Diagenesis, Depositional Environments, and Hydrocarbon Potential of the Basal Limestone, Green River Formation, Uinta Basin, Utah: ABSTRACT

Abstract

The basal limestone of the Eocene Green River Formation is well exposed along the southern margin of the Uinta basin. Surface and subsurface stratigraphy evidence a wide spectrum of mixed siliciclastic-carbonate rocks within a well-defined sequence. Although numerous stratigraphic and petrographic investigations of Green River rocks have been completed, none have dealt specifically with the basal limestone facies in detailed stratigraphic context. Rocks exposed along the southern basin margin reflect deposition in relatively shallow-water, mud-flat conditions. Shallowest conditions are marked by dolomitized ostracod and pellet grainstones. Shoreward of the grainstones in typically fresher water, sandy pelecypod-gastropod grainstones are presented and are commonly interbedded with silty mudstones. Deepest offshore conditions resulted in the deposition of dark-gray, kerogen-rich carbonates. Cores, electric logs, and subsurface mapping indicate rapid facies changes to the north (toward the basin center). Kerogen-rich carbonate potential source beds predominate toward the basin center and interfinger southward with lakeshore and lagoonal deposits, which are composed of ostracod packstone and sandy grainstone reservoirs. Interpretation of the detailed petrography of various environments has evolved a paragenetic sequence. Several authigenic clay and carbonate mineral phases were precipitated in the pore systems.