Ostracods from the Pennsylvanian glacial-postglacial successions in the Calingasta-Uspallata basin, CW Argentina.

SALAS, MARIA JOSE; STERREN, ANDREA FABIANA; CISTERNA, GRABRIELA

Salta

Congreso; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2022

Asociacion Paleontologica Argentina

In this contribution we present a preliminary study of the ostracod fauna recorded in the glacialpostglacial successions of three localities in the Calingasta-Uspallata Basin, San Juan province. The knowledge of Upper Paleozoic ostracodsfrom Argentina is scarce and very patchy, the Carboniferous ostracod records are included in a series of isolated papers mainly from Tepuel Genoa basin (Pampa de Tepuel and Las Salinas formations) and Río Blanco basin (Rio del Peñon Formation), with only some mentions in Calingasta–Uspallata basin. The studied fossils were collected in the mudstone intervals of the classical outcrops of the Hoyada Verde and Leoncito formations,where the ostracods appear associated to the Levipustula Fauna, and in the El Paso Formation, related with the AT/RM Fauna. The typical marine invertebrates that accompany these assemblages are brachiopods, bivalves, gastropods, cnidarians, crinoids and bryozoans. The age of these faunas is constrained to the late Serpukovian-Bashkirian, based on the brachiopod assemblages and palinological and radiometric data. The ostracod fauna is, in general, not very diverse and shows a poor state of preservation.However, seven different forms were recognized from the laminated mudstones interbedded with diamictic beds of the basal levels of Hoyada Verde Formation. Between that, one species of Aechminaand one possible species of Graphiadactylloideswere identified. In the middle levels of the El Paso Formation, over the most important diamictitc bed, four genera were registered, among which Aurikirkbya? and Aechminaare identified. Finally, only three species are recognized in the mudstone horizons located below the glacial level in the Leoncito Formation. So far, the most diverse association is that of Hoyada Verde, including the species recorded in the other two localities, except Aurikirkbyawho only is registered in El Paso. Although our knowledge of the ostracods in this region is in its infancy, and a detailed taxonomic analysis should be carried out, the taxa identified so far show affinities with the ostracod fauna from the relatively coeval postglacial levels of the Tepuel Genoa basin (Patagonia), based in the presence of Graphiadactylloides and Aurikirkbya. By other hand, the studied fauna does not present any genus in common with the association of Rio del Peñon Formation (Rio Blanco basin). Respect to their paleobiogeographical affinities, both Graphiadactylloides and Aurikirkbya, have North American affinities; while Aechmina, although it is an abundant and cosmopolitan genus since the Ordovician, during the early Carboniferous only one species from North America is known