TECTONOSTRATIGRAPHIC ANALYSIS OF THE NEOPROTEROZOIC MCCOY CREEK GROUP IN THE NORTHERN EGAN RANGE, EASTERN 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. The McCoy Creek Group at Cocomongo Mountain 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, the sequence-stratigraphic framework adopted in this mapping effort, coupled with carbon isotope chemostratigraphy, allows for effective correlation with equivalent regional units and development of a new age model. Furthermore, provenance analysis from detrital zircon geochronology and petrography of the McCoy Creek Group suggests recycling and local sediment derivation from a rift shoulder prior to the development of the Transcontinental Arch.