Fossil gastropods from relictic Pleistocene palustrine deposits of Tiopunco, Santa María Valley, Tucumán, Argentina

Abstract

This study documents a Pleistocene fossil gastropod assemblage from the Tiopunco area, Santa María Valley, Tucumán Province,
northwestern Argentina. Fossil material was recovered from two discrete fossiliferous levels within the Divisadero Chico profile, developed in fine-grained palustrine deposits that rest unconformably on the Andalhuala Formation. The assemblage includes freshwater, amphibious, and terrestrial gastropods, associated with scarce vertebrate remains represented by micromammals and possible birds. A detailed taxonomic revision refines previously reported identifications and allows recognition of Galba viator, Biomphalaria sp., Radiodiscus sp. aff. R. compactus, Succinea sp., Scolodonta semperi, and Rotadiscus amancaezensis, the latter two recorded for the first time at this locality. Gastropod shells are commonly preserved as complete or nearly complete specimens, with differential fragmentation related to shell size and thickness. Sedimentological and taphonomic evidence, including the absence of abrasion, the presence of in situ root structures, and pedogenic features, indicates low-energy depositional conditions and relatively rapid burial. Overall, the Tiopunco assemblage represents an autochthonous to parautochthonous record formed in shallow palustrine environments with episodic subaerial exposure, contributing new and chronologically constrained data to the Quaternary paleontological record of intermontane Andean valleys.