X-RAY FLOURESCENCE AND OPTICAL PHOTOGRAPH ANALYSIS TO EVALUATE THE PALEOREDOX CONDITIONS, PALEOPRODUCTIVITY AND DEPOSITIONAL ENVIRONMENT OF AN EOCENE LAKE SYSTEM: MAHOGANY ZONE, GREEN RIVER FORMATION, EASTERN UINTA BASIN, UTAH

The Green River Formation contains some of the most prolific oil-shale deposits in the world. As the demand for oil rises, so does the demand for unconventional oil sources. This research will focus on better understanding the ancient lake and depositional environment during the deposition of the most organic rich interval, the Mahogany zone of the Green River Formation in the eastern Uinta Basin. The Mahogany zone is thought to record a period of high lake level conditions in which high algal productivity combined with prolonged anoxia promoted the preservation of a world class source rock. Herein, the stratigraphic variability of paleoredox conditions, paleoproductivity and mud depositional processes through the Mahogany zone are further investigated using a newly drilled core (PR-15-7C) from the eastern Uinta Basin. High resolution stratigraphic (5 mm spacing) handheld X-ray florescence analysis has been performed on the Mahogany zone (~42 ft. thick) of the PR-15-7C core, which provides inorganic major and trace element abundance data. This was combined with quantitative RGB analysis of optical core photographs, which provides a proxy for organic richness at high stratigraphic resolution (up to a few hundred microns). These data were used to evaluate the paleoredox conditions and paleoproductivity, respectively, of the ancient lake system recorded in the Mahogany zone in the Green River Formation. In addition, standard thin section analysis of mudstone samples was used to determine different sedimentary processes of mud deposition (i.e. suspension settling versus hydrodynamic currents) in the lake system recorded by the Mahogany zone. These data indicate that the lake chemistry, specifically the paleoredox conditions and paleoproductivity as well as the depositional environment of the lake changed through the Mahogany zone over time. This suggests a more complex depositional history than was previously depicted. This will ultimately provide a more predictive model of how the oil shale resource changes spatially, providing a framework for more intelligent and responsible future development.