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the Wisconsin

Sciences,

Arts o

TRANSACTIONS

OF THE

WISCONSIN ACADEMY

OF SCIENCES, ARTS

AND LETTERS

Volume 71, Part I, 1983

OCT 4 19g3

viffiRARlES.

Co-editors

PHILIP WHITFORD

KATHRYN WHITFORD

Copyright © 1983

Wisconsin Academy of Science, Arts and Letters.

Manufactured in United States of America.

All Rights Reserved.

TRANSACTIONS OF THE

WISCONSIN ACADEMY

Established 1870

Volume 71

Part I, 1983

KATHERINE GREACEN NELSON 1

MILWAUKEE’S GENTLEMEN PALEONTOLOGISTS 5

Donald G. Mikulic

SILURIAN BENTHIC INVERTEBRATE ASSOCIATIONS OF

EASTERN IOWA AND THEIR PALEOENVIRONMENTAL

SIGNIFICANCE 21

Brian J. Witzke

OBSERVATIONS ON THE COMMENSAL RELATIONSHIPS

BETWEEN PLATYCERATID GASTROPODS AND STALKED

ECHINODERMS 48

Joanne L. Kluessendorf

MICROFAUNA OF THE SILURIAN WALDRON SHALE,

SOUTHEASTERN INDIANA 56

Susan M. Siemann-Gartmann

EVOLUTION OF A BIOSTRATIGRAPHIC ZONATION: LESSONS

FROM LOWER TRIASSIC CONODONTS, U.S. CORDILLERA 68

Rachel Krebs Pauli

CONODONTS AND BIOSTRATIGRAPHY OF THE MUSCATATUCK

GROUP (MIDDLE DEVONIAN), SOUTH-CENTRAL INDIANA

AND NORTH-CENTRAL KENTUCKY 79

Curtis R. Klug

WISCONSIN ACADEMY OF SCIENCES, ARTS AND LETTERS

The Wisconsin Academy of Sciences, Arts and Letters was chartered by the State Legislature on

March 16, 1870 as an incorporated society serving the people of the State of Wisconsin by

encouraging investigation and dissemination of knowledge in the sciences, arts and letters.

OFFICERS

PRESIDENT

Martha Peterson , Madison

PRESIDENT-ELECT

Kenneth Dowling

IMMEDIATE PAST PRESIDENT

Theodore N. Savides

VICE-PRESIDENTS

Koby T. Crabtree (Sciences), Wausau

William H. Tishler (Arts), Madison

Michael Sherman (Letters), Madison

SECRETARY-TREASURER

Robert E. Najem, Madison

COUNCILORS-AT-LARGE

TERM EXPIRES 1987

Joyce M. Erdman, Madison

Daniel O. Trainer, Stevens Point

TERM EXPIRES 1986

Margaret Fish Rahill, Milwaukee

Gerald Viste, Wausau

TERM EXPIRES 1985

Nancy Noeske, Milwaukee

F. Chandler Young, Madison

TERM EXPIRES 1984

Charles C. Bradley, Baraboo

Robert Ragotzkie, Madison

COUNCIL-APPOINTED POSITIONS

LIBRARIAN

Jack A. Clarke, Madison

DIRECTOR— W.A.S.A.L.

DIRECTOR— JUNIOR ACADEMY

LeRoy R. Lee, Madison

EDITORS

Kay and Philip Whitford, Transactions

Patricia Powell, Review

EDITORIAL POLICY

The TRANSACTIONS of the Wisconsin Academy of Sciences, Arts and Let¬

ters is an annual publication devoted to original papers, preference being given to

the works of Academy members. Sound manuscripts dealing with features of the

State of Wisconsin and its people are especially welcome; papers on more general

topics are occasionally published. Subject matter experts review each manuscript

submitted.

Contributors are asked to submit two copies of their manuscripts. Manuscripts

should be typed double-spaced on 8 Vi x 11 inch bond paper. The title of the paper

should be centered at the top of the first page. The author’s name and brief address

should appear below the title. Each page of the manuscript beyond the first should

bear the page number and author’s name for identification, e.g. Brown-2, Brown-3,

etc. Identify on a separate page, the author with his institution, if appropriate, or

with his personal address to be used in Authors’ Addresses at the end of the printed

volume.

The style of the text may be that of scholarly writing in the field of the author.

To expedite editing and minimize printing costs the Editor suggests that the general

form of the current volume of TRANSACTIONS be examined and followed when¬

ever possible. For Science papers, an abstract is requested. Documentary notations

may be useful, especially for the Arts and Letters papers, and should be numbered

for identification in the text. Such notations as a group, should be separate from the

text pages and may occupy one or more pages as needed. Literature Cited should be

listed alphabetically at the end of the manuscript unless included in notations. The

style of the references will be standardized as in the current volume to promote ac¬

curacy and reduce printing costs.

Figures should be prepared to permit reduction. Lettering should be large

enough to form characters at least 1 mm high after reduction. Only high contrast

glossy prints, not larger than 8 Vi x 11 inches, or good black ink drawings on bond

paper, are suitable for reproduction. (Copies run by dry photocopiers will do for the

second copy, but are not sharp enough for printing.)

Printing is expensive. Each paper will be subject to a per page charge to the

author, the rate being determined yearly. When a paper is accepted, authors without

departmental or grant funds for publication should request that the Director of the

Academy (at the Academy address) waive page charges. Galley proofs and edited

manuscript copy will be forwarded to the authors for proof reading prior to

publication; both must be returned to the editor within one week. Reprints should be

ordered when proof is returned; forms and instructions will be sent to the authors.

Each author will receive one complimentary copy of the volume of Transactions in

which his work appears.

Papers received after July 1 will be considered for the next annual volume.

Manuscripts should be sent to:

Philip & Kathryn Whitford

Co-Editors: TRANSACTIONS

2647 Booth St.

Milwaukee, WI 53212

DEDICATION

This memorial volume presents the results of a paleonto¬

logical symposium sponsored by colleagues, alumni and

students of The University of Wisconsin-Milwaukee, De¬

partment of Geological and Geophysical Sciences as a

tribute to the productive life of Dr. Katherine Greacen

Nelson. This symposium was held on the old Milwaukee

Downer Campus in Milwaukee on January i; 1983, and all

participants were Katherine’s students.

It is appropriate that this memorial volume, sponsored

by contributions from former students and industries that

employ her students, be published in the Transactions of

the Wisconsin Academy of Sciences, Arts, and Letters. She

worked for many years in a variety of capacities for the

Academy, and was the first woman elected as President.

To Katherine Greacen Nelson, geologist, educator, and

friend, we dedicate this volume with love for enriching the

lives of so many people.

1

Katherine Greacen Nelson

KATHERINE GREACEN NELSON

Katherine Greacen was born in Sierra

Madre, California on December 9, 1913. She

was married to Attorney Frank H. Nelson of

Milwaukee, Wisconsin. She died on Decem¬

ber 29, 1982 in Milwaukee after a short but

valiant fight against cancer.

After receiving the first Ph.D. in geology

from Rutgers University in 1938, Katherine

began her distinguished career of service at

Milwaukee Downer College. After World

War II duty in the oil fields of Texas, she

returned to Milwaukee and made contribu¬

tions at Milwaukee Downer Seminary, the

Y.W.C.A., and Wisconsin State College

before joining The University of Wisconsin-

Milwaukee Faculty in 1956.

Although Katherine’s professional accom¬

plishments include numerous scholarly

papers, she is best known for her devotion to

teaching others about the earth. Most uni¬

versity professors restrict their teaching to

college-level courses and the supervision of

graduate students, but not Katherine. She

was always generous in her educational en¬

deavors, and was equally available to, and

comfortable with, a bus load of school

children visiting the Greene Museum or

congressmen contemplating the potential for

the Ice Age Scientific Reserve. She never

undertook any assignment with thought of

personal reward or recognition. All she ever

cared about was helping an individual, a

group, or an organization. Such selfless

people are rare in our society.

In addition to being the first chairperson

of the Department of Geological and Geo¬

physical Sciences at UWM, Katherine found

time to serve the University on dozens of

committees, including two terms on the

Faculty Senate. She was a Fellow of the

Geological Society of America, and a

member of the Paleontological Society and

the American Association of Petroleum

Geologists.

Katherine held offices in a score of

service-oriented organizations. For special

contributions toward the establishment of a

Sigma Xi Club at UWM, she was elected

President. In recognition of assistance to the

Milwaukee Public Museum, she was ap¬

pointed an Honorary Curator. For long¬

term service to the Wisconsin Geological

Society, including a term as President, she

was appointed an Honorary Member. She

was President of Phi Kappa Phi, and was a

nominee for President of the Earth Science

Section of the American Association for the

Advancement of Science at the time of her

death. The Midwest Federation of Mineral-

ogical and Geological Societies honored

Katherine as Educator of the Year in 1982.

She was an active contributor to programs of

the National Association of Geology Teach¬

ers, and served as President of the Central

Section. In 1978, this organization selected

her as the first woman recipient of the

prestigious Neil Miner Award for dis¬

tinguished contributions to earth science

education.

There is much more one could record

about Katherine the doer, but what about

Katherine the person? She was tranquil and

energetic with a kind word and helping hand

to all; and always with a beautiful smile. To

her, the earth was a remarkable place — to be

understood, appreciated and enjoyed. She

labored tirelessly for this belief while

imparting warmth, enthusiasm and joy to

everyone with whom she came in contact.

3

ACKNOWLEDGMENTS

The Katherine G. Nelson Symposium and

Memorial Program presented at The Univer¬

sity of Wisconsin-Milwaukee on January 15,

1983 was coordinated by Richard A. Pauli,

and arrangements were facilitated by Frank

J. Charnon, Gregory Mursky, Rachel K.

Pauli and Robert W. Taylor; all of the

Department of Geological and Geophysical

Sciences at The University of Wisconsin-

Milwaukee. The other faculty, staff, and

students in the department generously

assisted in many aspects of the program.

Dennis D. Bollmann, Marmik Oil Company,

Denver, Colorado and Charles W. Gart-

mann, Placid Oil Company, New Orleans,

Louisiana acted as session chairpersons.

The memorial program was conducted by

L. Joseph Lukowicz, Ladd & Lukowicz,

Denver, Colorado; Frank E. Horton,

Chancellor, The University of Wisconsin-

Milwaukee; Douglas S. Cherkauer, The

University of Wisconsin-Milwaukee; Robert

E. Behling, West Virginia University; and

Rachel K. Pauli, The University of Wiscon¬

sin-Milwaukee.

Rachel K. and Richard A. Pauli directed

the preparation and critical review of the

manuscripts contained in this volume. How¬

ever, the encouragement and assistance of

LeRoy R. Lee, Executive Director of the

Wisconsin Academy of Science, Arts and

Letters; and Philip B. and Kathryn D. Whit-

ford, Co-Editors of the Transactions were

critical factors in making this publication

possible.

The papers included in this volume were

critically reviewed by: Dr. Timothy R. Carr,

Arco Oil and Gas Company (Texas); Dr.

James W. Collinson, The Ohio State Univer¬

sity; Dr. Robert E. Gernant, The University

of Wisconsin-Milwaukee; Dr. Markes E.

Johnson, Williams College (Massachusetts);

Dr. Bradford Macurda, Jr., The Energists

(Texas); Dr. Rachel K. Pauli, The University

of Wisconsin-Milwaukee; Dr. Dietmar Schu¬

macher, Pennzoil Exploration and Pro¬

ducing Company (Texas); Dr. Peter M.

Sheehan, Milwaukee Public Museum and

The University of Wisconsin-Milwaukee;

and Dr. Dale R. Sparling, Southwest State

University (Minnesota).

Financial support for publication of this

memorial volume of the Transactions

dedicated to Katherine Greacen Nelson was

provided by The Amoco Foundation

through the efforts of many geologists and

geophysicists employed by Amoco Pro¬

duction Company; Richard W. and Julie S.

Behling, Tulsa, Oklahoma; Conoco Incor¬

porated through the efforts of William E.

Laing; Cotton Petroleum Corporation

through the efforts of Arthur L. Paquette

and Donald E. Pauli; Exploration Logging

U.S.A. through the efforts of Robert J.

Rose and Howard Greene; Exxon Company

USA through the efforts of Robert L.

Sunde; Jeffrey C. Gruetzmacher, Leaf River

Group, Houston, Texas; The InterNorth

Foundation through the efforts of Julie S.

Behling; Dietmar Schumacher, Pennzoil

Exploration and Production Company,

Houston, Texas; Sohio Alaska Petroleum

Company through the efforts of M. J.

Marfleet and Edward A. Frankovic; Robert

L. Sunde, Kingsville, Texas; Union Oil

Company of California through the efforts

of Charles W. King, Larry H. Smith and

David E. Willis.

The generosity of the individuals and

organizations listed above is gratefully ack¬

nowledged by all of Katherine's students,

friends and colleagues.

In addition, thanks are offered to present

and future contributors to the Katherine G.

Nelson Scholarship fund established by the

Department of Geological and Geophysical

Sciences at The University of Wisconsin-Mil¬

waukee.

4

MILWAUKEE’S GENTLEMEN PALEONTOLOGISTS

Donald G. Mikulic

Illinois State Geological Survey , Champaign , IL 61820

Abstract

During the last half of the nineteenth century several large fossil collections

were assembled from Silurian and Devonian rocks quarried in the vicinity of

Milwaukee, Wisconsin. Conditions for collecting were favorable at that time

because the quarries were small, low volume, hand-operated and more numerous

compared to present-day operations. Low paid quarry workers were able to signif¬

icantly supplement their incomes by selling fossils which insured a continual supply

of specimens.

These collections were assembled by a few moderately wealthy, self-educated

naturalists, who had the time, money and interest to secure large numbers of

specimens. The most prominent of these gentlemen paleontologists were Increase A.

Lapham (collection destroyed by fire in 1884), Fisk Holbrook Day (collection now

at Harvard’s Museum of Comparative Zoology), Thomas A. Greene (collection at

The University of Wisconsin-Milwaukee), and Edgar E. Teller (collection at the

National Museum of Natural History).

By assembling collections and publishing a few papers, these individuals stimu¬

lated paleontologic and stratigraphic research in the area by such notable geologists

as James Hall, Robert Whitfield, Stuart Weller, and many others. Since most

quarries in the area are abandoned, and because of the mechanized nature of large-

scale quarrying at those remaining, it is impossible to assemble comparable

collections of new material. These old collections, therefore, are of critical

importance to future geologic work in the area, particularly in the fields of taxo¬

nomy, biogeography, biostratigraphy, taphonomy, paleoecology, and stratigraphy.

Introduction

During the last half of the nineteenth

century, several important collections of

Silurian and Devonian fossils were made in

the vicinity of Milwaukee, Wisconsin by

local naturalists, including I. A. Lapham,

F. H. Day, T. A. Greene, E. E. Teller, and

C. E. Monroe. These collections, which

represented a great expenditure of time and

money, stimulated the interest of many

prominent scientists in the geology and

paleontology of southeastern Wisconsin.

The most important result of the subsequent

research was the discovery and correct inter¬

pretation of Silurian reefs in the area — the

first Paleozoic reefs to be identified in North

America (Fig. 1).

Two primary factors influenced the as¬

sembly of these collections. Most important

was the availability of fossil specimens, due

to the methods and intensity of quarrying

for lime and building stone. Also important,

however, was the role of the naturalist in

nineteenth century science and his moti¬

vation for an interest in natural history.

Both of these factors have changed greatly,

and the decline of the local stone industry

has made it impossible to assemble compar¬

able material. Because the older collections

are irreplaceable, they remain a key element

in geological research of the Milwaukee area

and in Silurian and Devonian paleontology

in general.

This paper discusses the conditions under

5

6

Wisconsin Academy of Sciences , Arts and Letters

[Vol. 71, Part I,

Fig. 1. Reef structure in the west wall of the Schoonmaker quarry, Wauwatosa,

Wisconsin, 1899. This Silurian reef was the first Paleozoic reef described in North

America (Hall, 1862). This quarry was also the locality from which Day, Greene,

and Teller, as well as others, made extensive fossil collections. The area illustrated is

near the present intersection of 68th and State Streets in Wauwatosa. Photo by

W. C. Alden, Photo No. 115, U.S. Geological Survey Photo Library, Denver.

Fig. 2. Lithograph demonstrating typical nineteenth century quarrying methods. Quarry depicted was in Devonian

rocks at Mill No. 1 of the Milwaukee Cement Company shortly after the company began operations, ca. 1876. The area

shown in the lithograph is on the east bank of the Milwaukee River, near the old swimming beach in Estabrook Park,

Milwaukee. From Chamberlin (1877); drawn from a photo taken by J. C. Miller.

1983]

Mikulic— Milwaukee’s Gentlemen Paleontologists

1

which the collections were made, the prom¬

inent individuals who assembled them, and

the way in which this collecting activity has

contributed to geological research of south¬

eastern Wisconsin.

Milwaukee’s Stone Industry

Silurian and Devonian dolomite underlies

much of southeastern Wisconsin and was an

important source of building materials

throughout the 1800s. The development of

the local stone industry and the methods of

operation were important factors in the for¬

mation of the nineteenth century Milwaukee

area fossil collections. Because a fairly thick

cover of Pleistocene and Recent sediments

limits natural bedrock exposures in south¬

eastern Wisconsin, quarries were critical to

extensive collecting and the rate of fossil

discoveries was closely related to the growth

of the stone industry. Local quarrying

reached its peak in the late 1800s with the

development of the natural cement industy,

which utilized Devonian rock (Fig. 2).

Nineteenth century quarries were quite

different from the large mechanized oper¬

ations of today. Most were small, shallow,

and the rate of rock extraction was slow.

Due to the lack of mechanization, large

numbers of low-paid laborers were em¬

ployed. After blasting, blocks too big to be

handled were broken with sledge hammers.

All rock was picked up by hand and placed

in carts or wagons, and building stone was

trimmed with hammer and chisel (Fig. 2).

Probably most quarry workers had little

desire to start personal fossil collections

during their ten hour workdays. However,

the opportunity to supplement their incomes

was a compelling reason to develop an inter¬

est in paleontology. Milwaukee’s gentlemen

paleontologists supplied the financial in¬

centive by regularly purchasing fossils from

the workers. A single good specimen could

fetch a dollar or two, a sum which doubled

the daily wages of most quarry employees.

Thus, the methods of quarrying and the

active fossil market insured that few im¬

portant fossils would escape the notice of the

quarrymen.

Since the later 1800s, the number of

quarries in the Milwaukee area has decreased

from over thirty sites to only one. Most of

the former sites are completely filled and

covered, and the active quarries are un¬

favorable for collecting because of high

vertical walls and large-scale operations.

Also, quarry workers are no longer a de¬

pendable source of specimens since they

have little direct contact with the rock and to

double their daily wages through fossil pur¬

chases would be prohibitive. These changes

have all contributed to a significant decrease

in the availability of fossils, as well as rock

exposures, which severely limits modern

geological and paleontological research in

southeastern Wisconsin.

Gentlemen Paleontologists

Fossil collecting was greatly influenced by

the presence of several well motivated and

competent naturalists who lived in the Mil¬

waukee area during the time that quarrying

activities were at their peak. These individ¬

uals were typical of the self-educated and

self-supported researchers who were respon¬

sible for much of the advancement of science

throughout the nineteenth century.

In the 1800s, scientific research and edu¬

cation took place sporadically and the qual¬

ity was irregular. It was difficult to obtain

advanced education in new specialized scien¬

tific areas such as geology, and it was even

more difficult to find employment in these

fields. However, these constraints did not

prevent an increase in the popularity of all

aspects of natural history throughout the

nineteenth century.

Studying and collecting natural history

specimens for one’s “cabinet” became a

socially acceptable and popular pastime. The

quality of naturalist activities ranged from

mindless collecting of everything and any¬

thing to some of the best research of the

time. Milwaukee’s gentlemen paleontolo¬

gists fit into the middle of this range. While

8

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

Fig. 3. Portrait of Increase A. Lapham (from

Sherman, 1876).

men like I. A. Lapham did make substantial

contributions to many fields of natural his¬

tory, others were not as diversified in their

interests nor did they publish as many schol¬

arly papers. All were interested in several

different branches of natural history, and

these lifelong interests developed early.

None of these individuals had advanced

training in geology or other science, and

were generally self-taught. They all enjoyed

fairly high social standing and were success¬

ful enough in their chosen careers to have the

time and money to devote to paleontological

pursuits. The major contributions of these

naturalists were the professional interest

they stimulated in others and the compre¬

hensive collections they diligently assembled.

The following biographical sketches describe

Milwaukee’s best known gentlemen paleon¬

tologists and their activities.

Increase A lien Lapham

Increase Allen Lapham is well known as

Wisconsin’s first scientist and one of the

state’s most distinguished early citizens (Fig.

3). His numerous accomplishments in other

fields of natural history may overshadow his

paleontological contributions. However, he

was the first to collect fossils in the Milwau¬

kee area, and undoubtedly influenced the

activities of his contemporaries.

Lapham was born at Palmyra, New York,

on March 7, 181 1 . As a youth he worked as a

stone cutter during construction of the Erie

Canal at Lockport, New York (Sherman,

1876), and this work with fossiliferous

Silurian rocks stimulated a lifelong interest

in geology. He wrote his first scientific

article at the age of 17, a short paper pub¬

lished in the American Journal of Science

dealing with the geology around Louisville,

Kentucky (Lapham, 1828). After spending

several years as an engineer in Ohio, he

moved to Milwaukee in 1836 at the request

of Byron Kilbourn, and became chief

engineer and secretary of the Milwaukee and

Rock River Canal Company (Sherman,

1876). Soon after his arrival, he and Kil¬

bourn began to seach the area for econom¬

ically important rock and mineral deposits.

Lapham also began to make observations on

a variety of natural history subjects, which

he continued to do throughout his life.

In 1846 Lapham sent a collection of Mil¬

waukee area fossils to James Hall for identi¬

fication. With the help of Hall’s fossil

identifications, Lapham determined the cor¬

rect stratigraphic succession of rock units in

Milwaukee. By the time his 1851 paper was

published, he had defined the general Paleo¬

zoic stratigraphic section for eastern Wis¬

consin, established correlation with the New

York section, and recognized the eastward

dip of the rocks into the Michigan Basin.

In 1853 Lapham sent a manuscript entitled

“American Paleontology’’ containing over

2000 fossil descriptions to Hall for comple¬

tion and co-authorship (Winchell, 1894).

Collaboration with Hall would have greatly

elevated Lapham’s stature as a geologist and

paleontologist. Although Hall agreed to

complete the project, he apparently did

1983]

Mikulic— Milwaukee’s Gentlemen Paleontologists

9

nothing with it and it was returned in 1860 at

Lapham’s request (Bean, 1936).

In 1873 Lapham was appointed head of

the new state geological survey, and in this

capacity he assembled a noteworthy group

of young geological assistants, including

T. C. Chamberlin (Beloit College) and

Roland Irving (The University of Wiscon¬

sin). In 1875 he was replaced by a political

crony of the new governor, but his early

planning was in no small way responsible for

the later success of the survey. He died on

September 14, 1875, a few months after his

removal from office.

Lapham’s natural history collection,

which included “10,000 fossils, minerals,

shells, meteorites, and Indian relics” ( State

Journal, Dec. 16, 1884) was purchased by

the state for The University of Wisconsin.

Unfortunately, his entire collection was

destroyed in the Science Hall fire of De¬

cember 1, 1884 {Milwaukee Sentinel, Dec. 2,

1884). Only a partial list of Lapham’s mate¬

rial exists in the published catalogue of the

Wisconsin state mineral exhibit from the

Centennial Exposition at Philadelphia in

1876, which consisted predominantly of

specimens from his collection (Sweet, 1876).

Lapham was generous with his specimens

and many were given to, or exchanged with,

other scientists. Some of James Hall’s type

specimens from Wisconsin, now in the

American Museum of Natural History, are

probably Lapham’s specimens, although

they are not so labelled. The Worthen

Collection at the Illinois State Geological

Survey contains at least one Lapham

specimen and others are reported to be

located at the Milwaukee Public Museum

(Teller, 1912) and in the Greene Museum at

The University of Wisconsin-Milwaukee.

Fisk Holbrook Day

Fisk Holbrook Day, the son of Reverend

Warren Day and Lydia Holbrook Day, was

born at Richmond, New York, on March 11,

1826 (Fig. 4). He attended Jefferson Medical

College in Philadelphia, graduating in 1849

Fig. 4. Portrait of Fisk Holbrook Day (from Zimmer-

mann, 1979).

{Lansing Journal, 1903). Day moved to

Wauwatosa, Wisconsin, in 1854, and was a

prominent physician in Milwaukee County

for almost 40 years. Besides having a private

practice, Day was a physician for Milwaukee

County hospital and poor farm for many

years (Zimmermann, 1979).

Day was a naturalist with a wide variety of

interests, including geology, botany, and

archeology (Fig. 5). His paleontologic inter¬

ests probably stemmed from his father’s

acquaintance with James Hall while in New

York. Reverend Day had collected fossils

and occasionally corresponded with Hall

during the 1840s, and Hall visited the Day

household to examine his collections. Hall

later made several visits to Wauwatosa to

study the fossils in F. H. Day’s cabinet, and

a few specimens figured by Hall in 1867 and

1870 were from the Day collection.

Day published one paper on Milwaukee

area geology in 1877. This paper demon¬

strates that Day was very observant and an

original thinker, confident enough in his

10

Wisconsin Academy of Sciences , Arts and Letters [Voh 71, Part I,

Fig. 5. F. H. Day in his study, ca. 1870s. Photo

courtesy of Mary Dawson.

observations to dispute established geo¬

logical authorities such as James Hall and

Charles Doolittle Walcott. Day (1877) men¬

tioned working on another paper about the

general characteristics of trilobites that

apparently was never published. However,

he did supply a detailed faunal list from local

quarries to T. C. Chamberlin, which was

published in Volume 2 of The Geology of

Wisconsin.

Day specialized in collecting local Silurian

fossils, and by 1880 he had assembled a

collection of the best quality ever made in

southeastern Wisconsin. His cabinet con¬

tained may spectacular specimens, primarily

from the Schoonmaker quarry. These in¬

cluded an orthoconic cephalopod over seven

feet long, and a spectacular specimen of the

trilobite Bumastus dayi (named in his honor)

(Fig. 6).

In 1880 Day decided to sell his collection,

and offered it to The University of Wis¬

consin (through T. C. Chamberlin) and to

Harvard University. Most of the collection,

including the best specimens, was purchased

by Alexander Agassiz and donated to the

Museum of Comparative Zoology at Har¬

vard in 1881 (Raymond, 1916). While it may

seem unfortunate that Day’s collection was

Fig. 6. Two specimens of the trilo¬

bite Bumastus dayi collected from the

Silurian reef at the Schoonmaker

quarry by Day, named in his honor by

Raymond (1916). This was Day’s most

valued specimen, for which he was

offered $100. This specimen is now

No. 647 in the Museum of Compara¬

tive Zoology at Harvard.

1983]

Mikulie— Milwaukee’s Gentlemen Paleontologists

11

sent out of the state, had it been sold to The

University of Wisconsin probably it too

would have been destroyed in the 1884

Science Hall fire. Even after Day shipped

8265 pounds of material to Harvard (Mil¬

waukee Sentinel, Jan. 9, 1881), he still

retained over 5000 fossils. In 1884 he sold a

large number of the remaining specimens to

Thomas Greene and much of his library to

Edgar Teller. Day retired in 1893 and moved

to Lansing, Michigan, where he died on May

31, 1904. At the time of his death he had

several thousand specimens in his posses¬

sion, which were later sold to The University

of Michigan.

Day’s material at Harvard was placed in

the general collections and cannot be studied

as a comprehensive unit. Much of it has not

been catalogued, but it is in reasonably good

shape. Besides containing most of Day’s best

specimens, the Harvard collection has

material from Milwaukee area localities that

is not represented elsewhere. Day’s material

in the Greene collection cannot be identified,

but, based on the purchase price, it probably

represents a large part of Greene’s Wauwa¬

tosa material. The labels for many of Day’s

specimens at The University of Michigan

have been lost, and little of his collection has

been unpacked.

Thomas Arnold Greene

Thanks to the foresight of his family,

T. A. Greene’s correspondence, library,

and, more importantly, his collections have

been preserved in Milwaukee. This material,

including several biographical studies (Buck,

1884; Conrad, 1895; Nehrling, 1895; Grea-

cen and Ball, 1946a, b; Thomas, 1928) pro¬

vides the most detailed information available

for any of Milwaukee’s gentlemen paleontol¬

ogists.

Greene was born on November 2, 1827 in

Providence, Rhode Island (Conrad, 1895)

(Fig. 7). At the age of 16 he began training in

a drug store, and five years later he moved to

Milwaukee. Greene purchased a retail drug

store, and shortly afterward went into

Fig. 7. Portrait of Thomas A. Greene (from Thomas,

1928).

partnership with Henry H. Button. Their

firm became one of the largest wholesale

drug businesses in the city, making Greene a

wealthy man (Greacen and Ball, 1946a).

Greene was very interested in botany and

geology in his youth, and brought a collec¬

tion of Rhode Island minerals with him to

Milwaukee (Nehrling, 1895). During his first

thirty years in Milwaukee, Greene devoted a

little time to collecting and purchasing

minerals, but there was no apparent interest

in fossils. While he sustained an interest in

botany and mineralogy, in subsequent years

paleontology became his major concern.

Because of poor health in 1878, he was

advised by his physician to seek relief from

the pressures of business. As a means of

relaxing he began to collect and purchase

fossils, and continued to do so until his

death in the fall of 1893. Greene collected

primarily at the cement quarries, the 26th

Street quarry, and quarries at Racine and

Wauwatosa. He corresponded with fossil

collectors around the country to arrange

12

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

exchanges or purchases. He also corres¬

ponded with many scientists and loaned

specimens to them. James Hall, C. Wach-

smuth, and J. Newberry all illustrated a

number of Greene’s specimens.

Although Greene acquired a thorough

knowledge of Silurian and Devonian fossil

identification, he apparently had no interest

in writing scientific papers. His corres¬

pondence does reveal some geological data,

and it also contains information on how he

assembled his collection and gives insight

into his personality.

Greene was quite serious and methodical

in his efforts (Buck, 1884), and his goal was

to obtain a comprehensive collection of both

minerals and Silurian and Devonian fossils.

Although he wanted the best possible speci¬

mens for his collection, he also purchased as

many common specimens as possible. He

was aggressive in his quest for specimens, and

collecting soon became an obsession — cer¬

tainly not the type of relaxation his doctor

had prescribed. Greene’s persistence in

trying to convince other collectors to trade

or sell specimens to him often resulted in

their complete disinterest in further dealings

with him. Greene seldom revealed informa¬

tion on the availability of fossils to other

collectors, and in most letters he states that

collecting had been better a few years before

at all of his localities.

In addition to the large number of fossils

purchased from quarry workers in Wis¬

consin, Greene also dealt with collectors

and quarrymen in the Chicago area, and

obtained Waldron (Indiana) fossils from

J. Doty. His main supplier of Chicago area

fossils from 1884 to 1893 was A. G. Warner.

Warner appears to have earned a fair income

by selling fossils to a small group of wealthy

collectors, including Dr. J. Kennicott and

W. Van Horne of Chicago. When Greene

purchased Kennicott’s collection in 1885 he

also became Warner’s main, and possibly

only, customer. For the remainder of his life

Greene purchased specimens from Warner

on a regular basis, often receiving several

boxes of fossils a month during the summer.

It is interesting to note that Greene invari¬

ably paid Warner less than his asking price

for the fossils. There was seldom any bar¬

gaining over the price, and it is difficult to

determine whether Greene was always

underpaying or Warner was always over¬

charging. As a result of these transactions

Fig. 8. Mill No. 1 of the Milwaukee Cement Company, ca. 1885 (from Barton, 1886).

1983] Mikulic— Milwaukee’s Gentlemen Paleontologists 13

Fig. 9. Thomas Greene’s collection at his home, probably taken after his death in 1894 and before the dedication of

the Greene Museum in 1913. Photos courtesy of the late Katherine G. Nelson.

Fig. 10. Another view of Thomas Greene’s collection at his home. Photo courtesy of the late Katherine G. Nelson.

14

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

with Warner, Greene acquired the best col¬

lection of Chicago area Silurian reef fossils.

Greene’s interest in Devonian fossils led

him to purchase stock in the Milwaukee

Cement Company (Fig. 8). Greene possibly

made this investment more to .insure a

constant supply of fossils than to realize

financial gains, but he later became a mem¬

ber of the board of directors and vice pres¬

ident of the company (Greene and Berthelet,

1949).

He also had interesting and unusual deal¬

ings with the Horlick Lime and Stone Com¬

pany in Racine. At most quarries he ar¬

ranged to have workers and owners save

fossils for him to purchase, but at this

quarry he also paid to have workers break

rocks for him while he was on the premises.

He eventually arranged to have charges set in

specific parts of the quarry ready to go off

when he arrived. Anyone who has collected

fossils in recent years knows this type of

cooperation is unheard of in modern quar¬

ries, even if one could afford it.

Greene was a member of the Board of

Trustees of the Milwaukee Public Museum

from 1883 until his death in 1894. He

arranged fossil purchases for the museum

while on the board, but he also outbid the

museum for specimens he wanted in his own

collection (Greacen and Ball, 1946a).

Greene spent over $16,000 on his entire

collection, including many of the wooden

cases in which it is still housed. Of that

amount, over $5000 was spent on fossils

between 1878 and 1893. Greene’s collection

(Figs. 9 and 10) was kept by his family until

1911 when it was donated to Milwaukee-

Downer College (Greacen and Ball, 1946a).

The family also provided a fireproof build¬

ing for the collection. In 1964 the collection

was sold to The University of Wisconsin-

Milwaukee for the bargain price of $20,000,

and is now worth more than ten times that

amount.

The Greene collection is the sole major

nineteenth century Milwaukee area fossil

collection to remain intact and in the area.

Not only is it the largest collection of local

Silurian and Devonian fossils, but it is also

the largest single collection of Silurian reef

fossils from the Chicago area. Although the

Greene collection is undoubtedly the most

important paleontologic research collection

in the state, it has been only partially

examined by specialists. However, it will

remain a key element in any future geologic

research in the area.

Edgar Eugene Teller

Edgar E. Teller was born on August 3,

1845 in Buffalo, New York (Fig. 11). In 1875

he moved to Milwaukee where he worked as

a buyer for Plankinton and Armour (and its

successor firms) until his retirement (Teller,

1924). He became interested in paleontology

by stopping in at the Moody quarry (26th

Street quarry) on his way to and from work

in the early 1880s. Teller devoted most of his

time to collecting Devonian fossils from the

Milwaukee Cement Company quarries, but

he also collected a large amount of Silurian

Fig. 11. Portrait of Edgar E. Teller, ca. 1895. Photo

courtesy of Kathryn Teller.

1983]

Mikulic— Milwaukee’s Gentlemen Paleontologists

15

material from the Moody quarry and lesser

amounts from the Schoonmaker quarry and

the Horlick quarry in Racine (Fig. 12), as

well as some of the few complete trilobites

known from the Cambrian Lodi Shale of

Wisconsin.

Teller corresponded with, and loaned

specimens to, a number of professional

paleontologists, including James Hall,

Robert Whitfield, Stuart Weller, Charles

Eastman, Charles Walcott, and H. F. Cle-

land. Because of these associations, his

collection contained, or supplied, more

figured specimens than any other local

naturalist’s. He also wrote more scientific

papers than other local collectors (Teller,

1900; 1906; 1910; 1912; Monroe and Teller,

1899), providing some of the most detailed

descriptions of Wisconsin Devonian geology

ever published (also see discussion about

Monroe).

Teller was a major participant in the

Wisconsin Natural History Society. He

joined the society in 1885, serving as its

president on several occasions, and as an

editor and director until he returned to

Buffalo in 1915. The demise of the society at

this time was probably due in part to his

departure. Teller was also interested in

archaeology, and helped to establish the

Wisconsin Archaeological Society as a separ¬

ate organization from the Wisconsin Natural

History Society in 1901 (Teller, 1924).

In 1908 Teller gave a large part of his

collection to the Walker Museum at The

University of Chicago (now part of the

present-day Field Museum). Few of these

specimens can now be identified as collected

by Teller, but many of the Wisconsin Sil¬

urian and Devonian fossils in this collection

undoubtedly were his.

Teller died in Buffalo on July 19, 1923.

Both the National Museum of Natural

History and Yale University were interested

Fig. 12. Main quarry of the Horlick Lime and Stone Company located along the Root River near Racine, Wisconsin,

ca. 1888. The Silurian reef rock at this quarry supplied most of the fossils collected in the Racine area (from Art

Publishing Co., 1888).

16

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

in his collection, and on April 3, 1924 his

wife, Marie, gave the entire collection of

100,000 specimens and a library of several

thousand volumes to the National Museum.

This donation included nearly all of the type

specimens described from his collection.

Teller’s material was assimilated into the

National Museum’s general collections and

can no longer be examined intact. Several

drawers of his Silurian specimens remain

unsorted and uncatalogued. His books were

incorporated into the museum library.

Charles Edwin Monroe

Charles Monroe was born in 1857, and

later graduated from Oberlin College and

The University of Michigan Law School

(Milwaukee Journal, May 13, 1931) (Fig.

13). He moved to Milwaukee in 1884, and

began a long career as a prominent attorney.

He was apparently interested in several fields

of natural history, of which botany was fore¬

most.

Fig. 13. Portrait of Charles E. Monroe, ca. 1920s.

Photo courtesy of the Milwaukee Public Museum, Neg.

No. 417133.

In the 1890s and early 1900s, Monroe

spent a considerable amount of time collect¬

ing and studying the Devonian fossils of

Wisconsin. He was a close friend of Edgar

Teller, and the two of them share credit for

stimulating research on the Devonian rocks

of the area. Together they made comprehen¬

sive collections of all the localities and

stratigraphic units of the Wisconsin

Devonian. They were the first to publish

detailed descriptions of the stratigraphic

occurrence of Devonian fossils and to sub¬

divide Devonian strata. They published an

important report on Devonian rocks and

fossils encountered during excavation for

water intake tunnels at North Point in

Milwaukee. They also discovered the phyllo-

carid bed in the Silurian Waubakee Dolo¬

mite and supplied the phyllocarid specimens

described by Whitfield (1896). In 1900

Monroe published a description of the De¬

vonian rocks, which he discovered, at what

is now Harrington Beach State Park near

Lake Church, Ozaukee County, Wisconsin.

He contacted several individuals, including

Charles Schuchert and Stuart Weller, in an

attempt to have this new fauna described,

and it was probably a result of his efforts

that one of Schuchert’s students, H. F.

Cleland, began his work on the Wisconsin

Devonian.

Monroe was associated with the Milwau¬

kee Public Museum for many years. He held

the position of honorary curator of paleon¬

tology from 1897 until at least 1922, and was

the only person to work on the museum’s

fossil collections until Ira Edwards was hired

in 1916. A generous donor to the museum,

he gave nearly all of his Wisconsin Devonian

fossil collection to the museum between 1898

and 1900, including the spectacular jaw of

Eastmanosteus figured by Eastman (1900)

and Cleland (191 1) (Fig. 14). Other fossils he

collected became type and figured specimens

in papers by Cleland, Pohl, Penhallow, and

others.

After 1905 Monroe devoted almost all of

his spare time to botany, and he made

1983]

Mikulic — Milwaukee's Gentlemen Paleontologists

17

i

Fig. 14. Jaw of the Devonian fish Eastmanosteus

pustulosus collected in 1899 by C. E. Monroe in the

Milwaukee Cement Company quarries. The specimen is

approximately 10 inches long and is now in the

collection of the Milwaukee Public Museum (from

Cleland, 1911).

several donations of botanical material to

the Milwaukee Public Museum, including a

collection of over 15,000 specimens in 1924.

He moved to Oberlin, Ohio, in 1929, where

he died in May, 193 1 , at the age of 74.

Other Local Collectors

Several other individuals are known to

have made fossil collections in southeastern

Wisconsin during the nineteenth century,

but little specific information is known

about their activities. For the most part,

these collections have disappeared.

Professor Samuel S. Sherman, who taught

at Milwaukee Female College in the 1860s

and 1870s, collected and purchased fossils

from quarrymen in the 1860s. Sherman

moved to Chicago in 1879 where he worked

for Sherman Brothers, a family business.

Walter Rankin of Carroll College col¬

lected fossils in the Waukesha area and some

of his specimens are thought to be in the Day

and Greene collections.

Philo Romayne Hoy was a general natur¬

alist like Lapham, who confined his studies

to the Racine area. Hoy was born in Mans¬

field, Ohio, in 1816, and was trained as a

medical doctor. In 1846 Hoy moved to

Racine (McMynn, 1893) and later that same

year he and Lapham collected fossils to¬

gether in the quarries north of Racine. Hoy

also knew Day and Greene and accompanied

them to Racine area quarries on many occa¬

sions. James Hall also received specimens

from Hoy. Hoy’s collection was divided be¬

tween Day and the now defunct Racine

College (Teller, 1912). Ornithology and

botany are the fields of natural history for

which Hoy is most often remembered.

F. L. Horneffer collected fossils from the

cement quarries and the 26th Street quarry in

Milwaukee during the 1890s (Teller, 1912).

His fossils became part of Teller’s collection,

and included some of the type material in

that collection. Horneffer continued collect¬

ing into the early 1900s, and accompanied

Gilbert Raasch into the field on occasion

(G. Raasch, 1973, pers. comm.).

After the turn of the century, quarrying

activity in the area declined, and methods of

operation changed. Social values, education,

and employment opportunities also

changed, and the gentlemen paleontologists

faded from the scene. The only important

local collections made since that time were

assembled by Gilbert Raasch and Joseph

Emielity. Both these men are Milwaukee

natives who started collecting fossils as

children, and went on to become profes¬

sional geologists. Nearly all of their

collections are now located in the Milwaukee

Public Museum.

The Collections

Research Value

The four major surviving collections are

of primary importance to paleontological

research on the Paleozoic geology of south¬

eastern Wisconsin. The Day, Greene, Teller,

and Monroe collections are a source of

unique and unstudied fossils and contain

many type specimens. They cannot be dupli¬

cated in quantity, quality, or comprehensive¬

ness, because most of the bedrock outcrops

and quarries have disappeared and quar¬

rying methods have changed. In addition,

they are the only source of fossils and rock

samples for many of the vanished localities.

The later collections made by Raasch and

Emielity supplement the older collections by

18

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

covering more recent exposures, but do not

replace them.

Although many of the fossils were col¬

lected more than one hundred years ago,

they have not lost their usefulness for

paleontologic research. Locality information

accompanies most specimens, and by study¬

ing old geologic reports and the lithology of

the specimens, it is possible to determine the

exact geographic location and stratigraphic

horizon in which the fossils were collected. It

is also possible to determine reef or interreef

origins for most of the Silurian material.

These collections are invaluable for taxo¬

nomic studies because they include many

type specimens and numerous individuals of

single taxa which are necessary for popula¬

tion studies. While the Day, Teller, and

Monroe collections are no longer readily

available for comprehensive faunal studies

of specific localities, the Greene collection is

ideal. It contains the most complete collec¬

tion of North American Silurian reef fossils

found in any museum. These historic collec¬

tions are also important for research in

biogeography, paleoecology, biostratigra¬

phy, taphonomy, rates of evolution, and for

general and local stratigraphic studies.

Preservation of the Collections

Many other nineteenth century fossil

collections in the state, and throughout the

country, have virtually disappeared through

accident or neglect. Over 20,000 fossils were

collected by the Wisconsin Geological Sur¬

vey during the 1870s, and were equally

divided among twelve different educational

institutions in the state (Chamberlin, 1880).

Approximately 1200 specimens were de¬

stroyed along with Lapham’s collection in

the Science Hall fire in 1884, but the fate of

most of the others has not yet been deter¬

mined. Only a few hundred of these speci¬

mens are known to exist.

Even in recent years, important collections

have been seriously damaged by neglect. The

W. C. Egan collection of Chicago area fos¬

sils in the Chicago Academy of Science is a

good example. This collection was well

organized as late as 1946 (Ball and Greacen,

1946), but by 1967 it was in disarray and

many specimens, including types, cannot be

located. The University of Wisconsin-

Madison Geology Museum has also suffered

long periods of neglect during which fossils

disappeared and uncatalogued material was

rendered useless because of missing locality

information.

The Greene, Day, and Teller collections

are all vulnerable in varying degrees to the

same problems. Above all, a collection must

be completely catalogued to prevent the loss

of locality data. Once this is accomplished,

the Day and Teller collections will be in little

danger (although the Museum of Compara¬

tive Zoology is not exactly fireproof).

Greene’s collection is, and probably always

will be, vulnerable to the type of neglect that

small university collections often face. As

long as a dedicated individual, like the late

Dr. Katherine G. Nelson, took care of the

collection there was a little danger of this

happening. However, with her passing, the

awareness of the importance of the Greene

collection may fade. The University of Wis-

consin-Milwaukee faces an important obli¬

gation in preserving the Greene collection

and insuring its usefulness in the future.

Summary

The collecting activity of Milwaukee’s

gentlemen paleontologists continues to be a

major factor in geological research in the

Milwaukee area. They made important ob¬

servations, published papers, distributed

specimens, and assembled comprehensive

collections, all of which stimulated interest

in the geology and paleontology of the area.

They spent more time and money assembling

their collections than would have been

possible for any professional geologists of

that time. Their fossils were studied by some

of the most prominent paleontologists of the

nineteenth century, including James Hall,

F. B. Meek, J. S. Newberry, C. D. Walcott,

C. Wachsmuth, R. P. Whitfield, P. E. Ray-

1983]

Mikulic — Milwaukee's Gentlemen Paleontologists

19

mond, H. F. Cleland, C. R. Eastman, J. M.

Clarke, Stuart Weller, A. F. Foerste, E. O.

Ulrich, C. E. Resser, E. R. Pohl, and Frank

Springer. Most of these collections focused

attention on classic Silurian reefs in the area

with their abundant and diverse faunas. On

a local level, these collectors promoted and

actively participated in natural history soci¬

eties and museums.

It is no longer possible to assemble com¬

parable collections on the Milwaukee area

because of the change in quarrying methods,

the general decline of that industry, and the

lack of people willing to devote large

amounts of both time and money to this

pursuit. For these reasons the Day, Greene,

Teller, and Monroe collections are more im¬

portant than ever before.

Acknowledgments

I would like to thank Mary Dawson,

Samuel Riggs, Jr., and Mary Riggs for sup¬

plying information on F. H. Day; Kathryn

Teller, the late Edgar Teller, and the late

Eugene Richardson for information on E. E.

Teller; and the late Katherine G. Nelson for

information on T. A. Greene. Joseph Emiel-

ity, Gilbert Raasch, and Christine Beaure¬

gard supplied general information. Special

thanks are extended to Douglas Dewey and

Waukesha Lime and Stone Company for re¬

search support. Joanne Kluessendorf helped

gather information, provided suggestions,

and critically read the manuscript. Richard

A. Pauli and Rachel K. Pauli reviewed the

manuscript. This work is based, in part, on

doctoral research conducted under A. J.

Boucot of Oregon State University.

Literature Cited

Art Publishing Co. 1888. Racine. Picturesque

and Descriptive. George B. Pratt, Neenah.

Ball, J. R. and K. F. Greacen. 1946. Catalog of

the Egan Collection of Silurian invertebrate

fossils at the Chicago Academy of Sciences.

Chicago Acad. Sci. Spec. Pub. 7, 55 p.

Barton, E. E. 1886. Industrial history of Mil¬

waukee. E. E. Barton, Milwaukee.

Bean, E. F. 1936. Increase A. Lapham, geologist.

Wisconsin Archeologist 16: 79-96.

Buck, J. S. 1884. Milwaukee under the charter,

volume III. Symes, Swain and Co., Milwau¬

kee.

Chamberlin, T. C. 1877. Geology of eastern

Wisconsin. In T. C. Chamberlin (ed) Geology

of Wisconsin, volume 2, pt. 2: 91-405.

_ . 1880. Annual report of the Wisconsin

Geological Survey for the year 1879. Madison,

72 p.

Cleland, H. F. 1911. The fossils and stratigraphy

of the Middle Devonic of Wisconsin. Wiscon¬

sin Geol. and Nat. Hist. Surv. Bull. 21 , 232 p.

Conrad, H. L. 1895. History of Milwaukee

County from its first settlement to the year

1895. Volume 1. American Biographical Pub¬

lishing Co., Chicago and New York.

Day, F. H. 1877. On the fauna of the Niagara

and upper Silurian rocks as exhibited in

Milwaukee County, Wisconsin, and in counties

contiguous thereto. Trans. Wisconsin Acad.

Sci., Arts, and Letters 4: 1 13-125.

Eastman, C. R. 1900. Dentition of some

Devonian fishes. J. Geol. 8: 32-41.

Greacen, K. F. and J. R. Ball. 1946a. Studies of

Silurian fossils in the Thomas A. Greene Col¬

lection at Milwaukee-Downer College. Trans.

Wisconsin Acad. Sci., Arts, Letters 36: 415-

419(1944).

_ _ and _ . 1946b. Silurian invertebrate

fossils from Illinois in the Thomas A. Greene

Memorial Museum at Milwaukee-Downer Col¬

lege. Milwaukee-Downer College Bull., 61 p.

Greene, H. and W. T. Berthelet. 1949. The Mil¬

waukee Cement Company. Wisconsin Maga¬

zine of History 33: 28-39.

Hall, James. 1862. Physical geography and gen¬

eral geology. In J. Hall and J. D. Whitney,

Report of the Geological Survey of the State of

Wisconsin, volume 1. Madison, p. 1-72.

_ . 1867. Account of some new or little

known species of fossils from rocks of the age

of the Niagara group. 20th Ann. Rept. of the

Regents of the Univ. of the State of New York

on the conditions of the State Cabinet of

Natural History: 305-401.

_ . 1870. Descriptions of some new or little

known species of fossils from rocks of the age

of the Niagara group. 20th Ann. Rept. of the

Regents of the State of New York on the con¬

dition of the State Cabinet of Natural History

(revised ed.): 347-438.

20

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

Lapham, I. A. 1828. Notice of the Louisville and

Shippingsport canal and of the geology of the

vicinity. Amer. J. Sci. 14: 65-69.

_ . 1851. On the geology of the south¬

eastern portion of the State of Wisconsin being

the part not surveyed by the United States geol¬

ogists, in a letter to J. W. Foster by I. A.

Lapham of Milwaukee: In J. W. Foster and

J. D. Whitney. Report on the geology of the

Lake Superior land district, Pt. 2. U.S. 32nd

Congress, Spec. Session, Senate Executive

Document No. 4: 167-177.

McMynn, J. G. 1893. Philo Romayne Hoy,

M. D. Trans. Wisconsin Acad. Sci., Arts, and

Letters 9: 75-78.

Monroe, C. E. 1900. A notice of a new area of

Devonian rocks in Wisconsin. J. Geol. 8:

313-314.

_ and E. E. Teller. 1899. The fauna of the

Devonian formation at Milwaukee, Wisconsin.

J. Geol. 7:272-283.

Nehrling, H. 1895. In memoriam, Thomas A.

Greene. 13th Ann. Rept., Board of Trustees of

the Public Museum of the City of Milwaukee:

45-48.

Raymond, P. E. 1916. New and old Silurian trilo-

bites from southeastern Wisconsin, with notes

on the genera of the Illaenidae. Mus. Comp.

Zool. Bull. 60: 1-41.

Sherman, S. S. 1876. Increase A. Lapham,

LL.D., A biographical sketch read before the

Old Settlers’ Club. Milwaukee News Company

Printers, Milwaukee, 80 p.

Sweet, E. T. 1876. Catalogue of the Wisconsin

State Mineral Exhibit at Philadelphia, 1876.

State of Wisconsin, embracing brief sketches

of the history, position, resources, industries,

and a catalogue of the exhibits at the Cen¬

tennial at Philadelphia, 1876.

Teller, E. E. 1900. The Hamilton Formation at

Milwaukee, Wisconsin. Wisconsin Nat. Hist.

Soc. Bull. 1:47-56.

_ 1906. Notes on the fossil fish-spine

Phlyctaenacanthus telleri (Eastman). Wis¬

consin Nat. Hist. Soc. Bull. 4: 162-167.

_ 1910. An operculated gastropod from

the Niagara formation of Wisconsin. Trans.

Wisconsin Acad. Sci., Arts and Leters 16:

1286-1288.

_ 1912. A synopsis of the type specimens

of fossils from the Phanerozoic formations of

Wisconsin. Wisconsin Nat. Hist. Soc. Bull. 9:

170-271.

Teller, M. 1924. Memorial of Edgar E. Teller.

15th Ann. Mtg. Paleontol. Soc. Proc., Geol.

Soc. Amer. Bull. 35: 182-184.

Thomas, O. J. 1928. The Greene Collection of

fossils and minerals. Milwaukee-Downer Col¬

lege Bull., ser. 10, no. 3, 1 1 p.

Whitfield, R. P. 1896. Notice and description of

new species and a new genus of Phyllocaridae.

Amer. Mus. Nat. Hist. Bull. 8: 299-304.

Winchell, N. H. 1894. Increase Allen Lapham.

The Amer. Geologist 8: 1-38.

Zimmermann, H. R. 1979. The Dr. Fisk Hol¬

brook Day residence. In Dedication of the his¬

torical marker plaque on the Fisk Holbrook

Day residence by the Wauwatosa Landmark

Commission: 3-16.

SILURIAN BENTHIC INVERTEBRATE ASSOCIATIONS OF EASTERN

IOWA AND THEIR PALEOENVIRONMENTAL SIGNIFICANCE

Brian J. Witzke

Iowa Geological Survey

Iowa City , Iowa 55242

Abstract

The vertical and lateral distributions of benthic invertebrate associations in the

Silurian carbonate sequence of eastern Iowa are interpreted in terms of widespread

environmental changes created by relative changes in sea level and general water

circulation patterns. Previous studies (especially Johnson, 1975, 1980) delineated

three broadly-defined benthic invertebrate associations within the middle

Llandoverian-lower Wenlockian sequence of eastern Iowa, and similar associations

are recognized in younger Wenlockian strata in this study. The middle Llandoverian

through middle Wenlockian interval in eastern Iowa includes three recurrent benthic

associations characteristic of open-marine carbonate shelf environments: 1) coral-

stromatoporoid, 2) pentamerid brachiopod, and 3) stricklandiid brachiopod. Petro¬

graphic, sedimentologic, and stratigraphic information evaluated for this study is

consistent with the earlier suggestion that these associations respectively inhabited

different depth-related benthic carbonate environments: 1) at or near fair-weather

wave base, 2) generally below fair-weather wave base with episodic impingement of

storm wave base on the bottom, and 3) below effective reach of fair-weather and

storm wave base. However, the development of carbonate mounds (reefs) during

Silurian deposition in eastern Iowa adds additional complexity to the paleotologic

and sedimentologic framework. In addition, lateral biofacies variations suggest that

basinal geometry influenced the geographic distribution of specific benthic

associations.

The middle Wenlockian through Ludlovian interval in eastern Iowa is marked

by a change from open-marine to restricted-marine carbonate deposition. A general

offlap of the epeiric sea during that interval probably left eastern Iowa as a restricted

embayment, in part hypersaline. When compared to the Llandoverian through

middle Wenlockian interval, the younger Silurian benthic associations show a

marked decline in diversity, and several major taxonomic groups are commonly

absent. Abundant low-diversity brachiopod and coral-dominated faunas are well

developed in the younger Silurian carbonate mound facies, but benthic invertebrate

associations are characteristically sparsely developed to absent in the laminated

inter-mound facies. However, Upper Silurian mound and inter-mound benthic

associations generally increase in diversity eastward within the East-Central Iowa

Basin. The stratigraphic distribution of these younger Silurian benthic associations

is interpreted to be a joint response to relative changes in water depth and salinity

stresses on the carbonate shelf.

Introduction and Comments

150 years. My personal interest in Silurian

rocks was heightened during my teen and

college years in Milwaukee, and Katherine

Nelson played a significant role in cultivat-

Silurian rocks of the central midcontinent

region have been the subject of geologic and

paleontologic investigations during the past

21

22

Wisconsin Academy of Sciences , Arts and Letters

[Vol. 71, Part I,

ing that interest. Milwaukee is conveniently

located in the Silurian outcrop belt, and

Katherine took advantage of that fact by en¬

couraging class field trips to nearby quarries.

The Greene Museum collections (Univ.

Wise. -Milwaukee), tended by Katherine for

many years, were the envy of local fossil

collectors, like myself, and these collections

certainly helped kindle student interest in

Silurian paleontology.

While still living in Milwaukee, Don

Mikulic and I first visited Silurian outcrops

in eastern Iowa. These visits ultimately led to

further study and graduate research on the

Silurian rocks and fossils of Iowa (Witzke,

1976, 1981c; Mikulic, 1979). Although most

of the Iowa Silurian rocks are extensively

dolomitized, the contained fossils are

commonly abundant and diverse. Paleonto-

logic data obtained from the Iowa exposures

and subsurface cores, when utilized with

additional geologic information, form an

essential basis for the interpretations of

Silurian stratigraphy and depositional envi¬

ronments outlined in this report.

The general purpose of this report is to

evaluate the vertical and lateral distributions

of recurrent associations of benthic inverte¬

brates within the Silurian sequence of

eastern Iowa in terms of possible controlling

paleoenvironmental parameters. Previously

published paleocommunity models are re¬

viewed and supplemented with new informa¬

tion, and models relating the various benthic

associations to paleo-depth are indepen¬

dently tested utilizing petrographic and strat¬

igraphic data. The study was approached

through an analysis of paleontologic, sedi-

mentologic, petrographic, stratigraphic, and

structural information. Iowa Llandoverian

stratigraphic data was geographically ex¬

panded over previous studies by utilizing

subsurface cores (2 inch diameter). A first

attempt at synthesizing Iowa Wenlockian-

Ludlovian data in terms of regional sedimen¬

tation and benthic associations is presented

in this report.

This report is intended to summarize some

of the major conclusions of my dissertation

research and to compare these results with

some previous ideas. Because of the sum-

mary-and-review character of this paper,

complete details of stratigraphic, petro¬

graphic, and paleontologic documentation

cannot be presented in this volume. Further

documentation is presented in Witzke

(1981c).

Stratigraphy

The sequence of Silurian carbonate rocks

is exceptionally well exposed in the outcrop

belt of eastern Iowa, and supplementary ex¬

posures were examined in adjacent Illinois

and Wisconsin. Integration of surface and

subsurface (core) sections in Iowa has neces¬

sitated revision of previous stratigraphic in¬

terpretations. Following the lead of Wilson

(1895) and Calvin and Bain (1900), Iowa

Silurian lithostratigraphic relationships have

recently been delineated (Johnson, 1975,

1977a; Witzke, 1981a, 1981c; Bunker et al.,

1983). A generalized interpretation of the

composite eastern Iowa Silurian strati¬

graphic sequence is schematically illustrated

in Figure 1 . Units within the Hopkinton For¬

mation are informally labelled Hopkinton

A, B, and C which correspond, respectively,

to the “ Syringopora ” and “ Pentamerus

beds,” “ Cyclocrinites beds,” and

“ Favosites beds” of Johnson (1975).

Member names within the Hopkinton For¬

mation were recently proposed by Johnson

(1983), which in ascending order include the

Sweeney, Marcus, Farmers Creek, and Pic¬

ture Rock Members.

The Scotch Grove Formation has been

recently proposed as a stratigraphic unit by

Bunker et al. (1983) to include the interval

above the originally defined top of the

Hopkinton and below the laminated and

mounded carbonates of the Gower Forma¬

tion. The Scotch Grove is characterized by a

complex series of mounded (reef) and flat-

lying carbonate facies that have been given

informal facies names (see Fig. 1). The lower

Scotch Grove interval of this report was in-

1983]

Witzke — Silurian Benthic Invertebrate Associations

23

eluded within the upper Hopkinton Forma¬

tion by Johnson (1975, 1983). Johnson

(1983) recognized members within this inter¬

val which he assigned, in ascending order, to

the Johns Creek Quarry, Welton (“Emeline

facies” of this report), and Buck Creek

Quarry Members. Because of the recent

status of Johnson’s (1983) stratigraphic

classification, time did not permit complete

incorporation of the new terminology into

regressive

transgressive

ROCK

Benthic Assemblages

° °,\ very crinoidal dolomite

laminated dolomite

[ z ~ | shaly dolomite and shale

P large pentamerid brachiopods

S stricklandid brachiopods

B brachiopod-rich Brady Facies

Fig. 1. Generalized Silurian stratigraphic sequence in east-central Iowa. Formal and informal stratigraphic

terminology largely adapted from Johnson (1980), Witzke (1981c), and Bunker et al. (1983). Facies illustrated within

the Scotch Grove and Gower Formations are highly schematic; the distribution of very crinoidal dolomites is shown for

the Scotch Grove Fm. only. The sequence of Benthic Assemblages shown at left is generalized and adapted from

Johnson (1980) and Witzke (1981c). Vertical scale is time. CGMf-Castle Grove Mound facies.

DATUM (base Devonian)

24

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Witzke — Silurian Benthic Invertebrate Associations

25

this report, although union of informal ter¬

minology with the formal stratigraphic

schemes is recommended for future publica¬

tions. The Gower Formation includes three

general facies: 1) flat-lying laminated dolo¬

mites of the Anamosa facies, 2) mounded

(reef) brachiopod- and coral-rich rocks of

the Brady facies (Philcox, 1970a), and 3)

mounded to flat-lying crinoidal and brachio-

pod-rich rocks of the LeClaire facies. Many

mounded (reef) carbonate exposures previ¬

ously assigned to the LeClaire facies are now

assigned to the Palisades-Kepler Mound

facies of the Scotch Grove Formation.

The eastern Iowa Silurian sequence is

composed primarily of dolomite and cherty

dolomite. However, the dolomite sequences

are replaced, in part, to the west and north

by limestones and cherty limestones assigned

to the LaPorte City and Waucoma forma¬

tions (Witzke, 1981c). The fortuitous preser¬

vation of Silurian limestone facies in Iowa

allows direct comparison of limestone petro¬

graphic fabrics with their dolomitized

equivalents.

The thickest known sequence of Iowa

Silurian rocks (146 m) occurs within the

Silurian outcrop belt of east-central Iowa,

and the Silurian sequence thins beneath the

Devonian cover to the north, west, and

south. Recent investigations in Iowa identi¬

fied a Silurian structural and stratigraphic

basin centered in eastern Iowa (Bunker,

1981; Bunker et al„ 1983; Witzke, 1981c).

This paleobasin is termed the East-Central

Iowa Basin. Although the central basin area

was uplifted prior to Pennsylvanian deposi¬

tion (ibid.), and the area has been subjected

to extensive erosional truncation, thickening

of individual Silurian stratigraphic units

towards the center of the East-Central Iowa

Basin is clearly evident in cross-section (Fig.

2). Erosional remnants of Silurian strata

preserved in southwestern Wisconsin outliers

compare closely with Lower Silurian se¬

quences in the central basin area of eastern

Iowa (Bunker et at., 1983).

Brachiopod and conodont biostrati-

graphic studies in the eastern Iowa Silurian

sequence provided a basis for inter-regional

chronostratigraphic correlation (Johnson,

1975, 1979; Witzke, 1978, 1981c). The age

relationships of the Iowa Silurian sequence

are shown on Figure 1 .

BENTHIC FOSSIL ASSOCIATIONS

AND PALEOENVIRONMENTAL

INTERPRETATIONS

Benthic Associations

Recurring associations of fossils (com¬

monly termed communities) in the eastern

Iowa Silurian sequence, when supplemented

with stratigraphic, sedimentologic, and

petrographic information, provide a basis

for interpreting environmental changes

through time. Ziegler (1965) and Ziegler et

al. (1968) pioneered studies in Silurian com¬

munity paleoecology and documented recur¬

rent associations of brachiopods and other

fossils in the Llandovery Series of the Welsh

Borderland. They interpreted the distribu¬

tion of these fossil associations to be envi¬

ronmentally controlled, and they correlated

the controlling environmental parameters

with water depth. Later studies, most of

which are not enumerated here, identified

other supposed depth-related Silurian fossil

associations at other localities in Europe and

North America. Johnson (1975, 1977a,

1980) identified five basic and recurrent

fossil associations (or communities) in the

Iowa Llandoverian sequence that, in part,

paralleled Ziegler’s in the Welsh Borderland.

Johnson listed these in order of increasing

water depth: 1) Lingula, 2) coral-algal, 3)

pentamerid, 4) stricklandiid, and 5)

“Clorinda-Q quivalent.” Although some

brachiopod taxa are shared between the

Iowa and Welsh Borderland Llandoverian,

many important differences in taxonomic

composition between the two areas are

noted, in part because of contrasting sub¬

strates (carbonate vs. terrigenous clastic).

Most marine ecologists recognize modern

marine communities as unique congrega¬

tions of organisms, recognizable at the

26

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

species level (“Peterson Animal Commu¬

nity’’ concept of Watkins et al, 1973). In

this context, the recurrent associations of

fossils in the Iowa Silurian are not members

of the same communities present in the

Welsh Borderland. A broader community

concept, the “parallel community,’’ has also

been defined which includes “a grouping of

separate, related Peterson animal commu¬

nities, describing an ecologic unit of great

areal and temporal’’ extent recognized by

similar associations of “characteristic

genera’’ or “families” (ibid., p. 56).

In this study, the term “community” is

not utilized, primarily to avoid confusion

between the various community definitions,

and the general term, “association,” is

preferred. As utilized here, a benthic asso¬

ciation is defined to include a combination

of taxa (usually at the generic or family level)

that occur together in a specific stratigraphic

interval and collectively form a discrete

grouping unique from other associations.

Although benthic associations could be

defined and analyzed at any taxonomic level,

including species level, the stratigraphic

representation of the various associations is

dependent on the hierarchic level employed

by the observer (Anderson, 1973a). In a gen¬

eral sense, the benthic association definition

utilized in this report roughly coincides with

the “parallel community” concept.

The recognition and establishment of dis¬

crete benthic association types is, in part, an

artificial procedure, and a certain degree of

overlap in taxonomic composition between

some associations is noted. There may be a

degree of variation in the relative abundance

of individual taxa within single benthic asso¬

ciation types at different localities and in

different collections. Nevertheless, the

benthic association approach affords a

reasonably consistent way of categorizing a

mass of paleontologic information into envi¬

ronmentally and paleoecologically signif¬

icant entities. In this study, most benthic

associations are recognized and defined by

the co-occurrence of two or three prominent

key taxa in a single collection, and, although

additional taxa are usually noted within a

particular association, the full complement

of additional taxa may not be recovered in

all collections. The key taxa that define a

particular association must be relatively

abundant, although the name-bearing mem¬

bers of each association are not necessarily

the most abundant fossil types present. For

example, the skeletal volume of echinoderm

grains in many of the Iowa Silurian benthic

associations far exceeds that of the name¬

bearing members of the association. The

benthic association concept utilized in this

study is a broadly defined one that is suited

for field observations as well as numerical

assessment of dolomite block collections in

the laboratory. In addition, rock core from

Iowa subsurface Silurian intervals has

yielded macrofossil collections that provide

important data on the stratigraphic and geo¬

graphic extent of various benthic associa¬

tions, even though collection sample sizes

are comparatively small and the sampling

interval is generally thicker than in block

collections derived from surface exposures.

Rock core descriptions and fossil lists are

recorded in Witzke (1981c).

An abbreviated review of the various

benthic associations represented in the Iowa

Silurian sequence and their environmental

significance is presented later in this report.

To a large extent, the Iowa Llandoverian

associations used here closely parallel the

community definitions of Johnson (1975,

1980). The reader is referred to the studies of

Johnson (ibid.), Witzke (1976, 1981c),

Witzke and Strimple (1981), and Mikulic

(1979) for a more complete listing of the

taxonomic composition and diversity of the

various Iowa Llandoverian and early Wen-

lockian associations. In addition, valuable

information on community evenness, diver¬

sity, and lateral homogeneity (as determined

from block collection counts and “stretch¬

line” fossil censuses taken from Lower

Silurian strata in the Iowa outcrop belt) is

given by Johnson (1977a, 1980). A partial

1983]

Wiizke . Silurian Benthic Invertebrate Associations

27

taxonomic listing of the various mid Wen-

lockian through Ludlovian benthic associa¬

tions is given by Witzke (1981a, 1981c).

Benthic Assemblages

Boucot (1975, p. 11) introduced the term

“Benthic Assemblage” for “a group of

communities that occur repeatedly in dif¬

ferent parts of a region (during some times

even worldwide) in the same position relative

to shoreline,” and further suggested that

“Benthic Assemblages are probably temper¬

ature-controlled as well as highly correlated

with depth.” Because community structures

changed through time and individual taxa

evolved, the Benthic Assemblage approach

affords a method to compare the taxonomic

and environmental similarities of various

benthic associations on a broad temporal

and geographic scale. Boucot (1975) pro¬

posed a simple numerical listing of Benthic

Assemblages (B.A.), which increase in

number moving away from the shoreline

into progressively deepening water (e.g.,

B.A. 1 — near shore, B.A. 6 — farthest off¬

shore). Boucot and others have categorized a

great variety of Silurian fossil associations

from around the world according to their

general Benthic Assemblage position, and I

have utilized Boucot’s B.A. categories for

the various Iowa Silurian associations.

However, I have not uncritically utilized the

B.A. categories, but have attempted to

define the environmental parameters affect¬

ing each benthic association from sediment-

ologic, stratigraphic, petrographic, and

other criteria. “Meaningful paleoecologic

analysis of fossil assemblages is impossible

without using environmental data which are

independent of the paleontologic record,” as

stressed by Makurath (1977, p. 251). As

such, the assertion that Benthic Assemblages

are depth-related can be independently eval¬

uated for specific Iowa Silurian benthic asso¬

ciations.

In general, the Iowa Silurian sequence was

deposited in carbonate shelf environments

within a “dear-water” epeiric sea, and

terrigenous clastic influx was extremely low.

The temporal and geographic distribution of

the various benthic associations was related

to environmental and biotic influences

operating within the epeiric sea. Environ¬

mental factors that may have influenced the

distribution of the various Iowa associations

include water circulation patterns, salinity,

relation to wave base, water turbulence,

turbidity, light penetration, temperature,

substratum, and nutrient availability. Most

of these factors are strongly related to water

depth and shelf physiography in areas of

“clear water” carbonate shelf deposition

(Irwin, 1965). Irwin (1965) stressed the

importance of relative sea level change as a

major controlling factor on the temporal

sequence of environments on “clear water”

carbonate shelves, and Anderson (1971, p.

301) suggested that recurrent benthic inver¬

tebrate associations are directly correlated

with depth-related environmental zones in

the epeiric seas.

If the distribution of Benthic Assemblages

is depth-related, then the sequence of

assemblages can be locally used to charac¬

terize relative changes in sea level, as

previous workers have done for the Silurian

of North America and Europe. Although

some workers have criticized this approach

(e.g., Makurath, 1977; Watkins, 1979), as

will be shown, the stratigraphic and petro¬

graphic evidence from the Iowa Silurian

generally supports relative differences in

water depth for the various benthic assem¬

blage types. However, the sequence of ben¬

thic assemblages in the Iowa Silurian is not

necessarily a reflection of absolute changes

in water depth since there is no assurance

that each benthic assemblage maintained the

same absolute depth range through time in a

specific region. Sheehan (1980, p. 21) further

suggested: “Benthic Assemblages are depth

related in that, from shallow to deep, a

consistent pattern of communities is main¬

tained. But B.A.’s are not depth specific

since the actual depth a given community

inhabited probably varied significantly.”

Table 1. Thin section point-count data averages from LaPorte City Formation limestones. General stratigraphic positions listed according to dolomite

facies equivalents in the Hopkinton and Scotch Grove formations, (n = number of thin sections point-counted).

28

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Witzke — Silurian Benthic Invertebrate Associations

29

Depth-related environmental factors that

influenced carbonate depositional patterns,

in particular those related to wave current

activity, can be interpreted from petro¬

graphic and sedimentologic evidence. Such

independent lines of evidence provide in¬

formation critical for evaluating the relative

depth positions of the various Iowa Silurian

benthic associations.

Although the distribution of many Iowa

Silurian benthic associations was apparently

depth related, evaluation of additional non¬

depth-related environmental factors is also

needed for adequate classification. In this

report, all Iowa Silurian carbonate environ¬

ments and their contained benthic associa¬

tions are categorized into two general group¬

ings: 1) open-marine, and 2) restricted-

marine (varying degrees of elevated salinity).

Open-Marine Benthic Associations

General Characteristics

Iowa middle Llandoverian through middle

Wenlockian rocks contain paleontologic and

sedimentologic features suggestive of open-

marine (stable marine salinity) carbonate

depositional environments. 1) The contained

faunas are characteristically diverse and

include a number of biotic groups commonly

regarded as stenohaline (see Heckel, 1972).

In particular, echinoderm debris, commonly

in great abundance, is present in all benthic

associations here assigned to open-marine

environments. 2) Iowa Silurian open-marine

environments were generally characterized

by the deposition of skeletal wackestone and

packstone textures. All sedimentologic

evidence suggestive of elevated salinites

during deposition is absent. Unlike the

restricted-marine environments discussed

later, evaporite crystal molds, laminated

carbonates, and oolites are conspicuously

lacking.

Coral-Stromatoporoid Associations

Coral-stromatoporoid associations are

noted in the Tete des Morts and Blanding

formations, the Hopkinton A, B, and C

intervals, and the lower La Porte City

Formation. These associations are character¬

ized by conspicuous tabulate corals (Haly-

sites, Favosites, Syringopora) and disc¬

shaped stromatoporoids on outcrop. Other

macrofossils commonly encountered include

rugose corals ( Heliolites , Arachnophyllum,

solitary rugosans), brachiopods (Hesperor-

this , Leptaena ), nautiloids, and trilobites

(Stenopareia) . The brachiopod Cryptothy-

rella has also been recovered from the

Blanding Formation (Johnson, 1977a). This

recurrent coral-stromatoporoid association

is assigned a B.A. 2 position following

Boucot (1975). Although corals and stroma¬

toporoids are conspicuous on outcrop,

petrographic analysis reveals that the

dominant skeletal constituent of these asso¬

ciations is disarticulated echinoderm debris

(primarily crinoid with minor cystoid) less

than 2 mm in diameter (Witzke, 1981c).

Dolomitization has hampered recognition of

the crinoidal component, although petro¬

graphic study reveals that moldic or

dolomite-replaced crinoidal wackestone and

packstone fabrics predominate in these asso¬

ciations (ibid.). Strata equivalent to

Hopkinton C in the LaPorte City limestone

contain a conspicuous coral-stromatoporoid

fauna. However, petrographic study of these

limestones reveals skeletal wackestone and

packstone textures containing a great

abundance of small echinoderm debris (see

Table 1). Data in Table 1, due to thin section

size limitations, is only for the rock matrix

between the conspicuous coral and stroma-

toporoid colonies. Grid measurements (m2)

on vertical exposure faces indicate that

corals and stromatoporoids, on the average,

comprise less than 2% of the total rock

volume in limestone strata containing coral-

stromatoporoid associations (Table 2).

Cross-sectional dimensions of all

macroskeletal constituents within the m2 grid

whose long dimension exceeded 3 mm were

recorded. However, this data tended to over¬

estimate coralline skeletal volume since

30

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

corallite spar fillings were included in the

volumetric measurements.

Johnson (1975, 1977a, 1980) interpreted

the flat disc-shaped fossils in these asso¬

ciations as blue green algal stromatolites,

and labelled this benthic association the

“coral-algal community” accordingly.

However, Johnson (1980, p. 200) acknowl¬

edged that some stromatoporoids “were

undoubtedly included under this classifica¬

tion.” All these disc-shaped fossils are

herein interpreted as stromatoporoids and

not algal stromatolites for two reasons.

First, although the dolomitized or silicified

specimens are typically poorly preserved,

better preserved specimens bearing monti¬

cules and pillars are clearly stromatoporoids.

Where identical benthic associations were

examined in the LaPorte City and Waucoma

limestones, no stromatolites were observed,

and all laminar disc-shaped fossils were

consistently recognizable as stromato¬

poroids. Second, there are no modern or

ancient examples of isolated stromatolitic

discs occurring within a groundmass of

skeletal wackestone and packstone. Al¬

though normal-marine subtidal stromato¬

lites have been identified in modern oolitic

sand environments in the Bahamas (Dravis,

1983), the crudely laminated columnar heads

and the surrounding sediment differ signif¬

icantly from the Iowa Silurian examples. In

general, most post-Lower Ordovician stro¬

matolites are typically associated with envi¬

ronments of increased salinity or restricted

circulation, whereas the Iowa examples

occur in normal-marine associations.

Additional petrographic observations pro¬

vide useful information for evaluating envi¬

ronmental parameters during deposition.

Limestone fabrics include abraded skeletal

grains, and the grains are, in part, moder¬

ately well sorted, suggesting relatively high-

energy conditions in the B.A. 2 environ¬

ments. However, skeletal wackestone and

packstone textures indicate that carbonate

mud was not completely winnowed out dur¬

ing deposition. Micrite envelopes occur

around some skeletal grains in these associa¬

tions. Moderate to strongly agitated open-

marine conditions apparently prevailed in

the B.A. 2 environments, and bottom con¬

ditions were apparently within the photic

zone. Johnson (1980, p. 208) interpreted the

flat, disc-shaped morphology of the corals

and stromatoporoids as a probable response

to the hydrographic factors, and further

suggested that “effective wave base” may

have reached the bottom during deposition

of these intervals bearing such associations.

Pentamerid Brachiopod

and Related Associations

Associations of large-shelled pentamerid

brachiopods have been assigned a B.A. 3

position by Boucot (1975) and others. A

variety of large pentamerid taxa are repre¬

sented within the eastern Iowa sequence in

the following stratigraphic positions: 1)

Pentamerus oblongus, upper Hopkinton A,

basal Hopkinton C; 2) Harpidium (Isovella)

maquoketa (see Boucot and Johnson, 1979),

Hopkinton B; 3) Pentameroides subrectus,

basal and middle Scotch Grove (Johns Creek

and Buck Creek Quarry facies); 4) Penta¬

meroides (Callipentamerus) corrugatus,

middle Scotch Grove (Emeline and Buck

Creek Quarry facies); 5) Rhipidium sp.,

upper Scotch Grove (Waubeek facies). Due

to incomplete recovery or poor preservation,

H. maquoketa was not consistently dis¬

tinguishable from P. oblongus in subsurface

rock cores. Although all Hopkinton B

pentamerids are tentatively listed as

Pentamerus on the Figure 2 subsurface

cross-section, many of the Hopkinton B

specimens probably belong to H. maquoketa

(which was assigned to Pentamerus maquo¬

keta in earlier reports). In general,

Pentamerus and Harpidium associations are

spatially homogeneous and geographically

widespread within specific stratigraphic

intervals (Johnson, 1980). However, Penta¬

meroides, Callipentamerus, and Rhipidium

associations are not ubiquitous in specific

stratigraphic intervals, but occur in spatially

1983]

Witzke — Silurian Benthic Invertebrate Associations

31

disjunct facies accumulations or “banks”

(Witzke, 1981c). Although lacking large pen-

tamerids, additional benthic associations

laterally equivalent to the Rhipidium asso¬

ciation in the upper Scotch Grove Formation

(Buck Creek Quarry and Waubeek facies)

are recognized and tentatively assigned a

B.A. 3 position (Witzke, 1981a, b,c).

In general, the Iowa B.A. 3 associations

are taxonomically more diverse than the

B.A. 2 associations, although the brachio-

pod component is typically dominated by a

single species. Additional biotic elements,

not necessarily present in all pentamerid

associations, include corals (primarily tabu¬

lates and solitary rugosans, some colonial

rugosans), bryozoans, brachiopods (orthids,

strophomenids, spiriferids), gastropods,

nautiloids, trilobites, ostracodes, crinoids

(rare articulated cups), and calcareous algae.

Ecologic succession in the Hopkinton

pentamerid associations is discussed by

Johnson (1977b). Coralline developments or

biostromes (highest diversity coral faunas

noted in the Iowa Silurian) are evident in

portions of the middle Scotch Grove For¬

mation associated with abundant Pen-

tamer oides (Witzke, 1981c). Coralline

biostromes associated with Pentameroides

also occur within the basal Scotch Grove

(Johnson, 1977a). Upper Scotch Grove B.A.

3 associations that lack large pentamerids

are faunally varied and, although not

enumerated here, include scattered small

pentamerid (gypidulinid) brachiopods

(ibid.).

Pentamerus, Harpidium, and Pentamer¬

oides associations in portions of the

Hopkinton and Scotch Grove formations

include small numbers of stricklandiid

brachiopods, forms generally characteristic

of B.A. 4 stricklandiid associations. The

intermixing of pentamerid and stricklandiid

faunas may suggest a degree of gradational

overlap between B.A. 3 and B.A. 4 associa¬

tions at times during deposition of the Iowa

Silurian carbonates.

Pentamerid accumulations in the Iowa

Silurian are preserved in two general ways

with “a complete preservational spectrum”

between the two extremes: 1) articulated

brachiopod shells in life position with

scattered truncated “submarine erosion”

surfaces, and 2) “disarticulated shells

accumulated as coquinas” (Johnson, 1977b,

p. 86, 92). Johnson (ibid.) suggested periodic

“scouring of the sea bottom” as a mechan¬

ism for the origin of the truncation surfaces.

Many disarticulated pentamerid accumula¬

tions sampled by Johnson (1977a) showed a

preservational bias of pedicle valves over

brachial valves, suggesting a degree of cur¬

rent sorting. Bridges (1975, p. 89) described

“storm-generated coquinas of Pentamerus ”

from the Welsh Borderland, and Anderson

(1973b) suggested that pentamerid associa¬

tions in the Appalachian Basin area

inhabited skeletal sand substrates that were

“occasionally wave reworked.” Some

pentamerid accumulations in the Iowa

Silurian may represent storm lags. Iowa

pentamerid associations occur within rocks

displaying skeletal wackestone to packstone

textures, both in dolomite and limestone

facies. Echinoderm debris (most less than 2

mm diameter) is considerably more impor¬

tant volumetrically than macrofossil block

counts would suggest, and the echinoderm

component of the pentamerid associations

can only be adequately evaluated petro-

graphically (see Table 1; Pentamerus-

bearing limestones, Hopkinton B equiva¬

lents). Moldic and dolomite-replaced echino¬

derm grains are also abundantly evident

petrographically in the dolomite facies

(Witzke, 1981c). Pentamerus- bearing

limestones in the LaPorte City Formation

contain some abraded grains, and agitated

conditions were apparently present at times

during the deposition of the B.A. 3 associa¬

tions. However, abraded grains and current

sorting are not pervasive throughout the

pentamerid-bearing sequences, and agitated

high-energy conditions were probably pres¬

ent in the B.A. 3 environments only at

irregular intervals. Overall, the sedimentary

32

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

evidence in the B.A. 3 pentamerid associa¬

tions is consistent with a depositional

environment generally below wave base.

Johnson (1980, p. 208) also suggested that

the pentamerid associations generally

occupied a position “at or below effective

wave base.” The abundance of micrite and

articulated fossils generally supports this

interpretation. However, periodic turbulent

conditions produced truncation surfaces,

shell transport and sorting, and abraded

grains, perhaps as a result of periodic storms

in which storm wave base impinged on the

bottom.

Carbonate Mound (Reef)

and Related Associations

Open-marine carbonate mound (reef)

facies are noted at two positions in the

Scotch Grove Formation: 1) small-scale

mounds (about 5-10 m high, 30-70 m across)

informally included in the Castle Grove

Mound facies, and 2) large-scale mounds

(forming coalesced mounded complexes to

2.5 km across; single mounds up to 1 km

across, 45 m thick) informally included in

the Palisades-Kepler Mound facies (Witzke,

1981a, c). Both mound facies are laterally

replaced, in part, by flat-lying intermound

strata containing probable B.A. 3 associa¬

tions. Stratigraphic relations indicate that,

during deposition, the mound facies were

elevated on the sea floor relative to the

intermound facies. Since the B.A. 3 associa¬

tions in the Palisades-Kepler mounds lived in

shallower water than equivalent B.A. 3 asso¬

ciations in the intermound areas, the conten¬

tion that each benthic assemblage occupied a

distinct bathymetric zone characterized by a

specific absolute depth range is probably

incorrect. Mounds within the Castle Grove

Mound facies contain central “cores” of

dense dolomite with mudstone and wacke-

stone textures containing scattered large

colonies (to 3 m) of rugose and tabulate

corals and crinoid debris. “Flank” beds

(crinoid and fenestellid bryozoan packstone

textures) bury the central mounds and

contain a diverse assemblage of fossils.

Philcox (1970b), Johnson (1980), and Witzke

(1981c) noted a variety of brachiopods, cri-

noids, and other fossils in the “flank” beds

that are characteristic of B.A. 4-5 associa¬

tions. The “flank” beds post-date the

development of the mounds that they

enclose, and probably correlate with similar

faunas in the lower Emeline facies. Devel¬

opment of the Castle Grove mounds was

coincident with deposition of the flat-lying

Johns Creek facies containing a B.A. 3

pentamerid association. However, active

mound development apparently ceased

during C6 late Llandoverian as environments

changed and B.A. 4-5 associations became

established in eastern Iowa.

The benthic associations in the carbonate

mounds of the Palisades-Kepler Mound

facies are varied and diverse, although

crinoids are volumetrically the dominant

benthic invertebrate present in most of the

mounds. Echinoderm debris is characteris¬

tically large (more than 3 mm diameter), and

where identifiable echinoderms are present,

the fauna is dominated by a variety of

camerate crinoids (especially Eucalypto-

crinites, Siphonocrinus) with lesser numbers

of flexible and inadunate crinoids (especially

Crotalocrinites) and cystoids (Caryocri-

nites). The carbonate mounds are primarily

constructed of carbonate mud and crinoid

debris with lesser quantities of other fossils,

most notably corals and stromatoporoids.

“The distribution and orientation of

colonial coelenterates shows that in Iowa

they did not construct rigid, wave-resistant

frames, but were subordinate to crinoids in

the reef-building role” (Philcox, 1971, p.

338). Relict isopachous fibrous submarine

cements are observed petrographically, and

the mounds apparently became rigid features

on the sea floor primarily through sub¬

marine cementation processes (Witzke,

1981c). Favosites is the commonest coral in

the facies, and a variety of other tabulates

and solitary and colonial rugosans are also

present. Branching and fenestellid bryo-

1983]

Witzke— Silurian Benthic Invertebrate Associations

33

zoans are locally significant within the

mounds, especially in possible grain flow

deposits in the flanking beds. Nautiloid and

trilobite predators and scavengers in the

mound environments were commonly con¬

centrated by currents into fractures and

depressions (“pockets”) within the mound.

A variety of brachiopods are present in the

Palisades-Kepler mounds, but usually none

is abundant. Within crinoidal and bryozoan-

rich beds, the brachiopod fauna is primarily

characterized by A try pa, rhynchonellids,

and strophomenids. Large pentamerid

(' Conchidium , Lissocoelina) and trimerellid

brachiopods are locally present in the

mounds; these brachiopods are included in a

B.A. 3 position by Boucot (1975). In addi¬

tion, sponge spicules, gastropods, bivalves,

and calcareous green algae ( Ischadites ) are

noted in the mounds.

Faunas within the Palisades-Kepler

mounds are generally characterized by a

greater abundance of large and more robust

benthic invertebrates than contemporaneous

faunas in the intermound position. The

mound facies include an abundance of large

camerate crinoids, rugose and tabulate

corals (to 65 cm), and stromatoporoids,

whereas the intermound Waubeek and Buck

Creek Quarry facies associations are charac¬

terized by smaller crinoids and corals (rarely

exceeding 8 cm). Colonial tabulates are the

most abundant corals in the mound facies,

whereas small solitary rugosans dominate

the coral faunas in the intermound facies.

Large, relatively smooth-shelled trilobites

(e.g., Bumastus) were most successful in the

mound facies, whereas smaller, more ornate

trilobites (e.g,, Encrinurus) achieved greater

success in the intermound facies. Rhyncho-

nellid, large pentamerid, and trimerellid

brachiopods fared best in the mound facies,

whereas generally small and thinner-shelled

brachiopods (e.g., orthids, meristellids)

achieved a higher level of success in the

intermound facies. The general abundance

of benthic invertebrates was considerably

greater in the mound facies than in equiv¬

alent intermound facies, possibly reflecting

the greater availability of nutrient-rich

currents in the shallower water mound envi¬

ronments and greater habitat complexity.

The upper Scotch Grove Fawn Creek

facies faunas and lithologies are similar to

those in the mound facies, although the

volume of skeletal grains in the non-

mounded Fawn Creek facies is proportion¬

ately slightly less than in the mound facies,

and the coralline fauna is of generally

smaller size than in the mounds. The Fawn

Creek facies probably represents a skeletal

bank facies that occupied an intermound

environmental position intermediate be¬

tween the mound facies and the more distal

intermound Buck Creek Quarry and Wau¬

beek facies.

Stratigraphic relations clearly indicate that

the carbonate mound environments occu¬

pied a shallower water position than the

adjacent flat-lying intermound facies.

Correspondingly, evidence of wave and

current activity is more pronounced in the

mound facies. The abundance of skeletal

packstone and grainstone textures in the

Palisades-Kepler mounds suggests that

carbonate muds were partially to completely

winnowed during deposition of some beds.

Some beds with packstone-grainstone tex¬

tures consist of crinoidal debris of relatively

uniform size, which implies possible current

sorting. In addition, some packstones con¬

tain possible current-oriented crinoid stems.

Wedge-shaped grain flow deposits, some of

which exhibit graded bedding, flank some of

the mounds, suggesting periodic downslope

mass movements. Overturned and trans¬

ported corals are commonly observed, which

were probably moved during periodic in¬

fluxes of turbulent conditions across the

mounds.

Philcox (1971, p. 345) studied coral

growth forms and their relationship to the

surrounding sediment in the Palisades-

Kepler Mound facies, and suggested that

“reef sedimentation was an irregular

process” with “marked fluctuations in

34

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

sediment rates” across the mounds. He also

found “evidence for periodic local removal

of sediment.” These observations indicate

that periodic water turbulence, possibly

generated during storm events, played an

important role in mound sedimentation.

Less turbulent water currents were probably

present across the mounds on a more regular

basis. The abundant and diverse biota that

inhabited the mounds required a continual

influx of nutrients. The pervasive submarine

cementation that occurred in the mounds

probably required movement of large quan¬

tities of water through the mounds. Accu¬

mulations of nautiloids and trilobites within

the mounds are also indicative of current

activity (Mikulic, 1979). However, the lack

of a rigid skeletal framework suggests that

the mounds were not continuously exposed

to high-energy environments. Philcox (ibid.)

also concluded that “turbulence was nor¬

mally limited” during the growth of the

Palisades-Kepler mounds, although the

mounds apparently grew upward into more

agitated environments through time. The

vertical limits to mound growth may have

been controlled by normal fair-weather wave

base, since the lack of a skeletal framework

may have precluded further mound growth

into the highly agitated wave-washed envi¬

ronments. Corals are most abundant in the

upper portions of the mounds (Philcox,

1971), where presumably the greatest degree

of current activity would have been operat¬

ing during mound deposition. In summary,

all evidence indicates that current activity

and storm events exerted considerably more

influence on sedimentation in the mound

environments than in the laterally equivalent

and deeper-water B.A. 3 environments in the

intermound position.

Stricklandiid Brachiopod

and Related Associations

Stricklandiid brachiopod and related

associations occur at several positions in the

eastern Iowa Silurian sequence (stricklandiid

taxonomy after Johnson, 1979, 1983: 1)

middle portion of Hopkinton A (Strick¬

land ia lens progressa ), 2) lower to middle

Hopkinton B (S. laevis ), 3) lower Scotch

Grove Formation, Emeline and Buck Creek

Quarry facies (Costistricklandia castellana ),

and 4) mid Scotch Grove Formation, Eme¬

line, Buck Creek Quarry, and basal Fawn

Creek facies (C. castellana, C. multiliratd) .

Overall, the stricklandiid associations con¬

tain the most diverse benthic faunas re¬

covered in the entire Iowa Silurian sequence.

However, Stricklandia associations are inter-

bedded with coral-stromatoporoid associa¬

tions in one to several thin bands in the

middle portion of the Hopkinton A in the

eastern and northeastern Iowa outcrop belt,

and these stricklandiid associations, typic¬

ally characterized by corals and one to two

species of brachiopods (Johnson, 1977a), are

of generally lower diversity than younger

Iowa stricklandiid associations. Although

stricklandiid associations are usually

assigned a B.A. 4 position (Boucot, 1975),

interbedding of Hopkinton A stricklandiid

associations with B.A. 2 coral-stroma¬

toporoid associations suggests that the

Hopkinton A stricklandiids may have occu¬

pied a position more closely analogous to

B.A. 3 pentamerid associations. Johnson

(1980, p. 206) further suggested that “there

is very little difference” in general paleo-

community structure between the Hopkin¬

ton A “ Stricklandia community” and typi¬

cal Hopkinton “pentamerid communities,”

perhaps due to similarities in shell packing

(Johnson, 1979). Stricklandiids occur as a

minor component of pentamerid-dominated

brachiopod associations in younger intervals

of the Hopkinton and Scotch Grove forma¬

tions, suggesting that stricklandiids were

apparently adapted for life in some B.A. 3

environments.

On the other hand, stricklandiid and

related associations in the Hopkinton B and

lower Scotch Grove (Emeline and Buck

Creek Quarry facies) are very diverse and

include faunal elements, excluding the

stricklandiids, that are generally charac-

1983]

Witzke . Silurian Benthic Invertebrate Associations

35

teristic of B.A. 4 to B.A. 5 positions

(Boucot, 1975). These associations com¬

monly include: 1) sponge spicules, 2)

stromatoporoids, 3) tabulate and rugose

corals (most less than 10 cm diameter), 4)

inarticulate, orthid, strophomenid, rhyncho-

nellid, pentamerid, and spiriferid brachio-

pods, 5) bryozoans (abundant branching and

fenestellid forms), 6) gastropods, bivalves,

and nautiloids, 7) trilobites, and 8)

echinoderms. The echinoderm faunas are

dominated by a highly diverse assemblage of

camerate crinoids (Witzke and Strimple,

1981), although inadunate and flexible

crinoids, blastoids, paracrinoids, and

rhombiferan cystoids also occur (Witzke,

1976). Johnson (1977a, p. 38-91) recognized

additional stricklandiid-related associations

in the lower Emeline facies: 1) “a unique

bryozoan and trilobite fauna” and 2) “a

high diversity fauna comparable to a

cloridan community” (cloridan brachiopod

communities assigned B.A. 5 position by

Boucot, 1975). A similar bryozoan-rich

association containing brachiopods ( Atrypa ,

Protomegastrophia, Dicoelosia ), solitary

rugosans (including Palaeocyclus), crinoid

debris (including abundant Petalocrinus'),

and trilobites occurs above Pentameroides-

bearing beds in the middle Scotch Grove

Formation (Buck Creek Quarry facies).

Closely similar stricklandiid associations

occur within both the Buck Creek Quarry

and Emeline facies in the lower Scotch

Grove Formation, although the highly

crinoidal Emeline facies contains proportion¬

ately more skeletal material. Wackestone

and packstone textures are characteristic,

and crinoidal debris is the dominant skeletal

constituent in both facies (see Table 1 point-

count data for a limestone interval equiva¬

lent to the lower Buck Creek Quarry facies).

Petrographic and sedimentologic observa¬

tions pertinent to environmental interpreta¬

tions include: 1) skeletal grain abrasion/

breakage not observed, 2) absence of current

sorting or graded bedding, and 3) micrite

envelopes around grains not observed. These

features suggest relatively quiet depositional

conditions in deeper-water environments

than the B.A. 2 and 3 associations. In addi¬

tion, the benthic faunas that thrived in the

stricklandiid associations include forms

whose delicate or thin-shelled morphology

seems poorly suited for survival in agitated

environments (Johnson, 1980). The presence

of articulated echinoderms is consistent with

a quiet depositional environment. Johnson

(1980) proposed a relatively calm water

depositional environment for the strick¬

landiid associations, “well below effective

wave base.” Although effective wave base

can be substantially lowered during periodic

storm events, the B.A. 4-5 associations in the

Iowa Silurian lack sedimentologic evidence

of episodic turbulence and thus are reason¬

ably inferred to have occupied environments

generally below maximum storm wave base.

However, B.A. 4-5 environments in Iowa

occupied a position partially or wholly

within the photic zone (contrary to Boucot,

1981, p. 247), inasmuch as calcareous green

algae have been recovered in stricklandiid

associations in the Hopkinton and lower

Scotch Grove formations.

Conclusions and Geologic Implications

The distribution of open-marine benthic

associations in the Iowa Silurian was strong¬

ly controlled by depth-related environmental

factors, primarily general position with

respect to effective fair-weather and storm

wave bases. As such, the temporal changes

from one benthic association type to another

can be reasonably correlated with depth-

related environmental changes. The spatial

distribution of various associations within

specific stratigraphic intervals can also be

evaluated in terms of depth-related facies

changes over a geographic expanse. John¬

son’s studies within the eastern Iowa Lower

Silurian outcrop belt led him to conclude

several things about that region: 1) “the

generally flat, Iowa sea bottom supported

only a single spatially monotonous commu¬

nity at a time” (1977a, p. 118); 2) “their

36

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

lateral uniformity in composition and

structure was pervasive” (1980, p. 213); and

3) “contemporaneous facies, if present,

existed in such widely spaced belts as not to

be obvious in this particular region” (1975,

p. 130). However, comparisons of the Hop-

kinton benthic associations in the subsurface

west of the outcrop belt (Linn-Benton

counties; see map Fig. 2) with those in the

outcrop belt suggest lateral variations in the

distribution of benthic associations and

facies on a slightly broader geographic scale.

The Hopkinton Formation doubles in

thickness as one proceeds from the Benton

County subsurface to the central area of the

East-Central Iowa Basin (see Fig. 1), and the

interpreted distribution of the contained

benthic associations displays a pattern that is

consistent with the basinal geometry (Fig. 3).

Figure 3 is presented as a generalized and

interpretive model that attempts to rectify

the fossil distributions recognized in the

western subsurface cores with those known

in the Iowa Silurian outcrop belt. Subsurface

data cannot be elaborated here, although

core data recorded by Witzke (1981c, p.

486-544) forms the primary basis for the

illustrated interpretations. Although Strick-

landia associations occur in the middle Hop¬

kinton A in the outcrop belt, the thinned

Hopkinton A in the western subsurface has

yielded no elements of this association (Fig.

3). The most dramatic lateral change in

benthic associations apparently occurs in

I stricklandid o io 20 30 mi.

j association 1 . — ' 1 - d

O 10 20 30 40 50 km.

Fig. 3. Generalized interpretation of the vertical and lateral variation in the distribution of benthic associations in the

Hopkinton Formation of east-central Iowa. Cross-section line is essentially the same as that used in Figure 2. The

sequence of associations in the eastern outcrop belt is derived, in part, from Johnson (1975, 1977a). Subsurface

paleotologic data in western subsurface sections generalized from Witzke (1981c). Distribution of Hopkinton A

stricklandiid association is schematic, and is represented by several thin zones in the middle to upper “ Syringopora

beds.” The interpreted distribution illustrates an “Israelsky Wedge,” suggesting that Iowa Hopkinton deposition

occurred during a major transgressive-regressive bathymetric cycle.

1983]

Witzke — Silurian Benthic Invertebrate Associations

37

Hopkinton B. In the outcrop belt the

Hopkinton B is characterized by a lower

interval with a Stricklandia association and

an upper interval with a pentamerid associa¬

tion (Johnson, 1980). However, the western

subsurface Hopkinton B interval character¬

istically contains pentamerid associations in

the lower portion, and the upper portion

contains an abundant tabulate coral fauna

with additional fossils (cup corals, stroma-

toporoids, crinoids, bryozoans, orthids,

gastropods). The fauna in the upper interval

is tentatively assigned to the coral-stroma-

toporoid association, although it contains a

slightly more diverse fauna than that noted

in similar associations in Hopkinton A and

C. This association lacks the pentamerid and

stricklandiid brachiopods present in the

deeper water Hopkinton associations toward

the east (Fig. 3). These observations suggest

the following interpretations: 1) the lower

Hopkinton B Stricklandia association in the

central portion of the East-Central Iowa

Basin is replaced westward by pentamerid

associations, and 2) upper Hopkinton B

pentamerid associations in the central area

of this basin are replaced westward by a

coral-stromatoporoid association.

As illustrated in Figure 3, the interpreted

spatial distribution of the various Hopkin¬

ton benthic associations forms an “Israelsky

Wedge” (Israelsky, 1949) in which, at any

given time, deeper-water associations occu¬

pied the central basin area with stratigraph-

ically equivalent shallower-water associa¬

tions developed toward the basin margin.

These observations offer independent evi¬

dence of the depth significance of each

association type, since an “Israelsky

Wedge” records the “deepening and shal¬

lowing phases of a bathymetric cycle” as

determined by the relative positions of

“bathymetrically controlled” benthic asso¬

ciations (Krumbein and Sloss, 1963, p. 386).

A sequence of probable depth-related

open-marine benthic assemblages is identi¬

fied in the Iowa Silurian, and these assem¬

blages can be correlated with general depth-

related environmental zones of Irwin (1965)

and Anderson (1971). However, at any given

time during the Silurian, only one or two

benthic assemblage positions were repre¬

sented in eastern Iowa. The full complement

of onshore to offshore environments (B.A.

1-B.A. 6) at any one time, if developed,

probably spread over a much broader geo¬

graphic area in the epeiric sea. A hypo¬

thetical onshore-offshore transect depicts

the position of B.A. 1 to 5 environments

over a broad geographic area in the central

midcontinent (Fig. 4), presumably many

hundreds of kilometers across. The farthest

offshore environments (B.A. 4-5) are shown

in a position well below wave base. How¬

ever, in Iowa, these environments were

characterized by a diverse benthic biota that

would have required a degree of current

activity to replenish nutrients and maintain

stable salinities. B.A. 3 associations inhab¬

ited two general carbonate environments in

wave currents

damped

Fig. 4. Hypothetical onshore to offshore transect depicting environmental zones in the Early Silurian epeiric sea in the

central midcontinent. Transect is presumably many hundreds of kilometers across. Relative positions of Benthic

Assemblages 1 to 5 are shown in relation to fair-weather and storm wave bases. Stable open-marine salinities are

maintained across the area occupied by B.A. 2-5, but wind-generated currents are damped in the B.A. 1 position where

elevated salinities may be developed. The various environmental zones would migrate across the bottom during relative

changes in sea level.

38

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

the Iowa Silurian: 1) flat-lying substrate

(commonly pentamerid-bearing), and 2)

carbonate mound (reef) environments. The

flat-lying associations are positioned

generally below fair-weather wave base,

although periodic turbulent conditions

suggest that storm wave base occasionally

reached the bottom. On the other hand, car¬

bonate mound environments were subjected

to a greater degree of wave and current

activity than the flat-lying environments and

are placed in a position on Figure 4 where

they would have been recurrently subjected

to storm events but, in general, immediately

below normal fair-weather wave base. B.A.

2 environments are positioned near wave

base in the clear water epeiric sea, in part

above and in part immediately below wave

base (Fig. 4). B.A. 1 associations in Iowa

display evidence of restricted circulation and

elevated salinities and are discussed in the

next section.

Restricted-Marine Benthic Associations

General Characteristics

Restricted-marine benthic associations in¬

habited environments of elevated or fluctu¬

ating salinity. During portions of the Iowa

Silurian (early Llandoverian, late Wenlock-

ian-Ludlovian) these environments encom¬

passed a broad range of salinity variations

constrained between two general extremes:

1) salinities close to normal-marine, and 2)

hypersaline environments in which solutions

were occasionally concentrated high enough

to precipitate gypsum or halite. This spec¬

trum of environmental conditions influenced

sedimentation in a variety of ways, and a

variety of distinctive rock types occur in

intervals bearing restricted-marine associa¬

tions. General rock types include: 1) dolo¬

mites with skeletal wackstone, packstone, or

grainstone textures, 2) unfossiliferous or

sparsely fossiliferous dolomites with mud¬

stone textures, 3) domal and sheet-like

stromatolitic carbonates, 4) thinly-bedded

dolomites and shaly dolomites, 5) laminated

dolomites, and 6) dolomites containing

evaporite crystal molds. In addition, the

contained faunas are characteristically of

lower diversity than the open-marine faunas,

and several invertebrate groups commonly

regarded as stenohaline (see Heckel, 1972)

are absent in many of the associations.

Lingulid Brachiopod

and Related Associations

Deposition of the Mosalem Formation in

eastern Iowa occurred above an irregular

Ordovician shale surface along the margin of

the transgressing Early Silurian epeiric sea.

The surrounding shale hills supplied clays to

the Mosalem environments, where argil¬

laceous carbonate deposition prevailed.

Mosalem deposition in Iowa was restricted

to the eastern part of the state, apparently

within isolated cul-de-sacs and embayments

in a nearshore position. The Ordovician

shale hills were progressively buried by

Silurian sediments as the Silurian trans¬

gression progressed, and authochthonous

open-marine carbonate depositional patterns

became established across much of Iowa by

the middle Llandoverian (Blanding Forma¬

tion).

The benthic associations contained in the

Mosalem Formation are assigned a near¬

shore B.A. 1 position. Unlike the younger

Iowa Llandoverian environments where

normal-marine faunas are well represented,

the Mosalem biota is a low-diversity assem¬

blage locally dominated by lingulid brach-

iopods. Rhynchonellid and strophomenid

brachiopods and gastropods are also locally

noted (Johnson, 1975, 1977a). Corals,

stromatoporoids, echinoderms, and trilo-

bites are characteristically absent in the

Mosalem. Where the Mosalem Formation is

thin, a basal zone of stromatolitic algal mats

is observed (ibid.). Skeletal grains in the

Mosalem are non-abraded, suggesting gener¬

ally quiet depositional conditions. The

thinly-bedded argillaceous dolomites and

shales and horizontally-laminated stroma¬

tolites in the Mosalem are also consistent

with relatively quiet depositional environ-

1983]

Witzke — Silurian Benthic Invertebrate Associations

39

ments. The preservation of organic matter in

the Mosalem, including plant filaments

(ibid.), graptolites, and soft-bodied worms

(T. Frest, 1982, personal comm.), also sug¬

gests a non-agitated depositional setting.

The restricted fauna and low-energy B.A.

1 environment of the Mosalem Formation in

Iowa are characteristic of the “low-energy

zone” of Irwin (1965) and “restricted sub-

tidal” environment of Anderson (1971).

Wave current activity was probably damped

somewhere offshore (B.A. 2 position), re¬

stricting circulation in the nearshore zone

(see Fig. 4). The discovery of possible halite

pseudomorphs in the Iowa Mosalem sug¬

gests that elevated salinities may have been

present at times during Mosalem deposition.

However, some currents were occasionally

present in the nearshore Mosalem environ¬

ments, as evidenced by rare ripple marks low

in the sequence.

Stegerhynchus Association

The uppermost portion of the Scotch

Grove Formation (upper Waubeek and Buck

Creek Quarry facies) and basal Gower

Formation (Anamosa facies) in Linn and

Jones Counties, Iowa (Fig. 2 map) contain

benthic associations of considerably

different composition from those in under¬

lying Scotch Grove strata. Block collections

have produced a relatively low diversity

assemblage characterized by brachiopods

and, locally, small tabulate and solitary

rugose corals. This assemblage is termed the

Stegerhynchus association. In addition to

Stegerhynchus, other brachiopods, com¬

monly Protathyris, Spirinella, and Meris -

tina, are prominent members of this associa¬

tion. Of special interest is the absence of

bryozoans and trilobites and general absence

of echinoderms, which renders the associa¬

tion considerably different from the under¬

lying Scotch Grove associations. Protathyris

is known only from a B.A. 2 position (Bou-

cot, 1975), and the presence of Protathyris in

the Stegerhynchus association suggests the

same position.

The lowest occurrence of the Steger¬

hynchus association in the upper Scotch

Grove Formation is interbedded with strata

containing scattered small echinoderm

debris. Collections recovered from this

position contain a slightly more diverse

assemblage than Stegerhynchus association

collections identified a few meters higher

stratigraphically, and small colonial rugo-

sans (Heliolites), gastropods, bivalves, and

additional brachiopod taxa are present

(Witzke, 1981c, p. 409). However, Prota¬

thyris is absent in these collections. Higher in

the sequence, the uppermost Scotch Grove

Stegerhynchus association is further reduced

in diversity, contains fewer brachiopod taxa,

and completely lacks echinoderm debris.

Brachiopods are the only benthic group

represented in some uppermost Scotch

Grove collections. This general change in

benthic association diversity in the upper¬

most Scotch Grove is also marked by the

appearance of two brachiopod genera,

Protathyris and INalivkinia, not represented

lower in the sequence. The presence of an

atrypid tentatively identified by Boucot

(1981, personal comm.) as INalivkinia is

noteworthy, as the genus has previously been

identified only in central Asia. Elements of

the uppermost Scotch Grove Stegerhynchus

association survived past the close of Scotch

Grove deposition, and Protathyris and

rhynchonellids are prominent throughout

much of the Gower Formation.

The disappearance of several probable

stenohaline groups (most notably the bryo¬

zoans, trilobites, echinoderms) in the upper¬

most Scotch Grove Formation in the western

portion of the East-Central Iowa Basin

(Linn- Jones counties) suggests that elevated

salinities may be, in part, responsible for the

biotic changes. The major changes in benthic

association structure evident in the

uppermost Scotch Grove Formation imme¬

diately preceded, or were coincident with,

the appearance of laminated Gower carbo¬

nate deposition in eastern Iowa, and there

appears to be a close link between the

40

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

appearance of the Stegerhynchus association

and major changes in the patterns of carbo¬

nate deposition in Iowa. As will be discussed

later, the appearance of laminated carbonate

deposition in eastern Iowa probably marked

a significant change in the patterns of water

circulation that led to elevated salinities.

Uppermost Scotch Grove Stegerhynchus

associations, assigned a B.A. 2 position,

overlie normal-marine B.A. 3 associations,

and a relative drop in sea level towards the

close of Scotch Grove deposition in Iowa is

inferred. Unlike relative sea level drops

earlier in the Silurian, the probable drop in

sea level at the close of Scotch Grove deposi¬

tion created physiographic conditions that

led to the restriction of normal-marine

epeiric circulation in eastern Iowa. This

change is not only reflected in the patterns of

carbonate deposition, but also by a general

reorganization of benthic community struc¬

ture.

Laminated Carbonate Environments

and Associations

The onset of Gower deposition was

marked by the widespread appearance of

laminated carbonate sediments over much of

east-central Iowa. Although three general

facies are recognized in the Gower Forma¬

tion of Iowa, flat-lying sequences containing

laminated dolomites (Anamosa facies) typify

much of the formation. The bulk of the

Anamosa facies is comprised of laminated

dolomites; individual laminae generally

range between about 0.3 and 3 mm thick,

and laminae as thin as 30 microns are noted.

The laminated rocks include three general

lithologies: 1) wavy- or crinkly-laminated

rocks interpreted as subtidal algal stromato-

litic mats (Philcox, 1972; Henry, 1972); 2)

planar-laminated rocks, possibly represent¬

ing varved carbonate accumulations depos¬

ited by episodic or seasonal carbonate

precipitation (Witzke, 1981c); and 3) faintly-

laminated dolomites. In addition, the

Anamosa facies includes a variety of sec¬

ondary rock types: thinly-bedded dolomites,

dense to porous non-laminated dolomite

mudstones, intraclastic dolomites, dolomites

with evaporite crystal molds, and fossilifer-

ous dolomites with skeletal wackestone to

packstone textures. Individual laminae and

dolomite mudstone beds are laterally persis¬

tent on outcrop (up to distances of 3 km or

more), suggesting widespread quiet-water

depositional environments. The rare pres¬

ence of evaporite crystal molds (Henry,

1972), probably gypsum, along with the

general absence of benthic faunas, indicates

that the Anamosa facies was, at least in part,

deposited under conditions of elevated salin¬

ity. Similar laminated carbonate intervals

are present in evaporitic sequences in the

Salina Group of the Michigan Basin. Al¬

though the bulk of the Anamosa facies was

probably deposited under quiet conditions,

the occasional presence of truncated laminae

and intraclast beds in the sequence suggests

that periodic turbulent conditions, perhaps

generated during storm events, occurred

during deposition.

The Anamosa facies is characterized by a

general absence of benthic invertebrates

(including burrowers), although a few low-

diversity associations are scattered within

some Anamosa sequences. The beds contain¬

ing benthic faunas are typically quite thin,

indicating that benthic faunas lived in the

Anamosa environments for relatively short

periods of time. Benthic faunas are most

commonly encountered in the Anamosa

facies in the general vicinity of the Brady

facies mounds, where abundant brachiopod

and coral faunas thrived in the shallower

mound environments. These faunas are

included in the Prota//zj77S'-rhynchonellid

association, an association best developed in

the mound facies. This association inter¬

fingers with laminated Anamosa dolomites

near the mound margins. However, thin

beds bearing the Protathyris-vhynchoneWxd

associations are occasionally present within

the Anamosa facies at localities removed

from areas of Brady facies mound devel¬

opments; thus at times when laminated

1983]

Witzke — Silurian Benthic Invertebrate Associations

41

Anamosa deposition was interrupted, this

association may have briefly lived in the

intermound environments. In general, the

Protathyris- rhynchonellid association

typically includes an abundance of few taxa,

most notably athyrid {Protathyris, Hyat-

tidina) and indeterminate rhynchonellid

brachiopods and small tabulate and solitary

rugose corals. Gastropods, bivalves

( Pterinea ), and ostracodes have also been

observed. Echinoderm debris is character¬

istically absent throughout the Anamosa

facies, although some small echinoderm

debris has been locally noted, most com¬

monly near the contact with the underlying

Scotch Grove Formation.

A second benthic association, termed the

“rod”-algal mat association, is also iden¬

tified in the Anamosa facies. This associa¬

tion is not only noted at a position where the

Brady and Anamosa facies interfinger, but

also at localities far removed from any car¬

bonate mounds. The “rods” are enigmatic

cylindrical fossils generally about 1 cm by 2

mm in size, but occasionally reaching lengths

of up to 4 cm. They are usually associated

with algal-laminated beds. The “rods” were

apparently soft when deposited, as indicated

by draping of individual “rods” to conform

to bedding surface undulations (Henry,

1972). The “rods” have been variably inter¬

preted as fecal pellets or dwelling tubes of an

unknown benthic invertebrate. However, the

“rods” are exceptionally large for most

known fecal pellets. Gill (1977) illustrated

“rods” from algal-laminated dolomites of

the A-l carbonate in the Michigan Basin

which he interpreted as being of “fecal

origin,” probably produced by unknown

“mat-grazing organisms.” However, if the

abundant “rods” were produced by burrow¬

ing or grazing organisms, there should be

evidence of burrowing within the laminated

dolomites or truncated grazed surfaces on

individual algal laminae adjacent to the

“rod”-bearing beds. Such features have not

been observed in the laminated Gower dolo¬

mites. In addition, well-preserved “rods”

have a hollow central chamber, a feature not

easily explained if they are of fecal origin.

Henry (1972) alternatively suggested that the

“rods” were soft, gelatinous dwelling tubes

of an unknown “worm”-like organism. The

organisms that lived in these tubes may have

been filter feeders. The general exclusion of

a benthic fauna in most laminated Anamosa

environments suggests that benthic condi¬

tions were hostile to most invertebrates,

probably due to elevated salinities. How¬

ever, the “rod” organisms were apparently

uniquely adapted for survival in some of the

subtidal organic-mat environments.

Carbonate Mound ( Reef)

and Related Associations

Carbonate mound facies interfinger with

laminated dolomites of the Anamosa facies

within the Gower Formation of eastern

Iowa. Two mound facies are recognized,

each generally occupying a distinct geo¬

graphic region of eastern Iowa. The Brady

facies includes coral- and brachiopod-rich

mounds typically developed in the western

and central portions of the East-Central

Iowa Basin. Stratigraphic relations indicate

that the Brady mounds were deposited in

shallower-water environments than the

adjacent flat-lying Anamosa beds (Witzke,

1981a). Brady facies mounds and mound

complexes vary in size from about 150 m to 1

km in diameter; maximum vertical dimen¬

sions are unclear due to post-Silurian erosion

(up to 25 m preserved). Dips average about

20 to 50° in the mounds, and slump-folds

locally achieve dips up to 90° (Hinman,

1968).

The Brady facies is characterized by fossil-

iferous dolomite with skeletal wackestone-

packstone (some grainstone and bound-

stone) textures. Dense non-laminated to

laminated dolomites, in part with prominent

stromatolites, are interbedded with the

fossil-rich beds. Although, in a general

sense, Brady rock types resemble those of

the Anamosa facies, the Brady facies is

markedly more skeletal rich. The Brady

42

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

mounds lack a rigid skeletal framework,

and, as evidenced by abundant relict fibrous

isopachous cements, the mounds apparently

became rigid features on the sea floor

primarily through submarine cementation

processes.

A profusion of fossils is evident in the

Brady facies, but the faunas are of relatively

low diversity. As previously discussed, dense

brachiopod accumulations of the Prota-

t/2yr/s-rhynchonellid association comprise

much of the Brady facies. The abundant

small brachiopods are normally articulated,

and dolomite-replacement of delicate athy-

rid spiralia is not uncommon. The Fletcheria

association is well developed within some

Brady facies mounds, commonly intimately

associated with Protathyris-rhynchoneWxd

beds. This association is dominated by clus¬

ters of the solitary rugose coral, Fletcheria

sp., and small colonies (usually less than 20

corallites) of an indeterminate tabulate coral

are commonly encountered. Small solitary

rugosans, Haly sites, and Favosites are

locally present. The coral-rich Fletcheria

association intergrades with the Protathyris-

rhynchonellid association in the Brady

facies, and Fletcheria and small tabulates are

locally represented in the brachiopod-rich

beds. The abundance of corals and Prota-

thyris in these associations suggests a B.A. 2

position. Toward the edges of the Brady fa¬

cies mounds, the Protathyris-x\xynchoxxe\\\d

association interfingers with laminated dolo¬

mites of the Anamosa facies. At this general

position, algal-laminated dolomites, in part

containing “rods,” become prominent, and

domal stromatolites are locally observed.

“Rod” packstones are noted near the

mound edges.

A distinct benthic association is locally

present in the central mound areas of the

Brady facies, stratigraphically below

Fletcheria and Protathyris- rhynchonellid

associations. Large pentamerid ( Harpidium )

and trimerellid brachiopods are conspicuous

in this association, forms generally charac¬

teristic of a B.A. 3 position (Boucot, 1975).

In addition, spiriferid, strophomenid, and

rhynchonellid brachiopods are also repre¬

sented, although athyrids are absent.

Gastropods, bivalves, and nautiloids are

present, but corals are generally rare. The

F[arpidium-lnmerQ\\\(\ association locally

contains rare echinoderm debris, but trilo-

bites, bryozoans, and stromatoporoids have

not been observed.

The LeClaire facies occupies a position

near the southeast margin of the East-Central

Iowa Basin, and is best developed in Scott

County, Iowa (see Fig. 2 map) and adjacent

areas of Illinois. The LeClaire facies includes

mounded and flat-lying strata that inter¬

finger with the Anamosa facies in a complex

manner. The LeClaire facies contains several

different benthic associations. Unlike

benthic associations in the Brady facies, the

LeClaire facies locally includes associations

with an abundance of crinoidal debris, both

in flat-lying and mounded sequences. Large

crinoid debris, including identifiable cups

(especially Eucalyptocrinites, Crotalocri-

nites), is locally common in some LeClaire

mounds, and small indeterminate crinoid

debris is present in some flat-lying LeClaire

sequences. Trilobites also occur in some

LeClaire mounds. The presence of crinoid

debris and trilobites in the LeClaire facies

(these groups commonly regarded as steno-

haline) suggests that LeClaire environments

were developed, in part, in water of gener¬

ally normal-marine salinity. Crinoidal rocks

in the LeClaire facies resemble typical

lithologies in the Palisades-Kepler Mound

facies, although, unlike the Palisades-Kepler

mounds, the LeClaire facies occurs higher

stratigraphically and is laterally equivalent

to laminated dolomites. However, the

LeClaire facies also includes lithologies and

benthic associations that closely resemble

those in the Brady-Anamosa facies.

Fletcheria associations are well developed

in the LeClaire facies, both in flatlying and

mounded sequences, and are locally inter-

bedded with crinoidal or laminated dolo¬

mites. The LeClaire Fletcheria associations

1983]

Witzke — Silurian Benthic Invertebrate Associations

43

contain rugose and tabulate corals, brachio-

pods (rhynchonellids, atrypids), and rare

gastropods, but echinoderm debris is absent.

Additional brachiopod-dominated associa¬

tions, commonly containing rhynchonellids

and atrypids (aff. INalivkinia ), occur in the

facies. The LeClaire mounds also locally

contain a brachiopod association character¬

ized by large pentamerids ( Conchidium ) and

trimerellids; large bivalves (“ Megalomus ”),

gastropods, and solitary rugose corals also

occur. The LeClaire rhynchonellid-atrypid

and Conchidium- trimerellid faunas re¬

semble, in a general sense, the Protathyris-

rhynchonellid and Harpidium-tnmQveWid

associations, respectively, in the Brady

facies. A degree of faunal similarity between

the Brady and LeClaire mounds is apparent,

although important faunal differences, par¬

ticularly with respect to the crinoidal

component, need to be stressed.

As with the upper Scotch Grove mounds,

mound facies in the Gower Formation were

subjected to water currents during

deposition to varying degrees. These

currents brought a continuing supply of

nutrients to the abundant suspension¬

feeding invertebrates that lived on the

mounds, and also facilitated the movement

of water through the mound promoting sub¬

marine cementation. However, the charac¬

teristic preservation of abundant artic¬

ulated brachiopods implies that agitated

wave-washed conditions were not contin¬

ually present in the mound environments.

Although the LeClaire mounds, in part, con¬

tain crinoidal faunas suggestive of open-

marine conditions, more Gower mound

faunas, especially those in the Brady facies,

are characterized by low-diversity associa¬

tions lacking several biotic groups

commonly interpreted as having stenohaline

normal-marine environmental requirements

(most notably echinoderms, trilobites,

bryozoans). In addition, the Gower mound

facies interfinger with laminated Anamosa

carbonates that were probably deposited in

environments of elevated salinity. It is

consistent with those observations to suggest

that the Gower mound environments were

also subjected to conditions of fluctuating or

elevated salinities during their deposition.

Upper Gower Faunas and Environments

The final phases of Silurian sedimentation

in Iowa have been largely erased by pre-

Middle Devonian erosion. However, the

uppermost Gower rocks examined contain

faunal and lithologic characteristics distinct

from those in underlying strata. The upper¬

most portion of the Anamosa facies at one

locality in Jones County (see Fig. 2 map)

includes non-laminated to faintly-laminated

dolomites that are locally intraclastic.

Specimens of a large ostracode, Leperditia

sp., were found in this interval. No other

fossils were recovered, and the fauna was

undoubtedly one of very low diversity. The

presence of intraclastic rocks suggests the

development of shallower water conditions

during upper Gower deposition. Intraclasts

may have been incorporated into the enclos¬

ing fine-grained carbonate sediments during

episodic incursions of agitated conditions.

This shallowing trend evident in the upper

Gower led to eventual offlap of the Silurian

sea from eastern Iowa.

Gower Depositional Model

The progression of normal-marine benthic

associations in the middle Llandoverian

through middle Wenlockian sequence in

Iowa bespeaks long-term maintenance of

stable salinities and effective circulation in

the Iowa portion of the epeiric sea. How¬

ever, a profound change in benthic associa¬

tion structure and carbonate depositional

patterns occurred during the middle to late

Wenlockian. Epeiric water circulation pat¬

terns in Iowa were apparently disrupted at

that time. Diverse marine B.A. 3 associa¬

tions in the upper Scotch Grove are replaced

by relatively low-diversity restricted-marine

B.A. 2 associations near the contact with the

Gower Formation. A relative drop in sea

level may have contributed to these changes.

44

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

What other factors contributed to the

restriction of water circulation in eastern

Iowa during the late Wenlockian? I previ¬

ously suggested that the late Wenlockian

drop in sea level “left central Iowa emergent

at the beginning of the Gower deposition,

and open circulation across the carbonate

shelf was thereby cut off’’ leaving “east-

central Iowa as a restricted embayment of

the Silurian sea’’ (Witzke, 1981a, p. 17).

During marine regression, the seas would

retreat first from the structurally elevated

areas and be retained longest within the

basinal areas (in this case, the East-Central

Iowa Basin). A tentative model of Gower de¬

position is proposed in which a restricted

embayment of the Silurian sea in east-central

Iowa opened eastward into Illinois where

better circulation and more normal marine

salinities prevailed.

The onset of Gower deposition was

marked by the widespread appearance of

laminated carbonate sediments (Anamosa

facies) over much of east-central Iowa. I

concur with Henry (1972, p. 78) and Philcox

(1972, p. 701) in interpreting the deposi-

tional environment of the laminated Gower

carbonates as one of quiet conditions of

restricted circulation and high salinities.

However, equivalent carbonate mound fa¬

cies developed in waters that were generally

shallower than the laminated Anamosa

facies. The nearer-surface water conditions

in the mound environments were apparently

more favorable for the flourishing of benthic

organisms than the slightly deeper environ¬

ments where subtidal organic mats and

“evaporitic’’ carbonates were deposited.

These interpretations suggest that a vertical

stratification of the water column was devel¬

oped during Gower depositional in eastern

Iowa. The probability of hypersaline condi¬

tions in the Gower environments further sug¬

gests that the water column may have been

divided into two water masses by a halocline.

The halocline marked the boundary between

the denser, more saline bottom waters and

an upper surface layer of less saline and

better aerated waters. The Brady facies

mounds apparently developed in the shal¬

lower and more hospitable surface waters,

whereas deposition of the Anamosa facies

predominated beneath a halocline (Witzke,

1981a, p. 21). Because the Brady faunas,

while extremely abundant, are generally of

low diversity and characteristically lack

several normally stenohaline groups, the

waters of the upper surface layer apparently

still posed stresses that tended to exclude

several groups of marine organisms, and

somewhat elevated salinities are suggested.

Skeletal-rich Brady facies beds may have

spread laterally into the flat-lying Anamosa

facies at times when the halocline became

depressed or disrupted.

The LeClaire facies includes a more

diverse benthic fauna compared to the more

restricted faunas of the Brady facies,

suggesting that surface water conditions

were more favorable for marine faunas in

the eastern portion of East-Central Iowa

Basin than farther west. This can be ex¬

plained if surface water salinities increased

westward within the basin. Carbonate build¬

ups and skeletal/mud banks of the LeClaire

facies in the eastern portion of the basin may

have served to attentuate open marine cir¬

culation between Illinois and eastern Iowa.

The LeClaire facies may thereby have

formed an effective circulation barrier, pro¬

moting the development of a stratified water

column in the East-Central Iowa Basin. The

halocline must have vanished eastward into

Illinois, where saline bottom waters pre¬

sumably mixed with more open-marine wa¬

ters. The LeClaire-Anamosa facies belt lies

at a position transitional between the

western Brady-Anamosa facies belt, where a

relatively stable and long-lived halocline was

apparently developed, and an open-marine

facies belt in Illinois. The LeClaire facies,

occupying this intermediate environmental

position, contains both open-marine and

restricted-marine benthic associations.

Conclusions

The central objective of this report was to

evaluate the distribution of the Iowa Silurian

1983]

Witzke— Silurian Benthic Invertebrate Associations

45

benthic associations in terms of possible con¬

trolling paleonvironmental parameters. The

Iowa Llandoverian depth-related benthic

paleocommunity model of Johnson (1975,

1980) was tested using additional petro¬

graphic and stratigraphic information. In

general, the distribution of the three basic

level-bottom open-marine benthic associa¬

tions (coral-stromatoporoid, pentamerid,

stricklandiid) was found to be highly

correlated to depth-related paleoenviron-

mental parameters, in particular the relative

position of effective wave base. Open-

marine epeiric circulation patterns were

maintained across the carbonate shelf in

Iowa during the middle Llandoverian

through middle Wenlockian, and the tem¬

poral sequence of benthic asociations and

facies is linked to widespread depth-related

environmental changes. Open-marine

environments and faunas are correlated to

general Benthic Assemblage positions within

the epeiric sea, and the change from one

B.A. type to another in the Iowa strati¬

graphic sequence can be consistently inter¬

preted in terms of relative changes in sea

level. As illustrated in Figure 1, several

transgressive (deepening) and regressive

(shallowing) trends are evident. However,

the change from one B.A. type to another

only documents relative changes in sea level,

and absolute changes in water depth may not

be accurately reflected. This is particularly

evident in the open-marine mound facies.

Although the mounds typically contain B.A.

3 associations, water depths and environ¬

mental conditions in the mound facies were

considerably different than in the inter¬

mound environments where B.A. 3 associa¬

tions also occur. In many respects, the

environmental factors operating during

mound deposition share more similarities

with flat-lying B.A. 2 environments than

with the B.A 3 intermound environments.

The disruption of open-marine epeiric cir¬

culation patterns during the late Wenlockian

and Ludlovian resulted in a dramatic reorga¬

nization of benthic association structure and

carbonate depositional patterns. The tem¬

poral and geographic distribution of the

Late Silurian benthic assemblages was re¬

lated, not only to relative changes in sea

level, but more importantly, to salinity

stresses within the restricted eastern Iowa

sea. As salinity stresses increased within the

eastern Iowa seaway, several stenohaline

groups, notably the echinoderms, trilobites,

and bryozoans, were excluded from the

benthic associations. Although Benthic

Assemblage analysis, when utilized with

additional stratigraphic and sedimentologic

evidence, provides a basis for evaluating

relative changes in sea level, a strict

correlation of Benthic Assemblages with

specific water depths is overly simplistic.

Additional environmental parameters oper¬

ating on epeiric carbonate shelves, especially

those related to salinity, also exerted

significant influence on the distribution of

Benthic Assemblages and their contained

biotic associations. In general, relative

changes in sea level affected carbonate

deposition by modifying the position of

storm and fair-weather wave base and, in

combination with physiographic and cli¬

matic factors, water circulation patterns.

Acknowledgments

Many people freely offered assistance

during the course of this study, and the

efforts of J. Barrick, A. Boucot, M. Bounk,

B. Bunker, M. Carlson, T. Frest, W.

Furnish, B. Glenister, R. Heathcote, P.

Heckel, G. Klapper, J. Kluessendorf, G.

Ludvigson, D. Mikulic, and J. Swade are

especially appreciated. Review comments by

M. Johnson, P. Sheehan, and R. Pauli are

acknowledged. P. Lohmann prepared the

illustrations, and L. Comstock, typed the

manuscript.

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Witzke— Silurian Benthic Invertebrate Associations

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OBSERVATIONS ON THE COMMENSALISM OF SILURIAN

PLATYCERATID GASTROPODS AND STALKED ECHINODERMS

Joanne Kluessendorf

Illinois State Geological Survey , Champaign , IL 61820

Abstract

Commensalism of coprophagous platyceratid gastropods and stalked echino-

derms persisted from the Ordovician through the Permian. Reported examples from

the Silurian are few although this association was well established by that time.

Among Silurian crinoids only camerates are involved in this commensalism.

These taxa comprise only nine genera from seven families among the 57 genera

represented by 21 Silurian camerate families. Four of these genera ( Dimer ocrinites ,

Lyriocrinus, Macrostylocrinus, Saccocrinus) are found in the Rochester Shale of

New York and Ontario. Other host crinoid genera include Ptychocrinus (Power

Glen Shale, New York and Ontario), Periechocrinus (Waldron Shale, Indiana),

Scyphocrinites (Silurian-Devonian boundary, Morroco), and Marsupiocrinus and

Clematocrinus (Wenlock Limestone, England). Dimer ocrinites with attached platy-

ceratids are also known from the Hogklint beds at Haftingsklint, Gotland, Sweden.

The cystoid Caryocrinites from the Rochester Shale is also found as a platy¬

ceratid host. This is the only cystoid known as a host in the Silurian. Caryocrinites is

unique among cystoids because of its morphologic similarity to crinoids, par¬

ticularly camerates.

The non-camerate host crinoids (six genera of poteriocrinine inadunates and

one taxocrinid flexible) in the geologic record bear morphologic and behavioral

similarities to camerates, and these characteristics may influence host selectivity.

The tegmen and anus morphologies of host crinoids are variable, and the degree of

control which these features exert on host selectivity is uncertain.

Introduction

Platyceratid gastropods are found

attached to the tegminal area of certain

Paleozoic stalked echinoderms, primarily

crinoids and rarely cystoids and blastoids.

Presumably, the platyceratid settled during

its larval stage onto a young host echino-

derm and led a sedentary life situated over

the echinoderm’s anal opening where it fed

on discharged fecal material. This commen¬

salism was apparently successful since it

persisted from the Ordovician, when platy-

ceratids first appeared, through the Per¬

mian, when both platyceratids and the

echinoderms which served as hosts became

extinct (Bowsher, 1955). This platyceratid-

echinoderm relationship has been reviewed

in general by several authors (Keyes, 1888;

Clarke, 1921; Bowsher, 1955; Lane, 1978)

but little has been previously published

about Silurian occurrences even though this

association was well established by that

period. This paper will relate the known

Silurian commensal occurrences, describe

the types of echinoderms that serve as hosts,

and suggest some possible factors in host

selectivity by platyceratids.

Silurian Occurrences

The existence of this commensalism in

Silurian time has been known at least since

1851 when Hall figured (1851), PI. 49, fig.

48

1983]

Kluessendorf— Commensalism of Gastropods and Echinoderms

49

Id) the cystoid Caryocrinites ornatus from

the Rochester Shale of Lockport, New York,

with a platyceratid firmly attached to it. Hall

did not attempt an interpretation of this

relationship, but he concluded that it repre¬

sented an association in life and was not just

a fortuitous occurrence. The earliest report

of a Silurian crinoid host was provided by

Murchison (1854) who figured a specimen of

Marsupiocrinus caelatus with attached platy¬

ceratid from the Wenlock Limestone of

Dudley, England. Murchison believed that

this crinoid was carnivorous and the gastro¬

pod was its prey.

The oldest Silurian occurrence of the

platyceratid-echinoderm relationship is

known from the Llandoverian Power Glen

Shale of New York and Ontario (Brett,

1978a). Brett reported a high density of

platyceratids at one locality where Nati-

conema niagarense was found attached to

many of the more than 100 crowns of the

crinoid Ptychocrinus medinensis present.

Additional Silurian examples of this com¬

mensalism were found in the Wenlockian

Rochester Shale of New York and Ontario.

Bowsher (1955) and Brett (1978b) reported

Naticonema niagarense attached to the

crinoid Macrostylocrinus ornatus from this

unit. Naticonema was also found attached to

the cystoid Caryocrinites ornatus (Hall,

1851); Bowsher, 1955; Brett, 1978b) and to

the crinoids Lyriocrinus, Saccocrinus, and

Dimer ocrinites { C. Brett, 1977, pers. comm.)

in the Rochester Shale. The Wenlockian

HOgklint beds at Haftingsklint, Gotland,

Sweden, have also yielded Dimer ocrinites

with attached platyceratids (C. Franzen,

1978, pers. comm.). Saccocrinus and Cary¬

ocrinites from the Rochester Shale are illus¬

trated as playceratid hosts in figures 1 and 2,

respectively.

Platyceras haliotis has long been known as

a commensal on the crinoid Marsupiocrinus

caelatus from the Wenlock Limestone of

Dudley, England (Murchison, 1854);

Springer, 1926; Bowsher, 1955; Watkins and

Hurst, 1977). The crinoid Clematocrinus

Fig. 1 Naticonema in place on the crinoid Saccocrinus

(ROM 35797, Royal Ontario Museum) from the Roches¬

ter Shale of Ontario. Photo courtesy of C. E. Brett. (x2)

Fig. 2. Platyceras on the theca of the cystoid Cary¬

ocrinites ornatus (E25477, Buffalo Museum of Science)

from the Rochester Shale of New York. Photo courtesy

of C. E. Brett. (x2)

50

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

Fig. 3. Slab of abundant

well-preserved Clematoc-

rinus retiarius showing two

crowns with attached

platyceratids. This slab

(A 12749, Fletcher Collec¬

tion, Cambridge Univer¬

sity) is from the Wenlock

Limestone of Dudley,

England. (x2)

retiarius (figs. 3 and 4), previously

unreported as a host, also occurs with

attached platyceratids in the Wenlock Lime¬

stone at Dudley. Watkins and Hurst (1977)

described this monotaxic crinoid assemblage

Fig. 4. Crown of the crinoid Clematocrinus retiarius

(A12743, Fletcher Collection, Cambridge University)

with attached platyceratid, also from Wenlock Lime¬

stone at Dudley, England. (x4)

in detail (under the name Hapalocrinus) but

did not report the presence of platyceratids.

Several slabs of abundant well-preserved C.

retiarius from Dudley in the Fletcher Collec¬

tion (Cambridge University) show a rather

common occurrence of small commensal

platyceratids. The incomplete preparation of

the slabs and the small size of the gastropods

make it difficult to observe the relationship,

therefore, an even higher density of platy¬

ceratids possibly exists here.

Another previously unreported Silurian

example of this commensal behavior was

found in the Wenlockian Waldron Shale

near Waldron, Indiana, and was brought to

my attention by Jeff Aubrey and Kenneth

Sever. In this unit platyceratids are found in

situ on the crinoid Periechocrinus christyi.

Both the platyceratid and Periechocrinus

individuals are unusually large for Silurian

occurrences of this relationship. One unique

specimen of Periechocrinus, collected by

Kenneth Sever and loaned to me for this

study, bears two platyceratids (figs. 5-7).

The larger of the two gastropods has an

irregular apertural margin corresponding to

the distribution of the crinoid arm facets,

1983]

Kluessendorf— Commensalism of Gastropods and Echinoderms

51

Fig. 5. Large Periechocrinus christy i aboral cup

associated with two platyceratid gastropods, from the

Waldron Shale, near Waldron, Indiana. Specimen in

figs. 5-7 is in the collection of Kenneth Sever. Figs. 5

and 6 are x 0.8.

Fig. 6. Another view of the Periechocrinus specimen

in fig. 5.

Fig. 7. Close-up of the attachment

area on the Periechocrinus specimen

in figs. 5 and 6. Note the irregular

growth lines and apertural margin of

the larger gastropod and also the epi-

faunal organisms which are present on

both platyceratid shells, (xl.2)

52

Wisconsin Academy of Sciences, Arts and Letters

[Vol. 71, Part I,

and its aperture is oriented over the crinoid

tegmen. The smaller gastropod is displaced

with its aperture partly facing the other

gastropod. The apertural margin of the

smaller gastropod shows no modification to

accommodate the larger shell, but a portion

of its margin is irregular in outline, suggest¬

ing it may once have been attached to this or

another crinoid, but dislodged at the time of

burial. Several rhynchonellid brachiopods

are associated with the gastropods, three of

which are oriented with their pedicles

towards the smaller gastropod, suggesting

that they may have been attached to it in life.

The platyceratid shells are heavily encrusted

by ectoproct bryozoans, however, and the

brachiopod attachment site is concealed.

Several cornulitids are also attached to the

gastropod shells. The presence of the same

epifaunal organisms on both shells suggests

a living association may have existed be¬

tween the two platyceratids; however, it is

also possible that the presence of the smaller

gastropod is only fortuitous.

Examples of this commensalism have also

been found at the Silurian-Devonian bound¬

ary in southeastern Morocco. Lierl (1982)

reported both Platyceras (Orthonychia) ele-

gans and Ptychospirina sp. attached to

specimens of the crinoid Scyphocrinites

elegans there.

No examples of this commensal behavior

are known from the diverse North American

Silurian reef echinoderm faunas. Many of

the camerate host crinoids (Dimer ocrinites,

Lyriocrinus, Macrostylocrinus, Marsupio-

crinus, Periechocrinus) and the cystoid

Caryocrinites commonly occur in Silurian

reefs, as do platyceratids. The absence of

this relationship from the reef environment

appears to be an artifact of preservation

because the high energy and low sedimenta¬

tion rates characteristic of reefs are not

conducive to the type of rapid burial needed

to preserve articulated echinoderms. Once

an echinoderm begins to disarticulate any

attached platyceratids could be mechanically

detached from it, destroying evidence of the

original association. A brief survey of the

Greene Museum collections (University of

Wisconsin-Milwaukee) has revealed several

loose platyceratid specimens from the

Hawthorne and Bridgeport Silurian reefs

(Chicago, Illinois) with irregular apertural

margins suggesting that they may have been

attached to crinoids or cystoids.

Relation of Commensalism to Crinoid

Morphology and Behavior

Several of the Silurian crinoid taxa which

serve as hosts to platyceratids are not

anchored by holdfasts or roots and are

capable of some mobility. Some, such as

Dimer ocrinites, had prehensile distally-

coiling stalks to provide limited mobility.

One of the host crinoids, Scyphocrinites,

was eleutherozoic and drifted by means of

an air- filled, bulbous float (Strimple, 1963;

Lierl, 1982). Clematocrinus had nodal rings

of cirri on its stem suggesting it had the

ability to reorient itself on the soft sediments

on which it lived (Watkins and Hurst, 1977).

The lack of direct contact with the substrate

and the mobile lifestyles of some of the

Silurian host crinoids lend support to the

idea that platyceratids settled on their hosts

as free-swimming larvae.

Evidence for the sedentary lifestyle of

platyceratids is provided by several Silurian

examples in which the attached gastropod

has an irregular apertural margin which

conforms to irregularities on the host at the

attachment site. The large platyceratid

attached to the Periechocrinus specimen in

figure 7 provides a fine example of this

apertural modification.

The presence of a large, smooth, flat

tegmen has been proposed as the principal

factor in host selectivity by platyceratids

(Bowsher, 1955; Lane, 1978). The Silurian

crinoids which serve as hosts, however,

exhibit a variety of tegmen morphologies

ranging from flat to conical to depressed.

The type of anal area also varies among

these crinoids. The anus may be a simple

opening on the tegmen (e.g., Marsupioc-

rinus) or marginal to the tegmen (e.g.,

Macrostylocrinus ). In some taxa an anal

1983]

Kluessendorf —Commensalism of Gastropods and Echinoderms

53

ridge (e.g., Ptychocrinus ) or anal tube (e.g.,

Periechocrinus ) exists. The length of the anal

tube increases dramatically in some later

hosts, particularly in Carboniferous taxa

such as Stellar ocrinus. No matter what the

structure of the anus or the morphology of

the tegmen the platyceratid is always

associated with the anal opening. In those

taxa with a long anal tube or marginal anus

the platyceratid may have had no contact

with the tegmen at all. Factors other than

tegmen morphology apparently are signif¬

icant in controlling host selectivity.

Camerate crinoids and feeding adaptations

All of the Silurian crinoids to which

platyceratids are found attached belong to

the subclass Camerata. Among 57 genera (21

families) of known Silurian camerates nine

genera (seven families) are involved in this

commensalism (Table 1). The earliest known

example in the Ordovician also involved a

camerate host (Glypt ocrinus) (Bowsher,

1955), and of the numerous post-Silurian

host crinoid genera all are camerates except

for six genera in the inadunate suborder

Poteriocrinina and one genus ( Taxocrinus j

from the subclass Flexibilia. This relation¬

ship occurs rarely in the fossil record among

Table 1. Classification of Silurian crinoids serving as

platyceratid hosts.

Subclass Camerata

Order Monobathrida

Family Hapalocrinidae

Clematocrinus

Family Marsupiocrinidae

Marsupiocrinus

Family Patellocrinidae

Macrostyiocrinus

Family Scyphocrinitidae

Scyphocrinites

Family Periechocrinidae

Periechocrinus

Saccocrinus

Order Diplobathrida

Family Rhodocrinitidae

Lyriocrinus

Family Dimerocrinitidae

Dimerocrinites

Ptychocrinus

known host taxa; however, many other cam¬

erates were possible platyceratid hosts, but

specimens exhibiting this commensal associ¬

ation have yet to be found.

The three groups of crinoids which were

hosts to platyceratids shared similar

morphologic and behavioral adaptations.

Most camerate and some flexible crinoids,

particularly taxocrinids, are considered to

have been rheophilic, filtration-fan feeders

(Breimer, 1978). These crinoids maintained a

passive feeding posture with their highly

pinnulated or ramulated arms forming a fil¬

tration net oriented normal to the horizontal

current (Macurda and Meyer, 1974). This

feeding method provided an efficient means

of capturing plankton and other detritus. In

this orientation the crinoid had to have some

means of supporting its heavy crown. This

balance control necessitated a stalk which

was flexible enough to bend in the feeding

posture but rigid enough to provide ele¬

vation and anchorage. Most camerates pos¬

sessed a stalk capable of considerable flexure

in the middle while rigidity at the proximal

and distal ends provided maximum leverage.

The distally-coiling stalks of dimerocrinitids

(e.g., Dimerocrinites) and rhodocrinitids

(e.g., Lyriocrinus ) may have been very

useful in balance control because they were

able to yield somewhat to prevent too much

longitudinal stress in the stalk (Breimer,

1978). Movement of the pinnules provided

additional control. This passive rheophilic

feeding method did not require complicated

movements and was well suited to camerates

which lacked muscular contacts between

brachials (Breimer, 1978). Breimer (1978)

has also suggested that advanced inadunate

crinoids possessed pinnulate arms capable of

muscular control and could actively orient

their crowns into the current at a specific

angle in a rheophilic posture in order to

derive lift from the current. Although not all

poteriocrinine inadunates (the only inadu-

nates known as platyceratid hosts) had

developed muscular articulation, they had

earlier evolved pinnulate arms and were

capable of the rheophilic feeding posture

54

Wisconsin Academy of Sciences , Arts and Letters

[Vol. 71, Part I,

(Lane and Breimer, 1974; Breimer and

Webster, 1975).

Crinoids adapted to the alternative, rheo-

phobic feeding posture either rested directly

on the substrate or were supported by a

short, rigid stalk. Rheophobes are thought

to have lived in areas with very slight

currents, or none, where they fed on plank¬

ton and other detritus which settled gravita¬

tionally through the water column onto their

outstretched non-pinnulated arms (Breimer,

1978). No rheophobes have been reported as

platyceratid hosts.

What in particular made rheophiles attrac¬

tive, or rheophobes unattractive, to platy-

ceratids as hosts is unknown. Platyceratids

may have selected rheophilic hosts because

these crinoids could effect some balance

control and were capable of supporting a

gastropod while maintaining their feeding

postures. The most effective rheophiles may

have been camerates such as dimerocrinitids

and rhodocrinitids with prehensile stalks,

and several of the Silurian host crinoids are

of this type. The sessile rheophobic crinoids

may have possessed some chemical or

mechanical means of preventing organisms

from settling on them in order to keep their

feeding surfaces clear. Utilizing different

feeding methods at different feeding levels

rheophobes and rheophiles may have had

different food sources. Rheophiles may have

fed on smaller sized plankton and detritus

than rheophobes (Meyer and Lane, 1976;

Watkins and Hurst, 1977). The difference in

food source may have been reflected in the

crinoid’s fecal contents. Rheophobes were

probably less efficient feeders than rheo¬

philes. Also they may have had a lower

metabolic rate resulting in lower feces

production than rheophiles (D. B. Macurda,

1983, pers. comm.).

Morphology of Caryocrinites

The rhombiferan cystoid Caryocrinites

ornatus is the only Silurian cystoid known to

host platyceratids. Caryocrinites is an

unusual cystoid having many morphologic

similarities to crinoids, particularly camer¬

ates. A “legmen” of specialized plates

covers the mouth of Caryocrinites and bears

a morphologic similarity, but is not homol¬

ogous, to the tegmen of crinoids (Kesling,

1967). The long flexible stalk of Caryocrin¬

ites is also very crinoid-like and dissimilar to

most other cystoids which are eleutherozoic

or possess very short rigid columns. Brett

(1978b) compared the radix-type root of

Caryocrinites to that of some camerate

crinoids. The biserial arrangement and

pinnulation of Caryocrinites arms is unlike

most other cystoids, which have simple

unbranched brachioles, but is reminiscent of

camerate crinoid arm structure. Sprinkle

(1975) suggested that the development of

such arms in Caryocrinites increased its

food-gathering capacity. Also, the theca of

Caryocrinites is similar in appearance to

many camerate crinoid calices (Kesling,

1967). The commensal platyceratid is com¬

monly situated on the upper surface of the

Caryocrinites theca in a position correspond¬

ing to that occupied on many crinoids. Based

on its general morphology Sprinkle (1975)

believed that Caryocrinites was a top layer

rheophilic filter-feeder.

Caryocrinites is the only Silurian cystoid

known to be involved in this commensalism,

and it is the only one to possess numerous

camerate crinoid morphologic character¬

istics. This morphologic similarity to

camerates (which are the only Silurian

crinoids that host platyceratids) may have

been the reason that Caryocrinites was a

suitable host for these gastropods.

Summary

All Ordovician and Silurian host crinoids

as well as the majority of post-Silurian

hosts are camerates. The non-camerate hosts

comprise only six genera of poteriocrinine

inadunates and one flexible. These inadu-

nate and flexible crinoids bear resemblance

to camerates, and all three groups are

thought to have been rheophilic filter-

feeders. The only Silurian cystoid (Caryoc-

1983]

Kluessendorf '—Commensalism of Gastropods and Echinoderms

55

rinites) known to be a platyceratid host

mimics many camerate crinoid traits. This

evidence suggests that echinoderms possess¬

ing certain morphologic or behavioral

characteristics of camerate crinoids were

selected as hosts by platyceratids. What

specific characteristics possessed by these

echinoderms influenced host selectivity is

uncertain, but possibly this selectivity was

related to particular morphologic or be¬

havioral adaptations associated with rheo-

philic feeding. The variety of tegmen and

anus types exhibited by Silurian and later

crinoid hosts suggests that factors other than

the morphology of these features were crit¬

ical in host selection.

Acknowledgments

I would like to thank C. E. Brett, A. J.

Boucot, C. Franzen, and D. G. Mikulic for

kindly providing me with unpublished data.

C. E. Brett also generously provided photos

used in figures 1 and 2. J. Aubrey and K.

Sever kindly drew my attention to the exis¬

tence of this relationship in the Waldron

Shale, and special thanks are extended to

Mr. Sever for his patience and gracious loan

of the Periechocrinus specimen illustrated in

figure 4. I would also like to express my

appreciation to R. E. Gernant, D. R. Kolata,

D. B. Macurda, and D, G. Mikulic for criti¬

cally reviewing the manuscript.

Literature Cited

Breimer, A. 1978. Autecology. In R. C. Moore

and C. Teichert (eds) Treatise on Invertebrate

Paleontology, Part T, Echinodermata 2. 1:

T331-T343.

_ and G. D. Webster. 1975. A further con¬

tribution to the paleoecology of fossil stalked

crinoids. Koninkl. Nederl. Akad. Wetenschap-

pen- Amsterdam, Proc., Ser. B, 78: 149-167.

Brett, C. E. 1978a. Description and paleoecology

of a new lower Silurian camerate crinoid. J.

Paleontol. 52:91-103.

_ _ _ . 1978b. Systematics and paleoecology of

late Silurian (Wenlockian) pelmatozoan

echinoderms from western New York and

Ontario. Ph.D. thesis (Geology) Univ. of

Michigan, Ann Arbor, 595 p.

Bowsher, A. L. 1955. Origin and adaptation of

platyceratid gastropods. Univ. Kansas

Paleontol. Contrib., Art, 5 (Mollusca), 11 p.

Clarke, J. M. 1921. Organic dependence and

disease. New York State Museum Bull. Nos.

221,222: 113 p.

Hall, J. 1851. Paleontology of New York, Vol¬

ume 2, Albany, 362 p.

Kesling, R. V. 1967. Cystoids. In R. C. Moore

(ed) Treatise on Invertebrate Paleontology,

Part S, Echinodermata 1. 1: S85-S267.

Keyes, C. P. 1888. On the attachment of Platy-

ceras to paleocrinoids and its effect on modify¬

ing the form of the shell. Amer. Phil. Soc.

Proc. 25:231-243.

Lane, N. G. 1978. Mutualistic relations of fossil

crinoids. In R. C. Moore and C. Teichert (eds)

Treatise on Invertebrate Paleontology, Part T,

Echinodermata 2. 1: T345-T347.

_ and A. Breimer. 1974. Arm types and

feeding habits of Paleozoic crinoids. Konikl.

Nederl. Akad. Wetenschappen Amsterdam,

Proc., Ser. B, 77: 32-39.

Lierl, H.-J. 1982. Pseudoparasitare Schnecken

auf Kelchen der Seelilie Schyphocri n ites

elegans Zenker aus dem Obersilur-Unterdevon

Stidostmarokkos. Aufschluss 33: 285-290.

Macurda, D. B. and D. L. Meyer. 1974. Feeding

posture of modern stalked crinoids. Nature

247: 394-396.

Meyer, D. L. and N. G. Lane. 1976. The feeding

behavior of some Paleozoic crinoids and recent

basketstars. J. Paleontol. 50: 472-480.

Murchison, R. I. 1854. Siluria. John Murray,

London, 523 p.

Springer, F. 1926. American Silurian crinoids.

Smithsonian Institution Pub. 2871, 239 p.

Sprinkle, J. 1975. The “arms” of Caryocrinites,

a rhombiferan cystoid convergent on crinoids.

J. Paleontol. 49: 1062-1073.

Strimple, H. L. 1963. Crinoids of the Hunton

Group. Okla. Geol. Surv. Bull. 100, 169 p.

Watkins, R. and J. M. Hurst. 1977. Community

relations of Silurian crinoids at Dudley,

England. Paleobiol. 3: 207-217.

MICROFAUNA OF THE MIDDLE SILURIAN WALDRON SHALE,

SOUTHEASTERN INDIANA

Susan M. Siemann-Gartmann

Amoco Production Company

1340 Poydras Street

New Orleans , Louisiana 70150

Abstract

A distinctive microfauna developed around crinoid holdfasts on the soft-

bottomed environment of the Middle Silurian Waldron Shale of southeastern

Indiana. This microfauna was less diverse than the microfauna outside of the

crinoid meadows. The echinoderms exerted an unknown control on the microfauna,

that permitted selected foraminiferid (Psammosphaera and Saccamina) and

ostracode ( ICyrtocyprus and Leperditia) genera to monopolize the micro¬

environment. Scolecodonts were the faunal group least affected by the presence of

crinoids.

Introduction

This study examines the influence of

crinoids upon the distribution of micro¬

fossils in the Middle Silurian (Wenlockian)

Waldron Shale of southeastern Indiana.

Fig. 1. Diagrammatic sketch of Eucalyptocrinites

illustrating the basic structured parts of the animal.

Most crinoids inhabiting the shallow sea

during deposition of the Waldron muds pos¬

sessed root systems (holdfasts) that attached

to the sea bottom. The attachment device

was composed of cirri and radial rootlets

located at the base of the stem (Fig. 1). The

animals anchored themselves by wrapping

the roots around firm objects, such as

brachiopods, or by attaching directly to the

sea bottom. Because two species of Eucalyp¬

tocrinites, E. crassus (Hall) and E. tuber-

culatus (Miller and Dyer), are the most

abundant crinoids in the Waldron Shale, the

root systems examined in this study are

assumed to be of these species (Macurda,

1968; Halleck, 1973) (Fig. 2).

According to Halleck (1973, p. 239),

Eucalyptocrinites was so abundant locally

during Waldron deposition that they formed

crinoid “meadows,” which, along with algal

growths, acted as sediment traps. This

unique environment could have a micro¬

fauna distinctive from that of adjacent areas

without major crinoid beds. Furthermore,

because the crinoids acted as sediment traps,

the microfossils recovered from sediment

around the root systems should provide a

good record of the forms that existed in the

56

1983]

Siemann-Gartmann — Microfauna of the Waldron Shale

57

Fig. 2. Eucalyptocrinites holdfast or root system from the Middle Silurian Waldron Shale in southeastern Indiana.

Greene Museum specimen G27371 .

crinoid “meadows” at time of deposition.

This study was designed to evaluate these as¬

sumptions.

Previous Investigations

The celebrated invertebrate fauna in the

Waldron Shale of southeastern Indiana was

first detailed in the literature by James Hall

(1864). Elrod (1883) applied the name

Waldron Shale to the upper part of the Mid¬

dle Silurian (Wenlockian) calcareous shales

cropping out in southeastern Indiana, in

order to distinguish it from the underlying

Laurel Limestone. Reports on the Waldron

Shale during the early 1900s were completed

by Price (1900), Cumings (1900), and Kindle

and Barnett (1909).

Studies of ostracodes from the Waldron

Shale include the work of Berry (1931),

Coryell and Williamson (1936), and Morris

and Hill (1951, 1952). Other paleontological

work on the Waldron included foraminiferal

studies by Hattin (1960) and McClellan

(1966), and a study of acritarchs by Krebs

(1972).

Evolution and paleoecology of the Wald¬

ron fauna were evaluated by Tillman (1962),

McClellan (1966), Macurda (1968), and Hal-

leck (1973). Macurda (1968) described the

ontogenetic development of the crinoid

Eucalyptocrinites, while Halleck (1973)

studied the relations of crinoids to the

existence of a hardground at the Laurel-

Waldron contact.

Stratigraphy

The Waldron Shale crops out along a dis¬

continuous, elongated strip extending from

northern Indiana to western Tennessee,

where it was originally called the Newsom

58

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

Fig. 3. Part of the Middle Silurian stratigraphic sec¬

tion for southeastern Indiana. The relative position of

Middle Devonian Geneva, which unconformably over-

lies Silurian rocks, is also shown. The thickness of all

units is given in meters. Modified from McClellan

(1966, p. 451).

Shale. In the study area of southeastern

Indiana, the Waldron Shale is generally

underlain by the Laurel Limestone, and

overlain by the Louisville Limestone (Fig. 3).

However, at several localities, the Waldron

Shale is unconformably overlain by the

Middle Devonian Geneva Dolomite due to

erosion during Early Devonian time. The

Laurel, Waldron, and Louisville formations

are all of Middle Silurian (Wenlockian) age,

as established by the presence of ostracodes

of the Drepannellina clarki zone in both the

Laurel and the Waldron formations, and the

presence of the brachiopod Rhipidium in the

Louisville Limestone (Berry and Boucot,

1970).

The Waldron consists of nonresistant,

blue-gray, silty shale, which is easily

differentiated from resistant carbonates of

the underlying Laurel or the overlying Louis¬

ville or Geneva formations (Fig. 4). The

blue-gray shale pales to a buff-gray where it

is weathered or more calcareous, as at San¬

dusky, Indiana. The parting changes from

blocky to very fissile, depending on the

amount of carbonate present. The Waldron

is locally fossiliferous, especially where it is

Fig. 4. Waldron Shale at Tunnel Mill near Vernon, Indiana.

1983]

Siemann-Gartmann— Microfauna of the Waldron Shale

59

highly calcareous. According to Heele

(1963), the shale is composed of calcite and

dolomite, with lesser amounts of feldspar,

illite, kaolinite, pyrite and quartz.

The Waldron varies in total thickness

from 0 to 4 m, and thins to the north and

east. In western exposures, the formation is

about 2.5 m thick, and it reaches a maximum

of 4 m near Louisville, Kentucky (McClel¬

lan, 1966).

Paleogeographic Setting

During Wenlockian time, present-day

Indiana was covered by a tropical epicon¬

tinental sea with an extensive reef system.

These reefs developed in the southeastern

Trade Wind belt of the southern latitudes,

and formed around the margins of the

proto-Michigan basin and the Vincennes

basin in southern Illinois and Indiana

(Shaver, 1977) (Fig. 5). The Waldron muds

were deposited in shallow water on the

i i 1 i r

0 100 200 300 km

Fig. 5. Major reef systems (dotted lines) and paleo¬

geographic features in the central Great Lakes region

during the Silurian. Adapted from Shaver (1977, p.

1409 and p. 1422).

Wabash platform between the developing

basins (Shaver, 1977).

Methods

Samples

Twenty-eight of the 36 crinoid holdfasts

used in this study came from the Greene

Memorial Museum Collection at the Univer¬

sity of Wisconsin-Milwaukee. These samples

were purchased by Thomas A. Greene, a

Milwaukee pharmacist and amateur paleon¬

tologist, from J. T. Doty, a fossil collector

from Waldron, Indiana in the early 1880s.

Other samples were collected from 4 expo-

Fig. 6. Location of field localities discussed in the text.

60

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

sures of Waldron Shale in southeastern

Indiana. The 4 field localities were: Tunnel

Mill, Anderson Falls, Sandusky quarry, and

St. Paul quarry (Fig. 6). The only 2 crinoid

holdfasts found in place were collected at

Tunnel Mill, although 6 displaced specimens

were collected at the St. Paul quarry. Other

localities provided control samples from

areas where holdfasts were not present.

Laboratory Work

In order to recover microfossils, samples

were crushed to approximately 3 cm prior to

chemical treatment. The most satisfactory

Table 1. Summary of samples utilized in this study.

Explanation for Table 1: GM numbers 1 through 7 are composite samples of the Greene Museum

cataloged specimens listed in parentheses. There was sufficient material of Greene Museum samples

17740 and 17742 to run them separately. Indiana field sites are shown on Fig. 5. Sample locations are:

TM-Tunnel Mill, AF-Anderson Falls, SQ-Sandusky quarry, and SPQ-St. Paul quarry.

1983]

Siemann-Gartmann— Microfauna of the Waldron Shale

61

disaggregation technique utilized Quater¬

nary 0, a detergent with a good wetting

character. Although Zingula (1968, p. 102)

recommended a 20% solution of Quaternary

0, a concentration of 33% produced better

results for samples used in this study. The

disaggregated material was washed through

nested sieves of 35, 60, 120, and 170 mesh.

The 35 mesh fraction represented rock

material that did not break down, and it was

discarded. The other 3 fractions were

manually picked for microfossils, although

the 170-mesh fraction proved to be unfos-

siliferous. Over 1500 microfossils were

recovered, and 1328 of these could be iden¬

tified to generic level.

The size of the samples processed was de¬

pendent upon availability of material. Hold¬

fast samples were generally limited to about

100 gm, while 300 gm of non-holdfast field

samples were used. To have sufficient

material to process most of the Greene

Museum holdfast specimens, samples of

similar lithology from the same locality were

combined (Table 1).

As shown in Table 1, a total of 16 holdfast

samples totaling 1566 gm was processed. Of

these, 7 were composite samples. A total of

3600 gm from 13 field samples not asso¬

ciated with holdfasts was also processed.

This disparity in sample number and amount

created some problems in interpreting the

results of microfauna analysis. Furthermore,

the stratigraphic position of Greene Museum

samples within the Waldron was unknown.

Hence, the microfauna recovered must be

considered to be “time averaged” in that

they probably represent the accumulation of

fossils throughout the time represented by

deposition of the Waldron Shale.

Micropaleontology

Analysis

The microfossils recovered included 656

foraminifera, 443 ostracodes, 181 brachio-

pod fragments, 35 scolecodonts, 13 gastro¬

pods, and lesser numbers of echinoid spines,

bryozoan fragments, and crinoid parts.

Sources used in the identification of the

microfossils included: Coryell and Wil¬

liamson, 1936; Stewart and Priddy, 1941;

Morris and Hill, 1951, 1952; Hattin, 1960;

Moore, 1961, 1962, 1964; McClellan, 1966;

Lundin and Newton, 1970; and Glaessner,

1972. Generic identification was difficult in

many cases, because a majority of the

brachiopods, gastropods and ostracodes

were internal casts.

Because the gastropod casts probably

represent juvenile forms, no attempt was

made to classify them to genera. However,

the coiling pattern and shell shape were

distinctive enough to infer that at least 3

genera were present. The three gastropod

“form genera” were identified as “Bellero-

phontiform,” “Conispiral,” and “Plani-

spiral” (Fig. 7).

The brachipods presented the same prob¬

lem as the gastropods. Although distinctive

variations in the valves were evident, the

internal casts were not definitive enough to

identify genera. Based on valve shape and

the presence or absence of ribbing, at least

three “form genera” were inferred to be

present. These were designated as

“Ribbed,” “Spatulate,” and “Sulcate”

(Fig. 7).

For each sample studied, the 60 and 120

mesh fractions were analyzed individually.

In general, the 120 mesh yielded relatively

few microfossils and the forms were similar

to those present in the 60 mesh fraction.

Fig. 7. “Form genera” for microbrachiopods and

microgastropods described in this study.

62

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

Siemann-Gartmann (1979, p. 33-34) pro¬

vided detailed counts of the microfauna for

each sieve size and for each sample pro¬

cessed. However, this information only

served to establish that all the samples

processed could be combined into holdfast

samples and nonholdfast samples. Table 2

provides this summary.

Abundance and Diversity

Table 2 lists the individual genera

identified from the two basic lithogenetic

Table 2. Summary of the number of microfauna genera (“form genera’’ of brachiopods and gastroods)

and individuals recovered from 16 holdfast samples totaling 1566 gm and 13 nonholdfast samples totaling

3600 gm. The difference in the number and weight of samples in each category must be considered in this

comparison.

Holdfast Microfauna Nonholdfast Microfauna

(Genera) - Individuals (Genera) - Individuals

1983]

Siemann-Gartmann— -Micro fauna of the Waldron Shale

63

associations described above. The total

genera present is also provided in this table.

The holdfast samples yielded 23 genera,

while 33 genera were present in nonholdfast

samples. In spite of a large bias in the weight

of nonholdfast samples, it seems that they

contain a more diversified microfossil

assemblage than the holdfast samples.

All three brachiopod “form genera” are

present in the grouping of microfossil forms

from both primary lithologic associations.

Since more than twice as much nonholdfast

material was processed, it seems that micro-

brachiopods were present in essentially equal

numbers in the two groups under study. In

both instances, the most common brachio¬

pod form was the “Sulcate.”

All six genera of foraminifera which are

present in the holdfast samples are also pres¬

ent in the nonholdfast samples. Although 3

more genera are present in the latter

lithologic association, they are represented

by only 5 specimens. Although the foramini-

feral fauna is dominated by Psammosphaera

sp. and Saccammina sp. in both associa¬

tions, it is more abundant with holdfasts.

When one considers the biased sampling

against holdfast lithologies, this difference is

given more significance. Other foraminiferal

genera common to both lithologic associa¬

tions are lower in total number of

individuals per genus in the holdfast

samples. However, the total number of

foraminifera individuals is still higher in

holdfast samples (356) than in nonholdfast

rocks (300). This indicates that the holdfasts

contain more foraminifera, although the

fauna was less diverse, than the samples

without holdfasts.

Only two of the gastropod “form genera”

were found in association with holdfasts,

and these were each represented by only one

specimen. Eleven gastropods representing 3

“form genera” were identified from non¬

holdfast samples.

Holdfast samples contained only 10 of the

14 ostracode genera recovered during this

study. Of these 10 genera, 5 ( Bairdia ,

Beyrichia, ?Cyrtocyprus, Eridochoncha and

Leperditia) occurred in greater numbers than

in the nonholdfast control samples, and one

(Entomozoe) was represented by 4 specimens

in each rock type. The total number of

individual ostracodes recovered was 213

from holdfast samples and 230 from non¬

holdfast rocks. However, these numbers are

misleading if one does not consider that

approximately 2.3 times more nonholdfast

rock was processed.

Two genera of scolecodonts were found in

holdfast material, whereas four genera were

recovered from nonholdfast samples. How¬

ever, the 2 unique genera were each repre¬

sented by a single specimen. The two

scolecodont genera, Arabellites and

Nereidavus, that occur in both sample types

are present in almost equal numbers. Fur¬

thermore, the total number of scolecodonts

is similar in both associations (17 in holdfast

samples and 18 in nonholdfast rocks). Once

again, if sample bias is considered, the

holdfast samples are characterized by more

individual scolecodonts, but fewer genera.

The holdfast and nonholdfast faunas de¬

scribed above were tested with the Shannon

index, which provides a measure of diversity

for nominal scale data. The Shannon index

for each group was then utilized to deter¬

mine relative diversity of each group (Zar,

1974, p. 35). These tests verified the

apparent diversity differences noted in a

visual examination of Table 2. Although

both faunas have a moderately high diver¬

sity, the holdfast fauna is relatively less

diverse.

Interpretation

When I began this study, I presupposed

that the microfauna associated with crinoid

holdfasts would be more diverse and abun¬

dant than the control fauna. This assump¬

tion was based on the view that the Waldron

crinoids supposedly lived in well-circulated

marine waters with a constant supply of

food. Such an environment should also

allow a diverse microfauna to flourish.

Furthermore, I visualized effective entomb¬

ment of these organisms upon death because

64

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

the crinoids, along with algal mats, would

act as effective sediment traps (Halleck,

1973; Abbott, 1975). My conceptual model

was only half right. As previously described,

the microfauna associated with the crinoid

holdfasts is more abundant, than with non¬

holdfast rocks, but it is less diverse.

The percentage of each faunal group pres¬

ent in the total microfossil assemblage in the

holdfast and nonholdfast samples is sum¬

marized in Table 3. Based on these figures, it

is evident that brachiopods are relatively less

abundant in association with holdfasts than

they are in nonholdfast rocks. More than

half (54.9%) of the microfauna associated

with holdfasts consists of foraminifera,

Table 3. Percentage of microfaunal groups in

Fig. 8. Percent of genera for the foraminifera and

ostracode faunal groups.

while they comprise only 44.1% of the

microfauna in nonholdfast rocks. Gastro¬

pods are a minor element in both micro¬

faunas, but they are more abundant in

nonholdfast samples. Ostracodes made up

approximately one third of all the micro¬

organisms in both holdfast and nonholdfast

groups. Scolecodonts are present in equal

percentages in both rock types.

As described above, the foraminifera con¬

stitute 54.9% of holdfast samples, and

98.2% of this fauna is composed of two

genera, Psammosphaera (35.9%) and

Saccammina (62.3%) (Fig. 8). The

remaining 1.8% includes four genera

( Metamorphina , Sorosphaera, Sorostomas-

phaera, and Webbinelloidea). Foraminifera

make up 44.1% of the microfauna of non¬

holdfast samples, with five genera con¬

stituting 97.5% of the fauna. These genera

are Psammosphaera (36%), Saccammina

(52%), Sorosphaera (4.7%), Sorostomas-

phaera (2.7%) and Metamorphina (2.3%)

(Fig. 8). The remaining 2.4% consist of the

following genera: Hemisphaeramina, Psam-

monyx, Thurammina and Webbinelloidea.

Although the percentage of ostracodes in

both groups is similar, the relative amounts

of the genera represented are different.

Genera present in holdfast samples consist

of ?Cyrtocyprus (45.5%), Leperditia

(22.5%), Bairdia (12.2%), Eridochoncha

(6.1%), and Bythocyrus (5.2%) (Fig. 8).

These 5 genera represent 91.5% of the

ostracode fauna, while the remaining 8.5%

consists of Beyrichia, Entomozoe, Euprim-

itia, Halliella, and Primitia.

In nonholdfast samples, 88.7% of the

ostracode fauna is composed of six genera.

These are: ICyrtocyprus (36.5%), Leperditia

(18.7%), Primitia (9.6%), Bairdia (8.7%),

Bythocyrus (8.7%), and Euprimitia (6.5%)

(Fig. 8). The remaining 11.3% consists of

the following nine ostracode genera:

Beyrichia, Entomozoe, Eridochoncha, Hal¬

liella, Hemiaechminoides, Schmidtella, Thli-

puroides, and Waldronites. The two most

abundant ostracode genera, ICyrtocyprus

1983]

Siemann-Gartmann— Micro fauna of the Waldron Shale

65

and Leperditia , comprise 68% of the total

ostracode fauna in the holdfast samples

compared with only 55% in nonholdfast

rocks (Fig. 8).

Two foraminifera genera (Psammos-

phaera and Saccammina) and two ostracode

genera (ICyrtocyprus and Leperditia )

dominate the microfauna. These forms may

have been generalists, who occupied an

environment that was not highly specialized.

Since the 4 taxa listed above comprise 76.3%

of the total population of microorganisms

present in the holdfast assemblage, this

might indicate the environment associated

with the crinoid roots was not partitioned

into narrow ecological niches which would

have favored a wider range of micro¬

organisms. Once established in this non-

specialized environment, generalists would

flourish and probably crowd out other

genera. Hence, environmental factors

favoring a large population of nonselective

microorganisms could explain the lower

diversity previously described. However, it

may be that the most abundant taxa were

merely better adapted to the environment

associated with the holdfasts.

It is also possible the crinoids themselves

were responsible for lower diversity in the

microfauna associated with the holdfasts.

Watkins and Hurst (1977) constructed a

model of crinoid ecology for the Middle

Silurian Wenlock Limestone of Dudley,

England. These workers concluded that

crinoids affected the associated fauna by

their high-level suspension feeding habits. A

dominance of crinoids resulted in “high

crinoid species diversity, partitioning of

planktonic resources, and maintenance of

suspension feeding height over other fauna’’

(Watkins and Hurst, 1977, p. 216). Lane

(1973), who reported on Carboniferous

crinoids from Crawfordsville, Indiana,

arrived at similar conclusions in a study that

focused on a depositional environmental

receiving terrigenous sediment.

According to Watkins and Hurst (1977),

one key to the successful dominance of the

crinoids was their diversity, which allowed

for stratified feeding heights. Although

species diversity in crinoids of the Waldron

Shale was probably inhibited by the soft

bottom environment, they may have exerted

some control on the associated microfauna.

Size comparisons between the holdfast

and nonholdfast foraminifera and ostra-

codes do not indicate that crinoids selectively

filtered out some forms for food. Further¬

more, the rooted crinoids would feed well

above the level of the substrate where the

microfauna lived (Fig. 1).

The scolecodonts were the faunal group

that appears to be least affected by the

presence of crinoids. These microfossils are

the jaws of worms that inhabited the

substrate at least part of the time, and this

would minimize any influence by crinoids.

Based on the discussion above, there is a

difference between the microfaunas asso¬

ciated with holdfast and nonholdfast sam¬

ples. However, my work does not establish

what caused this difference. Certainly the

controls are somehow related to the presence

of crinoids, or crinoid holdfasts.

Conclusions

This study establishes that the microfauna

associated with crinoid holdfasts in the

Middle Silurian Waldron Shale of south¬

eastern Indiana is distinctive from control

samples not associated with holdfasts. The

crinoid holdfast microfauna is characterized

by a large percentage of foraminifera and

ostracodes. A small percentage of the micro¬

fauna is composed of brachiopods, scoleco¬

donts and gastropods. A total of only 23

genera represents the five faunal groups

present in the crinoidal microfauna, whereas

33 genera are present in the same 5 faunal

groups in nonholdfast samples. Thus, the

holdfast faunal assemblage is characterized

by a relatively abundant microfauna with

lower diversity than that recovered from the

control samples.

Crinoids, or crinoid holdfasts, exerted an

unknown controlling influence over the

66

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

microfauna, although several possibilities

are discussed. The genera that make up

76.5% of the crinoidal microfauna were

Psammosphaera and Saccammina (foramin-

ifera), and ? Cyrtocyprus and Leperditia

(ostracodes). The only faunal group that was

not significantly affected by the rooted

crinoids were the scolecodonts. These con¬

clusions support the findings of Watkins and

Hurst (1977), who also concluded that cri¬

noids exerted a control on the associated

fauna.

Acknowledgments

I would like to thank Dr. Katherine

Nelson for suggesting and guiding this study.

I also wish to acknowledge the following

individuals for professional assistance: J. M.

Berdan, U.S. Geological Survey, Frank J.

Charnon and Dr. Robert E. Gernant of The

University of Wisconsin-Milwaukee, Mr.

Kenneth Hodginson, a paleontologist with

Exxon Company U.S. A., Dr. Gary Lane of

The University of Indiana-Bloomington,

Drs. Richard A. and Rachel K. Pauli of The

University of Wisconsin-Milwaukee, and

Dr. Peter Sheehan, The Milwaukee Public

Museum. On a more personal note, I would

like to thank my parents for moral and

financial support, and my husband, Chuck,

for continual encouragement.

Literature Cited

Abbott, B. M. 1975. Implications for the fossil

record of modern carbonate bank corals. Geol.

Soc. Am. Bull. 86: 203-204.

Berry, W. 1931. Micro-organisms from the

Waldron Shale of Clifty Creek, Indiana. Proc.

Indiana Acad. Sci. 40: 207-208.

Berry, W. B. N. and A. J. Boucot. 1970.

Correlation of North American Silurian rocks.

Geol. Soc. Am. Special Paper 102. 289 p.

Coryell, H. N. and M. Williamson. 1936. A study

of the ostracode fauna of the Waldron Shale,

Flat Rock Creek, St. Paul, Indiana. Am. Mus.

Novitates 870. 7 p.

Cumings, E. R. 1900. On the Waldron fauna at

Tarr Hole, Indiana: Proc. Indiana Acad. Sci.

15: 174-176.

Elrod, M. N. 1883. Geology of Decatur County.

Indiana Dept. Geology and Nat. Hist. Ann.

Rept. 12: 100-152.

Glaessner, M. F. 1972. Principles of Micro¬

palaeontology. Hafner Publishing Co., New

York. 297 p.

Hall, James. 1864. Notice of some new species of

fossils from a locality of the Niagara Group in

Indiana, with a list of identified species from

the same place. Albany Inst. Trans. 4: 195-228.

Halleck, M. S. 1973. Crinoids, hardgrounds, and

community succession; The Silurian Laurel-

Waldron contact in southern Indiana. Lethaia

6: 239-251.

Hattin, D. E. 1960. Waldron (Niagaran) Fora-

minifera in Indiana (abs.). Geol. Soc. America

Bull. 71: 2016.

Heele, G. L. 1963. A study of the lateral textural,

mineralogical and chemical variations in the

Waldron Shale (Silurian: Niagaran) in

southern Indiana, western Kentucky, and

western Tennessee. Oxford, Ohio, Miami

Univ., Master’s thesis. 48 p.

Kindle, E. M. and V. H. Barnett. 1909. The

stratigraphic and faunal relations of the

Waldron fauna in southern Indiana. Indiana

Dept. Geol. and Nat. Res. Ann. Rept. 33:

393-416.

Krebs, E. A. 1972. Arcitarchs of the Waldron

Shale (Middle Silurian) of southeastern

Indiana: Cincinnati, Ohio, Univ. Cincinnati,

Master’s thesis. 161 p.

Lane, N. G. 1973. Paleontology and paleo-

ecology of the Crawfordsville fossil site (Upper

Osagian: Indiana). Univ. Calif. Pub. Geol.

Sci. 99: 1-141.

Lundin, R. F. and G. D. Newton. 1970. Ostra-

coda and the Silurian stratigraphy of north¬

western Alabama. Geol. Survey of Ala. Bull.

95: 1-64.

Macurda, D. B. 1968. Ontogeny of the crinoid

Eucalyptocrinites. Jour. Paleo. 42: 99-118.

McClellan, W. A. 1966. Arenaceous foramini-

fera from the Waldron Shale (Niagaran) of

southeastern Indiana. Bull. Am. Paleo. 50, no.

230:447-518.

Moore, R. C. (editor). 1961. Treatise on In¬

vertebrate Paleontology: Part Q Arthropoda,

Vol. 3. Geol. Soc. of America and Univ. of

Kansas Press. 442 p.

_ . 1962. Treatise on Invertebrate Paleontol¬

ogy: Part W Miscellanea. Geol. Soc. America

and Univ. of Kansas Press. 259 p.

1983]

Siemann-Gartmann — Microfauna of the Waldron Shale

67

_ . 1964. Treatise on Invertebrate Pal¬

eontology: Part C Protista, Vol. 2. Geol. Soc.

of America and Univ. of Kansas Press. 510 p.

Morris, R. W. and B. L. Hill. 1951. Shidelerites,

a new Silurian ostracode genus. Jour. Paleo.

25:698-699.

_ and _ . 1952. New Ostracoda from

the Middle Silurian Newsom Shale of Tennes¬

see. Bull. Am. Paleontology 34, No. 142. 22 p.

Price, J. A. 1900. A report upon the Waldron

Shale and its horizon, in Decatur, Barthol¬

omew, Shelby, and Rush Counties, Indiana,

together with such other information concern¬

ing the region surveyed, as is of probable

general interest. Indiana Dept. Geol. and Nat.

Res. Ann. Rept. 24: 81-143.

Shaver, R. H. 1977. Silurian Reef geometry—

New dimensions to explore: Jour. Sed. Pet. 47:

1404-1424.

Siemann-Gartmann, S. M. 1979. Microfauna

associated with crinoid root systems of the

Wenlockian Waldron Shale in southeastern

Indiana. Milwaukee, Wise., Univ. of Wisc.-

Milwaukee, Master’s thesis. 61 p.

Stewart, G. A. and R. R. Priddy. 1941. Arena¬

ceous foraminifera from Niagaran rocks of

Ohio and Indiana. Jour. Paleo. 15: 366-375.

Tillman, C. G. 1962. Stratigraphy and brachio-

pod fauna of the (Silurian) Osgood Formation,

Laurel Limestone, and Waldron Shale of

southeastern Indiana. Cambridge, Mass.,

Harvard Univ., Ph.D. thesis, 82 p.

Watkins, R. and J. M. Hurst. 1977. Community

relations of Silurian crinoids at Dudley,

England. Paleobiology 3: 207-217.

Zar, Jerrold H. 1974. Biostatistical Analysis:

Prentice-Hall, Inc. Englewood Cliffs, N.J.,

620 p.

Zingula, R. P. 1968. Technique— A new break¬

through in sample washing. Jour. Paleo. 42:

1092.

EVOLUTION OF A BIOSTRATIGRAPHIC ZONATION;

LESSONS FROM LOWER TRIASSIC CONODONTS, U.S. CORDILLERA

Rachel Krebs Paull

Dept . of Geological and Geophysical Sciences

University of Wisconsin-Milwaukee

Milwaukee , Wisconsin 53201

Abstract

Condonts have exceptional value as biostratigraphic tools, and more than 100

conodont biozones are recognized in Ordovician through Triassic rock. They facili¬

tate correlation in Triassic strata where stratigraphically significant ammonoids are

rare or absent. A biostratigraphic zonation for the entire Triassic System was first

developed in 1971 by integrating parts of a Lower Triassic zonation developed in

West Pakistan with zonations from the Cordillera of the western United States.

Conodonts were considered to be ‘facies breakers,” and paleoecologic influ¬

ences were not recognized in the Great Basin and Middle Rocky Mountains by many

earlier workers. This resulted in a number of proposed modifications for the

Smithian Stage. Additional conodont biostratigraphic studies extended the total

ranges of some conodont species and eliminated the utility of several overlapped

biozones. As regional biostratigraphic work on Lower Triassic conodonts con¬

tinued, it became apparent that simplification of the zonal scheme would make it

more useful in a variety of marine depositional environments on a worldwide basis,

if the spirit of Albert Oppel’s ‘‘ideal profile” were followed.

Lower Triassic conodont biozones are based on: Hindeodus typicalis for the

Griesbachian Stage, Neospathodus kummeli and Neospathodus dieneri for the

Dienerian Stage, and Neospathodus waageni for the Smithian Stage. The uppermost

Early Triassic Spathian Stage biozones are based on: Neospathodus triangularis,

Neospathodus collinsoni, Neogondolella jubata, and Neospathodus timorensis.

The refined Lower Triassic zonation presented here is a progress report that

extends the generic ranges of Gladigondolella and Platyvillosus downward into the

Smithian. Further biostratigraphic studies will modify this contemporary effort, as

total ranges of zone diagnostic conodonts are ultimately defined.

Introduction

Conodonts were widespread in early

oceans for a span of 400 million years, from

the latest Precambrian or earliest Cambrian

into the latest Triassic (Sweet and Berg¬

strom, 1981). Their resistant, phosphatic,

microskeletal components, while providing

very limited clues as to the biologic nature of

the conodont animal, possess exceptional

value as biostratigraphic tools.

Conodonts were probably small (up to

several centimeters in greatest dimension),

bilaterally symmetrical, free-moving orga¬

nisms which occupied pelagic to benthic

marine environments. A recently described,

elongate, soft-bodied animal with an ap¬

paratus of conodont elements, apparently in

place, shows similarities to both chordates

and chaetognath marine worms (Briggs and

others, 1983). The microscopic elements

served as teeth or as supports for respiration

or feeding activities, and were embedded in,

or covered by, fleshy tissue (Bengston, 1976;

Jeppsson, 1979; Clark, 1981a). After death,

68

1983]

Pauli— Evolution of a Biostratigraphic Zonation

69

these carbonate-apatite structures became

dissociated, so natural assemblages of hard

parts are rare. Crushing and processing rock

for recovery of conodonts further isolate

individual elements.

Within the past 35 years, coincident with

the use of the acetic acid method for dis¬

solution of carbonate rocks, conodont study

accelerated and the literature burgeoned.

Work during this period focused primarily

upon the stratigraphic distribution of diag¬

nostic forms. As a result, more than 100

conodont biostratigraphic units are recog¬

nized from Ordovician through Triassic rock

(Sweet and Bergstrom, 1981).

The widespread occurrence of conodonts

in diverse lithologies led to the general belief

that they were largely independent of envi¬

ronmental influences, and stratigraphers en¬

visioned a universal spread of individual

taxa in marine environments. The same spe¬

cies were observed, for example, in Ordovi¬

cian lithofacies that included shelly shelf

limestone, black graptolitic shale, and deep

water chert-shale sequences containing

sponge spicules and radiolaria. The ubi¬

quitous nature of some forms prompted an

unnamed geologist to remark that “Cono¬

donts are like God— they are everywhere”

(Lindstrom, 1976).

By 1950, conodont faunas from Ordo¬

vician through Permian rocks were described

for the United States. Muller (1956)

described the first fully-documented North

American Lower Triassic conodont fauna

from strata in Nevada. Clark (1957) pio¬

neered the use of conodonts to establish the

Triassic age for marine strata in the eastern

Great Basin. However, documentation of

Triassic conodonts lagged behind Paleozoic

efforts. Factors contributing to this situation

include the limited areal extent of marine

Triassic rocks, the remote, often desolate,

character of the Great Basin outcrop area,

the limited abundance of most Lower Tri¬

assic conodont faunas, and a small number

of persistent workers. Apparently, the

paucity of knowledge about the Triassic in

the western United States is only part of a

worldwide problem, for Derek Ager states,

“Much is hidden in the mists of the early

Triassic, which is probably the least known

episode in the long history of Phanerozoic

time” (1981, p. 99).

Conodont faunas of both the Late

Permian and Early Triassic lack diversity,

but include distinctive forms. An evolution¬

ary crisis in Early Permian time eliminated

many long-ranging Paleozoic taxa, and only

four or fewer major superfamilies survived

(Clark, 1972; Sweet, 1973; Sweet and

Bergstrom, 1981). The cosmopolitan nature

of Lower Triassic marine faunas reflects the

assembly of a single supercontinent, with the

Pacific and Tethyan oceans forming a con¬

tinuous water body around the shores of

Pangaea (Valentine and Moores, 1973).

Biozones and Correlation

Worldwide biostratigraphic zonation and

correlation of Permian and Triassic marine

rocks are historically based on ammonoid

faunas, which are arranged in a standard

succession. In North America, at least 35

ammonoid zonal units provide a biostrati¬

graphic framework for the marine Triassic

(Silberling and Tozer, 1968). Although

ammonoids were widely distributed in late

Paleozoic and Mesozoic seas, they are rare

fossils in many geographic areas. More

recently, conodonts were used to facilitate or

refine correlation where ammonoids are

scarce or absent (Clark and Behnken, 1971;

Sweet and others, 1971).

Regardless of the fossil content utilized,

the purpose of biostratigraphic zonation is

to provide a means by which the relative

timing of biologic and geologic events can be

determined and correlated on a worldwide

basis. These biozones must necessarily have

time significance, and may involve evolu¬

tionary changes, migrations, and extinctions

(Eicher, 1968).

Three principal categories of biostrati¬

graphic units are used, depending upon cir¬

cumstances and available fauna (North

70

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I

American Commission on Stratigraphic

Nomenclature, 1983). However, range

(interval) zones of various types are the most

widely employed. Interval zones are defined

by the lowest and/or highest, documented

occurrences of less than three taxa (Fig. 1).

They include: the interval between the lowest

and highest occurrences of a single taxon

(taxon range zone), the interval between the

lowest occurrence of one taxon and the high¬

est occurrence of another taxon (concurrent

range zone or partial range zone), or the

interval between successive lowest or highest

occurrences of two taxa (lineage zone or

interval zone). Unfossiliferous intervals are

also recognized between or within biozones

(barren interzones and intrazones).

An assemblage zone is characterized by

the association of three or more taxa, and in

practice, two different concepts are used

BIOSTRATIGRAPHIC

INTERVAL ZONES

Fig. 1 . Biostratigraphic interval zones, as defined by the North American Commission on Stratigraphic Nomenclature

(1983). Examples include: A) taxon range zone, Bl) concurrent range zone, B2) partial range zone, Cl) lineage zone,

C2) interval zone.

ASSEMBLAGE ZONE

OPPEL ZONE

Fig. 2. Assemblage zones, as defined by the North American Commission on Stratigraphic Nomenclature (1983).

Examples include: Left) assemblage zone, not based upon the ranges of the included species; Right) Oppel zone, a con¬

current range zone defined by more than two taxa.

1983]

Pauli — Evolution of a Biostratigraphic Zonation

71

(Fig. 2). One, the assemblage zone, is

characterized by a certain association of taxa

without regard to their range limits. The

second type is an Oppel zone, with bounda¬

ries based on two or more documented, first

and/or last occurrences of the taxa charac¬

terizing the zone. This is also a form of

concurrent range zone.

The third category, or abundance zone, is

characterized by quantitatively distinctive

maxima of relative abundance of one or

more taxa (Fig. 3). This is the acme zone of

the International Subcommission on Strati¬

graphic Classification (Hedberg, 1976).

Although all fossils, in a general sense,

may be considered “facies fossils” (Ager,

1981), some assemblage and abundance bio¬

zones may reflect strong local ecologic

control, and are not necessarily time

significant. The appearance of the included

ABUNDANCE ZONE

Fig. 3. Abundance zone, as defined by the North

American Commission on Stratigraphic Nomenclature

(1983). This biozone is based on a marked increase in

abundance of the defining taxon or taxa.

taxa in these cases may be due to the shift or

return of favorable, or optimal environ¬

mental conditions within a geographic area.

Whether based on the range of a single

taxon or of a specific combination of taxa, a

biozone conceptually includes all the rocks

deposited anywhere during the entire time

the defining taxon or taxa existed (total

range), whether their remains are recognized

or not. Most local range zones (teilzones) are

only fragments of the total taxon/taxa

record. The development and application of

biozones were elegantly detailed in 1856 by

young Albert Oppel during his study of

Jurassic biostratigraphy. Oppel visualized

the general succession of fossils as indepen¬

dent of the actual paleontologic or lithic

succession at any one place (Hancock, 1977).

In discussing correlation based on fossil

content, Oppel observed:

“This task is admittedly a hard one, but it is

only by carrying it out that an accurate corre¬

lation of a whole system can be assured. It

necessarily involves exploring the vertical

range of each separate species in the most

diverse localities, while ignoring the

lithological development of the beds; by this

means will be brought into prominence those

zones which, through the constant and exclu¬

sive occurrence of certain species, mark them¬

selves off from their neighbours as distinct

horizons. In this way is obtained an ideal

profile, of which the component parts of the

same age in the various districts are character¬

ised always by the same species” (translation

in Hancock, 1977, p. 12).

The search for the “ideal profile” became

the aim of all biostratigraphers who fol¬

lowed.

Lower Triassic Conodont Zonation

Early Zonations

Muller (1956) first suggested the possibil¬

ity of establishing a time-significant, cono¬

dont biostratigraphic succession within the

Triassic, and Clark (1960), Mosher and

Clark (1965), and Mosher (1968) identified

preliminary sequences. The first extensive

Lower Triassic zonal scheme based on

72

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

Fig. 4. Lower Triassic conodont zonation of Sweet

(1970), based on specimens from the Salt and Trans-

Indus ranges of West Pakistan.

Fig. 5. Lower Triassic stage names for North

America.

Fig. 6. Lower Triassic conodont zonation of Sweet

and others (1971), combining data from West Pakistan

and the Great Basin of the western United States.

conodonts was provided by Sweet (1970)

from the uppermost Permian and Lower

Triassic of West Pakistan (Fig. 4). The

Lower Triassic was divided into nine zones

based on the vertical distribution of six

genera, with the oldest zone spanning the

Permian-Triassic boundary (Sweet, 1970).

Five of the zones were also represented in

Triassic collections from Europe and North

America, but four were of utility only in

West Pakistan. Figure 5 provides series and

stage names for the Lower Triassic.

A cooperative effort by North American

conodont workers led to the development of

a biostratigraphic zonation for the entire

Triassic System (Sweet and others, 1971)

(Fig. 6). Thirteen Lower Triassic conodont

zones were established, and correlated with

the ten North American ammonoid zones of

Silberling and Tozer (1968). The type strata

for the lower Scythian zones are in the Salt

and Trans-Indus ranges of West Pakistan.

Type localities for all but the topmost upper

Scythian zones are in the Great Basin of the

western United States (Sweet and others,

1971).

Continuity between the Pakistan and

Great Basin portions was not immediately

confirmed, although some conodont species

were common to both regions. Diagnostic

Salt Range forms, such as Neospathodus

pakistanensis of zone 6, underlying the

suture, had not been found in the Great

Basin, while Neospathodus waageni of zone

7 was not yet reported from the Parachirog-

nathus-Furnishius Zone of North America

(Figs. 4 and 6) (Sweet and others, 1971).

The Parachirognathus-Furnishius interval

of Sweet and others (1971) was based on

work in Utah and Nevada, and it forms the

lowest zone of the North American part of

the combined zonation (Fig. 6). This dual

assignment was based on the suspicion that,

“there may be a facies relationship between

Furnishius- and Parachirognathus- bearing

strata” (Sweet and others, 1971, p. 452). To

evaluate this concern, Parachirognathus-

Furnishius ratio studies were conducted

along the margin of the Lower Triassic

1983]

Pauli — Evolution of a Biostratigraphic Zonation

73

seaway. The paleoecologic work of Clark

and Rosser (1976) assumed a basin to shelf

transect from the deeper parts of the

Cordilleran geosyncline on the west to

progressively shallower marine environ¬

ments to the east, where terrigenous red beds

intertongue with marine sediments. Regional

stratigraphic work (Koch, 1976; Collinson

and Hasenmueller, 1978; Pauli, 1980; Carr

and Pauli, 1983), however, established that

the geographic distribution of sections

sampled by Clark and Rosser (1976) was

biased toward the shelf (shallow transitional)

environment (Fig. 7). Although their western

sections are thicker than those to the east,

this did not mean deeper water, and a true

basin to shelf survey was not made.

The upper Scythian conodont biostratig¬

raphy reported by Solien (1979) from Fort

Douglas, Utah, was in the same relative

basin to shelf position and had a deposi-

tional environment similar to the sections

used by Clark and Rosser (1976). Progres¬

sive changes in the vertical distribution of

Furnishius and Parachirognathus in this

single section were included in a modified

zonation proposed by Clark and others

(1979) (Fig. 8).

Solien (1979) recovered Neospathodus

pakistanensis from the lower part of his

sequence, finally forging the link between

Pakistan and the Great Basin. N. pakis¬

tanensis was also conditionally reported by

Clark and others (1979) from southern

Idaho. Solien’s study, was well as the work

of Collinson and Hasenmueller (1978), also

confirmed the occurrence of Neospathodus

waageni with the Parachirognathus-

Furnishius fauna of western North America

(Fig. 4 and 6).

Fig. 7. Lithofacies map of the Lower Triassic during

the Smithian Stage. Dots represent study localities of

Clark and Rosser (1976) and Solien (1979).

Fig. 8. Comparison of Lower and Middle Scythian conodont zonations.

74

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

It is instructive to compare the three

zonations at this point (Fig. 8). The initial

scheme of Sweet (1970) utilizes a single

Smithian zone, and six lower Scythian

intervals. With the compilation of the 1971

biostratigraphy, the lower zones were re¬

tained. However, the Smithian was sub¬

divided and tailored to the Great Basin,

where the stratigraphic value of Neospath -

odus waageni had not yet been realized.

The zonation of Clark and others (1979)

reflects Smithian conodont distributions in

transitional despositional environments (Fig.

8). Dienerian biozones, although still based

on neospathodids, were reduced in number,

when compared to the scheme of Sweet and

others (1971). This change reflects the

limited abundances and diversity of cono¬

dont faunas from the Lower Triassic Din-

woody Formation.

Paleoecologic Influences

Most early workers believed that the

conodont animal was nearly independent of

depositional facies. Yet, as additional

distributional data were collected, it became

apparent that at least some conodont taxa

were prone to ecologic control. Recognition

of paleoecologic patterns led to a symposium

focused on conodont paleoecology, and two

opposing models of marine lifestyle were

proposed. Seddon and Sweet (1971) envi¬

sioned a depth-stratified, pelagic existence,

while Barnes and Fahraeus (1975) suggested

lateral variation of biofacies reflected a

nektobenthic or benthic habit. However, a

cautionary note was introduced by Klapper

and Barrick (1978), who found that distribu¬

tional data alone were not definitive of a

pelagic or a benthic habit for these extinct

organisms. Development of parallel zona¬

tions for major Triassic facies was suggested

as a way to avoid some paleoecologic pitfalls

(Sweet and Bergstrom, 1981; Clark, 1981b).

This would allow the use of two or more

semi-“ideal profiles.”

The sedimentological history of the upper,

or Dienerian, part of the Dinwoody Forma¬

tion was one of progressive progradation

from a shelf region to the east (McKee and

others, 1959). As terrigenous sediments

encroached basinward, the environment was

not favorable to the conodont animal. Also,

the rate of Dienerian sedimentation was

probably rapid. Observations indicate that

conodont numbers, as well as general faunal

abundance, decrease with increasing rates of

sedimentation (Lindstrom, 1964; Kidwell,

1981). Other factors adversely affecting the

presence and diversity of conodonts during

this time include evolution, extinction, and

migration. All of these items influence

current attempts to refine the zonation of the

Dienerian Stage in the western United States.

Paleoenvironmental work supported by

quantitative efforts continues. Two recent

studies of the spatial distribution of cono¬

donts in the Lower Triassic Thaynes Forma¬

tion of the western Cordillera distinguished

three discrete biofacies (Carr, 1981; Carr,

Pauli, and Clark, 1983). As a result, cono¬

dont species with little facies dependence,

and more temporal significance, were identi¬

fied. Amalgamation of this type of research

with stratigraphic distribution studies should

enhance the biostratigraphic utility of cono¬

donts, and improve further zonal subdivi¬

sions.

Proposed Zonation

Continued biostratigraphic and petro¬

graphic work in the western Cordillera

resulted in increased understanding of Early

Triassic depositional history and paleo-

geography, and the conodont biozonation

was again modified. Collinson and Hasen-

mueller (1978) suggested a zonation reminis¬

cent of Sweet’s original (1970) version (Fig.

8). Additional regional studies (Pauli, 1980;

Carr and Pauli, 1980; Carr, 1981; Pauli,

1982; Carr and Pauli, 1983) established a

workable zonation from basin to shelf that

resulted in additional reduction in biozones

(Fig. 8).

With this simplified zonation, what was

done in the name of refinement? The

1983]

Pauli— Evolution of a Biostratigraphic Zonation

75

philosophy behind Shaw’s (1964) graphic

method, which has the potential for a

detailed and more quantitative correlation,

may provide some insight. In order to arrive

at a composite standard reference section,

the technique seeks the maximum strati¬

graphic range for each taxon used, despite

local environmental influence or poor

preservation (Miller, 1977).

Refinements in correlation may proceed in

one of two directions as additional studies

are conducted. If the fauna is large and

diverse, the result should be a sequence with

greater resolving power and a corresponding

increase in significant biozones. If the fauna

is modest and of limited diversity, biostrati¬

graphic refinement consists of extending the

local stratigraphic ranges of faunal elements

toward their maximum values. As a result,

zonal units may be eliminated (Fig. 9).

Fig. 9. Extension of range, depicted by dotted line,

results in deletion of zone 2, previously a partial range

zone.

This latter situation describes the evolu¬

tion of Lower Triassic conodont zonation.

Extension of the local ranges of species

resulted in the deletion of the Neogondolella

Lower Triassic

GRIESBACHIAN

N>

CO

Ul

O)

00

oj n

n

05

SUBZONES

ISARC

HINDEODUS TYPICALIS

CELLA IsARCI(!a

NEOgAnDOlJlLA CAR I NAT A

NEOSPATHODUS KuAlMELI

neAspatkodus DlENERI

US ETH NGTON

PARACHIROGNATH

furnishiu! trise Bratus

neospathAdus conservativus

I I I

NEOSPATHODUS WAAGENI

I I I

NEOSPATHODUS BICUSPIDATUS

I

GLADIGONDOLELLA MEEKI

NEOGONDOLELLA MILLERI

I I I

NEOGONDOLELLA SP A -

I I I

NEOSPATHODUS TRIANGULARIS

NEOSPATHODUS HOMERI

PLATYVILLOSUS

NEOSPATHODUS COLLINSONI

I I I I

NEOGONDOLELLA JUBATA -

NEOSPATHODUS TIMORENSIS

J _ I _ -L I _

Fig. 10. Lower Triassic conodont zonation of Carr and Pauli (1983).

76

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

carinata Zone (Sweet, 1973, 1979; Collinson

and Hasenmueller, 1978), the Neospa thodus

conservations Zone (Collinson and Hasen¬

mueller, 1978; Solien, 1979), the Parachir-

ognathus ethingtoni Zone (Collinson and

Hasenmueller, 1978), and the Furnishius

triserratus Zone (Pauli, 1980, 1982) (Fig. 8).

Solien (1979) and Clark and others (1979)

recommended expansion of the Parachirog-

nathus-Furnishius Zone of Sweet and others

(1971), but retained these conodonts as zonal

indicators (Fig. 8).

In conclusion, the zonation proposed in

Figure 10 is a progress report, and the

following facts suggest that the biozones will

change again.

1) Gladigondolella, a stranger to North

America, makes a Smithian appear¬

ance. This genus was previously

known only from the Middle and

Upper Triassic of Europe and Asia

(Pauli, 1982, 1983) (Fig. 10).

2) Platyvillosus costatus, a lower

Spathian indicator, is reported with

Smithian forms (Goel, 1979; Wang,

1980; Pauli, in prep.) (Fig. 10).

With these observations in mind, and

others that undoubtedly will be made, one is

impressed with the wisdom often attributed

to Mark Twain, when he noted: “Research¬

ers have already cast much darkness on the

subject, and if they continue their investi¬

gations, we shall soon know nothing at all

about it.” Nevertheless, the search for the

ultimate Lower Triassic zonation goes on.

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CONODONTS AND BIOSTRATIGRAPHY OF THE MUSCATATUCK

GROUP (MIDDLE DEVONIAN), SOUTH-CENTRAL

INDIANA AND NORTH-CENTRAL KENTUCKY

Curtis R. Klug

Dept, of Geology

University of Iowa

Iowa City , Iowa 52242

Abstract

Eighty-two samples were collected and processed for conodonts from strata of

the Middle Devonian Muscatatuck Group of south-central Indiana and north-

central Kentucky. In this region, the Muscatatuck Group consists of two

formations, the Jeffersonville Limestone and the overlying North Vernon

Limestone. Although conodonts are abundant (over 20,000 specimens were

recovered), diversity is relatively low. Icriodus and Polygnathus are the dominant

faunal elements. Nineteen conodont species and subspecies are recognized including

one new subspecies, Icriodus angustus obliquus. Few of the recognized species are

diagnostic of the standard Middle Devonian conodont zones, making long-distance

correlations uncertain. Consequently, a zonation consisting of three local zones and

one standard subzone is adopted. These are, in ascending order, the Icriodus

latericrescens robustus Zone, the Icriodus angustus angustus Zone, the Polygnathus

pseudofoliatus Zone, and the Lower Polygnathus varcus Subzone. Examination of

the conodont faunas suggests an Eifelian age for the lower part of the Muscatatuck

Group and a Givetian age for the upper part.

Acknowledgments

The author very gratefully acknowledges

the invaluable assistance of Gilbert Klapper

during all phases of this study. Thanks are

also extended to Dale Sparling for making

available unpublished information on cono¬

dont faunas from the Columbus and Dela¬

ware Limestones of Ohio. The Graduate

College of The University of Iowa provided

funding and access to the JEOL JSM-35C

Scanning Electron Microscope with which

the photographs for the conodont figures

were made. The Department of Geology at

The University of Iowa provided access to

darkroom facilities, and thin-section and

conodont-processing laboratories.

Introduction

Since 1820, over 175 papers have been

published on the Devonian stratigraphy and

paleontology of the Falls of the Ohio and

surrounding area. Relatively few publica¬

tions, however, have included a detailed dis¬

cussion of the conodont faunas and bio¬

stratigraphy. One of the earliest papers to

report Middle Devonian conodonts from the

Falls of the Ohio was that of Branson and

Mehl (1938), which included the description

of a new species, Icriodus latericrescens. A

number of other papers (e.g., Rexroad and

Orr, 1967; Orr and Pollock, 1968; Klapper et

al., 1971) mention the occurrence of cono¬

donts in these strata but do not include

illustrations of specimens. Only a few

publications include both discussion and

illustrations of the Middle Devonian

conodonts of south-central Indiana and

north-central Kentucky (e.g., Orr and

Klapper, 1968; Klapper, Philip and Jackson,

1970; Klapper and Johnson, 1980). By far

the most important paper on this subject is

79

80

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

Orr’s (1946b) unpublished M.A. thesis.

Although the stress of this thesis is on the

Middle Devonian conodonts of southern

Illinois, four sections in south-central

Indiana were also included. Conodont

faunas are well illustrated, and a local zonal

scheme of six conodont zones was estab¬

lished. Since the writing of Orr’s thesis, the

understanding of Middle Devonian cono¬

dont faunas and biostratigraphy has been

considerably refined. The main purpose of

the present paper is to examine, in greater

detail, the conodont faunas of the Middle

Devonian Muscatatuck Group of south-

central Indiana and north-central Kentucky

and to provide an updated biostratigraphy

based on these faunas.

Procedures

Eighty-three samples were collected from

eight Middle Devonian sections in south-

central Indiana and north-central Kentucky.

The eight localities lie along a nearly north-

south trending line from Jennings County,

Indiana to Jefferson County, Kentucky (see

Figs. 1 & 2). An effort was made to visit type

localities of the lithostratigraphic units

under consideration; when not possible,

nearby alternate localities were substituted.

See the Appendix for detailed location of

sections. Samples were generally collected

from major beds with spacing no more than

1 meter apart, and with individual samples

including no more than 10 cm of vertical

section. When possible, one kilogram of

each sample was processed for conodonts

using standard acidizing procedures with

formic acid. In the case of particularly

argillaceous samples, the acidizing proce¬

dure was supplemented with Stoddard’s

solvent treatment as described by Collinson

(1963). Residues were washed through three

nested sieves of 20, 120, and 230 U.S.

standard mesh. Only the residue retained on

the 120 mesh sieve was picked for cono¬

donts. All specimens that retained the basal

cavity were picked to guarantee that only

individual elements were collected. In the

case of some particularly large samples, only

part of the residue was picked. The cono¬

donts illustrated in this paper were

photographed on the JEOL JSM-35C scan¬

ning electron microscope at The University

of Iowa, Iowa City. Lithologic nature of the

samples was determined by examination of

hand samples, polished slabs, insoluble resi¬

dues, and, in most instances, thin sections.

Lithostratigraphy

The stratigraphic terminology employed

herein is primarily that in use by the Indiana

Geological Survey as set forth by Shaver et

al. (1970) and modified by Perkins (1963),

Shaver (1974), and Droste and Shaver

(1975). The Muscatatuck Group, proposed

by Shaver (1974, p. 3), in south-central

Indiana and north-central Kentucky includes

two formations, the Jeffersonville Lime¬

stone and the overlying North Vernon

Limestone.

The Jeffersonville Limestone was named

by Kindle (1899, p. 8) for the “limestone

lying between the Sellersburg beds and the

Catenipora beds of the Niagara’’ as exposed

at the Falls of the Ohio between Jefferson¬

ville, Indiana, and the mouth of Silver Creek.

Droste and Shaver (1975) considered the

Jeffersonville Limestone to include three

members in generally ascending order: the

Dutch Creek Sandstone, Geneva Dolomite,

and Vernon Fork Members. They con¬

sidered the Dutch Creek Sandstone Member

to be equivalent to the basal Jeffersonville of

the southern Indiana outcrop. This sand¬

stone has a discontinuous distribution and

was not encountered in any of the sections

examined in this study.

The Geneva and Vernon Fork Members

are considered to be northern facies equiva¬

lents of the type Jeffersonville Limestone.

Of these two members, only the Vernon

Fork was sampled for conodonts in this

study. Orr (1964b), however, examined

samples from the Geneva Member for cono¬

donts, but found them to be nonproductive.

The Vernon Fork Member was examined,

1983]

Klug — Conodonts and Biostratigraphy

81

for this paper, only at its principal reference

section, the Berry Materials Corp. Quarry

(BMQ) (see Droste and Shaver, 1975, p.

405). The sampled strata consist of light

yellowish- to brownish-gray, slightly calcitic,

sandy, “dolomicrite.” Birdseye structures,

laminations, and intraclasts also occur in

this unit. The term “dolomicrite,” as used

above, refers only to the fine-grained nature

of these dolostones and does not necessarily

imply a primary origin for the dolomite.

Of greater concern to this study is the

southern facies of the Jeffersonville Lime¬

stone. This formation, as exposed at its type

locality at the Falls of the Ohio, has not been

subdivided into members, as it has in its

more northerly occurrences. Several

schemes, however, have been proposed to

subdivide the formation based on faunal

content (see, e.g., Kindle, 1901; Patton and

Dawson, 1955; Perkins, 1963; Conkin and

Conkin, 1976). To facilitate the discussion

of the Jeffersonville Limestone, the zonal

scheme as proposed by Perkins (1963, p.

1338) has been adopted. He recognized five

zones which are, in ascending order: (1)

coral zone; (2) Amphipora Zone; (3) Brevis-

pirifer gregarius Zone; (4) fenestrate

bryozoan-brachiopod zone; (5) Paraspirifer

acuminatus Zone (Fig. 2). A detailed de¬

scription of each of these zones and the

associated lithologies can be found in

Perkins (1963).

The Jeffersonville Limestone is overlain

by the North Vernon Limestone (= Sellers-

burg Limestone of authors). This unit was

named by Borden (1876, p. 160-161) for

strata occurring at North Vernon, Jennings

County, Indiana, and lying “at the horizon

of the hydraulic limestone” (Silver Creek

Member) of Clark County, Indiana. In

Borden’s concept, the North Vernon Lime¬

stone was overlain by gray, crystalline,

commonly crinoidal limestone (= Beech-

wood Member of present usage). Kindle

(1899, p. 8, 20) proposed the name Sellers-

burg beds for the strata underlying the New

Albany Shale down to the lowest beds

worked by the cement quarries. As used in

this sense, the Sellersburg beds include the

Beechwood and Silver Creek Members only.

More detailed discussions of the nomen-

clatural history of these strata can be found

in papers by Patton and Dawson (1955, p.

39-43) and Burger and Patton, in Shaver et

al. (1970, p. 120-122). Through time, usage

of the names North Vernon Limestone and

Sellersburg Limestone has come to be nearly

synonymous, referring to the strata under¬

lying the New Albany Shale and overlying

the Jeffersonville Limestone. In this paper,

North Vernon Limestone is used in this

sense. Three members are recognized in the

North Vernon Limestone. These are, in

ascending order: the Speeds, Silver Creek,

and Beechwood Members.

Sutton and Sutton (1937, p. 326) proposed

the name Speeds Member for an 18-inch

thick, shaly limestone below the cement rock

( = Silver Creek Member) in the Speeds

Quarry, near Sellersburg, Indiana. In thin

section, the Speeds is a slightly- to highly-

dolomitic, packed biomicrosparrudite.

Campbell (1942, p. 1060) considered the

Speeds to be of formational status, overlain

by the Deputy Formation, a blue to gray

limestone weathering light gray. He desig¬

nated the quarry 3/4 mile south of Deputy,

Jefferson County, Indiana, as the type local¬

ity. According to Campbell, the Deputy is

difficult to distinguish from the Speeds in

fresh material, except by the fossil content.

In thin section, the Deputy at the type

locality is a slightly- to moderately-dolomitic

biomicrosparite to biosparite. The Deputy is

only locally developed and is considered

herein as a facies of the Speeds Member.

The overlying Silver Creek Member was

originally proposed by Siebenthal (1901, p.

345-346) for “a homogeneous, fine-grained,

bluish to drab, argillaceous, magnesian

limestone, the calcined form of which has

the property of hydraulicity.” This unit is

typically exposed in the vicinity of Silver

Creek in Clark County, Indiana. Siebenthal

originally considered the Silver Creek to be

82

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

of formational status. Butts (1915, p. 118)

reduced it to the rank of member, as it is

considered herein. Thin section examination

shows the Silver Creek to vary from highly

dolomitic, argillaceous biomicrite to fossil-

iferous, argillaceous “dolomicrite.” The

Silver Creek Member thins northward from

its maximum thickness in Clark County,

Indiana. At the same time, the underlying

Speeds Member shows a corresponding

thickening. Based on stratigraphic position

and the inclusion of lentils or tongues of one

lithology in the other, the two members have

been considered to be contemporaneous

facies (see e.g., Patton and Dawson, 1955, p.

42).

The Beechwood Member is the youngest

member of the North Vernon Limestone.

The name was proposed by Butts (1915, p.

120) for a gray, thick-bedded, coarsely

crystalline crinoidal limestone containing

black phosphatic pebbles in the basal few

inches. Butts named this unit for exposures

near Beechwood Station, Jefferson County,

Kentucky, but did not establish a type

section. Orr and Pollock (1968, p. 2258)

proposed a principal reference section for

the Beechwood Member, about 4.5 miles

west of the old Beechwood Station in

Louisville, Jefferson County, Kentucky. In

thin section, the Beechwood varies from

echinoderm biosparite to biosparrudite.

Dolomitization is generally minimal to

moderate but may be extensive in some beds.

Phosphate pebbles and flattened, phosphatic

ooids(?) are frequently encountered at the

base of the unit.

Biostratigraphy

The conodont faunas of the Muscatatuck

Group in south-central Indiana and north-

central Kentucky include few diagnostic

species common to the standard zonation,

which is reviewed, for example, by Klapper

and Johnson (1980). The local zonal scheme

proposed by Orr (1964b) and modified by

Orr (1971) is further modified and used in

this paper (Fig. 3).

Conodonts were not recovered from the

Jeffersonville Limestone below the Brevis -

pirifer gregarius Zone. Oliver (1976, Fig. 3)

considered these lower strata to be of late

Emsian to early Eifelian age, as determined

from the coral faunas.

Icriodus latericrescens

robustus Zone

This, the lowest conodont zone recognized

in the study area, corresponds to the Icri-

odux latericrescens n. subsp. Zone of Orr

(1964b, p. 36-37). The lower limit of this

zone is defined by the lowest occurrence of /.

/. robustus, and the upper limit by the lowest

occurrence of /. a. angustus. Polygnathus cf .

P. angusticostatus, /. sp. A, and /. n. sp. E

of Weddige first occur near the top of the

Brevispirifer gregarius Zone below the low¬

est occurrence of P. c. costatus (see Fig. 4).

This association suggests that the /. /.

robustus Zone, of the study area, may be

equivalent, in part, to the P. costatus patulus

Zone of the standard zonation. For ranges

of the above-mentioned forms in the stan¬

dard zonation, the reader is referred to

Klapper and Johnson (1980, p. 420-422).

Icriodus angustus

angustus Zone

The lower boundary of this zone is defined

by the lowest occurrence of /. a. angustus.

The upper boundary is defined by the lowest

occurrence of Polygnathus pseudofoliatus.

Polygnathus c. costatus and P. /. lingui-

formis first occur in the /. a. angustus Zone.

In the examined sections, the /. a. angustus

Zone is recognized in the fenestrate bryo-

zoan-brachiopod zone and the Paraspirifer

acuminatus Zone of the Jeffersonville Lime¬

stone. Correlation of the I. a. angustus Zone

with the P. c. costatus Zone of the standard

zonation is suggested.

Polygnathus pseudofoliatus Zone

The base of the P. pseudofoliatus Zone is

defined by the lowest occurrence of the

nominal species. The top is defined, in the

study area, by the lowest occurrence of P.

timorensis. Icriodus n. sp. E of Weddige

1983]

Klug—Conodonts and Biostratigraphy

83

(1977), /. sp. A, and I. retrodepressus show

their maximum development in this zone.

Below this zone /. retrodepressus is

represented only by tentatively identified

specimens. Icriodus angustus obliquus first

occurs at the base of the P. pseudo foliatus

Zone. Faunas characteristic of the P.

pseudofoliatus Zone were recovered from

the Speeds (including the Deputy facies) and

Silver Creek Members of the North Vernon

Limestone.

A single, apparently weathered specimen

of Polygnathus timorensis was recovered

from a sample (SSQ-5) at the top of the

Silver Creek Member. In another sample

(OGQ-4), from the top of this member,

several fragmentary specimens of Icriodus /.

latericrescens were recovered below the first

occurrence of P. timorensis in the overlying

Beechwood Member. Also recovered from

this sample were a number of flattened

phosphatic ooids(?) like those typical of the

basal part of the Beechwood Member. The

presence of these ooids(?) and the weathered

appearance of the specimen of P. timorensis

suggest the possibility of stratigraphic leak.

Orr and Pollock (1968, p. 2261) also

reported I. /. latericrescens from a fauna

without “P. varcus ” from the top of the

Silver Creek Member at the Atkins Quarry,

in Clark County, Indiana. On evidence of

that occurrence, Orr (1971, p. 17) considered

the upper part of the Silver Creek Member to

belong to his I. L latericrescens Zone. This

zone, however, cannot be recognized with

any confidence in the present study.

The relationships of the Polygnathus

pseudofoliatus Zone with the standard

conodont zonation are far from straight-

forward. Correlation of this zone with part

or all of the sequence from the Tortodus

kockelianus australis Zone (Eifelian)

through the Polygnathus xylus ensensis Zone

(Eifelian-Givetian, Weddige, 1977) is possi¬

ble.

Lower Polygnathus varcus Subzone

The Lower Polygnathus varcus Subzone

of Ziegler, Klapper and Johnson (1976, p.

1 13) is recognized in the Beechwood Member

of the North Vernon Limestone. Polyg¬

nathus timorensis , P. linguiformis weddigei

and P. linguiformis klapperi make their first

appearance at the base of this member.

Several species, for example Icriodus

angustus angustus, Icriodus angustus

obliquus and Icriodus retrodepressus, range

upward into the lower P. varcus Subzone

(see Fig. 4). These forms are not known to

occur at this level outside of the study area

and many represent reworked elements in

the present collections.

One sample (SSQ-1) from the thin lime¬

stone at the base of the New Albany Shale

Group was also processed for conodonts. A

diverse fauna including Polygnathus crista -

tus was recovered from this sample but, be¬

cause of stratigraphic position, is considered

beyond the scope of this paper and will not

be discussed further herein. For a detailed

description of this fauna, the reader is

referred to the paper by Orr and Klapper

(1968).

Conodont-based correlations of the Mus-

catatuck Group with Middle Devonian strata

in surrounding areas are shown in Fig. 5.

Systematic Paleontology

Nineteen conodont species and subspecies

were recognized from among the 22,154

specimens recovered in this study. For

distribution of species see Figs. 6 and 7.

Emphasis is placed on platform and some

coniform elements. Multielement recon¬

structions have generally not been attempted

owing to the poor preservation of most non¬

platform elements. General associations,

however, are noted. Figured specimens are

reposited at the University of Iowa (SUI).

Belodella cf . B. resima (Philip, 1965)

Fig. 12 G,L

cf. Belodus resimus Philip, 1965, p. 98, PI.

8, Figs. 15-17, 19.

Remarks. — Proclined to erect, denticulate

coniform elements have been recovered from

several samples in south-central Indiana and

north-central Kentucky. These forms are

84

Wisconsin Academy of Sciences , Arts and Letters

[Vol. 71, Part I,

comparable in shape, denticulation, and the

development of anterolateral flanges, to

Belodella resima (Philip, 1965). In B.

resima, however, the cross-sectional shape is

a narrow isosceles triangle whereas in the

present material it is a narrow right triangle.

Also, the anterolateral flanges of B. resima

appear to be smooth whereas in the material

at hand they are made up of minute, con¬

fluent denticles similar to those of the

posterior keel. Uyeno, in Uyeno, Telford,

and Sanford (1982, PI. 5, Figs. 30-32) illus¬

trated three specimens of Belodella sp. which

also appear to have denticulated antero¬

lateral flanges.

Material. — 39 specimens

Occurrence. — Fenestrate bryozoan-brach-

iopod zone and Paraspirifer acuminatus

Zone of the Jeffersonville Limestone and

upper Speeds, Silver Creek and Beechwood

Members of the North Vernon Limestone.

Coelocerodontus cf. C. biconvexus

Bultynck, 1970

Fig. 12H-K, M-O

cf. Coelocerodontus biconvexus Bultynck,

1970, p. 94, PI. 27, Figs. 13-15.

Remarks. — Erect to slightly recurved

coniform elements comparable to Coelo¬

cerodontus biconvexus are common in the

Middle Devonian strata of south-central

Indiana and north-central Kentucky. The

present material differs, however, from

Bultynck’s specimens in that the cross-

sectional outline of the Indiana and

Kentucky specimens varies from biconvex to

triangular to concavo-convex, and none of

these specimens has a denticulated posterior

keel, although denticulation of the antero¬

lateral costa is commonly well-developed.

Paltodus sp. of Orr (1964a, p. 13, PI. 2,

Figs. 4, 7) and Coelocerodontus sp. of

Uyeno, in Uyeno, Telford, and Sanford

(1982, p. 34, PI. 5, Figs. 25-29) are

apparently conspecific with the present

form.

Material. — 686 specimens.

Occurrence. — Brevispirifer gregarius

Zone, fenestrate bryozoan-brachiopod zone,

Paraspirifer acuminatus Zone, and Vernon

Fork Member of the Jeffersonville Lime¬

stone; Speeds, Silver Creek, and Beechwood

Members and Deputy facies of the North

Vernon Limestone.

Icriodus angustus angustus

Stewart and Sweet, 1956

Fig. 8 A-F

Icriodus angustus Stewart and Sweet, 1956,

p. 267, PI. 33, Figs. 4, 5, 11, 15; Klapper

and Ziegler, 1967, PL 10, Figs. 1,?2, 3;

Klapper, in Ziegler, 1975, p. 75-76,

Icriodus — PI. 2, Figs. 6, 7; Klapper and

Johnson, 1980, p. 447, PI. 3, Figs. 3-6;

Uyeno, in Uyeno, Telford, and Sanford,

1982, p. 31, PI. 3, Figs. 1-4.

Remarks. — The specimens herein assigned

to Icriodus angustus angustus agree well

with those described by Stewart and Sweet

(1956, p. 267, PI. 33, Figs. 4, 5, 11, 15). See

also Klapper, in Ziegler (1975, p. 75-76) for

additional comments and relations. For

comparison with Icriodus angustus

obliquus, see remarks for that taxon.

Material. — 280 specimens.

Occurrence. — Fenestrate bryozoan-brach¬

iopod zone and Paraspirifer acuminatus

Zone of the Jeffersonville Limestone;

Speeds, Silver Creek, and Beechwood Mem¬

bers of the North Vernon Limestone. For

further discussion of occurrence, see section

on Biostratigraphy.

Icriodus angustus obliquus n. subsp.

Fig. 8 G-L

Derivation of name. —obliquus, Latin,

sloping; referring to the upper margin of the

bladelike extension.

Holotype. — SUI 49334, the specimen

illustrated on Fig. 8 J-L; from the Sellers-

burg Stone Company Quarry, sample

SSQ-14, 0-10 cm above the base of the

Speeds Member.

Diagnosis. — A subspecies of Icriodus

angustus with a segminiscaphate element in

which the posterior extension of the middle

1983]

King — Conod on ts and Biostratigraphy

85

row of denticles is bladelike and is made up

of about four to six laterally compressed

bluntly to acutely pointed denticles. Of

these, the anterior two to four denticles are

relatively slender and subequal to gradually

increasing in height posteriorly. The

posteriormost one or two denticles are

larger and gradually to distinctly higher than

the preceding denticles of the bladelike

extension. This extension begins near mid¬

length of the element.

Remarks. — Icriodus angustus angustus is

distinguished from the new subspecies by a

segminiscaphate element in which the poste¬

rior extension of the middle row of denticles

is made up of one to four subequal denticles

which, in most specimens, are abruptly

higher than all other denticles on the

platform. In some specimens, however, the

denticles of the posterior extension increase

gradually in height posteriorly as in one of

the paratypes (Stewart and Sweet, 1956, PI.

33, Fig. 4; also illustrated by Klapper, in

Ziegler, 1975, Icriodus — PI. 2, Fig. 6). In

such specimens, however, the denticles of

the posterior extension of the middle row are

subequal in the anteroposterior dimension

and are fewer in number than in the new

subspecies.

Elements of Icriodus obliquimarginatus

have posterior bladelike extension of the

middle row of denticles similar to that of /.

angustus obliquus. They can be dis¬

tinguished from the new subspecies,

however, by the outline of the basal cavity.

In I. angustus obliquus the outline is like

that of I. angustus angustus, in which the

inner margin extends farther posteriorly

than the outer margin and the two are con¬

nected by a diagonally oriented posterior

margin. The outline of the basal cavity of I.

obliquimarginatus is rounder and more ex¬

panded posteriorly than in the new sub¬

species. In addition, the posterior margin of

elements of I. angustus obliquus is not

inclined as strongly posteriorly, in lateral

view, as in I. obliquimarginatus, and it may

be vertical to inclined anteriorly as well.

One specimen assigned to the new sub¬

species from a sample from the Sellersburg

Stone Company Quarry (SSQ-14) shows

characteristics intermediate between Icrio¬

dus angustus obliquus and the nominal sub¬

species. It possesses a posterior extension of

the middle row of denticles in which the

anterior two dentiles are slender and sub¬

equal, as in I. angustus obliquus, but are

followed by four abruptly larger denticles

similar to those of I. a. angustus. Most of

the other specimens of /. angustus recovered

from this sample, however, clearly belong to

the new subspecies.

Material. — 23 specimens.

Occurrence. — North Vernon Limestone

(all members). For further discussion of

occurrence, see section on Biostratigraphy.

Icriodus brevis Stauffer, 1940

Fig. 12P-R

Icriodus brevis Stauffer, 1940, p. 424, PL

60, Figs. 36, 43, 44, 52; Klapper, in

Ziegler, 1975, p. 89-90, Icriodus — PI. 3,

Figs. 1-3; Uyeno, in Uyeno, Telford, and

Sanford, 1982, p. 31-32, PI. 5, Figs. 10-16,

21, 22 [see further synonymy].

Icriodus cymbiformis Branson and Mehl.

Orr, 1964b, p. 70-71, PI. 2, Fig. 5; Orr,

1971, p. 33-34, PI. 2, Figs. 1-6.

Icriodus eslaensis Adrichem Boogaert, 1967,

PI. 1, Figs. 9-12; Norris and Uyeno, 1972,

PL 3. Fig. 9; Huddle, 1981, p. B22, PL 4,

Figs. 1-29 [see further synonymy].

Remarks. — Segminiscaphate elements

assigned to Icriodus brevis are characterized

by an extension of the middle row of denti¬

cles posteriorly beyond the lateral rows. The

denticles of this extension stand at approx¬

imately the same height as the other denticles

on the platform. Some specimens in the

present collections have a longitudinal axis

that is apparently more curved than that of

the type material (Fig. 12 P-R) but are

similar in other respects. See Klapper, in

Ziegler (1975, p. 89) for further discussion of

this species.

Material. — 5 specimens.

86

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

Occurrence. — Beechwood Member, North

Vernon Limestone.

Icriodus latericrescens latericrescens

Branson and Mehl, 1938

Fig. 8 V-AD

Icriodus latericrescens Branson and Mehl,

1938, p. 164-165, PI. 26, Figs. 30-32, 34,

35 (only).

Icriodus latericrescens latericrescens

Branson and Mehl. Klapper and Ziegler,

1967, p. 74-75, PI. 10, Figs. 4-9, PI. 11,

Figs. 1-5 [see further synonymy]; Huddle,

1981, p. B22-B23, PI. 5, Figs. 1-6; Uyeno,

in Uyeno, Telford, and Sanford, 1982, p.

32, PI. 4, Figs. 27-30 [see further

synonymy].

Remarks. — This subspecies includes a

scaphate pectiniform element, the diagnostic

characteristics of which were given by

Klapper and Ziegler (1967, p. 75). It is

distinguished from the comparable element

of I. 1. robustus in that the main process

tends to be slightly bowed with a more or less

concave inner side and convex outer side.

In /. /. robustus, the main process is

generally straighter with a straight to convex

inner side and convex outer side. The

denticulation of the main process in the

nominal subspecies consists of three longi¬

tudinal rows. The lateral rows are composed

of discrete, round nodes, whereas the middle

row nodes vary from subround to elongate

to an irregular, discontinuous ridge. In I. 1.

robustus, the middle row nodes tend to be

more nearly round, although in some speci¬

mens they are slightly elongate longitudin¬

ally. The lateral row nodes of I. 1. robustus

are generally round but tend to be more

robust than those of the nominal subspecies.

In some specimens, they appear crowded to¬

gether, commonly becoming somewhat lat¬

erally elongate. In some large specimens of

both subspecies, the middle row denticles

may be much reduced or absent, in which

case the distinction between the two sub¬

species is more difficult and must be based

on the shape of the main process and the

lateral row nodes.

Material. — 1 5 1 specimens .

Occurrence. —Beechwood and upper part

of the Silver Creek Members of the North

Vernon Limestone.

Icriodus latericrescens robustus Orr, 1971

Fig. 8 M-U

Icriodus latericrescens robustus Orr, 1971,

p. 37-38, PI. 2, Figs. 14-17 [see further

synonymy]; Uyeno, in Uyeno, Telford

and Sanford, 1982, p. 32, PI. 4, Figs. 1-6,

8-15, 19-22, 25, 26 31-38 (I elements) [see

further synonymy].

Remarks — For diagnosis and description

see Orr (1971, p. 37-38) and remarks for

Icriodus l. latericrescens herein. Some of the

specimens from the Brevispirifer gregarius

Zone from the Falls of the Ohio (FOS) and

Oak and Vine (OVS) localities have middle

row denticles that are longitudinally elongate

(e.g., Fig. 8 T). Although this feature is most

characteristic of I. 1. latericrescens, other

features of these specimens are typical of /. /.

robustus, and they are assigned to the latter

subspecies. One specimen, which is complete

except for the anterior tip, is typical of I. 1.

robustus but occurs in the highest sample of

the Beechwood Member from the Sellers-

burg Stone Company Quarry (SSQ-2). Other

latericrescid Icriodus from this sample

belong to I. 1. latericrescens.

Material. — 530 specimens.

Occurrence. — Brevispirifer gregarius

Zone, fenestrate bryozoan-brachiopod zone,

Paraspirifer acuminatus Zone of the

Jeffersonville Limestone and ?Beechwood

Member of the North Vernon Limestone.

Icriodus retrodepressus Bultynck, 1970

Fig. 9 A-F

Icriodus retrodepressus Bultynck, 1970, p.

110-111, PI. 30, Figs. 1-6; Ziegler, in

Ziegler, 1975, p. 143-144, Icriodus— PI. 8,

Figs. 4, 5.

Icriodus nodosus (Huddle). Schumacher,

1971, p. 93-95, PI. 9, Figs. 4-6 (only).

Icriodus corniger retrodepressus Bultynck.

Weddige, 1977, p. 290-291, PI. 1, Figs. 10,

11, ? 1 2.

1983]

Klug — Conodonts and Biostratigraphy

87

Icriodus aff. I. retrodepressus Bultynck.

Uyeno, in Uyeno, Telford and Sanford,

1982, p. 33, PI. 3, Figs. 16-18, 25-27

(only).

Remarks. — Icriodus retrodepressus is

characterized by a segminiscaphate element

with reduced or absent middle row denticles

in the posterior part of the main process

resulting in a distinct depression immediately

anterior to the posteriormost middle row

denticle. For further remarks and diagnosis

see Bultynck (1970) and Ziegler, in Ziegler

(1975). Uyeno, in Uyeno, Telford, and

Sanford (1982), reported specimens of

Icriodus with a posterior depression of the

middle row denticles. He referred to these

specimens as /. aff. I. retrodepressus and

distinguished his material from I. retro¬

depressus sensu stricto by the more uniform

longitudinal spacing of the lateral row nodes

in the latter species. According to Klapper

and Barrick (MS), some specimens of /.

retrodepressus from the Couvinian Eau

Noire sequence above and below the type

stratum show greater longitudinal spacing of

the lateral row denticles anteriorly than

posteriorly. Specimens in the present

collection may also show this feature and are

considered within the range of variation of /.

retrodepressus. See also I. sp. A, herein, for

the distinction from I. retrodepressus.

Material. -—46 specimens, (mature forms

only.)

Occurrence. — North Vernon Limestone

(all members). For further discussion of

occurrence, see section on Biostratigraphy.

Icriodus n. sp. E. ofWeddige, 1977

Fig. 9 G-I, cf. J-L

Icriodus n. sp. E Weddige, 1977, p. 299-300,

PI. 2, Figs. 23-25 [see further synonymy].

Remarks. — For diagnosis and remarks,

see Weddige (1977). See also remarks for

Icriodus sp. A, herein, for comparison of I.

n. sp. E and I. retrodepressus.

Material. — 280 specimens (mature forms

only).

Occurrence. — Upper part of the Brevis-

pirifer gregarius Zone of the Jeffersonville

Limestone and all members of the North

Vernon Limestone.

Icriodus sp. A

Fig. 9cf. M-O, S-X

Icriodus nodosus (Huddle). Orr, 1964b, p.

77-78, PI. 2, Fig. 16?, 24-26; Orr, 1971, p.

38-39, PI. 2, Figs. 20-23; Schumacher,

1971, p. 93-95, PI. 9, Figs. 1-3, 7-9?,

10-13, 15, 16 (only).

Icriodus sp. aff. I. retrodepressus Bultynck.

Klapper and Johnson, 1980, p. 448, PI. 3,

Figs. 19-21, 22?, 23?

Icriodus aff. I. retrodepressus Bultynck.

Uyeno, in Uyeno, Telford, and Sanford,

1982, p. 33, PI. 3, Figs. 19?, 23.

Remarks. — This species is to be described

and named by Klapper and Barrick (MS). In

upper view, the segminiscaphate element of

this species is similar to that of I. n. sp. E of

Weddige (1977), and I. retrodepressus. I. sp.

A includes two morphotypes; one has a

posterior depression of the middle row

denticles as in I. retrodepressus; the other

lacks such a depression and is similar to I. n.

sp. E. I. sp. A, however, possesses a broader

basal cavity posteriorly than either I. n. sp. E

or I. retrodepressus. In the present collec¬

tions, specimens considered intermediate

between the three species have also been

recognized. In addition, specimens have

been recovered that have lateral row denti¬

cles that are rounder than is apparently

typical of the above-mentioned species.

These forms may also have two or three

more or less well-developed middle row

denticles posterior to the lateral rows, as

opposed to the more typical, single, large,

triangular denticle of the other forms. In

other respects, these specimens are compar¬

able to the three species discussed above (see

Fig. 9 J-O). The rounder lateral row denti¬

cles and the two to three posterior middle

row denticles are generally best developed in

the smaller, possibly juvenile forms. If these

are juvenile, it is often difficult or impossible

to determine with which of the three mature

forms they are associated. Faunas made up

entirely of these smaller forms are common

88

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

in the study material and have a stratigraphic

range greater than that of the larger

specimens. For the distribution of these

“juvenile” forms relative to that of the

mature forms, refer to Figs. 6 and 7.

Material. — 347 specimens (mature forms

only).

Occurrence. — Upper part of the Brevis-

pirifer gregarius Zone of the Jeffersonville

Limestone and all members of the North

Vernon Limestone.

Icriodus1. sp. B

Fig. 12S-X

Remarks. — The specimens treated here in

open nomenclature include scaphate

elements with a narrow anterior primary

process consisting of a single row of

denticles that are round to laterally

compressed in upper view. The denticles are

numerous, subequal, discrete to fused, and

bluntly pointed to round in lateral view. An

outer lateral process extends at right angles

to or is directed slightly posteriorly to the

posterior end of the anterior primary

process. The outer lateral process may have

a narrow ridge running along its upper

surface or may be weakly denticulate. A less

well-developed inner lateral process or spur

is also present. In lower view, the basal

cavity is broadly flared posteriorly, becom¬

ing narrower anteriorly and pinching out

slightly posterior of the anterior tip of the

element.

The specimens considered herein are mor¬

phologically intermediate between Icriodus

and Pelekysgnathus. Unfortunately, few

specimens were recovered and all are

fragmentary. A tentative assignment to

Icriodus is based on the following con¬

siderations: (1) specimens of Icriodus1. sp. B

are notably similar in lower view to Icriodus

latericrescens latericrescens with which this

form co-occurs; (2) no specimens definitely

assignable to Pelekysgnathus were recovered

from any of the samples in this study; (3)

Bultynck (1970, p. 111-112) reported a

similar situation for Icriodus regular i-

crescens. In his faunas, he found specimens

with well-developed lateral rows, with

reduced lateral rows, and with only the

middle row of nodes. In the present study,

however, no forms were found showing any

development of lateral rows of nodes. In

addition, the denticulation of the anterior

primary process of Icriodus1 sp. B is unlike

that of Icriodus I. latericrescens in both the

shape and number of denticles. Definitive

treatment of the form in question must await

recovery of larger and better preserved

faunas.

Material. — 7 specimens.

Occurrence. — Beechwood Member of the

North Vernon Limestone.

Polygnathus cf . P. angusticostatus

Wittekindt, 1966

Fig. 10A-C, G-I

cf. Polygnathus angusticostatus Wittekindt,

1966, p.631, PI. 1, Figs. 15-18.

Remarks. — The specimens under consid¬

eration are all fragmentary carminiplanate

elements, which are missing part or all of the

free blade. Although platform development

and ornamentation is apparently not as well

developed as in the type specimen of P.

angusticostatus, the present material appears

closer to that species than to the similar and

probably intergradational P. angustipen-

natus. Smaller specimens (see Fig. 10 A-C)

tend to have more restricted platforms and

appear to be closer to P. angustipennatus.

For more detailed discussions on the similar¬

ities and differences between P. angusti¬

costatus and P. angustipennatus the reader is

referred to the papers by Klapper (1971, p.

65), Weddige (1977, p. 307), and Sparling

(1981, p. 309-312).

Material. — 21 specimens.

Occurrence. — Brevispirifer gregarius and

Paraspirifer acuminatus Zones of the Jeffer¬

sonville Limestone and the Speeds and basal

1983]

King — Conodonts and Biostratigraphy

89

Silver Creek Members of the North Vernon

Limestone.

Polygnathus? caelatus Bryant, 1921

Fig. 10S-U, cf. V, W

Polygnathus caelatus Bryant, 1921, p. 27,

PI. 13, Figs. 1-6, 8, 12, 13 (not Figs. 7,

9-1 1 = Polygnathus collieri Huddle,

1981).

not Polygnathus caelata Bryant. Bischoff

and Ziegler, 1957, p. 86, PI. 18, Figs. 18,

19.

Polygnathus beckmanni Bischoff and

Ziegler, 1957, p. 86, PI. 15, Fig. 25;

Ziegler and Klapper, in Ziegler, Klapper,

and Johnson, 1976, PI. 4, Figs. 22, 23;

Bultynck and Hollard, 1981, p. 42, PI. 8,

Fig. 9.

Polygnathus aff. P. beckmanni Bischoff and

Ziegler, Bultynck and Hollard, 1981, p.

42, PI. 8, Fig. 1.

Polygnathus? caelatus Bryant. Huddle,

1981, p. B27, PI. 11, Figs. 15-18, PI. 12,

Figs. 12-18, 22-24 (only), PI. 13, Figs. 1-6,

12, 13.

Remarks.— Huddle (1981, p. B27)

considered Bryant’s original concept of

Polygnathus caelatus to include two species.

Specimens with an elongate, asymmetrical

platform, ornamented by irregular ridges,

and with little or no free blade, were referred

to Polygnathus? caelatus, whereas the re¬

mainder of Bryant’s specimens, character¬

ized by a large free blade and smaller basal

pit, were included in Polygnathus collieri.

Huddle (1981, PI. 13, Figs. 1-6, 12, 13) re¬

illustrated several of Bryant’s original speci¬

mens and designated the specimen illustrated

on PL 13, Figs. 6, 12, 13 (= Bryant, 1921,

PL 13, Fig. 2) to be lectotype of P. ? caelatus.

In addition, he considered P. beckmanni and

P. ? variabilis, both of Bischoff and Ziegler,

as junior synonyms of P. ? caelatus.

Bischoff and Ziegler (1957, PL 15, Fig. 25

a,b) illustrated only an upper and lateral

view of the holotype of P. beckmanni. P. ?

caelatus shows considerable variation in

nature and strength of ornamentation and in

shape of the platform in upper and lateral

views. In this respect, the holotype of P.

beckmanni, as well as the material in the

present study, appears to be within this

range of variation and assignment to P. ?

caelatus sensu Huddle, 1981, is adopted

herein.

Material. — 1 nearly complete and 10 frag¬

mentary specimens.

Occurrence. — Beechwood and upper part

of the Silver Creek Members of the North

Vernon Limestone.

Polygnathus costatus costatus Klapper, 197 1

Fig. 10D-F, J-L

Polygnathus sp. nov. B Philip, 1967, p.

158-159, PL 2, Figs. 4, ?5, 8.

Polygnathus costatus costatus Klapper,

1971, p. 63, PL 1, Figs. 30-36, PL 2, Figs.

1-7; Klapper, in Ziegler, 1973, p. 347-348,

Polygnathus — PI . 1, Fig. 3 [see further

synonymy]; Bultynck and Hollard, 1981,

p. 42, PL 3, Figs. 7, 8; Klapper, in

Johnson, Klapper, and Trojan, 1980, PL

4, Figs. 14, 15, 17; Sparling, 1981, p.

312-313, PL 1, Figs. 25-27 [P element] [see

further synonymy]; Uyeno, in Uyeno,

Telford, and Sanford, 1982, p. 28-29, PL

1, Figs. 11-13, 24, 25 [Pa element] [see

further synonymy].

Remarks. —The specimens considered

herein agree well with typical specimens of

Polygnathus costatus costatus. For diagnosis

and relations of P. c. costatus, see Klapper

(1971, p. 63) and Klapper, in Ziegler (1973,

p. 347-348).

Material. — 79 specimens.

Occurrence. — Specimens confidently

identified as P. c. costatus have been

recovered, in this study, only from the Para-

spirifer acuminatus Zone of the Jefferson¬

ville Limestone at the Sellersburg Stone

Company Quarry (SSQ) and from the Berry

Materials Corporation Quarry (BMQ).

90

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I,

Polygnathus linguiformis klapperi

Clausen, Leuteritz, and Ziegler, 1979

Fig. 11 R-T

Polygnathus linguiformis linguiformis

Hinde, epsilon morphotype Ziegler and

Klapper, in Ziegler, Klapper, and

Johnson, 1976, p. 123-124, PL 4, Figs. 3,

12, 14, 24; Klapper, in Ziegler, 1977, p.

465, Polygnathus — PI. 10, Figs. 5, 9, 10

[see further synonymy]; Bultynck and

Hollard, 1981, p. 44, PI. 7, Figs. 2-7, 9.

Polygnathus linguiformis klapperi Clausen,

Leuteritz, and Ziegler, 1979, p. 32, PI. 1,

Figs. 7, 8.

Remarks. — Polygnathus linguiformis

klapperi has a carminiplanate element with a

flatter outer platform margin than that of

the nominal subspecies. It can also be

distinguished from P. 1. weddigei by the

poorer development of the tongue in the

carminiplanate element of the latter

subspecies. For a complete diagnosis and

remarks, see Clausen, Leuteritz, and Ziegler

(1979) or Ziegler and Klapper, in Ziegler,

Klapper, and Johnson (1976).

Material.— 9 specimens.

Occurrence. — Basal Beechwood Member

of North Vernon Limestone.

Polygnathus linguiformis linguiformis

Hinde, 1879

Fig. 1 1 O-Q

Polygnathus linguiformis Hinde, 1879, p.

367, PI. 17, Fig. 15.

Polygnathus linguiformis linguiformis

Hinde gamma forma nova Bultynck,

1970, p. 126-127, PI. 11, Figs. 1-6, PL 12,

Figs. 1-6.

Polygnathus linguiformis linguiformis

Hinde. Weddige, 1977, p. 315-316, PL 5,

Figs. 80-82; Uyeno, in Uyeno, Telford,

and Sanford, 1982, p. 29-30, PL 2, Figs.

26-31 (Pa elements) [see further

synonymy].

Polygnathus linguiformis linguiformis

Hinde gamma morphotype Bultynck.

Klapper, in Ziegler, 1977, p. 463-464, Pol¬

ygnathus — PL 10, Fig. 2, Polygnathus—

PL 11, Figs. 4, 7 (P element) [see further

synonymy]; Bultynck and Hollard, 1981,

p. 43-44, PL 7, Fig. 1.

Remarks. — Polygnathus linguiformis

linguiformis has been divided into several

morphotypes (Bultynck, 1970; Ziegler and

Klapper, in Ziegler, Klapper, and Johnson,

1976, p. 122-124; Klapper, in Johnson,

Klapper, and Trojan, 1980, p. 102; Huddle,

1981, p. B30-B31). Most of these have since

been treated as subspecies of Polygnathus

linguiformis (Weddige, 1977, p. 312-316;

Clausen, Leuteritz, and Ziegler, 1979, p.

30-33). Weddige (1977, p. 312-316) con¬

sidered the gamma morphotype synonymous

with the nominal subspecies and this opinion

is followed in the present paper. Detailed

diagnoses and descriptions of this form can

be found in Weddige (1977); Klapper in

Ziegler (1977), and Bultynck (1970).

Material. — 943 specimens.

Occurrence. — Fenestrate bryozoan-brach-

iopod zone and Paraspirifer acuminatus

Zone of the Jeffersonville Limestone and all

members of the North Vernon Limestone.

Polygnathus linguiformis weddigei Clausen

Leuteritz, and Ziegler, 1979

Fig. 1 1 L-N

Polygnathus linguiformis linguiformis

Hinde. Wittekindt, 1966, p. 635-636, PL

2, Fig. 11.

Polygnathus linguiformis linguiformis

Hinde, delta morphotype, Ziegler and

Klapper, in Ziegler, Klapper, and

Johnson, 1976, p. 123, PL 4, Figs. 4-8;

Klapper, in Ziegler, 1977, p. 464-465,

Polygnathus— PL 10, Figs. 1, 3; Bultynck

and Hollard, 1981, p. 44, PL 7, Fig. 8.

Polygnathus linguiformis Hinde, delta

morphotype, Ziegler and Klapper.

Orchard, 1978, p. 944, PL 110, Figs. ?9,

?10,21,23,?28, ?30.

Polygnathus linguiformis weddigei Clausen,

Leuteritz, and Ziegler, 1979, p. 30-32, PL

1, Figs. 4, 9-12.

not Polygnathus linguiformis linguiformis

Hinde, form delta Huddle, 1981, p.

B30-B31, PL 15, Figs. 1-8.

(Text continues on page 108)

1983]

King — Conodonts and Biostratigraphy

91

0 5 10 20 miles c| SAMPLE LOCALITIES

iiilli-JLXi 1

0 5 10 20 30 kilometers ” COUNTY BOUNDARIES

llinl I I I

Fig. 1 . Locality map for measured sections (see Appendix of Localities for precise locations).

92

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I

Stratigraphy and conodont sample locations (numbered black rectangles) in the Muscatatuck Group, south-central Indiana and north-central Kentucky.

1983]

Klug—Conodonts and Biostratigraphy

93

ORR

(1964b)

ORR

(1971)

THIS

ST U DY

tcrio dus

/ a tericrescens

tatericrescens

ZONE

tcriodus

angustus

ZONE

/ criodus

tatericrescens

n subsp

ZONE

Pol y gnat has

v a r cus

ZONE

LOWER

Po lygnathus

v a rcu s

SUBZONE

tcriodus

tatericrescens

tatericrescens

ZONE

tcriodus

angustus

ZONE

— 7 -

Polygnathus

p seu dofot iatus

ZONE

Polygnathus

H , , . //

webbi

ZONE

“ - - ? -

i c r 10 Jus

angustus

angustus

ZONE

t criodus

tatericrescens

r opus f us

ZONE

tcriodus

tote ricr escens

robustus

ZONE

Fig. 3. Comparison of the conodont zonations of Orr (1964b), Orr (1971), and that of the present study.

94

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I

■ udddo /if s/ujj oj.;n 6 w / s nq / ou 6 A/ o <-/

■ / <? b/pp 9 m s/wj o//n6u// s nq / oub A/ o d

• suaosdj ou 9i Dj / snpouo/

• s / su 9 j olu / / s nq/DubA/o d

snnbf/qo sn/snbuo snpouo/

V ds snpouo/

snss9Jdapojj9J snpo/jo/

sn/Di/ojopnosd snq/ou6A/od

sn/o/soo o snq/oubA/Od

s/LUJOj/nbu// / snq/oubA/Od

sn/snbuo d snpouo/

U 261 ‘aBippaM) 3 ds u snpouo/

sn/o/sooi/snbuo d P snq/oubA/Od — -

sn/snqoj su 90 S9 j o/ j 9 / d / snpouo/

snx9 Auoo/q j p sn/uo po j 900 / 90 j

$ 3 2

^ O, O,

^ C;

O

C;

<0

^ ^ =3

^ t s

S -S 4

i 3 ?

Ranges of important conodont taxa in the Muscatatuck Group of south-central Indiana and north-central Kentucky.

1983]

Klug—Conodonts and Biostratigraphy

95

Biostratigraphic correlations of Middle Devonian conodont zones in south-central Indiana, north-central Kentucky and surrounding areas.

96

Wisconsin Academy of Sciences, Arts and Letters [Vol. 71, Part I

Fig. 6. Distribution of conodonts in the Sellersburg Stone Company Quarry (SSQ), Old Gheen’s Quarry (OGQ) and

Oak and Vine Streets (OVS) sections. For discussion of Icriodus “juveniles,” refer to remarks on Icriodus sp. A.

Sample numbers preceded by an asterisk (*) indicate partial picking.

1983]

King — Conodonts and Biostratigraphy

97

Fig. 7. Distribution of conodonts in the Berry Materials Corporation Quarry (BMQ), Type Deputy Quarry (TDQ),

Harrison Avenue (HAS), Falls of the Ohio (FOS) and Beechwood Reference (BRS) sections. For discussion of Icriodus

“juveniles,” refer to remarks on Icriodus sp. A. Sample numbers preceded by an asterisk (*) indicate partial picking.

98

Wisconsin Academy of Sciences, Arts and Letters

[Vol. 71, Part I,

Fig. 8. Conodonts from the Muscatatuck Group of south-central Indiana and

north-central Kentucky. All figures approximately X40.

A-F Icriodus angustus angustus Stewart and Sweet, 1956. A, B, C, upper,

lower and lateral views of SUI 49331, TDQ-5. D, E. F, upper, lower,

and lateral views of SUI 49332, BMQ-4.

G-L Icriodus angustus obliquus n. subsp. G, H, I, upper, lower, and lateral

views of paratype SUI 49333, TDQ-5. J, K, L, upper, lower, and lateral

views of holotype SUI 49334, SSQ-14.

M-U Icriodus latericrescens robustus Orr, 1971. M, N, O, lower, upper, and

lateral views of SUI 49335, FOS-6. P, Q, R, upper, lower and lateral

views of SUI 49336, OVS-6. S, T, U, lower, upper, and lateral views of

SUI 49337, OVS-6.

V-AD Icriodus latericrescens latericrescens Branson and Mehl, 1938. V, W, X,

lower, upper, and lateral views of SUI 49338, BRS-2, Y, Z, AA, upper,

lower, and lateral views of SUI 49339, OGQ-2. AB, AC, AD, lower,

upper, and lateral views of SUI 49340, BRS-2.

1983]

Klug—Conodonts and Biostratigraphy

99

100

Wisconsin Academy of Sciences , Arts and Letters

[Vol. 71, Part I,

Fig. 9 Conodonts from the Muscatatuck Group of south-central Indiana and

north-central Kentucky. All figures approximately X40.

A-F Icriodus retrodepressus Bultynck, 1970. A, B, C, upper, lower, and

lateral views of SUI 49341, BMQ-4. D, E, F, upper, lower, and lateral

views of SUI 49342, BMQ-4.

G-I Icriodus n. sp. E of Weddige, 1977. Upper, lower, and lateral views of

SUI 49343, BMQ-2.

J-L Icriodus cl. /. n. sp. E of Weddige, 1977. Upper, lower, and lateral views

of SUI 49344, OVS-6.

M-O Icriodus cf. /. sp. A. Upper, lower, and lateral views of SUI 49345,

FOS-5.

P-R Icriodus n. sp. E of Weddige, 1977 — Icriodus sp. A. Upper, lower, and

lateral views of SUI 49346, BMQ-4.

S-X Icriodus sp. A. S, T, U, upper, lower, and lateral views of SUI 49347,

TDQ-5. V, W, X, upper, lower, and lateral views of SUI 49348, BMQ-4.

1983]

Kiug—Conodonts and Biostratigraphy

101

102

Wisconsin Academy of Sciences, Arts and Letters

[Vol. 71, Part I,

Fig. 10. Conodonts from the Muscatatuck Group of south-central Indiana and

north-central Kentucky. All figures approximately X40.

A-C Polygnathus cf. P. angusticostatus Wittekindt, 1966. Upper, lower, and

lateral views of SUI 49349, BMQ-1 . Specimen missing most of free

blade.

D-F Polygnathus costatus costatus Klapper, 1971. Upper, lower, and lateral

views of SUI 49350, SSQ-17.

G-I Polygnathus cf. P. angusticostatus Wittekindt, 1966. Upper, lower, and

lateral views of SUI 49351, SSQ-15. Specimen missing free blade.

J-L Polygnathus costatus costatus Klapper, 1971. Upper, lower, and lateral

views of SUI 49352, SSQ-18.

M-R Polygnathus pseudofoliatus Wittekindt, 1966. M, N, O, upper, lower,

and laterial views of SUI 49353, SSQ-15. P, Q, R, upper, lower, and

lateral views of SUI 49354, SSQ-15. Specimen missing most of free

blade.

S-U Polygnathus? caelatus Bryant, 1921. Upper, lower, and lateral views of

SUI 49355, OGQ-1 . Specimen missing anterior tip.

V,W Polygnathus? cf. P. ? caelatus Bryant, 1921. Upper and lower views of

SUI 49356, HAS-3. Fragmentary specimen missing anterior portion

and posterior tip.

1983]

Klug—Conodonts and Biostratigraphy

103

104

Wisconsin Academy of Sciences , Arts and Letters

[Vol. 71, Part I,

Fig. 1 1 Conodonts from the Muscatatuck Group of South-central Indiana and

north-central Kentucky. All figures approximately X40.

A Bipennate element. Inner lateral view of fragmentary specimen, SUI

49357, FOS-10.

B-E Dolabrate elements. B, inner lateral view of SUI 49358, OGQ-1 . C, D,

E, inner lateral, outer lateral, and lower views of SUI 49359, HAS-5.

F-H Angulate element. Inner lateral, outer lateral, and lower views of SUI

49360, TDQ-5.

I-K Polygnathus timorensis Klapper, Philip, and Jackson, 1970. Upper,

lower, and lateral views of SUI 49361 , OGQ-1 .

L-N Polygnathus linguiformis weddigei Clausen, Leuteritz, and Ziegler,

1979. Upper, lower, and lateral views of SUI 49362, BRS-2.

O-Q Polygnathus linguiformis linguiformis Hinde, 1879. Upper, lower, and

lateral views of SUI 49363, SSQ-4.

R-T Polygnathus linguiformis klapperi Clausen, Leuteritz, and Ziegler,

1979. Lower, upper, and lateral views of SUI 49364, BMQ-2.

1983]

Klug—Conodonts and Biostratigraphy

105

106

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

1983]

Klug — Conod onts and Biostratigraphy

107

Fig. 12 Conodonts from the Muscatatuck Group of south-central Indiana and

north-central Kentucky. All figures approximately X40.

A-D Coniform elements. A, SUI 49365, OGQ-1; B, SUI 49366, TDQ-5; C,

SUI 49367, BRS-2; D, SUI 49368, SSQ-3.

E,F Genus and species indeterminate. Upper and lateral views of SUI 49369,

SSQ-4.

G Belodella cf. B. resima (Philip, 1965). Lateral view of SUI 49370.

OVS-3.

H-K Coelocerodontus cf. C. biconvexus Bultynck, 1970. H, posterolateral

view of SUI 49371, SSQ-3; I, J, K, inner lateral, outer lateral, and pos¬

terolateral view of SUI 49372, TDQ-5.

L Belodella cf. B. resima (Philip, 1965). Lateral view of SUI 49373, SSQ-4.

M-O Coelocerodontus cf. C. biconvexus Bultynck, 1970. M, N, posterior and

lateral views of SUI 49374, SSQ-3. O, lateral view of SUI 49375,

OGQ-1.

P-R Icriodus brevis Stauffer, 1940. Upper, lower, and lateral views of SUI

49376, OGQ-1.

S-X Icriodus? sp. B. S, T, U, upper, lower, and lateral views of SUI 49377,

SSQ-2. V, W, X, upper, lower, and lateral views of SUI 49378, GHE-2.

108

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

Remarks . —Polygnathus linguiformis

weddigei is distinguished from the nominal

subspecies by the flatter platform, the poorly

developed tongue, and a carina that extends

to, or nearly to, the posterior tip in the

former. For a detailed diagnosis, see

Clausen, Leuteritz, and Ziegler (1979) or

Ziegler and Klapper, in Ziegler, Klapper,

and Johnson (1976). P. 1. weddigei is a rare

form in the present faunas and was re¬

covered from only two samples.

Material.— 5 specimens.

Occurrence. — Basal part of the Beech-

wood Member of the North Vernon Lime¬

stone.

Polygnathus pseudof oliatus

Wittekindt, 1966

Fig. 10M-R

Polygnathus n. sp. Ziegler. Flajs, 1966, p.

232-233, PI. 23, Figs. 5-7.

Polygnathus pseudofoliata Wittekindt,

1966, p. 637-638, PI. 2, Figs. 20-23 [non

Fig. 19 = P. eiflius].

Polygnathus pseudof oliatus Wittekindt.

Klapper, 1971, p. 63-64, PI. 2, Figs. 8-13

[see further synomymy]; Klapper, in

Ziegler, 1973, p. 375-376, Polygnathus —

PI. 1, Figs. 8, 9 [see further synonymy];

Ziegler and Klapper, in Ziegler, Klapper,

and Johnson, 1976, PI. 3, Figs. 2, 3, 12,

13; Weddige, 1977, p. 317-318, PI. 4, Figs.

68-70 [see further synonymy]; Bultynck

and Hollard, 1981, p. 45, PL 5, Figs. 13,

14.

Polygnathus cf. P. pseudof oliatus Witte¬

kindt. Pedder, Jackson, and Ellenor,

1970, PI. 15, Fig. 26.

Remarks. — For diagnosis and description

of Polygnathus pseudof oliatus, see Witte¬

kindt (1966, p. 637-638). For amended diag¬

nosis see Klapper, in Ziegler (1973, p. 375).

P. pseudof oliatus includes a carminiplanate

element that may have a platform outline

similar to that of P. c. costatus. In P.

pseudof oliatus, however, the platform tends

to be shallower with shallower adcarinal

troughs, especially in the posterior part of

the platform. The ornamentation of P.

pseudof oliatus is less strongly developed

than in P. c. costatus and consists of

transverse rows of nodes to weakly devel¬

oped to broken transverse ridges. Rare speci¬

mens in the present study have unusually

elongate platforms (see Fig. 10, M-O) but

otherwise agree with specimens considered

herein as P. pseudof oliatus.

Material.— 44 specimens.

Occurrence. —North Vernon Limestone

(all members).

Polygnathus timorensis

Klapper, Philip, and Jackson, 1970

Fig. 11 I-K

Polygnathus varca Stauffer. Bischoff and

Ziegler, 1957, PI. 18, Fig. 34 (only).

Polygnathus varcus Stauffer. Kirchgasser,

1970, p. 351-352, PI. 66, Figs. 9-11; Orr,

1971, p. 53-54, PI. 5, Figs. 4-8.

Polygnathus cf. decorosa Stauffer.

Matthews, 1970, PI. 1, Fig. 10.

Polygnathus timorensis Klapper, Philip, and

Jackson, 1970, p. 655-656, PI. 1, Figs. 1-3,

7-10; Klapper, in Ziegler, 1973, p.

385-386, Polygnathus — PI. 2, Fig. 3;

Ziegler and Klapper, in Ziegler, Klapper,

and Johnson, 1976, p. 125, PI. 2, Figs.

27-32; Orchard, 1978, p. 949, PI. 112,

Figs. 13-15, 17, 18, 25, 28, 32, 35; Bultynck

and Hollard, 1981, p. 45, PI. 6, Figs. 8-14;

Uyeno, in Uyeno, Telford, and Sanford,

1982, p. 30, PI. 2, Figs. 7, 8, 13-16 (Pa

elements).

Polygnathus rhenanus marijae Huddle,

1981, p. B32, PI. 17, Figs. 10-12, 19-27

(only), PI. 18, Figs. 1, 2, 5 (only).

Remarks. — For diagnosis and remarks,

see Klapper, Philip, and Jackson (1970) and

Ziegler and Klapper, in Ziegler, Klapper,

and Johnson (1976).

Material. — 1 6 1 specimens.

Occurrence. — Uppermost part of the

Silver Creek Member, and the Beechwood

Member of the North Vernon Limestone.

See section on Biostratigraphy for comments

on occurrence in the Silver Creek Member.

1983]

Klug— Conodonts and Biostratigraphy

109

Genus and species indeterminate

Fig. 12 E, F

Remarks. . Three, slightly asymmetrical,

nongeniculate coniform elements of uncer¬

tain affinities have been recovered from two

of the examined samples. These elements

have a broad, circular to elliptical basal

margin. The thin-walled base occupies the

lower three-fourths to four-fifths of the

specimen. The cusp is proclined, oval in

cross-section, and bluntly pointed apically.

A low, narrow keel runs along the anterior

margin from the apex to the basal margin;

otherwise, the elements are smooth. These

specimens bear some resemblance to Coelo -

cerodontus cf. C. biconvexus in the develop¬

ment of the deep, thin-walled base. Paucity

of material and restricted distribution,

however, obscure the relationship, if any,

with that species.

Material.— 3 specimens

Occurrence. — Beechwood Member, North

Vernon Limestone.

Coniform Elements

Fig. 12A-D

Remarks. — Proclined coniform elements

that are generally either compressed or

nearly circular in cross-section are common

to abundant in many of the examined sam¬

ples. Similar coniform elements have been

included in multielement reconstructions of

species of Icriodus (see, e.g., Klapper and

Philip, 1971, p. 446; Johnson and Klapper,

1981, p. 1242; Clark et al., 1981, p. W125;

Uyeno, in Uyeno, Telford, and Sanford,

1982, p. 32). The comparable distributions

of the segminiscaphate elements of Icriodus

and of the simple cones, in the present study,

support those reconstructions (refer to Figs.

6 and 7). No similar reconstructions are

attempted in this paper, however, because of

the diversity of the simple cones and of

species of Icriodus.

Material. - -Compressed: 1,955; circular:

978.

Occurrence. —Brevispirifer gregarius

Zone; fenestrate bryozoan-brachiopod zone;

Paraspirifer acuminatus Zone and Vernon

Fork Member of the Jeffersonville Lime¬

stone; Speeds, Silver Creek and Beechwood

Members and Deputy facies of the North

Vernon Limestone.

Ramiform and Angulate Elements

Fig. 1 1 A-H

Remarks. —Ramiform and angulate

elements are common constituents of many

of the conodont faunas examined. Preser¬

vation tends to be poor, however, with most

specimens being fragmentary. Whenever

possible, specimens were placed into the

various shape categories (alate, bipennate,

dolabrate, and angulate). Elements belong¬

ing to these shape categories have been

included in reconstruction of species of

Polygnathus (see, e.g., Klapper and Philip,

1971, p. 431-433; Sparling, 1981, p. 308-309;

Clark et al., 1981, p. W162-W164; Uyeno, in

Uyeno, Telford, and Sanford, 1982, PI. 2).

The comparable distribution of the carmini-

planate elements of Polygnathus and the

ramiform and angulate elements in the pres¬

ent study support these reconstructions.

Material. — Alate elements: 51; bipennate

elements: 367; dolabrate elements: 235;

angulate elements: 117.

Occurrence. —Brevispirifer gregarius

Zone; fenestrate bryozoan-brachiopod zone;

Paraspirifer acuminatus Zone and Vernon

Fork Member of the Jeffersonville Lime¬

stone; Speeds, Silver Creek and Beechwood

Members and Deputy facies of the North

Vernon Limestone.

Conclusions

Conodont faunas from the Middle

Devonian Muscatatuck Group of south-

central Indiana and north-central Kentucky

contain few species diagnostic of the

standard conodont zonation. Consequently,

a zonation consisting of three local zones

and one standard subzone has been adopted.

By means of this local zonal scheme, a corre¬

lation of the Middle Devonian strata of the

110

Wisconsin Academy of Sciences , Arts and Letters [Vol. 71, Part I,

study area and surrounding areas can be

established. A late Emsian to early Givetian

age is suggested for the Muscatatuck Group

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