Eolian events in Médanos Grandes dune field (San Juan province) during the late Holocene

TRIPALDI, A.; FORMAN, S.L.

Malargüe, Mendoza, Argentina

Simposio; Reconstructing Past Regional Climate Variations in South America over the late Holocene: a new PAGES initiative; 2006

Past Global Changes, core project of the International Geosphere-Biosphere Programme (IGBP)

Although eolian sand is ubiquitous in western intermontane valleys of Argentina, reflecting significant climate variability in the Late Quaternary and Holocene, this record has not yet adequately deciphered. A first dating of eolian sand in Médanos Grandes dune field (MG) have allowed obtaining several ages from the last 2200 yrs. MG dune field, located to the south of San Juan province, is one of the largest and tallest intermountain eolian system in Argentina. It is placed in one of the driest region of Argentina, with a mean annual precipitation of 88.3 mm/yr and >80% of the precipitation occuring between October and March (1901-1990) and where austral summer temperatures can often exceed 40°C. The resultant drift potential are due north at 352°, characterized by low energy winds. MG dune field is formed by a complex dune-field pattern pointing out the superimposition of different dune types due to several episodes of eolian construction/reactivation. At Lizard section (31° 41,957’ S; 68° 9,76’ W), to the northwest of MG dune field, eolian units cover alluvial gravel and are represented by sand sheet deposits. OSL ages for quartz extracts from that eolian sands indicate depositional ages of 2070 ± 150, 600 ± 40, 400 ± 45 and 410 ± 40 yrs BP.