NEOPROTEROZOIC SYN-SEDIMENTARY TECTONISM IN DEATH VALLEY

Bennie Troxel and Lauren Wright constructed a tectono-stratigraphic framework for the beautifully exposed Proterozoic sediments in Death Valley, California, and interpreted the deposition of these units in a long-lived aulacogen that formed during the breakup of Rodinia. However, more recent geochronological and geologic studies demonstrate that these strata were deposited in multiple discrete basin-forming events, which are separated by major unconformities and formed >100 Myrs before the rift-drift transition. Here, we present geologic mapping, stratigraphic, sedimentological, and structural data from the Panamint Range, Saddle Peak Hills, and the Kingston Range that document Neoproterozoic tectonism sealed by ca. 635 Ma Marinoan glacial deposits of the upper Kingston Peak Formation. Both compressional and extensional Neoproterozoic structures, combined with spatially restricted episodes of uplift and deposition, suggest Tonian through Cryogenian strata of Death Valley were deposited along a strike-slip margin rather than within a long-lived rift basin, as previously proposed by Walker et al. (1986). Although Troxel et al. (1987) correctly pointed out that the thrust faults of Walker et al. (1986) are not structural contacts but olistolith boundaries, we suggest that discontinuous transpressional and transtensional regimes produced recognizable syn-sedimentary deformation, generating the topography responsible for large facies changes and multiple intervals of fanglomerates and olistostromes. These data compel a revised age model for the rifting of Rodinia in Southwest Laurentia, consistent with subsidence models that indicate significant crustal thinning did not occur until the late Ediacaran.