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A New Oil-Generation Model for Pine and Railroad Valleys, Nevada

PERRY, WILLIAM J., JR., CHARLES E. BARKER, and KAREN LUND, U.S. Geological Survey, Denver, CO

The two oil-productive areas of Nevada, Pine Valley and Railroad Valley, show remarkably similar structural patterns and thermal histories. Both valleys are bounded on the east and below by a major low-angle west-dipping extensional fault into which steeper east- and west-dipping normal faults gather. In both valleys, the major fault bounds a brittly deformed upper plate which contains Devonian, Mississippian, and Tertiary source or reservoir rocks or both. Both lower plates contain Cretaceous(?) intrusive rocks.

We propose that late Tertiary extension in both areas brought cool upper crustal rocks, including Paleozoic and Cenozoic sedimentary rocks that were immature with respect to hydrocarbon generation, into contact with hotter lower plate rocks that had been previously deeply buried--as deep as midcrustal levels in places along the eastern margin of Railroad Valley. We suggest that extension may have been sufficiently rapid that very high thermal gradients existed across the major low-angle extensional fault (structural detachment) in both areas. This model implies that Mesozoic to early Tertiary compressional deformation is not a major factor in contemporary oil occurrences in Nevada, and that late Tertiary extension and associated events probably destroyed any oils that may have been pr duced by earlier thermal maturation. The model also implies that oil generation is still occurring in areas where hotter lower plate rocks are producing increased heating of source rocks in the upper plate that have remaining oil-generative capacity. This model is being tested by a variety of petrographic, geochemical, isotopic, and other paleogeothermal techniques.

 

AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)