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Tectonic Alteration Of A Major Neogene River Drainage Of The Basin And Range, Stuart D. Parker

Graduate Student Theses, Dissertations, & Professional Papers

Depositional characteristics of the ‘Divide unit’ of the Cretaceous Beaverhead Group within the southern Beaverhead Mountains challenge previous interpretations. This study reassigns the Divide unit to the Neogene. This revised age assignment highlights a major influx of immature sediment at the onset of Basin-Range normal faulting. Syntectonic deposition in an active half-graben continued from Middle Miocene to the Pliocene, attaining a thickness of 800 m. Local clasts of carbonate, siliciclastic and orthoquartzite entered the channel from the immediate west through large mass-wasting events. Dacitic fluvial cobbles dated herein to 98 Ma were transported from an unknown southwesterly source. Clasts of …