Sedimentology of the Douglas Pass section of the lower Eocene Green River Formation, Picenace Creek Basin: Implications for lake levels in ancient lake uinta

The Green River Formation of the Piceance Creek Basin has been extensively studied due to its vast deposits of oil shale and sodium carbonate minerals. Previous workers have attempted to correlate the basin deposits using rich and lean zones of oil shale as stratigraphic intervals. Basin wide correlation has proven difficult due to the pinching out of the oil shale units into heterolithic marginal deposits. This study therefore focuses on determining the marginal subenvironments of the Green River Formation at Douglas Pass using comparative sedimentology to better understand the depositional processes and lake level fluctuations occurring at the basin margin. Five different facies have been identified from the measured section: Calcareous Mudstone Facies, Massive Mudstone Facies, Sandstone Facies, Cyclic Facies, and Laminated Kerogenous Dolomicrite Facies. The subenvironments fluctuated between fluvial to deep lacustrine. There was an overall shallowing then deepening upward trend in the lake level at Douglas Pass.