EVIDENCE OF SYN-DEPOSITIONAL TECTONISM IN THE NEOPROTEROZOIC REED DOLOMITE, WHITE-INYO MOUNTAINS, EASTERN CALIFORNIA

The timing and progression of Neoproterozoic-Cambrian rifting and passive margin development along the western margin of North America remains uncertain in the southern Great Basin of the western US. Limited volcanism, syndepositional faulting, and abrupt facies changes noted in the Kingston Peak Formation in the Death Valley region may suggest rifting initiated ca. 750-700 Ma. However, tectonic subsidence models would predict the development of a western Laurentia passive margin ca. 600-550 Ma. Some workers have proposed a two-phase rift scenario, whereas other workers support a scenario of multiple and/or stepwise rifting events along the Cordillera.

The White-Inyo succession represents a thick succession of Neoproterozoic-Cambrian strata that loosely correlates with the Death Valley succession to the southeast. Correlation between the Cambrian of the two sections is clear, but correlation of Neoproterozoic units (representing ~4000m of strata in the White-Inyo region) remains unclear. Here we report more than 100 meters of megabreccia within and in abrupt contact with the oolitic carbonates of the Lower Reed Dolomite in the White-Inyo succession, tentatively constrained between ca. 580-548 Ma and thought to correlate with the Stirling Quartzite (or perhaps the Johnnie Formation) in Death Valley. The megabreccia displays diverse, angular clasts likely derived from the Lower Reed Dolomite, as well as other lithologies. Minor evidence for syndepositional faulting exists but requires further investigation. The stratal stacking patterns observed to date are inconsistent with lowstand incised valley development. We therefore tentatively interpret the megabreccia in the Lower Reed Dolomite to provide evidence of tectonically controlled deposition, although (glacio?)-eustatic fluctuation cannot be completely ruled out at this time.