ANALYSIS OF PALEO-WIND DIRECTION FROM VEGETATION STABILIZED DUNES IN LA PAMPA, ARGENTINA

Pampean dune fields in central Argentina have experienced cyclical patterns of deposition and reactivation over at least the past 70 ka. Activation of the now vegetation stabilized dune fields last reached a peak in activity around ~20 ka when aridity was also high. The goal of this research was to better understand the orientation of geomorphically effective winds during phases of dune mobility to elucidate provenance of the eolian sediments and understand synoptic wind patterns during dry glacial periods in La Pampa. Mapping of dune orientations in La Pampa shows that geomorphically effective winds follow a cyclonic pattern (counter-clockwise rotation in the Southern Hemisphere) with a pole of rotation located ~36° S ~66° W. This pattern along with the distribution of loess and loessic paleosol in the northern and southern Pampas suggests rivers and floodplains west and south of La Pampa (e.g., Río Desaguadero and Río Colorado) were the primary sources of these eolian sediments during late Pleistocene glacial periods. This pattern is distinguishable from current near surface winds in the La Pampa which are primarily northerly and are associated with moist air of the Chaco lower-level jet. The pattern is also consistent with a ~5°–10° equatorward shift in the mean position of the westerly winds during glacial periods and lower import of moisture from the Atlantic Ocean into the La Pampa.