Late Quaternary aeolian record and paleoclimatic conditions at the distal Andean piedmont, southern Mendoza, Argentina

TRIPALDI, A..; ZÁRATE, M.A.; BROOK, G.

Berna

Congreso; XVIII Congress of the International Union for Quaternary Research; 2011

International Union for Quaternary Research

The eastern plain of Mendoza province, in the distal Andean piedmont of Argentina (32º ?36º S, South America) presents extensive aeolian sandy surfaces, in many cases with dunefields. The aeolian cover is partial stabilized by a shrub steppe of Larrea spp and Gramineae, with aeolian processes occurring barely at the crests and steep sides. This is a semiarid region with mean annual precipitation and temperature of 350 mm and 5ºC, respectively, dominated by summer rainfall of a monsoon-like system, influenced by the South Atlantic anticyclone. Aeolian sand grades laterally to fluvial deposits (Mendoza, Tunuyán, Diamante, Atuel and Desaguadero-Salado rivers), wetlands (e.g. Guanacache lakes) and saline mud flats. Late Quaternary records of these aeolian deposits were studied in river bank exposures from arroyos of southern Mendoza, together with some preliminary information from dune augering in the near Médanos de los Naranjos dunefield. In the river bank sections, channel, floodplain, fluvio-aeolian interaction, reworked pyroclastic and aeolian deposits were identified, described and sampled for OSL dating. Facies analysis indicates ephemeral fluvial aggradation between 40-60 ka and 31-21 ka, under generally semiarid conditions. During LGM (21-14 ka) there were significant aeolian activity represented by dune migration and aeolian sand sheet accretion. Médanos de los Naranjos dunefield, partially eroded in some zones, is formed by crescentic dunes and megadunes, with variable orientations. There are mainly NE-SW crests and leeward facing W-NW at the western area, while at the E crests show a NW-SE orientation and leewards to the NE. Augered sand from different hollows evidences aeolian sedimentation at ca. 10 ka (6 m depth sample), between ca. 4-6 ka (2 m depth samples) and at ca. 2.3 ka (1 m depth sample). These inferred paleoenvironmental conditions of southern Mendoza plain are in broad agreement with regional evidence.