Petroleum Source-Rock Potential and Crude-Oil Correlation in the Great Basin

Petroleum source beds in the Great Basin region include marine Paleozoic rocks and nonmarine upper Mesozoic and lower Cenozoic rocks. Many inactive and potential source beds have been identified in continental-rise deposits of the Ordovician Vinini and Devonian Woodruff formations in the eastern part of the Roberts Mountains allochthon (Antler orogen), in central and north-central Nevada; in flysch-trough and prodelta-basin deposits of the Mississippian Chainman Shale and equivalent rocks of the Antler foreland basin, in Nevada and western Utah: and in lake-basin deposits of the Cretaceous Newark Canyon Formation and the Paleogene Sheep Pass and Elk0 formations and equivalent rocks, in cenfral and eastern Nevada. All of the oil fields in the Great Basin are located within NeogeneQuaternary basins that formed during Neogene “Basin-Range” block faulting. Most of the oil shows and reservoir crude oils analyzed can be correlated with Mississippian or Paleogene source rocks. Regional petroleum sourcerock evaluation and crude-oillsource-rock correlation indicate that conditions necessary for crude-oil accumulation are present locally throughout this region. The Mississippian Chainman Shale is confirmed as the major petroleum source rock, having generated the oil in the Trap Spring, Bacon Flat, and Grant Canyon fields in Railroad Valley and the Blackburn field in Pine Valley. The Paleogene Sheep Pass Formation is the source of the oil in fhe Eagle Springs field and probably the Currant field in Railroad Valley. Oil occurrences in the northern Great Basin are believed to be derived from two or more other Terfiary lacustrine sequences. Geological and geochemical evidence indicate a much broader range of source-rocklreservoir-rock target combinations than would be pursued under a Tertiary sourcelreservoir exploration model. Regional evaluation indicates that the Chainman Shale, and possibly other Paleozoic units, may be effective source rocks for oilaccumulation in other valleys in the Great Basin.