POOLE, FORREST G., and CHARLES A. SANDBERG, U.S. Geological Survey, Denver, CO

ABSTRACT: Relation of Transitional-Facies Woodruff Formation to Late Devonian Continental Margin in Nevada

The Upper Devonian, upper Woodruff Formation occupies a narrow (50-km wide) belt extending southward 400 km from the Pinon Range in northeastern Nevada to Bare Mountain in southwestern Nevada The upper Woodruff comprises tan-weathering platy siltstone, spicular siliceous siltstone, and radiolarian chert deposited on the continental rise, continental slope, and outer shelf. Seaward, the transitional-facies upper Woodruff intertongued with the upper part of the western-facies Slaven Chert, and landward the upper Woodruff had local connections with the lower member of the Pilot Shale, which was deposited in a protoflysch basin within the carbonate platform. The upper Woodruff occurs both in the Roberts Mountains allochthon farther west and in continental-slope and shelf sequences of the utochthon, demonstrating a depositional connection between rocks of the two areas and indicating that oceanic rocks of the allochthon are not part of an exotic terrane.

The upper Woodruff has been dated at more than 15 localities by conodonts on bedding surfaces and from sparse micrite lenses and concretions. At localities such as the northern Roberts Mountains, northern Antelope Range, northern Hot Creek Range, and Bare Mountain, where depositional bases or tops or both are exposed, it is entirely Famennian (late Late Devonian) in age, ranging from late crepida to early expansa zone. Beds of this age are also identified by Angustidontus (crustacean appendages) on bedding surfaces. At many localities, it overlies the transitional-facies Upper Devonian Fenstermaker Wash Formation, outer shelf Devils Gate Limestone, or older Devonian rocks. Elsewhere, as in the southern Hot Creek Range and northern Monitor Range, older Famennian or Frasnian (lower Uppe Devonian) or both beds also present are in the upper Woodruff. At March Spring in the northern Toquima Range, only Frasnian (early hassi and late rhenana zones) beds are recognized. The upper Woodruff commonly forms the substrate on which Mississippian Antler foredeep sediments, beginning with the deep-water Kinderhookian Webb Formation, were deposited, prior to deposition of western-derived siliciclastic flysch and eastern-derived calciclastic turbidites.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.