Molluscan Systematics and Biostratigraphy: Lower Tertiary La Meseta Formation, Seymour Island, Antarctic Peninsula

206 Pages·017.436 MB·English

by  Jeffrey D. Stilwell, William J. Zinsmeister

Molluscan Systematics and Biostratigraphy
Lower Tertiary La Meseta Formation, Seymour Island, Antarctic Peninsula
Physical Sciences
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ANTARCTIC
Volume 55 RESEARCH
SERIES
Molluscan Systematics
and Biostratigraphy
Lower Tertiary La Meseta Formation,
Seymour Island, Antarctic Peninsula
Jeffrey D. Stilwell
William J. Zinsmeister
American Geophysical Union
Washington, D.C.
1992
ANTARCTIC
Volume 55 .RESEARCH
SERIES
Published under the aegis of the
Board of Associate Editors, Antarctic Research Series
David H. Elliot, Chairman
John B. Anderson, Steve Cairns,
Samuel C. Colbeck, Rodney M. Feldmann,
E. Imre Friedmann, Dennis E. Hayes,
Charles R. Stearns
Library of Congress Cataloging in Publication Data
Molluscan systematics and biostratigraphy : lower tertiary, La Meseta
formation, Seymour Island, Antarctic Peninsula 1 Jeffrey D.
Stilwell, William J. Zinsmeister, authors.
p. cm. - (Antarctic research series : v. 55)
Includes bibliographical references.
ISBN 0-87590-770-9
1. Mollusks, Fossil-Antarctic regionsseymour Island-
-Classification. 2. Paleontology, Stratigraphic. 3. Paleontology-
-Tertiary. 4. La Meseta Formation (Antarctic regons)
I. Stilwell, Jeffrey D. 11. Zinsmeister, William J. 111. Series.
QE801.M75 1991
564'.0998'9-dc20 91-44071
CIP
ISBN 0-87590-770-9
ISSN 0066-4634
Copyright 1992 by the American Geophysical Union
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March 15, 1992
Printed in the United States of America.
CONTENTS
The Antarctic Research Series: Statement of Objectives
Acknowledgments
Abstract
Introduction
Previous Investigations
Stratigraphy
Age of the La Meseta Formation
Biostratigraphy
Depositional Environments and Paleoecology
Paleoclimatology
Discussion of the Molluscan Fauna of the La Meseta Formation
Conclusions
Systematic Paleontology
Appendix 1
Fossil Localities and Descriptions of the La Meseta Formation,
Seymour Island, Antarctic Peninsula
Appendix 2
Section LM 86-1 Description
Appendix 3
Localities Used in the CHECKLIST I1 Program
References
The Antarctic Research Series:
STATEMENT OF OBJECTIVES
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of the series is partially supported by a grant from the National Science Foundation.
Board of Associate Editors
Antarctic Research Series
Revised 5113191
ACKNOWLEDGMENTS
Financial support for this investigation was provided through National Science Foundation (NSF)
grants DPP 7721585A01, 7920215A01, 823985A01, and 8416783A04 to William J. Zinsmeister.
Special and hearty thanks are extended to Louella Saul, Natural History Museum of Los Angeles
County, California, and Richard L. Squires, Department of Geological Sciences, California State
University, Northridge, who critically reviewed the manuscript and provided valuable suggestions.
We would also like to extend our appreciation to Mort Turner, Earth science program manager,
Division of Polar Programs, NSF, for his initial support of the field program during the late 1970s
and early 1980s, and to Anton Inderbitzen and Herman Zirnmerman, subsequent Earth science
program managers at the Division of Polar Programs, for their continued support of this work.
Special thanks are given to the following scientists for providing suggestions, insights, and aid in
acquiring data for this project: Michael Woodbume, Rosemary Aski, Marilyn Kooser, Peter
Sadler, and Judd Case, University of California, Riverside; Rodney Feldrnann, Kent State
University, Kent, Ohio; David Elliot, Institute of Polar Studies, Ohio State University, Columbus;
Daniel Blake, University of Illinois, Urbana; R. Ewan Fordyce. University of Otago, Dunedin,
New Zealand; Alan Beu and Phillip Maxwell, New Zealand Geological Survey, Lower Hutt, New
Zealand; Eduardo Olivero and Francisco Medina, Centro de Investigaciones en Recursos
Geol6gicos, Buenos Aires, Argentina; Daniel Frassinetti, Santiago, Chile; Char1es.R. Givens,
Nicholls State University, Thibodaux, Louisiana; Thomas Waller, Dan Chaney, and Warren Blow,
U.S. National Museum, Washington, D.C.; Norman Sohl, U.S. Geological Survey; and Miguel
Griffen, Purdue University, West Lafayette, Indiana. Luis Mario Paredes-Mejia, Purdue University,
provided both valuable lab and field assistance during the 1985 expedition. The writers are also
grateful to the many persons who collected and graciously gave up their mollusc specimens during
the many expeditions to Seymour Island. Jim Gardner, Giovanni Soto, and Matthew Stuve, Purdue
University, assisted in drafting the figures.
ABSTRACT
The La Meseta Formation of Seymour Island contains one of the most diverse, well-preserved
,early Tertiary invertebrate faunas from the southern hemisphere. During the course of this study,
which was based on five field seasons on Seymour Island, 170 species of molluscs were collected
from the nearshore sandstones and siltstones of the La Meseta Formation. The La Meseta
Formation has been divided into seven lithologic units (Telml-Telm7). Faunal diversity is low in
unit Telml but steadily increases up-section to a peak in the shell lenses of Telm5 followed by a
sharp drop in diversity near the contact of Telm5 and Telm6. This marked decline in diversity is
believed to be a reflection either of local facies change or of the onset of rapidly decreasing sea
surface temperatures in the southern oceans at the close of the Eocene. A fourfold biostratigraphic
zonation (Antarctodaminella ellioti, Antarctodanvinella nordenskjijldi, Struthiolarella steinmanni,
and Perissodonta laevis zones) for the La Meseta Formation is proposed based on changes within
the gastropod family Struthiolariidae. This biostratigraphic zonation for the Eocene of the Antarctic
Peninsula is considered to be provisional. The sediments of the La Meseta Formation are believed
to have been deposited in a barrier island to nearshore tidal and wave-dominated environment. The
faunas are typified by parautochthonous and autochthonous monotypic and polytypic assemblages
in which molluscs dominate. Although Seymour Island is located at a relatively high southern
latitude (a's), the presence of a number of warm-water taxa suggests that sea temperatures during
the Eocene may have been as high as warm-temperate. The molluscan fauna is found to be highly
endemic with a strong paleoaustral component. The fauna displays marked heterochroneity; many
taxa make their first appearance in the fossil record in the La Meseta Formation. The endemic
nature and diversity of the La Meseta faunas as compared with other southern hemisphere faunas
indicate that the Weddellian Province, which extended from Australasia to southern South America
during the Late Cretaceous, had been greatly reduced by the late Eocene. The 170 species of
molluscs recorded from the La Meseta Formation are based on more than 10,370 specimens of
molluscs collected from 196 localities. Of the 123 new species that are described, 24 are bivalves
and 98 are gastropods. In addition, one new species of scaphopod, 10 new genera, and three new
subgenera are proposed.
Frontispiece. View to the north of locality 453, a shell lens within the La Meseta Formation of
Seymour Island, Antarctic Peninsula. Note the abundance of molluscan shell material at this
locality. The robust bivalve Cucullaea raea Zinsmeister, 1984, dominates the macrofauna. The La
Meseta Formation of Seymour Island contains the most diverse, well-preserved representation of
early Tertiary life known from Antarctica and is important in our understanding of early Cenozoic
molluscan biogeographic disaibutions of the southern hemisphere. From the La Meseta Formation,
170 molluscan taxa are reported, of which 122 are new. Ten new genera and three new subgenera
are proposed. (Photograph by J. D. Stilwell, December 25, 1986.)