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Abstract: Taphonomy of fluvially deposited microvertebrates and systematic paleontology of the Pinnacles buttes in the northwest Great Divide Basin is examined. The Pinnacles buttes contain an early Eocene mammal assemblage of over 900 cataloged specimens from several prolific University of Michigan localities. The diverse assemblage is represented by a minimum of 56 species of 30 families. Sedimentology of the Main Body of the Wasatch formation in the basin margin of the Great Divide has not previously been examined. This thesis provides the first detailed descriptions and measurements of these specimens and explores the sedimentological and taphonomical environments in which this diverse assemblage accumulated in. The microvertebrate fossils were collected from chute-modified channel bar deposits at two fossiliforous horizons in the uppermost 40-50 m of the Main Body of the Wasatch Formation. Concentration of fossils to discrete horizons vertically associated with crevasse splays and gravel bed streams suggests that proximal channel facies played a pivotal role in preservation of fossils in this setting.

Abstract: The early Eocene (Gardnerbuttean) Cathedral Bluffs Tongue of the Wasatch Formation near South Pass, Wyoming preserves a succession of continental fluvial deposits, which interfinger with lacustrine strata of the Green River Formation in a basinward direction. This thesis focuses on the sedimentology of the Cathedral Bluffs Tongue and identifies the dominant influences on sediment accumulation. Previous studies focused primarily on the regional (basin-scale) lithostratigraphic architecture of Eocene strata in the Green River Basin. Detailed sedimentological analyses of the study interval have not previously been completed. Using whole-rock geochemistry, gamma spectrometry, outcrop description and petrography, fine-scale correlations were made through the study interval. As climate remained constant throughout the ~ 1. 5 million year study interval, and syndepositional structural influences can be demonstrated in the study area, it is shown that movement of the Wind River Thrust Fault, played a dominant role in Early Eocene sediment accumulation at South Pass.