Depositional and tectonic evolution of a supradetachment basin: Ar-40/Ar-39 geochronology of the Nova Formation, Panamint Range, California

The Nova Basin contains an upper Miocene to Pliocene supradetachment sedime ntary succession that records the unroofing of the Panamint metamorphic cor e complex, west of Death Valley, California. Basin stratigraphy reflects th e evolution of sedimentation processes from landslide emplacement during ba sin initiation to the development of alluvial fans composed of reworked, up lifted sections of the basin fill. Ar-40/Ar-39 geochronology of volcanic un its in middle and lower parts of the sequence provide age control on the te ctonic and depositional evolution of the basin and, more generally, insight s regarding the rate of change of depositional environments in supradetachm ent basins. Our work, along with earlier research, indicate basin depositio n from 11.38 Ma to 3.35 Ma. The data imply sedimentation rates, uncorrected for compaction, of similar to 100 m Myr(-1) in the lower, high-energy part to similar to 1000 m Myr(-1) in the middle part characterized by debris-fl ow fan deposition. The observed variation in sediment flux rate during basi n evolution suggests that supradetachment basins have complex depositional histories involving rapid transitions in both the style and rate of sedimen tation.