The Upper Paleozoic in Patagonia (Tepuel-Genoa Basin, Chubut Province, Argentina)

PAGANI, MARÍA ALEJANDRA

Melbourne, Australia

Simposio; First International Symposium and Field workshop on the Permian of Gondwana; 2008

School of Life and Environmental Sciences, Deakin University

The aim of this contribution is to present the recent taxonomic and biostratigraphical advances in Tepuel-Genoa Basin. The Upper Paleozoic outcrops in Argentina are mainly distributed along the western margin of the country. The Tepuel-Genoa Basin is located in the northwestern region of Patagonia in Chubut province, Argentina, and the outcrops are distributed from north-northwest to south-southeast trends, along 250 km approximately. This basin was located on the southwestern border of Gondwana, is thicker than 5000 m, and constitutes a continuous and complete sequence from the Early Carboniferous to the Early Permian. In this sense, the Tepuel-Genoa Basin is probably the most complete Upper Paleozoic sequence of Gondwana, and a potential pattern for regional correlation. Many authors have described the stratigraphy of the basin; the strata are unconformably underlain by Devonian granite and overlain by Lower Jurassic marine strata. The sediments, at the type locality of Sierra de Tepuel, include from base to top the Jaramillo, Pampa de Tepuel and Mojón de Hierro Formations. To the east-northeast, the sediments are exposed in the Sierra de Languiñeo and have been assigned to the Las Salinas Formation. Farther south, in the Río Genoa region, the basin is represented by the Río Genoa Formation. The marine Upper Paleozoic of Patagonia has yielded abundant and well preserved representatives of most invertebrate groups: brachiopods, bivalves, gastropods, cephalopods, hyolithids, crinoids, ostracods and cnidarians.  In the last years, the studies on the Patagonian faunas have originated substantial advances as well as different opinions on the ages that were assigned to fossils therein found. Particularly mollusks have been studied exhaustively and new species of bivalves, cephalopods, gastropods and hyolithids were described.    The biostratigraphic correlation in Tepuel-Genoa Basin is complex because of the high faunistic provincialism, as a consequence of the different climatic conditions in the Earth during Carboniferous and Permian times. For this reason, there are several hypotheses about the biostratigraphic zonation in the basin. Different biostratigraphic charts have been proposed following the stratigraphic distribution of different invertebrate groups, the most recent of which was based on mollusk faunas. In the last ten years, the biostratigraphic charts of this basin, and specially the age of biozones changed in many opportunities, mainly because of the different systematic proposals for brachiopods and the advances of studies on mollusks.  At the moment, in order to unify biostratigraphic criteria, we are working to achieve a complete record of the different faunistic associations, with an exact stratigraphic position in the section and more precise taxonomic determination. For this reason, an exhaustive stratigraphic and paleontological research is being done especially in the type section of Patagonian basin. The aim of this study is to obtain a correlation of the sequences of different outcrops of the basin and to propose a biostratigraphic chart. Once this goal is achieved, a global correlation can be conducted, especially with other section in Gondwana and the Arctic.