Radiolarian Biostratigraphy of the Quinn River Formation, Black Rock Terrane, North-Central Nevada: Correlations with Eastern Klamath Terrane Geology

Abstract

The Quinn River Formation, Black Rock terrane, Quinn River Crossing, is one of the few Nevadan sections of Permian and Triassic strata that are unaffected by Sonoman deformation. The formation consists of: (1) a basal tuff overlain by limestone and ferruginous dolomite, (2) interbedded radiolarian-bearing chert and argillite, (3) siltstone and carbonaceous shale, and (4) partly volcaniclastic rocks that include siltstone, shale, and minor sandstone and radiolarian-bearing argillite. Disconformities separate the dolomite from the radiolarian chert and the chert from the siltstone and shale. Abrupt lithologic and faunal changes indicate that the partly volcaniclastic unit is faulted. All but the uppermost (barren) chert samples contain Late Permian (Abadehian and Djulfian) radiolarian taxa belonging to Albaillella, Deflandrella, Ishigaum, Neoalbaillella, and Triplanospongos. These radiolarians suggest that early Wordian conodonts reported from near the top of the chert and argillite unit are reworked. Poorly preserved Early(?) or Middle Triassic radiolarians and Middle Triassic ammonites and pectenacid bivalves from the middle part of the volcaniclastic unit indicate that Early Triassic deposition cannot be documented at the Quinn River locality. Late Triassic (early to middle Carnian) radiolarians assignable to the Triassocampe nova Assemblage Zone of Yao occur about 21 meters below the top of the Quinn River section; diagnostic genera include Castrum, Corum, Poulpus, Pseudostylosphaera, Triassocampe, and Xipha. The ages of the Quinn River brachiopod, conodont, and radiolarian faunas resemble those of the Dekkas and Pit Formations, eastern Klamath terrane, northern California. The Early Triassic age for the lower part of the Pit Formation is questioned because the unit contains only unidentifiable primitive radiolarians and long-ranging (Late Permian and Early Triassic) neogondolellid conodonts. The analogous Quinn River and eastern Klamath rock types and faunal ages, as well as similar hiatuses in their stratigraphic records, suggest that they may be lateral equivalents that formed in the same island-arc sedimentary basin.