Brachiopods from the Serpukhovian Tonka Formation of Carlin Canyon, Elko, Nevada (USA): Systematics and biostratigraphy

Systematic study of a brachiopod assemblage from the upper Mississippian Tonka Formation in Carlin Canyon, Elko, Nevada, USA, led to the recognition of 13 species, representing 12 genera and seven orders: ?Antiquatonia sp., Flexaria sp., ?Marginatia sp., Echinoconchus sp. of the Productida, ?Orthotetes sp. of the Orthotetida, Rhipidomella sp., Schizophoria sp. of the Orthida, Cleiothyridina cf. sublamellosa Hall, 1858, Composita sulcata Weller, 1914 of the Athyridida, Anthracospirifer shawi shawi Gordon, 1975, Anthracospirifer aff. A. shawi of the Spiriferida, Punctospirifer sp. of the Spiriferinida, and Girtyella indianensis Girty, 1909 of the Terebratulida, with the addition of one undetermined linoproductid and one genus and possibly two undetermined species of the Delthyridina. The assemblage shares affinities with late Chesterian (middle Serpukhovian) Carlinia phillipsi and C. amsdeniana associations from western North American units, though the presence of Composita sulcata makes it also close to latest Chesterian faunas (Rhipidomella nevadensis and Composita popsiensis zones). The recorded faunal association, in terms of composition at the genus-level, is characteristic of brachiopod Unit 16 of Carter (1990a). Unit 16 spans the middle Chesterian (Gnathodus bilineatus conodont Zone) to upper Chesterian (Rachistognathus muricatus conodont Zone), corresponding to the upper Visean–Serpukhovian interval. A monospecific Volgegnathus postcampbelli conodont assemblage from the same locality confirms a late Chesterian (Serpukhovian) age of the fauna.