| The Grand Wash trough (GWT), a Miocene extensional basin in the Lake Mead region, had been interpreted by previous workers as a rift basin. This study's objective was to test this interpretation by analyzing basin deposits using stratigraphic sections, geologic mapping, and a gravity survey. The results reveal that the structure of the GWT and its axial and foot wall derived deposits resemble those of a rift basin. However, the basin is too shallow (∼1 km) and the hanging wall alluvial fan is larger and coarser grained than those in previously described rift basins. Instead, these aforementioned characteristics are comparable to supradetachment basins. Therefore, in contrast to previous studies the GWT is interpreted as a hybrid basin that contains features found in both basin types. Significantly the supradetachment-like depositional systems impacted the location and development of the rift-like facies. |
