Paleogeographic and structural significance of an Upper Mississippian facies boundary in southern Nevada and east-central California

Abstract

A major facies boundary separating Meramecian (lower Upper Mississippian) shallow-water, carbonate-platform rocks to the south-east from coeval to slightly younger relatively deep-water siliciclastic rocks to the northwest can be traced throughout southern Nevada and east-central California. Although the precise depositional relation between the two facies is not entirely clear, the outer margin of the shallow-water carbonate rocks almost certainly marks the edge of the carbonate platform in earliest late Meramecian time. This facies boundary is distinct and unambiguous enough that it and a parallel subfacies boundary within the carbonate-platform rocks can be used to estimate amounts of displacement on Cenozoic right-slip faults in the region. The carbonate-siliciclastic facies boundary is offset by about 170 km in a right-lateral sense parallel to the Death Valley-Furnace Creek fault zone between the west side of that fault zone and the northeast side of the Las Vegas Valley shear zone. This offset is Cenozoic in age and is interpreted to be distributed as follows: 45-50 km on the Las Vegas Valley shear zone, 80 km on the Death Valley-Furnace Creek fault zone, 30 km on the Stewart Valley fault, and an additional 10-15 km that is not specifically accounted for. Restoration of these offsets successfully reconstructs the Meramecian carbonate shelf edge and aligns several thrust faults now exposed on opposite sides of the right-slip faults.