LATE PENNSYLVANIAN-EARLY PERMIAN TECTONICS AND SEDIMENTATION IN CARLIN CANYON, NORTHEASTERN NEVADA

The Carlin Canyon area of northern Nevada (Basin and Range) displays a number of spectacular angular unconformities, which suggests long-term episodes of sedimentation were interrupted by short-lived events marked by tectonic uplift and erosion. The area lies east of the Roberts Mountain Allochthon, implying a direct linkage between renewed tectonic movements along Antler structures and Late Paleozoic sedimentation. In order to assess the extent to which Pennsylvanian-Early Permian sedimentation was affected by renewed tectonism, we conducted a biostratigraphic/microfacies analysis of the carbonate-dominated Lower Strathearn, Upper Strathearn and Buckskin Mountain formations. The Lower Strathearn comprises high-order sequences representing cyclical mixed clastic-carbonate to photozoan carbonate sedimentation on a warm-tropical ramp. This unit contains Late Pennsylvanian conodonts and represents a broad third-order unconformity-bounded transgressive-regressive sequence. The unit thins and ultimately pinches out to the east beneath the sub-Permian unconformity. The Asselian (Lower Permian) Upper Strathearn comprises a broad transgressive succession of heterozoan carbonate that represents a deep-water ramp under substantially cooler oceanographic conditions characterized by a shallow thermocline. It thins to the east and passes gradationally upward into thick Sakmarian spiculitic silty lime mudstone of the Buckskin Mountain Formation, which also thins to the east and represents a deep cool water ramp. The Buckskin Mountain shallows upward into an echinoderm-fusulinid-dasyclad grainstone that represents high energy mid to inner ramp deposition in proximity to the thermocline. This unit marks the end of a regressive trend that culminates around the Artinskian-Kungurian boundary. The Kungurian succession above is substantially deeper water comprising spiculitic chert and deeper water lime mudstone. Our study supports the interpretation that the Pennsylvanian-Early Permian succession of Carlin Canyon was deposited in a vast foreland basin affected by reactivated Antler structures. Episodic reactivation of these structures led to major uplift and unconformities up to the Carboniferous-Permian boundary and differential subsidence during the remainder of the Early Permian.