Molluscan Systematics and Biostratigraphy Lower Tertiary La Meseta Formation, Seymour Island, Antarctic Peninsula Physical Sciences ANTARCTIOC CEANOLOGY Joseph L. Reid, Editor ANTARCTIOC CEANOLOG11Y: THE AUSTRALIAN- NEW ZEALANDSE CTOR Dennis E. Hayes, Editor ANTARCTISCN OWA ND ICE STUDIES Malcolm Mellor, Editor ANTARCTISCN OWA ND ICE STUDIESI1 A. P. Crary, Editor ANTARCTISCO ILSA ND SOILF ORMINGP ROCESSES J. C. F. Tedrow, Editor DRYV ALLEYD RILLINGP ROJECT L. D. McGinnis, Editor GEOLOGICAINL VESTIGATIOINNS N ORTHERN VICTORIAL AND Edmund Stump, Editor GEOLOGYAN D PALEONTOLOGOFY T HE ANTARCTIC Jarvis B. Hadley, Editor GEOLOGOYF THE CENTRALTR ANSANTARCTIC MOUNTAINS Mort D. Turner and John F. Splettstoesser, Editors GEOMAGNETISAMND AERONOMY A. H. Waynick, Editor METEOROLOGICSATLU DIESA T PLATEAUS TATION, ANTARCTICA Joost A. Businger, Editor OCEANOLOGOYF THE ANTARCTICCO NTINENTASLH ELF Stanley S. Jacobs, Editor STUDIESIN ANTARCTIMC ETEOROLOGY Morton J. 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Kornicker, Editor POLYCHAETMAY ZOSTOMIDAANED SEDENTIAROIAF BIOLOGOYF THE ANTARCTISCE ASX I1 ANTARCTICA David L. Pawson, Editor Olga Hartman BIOLOGOYF THE ANTARCTISCE ASX I11 RECENTA NTARCTIACN D SUBANTARCTBIRCA CHIOPODS Louis S. Kornicker, Editor Merrill W. Foster BIOLOGOYF THE ANTARCTISCE ASX IV Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE ASX V Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE ASX VI Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE ASX VII Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE ASX VIII Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE ASX IX Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE ASX X Louis S. Kornicker, Editor BIOLOGOYF THE ANTARCTISCE AS XXI Louis S. Kornicker, Editor 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 2000 Florida Avenue, N. W. Washington, DC 20009 Figures, tables, and short excerpts may be reprinted in scientific books and journals if the source is properly cited. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by the American Geophysical Union for libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $1.00 per copy plus $0.20 per page is paid directly to CCC, 21 Congress Street, Salem, MA 10970. 0066-46341921$01.00+0 .20. This consent does not extend to other lunds of copying, such as copying for creating new collective works or for resale. The reproduction of multiple copies and the use of extracts, including figures and tables, for commercial purposes requires permission from AGU. Published by American Geophysical Union With the aid of grant DPP-89.15494 from the National Science Foundation 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 The Antarctic Research Series provides for the presentation of detailed scientific research results from Antarctica, particularly the results of the United States Antarctic Research Program, including monographs and long manuscripts. The series is designed to make the results of Antarctic fieldwork available. The Antarctic Research Series encourages the collection of papers on specific geographic areas within Antarc- tica. In addition, many volumes focus on particular disciplines, including marine biology, oceanology, meteorology, upper atmosphere physics, terrestrial biology, geology, glaciology, human adaptability, engineering, and environmental protection. Topical volumes in the series normally are devoted to papers in one or two disciplines. Multidisciplinary volumes, initiated in 1990 to enable more rapid publication, are open to papers from any discipline. The series can accommodate long manuscripts and utilize special formats, such as maps. Priorities for publication are set by the Board of Associate Editors. Preference is given to research manuscripts from projects funded by U.S. agencies. Because the series serves to emphasize the U.S. Antarctic Research Program, it also performs a function similar to expedition reports of many other countries with national Antarctic research programs. The standards of scientific excellence expected for the series are maintained by the review criteria established for the AGU publications program. Each paper is critically reviewed by two or more expert referees. A member of the Board of Associate Editors may serve as editor of a volume, or another person may be appointed. The Board works with the individual editors of each volume and with the AGU staff to assure that the objectives of the series are met, that the best possible papers are presented, and that publication is timely. Proposals for volumes or papers offered should be sent to the Board of Associate Editors, Antarctic Research Series, at 2000 Florida Avenue, N.W., Washington, D.C. 20009. Publication 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.)