--> The Hydrological Cycle During Deposition of the Mahogany Oil Shale Interval of Eocene Lake Uinta, Green River Formation, Utah

AAPG ACE 2018

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The Hydrological Cycle During Deposition of the Mahogany Oil Shale Interval of Eocene Lake Uinta, Green River Formation, Utah

Abstract

The Lower Eocene Green River Formation of Utah and Colorado represents a ~15 million-year record of unusually large, productive lakes which deposited an estimated 750 billion barrels of oil equivalent, one of the largest oil shales in the world. Multiple drill cores through the Parachute Creek Member, taken from both the basin margin and center, offer an excellent opportunity to construct high-resolution records of terrestrial conditions and explore their influence on organic matter deposition and preservation.

These drill cores record several negative carbon isotope excursions in the carbon isotopic composition of bulk organic carbon that can be potentially correlated to the marine record of hyperthermals through a radiosotopically anchored astrochronolgy. One of these transient intervals of rapid greenhouse warming occurred during deposition of the Mahogany Oil Shale, an unusually organic carbon-rich deposit (up to 40%) of interest for unconventionals.

In this study, the isotopic expression of mid-latitude hydrological change during rapid warming is investigated through compound-specific hydrogen isotopic analyses of n-alkanes extracted from the Mahogany Oil Shale Zone, Uinta basin, Utah. Comparison of this novel record with high-resolution sedimentary logs will allow for greater understanding of the hydrological cycle at the time of deposition of this key oil shale.

Disentangling the factors controlling deposition and preservation of organic matter in the Green River Formation will lead to greater understanding and predictability of the organic-rich layers in the oil shale, which will support the development of the U.S unconventional hydrocarbon industry, and petroleum independence in the region.