Regional Seismic Reflection Profile from Railroad Valley to Lake Valley, East-Central Nevada, Reveals a Variety of Structural Styles Beneath Neogene Basins
POTTER, C. J., J. A. GROW, K. LUND, W. J. PERRY, JR., J. J. MILLER, and M. W. LEE, U.S. Geological Survey, Denver, CO
Two seismic reflection lines that compose a 90-km east-west profile at approximately 38 degrees 25'N latitude, east-central Nevada, help define the structure beneath Railroad Valley, White River Valley, the southern Egan Range, Cave Valley, Muleshoe Valley, the southern Schell Creek Range, and Lake Valley. Preliminary seismic interpretations are being integrated with ongoing geologic mapping, gravity, and magnetic studies and with drill-hole data along this transect.
In the Grant Canyon oil field of Railroad Valley, a gently west-dipping normal fault appears to have controlled the development of the Neogene basin. The fault is clearly defined by fault-plane reflections and by terminations of east-dipping reflections from Tertiary and Paleozoic strata that have rotated toward the fault; the fault projects to nearby outcrops of a major low-angle extensional fault mapped in the Grant Range to the east. Interpretations of reflection patterns, a steep gravity gradient, and a line of springs along the east side of the valley all suggest the presence of listric normal faults that cut Paleozoic rocks and merge into the low-angle fault at depth. There is no evidence for significant offset of the low-angle fault by younger steep faults.
White River Valley at this latitude consists of three east-dipping half-grabens and two intervening basement highs. Two half-grabens in the western part of the valley are bounded by west-dipping faults with intermediate to steep dips. The largest half-graben occupies the east side of the valley and is bounded on the east by a west-dipping low-angle normal fault that is well defined on the seismic data but cannot be traced into the range at this latitude. Younger steep faults cut the basin-bounding fault and much of the Neogene strata; the surface trace of one of these steep faults corresponds to a line of springs along the east side of the valley.
East-dipping reflections in the southern Egan Range correspond to a homoclinal Paleozoic panel overlain by a veneer of Late Cretaceous and early Tertiary rocks. These reflections continue to the east beneath Cave Valley, which is bounded on the east by a moderately dipping normal fault that may become listric at depth. The deepest basin fill strata dip east (toward the fault), but most of the basin-fill produces subhorizontal reflections; deposition of these flat strata apparently postdated Neogene faulting. These patterns suggest that rapid, short-lived Neogene extension produced this basin.
The north end of Muleshoe Valley yields a narrow sag basin pattern between the southern Schell Creek Range and Dutch John Mountain, with no well-defined bounding faults. Lake Valley, on the east end of the profile, is a broad, complex basin containing normal faults with opposing dips. The progressive steepening of westerly dips in basin-fill beneath the west side of the basin suggests the presence of a major east-dipping listric fault.
AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)