Abstract

We have started a program of detailed mapping and sampling buried paleosols and paleodunes sequences that occur along the semiarid coast of central Chile (32-34ºS). Previous work has postulated these stratigraphic records afford evidence for past climate change linked to the latitudinal oscillations/intensification of the southern westerly winds (SWW): Bt horizons resembling humid conditions associated with north shifted SWW, and paleodunes with arid conditions and south shifted SWW. Nonetheless, multiple factors can affect long-term (e.g., orbital to suborbital time-frames) eolian dune variability (stabilization-reactivation, expansion-contraction, pedogenesis-morphogenesis), including sea level, sediment supply, wind intensity, and tectonics. It is therefore a pending work to expand our research in these eolian archives and understand their causes and environmental implications. Here, we present preliminary research results from the Ritoque paleodune, Comuna de Quintero, Chile (32ºS). The study site is a 15 m deep gully incision that allowed us to built a very complete sediment stratigraphic sequence postdating the Miocene-Pliocene marine Horcón Formation. Previous luminescence geochronologic control in nearby paleodune deposits indicate eolian morphogenetic and pedogenetic activity during the last glacial period. We interpret the geomorphic context together with standard sediment field and laboratory data to discriminate between stratigraphic units and their origin. A total of 13 sediment units were mapped, which include mostly couplets of buried paleosols (Bt horizons) and underlying paleodunes. Other units resembling rather paleowetlands and possibly sea side sand beaches were also found. We discuss our results in light of available evidence to unravel the environmental meaning of this extraordinary well-preserved terrestrial record in the SE subtropical Pacific.