The Cisuralian faunal succession in Patagonia

PAGANI, MARÍA ALEJANDRA; TABOADA, A. C.

Melbourne, Australia

Congreso; 6 th International Brachiopod Congress; 2010

Geological Society of Australia

Marine lower Permian deposits bearing the brachiopod genus Costatumulus Waterhouse (in Waterhouse et al' J 1983) are known from the Tepuel-Genoa basin, located in the Patagonian region (Chubut Province)of southern Argentina. The basin enclosed a wide embayment open to the Panthalassic Ocean at the southwestern border of Gondwana, and was infilled by a nearly 7000m continuous sequence (Tepuel Group) of clastic sediments from the early Carboniferous (late Tournaisian) to the Early Permian (Artinskian). Earliest Permian faunas were recognised in the upper part of the Pampa de Tepuel Formation, but the first record of a Costatumulus-like faunal assemblage starts at the lower section of the overlying Moj6n de Hierro Formation and ends at the uppermost RIo Genoa Formation. Costatumulus was first recognised in the early Permian of the Calingasta-Uspallata subbasin, western Argentina (Precordillera), with the species C. amosi Taboada (1998), formerly Cancrinella dr. farleyensis (Etheridge & Dun) Amos (1960). Recently, refined lithostratigraphy and biostratigraphy of the Moj6n de Hierro and Rio Genoa formations has allowed us to extend the stratigraphic range for the Costatumulus Biozone within the Tepuel-Genoa basin (Taboada & Pagani, 2009). New material collected from different localities and fossiliferous horizons throughout this basin suggests a greater number of species than previously thought (previously, only Costatumulus and an allied genus Magniplicatina Waterhouse were known from this biozone). Such adjustment in the taxonomic composition of the Costatumulus Biozone permits the recognition of six different and successive faunal assemblages within the basin. These are, in ascending order: the Cimmeriella fauna (~Late Sakmarian) bearing Costatumulus sp. 1 (formerly Cancrinella d. farleyensis of Amos, 1960); the newly recognised Costatumulus-Kochiproductus (~Latest Sakmarian-earliest Artinskian) assemblage bearing Costatumulus sp. 2, recovered from the upper section of the Mojon de Hierro Formation; the Costatumulus-Tivertonia assemblage (~early Artinskian) from the lower Rio Genoa Formation containing Costatumulus sp. 3, and the Jakutoproductus (~early late Artinskian), Piatnitzkya (~ early late-middle Artinskian) and Magniplicatina sp. (~middle Artinskian) assemblages from the uppermost section of the Rfo Genoa Formation. The taxonomic composition of the Costatumulus Biozone faunal succession in Patagonia appears to suggest strong faunal links with western Australia, Cimmeria (south and southeast Asia) and Siberia-Arctic and also, albeit subordinate, links with eastern Australia.