KASIMOVIAN–GZHELIAN (LATE PENNSYLVANIAN) CONODONTS FROM THE LOWER AND MIDDLE INFORMAL MEMBERS OF THE RIEPE SPRING LIMESTONE, ELKO COUNTY, NEVADA

A Late Pennsylvanian idiognathodid conodont succession is present in the cyclic, mixed carbonate-siliciclastic strata of the lower and middle informal members of the Riepe Spring Limestone at Spruce Mountain Ridge, Elko County, Nevada. The Upper Pennsylvanian strata of the North Spruce Mountain Ridge (NSMR) section measure approximately 220 m thick and comprise alternating deposits of variably quartzose limestone, calcareous siltstone, calcareous sandstone, replacement dolomite, and quartzose conglomerate. The conodont assemblage recovered from the Riepe Spring Limestone consists primarily of Idiognathodus and Streptognathodus morphotypes ranging in age from early-middle Kasimovian (lower Missourian) to late Gzhelian (late Virgilian). Adetognathus lautus and sparse, nondescript morphotypes of Hindeodus occur in the underlying uppermost part of the Ely Limestone. The occurrence of Adetognathus suggests a shallow-water setting for the uppermost part of the Ely Limestone, but neither Adetognathus lautus nor Hindeodus sp. provide adequate biostratigraphic control, and the Ely Limestone is therefore excluded from the study. Eight idiognathodid conodont species occur in collections from the lower and middle informal members of the Riepe Spring Limestone at Spruce Mountain Ridge. Kasimovian species include Idiognathodus cancellosus, Idiognathodus aff. confragus, Streptognathodus elegantulus, and Streptognathodus aff. firmus. Gzhelian species include Idiognathodus lateralis, Streptognathodus pawhuskaensis, Streptognathodus virgilicus, and Streptognathodus bellus. Integration of the accompanying Late Pennsylvanian fusulinid succession dominated by Triticites spp. provides additional age constraint throughout the lower and middle informal members of the Riepe Spring Limestone and allows for inferred correlation with equivalent sections in north-central Texas and the North American Midcontinent.