99 Paleontology (Posters) II: Extinction and Environment

Monday, 10 October 2011
9:00 AM - 6:00 PM
Hall C

AN UNUSUAL VERTEBRATE ASSEMBLAGE PRESERVED IN DISTAL ALLUVIAL FAN AND LAKE MARGIN DEPOSITS OF THE CATHEDRAL BLUFFS TONGUE, WASATCH FORMATION, BUSH RIM, RED DESERT, WYOMING

Paper number: 99-34
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The Cathedral Bluffs Tongue of the Wasatch Formation records latest early Eocene (earliest Bridgerian – Gardnerbuttean) deposition along the southern flank of the Wind River Mountains. This unit was deposited by generally southward flowing alluvial fans and braided to meandering fluvial systems. The deposits thin and, especially, fine rapidly to the south and southwest from granule to boulder conglomerates near the Wind River Fault through dominantly granule conglomeratic sandstones, siltstones, and mudstones in the Honeycomb Buttes region, to predominantly fluvial and lake margin mudstones with subordinate channel and splay sandstones in the Bush Rim Area. These Bush Rim deposits also record periodic inundation of the distal alluvial plain by Paleolake Gosiute as indicated by tree-encrusting stromatolites, lake shales, and carbonates and evaporate deposits as the Cathedral Bluffs Member interfingers with the Tipton Shale Member of the Green River Formation.

Fossil vertebrates recovered from these lake-margin deposits differ markedly from the terrestrial basin-margin assemblages typical of the Cathedral Bluff Tongue. As would be expected, basin-center and lake margin turtle taxa (trionychids, Baptemys, and Echmatemys) are common, but so is a new genus of normally upland emydid that is the only turtle found in the alluvial fan deposits of the Cathedral Bluffs. Among crocodylians, Pristichampsus, characteristic of basin-margin assemblages, occurs with lake margin alligatorids (Procaimanoidea utahensis) and crocodiles.

Mammals are represented by 80 individual specimens (mostly isolated teeth) from 12 orders, at least 16 families, and at least 22 genera. The most common mammals found include notharctine primates (16 specimens), hyopsodontid condylarthrans (12 specimens) and rodents representing at least three different genera (12 specimens). Curiously, four taxa that have previously only been documented from younger Bridgerian sediments (zone Br1b or later) are well represented at Bush Rim – these include the primates Notharctus robinsoni and Anaptomorphus aemulus, the plesiadapiform Microsyops elegans, and the palaeanodont Metacheiromys marshi. More proximal Cathedral Bluffs sediments lack these taxa and preserve a typical Br1a mammalian faunal assemblage.