WALKER, C. T., and ROBERT D. FRANCIS
California State University, Long Beach, Long Beach, CA 90840
The Basin and Range province has long been attributed to block faulting. However, some work has indicated attenuation and detachments in the ranges. It is difficult to have block faulted valleys and intervening attenuated ranges. Some recent work, based mainly on surface data, suggests that basins are partially or wholly formed by attenuation and detachment faulting. We have used surface and subsurface data to prepare a structure contour map of a detachment that extends from the White Pine and Grant ranges into Railroad Valley. This map also shows that significant range bounding faults are absent.
Railroad Valley began as a proto-basin formed by slight attenuation in the basement, causing gentle subsidence. The modern basin formed by increased attenuation along detachments in the basement and suprastructure together with domal uplifts along the eastern margin of the protobasin.
Petroleum discoveries in Railroad Valley have, at least in part, been serendipitous. Also, a consensus on structural models, especially for the Grant Canyon and Bacon Flat fields, is lacking. We propose that this lack of consensus is due to attenuation-related local variation in availability of, source rock, reservoir structures, and migration paths. ?Unconformity A? at the base of the Valley Fill is variable in age and partially coeval with attenuation and detachment faulting. Therefore, models invoking ?unconformity A? as the primary seal may not necessarily be accurate. Instead, traps may have been formed and sealed by attenuation and detachment faulting.
AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana