LATE QUATERNARY OSTRACODES AND CHAROPHYTES FROM LAGUNA DE LOS POZUELOS (NW ARGENTINA)

The Puna Plateau has a number of hydrologically-closed lakes whose strata potentially contain untapped archives of climate change for the sub-tropical central Andes. Accurate dating of Quaternary lake sediments from arid regions remains a challenge, but sequence stratigraphic interpretations can be improved by integrating lithofacies and bulk geochemical information with biofacies data. In this study, we analyzed calcareous microfossils recovered from modern sediment samples (n=3) and a ~372 cm long sediment core (n=34) collected from Laguna de los Pozuelos (LP), a large playa-lake located within an endorheic Puna basin in northwest Argentina. The goal was to clarify the past ~43,000 yr environmental history of the basin by developing the first paleoecological record of ostracodes and charophytes. Ostracodes were described based on carapace morphology and found to be more diverse than typically associated with high-altitude saline lakes. A minimum of three and a maximum of eleven species were recorded per sample. The ostracode record includes nine limnocytherids and three cypridids, some of which may be endemic. The record of calcareous algae is represented by gyrogonites of two Lamprothamnium species, which typically occur in brackish to saline aquatic ecosystems. Our analysis indicates that both ostracodes and charophytes responded sensitively to short-term lake expansion and contraction dynamics. In general, the ostracodes support the interpretation of an underfilled lake basin made from sequence stratigraphy and have helped to clarify the depositional context for certain lithofacies, especially those related to saline lake and wetland environments. Importantly, population densities, species assemblages, and taphonomy have resolved a key transition from lateral to axial deltaic inputs, which altered the paleogeography and hydrochemistry of LP in the late Quaternary.