Gravity Studies of Cave, Dry Lake, and Delamar Valleys, East-Central Nevada

Analysis of gravity anomalies in Cave, Dry Lake, and Delamar valleys in east-central Nevada defines the overall shape of their basins, provides estimates of the depth to pre-Cenozoic basement rocks, and identifies buried faults beneath the sedimentary cover. In all cases, the basins are asymmetric in their cross section and in their placement beneath the valley, reflecting the extensional tectonism that initiated during Miocene time in this area. Absolute values of basin depths are estimated using a density-depth profile calibrated by deep oil and gas wells that encountered basement rocks in Cave Valley. The basin beneath southern Cave Valley extends down to -6.0 km, that of Dry Lake Valley extends to -8.2 km, and that of Delamar Valley extends to -6.4 km. The ranges surrounding Dry Lake and Delamar valleys are dominated by volcanic units that may produce lower-density basin infill, which in turn, would make the maximum depth estimates somewhat less. Dry Lake Valley is characterized by a slot-like graben in its center, whereas the deep portions of Cave and Delamar valleys are more bowl-shaped. Significant portions of the basins are shallow (<1 km deep), as are the transitions between each of these valleys. A seismic reflection image across southern Cave and Muleshoe valleys confirms the basin shapes inferred from gravity analysis. The architecture of these basins inferred from gravity will aid in interpreting the hydrogeologic framework of Cave, Dry Lake, and Delamar valleys by placing estimates on the volume and connectivity of potential unconsolidated alluvial aquifers and by identifying faults buried beneath basin deposits.