Brachiopods and molluscs from the Permian Arcturus Formation, Nevada and Utah - BAP #303
The Arcturus Group, early Permian, of eastern Nevada and western Utah contains the Riepe Spring Formation at the base, Riepetown Formation, Pequop Formation, and Loray Formation at the top, and ranges in thickness from less than 1000 meters to greater than 2000 meters. The base of the Arcturus Group is early Wolfcampian in the western and northern parts of the area, and middle Wolfcampian in the center of the depositional area. Deposition of sediments continued without significant interruption until the late Leonardian. The Leonardian-Guadalupian boundary occurs in the overlying Kaibab Formation.
Normal salinity marine biotas are common throughout, and biotas representing hypersaline environments are present in the upperpart of the Arcturus Group. Biotas representing hyposaline (brackish) and fresh-water environments are not recognized and are probably absent.
Arcturus Group biotas are dominated by brachiopods and molluscs. Brachiopod diversity and abundances are low, except for the genera Squamaria, Costellarina, and Composita. The small productacean Costellarina is common in shallow-water molluscan-dominated biotas and is the most common brachiopod in the Arcturus. Brachiopods described as new are Costellarina kaasai, n. sp., Costellarina piasi, n. sp., Costellarina carlstroemi, n. sp., and Wilberrya fragilis, n. gen. and n. sp. The Costellarininae are transferred from the Strophalosiacea to the Productacea (Linoproductidae) on the basis of new information on the type genus Costellarina.
Mollusc diversity and abundance are high in almost all biotas. Scaphopods, rostroconchs, and bivalves of the superfamilies Ctenodontacea, Nuculanacea, Arcacea, Pinnacea, and Ambonychiacea are described in this part of the study. Molluscan taxa designated as new are the bivalves, Quadratonucula stella, n. sp., Polidevcia arctura, n. sp., and Girtyana stellara, n. sp., and Meckopinna, n. gen.
T.E. Yancy
Pages: 115, 10 pls.
Year published: 1978