WALKER, C. T., and ROBERT D. FRANCIS
California State University, Long Beach, Long Beach, CA 90840
Abstract: Attenuation
and Petroleum
Exploration in the Great Basin, Nevada
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