OSTRACODS FROM THE PENNSYLVANIAN GLACIAL-POSTGLACIAL SUCCESSIONS IN THE CALINGASTA-USPALLATA BASIN, CW ARGENTINA

SALAS, M.J.; STERREN, A. F.; CISTERNA, G.A.

Salta

Congreso; RCAPA; 2022

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. Theknowledge of Upper Paleozoic ostracodsfrom Argentina is scarce and very patchy, theCarboniferous ostracod records are included in a series of isolated papers mainly from TepuelGenoa basin (Pampa de Tepuel and Las Salinas formations) and Río Blanco basin (Rio del PeñonFormation), with only some mentions in Calingasta–Uspallata basin. The studied fossils werecollected in the mudstone intervals of the classical outcrops of the Hoyada Verde and Leoncitoformations,where the ostracods appear associated to the Levipustula Fauna, and in the El PasoFormation, related with the AT/RM Fauna. The typical marine invertebrates that accompany theseassemblages are brachiopods, bivalves, gastropods, cnidarians, crinoids and bryozoans. The age ofthese faunas is constrained to the late Serpukovian-Bashkirian, based on the brachiopodassemblages and palinological and radiometric data. The ostracod fauna is, in general, not verydiverse and shows a poor state of preservation.However, seven different forms were recognizedfrom the laminated mudstones interbedded with diamictic beds of the basal levels of Hoyada VerdeFormation. Between that, one species of Aechminaand one possible species ofGraphiadactylloides were identified. In the middle levels of the El Paso Formation, over the mostimportant diamictitc bed, four genera were registered, among which Aurikirkbya? and Aechminaareidentified. Finally, only three species are recognized in the mudstone horizons located below theglacial level in the Leoncito Formation. So far, the most diverse association is that of HoyadaVerde, including the species recorded in the other two localities, except Aurikirkbyawho only isregistered in El Paso. Although our knowledge of the ostracods in this region is in its infancy, and adetailed taxonomic analysis should be carried out, the taxa identified so far show affinities with theostracod 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 faunadoes not present any genus in common with the association of Rio del Peñon Formation (RioBlanco basin). Respect to their paleobiogeographical affinities, both Graphiadactylloides andAurikirkbya, have North American affinities; while Aechmina, although it is an abundant andcosmopolitan genus since the Ordovician, during the early Carboniferous only one species fromNorth America is known.