Paleontology and stratigraphy of middle Eocene rock units in the Bridger and Uinta Basins, Wyoming and Utah

Abstract

The Bridger Formation is located in the Green River basin in southwest Wyoming, and the Uinta and Duchesne River formations are located in the Uinta basin in Utah. These three rock units and their diverse fossil assemblages have great scientifi c importance and are also of historic interest to vertebrate paleontologists. Notably, they are also the stratotypes for the three middle Eocene North American Land Mammal “Ages,” the Bridgerian, Uintan, and Duchesnean, from oldest to youngest. The fossils and sediments of these formations provide a critically important record of biotic, environmental, and climatic history spanning ~10 million years (49–39 Ma). This article features a detailed fi eld excursion through portions of the Green River and Uinta basins that focuses on locations of geologic, paleontologic, and historical interest. In support of the fi eld excursion, we also provide a review of current knowledge of these formations with emphasis on lithostratigraphy, biochronology, depositional and paleoenvironmental history, and the history of scientifi c exploration. *pmurphey@sdnhm.org; btowns@midwestern.edu; tonyf@ucla.edu; emmett.evanoff@unco.edu. Murphey, P.C., Townsend, K.E.B., Friscia, A.R., and Evanoff, E., 2011, Paleontology and stratigraphy of middle Eocene rock units in the Bridger and Uinta Basins, Wyoming and Utah, in Lee, J., and Evans, J.P., eds., Geologic Field Trips to the Basin and Range, Rocky Mountains, Snake River Plain, and Terranes of the U.S. Cordillera: Geological Society of America Field Guide 21, p. 125–166, doi:10.1130/2011.0021(06). For permission to copy, contact editing@geosociety.org. ©2011 The Geological Society of America. All rights reserved.