Seismic reflection evidence for two phase development of Tertiary basins from east-central Nevada

Two east-west seismic reflection profiles crossing Antelope Valley, Smokey Valley, Railroad Valley and Big Sand Springs Valley demonstrate the evolution of Tertiary extension from broad sags to narrow, fault-bounded basins. Seismic reflection data was acquired for the Anschutz Corporation by the Digicon Corporation during the winter of 1988/1989. Reprocessing of a 480 channel, 60 fold, dynamite source experiment enabled good imaging of the basin stratigraphy. These data suggest two distinct phases of basin development occurred, separated by a regional unconformity. The early phase is characterized by development of a broad basin riddled with many small offset normal faults. The later phase shows a narrowing of the basin and subsidence along one dominant structure, an apparent planar normal fault. The unconformity separating the two phases of extension marks a transition from broad subsidence to local asymmetric tilting that took place over a short period of time relative to sedimentation rates. Antelope Valley and Railroad Valley clearly show strong evidence for two phase development, whereas Smokey Valley represents mostly the early phase and Big Sand Springs Valley represents only the later phase of extension. The absence of dating within the basins precludes the authors from determining if the abrupt tectonic transition withinmore » the basins resulted from differences in local strain rates or amounts, or was due to changes in regional stress fields.« less