BIOTIC AND TAPHONOMIC RESPONSE TO LAKE-LEVEL FLUCTUATIONS IN THE GREATER GREEN RIVER BASIN (EOCENE), WYOMING

Abstract

The Eocene Green River Formation (GRF) (United States) is one of the best-known and most extensively studied Konservat Lagerstatte in the world. As most studies have focused on the fossil fish and plants, few studies have examined the invertebrates, particularly the ostracodes of the renowned GRF fauna. Six species of ostracodes were recovered from 18 intervals within a 154 m section of the Laney Member (LM) in the Washakie Basin (WB). Ostracode species recovered occupied a variety of biological niches, including plant and mud dwellers as well as nektonic lifestyles. Ecological tolerances of these ostracodes were used to reconstruct environmental conditions of the lake through this portion of its history. The taphonomic mode of the ostracodes varied with lithology and depositional setting. Diversity analyses show that the ostracodes from the lower and upper Laclede beds of the LM are consistent with the lake- level fluctuation model constructed for the WB, which was based on independent, stratigraphic, isotopic, and sedimentological data. Ostra- code response to changing lake conditions within the LM demonstrates an environmental tracking (i.e., coordinated stasis) of the lake-level variation. In addition, the similarity of ostracode faunas between the LM and those reported from the Uinta Basin (UB) supports the possible paleohydrologic connection of various basins with deposits of the GRF, related to the tectonic uplift and concomitant climatic change during the Paleocene-Eocene Thermal Maximum. The establishment of these paleohydrologic connections provides important constraints pertaining to the tectonic and climatic history of this region.