Facies Architecture and Provenance of Ancient Dryland River Systems in the Eocene Wilkins Peak Member of the lacustrine Green River Formation, Wyoming

Kuwanna Dyer
University of Wisconsin-Madison Department of Geology and Geophysics
Madison, Wisconsin
kmdyer@geology.wisc.edu

Modern dryland systems have recently received considerable attention; however, ancient systems are not as well understood. Those such as the Caspian basin contain significant reserves of hydrocarbons, and therefore further study of ancient basins is warranted. The Caspian basin consists of sheet-like fluvial sandstones interbedded with mudstones, but has limited subaerial exposures. Like the Caspian basin, the hypersaline Wilkins Peak Member of the Green River Formation contains fluvial sandstones interbedded with mudstones. These beds are well exposed and provide abundant outcrop exposure suitable for detailed lateral and vertical lithofacies description and correlation; for this reason, they may serve as analogs to reservoirs in the Caspian basin, as well as basins elsewhere. The ubiquitous occurrence of climbing ripples and channel scours, together with the presence of insect burrows and interwoven paleosols, suggest that these sandstones were deposited by rivers and sheetfloods when lake levels were low (Eugster and Hardie, 1975; Smoot, 1983; Pietras, 2003). In this study we will investigate whether the sandstones are the deposits of ancient dryland rivers and determine their provenance. We are also interested in the relationship between sandstone deposition and lake level; i.e., whether the lake was at its driest, in the process of drying out, or beginning to refill. The results of this study will provide valuable insight into the depositional history of fluvial depositions within a lacustrine basin. This study is part of a larger collaborative effort underway at the University of Wisconsin-Madison aimed at reconstructing the evolution of the greater Green River basin.