAL & Karima Ghazali

Departement des Sciences de la Terre. Faculte des Sciences, Avenue I bn Batouia. Rabat. Maroc

ABSTRACT

The Sidi-Kassem Carboniferous basin is located in the northwestern Meseta. It unconformably overlies a basement of

Ordovician to Devonian age. strongly deformed by the major Variscan phase. The basin is filled by continental red rocks. flora

indicates a late Westphalian age. The sedimentological study shows that the basin is of intramontane type, feeded by braided

fluvial networks. Lacustrine and Hood plain deposits are periodically interrupted by high energy currents related to floods and

tectonic activity of the basin margins. Cartography and structural analysis show that deformations are represented by open

kilometric NE-SW trending folds. A rough cleavage appears occasionally. The main structures are NE-SW striking reverse or

thrust faults verging to the NW or to the SE. The kinematic analysis of microfaults systems indicates a compressionnal phase

with a N-S to NNW-SSE shortening. All these Late Variscan events are not precisely dated, but a Latest Permian to Earliest

Triassic age is probable.

RESUME

Le bassin westphalien de Sidi-Kassem (Massif Central, Maroc). Sedimentation continentale et deformation tardi-

va risque.

Le bassin carbonifere de Sidi-Kassem est situe dans la Meseta marocaine nord-occidentale. II est discordant sur un socle

d'age ordovicien ii devonien, fortement deforme par la phase majeure varisque. Le bassin est rempli de couches rouges

continentales, des flores indiquent un age westphalien terminal. L'etude sedimentologique montre que bassin est de type

intramontagneux, parcouru par un reseau fluviatile en tresses. Des depots lacustres et de plaine d'inondation sont

periodiquement interrompus par des courants de haute energie en relation avec des evenements pluviaux et une activitc

tectonique des marges du bassin. La cartographic et V analyse structural montrent que les deformations sont representees par

des plis kilometriques ouverts, orientes NE-SW. Une schistosite grossiere se devcloppc localement. Les principals structures

sont des failles inverses NE-SW et des chevauvements a vergence NW ou SE. L'etudc microtectonique de la fracturation

Hoepffner. C., El Wartiti, M.. Bensahal, A. & Ghazall K.. 2000.— The Westphalian Basin of Sidi-Kassem (Central

Massif. Morocco). Continental sedimentation and Late Variscan deformations. In : S. Crasquin-Soleau & E. Barrier (eds).

Peri-Tcthys Memoir 5: new data on Peri-Tcthyan sedimentary basins, Mem. Mus. natn. Hist, nat .. 182 : 11-22 Paris ISBN :

2-85653-524-0.

Source: MNHN, Paris

CHRISTIAN HOEPFFNER ETAL.

indique une phase compressive avec une direction de raccourcissement N-S a NNW-SSE. Tous ces evenements tardi-varisques

nc sont pas dates avec precision, mais un age Permien terminal-Trias basal est probable.

INTRODUCTION

The Late Carboniferous of Northern Africa was represented, during Westphalian time, by detritic

deposits which are interpreted as the erosional products of the Variscan belt. These deposits, exclusively

continental, indicate the eastward regression of the Palaeo-Tethys sea. We can distinguish: on one hand,

in the northern margin of the African shield, the weakly deformed deposits of the Tindouf and Bechar

basins; on the other hand, small basins included in the Hercynian chain, especially in Morocco. Here,

the Westphalian is represented in two areas: the paralic basin of Jerada to the east and the limnic basin

ol Sidi-Kassem to the west (Fig. I).

r |G . I.— Palaeozoic outcrops in North Africa. I: Variscan allochtonous terranes included in the rifo-tellian Alpine nappes; 2:

Variscan belt ol Northern Africa. Palaeozoic terranes strongly deformed; 3: West African craton margin. Palaeozoic

terranes weakly deformed; 4: Undeformed Palaeozoic terranes; 5: Panafrican belt (Hoggar); 6: Lower Proterozoic and

Archeozoic (Reguibat shield). S.K.: Sidi-Kassem: Je: Jerada.

F,a L ~ Affleurements paleozoiques en Afrique du Nord. 1: terrains varisques allochtones inclus dans les nappes alpines rifo-

telltennes ; 2 : chaine varisqne d'Afrique du Nord, terrains paleozoiques fortement deformes ; 3 : marge du craton

Uuest-Africain, terrains paleozoiques pen deformes ; 4 terrains paleozoiques non deformes ; 5 : chaine panafricaine

(Hoggar); ( : Proterozoique inferieur et Archeen (bouclier Reguibat). S.K. : Sidi-Kassem, Je : Jerada

The Sidi-Kassem basin, subject of this paper, is located in the northwestern Moroccan Meseta, in the

xirew ?! th fn^ ll 0 v Urib8a " 0ulmes anlicline < Fi g- 2 >- II is an elongated, rectangular basin trending ENE-

WSW (6 x 30 km).

The Sidi-Kassem basin has been discovered by TERMIER (1936) and described as limnic basin tvpe.

Piedmont plain and fluvio-lacusfrine basin continental deposits unconformably overlie a strongly

deformed basement ol Ordovician to Devonian age. They are conglomerates, red sandstones, shales with

thin coa levels and lacustrine limestones. Flora found in pelitic beds indicate a late Westphalian age for

the whole of the formation (Pruvost & TERMIER, 1949). Lithostratigraphic descriptions are old (Roch,

1950) or very localised (El WARTITI, 1990; CHAKIRI, 1991).

Informations about the structure are very scarce: the geological map of TERMIER (1936), and the

unpublished data which have been used to draw the geological maps of Morocco at 1/500 000

Source: MNHN . Paris

THE WESTPHALIAN BASIN OF SIDI-KASSEM (CENTRAL MASSIF, MOROCCO)

TE00ERS\

==^L° o o'*

-yfP o °

J°,o Voo

izohiiigay'

Khofouat

S8 Sokhrof es SDaa

A Akakou

KD Koudiot bou OoDlig

JK Jebel Krone:

imolo

KG Koudiot el Grome

SO Sokhror ed Drei'to

JT Jebel Tirmah

J0 Jebel Bedou:

JA Jebel el Afchone

JB Jebel Berkane

°“o“o

o o

|o> u> yi I

D | (J) (J> 01 '

9 p

- - -1 3

0 -0_0

Fig. 2.— Geological map of the Moroccan Central Hercynian Massif, area ot the NE-SW trending Khouribga-Oulmes anticline

(from the geological map of Morocco, 1/500 000). I: Ordovician; 2: Silurian; 3: Lower Devonian; 4: Lower and Middle

Devonian; 5: Lower Carboniferous; 6: Westphalian; 7: Permian and Triassic; 8: Cretaceous; 9: Miocene; 10: Recent

lavas; 11: Hercynian granites.

FiG. 2.— Cane geologique du Massif Hercynien central marocain, secteur de /’anticlinal cle Khouribga-Oulmes oriente NE-SW

(d'apres la cane geologique du Maroc a 1/500 000). I : Ordovicien : 2 : Silurien ; 3 : Devonien inferieur : 4 :

Devonien inferieur et nwyen ; 5 : Carbonifere inferieur ; 6 : Westp/ialien ; 7 : Permien et Trias ; 8 : Cretace ; 9 :

Miocene ; 10 : Laves recentes ; II : Granites hercyniens.

(Choubert, 1956) and 1/1 000 000 (HOLLARD, 1985). Main structures are open or tight folds and fault

systems trending NE-SW and NW-SE. An overthrust involving the Westphalian beds was mentioned in

a borehole by TERMIER & TERMIER (1951); at last, CHAK1RI (1991) and GHAZALI (1995) described a

spaced cleavage in conglomerates of the northern part of the basin.

This review demonstrates the lack of modern and detailed studies in the basin, although it is always

described as a very important reference for dating the major Hercynian phase in the western Moroccan

Meseta (Pique & Michard, 1989).

Source:

CHRISTIAN HOEPFFNER ETAL.

SEDIMENTOLOGY

Following TF.RMIER (1936), PRUVOST in ROCH (1950) and CHOUBERT (1951), the Sidi-Kassem

formation could be divided into two members:

— the lower member is constituted by conglomerates in die NW area (600 m) grading into shales

and sandstones with intercalations of coal veins and lacustrine limestones toward the SE (1200 m).

— the upper member is formed by shales, red sandstones and the “Sidi-Kassem conglomerate" (300-

400 m).

Flora indicates a Westphalian C (and D?) age for the formation (Cordaites, Cardioearpus,

Catamites, Odontoperis and Mixoneura, after ROCH, 1950).

With the aim at doing a sedimentological study of the basin, several sections have been made in the

lower member. Two sections are described here: the first is situated in the northern part, between the

Grou and Bou-Regreg rivers, the second, in the SW part is located near Sidi Mohammed ben Hammou

(Fig. 3).

FlG ' 3 ' ha ^ P '' fi , ed geol °8 ical map of the Sidi-Kassem basin. 1: late Westphalian red-beds; 2: Ordovician to Devonian

sancn,alre de S'di-Kassem ; KL : cWne de Ktab Lahmar. a. b : sin,a,ion des coupes siLeZlogiques. ' C '

Source: MNHN , Paris

THE WESTPHALIAN BASIN OF SIDI-KASSEM (CENTRAL MASSIF, MOROCCO)

Our sedimentological study involves determination and classification of the facies, according to

MlALL (1978), sequential analysis, and determination of the depositional environment.

Main facies of the Westphalian deposits

According to the MlALL's classification (1978), five facies can be distinguished in the lower member

of the Sidi-Kassem formation.

K1: this facies is characterised by lenticular beds of immature conglomerates. The pebbles,

sometimes imbricated, are principally sandstones and quartzites.

KM: this facies is organised in conglomeratic lenses poorly stratified, with erosional base level and

slumpings. Pebbles are small.

These facies are similar to the Gm facies of MlALL (1978) and they characterise a proximal deposit

in a braided fluviatile network or more accurately a deposit in a longitudinal bar.

K2: this facies is characterised by continous beds of thin to medium tickness (10-15 cm). They show

massive structures or horizontal laminations. It is analogous to the Sh facies of MlALL (1978) and

indicates sheet Hood distal deposits.

K3: red mudstones are organised in metric beds with horizontal bedding. This facies alternates with

sandstones or overlies the conglomerates. It is similar to the FI facies of MlALL (1978) and is related to

decreasing energy of the current transport.

K'3: green mudstones with horizontal bedding and vegetal remains. Very thin coal levels appear near

the bottom of the beds. Spore and pollen have been recently discovered in these coal levels (El Wartiti

et al ., in progress). This facies is similar to the Fh facies of MlALL (1978) and characterises a lacustrine

or a palustrine environment in a flood plain.

K4: this facies corresponds to thin (50 cm), lenticular, massive limestones interstratified in the green

mudstones. Identical with the P facies of MlALL (1978), they are palustrine or lacustrine deposits in a

quiet and shallow environment.

Examples of sections and sequential analysis

Section a (Fig. 4)

This section is located on the left side of the Bou-Regreg river (x= 143; y=321; Sidi Matla ech

Chems map at 1/50 000) near the Feddane Lebtam hills. This section shows four parts, two

megasequences can be distinguished.

MEGASEQUENCE I.— The bottom is formed by an alternation of the K1 and K3 facies. The

sequences characterise braided fluvial network, in proximal position.

The lower part is essentially formed by mudstones or siltstones with intercalations of conglomerates

and sandstones (K* 1). The main sequence indicates quiet environment like a sheet Hood plain.

This megasequence shows a upward fining grain size evolution. The very coarse early deposits

indicate a strong erosion of high reliefs, and a transport by fluvial currents in a proximal position. Later,

near the top of the megasequence, finer deposits indicate a sheet-flood environment in distal position

with temporary irruption of fluviatile high-energy currents.

Megasequence 2.— The medium part of the section is a conglomerate stacking with intercalations

of thin and lenticular pelitic beds. The sequences are formed by associations of the K* 1 and K3 facies,

which characterise a braided fluviatile network in proximal position.

The upper part is formed by repetitions of rythmic sequences with upward fining grain size. Each

sequence, from 4 m up to 6 m thick, contains alternations of sandstones, mudstones and centimetric beds

of conglomerates. The predominance of thin deposits indicates a fluviatile braided network in distal

position, probably located in the downstream part of an alluvial fan.

CHRISTIAN HOEPFFNER ETAL.

Fig. 4.— Lithostratigraphical column

and sequential analysis of the

section A. 1: massive conglome¬

rates; 2: conglomerates weakly

stratified; 3: sandstones; 4: peli-

tes; 5: pelites and sandstones;

6: limestone lenses.

Fig. 4 .— Colonne lithostratigra-

phique et analyse sequentielle de

la coupe A. I : conglomerals

massifs ; 2 : conglomerals mal

si ratifies : 3 : gres ; 4 : pelites ;

5 : pelites et gres : 6: [entitles de

calcaires.

Section A lithostrafigraphlc Log

In this megasequence, the conglomerates are well organised as in the first one. Their occurrence

probably indicates a new tectonic activity with rejuvenation of the marginal reliefs, followed by their

aplanation, as indicated by decreasing grain size in the upper part of the megasequence.

Section B (Fig. 5).

This section is located in the SW part of the basin near Sidi Mohammed Ben Hammou (x=398.7;

y=304.8; Sidi Matla ech Chems map, 1/50 000). The sedimentation is chiefly pelitic, with rare

occurrences of limestones.

Sequential analysis shows only one megasequence where four facies can be distinguished. Red

siltstones and mudstones with rare lenticular beds of conglomerates (K3), lenticular conglomerates with

Source: MNHN. Paris

THE WESTPHALIAN BASIN OF SIDI-KASSEM (CENTRAL MASSIF, MOROCCO)

Fig. 5.— Lithostratigraphical column of the section B (legend: see Fig. 4).

Fig. 5 .— Colonne lithostratigraphique de la coupe B (legende : voir Fig. 4).

Section B

siltstones and mudstones with rare lenticular beds of conglomerates (K3). lenticular conglomerates with

small pebbles (K' 1), green mudstones with plant debris and coal levels (K 3), massive and discommons

limestones (K4).

All these facies are organised in small sequences that indicate a quiet environment, a weakly dipping

hydrographic network and low energy currents. Limestones and plants indicate palustrine or lacustnne

environments temporarily invaded by high energy currents.

Therefore these observations concern only the lower member of the Sidi-Kassem formation, they

allow us to display the main characteristics of the sedimentary palaeoenvironment during part of the late

Westphalian in the western Moroccan Meseta. The Sidi-Kassem basin is an mtramountain type, it is

feeded by braided hydrographic networks whose direction of transport and current energy aie very

variable.

Erosional periods are probably related with raining seasons under warm and wet climate. Sediments

become finer toward the top of the formation, in relation with the peneplanation of the reliefs. 1 he

tectonic control of the sedimentation is certainly important, but the synsedimentary displacements along

the main faults in the basin are not yet well known.

CHRISTIAN HOEPFFNER ETAL.

TECTONIC SETTING

Southwestern part of the basin

The structural analysis is based on the mapping of the whole basin and some detailed studies, which

are carried out in the southwestern part. Map (Fig. 6) and cross-sections (Fig. 7) clearly show the major

unconformity of the Westphalian beds upon the Silurian-Devonian which is represented by shales,

sandstones and limestones.

Fig. 6.— Geological map of the southwestern part of the Sidi-Kassem basin. 1: Ordovician slates; 2: Ordovician quartzites

(Ashgillian); 3: Silurian-Devonian mudstones and sandstones; 4: Devonian limestones and greywackes (Ktab Lahmar

hill); 5: Westphalian conglomerates.

llG. 6. Cane geologique de la panic SW du bassin deSidi-Kassem. 1 : schistes ordoviciens ; 2 : quartzites ordoviciens

(Ashgill); 3 : pelites et gres du Siliiro-Devonien ; 4 : calcaires et grauwackes du Devonien (colline de Ktab Lahmar);

5 : conglomerats westphaliens.

The whole structure results from Late Variscan tectonic events. Westphalian beds are organised in

NE-SW trending belts. Thus, the limits between the Late Carboniferous and the basement appear as

reverse faults verging to the NW or to the SE, or sometimes, as normal faults.

Regional structures of Late Variscan age are kilometric, open folds like the Sidi-Kassem syncline

(Fig. 7a). Dips of bedding planes are moderate except near the faulted zones where they reach 50-60°.

Flexural folding is accomodated by layer-parallel-slip.

Source: MNHN, Paris

THE WESTPHALIAN BASIN OF SIDI-KASSEM (CENTRAL MASSIF, MOROCCO)

Fig. 7.— Cross-sections in the Sidi-Kassem basin. 7a.— Cross-section in the southwestern part of the Sidi-Kassem basin

showing the Klab Lahmar tectonic klippe. 1: Silurian-Devonian basement; 2: Westphalian conglomerates; 3:

Westphalian mudstones and sandstones (for location see Fig. 3). 7b. — Cross-section in the northern part ol the basin. 1:

basement (Ordovician to Devonian); 2: late Westphalian sandstones and conglomerates (for location, see Fig. 3).

Fig. 7.— Coupes dans le bassin de Sidi-Kassem. 7a.— Coupe dans la partie SVV du bassin de Sidi-Kassem montrant la klippe

tectonique de Ktab Lahmar. 1 : socle siluro-devonien ; 2 : conglomerais westphaliens ; 3 : gres et pelites du

Westphalien (situation, voir Fig. 3). 7b.— Coupe dans la partie nord du bassin. 1: socle (Ordovicien a Devonien) ; 2 :

gres et conglomerats du Westphalien superieur (situation, voir Fig. 3).

In the southwestern part of the basin, a major thrust fault outcrops from Ez-Zehiliga up to the Ktab

Lahmar hill, with an average dip of 50° SE. The displacement toward the NW along this fault is locally

important, as clearly illustrated by the Devonian tectonic klippe of Ktab Lahmar.

The Ktab Lahmar hill is very interesting. Devonian limestones and sandstones constitute a crest NE-

SW trending (spots height 767m and 732m) which rises above the Westphalian red beds. Since

TERMlER’s thesis (1936), this area was interpreted as a Devonian horst or an extrusive anticline.

However, recent detailed mapping and structural analysis show that the Ktab Lahmar hill is a tectonic

klippe overthrusting the Carboniferous (Figs 6 and 7):

— the abnormal contact which encompasses the hill is clearly a subhorizontal surface;

— Westphalian deposits are very coarse red conglomerates, where there is no Devonian pebble.

Bedding planes seem subhorizontal;

— structures in the Devonian are metric upright or overturned folds, EW trending.

Following these data it is not possible to root the Devonian basement below the conglomerates. The

only geometrical solution is a tectonic klippe.

South of the Ktab Lahmar hill, along the Ez-Zehiliga track, the Devonian outcrops in a ENE trending

belt. Its northern limit is the major SE dipping thrust-fault, many microfault zones show quartzose

slickensides where striae have a strong pitch (70-80°). Its southern limit is not clear on the field, but it

can be interpreted as the unconformity of the Westphalian on the Devonian.

CHRISTIAN HOEPFFNER ETAL.

Southwards, the deformations of the Westphalian conglomerates outcropping between Ktab Lahmar

and the Sidi-Kassem sanctuary correspond to layer parallel slip with striated slickensides, small metric

box-folds with a forelimb truncated by shear planes.

An important microfracturation characterises the internal deformation of the Westphalian. A fault-

slip data analysis has been made on several sites in the SW part of the basin (Fig. 8).

The "diedres droits" method has been used to determine the palaeostress field (ANGELIER &

MECHLER, 1977). The results indicate two phases. 1) A compressional phase with strike-slip and reverse

microfaults and a N-S to NNW-SSE trending shortening axis. It is compatible with the motion along the

major reverse faults. 2) An extensional phase with normal microfaults and a NE-SW trending elongation

axis.

Fig. 8.— Simplified representation of the deformation fields according to the fault-slip data analysis (“diedres droits’* method.

ANGELIER & Mechler, 1977). I to 5. see Fig. 6: 6: shortening direction; 7: stretching direction; 8: vertical extension; 9:

vertical shortening.

Fig. 8.- Representation simplifiee des champs de deformation obtenus par Fanalyse microtectonique de la fracturation

<methode des diedres droits, Angeuer & Mechler, 1977). I a 5. voir Fig. 6:6: direction de raccourcissement ; 7 :

direction d 'allongement; 8 : extension verticale : 9 : raccourcissement vertical.

Northern part of the basin

This area extends between the Grou and Bou Regreg rivers. Our observations are not as detailed as in

the southwestern zone. Cross-section (Fig. 7b) shows, like elsewhere, that the Westphalian overlies

uncontormably the Silurian-Devonian basement. The detrital red beds are deformed by larse open folds

NE-SW trending. J 5 P

Source: MNHN, Paris

THE WESTPHALIAN BASIN OF SIDI-KASSEM (CENTRAL MASSIF, MOROCCO)

In addition to folding and fracturing, the Late Hercynian deformation is characterised in this area and

especially near the northwestern border of the basin (Feddane Lebtam, northern flank of the Jebel

Hadid) by the development of a subvertical cleavage. NE-SW trending. Closely spaced in the red

sandstones and mudstones, the cleavage also cuts the conglomerates where it appears irregular and

spaced. Following microscopical observations, the flattening is accomodated by both mechanical

rotation and pressure-solution.

CONCLUSIONS

The main deformation of the late Westphalian Sidi-Kassem formation was controlled by motion

along NE-SW trending reverse faults. Displacements can be locally important, especially toward the

NW. with thrusting of the Devonian upon the Westphalian. The whole structure could be interpreted like

flat-ramp systems with the decollement level localised in the Silurian-Devonian mudstones.

Physical conditions have permitted the development of a spaced cleavage on the northern basin

border. But on the whole, the internal deformation corresponds to a pervasive microfracturation

indicating a N-S to NNW-SSE directed compressional phase.

The deformation age is not accurately determined. Indeed the Sidi-Kassem formation is the only late

Westphalian deposit in western Morocco, where erosional products of the Variscan belt are principally

represented by the Stephanian (western High Atlas: KONING, 1957; SABER. 1994) and the Early

Permian (Moroccan Meseta: ELWART1TI, 1990; El WARTITI £>/ at., 1990). Structural relationships

(conformity or unconformity) between Westphalian and Stephanian-Permian are not known. However,

the post-Permian/pre-Triassic tectonic events are well documented in the Meseta and we recognise an

important similarity between both style and direction of the deformations described in the Westphalian

and those described in the Permian. For instance: thrusting and reverse-faults in the Rehamna massif

(MULLER et at., 1991), fault-slip-data analysis in the Central Massif (AIT BRAHIM & TAHIRI, 1996).

Thus, the compressional late Variscan phase described here in the Sidi-Kassem basin could probably be

of Latest Permian-Earliest Triassic.

REFERENCES

AIT BRAHIM, L. & TAHIRI. A., 1996.— Rolation horaire des contraimes et mecanismes d'ouverture et de fermeture des bassins

permiens du Maroc central. In: F. Medina (cd.). Le Permien el le Trias du Maroc: dial des connaissances. Pumag.

Marrakech: 87-98.

ANGELIER, J. & MECHLER, P„ 1977. — Sur une methode graphique de recherche des contraintes principales egalemenl

utilisablcs en tectonique et en seismologie: la methode des diedres droits. Bulletin de la Societe geologique de France,

6: 1309-1318.

Chakiri, S.. 1991. — Le Paldozoique de la region de Tsili-Tiddas (Maroc central occidental). Stratigraphic, sedimentologie et

evolution structural hercynienne. These de 3 in " cycle, Universite Mohammed V, Rabat, Maroc: 1-227.

Choubert, G.. 1951.— Essai de chronologie hercynienne. Notes et Memoires du Service geologique du Maroc. Rabat. 83: 9-

78.

Choubert, G.. 1956 (ed.).— Carte geologique du Maroc a 1/500 00(f". feuille Rabat. Notes et Memoires du Service

geologique du Maroc, Rabat, 70.

El Wartiti, M.. 1990.— Le Permien du Maroc mesetien. Etude geologique et implications paleogeographiques. These d’Etat,

Universite Mohammed V, Rabat. Maroc: 1-501.

El Wartiti, M., Broutin, J., Freytet, P., Lahrib, M. & Toutin-Morin, N.. 1990.— Continental deposits in Permian basins

of the Mesetian Morocco. Geodynamic history. Journal of African Earth-Sciences, 10 (1/2): 361-368.

GHAZALI, K., 1995.— Contribution a l'etude geologique du bassin de Sidi-Kassem (Formation de Feddane Lebtam). Maroc

hercynien central. Memoire de DEA. Universite Mohammed V. Rabat, Maroc: 1-43.

Bollard. H.. 1985 (ed.).— Carte geologique du Maroc a 1/1 000 000 tm .Notes et Memoires du Service geologique du Maroc,

Rabat, 260.

KONING, G. DE, 1957.— Geologic des Ida-ou-Zal (Maroc). Stratigraphic, petrographie et tectonique de la partie SW du Bloc

occidental du Massif ancien du Haut Atlas. Edvard Ijdo N.V.. Leyde: 1-210.

Miall, A.D.. 1978.— Lithofacies types and vertical profile models in braided river deposits. In: A.D. Miall (ed.). Pluvial

sedimentology. Memoir- Canadian Society' of Petroleum Geologists, 5: 597-604.

CHRISTIAN HOEPFFNER ETAL.

Muller. J.. Cornee, J.J. & El Kamel, F.. 1991.— Evolution tectono-sedimentaire d'un bassin molassique post-orogenique-

I exemple des senes conglomeratiques stephano-triasiques de Mechra-ben-Abbou. Rehamna. Maroc. Geologic

mediterraneenne , 1 -2: 109-120. 6

Pique, A. & Michard, A 1989 — Moroccan Hercynides: a synopsis. The paleozoic sedimentary and tectonic evolution at the

northern margin ol the West Alnca. American Journal of Science, 289: 286-330.

Pruvost. P. & Termier, H.. 1949.- Sur Page de la formation houillere deSidi-Kassem (Bled Zaer, Maroc). Comptes Rendus

de l Academic des Sciences, Paris , 229: 7-9.

RoCH - ^Histoire -siraligraphique du Maroc. Notes el Memoires du Service geologique du Maroc. Rabat. 80: 1-435,

SABHR ' Ty'F Sedmientologie et evidence d’une tecionique tardi-hercynienne d'agc permien inferieur dans le bassin des

Ida ou Z.ki, SW du massd ancien du Haul Atlas (region d'Argana, Maroc). Journal of African Earth-Sciences. 19: 99-

Term| er H. 1936.--Eludes geologiques sur le Maroc central et le Moyen Atlas septentrional. I: Les Terrains primaires e. Ic

lermo-Tr as _ Les Terrains post-tnasiques^ 3: Paleonlologie, petrographie. 4: Atlas. Notes et Memoires du Sendee des

Mines el de la Carte geologique du Maroc , 33: 1-1566.

Termier H & Termier. G.. 1951 — Presence deViseen dans le bassin houiller de Sidi-Kassem. Comptes Rendus de

l Academie des Sciences, Paris. 232: 1310-1312.

Source: MNHN, Paris

Triassic series of Morocco: stratigraphy,

palaeogeography and structuring of the Southwestern

Peri-Tethyan Platform. An overview

Mostafa OUJ1DI Louis COUREL", Nciima BENAOUISS Ui , Mohcimed El

Mostaine ij \ Mohcimed El YOUSSI ", Mohamed Et TOUHAMI Driss

OUARHACHE , " 1 , Abdellcih Sabaoui "" & Abdel-Illah TOURANE 1

University Mohamed I er , Laboratoire de Geodynamique, route de Sidi Maafa. 60 000 Oujda, Maroc

l2 'Universitc dc Bourgogne et UMR 5561 CNRS. 6, boulevard Gabriel. 21 000 Dijon. France

"Faculte des Sciences Semlalia, boulevard Prince Moulay Abdellah. BP SI5. Marrakech. Maroc

(J 'ONAREP, 34, avenue Al Fadila. Rabat, Maroc

,5) University Mohamed V-Agdal. BP 1014, Rabat. Maroc

<ft 'Faculte des Sciences Dhar El Mahraz, BP 1796, Atlas Fes, Maroc

ABSTRACT

New biostratigraphic findings combined with earlier works allow' us to establish a new stratigraphic framework for the

epicratonic Triassic series of Morocco. The Tethyan transgression from the NE reached the Oujda area during the late Ladinian

time before subsequently spreading extensively across the central High Atlas during the Carnian. The transgression from the

Proto-Atlantic domain over SVV Morocco developed at the end of the Triassic (late Carnian/Norian) and during the Early

Jurassic. The structural-sedimentary history of the Triassic epicratonic platform can be divided into three major stages. Basalt

Hows and exceptional carbonate level deposition of the Oujda Mountains were related to reactivation of Hercynian and Late

Hercynian ENE-WSW and EW faults. The Carnian episode was marked by active extension. Maximum subsidence and basalt

Bows in the High Atlas troughs were controlled by N45° conjugated with N70-90 0 normal synsedimentary faults. Normal or

sinistral normal faulting guided the progressive transgression of the Tethys from the NE. Late Carnian/Norian eastward dipping

normal faults generally post-date the ENE-WSW to EW faults bounding the Atlasic tectonic troughs. In the west of Morocco,

from the late Norian up. grabens of the Proto-Atlantic domain were filled with clastic material mainly from SW tilted High

Atlas rift compartments. Above the debatable boundary between the Triassic and Lower Jurassic series, basalt Hows and thick

evaporite depocentres developed over the Proto-Atlantic domains. At the scale of the whole Moroccan platform the

homogeneity of the Late Triassic and early Liassic facies could be indicative of easier communication in coalescent basins

during marine onlaps.

OlIJIDl, M., COUREL. L..BENAOUISS, N.. El MOSTAINE, M., El YOUSSI, M., ET TOUHAMI. M.. OUARHACHE, D.. SABAOUI, A.

& Tourani. A.-L. 2000.—Triassic series of Morocco: stratigraphy, palaeogeography and structuring of the southwestern Peri-

Tethyan Platform. An overview. In: S. Crasquin-Soleau & E. Barrier (eds), Peri-Tethys Memoir 5: new data on Peri-

Tethyan sedimentary basins, Mem. Mus. nain. Hist . not.. 182 : 23-38. Paris ISBN : 2-85653-524-0.

Source: MNHN. Paris

MOSTAFA OUJIDI ETAL.

RESUME

Series triasiques du Maroc : stratigraphic, paleogeographie et structuration dc la plate-forme peri-tethysienne du

Sud-Ouest. Une revue.

Un nouveau cadre stratigraphique est propose pour les series triasiques du Maroc. base sur des donnees biostratigraphiques

anciennes et recentes. La transgression tethysienne venue du NE atteint la region d'Oujda au Ladinien superieur/Carnien

inferieur. avant dc s'etcndre plus largement jusqu’au Haut Atlas central pendant le Carnien. Une transgression venue du

domaine proto-atlantique se developpe plus tard sur I'Ouest du Maroc a la fin du Trias, au Norien et pendant le debut du

Jurassique. L'histoire sedimentaire de la structuration de la plate-forme epicratonique au Trias est divisee en trois stades

principaux. Des coulees de basalte et le depot localise de carbonates dans la region d‘Oujda sont lies a la reactivation de failles

hercynienncs ct tardi-hercyniennes ENE-WSW et EW. Le stade carnien est marque par une extension. Une subsidence

maximum et des coulees de basalte dans le Haut Atlas sont controlees par des failles syns^dimentaires N45° et N70-90 0

conjuguees. Une fracturation normale ou senestre normale a guide la transgression progressive de la Tcthys venue du NE. Des

failles normalcs d’age carnientardif/norien plongeant vers I’E reprennent les directions ENE-WSW des fractures limitant les

gouttieres atlasiques. Des grabens du domaine proto-atlantique, dans LOuest du Maroc, sont remplis a partir du Norien tardif

par du materiel clastique venant principalement de blocs bascules du Haul Atlas. Au dessus de la Iimite discutable entrc le Trias

et la base du Lias, des coulees de basaltes et des depots-centres a evaporites se developpcnt dans le domaine proto-atlantique. A

Lechelle de Lensemble de la plate-forme marocaine, Fhomogeneite des facies du Trias tardif et de la base du Lias temoignent

de communications plus faciles dans des bassins coalescents pendant des onlaps marins.

INTRODUCTION

Work on the Triassic deposits of Morocco began in the 1930s (TERMIER, 1936; ROCH. 1939). The

Marrakech symposium (1982) and the Rabat round-table (1995) presented compilations of the last thirty

years work of local character. Palaeogeographic syntheses have attempted to situate the Triassic series

of Morocco in a wider framework (Van HOUTEN, 1977; MANSPEIZER et al ., 1978; SAL VAN, 1984;

BEAUCHAMP. 1985, 1988). Such efforts have been thwarted, though, by the paucity of chronological

data. MANSPEIZER et al. (1978) and Salvan (1984) concentrated particularly on the basalt-claystone

sequences of Northeast Morocco and the Middle Atlas and on the High Atlas lava flows. It is suggested

that at least four volcanic episodes occurred from Ladinian to Sinemurian times. Evidence for this

hypothesis is the apparent difference in chemical composition of lava from these different provinces

(MANSPEIZER et al.. 1978). In the absence of reliable chronological markers. Van HOUTEN (1977)

considered that except for basal deposits in the High Atlas (probably from the Lower Triassic), the

Triassic deposits of Morocco do not pre-date the beginning of the Late Triassic. He further postulated

that the more widespread uppermost strata (basalts, claystones and evaporite facies) date back to the

Early Jurassic and may allow correlations to be made throughout Morocco.

This paper is one such attempt at correlating reference series from different Triassic basins in

Morocco. Recent and mainly biostratigraphic data are compared with earlier findings for the purpose of

proposing a new historical framework for the Moroccan domain during Triassic times. To this end,

palaeogeographical reconstructions are proposed which lead to the hypothesis about the structuring of

this Peri-Tethyan domain.

REGIONAL FRAMEWORK

The Triassic series lie unconformably over the deformed Palaeozoic basement or, locally, over

coarse intra-mountane basin deposits dated to the Early Permian by plant fossils (CAILLEUX et al ., 1983;

LARHRIB, 1996; SEBAN, 1996). The Triassic series is up to 2000 m. From outcrop and borehole data

supplemented by seismic profiles, 15 separate basins have been identified for the transition from the

Late Triassic to Early Jurassic, most of which are oriented NE or ENE (Fig. 1). Their boundaries are not

clearly identified, however, and some may be simple depocentres in a largely coalescent complex. In the

areas where subsidence was less intense, shallow series are made up of poorly dated evaporitic

claystones. LORENZ (1988) distinguished three types of basin according to the dominant facies,

including the evaporite levels of the lower Liassic whose thicknesses are quoted below:

Source: MNHN , Paris

TRIASSIC SERIES OE MOROCCO

— basins with thick sandstone and conglomerate series: Argana (>2500 m). Marrakech High Atlas

(1500 in). Central High Atlas (1000 tn) and Kerrouchen (600 in);

— basins with thick salt series: Essaouira (2300 in), Berrechid. Guercif, Ziz-Guir (500 m) and Hants

Plateaux (1200 in). Evaporite basins have also been detected along the present-day Atlantic coast and a

far offshore as Tarfaya Basin;

_ basins with detrital deposits overlain by thick halite series: Doukkala (1390 m), Rharb ( 11()0 m),

Khemisset (1095 m), Bou Fekrane (900 m) and Moyenne Moulouya (Tamdafet. 950 m).

Investigators agree that broad areas of non-deposition subsisted in the Meseta ot Central Morocco.

Th , d rinmain l0 the north is composed of allochthonous sheets whose palinspastic position is

lincertain'These^initsincludered detrital facies (BAUDELOT etal, 1984) or marme platform carbonates

(WlLDI, 1983). They are not discussed in this paper which only deals with the autochthonous epicu

domain.

Alborar

Sea

allochionous

! ' area J

RABAT

Marrakech

Triassic time; 20. Interbasin area covered mostly by evaponte mudstone.

/.— Principaux bassins marocains au Trias superieur (d apres Sal ™''- 1984 , V ' : 4.

Beauchamp et al. 1995). 1. Zone salifire ^ diapinqitede la marge ■ 9 . Khemissei; 10. Boa

Doukkala : 5. Haul Allas de Marrakech : 6 Haul Atlas central, 7 Berrechi , * plateaux; 16. Bassin

reconvert par des mudstones a evaporites.

Fig.

MOSTAFA OUJ1DI ETAL.

STRATIGRAPHIC FRAMEWORK

Chronological Data

Hie Tnassic series of Morocco arc poorly dated. Sedimentary strata have until recent years yielded

almost exclusively imprints and plant remains. A handful of animal fossils, despite their

palaeoecological value, were of little use in establishing a detailed stratigraphic scale. However,

advances in palynology have recently made it possible to be more specific about many levels. Basalts

have been weathered and radiochronological datings often lie outside the limits suggested by

biostratigraphy. This tool must therefore be used with caution. All the ancient and recent data allow us

Significant datings lor the main formations to attempt to make correlations between basins (Fig. 2).

The recent discovery of ostracod fauna in the Oujda Mountains (Crasquin-Soleau et al., 1997) has

allowed two beds to be dated. Limnocythere keuperea Will and Speluncella n. sp. Crasquin-Soleau el at.

date to the late Norian while Lutkevichinella kristanae Crasquin-Soleau et al.. which is similar to

Lutkevichinella lata Kozur. found in association with Anoplophora lettica Quenstedt, is ascribed to the

late Ladiman / early Carnian boundary. These latest data corroborate and supplement those of

OWODENKO (1946) in the same beds of that sector.

Recent studies have refined the biostratigraphic framework in the Middle Atlas south of Fes, between

Central Morocco and the Tazekka Massif. Carnian spore and pollen associations (SABAOUl, 1996;

BAUDELOT et al.. 1984, 1986) have been discovered in sedimentary levels beneath the first Triassic

basalt flows. In addition. OUARHACHE (1987) and BAUDELOT et al. (1986) described early to mid

Nonan ostracods Sulcocythere hajbensis Cohn associated with Darwinula in the El Hajeb inter lava

now bed. J

. pr YOUSS, (1986) subdivided the Oukai'meden Sandstone formation in the High Atlas south of

M'delt into three members (a, b. c) by facies and sedimentary environment. The top of the “a” member

has proved to have high late Carman spore and pollen content. In the Ourika region, COUSMINER &

MANSPEIZER (1977) considered that the entire Ouka.meden Sandstone formation is mid Carnian. In the

Argana Basin among the many vertebrate remains collected and described from 1962 to 1975 bv

IIUIT (1976), Jalil & DUTUIT (1996) and Jalil (1996), the presence of large Metoposaurids

(Metoposaurus ouazzoui Dutuit and M. lyazidi Dutuit) in T5 and of a Cyclotosaurus in T4 allows these

units to be dated to the middle to late Carnian.

In the Essaouira Basin. SLIMANE & El MOSTAINE (1997) reported ostracods Darwinula in borehole

MKL-i between 3027 and 3300 m and Lymnocvtliere at 2964 m in borehole MKL-104 The

corresponding clay-siltstones have been ascribed to the Carnian-Norian. Furthermore, K/Ar dating of a

Iresh doierite sampje located at the base of the Triassic series between 2768 m and 3163 m in borehole

JKP-1 yielded an absolute age of 210 Ma, making it Norian by Odin’s scale (1982).

In the Doukkala Basin, Slimane & El MOSTAINE (1997) reported ostracods at the base of the fine

clastic series located immediately below- the lower salt formation of boreholes BHL-1 and DOT-1 The

species recognised belong to Gemmanella in borehole BHL-1 at depths of 1654, 1680. 1812 and 1818 m

and Paracypris and Lutkevichinella in the DOT-1 borehole at depths of 1758, 1867 and 1875 m Those

authors dated these formations to the Carnian-Norian. Foraminifers and ostracods have allowed the

topmost clastic and salt formations to be dated to the Lower Jurassic (Sinemurian). Thus the age of the

claystone and salt formations in association with the volcanic lava flows may range from Carnian-

iNorian to oinemunan.

NEW STRATIGRAPHIC FRAMEWORK

We propose a new stratigraphic framework (Fig. 2) according

biostratigraphic findings combined with earlier works.

to correlations based

on the new

Source: MNHN , Paris

TRIASSIC SERIES OF MOROCCO

0^9 Vertebrates (jp) Esterids ❖ Palynoflora * Ostracods c-)Anoplophora

Q Foraniinifers ® Radiochronology

1 CHl3

l" l” l

7 bads

/ / s

v \ S

* i 4

Fig. 2.— Permian to lower Liassic Moroccan series: correlations. 1. gap; 2. conglomerate; 3, sandstones; 4. clayey sandstones;

5. silty claystones 6. gypsiferous claystones; 7, halite and claystones; 8. carbonates; 9, grey claystones; 10, doleritic

basalts. dtfv-Defretin & Fauvelet (1951): brpt-Bertrand (1991); duja-Dutuit (1976); Jalil & Dutuit (1996);

ely-El Youssi (1986); csma-Cousminer & Manspeizer (1977); lmjn-Le Marrec (1979x Jenny (1983); elw-El

Wartiti (1990); tl-Taugourdeau-Lanz (1978); mans-Manspeizer et al. (1978); bdal-Baudelot et al. (1990);

QUA-OUARHACHE (1987); SAB-SABAOUl (1987); BDCH-BAUDELOT & CHARRIHRE (1983); CRAL-CRASQUIN-SOLEAU et al.

(1997); owo-Owodenko (1946); slel-Slimanh & El Mostaine (1997).

Fig. 2.- Series marocaines, dti Pennien an Lias inferieur : correlations. I, lacune ; 2, conglomerat ; 3. gres . 4, gres

argileux ; 5, argilites silteuses ; 6. argilites gypsiferes : 7, halite et argilites ; 8, carbonates ; 9. argilites fetides : 10.

basaltes doleritiques. dtfv-Defretin & Fauvelet (1951) : brpt-Bertrand (1991) ; duja-Dutuit (1976). Jalil &

Dutuit (1996) ; ely-El Youssi (1986) ; csma-Cousminer & Manspeizer (1976) ; lmjn-Le Marrec ( 1977). Jenny

(1983) ; elw-El Wartiti (1990) ; tl-Taugourdeau-Lanz (1978) ; mans-Manspeizer et al. (1978) ; bdal-Baudelot et

al. (1990) ; oua-Ouarhache (1987) ; sab-Sabaoui (1987) : bdch-Baudelot & Charriere ( 1983) ; cral-Crasquin-

Soleau et al. (1997) ; owo-Owodenko (1946) : slel-Slimane & El Mostaine( 1997).

Source: MNHN. Paris

MOSTAFA OUJIDI ETAL.

No Permian deposits are recorded in Eastern Morocco. Permian intracontinental basins form in the

Meseta, and the Middle and High Atlas Mountains. These coarse, post-orogenic deposits are

lithologically distinct from those of the Triassic and have yielded Autunian and Stephano-Autunian flora

(VanHouten, 1976. 1977; LORENZ. 1988; El. Wartiti. 1990; Larhib. 1996; SEBBAN. 1996).

There is a large sedimentary gap between the Lower Permian and the upper Ladinian reflecting

weathering and erosional processes in an arid climate (LUCAS, 1942; ROBINSON, 1973).

The oldest Triassic deposits in Morocco outside the Rif dated late Ladinian/early Carnian are found

exclusively in the Oujda region (CRASQUIN-SOLEAU el al., 1997). This first Tethyan onlap is

materialised by a carbonate bar. The fauna is characteristic of brackish to marine conditions in an

intertidal to subtidal environment (OUJIDI, 1994). This bar overlies clay-siltstones deposited as mud flats

and the first basalt flow.

The Carnian deposits yield the earliest Triassic biostratigraphic assemblages in Morocco outside the

Oujda Mountains. In the High Atlas, mainly continental fluvial or alluvial fan sedimentation (F3 or T3)

overlies the Permian series (MATTIS, 1977; Van HOUTEN. 1977; PETIT & BEAUCHAMP. 1986; EL

YOUSSL 1986). The silt and clay formation (F4 or T4/5) was interpreted as floodplain deposits by

Mattis (1977) on the evidence of dispersed channels and bioturbation of the clay and silt deposits. By

contrast. PETIT & BEAUCHAMP (1986) interpreted ii as a margin-littoral tidal-flat type environment

because of the presence of symmetric ripples and marine bivalve tests. Formation F5 (or T6/7) or the

Oukaimeden Sandstones was interpreted by El YOUSSI (1986) as a delta environment with the main

SW-oriented flow. BENAOL'ISS (1996) and BENAOU1SS el al. (1996) recognised in this F5 formation of

the High Atlas intertidal structures which are indicative of brief marine incursions from the NE. the

direction of the Peri-Tethyan marine domain (Fig. 5). They also discovered eolianites at the top of the

formation. Contemporary series in Central Morocco reflect lagoonal clay sedimentation with a few

evaporite levels to the Khemisset Basin. These claystones are associated with 1 ignitic strata in the

Tazekka Massil (Sabaoui. 1987. 1996). A new basalt outflow (the second phase) is recorded in the

Carnian deposits of the Oujda Mountains. It is thought to correspond to the first phase of basalt outflow

in the El Hajeb Causse.

It is currently difficult to make out separations between the upper Carnian and Rhaetian deposits.

Assemblages of Norian ostracods are described in the Oujda Mountains, Middle Atlas, Essaouira Basin

and Doukkala Basin which are characteristic of oligo- to mio-haline, limnic to brackish environments

(CRASQUIN-SOLEAU et al., 1997). They are said to correspond to permanent lacustrine or possibly

lagoonal environments (Baudelotc? al., 1986). Their presence does not exclude upper Carnian and

Rhaetian deposits in the same facies. At that time, salt claystones sometimes containing basalt flows

largely dominated homogeneous sedimentation in coalescent basins (BEAUCHAMP, 1988).

It > s diflicult to locate the Triassic / Jurassic boundary. Carbonate beds are found above the Triassic

series in the Oujda Mountains in Eastern Morocco and in the Argana corridor in Western Morocco. This

suggests biostratigraphic dating should be possible, but new data are required yet. It seems that these

carbonates are less developed, or even absent in the central part of Morocco where lagoonal, evaporite

or stromatolite claystones are found. This is the case in the Khemisset Basin, for example, and

ETTOUHAMI (1994) assumed that this basin was the site of mixing of Tethyan and Proto-Atlantic

marine waters.

These correlations emphasise three main results:

on the scale of Morocco, basalt Hows occurred in succession from the Ladinian / Carnian

boundary to the early Jurassic and are on the whole more and more younger toward the West;

- the Tethyan transgression from the NE reached the Oujda area during the late Ladinian before

subsequently spreading extensively across the central High Atlas during the Carnian;

jhe transgression from the Proto-Atlantic domain over SW Morocco developed at the end of the

Triassic (late Carnian / Norian) and during the Early Jurassic.

Source: MNHN, Paris

TRIASSIC SERIES OF MOROCCO

STRUCTURING OF THE MOROCCAN EPICRATONIC DOMAIN

Most workers agree lhat the structuring of the Moroccan margin during the Triasslc was mainly

controlled by reactivation of Hercynian and late Hercynian faults (ENE-WSW to E-W) with, initially, a

virtually homogeneous NW-SE direction of extension. However, different geodynamic models have

been proposed to explain the formation of the Triassic basins of Morocco.

VAN HOUTEN (1977). MANSPEIZER et al. (1978). MaNSPFJZER (1988). LAVILLE (1981). LAVILLE &

PETIT (1984), Laville & Pique (1991, 1992) and PIQUE & Laville (1995) considered that the

structuring of the basins is related to a fault field with a high normal component forming part of a

megazone of sinistral shear faulting, corresponding to the reactivated "Atlas Palaeozoic transform zone"

to the South and the “Gibraltar-Azores transform zone" to the north.

FAVRE & STAMPFLl (1992), STAMPFLI (1994) and MEDINA (1995, 1996) postulated that the Atlantic

Rift probably developed in two major extensional stages. An initial Carnian, or slightly earlier stage, is

related to NNW-SSE extension. This apparently induced shear faulting in the Atlas rift, partly by simple

reactivation of inherited Hercynian and Late Hercynian structures. A late NW-SE extensional stage

seems to have produced pure shear at the end of the rifting episode (Sawyer & Harry, 1991). Ii is

thought to be related to the emplacement of a thermal dome along the rift centerline together with the

raising of the rift shoulders. However. LISTER et al. ( 1991) and MEDINA et al. (1996) observed that the

structural evolution of the Souss Basin in the Triassic was conlrolled by a deep detachment, probably an

old, gently NNW sloping, Hercynian plane of weakness, from which the entire system of the Tizi n'Test

fault zone arose.

EL Kochri & Chorowicz (1996), although dealing with the Jurassic rift, proposed an alternative

hypothesis to the pure slip stress regime acting along the E-W faults. They assumed that at the beginning

of the Jurassic, regional extension was oriented rather WNW-ESE. obliquely to the main lilting faults.

These faults, which were largely divergent to the direction of maximum extension, worked like normal

faults and were responsible for the titling of the different tectonic blocks. The faults parallel to the

direction of extension slipped and operated as transfer faults. The coexistence ot single- or double-curve

transfer faults defines a highly particular tectonic style to explain the kinematics of rift opening.

In the light of the new stratigraphic framework proposed and the review ot the structural models that

attempt to explain the opening of the basins on the Moroccan margin during the Triassic, we suggest

(hat the structural-sedimentary history of the Triassic epicratonic platform can be divided into three

major stages.

Pre-rift stage (before Carnian time)

Before the break-up of Pangea, the northwest edge of the African Craton was attached lo North

America between Nova Scotia and Newfoundland (BALLARD & UCHUPI. 1975: LORENZ. 1988). The

nearest open marine domain was the Tethys, some 1000 to 1500 km to the cast. During the stait ol the

Triassic, Morocco was the site of erosion, with no deposits being conserved, and with an eastward

palaeoslope (Van Houten et al., 1974; Van Houten & Brown, 1975. 1977). The oldest Triassic

deposits on the Moroccan Craton are found in the Oujda Mountains and are dated to late Ladinian times

(CRASQUIN-SOLEAU et al., 1997) (Fig. 4). The deposits are a very condensed marine carbonate bed

which was transgressive over tholciitic basalt. The structural framework ol the Oujda Mountains was

characterised by "small elongated depocenters several kilometers in length separated by shoals (Fig. 3).

The direction of marine influences between ihc Tethys and the Moroccan platform was mainly

controlled by WSW-ENE tectonic troughs. These synsedimentary extensional structures were related to

reactivation of Hercynian and Late Hercynian faults (ENE-WSW and E-W) (OUJIDL 1994, 1996). The

exceptional carbonate beds of the Oujda Mountains replaced in their structural context suggest marine

aggradation wedges from the Tethys to the northeast (CRASQUIN-SOLEAU et al., 1997).

MOSTAFA OUJIDI ET AL.

Fig. 3.— Isopach map of the “Barre carbonatee intercalaire" in the Oujda mountains (after Oujidi. 1994). 1. Area without

"Barre carbonatee intercalaire": 2. Maximum thickness of the "Barre carbonatee intermediaire”: II to 13 m thick: 3,

data point location. MT-J. Mctsila, MM-Moussa ou Mohammed. 12 et 13-maximum thickness of the "Barre carbonatee

intercalaire” in metres.

Fig. 3.— Carte des isopciques de la Barre carbonatee intercalaire dans les Monts d'Oujda. (d’apres OUJIDI, 1994) /. domaine

sans Barre carbonatee intercalaire ; 2. Epaisseur maximum de la Barre carbonatee intermediaire : II a 13 m : 3.

localisation des points de donnees, MT-J. Metsila. MM-Moussa ou Mohammed. 12 et 13-epaisseur maximale de la

Barre carbonatee intercalaire en metres.

Syn-rift Stage

— Carnian: the climax of the Triassic rifting in Morocco is of Carnian age. Subsidence reached its

maximum in the Triassic basins located in the High Atlas troughs and to a lesser extent in the Middle

Atlas (Kerrouchen Basin) (Fig. 5). This episode is characterised by active extension in a strike slip

system. N45° synsedimentary normal faults are highly developed and their movement is conjugated

with N70-90 0 normal faults. Half-grabens are thus delineated that are up to several hundred metres

thick, that link up to varying degrees and exhibit differential subsidence. This fracturation is responsible

for the outpouring of basalts in relation with the onsetting of rifting over the whole of the Moroccan

Margin. With the exception of the shallow marine carbonates of the Oujda Mountains, Carnian

sedimentary environments were mainly continental: fluvial, fluvio-lacustrine or alluvial fans. However,

reactivated normal or sinistral-normal faulting of the Hercynian and Late Hercynian structures (ENE-

WSW to E-W) guided the progressive transgression of the Tethys from the northeast over the North

African margin. Thus tidal marine interbeds appeared in the High Atlas (BEAUCHAMP et al ., 1995;

BENAOUIS et at., 1996).

Source: MNHN. Paris

TRIASSIC SERIES OF MOROCCO

Fl G 4 - Palaeogeographic map of the late Ladinian series in Morocco. 1. Triassic erosion or non-deposition area; 2,

ailochtonous domain; 3. marine limestone and dolostone; 4. marine tncurs.cn; 5. volcamsm. Ez-J. Ez Ztdour. C-

Casablanca. S-Safi. A-Agadir, O-Oran. T-Tanger.

Fic. 4 .- Carte paleogeographique du Maroc pendant le Ladiniensuperieur. 1. zone d'erosion triasiqueou de non depot ;2

domaine attach,one ; 3 calcaire e, dolomie marines ; 4. incurs,on marine ; 5 volcamsme. Ez-J. Ez Ztdour. C-

Casablanca, S-Safi. A-Agadir. O-Oran, T-Tanger.

Carnian

I—h & S 3

Fig. 5.- Palaeogeographic map of the Carnian series in Morocco. Lithologic and geographic captions, see the figure 6.

F,C. 5.- Carte paleogeographique du Maroc pendant le Carnien. Legendes lithologiques e, geographies, voir la figure 6.

Source:

MOSTAFA OUJ1DI ETAL.

~ Late Carman I Nonan: in (he Mesetian and (he Atlasic domains, the N-S normal faults with

medium to low eastward dipping generally postdate the ENE-WSW to E-W faults bounding the tectonic

troughs initiated in the Carman (Fig. 6). The direction of extension is NW-SE and the strike-slip

component weak. This structuring is said to be controlled by a deep detachment plane, probably an old

Hercynian plane ol weakness, dipping slightly NNW (MEDINA el ciL, 1996) according to the model of

LISTER el al (1991). It is related to the opening of the Proto-Atlantic domain, flooded by the

epicontinental Tethys Ocean which supposedly crossed the Gibraltar fracture zone (E-W or NE-SW-

R .! < l ou ;. 1 " t 4) f rom the North - The N S faults occur mainly in the west of Morocco (Fis. 6) in the basins

ot 1 arraya-Laayoun, Argana, Essaouira. Doukkala, Berrechid-El Gara and Khemisset N3Q-40°E faults

are interpreted (BlRON 1982; BEAUCHAMP. 1988) as neo-breaks engendered by oblique extension of

existing N70 E faults which operated as sinistral strike-slip / normal faults during the Triassic.

'Guercif.

RABAT

Taourirt

Doukkala

F4 Mekkam

Berrechid

Kerroucht

:mklZ-

--JRP

Norian

Alboran

Sea

F ' a 6 ‘7nmln e °fS hiC maP ° f N0ri f,f ries in Morocco - '• Triassic erosion or non-deposition-area: 2. allochtonous

clavstonev t w 7T i 8 °° nal 1 'acustrinc limestone and dolostone: 4. marine incursion: 5, mud Hal type silly

alhvd c ,0 Hr a ' C r gl ° mer n e: , 7 ' 1 7u l , Cl 77 sands,0l,e: *■ i'Hra-basinal transit direct on: 9. gypsmn and

MX, an l ippo™ V' I2 - fau " [Ch-J. Ech Chekhar. Tz-Massifde Tazekka. Hj-EI Hajeb. Kh Khemisset

Ag^%lKo™.x!!Sr ESSa ° U,ra baS ' n - 'drohalene. Ar-Argana. Al-Ai, Leqaq. C-Casablanca. S-Safi. A-'

FlG ' 6 f Ma T pe " <lwu ,e Norien - 1 Z0,,e d ‘ ir0si0n ,riasu l“ e O" de non dtp*' • T domaine

a gin es silteuSes dJ n’nl fr"7 '"""T’"’ marin pe " P r ° fo " d * %«" o-lacustre : 4. incursion marine : 5.

d ' E "°- ***** ***» «-«<

A number of arguments led Laville & Pique (1991) to distinguish between two rifting areas in

Ssto the P wT^ r y a NE ' SW i° rSt deV °o d of Triassic deposits: the Atlantic margin with its coastal

S?" h 1 | h f' (du ' p,r ! c 1 zone ' Essaouira Basin, Doukkala Basin) and the basins of the Atlas domains

in fbsencfofTrns'^d, T 'ti C ' h "if ^ steni Meseta is addcd - This Presumed horst is marked by

an absence ot Ti lassie deposits. This may be the result of subsequent erosion though. In the Oukaimeden

Source: MNHN. Paris

TRIASSIC SERIES OF MOROCCO

Sandstones, west of the Argana region, there is only evidence of westward and eastward running

currents (BENAOUISS et al ., 1996).

More generally on the Moroccan Margin, the late Carnian to Norian sedimentary environments are

highly diverse. The grabens of the Proto-Atlantic domain were filled with alluvial materials from High

Atlas rift compartments that were raised and tilted to the southwest (BEAUCHAMP et al.. 1995). Activity

along the Zemmour Fault (N30) produced the Tarfaya Laayoun Basin with southwesterly oriented

alluvial piedmont sedimentation. The subsiding basins opened to the Tethys (Tiouli. Hauts Plateaux,

Guercif, Ziz Guir and Khemisset) were the site of halite sedimentation in a shallow saline mud-flat type

environment. These are known as the lower salt deposits.

Late Norian / early Liassic

The boundary between the Triassic series and those of the base of the Jurassic is difficult to localise.

However, a clearly Jurassic stage of basalt flow is confirmed biostratigraphically in the Tazekka Massif

(SabaOUI, 1996) and in the Doukkala and Essaouira Basins (SUMANE & El MOSTAINE, 1997) (Fig. 7).

This episode is thought to be equivalent to the formation topping the Triassic series of Tarfaya, Argana,

the Central High Atlas, Kerrouchen, El Hajeb and Tazekka.

Fig. 7.— Palaeogeographic map of the Norian to early Liassic series in Morocco. Lithologic and geographic captions, see

figure 6.

Fig. 7.— Carte paleogeographique du Maroc, du Norien an Lias inferieur. Legendes lithologiques et geographiques , voir

figure 6.

While the Oujda Mountains in the northeast witnessed the progressive build-up of the Jurassic

carbonate platform, all the subsiding basins were marked by the extension ot mainly halitic evaponte

deposits. This was the case for Tethyan basins (Hauts Plateaux, Guercif, Haute Moulouya) but also tor

MOSTAFA OUJID1 ETAL.

those which opened onto the Proto-Atiantic domains (Berrechid El Gara, Doukkala, Essaouira, Tarfaya-

Laayoun and the Atlantic Margin) or the intermediate basins (Boufekrane, Khemisset, Rharb). The

bromine geochemistry in these deposits indicate an influx of sea water (PERETSMAN, 1985; HOLSER et

al r 1988; EtTouhami, 1996). Despite the lack of evidence, it may be wondered whether the basal part

of the evaporites known as the upper salt deposits capping what is recognised as the Triassic series are

not of Late Triassic age in some locations. Sulphate and halite pseudomorphs are known in the

uppermost Triassic beds of Argana. The onset of halite sedimentation may be diachronous, as shown in

Algeria (AIT Salem et al ., 1998). The homogeneity of the Upper Triassic and lower Liassic facies could

be also indicative of the fact that the basins were coalescent at the time of easier communication during

Tethyan marine onlaps.

CONCLUSION

A new biostratigraphic division has made possible to propose palaeogeographic maps of three key

periods in the history of the Triassic on the Moroccan epicratonic platform (Figs 4 to 6). Several major

results can be summarised. At the scale of Morocco, sedimentation began only at the end of Ladinian

times and the transgression over the Peri-Tethyan domain which was from the northeast both then and

during the Carnian. occurred earlier in eastern Morocco. The transgression over the present-day west

coast and Atlantic offshore area occurred later, from the late Carnian, from the Proto-Atlantic domain,

even if there were link-ups with Tethyan waters, via a corridor between Africa and Iberia. At the scale

ol Morocco, the basalt flows occurred in succession from Ladinian / Carnian through to Jurassic times.

These results may be compared with structural data. The geological history of Morocco during the

Triassic is of interest because the region was at the hinge-point "between the Tethyan and Atlantic

domains (Ricou, 1994). The Tethyan influence is seen in the direction of the marine advances over the

Moroccan epicratonic platform from the northeast, where the open marine domain lay. Fault directions

follow the Hercynian structures in part but the directions of extension and the major WSW-ENE

structures such as those of the Atlasic trough were the same as in other parts of the Peri-Tethyan

Maghreb until the late Carnian. The NS Atlantic fracturing was superimposed from late Carnian times in

Western Morocco. It superseded the WSW-ENE fracturing over the entire Atlantic Margin of Morocco.

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The Liassic carbonate platform on the western part of

the Central High Atlas (Morocco):

stratigraphic and palaeogeographic patterns

Abdellatif SOUHEL 111 , Joseph CANEROT' 21 , Fatma El BCHARI ",

Driss CHAFIKI ", Abdelhak Gharib ",

Khadija El Hariri & Aziz Bouchouata

"Departement de Geologie, University Chouaib Doukkali, El Jadida, Maroc

Laboratoire de Geologie des Bassins sedimentaires

URA CNRS 1405-ER 1746. Universite Paul Sabatier

F-31400 Toulouse, France

11 Departement de Geologie, Universite Cadi Ayyad, Faculte des Sciences et Techniques, Marrakech. Maroc

ABSTRACT

In the western part of the Central High Atlas, nine formations have been recognised within the Liassic (Hettangian-

Pliensbachian) record. They are organised into eight third order sequences involved in two second order cycles. Five stages

characterise the geodynamic evolution of the considered area. 1. Hettangian-early Sinemurian: wide dolomiticsabkhas; 2. late

Sinemurian: huge NE dipping open marine carbonate platform; creation of the southern Telouet basin and central Tilougguit

trough; 3. late Sinemurian-earliest Pliensbachian: marine regression and break down of the northern platform along the LPS

(“Limite Plate-forme-Sillon"-boundary between platform and trough) fault zone; 4, middle Pliensbachian: transgression and

drowning of the preceding troughs and platforms; 5. late Pliensbachian: tectonic activity leading to the infilling of the central

Tilougguit trough and the emersion of the surrounding carbonate platforms.

RESUME

La plate-forme liasique carbonatee dans la partie occidentale du Haut Atlas Central (Maroc) : stratigraphic et

paleogeographie.

Dans la partie occidentale du Haut Atlas Central, la serie liasique (Hettangien-Pliensbachien) a ete subdivisee en neuf

formations distinctes. Ces dernieres s’organisent en huit sequences de troisieme ordre. elles-memes comprises dans deux cycles

Souhel, A., CanSrot, J., El Bchari. F., Chafiki, D., Gharib. A., El Hariri. K. & Bouchouata, A., 2000.— The Liassic

carbonate platform on the western part of the Central High Atlas (Morocco): stratigraphic and palaeogeographic patterns. In: S.

Crasquin-Soleau & E. Barrier (eds), Peri-Tethys Memoir 5: new data on Peri-Tethyan sedimentary basins. Mem. Mus. mini.

Hist, nat., 182 : 39-56. Paris ISBN : 2-85653-524-0.

Source: MNHN. Paris

ABDELLATTFSOUHEL ETAL.

de deuxieme ordre Devolutioni geodynamique regionale comporte cinq etapcs successives. 1. Hettangien-Sinemurien ink-new

larges sabkhas dolomitiques ; 2. Sinemunen superieur: vaste plate-forme marine carbontee, ouverte vers le NE : creation du

bassin meridional de Telouet et du fosse central de Tilougguit ; 3, Sinemurien superieur-Pliensbachien basal : regression marine

et dislocation de la plate-forme septcntrionale le long de la /one de fracture LPS (“limite plate-forme/sillon") ; 4 Pliensbachicn

moyen : transgression et ennoyage des plates-formes et des bassins precedents ; 5. Pliensbachien superieur: activite tectoiiiaue

intense conduisant au comblement du fosse central de Tilougguit et a F emersion des plates-formes carbonatees avoisinantes

INTRODUCTION

In the western part of the Central High Atlas (Beni-Mellal area. Fig. 1) the main outcropping

formations are Jurassic (Sinemurian to Bathonian in age). These formations are folded into different

narrow NE-SW, N-S or NW-SE oriented and faulted anticlines, involving sometimes injected Triassic

materials, separated by wide synclines. So, the Mesozoic sedimentary cover shows a fan-shaped

structural organisation with a northern vergency on the northern edge opposed to a southern vergency in

the southern one. The compression rate related to Cainozoic structural inversion processes is rather low

10 to 15% along the Beni-Mellal section (BREDE et al. y 1992).

DU B A R (|96 °- ,962) . CHOUBERT & Faure-Murf.t (1 9 60-1 9 62), JOSSEN (1987) and El MI (1996)

provided the main palaeogeographic data for the Liassic period considered hereafter. These authors

described more particularly the further end of a Tethyan eastward opened gulf, surrounded to the north

the west and the south, respectively by the emerged Mesetan, Atlasic and Saharian Highs.

Recent stratigraphic and sedimentologic works allow us to propose a detailed analysis of the Liassic

sequence organisation and to present the different steps of the previously defined regional

palaeogeographic evolution during this Lower Jurassic period.

Cretaceous

Jurassic

Triassic

Paleozoic

32°-

Platform-Trough

Boundary Fault Zone

- Azilal-Ancrgui

Fault

- North Atlasic Fault

Tilougguit

Trough

Selected cross sections

1 - Adoumaz

2 - Tamadout

3- Jbel Taguendouft

4 - Barda

5 - Jbel Azourki

6 - Tizi N 'Targhist

7 - Rbat

Fig. 1.— Location map of the study area.

Fig. I .— Carte de localisation de la region etudiee.

Source: MNHN, Paris

LIASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

STRATIGRAPHIC SETTING

LlTHOSTRATIGRAPHY AND BIOSTRATIGRAPHY

The early to middle Liassic sedimentary supply of the study area involves nine different lithologic

formations, whose age has been provided by ammonite, benthic foraminifera and brachiopod faunas

(Fi>’. 2). These formations show important lateral sedimentary variations (Figs 2-4) leading to define

three main palaeogeographic zones: Beni-Mellal platform. Tilougguit trough and central (Amezraf and

AYt Bougemmez) platform, which deeply influenced the regional early and middle Liassic history. They

are organised as follows:

— Ait Ras (Beni-Mellal platform) and Tighanimine (Tilougguit trough and central platform)

Formations (JENNY. 1988). They correspond to the first carbonate deposits following the underlying

terrigenous, evaporitic and basaltic Triassic unit. They are made up of dolomitic and marly, red

coloured, decimetric beds (Ait Ras Formation) locally brecciated (Tighanimine Formation). Then-

stratigraphic position indicates a possible Hcttangian age.

— Ait Bou Oulli Formation (JENNY, 1988). Massive. 1 to 3 m thick limestone and dolostone beds are

rich in onchoids and oolites. The fauna is represented by Sinemurian brachiopods (Jerebratula moreh

Dubar. T. marucchensis Dubar and Zeilleria arethusa Di Ste. in JENNY, 1988), bivalves and benthic

foraminifera of the A biozone (SEPTFONTAINE, 1984).

— Jbel Rat Formation (JENNY. 1988), Beni-Mellal platform. This succession shows the same

stratonomic characteristics as the underlying Ait Bou Oulli Formation. Nevertheless, bird eyes vadose

pisolite and "tipi-like" stromatolitic structures are more frequent. It is Sinemurian in age. at the A and B

biozone boundary (SEPTFONTAINE, 1984).

— Jbel Taguendouft Formation (JOSSEN. 1988). Tilougguit trough. This unit represents the main

carbonate series developed in the central part of the Tilougguit trough. A rich ammonite fauna indicates

an early to middle Liassic age (EL HARIRI el ah, 1996). In the type-locality, some marly intervals

interfinger with the dominant limestones. The thick and dark Sinemurian limestones which involve

frequent flint nodules differ from the overlying, thin, light coloured. Phensbaclnan ones.

— Jbel Choucht Formation (SEPTFONTAINE, 1986). Amezraf platform. In the type-locality, on the

southern boundary of the Tilougguit trough, this formation is characterised by massive reel limestones

(Fig 5) The lower part cannot be described in detail because ol bad outcropping conditions related to

faulting and associated gabbro intrusions. The well developed uppermost part provided floated

ammonites” indicating a late Carixian interval (Du DRESNAY in SEPTFONTAINE, 1986).

- Aganane Formation (SEPTFONTAINE, 1986), Beni-Mellal platform It corresponds to a rythmic

succession of marls and dolomitic limestones, rich in benthic foraminifera and algae, accumulated

during the late Sinemurian-middle Domerian (early-middle Pliensbachian) (B. C, D and E biozones of

SEPTFONTAINE, 1984) period. The formation often provides an heterochronous intercalated unit made

up of red marls and conglomerates (marly and dolomitic member of SEPTFONTAINE, 1986 and Ait Bazzi

Formation of JENNY, 1988).

— Tamadout Formation (MONBARON, 1985). Tilougguit trough. In the Tamadout area, this

formation involves two different members (SOUHEL et ai. 1993) The lower one D o rnerian(lae

Pliensbachian) in age. is represented in the only Tamadout sector and mainly formed of brown to red

marls and shales, interbedded with decimetric bedded limestones with ammonites^

The following upper member, early to middle Toarcian in age. shows green to beige marls involving

sandstone beds in their upper part. It overlaps the underlying member, and covers the entue Tilougguit

area.

- Amezraf Formation (JOSSEN. 1988), Amezraf platform. This last unit show* a ^t es su n of thin

ripple-bedded sandstones, fossiliferous (bivalves gastropods and bl ‘ lc l ^ s s '' S

oobioclastic oblique laminated limestones (Fig. 5). The bach.opod tauna found in the lower part

indicates a Domerian age (BOUCHOUATA et ai, 1995).

ABDELLATIF SOUHEL ETAL.

— SUBSTAGES

- ZONES

i SUB ZONES

^ Havvskerense

3 Aperynum

DOMERIAN

D Gibbosus

2 Subnodosus

? Stokesi

P Figulinum

> Capricomus

3 Maculatum

Luridum

9 Valdani

Masseanum

n Jamesoni

j Polym. - Brevis.

Taylori

p 1

j Aplantum

2 Macdonnelli

^ Raricostatum

< Densinodulum

• Oxynotum

Simpsoni

Denotatus

Q Stcllarc

Obtusum

LOWER SINEM.

HETTANGIAN ?

Ammonites horizons

in Tilougguit trough

Sequence

Stratigraphy

[After SOUHEL

etcil. , 1998)

3rd

order

2nd

order

H 18" - Mazelieri

H 18'-Elisa

HIT- Emaciaticeras sp.?

H 17 (16')- Bertrandi

H 16 - R agazzon i_

H 15 - Cornacaldense

H 14 - Celebratum

H 13 - Marianii

H 12 - Portisi-Lavinianum

H 11 - Costicill.-Detractum

H 10 - Volubile-Pantanellii

_H 9 - Mellah ense-Peyrei

H 8 - Gemmellaroi

H 7 -ZiMi_(affjI

H 6 - Calliploaim

H 5 - Apertum

H 4 - Taguendoufi

H 3 - Parasteroceras ssp.

H 2 - Van, aff. interposita

H 1 - Rejectum

T2 1

R1,

FlG. 2.— Chronostratigraphic sketch diagram involving sequence stratigraphy of the described Liassic formations and

compared benthic foraminifera and ammonite zones.

FlG. 2.— Stratigraphie sequent idle el essai de correlation des echelles d'ammonites et de foraminiferes benthiques rencontres

dans les formations liasiques etudiees.

Sequence stratigraphy

A detailed analysis (SOUHEL, 1996) carried out in different sections of the northern part of the study

area, using sequence stratigraphy concepts, provided an interpretation of the early to middle Liassic

sediments. At a third order scale (sensu Vail et al ., 1987), eight sequences (SI to S8, Fig. 2) have been

described within the Sinemurian pro pcirte to Pliensbachian interval.

The different systems tracts which compose the middle Liassic sequences are well represented only

on the platform wedge (Tamadout section. Fig. 3) where thick submarine, well dated sediments have

been accumulated. The ammonite associations let us to recognise the corresponding systems tracts in the

Source . MNHN, Paris

LIASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO )

[~7~T) 1 EH33 (F^)4 R~^5 CC6 ^^7 S' 8

'^ 9S 5> X 11 —'—12 T T ’ ' 13 O 1114 99 C 15 ^16 17 >^18 ^19 ~20

S D 21 22 23 \/ 24

Fig 3_Described sections of the lower-middle Liassic formations in the northern part of the Central High Atlas (for location

of the selected sections, see Fig. I). 1. reef limestones; 2. shallow marine sandstones; 3. silts and clays: 4. oolitic

limestones; 5, Hint limestones; 6. marls involving reworked reef limestones; 7. interbedded hemipelagic mar s and

limestones; 8. interbedded peritidal marls and dolostones: 9. carbonate turbidites: 10. brecciated intertidal channels; 11,

brecciated coastal to continental channels: 12. exokarstic unconformity; 13. marine unconformity; 14, ammonite

horizon; 15. benthic foraminifera biozone; 16. brachiopods; 17. large bivalves; 18. corals; 19 tipis; 20. algal

laminations; 21. third order sequence; 22, lowstand systems tract: 23. transgressive systems tract; 24. highstand systems

tract: LPS: boundary between platform and trough; AAA: North Atlasic accident.

FlG. 3.- Coupes des formations du Lias inferieur et moyen decrites dans la partie septenmonale du Haul Atlas central (les

coupes decrites sent indiquees sur la figure 11 1, calcaires recifaux : 2. gres littoraux ; 3. silts et argiles ;4. calcaires

oolithiques ; 5, calcaires a silex ; 6. marries englobant des blocs de calcaires recifaux ; 7 alternances de marries et

calcaires hemipelagic,ues ; S. alternance de marries et de dolornies pent,dales; 9 calciturb,elites ; 10. breches

intertidales chenalisees : 11. breches cotieres ou continentales chenahsees ; 12 discontinuity exokarstique . 13

discontinuity sous-marine ; 14. horizon a ammonites : 15, biozone a forarnin, feres benthic,ues ;16. brachiopodes ; 17.

grands bivalves ; IS. reefs ; 19. tipis ; 20. laminations algaires ; 21. sequence de troisieme ordre ; 22. cortege debas

niveau marirt : 23. cortege transgressif; 24, cortege de haul niveau marin ; LPS : hmite Plate-forme - sdlon ; AAA :

Accident Nord-Atlasique.

Source: MNHN. Paris

ABDELLAT1F SOUHEL ETAL.

BARDA

JBEL

AZOURKI

lAA'Al

TIZI

N'TARGHIST

RBAT

►—<

= 35

Fig. 4.— Described sections of the lower-middle Liassic formations in the central part of the Central High Atlas (for location of

the sections, see Fig. 1). Legend, see Fig. 3.

Fig. 4— Coupes des formations du Lias inferieur et moyen dec rites dans la partie cent rale du Haut Atlas Central (les coupes

decrites sont indiquees sur la figure /). Meme legende que sur la figure 3.

Source. MNHN, Paris

CARIXIAN

LIASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

thin bedded and condensed sections of the central part of the trough (Jbel Taguendouft section. Fig. 3).

In the last area, the only observed unconformities involving condensed ammonite faunas (HI3 to HI8)

correspond to the main flooding surfaces (sensa Vail et al ., 1987).

On the platform, where nearshore, peritidal-type sedimentation occurred (Jbel Rat and Aganane

Formations, Adoumaz section, Fig. 3), only the highstand systems tracts have been clearly

distinguished. They correspond to carbonate series involving inter to supratidal facies made up of

dolomites and clays. The lowstand systems tracts are absent or represented by supratidal dolostones

associated with argilaceous palaeosoils indicating episodic emersion periods. The transgressive systems

tracts are characterised by the development of peritidal. thickening upwards cycles, progressively

dominated by subtidal environments related to the increase of the accommodation rate.

These sequences are organised into two second order cycles (sensu Vail et al ., 1991; JACQUIN et al .,

1992; GRACIANSKY et a !., 1993). The drowning unconformities are located (Fig. 2) in the late

Sinemurian (Obtusum zone, HI) and the Carixian-Domerian (Davoei-Margaritatus boundary, HI 1-HI2)

transition interval. The tectonically enhanced unconformities develop at the top of the early Carixian

(base of Ibex zone, H5-H6) and in the late Domerian (Spinatum zone, H17'-H 18‘).

PALAEOGEOGRAPHY

PALAEOSTRUCTURAL SETTING

Different palaeogeographic areas can be distinguished through facies and thickness changes within

the formations described above. During the early-middle Liassic period, the best characterised sectors

correspond to the Beni-Mellal platform, the Tilougguit trough, the Amezrai basin and the Ait

Bougemmez platform (Fig. 1).

From north to south, the structural elements controlling this palaeogeographic zonation are:

— the boundary between the Beni-Mellal platform and the Tilougguit trough which corresponds to a

complex flexure zone (“Limite entre Plate-forme et Sillon” = LPS. Fig. 1) involving two main elements,

oriented N10 and N45 in the Beni-Mellal Atlas (Chafiki. 1994). Its eastward prolongation corresponds

to the northern boundary of the High Atlas central part. The normal faulting along the LPS provided

important debris-apron southeast dipping slopes (CHAFIKI & SOUHEL. 1993; CHAFIKI. 1994) on the

Beni-Mellal platform edge;

— the Azilal-Anergui Fault Zone (AAA, Fig. 1) which corresponds to the southern boundary of the

Tilougguit trough. Oriented N 70, it stretches continuously along 150 kms. Its Liassic activity induces

local Toarcian wedges on the Pliensbachian slope deposits of the SW boundary of the trough (JOSSEN,

1988). In the other areas, the overlapping Middle Jurassic cover forbides field observations;

— the North Atlasic Fault (ANA, Fig. 1) which separates the Amezrai area from the Ait Bougemmez

platform. Located within the large N 70 North Atlasic Fault Zone of ROCH (1939, 1950) it stretches

along the northern side of the highest (more than 3000 m) atlasic mountains and corresponds to the

eastern prolongation of the Tizi-N-Test fault zone. In the study area, the ANA has been generally

considered as a normal fault dipping northward during the middle Liassic (BURGESS & LEE, 1978;

Laville, 1981). Our observations indicate several inverted polarities (thickness and facies) within the

Liassic sedimentary record, related to transverse faulting (works in progress).

Source:

JBEL CHOUCHT Fm.

ABDELLATIF SOUHEL ETAL.

Source: MNHN, Paris

AMEZRAI Fm

LIASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

Geodynamic evolution stages

The different stages ot the palaeogeographic evolution are defined using the above presented second

order cycles (Fig. 2) and complementary data collected in the Moroccan Atlasic realm (Du Dresnay,

1979; FEDAN, 1989; BOUTAKIOUT & ELMI, 1996) and compared with the NE Moroccan and NW

Algerian areas (ELMI, 1996). These cycles are considered (VAIL et al ., 1991; JACQUIN et al ., 1992;

GRACIANSKY et al.. 1993) as tectonic and eustalic units providing the best data for basin analysis. They

are from 3 to 50 Ma long and involve a transgressive stage followed by a regressive one. The first stage

corresponds to a subsiding and deepening period at a regional scale whereas the second indicates a

slackening of subsidence and/or a tectonic rise.

Maps of the figure 6 show the palaeogeographic history of the western part of the Central High Atlas

at the end of every transgressive or regressive steps within these second order cycles. They involve data

from the different authors (ROLLEY, 1973; MONBARON, 1985; JENNY. 1985; Le Marrec, 1985;

JOSSEN, 1988) of the Geological maps at scale 1/100 000.

The earliest Liassic (Hettangian?-early Sinemurian. Fig. 6A) is characterised by wide dolomite and

evaporite sabkhas indicating flat topography under shallow water conditions. The facies organisation

testifies coastal environments involving terrigenous influence. Tectonic activity is very low or absent.

The synsedimentary megabreccias of the Tighanimine Formation developed in the centre of the basin or

in its southern edge (Telouet basin of JOSSEN, 1988) indicate an early subsiding step on the southern

margin of the High Atlasic trough.

The late Sinemurian (Fig. 6B) corresponds to the first really open marine environments. The

carbonate formations reach the limits of the Atlasic area. They indicate a huge NE slowly dipping

platform which involves outlying intertidal (innershelf) sediments interfingering with subtidal

(outershelf) deposits in the centre of the basin. Two subsident basins characterised by euxinic supplies

can be observed: the southern one, created during the earliest Liassic period, persists in the Telouet area;

the northern one is newly individualised in the Tilougguit vicinity.

Low tectonic activity leads to a progressive deepening of the sedimentary basin, except in the last

central zone where faulting along the LPS and the AAA induces the creation of the Tilougguit trough .

The latest Sinemurian-early Carixian (lowermost Pliensbachian. Fig. 6C) times show a marine

regression all over the Central High Atlas, specially in the bordering zones (Du DRESNAY. 1979;

JOSSEN, 1987). In the Azilal (JENNY, 1988) and Zawiat Ahan?al (Tizi-N-Targhist section. Fig. 4) areas

the sedimentary gap reaches the Domerian (late Pliensbachian) interval.

In the late Sinemurian, the facies organisation shows two main environment types:

— intertidal to supratidal sediments with “tipi-like" structures (Jbel Rat Formation. Aganane section.

Fig. 3) located on the subtidal carbonate platform of the preceeding stage:

— circalittoral carbonate deposits (H3 and H4 horizons of the Jbel Taguendouft Formation, Jbel

Taguendouft section. Fig. 3), characterised by a high sedimentation rate and situated in the Tilougguit

trough area.

Fig. 5.— Middle-upper Liassic sedimentation in the Central High Atlas. A. The Amezrai (upper Domerian-lower Toarcian)

Formation in the Amezrai area (Fig. I). The calciturbidites (right), sandstones and marls involve reworked blocks and

slices (center) of the underlying Jbel choucht limestones. B. The Domerian (upper Pliensbachian) unconformity in the

Jbel Azourki area, (section 5, Fig. 1 and Fig. 4). The massive limestones of the Jbel Choucht Formation (left) have been

eroded then unconformably covered by slope breccias and calciturbidites (right), representing the Amezrai Formation.

Fig. 5 .— Sedimentation du Lias moyen-superieur dans le Haul Atlas Central. A. La formation Amezrai (Domerien superieur-

Toarcien inferieur) dans la region-type (Fig. I). Les calciturbidites (a droite), les gres et les monies presentent des

blocs et des lambeaux remanies (an centre) appurtenant aux calcaires sous-jacents du Jbel Choucht. B. La

discontinuite domerienne (Pliensbachien superieur) dans le secteur du Jbel Azourki (coupe 5. Fig. / et Fig. 4). Les

calcaires massifs de la formation du Jbel Choucht (a gauche) out ere erodes puis reconverts en discordance par des

breches de pente et des calciturbidites (a droite). appurtenant a la formation Amezrai.

Source:

A B DELL ATI F SOU H EL ETAL.

tz^e d. a. □» &

X 11 > ^"12 ^^13 ^14 C==>15 ^16 ^17 \)8 N \19

FlG 6 .- Palaeogeographic sketch maps (A lo E) of ihe Central High Atlas during the lower-middle Uassic period 1

continental area; 2. supra- to intertidal area; 3, inter- to subtidal area: 4 .subtidal area; 5. reef 1 ^13 deltas !

7 , limestones; 8 . marls; 9 . silts and clays; 10 . breccias; 11 . tipis; 12 . carbonate turbidites and slumped blocks, U, deltas,

14. thickening deposits; 15. distension; 16. subsidence; 17. uplift; 18. fault zone; \). supposed fault.

Fig. 6ernes paleogeographiques (A a E) du Hem, Adas Central an cours du Lias inferieur e, moyen. l. milieu continental;

2. zone supra a intertidale : 3. zone in,er- d subtidale ; 4. zone subtidale : S.calcatres recijaux : 6-dolomes 7

calcaires ; 8, marnes : 9. sills e, argiles : 10. britches ; 11. tipis ; 12. calcicrb,dues etblocs glisses . 13 deltas . 14.

epaisseurs croissantes ; 15. distension ; 16. subsidence ; 17, zones hautes ; 18, zone faillee . 19. faille supposee.

Source: MNHN, Paris

LIASS1C CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

Fig. 6B

Source: MNHN, Paris

ABDELLATIF SOUHEL ETAL

6°

Source: MNHN, Paris

LIASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

The transition between the two environments, observed in the Tamadout vicinity (Tamadout section.

Fig. 3), is represented by debris apron deposits indicating a newly individualised submarine slope zone

(CHAFIKI & SOUHEL, 1993). These sedimentary changes are related to the break down of the lower

Liassic platform along the active LPS fault zone.

The same palaeogeographic features are preserved during the early Carixian (lowermost

Pliensbachian). Temporarily emerged tidal flats with palaeosoils and karst surfaces on the northern side

of the High Atlas and tipi-dolostones on the southern one develop on the late Sinemurian subtidal

platform. The first Liassic large bivalve communities cover the main active fault zones.

During the middle Carixian-early Domerian (middle Pliensbachian) interval (Fig. 6D), marine

sediments can be newly observed all over the western part of the High Atlasic basin. The maximum

opening conditions are registered towards the Carixian-Domerian boundary, when the thin bedded marls

and limestones of the Tilougguit trough interfinger with the carbonate lurbidites of the SE edge of the

Beni-Mellal platform and the lateral subsiding lagoons.

On the southern edge of the High Atlas, the persisting Telouet basin shows shallow marine

conditions (Aganane Formation) to the west and open sea sedimentation to the east (JOSSEN, 1988;

MILHI, 1992).

Towards the late (not latest) Domerian (Fig. 6E), the regional palaeogeographic setting changes (Fig.

7). The important tectonic rise of the central Tilougguit and neighbouring zones (SOUHEL et al. 9 1995;

SOUHEL, 1996) induces:

— the emersion of part of the carbonate platform leading to the development of palaeosoils, exokarst

surfaces and lignitous deposits along the active fault zones (Demnat fault of Jenny. 1983);

— the carbonate and terrigenous infilling of the Tilougguit trough which involves different turbiditic

basins (Tamadout section. Fig. 3) separated by isolated highs showing condensed sedimentation (Jbel

Taguendouft, Fig. 3).

In the Atlasic axis, the increasing tectonic activity along the AAA leads to the deepening of the

central shallow marine Amezrai' platform newly converted into a turbiditic basin.

CONCLUSION

New stratigraphic and sedimentologic data allow us to separate five main stages within the

palaeogeographic evolution of the Central High Atlas during the early-middle Liassic period. The

lowermost Liassic sabkha conditions (stage I) are followed by the Sinemurian extended outer carbonate

platforms (stage 2), the earliest Pliensbachian regressive and diversified trough and platform

environments (stage 3), the middle Pliensbachian newly transgressive and rather homogeneous

sedimentation (stage 4) and finally the late Pliensbachian regressive period (stage 5).

The Liassic transgression sediments are generally deposited under low tectonic conditions, with a

largest extension and a strongest depth for the Sinemurian interval. The regressive steps correspond to

normal faulting periods inducing breakdown of the platforms, block tilting and creation of new

subsiding basins where central deep marine sediments interfinger with bordering tidal flats.

During the considered Liassic period, the sedimentary organisation and geometries indicate a NW-

SE sinistral transtensive setting (Fig. 7) involving NE-SW normal faulting and N70 inverted polarities.

This interpretation fits well with the oblique opening model proposed by EL KOCHRI et al. (1997) for the

genesis and evolution of the Central High Atlas Jurassic basins.

Extension processes seem to migrate (SOUHEL, 1996) from the south (Sinemurian in the southern

side of the Central High Atlas) to the north (Middle Jurassic in the Middle Atlas).

Source:

ABDELLATIFSOUHEL ETAL.

P LIENS BA CHI A N

(Lower Domerian)

Beni x

MelJ^I

—-

N Beni-Mellal Tilougguit Amezrat Ait Bouguemmez S

Platform Trough Platform Platform

Source: MNHN, Paris

LiASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

LATE PLIENSBACHIAN

LOWERMOST TO AROIAN

32 ‘

Beni ,

Mellals

>X ''

z Vx'V\

X XX/ X x

v x>x

40 km

Fig. 6E

Source: MNHN, Paris

A B DELL ATI F SOU H EL ETAL.

Source: MNHN , Paris

LIASSIC CARBONATE PLATFORM IN CENTRAL HIGH ATLAS (MOROCCO)

ACKNOWLEDGEMENTS

,hi<™LTf k iS f 3 con,, i ibution t0 Peri-Tethys Program. The authors would like to thank the leaders of

this project for financial support. S. CRASQUIN-SOLEAU, B. Bud-Duval and S. ELMI who improved the

first version of the text are also gratefully acknowledged.

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unconformity related to the regional nw-se upper Domerian sinistral transtension stage separates the subvertical

Hettang i an-Pliensbachian limestones (foreground on the right) from the fan-shaped SE dipping uppermost

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the snowy Jbel Azourki (3677 m. background on the left). B. The Assemsouk turbiditic basin. This basin created by

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surface de discordance liee a la transtension regionale senestre NW-SE separe les calcaires couvrant Fintervalle

Hettangien-Pliensbachien (premier plan a droite) des silts, gres et calcaires allant du Pliensbachien terminal an

Bajocien, disposes en eventail ouvert an SE (premier plan a gauche). Le paysage englobe les reliefs enneiges du Jbel

Azourki (3677 m, arriere plan a gauche). B. Le bassin turbiditique dAssemsouk. Ce bassin, cree par transtension

senestre NW-SE le long de la Faille Nord-Atlasique (ana. Fig. I), est empli de calciturbidites proximales du

Pliensbachien terminal en provenance de la plate-forme meridionale exhaussee de I'A'it Bouguemmez (d droite).

56 ABDELLATIF SOUHEL ETAL.

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Source: MNHN, Paris

The Jurassic events and their sedimentary and

stratigraphic records on the Southern Tethyan

margin in Central Tunisia

Mohamed Sou SSIRaymond ENAY' 2 ',

Charles MANGOLD ,2 '& Moncef TURKI "

Departement de Geologie, Faculte des Sciences de Sfax. B.P. 3038 Stax. Tunisie

;i Universite Claude-Bemard-Lyon 1. UFR des Sciences de la Terre

27-43. boulevard du 11 novembre 1918, F-69622 Villeurbanne Cedex. France

IJI Departement de Geologie, Faculty des Sciences de Tunis. B.P. 1060. Tunis. Tunisie

ABSTRACT

rhe Jurassic sedimentary record of Central Tunisia comprises shallow marine peritidal carbonates, black shales outer shell'

marls and limestones, ironstone, deep marine condensed sections and hard-grounds. The faunas, especially ammonites allow

increasingly precise age estimations and correlations referred to the biochronological standard for Submediterranean Europe.

I he faunas show a submediterranean character in open marine environments and the South Tethyan situation is attested by

abundant Emileia and Oramceras in lower Dogger as well as the lack of boreal and sub-boreal families all along Jurassic. In

fact, the Jurassic of Central Tunisia corresponds to five major transgressive-regressive tectono-eustatic second order cycles,

tour of which are separated by three sub-marine unconformities associated with Important hiatuses. The abrupt facies changes

and the frequency of condensed sections and/or hiatuses resulted from the interaction between global sea level fluctuations and

local to regional tectonic activities associated with Early Mesozoic Tethyan rifting. Central Tunisia (North-South Axis)

corresponded during the Jurassic to an uplifted mega-block acting as a carbonate outer shelf relayed to the north and to the

south by subsident basins. Due to the intense activities of deep marine currents, occurring especially during the major rises or

falls of sea level, this carbonate outer shelf has acted as a sediment-starved high. This latter has been maintained far from coarse

or abundant clastic influences. Sedimentation has been recorded only during aggradational-retrogradational highstand phases.

RESUME

Les evenements jurassiques et leurs enregistrements sedimentaires et stratigraphiques sur la marge Sud-

Tethysienne en Tunisie Centrale.

L'enregistrement sedimentaire du Jurassique de Tunisie centrale englobe des carbonates de plate-forme tres peu profonde,

des “black shales”, des marno-calcaires de plate-forme externe. des oolithes ferrugineuses. des series condensees et de

nombreuscs surfaces durcies. La faune d'ammonites a permis d'une part, de dater avec precision les corps sedimentaires et

Soussi. M., Enay, R., Mangold, C. & Turki, M., 2000.— The Jurassic events and their sedimentary and stratigraphic

records on the Southern Tethyan margin in Central Tunisia. In : S. Crasqijin-Soleal & E. Barrier (eds). Pcri-Tethys Memoir

5: new data on Peri-Tethyan sedimentary basins. Mem. Mus. natn. Hist. Nat.. 182 : 57-92. Paris ISBN : 2-85653-524-0.

Source: MNHN . Paris

MOHAMED SOUSSI ETAL.

d'autre part, d’etablir des correlations avec Fechellc biochronologique standard de FEurope submediteraneenne. La faune

montre un caracterc submeditcraneen d’environnements marins profonds et sa situation sud-Tethysienne est attestec par

I'abondance des Emile a eiOraniccras ainsi que Fabscnce des families boreales et sub-boreales tout le long du Jurassique. Le

Jurassique de Tunisie Centrale correspond a cinq cycles transgressifs-regressifs majeurs de deuxieme ordre d origine tectono-

eustatique Ouatre cycles sont separes par des discontinuity sous-marines majeures accompagnees de lacunes strati graph lques

importantes. Les changements abrupts des facies et la frequence des condensations et/ou des hiatus resultent de I interaction des

effets conioints des lluctuations eustatiques et de Factivite tectonique locale associee au rifting mesozoique de la lethys. bn

Tunisie Centrale. la region de FAxe Nord-Sud correspondait au Jurassique a un megabloc sous-mann Sieve tonctionnant

comme une plate-forme carbonatee. relaye au nord et au sud par des bassins subsidents. A cause de I intense activite des

courants profonds lors des elevations rapides ou des abaissements du niveau marin relatit. ce domaine immerge a lonctionne

comme une “plate-forme affamee” qui est restee durant de longues periodes a Fecart de loute influence detritique temgene. La

sedimentation etait active essentiellement pendant les phases transgressives et les periodes de haul niveau marin.

INTRODUCTION

In Tunisia, the Jurassic series crop out within the Saharan Platform (Jeffara area), along the so-called

North-South Axis (NOSA) and its northern extension the “Tunisian Dorsale”, and locally within the

Atlasic and Tellian zones (Fig. IB). Their subsurface analogues have been encountered in numerous

wells in Southern and Central Tunisia.

Jurassic rocks of Southern Tunisia consist of mixed evaporite, carbonate and siliciclastic sediments

corresponding to various depositional environments including sabkha and subaqueous evaporite basin,

tidal flats, shallow and open marine carbonate platform (BUSSON, 1967; KAMOUN, 1988; BF.N ISMAIL &

M'RABF.T, 1990; BEN ISMAIL, 1991; BOUAZIZ, 1995). In Central Tunisia, the Jurassic deposits are

essentially carbonates and partly shales. The lower part of the Lower Jurassic rocks are composed of

peritidal shallow marine platform carbonates, while the Middle and Upper Jurassic deposits are formed

of hemipelagic marls and limestones and external platform carbonates (BONNEFOUS, 1972; SOUSSI,

1990) . The latter include several discontinuities associated with stratigraphic gaps (SOUSSI, ENAY et al.,

1991) . In Northern Tunisia, the Jurassic rocks are also composed of shallow marine carbonates

succeeded by Middle-Upper Jurassic hemipelagic and pelagic facies; they comprise, in addition,

calciturbidites, radiolarites and local bioherms (CASTANY, 1955; BONNEFOUS. 1972; RAKUS & BlELY

1970; ALOUANI et a /., 1990; ALOUAN1, 1991; SOUSSI et al., 1992; SOUSSI et a /., 1994; SOUSSI. TURK! et

al., 1996; SOUSSI et al., 1998).

This northward variation from shallow to deep marine facies is related to the Late Palaeozoic-Early

Mesozoic rifting and drifting of the northern margin of the African Plate (M'RABET et al., 1989;

ALOUANI, 1991 TpeYBERNES, 1992; BOUAZIZ. 1995; BEN ISMAIL. 1991).

The reconstruction of the several palaeogeographic parts of this passive margin requires accurate and

homogeneous sedimentologic. tectonic and biochronologic data.

The main objective of the present paper is to analyse the palaeogeographic framework of the Jurassic

of Central Tunisia during the rifting of the Tethys. For this, we will refine the stratigraphic control using

ammonites, and re-examine in detail the facies distribution and the corresponding depositional

environments as well as their controlling factors.

A particular interest is reserved to the relationship between the facies record in space and time, the

morpho-structural framework, and sea level changes.

The tectono-stratigraphic framework and its sedimentary record, which are emphasised by the

presence of numerous condensed sections and hiatuses, will be correlated to the Jurassic of both

Northern and Southern Tunisia, then it will be compared to the sea level history curves proposed by

VAIL et al. (1987), HAQ et al. (1987) and HALLAM (1988). This comparison will offer the opportunity to

appreciate once again the effects of the tectonic and eustatic control on sedimentation. Within Central

Tunisia and especially on the NOSA. which acted as a starved platform, sedimentation has been recorded

particularly during aggradational-retrogradational highstand phases. Hiatuses characterise the highest

part of the tilted blocks where current activities were at a maximum during the rapid sea level rises or

falls. The frequency of the discontinuities and hiatuses is due to the combined effects of the local

tectonic factors and the global eustatic ones. Tectonic activities linked to the Tethyan rifting created a

Source: MNHN. Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

pattern of tilted blocks involving palaeohighs. These latter have been isolated from the sedimentary

supplies, notably during either the maximum regressive periods when sedimentation displaced towards

the basin or during transgressive phase when the shoreline displaced onto continental margin.

GEOLOGICAL SETTING

The Jurassic senes of Central Tunisia crop out along the so-called North-South Axis (NOSA)

stretching between Jebel Rheouis in the south and Jebel el Haouareb in the north (Fig I C) This area is

considered as a boundary between the Central Atlas fold belt to the west and the Pelagian Sea block to

the east This NOSA constitutes a singular component of the Tunisian geology. It has acted as a relative

high and unstable palaeogeographic domain, notably during the Mesozoic (BUROLLET 1956- M'Rabet

1975; Abbes, 1983; OUALl, 1984; SOUSSI, 1990).

Along this domain, bounded by a sub-meridian fault system, the Jurassic series are generally in

tectonic contact with Tnassic and even Cretaceous series. The normal Upper Triassic-Lower Jurassic

stratigraphic transition is locally preserved (e.g., Ain el Morra, Chaabet el Attaris and Loridga sections;

Soussi, Abbes etai, 1996; Soussi, Abbes & Belayouni, 1998).

FACIES ANALYSIS

Fodowing the first investigations (DUMON, 1936; SCHOELLER, 1937; CASTANY, 1951). BUROLLET

(19.16) defined the Jurassic Nara Formation with three terms: a lower dolomitic term a middle

argillaceous term and an upper dolomitic term.

The present sedimentologic study has led to distinguish within the Nara Formation, at least, six major

lithologic units, that could each have the rank ot formation. These major units have a regional extent and

may be easily distinguished in the field and sub-surface on the basis of their faunal and facies

characteristics. Furthermore, they are separated by three major unconformities. The different lithologic

units will be analysed using eight measured sections, from south to north, in Jebel Rheouis. Krecheni'el

Kelb, Chaabet el Attaris, Kef el Hassine, Kef el Khouadja, Guefaiet, Loridga and Jebel el Haouareb

(Fig. 1C).

The TYPE SUCCESSION OF Rheouis-Loridga area

The three terms of the Nara Formation can be observed from Jebel Rheouis to Jebel Loridga. They

have been subdivided in six lithological units (Fig. 2).

— U1: first unit. The lower Nara A peritidal dolomites.

These deposits are generally in tectonic contact with the Triassic evaporites of the Rheouis

Formation (BUROLLET, 1956). The transition from the Upper Triassic to the lower par of the Lower

Jurassic is well exposed at Ain el Morra. Jebel Chaabet el Attaris and Loridga sections (Kamoun et al..

1994; SOUSSI, Abbes et al., 1996). Its lower part is dated Rhaetian at Jebel Gamgouma-Loridga

(KAMOUN et al ., 1994), while the rest which forms the major part of the lower Nara is attributed to the

Hettangian-Sinemurian (BONNEFOUS, 1972).

This unit (up to 195 m thick) is composed of massive dolomitic beds forming decimetric to metric

shallowing-upwards parasequences characterised by the constancy of their sedimentary and diagenetic

characteristics in Central Tunisia. The typical parasequence is composed of a basal dolomitic breccia

(0.05 to 0.30 m) formed of angular dolomitic lithoclasts, pelletoids and algal debris. Locally, this term

contains asymmetric ooids and pisoids encrusted by algae and it was early lithified. The middle term is

generally thicker (0.70 m) and composed of homogeneous and bioturbated dolomite. The third term is

MOHAMED SOUSSI ETAL.

Fig. 1.— Location of the study; A, location map of the studied area. B. the main Jurassic outcrops in Tunisia; C. location of the

studied sections along the North-South Axis (NOSA) in Central Tunisia.

FlG.l .— Localisation de Velude ; A, localisation de la zone etudiee ; B. principaux affleurements jurassiques de Tunisie ; C,

localisation des coupes etudiees le long de I'Axe Nord-Sud (NOSA) en Tunisie Cent rale.

Source: MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

’EH] £Z3 ^ V 'E3

“EE3 15 CZ] ’OD ’US ’*S » Gl. | ^ W« [

•G3 ,0 S "S "CZi

Fig. 2.— The Jurassic lithologic synthetic succession of the nosa (Central Tunisia) and their deposilional environments. 1

gypsum; 2 peritidal dolomites; 3. compacted open marine carbonates; 4. limestone partly dolomitised, 5. shales ; 6

I am in lies; 7, ferruginous ooids; 8. pelagic muddy limestones; 9. calcareous ooids; 10. cherty carbonates; 11.

stromatolite and birds-eyes; 12. sheet cracks; 13, borings; 14. unconformity; 15. gastropods; 16. benthic foraminifera*

17, pelycepods; 18 , brachiopods; 19. glauconitic grains; 20. fish bones; 21. belemnites; 22 . Zoophxcos ; 23. ammonites-’

24. 1 )laments; 25. Saccocdma; 26. radiolaria.

F,a 2 '~ Succession lithologUjue synthetique et environnement de depot des series jurassiques le long de I'A.xe Nord-Sud

(Tumsie centrale). 1. gypse ; 2, dolomies peritidales : 3, carbonates compactes de milieu marin ouvert; 4, calcaires

partiellement dolomitises, 5, argiles ; 6. laminites ; 7, oolithes ferrugineuses ; 8, calcaires "mudstones" pelagiques : 9

oolithes calcaires ; 10, carbonates a silex; II, stromatolites et "birds-eyes " ; 12, femes de dessiccation ; 13,

perforations ; 14, discordance ; 15. gasteropodes ; 16, foraminif eres benthiques ; 17, pelecypodes ; 18, brachiopodes ;

19, grains de glauconite ; 20. squelettes de poissons ; 21. belemnites : 22, Zoophycos ; 23. ammonites ; 24. filaments •

25. Saceocoma ; 26. radiolaires.

Source ; MNHN. Paris

MOHAMED SOUSSI ETAL.

rich in algal stromatolitic laminations, tepees, birds-eyes, mud and sheet cracks partly filled with

dolomicritic internal sediment and/or dolomite cement. Locally, this term exhibits evaporitic

micronodules which are dissolved and cemented by white dolosparite. The top of the last term of the

parasequence is marked by residual green argilites locally containing black pebbles. The thickness ol

these peritidal parasequences varies from 0.4 to 2 m while their lateral extension is a few hundred

meters.

— U2: second unit. The lower Nara B bioclastic dolomites.

This unit (up to 5 m thick) constitutes the upper part of the lower Nara and is Carixian in age

(SOUSSI. ENAY et a!., 1991). It is composed of well-bedded decimetric dolomitic beds, usually

recrystailised and rich in benthic fauna (pelecypods, gastropods, textularids, ahermatypic corals and

echinoderm debris). The uppermost beds which are particularly rich in ammonites and belemnites at

Jebel Kef el Hassine correspond to condensed deposits. In Chaabet el Attaris. these dolomites are black,

compact and particularly rich in pelecypods and gastropods. In Jebel Loridga, they alternate with green

shales. In all analysed sections, the top of this unit, which exhibits borings, corresponds to a submarine

hard-ground (unconformity: UC1).

— U3: third unit. The middle Nara A "black shales".

This unit is composed of two distinct lithologic sub-units (U,, and U v2 ).

The lower sub-unit (U VI ) consists of black laminated marls and carbonates: "black shales" (5 to

10 m). This unit is early Toarcian in age. It consists of alternating laminated dolomitic limestone and

greenish to beige coloured marls in which the clay fraction is essentially composed of illite and traces of

kaolinite. The marl intervals are rich in brachiopods, pelecypods and ammonites, while the limestone

beds are marked by ammonites traces. Locally, at Jebel Chaabet el Attaris, these facies are dark grey to

black-coloured and rich in pyrite and organic matter. They correspond to true black shales in which the

total content of organic carbon is up to 12 % (SOUSSI et a!.. 1990; SAIDI et a!., 1992). Within the black

shales the carbonate beds have mudstone textures, often partly dolomitised. These carbonates are poor in

benthic fossils and rich in closely-spaced bituminous laminae, with carbonate or clay-organic rhythmic

sequences (millimetric in thickness). Early diagenitic pyrite fabrics, such as small cubes or micro-

framboidal aggregates have been observed.

The upper sub-unit (U, 2 ) consists of shales and white to beige nodular limestones. In contrast to U,,,

this sub-unit is relatively more argillaceous (with a clay fraction made essentially of kaolinite). The

carbonate intervals are particularly nodular and argillaceous. They are packstone in texture and contain

filaments, brachiopods, echinoderm debris, detrital quartz and abundant bioturbations. The thickness ol

this unit, well exposed in Krechem el Kelb (8 m), Chaabet el Attaris and Kef el Hassine, decreases

towards the north and is notably very reduced in the el Guefaiet area (4 m). This sub-unit terminates

with a submarine erosional surface, locally encrusted by ferruginous and phosphatic horizons

(unconformity: UC 2).

— U4: fourth unit. The middle Nara B ironstones and/or filaments and Zoophycos -rich carbonates

It is composed of four main sub-units (U 4 I - U 44 ). From bottom to top we distinguish:

The sub-unit 1 (U 4I ) consists of "ironstones" (0 to 1.6 m) rich in ferruginous ooids. It is generally

Bajocian in age. but locally (Jebel Loridga), it is Aalenian-Bajocian (SOUSSI, ENAY et al., 1991: SOUSSI,

M'RABET & ENAY, 1991). It extends up to the middle Bathonian mainly in the northern part of the

NOSA (Fig. 3). It is a few decimetres thick and formed of discontinuous lenses bodies well represented at

Krechem el Kelb (1 in). Kef el Hassine (0.90 m). Demet (0.7 m) and Loridga (1.8 m) (Figs 3 and 4).

In Jebel Chaabet el Attaris, the ooids are rare, reworked and disseminated in a microsparitic matrix.

The "ironstone" facies has been extensively described from the Jurassic of Europe (Van HOUTEN,

1985; Harder. 1989). In Central Tunisia, the facies consists of muddy-carbonate horizons, reddish or

bluish green in colour, very rich in phosphatic and ferruginous (goethite and hematite) pisoid- and ooid-

like grains and lithoclasts encrusted by ferruginous algal laminations. The ooids and pisoids exist in

Source. MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

clayey or dolosparite matrix. They are 0.3 to 3 mm in size, spherical to elliptical and have a cortex

composed of concentric layers enveloping a nucleus often represented by quartz grains. Some broken

bemhifan?nekmni c ’fnnn l ! at£ f f enerallon <>1 ooids These iron-rich grains are associated with both

benthic and nektomc fauna including gastropods, pelecypods, annelids, brachiopods, ammonites and

aig^emS' bedding. K ' eChem el Kelb and Lorid § a >- the y exhibit fming-upwards sequences and low

The sub-unit 2 (U 42 ) is composed ol filaments and Zoophycos -rich carbonates.

It is Bajoeian-early Bathoman in age, 7 to 13 m thick and formed of decimetric bedded limestones or

^ndTnmnnrm I ,n t ,n | g ^ lnlcr , ca ' atlons - Locally, at Krechem el Kelb. it is composed of reddish

“1, P f dolomites separated by thin clayey layers. The carbonates are mud-wackestone to

packstone in texture and contain ostracods. benthic foraminifers, filaments (probably thin pelagic-

pel ecy pod shells), gastropods, brachiopods, echinoderm debris, ammonites and belemnites P These

carbonates are particularly rich in bioturbations such as Zoophycos and Chondrites.

HoloInh^HmL!! ‘ h ' S SUb ' Uni ‘ is ': elative| y more developed (13 m) and composed of blue grey

ni l b T fT S Sh ° W , ing er0 " IVe , surfaces marked b y lhin siltstones particularly rich in belemnites

The thickness of this unit drastically decreases from the south to the north (Figs 3-4).

The sub-unit 3 (U 4 ,) consists of pyritised ammonite-rich shales.

carhonare hprk^‘irhIn’rvi'"' Const ' luted of shales , local| y intercalated with decimetric bioturbated

carbonate beds rich in Chondrites , Zoophycos and filaments. It is 1 to 3 m thick.

-.mm ( ? aab ri el ^ tta r 8, IS excIusive| y fo ™ed of green shales particularly rich in small pyritised

ammom es The clay fraction consists of illite and kaolinite: the latter being progressively more

abundant at the top. This sub-unit thins and disappears towards the north (Figs 3, 4 and 6).

The sub-unit 4 (U 4 J ) is formed of compacted carbonates.

K„aT hlS ,l Ub ‘ Uni i (3 ' S middl , e Balhonian in a §e and composed of compacted limestones or dolomitic

beds with very thin clay intercalations. These dolomitic beds are usually coarse-grained and reddish and

when preserved from dolomitisation, they are blue and particularly rich in filaments and brachiopods

I his sub-unit terminates with an erosional surface encrusted by thin phosphatic layers, associated with

teiruginous ootd-hke grams and ammonites (unconformity: UC3).

— U5: fifth unit. The upper Nara A carbonates.

The upper Nara term is subdivided into two distinct lithologic units (U5 and U6).

The basai one which is late Callovian-Oxfordian in age and up to 70 m thick, corresponds to the fifth

umt (U5). It is locally preserved from dolomitisation (Krechem el Kelb. Chaabet el Attaris Kef el

Hasstne and el Haouareb) and composed of decimetric bedded wack-packstone rich in ammonites

belemnites protoglobigerines. benthic foraminifers, ostracods. echinoid debris and abundant glauconitic

grains In the northern part of Krechem el Kelb. this unit starts with a limestone lens (0.30 m in thick

and 50 m in length) dated middle Callovian in age.

Ihese condensed beds (reduced thickness, diversified fauna, glauconitic grains) are overlain bv

mudstone-wackstone rich in planktonic microfauna (protoglobigerines). The^latter are overlain bv

packstone to grainstone limestone beds particularly rich in ooids.

— U6: sixth unit. The upper Nara B carbonates.

The major part of this unit (up to 130 m) is composed of decimetric dolosparitic beds, medium- to

coarse-grained and showing well-preserved radiolarian.

At Chaabet el Attaris, it starts with mud-wackestone containing echinoderm debris and pelagic

cnnoids ( Saccocoma ), calcispheres and rare ostracods.

MOHAMED SOUSSI ETAL.

Kef

e| Hassine

ChSabet

el Attaris

IKrechem

L_el Kelb_

Lorldga| [EL Haouarebj

el Khouaja

J UPPER

DOLOMITE

NARA

Middle

Toarclan

South

Rh6ouis|

~ T~

North

10 2||§ 6 HI 70 8^53 e 10- 11*

Fig. 3.— Stratigraphic correlation of the Middle Jurassic series of the measured sections along the North-South Axis (Central

Tunisia). 1. Upper Jurassic dolomites; 2. Oxfordian “ammonitico rosso” tacies; 3. lower Oxfordian muddy-hmestones;

4. upper Callovian lense (= Athleta bed); 5, middle Bathonian compacted carbonates; 6. lower Bathonian pyritised

ammonites-rich shales; 7. Bajocian-Iower Bathonian filaments and Zoophycos -rich limestones; 8. Bajocian-Bathonian

ironstones; 9. middle Toarcian hemi-pelagic marls and limestones; 10. unconformities; 11. after Gharbi (1989).

PlG. 3 .— Correlations straligraphiques des unites lithologiques du Jurassique moyen des coupes etudiees le long de I'Axe

Nord-Sud (Tunisie centrale). /. dolomies du Jurassique superieur; 2. facies "ammonitico rosso de l Oxfordien

inferieur; 3. calcaires pelagiques de I'Oxfordien inferieur; 4, lentille calcaire du Callovien superieur (banc a

Athleta); 5. carbonates compactes a filaments du Bathonien moyen : 6, argiles a ammonites pyrileuses du Bathomen

moyen ; 7. calcaires a Zoophycos et filaments du Bajocien-Bathonien inferieur ; 8. oolithes ferrugineuses du Bajocien-

Bathonien ; 9. marno-calcaires hemi-pelagiques du Toarcien moyen ; 10, discordances : II. d a pres Gharhi (1989).

THE LATERAL SECTION IN JEBEL EL HAOUARF.B AREA

In Jebel el Haouareb area, located 9 km to the north from Jebel Loridga. the outcropping Jurassic

sequence is thick and is very similar to that described within the Tunisian Dorsale (CASTANY, 1951;

BONNEFOUS, 1972; Gharbi.’ 1989). The Lower and Middle Jurassic are not exposed. Here, the section

starts with lower Callovian alternating marls and limestones particularly rich in filaments, calcispheres,

and foraminifers (spirillines and lenticulines).

The overlying succession is composed of mud-wackestone carbonates rich in calcispheres (7 m),

alternations of green shales and mud-wackestone carbonate beds (40 m), and the “ammonitico rosso’

facies, represented by nodular limestones, reddish- to greenish-coloured and rich in protoglobigerines,

calcispheres, belemnites and abundant ammonites indicating an early Oxfordian age.

Laterally to the north, the series continue with alternations of green shales and blue grey muddy-

limestones locally containing numerous calciturbidite beds. The carbonate horizons contain belemnites,

calcispheres, pelecypod echinoderm debris and pelagic crinoids ( Saccocoma).

The uppermost part of the section is dolomitised and conformably overlain by the Sidi Khalif shales,

the base of which is late Tithonian in age (BUSNARDO el al., 1976. 1980, 1985;M RABET, 1975, 1987).

Source: MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

BIOSTRATIGRAPHY AND BIOCHRONOLOGY (Figs 3 and 4)

Faunas, especially ammonites, provide the basis of the biochronological framework necessary to the

interpretation of the lithosequential analysis in a regional context. It allows the estimation of the

duration of the gaps in sedimentary discontinuities.

The biochronological reference framework is that used for Submediterranean Western Europe (in

Cariou & Hantz.PERGUE, 1997). Some of the data pointed here were obtained before, but only in

unpublished reports. This work incorporates the data briefly summarised in 1991 (SOUSSI 1990

SOUSSl. ENAY etui.. 1991, SOUSSI, M‘RABET&ENAY. 1991).

A recent work (PEYBERNES el at. , 1995) proposes for the same time span (Toarcian-Oxfordian) an

interpretation ot the depositional sequences and ammonite biochronozones of the NOSA, which

recognises most of our dating. Nevertheless, differences with our data appear and the resulting ages are

discussed below.

The identified fauna

Toarcian assemblages

They were not the subject of a systematic research except at the top with the aim to precise the age of

the base of the first unconformity (UC 1) and of the Middle Jurassic series above.

— The first fauna (FI), are Paltarpites sp. at Jebel el Guemgouma and Kef el Khouadja, Hildaites

sp. at Jebel Chaabet el Attaris from the lower Toarcian, already recognised by Rakus (1968,

unpublished) with Palraipites sp. too. According to PEYBERNES et al. (1995) Dcictylioceras sp. and

Paltarpites sp. at Jebel Chaabet el Attaris would indicate the Polymorphum Zone (earliest Toarcian).

— The presence of (he Falcifer (or Serpentinum) Zone of the late early Toarcian was established

(Rakus. 1968 unpublished) with Harpoceras cl. falcifer (Sow.). Hildaites sp. at Jebel Chaabet el

Attaris; also H. gr. serpentiniformis mentioned by PEYBERNES et al. (1995) indicates the same zone

(F2).

— The fauna ot the Bitrons Zone, Sublevisoni Subzone (F3) (middle Toarcian) is more constant and

often represented by the index species at Kef el Khouadja. Jebel Krechem el Kelb. We found Hildoceras

cf. sublevisoni Fucini at Kef el Hassine a few centimetres below the unconformity UC2 (middle Nara A,

U3. top of U,,) and the earliest Bajocian age deposits (middle Nara B. U4, base of U 4 ,).

— Furthermore, at Kef el Hassine, fauna from the late Toarcian, Variabilis or Thouarsense Zone

(F4), were reported by RAKUS (1968, unpublished). The phosphatised thin layer underlining the

unconformity has yielded Polyplectus sp. from the upper Toarcian too.

North of this locality, the Toarcian does not extend above the middle Toarcian.

Aalenian assemblages

Faunas of this stage and also of the upper Toarcian are everywhere nearly absent. They were

recognised only at Jebel Loridga where the lowest iron oolithic levels yielded Graphoceras (G.) sp. and

G. (G.) cf. limitation (Buckman) from the Concavum Zone (upper Aalenian) (F5).

Lower Bajocian Sonninia/Emileia and Stei>hanocer.as/Teloceras assemblages

Two profiles. Kef el Hassine and Jebel Krechem el Kelb. allow us to characterise the lower Bajocian

levels, which are undoubtedly present at other profiles according to the litho-sequential correlations, but

not yet attested and dated by faunas.

MOHAMED SOUSSI ET AL.

1 2

5 pm «[ZZ3 7 \m ® 9 -

Fig. 4.— Biochronology chart of

Jurassic ammonites of Central

Tunisia. 1. limestones; 2, shales; 3,

ironstones; 4. nodular limestones; 5,

proved hiatus;6, probable hiatus; 7,

ferruginous ooids-rich-limestone or

"ironstones"; 8, dolomites; 9.

unconformities.

Fig. 4 .— Charte biochronologique des

ammonites du Jurassique de Tunisie

Cent rale. 1 . calcaires ; 2, argiles ;

3, oolithes ferrugineuses ; 4, cal¬

caires nodulaires ; 5, lacune

stratigraphique prouvee ; 6. lacune

stratigraphique probable ; 7. cal¬

caires a oolithes ferrugineuses ; 8,

dolomites ; 9. discordances.

— The first Bajocian fauna (F6) identified at Kef el Hassine within the middle Nara B (U4, Base of

U 41 ) is dominated by frequent and large Emileia gr. polyschides (Waagen) associated with rare

Sonninia : 5. ( Euhoploceras) polyacantha (Waagen) and S. (E.) simplex Buckman. These species are

known from the Discites and Laeviuscula Zones. Throughout Europe (GABILLY et a! 1971; RlOULT et

a /., 1997), Emileia is rather common in the third zone (Propinquans Zone) of the lower Bajocian,

Source : MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

although already present in the Laeviuscula Zone. Sonninia , associated with the subgenus Euhoploceras

points to an early Bajocian age. This association would also indicate a condensed sequence during

P'.scites and Laeviuscula Zones. This is indicated by numerous phosphatised ooids and abundant

belemmtes both at the bottom and the top of the bed (= ammonites level).

- The next fauna with Stephanocercis and Teloceras (F7) is located at Jebel Krechem el Kelb in the

uppermost beds with ferruginous ooids (middle Nara B. U 4] ): Stephanoceras (S.) gr. humphriesianum

(Sow ), often of arge size (0.40 m) and Teloceras blagdeni (d’Orb. non Sow.). At Kef el Hassine. the

middle part ol the same beds with ferruginous ooids, here less thick, has yielded: Cenoceras so..

Cliondroceras ct. gervtllet (Sow.). C. cf. orbignyanum (Whright), Sphaeroceras gr. brongniarti (Sow )'

Dorsetensia (Nanmna) sp„ Normannites sp., Epalxites sp., Stephanoceras ( S .) cf tenuicostatum

Hochstetter.

Both associations belong to the Humphriesianum Zone. It is impossible to currently recognise the

!£ neS ™ e 1Z ° nS distinguished in Poitou (Gabii.ly e, a!.. 1971). in Subalpine ranges (PAVIA,

1 783). m NW Germany (MaSCKE. 1907) or in the Submediterranean province (RIOULT el al., 1997). At

Ket el Hassine, Dorsetensia and Cliondroceras would indicate that the basal Romani Subzone is better-

recorded.

Upper Bajocian Spiroceras assembiages

At Ket el Hassine, two levels in the filaments and Zoophycos-nch limestones (middle Nara B U,,)

have yielded: Cadomites sp and Spiroceras sp. from the lower bed. and one metre above: Spiroceras sp.

Zone n " rCOtl and ' s,ri goceras sp. (F8). The second association can be referred to the Niortense

Morphoceras and Oraniceras lower Bathonianassemblages

This is the best-characterised and the most widely represented fauna from Jebel Rheouis to Jebel

Londga. Its absence at Kef el Hassine probably results from bad outcrop condition. The marls with

pyntised ammonites are here covered by scree. At Jebel el Haouareb the beds below the early Callovian

do not crop out.

These taxa are present in several sub-units.

— The filaments and Zoophycos-nch limestones (Middle Nara, U 4 ,) have yielded Oraniceras

hamyanense Flamand at Jebel Krechem el Kelb and earlier Lobosphinctes sp., Planispliinctes of the

earliest Bathonian (Zigzag Zone, Parvum Subzone) at Jebel Chaabet el Attaris (F9).

— The marls with pyritised fossils (Middle Nara, U 43 ) have provided the richest associations (FI0):

at Jebel Rheouis, Phylloceras sp., Cadomites sp. juv., Procerites sp. juv., Morphoceras sp. cf. M.

macrescens (Buckman), Oxycerites cf. yeovilensis Roll., Ebrayiceras sp. (a calcareous mould perhaps

from the beds situated just above); at Jebel Krechem el Kelb. Procerites sp. juv., Parkinsonia sp. juv..

Morphoceras sp. juv. cf. jactation (Buckman), Ebrayiceras sulcatum (Hehl in Zieten), Asphinctites

replictus (Buckman), Polysphinctites polysphinctus Buckman, Oxycerites gr. yeovilensis Roll.,

Nannolytoceras tripartitum (Rasp.); at Chaabet el Attaris: Morphoceras sp. juv.’, M. aff. jactation

(Buckman). Cadomites sp., Oxycerites yeovilensis Roll. , O. seebachi Wetzel.

— The compacted carbonates overlying the marls with pyritised ammonites (middle Nara, U 44 ) still

contain the early Bathonian age fauna as at Krechem el Kelb: Oraniceras hamyanense Flamand,

Morphoceras egrediens Wetzel, Siemiradzkia sp. (F10). This is perhaps the bed yielding the calcareous

mould of Ebrayiceras found on the slope corresponding to the marls with pyritised fossils at Jebel

Rheouis (see the section UC2 unconformity).

— This fauna at Kef el Khouadja was collected from two calcareous beds with phosphatised nodules

and fossils below an iron ore identical with that of Oued Demet: Oraniceras hamyanense Flamand

(juv.), Morphoceras sp. (cf. M. macrescens Buckman), Ebrayiceras sulcatum (Hehl in Zieten),

Procerites sp. (F10).

Source

MOHAMED SOUSSI ETAL.

— The iron ores spreading out from Kef el Khouadja (without fauna) to the north are not very

fossiliferous: at Guefaiet, Asphinctires patrulii Hahn and Procerites gr. tmetolobus Buckman, at

Loridga, Oraniceras cf. hamyanense Flamand.

So, except at Jebel Chaabet el Attaris where ammonites from the filaments- and Zoophycos- rich

limestones point to the base of early Bathonian, Zigzag Zone. Parvum Subzone (F9), faunas are

homogeneous and nearly of the same age into the Zigzag Zone, Macrescens Subzone and Aurigera Zone

pars (F10). The genus Oraniceras is frequent in the Moroccan Middle Atlas and on both sides of the

Morocco-Algeria frontier where it is associated with European elements of these ages.

Middle Bathonian assemblages

They are less frequent than lower Bathonian faunas, but well represented at Jebel Krechem el Kelb

and Jebel Chaabet el Attaris (FI 1) in the uppermost beds of the compacted carbonates below the

unconformity (UC3). In the same position was discovered a single Bullatimorphites (B.) sp. juv.

— At Chaabet el Attaris, Hecticoceras (Prohecticoceras) sp., Cadomites (C.) cf. bremeri Tseret.

Bullatimorphites (Sphaeroptychins) marginatus (Ark.) and Siemiradzkia cf. pseudorjasanensis (Liss.)

bring precise the age as late middle Bathonian Bremeri Zone.

— At Jebel Krechem el Kelb, the lower calcareous bed with nodules and pyritised fossils includes

Cadomites (C.) orbignyi de Gross., the index species of the lower horizon of the Progracilis Zone.

While, it contains also a Bremeri Zone assemblage: Hecticoceras (Prohecticoceras) ochraceum Elmi. C.

(Cadomites) bremeri Tseret., Bullatimorphites (B.) sp.. Micromphalites sp., Choffatia (Subgrossouvria)

sp.

Above, the marly bed with phosphatised nodules has also yielded a Bremeri Zone fauna: Cenoceras

sp., Holcophylloceras sp. juv., Phylloceras plicatum Neum.. Hecticoceras (Prohecticoceras) ochraceum

Elmi, Oxycerites sp., C. (Cadomites) bremeri Tseret., B. (Bullatimorphites) gr. bullatimorphus

Buckman. B. (Sphaeroptychius) marginatus (Ark.), Choffatia (Subgrossouvria) sp., Procerites sp.

This assemblage also contains two forms known from the upper Bathonian, Retrocostatum Zone,

Blanazense Subzone: Hecticoceras (Prohecticoceras) cf. blanazense Elmi and H. (P.) crassum Elmi,

mixed together with the Bremeri Zone fauna.

— The only known elements of the early middle Bathonian (Progracilis Zone) were encountered at

Jebel Krechem el Kelb and Jebel Loridga, and those of the late Bathonian Retrocostatum Zone,

Blanazense Subzone at Krechem el Kelb. The Subcontractus and Morrisi middle Bathonian Zones and

the upper Bathonian Histricoides Subzone as well as the late Bathonian Discus Zone were not identified.

PEYBERNES et al. (1995, p. 596, Fig. 1) mentioned a Discus Zone fauna at Jebel el Haouareb below

the marls with pyritised fossils, which indicates us an assemblage of late early Callovian age. If this age

can be corroborated, it would be one of the rare late Bathonian age faunas known on the Southern

Tethyan margin.

Lower and middle Callovian assemblages

— The early Callovian is only present at Jebel el Haouareb, and elsewhere only the middle Callovian

fauna was recognised. At Jebel Krechem el Kelb, a discontinuous level at the bottom of the upper Nara

member has yielded: Putealiceras arkelli Zeiss, Lunuloceras romani (Lem.). L. gr. paulowi (de Tsyl.),

Sublunuloceras aff. nodosulcatum (Lah.), Lemoineiceras sp., Rehmannia (Loczyceras) cf. richei

(Flamand) from the middle Callovian Anceps Zone (FI3).

— Lower and middle Callovian are represented by rare and badly preserved fauna only at Jebel el

Haouareb. PEYBERNES et al. (1995) have attributed the first fauna with pyritised facies in the marls of

the lower part of the interval to *‘Bt 5 (= late Bathonian. Discus Zone and Subzone) or to Ca 0 ? (=

earliest Callovian, Macrocephalus Zone, Bullatus Subzone)'’. These ages are based on the presence of

Epistrenoceras sp. and Homoeoplanulites (H.) gr .furculus (Neum.) from the alternation overlying the

marls with pyritised fossils. In these alternations, we have collected Phylloceras sp., Holcophylloceras

sp.. Sowerbyceras sp. juv., Macrocephalites sp. juv., Dolikephalites gr. gracilis Spath, Jeanneticeras cf.

Source: MNHN , Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

meridionals Elmi, Choffatia sp. juv., Elatmites sp., Grossouvria sp. This fauna (FI2) belongs to the

Gracilis Zone (late early Callovian).

If the attribution of the underlying levels to “Bathonien terminal, Retrocostatum zone or Discus"

zone seems justified (see the section "Middle Bathonian assemblage"), the presence at this level of

Epistrenoceras is a problem. J I HIERRY, author of these determinations (oral communication) has given

thiee possibilities for this badly preserved fragment: Garantiana sp. (upper Bajocian), Epistrenoceras

sp. (upper Bathonian), Reineckeid (Callovien). The second one (accepted in PEYBERNES et at., 1995) is

invalidated by the pyntised ammonite fauna. In fact, all the specimens are of small size but in excellent

preservation and their generic determinations and age are beyond doubt.

The other lower Callovian fauna (Macrocephalitids ind. and Macrocephalites sp.) (F12) follow each

Cal^ovhn .iist^ 5 m m St h 0neS ■ tha, . has yidded at itS 1 o P : PorapatJeras sp. from lower to middle

Callovian. Just 2.5 m above. Orbignyiceras sp. is certainly of middle Callovian age (FI 3).

Uppf.r Callovian Collotia andPeltoceras assemblages

These faunas are widely distributed both in the upper part of the limestones with filaments at Jebel el

Haouareb and at the bottom of the upper member of the Nara Formation.

— At Jebel el Haouareb, the earliest bed of the alternations overlying the limestone bar has yielded-

Puteahceras sp. cf. P. rossiense (Teiss.), Collotia sp„ Subgrossouvria sp. (FI4) from the upper

Callovian Athleta Zone. The scarceness and the state of preservation of this fauna do not allow better

accuracy.

— At Chaabet el Attaris, a thin condensed ferruginous and nodular level (0.1 m), encrusting the

surface of the “compacted carbonates" (late middle Bathonian. Bremeri Zone) contains faunas from the

upper Callovian and Oxfordian. The lower, more calcareous part includes: Holcophylloceras gr

mediterranean i Neiim., Sowerbyceras cf. subtortisulcatum Pomp.. Lytoceras aff. eudesianum (d'Orb )

Lumdoceras alt. pseudopunctatum (Lah. in Jeannet), Choffatia sp indet., Collotia sp., Peltoceras

(Metapeltoceras) sp., Peltoceras cl diversiforme (Waag. in jeannet) (F14). This assemblage belongs to

the Athleta Zone, lowermost upper Callovian. In spite of numerous ammonite sections (and belemnites)

obvious on the outcrop, the "Athleta bed" of Jebel Krechem el Kelb has yielded a poor fauna difficult to

extract: Distichoceras sp., P. (Peltoceras) sp.. Perisphinctids indet. (FI4).

Lower Oxfordian assemblages

From Kef el Hassine toward the south, the lower Oxfordian (F15) is well characterised in all the

studied profiles at the base of the upper member of the Nara Formation, which has escaped

dolonutisation. For the first time a fauna of this age has been recognised at Jebel Rheouis (SOUSSI

M’Rabet & ENAY, 1991).

From Kef el Hassine to Jebel Rheouis

At Kef el Hassine they are: Holcophylloceras mediterraneani (Neum.), Taramelliceras

pseudoculatum (Bukow.), Euaspidoceras cf. douvillei Collot. Perisphinctes (Otosphinctes) sp.,

Properisphinctes gr. bernensis (de Lor. in Ark.) (FI5).

— The upper part of the condensed level at Jebel Chaabet el Attaris has yielded: Phylloceras sp.,

Holcophylloceras sp., Campylites (C.) delmontanus helveticus Jeannet, Perisphinctes (Kranaosphinctes)

cf. promiscuus Bukow., Euaspidoceras cf. knechti Jeannet and a little above: Lytoceras cf. eudesianum

(d'Orb.), Phylloceras gr .plication Neum (FI 5).

— This fauna is richer and much diverse at Jebel Krechem el Kelb: ? Cenoceras sp.. Phylloceras sp.,

Ptychophylloceras sp., Campylites (Campylites) delmontanus (Opp.), C. (C.) taeniolatus Jeann..

Taramelliceras cf. pseudoculatum (Bukow.), Prososphinctes cf. mazuricus (Bukow.), Perisphinctes

(?Dichotomosphinctes) cf. laisinensis (de Lor.), Perisphinctes (?Arisphinctes) cf. gyrus (Neum.),

Peltoceratoides cf. and gr. williamsoni (Phill.) (F15).

MOHAMED SOUSSI ETAL.

_The recently discovered fossiliferous beds of Jebel Rheouis (SOUSSI et a!., 1991) has yielded

badly preserved fossils at five levels: 1) Peltoceratoides sp.; 2) Campylites sp.; 3) Sowerbyceras

tortisulcatum (d'Orb.), Campylites (Campylites) cf. delmontanus (Opp.), C (C.) cl. delmontanus

helveticus Jeann., Passendorferia (Enayites) czentochovensis (Siem.) Euaspidoceras gr. wtluunsom

(Phill )' 4) Trimareinites sp., Perisphinctidae ind., Peltoceratoides gr. williamsoni (Phill.), 0)

Proper'ispliinctes cf. bernensis (de Lor. in Arkell). and Prososphinctes cl. mane, (de Lor.),

Properisphinctes cf. bernensis (de Lor. in Arkell), Peltoceratoides sp. (FI 5).

In summary, these assemblages which differ greatly in abundance, diversity and preservation, are in

fact very homogeneous and belong to the lower Oxfordian, including forms of the Marine and Cordatum

Zones Distinction of the subzones (to say nothing on the horizons) recognised in Submediterranean

Europe is not actually possible. The absence of boreal cardioceratids and more curiously ot tethyan

groups like hecticoceratids obliges us to base the age determination on other groups. Such parallel

zonations have been proposed or are now in use: (CARIOUS al„ 1997), based on Taramelhceras

(TARKOWSKI. 1990), some Perisphinctidae (BROCHWICZ-LEWINSKI, 1981: MELENDEZ et at.. 1983) or

Peltoceratidae and Aspidoceratidae (BONNOT, 1995).

The lower part of the Marine Zone (Scarburgense Subzone) is not recognised and the zone is

represented only by the Praecordatum Subzone. It is the same for the Cordatum Zone; its fauna points

certainly to the Submediterranean equivalents of the Bukowskii and Costicardia Subzones:

Claromontanus Zone of BROCHWICZ-LEWINSKI: Mirus Zone. Baccatum Subzone and Patturattensis

Zone, Oculatum Subzone of TARKOWSKI. The upper Cordatum Subzone is not represented or only by its

lower part.

Jebel el Haouareb

The first nodular bedded limestone (“ammonitico rosso facies”) has yielded the same fauna of the

early Oxfordian (FI5).

— On the right bank of the wadi Souyah, 11 m thick, we found successively :

1) Sowerbyceras cf. tortisulcatum (d'Orb.), Peltoceratoides sp.; 2) Passendorferia (Enayites) cf.

birmensdorfensis (Moesch in Broch.-Lew.), Perisphinctes (Kranaosphinctes) cf. promiscuus Bukow.;

-\) Euaspidoceras sp.; 4) Phylloceras sp., Campylites (Campylites) delmontanus (Opp.), Passendorferia

(Enayites) czentochovensis (Siem.); Taramelhceras aff. T. argoviense Jeann.; 6) Campylites

(Campylites) delmontanus helveticus Jeann.. Lissoceratoides sp.; 7) Campylites (Campylites) gr.

delmontanus (Opp.), Properisphinctes sp.; 8) Passendorferia (Enayites) czentochovensis (Siem.);

9) TarameUiceras argoviense Jeann.. I pseudoculatum (Bukow.), Prososphinctes sp.; 10) Phylloceras

sp., TarameUiceras pseudoculatum Bukow.; 11) Prososphinctes sequeirosi Broch.-Lew.;

12) Perisphinctes (?Dichotomosphinctes) cf. episcopalis de Lor., Peltoceratoides cf. williamsoni

constantii (d'Orb.); 13) Phylloceras sp., Holcophylloceras sp., Sowerbyceras tortisulcatum (d Orb.),

Passendoiferia sp.

— On the left bank, the upper four metres of the same sequence approximately equivalent to faunas 8

to I 1 mentioned above contain: 8) Perisphinctidae ind., Aspidoceratidae ind.; 9) TarameUiceias cl.

baccatum (Bukow.). Properisphinctes cf. bernensis (de Lor. in Arkell); 10) Phylloceras sp.,

TarameUiceras argoviense Jeann., Properisphinctes gr. bernensis (de Lor. in Arkell). Perisphinctes

(?Dichotomosphinctes ) cf. laisinensis de Lor.. Peltoceratoides cf. stephanovi (Sap.); 11) TarameUiceras

aff. T. callicerum (Opp.).

In spite of the more important thickness, the fauna ol the nodular limestones leads to the same

biostrati graphical conclusions as for the Cordatum Subzone. Several forms have been attributed or

closely related to species with a poorly established range, often quoted from younger levels

(TarameUiceras argoviense. P. (?Dichotomosphinctes) cf. laisinensis).

The middle and upper Oxfordian faunas

The dolomitised limestones term of upper Nara Formation contain a poor macrofauna. The facies is

unfavourable to their preservation and complete specimens are rare in good condition.

— Bad and undetermined perisphinctids, probably from the middle Oxfordian, have been found in

Source ; MNHN. Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

ttnck calcareous beds at Kef el Hassine and at Chaabet el Attaris. The nodular levels at Jebel Krechem el

Ke!b are more or less rich with: Coenoceras sp., Trimarginites arolicus (Opp.) (m), Protophites christoli

'Beau /Fl The middle Oxfordian is attested at Jebel el Haouareb, according to the quotation by

Gharisi (1989) of P. christoli (Bcaud.) and Gregoryceras riazi (de Gross.).

Some upper Oxfordian fauna (FI7) have been collected at Jebel el Haouareb (300 m to the north

°J P uec | So “y ah) U '°™ the more calcareous intercalations of the upper Member of the Nara Formation.

A first level has yielded: I) Orthosphinctes (Orthosphinctes ) sp.; 2) Taramelliceras (Strebliticeras) cf.

externnodosum (Dorn); 3) Orthosphinctes (Orthosphintes J; higher, from a second outcrop we have

collected. 4) Aspidoceras circumspinosum (Opp.); 5) Taramelliceras sp.; 6) Laevaptvchus sp • 7)

Trimarginites stenorhynchus (Opp.); 8) Taramelliceras cf. costatum (Qu.); 9) Perisphinctidae ind These

isolated forms represent homogeneous assemblages close to those in the Bimammatum Zone.

AGE OF THE SEDIMENTARY BODIES AND ASSOCIATED UNCONFORMITIES

Age of the sedimentary bodies

Ages are constrained by new biostratigraphical data only for the upper part of the middle Nara

member, from and above the second unconformity (UC 2). Uncertainties still exist on the ages of several

sub-units of the series for which we use the ages established in the closest sections (Figs 3 and 4).

— The peritidal carbonates (lower Nara A, Ul ) and the bioclastic carbonates (lower Nara B, U2) are

attributed to early Lower Jurassic up to the Carixian. The later is suggested bv the presence of the

aimrionite Metaderoceras sp. collected 2 m below the top of U2 at Kef el Hassine (SOUSSI, Enay et al .,

— The alternation of limestones and marls (middle Nara A, U3) includes early Toarcian age “black

shales" (U 3 ,) and middle Toarcian argillaceous limestones (U 32 ).

— The ferruginous and/or phosphatised ooids limestones: “ironstones " (middle Nara B, U 4I ) are

distinguished by their fauna and ages.

In the south, from Kef el Hassine to Krechem el Kelb, the ferruginous and/or phosphatised ooids

limestones are early Bajocian, ranging from Discites Zone (Kef el Hassine) to the Humphriesianum

Zone (Krechem el Kelb). The same range is admitted at Chaabet el Attaris where fauna are missing and

the facies are poor in ferruginous or phosphatised ooids. Not all of the subzones of the recognised zones

are represented and the sequence can be incomplete. So, at Kef el Hassine, a hard-ground with a

ferruginous crust separates beds with Sonninia and Emileia (Discites and Laeviuscula Zones) from

levels with Chondroceras and Stephanoceras (Humphriesianum Zone, mostly Romani Subzone).

The so- called ironstones, spreading out from Kef el Khouadja to the north, are restricted to the early

Bathonian (Zigzag Zone, Macrescens Subzone at Kef el Khouadja and at Jebel Guefai'et; Aurigerus

Zone at Demet). Thus, they are the lateral equivalent of the marls with pyritised fossils of Chaabet el

Attaris, Krechem el Kelb and Rheouis. On the other hand, the ironstone of the old mine of Jebel Loridga

ranges up from late Aalenian (Concavum Zone) to early middle Bathonian (Progracilis Zone, Orbignyi

Subzone) with the possibility of discontinuities and gaps particularly in the upper Bajocian and lower

Bathonian, pars (see the section Age of the sedimentary bodies and associate unconformities).

— The filaments- and Zoophycos-mV? limestones (middle Nara B. U 42 ) underlying the marls with

pyritised fossils at Rheouis, Krechem el Kelb, Chaabet el Attaris, ? Kef el Hassine and the ironstone at

Kef el Khouadja, ? Demet, begin with the upper Bajocian at Kef el Hassine. This is the only outcrop

where the upper part of the stage is recognised. Their upper part is of early Bathonian age (Zigzag Zone,

Macrescens Subzone) at Kef el Khouadja. The same interval is admitted for Rheouis, Krechem el Kelb,

Chaabet el Attaris and for the upper beds without fauna at Kef el Hassine.

— The pyritised ammonites rich shales (middle Nara B. U 43 ) are an excellent marker bed for the

southern half of the NOSA from Rheouis to Chaabet el Attaris, certainly also at Kef el Hassine where

they are covered by scree. They occupy a constant level into the lower Bathonian: Zigzag Zone,

MOHAMED SOUSSI ETAL.

Macrescens Subzone. Towards the north, they laterally pass into the ironstone of Kef el Khouadja.

Demet and Jebel Guefai'et.

— The compacted carbonates (middle Nara B, U 4 . 4 ) with the third unconformity (UC3) at the top are

everywhere fossiliferous. The bottom still belongs to the lower Bathonian (Zigzag Zone, Macrescens

Subzone and Aurigerus Zone) at Jebel Krechem el Kelb. where the sequence is the thickest (7 m). It is

organised into several parasequences with marly or nodular intervals. At other places, the sequences are

reduced and more calcareous (0.8 m at Rheouis; 0.7 m at Kef cl Hassine; 1.5 m at Kef el Khouadja: _ m

at Chaabet el Attaris). The upper part is better dated from middle Bathonian, Bremen Zone at Krechem

el Kelb. Chaabet el Attaris and Kef el Khouadja.

_ The dolomitised limestones of the upper Nara member (upper Nara A, base of U5) locally begin

with middle Callovian, Anceps Zone (at Krechem el Kelb). more widely within upper Callovian Athleta

Zone Collotiformis Subzone (Chaabet el Attaris). and also in the whole study area within lower

Oxfordian Mariae Zone. Praecordatum Subzone (Kef el Hassine, Rheouis). The upper Nara Membcr

inchides Oxfordian. Kimmeridgian and partly Tithonian, but without precise ages lor the highest levels.

At the top. the Sidi Khalil Formation, including Berriasian, is diachronous and begins earlier in the

south (Rheouis, Bou Hedma) within the upper Tithonian (Microcanthum Zone), later (lower Berriasian,

Euxinus Zone. Jacobi Subzone) at Jebel Sidi Krai if and Jebel Nara ( BUSNARDO et a!., 1976; 1980: 1985;

M'RABET. 1975. 1987).

— The sequence of Jebel el Haouareb is similar to these of the “Dorsale tunisienne” (Figs 3-5).

The limestones with filaments, here without Zoophycos , are dated upper Bathonian by PEYBERNES et

at. (1995). They extend through lower and middle Callovian. and the highest beds are from upper

Callovian (Athleta Zone).

The grey-green to wine-coloured nodular limestones (“ammonitico rosso” facies) underline a major

lithological change during early Oxfordian time, Mariae Zone. Praecordatum Subzone), and range up

into middle Oxfordian steeply invaded by secondary dolomitisation.

Unconformities (Fig. 4)

Three unconformities have been clearly recognised within the middle Nara member. In several

sections, ammonites below and above of these unconformities have allowed age correlations and the

measurement of their relative duration through the biochronological reference scale.

UCI UNCONFORMITY

UC1 falls between the bioclastic dolomites (U2) and the black shales facies (U3). This unconformity

materialised by a submarine bored hard-ground is the less characterised one. because of the total lack of

fauna within the bioclastic dolomites. Badly preserved fragments or moulds at the topmost of the

bioclastic dolomites were determined in situ as Microderoceras sp. This unconformity underlines a

stratigraphic hiatus which may correspond to a part of the Carixian and the Domerian pro parte (time

average of 4 Ma. Haq et al., 1987). In fact, the last two metres of the bioclastic carbonates remain

undated and thus could be Domerian p. in age.

UC2 UNCONFORMITY

UC2 passes through the middle Nara member and was unnoticed for a long time. It corresponds to a

submarine erosional surface encrusted by thin phosphatic and/or ferruginous layer. The systematic

collecting of fauna has allowed us to date UC2 in several places. The base of the unconformity and the

sedimentary break are of middle Toarcian age (Bifrons Zone, Levisoni Subzone). The renewal of

sedimentation occurred generally during the early Bajocian (Discites Zone) (Krechem el Kelb. Kef el

Hassine). This unconformity marked a long hiatus varying from 4 to 12 Ma (HAQ et al.. 1987). At Jebel

Loridga the deposition of ironstones began, exceptionally, in the late Aalenian Concavum Zone. During

this time interval, locally (Kef el Hassine), encrusting layers or lenses developed in the late Toarcian.

Source. MNHN. Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

South

Krechem

Chaabet

Kef el

el Kelb

el Altaris

Hassine

12km

10 km

Loridqal

North

Ftc.. 5. Lithostratigraphic correlation showing the thickness variation within the Jurassic series in the nosa (Central Tunisia)

l, Tnassic gypsum;2, lower Liassic peritidal dolomites; 3. Toarcian black shales; 4. Bajocian-Bathonian ferruginous

ooids or ironstones ; 5. Callovian-Oxfordian pelagic muddy-limestones: 6, shales; 7. Oxfordian calciturbidites* S

unconformities; 9, slumps; 10, hard ground; 11, fault contact (F).

h'C. 5.— Correlations lilhostratigraphiques montrant les variations des epaisseurs dans les series jurassiques de I‘Axe Nord-

Sud (Tiimsie cent rale). I . gypses dn Trias ; 2. dolomies peritidales du Lias inferieur ; .1. “black shales " da Toarcien ; 4

oollines ferrngmeuses du Bajocien-Bathonien : 5. calcaires pelagiques da Callovien superieur-Oxfordien : 6. argiles

7, calciturbidites de / Oxfordian ; 8, discordances ; 9. slumps : 10. surface durcie ; II. contact par faille (F).

Al Jebcl Guefaiet, and probably at Dcmet also, the renewal of deposition began later (early

Bathonian) if the marls and limestones situated below the ironstones are Toarcian. At Kef el Khouadja.

UC2 was observed but has not been dated precisely. It is underlain by a clay layer with phosphatised

grains resting over the limestones and marls of “Toarcian” type. Only about’one metre of dolomitised

limestone, beds with phosphatised ooids, scattered at the base, separate it from the bed with lower

Bathonian fauna, below the ironstones. The numerous faults in the Rheouis area do not allow us to

observe UC2: they also explain the differences between our observations and the sequence described by

PHYBERNES el al. (1995), particularly the unit bounded by two faults and noted Bj3-Bj5. The existence

of upper Bajocian beds <Bj3) agrees well with what is known elsewhere in the NOSA. The lower

Bathonian marls with pyritised fossils discovered in 1988 (SOUSSI. ENAY el til., 1991; SOUSSI.

M’Rabf.T & ENAY, 1991) are the marls noted Bt4 (upper Bathonian) below the “dolomies boudinees”

which are overlain by D3 and the limestones with lower Oxfordian fauna (0x2).

VC3 UNCONFORMITY

UC3, as UC2, corresponds to a submarine erosional surface encrusted by thin phosphatic and/or

ferruginous layer locally rich in iron-rich ooids. It is lithologically and palaeontologically well

MOHAMED SOUSS1 ETAL.

characterised only in the southern part of the NOSA. Beyond the Ket el Khouadja, toward the north

(GuefaTet Demet, Loridga), dolomitisation invaded the base of the upper member of Nara Formation

down the contact with the ironstones (Figs 3-4). At Jebcl Loridga. if a stratigraphic gap is present (see

Soussi, ENAY et al.. 1991: PEYBERNES el al.. 1995) as wide as in the south, it is completely obscured

by dolomitisation.

The latest deposits below the discontinuity are often condensed and locally (Krechem el Kelb)

contain an earliest upper Bathonian fauna, but nearly everywhere else their age is latest middle

Bathonian (Bremeri Zone) at Krechem el Kelb. Chaabet el Attaris. Kef el Khouadja. We have used the

same age aap for UC3 at Kef el Hassine and Jebel Rheouis but without any evidence. PEYBF.RNES et al.

(1995) mentioned (without explanation) a fauna from the base of sequence Bt4 at Jebel Rheouis. This

introduces a discontinuity essentially of middle Bathonian age (Btl to Bt3). This was not conitrmed by

our observations, in particular with the position of marls with pyritised fossils of early Bathonian, which

are, for us, those designated Bt4.

The renewal of sedimentation began locally at Krechem el Kelb with a lenticular deposit ot middle

Callovian (Anceps zone). It developed more clearly during the late Callovian (Athleta Zone,

Collotiformis Subzone) at Krechem el Kelb and Chaabet cl Attaris, but probably still with interruptions.

The Athleta zone is unknown at Jebel Rheouis and Kef el Hassine where the earliest fauna is early

Oxfordian. Moreover we do not know any fauna of the Mariae Zone, Scarburgense Subzone ol the

lowest Oxfordian. The renewal of sedimentation became widespread during early Oxfordian, (Mariae

Zone Praecordatum Subzone) (= 0x2 in PEYBERNES et al. 1995). The nodular limestones were

deposited at Jebel el Haouareb at this time (SOUSSI. Enay et al.. 1991). Thus, this unconformity is

accompanied by a gap of a duration which varies from 4 to 9 million years (Haq et al., 1987) which

covers a relative time from Retrocostatum Zone to Lamberti Zone and also the lower part ot Mariae

Zone.

Other unconformities

Despite the lack of a significant faunal argument, other unconformities can be considered. In the

ironstones, particularly at Jebel Loridga, several diastems made this hypothesis credible. SOUSSI, ENAY

et al. (1991) had already considered it for the most important diastem that separates the lower part with

fauna of the upper Aalenian (Concavum Zone) - lower Bajocian (Discites Zone) (Figs 3 and 4) Irom

higher levels with lower Bathonian (Aurigerus Zone) and lowest middle Bathonian (Progracilis Zone,

Orbignyi Subzone). PEYBERNES etal. (1995) went further in adding a discontinuity with a gap of a part

of the middle Bathonian between lower Bathonian (SD Bt5 and Btl possibly) and the highest middle

Bathonian (SD Bt3).

At Chaabet el Attaris, the discontinuity with a lower and middle Bathonian gap suggested by

PEYBERNES et at. (1995) is not justified. In fact, the lower Bathonian (Aurigerus Zone) is well

characterised by fauna in the filaments and Zoophycos -rich limestones, and in the overlying marls with

pyritised fossils. Moreover, below the beds dated from the Bremeri Zone, two metres of compacted

carbonates (U 44 ) representing the rest of the middle Bathonian do exist.

In the sequence of “Dorsale tunisienne” type, at Jebel el Haouareb, no fauna was collected in the

alternation of limestones and marls (7.5 m) between the latest upper Callovian fauna, Athleta Zone and

the earliest lower Oxfordian fauna of the Mariae Zone. Here, a discontinuity with a gap is very probable,

underlined by an important facies change. This was recognised by PEYBERNES et al. (1995), but we

limit it to the Lamberti Zone and the lower part of the Mariae Zone (SD Ca5-OxO for Ca4-0xl). We do

not consider that a gap exists within the lower Callovian Gracilis Zone developed on 30 to 40 m, from

the marls dated by a pyritised fauna (base of SD Bt5) up to the base (or the top ?) ot the first calcareous

bar of SD Ca2. It will be noticed that in the PEYBERNES et al. figure 1, SD kfc Cal ?” is wrongly situated.

If their figure 2 is correct, its place would be at the top of PHN of CaO ? or Bt5 that we have dated as

lower Callovian, Gracilis Zone.

Source:

THE JURASSIC EVENTS IN CENTRAL TUNISIA

DEPOSITIONAL ENVIRONMENTS

The vertical facies succession described here suggests that Jurassic sedimentation occurred in Central

Tunisia in a full marine environment (Fig. 2).

Hettangian-Sinemurian peritidal carbonate platform

The sedimentary and early diagenitic characteristics recorded within the lower Liassic carbonates

suggest a very shallow marine and restricted platform environment with tidal fiats. The latter are

characterised especially by algal (microbial) stromatolites and locally by the formation of low energy

ooids and pisoids. The various terms of the peritidal cycles indicate relative fluctuation in the

environments of deposition varying between shallow sub-tidal to supra-tidal (with aerial exposures)

(Fig.E2). The various peritidal cycles have a total thickness of more than 150 m suggesting an

equilibrium between subsidence and sedimentation rates. Although the depositional environments were

very shallow, they appear clearly as aggradational to retrogradational over the underlying continental to

paralic Triassic siltstones and evaporites (BUROLLET, 1956; SOUSSI, ABBES et al., 1996). These inter-

supratidal or tidal environments extend to the Atlasic zone to the north and to the Chott Basin to the

south (more than 400 km). The lower Liassic sediments of Tunisia could be compared to the Holocene

deposits described by SHINN el al. (1969) and to the Late Triassic “Dolomie Principale” in the Southern

Alps (BOSELLINI & HARDIE, 1985). Relative sea level changes on a 10 3 -10‘ years scale (Milankovitch-

type eustasy cycles) have been evoked to explain the formation of this peritidal type cycles (GlNSBURG,

1975; HARDIE et al., 1986).

Carixian open marine carbonate platform

With the Carixian bioclastic limestones, especially those containing belemnites and ammonites, the

depositional environment became slightly deeper. This deepening, caused by an important and

regionally widespread marine transgression, was accompanied by a drastic slowing of sedimentation as

indicated by the submarine hard-ground identified at the top of U2 over the whole study area. This

transgression had been preceded, at least since the upper Sinemurian-Carixian, by the dislocation of the

wide and homogeneous shallow marine platform. This first important tectonic event has been well

documented both to the north within the Tunisian Dorsale (BONNEFOUS. 1972; ALOUANI, 1991; SOUSSI,

Davaud et al., 1993) and to the south within the Chott Basin (POGACSAS et al.. 1998; HLAIEM, 1998).

The fragmentation of the “initial” platform has led to a new structural setting comprising tilted blocks

and horsts and relatively subsidenl grabens (Fig. 7).

Toarcian drowned platform and associated anoxic sub-basins

The carbonate sedimentation of the lower Liassic was replaced in the Toarcian by shaly and

laminated limestone deposition containing both pelagic and benthic faunas. The latter suggests a marine

deepening in relation to a new widespread transgressive episode.

The local presence of high organic matter content within these facies, their laminated character, the

absence of burrows, the presence of pyrite and the excellent preservation of fish bones indicate oxygen

deficiency and signify anaerobic bottom water conditions, in association with sulphate-reducing

bacterial activity. In addition, the lateral variations in thickness indicate differential and rather slow

subsidence (Fig. 5). The Chaabet el Attaris and the northern part of Krechem el Kelb formed a relatively

subsident graben; while the Kef el Hassine-Loridga zone constituted a high and resistant horst block.

MOHAMED SOUSSI ETAL.

In summary, during the early Toarcian the environment of deposition corresponded to an irregular

outer shelf including horsts and grabens or half grabens, which locally acted as narrow anoxic basins.

On the other hand, the presence of the "black shales" confirms that the Toarcian Oceanic Anoxic Event

(JENKYNS. 1985; BAUDIN et al., 1988) had a worldwide extension and was recorded in numerous basins

not only of the Tethyan Northern Margin but also of the Tethyan Southern Margin (SOUSSI et al., 1990).

These anoxic conditions stopped during the middle Toarcian. The depositional facies became more

clayey and rich in detrital quartz, abundant bioturbations and benthic fauna, thus suggesting oxic

conditions in relation with the initiation of a regressive and prograding carbonate facies.

Bajocian-Bathonian starved carbonate shelf

During Bajocian-Bathonian time. Central Tunisia recorded the maximum variation in sediment facies

and thickness and two distinct depositional environments existed simultaneously. The Bajocian

ironstone deposits, following the second major stratigraphic gap (UC2), indicate a renewal of

sedimentation during a transgressive phase. The origin of the Jurassic "ironstones of NW Europe and

their depositional environments have been extensively discussed (BROCHERT, I960; Hallam. 1975;

Harder. 1989; Van Houten. 1985; Teyssen, 1984).

In Central Tunisia, the lack of any evidence of emersion, the presence of mixed benthic and nektonic

fauna, associated with low angle cross-bedding suggest a submarine environment characterised by high

energy conditions in relation to submarine current activities. These ironstones are syngenetic in origin

and reflect particular physico-chemical conditions with abnormal enrichment in iron and phosphate

(SOUSSI & M'RABET, 1991).

The regional thickness and facies distribution of these “ironstones”, in addition to the presence of

frequent hard grounds with borings, phosphatic and ferruginous encrusting laminations, clearly

demonstrate that these facies have been formed on upthrown and weakly subsiding blocks (horsts).

Within the latter, the sedimentation rate was very slow, varying from 0.1 to 0.25 m per million years

compared to the Bajocian-Bathonian facies which are 200 m thick (in the range of 14 m per million

years) to the north within the Tunisian Trough (Bou Kornine of Hammam Lif) or in the south within the

Chott Basin (BONNEFOUS, 1972; MZOUGHI et al., 1992).

The adjacent and overlying Bajocian-Bathonian facies represented by filaments and Zoophycos-nch

carbonates correspond to hemipelagic facies. During Bathonian sedimentation, detrital clay supply

became more important as suggested by the increase in kaolinite. During the middle Bathonian. platform

carbonate sedimentation characterised the whole area, except the palaeohigh of el Guefaiet and Loridga

where ferruginous ooids continued to develop.

Callovian-Tithonian deep carbonate shelf to basin transition

The Callovian-Oxfordian muddy-limestones (the lower part of U5) which overlie the third major

unconformity (UC3), inducing a clear angular discordance (also identified on seismic data within the

Chott area), reflect a new transgressive sedimentation pattern. The depositional environments became

deeper and apparently homogenous; this corresponds to a calm and deep marine carbonate platform

replaced to the north by a marginal slope (el Haoureb) with mostly debris flow deposits initiated by syn-

sedimentary tectonic activity.

The uppermost Oxfordian limestones become rich in benthic fauna and locally in high energy

calcareous ooids, which indicate a regional shallowing-up ot the depositional environment.

The upper Oxfordian temporary regression was followed by a new deepening phase, which occurred

from the early Kimmeridgian. This is attested by the development ot muddy limestones rich in pelagic

fauna such as crinoids ( Saccocoma ), radiolarians and calpionnelids during the lower Tithonian.

Source MNHN . Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

PALAEOGEOGRAPHIC FRAMEWORK AND SEDIMENTATION CONTROLS

Liassic shallow marine carbonate sedimentation was replaced during the Middle-Upper Jurassic by

various types of lithotac.es deposited in distinct and quite different palaeoenvironments (anoxic

environment, shelf and outer shelf...). In addition, the sedimentary record includes major submarine

unconformities accompanied by hiatuses recorded over considerable extents. Vertical and lateral

changes oi thickness and facies suggest the presence of two main, but quite different, palaeogeographic

domains in the studied area. A resistant block extends from Rheouis to Loridga to the south, relayed to

the noith by a subsident basin (el Haouareb graben). The relatively low modification of sedimentation

coinciding with faunal changes between the major unconformities, in addition to the regional changes in

thickness, suggests that sedimentation has been controlled both by global eustatic fluctuations and"local

tectonic activity.

Tectonic control (Fig. 6)

The variations of sediment thickness and of depositional environments, observed within the upper

Liassic and Middle Jurassic deposits (Fig. 5), suggest a major modification in the palaeotopography.

The latter became irregular and unequally subsident. In fact, the relatively homogeneous and widespread

Liassic shallow marine platform had been dislocated at least since the Lotharingian into an irregular and

South

North

Fig. 6 .— Interpretative diagram showing relationships between the Jurassic facies and the major tectonic events in the nosa,

Central Tunisia. 1. Liassic shallow marine platform dolomites; 2, Carixian condensed section; 3. Toarcian marl and

limestone alternations, 4. Toarcian black shales; 5. Bajocian-Bathonian ferruginous ooids; 6. middle Bathonian

filament-rich compacted carbonates; 7, upper Callovian pelagic mud-limestones; 8^early Oxfordian calciturbidites with

slump; 9, major unconformities; FO, M'KIula-Kairouan lault; FI, Touila fault (approximately E-W trending). F2.

Chaabet el Attaris fault; F3. South Krechem el Kelb fault (branch of the approximately E-W Kasserine-Chorbane fault).

The thickness are not proportional from south to north.

F /G. 6.— Diagramme interpritatif montrant la relation entre les facies du Jurassique el la structuration en blocs bascules dans

le NOSA (Tunisie Centrale). /, dolomies de plate-forme tres pen profonde du Lias : 2. sediments condenses du Carixien :

3. alternances marno-calcaires du Toarcien ; 4. black shales du Toarcien ; 5. oolithes ferrugineuses du Bajocien-

Bathonien ; 6, carbonates compactes a filament du Bathonien moyen : 7. calcaires pelagiques du Callovien superieur ;

8, calciturbidites avec slumps de I'Oxfordien inferieur ; 9, discordances majeures ; FO. faille de M'Rhila-Kairouan ;

FI, faille de Touila (approximativement E-W); F2, faille de Chaabet el Attaris ; F3, faille de Krechem el Kelb Slid

(branche de la faille de Kasserine-Chorbane de direction approximative E-W). Les epaisseurs ne sont pas

proportionnelles du sud an nord.

MOHAMED SOUSS1 ETAL.

: 1

: 2

: 3

North

(Ichkeul)

South

North-South Axis

Tunisian Dorsals

North

Tunisian Trough

Fig. 7.— Simenurian-Carixian palaeogeography: A: The geographic distribution of the upper Sinemurian-Carixlan facies. 1,

Jurassic outcrops; 2. condensed facies; 3. thick deep marine carbonates. B 1: simplified diagram showing the

Hettangian-Sinemurian palaeogeographic setting dominated by a wide peritidal shallow marine carbonate platform. B2:

interpretative diagram illustrating the upper Sinemurian-Carixian facies variation. This pattern is closely related to the

dislocation of the initial platform during the Liassic rifting. 1. peritidal carbonates (Lower Nara and Oust formations); 2.

upper Sinemurian bioclastic carbonates; 3. condensed sedimentation rich in ammonites, belemnites and glauconite; 4.

pelagic cherty muddy-limestones rich in radiolaria and schizosphers (Zaghouan formation); 5. major faults.

FlG. 7— Paleogeographie du Sinemurien - Carixien ; .4 : distribution geographique des facies du Sinemurien superieur-

Carixien. 1. affleurements jurassiques : 2, facies condenses : 3. serie epaisse de calcaires profonds. Bl : diagramme

simplifie montrant les diffe rents domaines paleogeographiques durani Fintervalle Hettangien-Sinemurien . domine par

une vaste plate-forme carbonatee ti es pen profonde : B2 : diagramme interpretatif montrant les variations de facies de

Fintervalle Sinemurien superieur-Carixien. Cette evolution est etroitement associee a la dislocation de la plate-forme

initiate lors du rifting du Lias inferieur. I . carbonates peritidaux (formations: Nara inferieure el Oust): 2. carbonates

bioclastiques du Sinemurien superieur : 3, sedimentation condensee riche en ammonites, belemnites et glauconite : 4,

calcaires pelagiques a silex. riches en radiolaires et schizospheres (formation Zaghouan): 5. failles majeures.

Source : MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

relatively deep shelf composed of blocks tilted towards the south. This new structural pattern includes

three depressions or half grabens (el Haouareb. Chaabet el Attaris and Rheouis) separated by relatively

resistant highs or horsts (Jebel Krechem el Kelb towards the south and Kef el Hassine-Nara Loridga

block towards the north) especially during Bajocian time. The differentiation of these tilted blocks is

related to h-W or near E-W synsedimentary Jurassic faults. In this connection, these E-W faults alon<>

the NOS A especially at the latitude of the El Gamgouma and Krechem el Kelb areas could correspond to

the Touila E-W fault (ABBES, 1983; Ouali, 1984) and one of the branches of the FaYd faults

respectively. I he lirst could be the lateral extension towards the east of the M'rhilla fault or one of its

branches while the second may be related to the nearly E-W Kasserine fault (Ben Ayed, 1986) In

addition local N-S synsedimentary antithetic faults are present.

The Kef el Hassine-Loridga horst is bordered towards the north by the E-W Touila fault which had

been active since the Early Jurassic. This Touila fault is bordered to the north by an important down-

laulted block or graben where sedimentation has been more continuous and thick during both Jurassic

and Cretaceous (ABBES. 1983; OUALI, 1984). During the Jurassic the control of this fault is

demonstrated by the evolution of Callovian-Oxfordian thickness and facies. The latter, reduced to the

south to a few metres of mud limestones, is represented towards the north (El Haoureb area) by a thick

deep marine sequence (more than 200 m) comprising debris flow deposits with slumps (Fig. 6).

Within this tectonic framework, the Chaabet el Attaris graben has acted during the lower Toarcian as

a narrow anoxic basin (SOUSSI et al., 1990). while the Kef el Hassine-el Guefaiet and Loridga blocks

corresponded to a condensed sedimentation especially during the Toarcian-Bathonian time interval. This

is indicated lirst by the progressive thinning to the north of the several sedimentary units secondly by

the development of ironstones especially to the north and the superposition of these onto the Toarcian at

el Guefaiet area.

I he lack of ferruginous ooids at Krechem el Kelb during the Bathonian suggests a local readjustment

of the structural system with reactivation of the Oued Abiod fault (F2) and the drowning of Krechem El

Kelb block (Fig. 6).

The Jurassic tectonic activity is well illustrated at a regional scale. In fact, to the north, both in the

Tunisian Dorsale and the Tunisian Trough, at least three major tectonic phases have been recognised.

The first major phase occurred during the middle Liassie (upper Sinemurian-Carixian) and led'to the

dislocation of the initial shallow marine platform and the development of condensed horizons on the

highs of the tilted blocks. Within the grabens were deposited a thick pelagic cherty muddy-limestones

rich in radiolarian and schizospheres (Zaghouan Formation) (Fig. 7). (BONNEFOUS, 1972; Rakus &

BlELY. 1970; HJRK1, 1988; RAIS et al., 1991; ALOUANI. 1991;SOUSSI. BUSSON et al.. 1993). The

second tectonic event occurred during Bajocian-Bathonian time and is well recorded in Jebel Bou

Gamine of Hammam Lif graben by the presence within the Bathonian deposits of two main

conglomeratic horizons including resedimented Liassie dolomitic and cherty carbonates (BONNEFOUS,

1972; COSSEY & EHRLICH. I981;TURK1, 1988). The third event is demonstrated by the resedimentation

ol Callovian Bent Saidane limestones and shales within the early Oxfordian “ammonitico rosso facies”.

To the west and the south of Central Tunisia, Jurassic sedimentation has also been strongly

influenced by the tectonic framework characterised by E-W, N-S and NW-SE fault systems (BEN AYED

& Khessibi, 1983; BEDIR, 1995; BOUAZIZ et al., 1998). To the south of Central Tunisia, two main

subsident basins have been formed in relation to the Late Palaeozoic-Early Mesozoic rifting. The Chott

basin where Jurassic is up to 2000 m thick (BONNEFOUS. 1972; MZOUGHI et al., 1992). and the

Tataouine Remada graben also characterised by a thick Jurassic sequence (BUSSON, 1967:KAMOUN,

1988; BEN Ismail. 1994). These basins are separated by ridges bounded by major normal faults

(BOUAZIZ et al., 1998). The Medenine platform or “Tebaga high" is bordered towards the north by the

E-W Tebaga fault and to the south by the E-W Zmilet el Ghar fault (Fig. 8). The Tataouine Remada

graben is separated from the uplifted zone of Jebel Nefzaoua in Libya by the E-W Azizia fault

(ASSERTO & BENELI, 1971; El ZOUKI, 1980).

Some of the horsts bordered by E-W faults acted as a structural barrier blocking the terrigenous

progradation phase during the Bathonian or as a platform edge favourable to the installation of sponge-

coral bioherms during the Callovian (BEN ISMAIL & M'R.ABET. 1990).

In summary, the palaeogeographic framework of Tunisia clearly corresponds to a system of tilted

blocks initiated at least since the Permian in Southern Tunisia and during the Pliensbachian in Central

Source:

MOHAMED SOUSS1 ETAL.

and Northern Tunisia (Figs 8 and 9). Such geodynamic evolution is comparable to that outlined in

Algeria (BUREAU, 1986). Morocco (WARME. 1988) and in the Western Alps (WlLDi. 1 983; LEMOINE,

1985: BOUILLIN, 1986) and it results from Late Palaeozoic-Early Mesozoic ntting and associated

distentional drifting of the North African Tethyan margin.

TUNISIAN TROUGH

^>Tunis;

PLATFORM DOMAIN

SFAX

CHOTTS BASIN

TATAOUINB BASIN

Jurassic outcrops

FI: Zaghouan tault

F2: Mrhilla-Kairouan fault

F3: Kasserine-Chorbane fault

F4: North-South Axis fault

F5: Chotts fault

F6: El Melaab fault

F7: Tebaga of Medonine fault

F8. Zemlet el Ghar fault

F9: Azizia fault

F10: Tajera fault

| Subsiding basin

I I Platform

Fit: Jeffara fault

FlG. 8.— Simplified structural sketch

map showing the main probable

faults controlling the Jurassic

palaeogeography and thickness

(isopachs at 100 m intervals) in

Tunisia (after Ben Ferjani el al .,

1990. modified).

Fig. 8 .— Carle structurale simp I if ice

montrant les failles ayant probable-

merit controle la paleogeographie el

les dpa is sears (isopaques tons les

100 m) da Jarassiqae en Tunisie

(d'apres Ben Ferjani et al.. 1990.

modi fide).

EUSTATIC CONTROL

In addition to tectonic control. Jurassic sedimentation has been strongly influenced by sea level

changes. The detailed facies analyses and accurate biostratigraphic control have led us to define with

more precision the major transgressive and regressive episodes and their separating unconformities.

Source: MNHN. Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

The major transgressive episodes which are undoubtedly linked to sea level rises occurred during late

Sinemurian-Carixian, early Toarcian, early Bajocian. late Callovian and early Kimmeridgian (Fig. 2).

Their corresponding deepening phases have been recorded in different ways including condensed

sections, fine-grained pelagic limestones or black shales. These transgressive episodes were attested by

the renewal of sedimentation and facies changes, occurring just after the starvation phases (non¬

deposition or submarine erosion materialised by the three major discontinuities). In Southern Tunisia,

these different phases have been established not only by deepening but also by coastal onlap such as the

middle Liassic Zmilet Haber and the Bajocian Krachoua carbonates. The Callovian transgression is

represented in the Tebaga of Medenine mountain by a transgressive contact between the Permian and

the Jurassic series.

Fig. 9.— Palinspastic recons¬

truction of the North African

margin in Tunisia along a

north-south cross section

during middle-late Liassic.

The diagram shows the main

palaeogeographic domains.

FlC. 9.— Reconstruction palins-

pastique de la marge Nord

Africaine en Tunisie durant

le Lias moyen et superieur

selon un transect nord-sud.

Ce diagramme montre les

principaux domaines paleo-

geographiques.

A number of significant regressive episodes can be also recognised. The first episode started during

the middle Toarcian and continued through the late Toarcian and probably the whole Aalenian. The

second started during early Bathonian and attained its maximum during late Bathonian-early Callovian.

These two regressive phases were characterised by the installation of mixed (marly-calcareous)

sedimentation with supply of elastics (quartz and detrital clay). The development of shallow marine

carbonates particularly those rich in ooids, during the late Oxfordian indicate a shallowing-up phase of

the environment of deposition in relation to a regressive episode. It is important to note that the absence

of the lower and middle Callovian within the specific NOSA series could be linked to tectonic control

rather than eustatic fall (see discussion).

REGIONAL CORRELATION (Fig. 10)

Before comparing the Jurassic sedimentary record of Central Tunisia to global sedimentary cycles

and associated events, it is appropriate to attempt correlations with the Jurassic series of Northern and

Southern Tunisia. Taking into account biostratigraphic and sedimentologic data, correlations led to the

recognition of regional transgressive and regressive phases in Northern, Central and Southern Tunisia.

Transgressive phases

In Northern Tunisia (the Dorsale and adjacent areas), the upper Sinemurian-Carixian transgressive

episode is recorded within the transitional series from the shallow marine peritidal limestones (Oust

Formation) to the bioclastic and condensed section or their lateral equivalent facies represented by

cherty muddy-limestones of the Zaghouan Formation (RAKUS & BlELY, 1970; BONNEFOUS, 1972;

Faure & PEYBERNES, 1986; SOUSSI. BUSSON et at ., 1993). As shown in the figure 10. the lower Nara

(U1) and Oust Formation are similar and correspond to peritidal deposits. Their uppermost parts are also

similar and represented by open marine carbonates particularly rich in ammonites and belemnites.

In Southern Tunisia, the sedimentary response of the first Jurassic transgressive episode was

recorded within the Pliensbachian Zmilet Haber oolitic limestones (B Horizon for petroleum geologists).

The latter constitutes a major onlap and could be. at least in part, the equivalent of the uppermost

Carixian and ammonite-rich carbonates along the NOSA and the Dorsale zone.

MOHAMED SOUSSI ETAL.

1 ES’B tU! 4 * •S 10 ^ 1 ® ? ^ ,3 ^BEE ,5 ^*a i7 ^ ,, [GiD 1# !Xl

Pig 10.— Tentative lithostradgraphic correlation between the Jurassic series of Southern, Central and Northern Tunisia. 1.

Triassic gypsum; 2. peritidal dolomites; 3, limestones partially dolomitised; 4, black shales: 5, ferruginous ooids or

ironstones; 6. compacted carbonates; 7. nodular limestones; 8. "ammonitico rosso" facies; 9. radiolarites; 10,

resedimented limestones; 11, calciturbiditcs: 12, cherty limestones; 13, reefs: 14. calcareous ooids; 15. sandstones; 16.

unconformities: 17. hiatus; 18. glauconitic grains; 19. bipyramidal quartz cristals; 20. sheet cracks; 21. birds-eyes; 22.

cross-bedding; 23. wood fragments; 24. slump; 25. algal laminations; 26. oncoliths; 27, benthic foraminifera; 28,

pelecypods; 29, brachiopods; 30, gastropods; 31, echinoderms: 32, fish bones; 33. Zoophycos\ 34, filaments; 35.

ammonites; 36, belemnites; 37. Protoglobigerina; 38. radiolaria; 39. Saccocoma: ; 40. Aprycus: 41. calpionnellids.

FlG. 10 .— Tentative tie correlation I it host rat ig raph i q u e entre les series du Jurassique de la Tunisie Meridional Centrale et

Septentrionale. 1. gypses du Trias ; 2, dolomiesperitidales ; 3. calcairespartiellement dolomitis&s ; 4. “black shales'' ;

5. oolithes ferrugineuses on "ironstones ” ; 6. carbonates compactes : 7, calcaires en mic/ies ou pseudonodulaires ; 8,

facies "ammonitico rosso" : 9. radiolarites ; 10. calcaires residimentes ; II. calciturbiditcs ; 12. calcaires a silex ; 13,

recifs ; 14. oolithes calcaires; 15. sables et silts ; 16. discordance ; 17. lacune stratigraphique : 18, grains de

glauconie ; 19. quartz bipyramidal; 20. fentes de dessiccation ; 21, "birds-eyes" ; 22, stratifications obliques ; 23,

fragments de bois ; 24. "slump" : 25. laminations algaires ; 26. oncolithes : 27. foraminiferes benthiques ; 28.

lamellibranches ; 29. brachiopodes ; 30, gasteropodes ; 31. echinodermes ; 32, os de poissons : 33, Zoophycos ; 34,

filaments : 35, ammonites ; 36. belemnites ; 37. Protoglobigerina ; 38, radiolaires : 39. Saccocoma ; 40, Aptycus . 41.

calpioneUes.

The lower Toarcian transgressive episode locally represented in Central Tunisia by the “black

shales” (U V! ) has been recorded in the Tunisian Dorsale and adjacent areas by black laminated marl-

limestones rich in organic matter and fish traces (RAKUS & BlELY, 1970; Gaudant et a! 1972; SOUSSI

eta!., 1992).

In Southern Tunisia, during the Toarcian(7), the sedimentation was dominated by the Mestaoua

gypsum deposited in sub-aqueous evaporite basin (BEN ISMAIL & M’RABET, 1990), but in our opinion a

Source. MNHN. Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

part of the Zmilet Haber could correspond to the early Toarcian and the Mestaoua gypsum to the upper

Toarcian-Aalenian. This hypothesis has to be confirmed by faunal arguments.

The Bajocian transgressive phase represented in Central Tunisia by the development of ironstones

and hemipelagic limestones (U 3I , U 32 ) corresponds in Northern Tunisia to the mud-limestones rich in

radiolarian, filaments, calcispheres and Zoophycos of the Kef el Orma Formation (BONNEFOUS, 1972:

FAURE & PEYBERNES. 1986). In Southern Tunisia, it corresponds to the shallow marine Krachoua

carbonates overlying the Mestaoua gypsum (BUSSON, 1967; BEN ISMAIL & M'Rabet, 1990; KAMOUN.

1988; ZARBOUT&Ghanmi. 1997) (Fig. 10).

The major and widespread transgressive episode, occurring at the late Callovian, is represented in

Central Tunisia by the deposition ol a pelagic condensed section unconformably overlying middle

Bathonian rocks. In Southern Tunisia, it corresponds to the relatively deeper carbonates of Beni Oussid

member (Foum Tataouine Formation; BEN ISMAIL et al ., 1989), attributed to the late Bathonian by

KAMOUN (1988) and recently to the Callovian on the basis of ostracods (METTE, 1997). These facies

may be considered then as the equivalent of the marl and limestone alternations of the lower part of El

Haouareb section in Central Tunisia. In Northern Tunisia, the Callovian transgressive event has been

marked by a marine deepening illustrated by the development of pelagic and radiolarite beds

(BONNEFOUS, 1972; ALOUANI et al., 1990; SOUSSI et al ., 1998). This major transgressive phase is

marked within the Chott basin by an angular unconformity and at Jebel Tebaga de Medenine by the

juxtaposition of the Jurassic series to the Permian rocks.

The Kimmeridgian transgression was recorded both in Central and Northern Tunisia by the

deposition ot Saccocoma -rich muddy limestones, while in Southern Tunisia it was represented by the

deposition of the Bir Miteur bioclastic carbonates overlying the Merbah el Asfer silisiclastics Formation

(KAMOUN et at. 1994: BEN ISMAIL. 1991).

Regressive phases

The major regressive phases are recorded in Southern Tunisia by; first the evaporitic deposits (upper

part of the Mestaoua gypsum) upper Toarcian-Aalenian, second the ramp silisiclastic deposits of the

Bathonian Techout Formation and thirdly the Oxfordian Merbah El Asfer siliciclastic deposits.

In Northern Tunisia, the regressive phases are difficult to distinguish, but they are particularly

marked by an increase of detrital supply during the late Toarcian and Bathonian.

Unconformities and hiatuses

The three major unconformities and their associated hiatuses identified in Central Tunisia are not yet

well defined in Northern Tunisia, and particularly so in Southern Tunisia where environments of

deposition were often shallow and chronostratigraphic resolution is poor. In this latter region, they

correspond rather to lithologic and environmental discontinuities.

In the Tunisian Dorsale and adjacent areas, discontinuities exist but they are not marked by hiatuses

as important as in Central Tunisia. They are, rather, expressed by condensed deposits with small

hiatuses, notably within the upper Sinemurian-Carixian, Aalenian (FAURE & PEYBERNES, 1986) and

lower Oxfordian (SOUSSI et al., 1999).

In Northern Tunisia, the transition from the lower Bajocian muddy limestones to the upper Bajocian

shales and packstones (Bent Sai'dane Formation) is marked by centimetric conglomeratic horizons rich

in reworked pebbles derived from the underlying carbonates. Locally, in Bou Gamine of Hammam Lif.

the two mega-breccias composed of Liassic blocks redeposited within Bajocian-Bathonian marls, were

mostly created by local tectonic activity (COSSEY & Ehrlich, 1981). The possible equivalent of the

discontinuity that marks the upper Bathonian-lower Callovian in Central Tunisia is not currently

identified in the Dorsale, neither by fauna nor by sedimentologic criteria.

Within the “ammonitico rosso facies” (upper Callovian-upper Oxfordian), condensed deposits are

frequent and the lower Oxfordian is usually lacking.

MOHAMED SOUSSI ETAL.

In Southern Tunisia, due to the absence of biostratigraphic markers, hiatuses are not easy to

demonstrate. The two first intra-Jurassic unconformities identified in the nosa (UCI+UC2) could

correspond in Southern Tunisia to the major lithologic changes occurring from the middle Liassic

Zmilet Haber limestones to the Toarcian-Aalenian (?) Mestaoua gypsum and from the Bajocian

Krachoua limestones to the Bathonian Techout sandstones.

This regional correlation demonstrates clearly that the several Jurassic deepening and shallowing

episodes and their correlative transgressions and regressions have been recognised simultaneously in

Northern. Central and Southern Tunisia. This implies that in Tunisia the eustatic factor has played a

great part in controlling Jurassic sedimentation. Nevertheless, a number of sedimentological and

strdtigraphical events (hiatuses) occurring particularly in Central Tunisia, have been controlled by

regional tectonics. This will be demonstrated by comparing the Central Tunisia sedimentary record to

the Jurassic sea level curve of HALLAM (1988) and the global diagram of Jurassic sedimentary cycles ol

Vail et al. (1977) and HaQ et al. (1987).

JURASSIC SEDIMENTARY RECORD IN CENTRAL TUNISIA

AND GLOBAL SEA LEVEL CHANGES (FIG. 11)

One century ago. E. Suess recognised the importance of sedimentary cycles in stratigraphy and

attributed them to fluctuations of sea level. Then, several works demonstrated that some of these cycles

could have extensive repartition and could then be used as a tool in global correlation. More recently,

the sequence stratigraphy approach, largely developed since the first publication of Vail el id. (1977).

stimulated the re-examination of basin sedimentary records. It is well established now that eustasy and

tectonics constitute the major factors controlling the relative changes in sea level which create the

available space for accommodation of the sediments (SARG, 1988).

On the basis of abundant data collected essentially from NW Europe. Vail et id. (1977) and Haq et

al. (1987) constructed a global diagram or chart including a global eustatic curve and the main orders of

sea level fluctuations (first, second and third order). From the lower Hettangian to the upper Tithonian,

their diagrams showed seven second order cycles including 27 third orders cycles separated by 26 type 1

or 2 unconformities (Haq et al.. 1987).

Our objective is not to deduce these cycles and their separating discontinuities from the chart using

the ammonite zones detected in the NOSA, but to test the curve and the global cycles by reference to our

data in order to distinguish the global eustatic signal from regional tectonics.

A comparison of the framework of sea level history documented by HALLAM (1975, 1988), VAIL et

al. (1987) and Haq et al. (1987) to the sedimentary record and sea level evolution of Jurassic in Central

Tunisia requires the following comments.

— The overall trends of the sea level curve constructed for the NOSA, on the basis of detailed facies

analysis coupled to precise dating using ammonites, compared to the curve of theses authors are closely

similar. Both curves show major transgressive pulses during the Pliensbachian, the early Toarcian, the

early Bajocian. the late Callovian and the Kimmeridgian (Fig. 1 I). The regressive tendency signalised

during the Domerian. the late Toarcian. the late Bathonian and the late Oxfordian (HALLAM. 1988) in

NW Europe have also been identified in Tunisia.

— The third order cycles or depositional sequences reported in the Haq et al. (1987) diagram, from

the Hettangian to the Tithonian, are not completely recorded in Central Tunisia. Here, only five

significant (second order) major transgressive-regressive cycles have been distinguished.

These cycles extend from the Hettangian to Carixian. the early to middle Toarcian, the early

Bajocian to middle Bathonian and the upper Callovian to upper Oxfordian. The fifth sequence is not

well dated but may have started during the Kimmeridgian and extends to the upper Tithonian. They are

separated by three major unconformities associated with hiatuses, the duration of which ranged from 4

to 12 Ma. These cycles approximately correlate with the second order cycles recognised in NW Europe

by HAQ et al. (1987). The first, constituted of Uland U2 lithologic units, corresponds to amalgamated

sequences situated since 21 1 to 188.5 Ma in the chart of HAQ et al. (1987). The Toarcian transgressive

part of the second order sequence corresponds in part to the major cycle situated between 188.5 and 177

Source: MNHN. Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

Ma. while the Aalenian cycle is completely absent within the NOSA series. The third Bajocian-Bathonian

transgressive-regressive cycle, recognised in Central Tunisia, correlates quite well with the major cycle

ot Haq et al. (1987) situated between 169 and 158.5 Ma. While the fourth and the fifth transgressive-

regressive cycles in Central Tunisia could correspond to the cycles comprised between 158.5 and 138 or

136 Ma (?).

— The major sea level tails recorded during the Jurassic and shown within the Haq and Vail

diagrams, coincide perfectly with the unconformities identified in Central Tunisia (Fig. I 1).

The first unconformity (UC1), which is accompanied by the Carixian /x/x-Domerian hiatus,

coincides with the eustatic fall noticed al 188.5 Ma. The second unconformity (UC2), accompanied by

the gap of the upper Toarcian-Aalenian, coincides with the eustatic fall dated 177 Ma. The third

i£SS 2 f~~^ 4©J uc

Fig. I I.— Comparison of the Jurassic stratigraphy and sedimentary cycles of Central Tunisia to the global cycles of Haqc/ al.

(1987) (for the lithological legend see figure 2). 1, stratigraphic hiatus (submarine non-deposition/erosion); 2.

unconformity; 3, second order tectono-eustatic transgressive-regressive cycle, black = transgressive half-cycle, grey =

regressive half-cycle; 4. major extensional tectonic event: 5. UC: major unconformity.

F/G. II — Comparaison de I'enregistrement stratigraphique et des cycles sedimentaires dn Jurassique de Tunisie cent rale aux

cycles globaux de Haq et al.. 1987 (pour la legende lithologique, voir legende de la figure 2). I. lacune

stratigraphique ; 2, discordance ; 3. cycle transgress if- regressif de deuxieme ordre d'origine tectono-eustatique, noir =

demi cycle transgressif gris = demi-cycle regressif: 4. evenement tectonique distensif majeur : 5. UC : discordances

majcures.

Source.

MOHAMED SOUSS1 El' AL .

unconformity (UC3), accompanied by the hiatus of the upper Bathonian-lower Callovian, could be

correlated to the eustatic fall of 158.5 Ma (Haq el al.. 1987).

The sequence boundaries indicated at 188.5. 188 and 186.5 Ma converge to the major unconformity

(UC1). Those dated 184. 179.5 and 177 Ma meet the unconformity UC2 and those attributed to 155.5,

158.5 and 159.5 match the unconformity UC3 (Fig. 11).

— The Jurassic condensed sections of the specific series of the NOSA (Central Tunisia), which

consist in thin pelagic deposits characterised by abundant and mixed planktonic and benthic fossils

associated with authigenic minerals such as glauconite, phosphate and iron oxides, occurred during

Carixian. early Toarcian, Bajocian. late Callovian-early Oxfordian times. They coincide with the second

order peak transgressions indicated within HAQ et al. (1987) at 191.5 Ma, 183.5 Ma, 170 Ma, 153.5 Ma

and 150 Ma? (Fig. 11).

DISCUSSION

The sedimentary cycles of Central Tunisia are not complete and their separating unconformities are

considerably longer than the duration of unconformities dividing the Jurassic supercycles of HAQ el al

(1987).

The hiatuses identified within the Jurassic series in Central Tunisia, separate deep marine facies and

their corresponding discontinuities did not show any trace of emergence features. Thus, they have to be

considered as deep marine hiatuses caused by erosion or non-deposition. The lack of sediments or the

slowing of sedimentation within deep-water facies may be caused by rapid and drastic changes of sea

level. Maximal of hiatuses occurred in Central Tunisia in the Domerian. late Toarcian-Aalenian and late

Bathonian. Their correspondence with the major falls of sea level indicated within the Haq et at. (1987)

chart is remarkable and suggests at first sight that these major sea level falls should have played an

important role in the development of these hiatuses.

This could be the case for the upper Toarcian-Aalenian and upper Bathonian gaps which coincide

with the maximum point of the regressive parts of the second order cycles of HAQ et al. (1987) (Fig.

I 1). The gaps associated with the condensed sections occurring during the late Carixian, Bajocian and

Callovian seem to be associated with the maximum water depth following a rapid rise of sea level. In

tact, it is well known nowadays that during sea level high stands, especially when they follow a rapid

rise of sea level, sediment supply tends to be trapped close to the shore line and the outer shelf regions

become starved of sediments or characterised by slow sedimentation.

In Tunisia, the greatest hiatus abundance occurred within the NOSA and the duration of each hiatus

varies from Central to Northern Tunisia and appears to depend upon the position of the section on the

continental margin (Fig. 9). In addition, the studies carried out towards the west of the NOSA (BEDIR.

1995) demonstrated the existence of the major second order cycles identified by HAQ et al. (1987) and

the seismic profiles also clearly show that the Jurassic series are relatively thick and more complete to

the west (Majora et Sidi AYch blocks).

Such differences result from the tectonic configuration of Central Tunisia which corresponded during

Jurassic and Cretaceous time to a platform structured into horsts and grabens delimited by N-S and

nearly E-W faults. Within this platform, the NOSA has acted as an active uplift block characterised by

very condensed sedimentation compared to other domains where the Jurassic series are more complete

and very thick, such as the Chott Basin to the south and the Tunisian trough to the north (Fig. 9). The

unconformities identified within the NOSA area, have also been identified in other areas of the Tethyan

realm (HALLAM, 1978; GABILLY et al.. 1985), but their duration is nowhere greater than in Central

Tunisia. Thus, these unconformities could be inteipreted as the result of the effects of major sea level

fluctuations (transgressions or regressions) enhanced by local tectonic activities.

hi tact, the hiatuses identified in Northern and especially in Central Tunisia within the middle Liassic

and the Dogger are very close to the tectonic movements associated with the rifting of the Tethys. On

the NOSA mega-block (from Jebel Rheouis to Jebel Loridga), the sedimentation was particularly very

condensed and hard-grounds coalesce to form composite condensed sections particularly on the highs of

the block (Loridga area). Submarine erosional activities during the falls or rises of sea level constituted

Source: MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

the rule on this submerged swell. The activity ot currents is recorded by the presence of reworked

Toarcian lithoclasts within the Bajocian rocks, the cross bedding stratification, the association of

numerous ammonite zonal marker species in the same bed. in addition to the local record of upper

Toarcian, Aalenian and lower Callovian as lenses bodies delimited by erosional surfaces. Only during

the highlands 'maximum transgression), the NOSA block has recorded sedimentation processes

Sedimentation occurred approximately during the second order transgressive phases of the second order

cycles or HAQ et al. (I Vo /).

™ U 'Y ll l l l n , g ‘I 16 majo1 ,' falls or rises of sea level - especially those, which coincide with tectonic

events the NCSA has acted as a starved platform. The unconformities identified within the Jurassic of

Central Tunisia are abruptly overlain by more marine facies. The five second order transgressive-

regressive cycles identified within the NOSA Jurassic series have been clearly controlled both by sea

level changes and the tectonic phases associated to the Tethyan rifting. They can be assimilated to

second order tectono-eustatic cycles and their separating unconformities and hiatuses result from the

combination ot sea level changes with the tectonic activities (Graciansky et al., 1993).

CONCLUSION

The faunas

The faunas show a sub-mediterranean character and are known in open sea environments of Peri-

Tethyan platforms: Morphoceras, Ebrayiceras in the Bathonian; Rehmannia , Collotia and

Hecticoceratidae in the Callovian; Taramelliceras, Campylites, Peltoceratoides and several

Perisphinctidae in the Oxfordian. Thus, they integrate well in the palaeogeographic schemes which

underline the faunal homogeneity of the western part of the Tethys where the ibcro-moorish strait

allowed faunal exchanges. Tunisia as well as Sicily and the Malta scarp mark the eastern boundary of

the extension of the dominant submediterranean faunas on the Southern Tethyan margin. Eastwards, in

southern Turkey and as far as Malagasy, the submediterranean European laxa are only episodically

As a result, ages and correlations are referred to the biochronological standard for the

submediterranean Europe. However, in the beds at the Callovian-Oxfordian boundary, boreal

caidioceratids which are the basis of the zonation used in Europe are missing, especially for the

Oxfordian,. So, the more typical sub-mediterranean taxa (oppeliids. perisphinctids, peltoceratids and

euaspidoceratids) and the parallel zonations based on these families have been used.

Concerning biogeography, as in Algeria and Morocco, abundant Emileia in the lower Bajocian and

Oramceras in lower Bathonian attest the South Tethyan character of the faunas, as well as the lack of

the boreal and sub-boreal families (cardioceralids and kosmoceratids) at the Callovian-Oxfordian

boundary. The lack of sub-mediterranean hecticoceratids of the same age is not so easy to understand, as

the occurrence of Phylloceras and Lytoceras from the upper Callovian up to the lower Oxfordian

indicates a clear deepening of the sea which normally is auspicious for oppeliids.

The deeper marine environments of the Jurassic of the NOSA explain the lack of Arabian taxa, which

are known westwards in Western Algeria and Morocco, although Tunisia is on the south Tethyan

migration route often used by the Arabian taxa. The migration route was probably south of the NOSA,

probably in the Chott area where environments were very shallow in which the Arabian taxa were

adapted. Except for the Fount Tataouine Formation yielding upper Callovian Pachyerymnoceras, other

South Tunisia formations do not contain ammonites. Old collections of M. Rakus include one specimen

of Ermoceras gr. coronatoides (Douv.). badly preserved, especially the ventral area, from the Bajocian

limestones with ferruginous ooids at Kef el Hassine. The existence of the Arabian genus Ermoceras in

Tunisia is very probable, but needs to be confirmed by new better-preserved specimens.

MOHAMED SOUSSI ETAI..

THE SEDIMENTARY RECORD

Five major transgressive-regressive cycles have been at least recognised in Northern, Central and

Southern Tunisia. The transgressive episodes occurred during the Pliensbachian. early Toarcian, early

Bajocian, late Callovian and Kimmeridgian. The corresponding palaeogeographic evolution has been

influenced by both tectonic and eustatic factors. In Central and Northern Tunisia, tectonic events

occurred during the late Sinemurian. Bajocian. Callovo-Oxfordian and early Tithonian and led to the

differentiation of faulted blocks with horsts and grabens.

Since the Pliensbachian, Central Tunisia acted as a pelagic platform structured into horsts and

grabens limited by approximately E-W faults. Within this structural framework, the North-South Axis

area has acted as a resistant block (uplift) characterised, especially during Middle Jurassic, by condensed

deposits and hiatuses. The NOSA Jurassic series presents specific features compared to those of

Centralwestern and Northwestern Tunisia. It is less thick and includes specific facies (ironstones) and

numerous stratigraphic hiatuses. The hiatuses and discontinuities, particularly frequent in the high

domains of the structural framework, are closely related to the tectonic instability and the increase of

erosive activity by submarine currents on highs during the major eustatic changes. The active circulation

of the deep currents and their corrosive action (sweeping and dissolution) on the biogenic material,

notably on the highs of the tilted blocks during major transgressions or regressions, have notably

reduced the sedimentation rate and consequently controlled the extent and duration of the sedimentary

hiatuses.

The three unconformities accompanied by hiatuses correspond to the superposition of several

discontinuities (VAIL el a /., 1987) and can be interpreted as enhanced tectonic sequence boundaries. The

frequency of the unconformities and hiatuses is then due to the combined effects of the local tectonic

factor and the global eustatic one. Tectonic activity which is linked to the Tethyan rifting created a

pattern of tilted blocks involving palaeohighs which were isolated from sediment supplies, notably

during either the maximum regressive periods when sedimentation was displaced towards the basin

(progradation phase) or during rapid sea level rise when sediments were caught on the inner shelf.

Sedimentation has been recorded only during the aggradational-retrogradational phases of the second

order cycles.

Comparison of the NOSA Jurassic sedimentation pattern with the global cycles shows clearly that

numerous third order cycles of the chart of Haq el al. (1987) are not registered in this part of the

margin. Only the second order ones, marked by major faunal and sedimentological changes, are

recognisable. The Jurassic sedimentary and stratigraphic records of Central Tunisia represent a good

illustration of the interaction between the global eustatic signal and regional tectonic activities. It

demonstrates what was suggested by H.ALLAM (1988): “there is no region that can give a definitive

picture of the sequence boundaries for the whole world, and that regional tectonics can be discounted".

Because of the abundant hiatuses and their long duration, the NOSA region cannot be used as a

standard for eustatic analysis. The third order sequences recorded al a global scale are usually missing

especially on the highs of the tilted blocks.

ACKNOWLEDGEMENTS

This work is a part of research projects sponsored by CONOCO. ETAP, and Peri-Tethys Program

(Proposal 96/128). We are thankful to these for their logistic support. We gratefully acknowledge Mr A.

M'RABET for stimulating many discussions and helpful comments. Thoughtful reviews by .1. THIERRY

and two anonymous reviewers greatly helped in improving the paper. We also especially thank CH.

ABBES for productive discussions.

Source. MNHN, Paris

THE JURASSIC EVENTS IN CENTRAL TUNISIA

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Source: MNHN. Paris

The Tethys southern margin in Morocco; Mesozoic

and Cainozoic evolution of the Atlas domain

Alain PIQUE'", Mohamed CHARROUD 121 , Edgard Laville ",

Lahcen An BRAHIM " & Mustafa AMRHAR "

(I) Departement des Sciences de la Terre et IUEM. Universite de Bretagne Occidentale

Place Nicolas Copernic. F-29280 PIouzan6 Cedex, France

(2) Departement de Geologic. Faculte des Sciences ct Techniques du Sai's, route dTmouzzer. B.P 2202. Fes. Maroc

(3) Departement de Geologie, Universite de Caen, Esplanade de la Paix. B.P. 5186, F-14032 Caen Cedex. France

(4) Departement de Geologie, Faculte des Sciences, Avenue Ibn Batouta, B.P. 1040. Rabat. Maroc

(5) Departement de Geologie. Faculte des Sciences Scmlalia, Boulevard Amir Moulay Abdallah. B.P. 2390. Marrakech, Maroc

ABSTRACT

As the central and southern Rif. the Atlas domain of Morocco constituted the southern margin of the Tethys during the

Meso-and Cainozoic. Its polyphase development recorded the geodynamic evolution of the African plate and the correlative

opening ol the Tethys ocean: I) the Late Triassic-earliest Liassic times have been characterised by the initiation and

development of the NE-SW trending Atlasic rift which aborted during the early Liassic; 2) the Middle and High Atlas troughs,

respectively NE-SW and WSW-ENE trending, developed in response to a sinistral transtensive motion along the N 70°E

trending faults, inherited from the Hercynian orogeny: 3) the Atlasic inversion was realised in two times: by a sinistral

transpressive deformation during the Late Jurassic-Early Cretaceous, and by the uplift of the chain during the Neogene.

RESUME

La marge sud de la Tethys au Maroc : evolution du domaine atlasique au Mesozoique et au Cenozoique.

Tout comrnc le Rif central et sud. le domaine atlasique du Maroc constiluait la marge meridionale de la Tethys au

Mesozoique et au Cenozoique. Son developpement a done enregistre les etapes successives de^ revolution de la plaque Afrique

et de rouverture de Focean Tethysien. avec notamment : I) le developpement puis ravortement du Rift atlasique, NE-SW. au

Trias superieur-Lias basal : 2) I 'individualisation des Sillons moyen- et haut-atlasique, respectivement NE-SW et WSW-ENE.

en reponse a un mouvement transtensif senestre le long de failles N 70°E heritees de Forogenese hercynienne ; 3) I'inversion

atlasique, elle-meme realisee en deux temps : une transpression senestre au Jurassique superieur-Cretace inferieur, ct le

soulevement de la chaine au Neogene.

Piqub. A., Charroud, M.. Laville, E.. AItBrahim, L. & Avirhar. M., 2000.— The Tethys southern margin

in Morocco : Mesozoic and Cainozoic evolution of the Atlas domain. In: S. Crasquin-Soleau & E. Barrier (eds). Peri-

Tethys Memoir 5: new data on Peri-Tethvan sedimentary basins. Mem. Mits. natn . Hist. Nat., 182 : 93-106. Paris ISBN :

2-85653-524-0.

Source: MNHN , Paris

ALAIN PIQUE ETAL.

INTRODUCTION

At the beginning of the Mesozoic, the Central Atlantic ocean opened between North America and

Western Africa. The continental rift was limited to the east by the unstretched continental crust of the

Central Moroccan Meseta and to the north by a transform fault zone which corresponds to the eastern

prolongation of the present Azores-Gibraltar zone and represented at that time the northern limit of the

individualising African plate (PIQUE & Laville, 1996). This WNW-ESE to E-W transform fault

separated east-travelling Africa from Eurasia (DERCOURT et al., 1993) and it corresponded to the

western end of the Tethys ocean, propagating to the west (Tethyan reconquest: AUBOUIN, 1980).

Consequently, Morocco corresponded to a triple point, at the intersection of a NNE-SSW continental rift

— the Central Atlantic rift— and the western extremity of the Tethys, between Africa and Eurasia.

Later, the eastern passive margin of the Central Atlantic ocean remained undeformed, while the southern

margin of the Tethys in Morocco was affected by the Alpine orogeny. Since this transform boundary has

been intensively reworked and integrated in the allochthonous units of the Rif belt, it is not possible to

reconstruct the Meso- and Cainozoic palaeogeographic evolution of the southern Tethysian platform.

This evolution can. however, be studied south of the Alpine Rif belt, in the relatively weakly deformed

and unmetamorphosed Atlas. The aim of the present paper is to analyse the Meso- and Cainozoic

evolution of the Moroccan Atlas domain, especially in its central part, through the presentation of

palaeogeographic maps drawn for several key-periods. A preliminary short presentation of the

Hercynian basement structures will help to discuss their control on the Mesozoic palaeogeography.

THE PALAEOZOIC INHERITED STRUCTURES

In Morocco, except in its southernmost part, the Tindouf basin, which belongs to the West African

craton, the Palaeozoic sedimentary series were deformed, metamorphosed and intruded by granitoids

during the second half of the Palaeozoic (PIQUE & MlCHARD, 1989). The resulting chain corresponds to

and prolongates the Hercynian (=Variscan) belt of western Europe. Its main characteristics is the

inhomogeneous nature of the regional deformation: intense folding and faulting and a relatively high

grade metamorphic evolution concentrated along narrow and elongate regional shear zones that separate

wider areas which remained poorly deformed. The most important of these regional shear zones (Fig. 1)

are :

— the Atlas Palaeozoic transform zone (APTZ). Trending 70°E to E-W. it separates the Hercynian

orogenic domain to the north from the pericratonic Anti-Atlas to the south. It acted with an important

transcurrent component and its dip is generally steep:

— the Marrakech-Oujda shear zone, or lineament (MOL), which trends NE-SW, parallel to the axis

of the eastern belt of the Moroccan Hercynian chain. It dips at low angle to the southeast;

— the Western Meseta shear zone (WMSZ), N 20°E, characterised locally by an important

metamorphism and a strong deformation (PIQUE et al.. 1980). It corresponds to the western limit of the

late Dinantian-Early Carboniferous Sidi-Bettache basin;

— the Sehoul shear zone, which trends E-W. It limits to the south the Sehoul “Caledonian" belt and

it was reactivated during the Hercynian orogeny.

The last period of the Palaeozoic times, i.e. the Permian, is scarcely represented by red sandstones

conglomerates and felsic lavas. All of these rocks, either sedimentary or magmatic, yielded Early

Permian ages (e.g.. BROUTIN et a !., 1989; YOUBI et al ., 1995; etc.) and, as far as we presently know,

neither Late Permian nor Early Triassic are represented.

Source: MNHN. Paris

THE TETHYS SOUTHERN MARGIN IN MOROCCO

Fig. 1.—The Hercynian regional structures in Morocco. APTZ: Atlas Palaeozoic Transform Fault: MOL: Marrakech-Ouida

Lineament; WMSZ: Western Meseta Shear Zone

Fla s structures hercyniennes d'importance regionale an Maroc. APTZ : Zone transformante paliozoique de TAtlas •

MOL : Lineament Marrakech-Oujda : WMSZ: Zone cisaillee de Meseta occidentale.

LATE TRIASSIC-EARLY LIASSIC: THE ATLANTIC AND ATLASIC RIFTING

The Mesozoic sedimentary rocks known in Morocco unconformably cover the folded and eroded

Palaeozoic rocks. The oldest Triassic sedimentary sequences are Camian in age (locally late Ladinian in

northeast Morocco: OUJIDI et al. 1997). They are found: i) in faulted basins distributed in the present

Atlantic margin. They correspond to the synsedimentary deposits of the Atlantic rift (LeRoy, 1997; LE

Roy et al, 1997) and they are not considered here; ii) in halfgrabens located from Middle to Central

High Atlas (Fig. 2). Their active border faults, mainly NE-SW trending, are reactivated Hercynian

thrusts and reverse faults (LAVILLE et al, 1995). The left-lateral oblique faults like the Tizi n'Test fault

correspond to Hercynian N 70° strike-slip faults (Beauchamp, 1988). The synsedimentary activity of

the halfgrabens is indicated by the facies distribution and the thickness lateral changes of the

sedimentary sequences. The subsidence decreased during the Norian and the halfgraben border faults

were sealed up by the lower Liassic carbonates. Contemporaneously with this crustal extension,

tholeiitic magmas were emplaced (BERTRAND et al, 1982) and a thermal How occurred, indicated by

the alteration of the uppermost Triassic-lowermost Liassic basalts and by the development of a very low

grade paragenesis (BENCHEKROUN et al. 1987). probably hydrothermal, dated al about 200 Ma (HUON

et al, 1993; CLAUF.R et al, 1995: Rais, work in progress). All of these structural, metamorphic and

magmatic arguments suggest that an intracontinental rift, the Atlasic rift, developed from the Middle

Atlas to Central High Atlas, in a NE-SW direction parallel to the Atlantic rift. Contrary to the Atlantic

rift, which led to the oceanic accretion, the Atlasic rift aborted during the earliest Liassic.

The postrift early and mid-Liassic carbonate shelf extended over a large part of northern Morocco,

tar from the limits of the former Atlasic rift. During the Carixian for instance, various sedimentary

facies characterised this shelf (Fig. 3):

— chert limestones which sometimes graded laterally to reefal buildings. These limestones are

restricted to the axis of the future Atlasic troughs;

— oolitic limestones;

Source:

ALAIN PIQUE £T/\Z..

Fig. 2.— The Late Triassic-earliest Liassic Atlasic rift (from LavilLE & Pique, 1991). I. TnT: Tizi n'Test Fault: 2, Lower

sequences (Carnian): 3. Upper sequences (Norian); 4. post-Triassic; 5. doleritic dike.

FlG. 2. - Le rift atlasique du Trias superieur-Lias basal (dapres LAVILLE & PlQVE. 1991). I, Tnt : Faille dit Tizi n'Test ; 2,

series inferieures (Carnien); 3. series superieures (Norien); 4, terrains pust-triasiiqnes ; 5. dykes doleritiques.

— transitional facies: dolomitic limestones and shelly Hesperithyris limestones with argillaceous

intercalations. These “Itzer beds" are located on some intrabasinal highs, as the Haute Moulouya

threshold, in the Midelt area.

LATE LIASSIC-BATHONIAN: THE ATLAS TROUGHS

At the limit between the Domerian and the Toarcian. a transtensive fracturation of the former

carbonate shelf occurred, individualising the Middle Atlas and High Atlas troughs made of coalescent

lozange-shaped depocentres which were limited by synsedimentary normal and transcurrent faults,

N 50°E in the Middle Atlas and N 70°E in the High Atlas (Fig. 4). The fracturation of the mid-Liassic

shelf was contemporaneous with the beginning of the oceanic accretion in the Central Atlantic. At that

time, the eastward drift of Africa was triggered, inducing new intracontinental stresses in the northern

part of the Africa plate. As a result, the crustal weakness zones were reactivated in this new stress field

and, as for the Late Triassic rifting episode, in many cases one can effectively demonstrate that the

border faults of these basins correspond to Hercynian structures. This is obvious for the southern limit of

the High Atlas basin, which corresponds to the former Atlas Palaeozoic transform fault, and for the

southeastern limit of the Middle Atlas trough, parallel to the former Marrakech-Oujda shear zone.

In the two subsident troughs a thick pile of marine sedimentary sequences was deposited from the

late Liassic to the end of Dogger, in contrast with thin or even absent contemporary deposits outside the

troughs. The main sedimentary facies which characterise this period are:

— yellow cephalopods marls which often contain turbiditic horizons, deposited in the Atlasic trough

axis;

— encrinitic limestones indicative of inner shelf conditions at the margins of the Atlasic troughs;

— red clays (Mibladen series), which were deposited in the Moulouya and Oranese Meseta areas in a

lagoonal environment with tidal flats and frequent emersions.

Source. MNHN , Paris

THETETHYS SOUTHERN MARGIN IN MOROCCO

Fig. 3 — Palaeogeography ol the central Atlasic domain during Carixian times from CHARROUD (unpublished). Location of the

represented area: see Fig. 4. 1. intrabasinal heights; 2. transitional facies (Itzer beds); 3, reefal formations- 4 inner shelf-

lnner she *‘ : ooliIIC limestones with continental influences; 6, outer shelf and basinal facies. Bedded and chert

limestones; 7, continental inland.

Fic. 3.— Paliogiographie du domaine atlasique central an Carixien, d’apris Charroud (inedit). Localisation de la zone

representee : voir hg. 4. I. hauts-fonds ; 2, facies de transition (facies d'Itzer ).- 3. recifs ; 4. plate-forme interne • 5

plate-forme interne : calcaires oolitiques a influences commentates : 6. plate-forme externe el facies de ba'ssin

Calcatres en plaquettes et a cherts : 7. terres emergees.

The maximum depth of the basins was attained between the early Aaleno-Bajocian and the late

Bajocian, with the deposition of deep basin facies: the early Aaleno-Bajocian Posidohomva Boulemane

marls with turbiditic intercalations. The deposition of the late Bajocian, so-called “Calcaire comiche”, a

reefal and oolitic limestone indicative of open shelf environments, marked the progressive filling of the

troughs. However, deep basin conditions persisted as long as the late Bajocian in the northeastern part of

the Middle Atlas trough where they are represented by the “Marnes de Sakka superieures”.

In the Middle Atlas domain deposition of the the late Bajocian “Calcaire corniche” marked the

beginning of the northeastward retreat of the sea. In the main part of the Atlas trough, the "Calcaire

corniche” was covered by red beds, mostly aerial, deposited in a para-deltaic and deltaic system (Fig. 5).

The numerous dinosaur tracks which were found in these strata indicate that they correspond to the Late

Jurassic and part of the Early Cretaceous. The orientation of the palaeo-currents and the nature of the

clasts suggest that they were originated from the Saharian domain like the contemporary Algerian Ksour

sandstones (DELFAUD & ZELLOUF. 1993). However, other source lands were represented by several

physiographic-ally high areas which furnished relatively immature clasts. Meanwhile, marine conditions

persisted in northeastern Morocco, where deep deltaic sediments were deposited (CATTANEO, 1991) and

in the western part of the High Atlas, connected to the young Atlantic (e.g., AMRHAR, 1995).

From a structural point of view, the rhomboida! shape of the depocentres and the arcuate shape of the

plutonic alkaline bodies (ZAYANE, 1992 and Fig. 6) emplaced in the central High Atlas during the Late

Jurassic argue for a strong transcurrent, sinistra! component in the Atlasic troughs along N 70°E faults

(Laville. 1988), perhaps associated with a normal N-S extension (Warme. 1988). In the eastern High

ALAIN PIQUE ETAL.

KS553 3

Fig. 4.— "Palaeostructural maps” of ihe central Atlasic domain from middle Toarcian to late Bajocian from Charroud

( unpublished, modified). Cartoon: studied area: a. marginal basins; I), Atlasic belt. 1, deltaic; 2, paradeltaic; 3, residual

shelf: 4. continental basins; 5. emerged area; 6. intrabasinal height: 7. tidal flats and lagoonal facies; 8. reefs; 9. shelf;

10. basin.

Fig. 4.— "Cartes paleostructurales " du domaine atlasique central du Toarcien moyen an Bajocien superieur d'apres

Charroud (inedit, modifie). Cartouche : zone etudiee ; a, hassins marginaux ; b, chaine atlasique. 1, deUnique ; 2.

parade Itaique ; plate-forme residuelle ; 4. bass ins continentaux ; 5, lerres enter gees ; 6, hauts-fonds ; 7. facies

lagunaires el tidal flats ; 8. reefs ; 9. plate-forme ; 10. facies de bassin.

Atlas, El Kochri & CHOROWicz (1996) suggested that the N 70°E trending faults were normal faults,

connected by NW-SE transfer faults. On the other hand, it is important to note that the Palaeozoic

basement is practically never represented in the Atlasic anticlines, where Triassic siltstones and/or

plutonic massifs crop out. This suggests that the deformation of Central Atlas was coeval with a general

decollement of the Mesozoic cover at the level of the Late Triassic sequences.

The main shortening in the Atlas axis was expressed by open folds locally accompanied by the

development of an incipient cleavage (Fig. 8). It occurred during the Late Jurassic-Early Cretaceous,

since the eroded hinges of some folds (in particular those which contain plutonic rocks) were

unconformably covered by transgressive strata of late Early Cretaceous age (Fig. 7). This tectogenesis

was not followed by any uplift of the mountain range.

Source MNHN. Paris

THE TETHYS SOUTHERN MARGIN IN MOROCCO

rif

Cenomanian

Idrissides land

Senonian • RIF .

. * Fes .. • •

. bobdou

Fig. 5.— “Palaeostructural maps" of the central Atlasic domain from Callovo-Oxfordian to Senonian from Charroud

( unpublished, modified). Same legend as Fig. 4.

Fic. 5.— "Cartes paleostruclurales" du domaine atlasique central du Callovo-Oxfordien au Senonien d'apres Charroud

( inedit, modifie). Mime lege tide que Fig. 4.

THE EARLY-LATE CRETACEOUS AND PALAEOCENE-EOCENE

This period was dominated by the general eustatic transgression which, in Morocco, proceeded

northeastward from the Atlantic and southwestward from the Tethys.

On the basis of sedimentological evidence (presence of marine sedimentary rocks in the western part

of the Atlasic domain and littoral conditions in the east), the marine Albo-Aptian deposits of Beni-

Mellal (Ouaouizart and Ait Attab basins) in the High Atlas and Boulemane (Tighboula-Oudiksou and

Ain Nokra basins) in the Middle Allas are classically considered as Atlantic-related, although faunal

similarities would suggest Tethysian affinities (CHARRIERE & Vila, 1991).

Evaporitic sediments with colored marls and gypsum were deposited during the early and middle

Cenomanian (Fig. 5). They grade westward into the marls and limestones of the inner carbonate shelf.

During the late Cenomanian-early Turonian, the transgression attained its maximum and the shelf facies

became homogeneous within the whole Atlasic domain. To the west, they covered the western Meseta

although small areas remained however emerged. To the north, the Idrissides land (CHOUBERT &

Faure-Muret, 1962) constituted the northern border of the seaway.

100

ALAIN PIQU£ E7 AL.

Eastern (Oranese)

53 6 4 2

5 ES3 3 CZD 1

Figs 6-8.— 6.—The Atlasic structures in the central High Atlas. Depocentres and plutonic massifs in the central High Atlas (a)

and schematic structural model of their distribution (b). From Laville (1988). 1. depocentre; 2. plutonic massif; 3,

transcurrent fault; 4. synsedimentary fold.

7. — The Tasraft ridge and anticline, central High Atlas, from Laville (1988). 1. Late Triassic-early Liassic doleritic

basalts: 2. Jurassic pluton; 3, Triassic siltstones; 4. Jurassic carbonates; 5. Callovian-Lower Cretaceous: 6. Upper

Cretaceous.

8. — Distribution of the cleavage in the central High Atlas from Laville et al.. (1991). 1. pluton: 2. Liassic to Bajocian;

3. Balhonian; 4. Upper Jurassic-Lower Cretaceous; 5, cleavage trajectory; 6. dyke.

FlGS 6-8.— 6 .— Les structures atlasiques dans le Haul Atlas central. Depocentres et massifs plutoniques dans le Haut Atlas

central (a) et modele structural schematique de leur disposition (b). D'apres Laville (1988). /, depocentre ; 2. massif

plutonique : 3. faille transcurrente ; 4, pli synsedimentaire.

7. La ride et F anticlinal de Tasraft. Haut Atlas central, d'apres Laville (1988). /. basal les doleritiques du Trias

lerminal-Lias basal ; 2. pluton jurassique : 3, siltites triasiques ; 4, carbonates jurassiques ; 5. Callovien-Cretace

inferieur ; 6. Cretace superieur.

8. Repartition de la schistosile dans le Haut Atlas central, d'apres Lwillec t al., 1991. I . pluton : 2. Lias a Bajocien ;

3. Bathonien ; 4, Jurassique superieur-Cretace inferieur : 5. trajectoires de la schistosite : 6, dyke.

The Senonian palaeogeography remained practically similar to that of the Turonian. the facies

changes resulting from the general regression. In the Atlasic domain, the fracturation of the Turonian

shelf produced small basins where confined facies (bituminous marls) were deposited between uplifting

and emerging areas characterised by phosphorite sediments (CHARROUD et ai , 1993). These Atlasic

bituminous marls (BENALIOULHAJ. 1991) were coeval with the Western Meseta phosphoritic deposits

indicative of the Atlantic shallow shelf. The Eocene marls, dolomites and gypsum are the last marine

deposits in the Atlas domain, sometimes covered by sandstones attributed to the Oligocene.

Noteworthy is the emplacement of Eocene alkaline magmas in two massifs, Taourirt (AGARD, 1950)

and Tamazert (BOUABDELI, 1987) of the Atlas domain (Fig. 9).

Source. MNHN, Paris

THE TETHYS SOUTHERN MARGIN IN MOROCCO

101

Mediterranean sea

Hg - 9 — Eocene magmatic rocks. Neogene and Quaternary structures and volcanic rocks in the Atlasic domain (from Ait

Brahim, unpublished, modified). I, Allas belt; 2. Neogenc basins (SB: Souss basin, OB: Ouarzazate basin); 3, Neogene

alkaline volcanic rocks. Arrow: Transmoroccan lineament: T: Toundoute nappe; *: Eocene alkaline rocks.

f, c. 9Roches mcigmatiques eocenes, structures neogenes et quciternaires dans le domaine atlasique (d'apres Air Brahim

inedit, nwdtfie). 1, Atlas : 2, Bassins neogenes (SB : Bassin du Souss ; OB : Bassin de Ouarzazate ; 3. roches

volcaniques alcalines neogenes ; Fleche : lineament transmarocain ; T: nappe de Toundoute ; * ; roches alcalines

eocenes.

THE NEOGENE

In northern Morocco, the Africa-Europe convergence during the Neogene was at the origin of the Rif

orogeny, with the development of south- and southwest-vergent nappes, HP metamorphism, etc. The

late Miocene "post-nappes" basins of the Rif (e.g., AiT Brahim & CHOTIN, 1989) register the

successive stress fields acting from the Tortonian to Present.

Meanwhile, the Atlas domain reacted to the same regional N-S shortening. South of the High Atlas,

the Souss and Ouarzazate basins tilled up with detrital sandstones and conglomeratic sequences. At the

base of the Ouarzazate sequences, the Hadida Formation (GORLER el al ., 1988) represents the Oligocene

(and early Miocene?). The clasts have a southern (Anti-Atlas) origin. The overlying sequence, the

Kandoula Formation, represents the early -(?)middle Miocene. It" exhibits proximal alluvial fans

originated from the north, registering henceforth the surrection of the High Atlas. Laterally, these clastic

sequences correspond to the Toundoute pellicular and gravity-driven nappe (Laville et al. 1977), itself

issued from the High Atlas domain. The upper part of the Kandoula Formation represents the middle

Miocene-early Pleistocene and it is composed of fluviatile and torrential sequences of northern (High

Atlas) origin. Final emplacement of the clastic sequences was contemporaneous with the development of

flat-lying and south-vergent shear zones (OUTTANI el al.. 1995). The High Atlas northern border is

represented by north-vergent. E-W trending reverse faults, with a right-lateral component (MOREL et al.

1993).

Like the High Atlas, the Middle Atlas is limited by reverse faults, here NE-SW, often showing a left-

lateral component (DUEE et al. 1977: Laville & FEDAN. 1989). Some of them, e.g., the Ait Oufella

fault at the southeastern limit of the Middle Atlas, are flat-lying thrusts related to a decollement at the

base of the Mesozoic cover (MOREL et al. 1993).

Source:

102

ALAIN PIQUE ETAL.

The Neogene and Quaternary volcanism is distributed along the Transmoroccan lineament (A IT

BRAHIM. 1986) which runs from Oujda to Agadir (Fig. 9). Its alkaline nature is attributed to a mantellic

origin and its emplacement along the NE-SW axis has been related to the left-lateral motion along this

lineament (PIQUE et al.. 1998a).

DISCUSSION AND CONCLUSIONS

The Moroccan Atlas displays several particular points which distinguish it from the other segments

of the Maghrebian Atlas chain. Their enumeration sheds light on its particular geodynamic evolution.

THE ATLASIC RIFT OF MOROCCO AND THE DEVELOPMENT OF THE ATLASIC TROUGHS

WARME (1988) among others described the Jurassic “Atlasic rift” of Morocco as the result of N 70°E

to E-W trending normal faults which merge into a crustal detachment zone weakly dipping to the North.

A similar model was developed later for the Algerian Atlas (VlALLY et al., 1994). Others argued, on the

contrary, for an oblique opening of the Moroccan Atlasic basins. In the Middle Atlas and the central

High Atlas, Laville & PETIT (1984) and Laville et al. (1995) showed that, since the end of Triassic

times, the NE-SW Hercynian directions (e.g., the Marrakech-Oujda shear zone) were reactivated as

normal faults which delimitated halfgrabens while the N 70°E to E-W faults (e.g.. those which

constituted the Atlas Palaeozoic Transform Zone) acted as sinistral transcurrent faults. Later, during

Jurassic times, the distribution of the depocentres and the plulonic massifs suggest their en-echelon

pattern along the sinistral transcurrent N 70°E trending faults.

The important lateral component of the motion along the N 70°E to E-W faults during the Jurassic,

already proposed by MATTAUER et al. (1977), implies that the "Atlasic rift" of WARME (1988). SOUHEL

et al. (1993) and CANEROTer al. (1996) corresponds rather to a transtensive zone referred to above as

the “Atlasic troughs". Between the northern limit of the Africa plate, parallel to the present Rif

mountain, and the south-Atlasic line, the Atlas domain was a sinistral mega-shear zone where the

development of the Middle and High Atlas troughs resulted from sinistral motions along the N 70°E to

E-W faults, while the NE-SW faults acted preferentially as normal faults. At that time, the Atlasic

domain was connected to the Atlantic, to the southwest, and the Tethys, to the northeast. The filling of

the Atlasic troughs occurred during the end of the Jurassic, when the sinistral transcurrent, probably

transtensive, movement decreased progressively.

The Central Atlas main deformation

Along the axis of the High Atlas, the main tectogenesis, i.e. the development of the penetrative

structures, occurred during the Late Jurassic-Early Cretaceous, certainly before the deposition of the

marine Cretaceous sequences (Laville & FEDAN, 1989). Since the Cretaceous transgression covered at

least parts of the Atlas domain, it is clear that the orogenesis (i.e. the uplift of the Atlas mountain range)

did not immediately follow its tectogenesis (LAVILLE et al., 1991). The explanation for the absence of

post-tectonic uplift is that the tectogenesis did not create a crustal thickening and a subsequent isostatic

rebound, that is compatible with a transpressive regime for the Late Jurassic-Early Cretaceous

tectonism.

Now. it is important to note that the Mesozoic shortening of the Moroccan Atlas did not affect the

other segments of the Maghrebian Atlas which were deformed later, during the Eocene in Algeria (e.g.,

Vi ALLY et al.. 1994) and the Neogene in Tunisia (e.g., PHILIP et al., 1986). Reasons for this diachronous

deformation are not clear yet. The oblique convergence between Africa and Europe could have been

realised earlier in Morocco, in front of the Iberian microplate, than in easternmore segments of the Atlas

(PIQUE et al., 1998b).

Source. MNHN, Paris

THETETHYS SOUTHERN MARGIN IN MOROCCO

103

The alkaline magmatism in the Atlas domain

The alkaline magmatic activity occurred during three periods in the Moroccan Atlas:

— during the Late Jurassic, alkaline magmas emplaced in the central High Atlas. The geometry of

the small plutons suggests that they emplaced in connection with the sinistral transcurrent motion along

N 70°E trending faults (Fig. 6);

— during the Eocene in the Taourirt and Tamazert massifs;

— during the Neogene and the Quaternary. The three main volcanic provinces, i.e. Oujda Mountains,

Middle Atlas and Siroua are aligned along the NE-SW Transmoroccan lineament (Fig. 9).

The Jurassic alkaline rocks are not represented in the western nor the eastern High Atlas, but only in

the Central High Atlas axis, along the former Atlasic rift. It is thus probable that their emplacement has

been favoured, within the Atlas transcurrent domain, by the earlier crustal thinning previously realised

during the Late Triassic-early Liassic rifting.

The Eocene and Neogene-Quaternary alkaline rocks are distributed along NE-SW trending zones. It

is suggested that their emplacement is related to a N-S regional shortening, attributed to the Africa-

Europe convergence.

The Atlas uplift

In the course of the continuing Africa-Europe collision, the uplift of the High Atlas and at a lesser

degree the Middle Atlas was due to the reactivation of the crustal faults in a roughly N-S compressive

stress field (Gomez et at ., 1996). The High Atlas N 70°E faults acted then as reverse faults, north- and

south-vergent thrusts developed along the borders of the chain, and a sinistral component was present on

the Middle Atlas NE-SW faults.

In conclusion, the main tectonic event (i.e. the development of regional folds, themselves derived

from sedimentary ridges and depocenters) in the Central Atlas was achieved prior to the deposition of

the Cretaceous transgressive beds. It resulted from the adaptation of the Mesozoic cover to a

transpressive reactivation of Hercynian faults and a general decollement of this cover from its Hercynian

basement.

By contrast, along the Atlas borders, the main deformation occurred later, during Neogene times. It

was characterised by reverse faults and Hat-lying thrusts divergent with regard to the Atlas axis. The

kilometric-scale thrusts (Laville et at., 1977; Morel et at ., 1993; Lowell, 1995; Outtani et at

1995; etc.) are of particular interest since they are the manifestation of a decollement tectonics, perhaps

initiated during the Mesozoic and strongly reactivated during the Neogene. Whether or not they are

limited to the Atlas borders or played a significative role in the deformation and the uplift of the whole

chain is not determined yet.

ACKNOWLEDGEMENTS

The paper is the result of a grant from the Peri-Tethys program. It has been improved thanks to

thorough scientific reviews made by Drs G. DUEE and D. FRIZON DE LAMOTTE and a careful editorial

review by Dr. S. CRASQUIN-SOLEAU.

104

ALAIN PIQUE ETAl..

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Hercynian belt of Morocco. Journal of Structural Geology. 2: 55-61.

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the northern margin of West Africa. American Journal of Science. 289: 286-330.

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21:235-255.

Piqu£, A.. An Brahim, L.. B. Azzouzi, M'H.. Maury. R.. Bellon. H.. Semroud, B. & Laville, E., 1998a.— Le Poin^on

maghrebin: contraintes structurales et geochimiques. Comptes Rendus de VAcademie des Sciences, Paris, 326: 575-581.

Piqu£, A., Ait Brahim, L., Ait Ouali, R., Amrhar, M., Charroud, M., Gourmelen, C., Laville, E., Rekhiss, F. &

Tricart, P., 1998b.— Evolution structural des domaines atlasiques du Maghreb au Meso- et Cenozoique: le role des

structures heritees dans la deformation du domaine atlasique de FAfrique du Nord. Bulletin de la Societe geologique de

France, 169: 797-810.

SOUHEL. A., Canerot. J.. Bouchouata, A.. Chafiki. D., El Hariri. K. & Gharib. A., 1993.— Le Rift atlasique sur la

transversale de Beni-Mellal (Haut Atlas central). VI. Essai de synthese geodynamique. In: I4 lh International Meeting of

Sedimentology, Marrakech. Avril 1993, Abstract. Universite de Marrakech, Marrakech: 305-306.

Vially, R.. Letouzey, J.. Benard. F., Haddadi, N., Desforges, G., Askri. H. & Boudjema. A., 1994.— Basin inversion

along the North African margin: the Saharan Atlas (Algeria), hi: F. Roure (ed.), Peri-Tethyan Platforms: Proceeding of

the IFP Peri-Tethys Research Conference held in Arles. France, March 23, 1993. Technip, Paris: 79-118.

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(ed.). The Atlas system of Morocco studies on its geodynamic evolution. Lectures and Notes in Earth-Sciences . 15:

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Khenifra (Sud-Est du Maroc central). Geodinamica Acta , 8: 158-172.

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1 - 201 .

Source: MNHN, Paris

The Southern Tethyan margin

in Northeastern Morocco; sedimentary characteristics

and tectonic control

Pierre CHOTIN"', Lahsen Ait BRAHIM ,2 ‘ & Hassan TABYAOUI i:>

( 1) University Pierre et Marie Curie, Dcpartement de Geotectonique, Tour 26-16, El

4, place Jussieu, F-75252 Paris Cedex 05, France

(2) Universite Mohamed V, Departement de Geologic, Avenue Ibn Batouta, Rabat. Maroc

ABSTRACT

Palaeostress analysis in northeastern Morocco allows the reconstruction of the tectonic and palaeogeographic evolution of

northeastern Morocco from Triassic to Eocene. The studied area is part of the West African Tethyan margin. From field work

and from space imagery analysis, we establish maps of the main regional faults and examine their movement in each

succeeding tectonic phase. Stress tensor calculation has showed that these faults acted as normal faults during the period

comprised between the Triassic and the Late Cretaceous. The extensive stress was oriented NNW-SSE to N-S during the

Triassic and NNW-SSE to N-S and E-W during the Late Jurassic to the Early Cretaceous. During the Liassic and the Dogger

the faults created horsts and grabens structure on the Tethyan margin and from Late Jurassic to Early Cretaceous, north verging

tilted blocks appeared. In the Late Cretaceous sequences, a strike-slip tectonic regime prevailed. The calculated tensors show a

maximal compressive stress oriented E-W. A last stress pattern reconstructed from faults in the Eocene formations gives a

maximal compressive stress oriented N-S. Three successive stages mark the evolution of the Tethyan margin: the creation of an

horts and grabens structured margin during the Triassic and the related effusion of basalts; a transgression during the Liassic

accompanied by an important subsidence; the creation of a tilted blocks structured margin from Late Kimmeridgian to Early

Cretaceous. At the end of the Early Cretaceous the whole region emerged. During the Late Cretaceous a compressive stress

regime led to the formation of ENE-WSW and NW-SE strike-slip faults and N020° folds. Finally, during the Eocene, a

compressive event created NNE-SSW and NW-SE strike-slip faults and ENE-WSW to E-W folds. In conclusion, the northeast

Moroccan margin of the Tethys evolved during the period comprised between the Triassic to the Early Cretaceous as a passive

margin related to the breakup of the Pangea and the opening of the Atlantic and Atlasic domains. This margin evolved later in

an active compressed zone from Late Cretaceous to Neogene.

Chotin, P., Ait Brahim, L. & Tabyaou, H., 2000.— The Southern Tethyan margin in Northeastern Morocco;

sedimentary characteristics and tectonic control. In: S. Crasquin-Soleau & E. Barrier (eds), Peri-Tethys Memoir 5: new data

on Peri-Tethyan sedimentary basins. Mem. Mus. natn. Hist, nut ., 182 : 107-128. Paris ISBN : 2-85653-524-0.

Source. MNHN. Paris

108

PIERRE CHOTIN ETAL.

RESUME

La marge sud-tethysienne an Maroc nord-oriental: caracteristiques sedimentaires et eontrole tectonique.

L'analyse des paleocontraintes dans Ic Maroc nord-oriental permet de reconstruire revolution tectonique et

paleoizeographique de ces regions, du Trias a I* Eocene. La zone etudiee fait partie de la marge tethysienne nord-africaine. Nous

avons etabli la carte des failles principales a partir de travaux sur le terrain et de l’analyse des images spatiales et nous avons

examine leur mouvement au cours de chaque phase tectonique. Ces failles ont un mouvement normal entre le Trias el le Cretace

superieur. La contrainte cn extension est alors orientee NNW-SSE a N-S pendant le Trias et NNW-SSE a N-S et E-W pendant

la periode qui s’etend du Jurassique superieur au Cretace inferieur. Au cours du Lias et du Dogger, des horsts et grabens se

forment sur la marge tethysienne el, du Jurassique superieur au Cretace inferieur, des blocs bascules a vergence Nord y

apparaissent alors. Dans les series du Cretace superieur, e’est un regime tectonique en decrochement qui se met en place. Les

tenseurs calcules montrent que la contrainte compressive est orientee E-W au cours de cette periode. Enfin, dans les formations

eocenes nous observons une contrainte compressive orientee N-S. Le eontrole tectonique de revolution de la marge tethysienne

nous permet de reconnaitre le scenario suivant : la creation d’une marge structuree en horst et grabens pendant le Trias et

Leffusion simultanee de basaltes : une transgression au cours du Lias accompagnee par une important subsidence ; la creation

de blocs bascules du Jurassique superieur au Cretace inferieur. A la fin du Cretace inferieur. la region emerge. Au cours du

Cretace superieur. une phase compressive conduit a la formation de failles decrochantes orientees NNE-SSW et NW-SE ainsi

quo de plis orientes ENE-WSW a E-W. En conclusion, la marge tethysienne du Maroc nord-oriental evolue du Trias au Cretace

inferieur comme une marge passive en relation avec la rupture de la Pangee et Louverture des domaines atlantique et atlasiquc.

Cette marge evolue en zone de compression au cours du Cretace superieur et de V Eocene.

INTRODUCTION

The studied area is located in northeastern Morocco (Fig. 1). between the Oranesan ineseta in the

south and the Rif-Tell belt in the north. Within this area, the Beni Snassen mounts are located in the

Fig. 1.— Geographical map with the studied area in

northeastern Morocco.

FlG. /.— Carte geographique et situation de la zone etudiee

dans le Maroc nord-oriental.

Fig. 2.— Geological sketch map of the studied area. I.

Palaeozoic basement: 2. Mesozoic sediments; 3, Cainozoic

sediments.

FlG. 2.— Schema geologique de la zone etudiee. /. socle

paleozoique : 2. sediments mesozoi'ques : 3, sediments

cenozoiques.

Gareb valley

Driouch .Tistoutine,

rifa valley

Berkanc ^

eastern Rif

Ben I snassen

LaTounc,

iTaourirt

Gucrcif

High Plateaux

Ain Beni Mathar

Middle Atlas

34°b

Source: MNHN, Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

109

north, and the Taourirt-Oujda mounts in the south, following an ENE-WSW direction over a distance

between 80 to 120 km and are separated by the Taourirt-Oujda basin (Fig. 2). These mounts are

essentially constituted by a Mesozoic sedimentary cover (an average altitude of 1200 m) in which the

Palaeozoic appears in antiforms. In the east, we find the Tlemcen mounts (outside the map, in the

Algerian regions) and in the west, the Beni Bou Yahi mounts and the Guercif basin (Fig. 2). Previous

studies in the region were largely concerned with the biostratigraphy and the sedimentology of the

Triassic to Early Cretaceous series (CATTANEO, 1984. 1987, 1991; NACIRI, 1994; CUAHHABI, 1994;

OUJIDI. 1994; MEHDl, 1995; Ouahbi, 1996). These detailed studies have greatly increased the

understanding of the organisation and dating of the different sedimentary facies.

The cartography of faults in this region is based on the analysis of Landsat, SPOT and ERS1 SAR

space imagery (AIT BRAHIM et al., 1994, 1996; TABYAOUI et ai , 1996) and field work (Fig. 3). The aim

of this paper is, (1) to constrain the timing of the tectonic evolution, (2) to clarify the tectonic control of

sedimentation, (3) to determine the succession of palaeostress fields and (4) to relate these data with

geodynamic setting.

REVIEW OF THE SEDIMENTARY CARACTERISTICS OF THE TETHYAN SERIES

The Triassic period

The Triassic deposits contain red beds with a coarse detritical basal level composed of Palaeozoic

elements, overlaying unconformably the hercynian basement (Fig. 4). This sedimentation has been

perturbed by the effusion of volcanic dolerites (Bertrand &Prioton, 1975; Cherotsky, 1973;

OUJIDI, 1994) and basalts (LAPIERRE et at 1984) which are 215 Ma old (MANSPEIZER et al. 9 1978).

This tholeiitic magmatism originated under tidal conditions characteristic of brackish water domain

(COGNEY & FAUGERES, 1975). This can be deduced from the presence of inter-stratified dolomitic

limestones containing gasteropods and lamellibranchs in particular Annaplophora littica Quenst. of the

late Ladinian (OwoDENKO, 1946). The distribution and thickness of the Triassic series testify to a

palaeo-relief, structured by relatively rapid subsident zones (Taourirt. Oujda and Tiouli areas) (Fig. 3)

and by shallow zones. Outside these areas, the deposits are either very reduced, corresponding to local

palaeoreliefs (Tanouralt and Bourdine areas) (Fig. 3), or are absent (uplifted blocks of Touissit, Rhar

Roubane, Debdou and Boudoufoud).

South-Gareb fault

[Moulay Idris:

North Beni-Snassen

SoutiyBeni Snasscn I'

Taforall F.

[Rhar

[Roubane

El Aloun-Nalma f.

|E1 Aioun-Naima

Touissit

_ North Taouml-Ouida f

Taourirt

Oued

Himmcr

Guercif f.

Guefait-Tiouli fault

[Tanouralt

Ain Beni

Mathar

Rekanie Mekam

[ekame-Sidi HI Abed f

L>ucd Kiss

C iuercil

Hauts Plateaux

0 20 km

Fig. 3.— Map of the faults identified

by space imagery analysis and

field observations. Location of the

horsts and grabens.

Fig. 3.— Carte des failles identifiees

par I'imagerie spatiale et les

observations de terrain. Loca¬

lisation des horsts et grabens.

Source

PIERRE CHOTIN ETAL.

The Early Jurassic period

The installation of a uniform and shallow carbonate shelf took place during the early Liassic. It is

characterised by the deposition of conglomerates and limestones (Fig. 4). The nature and the distribution

of these deposits reflect the persistence of palaeo-highs as in the northern part of the Beni Snassen

mounts (CATTANEO, 1987; Naciri, 1994) and in the Touissit. Titeft and Debdou areas (Fig. 3).

Fig. 4.— Lilhostratigraphic column

and simplified sequencial analysis

of the Mesozoic formations in

northeastern Morocco (Cattaneo,

1987).

FlG. 4 — Colonne I i t host rat ig raph iq ue

el analyse seqaentielle simplifiee

des formations mesozoi'ques du

Maroc nord-oriental (Cattaneo,

1987).

Source: MNHN , Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

111

During the Carixian times, this carbonated shelf changed (Fig. 5). In the Beni Snassen area, three

zones ol deposits develop from north to south. In the north, the first zone now presents proximal

platform facies where we find Megalodontidae limestones; in the central part, the second one shows

facies of external, proximal to distal platform represented by cherty limestones and the third one, in the

south presents deep deposits of external platform of mud type (CATTANEO, 1987; NACIRI, 1994). In

the Taourirt-Oujda area, the cherty limestone facies testifies to a north and westwards deepening. To the

east and to the south, limestones of shallow intra- to supratidal environment are found (limestones with

Megalodontidae, oolitic limestones, subrecifal limestones). Their thickness decreases quickly to the

Touissit horst (Fig. 3). Further to the south, a brackish water domain sets up in the High Plateaux.

The Domerian time is characterised by a general spreading of the transgression. The deposit

environment is now becoming increasingly deeper and is evolving in an outer carbonaceous shelf or

basin. In the Taourirt-Oujda axis and in the Beni Snassen area, a marly limestone facies with ammonites

can be found. South and northwards, the deposits are replaced by a reduced sequence of limestones and

dolomites of outer distal shelf. Southwards, in the High Plateaux, clays and red marls are deposited in a

inner epi-continental shelf.

The Toarcian time is characterised by the “ammonitico-rosso” facies developed in an outer shelf

environment. We find it in the Beni Snassen area and in the Taourirt-Oujda axe. Southwards, the

deposits consist of marls and sandy limestones of shallow distal shelf with a strong continental

influence.

The Middle Jurassic period

Fig. 5.— Palaeogeographical map

during the Carixian. I. proximal

shelf; 2. outer shelf; 3, epi¬

continental shelf; 4. emerged land;

5. faults.

Fig. 5 .— Carte paleogeographique an

Carixien. 1. plate-forme proxi¬

mal e ; 2. plate-forme ext erne ;

3. plate-forme epicontinentale ;

4, terres emergees; 5, failles .

During the Aalenian and the middle Bajocian times, the decrease of subsidence in the Taourirt-Oujda

area permitted the development of inner to supratidal shelf facies (Fig. 4). north and westwards of the

Taourirt-Oujda axis, these facies changed into Zoophycos marls and black limestones deposited in an

open outer shelf (NACIRI, 1994).

During the Bathonian and Callovian times, the sedimentary environment changed suddenly and the

detritical sedimentation came back (Fig. 6). These deposits marked an important filling phase of the

subsident areas.

During the Bathonian times, the facies were both deeper and more diverse, containing organo-

detritical marls and 800 m thick limestones, north of the Taourirt-Oujda axis. South of Oujda,

112

PIERRE CHOTIN ETAL.

limestones with iron oolites and ammonites were simultaneously being deposited (LUCAS, 1942; ELMI,

1973). Further to the south, in the High Plateaux, gypsum marls developed.

The Callovo-Oxfordian time is characterised by a flysch sedimentation of deep sea fan type, which is

well developed south of Oujda. Deposits are thicker in the grabens (200 to 250 m in Jebel Azira and Bou

Beker) than in the horsts (12 to 15 m)(CLAVEAU, 1952).

The upper Jurassic period

Fig. 6.— Palaeogeographical map

during the Bathonian-Callovian. 1.

basin (marls); 2, marls and organo-

dctritical limestones; 3, iron oolitic

limestones; 4. marls and sandy

limestones; 5. emerged lands; 6,

faults.

Fig. 6 .— Carte paleogeographique an

Bathonien-Callovien. 1, bass in

(marnes) ; 2. marnes et calcaires

organo-detritiques ; 3. calcaires

oolithiques ferrugineux : 4. marnes

et calcaires sableux : 5. terres

ernergees ; 6, failles.

From the middle Oxfordian to the early Kimmeridgian, a deltaic structure formed by several hundred

meters of sandstones and sandy marls developed south of Oujda (Figs 4 and 7). These deposits were

interrupted at the end of the early Kimmeridgian by a shallow water calcareous episode which ends to

the Mesozoic sedimentary cycle in the Taourit-Oujda region. Benio Ourimeuch sandstone formations

were simultaneously being deposited in the Beni Snassen area (CATTANEO, 1987).

Fig. 7.— Palaeogeographical map

during the Oxfordian-early Kim¬

meridgian. 1. basin; 2. carbonate

margin; 3. littoral domain; 4. del¬

taic plain; 5. emerged lands; 6,

faults.

Fig. 7.— Carte paleogeographique

a I'Oxfordien-Kimmeridgien infe-

riettr. 1 . bass in ; 2 . bordure

carbonatee ; 3, domaine littoral ;

4. plaine deltaique ; 5. terres

emergees; 6, failles.

Source. MNHN, Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

113

The late Kimmeridgian and the early Berriasian periods

During this time, a return of the carbonated sedimentation can be observed (Figs 4 and 8) These

deposits are organised in three series (CATTANEO, 1987): the limestones of Mechraa Klila from the late

Kimmeridgian, the marly limestones and limestones of Ahmer Akhdar from the early Portlandian and

the marly limestones of Bou Rhennja from the late Portlandian to early Berriasian ages. The thickness of

the early Kimmeridgian sedimentary sequence increases from south to north. Deposits are thicker in the

Beni Snassen area (550 m) than in the Taourirt-Oujda axe where they do not exceed 180 m (OUAHBI,

1996). To the south, they are reduced or absent. These series show also lateral variations of facies.

These deposits testify to the installation of an inner carbonated shelf organised in a sub-tidal zone which

pass southwards to an estran regime. The Taourirt-Oujda region has emerged definitely.

By the end of the early Berriasian, the whole of northeastern Morocco had emerged.

□ «

^ 5

Fig. 8.— Palaeogeographical map

during the late Portlandian. 1,

carbonated outer shelf; 2. barrier;

3. epicontinental carbonated shelf;

4. emerged lands; 5, faults.

Fig. 8 .— Carte paleogeographique ait

Portlandien superieur. 1. plate-

forme externe carbonatie ; 2,

barriere ; 3, plate-forme car bo-

natee epicontinentale . 4. terres

emergees; 5, failles

STUDY OF FAULT SYSTEMS AND STRESS PATTERNS

Detailed investigation of the brittle fracturing were carried out in the research area to establish the

stress pattern from Triassic to Eocene. It led to the reconstruction of the palaeostresses responsible for

the deformation of eastern Morocco. The analysis of fault planes and slickenside lineations from field

measurements enables us to reconstruct the orientations (trend and plunge) of the principal stress axes.

More than 600 measurements of slip data were collected in the Beni Snassen mounts and in the

Taourirt-Oujda mounts. In most of the sites we characterised two or more successive episodes of

deformation. We separated the successive tectonic events using observations of field relative chronology

criteria, the fossilised structures, crosscutting relationships between faults and superposition of

slickensides on a fault plane. We used the ANGELIER (1979, 1984, 1989, 1990) inversion method to

reconstruct the orientation of the maximum, intermediate and minimum principal stress axes (a 1, a2,

a3) and shape ratio O. The results are reported on the synthetical stratigraphic column (Fig. 9), on the

Table 1 and on structural maps of the Beni Snassen and the Taourirt-Oujda regions.

114

PIERRE CHOTIN ETAL.

Geological Synthetical Stratigraphic

stage Column

Calcareous and

marly facies

Direction of

Palacostress

Compression

Sandstone and

shaly sand

Shale and

sandstone

Ammonite marly

Cherty laminated

limestone

Red beds, Dolerite

with carbonated

bar

+ + Granite, Schist

+ + Sandstone, quartzite

Distension

Structuration

Geodynamic events

decametric

E-W folds

convergence between

Africa and Iberia

oblique

strike-slip faults

conjugated

strike-slip faults

anticlockwise rotation

of Iberia recorded by

the ending of the

sinistral movement

of Africa.

normal faults

tilted blocks acceleration of the

dipping north Atlantic ocean

opening.

(160 Ma)

normal faults

horsts and

grabens

opening of the

Ligurian Tethys

Start of the Atlantic

accretion

end of Liasic 180 Ma

paleohighs and

small tearing

basins

differential

subsidence

proto-Atlantic

distension

between Laurasia and

Gondwana plates

Norian 210 Ma

opening of the Tethys

Fig. 9.— Palacostress fields and geodynamical setting in the southern tethyan margin of northeastern Morocco.

Fig. 9 .— Champs de contraintes et evolution geodynamique de la marge sud tethysienne du Maroc nord oriental.

Source: MNHN, Paris

Table 1.— Location of fault stations (Nbr: number of measured faults) and reconstruction of stress tensors that correspond to

the orientation of stress axes and to the ratio O = (a2-a3)/(a l-o3) between principal stress values (ol>o2>o3)

(ANGELIER, 1984). ANG: average angle between computed shear stress and observed slickenside lineations (a in

degrees). Average RUP: ratio upsilon (ranging from 0 to 200%) of the INVDIR method (ANGELIER. 1990); values

below 50% correspond to good fits between actual fault slip data distribution and computed shear distribution. T= type

of predominant faulting (N: normal faults; I: reverse faults; D: strike-slip faults).

TABLEAU I. — Localisation des stations de mesures (Nbr : nombre de failles mesurees ) et reconstruction du tenseur des

contraintes qui correspond d Torientation des axes de contraintes et au ratio & = (o2 - g 3) / (ol - 03) entre les valeurs

des axes principaux ( gI>g2>g3) (Angeuer 19X4). ANG : angle moyen entre la contrainte tangentielle et la strie

mesuree (aen degres). RUP : ratio (entre 0 et 200%) de la methode INVDIR ( ANGEUER . 1990) : les valeurs en dessous

de 50% donnent une bonne correspondance entre la distribution des donnees des Stries mesurees et la distribution de la

contrainte calculee. T: ty pe de failles (N: faille normale : I. faille inverse ; D : faille decrochante).

Site

number

Lat /long

In degrees

Number of

faults

trend

plunge

trend

plunge

trend

plunge

Meth

ANG

RUP

stress

Regime

34 40/2 53

204

342

INVD

0158

34 43/2 48

106

282

INVD

0334

34 44/2.43

331

211

117

INVD

0275

34 48/2 25

339

162

INVD

0 277

34 53/2 18

187

283

INVD

0250

34 55/2 03

273

178

INVD

0227

34 46/2 1 7

291

122

INVD

0 3C6

34 13/2 45

127

218

INVD

0069

34 20/2 48

274

179

INVD

0211

34 18/2 15

106

282

INVD

0334

34 30/2 05

266

148

INVD

0536

34 37/1 53

342

165

INVD

0.191

34 30/1 47

350

149

240

INVD

0 646

34 24/1.50

322

232

142

INVD

0.244

34 40/2 55

281

188

INVD

0 367

34 50/251

287

177

INVD

03®

34 44/2.38

171

160

INVD

0312

34 48/2 25

276

116

INVD

0.417

34.51/2.24

316

179

INVD

0350

34 55/2 03

282

187

INVD

0 199

3447/2.21

222

352

INVD

0 3C0

34 2/2 48

339

€9

117

INVD

0202

34 14/2 35

191

327

INVD

0132

34.17/214

195

INVD

0356

34.2/2 16

100

281

190

INVD

0475

34 35/1 52

108

200

INVD

0 220

34 29/1 47

106

204

INVD

04C0

34 21/1 52

207

INVD

0 282

34 40/2 56

187

INVD

0.427

34 43/2 49

356

133

266

INVD

0286

34 45/2 46

190

334

INVD

0361

34 42/2 34

190

286

INVD

0138

34.47/2 55

185

275

INVD

0469

34 55/2 04

239

106

INVD

0396

34 46/2 14

181

271

INVD

0696

34 20/2.48

173

279

INVD

0.329

34 22/2 44

184

331

INVD

0346

34 26/2 17

187

277

INVD

0393

3417/214

190

335

INVD

0.302

34.34/1 51

179

294

INVD

0.338

34 29/1 47

192

314

100

INVD

0.314

34.21/1 52

359

188

INVD

0375

Source: MNHN , Paris

116

PIERRE CHOTIN ETAL.

Normal faulting tectonic regimes

The Triassic volcanic and sedimentary series are affected by normal synsedimentary faults oriented

N70°E to N90°E. These faults gave rise to the effusion of tholeiitic volcanism and the structure of

subsident basins limited by highs. In this extensional regime we calculate a minimum principal stress of

G3 oriented NNW-SSE to N-S (Figs 10 and 1 1).

Late Jurassic to Early Cretaceous series are affected by metric to decametric ENE-WSW to E-W and

NW-SE groups of normal faults. The fault slip data analysis allows the reconstruction of two

palaeostress tensors with an horizontal g 3 axis oriented NNW-SSE to N-S and NE-SW to E-W

respectively. During the Liassic and the Dogger, the faults with ENE-WSW and E-W directions are

again active and permit the development of ENE-WSW to E-W directed hoists and grabens. During the

Late Jurassic and the Early Cretaceous, the same faults were responsible for the formation of northwards

verging tilted blocks of the Tethyan margin. Normal faults which are progressively damped, variation of

thickness at each side of the faults, synsedimentary block tilting, intraformational breccias.

Strike-slip faulting regimes

A conjugated system of dexlral strike-slip faults trending ENE-WSW and sinistral strike-slip faults

trending NW-SE is present throughout the investigated area. The stress pattern registered in the pre-

Miocene series shows that the maximum principal stress a I was oriented E-W and the g 3, N-S (Figs 12

and 13). Some of these faults are neoformed. others correspond to normal faults which have undergone

strike-slip reactivation. This is illustrated by the presence of vertical slickensides intersected by

horizontal ones. Locally, some normal synsedimentary faults trending NW-SE were reactivated as

reverse faults. A maximum compressive stress oriented E-W with a permutation between g 2 and a3 was

calculated. This stress pattern is discrete in the Beni Snassen and the Taourirt-Oujda Mounts and it is

better registered in the Terni Masgout Mounts by N20°E folds related to sinistral strike-slip faults

trending N160°E. Some E-W directed faults were reactivated as sinistral strike-slip faults.

A second stress pattern has been registered with the maximal horizontal compressive stress ol

trending N-S and g 3, trending E-W (Figs 14 and 15). This is showed by dextral strike-slip faults

trending NW-SE. sinistral ones trending NE-SW and folds trending E-W. Some normal faults oriented

ENE-WSW to E-W were reactivated as reverse faults. Some NW-trending faults of the preceding stage

of E-W compression were also remobilized into dextral strike-slip faults under this N-S compression.

Fig. 10.— Location of fault stations and orientation of the principal stress axes during the Triassic to Early Cretaceous in the

Beni Snassen mounts. Geological space imagery sketch map of the Beni Snassen mounts. 1 , Quaternary; 2 . Neogene to

Quaternary volcanism; 3 , Mio-Pliocene; 4 . Miocene; 5 , Cretaceous; 6 , Callovian, Oxfordian; 7 . Oxfordian,

Kimmeridgian; 8 . Kimmeridgian, Portlandian; 9 . Dogger; 10 , Liassic; 11 , Triassic; 12 . granite; 13 , Palaeozoic; 14 ,

faults; 15 . normal faults; 16 . strike-slip faults; 17 . reverse faults; 18 . stratigraphic bedding. 1 to 7: stereographic

projections in this and subsequent figures, illustrate fault plane solutions in Schmidt lower hemisphere projection: fault

planes are shown as curves and poles as open squares, slickenside lineations as small centrifugal arrows (normal faults),

centripetal arrows (reverse faults) or double arrows (strike-slip faults). 5 branchs star: ol; 4 branchs star: o2; 3 branchs

star: o3; centrifugal black arrows indicate the direction of extension and centripetal ones, the direction of compression,

in the horizontal plane.

Fig. 10.— Localisation des stations de mesures el determination des directions de contraintes principales dtt Trias an C ret ace

superieur dans les monts Beni Snassen. 1. Quaternaire ; 2, volcanisme neogene a Quaternaire ; 3. Mio-Pliocene : 4 .

Miocene ; 5. Cretace ; 6. Callovien-Oxfordien ; 7. Oxfordien-Kimmeridgien ; 8. Kimmeridgien-Portlandien : 9.

Dogger ; 11). Lias ; II. Trias ; 12, Granite : 13. PaleozoYque ; 14. faille : 15, faille normale ; 16, faille decrochante ;

17. faille inverse ; 18. bancs stratigraphiques ; 1 a 7 : projection stereographique des plans de failles stir diagramme

de Schmidt, hemisphere inferieur : les plans de faille sont represents par des courbes el les poles par des carres

blancs, les stries par des petites fleches centrifuges pour les failles “normales ", des fleches centripetes pour les failles

inverses ou des fleches doubles pour les failles pour les decrochements ; etoile a 5 branches : a I ; etoile a 4 branches :

o2 ; etoile a 3 branches : o3.

Source : MNHN, Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

117

4 ♦

o \

/ w " \

/ * \

/ V \ \ \

°°\

/ \'J \\ \

\ MJJ i

\ y

\ D

0 *•

♦ ‘ -

Source: MNHN. Paris

Fig. 11.— Location of fault stations and orientation of the principal stress axes during the Triassic to Early Cretaceous

extension in the Taourirt-Oujda mounts geological sketch map. 1. Quaternary; 2, Moulouyan surface; 3. Neogene to

Quaternary volcanism;4, Plio-Quaternary; 5. Mio-Pliocene: 6, Miocene; 7. Aquitanian: 8. Malm; 9, Dogger; 10,

Liassic; 11, Triassic; 12. Palaeozoic; 13, stratigraphic bedding; 14. faults; 15. normal faults; 16, strike-slip faults; 17.

reverse faults. 8 to 14: Schmidt lower hemisphere projection of fault planes (same legend as figure 10).

Fig. 11 .— Localisation des stations de mesures el determination des directions de contraintes principals du Trias an Cretace

superieur dans les monts de Taourirt-Oujda. I. Quaternaire ; 2, surface du Moulouyen ; 3, volcanisme neogene a

quaternaire ; 4. Plio-Quaternaire : 5, Mio-Pliocene ; 6, Miocene ; 7. Aquitanien :8. Malm : 9, Dogger; 10. Lias : 11.

Trias ; 12, Paleozoi’que : 13. bancs stratigraphiques ; 14. faille ; 15, faille normale ; 16, faille decrochante ; 17, faille

inverse ; 8 a 14 : projection de Schmidt hemisphere inferieur (meme legende que figure 10).

Source : MNHN, Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

119

Fig. 12.— Location of fault stations and orientation of the principal stress axis during the Late Cretaceous in the Beni Snassen

mounts. 15 to 21: Schmidt lower hemisphere projection of fault planes (same legend as figure 10).

Fig. 12 .— Localisation des stations de mesure des failles el determination de la direction de contrainte principal an cours du

Cretace superieur dans les monts Beni Snassen. 15 a 21 : projection de Schmidt hemisphere inferieur (meme legende

que figure 10).

Source. MNHN. Paris

120

PIERRE CHOT1N ET AL .

Fig. 13.— Location of fault stations and orientation of the principal stress axis during the Late Cretaceous in the Taourirt-Oujda

mounts. 22 to 28: Schmidt lower hemisphere projection of fault planes (same legend as figure 11).

FlG. 13 — Localisation des stations de me sure des failles el determination de la direction de contrainte principale au cours du

Cretace superieur dans les moms de Taourirt-Oujda. 22 a 28 : projection de Schmidt hemisphere inferieur (merne

legende que figure II).

Source MNHN, Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

121

Fig. 14.— Location of fault stations and orientation of the principal stress axis during the Eocene compression in the Beni

Snassen mounts. 29 to 35: Schmidt lower hemisphere projection of fault planes (same legend as figure 10).

FlG. 14 .— Localisation des stations de mesure des failles et determination de la direction de contrainte principale an coins de

F Eocene dans les monts de Beni Snassen. 29 a 35 : projection de Schmidt hemisphere inferieur (me me legende que

figure 10).

122

PIERRE CHOTIN ETAL.

Fig. 15.— Location of fault stations and orientation of the principal stress axis during the Eocene compression in the Taourirt-

Oujda mounts. 36 to 42: Schmidt lower hemisphere projection of fault planes (same legend as figure 11).

Fig. 15.— Localisation des stations de mesure des failles et determination de la direction de contrainte principale an cours de

I'Eocene dans les monts de Taourirt-Oujda. 36 a 42 : projection de Schmidt hemisphere inferieur (mime legende (pie

figure 11).

Source MNHN , Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

123

^from Liassic to Bathoman ^

BENI SNASSEN TAOURIRT-OUJDA

I tiff* Bcvstii ElAtoua 7x kk»n Toni«i«

NNE (from Kimmcridgmn to Lower Cretaceous) SSW

KEBDANA BENI SNASSEN ELAIOUN TAOURIRT-OUJDA

Basin outer shelf inner shelf littoral domain emerged area

Fig. 16.— Palaeogeographic synthetic profiles through the

studied area showing: a. the horsts and grabens structure

from Liassic to Bathonian; b. the tilted blocks structure

during Kimmeridgian to Early Cretaceous.

Fig. 16.— Coupe paleogeographique synthetique an I ravers

de la zone etudiee monIrani : a, la structure en horsts et

grabens se mettant en place du Lias au Bathonien ; b. la

structure en blocs bascules formes du Kimmeridgien au

Cretace superieur.

TECTONIC CONTROL OF THE EVOLUTION OF THE TETHYAN MARGIN

IN NORTHEASTERN MOROCCO

From the data presented above, we can infer that the evolution of the northeastern Morocco from the

Triassic to the Eocene periods occurred in several steps. The correlations between global and detailed

biostratigraphic, sedimentary and major tectonic events and the key periods of the Tethys evolution

show that these main steps are as follows.

Bi-directional distension from the Triassic to the Early Cretaceous

During the Late Triassic period, the tectonic regime was characterised by extensional deformation

caused by the principal minimum stress o3 oriented NNW-SSE to N-S. Old inherited ENE-WSW to E-

W oriented late-hercynian faults have been reactivated as normal faults. This event led to the formation

of horts (Debdou, Touissit, Rhar Roubane, Tanouralt. Bourdine) and basins with differential subsidence

(Tiouli, Oujda, Taourirt. Metroh, Oued Himmer, Guercif, High Plateaux) (Figs 3 and 16a). This

extensive regime induced the effusion of basalts and dolerites within the red clays and the evaporites,

marking the beginning of the rifting at 215 Ma.

During the early Liassic, northeastern Morocco was structured by narrow and elongated horsts

(Touissit, Debdou and El AYoun-Nai'ma) and by narrow graben in a ENE-WSW direction (Figs 3 and

16a). It corresponds to an unstable subsident area located between two stable and shallow zones namely

the northern border of the Beni Snassen area and the High Plateaux in the south. Among the normal

faults oriented ENE-WSW which controlled the structure of these zones, we find (Fig. 3) the fault of

Rekame-Sidi El Abid. Guefait-Tiouli, Taourirt-Oujda, the faults of El AToun-Naima. the fault south of

the Beni Snassen area, the fault north of the Beni Snassen area, Ihe fault south of the Gareb area, and the

fault of Tafouralt (Fig. 3). The extensional stress responsible for the reactivation of these faults trends

NNW-SSE, and is secondly associated with a new extension trending NE-SW to E-W. This fault

activity coincides with the transgressive deposition of carbonates in the grabens where we can observe

an important accumulation. This event is related to the eastwards translation of the African plate. The

opening of the Atlantic rift goes ahead and the separation between Africa and America is effective

(J.ANSAL & Wade, 1975; Lancelot & Winterer. 1980).

During the middle Liassic. the effect of generalised eustatism (Vail el al., 1977) is associated with

an important subsidence brought about by the reactivation of synsedimentary faults oriented ENE-WSW

to E-W and NW-SE as a resull of a bi-directional extension NNW-SSE to N-S and ENE-WSW to E-W.

This tectonic and sedimentary transgressive evolution is materialised by the progressive advance of the

124

PIERRE CHOTIN ET AL.

Tethyan Sea onto the coastal or emerged palaeo-highs (El Aioun-Naima horst, Moulay Idriss horst. High

Plateaux, northern border of the Beni Snassen area) and the deepening of subsident zones (Beni Snassen

graben, Taourit-Oujda graben. Guercif graben) (Fig. 3).

During the late Liassic the tectonic regime underwent no change. Most of the faults oriented as ENE-

WSW to E-W and NW-SE, previously active, were remobilised as normal faults and contributed to the

fragmentation of the Tethyan margin. This tectonic period was characterised by terrigenous flows

relatively moderate and the generalisation of the marly facies deposits, indicating a modification of the

climate which became more temperate. Progressive filling up of grabens is related to the beginning of

oceanic accretion in the Central Atlantic Ocean at around 180 Ma (OLIVET el at., 1984).

From the Aalenian to the Bajocian times, and owing to marine advance, the tectonic of horsts and

grabens was accentuated under the same distensive regime. The palaeogeographic scheme shows the

deposition of an external carbonated shelf facies, open onto the slope in the Beni Snassen area and in the

Guercif basin, and a carbonated neritic facies in the Taourirt-Oujda axis and in the High Plateaux

regions.

During the middle Bathonian times, the opened deposit areas evolved in restrained environments in

which argillaceous and sandy materials had been deposited, attesting the retreat of the sea toward the

NE. During that time, the Moroccan Atlasic basins and the Moroccan High Plateaux emerged. The

northeastern Morocco was integrated to the Rif-Tell domain and constituted its southern margin. The

distensive movements created a more rapid deepening of the basement, compensated by a more

important sedimentary drift. Most of the syn-sedimentary deformations are concentrated along the major

normal faults oriented ENE-WSW and NW-SE. The permanent movement of these faults is responsible

for the facies variation and the thickness of the sedimentary series.

During the Callovian, the subsidence continued to take place in the whole of northeastern Morocco.

During the Oxfordian, horsts and grabens were structured by ENE-WSW to E-W normal faults. We

observe wjthin the sedimentary series, slumps, syn-sedimentary normal faults, and brecciated levels.

Numerous normal faults were reactivated during the early Kimmeridgian and brought about the

instability of the Rif foreland in these areas (DE LUCA, 1982; HERVOUET, 1985). During this period, the

relative movement of Africa always occurred eastwards and coincided with the first phase of

acceleration of the Atlantic oceanic accretion.

From the late Kimmeridgian to the Early Cretaceous, the structural control led to an important

increase in the subsidence of these areas. The reactivation of the ENE-WSW to E-W and the NW-SE

normal faults induced to the formation of tilted blocks in the northeastern Morocco (Fig. 16b). The

thickness of the sedimentary series increases from south to north. This tectonic regime induced the

formation of carbonated sedimentation which was deposited in the whole maghrebian margin of the

Telhys. The Taourirt-Oujda and High Plateaux areas emerged. The reactivation of the faults is also

attested by the superposition of filling sequences which correspond to alternative periods of downlift

and stability. This new structural scheme was conserved until the end of Early Cretaceous. Therefore,

during the late Kimmeridgian the deposits vary in thickness; they are thicker in the Beni Snassen area

(550 m) than in the Taourirt-Oujda area (180 m) (OUAHBI, 1996). In the south, they are less thick in the

Taourirt-Oujda Mounts and absent in the High Plateaux. The extension controlled the tilting of the

blocks, the formation of breccias and the collapse of cliffs in the Mechraa Klila formation. NW-SE

directed faults such as the Tafouralt or the Oued Kiss fault (Fig. 3) with an horizontal slip component,

controlled the shape of the sedimentation area. During the early Portlandian, the palaeogeographic

scheme and the structural framework were comparable to those of the late Kimmeridgian because of the

polarity and the orientation of palaeogeographic lines and direction of tectonic lines. The dislocation of

the late Kimmeridgian carbonated shelf and the installation of a new subtidal carbonated shelf was

initially caused by the reactivation of the faults in the Beni Snassen and the Taourirt-Oujda areas. The

High Plateaux and the Taourirt-Oujda mounts corresponded to emerged areas. This contrast between the

depth of the deposit and the thickness of the sedimentary series implies a progressive subsidence which

lasted throughout the Portlandian under the control of subvertical normal faults oriented N70° to N90°E.

These faults, fossilised by the upper layers, indicate the existence of a distensive tectonic activity.

The dislocation of the early Portlandian carbonated shelf induced the birth of high zones and

subsident ones. Then we observe the formation of a shallow epi-continental carbonated shelf

materialised by the generalisation of marly-calcareous facies of Bou Rhennja.

Source: MNHN , Paris

THE SOUTHERN TETHYAN MARGIN IN NORTHEASTERN MOROCCO

125

After the last argillaceous and sandy terrigendus deposits of the Early Cretaceous, northeastern

Morocco emerged definitely. The deposit area is displaced by progradation toward the Rif Basin in the

north, as a result of the Purbeckian regression (CATTANEO. 1987).

Late Cretaceous E-W compression

This compression direction, attributed to the Late Cretaceous, is the oldest compressive tectonic

event registered in this part of the Tethyan African margin. It is represented in the Beni Snassen and

Taourirt-Oujda mounts. It postdates the Early Cretaceous deposits and predates the first Miocene

deposits. It is recorded by conjugate dextral strike-slip faults trending ENE-WSW and sinistral strike-

slip faults trending NW-SE and by N20°E folds related to N160°E sinistral faults. This tectonic event is

related to an contre-clockwise rotation of the regional direction of Iberia, registered by the stopping of

the sinistral strike-slip movement of Africa along E-W fractures, which became dextral strike-slip

motion (between 80 ± 5 Ma) (BIJU-DUVAL et al ., 1977; PATRIAT et ai, 1982)

Eocene N-S compression

This compressive direction corresponds to the main tectonic event in the maghrebian regions. It is

recorded by NNE-SSW dextral and NW-SE sinistral strike-slip faults. It also caused the creation of

decametric folds oriented ENE-WSW to E-W the organisation of which will be perturbed by Neogene to

Quaternary tectonic events. The Miocene series overlay unconformably the Jurassic series which are

affected by this event. This tectonic event, attributed to the Eocene is directly related to the main

direction of the maghrebian orogeny. It is linked to the close-up between Africa and Eurasia lithospheric

plates.

CONCLUSION

Northeastern Morocco registered the main tectonic events which occurred onto the Tethyan African

margin. First an opening attempt during the Triassic allowed the effusion of tholeiitic basalts. This

period, characterised by active distension, allowed the transgression of the Tethyan sea onto the African

margin. This distensive regime is related to the break up of the Pangea, the opening of the Tethyan sea

and the formation of the Atlantic margins. Then, during the Liassic and the Dogger, the sedimentation is

typically Atlasic. The synsedimentary fracturing, induced by ENE-WSW to E-W and NW-SE directed

faults, led to the creation of a horst and graben system in a bi-directionnal N-S and E-W extensional

regime which affected the whole area. This fracturing is directly related to the proto-Atlantic rifting.

Finally, from the middle Oxfordian to the Early Cretaceous, the shelf sedimentary systems registered the

effect of a distensive tectonic regime, leading to the formation of tilted blocks and rapid downlifting.

This allowed the transgression on the Tethyan margin. The structures were controlled by ENE-WSW to

E-W and NW-SE directed faults which were in permanent motion during that period. Thus, the

distribution of sedimentary areas from the Triassic to the Cretaceous in the northeastern Morocco, was

produced by the conjugate effect of tectonic and eustatism.

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Subsidence history of the Essaouira basin (Morocco)

Kama! Labbassi", Fida Medina m , Abdelkrim Rimi

Hosna Mustaphi 141 & Rkia Bouatmani <’>

111 Departement de Geologie, Faculty des Sciences, B.P. 20, El Jadida, Maroc

121 Departement de Geologie, Institut Scientifique, B.P. 703, Agdal, Rabat, Maroc

" Departement de Physique du Globe, Institut Scientifique. B.P. 703, Agdal. Rabat. Maroc

,J> Centre regional de la Geologie. B.P. 421, Laayoune, Maroc

,S| ONAREP, 34, avenue A1 Fadila et Departement de Geologie, Faculte des Sciences, B.P. 1040, Rabat. Maroc

ABSTRACT

Subsidence history of the Essaouira basin from the Triassic to present times was studied on the base of data from 28 wells

and newly determined decompaction curves. The general (average of 25 curves) and selected local curves (4) include several

phases of rapid subsidence: (I) a synrift phase during the Late Triassic-earliest Liassic associated with the extensional

tectonism; (2) postrift phases during the late Liassic, in Late Jurassic-Early Cretaceous times, and from Hauterivian to Aptian.

The synrift apparent amount of extension inferred from subsidence curves is 1.56 to 3.8 for a uniform stretching model and

between 1.19 and 2.26 for a non-uniform extension model. This amount reduces to 1.17 when the area of Triassic sediments is

distributed in a uniform basin upon the basement top, and is then similar tothat calculated from fault restoration. These curves

constitute a database for studying the thermal evolution of the basin, which led to hydrocarbon generation.

RESUME

L'histoire de la subsidence du bassin d'Essaouira (Maroc).

L'histoire de la subsidence du bassin d'Essaouira du Trias a TActuel a ete etudiee & partir des donnees de 28 forages et de

nouvelles courbes de decompaction. Les courbes generates (moyenne de 25 courbes) et locales (4 courbes choisies) component

plusieurs phases de subsidence rapide : (1) une phase syn-rift pendant le Trias superieur-Lias basal, liee a la tectonique

distensive ; (2) des phases post-rift pendant le Lias superieur, au Jurassique superieur-Cretace inferieur et de I’Hauterivien a

f Aptien. La quantite d'extension apparente au cours de la periode syn-rift determinee a partir des courbes est de 1.56 a 3.8 pour

un modele d’etirement uniforme et entre 1,19 et 2,26 pour un modele d'extension non-uniforme. Cette quantite se reduit a 1.17

quand la surface occupee par les sediments triasiques est repartie sur un bassin uniforme au dessus du toit du socle; la quantite

d'extension obtenue est alors similaire a celle calculee a partir de 1'equilibrage des failles. Ces courbes constituent une base de

donnees pour I'etude de Revolution thermique du bassin qui a conduit a la generation d’hydrocarbures.

Labbassi, K.. Medina, F., Rimi, A., Mustaphi, H. & Bouatmani, R., 2000. — Subsidence history of the Essaouira basin

(Morocco). In: S. Crasquin-Soleau & E. Barrier (eds). Peri-Tethys Memoir 5: new data on Peri-Tethyan sedimentary

basins, Mem. Mus. natn. Hist. not.. 182 : 129-142. Paris ISBN : 2-85653-524-0.

Source MNHN. Pans

130

KAMAL LABBASSI ETAL.

INTRODUCTION

The birth and later evolution of the Central Atlantic Ocean has led to the development of several

coastal basins on both margins of the rift, i.e. along the present-day margins of northwestern Africa and

northeastern North America. Along the Moroccan coast, the productive Essaouira (sub-) basin

(DORREEN, 1987; BOUCHTA, 1992), structurally classified by petroleum geologists as a pull-apart basin

(CHATELLIER & Slevin, 1988), is located in the central part of the larger El Jadida-Agadir basin

(MEDINA, 1989a), which represents a Mesozoic-Cainozoic platform that was uplifted during the

collision between Africa and Europe in Late Cretaceous and Tertiary times (Fig. 1).

The major stages of the structural evolution of the Essaouira basin during Mesozoic times can be

retraced using seismic profiles (e.g., BROUGHTON & TREPANIER, 1993; MEHDI, 1994) and gravimetry,

which gives the shape of the faulted basement top (MEHDI, 1994), but these methods remain insufficient

for constraining the tectonic and thermal processes that may have controlled the evolution of the basin

and hydrocarbon generation within it. They require quantitative studies, such as subsidence analysis

which appears to be a powerful technique, as already shown by its application to surface and subsurface

sections of the El Jadida-Agadir basin (MEDINA, 1992; Mustaphi & BOUATMANI, 1996; MUSTAPHI,

1997). However, the database used in the previous studies was too small for being conclusive, since

isolated sections, which represent one-dimensional evolution, may only reflect local phenomena - such

as a horst structure, for instance - , and cannot be used for thermal modeling and setting subsidence

maps. Therefore, we analyse in this paper the structural aspects of the subsidence history of the

Essaouira basin, with the help of a large database, collected mainly from subsurface information

(boreholes and fictitious wells) supplied by ONAREP (Rabat), within the productive zone of the basin.

Fig. I.— Simplified structural map of

the Essaouira basin and adjacent

areas, and location of the studied

wells. 1. Precambrian and Palaeo¬

zoic; 2. Triassic (and Permian

p.p.)\ 3, Jurassic to Early Tertiary;

4, Pliocene and Quaternary; 5.

anticlinal axis; 6. thrust; 7. normal

fault; 8. strike-slip fault; 9. diapir.

H , Jbel Hadid anticline; K,

Kechoula diapir; T, Tidsi diapir;

A. Amsitten anticline; ZZ, Zem

Zem anticline; SA. Sidi Amara

fault; C.Chichaoua. Fictitious well

ESPRF is located west of the area

shown in the figure.

FlG. 1 .— Carte structurale simpli¬

fies du bassin d'Essaouira, et

localisation des forages studies.

1. Precambrien el Paleozoique ;

2. Trias (et Permien p.p.J;

3. Jurassique a Tertiaire infe-

rieur ; 4. Pliocene et Quaternaire ;

5, axe anticlinal ; 6, faille inverse ;

7. faille normale ; 8, decroche-

ment ; 9. diapir. H, anticlinal

du Jbel Hadid ; K. diapir de

Kechoula ; T. diapir de Tidsi ; A .

anticlinal d' Amsitten ; ZZ.

anticlinal du Zem Zem ; SA, faille

de Sidi Amara ; C, Chichaoua. Le

puits fictif ESPRF est situe a

Fouest de la region representee

dans la figure.

Source. MNHN, Paris

SUBSIDENCE HISTORY OF THE ESSAOUIRA BASIN (MOROCCO )

131

STRUCTURAL SETTING

The Essaouira basin (Fig. 1) appears as an east-west trending synclinorium with Mesozoic (mainly

Cretaceous) sediments, affected by weak deformations (SOUID AHMED. 1983: MEDINA, 1989b: MEHDI,

1994) consisting of NE-SW to WNW-ESE folds at the basin edges (Amsitten, Zem Zem, Chichaoua and

Hadid shear zones), diapiric structures (e.g.. Kechoula) and NNW-SSE to ENE-WSW strike-slip faults

or fault zones injected or not by Triassic salt (Sidi Amara. Tidsi). All these deformations were produced

by the Late Cretaceous to Quaternary compressions related to the collision between Africa and Europe.

The older Mesozoic structures appear along E-W seismic sections, which show: (i) a Late Triassic to

earliest Liassic synrift series deposited within westwards-dipping half-grabens bounded by N-S-

trending, moderately-dipping, normal faults, and (ii) a relatively undeformed Jurassic and Cretaceous

post-rift sequence disrupted by salt diapirs (Fig. 2). The half grabens are isolated from the final rift zone,

located westwards, by horsts such as the Meskala-Zelten horst structure (BROUGHTON & TREPAN1ER,

1993; BOUATMANI, 1995). The amount of extension at the surface, calculated by restoration of cross-

sections attains 17% (BOUATMANI, 1995). Some of the seismic sections clearly show that the faults

merge into a detachment plane at 4 sTWT (MEDINA, in press), as in the Souss basin located southwards

(MEDINA et al., 1996; MUSTAPHI et al., 1997). Contrary to the synrift period, deposition and

palaeogeography during the postrift stage was mainly controlled by sea level changes, diapirism, and

some mild tectonics (e.g., WlEDMANN etal.. 1982; TAJ-EDD1NE & BEN ABBES TAARJI, 1996).

W E

Fig. 2.— Interpretation of an E-W oriented seismic profile across the Essaouira basin (from Bouatmani & Ait Salem,

unpublished). Vertical scale in metres.

Fig. 2 .— Interpretation d'un profit de sismique-reflexion, de direction E-W . a travers le bassin d‘Essaouira (d'apres

Bouatmani & AiT Salem, inedit). Echelle verticale en metres.

132

KAMAL LABBASSI ETAL.

SUBSIDENCE HISTORY

Subsidence history of the Essaouira basin can be visualised through burial and thermo-tectonic

curves and subsidence rate histograms. Computation was carried out with the help of the computer

program BURSUB (STAM et al 1987) for 28 wells (two are offshore) and one Editions well. For

clarity, only the three most complete wells (JRPI, MKL1 and ADM1), which are those that reach the

basement, and a Editions well (ESPRF1) are shown (Fig. 1).

Input parameters

Lithostratigraphic column. The Mesozoic series drilled in the Essaouira basin (see DUFFAUD et al .,

1966; BROUGHTON & Trepanier, 1993) can be simplified as the following, according to

biostratigraphic datings (Fig. 3): (I) Late Triassic to earliest Liassic syn-rift detritics (mainly sandstones

and siltsones with halite) and volcanic rocks located within the half-grabens (levels T1 to JO); and (2)

Jurassic (JI to J9), Cretaceous (Cl to C6) and Eocene postrift deposits, consisting of carbonates, elastics

and minor evaporites. Thickness of the formations generally increases westwards. It may be noted that

the biostratigraphic datings given by ONAREP reports have not been revised; therefore, the formations

encountered in the wells may show some sligth diachronism with the surface formations that have been

extensively studied during the last years. However, the presumed difference has not an important

influence on our study, because we work at a relatively large scale.

W ESRIX ESW 1 ADM I MK1J01 JRPI JBLI bis E

FlG. 3.— Lithologic columns of the Mesozoic formations in Essaouira basin (location on figure 1).

FlG. 3. — Colonnes lithologiques des formations mesozotques du bassin d‘Essaouira (localisation sur la figure I).

Source: MNHN. Paris

SUBSIDENCE HISTORY OF THE ESSAOUIRA BASIN (MOROCCO)

133

Decompaction parameters. Decompaction curves and parameters were newly determined on the base

on 2680 datapoints obtained from sonic logs (LABBASSI, in press) for five different lithologies: clay,

sandy clay, sandstones, limestones and dolomites. The values obtained for surface porosity (Oo) and for

constant c (Fig. 4) appear to be reliable since they are not very different from those determined by other

POROSITY

0,0 0,2 0,4 0,6 0,8 1.0

POROSITY

Fig. 4.— Porosity vs. depth datapoints and curves for 5 lithologies, determined from sonic logs. A. sandy clay (Oo=0.62;

c=0.57); B, clay (Oo=0.71; c=0.77); C. sandstones (00=0.35; c=0.59); D. limestones (0)=O.46; c=0.23); E. dolomites

( 00 = 0 . 21 ; c=0.6).

Fig. 4 .— Points de mesure et combes de porosite en fonction de la profondeur pour 5 lithologies, determines a panir des

diagraphies. A. argiles greseuses (dm=0.62 ; c=0,57); B. argiles (dxi=0,71 ; c=0,77); C. gres (dX)=0,35 ; c=0.59):

D. calcaires (dX)=0,46 ; c=0,23); E. dolomies (dm=0.21 : c=0,6).

Source:

134

KAMAL LABBASSI ETAL.

authors in the same area (MEDINA & RlMl, 1992) or in other regions (ROYDEN & KEEN, 1980; JtLATER

& CHRISTIE. 1980; BRUNET, 1991).

Depth of deposition. According to sedimentological and palaeontological data, sediments in

Essaouira basin were deposited in a shallow environment, the depth of which did not exceed 100 m, as

indicated for instance by the ubiquitous presence of evaporites in Late Jurassic and Middle to Late

Cretaceous times (ETTACHFINI et a!.. 1989; ALGOUTI et al ., 1993). These depth values do not therefore

introduce large estimation errors. Maximal depths were recorded during Late Jurassic and Middle

Cretaceous times (Fig. 5, A).

200

100

Age (Ma)

Fig. 5.— Depth of deposition values for the Essaouira basin formations (A) and sea level changes (B). B from Haq et al.

(1987).

FlG. 5.— Profondeur de depot des formations du bassin d'Essaouira (A) et variations du niveau marin (B). B d'apres Haq

et al. (1987).

Sea level changes. Values of sea level changes were taken from the long-term curves of Haq et al.

(1987), which show a maximum of about 270 m during the Middle Cretaceous (Fig. 5, B ).

Chronostratigraphic scale. In order to maintain homogeneity with chronology of sea level changes,

the chonostratigraphic scale was also taken from Haq et al. (1987).

Results

Subsidence curves

Subsidence curves were established for the top of the Palaeozoic basement in each well (Fig. 6). The

lower and upper curves respectively represent burial (with or without compaction) and unloaded

thermo-tectonic subsidence for a local. Airy-type isostatic compensation. We also present histograms of

tectonic subsidence rates, which allow visualising the main phases.

Source: MNHN. Paris

SUBSIDENCE HISTORY OF THE ESSAOUIRA BASIN (MOROCCO)

135

Age (Ma)

100

200 100

Age (Ma)

Fig. 6.— Total and thermo-tectonic subsidence curves and histograms of rates of subsidence for wells JRP1. MKL1 and ADM1

and fictitious well ESPRF1. 1, depth of deposition: 2. thermo-tectonic subsidence; 3, total subsidence without

decompaction: 4. total subsidence with decompacted sediments.

FlG. 6 .— Courbes de subsidence tolale et thermo-tectonique, et histogrammes de taux de subsidence pour les forages JRPI,

MKLJ et ADM I. et le puits fictif ESPRF1. 1, profondeur de depot ; 2, subsidence thermo-tectonique ; 3. subsidence

totale sans decompaction ; 4, subsidence totale avec sediments decompactes.

Source: MNHN, Paris

136

KAMAL LABBASSI ETAL.

Analysis of subsidence curves shows several rapid (tectonic) phases which, however, are not

necessarily common to all the sections.

Thus, the first phase of rapid subsidence was recorded during the Triassic (probably Late Triassic)-

earliest Liassic (230-194 Ma). Initial fault-controlled subsidence reaches 1200 m to 1500 m and

represents 40% to 70% of the total tectonic subsidence. We note that well MKL shows a slight uplift

before the inception of subsidence, which may be interpreted as due to footwall uplift related to

extensional faulting. During the Liassic and Middle Jurassic (194-143 Ma), subsidence generally slows

down, although some anomalies, expressed by a steep slope during the late Liassic (183-177 Ma) may

disturb this calm period. During the Callovian-Oxfordian (158-143 Ma) some wells show no subsidence

at all.

In Late Jurassic-Early Cretaceous times (143-129 Ma), a second major phase is recorded in all the

sections. This rapid subsidence is followed by a calm period with an acceleration phase during the

Hauterivian (113 Ma). During Middle and Late Cretaceous times, there is generally no tectonic

subsidence, but rather some tendency to uplift.

The figure 7 shows the spatial evolution of subsidence through the plot of the four tectonic curves;

thus, well MKL, located on the Meskala-Zelten horst structure, has undergone less subsidence than

ADM and JRP which are located on either side of the horst. On the contrary, fictitious well ESPRF

shows a very large amount of subsidence reflecting its distal position.

Fig. 7.— Plot of the studied four

thermo-tectonic curves.

FlG. 7.— Diagramme des quatre cour-

bes thermo-tectoniques etudiees.

Age (Ma)

Since almost all subsidence curves show differences that may be caused by different effects, we have

tried to remove the latter by constructing a “regional” smoothed curve for tectonic subsidence, based on

averaging the data of 25 curves (Fig. 8). It is important to note that because most wells do not reach the

basement, we are only interested in the variation of the subsidence, not in its absolute value, which

needs normalizing the curves with respect to the oldest level that can be found in all wells (e.g.. BRUNET

& LE PlCHON, 1981). The smoothed curve, which may best reflect the subsidence history of the

Essaouira basin, shows four stages of rapid (tectonic) subsidence followed by a slow (thermal)

subsidence; the rapid subsidence stages are recorded during the Triassic (240-201 Ma), from the

Toarcian to the Bajocian (187-167 Ma), during the Tithonian-Berriasian (141-130 Ma), and from the

late Hauterivian to the Aptian (120-108 Ma). As we have indicated before, the chronology of these

stages is strongly dependent on the biostratigraphic dates made by ONAREP, which have not been

revised.

Source. MNHN, Paris

SUBSIDENCE HISTORY OF THE ESSAOUIRA BASIN (MOROCCO )

137

age (My)

200 150 100 50 0

Fig. 8.— Average thermo-tectonic

subsidence curve for the Essaouira

basin, based on data from 25

subsidence curves. O1 to 04.

stages of subsidence.

FlG. 8 .— Courbe de subsidence

thermo’tectonique moyenne du

bassin d'Essaouira, basee sur les

donnees de 25 courb.es de

subsidence. 0/ a 04, stades de

subsidence.

Amount of extension

The amount of extension, expressed by the parameters (3 and 5, was evaluated by comparing the

observed curves to the theoretical ones established for different models, especially the uniform

(McKenzie, 1978) and non-uniform (ROYDEN & KEEN. 1980; HELLINGER & SCLATER, 1983; LISTER el

al ., 1991) stretching models, assuming normal thicknesses of the crust (30-33 km) and the lithosphere

(125 km) for the synrift phase, and an attenuated crust and lithosphere during the post-rift stages.

SYNRIFT PHASE. — Comparison of the observed subsidence curves to the theoretical ones for a

uniform stretching model, shows that the amount of extension is variable, attaining 3.8 in the west, and

1.56 at the eastern border. These values appear to be too high with respect to estimations from fault

restoration (BOUATMANI, 1995), and are not common to continental proximal areas. In addition, most

subsidence curves show an amount of thermal subsidence much smaller than that expected from the

value of initial tectonic subsidence. We conclude that the use of the uniform extension model may not

be adequate, and we investigate in the following the use of a non-uniform extension model. Although

the estimation of crustal and subcrustal extension in this case is made difficult by the second subsidence

phase (Liassic-Middle Jurassic), which breaks the trend of the thermo-relaxation curve, the very small

amount of thermal relaxation during the Liassic (only 10 m during the 10 Ma that immediately follows

the rapid subsidence phase), suggests very small amounts of subcrustal streching, and even no subcrustal

stretching at all; so if we fix the latter to unity (p=l), then the amounts of crustal stretching 5 are,

depending on the adopted models (HELLINGER & SCLATER, 1983; ROYDEN, 1986), between 1.19 and

1.56 onshore and 1.97 and 2.26 offshore. It can be readily noticed that this amount is much smaller than

that obtained using the uniform extension model, and are closer to - although still higher than- the

values obtained from faults. We will review this point in the discussion. Another explanation for the

almost flat thermal relaxation phase could be a border effect, according to which the walls of

extensional basins cool very rapidly because of lateral conduction of heat. Thus, narrow basins and

borders of wider basins may show little thermal subsidence. In the case of Essaouira basin, we believe

that both mechanisms (simple shear and border effect) have taken place.

POST-RIFT PHASES. — Post-rift subsidence phases are relatively less important as can be seen on the

different curves, and excepting ESPRF1. even the rapid subsidence observed during the Late Jurassic

becomes difficult to discern when reducing the vertical scale, as in figure 6. Assuming that the

lithosphere has been sufficiently weakened by the previous event, as indicated by the extrusion of

volcanics, a uniform stretching model seems to be more adequate than a non-uniform one. Taking into

account the previous event for the calculations, i.e. a stretched crust and no subcrustal stretching, the

values of (3 (=5) are around 1.05 for well MKL as well as for the other sections where the event is clear.

The same can be said for the Late Jurassic-Early Cretaceous event, which shows larger values of (3

(1.11). The apparent cumulative stretching since the onset of rifting is about 1.3. However, one must

138

KAMAJL LABBASSI ETAL.

keep in mind that the Cretaceous events may not be indicative of any real tectonic stretching, since: (1)

the faults sole out into detachment levels located within the sedimentary cover, and therefore can be

considered as growth faults, the effects of which are recorded by the sedimentary column, and (2) the

region comprises several diapiric structures that had some important influence on the sedimentary

record, especially in Cretaceous times (e.g., Taj-Eddine & BEN ABBES Taarji, 1996).

DISCUSSION

In the following, we discuss the obtained results, by comparison to those obtained with the help of

other methods such as gravimetry and seismic reflection.

According to gravimetric data taken from TADILI et al. (1986) and BERNARD1N (1988), thickness of

the crust beneath the Essaouira basin is roughly 30 km in the east and 25 km in the west. Although the

basin is located at the foreland of the Atlas chain, no major thickening of the crust can be inferred from

gravimetry (BERNARDIN, 1988). The value of crustal thinning is then 0 to 17% for an initial crustal

thickness of 30 km, and 14 to 28% for a 35 km-thick crust. The maximum value of 8 is 1.28.

Restoration of cross-sections by removal of the offsets induced by the activity of normal faults gives

stretching values of 15-17% only (BOUATMANI, 1995), which fit well with those determined through

gravimetry. Unfortunately, no other measurements can be made on fault blocks since the synrift

sequence becomes deeply buried westwards.

Although we admit that most stretching occurred during the synrift phase, the values of crustal

thinning determined from subsidence curves (1.19 and 1.56 onshore and 1.97 and 2.26 offshore) remain

too high.

Some similar disparities have been found by several authors, in the North Sea (Coward, 1986), in

the Celtic basin (DYMENT. 1989) and in the Gulf of Lions (BURRUS, 1989). Different explanations have

been suggested, such as: (1) variable amounts of stretching at different levels of the crust (North Sea),

(2) neoformation of the Moho discontinuity (Celtic basin) removing the effects of crustal thinning

during the previous extension, and (3) phase changes at the deepest levels of the crust (Gulf of Lions).

We think that evaluation of the extension in Essaouira basin from subsidence curves is

overestimated, because it only takes into account particular sections, which may not be representative of

the whole basin: on the other hand, petroleum exploration wells are drilled on particular structures. The

amount of extension obtained is then only apparent. A much better approximation could be the

estimation of the area produced by the extension, and then a mean thickness of the Triassic strata. In our

case, it appears obvious that initial subsidence determined from thickness of the synrift section within

more or less triangular half-grabens will lead to overestimated amounts of extension when the borehole

crosses the thickest part of the half-graben, and to underestimated values in the thinnest parts. If we

replace the triangular basin by a rectangular one with the same area, we obtain a uniformly stretched

shape, to which the uniform stretching model can be compared.

We have applied this method to the studied section. From the figure 9, the total area covered by

synrift sediments within the triangular half-grabens is about 50 km 2 . When converting the area from

triangles to a single rectangle, the depth of the sediment-filled basin becomes 1 km. For a sediment of

density 2.2 g/cm , the value of (3 obtained is 1.17 which fits exactly with that measured through normal

faults.

From gravimetric data, the Moho raises from approximately 30 km in the east to 25 in the west; the

created area is about 125 km : , which is larger than that created at the surface. The difference can be

explained by the uncertainties on density contrasts, which may lead to large errors on Moho depth.

A more important problem is the occurrence of basalts within the Triassic series and at its top, since

adiabatic decompression and subsequent melting beneath a normal lithosphere, i.e. the base of which is

at 1333°C need large amounts of extension (>2 according to LE PlCHON & SlBUET, 1981). This can be

readily solved by admitting that subcrustal extension occurred westwards, in the direction of the final

Source: MNHN , Paris

SUBSIDENCE HISTORY OF THE ESSAOUIRA BASIN (MOROCCO)

139

rift axis, so the basalts were generated at some distance of the basin. The overall absence of feeder dykes

or necks in the area is in good agreement with this assumption.

Fig. 9.— Sketch showing the

effect of distributing the area

occupied by the Triassic

formations on a rectangle

instead of triangles (half

grabens).

FlG. 9 .— Schema mantrant Feffet

de repartition de la surface

occupee par les formations

triasiques stir an rectangle

an lieu d'un triangle (demi-

graben).

CONCLUSION

Subsidence history of the Essaouira basin reveals several phases of rapid subsidence: (1) a synrift

phase during the Triassic-earliest Liassic (240-201 Ma) associated with the extensional tectonism; (2)

postrift phases during the late Liassic (187-167 Ma), in Late Jurassic-Early Cretaceous times (141-130

Ma), and during the Hauterivian to Aptian (120-108 Ma). The synrift apparent amount of extension

inferred from subsidence curves is 1.56 to 3.8 for a uniform stretching model and between 1.19 and 2.26

for a non-uniform extension model. This amount falls to 1.17 when the area of Triassic sediments is

distributed in a uniform basin upon the basement top, and is then similar to that calculated from fault

restoration.

ACKNOWLEDGEMENTS

This paper is part of the State Thesis of one of us (K. LABBASSI), which was funded in part by the

Peri-Tethys Program. We would like to thank ONAREP (Rabat) for providing the well data, and

R. Stephenson and an anonymous reviewer for their comments.

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Hydrocarbon systems of Morocco

Haddou JABOUR, Al Moundir MORABET & Ret bah BOUCHTA

ONAREP, P.O. Box 8030. Rabat. Maroc

ABSTRACT

Available data base interpretation along with MAGOON & Dow’s (1994) petroleum system concept is utilised in this paper

to evaluate the origin of the proven hydrocarbon resources of Morocco, which lie chiefly in the Essaouira. Pre-Rif. Rharb and

offshore Tarfaya Basins. Several systems are interpreted, in which the confidence in the source/petroleum lie varies from

"known" to "hypothetical", involving charge from Silurian (eastern Essaouira). Palaeozoic-Liassic (Sidi Fili trend of Pre-Rif),

Liassic (Bou Draa and Haricha fields of Pre-Rif). Oxfordian (western Essaouira), Cretaceous (Ain Hamra) and an intra-

Miocene biogenic system in the Rharb Basin. The origin of the Cap Juby heavy oil accumulation in the offshore Tarfaya basin

is uncertain, we favour an offshelf Jurassic and/or Cretaceous sources interpretation. The hydrocarbon system concept is

extended in this paper to predict further, currently undrilled or unproven, systems. These include areas where the proven source

rocks referred to above are likely to be developed and be mature, plus systems that can be predicted on the basis of analogues

from surrounding regions. An example of the latter is a series of postulated Triassic systems developed in lacustrine deposits in

Atlantic offshore and coastal half graben. Palaeozoic source rocks may be regionally developed and may still be in the oil and

gas windows over wide, generally unexplored, regions. Early to Middle Jurassic source rocks occur mainly in lagoonal.

platform sags and outer shelf environments while Cretaceous-Eocene source beds occur in continental rift complexes and

deltaic basins. Biogenic gas potential is probably confined to Neogene deposits in foreland and divergent margin basins. Further

application of the hydrocarbon system concept should help to significantly reduce geologic risk particularly in frontier

exploration areas.

RESUME

Les systemes petroliers au Maroc.

L'interpretation de la base de donnees disponibles et le concept de systeme petrolier etabli par MAGOON & Dow (1994) sont

utilises dans cet article pour evaluer les origines des ressources d'hydrocarbures prouvees au Maroc. Ces ressources se situent

essentiellement dans les bassins d'Essaouira. du Pre-Rif. du Rharb et dans I'offshore de Tarfaya. Plusieurs systemes. dont le

degre de confiance de correlation huile-roche mere varie de "connu" a "hypothetique”. sont egalement interprets. Ces systemes

impliquent des charges du Silurien (Est d'Essaouira). du Paleozoique-Lias (trend de Sidi-Fili dans le Pre-Rif), du Lias (champs

de Bou Draa et Haricha dans les rides prerifaines), de FOxfordien (Ouest d'Essaouira), du Cretace (Ain Hamra) et d'un systeme

intra-Miocene de gaz biogenique dans le bassin du Rharb. L’origine de fhuile lourde accumulee dans la structure de Cap Juby

dans I’offshore de Tarfaya est incertaine. Notre interpretation favorise une origine de roche mere de type bassin du Cretace

et/ou Jurassique. Le concept de systeme petrolier est etendu. dans cet article, pour inclure les systemes non encore prouves ou

non encore testes par forage. Ces systemes comprennent des zones ou les roches meres sus-mentionnees peuvent ctre

JABOUR, H.. MORABET, Al M. & Bouchta. R.. 2000.— Hydrocarbon systems of Morocco. In: S. Crasquin-Soleau & E.

Barrier (cds), Peri-Tethys Memoir 5: new data on Peri-Tethyan sedimentary basins, Mem. Mus. natn. Hist, nat ., 182 : 143-

158. Paris ISBN : 2-85653-524-0.

Source: MNHN , Paris

144

HADDOUJABOUR ETAL.

developpees et matures ainsi que les systemes pouvant etre anticipes par analogic avcc les zones avoisinantes. Un exemple de

ces systemes consiste en une serie de structures en demi-graben dans Poffshore atlantique et dans les bassins cotiers dans

lesquels se sont developpees des roches meres lacustres. Les roches meres paleozoiques peuvcnt etre regionalement

developpees et dans de larges regions non encore explorees; ces regions pcuvent se situer dans la fcnetre a huile. Les roches

meres du Jurassique inferieur et moyen se sont deposees essentiellement dans des environnements lagunaires, de sillons de

plate-forme ou de plate-forme externe. Les roches meres du Cretace-Eocene sont des depots de rifts continentaux complexes et

de bassins deltai'ques. Les roches meres a Lorigine du gaz biogenique sont des sediments probablement Iimites au Neogene

deposes dans les bassins type foreland ou de marge passive. L’application future du concept des systemes petroliers devrait

aider a reduirc, de fa?on significative, le risque geologique et particulidrement en limite des zones d'exploration.

INTRODUCTION

Although most of Moroccan sedimentary basins are still largely unexplored and justifiably

considered frontier exploration areas, the database so far acquired in the exploration of these basins

requires a modern conceptual interpretation. As more geological, geophysical and geochemical

information about known petroleum occurrences is acquired, there is a need to adequately document and

review the models and geologic processes pertinent to these proven systems and use these as analogues

to accurately and adequately assess the hydrocarbon potential of less explored basins or those in which

hydrocarbons have yet to be proven.

Basin evaluation to date in Morocco has relied on analytical studies that emphasise structural

evolution and sediment fill, regardless of their relationship to any petroleum deposits. The petroleum

system concept, as proposed by MaGOON & Dow (1994) is a more holistic approach, which emphasises

the genetic relation between a particular source rock and the resulting petroleum accumulation. These

basic elements include the petroleum source rock, migration path, reservoir rock, seal, and trap and the

geologic processes that create each of these basic elements.

The purpose of this paper is to define, where the data base allows, the established petroleum systems

in Morocco, to determine the level of certainty of a specific system and attempt a classification, and

additionally to predict where further, currently unproven, petroleum systems may lie elsewhere in the

country.

The terminology used in this paper is a composite of that applied by MAGOON & Dow (1994), by

MaGOON (1988) and by DEMAISON & HUIZINGA (1991). The definition of the key-terms used is given

below.

An established petroleum system (one in which the occurrence of hydrocarbons is proven) can be

identified at three levels of certainty in terms of the geochemical correlation of petroleum and source

rocks (MaGOON & Dow, 1994). These can be listed as follows:

— known petroleum system; where a good geochemical match must exist between the active source

rock and oil or gas accumulation.

— hypothetical petroleum system, in which geochemical information is sufficient to identify a

source rock but where no geochemical match exists between source and petroleum deposits.

— speculative petroleum system, where the existence of both source rock and petroleum

accumulation is postulated entirely on the basis of geologic and/or geophysical evidence.

MaGOON & Dow (1994) proposed naming systems based on the predominant source and reservoir

within the relevant system, using 1 ithostratigraphic schemes. The absence of a common accepted

lithostratigraphy throughout Morocco presents problems here, therefore, chronostratigraphic terms are

used. These have to be used in conjunction with the basin name concerned.

The migration system can be further described using the following defined terms: a pure-bred

petroleum system exists in a geological setting in which the structural framework has not changed

significantly during the geological life of that system; a hybrid system exists in areas of major structural

reorientation, without which the petroleum system would not occur in its current form; high-impedance

migration systems are characterised by laterally continuous seals coupled with a moderate to high

degree of structural deformation; low-impedance migration systems are characterised by either a high

Source ; MNHN, Paris

HYDROCARBON SYSTEMS OF MOROCCO

145

degree of regional seal continuity or a low degree of structural deformation. Data available on the

petroleum systems of Morocco at this stage are generally not sufficient to estimate charge factor or gross

accumulation efficiency (GAE). However, in some cases, observations on trap fill allow an evaluation

of whether the system is under, normally or super-charged.

BASIN DEVELOPMENT. REGIONAL STRATIGRAPHY AND SOURCE FACIES OCCURRENCES

A large number of discrete sedimentary basins are recognised in Morocco (Fig. 1), varying in their

style from intramontane through inverted rifts to thrust belts, forelands and passive margin. Most of

these basins remain underexplored, with as a result, their potential petroleum systems and resources ill-

understood. Production is currently limited to onshore basins in the coastal area of northern and central

Morocco.

TANC

Rifan Neogene Foldbelt

Atlas Foldbelt

Palaeozoic and Precambrian outcrops

vy\ Panafrican Craton

LAGWIRA

Continental margin

Deep water exploration area

Fig. 1.— Structural units and major sedimentary basins of Morocco.

Fig. 1 .— Les unites structurales et les principaux bassins sedimentaires clu Mciroc.

Our current state of knowledge of the history of basin development and stratigraphy of the country is

summarised below. The figure 2 presents a summary of the most important tectonic events within a

typical onshore Moroccan basin.

A stratigraphic section of the area of fullest control, the Atlantic Coastal basins, is illustrated (Fig. 2).

Source: MNHN. Paris

146

HADDOUJABOUR ETAL.

.WESL

SEA LEVEL

CURVE

Pliocene

LMIoc.

U. CreL

Con la dan

Maaslrtch.

Channel

Upper

Jiir.'V.-'C

L. & M.

Jurassic

L^ - 4 Siliceous

Low energy Platform carbonates

IfiSfAljfl High energy Bank Front carbonates

Mari

1 ’ j Sandstone

Deltaic & nearshore Sand /shale

I \ Black shale

Shale

ISSSoSl Coarse grained Continental elastics

liiH'A Evaporltes

Volcanics (basaltic)

Deformed palaeozoic sedimonts

Basment (Procambrian)

Fig. 2.— Lilhosiratigraphic column of the atlasic coastal basins to the South of Agadir.

Fig. 2.— Colonne lithostratigraphique des bass ins coders atlasiques an Slid d'Agadir.

Palaeozoic

The oldest rocks encountered in Morocco belong to the Precambrian and outcrop in the Anti-Atlas.

Lower and Middle Cambrian strata have not been drilled but geophysical data, tied to surface geological

control, suggest that the succession is 100 to 3000 m thick; consisting of grey green shales, sandstones,

quartzites, and volcanoclastics. The Ordovician is represented by 1000 to 2500 m of grey to black

shales, siltstones, sandstones and quartzites and the Silurian by 100 to 200 m of graptolitic, locally

carbonaceous, black shales. Devonian rocks are mostly shales, often black, with thin sandstones and

deeper water reefal limestones locally developed. The Carboniferous succession, up to 4000 m thick in

depocenters, is represented by Visean, Namurian and Westphalian shales, sandstones, conglomerates,

turbidites and platform carbonates. Thin carbonaceous shales and coal beds are also present locally. The

Carboniferous rocks are bounded by the overlying erosive Hercynian unconformity.

The main potential Palaeozoic source rock is the Silurian sapropelic, radioactive graptolitic black

shales, rich in kerogen of Type II. Black carbonaceous shales also occur frequently in the Late

Ordovician and Early Devonian locally in the Westphalian. These systems are tightly controlled and

determined by the geodynamic characteristics of the basins.

The tectonic evolution of the onshore intracratonic basins, where the Palaeozoic succession is best

represented, is complex and results from successive tectonic episodes (Fig. 3). The first main event, the

Hercynian orogeny, caused strong deformation of the Palaeozoic sequence. Hercynian events begun at

the end of the Devonian with very large scale folding, and strike-slip faulting resulting in the creation of

a number ol deep Carboniferous basins. Subsequent deformation occurred during late Westphalian and

with tight folding, thrusting, nappe development and strike-slip faulting, associated with dyke

emplacement and granite intrusions.

These compressional events have a crucial and positive impact on the maturity history of Palaeozoic

source rocks in many of the intracratonic basins. In the Tadla Basin, Early Palaeozoic source rocks are

still present within the oil window in uplifted and thrusted blocks (Fig. 3), generally in areas which not

Source: MNHN . Paris

HYDROCARBON SYSTEMS OF MOROCCO

147

suffer from deep Carboniferous burial. It is likely that recent burial (Tertiary) resulted in renewed

hydrocarbon generation in at least some of these basins. Examples are the western Meseta. High

Plateaux, Pre-Rif, western Tindouf and part of Errachidia-Boudenib areas.

Fig. 3.— Tectonic evolution and subsequent critical events of petroleum systems in Morocco based on the example of theTadla

and other basins bordering the Atlas foldbelt.

FlG. 3. — L'evolution tectonique et les evinements critiques consequents des systemes petrotiers au Maroc, buses sur le bassin

de Tadla et les bassins en bordure de la chaine atlasique.

Mesozoic

Triassic grabens and half grabens associated with fragmentation of the continents occur throughout

Morocco, filled with continental coarse elastics, red beds and locally by lacustrine deposits (Brown,

1980). Crustal extension and rifting started in the latest Triassic massifs and Hercynian highs.

Transgressive sediments associated with the Tethys seaway spilled into the proto-Atlantic oceanic rift

later in the Triassic, leading to the development of hypersaline lagoon conditions over a large part of

coastal Morocco and the formations of thick salt deposits in, for example, the Essaouira Basin, Pre-Rif

and High Plateaux. These should provide excellent seals for hydrocarbons generated from both

Palaeozoic and Triassic source rocks.

The opening of the Atlantic Ocean was preceded by further (Triassic-Early Jurassic) rifting. This was

followed by massive regional subsidence during the Jurassic as is well illustrated in the Tarfaya region

and along the Atlantic shelf. Tethyan-related rifting occurs during the Jurassic in the Atlas Such Tethyan

rift are often discordant to the Atlantic-related rifts, with the former trending NE-SW and the latter N-S.

The Tethyan rift system was later inverted during the Alpine orogeny to form the mountains of the High

and Middle Atlas.

Liassic and Dogger (pre-Callovian) sedimentation is dominated by intertidal to supratidal conditions,

extending across most of the coastal basins. A sediment pil of carbonates, anhydrite and red-brown to

148

HADDOUJABOUR ETAL.

green shales accumulated. The Bajocian (Middle Jurassic) is characterised by an important clastic influx

especially in the Pre-Rif ridges areas. Open subtidal carbonates and minor grey shale were deposited

during the Callovian and early Oxfordian times. A gradual regression began in middle Oxfordian time.

This resulted in renewed intertidal to supratidal facies deposition. A marked drop occured in sea level

during the Late Jurassic.

Jurassic potential source rocks range in age from Early Jurassic (Tarfaya) margin, Pre-Rif and the

Inter-Atlasic basins) to Oxfordian (Essaouira basin). These source rocks contain predominantly

sapropelic Type II kerogen.

Early Cretaceous rocks, which are particularly well-represented in the Dakhla-Layoune-Tarfaya

basin, are characterised by thick regressive cycles, thick continental and deltaic elastics accumulated

unconformably over Jurassic platform carbonates. The Aptian and Albian succession is composed of a

thick interval of shallow marine, lagoonal and intertidal sediments represented by lithofacies such as

shales, sandstones and shelly limestones. Thick marls, that may be rich in organic matter, are also

widespread. The Late Cretaceous throughout Morocco is composed of carbonates and shales, with

common minor transgressive events. Potential source rock development is tied to these transgressions,

with an extensive organic rich shale recognised in the Turonian organic shale is seen as a 50 m (gross)

in the onshore Tarfaya Basin with TOC of 6-19 % (ElNSELE & WiEDMANN, 1982).

As the Atlantic Ocean widened and deepened, the relative movement between the African and

Eurasian plates reversed direction by Late Cretaceous time. Collision and subduction in Early Tertiary

time resulted in the Alpine orogeny which had a major impact on northern Morocco. The Rif Domain

developed Alpine style nappes at this time. Subsidence continued in several marginal sedimentary

troughs, associated with continued opening of the Tethys seaway, such as the Pre-Rif Ridges and the

Morocco-Algeria Atlas. A thick sedimentary pile in the Atlas sedimentary trough, which may have

developed above earlier incipient rifts, was inverted during the Early Tertiary, when the Atlas

Mountains were overthrust to the west and south.

Tertiary sediments are represented by marine and continental deposits. Palaeocene to Eocene marine

elastics are overlain by Oligocene continental elastics. During the Tortonian the Pre-Rif nappe was

emplaced. This appears on seismic reflection profiles as an interval of chaotic internal structures. The

Pre-Rif nappe, which is up to 3000 m thick, contains Triassic salt and volcanics together with Late

Cretaceous and Early Tertiary strata. Post-nappe sediments up to 2000 m thick, are mostly fine-grained

foreland basin elastics. Miocene transgressive sandy carbonates are present in the sub-nappe.

Table 1.— Petroleum systems (established hydrocarbon accumulation).

Tableau 1. — Systemespetroliers (accumulations d'hydrocarbures etablies).

BASIN

Petroleum system name

(source age/main reservoir age)

Reservoir

facies

Representative

discovery

Status of

geochimical correlation

Migration

path

Prerif

Cretaceous-Miocene

Clastic

deposits

Ain Harma

Good

Faults

Lias-Domerian

Lias-Palaeozoic

Dolomite

Granite * Wash

Quartzite

Haricha

Sidi Fili trend

Good

Fair

Faults

Rharb

Miocene-Miocene

Turbidite

Sands

Ksiri

Fair

Local

expulsion

Essaouira

Oxfordian-Oxfordian

Silurian-Triassic

(also Oxfordian reservoir)

Dolomite

Non - marine

sands

Sid Rhalem

Meskala

Good

Fair

Lateral

faults,

subcrop

Tarfaya

Lias-Upper Jurassic (?)

L.& M. Jurassic

carbonate bank

MO-2 heavy oil

(Cap Juby)

Poor but

carbonate

source favoured

Lateral

Source. MNHN, Paris

HYDROCARBON SYSTEMS OF MOROCCO

149

ESTABLISHED PETROLEUM SYSTEMS (WITH PROVEN HYDROCARBONS)

This section of the paper presents the current level of understanding of the established petroleum

systems of Morocco (i.e. where moveable hydrocarbons have been encountered) and classifies these

(Table 1) in terms of our confidence in the source to oil tie according to the terminology of MAGOON &

DOW (1994).

0 Oilfield

Gas field

Oil seeps

Tertiary prospecl

Jurassic prospecl

Palaeozoic prospecl

Gas pipe line network

Refinery

Rif foldbelt

Fig. 4.— Map showing the areal extends of two petroleum systems defined in the Pre-Rif ridges area. The Liassic-Domerian

system may extend to the north whereas the Palaeozoic-Liassic system may extend to the northwest.

FlG. 4.—Carte montrant Vextension des deux systemes petroliers deftnis dans la zone des rides prerfames. Le systeme Lias-

Dome rien pent s’etendre plus au nord tandis que le systeme Paleozoi'que-Lias pent s’etendre dans la partie nord-west.

Source

150

HADDOUJABOUR ETAL.

Pre-Rif producing basin

In the Pre-Rif compressional belt, developed basinward of the Rif Nappe, available data is used to

define 3 petroleum systems.

The first (Cretaceous-Miocene) lies to the north of the Rharb Basin, and is represented by the first oil

discovery in North Africa, Ain Hamra, made in 1923. Oil is reservoircd in shallow late Miocene sand

lenses (200 m), within steep compressional structures in the post-nappe series and has been typed to a

Late Cretaceous source. The complex structural setting suggests a hybrid system. The two other systems

occur in the Pre-Rif Ridges, as illustrated on the figure 4.

A series of oil occurrences in structures along the northeast-southwest trending Sidi-Fili fault (Fig. 4)

is reservoired in washed/weathered hercynian granites and fractured Palaeozoic sandstone reservoirs.

The most likely source is the Early Jurassic though Triassic and Palaeozoic contributions can also be

postulated. A hybrid system is suspected. This system is labelled as the Palaeozoic system on the

figure 4.

The third system (Liassic-Domerian) occurs in the eastern part of the Pre-Rif (Fig. 5). Oil is sourced

mainly from Early Jurassic and reservoired in Domerian reefal carbonates and Middle Jurassic arkosic

sands. Some oil may also be reservoired in early Miocene sandy carbonates. Oil is produced, as tar, in

hanging wall anticlines and imbricate ramps at a relatively shallow depth. Recent studies suggest that

the oil so far produced could be a product of dismigration via major faults from deeper accumulations

within sub-thrust anticlines.

Rharb producing basin

The Rharb Basin is a Neogene foreland basin filled by a thick Miocene-Pliocene clastic series

deposited coeval with uplifting of the Rif and Pre-Rif. Palaeozoic and Mesozoic basement outcrops

along its southern edge and is drilled in the basin centre and in the northeast, where the basin passes into

the Pre-Rif folded belt. The Rharb basin deep contains several sub-basins developed along major listric

faults.

A significant amount ot biogenic gas is reservoired and produced from Tertiary rocks deposited in

this foreland basin. This geologic setting is classified as a purebed system. Biogenic gas is expelled from

thermally immature Miocene source rock into adjoining medium- to fine-grained, well-sorted Late

Miocene sand reservoirs. Recent seismic processing techniques have considerably improved the success

ratio in exploring for biogenic gas in this petroleum system. More than 80 seismic amplitude anomalies

are identified in this region.

Essaouira producing basin

A detailed description of the Essaouira basin is provided by BROUGHTON & TREPANIER (1993). This

basin, which is currently the most important producing basin in Morocco, is a Mesozoic-Cainozoic

earlier trend basin passive margin basin developed over earlier fault trends. The basin trend basin

contains numerous extensional salt-related structures.

In the Essaouira Basin, two petroleum systems are identified (Fig. 6). Wet gas is sourced from

Silurian (cf. CLIFFORD, 1986) and possibly additional Ordovician and Devonian source rocks and

reservoired below a Triassic salt seal in siliciclastic sediments (termed Silurian-Triassic system). Highly

mature west gas is vertically drained from source to reservoir in the Meskala-Zelten horst. The system is

interpreted to be normally charged. We also favour a Palaeozoic source for the gas fields in the eastern

part of the basin, reservoired in fractured Oxfordian dolomites, as these fields are distant from any

conceivable Oxfordian gas kitchen.

Source: MNHN, Paris

1 0 Oilfield

2 Q Qae fields

3 ^3 JUn, "' C PrMpW: “ 5 0

4 Trlasslc Prospects 6 ^

Jurassic Source Rocks

Normal faults

Fig. 5.— Map showing the area extends of the two petroleum systems defined in the Essaouira basin. The Silurian-Triassic

system most likely extends to the north into the Doukkala and Casablanca basins. Note the mapping of an additional

kitchen in the west of the Oxfordian system, which has, as yet, no discoveries associated.

Fig. 5 .— Carle montrant l'extension des deux systemes pel rollers definis dans le bassin d'Essaouira. Le systeme Silurien-Trias

pent vraisemblablement s 'etendre plus au nord pour inclure les bassins de Doukkala et de Casablanca offshore. A noter

la canographie d'une cuisine a huile supplernentaire. a I'ouest du systeme Oxfordien. qui n'est pas encore associee a

une decouverie.

Source: MNHN, Paris

152

HADDOU JABOUR ETA/..

SYSTEM

CRET.

500 “

SILURIAN

1000 m-

AVERAGE TOC (%)

iu-t

4 0.39

2.21

1.08

23 4 - 04

yvT3.39

J 3 - 9

4.46

1 16

~P96

VITRINITE REFLECTANCE (or) Re %

I 12.12

earl

matu

Immature

0.6

1.3

•••

Mature

Peak

Wet

Gas

Dry

Gas

Fig. 6. Geochemical daia on ihe KAT-I well (Tadla basin), illustrating good quality source rocks still within the oil window.

I- ig. 6.—Les donnees geochitnii/iies du /mils KAT -/ du bassin de Tadla illusireni une roche mere paleozotaae de bonne aualile

a I interieur de la fenetre a I'huile.

The oil in the Essaouira Basin is formed in a purebred petroleum system (Oxfordian-Oxfordian). The

entire petroleum system, including the seal, is confined to the Oxfordian, with the source developed in

the early Oxfordian (BROUGHTON & TREPANIER, 1993). The reservoir in a late Oxfordian (Argovian)

fractured sandy dolomite is sealed by late Oxfordian anhydrite. Data from the Sidi Rhalem oil field

suggest this system to be undercharged. Recent studies, however, suggest a normally charged portion of

the system to the west in Neknafa syncline where oil and/or wet aas accumulations may be found

against salt walls and overhangs (Fig. 5).

Tarfaya basin (Cap Juby discovery)

Well MO-2 offshore Cap Juby in the Tarfaya basin discovered a significant heavy oil (11° API)

accumlation in a fractured Late Jurassic carbonate bank.which was unfortunately partially breached on

an Oligocene shelf collapse unconformity. Jurassic petroleum system defined in Tarfaya Basin is

classified as purebred system. A small amount of light oil is also found in Middle Jurassic reservoirs.

Many attempts have been made at source to oil correlation, none of which have been conclusive, though

the bulk of the evidence tends to favour a Jurassic carbonate source rock. This seems most likely

developed in the Early Jurassic either in intra-platform sags behind the shelf edge. An alternative

interpretation ot a shalier facies source, developed in the present day adjoining deep water area, cannot

be ruled out. Exploration drilling carried out in this area has mainly targetted the Late Jurassic shelf

edge. Recent studies, however, tend to favor Early and Middle Jurassic objectives surrounding the

possible interior platform source rock depocenter, which are less likely to have suffered from reservoir

breaching or input of groundwater.

Source: MNHN , Paris

HYDROCARBON SYSTEMS OF MOROCCO

153

PREDICTED PETROLEUM SYSTEMS IN FRONTIER BASINS

This section of the paper presents an interpretation of where further petroleum systems and resources

lie undiscovered in the underexplored basins of Morocco. As the occurrence of petroleum has yet to be

proven in these cases, the term petroleum system as applied by MAGOON & Dow (1994) cannot be used.

Therefore, these interpretations will be presented as “predicted petroleum systems”. The evidence

supporting these included identification of source rocks from geochemical analysis, extrapolations of

source rock extents from palaeogeographic mapping, extrapolations based on regional analogue basins,

basin modelling and in some cases, the occurrence of shows and/or seeps. The predicted systems are

grouped by the age of the inferred source rock.

Predicted Palaeozoic sourced systems

The main regional Palaeozoic source rocks, particularly those in the Silurian and Devonian are

predicted to have extended over Morocco, being effective source rocks in adjoining areas of Algeria and

in the Appalachian Basin (USA), which originally lay in close palaeotectonic position to Morocco

where stratigraphic data is available, the Silurian source rock can usually be identified, though at a wide

range of possible levels of maturity. The highest levels of maturity would be expected to occur over

uplifted Carboniferous depocentres, and it may be the tendency for such areas to present good outcrop

data that has led to a perception that the Palaeozoic of Morocco is regionally overcooked. This is clearly

not the case in the Essaouira and Tadla (Fig. 6) basins and it remains possible that large areas of

Morocco contain Palaeozoic source rocks that retained and generated much of their potential in post-

Hercynian time (Fig. 3). Such regions include the following.

Tadla basin

A scarcity of exploration boreholes in this basin (1 well per 3000 sq km) places the emphasis for

exploration on geological, geochemical and geophysical evidence. Geochemical analyses show that oil-

prone Silurian and Early Devonian source rocks (TOC up to 12%) are still within the oil window on

uplifted blocks (Fig. 6) (JABOUR & NAKAYAMA, 1988). Generation of oil and gas is predicted to have

occurred from Carboniferous to Cretaceous (JABOUR & NAKAYAMA, 1988). Resevoir objectives occur

in basal Triassic and Middle Jurassic siliciclastics which display excellent reservoir characteristics.

DOUKKALA BASIN

In the Doukkala Basin, a Palaeozoic petroleum system is predicted as an extension of that developed

in the Essaouira basin (Fig. 5). Oil and gas produced from Silurian-Lower Devonian source rocks could

be reservoired, as in Essaouira, in Permo-Triassic siliciclastic reservoirs. Such sub-system would be

vertically drained and normally charged. A further potential reservoir is a postulated Middle Devonian

reef complex.

Casablanca offshore basin

The Doukkala Basin passes northwards into the Casablanca offshore area, in which large structural

closures are defined on seismic. No wells have been drilled in this large exploration area. Oil is

postulated to be sourced from Silurian-Early Devonian oil prone source rocks and reservoired in

fractured and weathered Ordovician quartzitic sandstones. The system is laterally drained and postulated

to be normally charged with a high impedance entrapment style. The system is very similar in both size

and system components to the Hassi-Messaoud oil field in Algeria.

154

HADDOUJABOUR ETAL.

INTERATLASIC BASINS

Additional Palaeozoic petroleum systems are predicted in the Inter-Atlasic Basins. Oil and/or gas

probably originates from Carboniferous and Silurian source rocks (which are still in the generating

stage, particularly on uplifted blocks). Shows have been observed in basal Triassic sands and

conglomerates. The oil and/or gas is thought to be vertically drained and sealed by a thick, high

impedance salt sequence.

The Palaeozoic petroleum system of the interatlasic basins may be developed in three areas, namely

the High Plateaux, the Missour Basin and the Zekkara-Jerada area. No direct correlation has yet been

found between the oil and gas seen as shows and seeps and the likely source rock. Currently, no data is

available to confidently map the areal extend of these plays, though kitchens can crudely be defined

from sparse geochemical data.

Predicted Triassic sourced systems

The postulated Triassic system is comprised of lacustrine deposits rich in type I similar to these

recorded in the coeval Newark basin (OLSEN & SCHLISCHE 1990). This oil prone source can be

expected to charge alluvial fan and fluvial clastic reservoirs in both the hanging wall and the footwall of

the half graben (Fig. 7). Thick Late Triassic-early Liassic salt provides adequate sealing for this system.

The Triassic systems are predicted to have the character of pure-bred systems with a high impedance

associated with a mainly vertically drained system. The areal extent of these systems is very limited, and

in most cases corresponds only to the area encompassed by the half graben.

A study integrating seismic, gravity and magnetic data has identified at least 8 such buried Triassic

half-grabens along segments of the Atlantic margin between Casablanca and Tarfaya.

Predicted Jurassic sourced systems

Early Jurassic source rocks, as established in the Tarfaya marin and Pre-Rif are expected to extend

into the Inter-Atlasic Basins, including the southeastern part of the High Plateaux, the southeastern and

western parts of the Missour basin, and the Guercif Basin and the Zekkara area. Here again, the extent

of the kitchen and petroleum system is speculative, due to lack of seismic coverage.

Predicted Cretaceous sourced systems

Regional source rocks tied to transgressions and oceanic anoxic events are predicted in the Albian

and Turonian. Interest is focused on the former due to maturity consideration. The main areas of interest

are those in which a thick cover is developed of maturity above potential Cretaceous source rocks.

These are the following:

Dakhu-Laayoune basin

In the Layoune-Dakhla basins. Early Cretaceous source rocks matured below a thick deepwater

argillaceous section may charge Albian rollover structures generated along listric faults. In addition,

Late Cretaceous source rocks, il mature, may charge Maastrichtian carbonate reservoirs. Such

Cretaceous sources may be the origin of residual oil stains observed in the 51 A-l well, within Senonian

and Eocene carbonates.

Source: MNHN, Paris

HYDROCARBON SYSTEMS OF MOROCCO

155

Reservoir rocks

Source rocks

Fool wall

sourced

alluvial

fans

Hanging wall

Alluvial cones

Fig. 7.— Sedimentary model of a Triassic Newark-style half-graben illustrating the various components of the postulated

Triassic petroleum system.

FlG. 7.— Modele sedimentaire d'un hemi-graben triasique type Newark Must rant les differentes composantes d'un systeme

petrolier triasique postule.

Agadir-Essaouira OFFSHORE BASINS

Cretaceous petroleum systems are predicted to exist in offshore Agadir-Tarfaya segment. Excellent

Apto-Albian source rocks, mature basinward. potentially charging a Jurassic faulted and karstified bank

edge in Agadir and parts of the Tarfaya offshore basins.

In the Agadir-Essaouira offshore area, recent study has developed a new exploration concept. The

primary exploration objective is a faulted carbonate shelf edge where porosity is enhanced by subareal

exposure and consequent karstification. A hypothetical source rock would be Early Cretaceous shales

deposited beyond the Jurassic shelf edge. Geochemical basin modeling has defined a possible kitchen

area from which oil is generated. No exploration drilling has tested this concept yet.

TAD LA BASIN

For the Cretaceous system, rich (up to 13% TOC) oil prone Cretaceous source rock are interpreted to

enter the oil window under an interpreted low angle thrust marking the Atlas front. The additional

loading and burial acquired is predicted to be sufficient for maturity to be attained.

Predicted Neogene sourced systems

By analogy to the established Neogene hydrocarbon systems of the Rharb and Pre-Rif basins,

shallow biogenic gas systems are predicted in areas of high Neogene subsidence rate in offshore Rharb.

the offshore Mediterranean and Laayoune-Dakhla basins.

156

HADDOUJABOUR ETAL.

CONCLUSION

The present geological, geochemical and geophysical coverage has permitted us to predict a number

of petroleum systems in Morocco (Table 2) in addition to those already established as producing

provinces. These are defined on rather general information over relatively large areas. Any petroleum

system identified on a subsurface data, be subdivided into smaller sub-systems. Furthermore, some areas

such as the Atlas domain. Rif domain and south Atlas and Sahara domain where little or no seismic-

coverage is acquired, will probably provide, once investigated, a large variety of additional petroleum

systems.

Table 2.— Predicted petroleum systems (no discoveries to date).

Tableau 2.— Syst ernes pet rollers predits (pas de decouvertes a ce jour).

Age of

proposed

source

Basin

Proposed reservoir

age

Shows

Comments/critical

factors

Proposed

migration path

Tadla

Tnasstc(Ci.)

Middle Jurassic (G.)

Shows

Timing of

Vertically drained

Caboniferousfci.)

Paleozoic

(Silurian.*

? Ordovician)

Doukkala

Permo-TriassicfCi.)

Devonian Build-

Ups<Cb.)

Shows

Extenuon of

Essaouira system

Vertically up-faults

Laterally drained

Casablanca

Factured

Timing +

Laterally drained

Ordovician ssl(C1.)

? overmaturity

Boudenib

Devonian

carbonates(Cb-)

Timing +

? overmaturity

Vertically up-faults

Tnassic

Coastal Rift

Tnassic fluvial

Based on Newark

Laterally and

Lacustrine

ball-grabens

clastic deposits (Ci.)

rift system analogue

vertically drained

Lower

Jurassic

Interatlasic

Basins

(GuerciLMissour.

High Plateau)

Mid Jurassic(Cb.)

Shows

Seeps

Timing of

generation w.r.L

trap formation

Laterally drained

Tarfaya

Cretaceous, U.

Jurassic(Cb./Ci.)

Shows

Laterally drained

Cretaceous

(Albian*

Agadir

L. Cretaceous

(Ci.)

Shows

Laterally drained

?Turonian if

Dakhla

GetaceousfCi +

mature)

Cb.)

residual oil in

Tadla

Laic Cretaceous

51-A-l >

Maturity predicted

below Atlas

Laterally drained

(Ci.)

overthrust

Neogene

biogenic

Dakhla

Ncogene sand lenses

Compare Rharb

Local generation

analogue

& expuluon

systems

Mediterranean

Neogene sand

Compare Rharb

Local generation

analogue

& expulsion

Several large basins in Morocco still have much unexplored acreage. Drilling to date has tended to

concentrate on relatively shallow objectives, drilling large, often recent structures without the modern

appreciation of petroleum system concepts or the benefit of high quality seismic. The application of

these concepts leads one to concentrate on very specific plays and regions, often unexplored, where

petroleum is most likely to have been generated and preserved, e.g., in'”Palaeozoic-sourced plays over

areas not deeply buried in pre-hercynian times and in regions close to potential Jurassic and Cretaceous

kitchens, that may because of limited source facies extent or maturity considerations, be of limited

lateral extent. Very little is known about deep offshore plays. The results so far obtained from the

Campos Basin on the western side of the Atlantic ocean illustrate the potential attractiveness of such

areas. In salt basins, great strides have been made with new technology in deciphering the architecture

ol subsalt formations. A better knowledge of the petroleum systems and the characterisation of the

geology of the Moroccan sedimentary basins should therefore considerably enhance the chances of

eventual exploration drilling success.

Source: MNHN, Paris

HYDROCARBON SYSTEMS OF MOROCCO

157

ACKNOWLEDGEMENTS

This work, presented as an oral communication in its first version during the Hydrocarbon geology

of North African conference held in London (1995) then in the Peri-Tethys conference held in Rabat

(1997) expresses ideas evolved from discussion with several individuals working in both academia and

industry. The authors would like to acknowledge the comments of ALTON BROW r N, who refereed the

manuscript, and DUNCAN MACGREGOR, who made the publication of this work possible. The authors

are grateful to the last comments of a peer reviewer and the editing of the manuscript by Sylvie

CRASQUIN-SOLEAU of the Peri-Tethys program.

REFERENCES

Broughton. P. & Trepanier, A., 1993.— Hydrocarbon generation in the Essaouira basin of western Morocco. AAPG Bulletin,

77 (6): 999-1015.

Brown. R. 1980.— Triassic Rock of the Argana Valley south Morocco and their regional structural implication. AAPG

Bulletin, 64 (7): 988-1003.

Clifford. A.C., 1986.— African oil past, present & future. In: M.T Halbouty (ed.). Future petroleum provinces of the world.

AAPG Memoir, 40: 339-372.

Demaison, G. & Huizinga. B.J.. 1991.— Genetic classification of petroleum systems. AAPG Bulletin. 75 (10): 1626-1943.

ElNSELE, G. & Wi edmANN, J., 1982.— Turonian black shales in the Moroccan coastal basins. In: U. von Rad. K. Hinz. M.

SARNTHEIN & E. SEIBOLD (eds). Geology of the Northwest African Continental Margin. Springer. Berlin: 396-414.

Jabour. H. & Nakayama, K.. 1988.— Basin Modelling of Tadla Basin. Morocco, for Hydrocarbon potential. AAPG Bulletin.

72(6): 1059-1073.

Magoon. L.B.. 1987.— The Petroleum system-a classication scheme for research, resource assessment and exploration. AAPG

Bulletin, 71 (5): 587.

Magoon, L.B., 1988.— The Petroleum system-a classification scheme for research, exploration, and resource assessment. In:

L.B. MAGOON (ed.), Petroleum systems of the United-States. Bulletin - Geological Survey of America, 1870: 2-15.

Magoon. L.B. & Dow, W'.G. (eds), 1994.— The Petroleum system: from source to trap. AAPG- Memoir . 60: 1-655.

Olsen, P.E. & Schlische. R.W., 1990.— Transtensional arm of early Mesozoic Fundy rift basin: penecontemporaneous

faulting and sedimentation. Geology. 18: 695-698.

The Jurassic in Syria: an overview.

Lithostratigraphic and biostratigraphic

correlations with adjacent areas

Mikhail MOUTY

Department of Geology, Damascus University, Damascus, Syria

ABSTRACT

The carbonated Jurassic sediments in Syria and the adjacent areas are generally dominated by limestones, dolomitic

limestones and restricted marly intercalations, precipitated in shallow marine environments. Since the Jurassic marine onset,

transgressions covered the entire region of Syria with the exception of two NE-SW eiongated uplifts in the E-SE (Hamad

Uplift) and in the N-NE of the country (Aleppo-Mardin High). Before the end of the Middle Jurassic (early Bathonian). the sea

regressed from the interior of Syria northwards, moving the Tethyan Ocean shore line westward to the Levantine zone. There,

subsidence continued and the Jurassic sediments are locally thicker than 1300 m (Mount Hermon, Galilee). Before the end of

the Upper Jurassic (late Kimmeridgian), the sea further regressed from the last submerged areas. Consequently, the entire

Syrian platform remained emerged until the Cretaceous transgression initiated in the Barremian-Aptian time. As elsewhere in

the Levant, volcanic activity characterises locally the beginning and the end of the Jurassic serie in Syria.

RESUME

Le Jurassique de Syrie : une vue d’ensemble. Correlations lithostratigraphiques et biostratigraphiques avec les

regions avoisinantes.

Les sediments carbonates du Jurassique de Syrie et des regions adjacentes sont generalement domines par des calcaires, des

calcaires dolomitiques et de fagon moindre par des intercalations de marnes. deposes dans des environnements matins peu

profonds. Depuis le debut du regime marin au Jurassique. les transgressions couvrent P ensemble de la Syrie a 1’exception de

deux zones surelevees allongees, de direction NE-SW, dans Pest-sud est (zone surelevee de Hamad) et dans le nord-nord est du

pays (zone surelevde d'Aleppo-Mardin). Avant la fin du Jurassique moyen (Bathonien inferieur), la mer regresse de

Pinterieur de la Syrie vers le nord, deplagant la ligne de rivage de la Tethys vers POuest, vers la zone Levantine. La, la

subsidence continue et les sediments jurassiques, localement, onl une epaisseur superieure a 1300 m (Mont Hermon, Galilee).

Avant la fin du Jurassique superieur (Kimmeridgien superieur), la mer se retire des dernieres zones submergees. En

consequence, la totalite de la plate-forme syrienne reste emergee jusqu’a la transgression du Cretace. debutant au Barremien-

Aptien. Comme ailleurs dans le Levant. Pactivity volcanique caracterise localement le debut et la fin du Jurassique.

MOUTY, M., 2000.— The Jurassic in Syria: an overview. Lithostratigraphic and biostratigraphic correlations with adjacent

areas. In: S. Crasquin-Soleau & E. Barrier (eds), Peri-Tethys Memoir 5: New data on Peri-Tethyan sedimentary basins.

Mem. Mus. natn. Hist, not., 182 : 159-168. Paris ISBN : 2-85653-524-0.

Source. MNHN . Paris

160

MIKHAIL MOUTY

INTRODUCTION

Jurassic strata crop out in the main chains in Syria: the Anti-Lebanon Chain, the Coastal Chain (Jibal

As-Sahilyeh), the Kurd Dagh Chain and the Palmyrides Chain (Fig. I). A large number of boreholes

penetrating the Jurassic in different areas, and the sections measured in the Jurassic outcrops give an

important insight on its development in Syria.

The earliest works on the Jurassic of Syria date from the 19th century (LARTET, 1869; FRAAS, 1877;

NOETLING, 1887). Several important studies have described the Jurassic sequences in Syria (Vautrin,

1934; DUBERTRET, 1949-1975; PONIKAROV, 1966; MOUTY, 1976, 1978).

The recent lithological and palaeontological studies conducted on several formations, units and

biozones within the Jurassic series (MOUTY, 1997a, b; FOURCADE & MOUTY, 1995; FoURCADEcv al.,

1997) gave precise correlations between different Jurassic sections in Syria and in the neighbouring

countries, allowing an accurate palaeogeographic reconstruction of the Syrian platform during the

Jurassic.

The aim of the present paper is to correlate Jurassic formations in Syria and other neighbouring

countries on lithological and palaeontological basis.

40°E

35°N

Fig. 1.— Location map.

Fig. I .— Carle de localisation.

Source: MNHN, Paris

JURASSIC OF SYRIA

161

STRATIGRAPHY (Fig. 2)

Early Jurassic (Liassic)

The Early Jurassic in Mount Hermon (Anti-Lebanon) is represented by the Aarne Formation

(MOUTY, work in progress). It is essentially composed of numerous thin beds of multicoloured (black,

yellow,...) argillaceous marls with thin beds of limestones which predominate in the upper part of the

formation. A 50 m thick volcanic layer (spilite) is interbedded within this formation. Some limestone

beds in the tipper part of the formation contain Pseudocyclammina liasica Hottinger Foraminifera which

is characteristic of the late Liassic (Pliensbachian-Toarcian).

The thickness of this formation in the type section (Mount Hermon) reaches 150 m. It overlies

intercalations of black argillaceous marls and black thin bedded limestones (Rime Formation,

DUBERTRET, 1960) with Aulotortus sinuosus (Weynschenk) which characterises the Late Triassic

(Norian-Rhaetian).

The Aarne Formation is correlated in Lebanon with the lower part of “niveau 2" of Wadi Nahr

Ibrahim (RENOUARD, 1951) which is composed of limestones, dolomitic limestones with rare marl

intercalations and overlies a 300 m thick of dolomites and dolomitic limestones (“niveau 1") with

probable Triassic Nodosaridae (NOUJEIM-Clark & MOUTY, work in progress).

The Early Jurassic in the Palmyrides Chain is represented by the lower part (Unit A) of Satih

Formation (MOUTY, 1997a), which is composed of thin beds of limestones and dolomitic limestones

with some marl intercalations containing Liassic Foraminifera (Mayndna termieri Hottinger) in its

upper part.

In the boreholes drilled in central, north and northeast Syria, the Early Jurassic is represented by

limestones in the upper part of the Dolaa Group ( DUBERTRET & DANIEL. 1962, according to DUBERTET,

1963).

The Early Jurassic in the Coastal Chain (Jibal As-Sahilyeh) is represented by Treize Formation

(MOUTY, 1997b) which is composed of thin beds of light yellow marls, marly limestones and

limestones. Fossils found in this formation are Brachiopoda, Liospiriferina undulata (Seguenza), and

Foraminifera, Pseudocyclammina liasica Hottinger which indicate a Pliensbachian-Toarcian age. The

thickness of this formation in its type locality reaches 40 meters. It underlies a thick serie of dolomites

and dolomitic limestones (200-300 m) with Late Triassic Foraminifera: ( Galeanelia aff. laticarinata A1

Shaibani, Gsollbergella spiriloculiformis (Oroveczne-Scbeffer).

In the Kurd Dagh Chain, the Early Jurassic is represented by thick beds of micritic and pelbiomicritic

limestones (the lower part of the Dodo Formation: "Lithiotis Limestone") (MOUTY, work in progress),

with big, undulated and plated Pelecypoda: Lithiotis sp.. which characterises the basal beds of the

Jurassic in Iran (KENT et ai, 1951).

The numerous boreholes, which penetrated the Jurassic series, are located in the interior of Syria.

The Early Jurassic encountered in these boreholes is undifferentiated in the upper part of Dolaa Group

(DUBERTRET & Daniel, 1962, according to DUBERTRET. 1963). and consisting in limestones

underlying evaporates with some intercalations of thin beds of marls and marly limestones containing

Late Triassic microfossils (Bash Imam & Sigal, 1985).

In this respect, it is very important to mention that the entire Jurassic serie is missing on the Aleppo-

Mardin High (PONIKAROV, 1966; Kammar. 1994) and on the Hamad Uplift (MOUTY & AL MALEH,

1983; MOUTY, 1997a).

The Early Jurassic formations or units in Syria are correlated with the Ubaid Formation

(DUNNINGTON, 1954, according to DUBERTRET, 1959) in west Iraq (Rutbah area) which is composed of

limestones, dolomitic limestones and rare marl intercalations containing Liassic Foraminifera

(DUNNINGTON, 1954 cited in DUBERTRET, 1959). They are correlated, in the northwestern Iraq, with the

162

MIKHAIL MOUTY

lower part of the Sargelu Formation which is composed in its type locality of “thin bedded black,

bituminous limestones, and black laminated shales" containing Liassic fauna at the base (BELLEN cited

in DUBERTRET, 1959). They are also correlative with the upper part of the “Gres a plantes de Subeihi”

(WETZEL & Morton, 1959) in the northwest Jordan (Wadi Nahr Az-Zarqua).

The Early Jurassic volcanic serie, which outcrops in the Mount Hermon, reaches its maximum

thickness in the Galilee to the west and southwest where it is represented by Asher volcanic Formation

(Garfunkel & Derin, 1985). The dolerite flow in the Abba borehole, 54 km NE by N of Raqqa

(Daniel cited//? Dubertret, 1963) and the volcanic flow in the SE of Turkey (ALTINLI, 1966) are

about of the same age.

^\Localil>

Age

Galilee

Hermon

Lebanon

Coastal Chain

J. As Sahilyeh

Kurd Dagh

Palmyrides

West Iraq

Jordan

_ Aptian -

Cenomanian

Tayasir

Gres de base

Gr6s de base

Bab Janneh

Gres de base

Palmyra

Rutbah

Hathira

Tithonian

absent

Kimmeridgian

Haifa Bay

Batroun

Salima

Nasirah

Oxfordian

Callovian

Bathonian

Bajocian

Aalenian

Bloudane

Bikfaya

Majdal Chams

Bhanness

Wadi Al Ouyoun

Haifa

Asher

Hermon

Kesrouane

Machta

Bqassem

niveau 4a

niveau 3

Muhaiwir

Huni

Kalaat Jandal

niveau 2

Ouyoun

Toarcian

Pliensbachian

Lower Triassic

Aarne

Treize

■a

P <o

D a

1 A

•J

Ubaid

Subeihi

Norian-

Rhaetian

Mohilla

Rime

niveau 1

Jweikhate

Smalek

Hayan

Zor Hauran

Zarqa

Fig. 2.— Correlation of the Jurassic formations in Syria and neighbouring countries.

Fig. 2.— Correlations des formations jurassiques en Syrie et dans les regions avoisinantes.

Middle Jurassic (Dogger)

The Middle Jurassic is the thickest serie of this stage in Syria. It is represented by many formations

and units, especially along the coasts of the Eastern Mediterranean, from the Coastal Chains in Syria, all

the way down to northern Sinai (Egypt).

The Kalaat Jandal Formation in the Mount Hermon was first defined by DUBERTRET (1960), as

“Calcaire de Kalaat Jandal”. It was modified recently (MOUTY, work in progress) by the separation of

its lower part (Aarne Formation), due to the fact that it is lithologically different. It is essentially

composed, in its type section, of medium to thick beds of micritic and pelbiomicritic limestones which

are partly dolomitised. Its facies indicates a shallow marine environment of low energy. Its thickness is

approximately 400 m.

I he formation yields relatively abundant fossils, mainly Foraminifera. The most important ones are:

Iimidonella sarda Bassoullet, Haurania deserta Henson. Amijiella cimiji (Henson). These fossils

indicate an Aalenian-Bajocian age.

This formation is correlated with the Ouyoun Formation in the Coastal Chain in the NW Syria

Source: MNHN , Paris

JURASSIC OF SYRIA

163

(MOUTY, 1997b) which is composed of thick beds of limestones, dolomites, and dolomitic limestones

containing Timidonella sarda Bassoullet, Haurania deserta Henson. Amijiella amiji (Henson). It is

correlated with the B unit of Dodo Formation (MOUTY et al., work in progress) in the Kurd Dagh, which

consists in micritic and pelbiomicritic limestones containing Timidonella sarda Bassoullet. and with the

B unit of Satih Formation in the Palmyrides Chain (MOUTY, 1997a) which consists in massive

dolomicritic limestone containing Haurania deserta Henson and Amijiella amiji (Henson).

The correlation of this formation with its rivals in the neighbouring countries bears some problems. It

could be preliminarily correlated in age with the lower part of Haifa Formation (DERIN, 1974) in

Galilee, with the upper part of “Niveau 2" in Lebanon (RENOUARD, 1951), with the limestones and

marly sandstones of the Huni Formation in Wadi Az-Zarqa (WETZEL & MORTON, 1959), in the

northwest Jordan, with the lower part of Muhaiwir Formation (WETZEL, 1951 cited/'// DUBERTRET,

1959) in the southwest Iraq, which contains Haurania deserta Henson. Amijiella amiji (Henson) and

with the middle part of Sargelu Formation (WETZEL, 1951 cited/// DUBERTRET, 1959) in the northwest

Iraq, which contains abundant macrofossils (ammonites, Rhynchonellidae).

Bqassem Formation, in the Mount Hermon, overlies the Kalaat Jandal Formation. It was first defined

by DUBERTRET (1960) as “Calcaire jaune de Bqassem". It is composed of limestones with marl

intercalations, very thick in the lower part of the formation. It represents shallow marine environment

sediments of relatively high energy. It overlies an important hard ground surface on the top of Kalaat

Jandal Formation. Its thickness in its type locality is 150 m. According to VAUTRIN (1934) and

DUBERTRET (1960), fossils are abundant. The formation fossil assemblage consists of Rhynchonella

hopkinsi McCoy. R. absoleta Sowerby, Terebratula superstes Douville, T. quillyensis Bayle. The

presence of characteristic Foraminifera, Haurania deserta Henson, Amijiella amiji (Henson), indicates

an upper Bajocian-Bathonian age.

The formation has no proved correlation except the age with its rivals in the neighbouring countries.

It could be correlated with the upper part (Unit C) of Satih Formation (MOUTY, 1997a) in the

Palmyrides Chain which contains brachiopods, Daghanirhynchia subversabilis (Weik), and

Foraminifera, Haurania deserta Henson. Amijiella amiji (Henson), with the lower part of Machta

Formation (MOUTY, 1997b) in the Coastal Chain in the NW Syria, which consists in few metres of marl

and limestone intercalations with a typical surface of emersion (palaeosoil surface). This surface is

marked in the interior Syria, in the west of Iraq and in the northwest of Jordan, by an erosion surface,

covered by clastic continental sediments of Early Cretaceous.

The Hermon Formation overlies the Bqassem Formation in Mount Hermon. It was first defined by

DUBERTRET (1960) as “Calcaire de PHermon". It consists in thick beds of micritic, biomicritic and

pelbiomicritic limestones. The depositional environment of this formation is neritic and normal saline,

subject to long period of subsidence. Its thickness, in its type locality, is about 700m.

Fossils in the type locality are relatively frequent, consisting in lower part of Paleopfenderina

salernitana (Sartoni & Crescenti), P. trochoidea (Smouth & Sugden), Kilianina blanched Pfender,

EndersoneUa palastiniensis (Henson), and in the upper part, are rich in Steinekella steinekei Redmond.

S. crusei Redmond. Praekurnubia crusei Redmond. Redmondoides lugeoni (Septfontaine) with

Dasycladacea: Salpingoporella annulata Carozzi, Thaumatoporella parvovesiculifera (Raineri).

Fossil assemblages mentioned above indicate a Bathonian-lower Callovian age.

The formation can be correlated with the upper part of the Haifa Formation in the Galilee area

(DERIN, 1974). It is correlated with massive limestones of the Kesrouane Formation in Lebanon

(DUBERTRET, 1960).

The Hermon Formation has no proper lithologic correlation with the Coastal Chain in the northwest

Syria. It is correlated, essentially in age, with the upper part of the Machta formation, and the lower part

of Wadi Al-Ouyoun formation (MOUTY, 1997b). since Machta Formation consisted in an alternation of

thick lithological units of limestones and marls, that contain, from the base to the top, Paleopfenderina

trochoidea (Smouth & Sugden), P. salernitana (Sartoni & Crescenti), Kilianina blanched Pfender,

which indicate a Bathonian age, and the lower part of Wadi Al-Ouyoun formation which contains

Steinekella steinekei Redmond, S. crusei Redmond and which indicate a Callovian age.

The Hermon Formation is missing in the entire interior Syria, except for west Palmyrides Chain

(Sherifeh area) which contains Valvulinella jurasica (Henson).

164

MIKHAIL MOUTY

Late Jurassic (Malm)

The Majdal Chains Formation overlies the Hermon Formation in the southwest flank of Mount

Hermon (Majdal Chains village). It was first defined by DUBERTRET (1960) as “Marnesgris-clair de

Mejdel Chems” (in Hermon geological map). It is composed of argillaceous marls with limonitic

concretions at the base and intercalations of thin beds of limestone and marl.

Fossils are abundant throughout, specially in ammonites and brachiopods. According to NOETLING

(1887), Vautrin (1934), Haas (1955), Arkell (1956), Dubertret (1960). Razvalyaev (1966),

CARIOU & HANTZPERGUE (1997), CARIOU et al. (1997), this fauna indicates an Oxfordian age.

The thickness of Majdal Chams Formation in its type locality is about 150-200 m. It decreases in

thickness northwards. It drops to 50 m in Wadi Al-Karn, 40 km northeast of Mount Hermon: “Marne

jaune de Wadi Al-Karn" (DUBERTRET, 1950), yielding abundant fossils: stromatopora, corals, echinoids,

brachiopods (Somalirhynchia africana Uhlig. Bihenithyris weiri Muir-Wood) which indicate a middle

Callovian age ( Erymnoceras and Pachyerymnoceras horizon) (ALMERAS, personal communication).

The upper part of the Majdal Chams Formation is partly correlated in age with the upper part of

Wadi Al-Ouyoun Formation (MOUTY. 1997b) in the Coastal Chain, in the northwest Syria, which yields

Foraminifera, Steinekella steinekei Redmond, 5. crusei Redmond, and brachiopods, Bihenithyris sp.,

Kutchirhynchia indica (d'Orbigny), indicating a middle Callovian age.

A 30 m thick remarkable volcanic horizon termed “Niveau volcanic de Bhanness" (DUBERTRET,

1950) occurs in Lebanon.

The Late Jurassic is represented in the Levantine coastal chains. Above the Majdal Chams Formation

follows the Bloudane Formation (MOUTY, work in progress) which is the “Calcaire a Balanocidaris

glandifera" (VAUTRIN. 1934). It consists in massive limestones presenting a very distinctive 15-25 m

high cliff. It yields relative abundant fossils, mainly echinoids (Balanocidaris glandifera Munster) and

Foraminifera. The most important Foraminifera is Levantinella egyptiensis (Fourcade, Mouty &

Teherani) which indicates an Oxfordian age (Levantinella egyptiensis biozone). The alga Clypeina

jurassica Favre characterises this formation.

The depositional environment of the formation is clearly neritic.

It is followed by the “calcaires jaunes superieurs". This formation is correlated with the “Falaise de

Bikfaya” (DUBERTRET, 1949. 1950) which forms in the Lebanon a high cliff (80 m) of massive

limestone. The absence of micropalaeontological analysis makes difficult a precise correlation. It is

probably equivalent to the Haifa Bay Formation.

Nevertheless, the Bloudane Formation is correlated in age with the lower part of Nasirah Formation

(MOUTY, 1997b) in the Coastal Chain, in northwest Syria, which consists in pelbiomicritic limestone

with Levantinella egyptiensis (Fourcade, Mouty & Teherani) and Alveosepta jaccardi (Schrodt). It is

also correlative with the Haifa micrite levels containing Levantinella egyptiensis (Fourcade, Mouty &

Teherani) in the Galilee (PICARD & HlRSCH, 1987).

The Late Jurassic is represented in the Anti-Lebanon by the Batroun Formation or “Calcaire jaune de

Batroun" (DUBERTRET, 1950) which is composed of light yellow micritic, pelbiomicritic and oolitic

limestones with abundant marl intercalations. In the SW flank of Mount Hermon, near Hadar village,

two 20 cm thick basalt beds are present at the top of upper part of the formation.

The thickness of this formation in the Anti-Lebanon is about 20-40 m.

Fossils in the Hermon area are, according to VAUTRIN (1934): Terehratula subset la Leym.,

Pyguropsis noetlingi De Loriol. Near the Batroun locality (Rawda), SW of Zebdani plain, the fossils are

abundant: Alveosepta jaccardi (Schrodt), Kurnubia palastiniensis Henson. Alveosepta (Iberina)

prealusitanica (Maync). The presence of the latter species characterises the Kimmeridgian in this

region.

The formation is correlated with the Calcaire de Salima (DUBERTRET, 1950) in Lebanon which is

Source MNHN, Paris

JURASSIC OF SYRIA

165

composed of light yellow oolithic and clastic limestones (150 m thick) locally interbedded by some

volcanic levels.

The formation is correlated in age with the upper part of Nasirah Formation (MOUTY, 1997b) in the

Coastal Chain in the northwest Syria, which yields Alveosepta jaccardi (Schrodt), A. (Iberina)

prealusitanica (Maync) and Kurnubia pdlastiniensis Henson.

It is also correlated with the Haifa Bay Formation in Galilee which contains Alveosepta (Iberina)

prealusitanica (Maync) (MAYNC, 1966).

The Late Jurassic is missing in the entire interior Syria, except for the Sherifeh area (W ol

Palmyrides Chain), which was submerged during that time: its sediments contain Levantinella

egyptiensis (Fourcade, Mouty & Teherani) (HENSON, 1948).

It is also missing in west Iraq (BUDAY, 1980) and in Jordan (WETZEL& MORTON, 1959).

The Late Jurassic is restrictively present along the coastal chains of the East Mediterranean: Jabal

Akraa, Coastal Chain (Jibal As-Sahilyeh), Lebanon Chain, Anti-Lebanon Chain and Galilee (Coastal

Basin).

The Tithonian is missing in Syria and probably in the neighbouring areas due to an important hiatus

which reaches the end of Neocomian.

Amanos High

Afrine basin

Kurd Dagh

(

Aleppo High

Aleppo

(well)

Palmyrean Basin

Palmyrides

Hamad Uplift

N. Hamad

(well)

S. Hamad

(well)

Rutbah Basin

Rutbah

rIOOm

- 50

- 0

|; •; • ;| Cretaceous \

V/A Lower and Middle Jurassic \

^ Upper Triassic

!****! Palaeozoic

Fig. 3.— Correlation between sections from Amanos High to Rutbah Basin (NW-SE).

Fig. 3.— Correlations entre les coupes depuis la sur/elevation d'Amanos jusqu'an Bassin de Rutbah (NW-SE).

CONCLUSION

The palaeogeographic development during the Early and Middle Jurassic in Syria is controlled by

two ENE-SW oriented huge uplift zones:

Hamad Uplift (MOUTY & ALMALEH. 1983: MOUTY, 1997a). Aleppo-Mardin high (PONIKAROV,

1966: KAMMAR. 1994) and Amanos High (LOVELOK, 1984) within the Syrian platform, separated by

intracratonic rifted zones: the Rutbah basin (SW Iraq), the Palmyrid basin, the Afrine basin: and

bordered in the west by the western margin of a N-E oriented rift zone (the Coastal basin) which

represent the oldest manifestation of the Levant Fault-Zone (Dead Sea Fault) well developed at Late

Tertiary (MOUTY, work in progress) (Figs 3 and 5).

These structures were the result of the Gondwana breakup, reflected by the opening of the Tethyan

Ocean at the end of Upper Triassic.

166

MIKHAIL MOUTY

The palaeogeographic development during the Early Jurassic is characterised by progressive

transgression started just before the end of Late Triassic (MOUTY. 1997a) onto the Syrian platform, that

did not submerge the huge uplifted zones. The evaporitic sediments precipitated under lagoonal

conditions during the Triassic were replaced by marine sediments. The volcanic rocks within the Early

Jurassic sediments (Mount Hermon. Galilee. Dolaa well) indicate the activity of these rifted zones at

that time.

These marine conditions were continued during the Dogger, represented by frankly marine

sedimentation, mostly neritic calcareous-micritic, politic or arenaceous sedimentation, the west

marginal rift zone (Levantine basin) differs from the other basins, especially in its southern part

(Lebanon. Anti-Lebanon and Galilee) which was being of more expressive mobility and subsidence

(Vautrin, 1934; Renouard. 1951; Dubertret, 1966; Picard & Hirsch. 1987; HlRSCH & Picard.

1988).

The Dogger sedimentation locally ended by an emergent phase. Before the end of the Dogger, at the

base of the Bathonian. a regressive phase marks the end of the marine cycle on the entire interior Syrian

platform.

Fig. 4. Stratigraphic sections of East Mediterranean Chains. 1. limestones; 2. dolomites; 3, marls: 4. basalts- 5 sandstones*

6. gypsum.

Fig. 4.— Correlations stratigraphiques des Chaines est-mediterraneennes. 1, calcaires ; 2. dolomies ; 3, marnes * 4 b a mites •

5. gres ; 6, gypse.

The regressive phase began at the base of the Bathonian. The Jurassic sea withdrew from the interior

rifted basins to the Tethyan Ocean in the north and to the East Mediterranean basin in the west forming

an embayement in the Sherifeh area. This basin on the western margin of the Syrian platform continues

to subsidise, especially in its southern part (Lebanon. Anti-Lebanon and Galilee) until the end of

Kimmeridgian (Fig. 4) where the latest regressive phase began, with some volcanic activity locally

(Mount Hermon and Lebanon), and the entire Syrian platform became emerged during the fithonian

stage.

Source MNHN, Paris

JURASSIC OF SYRIA

167

40°E

35°N

Fig. 5.— Schematic palaeo-

geographic map of Syrian

Platform during the Early

and the early Middle

Jurassic.

Fig. 5.— Carte paleogeo-

graphique schematique de

la plate-forme syrienne

durant le Jurassique infe-

rieur et le debut du

Jurassique moyen.

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Source MNHN, Paris

Basin development and tectonic history

of the Euphrates graben (Eastern Syria):

a stratigraphic and seismic approach

Cecile CARON Maher JAMAL 121

Hassan ZEINAB 131 & Francis CERDA

in Mazzeh Dar Es Saada, 16 Villai Gharbia, BP 9645. Damas. Syric

Ministry of Petroleum and Mineral Resources, Adawi Aulostrade. Damas, Syrie

<J ' Syrian Petroleum Company. P.O. Box 2849 - 668, Damas, Syrie

ABSTRACT

The Euphrates graben (Eastern Syria) is a E-W to NW-SE trending basin developed during the Late Cretaceous within the

northern Arabian platform. This basin holds significant hydrocarbon reserves and is a major petroleum province in Syria. The

present study intends to reconstruct the structural evolution of this graben system from the Early Cretaceous to the Oligoccne,

on the basis of detailed isopach maps and regional 2 D seismic profiles. Early NE-SW extension and associated basaltic activity

are attested in Eastern Syria as soon as in Albian times. Intense block-faulting and graben formation are reported later, during

the Turonian-Coniacian. After a period of relative tectonic quiescence by the Santonian, the main pulse of “rifting” occured in

Campanian times, with the opening of a deep N120-140E trough, filled with a 1500 m thick “syn-rift” sequence. At that time,

major northeast-vergent listric faults formed in the southern part of the Euphrates graben. This graben may correspond to a

flexural basin induced by the obduction of the Tethyan oceanic crust onto the northern margin of the Arabian plate during the

Late Cretaceous. The early Maastrichtian period is characterised by an counterclock-wise rotation of stress orientation (from

NE-SW to N15E). This change may be explained either by the stopping of lateral eastward expulsion (folding of the Zagros

foreland) or by the obduction stage along the Bitlis axis. N-S compressive movements in late Maastrichtian times caused the

Euphrates "rift” system to abort. Structural inversion was particularly active in the northwestern part of the Euphrates graben. at

the junction with the Palmyrides belt. Mesozoic basin first inverted at that time. Palaeogene is the time of global compressive

tectonics. The response of the Euphrates graben to compression is diachronous over the northwestern area, with a propagation

of structural inversion from north to south. Northern grabens are inverted in the Palaeoccne, whereas southern grabens are

inverted later in the Eocene. This pattern is consistent with the global tectonic setting of the Northern Arabian plate at that time,

implying southward migration of deformation from the site of the Bitlis convergent zone to the foreland domains. The

Oligocene period corresponds to the reactivation of N120E normal faults in the northwestern pail of the study area.

Caron, C., Jamal, M., Zeinab, H. & Cerda. F.. 2000. — Basin development and tectonic history of the Euphrates graben

(Eastern Syria): a stratigraphic and seismic approach. In : S. Crasquin-SOLEau & E. Barrier (eds). Peri-Tethys Memoir 5:

new data on Peri-Tethyan sedimentary basins. Mem. Mus. natn. Hist. nut.. 182 : 169-202. Paris ISBN : 2-85653-524-0.

Source. MNHN , Paris

170

CECILE CARON ETAL.

RESUME

Developpement du bassin el histoire tectonique du graben de I'Euphrate (Syrie orientale): approche stratigraphique

et sismique.

Le graben de I’Euphrate (Syrie orientale), d'orientation E-W a NW-SE, se developpe au Cretace superieur au sein de la

plate-forme arabe septentrionalc. Ce bassin renferme cTimportantes reserves d’hydrocarbures qui en font unc province

petrolifere majeure en Syrie. La presente etude se propose de reconstituer revolution structural de ce graben du Cretace

inferieur a I’Oligoc&ne, sur la base de cartes en isopaques detaillees et de profils sismiques regionaux 2 D. Des LAIbien, Lest de

la Syrie est le siege d’une extension NE-SW s'accompagnant d’une activite basaltique marquee. L’intense morcellement en

blocs marquant la formation du graben de I’Euphrate se produit cependant plus lard, au cours du Turonien-Coniacien. Apres

une periode de relative stabilite tectonique au Santonien. la phase de "rifting” atteint son climax au Campanien. avec

I'ouverture d'un graben NI20E ou les depots “syn-rift" excedent une epaisseur de 1500 m. A cette epoque, des failles listriques

majeures a vergence nord-est s’individualisent dans la partie sud du graben. Le graben de I’Euphrate pourrait corresponds a un

bassin flexural induit par Lobduction de la croute tethysienne sur la marge nord de la plaque arabe au cours du Cretace

superieur. Une rotation anti-horaire de la direction d'extension (NE-SW a NI5E) est observee au Maestrichtien inferieur, peut-

etre lice a un blocage de Lextension vers Lest (plissement de I’avant-pays de la chaine du Zagros) ou bien a Lobduction de la

croute tethysienne qui intervient a cette epoque le long de la zone de suture de Billis. Le Maestrichtien superieur voit I'arret de

Lactivite du "rift” de I’Euphrate et son inversion locale, sous Leffet d’une compression N-S. L’inversion du graben est surtout

sensible dans sa partie nord-ouest, a la jonction avec la chaine des Palmyrides, bassin mesozoi'que majeur en Syrie. qui connait

sa premiere phase d’inversion a cette epoque. Cette inversion se poursuit au Paleogene et se propage dans le graben de

I'Euphrate du nord vers le sud. Les grabens les plus meridionaux s’inversent a LEocene, alors que ceux du nord s’inversent des

le Paleocene. Ce resultat est coherent avec le cadre geodynamique general de la bordurc nord de la plaque arabe a cette epoque.

impliquanl une migration de la deformation depuis la zone de convergence de Bitlis vers Lavant-pays au sud. La periode

oligocene correspond a la reactivation des failles normales N120E dans le secteur nord-ouest de la zone d’etude.

INTRODUCTION AND SCOPE

The Euphrates graben (Eastern Syria) is commonly described as an intracratonic E-W to NW-SE

trending rift developed within the northern Arabic Platform during the Late Cretaceous. This basin is

totally hidden by a “post-rift" sequence reaching more than 3000 m in thickness. It holds significant

petroleum reserves that have been discovered during the past decade. The main proven play is a

Triassic/Early Cretaceous clastic reservoir (Mulussa/Rutbah formations) covered and laterally oil-

sourced by Late Cretaceous limestones.

Despite the great amount of structural and sedimentological studies carried out at the scale of the

field, no comprehensive analysis of the development of this graben system was available up to now. The

produced maps are regional structural maps drawn on top of selected levels. No detailed isopach

mapping has been published, even though it can provide substantial information about the tectono-

sedimentary evolution of this basin. Moreover, the global geotectonic setting is not fully understood.

How to explain for example the occurrence of a rifting phase during a period dominated by plate

convergence in the Late Cretaceous?

The present study intends to elucidate this question or. at least, to propose clues for understanding.

The main data used for this study include 4 seismic reflection profiles (7 regional 2D lines) and

information from up to 100 exploratory and appraisal wells distributed over some 5600 km 2 .

GEOLOGICAL SETTING OF THE EUPHRATES GRABEN

The Euphrates graben is located in the northwestern part of the Arabian plate, at the eastern edge of

the Syrian territory (Fig. 1). This basin extends approximately 160 km from the E-W trending Anah

graben in Iraq to the northeastern edge of the Palmyrides fold belt (Fig. 2) with 90 km in width. This

graben is bounded to the south by the Hamad high and to the north by the Derm high (Fig. 2). which

could lepreseni the northeastern extension of the Palmyra belt into the Sin jar trough region lying to the

north (Sawaf et al„ 1993). The Euphrates graben shows a bi-directional fault paUern resulting"from a

multiphase history of deformation (LlTAK et al., 1998). The northwestern tracts of the basin show

Source: MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

171

predominantly east-west oriented normal faults, whereas its southern portion displays a northwest-

oriented array of normal faults.

Global geodynamic framework

The Arabian plate was separated from the African plate in the early to the middle Miocene along the

Read Sea rift (Fig. 1). The western boundary of the Arabian plate is marked by the left-lateral Levant

fault system, which extends from the Gulf of Aqaba in the south to the Bitlis suture zone in the north.

The Levant transform fault marks the boundary between the Arabian plate to the east and the Levantine

(Eastern Mediterranean) sub-plate to the west. The Bitlis suture is the site of convergence between the

Arabian and Eurasian plates. Continuing movement along the northern boundary is accommodated by

thrusting along this suture as well as extension along the left-lateral east Anatolian fault zone (Turkey

block). To the east of the Arabian plate, the Neogene-Quaternary Zagros fold belt represents the

collision zone of the African/Arabian plate with Iran.

Global structural setting: a review

The Euphrates graben is one of the three major basins active during the Mesozoic in Syria (Fig. 2).

The Palmyrides and Sinjar troughs are organised along an ENE/WSW trend whereas the Euphrates

graben follows a NW/SE trend (Fig. 2). Palmyrides and Euphrates trends are believed to represent

suture or shear zones along which the northern Arabian platform accreted during Late Proterozoic time.

This is suggested by the difference in metamorphic basement depth on both sides of the Palmyrides and

3 /ss

Fig. 1.— Geodynamical setting of the

Arabian plate. I. crystalline base¬

ment; 2, relative movements at

plate boundaries; 3, major tectonic

lineaments. EAF, East Anatolian

Fault.

Fig. /.— Cadre geodynamique de la

plaque arabe. I. socle cristallin :

2, mouvemehts relatifs aux limites

de plaques ; 3, lineaments tecto-

niques majeurs. EAF. faille est-

anatolienne

172

CECILECARON ETAL.

the Euphrates graben system ( Brew et a/., 1997). These suture/sheai /ones could have acted as zones of

weakness that still control the intracontinental deformation in Syria. Between these Mesozoic

intracratonic basins (Palmyrides, Euphrates, and Sinjar) are located several uplifted areas: the Aleppo

plateau to the north, the Hamad uplift to the south, the Khleissia and Mardin highs to the east and

northeast respectively (Fig. 2).

35 “

JORDAN

50km

-^ G *0 S

MARDIN

HIGH

ABOAL AZg

a fmcuk

IRAQ

SINJAR

KHLEISSIA

HIGH

Fig. 2.— Geological setting of the

Euphrates graben (East Syria). 1.

Mesozoic outcrops; 2. grabens/

troughs; 3. volcanic outcrops.

Fig. 2.— Cadre geologique du graben

de I'Euphrate (Syrie orientate).

1. affleurements mesozoiques ; 2 .

grabens/depressions ; 3, affleure¬

ments volcaniques.

The Palmyrides trough has been a centre of deposition from Carboniferous times onwards, with two

major phases ot lilting: from Carboniferous to Triassic times and from Aptian to Late Cretaceous

(LOVELOCK. 1984). The second subsidence episode accompanied the development of the Levant passive

margin to the west, in relation with the opening of the Eastern Mediterranean basin (BESTel al. 1993).

The Palmyrides rift was first inverted and deformed by the Late Cretaceous (Nil OE compression) until

the Upper Eocene (SALEL, 1993; CHAIMOV et al. 1993).

The Sinjar trough, on trend with the Palmyrides depression to the northeast and continuing into the

Mesopotamian basin in Iraq, is contemporaneous with the second phase of rifting in the Palmyrides

(Best et al. 1993; RUITER et al, 1994).

The Sinjar trough and the northern part ol the Euphrates graben (E-W trending basin) are believed to

develop as a northeastern dependence of the Palmyrides trough (BEST et al.. 1993). The southern part of

the Euphrates graben (N140E-trending basin) is conceived to develop later, during the Late Mesozoic

( Best et al. 1993). According to LlTAK et al. (1998), N140E-striking faults of the southern area appear

to accommodate more strike-slip movement than the E-W normal faults of the northern part of the

Euphrates graben. I hese authors conclude that Late Cretaceous extension may have been initially

accommodated by the N140E inherited fault system (Proterozoic shear zone), but later broke through a

new set of more favourably oriented structures (NI00E). This is in line with Lovelock’s interpretation

Source : MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

173

(1984) in which the Euphrates graben is viewed as a transtensional fault system which, after an eastward

step at the Anah graben, continued along the southeast-striking “Abu Jir" N140E trend in Iraq (Fig. 2).

Alternately, LlTAK et al. (1998) suggested that the bi-directional fault pattern of the Euphrates graben

might reflect a change in the pre-existing structures when approximating the Palmyrides N50E structural

trend. Hence, the structural pattern of the northwestern area, with predominantly N100E faults, would

result from the overprint of east-west oriented structures associated with Cainozoic compression, over a

set of mostly northwest-trending Mesozoic normal faults.

The Euphrates graben as a whole is conceived as an aborted intracontinental rift system. A Coniacian

age is proposed for the beginning of block faulting and the development of a regional unconformity

(LlTAK et al ., 1998). Rifting activity is shown to culminate during the Campanian-Maastrichtian.

LlTAK et al. (1998) also noted that the Euphrates graben displays several features, which are unusual

within classical rift structures:

— its aspect ratio length/width (160 x 90 km) is approximately one-half that of typical rifts;

— the estimated maximum total extension (about 6 km; (3= 1.06) is lower than that reported in the

literature for most other continental rifts. Stretching factor P ranges from 1.1 to 1.3 in the Rhine graben.

from 1.55 to 1.9 in the North Sea central graben. from 1.1 to 2.0 in the Gulf of Suez (see LlTAK et al.,

1998 for references);

— the Euphrates graben does not exhibit sharp edges characterised by major listric bounding faults.

Instead, numerous high-angle, planar normal faults are distributed over a broad zone to accommodate

minimal extension.

LlTAK et al. (1998) considered that this peculiar configuration is a common feature of rift basins in

their initial formation stages. Therefore, ihe Euphrates rift is suggested to have aborted early in its

history. RUITER et al. (1994) proposed that the Euphrates graben developed as a result of the subduction

of the Arabian plate beneath the Eurasian plate. BEST et al. (1993) suggested to connect this rifting

phase to the obduction events operating around the periphery of the Arabian plate during the Late

Cretaceous.

STRATIGRAPHICAL SETTING OF THE EUPHRATES GRABEN

The generalised stratigraphical succession within the Euphrates graben is shown in the figure 3. The

lithostratigraphic nomenclature adopted in this study is the one used since 1980 by the Pecten/Shell oil

company in Syria, which introduces Iraqi formation names. The Palaeozoic to recent sedimentary

sequence over the Euphrates graben is composed of a number of discrete depositional cycles separated

by periods of erosion and/or non-deposition. Only during the Late Cretaceous and Tertiary has

deposition been relatively continuous.

In the Euphrates graben, the maximum depth to the top of the “pre-rift" sequence is about 5 km

(LlTAK et al., 1998). The sequences deposited prior to the “rifting" event and reached by exploration

drilling range from Early Silurian to Lower Cretaceous in age and correspond to various depositional

environments.

The oldest deposits drilled in the Euphrates graben (Fig. 3) are composed of black micaceous shales

with minor silstones and thin beds of fine-grained sandstones of the so-called Abba formation. These

organic-rich graptolite shales, of Silurian age, record deep marine conditions. No Devonian deposits are

known in the Euphrates graben. More generally, the Devonian stratigraphic record is very sparse in

Syria (BEST et al., 1993). Whether it is absent by non-deposition, by erosion at the base Carboniferous

unconformity or by a combination of both is still unclear. The Carboniferous Doubayat formation,

composed of sandy shales and minor terrigenous carbonates, overlies the Lower Palaeozoic section with

a slight angular unconformity. The Carboniferous sedimentary cycle is a transgressive-regressive

sequence. The transgression starts with the sandy marine shale of the Lower Doubayat and evolves to a

fully marine dolomite interval (intra-Carboniferous Dolomite). The Upper Doubayat section is a

regressive sequence of sandstones and interbedded shales, deposited in a deltaic environment grading

upwards into a continental one.

174

CECILE CARON ETAL.

TECTONIC EVENTS

(Euphrates graben)

(as defined in this study)

Plio-Quaternary

last compression phase

Late Oligocene

extension

Upper Maastrichtian

to Palaeogene

compression associated

with Palmyrides folding;

Euphrates graben inversion

N 15 E

L. Maastrichtian extension

Turonian toCampanian

peak rifting phase

N45E Syn-rift unconformity

Albian to Cenomanian

- _ early extension

(7) Up. Jurassic major uplift

w (Al Hamad Uplift)

MiddleTriassic

extension

Before Permian

compression (?)

responsible for

NNE-SSW structures

(Hail and Joura Ridges)

Devonian compression (?)

responsible for NW-SE

structures.

Fig. 3.— Chronostratigraphic chart of the Euphrates graben.

Fig. 3 .— Charte chronostratigraphique da graben de FEuphrate.

Source: MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

175

The Palaeozoic-Mesozoic boundary is characterised by a Carboniferous/Triassic unconformity, as no

Permian deposits are recorded in the Euphrates graben and more generally in Eastern Syria. This time

boundary also corresponds to a change from clastic to carbonate sedimentation. As a matter of fact, the

Upper Permian-Lower Triassic period is marked by the creation of the Eastern Mediterranean basin to

the west and by the development of the Levantine passive margin (BEST et al., 1993). Within the

Triassic interval, marine to supratidal dolomite and anhydrite (Mulussa B to E members) evolved

upwards into a fluvial channel sand-dominated unit (Mulussa F formation, average thickness: 200 m)

that forms the lowermost part of the reservoir-bearing sequence in the Euphrates oil province (Fig. 3).

Following the deposition of the Triassic sequence (700 m thick in the deepest parts of the Euphrates

depression), a major stratigraphic gap covers the period from Jurassic to Lower Cretaceous (some 1 10

Ma). In most of the studied wells. Lower Cretaceous series (Rutbah elastics) directly overlie the Triassic

sediments. These deltaic to interdeltaic sandstones, up to 250m thick, constitute with the Mulussa F

sandstones, the main reservoir of the Euphrates graben oil province. They are conformably overlain by a

Cenomanian carbonate 10-90 m thick sequence (Judea formation).

The base of the Turonian in the Euphrates graben is marked by the presence of an unconformity

which dates the onset of rifting in that area (Fig. 3). This unconformity is overlain by a thick Upper

Cretaceous section, which reaches more than 2200 m in the deepest parts of the Euphrates rift system.

The Palaeogene sedimentary package, 500-1500 m thick, mainly consists of argillaceous limestones

interbedded with claystones. The final depositional stage is represented by shelf and shallow water

carbonates, lagoonal deposits, continental sands and conglomerates of Neogene and Quaternary age with

cumulative thicknesses increasing northeastward in the Euphrates graben, from 400 m to 1400 m.

DATABASE - METHODOLOGY

The zone under study has been constrained to the “Deir Ez Zor permit" area (Fig. 2), as this permit

covers most of the Euphrates graben.

Well data

Well data are widely used in this study. Among these wells, 46 were drilled either by Elf (EAS/EHS)

or by the operating company DEZPC (Deir-Ez-Zor Petroleum Company). 36 wells were drilled either

by the Pecten Shell/SSPD/AFPC group or by SAMOCO before 1988. On December 15' h , 1988, Elf

Aquitaine Syrie secured exploration rights in the Deir Ez Zor contract area and duly acquired

information on the 36 wells drilled before that date. 6 wells drilled after 1988 by the AFPC/SSPD group

were obtained by well data exchange in 1994 and 1996. Complementary set of wells has been provided

with the kind authorisation of SPC (Syrian Petroleum Company), owner of the data.

Within each studied period of the graben history, the successive horizons are described step by step,

following the chronology of sediment deposition. For each horizon considered, formation tops picked on

electric logs are contoured as isopach maps. In most of the presented maps, the structural framework is

taken at the Late Cretaceous/Early Cretaceous unconformity (Fig. 4). The base of the Late Cretaceous

(Turonian) corresponds to the “syn-rift” unconformity located at the top of the Mesozoic “pre-rift"

series (Fig. 3). This framework is used as a guideline to extrapolate isopach curves wherever well data

coverage is scarce, except for the Palaeogene period, for which the iso-contouring method is applied.

Seismic data

The database used in this study is shown in the figure 4 and consists of 190 km of conventional

seismic, respectively 155 km of dip and 35 km of strike sections. Among the seven 2D seismic lines

interpreted in this work, 3 were shot by Pecten Shell in 1985 and 1986 and 4 by Elf from 1989 to 1992.

Pecten Shell seismic data were duly acquired on December 15 th , 1988, when Elf Aquitaine Syrie held

exploration rights on the Deir Ez Zor permit area. 2D surveys were acquired and processed by various

contractors: GSI, CGG, and GECO-PRAKLA. The main acquisition source was vibroseis, but dynamite

was also employed when crossing the Euphrates River.

176

CHCILH CARON ETAL.

The 2D grid is wide and irregular (Fig. 4), about 6 to 20 km spacing between dip lines (NE-SW).

However, this grid covers most of the graben extension. It was mainly chosen to define NE-SW

transects spanning the width of the Euphrates graben. with cross-line control across the Hamad uplift to

the south and the Derro high to the north.

35^0 - -

DEIR-EZ-ZOR

CONTRACT

AREA

CENTRAL PLATFORM

Fig. 4.— Location of the selected seismic lines and calibration wells on the Upper Cretaceous structural map of the Euphrates

graben.

FlG. 4.— Localisation des lignes sismiques selectionnees et des puits de calibration sur le schema structural du graben de

rEuphrate au Cretace superieur.

Time/depth calibrations were provided by Well A. Well B. Well C. Well D. Well E, Well F within

the northern area. Wells G to L were used as drill-hole controls within the southern area. 2D seismic

lines have been scanned and directly loaded on Schlumberger-Charisma workstation. Picked horizons

were chosen for their interest in delineating the major structures.

Finally. NE-SW geo-seismic sections have been drawn, with special focusing on the successive

stages of the structural evolution of the Euphrates graben. This sketch scenario is obtained by flattening

the cross-sections at representative time levels.

GEOLOGICAL EVOLUTION OF THE EUPHRATES GRABEN: SEDIMENTARY APPROACH

In this section, we attempt to document the structural evolution of the Euphrates graben on the basis

ol the stratigraphic approach, i.e. by integrating successive isopach maps into'' a comprehensive

Source . MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

177

cinematic history. Note that this broad approach will serve as a basis for a more detailed discussion of

the whole tectono-sedimentary evolution, when dealing with seismic data.

The “early rifting" phase: where to place the “first rift pulse"?

The first “rift" pulse is commonly reported at the Late Cretaceous/Early Cretaceous unconformity

(LlTAK et al., 1998) (Fig. 3). However, initiation of the “rift" system as early as in Albian times is

manifested by isopach mapping of the late Albian deposits (Upper Rutbah shales) (Fig. 5). Mapping of

the shaly-silty sequence reveals that the “Upper Rutbah" isopachs exhibit a clear NW-SE trend with a

well-defined central depression where the shales may be up to 100 m thick. These shales are of marine

affinity, as their palynofloral assemblages contain a mass occurrence of dinoflagellates. The decrease in

thickness appears symmetrical on either side of that depression. We interpret this feature as suggestive

of early tectonic faulting at the site of the future Late Cretaceous graben rather than post-depositional

erosion.

The absence of Upper Rutbah shales in the northwestern part of the Deir Ez Zor permit area suggests

the emergence of a positive structure (Fig. 5). This structure, hereafter named “Joura Ridge" will play an

important role in the subsequent depositional history of the Euphrates basin. This NE-SW tectonic high

will divide the northern part of this basin into two zones showing distinct tectono-sedimentary

evolutions: an eastern zone controlled by N120E faults (graben opening) and a western zone mainly

influenced by the sedimentary dynamics of the westerly Bishri trough. The latter corresponds to the

northeastern part of the Palmyrides rift formed during the Triassic (Fig. 2) and later inverted to form a

broad (approximately 75 km wide) northeast-plunging anticlinorium that terminates in a domal uplift

39<40 40^0 40°2 0 40«40 41«O0

Fig. 5.— Isopach map of the upper Albian deposits (Upper Rutbah formation) within the Euphrates graben.

Fig. 5 — Carte en isopaques cles depots de I’Albien superieur (formation dit Rutbah superieur) dans le graben de I'Euphrate.

178

CECILE CARON ETAL.

(Jebel Bishri. Me BRIDE et al ., 1990). The Joura Ridge could be the northeastern expression of the A1

Hamad uplift (MOUTY, 1997). The NE-SW trending Al Hamad uplift, recognised from Jordan to NE

Syria, separated from the Late Triassic to the Early Cretaceous two subsiding sedimentary basins in

Syria: the Palmyrides basin to the northwest and the Rutbah basin to the southeast (MOUTY, 1997).

The following period corresponds to the deposition of the Judea carbonates during the Cenomanian

transgression (MAY, 1991) that Hooded the Joura Ridge (Fig. 6). In the northwestern part of the

Euphrates graben. the thickness of the Judea formation increases towards the west. This depositional

pattern illustrates the proximity of the Bishri subsiding trough to the west. The Judea carbonates are

notably thicker over the southeastern area, i.e. over the zone of incipient “rifting'’, and contain marine

palynoflora.

At that time, the early “rifting” phase (NE-SW extension) is yet accompanied by basaltic activity.

K-Ar ages as old as late Albian-early Cenomanian (95 Ma) have been obtained on the volcanics

associated with the “syn-rift” unconformity (in-house ELF data). In the Abd Al Aziz trough, which is on

trend with, and possibly of similar origin as, the Sinjar trough (KENT & HICKMAN, 1997) (Fig. 2), the

first “rift” pulse is also recorded at the base of the Early Cretaceous sequence (KENT & HICKMAN,

1997).

SHALLOW MARINE

(POLLENOSPORES)

> 100 m

50-100m

35-50m

15-35m

m JUDEA REDUCED

OR ABSENT

0_ 10_2 0 K m

"MARGINAL" MARINE

(DINOFLAGELLATES)

BASINWARD

Fig. 6.— Facies and isopach map of the Cenomanian deposits (Judea formation) within the Euphrates graben.

FlG. 6.— Carte montrant la repartition des facies et les variations d'epaisseur des depots du Cenomanien (formation Judea)

dans le graben de VEuphrate.

Source. MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES CiRABEN

179

The “syn-rift** phase: Turonian to early Maastrjchtian period

The Turonian to Coniac/an period: deposition of the Derro-Kometan formation

The Derro and Kometan formations correspond to distinct depositional environments but are

considered as time-equivalent units of Turonian to Coniacian age (in-house ELF reports).

The Derro formation consists in thick layers of volcanic ashes interbedded with and crosscut by

abundant laminae and veins of crystalline dolomite. This unit is also made of volcanoclastic sediments

corresponding to a mixing of tuffaceous siltstones and tuffaceous sandstones. The Derro is described as

continental “red beds’* interlayered with shales, tuffaceous silts and lavas, highly variable sands and

locally evaporitic deposits (interlayered shale and anhydrite). The Kometan marine formation is

composed of dolomites and argillaceous limestones.

The facies and isopach maps shown on the figures 7 and 8 reveal that, by the Turonian, the Joura

Ridge was reactivated and acquired a NNE-SSW shape. This high divides the northern part of the

Euphrates graben into two zones showing contrasting tectono-sedimentary evolutions. The western zone

is characterised by the deposition of the dolomites and argillaceous limestones of the Kometan

formation, which are thickest towards the West (from 25 m to 160 m) (Fig. 8). This depositional pattern

is similar to that of the preceding period (Cenomanian Judea carbonates. Fig. 6) and illustrates the

Fig. 7.— Facies map of the Turonian deposits (Derro-Kometan formations) within the Euphrates graben.

FlG. 7.— Carte de repartition des facies du Turonien (formations Derro-Kometan) dans le graben de VEuphrate.

180

CECILE CARON ETAL.

proximity of the Bishri subsiding trough to the west. East of the Joura Ridge. Turonian deposits consist

of the so-called Derro volcanoclastic series. In the northeastern and central areas, sandstones interbeds

are recorded within the Derro formation. They show a limited spatial extent to the South and a

coarsening trend to the north-northwest (Fig. 7). Very coarse to conglomeratic sands are recorded over

the Atalla Terrace. These sands are probably derived from a north-northwestern source, located at the

present site of the northern platform of the Euphrates graben. Anhydrite occurrences in the Derro

formation are also described in the northernmost reference wells. As a whole, these features point to

regressive conditions, which are also found in the southern part of the study area, with the occurrence of

numerous salt layers in the Derro deposits (Fig. 7). Weathered basalts are exclusively encountered in the

northeastern area, all along a NNE-SSW trend mostly parallel to the Joura Ridge at that time.

Elsewhere, the Derro formation consists of tuffaceous claystones and volcanic tuffs.

On a regional scale, the thickest Derro deposits (>200 m) are distributed along elongated depressions

associated with normal faulting (Fig. 8). These grabens develop along a N 160E to submeridian direction

over the southern area (Jido. Shwema, El Ward grabens) and along a NI40E to N120E direction over

the central and western parts of the study area (A1 Furat-Khabour and Thayyem-El Liel grabens). Derro

deposits are absent on top of tilted blocks and hoists (Maezalieh block, El Ward block, Tanak-Jido high,

El Hamra block, Joura high: Fig. 8). Deposition of the Derro formation is synchronous with a major

structuration phase responsible for the formation of horsts and grabens in a global NE-SW extensional

regime.

Fig. 8.— Isopach map of the Turonian deposits (Derro-Kometan formations) within the Euphrates graben.

Fig. 8.— Carte en isopaques des depots du Turonien (formations Derro-Kometan) dans le graben de VEuphrate.

Source. MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

181

The Santonian to Campanian period: deposition of the R 'mah formation

The R'mah formation, of Santonian to Campanian age, is composed of a lower dolomitic unit often

containing a basal sandy layer and an upper unit made of cherty limestones. In the northwestern part of

the Euphrates graben, the R'mah unit may contain well-developed sandy levels (up to 160 m thick).

These sands are coarse-grained, clean and massive with less permeable bioturbated intervals enriched in

organic matter and clay minerals. They constitute an oil-bearing unit located above the classical Early

Cretaceous reservoir.

Isopach mapping of the R'mah deposits is expected to provide substantial informations concerning

the “rifting” stage itself, as these deposits directly overlie the Derro-Kometan units. From NW to SE,

three zones may be distinguished (Fig. 9):

— a western zone where the R'mah carbonates are more than 100 m thick and where they thicken

gradually towards the NW (>450 m in westernmost wells). In that zone, the sedimentation is clearly

controlled by NE-SW structures, mimetic of the Joura Ridge orientation at that time;

39*40

40*00

-35*20

-35*00

41*00

Fig. 9.— Facies and isopach map of the Santonian deposits (Rmah formation) within the Euphrates graben.

FIG. 9 .— Carte en facies et isopaques des depots du Santonien (formation Rmah) dans le graben de FEuphrate.

Source

182

CECILS CARON ETAL.

— an intermediate zone where the R'mah carbonates do not exceed 40 m in thickness. This zone

defines a NE-SW belt of some 20 kilometres in width. It corresponds to the so-called "Joura Ridge”;

— an eastern and southern area, where the deposition of the R'mah carbonates is apparently

controlled by NW-SE structures linked to the "rifting" phase (A1 Furat-Khabour, Jido, Shwema and El

Ward grabens).

Sands are deposited at the footwall of the Joura Ridge and are progressively dispersed towards the

Bishri mobile zone to the west. They probably come from the erosion of temporarily emergent areas

over the Joura High.

The Campanian to early Maastrichtian period: deposition of the Erek formation

The Campanian to early Maastrichtian Erek formation directly overlies the R'mah cherty limestones.

This unit is composed of dark brown/blackish argillaceous limestones with interbeds of sparitic

recrystallised white limestones.

The Campanian to early Maastrichtian period is the time of substantial changes in the sedimentary

dynamics of the Euphrates graben. The comparison between isopach maps of Erek (Fig. 10) and R'mah

(Fig. 9) formations shows a completely distinct distribution in carbonate deposits.

Fig. 10.— Isopach map of the Campanian deposits (Erek formation) within the Euphrates graben.

FlG. 10 .— Carte en isopaques des depots du Campanien (jformation Erek) dans le graben de PEuphrate.

Source: MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

183

Rather isopach limestones fill in the northwestern area, which behaved since the Albian as a

dependence of the Bishri trough and was characterised by high sedimentation rates. In other words, the

NE-SW (structural?) control on R'mah deposits no longer existed during the deposition of the Erek

limestones.

Actually, the Joura high is entirely transgressed by Erek carbonates. In its northern part, this ridge is

incised by a NW-SE deep trough (A1 Furat-Khabour graben). Along this narrow trough, Erek deposits

are composed of argillaceous, partly silicified limestones containing abundant planktonic

microforaminifera. This N140E depression may be interpreted as a northern esxtension of the A1 Furat

Khabour graben initiated in Turonian times (Fig. 8).

In the northeastern area, a complex terrace (Atalla terrace) forms between the deep mobile A1 Furat-

Khabour graben and the stable northern platform. No Erek deposits are found in that area (Fig. 10). In

the southern area, the Tanak-Jido, El Hamra and El Ward blocks are completely transgressed at that lime

(Erek deposits <100 m). The Campanian period corresponds to the maximum extension of the Euphrates

graben system and may be viewed as the peak “rifting" phase in that area during the Late Cretaceous.

The earlyMaastrichtian period: deposition oe the Lower Shiranish formation

The Lower Shiranish formation, of early Maastrichtian age, consists in brown argillaceous

limestones (mudstones, wackestones) overlain by withish limestones (Tayarat formation).

Isopach mapping of the Lower Shiranish deposits (Fig. 11) shows a considerable widening of

regional subsidence throughout the Euphrates graben. The global broadening of depocenters and gradual

Fig. 11.— Isopach map of the lower Maastrichtian deposits (Lower Shiranish formation) within the Euphrates graben.

Fig. II .— Carte en isopaques des depots du Maestrichtien inferieur (formation Shiranish inferieur) dans le graben de

l 'Euphrate.

184

CECILE CARON ETAL.

blanketing of the Atalla Terrace, which corresponded to a low-relief area in the preceding Erek period,

suggest this interpretation. As such, the northwestern area (west of the Joura high) and the domains

located between the Chibli and Shwema grabens are strongly deepening and filled with a 400 to 700 m

thick Lower Shiranish section. To the northeast, a depression is highly active along N120E to N140E

master faults (A1 Furat-Khabour graben), with a Lower Shiranish section more than 1000 m thick.

However, its extension to the NW is rather limited, at least when compared to the Erek configuration

(Fig. 10).

Moreover, the Lower Shiranish isopach map shows a considerable reduction of fault-induced

subsidence along N140E-N160E faults of the southern area (El Ward. Jido, Schwema grabens). These

faults are much less active than the N100-120E faults of the northern area. This suggests a change in

stress orientation, from N45E to N15E.

THE “POST-RIFT" PHASE

The late Maastrichtian period: deposition of the Upper Shiranish formation

The Upper Shiranish formation, of Maastrichtian age, is composed of argillaceous limestones

(mudstones-wackestones) grading to marl, with local interbeds of white limestone (packestone)

containing calcite and glauconite.

35*20-

35*00

34*40-

SOUTIflERN

PLATFORM

39*40

40p00 40j°20

NORTHERN

' PLATFORM I

40*40

41f00

Axis of a possible

ancient high|

500-700m

400-500m

300-400m

200-300m

< 200m

UPPER SHIRANISH

ONLAP OVER THE

JOURA HIGH

2 0 K m

NOTE: STRUCTURAL FRAMEWORK

AT THE BASE OF UPPER CRETACEOUS

HIGH

Fig. 12 — Isopach map of the upper Maastrichtian deposits (Upper Shiranish formation) within the Euphrates graben.

Etc. 12.— Carte en isopaques des depots du Maestrichtien superieur (formation Shiranish superieur) dans le graben de

/ 'Euphrate.

Source MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

185

The Upper Shiranish marks the end of fault-induced subsidence throughout the Euphrates graben.

This configuration is visible in the northeastern area, where the Alalia terrace is overstepped by Upper

Shiranish limestones. At that time, the thickest deposits (>500m) developed within a very localised

basin, centered along the axis of the former graben system (N120E-trending A1 Furat-Khabour graben)

(Fig. 12). Noticeable is the limited extent of this basin to the southeast. From Campanian to late

Maastrichtian times, this basin appeared to terminate against a N45E to N20E zone, which corresponds

to a structural high on the Albian and Cenomanian maps (Figs 5 and 6). Moreover, this trend is globally

parallel to the Joura Ridge and appears to guide the extension of Derro volcanics (Fig. 7).

The Late Maastrichtian period corresponds as well to the renewed uplift of the El Ward, Tanak-Jido

and El Hamra blocks and onlap pattern of the Upper Shiranish against these blocks. A residual block of

the Joura high (its southern edge) was also reactivated at that time. The movements associated with the

first phase of the Palmyridian orogeny (first inversion stage of the Mesozoic Bishri basin, SALEL, 1993)

may account for this change in sedimentary dynamics over the Euphrates graben. This hypothesis will

be further tested with the seismic data.

The Palaeocene period: deposition oe the Aaliji formation

The Aaliji formation, of Palaeocene age, consists in grey to grey-brown argillaceous limestones

(mudstones/wackestones) often grading to calcareous claystones and shales.

34*0

500 - 600m

400 - 500m

300 - 400m

200 - 300m

100 - 200m

< 100m

SOUTHERN

PLATFORM

2 0 K m

40-00

40-20

41-00

Fig. 13.— Isopach map of the Palaeocene deposits (Aaliji formation) within the Euphrates graben.

Fig. 13.— Cane en isopaques des depots da Paleocene (formation Aaliji) dans le graben de TEuphrate.

186

CECILE CARON ETAL.

The depocenters, which were active during the Late Cretaceous (Thayyem-El Liel, El Ward, Shwema

grabens), were continuously active by the Palaeocene (Fig. 13). Localised horsts and long-lived interior

highs (Maezalieh. Jido-Tanak, El Hamra blocks), which were so far partly submergent blocks, are

buried by the Palaeocene below an isopach series (300-400 m). Regular infilling of subbasins and

smoothing of the former dissected “rift” bathymetry characterise the Aaliji stage.

In the northwestern area, a clear NE-SW zonation is evidenced, with a global trend opposite to that

of the Late Cretaceous period (Fig. 9). Actually, Palaeocene deposits display a gradual decrease in

thickness with proximity to the Bishri trough. Anomalous high thicknesses are recorded at the footwall

of tilted blocks and over updip zones (northern part of the residual As Sirra Joura block in Fig. 13).

Moreover, the axis of the A1 Furat-Khabour graben, which was so far the main depocenter, corresponds

to a relative sediment-starved basin in Aaliji times.

In order to explain this peculiar configuration, we suggest that the basin inversion occured during

Aaliji time. The Aaliji section is thicker over previous positive structures and thinner over older

depositional sinks (Fig. 13). We propose the following scheme: reverse displacement took place on the

same fault as the initial normal movement. In that frame, normal faults bounding horsts and tilted blocks

were reactivated as reverse faults and induced a relative thickening of the Aaliji section over the

downthrown panel of the inverted fault. Conversely, downdip areas were capped by relatively thinner

40^40

3540

34*40 -

41 “00

SOUTHERN

PLATFORM

39«40

40r00 40“20

1 I

NORTHERN

PLATFORM

Hi 600 - 700m

500 - 600m

1 400-500m

I 300 -400m

Fig. 14.— Isopach map of the Eocene deposits (Jaddala formation) within the Euphrates graben.

F/g. 14Carte en isopaques des depots de l'Eocene (formation Jaddala) dans le graben de VEuphrate.

Source: MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES CiRABEN

187

deposits, over the upthrown panel of the inverted faults. As a whole, an anticline-shaped structure was

created. This pattern is illustrated by the idealised cross-section in the figure 16. This configuration will

be exemplified in the foregoing seismic section.

In Palaeocene times, the northern part of the Euphrates graben as a whole was probably subject to

tectonic inversion. This structural inversion could have begun as soon as in Upper Shiranish times and

could be related to the first phase of deformation in the Pal my rides area (SALEL, 1993). The normal

faults bordering the A1 Furat-Khabour depression were presumably reactivated as reverse faults at that

time. This would explain the unexpected low thickness values recorded along this structure (Fig. 13).

Aside from the NE-SW zonation of Aaliji isopachs in the northwestern part of the study area, the

high rates of subsidence persisting along N140E normal faults in the southern part of the Euphrates

graben further suggest that compression was NW-SE orientated in Palaeocene time.

The Eocene period: deposition of the Jaddala formation

The Jaddala formation, of Eocene age, is composed of whitish to medium-grey argillaceous

limestones (mudstones, packestones) grading to packestones. A basal term is identified consisting of

marls to very argillaceous limestones. Abundant light brown to brown cherts are encountered in the

middle portion of the interval.

Comparison of Aaliji and Jaddala isopach maps (Figs 13 - 14) reflects the completely different

distributions of relative depositional highs and lows between the two periods. In the southern part of the

Fig. 15.— Interpretative structural map of the Eocene period within the Euphrates graben.

Fig . 15 .— Schema structural interpretatif a I'Eocene dans le graben de FEuphrate .

188

CECILE CARON ETAL.

study area, the El Ward graben was less active than in Palaeocene times. The NE-SW zonation that

characterised the northwestern part of the Euphrates graben in Palaeocene times is no more apparent on

the Eocene isopach map. This configuration suggests the local transgression of the Palaeocene folds and

a global change in stress orientation. Furthermore, from south to north, one can notice that:

— in Aaliji times, the Thayyem-El Liel graben received the thickest deposits (>500 m). In Jaddala

times, the sedimentation was reduced along this depression (<400 m) and could be compared to the

sedimentation growth over the Atalla Terrace;

— in Aaliji times, the A1 Furat-Khabour graben acted as a sediment-starved basin with a

sedimentation rate fairly comparable to that taking place over the Atalla terrace. In Jaddala times, this

graben showed average sedimentation rates with the development of a 500-600 m section;

— in Aaliji times, the As Sirra-Joura block was characterised by moderate sedimentation rates, fairly

comparable to those observed at a regional scale over the entire Euphrates graben system. In Eocene

times, this block was overfilled by Jaddala deposits, which are. there, the thickest recorded throughout

the Euphrates graben (> 660 m).

The figure 16 is an idealised N-S cross-section showing the contrasting evolutions between Aaliji

and Jaddala times.

In Aaliji times, the north-dipping Central Fault Zone (CFZ) that bounded the As Sirra-Joura block to

the north was reactivated by tectonic inversion and delineates to the north an upthrown, sediment-

starved panel, which was, up to that time, the site of maximum subsidence (A1 Furat-Khabour

graben)(Fig. 16). In the meantime, normal fault-induced subsidence was proceeding within the

Thayyem-El Liel graben. not yet affected by structural inversion.

In Jaddala times, ongoing reverse motion along the Central Fault Zone caused the southern

compartment (As Sirra-Joura block) to downwarp and the Jaddala unit to thicken at that site. The As

Sirra-Joura block is bounded to the south by a south-dipping master fault, which corresponds to the

northern bounding fault of the Thayyem-El Liel graben (Fig. 16). In Jaddala times, this fault

experienced reverse motion, resulting in the deposition of a sequence thinner within the southern

upthrown panel (Thayyem-El Liel graben) than in the northern compartment (As Sirra-Joura block).

On the structural interpretative map of the Eocene period (Fig. 15), relative mobile and stable areas

are shown, as well as the local thickening of Eocene deposits at the footwall of tilted blocks. The global

inversion of the As Sirra-Joura block and the Thayyem-El Liel graben suggests that these E-W

structures were favourably oriented with respect to Eocene compression. Stopping of subsidence along

the El Ward graben and interruption of N45E inversion over the northwestern area (Fig. 15) further

suggest a change in stress orientation from NW-SE (Palaeocene) to N-S (Eocene) compression.

One important result relies in the delay observed between the timing, of inversion over the

northwestern area. The response of the Euphrates graben to compression was diachronous there, with a

propagation of structural inversion from north to south. This pattern is consistent with the global

tectonic setting ol the Northern Arabian plate at that time, implying southward migration of deformation

from the site of subduction (suture zone recognised along the frontier between Syria and Turkey) to the

foreland domains (Salel, 1993).

The Oligocene period: deposition of the Chilou formation

The Chilou formation, of Oligocene age. is composed of cream to light grey argillaceous limestones

(mudstones/wackestones), with traces of very fine to fine bioclasts, interbedded with claystones.

I he distribution of Oligocene deposits over the Euphrates graben is quite similar to that of the

Eocene period, with the persistence of the same depositional highs and lows. However, a global N140E

depression newly appeared over the northern area, involving the northern part of the previous Al-Furat

Khabour graben (Fig. 17). We suggest that the Oligocene was the time of chance in stress regime, from

NW-SE to N-S compression in Palaeocene - Eocene to NE-SW extension in Oligocene. This extension

is limited to the northwestern part of the study area and possibly implies the reactivation of pre-existin«

N120E faults.

Source: MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

189

NORTH SOUTH

VERTICAL SCALE EXAGGERATED

NO HORIZONTAL SCALE

^ 1 2 3 jl5 6

Fig. 16.— Schematic cross-section showing the tectonic control on Palaeocene and Eocene deposition in the northwestern part

of the Euphrates graben. Location of this section is given in Fig. 14. 1, “pre-rift" section; 2. “syn-rift” to “late-rift"

sequence; 3, Palaeocene (Aaliji deposits); 4. Eocene (Jaddala deposits); 5, tectonic control on Palaeocene deposition; 6,

tectonic control on Palaeocene and Eocene deposition by reverse motion of pre-existing normal faults. CFZ: Central

Fault Zone.

FiG. 16. — Coupe schematique Ulustrant le coni role tectonique de la sedimentation ail Paleocene et a 1'Eocene dans la partie

nord-ouest da graben de FEuphrate. La localisation de cette coupe est donnee sur la Fig. 14.1 . sequence “ pre-rift ” ; 2.

sequence “syn a post-rift " ; 3. Paleocene (depots Aaliji ) ; 4. Eocene (depots Jaddala) ; 5. contrdle tectonique de la

sedimentation au Paleocene (Aaliji) ; 6, contrdle tectonique de la sedimentation an Paleocene et a I'Eocene par

inversion des failles normales preexistantes. CFZ: zone de la Faille Centrale.

GEOLOGICAL EVOLUTION OF THE EUPHRATES GRABEN: THE SEISMIC APPROACH

The aims of this section are to precise and eventually criticise the structural scenario proposed in the

previous section by integrating the interpretation of 2D seismic data. The objective is threefold:

— to check the validity of the morphostructural schema issued from isopach mapping (location of

the main rotated fault blocks and stable domains);

— to precise the structural relationships between ihe Mesozoic active blocks and the Tertiary

tectonically inverted areas;

— to obtain by horizontal flattening an image of the Euphrates graben at different key-phases of its

evolution and over selected areas.

The choice of the seismic lines has been guided by their location with respect to the calibration wells.

Location map of these lines is exhibited on the figure 4.

Whenever possible, up to 16 horizons have been followed. Silurian, Intra-Carboniferous,

Carboniferous, Norian (Mulussa E formation), Albian (Rutbah formation) and Cenomanian (Judea

formation) tops provide interpretation of the pre-Late Cretaceous structures. Picking of the Turonian

(Derro), Santonian (R’mah), Campanian (Erek), early and late Maastrichtian (Intra-Shiranish and

Shiranish) tops is expected to reflect the evolution of the “syn-rift” sequence. Palaeocene (Aaliji),

Eocene (Jaddala), Oligocene (Chilou) and early Miocene (Euphrates. Jeribe) tops enable to interpret the

evolution of the “post-rift” sequence.

190

CECILE CARON ETAL.

40“20

°00

SOUTHERN

PLATFORM

35*20 -

35*00 -

300- 400m

200- 300m

100 - 200 m

34 <*40— —

Fig. 17.— Isopach map of the Oligocene deposits (Chilou formation) within the Euphrates graben.

Fig. 17 .— Carte en isopaques des depots de l'Oligocene (formalion Chilou) dans le graben de FEuphrale.

Description of the structural styles

Structural styles in the northwestern area

Seismic line 1 (Fig. 18) is a strike line, about 35 km long, which covers most of the northwestern part

of the study area (see location on Fig. 4). This line transects the Joura-As Sirra block and part of the

southern border of the A1 Kharrata graben. Calibration of line 1 has been possible after production of

synthetic seismograms and time-converted logs for three wells, which are from west to east: Well A,

Well B and Well C (purple vertical lines on Fig. 18).

Seismic line 1 shows that the As Sirra-Joura block is dissected into a series of tilted blocks bounded

by northwest dipping master faults. Southeast-dipping antithetic faults develop within individual blocks.

Block tilting and normal faulting operate within the pre-Maastrichtian section and reach down to the

Palaeozoic units. Fault network is very dense with generally planar and steep contact surfaces. Top of

Silurian shales (in brown on Fig. 18) is shifted down on the eastern side of the section. Prominent faults

extend within the Cainozoic section, up to the Miocene. Large-scale folding of the post-Miocene series

traduces the last and major structuration phase in that area (Fig. 3), contemporaneous with the Plio-

Quaternary orogeny that produced the present Taurus and Zagros ranges (LOVELOCK, 1984).

Source: MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

191

WNW

Al Kharrata graben

Joura - As Sirra block

ESE

Nonan

Lower Miocene

Up. Maaslnchtian

Altlan

Silurian

mmom

%mm

MMS

■ill

H i, Well Cjlllll

II ..

i|![||||i|

‘>'‘\ y .■•••

FlG. 18.— Seismic interpretation of line I. Vertical scale is two-way travel time in ms. Datum plane is 300 m amsl.

FlG. 18 .— Interpretation du profit I. L'echelle verticale est en ms temps double. Le plan de reference sismique est de 300 m

niveau mer.

Structural styles in the northeastern area

The northeastern part of the Deir Ez Zor contract area covers a complex terrace area (Atalla Terrace)

located between the deep mobile Euphrates graben to the south (Al Furat-Khabour graben) and the

stable northern platform to the north. The figure 19 shows a geo-seismic cross-section elongating from

southwest to northeast over the area covered by the 2D data. Three 2D seismic lines have been

composed to obtain this cross-section over the northeastern area (lines 2, 3 and 4). Well D. Well E and

Well F were used for seismic calibration of the seismic lines 2, 3 and 4 respectively.

The outstanding structural style is a complex system of tilted blocks, horsts and grabens (Figs 20

and 21). However, in opposition to the northwestern area, faults rarely extend up to the Palaeocene

section.

From north to south, several relevant structural features may be discussed:

— within the northern platform (line 2, Fig. 20), the top Palaeozoic marker is found at around

1750 ms twt and is quite easy to follow over this area. This zone is characterised by the lack of

Cenomanian to early Maastrichtian deposits. The late Maastrichtian formation is directly overlapping

the Albian sandstones;

— immediately south of the northern platform lies a master normal fault, which offsets the top

Palaeozoic marker at 2400 ms twt. This master fault flattens with depth, causing collapse of the hanging

wall and formation of inclined antithetic panels. Synthetic dip development adjacent to the fault plane

(A on Fig. 20) and tilting of pre-Turonian units indicate that this fault was active from the Turonian to

192

CECILE CARON ETAL.

the early stages of upper Mastrichtian, with a break of activity during the Santonian (B on Fig. 20). This

fault activated a northeastern upthrown panel (northern platform) over which the Albian section is partly

eroded. The platform was therefore a structural high continuously emergent during most of the “syn-

rift" phase of the graben evolution;

— to the south (Fig. 20), the structural pattern consists in the so-called Atalla Terrace, characterised

by a series of narrow hoists, grabens and half grabens with horizontal dips and a top Carboniferous

marker at 2250 ms;

— line 4 (Fig. 21) illustrates the deepest parts of the A1 Furat-Khabour graben system, where the

Late Cretaceous time isopach reaches 1500 ms twt. whereas this section may be less than 600 ms in

thickness over the upthrown El Liel panel. The steep master normal fault that bounds this panel to the

northeast is inverted in late Maastrichtian-early Palaeocene times.

EL LIEL PANEL AL FURAT GRABEN

ATALLA TERRACE NORTHERN

PLATFORM

FlG. 19. — Coupe geosismique schematique de la partie nord-est du graben de I'Euphrate.

Structural styles in the central area

Seismic line 5 (Fig. 22) is a dip line that transects the central part of the Euphrates graben (Fig. 4).

Calibration was obtained by wells G and H. 12 horizons have been followed up. The “pre-rift" sequence

is dissected into grabens, horsts and tilted blocks. Major normal faults that offset the “pre-rift" markers

up to 350 ms twt are typically NE-vergent and reactivated as reverse faults in late Palaeocene times.

They typically flatten at depth and control planar roll over processes (SHAW et at., 1997) within

associated antithetic panels.

Source. MNHN , Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

193

Fig. 20.— Seismic interpretation of line 2. Vertical scale is two-way travel time in ms. Datum plane is 300 m amsl. A: fault-

controlled deposition of Turonian deposits. B: Onlap pattern of the Santonian section against the underlying Turonian

strata.

FlG. 20.—Interpretation du profit 2. L’echelle verticale est en ms temps double. Le plan de reference sismique est de 300 m

niveau mer. A : coni role par faille du depot du Turonien. B : onlap du Santonien stir les unites turoniennes sous-

jacentes.

Structural styles in the southern area

Line 6 (Fig. 23) transects from NE to SW the Dablan-Shwema High and the Shwema- El Ward

South graben. Within the Shwema-Dablan High, the •■pre-rift” sequence is dissected into horsts and half-

grabens delineated by a system of planar steep faults with no or moderate offset. The Shwema-El Ward

South graben is a well-defined graben structure with bounding master faults characterised by offsets no

more than 200 ms twt. The northeastern side of line 6 shows the reactivation of a syn-rift fault resulting

in a newly formed reverse fault implying the whole post-rift sequence, reflecting the Plio-Quaternary

last structuration phase.

Line 7 (Fig. 24) clearly shows antithetic and roll-over features along NE-facing master normal faults,

characterised by a maximum offset of 250 ms twt.

The figure 25 is a geo-seismic section elongating from SW to NE over the area covered by 2 regional

seismic lines (line 6 with Well I as calibration well, line 7 with Well J. Well K and Well L as control

wells).

194

CEC1LE CARON ETAL.

IAI Furat - Khabour graben

ilHlllfllliilHiflfliililllUiL

,3ntoman

Albian

Norian

• • •’

3000

4000 1

4500-

Lower Mtocore

Otigocane

Eocene

Pafeocene

Up. Maastnchtmn

L Maastnchban

Campanian

■

Fig. 21.— Seismic interpretation of line 4.

Vertical scale is two-way travel time in

ms. Datum plane is 300 m amsl. A:

fault-controlled deposition of Turonian

to Campanian deposits. B: on lap

pattern of the early Maastrichtian sec¬

tion against the underlying Campanian

strata.

Fig. 21 .— Interpretation du profit 4.

L'echelle verticale est en ms temps

double. Le plan de reference sismique

est de 300 m niveau mer. A : controle

par faille des depots du Turonien au

Campanien. B : onlap du Maestrich-

tien inferieur sur les unites campa-

niennes sous-jacentes.

Recognition of successive tectonic phases within the pre-Oligocene section

This section attempts to characterise the successive tectonic phases by horizontal flattening of

selected seismic lines at representative time levels. For that purpose, the recognition of onlap patterns,

truncations, fan-shaped deposition, structural erosion on top of lilted blocks, character of fault motion is

fundamental.

Turonian to Santonian interval

The thickness of the Turonian Derro formation is highly changing and largely fault-controlled in the

northern part of the Euphrates graben (Figs 20 and 21). Derro deposits are typically eroded on top of

tilted blocks (see Well J block on Fig. 24, see Santonian onlap on Well D block on Fig. 20). Their

deposition is synchronous with the first structuration phase of the study area into horsts, grabens and

tilted blocks. However, on line 7 (Fig. 24) and more generally over the southeastern area, the Derro

sequence is rather isopach within antithetic zones and conformably overlies the Early Cretaceous (“pre-

rift”) sequence. This pattern suggests that, in the southeastern area, the antithetic phase occured in post-

Iuronian times and even after the Santonian. Actually, tectonic activity seems to slightly resume after

the Derro deposition, as evidenced by the unconformable deposition of the Santonian formation onto the

Turonian strata and the moderate thickness variations of this section alone master normal faults (Figs 20

and 22).

Campanian interval

The northeastern sides of lines 6 and 7 (Figs 23 and 24) show that Campanian deposits are notably

thicker within graben and half-graben structures and reduced on top of tilted blocks. The important

thickness variations observed between the top Santonian and top Campanian markers traduce the onset

Source MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

195

Well H

2000

Santonian

_ Lower Miocene

OUgocene

Turonian

Cenomanian

Paleoceno

Albian

Up. Maestnchtian

Norton

L Maastrichtian

Campanian

Fig. 22.— Seismic interpretation of line 5. Vertical scale is two-way travel time in ms. Datum plane is 300 m amsl. A; NE-

vergent listric fault with associated antithetic panels. B: onlap pattern of the Santonian section against the underlying

Turonian strata. C: Campanian major phase of “rifting".

FiG. 22 .— Interpretation du profit 5. L'echeUe verticale est en ms temps double. Le plan de reference sismique est de 300 m

niveau mer. A : faille listrique a vergence NE el panneaux antithetiques associes. II : onlap du Santonien sur les unites

luroniennes sous-jacentes. C : Phase majeure de “rifting" an Campanien.

of a major “rifting” phase in the southeastern area by the Campanian. Antithetic panels correlatively

developed (line 7, Fig. 24) and are always connected at depth with NE-vergent listric faults.

Early Maastrichtian interval

No thickening of the early Maastrichtian series is observed along the N140E master normal fault

bordering the Well J block to the northeast nor along the NI40E fault bordering the Well L block (Fig.

24). The two major N 140E-trending normal faults of the northeastern side of line 5 (Fig. 22) inverted by

the late Palaeocene also did not guide the early Maastrichtian sedimentation. These N140E-trending

faults probably acted as transfer fault zones at that time. Concomitantly, in the northern area, seismic

data reflect high rates of subsidence along mostly E-W to N120E normal faults (Fig. 4). guiding the

deposition of a thick early Maastrichtian section (Line 4. Fig. 21). Line 4 (Fig. 21) also shows the onlap

pattern of the early Maastrichtian markers over Campanian strata. As the El Liel panel is entirely

transgressed by the Campanian series (no residual relief), this onlap was caused by the reactivation of

the fault system during a new tectonic phase of early Maastrichtian age. This configuration as a whole

suggests a change from NE-SW extension in Campanian times to N15E extension by the early

Maastrichtian. This result is in line with the stratigraphic data previously discussed.

196

CECILE CARON ETAL.

Dablan - Shwema High

Shwema * El Ward South graben

Lower Miocene

Poioccene

Up. Maastnchtian

L. MaasIricWian

Campanian

Turoman

Cenomanian

Alb,an

Nonan

Fig. 23.— Seismic interpretation of line 6. Vertical scale is two-way travel time in ms. Datum plane is 300 m amsI.A: First

phase of graben inversion during the late Maastrichtian.

Fig. 23.— Interpretation du profit 6. L'echelle verticale est en ms temps double. Le plan de reference sismique est de 300 m

niveau mer. A : Premiere phase d‘inversion des grdbens an cours du Maestrichtien superieur.

iMte Maastrichtian interval

Picking of the top Maastrichtian horizon shows a characteristic pattern, with the Upper Shiranish

marker blanketing the “rift"-interior highs and platforms (Fig. 20). This capping of the topography

might represent the late “syn-riff'/early “post-rift" stage. Moreover, the southwestern side of line 6 (Fig.

23) shows that the late Maastrichtian series are gradually thinner over a tectonically inverted N140E

master normal fault. Inversion occured prior to the deposition of the latest Maastrichtian deposits, which

are clearly sealing the inverted fault. This is the older evidence of structural inversion of the pre-existing

grabens and half-graben systems. The late Maastrichtian and following periods may thus be considered

as taking part ol the “post-rift" stage. This inversion stage is not detected over the northwestern area. As

N140E-trending interior highs and the N45E-trending Joura Ridge are reactivated (Fig. 12), we might

inter that the direction of the late Maastrichtian compression is NW-SE.

Post-rift interval

Globally, picking of the “post-rift" sequence in the northwestern area (Figs 18 and 23) shows

numerous evidence ot graben and half-graben inversion, resulting from the compressive movements that

prevailed from Late Mesozoic to Quaternary. Numerous Late Cretaceous normal faults were propagated

up into the “post-rilt" section and reactivated as reverse faults, causing inversion of the previous grabens

and lormation ol broad anticlines (Fig. 18). However, this configuration does not apply to the central

Source: MNHN. Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

197

Well J

Well K

Well L

Fig. 24.— Seismic interpretation of line 7. Vertical scale is two-way travel time in ms. Datum plane is 300 m amsl. A: NE-

vergent listric fault with associated antithetic panels.

Fig. 24 — Interpretation du profit 7. L'echelle verticale est en ms temps double. Le plan de reference sismique est de 300 m

niveau mer. A . faille listrique a mergence NE et panneaux antithetiques associes.

Horizontal Scale

Fig. 25.— Geoseismic cross-section across the southern part of the Euphrates graben.

Fig. 25 .— Coupe geosismique de la partie sud du graben de FEuphrate.

Source: MNFIN, Paris

198

CECILK CARON ETAL.

and southern parts of the Euphrates graben. where the base of the Eocene series (Jaddala formation)

seals most of the faults (Figs 22 and 24).

The figure 26 corresponds to a flattening of the line 1 (Fig. 18) at top of Eocene. This section

illustrates the discussion held in the stratigraphic section of this paper (Fig. 16). The thickening of the

Eocene Jaddala section over the pre-existing Joura block is explained by reverse motion of normal

faults.

The Palaeocene-Eocene transition is imaged on seismic by an unconformity characterised by onlap

termination (Figs 22 and 24). This pattern traduces the local sealing of Palaeocene faults and the global

change in stress orientation between the Palaeocene and Eocene periods, as already discussed in the

stratigraphic section.

The NE-SW extension suspected to occur in Oligocene times (Chilou deposition) is confirmed by

flattening of line 1 (Fig. 18) at top Chilou (Fig. 27). The Cretaceous A1 Kharrata graben inverted in Late

Cretaceous-Palaeocene-Eocene times was reactivated by normal faulting in Oligocene times.

WNW

Joura block

Nonan

Sdunon

Up. Maastnchban

Albiai

1raw

Ms mut/Ai

Fig. 26.— Seismic interpretation of line 1 flattened at top of Eocene.

FlG. 26 .— Interpretation du profit I horizontalise an toit de 1'Eocene.

CONFRONTATION OF STRATIGRAPHIC AND STRUCTURAL DATA: TECTONIC EVOLUTION

First movements announcing the major phase of “rifting” and associated basaltic activity are

recorded at the future site of the Euphrates graben as soon as in Albian times, along the southern

segment of the depression. The NE-SW extension was maintained in Turanian times (Fig. 28), with the

development of N160E to N120E-trending grabens and associated volcanic activity. A period of relative

tectonic quiescence followed the Turanian phase, with the deposition of Santonian limestones in a

global transgressive context.

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

199

The main pulse of “rifting” occured in Campanian times, with NE-SW extension and block tilting. A

deep N120-N140E trough opened, extending to the northern platform of the Euphrates graben.

Northeast vergent listric faults developed at that time in the southern part of the Euphrates graben. This

northeastward tilting was contemporaneous with the obduction of the Tethyan oceanic crust onto the

northeastern margin of the Arabian plate (Oman and Zagros ophiolites; KAZMIN et al., 1986; DERCOURT

el al ., 1993). As the fault network within the Euphrates graben (N140E) roughly parallels the obduction

axis (Zagros trend), the Euphrates graben could represent a flexural basin formed in response to the

loading of the subducting Arabian plate (Fig. 28).

The early Maastrichtian period is characterised by a change in the direction of extension, from NE-

SW (from Turonian to Campanian) to NI5E. Extension occured along N100-N120E faults and

transtension along N160E faults. This structural setting accords with the tectonic evolution described by

KENT & HICKMAN (1997) in the Abd Al Aziz and Sinjar areas. An early stage of Zagros folding at the

eastern margin of the Arabian plate may have stopped the lateral eastward tilting and caused the

direction of extension to rotate. Alternately, the N15E extension recorded during the Early Maastrichtian

Al Kharrata graben

WNW

vWell

Albian

Nonan

Srfunan

Up Maaslnchlian

'imm

i mm

Fig. 27.— Seismic interpretation of line I flattened at top of Oligocene.

FlG. 27 .— Interpretation du profit I horizontalise ait toil de /' Oligocene.

may have been induced by the obduction stage strongly active at that time along the globally E-W Bitlis

axis, with the tectonic emplacement of ophiolites (KAZMIN et al.. 1986; ORSZAC-SPERBER et a /., 1989;

Sage & LETOUZET, 1990; DERCOURT et al.. 1993).

In late Maastrichtian and early Palaeogene times, NW-SE compressive movements caused the

Euphrates “rift” system to abort. Structural inversion occured west to the Joura Ridge, mainly along NE-

SW structural trends. The area of structural inversion covers the hinge zone of two megatectonic trends:

the NW-SE trend of the Euphrates graben and the northeastern part of the Palmyra fault zone (inverted

Bishri trough) with predominantly SW-NE structures. Early Palaeogene was the time of global

Source:

200

CECILE CARON ETAL.

NORTHERN PASSIVE MARGIN OK TIIK ARABIAN PI-ATE

UPPER CRETACEOUS EVOLUTION OF THE

EASTERN PASSIVE MARGIN OK THE ARABIAN PLATE

LATE ALBIAN - CENOMANIAN

I IKS'! MOVEMENTS

g Wl l HI

* ' CRA

v * + + + * *r r * *

N sw

b c —

II.OI K FAULTING

V4T”

TURONIAN TO SANTONIAN

EXTENSION

ISLAND ARC

S BLOCK FAULTING

CAMPANIAN

CLIMAX OF •RIFTING*

ISI^NDARC

COI1ABI

NORTHEASTWARD

TILTING

OEDUCTION STAGE

ZAGROS BASIN J|t»

LOWER MAASTRICHTIAN

COLLArSt

NORTHWARD

TILTING OBDllCTION STAGE

-si

ZAGROS BASIS i,V

EACROS BASIS 0|F

CARBON AIE PLATFORMS

UPPER MAASTRICHTIAN

COMPRESSION

Fig. 28.— Conceptual model for the structural evolution of the Euphrates graben.

Fig. 28 .— Modele schematique d'evolution struct unde du graben de I'Euphrate.

Source: MNHN, Paris

DEVELOPMENT AND TECTONIC OF THE EUPHRATES GRABEN

2(31

compressive tectonics. This compression is clearly associated with the subduction of the Afro-Arabian

plate beneath the Eurasia plate, along the Bitlis suture zone to the north and Zagros suture zone to the

northeast. Structural inversion locally affected the deposilional trends over the northwestern part of the

Euphrates graben and migrates in time from north to south. However, the Euphrates graben appears to

be moderately deformed with respect to adjacent Mesozoic basins (Palmyrides, Sinjar and Abd El Aziz

troughs).

Palaeostress orientation changed from N-S compression to NE-SW extension by the Oligocene,

inducing over the northernmost part of the Euphrates graben the reactivation of Late Cretaceous N120E

faults.

REFERENCES

Best, A.J., Barazangi. M„ Al Saad, D., Sawaf. T. & Gegran, A.. 1993.— Continental margin evolution of the Northern

Arabian Platform in Syria. AAPG Bulletin, 77: 173-193.

Brew. G.E.. Dogan, R.K.. Seber, L., Al Imam, A. & Sawaf, T., 1997.— Basement depth and sedimentary velocity structure

in the Northern Arabian platform. Eastern Syria. Geophysical Journal International, 128: 617-631.

Chaimov, T.A., Barazangi, M., Al Saad, D., Sawaf. T. & Kmaddour, M., 1993.— Seismic fabric and 3D structure of the

Southwestern Intracontinental Palmyride fold belt, Syria. AAPG Bulletin. 77: 2032-2047.

Dercourt, J., Ricou, L.E. & Vrielynck, B., 1993.— Atlas Tethys Paleoenvironrnental Maps . Gauthier-Villars, Paris: 1-307.

14 maps, 1 pi.

Kazmin, Y., Ricou, L.E. & Sbortshikov, I.M., 1986.— Structure and evolution of the passive margin of the Eastern Tethys.

Tec ton op hy sics, 123: 153-179.

Kent, N. & Hickman, R.G., 1997.— Structural development of Jebel Abd Al Aziz. Northeast Syria. GeoArabia, 2: 307-330.

Litak, R.K., Barazangi, M.. Brew, G., Sawaf, Al Imam, A. & Al Youssef. W., 1998.— Structure and Evolution of the

Petroliferous Euphrates Graben System, Southeast Syria. AAPG Bulletin. 82: 1173-1190.

Lovelock, P.E.R., 1984.— A review of the tectonics of the northern Middle East region. Geological Magazine , 121: 577-587.

McBride, J.H., Barazangi. M.. Best. J.. AlSaad, D., Sawaf, T., AlOtri M. & Gebran, A., 1990.— Seismic reflection

structure of the intracratonic Palmyride fold-thrust belt and surrounding Arabian platform in Syria. AAPG Bulletin. 74:

238-259.

May, P.R.. 1991.— The Eastern Mediterranean Mesozoic Basin : evolution and oil habitat. AAPG Bulletin, 75: 1215-1232.

MOUTY. M.. 1997.— Le Jurassique de la chaine des Palmyrides (Syrie centrale). Bulletin de la Societe geologique de France,

168 (2): 181-186.

Orszac-Sperber, F., Rouchy, J.M. & Elion, P.. 1989.— The Sedimentary expression of regional tectonic events during the

Miocene-Pliocene transition in the Southern Cyprus basins. Geological Magazine. 126: 291-299.

Ruiter, R.S.C., Lovelock, P.E.R. & Nabulsi, N., 1994.— The Euphrates graben of Eastern Syria : a new petroleum province

in the Northern Middle East. In: M.I. Al Hussein (ed.). Geo' 94: The Middle East petroleum geosciences. Volume 1:

Maname, Bahrain. Gulf Petrolink: 357-368.

Sage, L. & LETOUZEY, J.. 1990.— Convergence of the African and Eurasian plate in the Eastern Mediterranean. In: J.

LETOUZEY (ed.). Petroleum and Tectonics in Mobile Belts. Technip. Paris: 49-68.

SALEL, J.F., 1993.— Tectonique de chevauchement et inversion dans la chaine des Palmyrides et le graben de I'Euphrate

(Syrie). Consequences sur Tevolution de la plaque arabe. These, Universite de Montpellier. Montpellier, France: 1-288.

Sawaf, T.. Al Saad, D., Gebran, A., Barazangi, M., Best, J.A. & Chaimov, T.A., 1993.— Structure and stratigraphy of

Eastern Syria across the Euphrates depression. Tectonophysics , 220: 267-281.

Shawl J.H.. Hook, C.S. & Sitohang, E.P., 1997.— Extensional fault-bend folding and synrift deposition: an example from the

central Sumatra basin, Indonisa. AAPG Bulletin, 81: 367-379.

Palaeogeography and palaeotectonic of the jointing

area between the Eastern European Basin and the

Tethys Basin during Late Carboniferous (Moscovian)

and Early Permian (Asselian and Artinskian)

Boris 1. CHUVASHOV" & Sylvie CRASQUIN-SOLEAU

<n Institute of Geology and Geochemistry of the Urals Branch of Russian Academy of Sciences

Pochtovy pereulok 7. 620 151, Ekaterinburg, Russia

121 CNRS UPRES-A 7073, Universite Pierre et Marie Curie, Departement de Geologie sedimentaire

T. 15-25, E.4. case 104. F-75252 Paris Cedex 05, France

ABSTRACT

During the Moscovian. the Eastern European sedimentary Basin (EEB) occupied an extensive territory on the Eastern

European continent, from the meridian of Arkhangelsk to the west up to the Urals to the east. On the territory of the present

eastern slope of Urals, the narrow and long Eastern Uralian Gulf (EUG) incorporated to the south the basins of Turansk Plate

and Precaspian Depression. In its southwestern part, the EEB is separated from the Donetsk gulf by the Voronezh Peninsula.

The EEB territory was subdivided in two unequal seas: the Volga-Kama Sea and Preuralian Sea (the last one included the

Eastern Uralian Gulf). In the Volga-Kama Sea. the carbonate shallow-water sediments prevail. In the rather deep-water

Preuralian Sea, lateral facies belts are present from coarse clastic marine and continental facies to the east, passing to mainly

carbonated to the west. The uplift of the Palaeouralian mountain system separated the Preuralian Basin from the Eastern Uralian

Gulf. During the Asselian. the main changes in the palaeogeography of the considered territory marine realms occurred. The

reduction of the EUG took place at the end of the Carboniferous. During the middle Asselian. the sea left the Donetsk Gulf. The

isolation and deepening of Precaspian Basin step up, allowing the connection between the Preuralian Basin and the northern

part of the Tethys Ocean. The important feature of the Asselian palaeogeography is the built up of a strong reef barrier, which

surrounds the Precaspian Basin and in a north-south direction (= along 60°E meridian). It separated the Volga-Kama Sea from

the Preuralian Sea. In the Preuralian Sea territory, lateral sediment belts, similar to the Moscovian ones, occur from coarse

clastic sediments to the east to mainly carbonated sediments to the west. On the immersed edge of the platform, the most thick

reef barrier for the whole Early Permian history was generated. During middle Asselian, the maximum transgression level was

reached, then, from Shikhanskian time, began the regression and the quick reduction of the Volga-Kama Sea. During the

Artinskian, the last existence of a marine basin with normal salinity is recorded. The EEB width was strongly reduced (500 km

against 1500 km during Asselian). On a great part of the Volga-Kama Sea territory, the salinity increased: the dolomites and

anhydrites set down everywhere. During the first half of the Artinskian, the sea left the Turansk plate territory and its southern

adjacent parts. During the late Artinskian, the marine transgression occured in the south, where the Tethyan belt reached the

Precaspian area. This geological history for these three time-slices is presented on three pairs of palaeogeographic maps. The

palaeobiogeographical relationships and palaeoclimatic conditions arc considered.

CHUVASHOV, B.I. & Crasquin-SoleaU, S., 2000. — Palaeogeography and palaeotectonic of the jointing zone between the

Eastern European Basin and the Tethys Basin during Late Carboniferous (Moscovian) and Early Permian (Asselian and

Artinskian). hr. S. Crasquin-Soleau & E. Barrier (eds). Peri-Tethys Memoir 5. new data on Peri-Tethyan sedimentary

basins. Mem. Mus. natn. Hist, nat., 182 : 203-238, Paris ISBN : 2-85653-524-0.

Source : MNHN, Paris

204

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

RESUME

Paleogeographie et paleotectonique d’une zone de jonction entre le Bassin Est Europeen et Ie Bassin de la Tethys an

cours du Carbonifere superieur (Moscovien) et du Permien inferieur (Asselien et Artinskien).

Au cours du Moscovien, Ic Bassin sedimentaire Est Europeen (EEB) occupe un large territoire sur le Continent Est-

Europeen, depuis le meridien d’Arkhangelsk a I'ouest jusque I'Oural a Test. Sur le versant oriental actuel de I’Oural, existe

1’etroii et long Golfe Est Ouralien (EUG), integrant, vers le sud. les bassins de la plaque de Turan et de la Depression

Precaspienne. Dans sa partie sud-ouesl, le Bassin Est Europeen est separe du Golfe du Donetz par la peninsule de Voronezh. Le

Bassin Est-Europeen est subdivise en deux mers de superficies inegales : la Mer de Volga-Kama et la Mer Preouralienne (cette

derniere incluant le Golfe Est-Ouralien). Dans la Mer de Volga-Kama, les sediments carbonates d'eau peu profonde dominent.

Dans la Mer Preouralienne, relativement profonde, se developpcnt des ceintures de facies depuis des sediments grossiers

clastiques marins et des facies continentaux a Pest jusqu'a des depots principalement carbonates a I'ouest. La surrection de

I'Oural separe le Bassin Preouralien du Golfe Est Ouralien. Durant I'Asselien, se produisent les principales modifications

paleogeographiques des domaines marins de cette region. A la fin du Carbonifere. I’EUG s’est notablement reduit. A P Asselien

moyen. la mer se retire du Golfe du Donetz. L'isolement et Papprofondissement du Bassin Precaspien et de la partie nord de la

Tethys se produisent. Le caractere important de la paleogeographie de PAsselien est la construction d'une barriere recifale

majeure sur le pourtour du Bassin Precaspien et en direction nord-sud, le long du meridien 60°E. Cette barriere separe la Mer de

Volga-Kama de la Mer Preouralienne. Dans la Mer Preouralienne, des ceintures de facies, similaires a celles du Moscovien, se

developpent depuis des facies grossiers clastiques a Pest jusqu'a des facies principalement carbonates a I'ouest. Sur la partie

immergi*e de la plate-forme, la plus iniportante barriere recifale de toule Phistoire du Permien inferieur s'edific. Durant

PAsselien moyen. le maximum de transgression est atteint puis, a partir du Shikhanskien. commence la regression avec une

rapide reduction de la Mer de Volga-Kama. Au cours dc P Artinskien, le dernier bassin marin a salinite normale est reconnu. Le

Bassin Est-Europeen est considerablement reduit (500 km de large pour 1500 a PAsselien). Sur la majeure partie du territoire

de la Mer de Volga-Kama, la salinite augmente fortement: des dolomies et des anhydrites se deposent partout. Durant la

premiere moitie de PArtinskien, la mer quitte la plaque dc Turan et ses regions mcridionales adjacentes. A PArtinskien

superieur. la transgression marine se produit au sud, la ou la Tethys rejoint la zone Precaspienne. Cette histoire geologique pour

les trois intervalles de temps est presentee sur trois paires de cartes paleogeographiques. Les relations paleobiogeographiques et

les conditions paleoclimatiques sont abordees.

INTRODUCTION

We discuss here the relations between the Eastern European Basin (EEB) and the seas of the Tethys

Basin for three time slices: Moscovian (Late Carboniferous). Asselian and Artinskian (Early Permian).

The historical study of the Carboniferous-Permian communications between the Urals and Russian

Platform, on one side, and the Tethyan Basin, on the other, was previously published (CHUVASHOV,

1977).

The EEB was divided here in two parts: the Volga-Kama Sea to the west and the Preuralian Sea

alongside the Urals.

The Moscovian was marked by wide biogeographical connections and large transgression of the

ocean on shallow-water carbonate platforms. Some important geological events occured during this

period: the development of the Preuralian Sea: the Uralian Basin, uniform before, was divided by the

uplift of Palaeourals Mountain system in two parts: Preuralian Sea and Eastern Uralian Gulf; the

Precaspian Depression was perfectly delimited at this moment.

During the Asselian, the Early Permian had a maximum variety of biota, due to the maximum of the

transgression. During this period, several important geological events occured: the Donetsk Gulf was

closed, the Preuralian Sea and the Precaspian Basin had their maximum of extension. The strong

influence of Tethyan biota is displayed on the organic communities of southern Preuralian Sea and

could be followed up to 55°N.

During the Artinskian, a significant reduction of the EEB area occurred and its Volga- Kama part

was transformed in an extensive very shallow-water lagoon with poor and uniform fauna. The typical

marine basin with diverse sediments and biotopes was preserved on the borders of the Preuralian Sea

and it's nearest western frame. The communications with the Tethys Basin at this time were reduced to

the minimum.

Source : MNHN, Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

205

FIG. I.— Location, on a present day map, of the main geographical terms used in this paper.

Fig. I .— Localisation, sur line carte geographique acme lie, cles principaux tennes utilises dans cel article.

Source: MNHN , Paris

206

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

The general palaeogeographic map of the Eastern-European Basin is established on the base of

1: 5 000 000 map, the palaeogeographic map of Preuralian Sea on the basis of 1: 2 500 000 map and

map of the jointing zone of Preuralian Sea and Tethyan Basin, scale I: 5 000 000. All the geographic

localities are reported on a present day map (Fig. 1). The legend used for all palaeogeographic maps and

profiles is drawn on the figure 2.

Our approach to restore the palaeogeographic situation is defined by the study of the Preuralian Sea

sediments and biota as well as data on the Volga-Kama Sea. In terms of tectonic, the Volga-Kama Sea

corresponds to the eastern rim of the Russian Platform and the Preuralian Foredeep. All facial zones

(belt of sediments) of this territory are traced from the Polar Urals and Preuralie to the Precaspian

Depression. The most difficult problem is the reconstruction of the Precaspian Depression and Turansk

Plate palaeogeography. where the studied formations are reached at significant depth, and drilled by far

separate boreholes, with very partial selection of cores. All direct and indirect informations are used.

AAA

EEB

° ° Y 1

I°°l

v—\r

v v

i!!

WIT

JjJjIlLl

Fig. 2.— Legend for palaeogeographic maps and profiles. 1. shallow-water limestones (carbonated platform); 2a, organic

buildups for palaeogeographic maps: established (black) and suggested (white); 2b, organic buildups for profiles:

established (black) and suggested (hachures); 3, dolomites: 4. deep water argilites with limestone and marl interlayers;

5, deep water argilites: 6, coal-bearing paralic deposits; 7. sandstones with shallow-water limestones; 8, organic

buildups on the sandy basement; 9. pebble and boulder conglomerates: 10, volcanic rocks: 11, sandy flysh; 12,

sandstones (for profiles); 13. gravelstone (for profiles); 14. evaporates; 15. suggested areas of marine sediments

distribution; 16, land and island with hilly relief: 17. land and island with middle mountain (1-2000 m) relief; 18. high

mountain (above 2000 m) relief; 19, limits of facial zones; 20, area of shore - line shifting during the map time slice; 21,

emerged land with low relief; 22. direction of distribution of denuded material.

FlC. 2.— Ugende pour les cartes paleogeographiques et les pro fils. 1, calcaires d'eau pen profonde (plate-forme carbonatee) ;

2a, contractions organiques sur les cartes paleogeographiques : prouvee (noir) et supposee (blanc) ; 2b, contractions

organiques sur les profits : prouvee (noir) et supposee (hachures) ; 3. dolomies ; 4, argilites d'eau profonde avec

niveaux intercales de calcaires et de marries ; 5. argilites d'eau profonde ; 6. depots paraliques avec charbon ; 7, gres

avec des calcaires d'eau pea profonde ; 8, contractions organiques sur an sous-bassement sableux : 9, conglomerats a

blocs et galets ; 10, roches volcaniques ; 11, flysch sableux ; 12, gres sur les profiles ; 13, roches gravelleuses (sur les

profits); 14. evaporites ; 15, aire de repartition supposee de facies marins ; 16, terres emergees et lies avec an relief de

collines ; 17, terres emergees et lies avec an relief de moyenne montagne (1200 m) ; 18, relief de haute montagne

(superieur a 200 m); 19, limites des zones de facies ; 20, zone de deplacement de la ligne de rivage dans I'intervalle de

temps de la carte ; 21, zones emergees avec faible relief; 22, sens de distribution du materiel detritique.

Source . MNHN , Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

207

The “Atlas of the lithological and palaeogeographic maps of the Russian platform ...”

(Vinogradov. 1961) is used for the reconstruction of Russian Platform, and for the Urals, the “Allas of

Palaeozoic-Mesozoic lithological-palaeogeographic maps of the Cis-Urals” (CHERMNYSK, 1972). The

palaeogeographic reconstruction of the Pamir and Tyan Shan region areas largely lake in account the

work of BENSH (1982) and informations were extracted from numerous publications about stratigraphy

and lithology, as well as being the results of private investigations. Only a small part of the publications

used are mentioned in the reference list. The characteristics of palaeogeographic situation for the three

time slices are given below.

THE MOSCOVIAN

The Moscovian stage is subdivided in two substages (Table 1): lower and upper. For the lower

Moscovian, the Vereiskian and Kashirskian horizons are recognised. The upper Moscovian is

subdivided in Podolskian and Maychkovskian horizons. All horizons have other names in the Urals, but

we use above divisions because they are relatively well known and well correlated with Uralian

horizons. A correlation table between Donetz, Moscow and Urals formations is proposed (Table 2,

modified after IZART et al ., 1998) for Late Carboniferous and Early Permian.

Table 1.— Correlations of the formations and units used in the text.

Tableau L — Correlation des formations et unites appelees dans le texte.

Artinskian

upper

Saraninskian

Timaksk suite

Tabolask suite

Visikovsk suite

Sarginskian

lower

Irginskian

Burtsevskian

Sakmarian

Shikhanskian

S. sphaerica - P. firma zone

Skosyrsk suite

Kramatorsk suite

Asselian

S. moelleri - P fecunda zone

Slavyaksk suite

Kholodnolozhskian

S. fusiformis zone

Kalitvensk suite

Nikotovsk suite

D. bosbytauenis - D. robusta zone

Kartamishsk suite

Kazimovian - Gzelian

upper

Maychkovskian

C2me

Podolskian

C2md

Moscovian

Bukhana suite

C2mc

Kashirskian

C2mb

lower

Ordynsk mb

Vereiskian

Alyutovsk mb

Shazk mb

C 2 ma

Moscovian palaeogeography of the European Eastern Basin

The Moscovian Eastern European Basin covered a large territory of the Eastern Russian Platform.

The width of this basin is almost 1500 km on the Moscow latitude. Northern part of the EEB was

located in recent Arctic Ocean.

The EEB can be divided in different seas and gulfs (Fig. 3), according to their size, depth, and type

of sediments. The large Donetsk Gulf, filled by a thick sequence of coal-bearing paralic deposits,

connected with the EEB in the south. A very large western part of the EEB could be treated like Volga-

Source:

208

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

Table 2.— Correlation table of the formations used in Russia (after Izart et td, 1998).

Tableau 2. —Tableau de correlation des formations utilisees en Russie (d'apres Izart et al., 1998).

Western

European

stages

Eastern European horizons

Eastern

European

stages

Donetsk Basin

Russian Platform

Ural

Irenskian

Philippovskian

Kungurian

Saxonian

Saraninskian

Sarginskian

Irginskian

Burtsevskian

Artinskian

Kramatorsk

Sterlitamakskian

Tastubskian

Sakmarian

k—

Slavjansk

Shikhanskian

Autunian

Nikitovsk

Kartamysh

Sukoljegorskian

Kholodnolozhskian

Asselian

Mironovsk

Noginskian

Mortukskian

Gzhelian

c/>

Stephanian

Kalinovsk

Klyazminskian

Azantashskian

Torezk

Dorogomilovskian

Khamovnichinskian

Krevyakinskian

Kerzhakovskian

Orlovskian

Kasimovian

V—

Westphalian D

Sanjarovsk

Sabovsk

Myachkovskian

Podolskian

Moscovian

Westphalian C

Mariesvk

Kamensk

Kashizskian

Vereiskian

k—

*4—

Westphalian B

Krasnodonsk

Melekeskian

Asatauskian

-Q

Westphalian A

Makeevsk

Zuevsk

Cheremshanskian

Tashastinskian

Bashkirian

“O

Namurian C

Blagodatnensk

Manuilovsk

Prekamskian

Askynbashkian

Akavaskian

Siuranskian

Namurian B

Feninsk

Kzasnopolyanskian

Source: MNHN, Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

209

MOSCOVIAN

Timan Archipel;

lountains

Arkhangelsk Lagoon

WEST SIBERIAN

&Ov LAN °

xxxkx Tobolsk

_,-Timan.

LM^iagoon

H . UkhtXK

rkhangelsk 5 ^ ^

Syktyvkar ^

istern Uralian

$$Gulf

^^Mourfiains'

CENTRAL

EUROPEAN LAND

Preuralian-

Sea^

Chelyabinsk

^ Eastern European Basin

(Volga - Kama Sea)

lountains

o ^

Moscow

Samara

Smolensk

Mugodzhary

^.Peninsula

^Voronezh Peninsula^

Donetsk

Astrakhan

Turanskian

1 1 Sea 1 1 1 1 1 1

50°

25°

35°

45°

Fig. 3.— Palaeogeography of the Eastern European Basin during the Moscovian. See legend on Fig. 2.

Fig. 3 .— Pcdeogeographie da Bassin Esi-Europeen durant le Moscovien. Legende voir Fig. 2.

Source: MNFiN . Paris

210

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

Kama Sea with essentially shallow-water carbonate sediments and rather diverse biota. A very long and

narrow Preuralian Foredeep was occupied by the deep-water of Preuralian Sea. Its southern part was

connected with the large and deep-water Precaspian Sea. The growing mountain chains of the

Palaeourals have separated Preuralian Sea from the Eastern Uralian Gulf (Fig. 3). Both were united to

the south with Precaspian and Turanskian Seas.

Within the Preuralian Sea, there was a general uniformity of the sediments distribution: coarse¬

grained terrestrial and near-shore sediments in the east and replaced in western direction by the deep¬

water mainly clay sediments, themselves gradually replaced by shallow water carbonates. A very

concise description of facial belts is given below (Figs 3-5).

C2B

Locality B

be- be-

•oc • OG-

• ■ • oe—

• • • DC- • • ■

X X :

o o^Co O

• • oc

^ •

• • 3o7 ■ •

° OX0O

' Xv S-

?.9JX-Q-P

.. . .

°yo ox>

• X ■ X •

L •

^ y.^;

f—■—1— ->.

l_1

o^°.0

oXDO

0° °o"

?oQo

j K° O O 5^5

o o ol o o o

loX o o o X o

0 o o Xo o O

•X- • • -X-

AooXo

) o oAo o oA

• X * • *A* • •

X-• y-« • x

"S —

r~^~i

C2b

i_i

Locality A

Fig. 4.— Main types of Moscovian sequences of the Preuralian Sea and their distribution within Ufa Amphitheatre . 1, fields of

Asyamsk Suite distribution; 2. belt of distribution of types II (to the east) and III (to the west); 3, area of type IV

distribution; 4. distribution of type V sediments - shallow water carbonates. C2/b. limestones of Bashkiria!!. Section see

figure 5.

Fig. 4 .— Principali.x types de facies dans les sequences du Moscovien de la Mer Preouralienne et leur distribution dans

l'Amphitheatre d'Ufa. I, zone de distribution de la suite d'Asyamsk ; 2. zone de distribution des facies de types II (a

Pest) et III (a I'ouest) ; 3, zone de dsitribution des facies de type IV; 4. zone de distribution des facies de type V -

carbonates d'eau pen profonde : C2/b, calcaires du Bashkirien. Trait de coupe voir figure 5.

Source: MNHN. Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

21 1

— The terrestrial coarse-grained sediments are distributed within restricted and separated areas: in

the eastern shore line of the north island of Novaya Zemlya archipelago (76°ION), in the Polar Urals

(between 69°N and 67°10N), within the Ufa Amphitheatre (from 57°10N up to 55°N). The local

distribution of the type of sediments along the Urals can be explained by the post Palaeozoic erosion.

Sandstones, gravelstones and conglomerates compose the Eksinsk suite in the North Island (Matveev

et al ., 1989). The Moscovian stage of Polar Urals is composed by similar sediments. The Moscovian

carbonate breccias, sandstones, gravelstones and conglomerates are distributed along of the Ufa

Amphitheatre. The thickness is 200-400 m.

— The near-shore marine coarse-grained sediments are also located in restricted areas along the

western slope of the Urals, but are more widely distributed. Along the eastern slope of the Pay-Khoy

Mountains within the Karsk Depression (between 69°N and 69°20N; Fig. 1), there are mainly

sandstones (200-250 m) with fusulinids (CHERMNYKH. 1976). Similar sediments are distributed in the

Pechora River upper stream area (between 60° and 60°20N). A rather thick sequence of conglomerates,

gravelstones and sandstones, with marine fauna in some sandstone interlayers, occurs in the Ufa

Amphitheatre (Figs 4-5). These sediments are considered as Abdresyakovsk Suite (Fig. 4) with a

thickness up to 1000 m. Locally, this suite includes levels with large (up to 5-7 m) carbonate blocks,

which represent partly the destroyed near-shore reefs and bioherms (CHUVASHOV, 1980). A similar

sandstone-conglomerate sequence was studied in the Ural and Ilek Rivers basins (Fig. 1), between 52°

and 51°N (Khvorova, 1961: Rauser-Chernoussova & KOROLUK, 1981). Some Targe (100-200 m)

and thick (up to 15 m) lenses of alga and stromatolite limestones are included in this section with a total

thickness averaging 800 m. Similar sandstone-conglomerate sediments with blocks of the biohermal

limestones (2-3 m of diameter) have been found 30 km eastwards from Aktyubinsk.

Fig. 5.— Palaeotectonical and facial profile of Moscovian sediments along the line of the figure 4. crossing different facial

zones (roman numerals) from northwest to southeast.

Fig. 5 .— Profit paleotectonique et faciologique des sediments du Moscovien, le long de la ligne de la figure 4, recoupant les

differentes zones de facies (chiffres romains) du nord-ouest an sud-est.

— Flysh-like sediments. On the Polar Urals (between 69° 40N and 66°N), the lower part of Kech-Pel

Suite (ROGOV et a !., 1988), a regular repetition of rather thin interlayers of fine-grained sandstones and

argilites, could be dated as Moscovian (thickness up to 200 m). To the south, on a large extent of the

western slope of the Urals (between 60°N and 55°50N) this facial zone was destroyed by the post-

Permian erosion. The thick (up to 700-800 m) marine sequence of sandstones, argilites with rare

interlayers of pelitic and detrital limestones, carbonate breccias, is traced to south till 56°50N (Figs 4-5).

Southernmost, this type of sediments is present in the Sakmara and Ural Rivers basin (between 51°50N

and 50°N). The thickness of sandstones, argilites with rare bed of detrital and micritic limestones could

be up to 1500 m near the eastern boundary of this facial belt. The thickness decreases near the western

boundary (400 m in the borehole at the latitude of Samara: Tschekotova, 1990). Similar sediments are

distributed between the Mugodzhary Mountains and the Precaspian Depression (Fig. 3) where they were

drilled by numerous prospecting holes (Fig. 6) in oil fields: Alibek-Mola (17a on Fig. 6), Zhanazhol (17

212

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

on Fig. 6), Tortay (9 on Fig. 6), Emba (GRACHEV, 1956; AVROV et al ., 1962; AVROV &

KROSMACHEVA, 1963; Ivanov, 1962 and 1966; DNEPROV, 1962; BULEKBAEV et al 1967;

Karstseva et al., 1985). Usually, the Moscovian stage is here underlayered by limestones of the

Serpukhovian and different levels of the Bashkirian. In Alibek-Mola area (17a on Fig. 6) the lower part

of Moscovian is mainly represented by limestones (Vereiskian horizon: 48 m and Kashirskian: 160 m;

Table 1). Essentially terrigenous sediments are distributed in the upper Moscovian, but significant

(thickness up to 60 m) limestone packets are present in this part of the section. The thickness of the

Podolskian horizon is close to 300 m and that of Myachkovskian to 129 m. In Tortay area (9 on Fig. 6),

the terrigenous sediments are prevailing in the lower part of the Moscovian and carbonates are

concentrated in the upper part.

Fig. 6.— Location of main prospecting areas on the territory of Precaspian Depression. 1. Carbonate frame of the Precaspian

Depression: 2. Precaspian Depression; 3. boreholes and prospecting areas; 4. large prospecting area; 5. boundaries of

Precaspian Depression.

FlG. 6 .— Localisation des principanx gisements de prospect ion sur le territoire de la Depression Precaspienne. 1, cadre de la

Depression Precaspienne, roches carbonatees ; 2, Depression Precaspienne ; 3, forages el zones de prospect ion : 4 .

zones etendues de prospection ; 5. limites de la Depression Precaspienne.

1. Sukhotinsk ; 2. Karakulsk : 3. Vysokovsk : 4. Dolgozhdann : 5. Aslrakhansk ; 6. Zavolzhsk : 7, Karaton : S.

Tugarakchan : 9. Tortay : 10. Turesay ; 11. Biikzhal : 12. Zhanasu : 13. Teresken ; 14. Severny Kindisay ; 15, Kursay ;

16. Kokpekty : 17. Zanazhol : 17a. Alimbek - Mola ; 18. Blansay ;19, Ostansuk : 20. Temir ;21, Krasnokhuduksk ; 22.

Tengiz : 23. Buzachi ; 24. Karachaganak.

— The essentially clay and cherty-clayey sediments (depressional type) are traced almost

everywhere from the Novaya Zemlva archipelago up to the Precaspian Sea. On the southern island of

Novaya Zemlya archipelago, undivided Middle Carboniferous sediments are represented by very thin

sequence (6-28 m) of cherty argilites, argilites and manganese bearing carbonates (PLATONOV et a !.,

1992). These sediments are present in the Vaigach Island (Fig. 1) and on the eastern slope of the Pay-

Khoy Mountains (between 70° and 68°N).

Source: MNHN, Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

213

In the Lemva River area (between 68° and 66°N), from east to west, are recognised the series of

undivided Middle-Upper Carboniferous (CHERMNYKH. 1976; ELISEEV, 1973, 1978). In the eastern part

of this zone, the Moscovian stage is a part of Kharotsk series, a sequence of argilites and cherty argilites,

deep-water limestones and dolomites; the thickness of this series exceeds 500 m. Next to west, the

Kharutsk series is represented by a very thin (20-30 m) repetition of cherty and argilites. And

westwards, the Worgashor series is composed of argilites and cherty argilites with interlayers of spongy

limestones and silts (150 m). These sediments can be found in the upper stream of Pechora, Kolva,

Vishera Rivers (Fig. 1) in the Northern Urals (between 62° and 61°N).

This type of Moscovian sediments is distributed without interruption from 56°40N to the Precaspian

Basin. The depressional and other types of Moscovian sediments are shown on the figures 4 and 5. The

relatively narrow belt of depressional sediments, distributed along the Urals, becomes very wide within

the Precaspian Depression. On the perimeter of the Precaspian Depression (oil fields of Karachaganak in

the north; Astrakhan Dome in the southwest; Yuzhno-Embensk uplift in the southeast; Tengis in the

east; Fig. 6) is observed, above the Bashkirian shallow-water limestones, a monotonous sequence (60-

250 m) of black argilites, marls, micrites with very rare and uniform fauna (radiolaria, sponges,

ammonoids, fish remains, conodonts; KARIMOV et al ., 1990). Miospores were identified in some

intervals. Within this sequence, there are thin grainstone beds with Middle and Late Carboniferous and

Early Permian foraminifera. Usually, these organic remains are considered as reworked.

The Artinskian dating of the uppermost part is generally acknowledged. For the lower part, the age

attributed could be: Artinskian (MOVSHOVICH, 1977; LAPKIN & MOVSHOVICH. 1978, 1994; LATSKOVA,

1976, and others), adopting a long time break between Bashkirian limestones and clay and marl

sediments; late Bashkirian-Sakmarian (DALYAN, 1990; this paper) if we consider a continuous

sedimentation. We shall consider each hypothesis in light of available material.

To the south of Karachaganak oil field reef formation (24 on Fig. 6) (ILYN et al ., 1987), above

Bashkirian limestones, there are black argilites and marls (up to 60 m). Early Asselian conodonts were

found in its middle part; the upper part contains Artinskian radiolaria and miospores.

In the Astrakhan uplift area (MOVSHOVICH, 1977) above Bashkirian limestones, was drilled a

formation of black argilites and marls in the lower part; the numerous silt and sandstone interlayers

occur in the top formation (whole thickness is 160 m). Some thin grainstone interlayers, with Middle-

Late Carboniferous and Asselian foraminifera, are found in lower and middle part of the formation. The

upper part contains Artinskian radiolaria and miospores and the age of the formation as a whole is

adopted as Artinskian (MOVSHOVICH, 1977; Lapkin & Movchovich. 1994). All above mentioned

foraminifera are considered as reworked, according to existing pattern. Similar situation is observed

everywhere along the borders of the Precaspian Depression.

The depressional sediments of the Preuralian foredeep were gradually replaced westwards by the

shallow-water, sequence, mainly carbonated, representing deposits of the Volga-Kama basin (Figs 3-5).

It is very important to note that on the border of the Russian Platform and Foredeep, organic build-ups

did not exist and the transitional zone is rather narrow (1-3 km). Numerous islands, with low relief, were

present on the Volga-Kama territory at the beginning of Moscovian as a result of the Bashkirian

regression. These islands were baring areas during the early Moscovian. Such conditions of

sedimentation have defined lithological composition of the lower substage (Vereiskian and, at a smaller

scale. Kashirskian horizon sediments): usually argilites and marls, less often sandstones, gravelstones

and carbonate breccias. At the top of the Moscovian, except with prevailing detrital and biogenic

carbonates, dolomites became rather common and locally evaporates are present.

In the Pechora River basin (on right bank), the thickness of Moscovian shallow water carbonates

could reach 200-300 m (CHERMNYKH, 1976). The numerous packets of carbonate breccias, with blocks

up to 1-5 m, are present in this area (CHUVASHOV. 1994). The upper Moscovian contains significant

thickness of dolomites and anhydrite along of the left side of the Pechora valley near Timan (Fig. 3).

On the large territory of the Western Urals and Cis-Urals, from the Kolva River to the Ay River

(between 61°20 and 56°N) (Fig. 1), there are two folded types of Moscovian. The lower one (Vereiskian

and Kashirskian horizons in whole) is represented by argilites and marls with interlayers of limestones,

silts and sandstones. The upper part is composed mainly of detrital and biogenic limestones with rich

and diversified fauna (Rauser-Chernoussova, 1961b). To the west of the Urals, secondary dolomites

214

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

significantly increase. The most important thickness of the Moscovian stage (350-400 m) is recorded

near Staroutkinsk Settlement (Chussovaya River Basin; Fig. 1, ~57°N; PAKHOMOV & DOSORTSEV,

1966; Tscherbakov & Tscherbakova, 1966).

Along of the Middle Volga (north of Samara. Fig. 3). the Vereiskian horizon (25 m) is a sequence of

the reddish and greenish-grey argilites with dolomites, silts and sandstones. Dolomites and limestones

prevail in the Kashirskian horizon (80 m); silts and sandstones at the bottom. Podolskian (113 m) and

Myachkovskian (124 m) horizons are represented by limestones and dolomites with prevalence of first

one (Rauser-Chernoussova, 1961a).

In the Volgograd region (Figs 1-3), contiguous with the northwestern Precaspian Depression, there is

the next sequence of M^oscovian (SEMIKHATOVA. 1961). Vereiskian horizon (22-125 m) is composed of

argilites and silts with sandstone and limestone interlayers. The thickness of this horizon decreased to

the northwest. The Kashirskian horizon (100-324 m) is represented by argilites and marls with

numerous carbonate beds. Both Podolskian (140 m) and Myachkovskian (124 m) horizons are

represented by limestones and dolomites with beds of marls and argilites.

Within the Moscow Synclinal, the Moscovian stage is represented by such sequence (Ivanova &

SHIK, 1978; MAKHLINA et at., 1997). The Vereiskian horizon contains three members (from bottom to

top; Table 1): Shazk member (3-10 m), argilites and sandstones with thin limestone and marl interlayers

containing brachiopods and fish remains; Alyutovsk member (5-19 m), argilite-limestone alternation

with sandstones in the middle part of section; Ordynsk member (5-10 m), argilites and clayey

limestones.

The Kashirskian horizon (60-70 m) combines carbonates with some interlayers of red and pink

argilites and silts. Fusulinids, corals and brachiopods are recognised. A conglomerate bed marks the

bottom of the stratotype of the Podolskian horizon near Podolsk (Fig. 1); above, thin-bedded limestones

with rich and diverse fauna of foraminifera (including fusulinids), corals, brachiopods, crinoids and

calcareous algae. The Myachkovskian horizon (19-24 m) is represented by white and white-grey detritic

and biogenic limestones with algae and a very rich fauna.

The original sequence of Moscovian sediments is present in the Donetsk Gulf (Fig. 3), where coal¬

bearing paralic deposits are accumulated (1800-3000 m thick). The rare and wonderful combination of

normal marine (fusulinids, corals, brachiopods, bivalves, ammonoids, ostracods and conodonts) and

terrestrial (bivalves, plants, miospores) organic remains could be noted for this section. A short

summary description is given below (after AlSENVERG & ROTAY, 1978).

At the basis of the Moscovian stage, the sediments belong to the biostratigraphic zone C2 m/a (450-

600 m): alternation of sandstones and argilites with 6 or 7 limestone beds. Some coal seams (part of

them industrial) occur in this sequence. The next zone C2m/b (150-500 m) differs from the underlying

by smaller development of sandstones. The zone C2m/c (250-450 m) contains 5 thick limestone beds,

some industrial coal seams and a lot of coal interlayers. The zone C2m/d (250-400 m) contains 5-8

limestone beds. The highest Moscovian zone C2m/e (360-600 m) includes up to 10 limestone beds 5-6

of which are widely distributed.

At the east of Palaeourals, the Eastern Uralian Gulf (EUG) is traced along the mountain system on

more than 1000 km (Figs 3-5). The width of this gulf (before folded and thrusting shortening) was about

200-250 km. Biostratigraphy and palaeogeography of the EUG were previously described (CHUVASHOV

et at., 1984). A very concise conclusion is presented below.

A thick sequence of coarse-grained terrestrial sediments (red argilites, silts, sandstones and

conglomerates), with locally lenses of gypsum and anhydrite, could be followed along western and

eastern shore lines of the EUG. On the eastern border of gulf (Tobol River Basin, latitude 52°30N; Figs

I, 3, 9), volcanic rocks and tuffs with clastic terrestrial sediments, are recognised with a thickness up to

1000 m.

The inner part of the EUG, in its northern half, is filled by marine flysh-like sediments. Beds and

packets of limestones, conglomerates and gravelstones are distributed locally within the flysh-like

sequence. The carbonates increase southwards and the Moscovian in whole is composed by shallow-

water carbonates with prolific fauna and calcareous algae near the southern end of the EUG (Figs 3, 9).

To the east of the EUG (Figs 3. 9), an extensive continent took place. In the restricted intermountain

Source: MNHN, Paris

PALAEOGEOGRAPHY OE EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

215

depressions, occur red-coloured clay-sandstone deposits or conglomerates and gravelstones-sandstones.

In numerous areas of the recent West-Siberian plate, those sediments are associated with the thick

blocks of volcanic rocks and tuffs. The poor palaeontological data (bivalves, plants and miospores)

permit, after all, to consider that these terrigenous sediments and volcanic rocks were accumulated

during a long time, from the second half of Bashkirian up to the end of the Permian.

The southern edge of the EUG (Figs 3, 9) was separated from the Precaspian Sea by the Mugodzhary

Peninsula. To the south of the Precaspian Sea, the EUG was merged in the Turanskian Sea. There are

some arguments to follow the EUG to the south in the region of Aral Sea, where, on geophysical data

(Pak, 1988; Babadzhanov et at ., 1989; PlLlPENKO, 1990), the Aralo-Murgabsk rifts dissected, from

north to south, the middle part of the Turansk plate. The northern branch of this zone passed along the

western shore line and jointed the middle part of the Aral Sea. In this graben. Upper Palaeozoic-

Mesozoic sediments are recognised with a total thickness up to 8-10 km. Amongst this sequence, under

the Jurassic, are defined by geophysical methods, the Upper Palaeozoic-Triassic rocks with a thickness

\ /

\ \ \

\ \

r r

-!9

•

Fig. 7.— Geological map of the Usturt territory without Jurassic-Quaternary deposits (after Kartseva & Kirl khin. 1974). 1.

Upper Permian-Triassic; 2. Upper Carboniferous-Lower Permian; 2a, slates: 2b. volcanic rocks; 3, Lower

Carboniferous; 4. Lower-Middle Carboniferous; 5. Middle Palaeozoic (Silurian - Lower Carboniferous); 6. Precambrian

and Palaeozoic; 7. Precambrian only; 8, diabases of porphyrite; 9. faults: a- real and b- suggested; 10. boreholes: 1-

Baiterek; 2- Sarytekis: 3- Karakunduk; 4- Priozerny: 5- Kisylshaly; 6- Koskala; 7- Shakhpakhty.

FlG. 7. — Carte geologique ecorchee du territoire d'Usturt, sans les depots du Jurassique ait Quaternaire (d'apres Kartseva &

Kirukhin, 1974). I. Pennien superieur - Trias ; 2 , Carbonifere superieur - Permien inferieur : 3, Carbon if ere

inferieur: 4, Carbonifere inferieur et moyen ; 5. Paleozo’ique moyen (Silurien a Carbonifere inferieur) ; 6,

Precantbrien et Paleozoique : 7. Precambrien seul: S. diabases de porpliyrites ; 9. failles: a - prouvees, b - suggerees :

10. forages : / - Baiterek : 2 - Sary tekis ; 3 - Karakunduk : 4 - Priozerny ; 5 - Kisylshaly : 6 - Koskala : 7 -

Shakhpakhty.

216

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

0.4-0.2 km. In this interval, there is a zone (2-3 km in width) with very irregular reflection of the seismic

waves, related to reef distribution. This suggestion is supported by the drilling data. In the Karakuduk

bore-hole (3 on Fig. 7), the Upper Palaeozoic carbonates are reached. Marine clayey silts are penetrated

by Priozerny borehole (4 on Fig. 7). The exact age of the formations is not established, but the general

regularity of more wide Moscovian sediments distribution compared with Upper Carboniferous-

Asselian, suggests the existence of Moscovian polyfacial sediments near and within the Aral Sea area.

The synthesis on Upper Palaeozoic of the Aral region according to drilling data was made by

KARTSEVA & Kirukhin (1974). They have shown (Fig. 7) that, under Jurassic sediments, are widely

distributed Asselian-Upper Carboniferous and Triassic-Upper Permian deposits. The regularity of

sediments permits to assume a wide distribution of Moscovian stage here.

The palaeogeography of the southeastern part of the Turanskian Sea is reconstructed mainly

prospectively (Fig. 9) (COOK et al., 1994). The very thick, mainly carbonated, Famennian-Bashkirian

sequence has been studied in the Kara-Tau Ridge. To the west, a borehole drilled, on more than I km,

evaporates (gypsum), which are considered as the higher part of the section. The Moscovian and

younger sediments could be amongst the evaporites. This kind of deposits could be accumulated only

within a large lagoon (Kara-Tau Lagoon).

The western extremity of this lagoon was represented by the shallow-water marine carbonate-

terrigenous sediments of the Nura-Tau Mountains area, which was located immediately to the west of

Kara-Tau Lagoon (Fig. 9; IBRAGIMOV et al ., 1989). Above the late Bashkirian conglomerates and

sandstones, the lower Moscovian bioherms, up to 50 m in thickness, are overlapped by a thick (up to

700 m) sequence of argilites, silts, sandstones with lenses and beds of conglomerates, tuffs and

limestones.

In the central Kisyl-Kum (area of Tokhtinikhtau Mountains; Fig. 9), the Moscovian stage is

represented by Tokhtatausk series, subdivided into three members. The lower (490 m) is composed by

sandstones, gravelstones and conglomerates with rare limestone beds. The middle member (700 m) is

represented by sandstones, gravelstones, silts, argilites and limestones. The upper member (650 m) is

very similar to the lower one. All this sequence could be considered as marine near-shore sediments

(Kalashnikov & Askarov, 1989).

Very sketchy data exist on the Moscovian of the western part of the Turansk Sea on the Busachy

Peninsula (Fig. 6; KARTSEVA, 1979). A borehole (23 on Fig. 6) drilled (interval 2000-3500 m) dark-

grey micritic and detrital limestones with interlayers of carbonate breccias and rudstones. Upper

Carboniferous and Asselian foraminifera are determined in the interval 2172-2924 m.

In the Bukhara-Karsha region (right side of the Amu-Darya River Valley; Figs 8-9), the Upper

Palaeozoic deposits were drilled by numerous boreholes (USAKOV, 1985) with Moscovian limestones

holding foraminifera. For other prospecting areas, the Moscovian stage could be supposed under the

Upper Carboniferous and Lower Permian.

The Moscovian stage in the region of Balkhash Lake or within the Balkhash Bay (Fig. 9) is

subdivided into three palaeogeographic members (BOGUSH et al., 1976; YUFEREV & SOKOLOV, 1976):

— with Choristites fritchi (118-183 m): alternation of sandstones, silts, cherty argilites and tuff beds

and packets; organic remains are represented by foraminifera, corals, brachiopods. bivalves, gastropods

and ammonoids;

— with AUjutovella (35-47 m): represented in the southern area by limestones with foraminifera,

corals and brachiopods. In the northern part, the coeval sediments are composed of sandstones and tuffs.

A limestone packet (27-32 m) with foraminifera, solitary and colonial corals, brachiopods and algae

overlies them;

— with Profusulinella rhomboides\ this member, on the southern part of synclinal, is represented by

alternation of cherty-clays, argilites, silts and sandstones, detrital limestone beds and packets (78 m). On

the northern edge of this structure, there are three groups. The lower one (31 m) is composed of the silts

with tuffs and sandstones. The middle one (77 m) is represented by calcareous silts with brachiopods

and numerous cephalopods. The upper one (92 m) is composed of coarse-grained sandstones and tuffs

with small pebbles. Brachiopods, gastropods, cephalopods and large wood trunks are present.

Source: MNHN, Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

217

62° 64° 66°

Fig. 8.— Area of Upper Palaeozoic distribution on the right side of the Amu-Darya River (after USAKOV, 1985). 1.

conglomerates, gravelstones; 2. sandstones; 3, silts: 4. argilites; 5. limestones; 6. outcrops of pre-Mesozoic rocks; 7.

Prospecting areas: 1- Daulepe; 2- Yankikasgan; 3- Khatar; 4- Sverdlov: 5- Kandym; 6- Chandyr; 7- Zekry; 8-

Bayshirin: 9- Pamuk; 10- Severny Mamanak; 11- Severny Karaktay; 13- Sapadny Karaktay; 14- Shurtan. 8. numbers of

boreholes with Upper Palaeozoic; Cl- Lower Carboniferous; C2- Middle Carboniferous; C3- Upper Carboniferous; P-

Permian; J- Jurassic.

FlG. 8 .— Zone de distribution du PaleozoYque supdrieur sur la rive droite de l'Amu-Darya (d'apres USAKOV, 1985). /.

con glome rats, graviers ; 2, gres : 3. silts ; 4. argilites ; 5. calcaires ; 6, affleurements de roches antd-mesozoYques ; 7.

zones de prospections: / - Dautepe ; 2 - Yankikasgan ; 3 - Khatar ; 4 - Sverdlov ; 5 - Kandym ; 6 - Chandyr ; 7-

Zekry; 8 - Bayshirin ; 9 - Pamuk ; 10 - Severny Mamanak ; 11 - Severny Karaktay ; 13 - Sapadny Karaktay ; 14 -

Shurtan ; 8, numeros des forages avec du PaleozoYque superieur : Cl - Carbonifere inferieur ; C2 - Carbonifere

moyen ; C3 - Carbonifere superieur ; P - Permien ; J - Jurassique.

YUFEREV & Sokolov (1976) considered that the marine Balkhash Gulf was merged to the south

with the Ob-Saisan Sea (to the east on the map. Fig. 9) and was surrounded to the west, the north and the

northeast by the mountainous land with active volcanic activity. If the second part of this assertion can

be adopted without any comment, the first one. about gulf communications, can not be accepted. The

whole fauna and alga assemblages of the Moscovian Balkhash Gull show the connection ot this gull

with biotas of both Tethyan and Eastern European Basins (Fig. 9) without any incursion of the very

specific fauna of the Ob-Saisan Sea.

MOSCOVIAN PALAEOBIOGEOGRAPHY

The Moscovian palaeogeographic situation is supported by the biogeographic data, showing the wide

and free communications between Tethyan and Uralian biotas. The results of fusulinid study were used

for restoration of the connection ways between Arctic, Eastern European and Tethyan Basins (IVANOVA

& CHUVASHOV, 1990). The fusulinid fauna of the Preuralian Sea shows a significant influence of the

Northern American biota (genera Pulchrella. Pseudofusulinella, Wedekindellina). A migration way of

those fusulinids along of the Palaeourals shoreline is distinctly traced. The southernmost distribution ot

these American genera is limited to 53°N. To the south of this latitude, the fusulinid tauna are closer to

Tethyan and Donetsk Gulf ones (some genera as Pulrella , Eofusttliiui, HemifusuUnd).

Source .

218

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

Preuralian Sea Eastern Uralian Gulf

50° 54° 58° 62° 66° 70° 74° 78° 82° 84°

Fig. 9.— Palaeogeographic map of jointing zone of the Eastern European and Tethyan Basins during Moscovian (late

Moscovian). 1. area of Tobol River - terrestrial terrigenous sediments with volcanic rocks. 2. Toktynyktau Mountains;

3. Nura-Tau Mountains. Legend: see Fig. 2.

Fig. 9.— Carte paleogeographqiue de la zone de jonction du Hass in Est Europeen et de la Tethys an Moscovien (Moscovien

terminal). I, region de la riviere Tobol, sediments continentaux terrigenes avec roches volcaniques ; 2, Montagues de

Toktynyktau ; 3. Montagues de Nura-Tau. Legende : voir Fig. 2.

New results on the Moscovian fusiilinids of southwestern Darvaz, Pamir were recently published

(LEVEN, 1998). Most of Moscovian fusulinid genera and species of this area are identical with fusulinid

biota of the Eastern European Basin. Only some genera are endemic. Undatofusulina is known in the

Pamir and the Middle Asia in whole and in the Donetsk Basin. Putrella is distributed within the same

territory and in the southern part of Eastern Uralian Gulf.

A great similarity could be noted between Moscovian fusulinids of Eastern European and Tethyan

Basins. For example, Moscovian foraminifera of Vietnam (NGUEN Van LlEM, 1982) and Thailand

(Toriyama el al ., 1975). according to the present genera, are very close to fusulinid biota of the

Russian Platform or, in other words, of the Volga-Kama Sea.

Taxonomic assemblages between the Moscovian brachiopods of Near-Polar Urals and Central Kisyl-

Kum (Kalashnikov & Askarov, 1989) share a lot of genera and species: Choristites priscus

(Eichw.), Ch. sower by (Fish.). Brachithyrina subcarnica (IIov.), Chaoiella gruenewaldti (Krotov),

Linoproductus simensis (Tchernyshew), Meckel la eximia (Eichw.), Enteleies lamarcki (Fish.),

Neospirifer postriatus Nik.

Source: MNHN , Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

219

Three biogeographic assemblages of calcareous algae are recognised (CHUVASHOVeT ai, 1995). One

of them characterises both slopes of the Southern Urals in the basin of the Urals and in Mugodzhary

Mountains (CHUVASHOV & ANFIMOV, 1988). A specificity of this assemblage is a great diversity of

green algae ( Anchicodium, Neoanchicodium, Epimastopora , Gyroporella , Macroporella , different

Beresellids) and similarity with coeval Tethyan assemblages (Middle Asia. KHODZHANYAZOVA, 1991:

Pyrenees Mountains, Ra'CZ, 1966). It is possible to assume, that the distribution of this Uralian alga

association goes up to 53°N.

The importance of the green algae and their diversity is regularly decreasing to the north, along the

Urals. The Middle Urals and the most part of the Russian Platform at the same latitudes show

assemblages belonging to the Beresellid realm ( Dvinella. Beresella, Uraloporella). Mainly red algae

( Ungdarella , Kornia , Pechoria) were recognised in the northern part of the Urals and northeastern part

of the Russian Platform. This alga distribution could be explained by the decrease of the temperature

from south to north along the Palaeourals Mountains.

All these data show the mutual and stable connections between Tethyan and Eastern-European Basin

biotas.

THE ASSELIAN

The Asselian stage is subdivided into two horizons (from bottom to top): Kholodnolozhskian and

Shikhanskian. In the first one, the following fusulinid zones are identified: Daixina bosbytauensis -

Daixina robusta zone; Sphaeroschwagerina fusiformis zone; Sphaeroschwagerina moelleri -

Pseudofusulina fecunda zone. The Shikhanskian horizon corresponds to the Sphaeroschwagerina

sphaerica - Pseudofusulina firma zone. The maximum of the Asselian transgression is linked with the

“moelleri-fecunda” zone. The palaeogeographic situation shown on the maps (Figs 10-12). basically

reflects this phase of the geological history.

Asselian palaeogeography of Eastern European Basin

During the Asselian, the area of Eastern European Basin is reduced; its width, at Moscow latitude,

does not exceeded 1000 km (Fig. 10). Some very important geological events between the Moscovian

and the Asselian and during the Asselian should be pointed out. At the beginning of the Late

Carboniferous, the Eastern Uralian Gulf, and at the end of middle Asselian, Donetsk Gulf, were closed.

With the development of the Preuralian Foredeep, the Preuralian Sea boundaries received a more sharp

geomorphological impression; a reef barrier arose on the boundary with Volga-Kama Sea or, in other

words, on the border of the Russian Platform. This barrier is traced from the Arctic Ocean to the

northern rim of the Precaspian Depression. This last one is deepening in relation with the structural

environment (Palaeourals and Mugodzhary Mountains, Russian and Turansk Plates).

On the borders of the Preuralian Sea, from east to west, some facial zones could be traced. They are

defined before for the Moscovian. but for the Asselian the differentiation between facial zones is clearer

and the preservation of the eastern facies is better. All the Asselian facies of the Preuralian Sea can be

described as follow (Figs 11-12).

— Mainly sandstone sequence with lenses and packets of the boulder-pebble conglomerates;

numerous interlayers of silts and argilites, and some beds of detritic limestones. A grading bedding is

typical for sandstones and detritic limestones. Among this sequence, rather thin (up to 3-2 m)

stromatolite, brachiopod, bryozoan, algae and Palaeoaplysinci organic build-ups could occur. Significant

olistostromes (2-20 m) are sometimes present. Rather thick (up to 250 m) carbonates breccias could be

recognised in uppermost part of the sequence. The thickness of the serie reaches 1500 m in the Southern

Urals and 700-800 m in the Middle Urals.

220

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

75°

-V—

ASSELIAN

Tobolsk

elyabinsk

Kustanay

Fig. 10.— Palaeogeographic map of the Eastern European Basin during the Asselian. Legend: see Fig. 2.

Fig. 10 .— Carte paldogeographique du Bassin Est Europeen durum I'Asselien. Legende : voir Fig. 2.

Source: MNHN. Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

221

Recent distribution , lc

of Asselian Sediments-*-. pi=,

Fig. 11.— Palaeogeographic map of the Preuralian Sea during the Asselian. Section A-Al: see figure 12; Legend: see Fig. 2.

Fig. II .— Carte paleogeographique de la Mer Preouralienne durant FAsselien. Coupe A-Al : voir figure 12.

Legende : voir Fig. 2.

Source: MNHN. Paris

222

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

E-NW

Fig. 12. — Palaeotectonical and facial profile of Asselian sediments on the Perm latitude (section A-AI on Fig. II). Legend: see

Fig. 2. Arrows show the used sections.

flG. 12 — Profit paleotecionique el faciologique des sediments de I'Asselien a la latitude de Penn (coupe A-AI sur la figure

11). Legende : voir Fig. 2. Les fleches montrent les forages utilises.

This type of section differs by richness and diversity of the organic communities. The detritic

limestones contain small foraminifera, fusulinids, corals, fragment of brachiopods and bryozoans,

crinoids, ostracods, algae, which were displaced by grainflows from shallow water coastal areas to the

deeper parts of the basin. The set of marls, argilites and micritic limestones, cherts, which are intersected

by the turbidite beds, contain an another autochthonous association of organisms: radiolaria, sponges,

bivalves, ammonoids, nautiloids, trilobiles, conodonts, fish remains, worm trails. This facial type is

distributed within two restricted areas. The northern one is located (Figs 10-11) between 57°30 and

56°50N, and the southern area corresponds to the basin of the Sakmara and Ural Rivers (between 52°

and 50°N). This belt of the coarse-grained sediments is traced on the eastern rim of the Precaspian

Depression (BOGATYREV & EVENTOL, 1962) (Fig. 13).

— To the west, the next facial zone is also represented mainly by sandstones, but there is here a

rather regular alternation of thin (5-15 cm, seldom up to 50-70 cm) sandstone beds with silt and argilite

interlayers. Usually, rare beds of detrital limestones, thinner than in the eastern facial zone, are included

in this uniform sandstone-argilite sequence. Organic remains could be divided into two groups:

allochtonous in turbidites (foraminifera, including fusulinids, corals, brachiopods, bryozoans, crinoids

and algae) and autochthonous, within clay interlayers between sandstone beds: radiolaria, sponges,

bivalves, ammonoids, fishes, conodonts. The thickness of this type seldom exceeds 500 m.

The distribution of these deposits is more uniform than for the first type. This type is absent only in a

restricted area located between 58° and 60°N (Fig. 10).

— Further west, the third facial zone is distributed almost everywhere from the Novaya Zemlya

archipelago to the north up to the Precaspian Depression to the south. The most significant width in the

latitudinal direction is 70-75 km. This type of section is represented mainly by argilites, cherty argilites,

marls and micritic limestones. Three subtypes could be recognised amongst these deposits

(Chuvachov & DYUPINA, 1973; Tscherbakova et al ., 1979; CHUVASHOV et <//., 1990): eastern,

central and western (Fig. 12). The eastern subtype is characterised by presence of the sandstone beds,

packets and a small increase of thickness (up to 120 m). The central subtype is composed mainly of

marls and argilites with cherts and has an insignificant thickness (20-50 m). The western subtype is

characterised by limestones and marls with carbonate breccias and conglomerate packets and lenses.

The thickness of this type could be up to 150 m.

The biota could be divided into two assemblages: alio- and autochthonous. The first group contains

the shallow-water organisms: foraminifera (including fusulinids), single and fragment of colonial corals,

brachiopods, bryozoans, crinoids, algae, which are transported in the deep part of basin by the sandy

grainflows from the premountain shallow-water. Similar assemblage is present within carbonate

turbidites and breccias, which are displaced from the western rim of Russian Platform to the east by

grainflows.

Source. MNHN , Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

223

East - European Basin f

c’T-t — 3 Orenburg m

Precaspian Sea

Mugodzhafy Peninsula

1111111111111111*,.;.

Kara - Tau Lagoori;

i i| I | I | I i I | l| II i | i | I r -

1 1 Turanskian Sea

M M I .... I i I .... I i I i | i I •

Tyari Shan Peninsula-

,Pamir - Tya'n Shan Sea

1111111111111111111111111111111

Preuralian Sea

1 ASSELIAN

Karaganda

^ 0 140 280 420 km

i i i i

=> Eastern - Tyan Shan Sea

Big Pamirskian Island

Fig. 13.— Palaeogeographie map of the Eastern European and Tethyan Basins jointed area during the Asselian.

Legend: see Fig.2.

FlG. 13 .— Carte paleogeographique de la zone de junction des Bassins Est Europeen ei Tethysien d I'Assilien.

Legende : voir Fig. 2.

The autochthonous group is represented by some genera of small foraminifera, radiolaria, siliceous

sponges, small-size solitary corals, bivalves, trilobites, thin-shelled brachiopods. ammonoids and

nautiloids, fishes, conodonts, worm-trails. According to the whole data, those sediments could be

interpreted as deep-water, compared with other Asselian facies. This type of the sequence is named

below as depressional.

The depressional type of sediments along of the Precaspian Depression rim was established on

numerous prospecting fields. Some informations were given before in the description of the Moscovian

sediments and palaeogeography. The idea of depressional deposits distribution on the whole territory of

the Precaspian Depression is now really validated.

— The Asselian reef is the most important during all the Early Permian and can be followed from the

Kolguev Island (Fig. 1) in the Barents Sea (PREOBRAZHENSKAYA el al. , 1993), along the western edge

of the Pechorsk Depression (KONOVALOVA et al ., 1995; KUZKOKOVA & CHERMNYSKH, 1987) and,

further to the south, along the eastern rim of the Russian Platform until the Orenburg latitude. Southern,

the reef belt is turning westwards along the northern border of the Precaspian Depression

Source: MNHN, Paris

224

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

(YAROSHENKO. 1985). The Asselian reefs outcrop in the basins of the Pechora. Kolva. Vishera Rivers

(between 61°50 and 60°30N), along ihe Chussovaya River (58°ION). The most impressive outcrops of

these build-ups are present near Sterlitamak and Ishimbay (53°30N - 53°40N). The Sterlitamak reefs

were described by SHAMOV (1958), KOROLUK (1985) and RAUSER-CHERNOUSSOVA & KOROLUK

(1993). The general characteristics of the Early Permian reefs were given by CHUVASHOV (1983).

The relationships between the Asselian reefs and the under- and overlying formations, as well as

their thickness, are variable in the different parts of the reef belt. They lie down on Upper Carboniferous

reefs, or locally with unconformity on Middle Carboniferous limestones. Usually, the Asselian build-ups

are shifted to the west, at least on 10 km, from the Late Carboniferous organic constructions. The reefs

of the northern border of the Precaspian Depression have a thickness up to 250 m. The thickness could

reach 500 m on the western border of the Preuralian Foredeep between Orenburg and Ufa latitudes. In

the Middle Urals (at Perm latitude), the thickness of Asselian reefs is 300-350 m. A similar thickness is

recorded in the Northern Urals, between the Vishera and Kolva Rivers, and in the upper and middle

streams of the Pechora River. The organic build-ups of the western border of the Pechorsk depression

are represented by biostromes and bioherms (5-25 m), composed of Palaeoaplysina.

The Asselian reefs are usually composed by a rather stable assemblage of organisms: sponges,

bryozoans. brachiopods, Palaeoaplysina and problematic algae ( Tubiphyies ). The importance ot

Palaeoaplysina , as reef-building organism, is more significant in Near-Polar and Northern Urals. In

Middle and Southern Urals, these organisms have a rock-building importance only at the beginning of

late Kholodnolozhskian (Table 1). A very rich and diverse assemblage of the calcareous algae is

connected with the Asselian organic build-ups. Some levels are composed of stromatolites.

— To the west, the Asselian reef belt is replaced by a rather thick sequence of bedded limestones

with some dolomites in the lower part of section. Most part of this sequence is represented by the

detritic limestones; Palaeoplysina and colonial coral bioherms are locally distributed (no more than 1-5

m). The organic limestone components are small foraminifera, fusulinids, corals, bryozoans,

brachiopods, crinoids and Tubiphytes. Other algae are very unusual in this facial zone (THEODOROVICH,

1949; Chuvachov & Dyupina, 1973; Zolotova et ai, 1973).

In these detritic and biogenic limestones, rather thick (2-5 m usually; up to 10 m) packets of dark-

grey and black thin-bedded bituminous marls, clayey limestones and argilites with concretion and lenses

of black cherts are developed. Such deposits were laid down in rather small (some metres deep and up to

100-300 m long) quite-water depression, where clay and carbonate material enriched by the organic

matter were accumulated. The assemblage of fauna is represented by numerous fusulinids, small (up to

20-30 cm in diameter) colonial corals, bryozoan colonies (usually complete and large, up to 20 cm).

These Asselian deposits are distributed to the west of the coeval reef belt on 80 to 100 km. A change

in deposits distribution is shown on the profile along the Chussovaya River (Figs 1 and 1 1). The

Asselian thickness in the eastern part is about 170-220 m, decreased to 100-120 m near Perm (110 km

westwards of the reef belt) and reached 50-65 m further to the west (mainly with dolomites). On the

Oka-Zna uplift (250 km eastwards of Moscow), the Asselian stage (40-45 m in thickness; SEMINA,

1961) is composed by an alternation of limestones and dolomites. Further westwards, a section of the

Asselian (about 80 km to the east from Moscow) presents mainly dolomites (MAKHLINA, 1978) with a

thickness of 25 m.

These data could be used for the interpretation of change in the bedded carbonates from east to west

in the Volga-Kama Sea territory:

— gradually decrease of thickness from east to west (200 m to 25 m); disappearance of biogenic

beds;

— increase of dolomite content as result of salinity rising;

— standardisation and poverty of fauna become more significant to the west. These data emphasise

the stronger differentiation (biological and sedimentological) in the Asselian than in the Moscovian,

near eastern and western boundaries of the Volga-Kama Sea.

The Donetsk Gulf, with normal salinity, exists only during the Kholodnolozhskian (lower Asselian).

In the central part of the gulf, a next sequence exits, with from bottom to top (NESTERENKO, 1978;

Alekseeva et al., 1983) (Table 1):

Source. MNHN , Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

225

— Kartamishsk Suite: mainly red sandstones with packets and beds of argilites and some limestone

beds; it disappears northwards; 500-1200 m thick.

— Nikitovsk Suite: grey sandstones and argilites with packets and beds of dolomites, limestones and

anhydrites; in the northern part of the gulf, rock-salt lenses (40 m) are recognised; 100-250 m thick.

— Slavyansk Suite: mainly anhydrites, gypsum, rock salts, packet of limestones (10-15 m)

containing a very diverse and rich fauna: foraminifera (small ones and fusulinids), corals, bryozoan,

brachiopods, crinoids and algae. The thickness is up to 600 m. These three suites, on the whole, could be

correlated with Asselian Kholodnolozhskian horizon.

— Kramatorsk Suite: mainly evaporates (anhydrites and rock-salts); in the upper part of the suite

there is a packet of potash salts. Rather thick alternation of red sandstones and argilites subdivide

evaporates; thickness of this suite is 530 m. The Kramatorsk Suite is compared with the upper Asselian

(Shikhanskian Horizon) and lower Sakmarian (Tastubskian Horizon).

In the northern part ot the Donetsk Gulf was established an other Asselian sequence based on

Skosyrsk borehole example (ALEKSEEVA etal., 1983). it is located at the junction zone of the southern

slope of the Voronezh dome and the Donetsk Folded belt or, in other words, at the junction of the

Russian and Scythian Plates. The Asselian deposits are composed as follow (from bottom to top).

— Kalitvensk Suite: dark-grey silts and argilites with interlayers and blocks of sandstones and

micrites or detritic limestones (1-3.5 m). The detritic limestones contain: small foraminifera, fusulinids.

brachiopods, crinoids, conodonts and algae: plant remains and miospores are present in argilites and

sandstones. This suite corresponds to the two lowermost Asselian biozones: Ultradaixina bosbytauensis-

Daixana robusta zone (Orenburgian in IZART el al„ 1998) and Sphaeroschwagerina fusiformis zone;

thickness of the suite is 1 18 m.

— Skosyrsk Suite: mainly limestones with thin (up to 1.2 m) argilite and marl interlayers. The

limestones as well as in the Kalitvensk Suite contain diverse fauna and calcareous algae. The suite

corresponds to the two biostratigraphical zones: Sphaeroschwagerina moelleri-Pseudofusulina fecunda

zone and Sphaeroschwagerina sphaerica-Pseudofusulina firma zone; thickness are 81.6 m and 42.6 m.

The usual thickness of the Asselian here is about 242 m.

In the Precaspian Depression, a deep water Asselian basin is now well known. The reef belt is traced

along the northern and northwestern border of the Precaspian depression. On palaeogeographic maps

(Figs 10, 11, 13), is shown a shallow-water sea with essentially carbonate sediments and organic build¬

ups. As we saw before, in the Astrakhan borehole, in the middle part of the argilite-marl sequence (in

stratigraphical interval between early Bashkirian and Artinskian), there are many reef limestone

fragments without any mixture of the terrigenous material. The area of baring should be located very

close to the south of the Precaspian depression border. It is important to note also, that some horizons of

carbonate breccias with numerous reef fragments were established within Asselian interval of the

borehole on Busachi Peninsula (23 on Fig. 6) immediately to the south of the discussed area

(Kartseva, 1979).

The distribution of the Asselian marine sediments in the region of western and southern parts of the

Aral Sea (Turanskian Sea in palaeogeographic mean) is also rather probable from results of geophysical

researches. There are direct borehole data (Figs 7, 13) which prove the existence of carbonate and

terrigenous Asselian rocks in the western and south-western areas of Aral Sea (KARTSEVA & KiRUKHIN,

1974). The wide distribution of them in Tyan Shan-Pamir region is supported by series of sections in

Fergana and Darwas areas (BENSH, 1982; LEVEN & TSCHERBOVICH, 1978).

Asselian palaeobiogeography

The palaeogeographic situation (Figs 10 and 13) is supported by the biogeographical data. During the

Asselian, very diversified and rich fauna and algae flora exist and the basin have its largest expansion.

The diversity falls down during the middle Asselian ("moelleri-fecunda 7 ' time). The taxonomic variety

of the biota is favoured by the wide biogeographical communications. An homogeneous fauna is present

226

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

on whole Preuralian Sea (CHUVASHOV. 1991) with slight differentiation to the north which could be

explained by a low decreasing of water temperature in south-norlh direction. Indeed, almost same

sediments are deposited along the western Hank of Urals Mountains with a general similar fauna. The

main differentiation is recorded in fusulinids with two assemblages.

A typical Tcthyan genus (Ultradaixina) from the base of the Asselian, is distributed only in the south

of the Urals and' Preuralie and is not known north of 51°30N. A group of the Tethyan genera

( Dutkevichia, Likharevites, Dutkevichiles) grows at 55°N. Between 55° and 58°N. the species diversity

of the genera Rugosofusulina and Paraschwagerina is strongly reduced. Quite the reverse,

Pseudofusulineila and Globifusulina (G. krotowi, G. mix, G. caudata), rare or absent in southern

latitudes, become very abundant, especially in the Middle, Northern and Polar Urals. This differentiation

between fusulinid fauna of the northern and southern flanks of the Preuralian Sea becomes more marked

during the Sakmarian.

The fusulinids of the Donetsk Gulf ( Ultradaixina , Dutkevichia, Likharevites without

Pseudofusulineila and Globifusulina) have a significant similarity with the South Uralian and Tethyan

assemblages. A free communication between the Donetsk Gulf and the Tethyan Sea and a rather

complicated relation with the Preuralian Sea (through Prccaspian deep-water sea and waters with high

salinity of the Volga-Kama Sea) can explain this phenomenon.

Almost the same regularity could be noted in the distribution of calcareous algae. Rich assemblage is

established within the reef facies and it is possible to compare them along the Preuralian Sea and with

other basins. There is a more diversified algae association in the Asselian-Sakmarian reefs of the

Southern Preuralie (KUI.IK. 1978; KULIK et al., 1978). This association is recognised (CHUVASHOV,

1974) as far as the latitude of Perm (58°N) with the genera: Tubiphytes, Anchicodium, Eugonophyllum,

Neoanchicodium, Globuliferoporella, Epimastopora, Pseudoepimastopora, Gyroporella,

Sphaenoporella, etc. In the North Urals, this list is reduced to Tubiphytes, Epimastopora and

Pseudoepimastopora. At least, in the Near-Polar Urals (65°40N), only numerous Tubiphytes are found

in the reef limestones.

An interesting conclusion could be drawn from the comparisons of the Uralian alga assemblages with

the associations from other parts of the Asselian ocean. The richest Asselian alga assemblage has been

studied in the Karachatyr Mountains (KHODZHANYAZOVA, 1991). This alga flora is close to Carnic Alps

(FLUGEL, 1966) and Slovenia (KOKHANSKY & HERAK, 1960) coeval assemblages. There is a possibility

to adopt for these points the same palaeolatitude. The Southern and Middle Uralian alga association

could be compared with the assemblage of the Arctic Canada (MAMET et al 1987) and the

palaeolatitudes of both areas could be similar.

The penetration of some Tethyan brachiopod genera and species, along the Preuralian Sea up to

58°N (Kalashnikov, 1998), can give an additional information about free relation and permanent

exchanges between the Tethyan and Eastern European faunas.

ARTINSKIAN AGE

The Artinskian stage is subdivided into two substages: lower and upper (Table 1). The lower

substage includes (from bottom to top) two horizons, Burtsevskian (Pseudofusulina concavutas - P.

pedissequa zone) and Irginskian (Pseudofusulina juresanensis zone). The upper substage contains

Sarginskian (lower) and Saraninskian horizons. The Sarginskian horizon corresponds to the Parafusulina

solidissima zone. The Saraninskian horizon does not contain fusulinids and its bottom is marked by the

first occurrence of the conodont Neostreptognathodus pnevi. This level could be used for interregional

correlation. In the Preuralian Sea, the Saraninskian horizon could be defined by small foraminifera,

bryozoans, ostracods and miospores. The complete correlations of the Artinskian fusulinid, ammonoid,

ostracod and conodont zones were given by CHUVASHOV et al. (1994).

Source: MNHN. Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

227

Timan Archipelago

Arkhangelsk

Chelyabinsk

Volga-\;

Island -

Kazan

nver

amara

Smolensk

Precaspian Sea

Volgograd

Astrakhan

,«»l lllll

ICaspian Archipelago

11111111111111

Turanskian Sea

60°

55°

-50°

60°

ARTINSKIAN

West Siberian Land

7 L

/ CENTRAL

y EUROPEAN LAND

./ Eastern European Basin

.7 Eastern European Basin^p 0^ (Preuralian Sea)

7 ( Volga - Kama Sea)

A ZEE SE

•V-7 V v - s \ - V * - g ~

Moscow

500 km

Fig. 14. Palaeogeographic map of the Eastern European Basin during the Artinskian. Legend: see Fig. 2.

Fig. 14. — Carte paleogiographique dit Bass in Est Europeen durant I'Artinskien. Legende : voir Fig. 2.

Source: MNHN, Paris

228

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

Artinskian palaeogeography of Eastern European Basin

During the Artinskian. there is the strong reduction of the Eastern European Basin area; its width at

Moscow latitude is up to 500 km including about 100 km of the Preuralian Sea, where deep-water

conditions of sedimentation and relatively rich biota are preserved (Figs 14 and 15). Important

palaeogeographic changes took place in the junction area of the Preuralian Sea and Tethys Basin.

During the second half of the Sakmarian and the early Artinskian. the sea left a large part of the modern

Tyan Shan and Pamir territories, except its southeastern part. Most part of the Turanskian Sea (near the

Aral Sea) also disappeared. Marine conditions were probably saved in the south of the Precaspian Sea.

In the second half of the Artinskian, an extensive transgression of the Tethys began, but its influence

did not carry on for long, and at the beginning of the Kungurian, on the whole territory of the Eastern

European Basin, an extensive shallow-water lagoon with evaporite accumulation is established. A deep¬

water evaporite sedimentation took place in the Precaspian Depression: anhydrites, potash and salt.

Exceptionally, in a narrow stripe of the Preuralian Sea, contiguous to the Palaeourals, the influence of

fresh water and periodical transgression from the north (Arctic Basin) established, for a short time,

normal marine conditions.

The characteristic Artinskian facies of the Eastern European Basin are present along the Palaeourals

Mountains. A regular east-west row of facial zones (I to V: Figs 16-17) could be traced along of the

Preuralian Sea (F^gs 15-17). A concise description is given below.

The first facial zone (I) is composed of an alternation of coarse-grained sandstones, gravelstones,

pebble and boulder conglomerates with some packets of sandstones, silts and argilites. Numerous

olistostromes (2-50 m thick) could be present in this sequence. These sediments contain a rather rich and

diversified fauna (fusulinids and small foraminifera, colonial and solitary corals, bryozoans, bivalves,

brachiopods, ammonoids and nautiloids, crinoids, trilobites, ostracods, fish and conodont remains).

Large (up to 3-5 m) wood trunk and numerous leaves could be met locally. This series, which can be

named “coarse Ilysh^. is distributed in wide areas (Figs 14-17). From north to south, in some areas,

these sediments are replaced by a sandstone-silt-argilite sequence: area between the Vaigach Island and

the Tschugor River (from 70° 15 to 64° 10N); area between the Vishera and Kosva Rivers (from 60°20 to

58°30N); basin of the Jurusan and Ay Rivers (between 55°30 to 55°N).

The whole territory of the Western Urals could be divided into two large areas, the boundary

between them is located at 6I°N. The southern part of this area is characterised by relatively rich and

diversified fauna. The Artinskian sediments of the large territory north of 61°N (Pechora River Basin)

contain uniformly very rare organic remains (Chuvashov, 1991). It could be explained by the gradual

decrease of the water temperature. The thickness of this sequence varies from 700 to 2000 m.

For the Preuralian Sea whole territory, a very important regularity can be marked in the construction

of Artinskian terrigenous sequence. Its lower part, which corresponds to Burtsevskian and Irginskian

horizons (Table 1), is represented by relatively thin-grained sediments, argilites, silts and sandstones.

The Sarginskian horizon is composed by more coarse-grained deposits: conglomerates and gravelstones,

coarse-grained sandstones; to the west, this sequence is formed essentially by sandstones. In the

uppermost horizon, Saraninskian, relatively thin-grained terrigenous sediments prevailed in the eastern

part of the facial zone; argilites, marls and limestones are common westwards. This sediment fineness

reflects two very important events: tectonic movements in the Palaeourals folded belt and change of the

ocean level and the late Artinskian transgression.

The next facial belt (II) is represented by “thin flysh", an uniform alternation of sandstones and

argilites with rare thin (5-15 cm) micrite, marl, detritic limestone and silt interlayers. Thickness of

sandstone and argilite beds are usually 5-30 cm and could reach sometimes 50-70 cm. The organic

remains are rarer in this facial zone than in the previous one and can be divided into two groups:

allochthonous in sandstone turbidites beds with foraminifera (including fusulinids), bryozoan and

brachiopod fragments, ammonoids, crinoids, calcareous algae; autochthonous in argilites, marls and

limestones with small foraminifera, radiolaria, sponges, bivalves, trilobites, ostracods, fish remains and

conodonts.

Source ; MNHN , Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

229

Fig. 15.— Palaeogeographic map of the Preuralian Sea during the Artinskian. A-Al and B-Bl: position of profiles represented

on Figs 16 and 17. Legend: see Fig. 2.

FlG. 15 .— Carle paleogeographique de la Mer Preouralienne dur'nt ’’ Artinskien. A-Al et B-Bl : position des profits des Figs

16 et 17. Legende : voir Fig. 2.

Source: MNHN, Paris

230

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

These more deep-water sediments are traced throughout the Preuralian Sea. The thickness of sections

near the eastern border of this zone is up to 1000-1200 m. The western boundary of this belt is defined

by dominance of argilites, marls and micritic limestones with rare interlayers of sandstones and silts; the

thickness is about 150-200 m.

To the west, a next facial zone (III) is represented mainly by carbonate-clay sediments; in the eastern

part of this belt, there are some interlayers of sandstones and silts; the western sequence contains

numerous beds of limestones and marls. A very rich and diversified fauna exists on the western part of

the zone: small foraminifera and fusulinids. radiolaria (locally), calcareous and siliceous sponges, corals,

brachiopods, bivalves, bryozoans. ammonoids and nautiloids, trilobites, fishes, crustaceans, ostracods,

conodont-bearing organisms. The thickness of the upper Artinskian substage varies from 80 to 200 m.

Westwards, the fourth zone (IV) is composed of similar carbonate-clay deposits, but here they

contain locally numerous organic build-ups. which could be treated like patch-reefs. The reef thickness,

in the eastern part of the zone, can be up to 300 m, in the western part it decreases to 10-20 m and

locally only some metres. These reefs are constructed by numerous Tubiphytes , stromatolites, and (more

rare) phylloid algae, bryozoans and brachiopods.

The westernmost facial zone (V) is considered as part of the Volga-Kama Sea. The Artinskian is

represented by an uniform sequence of dolomites and dolomitic limestones with small foraminifera,

single and colonial corals, bivalves and brachiopods. The thickness is about 100-150 m and quickly

decreases to the west. The western territory, on the whole, is occupied by a shallow-water sea with

significant increase of salinity. The sediments of the Volga-Kama Sea area are represented by dolomites

only, with uniform and scanty organic remains: rare levels with small foraminifera, colonial corals,

brachiopods and bivalves. Anhydrite beds and packets are locally distributed in the Artinskian sections

of the Volga-Kama Sea eastern and central parts and are present almost everywhere near the western

border of the basin (Figs 14-17).

w E

v IV III II i

Fig. 16.— Palaeotectonical and facial profile (W-E) of sediments during the Artinskian. through southern part of the Preuralian

and eastern part of Volga-Kama Seas (Orenburg latitude). A-Al: position of profile on Fig. 15. Legend: see Fig. 2.

Arrows show most important sections. Roman numbers locate the different facial belts.

F/G. 16 .— Profit paleotectonique el faciologique des sediments de I'Artinskien d trovers la partie medicine de la Mer

Preouralienne et de la partie orientate de la Mer de Volga-Kama. A-A! : position dn profil sur la Fig. 15. Legende :

voir Fig. 2. Les fleches positionnent les coupes les plus importantes. Les chiffres romains positionnent les differentes

zones de facies.

Source: MNHN , Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

231

Fig. 17.— Palaeotectonical and facial profile (W-E; NW-SE) ihrough the middle part of the Preuralian and eastern part of

Volga-Kama Sea (Perm latitude). The position of this profile (B - B1) on Fig. 15. Legend see Fig. 2. Arrows show most

important sections. Roman numbers locate the different facial belts.

FlC. 17 .— Profit pfildotectonique et faciologique des sediments de l'Artinskien a trovers la partie meridionale de la Mer

Preouralienne et de la partie orientate de la Mer de Volga-Kama. B-BI : position du profit sur la Fig. 15. Legende voir

Fig. 2. Les fleches positionnent les coupes les plus importantes. Les chiffres romains positionnent les differentes zones

de facies.

These facial zones (I-V) are traced from the southern part of the Preuralian and Volga-Kama Seas as

far as the region of the Precaspian Sea. The facial zones I and II are followed along the eastern boundary

of the Precaspian Depression (Avrov et at ., 1962; Avrov & KOSMACHEVA, 1963; AlSENSTADT &

PlNCHUK, 1961: TURKOV & Umirshin. 1980) (Fig. 18). The very large central part of the Precaspian

Depression is filled by sediments very similar to the deposits of facial zone III. The facial zones IV and

V could be easily recognised along the northern and northwestern rims of the Precaspian Depression

(Fig. 14).

Along the edges of the Precaspian Depression, the Artinskian sequences were studied in numerous

boreholes. We give below concise informations, because the stratigraphy problem of the depressional-

type sequence was discussed before during description of the Moscovian and Asselian stratigraphy and

palaeogeography.

To the south of the reef formation of the Karachaganak oil field (Ilyn et at ., 1987) on the northern

border of the Precaspian Depression, above the Bashkirian limestones, there are black argilites with rare

interlayers of micrite, marls; the thickness is 14-57 m. The upper part contains Artinskian radiolaria and

miospores.

Similar sediments, drilled by the Astrakhan borehole (MOVSHOVICH, 1977) reach 160 m; some beds

of silts and fine-grained sandstones are present in the upper part of the sequence. Artinskian radiolaria.

ammonoids and miospores were recognised here. The presence of terrigenous sediments in the southern

part of the Precaspian Depression is explained by the appearance of the low mountain ridge (Karpinsky

Kryazh) along the southern border of the Precaspian Depression. Between this border and the Karpinsky

Kryazh, the next Artinskian terrigenous sediment sequence, from bottom to top, is the following

(Levina etal ., 1991):

— Visikovsk Suite (50-1000 m): alternation of sandstones, silts and argilites; with early Artinskian

fusulinids and ammonoids;

— Tabolassk Suite (80-500 m): silts and sandstones with fusulinids and ammonoids;

Source:

232

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

— Tinaks Suite (50-300 m): argilites, marls and limestones with marine organic remains. The wide

distribution of carbonate sediments could prove that the Karpinsky Kryazh was covered by the sea at

end of the Artinskian.

The boundary between lower and upper Artinskian is located in the middle part of the Tabolassk

Suite. It is very important to note that the three Artinskian terrigenous sequences are easily recognisable

also near the Precaspian Depression. It can be used as an additional feature for correlation and

reconstruction of the geological history.

Near the eastern border of the Precaspian Depression (Yuzhno-Embensk uplift. Fig. 6) above the

lower Bashkirian limestones, there is a rather thick (225 m) member of black argilites. marls and

micrites (LAPKIN & MOVSHOV1CH. 1994). Artinskian miospores were found in the upper part of this

sequence.

Along the eastern border of the Precaspian Depression, in Tengiz (22 on Fig. 6) and Karaton (7 on

Fig. 6) oil fields, above the Bashkirian limestones, numerous boreholes drilled a sequence of black

argilites, marls, spongy limestones and carbonate breccias with a maximal thickness of 300 m

(ZOLOTUKHINA et aC. 1989; COOKer al„ 1994). The upper part belongs, without doubt, to the

Artinskian.

This information allows to conclude that the Precaspian Depression, on the whole, is filled

essentially by clay sediments with rare interlayers of cherts, marls and limestones. Some sandstones and

silts are present in the lower and in the lower upper Artinskian substages along of the southern,

southeastern and eastern rims of the depression. The thickness of Artinskian. near the outer border ot

depression, could be some dozens of metres; a thicker section should exist along southern and eastern

borders. In the central part of the depression, the thickness of the Artinskian, essentially clayey, could be

some metres only.

Artinskian palaeobiogeography

There is an important problem for the reconstruction of the Artinskian palaeogeography in the area

located south of the Eastern European Basin edge. All informations given above confirm the thesis that

a continuous sedimentation took place during the Artinskian in the Preuralian Sea. In the Tethyan Basin,

the situation is totally different. The nearest best studied sequence (Fergana Valley; BENSH, 1982)

shows that the upper part of the Dangibulak Horizon (early Sakmarian) is represented by lagoon facies,

but at the same time, in the Darvaz region (Western Pamir), Dangibulak and Uluk (late Sakmarian)

horizons are represented by marine sediments. These data could be used to assess the slow retreat of the

Tethys (Turanskian and Pamir-Tyan Shan Seas) shore line to the south.

We have no data about the lower Artinskian sediments on the eastern territories presented in the

figure 18. The suggestion of a wide distribution of a sedimentation break on the territory of the Middle

Asia and Pamir during early Artinskian could be realistic. The large scale of this break could be

confirmed by biostratigraphic researches in China (CHUVASHOV, 1984; LEVEN el al., 1996).

The next Tethyan transgression northwards could be dated from late Artinskian or, more

exactly, from Sarginskian and Saraninskian. The significant similarities between some groups of late

Artinskian fauna (brachiopods, bryozoans, ammonoids) could be used for reconstruction of the

communications between the Eastern European and Tethyan Basins. A possible way for these

connections could be a narrow strait in the jointed area between Karpinsky Kryazh and Mugodzhary

Peninsula. This palaeogeographic situation is represented on the map (Fig. 18).

CONCLUSION

The palaeogeographic situation for an investigated series of time slices (Moscovian, Asselian and

Artinskian) reflects, in full, the evolution of biota and sedimentogenesis of the Eastern European

sedimentary basin and its connection with the Tethys.

Source: MNHN, Paris

PALAEOGEOGRAPHY OF EASTERN EUROPEAN BASIN DURING UPPER PALAEOZOIC

233

Preuralian Sea

50° 54° 58° 62° 66° 70° 74° 78° 82° 86° 90°

Fig. 18.— Palaeogeographic map of jointing area of the Eastern European and Tethyan Basins during the Artinskian.

Legend: see Fig. 2.

FlG. IS .— Carte paleogeographique de la zone de jonction des Bassins Est Europeen et Tethysien a I'Artinskien.

Lege tide : voir Fig, 2.

The Moscovian stage is characterised by wide and free connections between EEB and Tethyan seas;

the communications between these two large global Carboniferous and Permian water-bearing domains

are significantly reduced during Early Permian. The boundary between the Eastern European Basin and

the Tethyan Basin can be determined on the basis of biogeographical data. For the Moscovian, it can be

traced on 55°N latitude. To the south of this latitude, the composition of fusulinid assemblage varies;

among brachiopods and algae, there are numerous Tethyan genera and species. During the Asselian,

some typical Tethyan fusulinid genera reach the 55°N latitude, but the ammonites community of the

Eastern European Basin stays different from Tethyan association. According to these data, the boundary

between the Eastern European and Tethyan Basins for the Moscovian and the Asselian can be traced on

55°N latitude. During the second half of Sakmarian and Artinskian, the boundary between these basins

is displaced to the south. The fusulinids of the Eastern European Basin (up to the southern margins of

the Precaspian sea) are clearly different from Tethyan ones. For the Artinskian, the boundary between

the EEB and Tethyan Basin biotas can be traced on 40°N latitudes.

The palaeogeographic reconstructions allow to assume the wide development of marine, including

carbonated, Middle-Late Carboniferous sediments on territory of the Caspian Sea (from the Karpinsky

Kryazh, to the south, and on the whole area of Caspian up to Aral); that significantly increases the

potential for oil and gas fields of this age on the extensive territory of the Turansk plate.

Source: MNHN , Paris

234

BORIS I. CHUVASHOV & SYLVIE CRASQUIN-SOLEAU

New studies confirm that a Precaspian deep water basin was generated during late Bashkirian time

and remained up to the end of Artinskian; during the Kungurian, this deep water depression was filled

by thick Kungurian and Late Permian evaporates.

During the second half of the Sakmarian and the first half of Artinskian. the EEB were almost

completely isolated from the influence of Tethyan biota, due to the appearance of an extensive land on

the modern territories of Northern Precaspian, Prearalian and Tyan Shan. Mutual palaeobiogeographical

isolations of EEB and Tethyan seas was also determined by the depth of Precaspian Basin and the

salinity increase in the greatest part of the Volga-Kama sea.

ACKNOWLEDGEMENTS

The authors are very grateful to the reviewers of the paper, Pr Maurizio GAETANI (University of

Milano) and Dr Alain IZART (Universite de Metz). We thank very sincerely Michel PETZOLD

(Universite Pierre et Marie Curie, Paris) for the drawing of maps and profiles.

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Source

Palaeotectonic conditions of Cretaceous basin

development in the southeastern segment

of the Mid-Polish Trough

Jolanta SWIDROWSKA & Maciej HAKENBERG

Institute of Geological Sciences, Polish Academy of Sciences. Twarda 51/55, 00-818 Warszawa. Poland

ABSTRACT

The analysis of the deposit accumulation rates, treated as a reflection of subsidence rates, coupled with the recognition of

sedimentary conditions, made possible to distinguish synsedimentary fault patterns for six time-spans of the Cretaceous. The

zones of major subsidence gradients were interpreted as synsedimentary faults. They determined the location of palaeouplifts

and depocentres. Two main fault zones were distinguished which separated the axial part of the trough from its marginal

portions. Asymmetry of the basin, observed in its transversal section up to the Turonian (inclusive), resulted from these

discontinuities. The axis of subsidence was shifted towards the NE boundary of the trough until the Cenomanian, during the

Turonian it was shifted towards the SW boundary. Since the Coniacian, the role of the bounding faults decreased. Subsidence

increased at the beginning of the late Albian transgression; however, the rate of sediment accumulation during the Albian did

not reach high values. The significant increase of subsidence during the Turonian, combined with the synsedimentary activity

of the southwestern zone of the bounding fault, shows the important role of a tectonic factor for the basin opening. We made an

attempt to determine palaeotectonic conditions controlling basin development. The evolution of palaeostress fields has been

proposed on the basis of the fault patterns. A clockwise rotation of a strike-slip stress field occurred, during Cretaceous times. It

is expressed by a change of the WNW-ESE azimuth of a, axis, deduced for the Early Cretaceous, to the NE-SW direction at the

end of Cretaceous time. This rotation was followed by variation of character of strike-slip movement component along

Teisseyre-Tornquist Zone: from sinistral component (till the middle Albian) to the dextral one (from the Turonian till inversion

time). Basins developed in the transtensional regime till the end of the Turonian and later in the transpressional regime. The

succession of palaeotectonic conditions of Cretaceous basins opening seems to be compatible with the relative movements

between Africa and Eurasia plates during this time.

RESUME

Conditions paleotectoniques de developpement du hassin cretace dans la partie sud-est du Bassin Polonais.

Le taux d’accumulation des sediments est analyse et interprets comme le reflet du taux de subsidence. II est couple a

I’identification des environnements sedimentaires dans le but de reconstituer le reseau des failles synsedimentaires. Le Cretace

est divise en six periodcs caracteristiques. Les zones de fort gradient de subsidence sont assimilees a des failles

SWIDROWSKA, J. & HAKENBERG, M.. 2000.— Palaeotectonic conditions of Cretaceous basin development in the

southeastern segment of the Mid-Polish Trough. In: S. Crasqi'IN-Solhai & E. Barrier (eds), Peri-Tethys Memoir 5: new data

on Peri-Tethyan sedimentary basins. Mem. Mus . natn. Hist, nat .. 182 : 239-256. Paris ISBN : 2-85653-524-0.

Source: MNHN. Paris

240

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

synsedimentaires. Ellcs individualisent des domaines dc soulevemcnt ct de depot-centre. Deux zones faiI lees principales

limitent la panic axialc du bassin. En coupe transversale. le bassin apparait asymetrique en raison du jcu des deux zones faillees

principales jusqu'au Turonien (inclus). Des le debut du Cretace et jusqu’au Cenomanien, le depot-centre est situe sur la marge

NE du bassin. Puis pendant le Turonien. le depot-centre bascule sur la marge SW. A partir du Coniacien. le role des failles

bordant le bassin diminue. Lors de la transgression a I'Albien superieur, le taux de subsidence augmente. Cependant, le taux

d’accumulation des sediments pendant EAlbien n'atteint pas de fortes valcurs. Au contraire, la hausse de la subsidence pendant

le Turonien s’accompagne d'un taux eleve d'accumulation des sediments. Celle periode est de plus caractcrisee par I’activite

synsedimentaire dc la zone faillec dc la marge SW. confirmant le role majeur de la subsidence tectoniquc. Nous avons tente de

reconstitucr les conditions paleo-tectoniques controlant le developpement du bassin. Lcs reseaux de failles sont interpretes cn

termes de champs de contraintes. Pendant le Cretace. le regime decrochant evolue cn tournant dans le sens horaire. II s’ensuit

un changement de sens de la composante decrochante le long de la Zone Teisseyre-Tornquist. Jusqu'a I'Albien moyen. la

composante decrochante est senestre. Elle devient dextre a partir du Turonien etjusqu’a I'inversion tectonique du bassin. Le

bassin se developpc dans un regime tectonique transtensif jusqu'a la fin du Turonien. puis le regime tectonique devient

transpressif. L’evolution du contexte paleo-tectonique controlant I’ouverture du bassin cretace est compatible avec le

deplacement relatif des plaques Afrique et Eurasie a cette epoque.

INTRODUCTION

The Mid-Polish Trough (MPT) developed during Permian and Mesozoic times (DADLEZ, 1989:

DADLEZ et a!.. 1994. 1995) over the Trans European Suture Zone (TESZ) joining the Eastern European

Platform of Precambrian and the Western European Platform formed by the Palaeozoic orogens. In

Poland, the northeastern part of the TESZ coincides with the Teisseyre-Tornquist Zone (TTZ), a crustal

weakness zone extending from Scania through Bornholm south-easterly to the Black Sea (GUTERCH el

cil., 1994: DADLEZ. 1997; BERTHELSEN, 1998). At the turn of the Maastrichtian/Early Tertiary an

inversion of the trough occurred and the Mid-Polish Swell has originated with two adjacent synclines

(Fig. 1).

The investigated area is located around the Palaeozoic of the Holy Cross Mountains (HCM). From

the palaeotectonic point of view, the studied area includes three distinct regions. The first was connected

with the axial and near-axial parts of the Mid-Polish Trough extending southeastwards. The subsidence

and the thickness of sediments in this region during the Permian and the Mesozoic were relatively of

high values, and breaks in sedimentation and erosional episodes were rare and short. The second and

third regions situated on both sides of the trough occupy the present areas of the Miechow Syncline and

the Warsaw-Lublin Syncline. Reverse trends in sedimentary conditions as compared with those in the

Mid-Polish Trough are the characteristic features of both zones (GLAZEK & KUTEK, 1970; DADLEZ.

1989: MORAWSKA. 1996; HAKENBERG & SWIDROWSKA. 1996. 1997).

We have tried to reconstruct the palaeotectonic conditions, which controlled basin development. An

analysis of subsidence and tectonic factor for all MPT was carried out by STEPHENSON (1993) and

DADLEZ et al. (1994. 1995). A restriction of studied area to southeastern part of MPT allowed to show

similar problems in more detail and to focus our efforts on the identification of synsedimentary faults.

We based our analysis on the relationships between sedimentation, basin subsidence and fault activity.

Data were acquired from outcrops of the Cretaceous and from wells situated in the marginal synclines.

Both archival and published descriptions of profiles were analysed (HAKENBERG & SWIDROWSKA.

1998). Abundant bibliography dealing with Cretaceous sediments in the Mid-Polish Trough is contained

in the papers of ClESLINSKl & POZARYSKI (1970) and MAREK & Pajchlowa (1997).

METHODS

This study is based on the thickness and lithofacies patterns. The thickness maps for particular stages

of the Cretaceous (HAKENBERG & SWIDROWSKA, 1998) provided a base for palaeotectonic analysis.

Isopach maps compared with maps of regions of similar lithological successions made possible to

distinguish regions of different palaeogeographical locations in the basin.

Presently, the basin analysis is based on high-quality seismic profiles. In this case no effort has been

made so tar in this area to carry out a new seismic survey or to reprocess and reinterpret available

seismic sections. Synsedimentary breccias or poorly sorted conglomerates, as lithofacies that normally

Source: MNHN, Paris

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

241

PALAEOZOIC

PLATFORM

Krakbvv

CARPATHIANS

100km

EAST

EUROPEAN

PLATFORM

Warszawa

Lublin

Fig. I.— Location of investigated

area. 1. Palaeozoic; 2, Triassic and

Jurassic of the Polish Swell; dash¬

ed line, boundary of Teisseyre-

Tornquist Zone; closed triangle

line, boundary of Carpathian

thrust.

FIG. I .— Localisation de la zone

d'etude. 1. Paleozoic/tie ; 2. Trias

et Jurassic/ue du "Polish Swell" ;

grands tirets, limite de la Zone

de Teisseyre-Tomquist; ligne a

triangles noirs, limite des chevau-

chements des Carpates.

ai ; e f ° rm f d at the /oot of underwater fault escarpments developing on the basin floor, could not be

identified in any of the profiles.

Only an indirect way could be employed in an effort to identify synsedimentary faults when there is a

lack ol geophysical and lithological evidences. Zones of relatively fast changes in the basin subsidence

have been considered as testifying the activity of synsedimentary faults. They are visible on the maps

where isopachs or isolines of rates of persistent accumulation of sediments are dense and probably also

document high gradients oi subsidence rates. Synsedimentary faults delineated this way. may have acted

in the basin basement without reaching its floor or producing a fault-scarp relief and high-energy, poorly

sorted sediments. It is most likely that in upward direction they decreased, passing in flexures; their

synsedimentary role resulted in a differentiation of subsidence rate of the basin floor (Fig. 2).

A comparison of facies and isopach patterns was also used in the analysis of tectonic subsidence and

the identification ol synsedimentary faults. Where the isopachs and lithofacies boundaries are parallel to

each other it means that the subsidence was a decisive factor governing the sedimentary conditions in

this part of the basin: the rate of subsidence was often higher that "the rate of sedimentary infill.

Recurrent coincidence of lithofacies boundaries with zones of increased thickness gradients was

considered a strong argument for the identification of synsedimentary faulting.

Transverse faults can be inferred where rapid changes of isoline directions occur, though in this case

a later origin of such faults cannot be excluded. Sometimes only local disturbances are visible in general

isoline course which may indicate mechanical weakness zones, probably of fault origin. Such a situation

can be reflected by a local increase in the accumulation of sediments.

The interpolation of facies boundaries and of isopachs was based on well data (black circles on Fie.

3). As some of these wells are situated at large distance one from another, faults shown on the Mesozoic

map of this area were taken into consideration when the facies boundaries and the isopachs were plotted.

An assumption was made that the faults manifested during inversion might have been active earlier as

synsedimentary faults.

242

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

65Ma

sandy limestonos and

calcareous sandstones

IrFH oligosleginian limestones

EE3 chalk

b ~ m limestones

E3 9 aizes

B5 spongolites

f' twodasts

• terruglnoous colds

phosphorite

Cenomanian

upper Albian

Maastrichtian

Campanian

Fig. 2. Chronostratigraphic diagram of lithofacies and sedimentary environments characteristic for Holy Cross segment of the

Mid-Polish Trough (after Hakenberg & Swidrowska. 1998, modified). 1-4. fault zones reflected in facies changes;

main fault zones 1. Przedborz - Checiny - Mielec fault. 2. Nowe Miasto - Ilza fault.

Fig. 2. Diagramme chronostratigraphique des lithofacies el des environnements caracieristiques de la Montague Sainte

Croix. Bassin Polonais (d'apres Hakenberg & Swidrowska. 1998, modifie). 1-4, zones de failles marquees dans les

changements de facies ; principals zones de failles 1. faille de Przedborz - Checiny - Mielec. 2. faille de Nowe Miasto

- Ilza.

Source: MNHN. Paris

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

243

GENERAL EVOLUTION OF DEPOSITIONAL CONDITIONS

The development of lithofacies and the sequence of sedimentary environments are shown in a

synthetic way on the chronostratigraphic diagram (Fig. 2) based on a cross-section running’from

headwaters of the Pilica River through Radom to the line of the Wisla River (Fig. 3). Two sedimentary

megacycles are visible. The first one is a regressive member of the Jurassic-Early Cretaceous megacycle

(K.UTEK, !994), preserved in fragmentary way only and represented by sediments of the upper

Valangiman and lower Hauterivian. The second, the main Cretaceous cycle, is composed in this section

ol sediments o! the middle Album to the Maastnchtian (ClESLlNSKI & FbZARYSKI. 1970) Sedimentary

cycles of lower order, are recorded due to biostratigraphic documentation of stratigraphic gaps as well as

a detailed recognition of lithology. They include cycles of the Albian, the Cenomanian, a early part of

the lower Turonian. an upper part of the early to late Turanian, and the last, the Coniacian to the

Maastnchtian (ClESLlNSKI & POZARYSKI. 1970; WALASZCZYK, 1987, 1992; Hakenbf.rg 1986'

MARC1NOWSKI & RADWANSKI. 1983). They could not be included in the diagram.

Sedimentation began (Fig. 2) in the environment of a shallow siliciclastic shelf (mostly during the

Albian), then developed through the phase of the deepening siliciclastic shelf, with increasing content of

sdica derived from sponges (in Cenomanian depocentres). Then carbonate-siliciclastic shelf (in places,

during the Cenomanian and the Turonian) occurred and a carbonate platform with organodetritic

sedimentation (in the marginal zone of the Turonian basin) until pelagic environments developed. The

latter are characterised by the inflow of finest terrigenous fractions (marls and siliceous marly chalk).

They appeared in the central parts of the trough during the Turonian; later, they successively expanded

towards NE and SW. A pure carbonate pelagic environment was the last member of this succession; it

was deprived of the inflow of terrigenous material so chalk deposits could have developed. The

tendency of the earlier appearance of open-sea members is observed in the northeastern flank of the

trough by the way of a decrease of content of terrigenous material with an increased productivity of

carbonates instead.

The deepening sedimentary environments, with decreasing share of terrigenous material, are

contemporaneous with the disappearance of areas affected by erosion (also those without sedimentation)

which reflects the advancement of transgression. It reached its maximum during the Campanian. Till the

Campanian, the boundaries of inferred sedimentary environments were spreading, larger and larger area

became covered with pelagic facies and the areas of shallow shelf disappeared. Maastnchtian sediments

represent a regressive part of this megacycle, mainly in the axial and southwestern part of the trough.

SUBSIDENCE CHARACTERISTICS

In order to present changes in subsidence rates, a backstripping method is usually applied, so that

quantitative data of real thicknesses (before compaction) could be referred to selected time intervals.

These results for NW and central part of MPT were presented by DADLEZ et at. (1994, 1995). As such

method was unavailable in our work, a set ol 6 maps of preserved sediment accumulation rates was

plotted (Fig. 3). Ratios of sediment thicknesses to respective time intervals were determined (the ODIN

& ODIN (1990) time scale was used). In order to better compare carbonate sediments with clastic ones,

an approximate factor was used to multiply the values of thicknesses of clastic sediments (affected by

stronger compaction than carbonate ones). It should be noted that the time spans of gaps of various

origin (such as non-deposition, submarine erosion or uplifting combined with sub-aerial erosion) were

also used to select the stratigraphic time intervals (characterised on maps in Fig. 3). Rates of subsidence

can be, to some extent, an ‘‘artificial" effect of opposite movements of the basin floor. An assumption

can be made that, approximately, the range of subsidence is directly proportional to the rate of

accumulation of sediments.

244

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

NEOCOMIAN-

MIDDLE ALBIAN

36 My v

IRADOM

extent ol epigenetic erosion y

boreholes or outcrops

synsedimeniary faults with decreasing - Y

influence upon the subsidence ' '//■

hypothetical synsedimentary faults

'/////jbys/s

synsedimentary faults

with unknown throw /<^/%///

0 10 40 100

m/My

Source: MNHN, Paris

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

245

CAMPANIAN

11 My

KRAKOW t

m/My

Fig. 3. Maps ol sediment accumulation rates for the particular Cretaceous time-intervals (A-F). Localities:G. Groiec NM

™ £ omaszow Mazowiecki: PT.Piotrkow Trybunalski: Pd. Przedhor/.: R. Radomsko: K. Konskic: I.

\!r Mi Hpr a n yS n h 0siro ^ iec Sw , iet0 !P£ ski: ?’ Sand °“; St - Staszou : Ch. Chcciny: M. Miechow;

xAk* D ; P C w ^ ' DT * Dab [Owa Tarnowska: I. Tarnow. On map A extents of: a. late Berriasian: b. early

valanginian, c. late \ alangiman and early Hauterivian: d. Barremian and Aptian; e. middle Alhian.

Fig. 3.— Carles tin max d accumulation des sediments pour des intervalles de temps particuliers da Cretace (A-F) I ocalites •

O. Grojec ; NM Nowe Miasm ; TM. Tomaszdw Mazowiecki ; PT. Piotrkdw Trybunalski : Pd. Przedhor- • K

tt'- rt h ri K ° nSk “\, \ Z “, SK-Jtorzys/co-Kamienna : OS. Ostrowiec Swietokrzyski : S. Sandomierz : St.

Stasmu . Clt. Cherniy : M. Miechow : Me. Mtelec ; I). Debica ; DT. Dabrowa Tarnowska : T. Tarnow. Sur la figure

pension du Berrtasten :b. extension da Valangmten inferieur; c. extension da Valangmien superieur et de

I Haateuvien mferteur; d. extension da Barremien el de I'Aptien : e. extension de I'Albien moyen.

Neocomian-middle Albian

The character of subsidence from the Neocomian to the middle Albian (Fig. 3A) was complicated

due to substantial differentiation of sedimentary processes and erosion with time, combined with the

lrequent lack of biostratigraphic record. There is a discontinuous stratigraphic record, with stratigraphic

gaps noted on the contacts between: (I) middle Volgian-late Berriasian, (2) late Berriasian-early

Valanginian ( Platylenticeras ), (3) early Valanginian (Polvptvchites )-late Valanginian, (4) early

Hauterivian-middle Albian (KUTEK e/ al ., 1989). Transgressive pulses of increasing extents appeared

(op. cit.): (I) late Berriasian, (2) early Valanginian, (3) late Valanginian, and (4) middle Albian. Time of

erosion that changed the lines of extents of the Berriasian and early Valanginian was relatively short, as

it was limited by later transgressions (Fig. 3A). Only the extent of the late Valanginian and Hauterivian

sediments in the area between Radom and the Wisla River is, in main part, erosional as undetermined (in

respect of their age) sediments conventionally considered Barremian and Aptian (MAREK. 1983) are less

extended and located north of the Pilica River.

Source

246

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

The extents of sediments of the first two transgressions are closely connected with the axial part of

the trough, two consecutive transgressions also comprise a part of its eastern margin. However, all of

them were connected with the NW-SE direction. The transgressions that followed during the late

Valanginian and the middle Albian were facilitated by the activation of the Nowe Miasto-Ilza fault of

the same direction (Fig. 3A). This fault was synsedimentary active already in the Early and Middle

Jurassic (HAKENBERG & SWIDROWSKA, 1997).

The two longest regressive events document the uplifting of the central part of the area, the axis of

which extends accordingly to a line running WNW-ESE (Fig. 3A) through Radomsko-Kielce-

Sandomierz (Vistula Swell: CIESLINSKI, 1976; Meta-Carpathian Arc: KUTEK et al ., 1989; KUTEK.

1994). The first was at the turn of the Jurassic/Cretaceous, and the second one, comprised the

Barremian-early Albian. The Purbeckian facies of the early and middle Volgian are present north of the

Piotrkow Trybunalski-Radom line and sediments considered to be of Barremian-Aptian age occur

exclusively north of the Pilica River (Fig. 3A). It is accepted that the expansion of Tethyan species of

ammonites was connected with transgressions while periods of regressions showed domination of boreal

forms (KUTEK & Marcinowski, 1996). It is a question whether the appearance of tethyan/boreal fauna

resulted only from sea level changes or from tectonically facilitated communication between Tethyan

and boreal domains. The different structural directions observed in transgression and regression time

spans can be admitted as contra-argument against the exclusive role of an eustatic control.

The first period of development of the Cretaceous basin (36 My; Fig. 3A) exhibits a very low rate of

accumulation of sediments. A fault along the lower course of the Pilica River (the line running through

Tomaszow Mazowiecki-Nowe Miasto-Grojec) was active. Transversal asymmetry of the middle Albian

basin changed along its line, and the axis of depocentre became Z-shaped. Its action in earlier times

(Berriasian-Aptian) resulted in more intensive subsidence in the N and NNE areas.

Late Albian

The trangression in the late Albian is a continuation of the transgression started in the middle Albian;

however, its range is different qualitatively and quantitatively as this transgression covered a dominant

part of the area and the sediment accumulation rate has considerably increased (Fig. 3B). The Nowe

Miasto-Grojec fault was only a weakness zone, which caused an increased subsidence there. Tectonic

activity during the late Albian affected mostly the western part of the area, where a set of short faults

delineating elevations and depocentres of NW-SE direction has developed along the upper course of the

Pilica River. In this zone of N-S to NNE-SSW direction, the Pilica fault was intensively active during

the Permian till Middle Jurassic (Morawska. 1996; HAKENBERG & Swidrowska, 1996). The Pilica

fault was inherited after the Late Palaeozoic structural setting. It was rejuvenated during the Albian and

is manifested in this basin as a zone of several small oblique faults.

Cenomanian

The main axis of the trough remains in the place where it was previously (between Kielce and

Radom, Fig. 3C). However, the location of a new subsidence depocentre shows that a rigid (so far)

southwestern rim ot the trough has lost its stability. This is a continuation of the process that started

during the late Albian, although elevated and depressed areas are inversed. The Albian peninsula, shown

in the SW part of the map (Fig. 3C), changed into a narrow through developed during the Cenomanian.

It had a character of a graben where the sediment thickness is the highest in comparison with the whole

Poland territory deposits. The graben is S-shaped which most likely results from the rejuvenation of E-

W and N-S faults known in this area in the Palaeozoic structural stage (JURKIEWICZ, 1975;

Hakenberg, 1978, 1986; Morawska, 1996; Hakenberg & Swidrowska, 1996).

Source:

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

247

Turonian

A substantial increase of sediment accumulation rate occurred in the Turonian: it is likely that

subsidence was also much faster (Fig. 3D), especially so that deeper facies appeared at that time

(compare with Fig, 2). A large zone of very rapid increase of sediment thickness appeared along present-

day SW Mesozoic margin of the Holy Cross Mountains (compare Fig. 3D with Fig. 1). Thus, it is also

the zone, along which the central part of the trough was inverted and uplifted together with the

Palaeozoic of the HCM.

We identify a set of smaller feathering faults at the SW the Przedborz-Checiny-Mielec main fault

zone. They are genetically connected with it. The strikes of faults, against the main fault, suggest their

tensional origin and also dextral slip component of the main fault zone. Tensional character of this set

seems to be confirmed by pattern of sediment accumulation rate. These faults manifest themselves by

tne occurrence ol tilted blocks (Fig. 3D) with upthrown western sides and downthrown eastern sides.

These faults can explain also a facies differentiation of early Turonian sediments, which is observed in

the NW-SE line of outcrops paralleling Palaeozoic/Mesozoic contact (HAKENBERG, 1978;

WALASZCZYK, 1992; HAKENBERG & SWIDROWSKA, 1998). Three short approximately N-S faults are

visible in the eastern part of the trough: they also can be considered as indicating a dextral slip

movement along the Nowe Miasto-llza fault.

The considerable acceleration of sediment accumulation rate in the Turonian and the existence of

good documented synsedimentary zone of Przedborz-Checiny-Mielec fault testify that intensive tectonic-

subsidence was going on at that time.

CONIACIAN AND SANTON1AN

Two consecutive stages of the Cretaceous are considered jointly (Fig. 3E) due to serious

discrepancies on their estimated duration (compare the time scales in GRADSTEIN et a!., 1995 and Odin

& ODIN, 1990). A more distinct differentiation in subsidence was pronounced in the area south of the

line of the Wisla River. Small areas of faster and slower accumulation of sediments are elongated there

consistently with the axis of the trough. The Kurdwanow-Zawichost fault strikes between Krakow and

Sandomierz. It probably existed during the Coniacian and Santonian and acted as a transfer fault, as it

was suggested for the Tomaszow Mazowiecki - Nowe Miasto - Grojec fault during Late Permian-Late

Jurassic times (HAKENBERG & SWIDROWSKA, 1997).

Campanian

During the Campanian, the transgression of the Late Cretaceous reached its maximum (Fig. 3F).

Regions that are devoid of sediments (either land or omission ones) do not exist within the limits of the

studied area. Already since the Turonian, the subsidence rate was higher in the southwestern part of the

trough; however, the synsedimentary faults had a very limited role. Subsidence during the Campanian

could be compared with that in the Late Jurassic: sufficiently high rates but without great gradients

(HAKENBERG & SWIDROWSKA. 1997). "

It > s likely that several faults existed in the south, along the Wisla line, that could indicate a sinistral

slip component of the Kurdwanow-Zawichost fault. Isolines of sediment accumulation rates changed

their directions in the south and became to be W-E in course.

Source:

248

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

MAASTRICHTIAN

As the complete thickness of sediments in this stage is preserved only in a narrow belt along the

parallel course of the Wisla River, with overlying Danian sediments, no data were available to draw a

map of the Maastrichtian. In this belt, the thickness of the Maastrichtian is more than 350 m. Most often

the Maastrichtian is covered with the Quaternary only. The process of shallowing of the basin with

effective increase of clastic material supply was observed in the Maastrichtian (HAKENBERG &

SWIDROWSKA, 1998). This process was asymmetric, because it occurred earlier and was more intensive

in the southwestern part of the basin. It is suggested also by the lack of upper Maastrichtian sediments in

the Miechow Syncline and by the development of chalk facies in the northeastern limb. This last fact

testifies to a decay of inflow of terrigenous material in this direction.

LONGITUDINAL ZONATION AND SYNSEDIMENTARY ACTIVITY OF BASIN FLOOR

The parallelism of facies zones with longitudinal basin axis is expressed (Figs 2 and 3) by the

presence of axial parts subjected to the earliest sedimentation and the earliest appearance of deep

siliciclastic shelf environments replaced later by pelagic sedimentation. Two marginal zones in the NE

and the SW display symmetry in sediment development only during the Albian and (partly) the

Turonian. Usually, the southwestern slope of the trough was different from the northeastern one due to:

(1) the increased share of terrigenous material, (2) long-lasting existence of areas subjected to erosion or

only omission ones, (3) diversity in sedimentary conditions, and (4) a higher energy of sedimentary

environments. The two last points concern time span till the Turonian (inclusive). These differences

decreased during the Campanian, but during the Maastrichtian they were effective again due to the

regression.

When analysing the chronostratigraphic diagram (Fig. 2), it should be noted that the boundaries ot

various sedimentary environments manifest themselves in the same places at different periods of time.

This suggests that the variable rate of the basin subsidence was connected with the presence of tectonic

discontinuities, an important factor for the basin depth. Four fault zones can be distinguished out of

which two main zones (Figs 2 and 3) delimit the axial part of the trough and its marginal limbs.

The first fault zone appears on the SW from Radom (Figs 2 and 3) where boundaries of dillerent

environments contacted in the Hauterivian and from the Albian to the Santonian, constituting a NE limit

of the axial part of the trough. Effects of faster subsidence in this zone are evidenced by the facts that

Valanginian sediments are preserved there and transgressive sediments of the middle Albian appear

earlier at the beginning of the next sedimentary megacycle. Another argument is provided by the

appearance - at the turn of the Albian and the Cenomanian - of deeper facies that spread not earlier than

in the upper stages of the Cretaceous. Only bigger share of organic silica and the inflow of terrigenous

material are decisive factors for specific sedimentary conditions in the axial part of the trough during the

Coniacian and the Santonian. In this way the Nowe Miasto-Ilza fault displayed its synsedimentary

activity during the Cretaceous. This fault was also the NE limit of the trough during Triassic and Early-

Middle Jurassic times (Hakenberg & Swidrowska, 1997). Its role decreased during Cretaceous times

as high thickness gradients did not appear there.

The second fault zone, being active from the late Albian to the Turonian (Fig. 2), runs in the vicinity

of the southwestern contact of the Mesozoic with the Palaeozoic of the HCM. It is Przedborz-Checiny-

Mielec fault zone (Fig. 3), the fragment of bigger Poznan-Rzeszow fault zone. The considerable

thickness gradients are also linked with this zone during the Turonian. An assumption can be made that

a great synsedimentary fault bounding the trough in the SW acted here. Its maximum activity occurred

during the Turonian. It could be consistent with the zone of intensive deformation of the Mesozoic,

which was manifested during the inversion of the trough (STUPNICKA, 1971; POZARYSKI, 1971).

The transversal asymmetry of the basin can be suggested accordingly to the activity of the bounding

faults. At the beginning of the Cretaceous and until the Cenomanian the axis of deposition would be

shifted towards the NE boundary of the trough, and later - during the Turonian - towards the SW

Source:

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

249

boundary. From the Coniacian the role of bounding faults has decreased. When drawing conclusions on

the subsidence during the Maastrichtian. one should consider not only the thickness of sediments but

also a probable increase in depth of the basin, with this trend advancing to NE where pelagic lithofacies

of siliceous marly chalk (opokas) and chalk appeared.

Rate of subsidence

In order to compare the rate of subsidence (or more precisely, the sediment accumulation rate,

probably proportional to the rate of subsidence), average thicknesses of sediments were calculated for

the consecutive stages (Fig. 4). The simplified method used here does not allow to quantify rates of

subsidence or to distinguish tectonic factor of an external strength from an isostasy induced by sediment

and water column loading. A full backstripping procedure was applied for the central and NW parts of

the MPT by DADLEZ et al. (1994, 1995). We could only relatively compare sediment accumulation rates

and interpret them in relation to the fault patterns.

After several long-lasting repeatable episodes of the uplift at the turn of Jurassic/Cretaceous time

(ClESLlNSKl, 1976: KUTEK, 1994; KUTEK et al., 1989), subsidence increased at the beginning of the late

Albian transgression. However, the sediment accumulation rate did not reach important values. During

the Cenomanian, subsidence decreased. It is illustrated by the flat segment of “subsidence” curve (Fig.

4) and by the light grey-tones of the Cenomanian map (Fig. 3C). The next stage, the Turonian, Ts

characterised by the significant acceleration of subsidence. The rate values reached over 100 m/My (i.e.

more than during Late Jurassic time) in aerial restricted elongated axial belt. During Coniacian,

Santonian and Campanian times the average sediment accumulation rate decreased a little. The different

style of subsidence consists in the lack of deep depocentres, nevertheless an intensive subsidence

embraced almost the all area.

Fig. 4.— Curve of medium rate of sediments accumu¬

lation (time scale according to Odin & Odin, 1990).

Fig. 4.— Courbe du tau.x moyen d’accumulation des sedi¬

ments (echelle des temps geologiques d'apres Odin &

Odin, 1990).

Our views concerning the evolution of the Mid-Polish Trough during the Cretaceous agree with those

of Stephenson (1993) and Dadlez et al. (1994, 1995) only in part. One event of subsidence

acceleration was stated by all the authors in the Cretaceous basin. We found an acceleration of

subsidence in the southeastern part of the trough during the Turonian and STEPHENSON (1993) and

Dadlez et al. (1994, 1995) during the Cenomanian in the entire Mid-Polish Trough. The difference

may result from the fact that in the first case the Cenomanian was compared with the whole Albian

whereas in the second one it was compared with the late Albian only. In the first case, the difference of

subsidence was related to older Cretaceous stages whereas in the second one, the subsidence

acceleration is to be observed but a clear contrast is noted with the late Albian. A comparison of

thickness maps of the Cenomanian and Turonian in Poland (Marek & PAJCHLOWA, 1997) allows to

assume that such a subsidence acceleration had taken place during the Turonian (SwiDROWSKA &

Hakenberg, 1999).

Source:

250

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

HYPOTHETICAL PALAEOSTRESS FIELD EVOLUTION

BASED ON SYNSEDIMENTARY FAULT PATTERNS

Based on the maps of sediment accumulation rates, some simplified maps were constructed showing

the main palaeotectonic elements such as synsedimentary faults, axes of palaeoelevations and

depocentres for the particular stages of the Cretaceous (Fig. 5). Geometric relationships between those

elements made the basis for an attempt to define the evolution of hypothetical palaeostress fields during

the Cretaceous.

The turn of the Jurassic/Cretaceous in broad understanding (from the beginning of the late

Kimmeridgian to the middle Albian) was characterised by quite different palaeotectonic conditions than

those ones in earlier time and those in stages to come. Two series of events can be distinguished in the

alternating appearance of regressive and transgressive periods; both series seem to be joined together in

a cause-and-effect interdependence. The first one is: regression, limitation of influence of the Tethyan

Ocean (decline of connections), an uplift of the area (in the central part) with its axis running WNW-ES-

E. remaining of sedimentary basins only in the northern part of the area. The conclusion could be that

geodynamic conditions resulted from the course of the border of the Eurasia plate. The second series is:

transgression, facilitated contact with the Tethys (opening of connections), origin of tectonic depressions

of graben type, with their NW-SE axes consistent with the extent of the trough. It suggests that

geodynamic factors have activated the Teisseyre-Tornquist Zone (Fig. 5).

At that time, development of tectonic structures of NW-SE trend was not contined to the Mid-Polish

Trough onlv. On its northeastern flank, already in the East European Platform, narrow grabens were

formed (BaC-Moszaszwiu & MORAWSKA. 1975; MAREK, 1983). This testifies that stresses expanded

northwards. The grabens are long and very narrow; this suggests that their tensional origin is

“restricted”. Instead, their development can be connected with the presence in the basement of steep

strike-slip faults that were split upward in a flower-like manner and made that way the structures ol

grabens with slip component of transtension.

Repetitive erosional and depositional periods could have been connected with the permutation ol

principal stress axes o, and o,. Extensive regime: a, vertical. a : horizontal trending WNW-ESE -

regression. Strike-slip regime: a, vertical, a, horizontal trending WNW-ESE - transgression. In both

cases principal minimum stress axis a, was similarly oriented (NNE-SSW) (Fig. 5). A phase of

intensified rifting process with slip component during the Early Cretaceous is known from various areas

of Central and Western Europe as the so-called "Late Cimmerian" rifting pulse (ZIEGLER. 1990).

Tectonic activity during the Albian was noted within the southwestern limb of the trough. A set of en

echelon faults developed above the Pilica fault existing in Palaeozoic basement (Fig. 5). They can be

defined as tensional fractures that caused a number of elevations and depocentres of short axes. This

arrangement suggests a strike-slip regime of stresses with the principal maximum stress axis o, close to

NW-SE. thus parallel to the trough axis. As compared with the former stage, a dextral rotation happened

by approximately 22°; this was probably followed by an increase of the difference between a, and a,.

This resulted in a sinistral-slip component along the Pilica fault.

A graben that developed over the Albian peninsula during the Cenomanian was a dominant and

clearly identified structure (Fig. 3C, B). So, the process of disruption of the SW frame of the trough

continued, and only a permutation of stress axes a, and o 2 happened (Fig. 5) due to relaxation of

principal maximum stress. Extensional regime became decisive and the position of the axis a, could be

defined from the S-shaped graben: only the axis a, of principal minimum stress of NE-SW direction

could ensure opening of the graben in all its segments (Fig. 5). The Cenomanian fault pattern in this area

does not allow to interpret tectonic conditions as “a response of the lithosphere to compression"

suggested for the central and NW parts of the MPT by STEPHENSON (1993) and DADLEZ el al. (1994,

1995).

Consequences of an intensive basin opening had taken place during the Turonian. A long fault zone

(the Przedborz-Checiny-Mielec fault) developed southwest of Kielce. This fault is expressed by very

high thickness gradients (Fig. 5). It means that the process of pulling of the southwestern region into the

Source: MNHN. Paris

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

251

0_100 km

Fig. 5.— Hypothetical palaeostress field evolution based on synsedimentary fault patterns. 1, active basement faults; 2, axes of

depocentres; 3. axes of uplifted areas; other explanations see Fig. 3. Stress regimes; extensive or transtensive: stress

pattern with o, marked with a solid circle in the centre; pure strike-slip or transpressive: stress pattern with o : marked

with a dot in the centre. Horizontal stress axes: black inward arrows: compressional stress axes o,. white outward

arrows: extensional stress axes a 3 .

Fig. 5.— Evolution hypothetique du champ des paleocontraintes basees sur le reseau de failles synsedimentaires. I. failles

actives dans le substratum ; 2, axe de depot-centre ; 3, axe des zones soulevees ; autres figures voir Fig. 3. Regime des

contraintes : extensif on transtensif: o, figure par un gros point noir an centre ; decrochant pur on transpressif: o\

figure par un petit point noir au centre. Axes des contraintes horizon tales : compression a, figuree par des flee lies

noire s cent ripe tes ; extension G i figuree par des fleches blanches centrifuges.

trough was restrained. It should be noted here that during the Turonian this region was left on the

southwestern limb of the trough. A set of T-fractures turned into normal faults in the SW sector of the

main fault zone, definitely points to a dextral-slip component during opening of the Turonian basin in

transtensional regime. Similar dextral-slip component along the Nowe Miasto-Ilza fault could be

suggested by three faults running northwestwards as well as southeastwards of Radom. The stress

pattern was most likely affected by further clockwise rotation, which resulted in the change of axis

orientation a, into NNW-SSE and of o } into WSW-ENE (Fig. 5).

Source: MNHN. Paris

252

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

The style of subsidence during Coniacian-Campanian times has changed. An overall decrease of fault

activity is observed (Fig. 5). Relatively intensive subsidence concerned a significant part of the studied

area but it was not related to fault zones. The southern part of area was tectonically activated and

separated from the central part of the basin by the Kurdwanow-Zawichost transfer fault (Fig. 5). Though

subsidence was intensive especially during the Campanian and the eroded areas disappeared, the closing

of the basin is visible in its south-western part. It is evidenced by the isolines of subsidence rate turning

E-W in the area south of the Wisla line. Several faults situated along the upper course of this river may

point to a sinistral-slip component along the Kurdwanow-Zawichost fault (Fig. 5).

It seems likely that the development of the basin during the Coniacian, Santonian and Campanian

occurred in different tectonic conditions than previously. Observations noted in other basins

(STEPHENSON et aL, 1990, 1992) suggested the interpretation of the compressional origin of tectonic

control of the MPT development during the time prior to inversion; in this case it was dated as

Cenomanian-Maastrichtian time span (STEPHENSON, 1993; Dadlez et aL, 1994. 1995). According to

our results, an increase of the compression seems very probable, but in a shorter time (Coniacian-

Maastrichtian). A different interpretation presented here (for the SE part of MPT) consists also in

understanding the effects of compression as a deflection of the axial part of the basin till the end of

Campanian times. An inversion in the axial part of the entire MPT since Coniacian was suggested

(Dadlez etal, 1994, 1995).

As a consequence of the increase of compression, the method of fault identification applied here fails

because faults did not manifest in form of upthrown and downthrown sides which obviously did not

control accumulation rate. The increase of compression in the NNE-SSW direction (suggested by

sinistral component along Kurdwanow - Zawichost fault zone) may explain considerable subsidence of

the trough during Coniacian-Campanian times. Simultaneous uplift of SW limb of the Mid-Polish

Trough (the Sudetes and Fore-Sudetic Monocline areas; MlLEWICZ, 1973) seems to confirm the deduced

flexural mechanism (compare with CLOETINGH & KOOI, 1992) of effective subsidence during

Coniacian-Campanian times.

STRIKE-SLIP COMPONENT ALONG THE TEISSEYRE-TORNQUIST ZONE

IN RELATION TO PLATE KINEMATICS

During the Mesozoic, the Mid-Polish Trough developed on the Eurasia plate, over the contact of the

Precambrian and Palaeozoic Platforms (TESZ) the basement structure of which is similar to the East

European Craton (BERTHELSEN, 1998). The basement is weakened there by the deep-seated zone of the

crustal discontinuity (TTZ). Stresses from collisional plate edges can be transferred over thousands of

kilometres toward the plates (CLOETINGH. 1988; ZIEGLER. 1990; ZOBACK et aL, 1993). The movement

of Africa relative to Eurasia has been determined (LE PlCHON et aL, 1988). A question arises: what

relation exists between hypothetical intraplate stress fields in the TTZ, which was deduced in the

previous section of this paper, and the theoretical strike-slip component that could occur along the TTZ

due to relative movement of the both plates?

Tracks of two points (Tunisian Bay and Suez) situated in the Africa plate were taken into

consideration (Fig. 6A); among other points analysed in the reference work both are at shortest distance

to Poland. From the Early Jurassic (190 Ma) to the Santonian (80 Ma) the relative movement path of

Africa towards Eurasia was more or less parallel to the TTZ. Africa shifted relatively to the left (Fig.

6A) thus there was a relative sinistral motion between the plates (ZIEGLER. 1990). The parallelism of

relative movement path of Africa against Eurasia to the crust weakness zone of TTZ theoretically

suggests that sinistral component along the TTZ could be very probable during that time. Conclusions

drawn from the distribution of palaeotectonic elements since the Early Cretaceous to the Middle Albian

(Fig. 5) seem to be in line with the sinistral drift resulting from plate kinematics. Also, the distribution

of synsedimentary fault pattern in the Early Jurassic induced the authors (HAKENBERG & SWIDROWSKA,

1997) to assume that the sinistral component of strike-slip stress field was common during that epoch

and that the axis a 3 of the principal minimum stress was oriented NNW-SSE.

Source:

CRETACEOUS TECTONIC DEVELOPMENT OF SE MID-POLISH TROUGH

253

Fig. 6.— Strike-slip component along the Teisseyre-Tornquist Zone (TTZ) during Cretaceous time shown in relation to plate

kinematics presented by LePiCHON et al. (1988. fragments of Figs I and 2). A. relative motion history of Africa with

respect to Eurasia from Early Jurassic (190 Ma) to Present time; B-E. simplified plate tectonic schemes along northern

boundary of Tethys. Schematic plate boundaries: continuous line, transform: open triangles, oceanic subduction; closed

triangles, continental collision: double dotted line, oceanic accretion; hachured pattern, oceanic crust; dotted pattern,

thinned continental crust.

FlG. 6.— Comptisante decrochante le long de la Zone de Teisseyre-Tornquist (TTZ) pendant le Cretace en relation avec la

cinematique des plaques {Le Pichon et al.. 1988). A. reconstruction du mouvement relatif de I'Afrique par rapport a

I'Eurasie du Jurassique inferieur (190 Ma) a I'Actuel. B-E , schemas simplifies de la tectonique des plaques le long de

la bordure nord de la Tethys. Limites de plaques : ligne continue, transformantes ; ligne a triangles blancs.

subduction ; ligne a triangles noirs, collision ; ligne pointillee double, accretion oceanique ; hachures. croiite

oceanique ; pointilles, croiite continental amincie.

During the Turonian the dextral-slip component along the NW-SE direction of TTZ came into

evidence in transtensional regime. It may be a reflection of overthrusting in the Western Inner

Carpathians (Matejka & Andrusov, 1931).

A rapid break in the track of relative motion occurred at the point characterising the Santonian (80

Ma): Africa started to move towards Eurasia (Fig. 6A); this motion was decisively northwards (LE

Pichon et al.. 1988). Guiraud & BOSWORTH (1997) presented a comprehensive compilation of

tectonic processes going on in intracratonic sedimentary basins over the Africa, Arabia and India plates.

Their compilation is intended to prove that a close relation exists between the Senonian inversion of

many basins and the change in direction of relative movement of the southern plates toward Eurasia.

A comparison of the stress field, supposed here for the Santonian-Campanian (Fig. 5) with the

GlRAUD & BOTHWORTH (1997) and LE PICHON et al. (1988) findings, allows to conclude about the

coherence of these data. The compression nearly N-S ought to create dextral-slip component along the

trend of the TTZ. The analysis of brittle deformation observed in the Mesozoic rocks of the investigated

area carried out by LAMARCHE et cd. (1998) show a N-S compression, which is suspected to occur

before the main stage of the Laramide tectonic inversion (compression NE-SW; JAROSZEWSKI, 1972;

Swidrowska, 1980; Lamarche et. al., 1998). It could be dated as the Santonian-Campanian

compression.

Another comparison of evolution of stress conditions proposed here (Fig. 5) with tectonic events

occurring in the northern border of Tethys (Fig. 6 B-E) is necessary. It leads to the conclusion that

continuous change in the stress regime from sinistral transtensional to dextral transpressive is not

Source:

254

JOLANTA SWIDROWSKA & MACIEJ HAKENBERG

contradictory to the distribution of zones of spreading, subduction and overthrusts already identified in

the northern Tethyan area (LE PlCHON et al.. 1988).

It should be stressed that strike-slip movements along TTZ. which could result from the suggested

transtensional to transpressional stress regimes. were of small scale, and did not exceed few tens of

kilometres. It pertains both to the movements leading to basin opening and to those ones acting during

inversion.

CONCLUSION

The analysis of the deposits accumulation rates, treated as a reflection of subsidence rates, was

coupled w'ith the recognition of basin sedimentary conditions. It made possible to distinguish

synsedimentary fault patterns for six time-spans of the Cretaceous. The fault patterns gave a base for the

reconstruction of the palaeostress field evolution controlling basins development.

The extensional regime came into evidence twice in the history of Cretaceous basin: at the beginning

of the Cretaceous but during regressions only, and then during the Cenomanian. These episodes were

connected with a decrease of subsidence rates. Strike-slip stress field characterised the remaining time-

periods of the Cretaceous basin development from the beginning of the Cretaceous but during

transgressions only till the Campanian (the Cenomanian excluded). The main episode of accelerated

subsidence during the Turonian was controlled by accentuated activity of SW bounding fault.

The evolution of tectonic regime can be characterised by the clockwise rotation of the strike-slip

stress field in transtensional regime from the beginning of Cretaceous (a, WNW-ESE) till the end of

Turonian (G, NNW-SSE), and later on. from the Coniacian-Santonian. in transpressional regime (a, N-S

to NNE-SSW) till the inversion time (a, NE-SW) at the turn of Cretaceous/Tertiary. This rotation was

followed by change of character of a strike-slip component along the Teisseyre-Tornquist Zone: from

the sinistra] component (till the middle Albian) to the dextral one (from the Turonian till inversion time).

The beginning of increase of compression during the Turonian, resulted in basin opening in well

expressed strike-slip stress field, but still in transtensional regime. The succession of palaeotectonic

conditions of Cretaceous basins opening seems to be compatible with the relative movements between

Africa and Eurasia plates during this time. The extensional stress field manifested at the transition from

the Jurassic to the Cretaceous during regressions times could be interpreted as a reaction of southern

edge of Eurasia plate to spreading in the northern Tethys.

ACKNOWLEDGEMENTS

We are indebted to Dr F. BERGERAT for discussion and comments on earlier version of the

manuscript. Critical comments and constructive suggestions made by Dr R.A. STEPHENSON and an

anonymous reviewer contributed to improve the manuscript. Their efforts are highly appreciated. The

manuscript benefited also from Prof. J. LEFELD helpful remarks. Dr J. LAMARCHE is thanked for the

translation of the abstract into French.

The study has been performed within the framework of the statute problem in the Geological Institute

of Polish Academy of Sciences titled “Palaeotectonics of the Holy Cross Mountains area during the

Cretaceous”.

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INDEX

Aalenian 62; 65; 71; 72; 74; 83; 84; 85; 87; 111; 124; 162

Aaliji 185; 186; 187; 188; 189

Abba 162; 173

Abd Al Aziz 178; 199; 201

Adoumaz 45

Africa 12; 34; 94; 96; 101; 102; 103; 123; 124; 125; 130; 131;

150; 239; 252;253

Agananc 41; 47; 51

Ahmer Akhdar 113

Ain el Morra 59

Ain Hamra 143; 150

Ain Nokra 99

Ail Allab 99

AH Bougemmez 41; 45

Ail Oufella 101

Aktyubinsk 211

AIFural 180; 182; 183; 184; 185; 186; 187; 188; 191; 192

AI Kharrala 190; 198

Albian 148; 155; 169; 177; 178; 183; 185; 189; 192; 198; 239;

243;245;246; 248; 249; 250; 252

Aleppo 159; 161; 165; 166

algae 41; 59; 214; 216; 219; 222; 224; 225; 226; 228; 230

Algeria 34; 68; 80; 87; 102; 148; 153

Alibek-Mola 211; 212

Alljutovella 216

Alps 75; 80; 226

Alveosepta (Iberina) prealusitanica 165

Alveosepta jaccardi 164; 165

Amanos 165

America 29; 94; 123; 130

AmezraV 41; 45

Amijiella amiji 162; 163

ammonite 41: 45; 57; 58; 62; 63; 64; 65; 68; 69; 71; 81; 82;

84;87; 111; 112; 163; 164; 233;246

ammonoid 213; 214; 216; 222; 223; 228; 230; 231; 232

Amsitten 131

Amu-Darya 216

Anah 170; 173

Anceps Zone 68; 72

Anchicodium 219; 226

Anergui 45

Annaplophora littica 105

annelid 63

Anoplophora letlica 26

Antakia 165

Anli-Allas 94; 146

Anti-Lebanon 160; 161; 164; 165; 166

Appalachian Basin 152

Aptian 129; 136; 139; 148; 159; 172; 245; 246

Aqaba 171

Arabian platform 169; 170; 171

Aral Sea 215; 216; 225; 228

Arctic 207; 217; 219; 226; 228

Argana 25; 26; 28; 32; 33; 34

Argovian 152

Arkhangelsk 203; 204

Artinskian 203; 204; 213; 225; 226; 228; 230; 231; 232; 233;

234

AsSirra 186; 188; 190

Asia 218; 232

Asphinctites patrulii 68

Asphinctites replictus 67

Aspidoceras circumspinosum 1 1

Aspidoceratidae 70

Assetian 203; 204; 213; 216; 219; 223; 224; 225; 226; 231:

232; 233

Astrakhan 213; 225; 231

Atalla 180; 184: 185; 188; 191; 192

Athleta Zone 69; 74

Atlantic 23; 25; 28; 32: 33: 34; 94: 95; 96; 97: 99; 100; 102:

107; 123; 124;125;130;143:145; 147;148;154;156

Atlas 21: 23; 24: 25; 26; 28; 29; 30; 32; 33; 39; 40; 45; 47; 51;

59; 68; 93; 94; 95; 96: 97; 98; 99; 100; 101; 102; 103: 138:

147;148:155:156

Aulotortus sinuosus 161

Aurigera Zone 68

Aurigerus Zone 71; 72; 74

Autunian 28

Ay 213:228

Azilal 45: 47

Azira 112

Azizia 79

Azores 29; 94

Bajocian 62; 63; 65: 66; 69: 71; 73; 74; 76; 79; 81; 83; 84; 85;

86:87:97: III; 124; 136; 148

Balanocidaris gland if era 164

Balkhash Lake 216

Barents Sea 223

Barremian 159; 245

Bathonian 40: 62; 63; 67; 68; 69; 71: 72: 73: 74; 76; 79; 81;

83; 84; 85: 86; 87; 96; 111; 124; 159; 163: 166

Bat rou n 164

Source:

258

INDEX

Bechar 12

belemnite 62; 63; 64; 67; 69; 75; 81

Beni Bou Yahi 109

BeniSnassen 108; 11 I; 112; 113; 116: 123: 124; 125

Beni-Mellal 99

Beni-Mellal 40: 41; 45

Be reset la 219

Beresellid 219

Berrechid 25: 32: 34

Berriasian 72; 113: 136; 245

Bifrons Zone 65; 72

Bihenithyris sp. 164

Bihen ithyris weiri 164

Bimammatum Zone 71

Bishri 177; 180; 182; 185; 199

Bitlis 169; 170; 199

bivalve 41: 214: 215; 216; 222: 223; 228; 230

Black Sea 240

Bornholm 240

Bou Beker 112

Bou Draa 143

Bou Fekrane 25

Bou Gamine 79: 83

Bou Hedma 72

Bou Kornine 76

Bou Rhennja 113; 124

Boudenib 147

Boudoufoud 109

Bou fekrane 34

Boulemane 97; 99

Bourdine 109: 123

Bou-Regreg river 15

Bqassem 163

brachiopod 41; 62; 63; 163; 164; 214; 216; 218; 219: 222;

223; 224; 225;226:228:230;232

Brachithyrina subcamica 2 18

Bremeri Zone 68; 69; 72; 74

bryozoan219; 222: 224; 225; 226;228;230:232

Bukhara-Karsha 216

Bullatimorphites (Bullatimorphites) gr. bullatimorphus 68

Bullatimorphites (Bullatimorphites) sp. 68

Bullatimorphites (Bullatimorphites) sp. juv. 68

Bullatimorphites (Sphaeroptychius) marginatus 68

Busachi Peninsula 216; 225

Cadomites (Cadomites) bremeri 68

Cadomites (Cadomites) cf. bremeri 68

Cadomites (Cadomites) orbignyi 68

Cadomites sp. 67

Cainozoic 40; 93; 94; 130; 150; 173: 190

Catamites 14

Caledonian 94

Callovian 63; 64; 67; 68; 69; 72; 74; 76; 79; 81: 83; 84: 86;

87; 88: III; 112: 124; 136:147;148: 163; 164

calpionnelid 76

Cambrian 146

Campanian 169; 173; 181; 182; 183: 185; 189; 194: 195; 199;

243; 247; 248; 249; 252; 253;254

Campos 156

Campylites 70: 87

Campylites (Campylites) cf. delmontanus 70

Campylites (Campylites) cf. delmontanus helveticus 70

Campylites ( Campylites ) delmontanus69 ; 70

Campylites (Campylites) delmontanus helveticus 69; 70

Campylites (Campylites ) gr. delmontanus 70

Campylites (Campylites) taeniolatus 69

Canada 226

Cap Juby 143; 152

Carboniferous 11: 12: 18:94; 146; 147; 153: 154; 172; 173;

175: 189; 192; 203; 204; 207; 212; 213;216;219;224

Cardiocarpus 14

cardioceratids 70; 87

Carixian 41; 45; 47; 51; 59; 71; 72; 75; 79; 81; 84; 85: 86

Carnian 23: 26; 28; 29; 30; 32; 33; 34; 95

Casablanca 154

Caspian Sea 233

Celtic basin 138

Cenoceras sp. 67; 68: 69

Cenomanian 99; 175; 178; 179: 185: 191; 239; 243; 246: 248;

249:250;252; 254

cephalopod 96; 216

Chaabet el Attaris 58; 59; 62; 63; 65; 67; 68: 69; 71; 72; 74;

75; 79

Chaoiella gruenewaldti 2 18

Checiny 247; 248; 250

Chibli 184: 188

Chichaoua 131

Chilou 188: 189; 198

China 232

Choffatia (Subgrossouvria) sp. 68

Choffatia sp. indet. 69

Choffatia sp. juv. 69

Chondrites 63

Chondroceras 67; 71

Chondroceras cf. gervillei 67

Chondroceras cf. orbighyanum 67

Choristites fritchi 2 16

Choristites prisons 2 18

Choristites sower by 2 18

Chott 75: 76; 79; 83; 86; 87

Chussovaya 213; 224

Cimmerian 250

Claromontanus Zone 70

Clypeina jurassica 164

Coenoceras sp. 71

Col lot ia 69; 87

Collotia sp. 69

Concavum Zone 65; 71; 72; 74

Coniacian 169; 173: 179: 239; 243; 247: 248; 249; 252; 254

conodont 213: 214; 222: 223; 225; 226; 228; 230

coral 79: 164: 214; 216; 222; 223; 224; 225: 228; 230

Cordaites 14

Source ; MNHN. Paris

INDEX

259

Cordatum Zone 70

Cretaceous 59; 79; 86; 93; 97; 98; 102; 103; 107; 109; 116;

123;124; 125; 129; 130; 131; 132; 134; 136;137;138;

139;143;148;150;135;154;156;159;163;169;170;

172; 173; 175; 177;178;181: 183: 186;189;192; 194;

196;201:239:240;243;246; 247; 248; 249; 250; 252; 254

crinoid 63; 34; 76; 214; 222; 224; 225; 228

Cyclotosaur 26

Dactylioceras sp. 65

Daghanirhynchia subversabilis 163

Daixina bosbytaucnsis - Daixina robusta zone 219

Dakhla 148; 154

Danian 248

Darvaz 218; 232

Darwinnla 26

Dasycladacea 163

Davoei zone 45

Dead Sea 165

Debdou 109; 123

DeirEzZor 175: 177; 191

Demet 62; 67; 71; 72; 73

Demnat 45

Derro 170: 176; 179; 180: 181: 185; 189; 194

Devonian II ; 12; 18; 19; 20; 21: 146; 150; 173

Dikfaya 164

Dinantian 94

Discites zone 67: 71: 74

Discus zone 68; 69

Distichoceras sp. 69

Dogger 57; 86; 96; 107; I 16; 125; 147; 162: 166

Dolaa 161; 166

Dolikephalites gr. gracilis 68

Domerian 41; 45; 47; 51; 72; 84; 85; 96; 111; 150

Donetsk 203; 204; 207; 214; 218: 219; 225: 226

Dorsetensia 67

Dorsetensia (Nannina) sp. 67

Doukkala 25; 26; 28; 32; 34; 153

Dutkevichia 226

Dutkevichites 226

Dvinella 219

Eastern European Basin 203; 204; 206; 217: 218: 219; 232;

233

Eastern European Platform 240

Eastern Uralian Gulf 203; 204; 210; 214; 218

Ebrayiceras 67; 87

Ebrayiceras sp. 67

Ebrayiceras sulcatum 67

eehinoderm 62; 63; 64

echinoid 63; 164

Egypt 162

El Ai'oun 123; 124

El Gamgouma 79

El Gara 32; 34

el GuefaVet 79

El Hajeb 26; 28; 33

El Hamra 180; 183; 185; 186

El Haoureb 77; 79

El Jadida 130

El Liel 180: 186; 188; 192

El Ward 180: 182; 184; 185; 186; 188; 193

Llatmites sp. 68

Emba 212

Emileia 57; 65; 66; 71; 87

Emileia gr. polyschides 66

Endersonella palastiniensis 163

Enteletes lamarcki 218

Eocene 99; 100; 103; 107; 113; 123; 125; 132: 143: 148; 154;

169:172;188;189; 198

Eofiisulina 2 17

Epalxites sp. 67

Epimastopora 219; 226

Epistrenoceras 68; 69

Epistrenoceras sp. 68: 69

Erek 182; 183; 184

Ermoceras 87

Ermoceras gr. coronatoides 87

Errachidia 147

Erymnoceras 164

Essaouira 25; 26; 28: 34; 129; 130; 131; 132; 134: 137; 138:

139; 143; 147; 148; 150; 152;155

Euaspidoceras cf. douvillei 69

Euaspidoceras cf. knechti 69

Euaspidoceras gr. williamsoni 70

Euaspidoceras sp. 70

euaspidoceratids 87

Eugonophyllum 2269

Euhoploceras 67

Euphrates 169; 170: 171: 172: 173; 175: 176; 178: 180: 181:

183;185: 187;188;189; 191; 192; 194; 198; 201

Eurasia 94; 125; 148; 201; 252; 253

Europe 58: 62; 65; 66; 76; 84; 94; 101: 102; 103: 130: 131:

240

Euxinus Zone 72

F/-Zehiliga 19

FaVd 79

Falcifer zone 65

Feddane Lebtam 15; 21

Fes 26

fish 75: 81; 213; 214; 222; 223; 228: 230

foraminifera 41; 161; 162; 163: 164; 183; 213; 214; 216; 218;

222; 223; 224; 225;226;228;230

Foraminifers 26; 63; 64

fusulinids 211; 214; 217; 218; 219; 222; 224; 225; 226; 228;

230: 231; 233

Source:

260

INDEX

Galeanelia aff. laticarinata 161

Galilee 159; 162; 163; 164; 165: 166

Garantiana sp. 69

Gareb 123

gastropod 41; 62; 163; 216

Gemmanella 26

Germany 67

Gibraltar 29; 32; 94

Globifusulina 226

Globifusulina caudata 226

Globifusulina krotowi 226

Globifusulina nux 226

Globuliferoporella 226

Gondwana 165

Gracilis Zone 69; 74

Graphoceras (G.) cf. limitation 65

Graphoceras (G.) sp. 65

Gregoryceras riazi 71

Grojec 246; 247

Grossouvria sp. 69

Grou river 15; 20

Gsollbergella spiriloculifprmis 161

Guefaiet 59; 68; 71; 72; 73; 76; 79

Guefait 123

Guereif 25; 33; 109; 123; 124; 154

Gulf of Lions 138

Gulf of Suez 173

GyroporeUa 219; 226

Hadar 164

Hadid 21; 131

Haifa 163; 164

Hamad 159; 161; 165; 170; 172; 176; 178

Hammam Lif 76; 79

Haricha 143

Harpoceras cf. falcifer 65

Hassi-Messaoud 153

Haurania deserta 163

Haute Moulouya 33; 99

Hauterivian 129; 136; 139; 243; 245; 248

Hauts Plateaux 25; 33

Hecticoceras (Prohecticoceras) cf. blanazense 68

Hecticoceras ( Prohecticoceras) crass urn 68

Hecticoceras ( Prohecticoceras) ochraceum 68

Hecticoceras (Prohecticoceras) sp. 68

Hemifusulina 217

Hercynian 13; 21; 23; 29; 30; 34; 88; 93; 94

Hesperithyris 96

Hettangian 39; 41; 45; 59; 75; 84

High Atlas 21; 23; 24; 25; 26; 28; 30; 32; 33; 39; 40; 45; 47;

51; 93; 95; 96; 97;99;101; 102; 103; 147

High Plateaux 1 11; 112; 123; 124; 147; 154

Hildaites gr. serpentiniformis 65

Hi/daites sp. 65

Hildoceras cf. sublevisoni 65

Holcophylloceras gr. mediterraneani 69

HolcophyUoceras mediterraneum 69

Holcophylloceras sp. 68; 69; 70

HolcophyUoceras sp. juv. 68

Holy Cross Mountains 240; 247; 254

Homoeoplanulites (H.) gr . furculus 68

Humphricsianum Zone 67; 71

Iberia 34; 125

Ibex zone 45

Idrissides 99

Ilek River 211

Ilza 246; 247; 248; 251

Iran 161; 171

Iraq 161: 163; 165; 170; 173

Ishimbay 224

Jabal Akraa 165

Jaddala 187; 188; 189; 198

Jbel Taguendouft 45; 47

Jeanneticeras cf. meridionale 68

Jebel Bishri 177

Jebcl Chaabet el Attaris 58; 59; 62; 65; 67; 68; 69

Jebel el Guemgouma 65

Jebel el Haouareb 59; 63; 67; 68; 69; 71; 72; 74

Jebel Hadid 21

Jebel Krechem el Kelb 58; 62; 63; 65; 67; 68; 69; 71; 72; 74;

Jebel Nara 72

Jebcl Nefzaoua 79

Jebel Rheouis 59; 67; 69; 70; 74; 86

Jebel Sidi Kralif 72

Jeffara 58

Jerada 12; 154

Jeribe 189

Jibal As-Sahilych 160; 161; 165

Jido 180; 182; 183; 184; 186

Jordan 162; 163;165; 178

Joura 177;178; 179; 180; 182; 183; 185; 186; 188; 190; 196;

199

Judea 175; 178; 179; 189

Jurassic 23; 24; 26; 29; 33; 34; 40; 45; 51; 57; 58; 59; 62; 64;

65; 71; 75; 76; 77: 79; 81; 83; 84; 85; 86; 87; 88; 97; 98;

102; 103; 107; 1 10; 112: 116: 125; 129; 131; 132; 134;

136;137:139;143; 147; 148;150;152;153;154;155;

156; 159; 160; 161; 162: 164; 165; 166; 175; 216; 243;

246; 247;248;249;250;252;254

Jurusan 228

Source: MNHN, Paris

INDEX

261

Kama 203; 204; 206; 211; 213; 218; 219; 224; 226; 230; 231;

234

Karachaganak 213; 231

Karpinsky Kryazh 231; 232; 233

Karsk 211

Kasserine 79

Kechoula 131

Kef el Hassine 62; 63; 65; 66; 67; 69; 71; 72; 74; 76; 79; 87

Kef el Khouadja 65; 67; 68; 71; 72; 73; 74

Kerrouchen 25; 30; 33

Khabour 180; 182; 183;184; 185;186;187; 188;191; 192

Khemisset 25; 28: 32; 33; 34

Khouribga 12

Kielce 246:250

Kilianina blanched 163

Kimmeridgian 72; 76; 79; 83; 84: 88; 107; 112; 112; 124; 159;

164: 166:250

Kisyl-Kum 216: 218

Kolguev Island 223

Kolva 213; 224

Komia 219

kosmoceratids 87

Ksour97

Ktab Lahmar 19: 20

Kumubia palastiniensis 164: 165

Kurd Dagh 160: 161; 163

Kurdwanow 247; 252

Kutchirliynchia indica 164

Laayoune 154

Laayoun 32; 33; 34

Ludinian 23; 24; 26; 28; 34; 95; 109

Laevaptychus sp. 71

Laeviuscula Zone 67; 71

Lamberti Zone 74

Lebanon 161; 163; 164; 165; 166

Lemoineiceras sp. 68

lenticulines 67

Levant 159; 165

Levantine I la egyptiensis 164; 165

Levantinella egyptiensis biozone 164

Liassic 23; 24; 33; 34; 39; 40; 41; 42; 45; 47; 51; 75; 77; 79:

83; 93; 95; 96; 103; 107; 110: 116; 123: 124; 125; 129;

131; 132: 136;137; 139; 143; 147; 150; 154; 161: 162

Libya 79

Likharevites 226

Limnocythere keuperea 26

Linoproductus simensis 2 18

Liospiriferina undulata 161

Lissoceratoides sp. 70

Li that is up. 161

Lobosphinctes sp. 67

Loridga 58; 59; 62; 63; 65; 68; 71; 72; 74: 76; 77; 79; 86

Lublin 240

Lunuloceras aff. pseudopunctatum 69

Lunuloceras gr. paulowi 68

Lunuloceras romani 68

Lutkevichinella 26

Lutkevichinella kristanae 26

Lutkevichinella lata 26

Lytoceras 69; 87

Lytoceras aff. eudesianum 69

Lytoceras cf. eudesianum 69

Maastrichtian 154; 169; 173; 179; 182; 183; 185; 189; 190:

191; 192: 195; 196; 199;240;243;248;249;252

Macrocephalites sp. 69

Macrocephalites sp. juv. 68

Macrocephalitids 69

Macrocephalus Zone 68

Macroporella 2 19

Maezalieh 180: 186

Maj dal Chains 164

Majora 86

Malagasy 87

Mardin 159; 161: 165; 172

Margarilatus zone 45

Mariae zone 70; 72; 74

Marrakech 24; 94: 96

Mayncina termieri 161

Medenine 79; 81; 83

Meekella eximia 2 18

Megalodontidae 111

Meseta 11; 12; 13; 17; 21; 28; 32; 94; 96; 99; 147

Meskala 131: 136: 150

Mesopotamian 172

Mesozoic 40; 57: 58; 75; 80; 93; 94; 98; 101: 120; 103; 109:

112; 130:131;132; 147:150:169; 171; 172; 175; 189;

196; 201; 207; 215; 240; 241; 247:248; 253

Metoposaurids 26

Metoposaurus lyazidi 26

Metoposaurus ouazzoui 26

Metroh 123

Microcanthum Zone 72

Microderaceras sp. 72

Micromphalites sp. 68

Middle Atlas 24; 26; 28; 30; 32; 68; 93; 95; 96: 97; 99: 101;

102: 103: 147

Midelt 26; 96

Mid-Polish Trough 239; 240; 249; 250; 252

Miechow 240: 248

Mielec 247; 248; 250

Miocene 101: 116;125; 143;148; 150; 171; 189

miospore 213; 214; 215; 225; 226; 231; 232

Mirus Zone 70

Mixoneura 14

Source:

262

INDEX

Morocco 11: 12: 21; 23: 24: 26: 28: 29; 30: 32: 34; 39; 68; 79:

87: 93; 94; 95; 97; 99; 102; 107; 108; 113; 123; 124; 125:

129; 143: 144:145; 146; 147;148; 149; 150;153;156

Morphoceras 67; 87

Morphoceras aff. jactation 67

Morphoceras egrediens 67

Morphoceras sp. 67

Morphoceras sp. cf. M. macrescens 67

Morphoceras sp. juv. 67

Morphoceras sp. juv. cf. jactation 67

Morrisi zone 68

Moscovian 203: 204; 207; 211; 212; 213: 214: 216: 217: 218;

219:224; 231; 232; 233

Moscow 207; 214: 219; 224; 228

Moulay Idriss 124

Moulouya 25: 33: 96

Mount Hermon 159: 161; 162; 163; 164: 166

Moyenne Moulouya 25

M'rhilla 79

Mugodzhary Mountains 211; 219

Mugodzhary Peninsula 215: 232

Mulussa 170: 175: 189

Naima 123; 124

Namurian 146

Nannolytoceras tripartition 67

Nara Loridga79

nautiloids 222; 223; 228; 230

Neknafa 152

Neoanchicodium 219: 226

Neocomian 165; 245

Neogene 93:101;102; 103; 125:143;150:155:171;175

Neospirifer postriatus 2 18

Neostreptognathodus pnevi 226

Newfoundland 29

Niortense Zone 67

Norian 23; 26: 28; 32; 33; 95; 161; 189

Nonnannites sp. 67

North America 29; 94: 130

North Sea 138; 173

Nova Scotia 29

Novaya Zemlya 211: 213; 222

Nowe Miasto 246: 247; 248; 251

Nura-Tau Mountains 216

Obtusum zone 45

Odontoperis 14

Oka-Zna 224

Oligocene 100; 101: 148; 152; 169; 188; 189; 198; 201

Oman 199

oppeliids 87

Oranesan meseta 108

Oranese Meseta 96

Oraniceras 57: 67; 68: 87

Oran ice ras cf. hamyanense 68

Oraniceras hamyanense 67

Ordovician 11:12; 146: 150: 153

Orenburg 224

Orcnburgian 225

Orthosphinctes (Orthosphinctes) sp. 71

ostracod 26: 28; 29; 30; 33; 94; 96; 102; 103: 109; 111: I 12;

113; 116; 124; 125

Ouaouizart 99

Ouarzazatc 101

Oued Abiod 79

Oued Himmer 123

Oujda 23; 26: 28; 29: 30; 33; 94; 96; 102; 103: 109; 111; 112:

113:116:123;124;125

Oulmes 12

Ouriak 26

Oxfordian 63: 64; 65: 69; 70; 71; 72; 73; 74; 76; 79: 83; 84;

86; 87; 88; 112; 124; 136; 143; 148: 150: 152; 164

Oxycerites cf. yeovilensis 67

Oxycerites gr. yeovilensis 67

Oxycerites seebachi 67

Oxycerites sp. 68

Oxycerites yeovilensis 67

Pachyerynmoceras 87; 164

Palaeoaplysina 219; 224

Palaeocene 99: 148; 169; 185; 186; 187; 188; 189; 192; 198

Palaeogene 169; 175

Palaeo-Tethys 12

Palaeozoic 24: 29: 58; 79; 80; 94; 96; 102; 109; 134; 143; 146:

150; 153; 154; 173; 190; 207; 211; 216; 240:246; 248:

250:252

Paleopfenderina salernitana 163

Paleopfenderina trochoidea 163

Palmyra 170; 199

Pal my rides 160; 161: 163; 165; 169; 170; 171; 172; 177: 178;

187

Paltarpites sp. 65

Pamir 207; 218; 225: 228; 232

Pangea 29: 107; 125

Paracypris 26

Parafusulina solidissima zone 226

Parapatoceras sp. 70

Paraschwagerina 226

Parkinsonia sp. juv. 67

Passendorferia (Enayites) cf. binnensdorfensis 70

Passendorferia (Enayites) czentochovensis 70

Pay-Khoy Mountains 211:212

Pechora 213; 224;228

Pechoria 2 19

Pelagian Sea 58

Source: MNHN. Paris

INDEX

263

pelccypod 62; 63; 64

Pelecypoda 161

Peltoceras (Metapeltoceras) sp. 69

Peltoceras (Peltoceras) sp. 69

Peltoceras cf. divers forme 69

Peltoceratidae 70

peltoceraiids 87

Peltoceratoides 70; 87

Peltoceratoides cf. stephanovi 70

Peltoceratoides cf. williamsoni 69; 70

Peltoceratoides gr. williamsoni 69

Peltoceratoides sp. 70

Perisphinctes (?Arisphinctes) cf. gyrus 69

Perisphinctes (?Dichotomosphinctes) cf. episcopal is 70

Perisphinctes (?Dichotomosphinctes) cf. laisinensis 69

Perisphinctes (Kranaosphinctes) cf. promiscuus 69; 70

Perisphinctes ( Otosphinctes) sp. 69

Perisphinctidae 70; 71; 87

perisphinctid 70

Peri-Tethyan domain 27

Peri-Tethyan Platform 27; 83

Permian II; 21; 24; 27; 79; 83; 94; 175; 203; 204; 211; 213;

215; 216; 223; 233; 234; 240; 246;247

Phylloceras 67; 68; 69; 70; 87

Phylloceras gr. plication 69

Phylloceras plication 68

Phylloceras sp. 67; 68; 69; 70

Pilica 343; 345; 346; 250

Piotrkow Trybunalski 246

Planisphinctes 67

Platylenticeras 245

Pleistocene 101

Pliensbachian 39; 41; 42; 45; 47; 51; 79; 88; 161

Pliocene 150

Podolsk 214

Poitou 67

Poland 240; 246

pollen 15; 26

Polymorphum Zone 65

Polyplectus sp. 65

Pofyptychites 246

Polysphinctites polysphinctus 67

Portlandian 113; 124

Posidonomya 97

Poznan 248

Praekurnubia crusei 163

Precambrian 146; 240; 252

Precaspian Basin/Depression 203; 204; 206; 211; 213; 214;

219; 222; 223; 224; 225; 228; 231; 232

Pre-Rif 143; 147; 148; 150; 154; 155

Procerites gr. tmetolobus 68

Procerites sp. 67; 68

Procerites sp. juv. 67

Profiisulinella rhomboides 2 16

Progracilis Zone 68; 71; 74

Properisphinctes cf. be me ns is 70

Properisphinctes gr. be me ns is 69

Properisphinctes sp. 70

Propinquans Zone 66

Prososphinctes cf. mairei 70

Prososphinctes cf. mazuricus 69

Prososphinctes sequeirosi 70

Proterozoic 171; 172

Proto-Atlantic 23; 28; 32; 33; 34

protoglobigerines 63

Protophites christoli 1 1

Przedborz 247; 248; 250

Pseudocyclammina liasica 161

Pseudoepimastoipora 226

Pseudofusulina concavutas - P. pedissequa zone 226

Pseudofusulina juresanensis zone 226

Pseitdofusulinella 217; 226

Ptychophylloceras sp. 69

Pulchrella 2 17

Purbeckian 125; 246

Putealiceras arkelli 68

Putealiceras sp. cf. P. rossiense 69

Putrella 217; 218

Pyguropsis noetlingi 164

Pyrenees 219

Quaternary 102; 103; 125; 131; 171; 175; 190; 193; 196; 248

radiolaria 63; 76; 79; 213; 222; 223; 228; 230; 231

Radom 243; 245; 246; 248; 251

Radomsko 246

Raqqa 162

Rawda 164

Read Sea 171

Redmondoides lugeoni 163

Rehamna massif 21

Rehmannia 68; 87

Rehmannia (Loczyceras) cf. richei 68

Reineckeid 69

Rekame 123

Retrocostatum Zone 68; 69; 74

Rhaetian 28; 59; 161

Rhar Roubane 109; 123

Rharb 25; 34; 143; 150; 155

Rheouis 58; 67; 69; 70; 71; 72; 74; 77; 79; 86

Rhynchonel/a absoleta 163

Rhynchonella hopkinsi 163

Rif 25; 28; 93; 94; 101; 102; 108; 124; 143; 147; 148; 150;

154;155;156

Rif-Tell 108; 124

Rugosofusulina 226

264

INDEX

Russian Platform 204; 206; 207; 213; 219; 222; 224

Rutbah 161; 165; 170; 175; 189

Rzeszow 248

Saccocoma 63; 34; 76; 83

Sahara 156

Saharan Platform 58

Sakmara 211; 222

Salpingoporella annulata 163

Samara 211; 214

Sandomierz 246; 247

Santonian 169; 181; 189; 192; 194; 247; 248; 249; 252; 253;

254

Scania 240

sehizosphere 79

Schwema 184

Schoul 94

Senonian 100; 154; 253

Serpentinum zone 65

Sheri feh 163; 165; 166

Shiranish 184; 185; 189; 196

Shwema 184; 186; 193

Sidi AVch 86

Sidi Amara 131

Sidi El Abid 123

Sidi Khalif 64; 72

Sidi Mohammed ben Hammou 14; 16

Sidi Rhalem 152

Sidi-Kassem 12; 14; 15; 17; 18; 21

SiemiradzJda cf. pseudorjasanensis 68

Siemiradzkia sp. 67

Silurian 18; 21; 143; 146; 150; 153; 154; 173; 190

Sinai 162

Sinemurian 24; 26; 39; 40; 41; 51; 59; 75; 79; 81; 88

Sinjar 172; 178; 199

Siroua 102

Slovenia 226

Somalirhynchia africana 164

Sonninia 66; 71

Sonninia (Euhoploceras) polyacantha 66

Sonninia (Euhoploceras) simplex 66

Souss 29; 101; 131

Sowerbyceras cf. subtortisulcatum 69

Sowerbyceras cf. tortisidcatum 70

Sowerbyceras sp. juv. 68

Sowerbyceras tortisidcatum 70

Speluncella n. sp. 26

Sphaeroceras gr. brongniarti 67

Sphaeroschwagerina fusiformis zone 219; 225

Sphaeroschwagcrina moelleri - Pseudofusulina fecunda zone

219;225

Sphaeroschwagerina sphaerica - Pseudofusulina firma zone

219; 225

Spinatum zone 45

spinllines 64

Spiroceras sp. 67

Spiroceras sp. cf. 5. bifurcati 67

sponge 79; 213; 222; 223; 224; 228; 230; 243

spore 26

Staroutkinsk 214

Steinekella cnisei 163; 164

Steinekella steinekei 163; 134

Stephanian 21

Stephanoceras 67; 71

Stephanoceras (S.) cf. tenuicostatum 67

Stephanoceras (S.) gr. humphriesianum 67

Sterlitamak 224

Strigoceras sp. 67

stromatopora 164

Subcontracts zone 68

Subgrossouvria sp. 69

Sublunidoceras aff. nodosulcatum 68

Suez 173; 252

Sulcocythere hajbensis 26

Syria 159; 160; 161; 162; 163; 164; 165; 169; 170; 171; 173;

175;178;188

Tadla 146; 153; 154

Tafouralt 123; 124

Tamadout 42; 47

Tamazert 100; 103

Tamdafet 25

Tanak 180; 183

Tanouralt 109; 123

Taourirt 100; 103; 108; 109; 111: 113; 116; 123; 124

Taramelliceras 69; 70; 71; 87

Taramelliceras aff. T. argoviense 70

Taramelliceras aff. T. callicerum 70

Taramelliceras argoviense 70

Taramelliceras cf. baccatum 70

Taramelliceras cf. costatum 71

Taramelliceras cf. pseudoculatum 69

Taramelliceras pseudoculatum 69; 70

Tarfaya 25; 32; 34; 143; 148; 152; 154; 155

Tataouine Remada 79

Taurus 190

Tazekka 26; 28; 33

Tebaga 79; 83

Teisseyre-Tomquist Zone 239; 240; 250; 254

Teloceras 67

Teloceras blagdeni 67

Telouet 41; 47; 51

Terebratula marucchensis 41

Terebratula moreti 4 1

Terebratula quillyensis 163

Terebratula subset hi 164

Terebratula superstes 163

Terni Masgout 116

INDEX

265

Tertiary 130: 147; 148; 150; 165; 173; 189; 240; 254

Tethyan 23; 28; 34; 57; 58; 68; 76; 79; 86; 87; 94; 107; 116;

123; 124; 147; 159; 165; 166; 169; 199: 204: 206;217;

218;226;232;233;234;250;254

Tethys 23; 29: 30; 58; 86: 88; 93; 99; 102; 103: 107; 123; 124;

148: 203: 204: 228; 232;250;253;254

Thailand 218

Thaumatoporella parvovesiculifera 163

Thayyem 180: 186: 188

Thouarsense Zone 65

Tidsi 131

Tighboula-Oudiksou 99

Tilougguit 39; 41; 45; 47

Timidonella sarda 162: 163

Tindouf 12; 94; 147

Tiouli 33; 109: 123

Titeft 109

Tithonian 64; 72; 76; 84; 88; 136; 165: 166

Tizi n'Test 29: 95

Tizi-N-Targhist 147

Tizi-N-Test 45

Tlemcen 109

Toarcian 41; 45; 59; 65; 71; 72; 73: 75; 76; 79; 81: 82: 83: 84;

85:86; 96; 111; 136: 161

Tobol 214

Tokhtinikhtau Mountains 216

Tomaszow Mazowiecki 246; 247

Tortay 212

Tortonian 101: 148

Touila 79

Touissit 109; 110; 111; 123

Triassic 11; 21; 23; 24; 26; 28; 29; 30; 33; 34; 41; 59: 75: 93:

94; 95; 96; 98; 102; 103: 107; 109; 113; 116: 123; 125;

129: 131; 132: 136; 138; 139: 143;147: 1550; 153;154:

161: 165; 166: 170; 172; 175; 178:216; 248

trilobites 222; 223; 228; 230

Trimarginites arolicus 1 1

Trimarginites sp. 70

Trimarginites stenorhynchus 1 1

Tschugor River 228

Tubiphytes 224: 226; 230

Tunisia57; 58; 59: 62; 74; 75; 76; 79; 80: 81; 82; 83; 84; 85;

86; 87; 88;102;252

Turansk 203; 206; 219

Turkey 87; 162; 171: 188

Turonian 99; 100; 148; 154; 169; 175; 179: 183; 189: 191:

194;198;199:239:243;247;248;249;250;253;254

Tyan Shan 207; 225; 232; 234

Ufa 211; 224

Ultradaixina 226

Ultradaixina bosbytauensis-Daixana robusta zone 225

Ungdarella 2 19

Ural (river) 211; 222

Uraloporella 219

Urals (mountains) 203; 204: 206; 207: 213: 214; 218; 219;

224: 226:230; 231 ;234

Vaigach Island 212; 228

Valanginian 243; 245; 246; 248

Valvtdinella jurasica 163

Variabilis Zone 65

Variscan 11; 12; 18; 21; 94

vertebrate 26

Vietnam 218

Visean 146

Vishera 213; 224; 228

Volga 203; 204; 206; 207; 213; 214; 218; 219; 224; 226; 230:

231; 234

Volgian 245

Volgograd 214

Voronezh 203; 225

Wadi Al-Karn 164

Wadi Nahr Az-Zarqua 162

Wadi Nahr Ibrahim 161

wadi Souyah 70

Warsaw 240

Wedekindellina 2 17

Westphalian II; 12; 13; 14; 15; 17; 18; 19; 20; 21; 146

Wisla 243; 245; 247; 248; 252

worm trails 222; 223

Yuzhno-Embensk 213; 232

Zagros 169; 171; 190: 199

Zawiat Ahangal 47

Zawichost 247; 252

Zebdani 164

Zeilleria arethusa 41

Zekkara 154

Zelten 131; 136; 150

Zem Zem 131

Zemmour 33

Zhanazhol 211

Zigzag Zone 68; 71; 72

Ziz-Guir 25

Zmilet el Ghar 79

Zoophycos 62; 63: 67; 68: 71; 72: 74; 76: 83; 111

Remerciements aux rapporteurs / Acknowledgements to referees

La Redaction tient a remercier les experts exterieurs au Museum national d'Histoire naturelle dont les noms suivent, d'avoir

bien voulu contribuer. avec les rapporteurs de FEtablissement. a revaluation des manuscrits (1997/2000) :

The Editorial Board acknowledges with thanks the following referees who, with Museum referees, have reviewed papers

submitted to the Memories du Museum (1997/2000):

Adkison D. L.

Macon

USA

Lowrie J.

Zurich

Suisse

Akam M.

Cambridge

Grande-Bretagne

Machida Y.

Kochi

Japon

Andersen N.

Copenhague

Danemark

MacKinnon D.

Christchurch

Nouvelle-Zelande

AUGELLI I.

Milan

Italie

MacPherson E.

Barcelona

Espagnc

Baba K.

Kumamoto

Japon

Maddison D.

Tucson

USA

Banks T.

Egham

Grande-Bretagne

Manning R.

Washington

USA

Barrier E.

Paris

France

Markle D.

Oregon

USA

Baud A.

Lausanne

France

Marshall B.

Wellington

Nouvelle-Zelande

Bernet-Rollande M.C.

Paris

France

Masaki S.

Hirosaki

Japon

BesseJ.

Paris

France

Masse P.

Paris

France

BestM.

Leiden

Pays-Bas

McLaughlin P.

Washington

USA

Biju-DuvalB.

RueiLMalmaison

France

McLennan D.

Toronto

Canada

Bonavia F.

Paris

France

Messing C.

Dania

USA

Bourdon R.

Roscoff

France

MeulenkampJ.

Utrecht

Pays-Bas

Bourseau J.P.

Villeurbanne

France

Morand S.

Perpignan

France

Bruce J.

Helensvale

Australie

MORETTI I.

Rueil-Malmaison

France

Bruce N.

Copenhague

Danemark

MoutyM.

Damas

Syrie

Brunton H.

Londres

Grande-Bretagne

MlJGNIER J.L.

Grenoble

France

Carpenter J.

New York

USA

Nakamura l.

Kyoto

Japon

Cassagneau P.

Toulouse

France

Naumann C.

Bonn

Allemagne

Castle P.H.J.

Wellington

Nouvelle-Zelande

Newman W. a.

San Diego

USA

Chace F. A.

Washington

USA

NgP.

Singapore

Singapour

Child C. A.

Washington

USA

OOSTEN J.G.

Leiden

Pays-Bas

Cherix D.

Lausanne

Suisse

OroussetJ.

Paris

France

Clobert J.

Paris

France

Packer L.

York

Canada

Cohen D.

Los Angeles

USA

Plateaux C.

Nancy

France

Cook P. L.

Victoria

Australie

Proust J. N.

Lille *

France

Cordey F.

Lyon

France

Ravenne C.

Rueil-Malmaison

France

Darlu P.

Paris

France

Rentz D. C. R.

Canberra

Australie

Danchin E.

Paris

France

ReymaneJ.

Neuchatel

Suisse

Dejean A.

Villetaneuse

France

Richards W.

Miami

USA

Deleporte P.

Paimpont

France

Richter S.

Berlin

Allemagne

Dietrich C.

Champaign

USA

Roberts C.

Wellington

Nouvelle-Zelande

Duffels J. P.

Amsterdam

Pays-Bas

Saldanha L.

Cascais

Portugal

Ellouz N.

Rueil-Malmaison

France

Salomon M.

Marseille

France

Fahay M.

Highlands

USA

Sazonov Y.

Moscou

Russie

Felder D.L.

Los Angeles

USA

SchaerJ.P.

Neuchatel

Suisse

FloquetM.

Marseille

France

SCHOLTZ C.

Pretoria

Afrique du Sud

Fodor L.

Budapest

Hongrie

Stampfli G.

Lausanne

Suisse

Gagne R.

Washington

USA

Stephenson R.A.

Amsterdam

Pays-Bas

Galtier J.

Montpellier

France

Stewart A.

Wellington

Nouvelle-Zelande

GranathJ

Houston

USA

Thierry J.

Dijon

France

Gull an P.

Canberra

Australie

Thorne B.

Maryland

USA

Hamayon R.

Paris

France

Tribovili.ardN.

Paris

France

Hancock P.

Bristol

Grande-Bretagne

Van Baaren J.

Rennes

France

Harvey AAV.

New' York

USA

Vernon P.

Paimpont

France

Harmelin J.G.

Marseille

France

Vi ally R.

Rueil-Malmaison

France

Hayward P.J.

Swansea

Grande-Bretagne

Vickery Vernon R.

Ste-Annc / Bellevue

Canada

Heemstra P.

Grahamstown

Afrique du Sud

Wagele J. W.

Bielefeld

Allemagne

Hodgson C.

Ashford

Grande-Bretagne

Waren A.

Stockholm

Suede

Holthuis L. B.

Leiden

Pays-Bas

Wenzel J.

Colombus

USA

Hue A.Y.

Rueil-Malmaison

France

Wicksten M.K.

College Station

USA

Humphrey C.

Cambridge

Grande-Bretagne

Wiegmann B.

Maryland

USA

Ingrisch S.

Frankfurt

Allemagne

Wilson M.

Cardiff

Grande-Bretagne

Rabat A.

Washington

USA

WilsonS.

Warrensburg

USA

KerpH.

Munster

Allemagne

Yeates D.

Brisbane

Australie

Komai T.

Chiba

Japon

Young P.S.

Rio de Janeiro

Bresil

Krapp F.

Bonn

Allemagne

Zappatera E.

Londres

Grande-Bretagne

Kristensen N.

Copenhague

Danemark

Zezina O.

Moscou

Russie

Ledouaran S.

Paris

France

ZlBROW'IUS H.

Marseille

France

Lemaitre R.

Washington

USA

Ziegler P. A.

Binningen

Suisse

Lovelock P. E. R.

La Haye

Pays-Bas

Source : MNHN. Paris

ACHEVS D IMPRIMER

E\ MARS 2000

SI R LES PRESSES

l'imprimerie K. PAlLLART

A ABBEVILLE

Date de distribution : 17 mars 2000.

Depot legal: Mars 2000

N° d'impression : 10841

Source: MNHN, Paris

2 1 m 2080

Source: MNHN, Paris

DERNIERS TITRES PARUS

RECENTLY PUBLISHED MEMOIRS

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The Peri-Tethys Programme, started in 1993, examines the influence of the Tethyan evolution

on the bordering cratons since the break-up of the Pangea through the accretion of oceanic domains

and finally the collision between the major bordering plates which led to inversions within the epi-

cratonic basins.

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volume like the two previous ones (Peri-Tethys Memoirs 3 and 4) deals with the two great geo¬

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particularly to Morocco (seven papers). Only two papers concern the Northern Platform.

In the first part, the first paper analyses the Late Carboniferous of Morocco, the second and the

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sents the Jurassic global events and their records in Tunisia. The paper 5 presents the Mesozoic and

Cainozoic evolution of the Moroccan Atlasic domain. The two next papers deal with the tectonic

evolution and the subsidence history of Morocco. The eighth paper presents the hydrocarbon sys¬

tem of Morocco. The next one is an overview of the Syrian Jurassic. The last paper of this first part

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data.

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European basin during the Late Palaeozoic. The last paper focuses on the palaeotectonic evolution

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Sylvie Crasquin-Soleau and Eric Barrier (CNRS - Universite Pierre et Marie Curie, Paris) coor¬

dinated this volume which follows the International Peri-Tethys Meeting held in Rabat (Morocco

in June 1997).

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