Late Quaternary continental and marine sediments of northeastern Buenos Aires province (Argentina): Fossil content and paleoenvironmental interpretation

Abundant invertebrate and vertebrate fossil remains that exhibit excellent preservation and were collected from deposits of both continental and marine origins at Pilar (Buenos Aires, Argentina) add paleoenvironmental data from the northeastern Buenos Aires province area linked to sea-level oscillations and climate variability since approximately 120 ka BP (marine oxygen isotope stage [MOIS] 5e). Two new fossiliferous localities discovered in the Luján River Valley allow for detailed geological studies and new dating of molluscan shells and bones. The studies suggest salinity changes during the Last Interglacial (8 m above m.s.l., min. 14C>40 ka) and the mid-Holocene transgression (5 m above m.s.l., 7-3 14C ka BP) compared with the modern pattern along the adjacent littoral (Río de la Plata). The marine sequences represent the innermost boundary of the sea-level transgression in that area and contain a biogenic record (bivalves, gastropods, forams, ostracods) that indicates marginal marine environments (higher salinity than at present). Vertebrates and molluscs from the continental sequence suggest a freshwater habitat in which remains of marine fish must be allochthonous, probably incorporated by postmortem fluvial transport to the final depositional environment.