Upper Quaternary Palaeoclimates of the Mar Chiquita area, North Pampa, Argentina

The Mar Chiquita shallow lake is the largest water body in Argentina, locat ed in a Quaternary tectonic depression (30 degrees 45'S and 62 degrees 30'W ). The southern margin of the depression is dominated by fluvial sediments transported by the Rio Segundo, and aeolian deposits. A 65 km wide alluvial fan is the most significant geological unit. The sequence of climatic even ts in the area is: (I) Upper Pleistocene Dry Period (IS4): development of a large sand sea. (II) Complex Upper Pleistocene Humid Period (IS3): first p hase of pedogenesis on the aeolian landforms and fluvial deposits (Marull S ands). General dissipation of the inherited relief (Carcarana Fm) and proba ble formation of the large alluvial fan (Lagunilla del Plate Fm). Second ph ase of pedogenesis in a flat landscape. During this phase the Mar Chiquita lake acted as local base level. (III) Late Pleistocene Dry Period (IS2; LGM ): deposition of a loess mantle on the surface of the fan (Tezanos Pinto Fm ). (IV) A Subhumid Phase (16,000 yr BP): redistribution of sand dunes (Lomi ta del Indio Fm) and precipitation of pedogenic carbonates in the loess. De velopment of a fluvial terrace. (V) Younger dryas (s.l.): development of de flation hollows associated with lunettes. (VI) Hypsithermal Humid period: g eneral pedogenesis. Rise of the lake level. (VII) Upper Holocene Dry Period : deposition of a loess sheet (San Guillermo Fm), formation of deflation ho llows. (VIII) Little Ice Age: reduction of the lake surface area and format ion of a dune field (Campo Maare Sands). (C) 1999 INQUA/Elsevier Science Lt d. All rights reserved.