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ABSTRACT: Geology and Petroleum Resources, Eastern Great Basin, United States

James A. Peterson

The complex geology of the eastern Great Basin involves a great thickness and diversity of sedimentary facies and major episodes of late Paleozoic and Mesozoic compressional deformation and igneous activity, followed by extensive late Tertiary block faulting. The original sedimentary cover is primarily late Precambrian to Early Triassic in age, comprising as much as 50,000 ft (15 km) of mostly shallow-water marine carbonate and clastic deposits. Lacustrine and fluvial beds of Late Cretaceous to middle Tertiary age are present over a large part of central and eastern Nevada. Late Tertiary lacustrine beds intermixed with volcanic sediments are widespread in northeastern Utah, southeastern Idaho, and southeastern Nevada. The petroleum geology of these rocks is severely compl cated by the overprint of late Tertiary basin and range extensional faulting and extrusive igneous activity. As much as 10,000 ft (3 km) or more of horst-derived late Tertiary and Pleistocene fluvial and lacustrine fill is present in some valleys. Approximately 300 exploratory oil and gas wells have been drilled in the eastern Great Basin region. As of 1989, ten oil fields, ranging in size from an estimated few hundred thousand to approximately 20 million bbl of oil had been found in Railroad and Pine valleys, Nevada. Cumulative production from these fields is approximately 25 million bbl of oil. Production is from fractured Devonian carbonate, Mississippian sandstone, and middle Tertiary volcanic reservoirs. Organic-rich source rocks are present in the Ordovician, Devonian, Mississippia , and upper Paleozoic section and in the lower Tertiary lacustrine beds. Most of the fields are sealed by the basal valley-fill unconformity. Deep-seated igneous intrusives are associated with several of the fields. Despite geologic and thermal complexities, the region retains significantly favorable aspects of an important petroleum province. Of significance to future exploration programs, in addition to structural and stratigraphic mapping, are factors such as paleostructural history and timing of petroleum migration; source rock maturity and temperature history; timing of thrusting, extensional faulting, and igneous intrusions; palinspastic restoration studies; and regional and local hydrology studies.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990