Molluscan Systematics and Biostratigraphy: Lower Tertiary La Meseta Formation, Seymour Island, Antartic Peninsula
Copyright 1992 by the American Geophysical Union.
Editor(s): Jeffrey D. Stilwell, William J. Zinsmeister
Published Online: 14 MAR 2013
Print ISBN: 9780875907703
Online ISBN: 9781118667705
Book Series: Antarctic Research Series
About this Book
Published by the American Geophysical Union as part of the Antarctic Research Series, Volume 55.
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 (Telm1-Telm7). Faunal diversity is low in unit Telm1 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 (Antarctodarwinella ellioti, Antarctodarwinella nordenskjöldi, Struthiolarella steirunanni, 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 (64°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.