Paleoenvironmental Reconstruction of the Pleistocene Regressive Marine Successions from Salado Basin, Northeastern Buenos Aires (Argentina)

Paleontological content (both trace fossils and microfossils) of two outcrops of the Puente de Pascua Formation (Late Pleistocene, Salado Basin, northeastern Buenos Aires, Argentina) are studied in order to reconstruct the paleoenvironmental and paleoecological conditions. Successions are located at the modern coastal plain and were deposited during the last interglacial MIS 5 (∼120 ka). At the Puente de Pascua site, the type locality of the Puente de Pascua Formation, the trace fossil assemblages and the lithofacies associations were analyzed, whereas an integrated sedimentological and micropaleontological analysis was carried out at Pipinas city. At the Puente de Pascua site, sediments were accumulated in subtidal to intertidal back-barrier tidal flat and subsequently in a continental setting. Six ichnotaxa, three trace fossils in open nomenclature and one belonging to a bioclaustration structure of both soft- and firmground were recognized: Ophiomorpha nodosa, Nereites uniserialis, N. biserialis, N. missouriensis and N. multiserialis. Additionally, the bivalve trace fossil Scalichnus isp, produced by the solecurtid bivalve Tagelus plebeius, was recognized. Rhizoliths and vertebrate burrows indicate loessoid continental settings in which burrowing may have been relatively hard. Towards the northwest, at Pipinas city, shelly ridge/bar facies with low diversity of benthic foraminifer assemblages are interpreted as a brackish settings corresponding to high energy foreshore. In the shallow, marginal marine facies defined, Skolithos, Nereites and Psilonichnus ichnofacies are recognized.