Upper Quaternary geology of the lower Carcarana Basin, North Pampa, Argentina

The geological evolution of the lower Carcarana Basin reflects a sequence o f dry and humid climates. From a geomorphological point of view, the area b elongs to the Pampean Eolian System. The geomorphological units comprise se veral fluvial geoforms, partially masked by a loess carpet, on which eolian erosive forms developed. The sedimentary record is not simple. The typical profile begins with a predominantly eolian unit, composed of silty sand an d including two pedogenic levels (Carcarana Fm). The formation is the resul t of the reworking of a dune field in the Pampean Sand Sea (IS4). It is upp er Pleistocene in age (IS 3). Another, somewhat different, climatic deterio ration followed (related to the begining of the Last Glacial Maximum -IS 2) , which caused the deposition of a loessic mantle (Tezanos Pinto Fm). Subse quent evolution of the climate involved a shift to humid conditions during the Hypsithermal period, generating a well-developed soil at the top of the formation. An upper Holocene eolian layer (San Guillermo Fm) covers the wh ole sequence. At the river margins of the basin the late Pleistocene/lower Holocene eolian deposits are replaced by a complex silty-clayey sequence, m ainly paludal, with a soil complex in the middle of the section (Lucio Lope z Fm). (C) 1999 INQUA/Elsevier Science Ltd. All rights reserved.