Abstract: Seismic Reflection Studies in Eastern Nevada

John A. Grow, Christopher J. Potter, John J. Miller

The U.S. Geological Survey has recently purchased over 600 km of multifold seismic reflection profiles in eastern Nevada in the vicinity of Railroad and White River Valleys to understand the regional structural setting of the Railroad Valley oil fields (35 million barrels produced through 1992). One profile extends west of Railroad Valley through the Pancake Range and into Big Sand Springs Valley; another line extends east of White River Valley into Cave, Muleshoe, and Lake valleys. Over 200 exploration wells have been drilled in the area, allowing a unique opportunity to understand extensional processes in this part of the Basin and Range Province using both geophysical and drilling control.

Analysis of sonic logs from over 50 wells indicate that Miocene and younger valley-fill deposits vary from less than 7,000 ft/sec, average velocity in the center of Railroad Valley (from surface down to either Oligocene welded tuffs or older rocks), to more than 16,000 ft/sec near the mountain fronts where conglomerates composed of Paleowic carbonate clasts occur. The conglomerates above and east of the Grant Canyon oil field (18 million barrels as of 1992) appear to have the highest velocities, and these may be due to cementation effects caused by hydrothermal upwelling.

Normal faults are generally too steep to be seen as fault-plane reflections (>40°), except in the vicinity of the prolific Grant Canyon oil field, where a low-angle normal fault (approx. 20°) can be seen on two profiles. The overall extension in the study area appears to be in the range of 25 to 50% except beneath eastern Railroad Valley and the adjacent Grant Range where 80 to more than 100% extension probably has occurred.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994