TECTONIC AND STRATIGRAPHIC MAP OF LATE NEOPROTEROZOIC MCCOY GROUP AT COCOMONGO MOUNTAIN, EGAN RANGE, NEVADA

The McCoy Creek Group of northern Nevada provides ample opportunity to constrain the evolution of the late Neoproterozoic margin of western Laurentia. Located north of Ely, NV, in the Egan Range on the western edge of the Steptoe Valley, Cocomongo Mountain contains extensive exposures of the McCoy Creek Group. A new sequence stratigraphic framework for the McCoy Creek Group was adopted to inform new geologic mapping on Cocomongo Mountain, which enables sequence-based correlation with McCoy Creek Group exposures in neighboring ranges. At Cocomongo Mountain, the McCoy Creek Group records deposition within an underfilled, active late Neoproterozoic rift basin, followed by deposition in a developing marine delta front environment, and finally a transition to passive margin deposition. Despite significant variability in both thickness and facies in McCoy Creek group rocks, the sequence-stratigraphic framework adopted in this mapping effort allows for effective correlation with equivalent regional units. Furthermore, during mapping, two sets of strain regimes were observed to have created various faulting along the range, including Eocene and Miocene normal faults related to regional Basin and Range extension. This new work will contribute to ongoing efforts to characterize the marginal environment and tectonic evolution of late Neoproterozoic western Laurentia.