TIMING AND STYLE OF DEPOSITION AND DEFORMATION OF THE MIOCENE RED SANDSTONE UNIT OF THE WHITE BASIN, SOUTHERN NEVADA, AND IMPLICATIONS FOR TECTONIC MODELS OF CENTRAL BASIN AND RANGE EXTENSION

The central Basin and Range in southern Nevada has long been recognized as an outstanding place to study continental extension. Both older, upper-crustal rocks involved in extension, as well as syntectonic deposits that record the entire timespan of extension, are well-exposed in the Lake Mead area. Many ground-breaking tectonic models of continental rifting and upper-plate deformation have been proposed based on studies from this region. These include the rolling hinge hypothesis (Wernicke and Axen, 1988), the synchronous slip model of extension (Brady et al., 2000), and the role that tectonic escape and contractional deformation play in extensional settings (Anderson and Barnhard, 1993). As part of a larger study to test and refine these models, we are examining the informally named red sandstone unit of Bohannan (1984) in the White Basin. This unit records the later stages of extension and is therefore specifically relevant to defining the timing, location and role of north-south contraction.

The red sandstone unit contains well-exposed but highly variable strata, including siliciclastics, evaporites, limestone and volcanic tuffs. Detailed mapping of these units reveals an interfingering of finer, distal deposits with fault-related, basin-margin, coarse clastics. On the west side of the basin, conglomerate facies were deposited within the hanging-wall of the active Muddy Peak Fault, as coarse sediment was shed eastward from the Muddy Mountains. Sedimentary deposits throughout the basin are interbedded with several unique volcanic tuff layers, which allow for detailed stratigraphic correlation across the many fault blocks within the basin. The White Basin was created in part by the major left-lateral oblique normal faults of the Lake Mead Fault System and deformed by numerous right-lateral, east-dipping oblique-normal faults. Correlating and dating the tuffs will allow for the creation of paleogeographic reconstructions and help determine a more precise timing and spatial evolution of this deformation. We are also examining cycles of lacustrine versus fluvial deposition to consider the role that global climate variations might play in creating the highly-variable stratigraphy.