The late Pleistocene-Holocene climatic transition record in the alluvial sequences of central Argentina (33-38° S)

MEHL, ADRIANA E.; ZÁRATE, MARCELO A.

Dona Paula, Goa

Congreso; PAGES 4º Open Science Meeting and 2º Young Scientists Meeting; 2013

National Centre for Antarctic and Ocean Research (NCAOR) and PAGES International Project Office

Alluvial records of central Argentina (33-38° S) have been the focus of detailed sedimentological, stratigraphical and geochronological studies along a west-east climatic transect encompassing the Andean piedmont, the central Pampas and the eastern Pampas of Buenos Aires province, from arid (200 mm/yr mean annual rainfall) to humid (900 mm/yr mean annual rainfall) dominant climatic conditions. The results obtained permitted to infer paleoenvironmental conditions during the late Pleistocene -Holocene climatic transition. At the Andean piedmont between 33-34º S, located in the South American Arid Diagonal, the Late Pleistocene -Holocene alluvial record is composed of sandy and silty deposits accumulated by braided streams in alluvial fan environments punctuated by episodes of volcanic eruptions and the formation of limnic levels. Aeolian process dominated the piedmont during the Last Glacial Maximum and the Late Glacial contributing with fine sediments. A soil stability interval followed documented by a conspicuous paleosoil (12-10 cal yrs BP) developed in a floodplain environment. The early Holocene alluvial deposits record a higher frequency of flooding events and the development of relative more abundant limnic levels reflecting higher organic production in the alluvial environments or higher organic matter inputs to them. The late Pleistocene -Holocene transition in the central Pampas and the eastern Pampas of Buenos Aries province is also recorded by sandy silt fluvial facies with paleosoil developed on top. In the central Pampas this paleosoil was dated in 11.601-12249 and 11.592-12.400 cal yrs BP. Paludal-like aggradation dominated during the early Holocene. Although analyzed alluvial sequences are located in a west-east climatic transect, they show a quasi synchronic behavior during the late Pleistocene -Holocene climatic transition. Paleosoil development indicates a climatic amelioration after arid-cold Late Glacial Maximum and Late Glacial conditions; in turns early Holocene records greater vegetation productivity in the fluvial basins. The conditions reflected across the west-east transect during the early Holocene -Andean piedmont more frequent flooding events and paludal-like environments of the Pampas- might have been linked with summer rains influenced by the South Atlantic anticyclonic center favoured by a southward displacement of the South Pacific anticyclonic center as it has been suggested by many authors (among them Markgraf, 1993; Villagrán, 1993;Zárate y Páez, 2002; Jenny et al.; 2002; Abarzúa,2009; Labraga y Villaba, 2009). References: Abarzúa, A.M, 2009. PhD thesis. Universidad Austral de Chile.74 pp. Jenny. B., Valero-GarcÉs, B.L., Villa-Martínez, R., Urrutia, R., Geyh M., y Veit, H., 2002. Quaternary Research 58,160-170. Labraga, J.C y Villalba, R., 2009. Journal of Arid Environments 73,154-163. Markgraf, V., 1993. In: HE. Jr. Wright, J.E. Kutzbach, T. Webb III, W.F. Ruddiman, F.A. Street-Perrott y P.J. Bartlein (Eds.), Global Climates since the Last Glacial Maximum. University of Minnessota Press, pp. 357-385. Villagrán, C., 1993. Bull. Inst. fr. Études andines 1,243-258. Whitlock, C., M.M. Bianchi, P.J. Bartlein, V. Markgraf, M. Walsh, J.M. Marlon y N. Mc Coy, 2006. Quaternary Research 66,187-201. Zárate, M.A. y Páez, M.M., 2002. In: Trombotto, D., Villalba, R. (Eds.): IANIGLA, 30 años de investigación básica y aplicada en ciencias ambientales. Pp.117-121. IANGyCA, Mendoza, Argentina.