A LOWER PERMIAN MIXED FAUNA FROM CARBONATE SUCCESSIONS OF CHILE AND ITS IMPLICATIONS IN THE PALEOBIOGEOGRAPHY OF THE SOUTHWESTERN GONDWANA MARGIN

CISTERNA, G.A.; STERREN, A.F.; NIEMEYER, H.

Mendoza

Congreso; 4º International Palaeontological Congress; 2014

Outcrops of the early Permian marine deposits from Chile are located in two regions: the Coquimbo area, around the central part of the country (Huentelauquén Formation), and in the north, the widely extended sequences of Juan de Morales, Cerros de Cuevitas and Cerro El Árbol formations. Brachiopods dominate the marine fauna of the Huentelauquén Formation although scarce trilobites, bivalves and bryozoans are mentioned. The group of brachiopod genera described is composed of Boreal type faunas (Yakovlevia (Muirwoodia) Fredericks and Spiriferella Tschernyschew), with other that exhibit Tethyan affinities (Liosotella Cooper, Alpavlia Lazarev and Gypospirifer Cooper and Grant). Cosmopolitan elements (Hustedia Hall and Clarke, Cleiothyridina Buckman), as well as, the genus Anidanthus Hill characteristic from Boreal-Tethyan transitional zones, have been also recognized. Faunal assemblages from carbonate deposits of northern Chile are relatively more diversified than those of the Huentelauquén Formation, and they are characterized by abundant brachiopods accompanied by bivalves, gastropods, crinoids and bryozoans. Two brachiopod genera are dominant in these assemblages: Waagenoconcha Chao, restricted to the Juan de Morales Formation (Iquique area) and Kochiproductus Dunbar that appears accompanied by Kozlowskia Fredericks, Gypospirifer, Hustedia, Cleiothyridina and Dielasma King, in the Cerros de Cuevitas and Cerro El Árbol formations (Antofagasta area). Waagenoconcha and Kochiproductus are common but not restricted to the Boreal Province and they have been also studied from mixed Boreal-Tethyan brachiopod faunas. In Argentina, Kochiproductus has been described from the early Permian carbonate deposits of the Arizaro Basin, as well as from the Precordillera, where it is related to a group of gondwanic genera that characterizes the latest Carboniferous Tivertonia jachalensis-Streptorhynchus inaequiornatus Zone. The bivalve fauna associated with the brachiopods from northern Chile is characterized by the genera Myalina De Koninck, Heteropecten Kegel and Costa and Wilkingia Wilson, which show an extensive latitudinal distribution. However, some of these elements (i.e. Wilkingia, Heteropecten) also described from central-west Argentina and Bolivia, appear usually associated with warm faunas. This mixed character has been previously identified in the late Carboniferous-early Permian bivalves from the central western Argentinean basins. From a paleobiogeographic viewpoint, early Permian faunal assemblages from Chile, particularly the brachiopods, have been generally defined by their Tethyan affinities, closely related to those from Copacabana Formation in Bolivia and Perú. The new studies indicate that these assemblages can be understood as a mixed fauna, which allows reconsider the paleobiogeography of the southwestern Gondwana margin.