Structural Control of Ground-Water Movement in Miogeosynclinal Rocks of South-Central Nevada
Regional interbasin movement of ground water in highly deformed miogeosynclinal carbonate rocks of the eastern Great Basin has received considerable attention in the literature since 1960. That these regional carbonate aquifer systems — some of which may integrate as many as 13 intermontane basins — are actually compartmentalized by major structural features, has not received adequate emphasis.
In south-central Nevada, major wrench, thrust, and normal faults and folds exert marked control on ground-water movement. Deformation of the carbonate rocks results in regions of high transmissibility, but juxtaposition by faulting or folding of thick clastic strata against carbonate aquifiers results in prominent ground-water barriers, some of which are more than ten miles long. The apparent hydraulic gradients across the thick clastic aquitards vary from 150 to 1300 ft per mile; by contrast gradients in the adjacent carbonate aquifers vary from 0.5 to 10 ft per mile. Barriers may also result from gouge developed along the major fault zones.
Recognition of the structural barriers as well as the conduits is essential for construction of an initial working flow net of a region. In upland areas the clastic aquitards may exert control on distribution of recharge. Where present in central parts of the flow system, the aquitards act as prominent ground-water dams, and localize minor spring discharge. In discharge areas they localize major spring lines.
Major structures with hydrologic reflections include the Las Vegas Valley shear zone and the Tippinip thrust fault.