Late Quaternary aeolian and fluvial-aeolian deposits from southwestern Pampas of Argentina, southern South America

Abstract

The central region of Argentina, southern South America, is characterized by an extensive Quaternary aeolian record. In this context, three locations from the southwestern Pampas, an Andean foreland region bearing a rich fossil mammal record that contributed to the South America biostratigraphic scheme, were selected to carry out a comprehensive sedimentological analysis of the late Quaternary deposits. The case studies are located at the Transverse Valleys of La Pampa province (Chapalcó, Quehué and Utracán-Argentino valleys), and exhibit a high resolution of the late Quaternary in comparison with others areas of the southwestern Pampas. The Toay locality (~36° 41′S, 64° 24′W) records aeolian-dominant activity since the end of the Late Pleistocene (~30 ka) onwards, soil formation at some point during the Holocene and early–mid 20th century reactivation of aeolian process. The Arroyo Quehué locality (~37°04′S, 64°42′W) presents a Late Pleistocene-Holocene succession mostly related to an ephemeral endorheic fluvial system, with an interval of relative surface stabilization and aeolian aggradation during the Late Holocene. The Utracán locality (~37°17′S, 64°35′W) exhibits a prevailing aeolian and fluvial-aeolian interaction succession developed in the mid-to Late Holocene in a sand-mud flat environment of a shallow saline lake. The three studied cases are representative of aeolian aggradation in association with ephemeral fluvial, shallow lake and pedogenic processes in a currently subhumid-dry region. Numerical ages indicate sedimentation during the last ~30 kyr. They allow constraining and evaluating the paleoenvironmental conditions in this inland region of southern South America, and provide age constraints for the regional databases of paleoclimatic proxies. The results are in agreement with other late Quaternary paleoclimatic-paleoenvironmental archives of central Argentina and show a fragile aeolian landscape that is susceptible to deterioration under extreme conditions, including both aeolian reactivation during dry phases and erosion of sandy-silty sediments during wet phases.