Facies, stratigraphic architecture, and lake evolution of the oil shale bearing Green River Formation, eastern Uinta Basin, Utah.

摘要

Lacustrine basin systems have historically been valued for their abundant conventional oil and gas reserves, but they also contain a vast potential for unconventional petroleum development. To better understand the evolution of Utah's Eocene Lake Uinta and to help facilitate prudent and economic development of its oil shale resource, a predictive genetic model of the basin's lacustrine strata has been refined here. This model provides a better understanding of facies distribution, stratigraphic architecture, and a precise history of depositional evolution of Lake Uinta in eastern Utah.;This study evaluates the upper Douglas Creek and Parachute Creek Members of the Green River Formation, exposed along the Evacuation Creek outcrop on the eastern flank of the Uinta Basin. In addition to the outcrop, the Asphalt Wash-1 core, located about 13.7 km (8.5 mi) to the northwest of Evacuation Creek, was described. Ten different facies are defined and grouped into four facies associations: siliciclastics, carbonates, saline deposits, and volcanic-derived deposits. These datasets provide an exceptional opportunity to highlight lateral changes in facies architecture on the east side of the basin. The sections record meter-scale shallowing upward successions, with an overall shallow to deep to shallower transformation of the lake system. Periods of high sediment supply are recorded by laterally extensive sandstone associations, whereas low siliciclastic sediment supply conditions are recorded by carbonate-dominated organic-rich zones and organic-poor microbialite intervals.;This research further defines a genetic framework that recognizes small-scale phases in lake evolution which are defined by the relationship between absolute lake level, accommodation, siliciclastic input, and salinity. The combination of short-term climatic changes and longer-term tectonics shaped the evolution of Lake Uinta from an overfilled basin with fluctuations in sediment supply and accommodation that vary in both frequency and length (lake phases 1a and 1b), to a balance-filled basin with little to no sediment input with a high lake level (lake phases 2a, 2b, and 3a), to an underfilled basin with abundant saline minerals (lake phase 3b). This research provides a key dataset towards developing a regional genetic framework for lake evolution in the eastern Uinta Basin.