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

Abstract

The geological evolution of the lower Carcarañá Basin reflects a sequence of dry and humid climates. From a geomorphological point of view, the area belongs to the Pampean Eolian System. The geomorphological units comprise several 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 and including two pedogenic levels (Carcarañá Fm). The formation is the result of the reworking of a dune field in the Pampean Sand Sea (IS4). It is upper Pleistocene in age (IS 3). Another, somewhat different, climatic deterioration followed (related to the begining of the Last Glacial Maximum -IS 2), which caused the deposition of a loessic mantle (Tezanos Pinto Fm). Subsequent 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 whole sequence. At the river margins of the basin the late Pleistocene/lower Holocene eolian deposits are replaced by a complex silty–clayey sequence, mainly paludal, with a soil complex in the middle of the section (Lucio Lopez Fm).