Attenuation
in Railroad Valley, Nye County, Eastern Nevada,
and its Significance for Petroleum Exploration in the Eastern Great Basin
Charles T. Walker and Robert D. Francis
Data from over 100 wells suggest that the boundary between the Grant Range
and Railroad Valley is a low angle detachment fault at or close to a metamorphic
core complex. The White Pine Detachment, mapped previously in the White Pine and
Grant Ranges, is penetrated by many wells because it occurs at a high structural
level. A structure contour map based on both surface and subsurface data
indicates that the detachment dips uniformly into the subsurface and is not
displaced significantly by a high angle fault. In the Grant Range subparallel
detachments are developed in the more ductile units. Because the White Pine
Detachment is not displaced by high angle faults Railroad Valley cannot have
formed by steep normal faulting but instead by attenuation
along a series of
subpara lel detachments.
Generation and accumulation of hydrocarbons in Railroad Valley and similar
basins may be related to the attenuation
that created the basins. For example,
the extent to which
attenuation
juxtaposed potential source rocks and hot
infrastructure rocks may influence maturity. Consequently, areas normally
considered too shallow for petroleum generation should not necessarily be
discounted. Furthermore, failure to find petroleum in a favorable structure may
not mean that the basin lacks potential because, as in Railroad Valley, source
rocks may be locally absent as a result of
attenuation
. Reservoir structures
formed by
attenuation
, such as lenticular stretch structures and localized
fracture zones in otherwise impermeable formations, may exist.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California