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Structure, Stratigraphy, And Hydrocarbon Potential of Butte Valley, White Pine County, Nevada

Alfred H. Pekarek, Dept. of Earth & Atmospheric Sciences, St. Cloud State University, MS 47, 720 Fourth Ave. S, St. Cloud, MN 56301, phone: 320-308-4127, fax: 320-308-4262, [email protected]

Butte Valley in east-central Nevada occupies a tectonic transition zone between the weakly deformed Butte Mountains on the west and a strongly deformed core complex to the east. East-central Nevada underwent compressional tectonism in the Paleozoic and in the Mesozoic and extensional tectonism in the Cenozoic. Consequently it contains both compressional and extensional structures favoring the development of a variety of hydrocarbon traps. An essentially complete Paleozoic section (Permian strata are missing locally) exceeds 20,000 feet of predominantly carbonate strata. A relatively thin Tertiary cover (commonly only a few thousand feet thick) includes Oligocene volcanics and younger valley fill sediments. Source rocks include nearly 2000 feet of the Mississippian Chainman Shale, the primary petroleum source rock in east-central Nevada, the Pilot Shale and some organic-rich carbonates. Published geochemical data from well cuttings show the Chainman to be in the oil generating window. Multiple carbonate reservoirs with solution enhanced fracture porosity are the primary objectives. Paleozoic sandstones and Tertiary volcanics provide secondary objectives. Gravity data and detailed photogeologic mapping allows Butte Valley to be subdivided into 5 areas, each with unique geologic features. The northern areas appear less prospective than the southern areas. Residual gravity data suggest a variety of potential hydrocarbon traps, including reentrants and horsts. Photogeologic mapping suggest domal traps under the valley fill adjacent to the Butte Mountains and fault block traps adjacent to the Eagan Range. Geochemical data (primarily soil gas) indicate some of these traps may contain accumulations of hydrocarbons.