ABSTRACT

About 10,000 feet of Ordovician through Permian rocks crop out within the Arrow Canyon Range, Clark County, Nevada. Cambrian black dolomite and argillaceous limestone also are exposed. Ordovician rocks include about 2,400 feet in the Pogonip Group, about 100 feet of Eureka Quartzite, and about 400 feet of Ely Springs Dolomite. The Silurian Laketown Dolomite thins southward from 400 to about 250 feet because of pre-Devonian erosion. Devonian rocks are approximately 2,000 feet thick. The Piute Formation, about 300 feet thick, consists of buff dolomite and contains Acrospirifer kobehana at the base and a Stringocephalus sp. biostrome at the top. The bench-forming, buff dolomite Moapa Formation, 300 feet thick, which succeeds the Stringocephalus biostrome is overlain by about 1,100 feet of dark, cliff-forming limestone of the Arrow Canyon Formation which includes several prominent interbedded sandstone layers. The uppermost Devonian formation, the Crystal Pass Limestone, is about 250 feet thick and is disconformably succeeded by black limestone of the Mississippian Monte Cristo Group. The Monte Cristo Group is about 1,500 feet thick and all of the sub-units named by Hewett excepting the Arrowhead Limestone are recognized. Pennsylvanian and Permian rocks, referred to the Bird Spring Group, include about 3,500 feet of rock assigned to five formations. The basal formation consists of about 80 feet of limestone resting on a basal sandstone. This unit is succeeded by a detrital formation assigned to the Indian Springs Formation. Rhipidomella nevadensis occurs at the base of the overlying cyclic Umestone of Pennsylvanian and Permian age. This formation is overlain by 300 feet of limestone and shale which are, in turn, succeeded by a Permian limestone formation in the Bird Spring Group.

Comparison with sections on the southeast and northwest and computation of approximate rates of sedimentation suggest that a hinge-line between the Paleozoic shelf and miogeosyncline may have shifted back and forth across this area during Ordovician through Permian time. The apparent hinge-line may have resulted from pre-Devonian erosion on the southeast, local basin development on the northwest during Devonian time, and introduction of detrital rocks from the northwest during the Mississippian and from the southeast during the Pennsylvanian and Permian. Rates of sedimentation appear to have been relatively uniform in the Arrow Canyon Range during the Paleozoic.

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