A Lower Permian mixed fauna from carbonates successions of Chile and its implications in the paleobiogeography of the southwestern Gondwanan margin

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

Congreso; 4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS,; 2014

Outcrops of the early Permian marine deposits from Chile are located in two regions: the Coquimboarea, around the central part of the country (Huentelauquén Formation), and in the north, thewidely 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 ofBoreal type faunas (Yakovlevia (Muirwoodia) Fredericks and Spiriferella Tschernyschew), with otherthat exhibit Tethyan affinities (Liosotella Cooper, Alpavlia Lazarev and Gypospirifer Cooper and Grant).Cosmopolitan elements (Hustedia Hall and Clarke, Cleiothyridina Buckman), as well as, the genusAnidanthus Hill characteristic from Boreal-Tethyan transitional zones, have been also recognized.Faunal assemblages from carbonate deposits of northern Chile are relatively more diversifiedthan those of the Huentelauquén Formation, and they are characterized by abundant brachiopodsaccompanied by bivalves, gastropods, crinoids and bryozoans. Two brachiopod genera are dominantin these assemblages: Waagenoconcha Chao, restricted to the Juan de Morales Formation (Iquiquearea) 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 BorealProvince and they have been also studied from mixed Boreal-Tethyan brachiopod faunas. InArgentina, Kochiproductus has been described from the early Permian carbonate deposits of theArizaro Basin, as well as from the Precordillera, where it is related to a group of gondwanic generathat characterizes the latest Carboniferous Tivertonia jachalensis-Streptorhynchus inaequiornatus Zone.The bivalve fauna associated with the brachiopods from northern Chile is characterized by thegenera Myalina De Koninck, Heteropecten Kegel and Costa and Wilkingia Wilson, which show anextensive latitudinal distribution. However, some of these elements (i.e. Wilkingia, Heteropecten)also described from central-west Argentina and Bolivia, appear usually associated with warmfaunas. This mixed character has been previously identified in the late Carboniferous-early Permianbivalves from the central western Argentinean basins. From a paleobiogeographic viewpoint, earlyPermian faunal assemblages from Chile, particularly the brachiopods, have been generally definedby 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 allowsreconsider the paleobiogeography of the southwestern Gondwana margin.