Abstract

Pennsylvanian sediments in northeast Nevada consist of limestone (80-90%) with smaller quantities of quartz sandstone, siltstone, and chert conglomerate. Outcrop patterns and details of lithology show cyclic alternations. Mechanically deposited limestone exceeds 25% of the total limestone, and includes bioclastic calcarenite and calcirudite and some oolite. Detrital quartz impurities are characteristic. Non-mechanical coquinoid limestones alternate with mechanical varieties. Characteristic nodular chert is secondary (diagenetic) and occurs in very cherry units alternating with non-cherty units. Fossils are not well preserved except where silicified. Algal remains, fragmented fossils, detrital quartz, oolite, and numerous diastems indicate shallow water, frequent agitation, winnowing, and redeposition. Alternating with these conditions were periods of less intense stirring of accumulating sediment, producing cyclic patterns. Orogeny in the eugeosyncline produced lands which shed quartz and chert detritus eastward into the miogeosyncline. Presence of notable quartz sandstones and limestones in the eugeosyncline contradicts popular concepts of only impure "graywacke" sands in such provinces to the near exclusion of all other sediment types. Local upwarps and platforms within the miogeosyncline subsided less rapidly and furnished clastics to adjacent negative areas. The limestones and associated quartzose sandstones lithologically qualify as stable shelf deposits like typical sequences of the craton. The Nevada ones are much thicker however, indicating more rapid subsidence in a relatively unstable geosynclinal belt. While depositional environments in the two provinces were identical, tectonic environments differed considerably as evidenced by significantly thicker deposits, local angular unconformities and appreciable chert detritus in Nevada.

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