Abstract
Stratigraphic studies on loess deposits in the intramontane basin of Valle de Tafı́ (27°S, 66°W) revealed up to 31 intercalated paleosols. In order to clarify the chronostratigraphic position of the sediments, we performed paleomagnetic investigations in the 50-m-thick Las Carreras section. The characteristic remanent magnetization (ChRM) obtained after alternating field (AF) demagnetization gives clear evidence of the Matuyama-Brunhes boundary (MBB) at a profile depth of 26.7 m , and of the Jaramillo subchron at depths from 38.7 to 44.9 m . We assign a minimum age of 1.15 Ma to the onset of loess sedimentation, which calls for a complete reassessment of the antiquity of loess in the region. Thus, the Las Carreras sequence, which is probably continuous and complete, represents one of the longest Quaternary terrestrial paleoclimatic records reported from the southern hemisphere. The magnetic susceptibility signal follows the behavior known for Argentinian eolian sediments — though with certain restrictions and an overall weak correlation with pedostratigraphy. This behavior is opposite to the pattern reported from the Chinese Loess Plateau (CLP) and seems to be influenced strongly by changing source materials contributing to the susceptibility signal in Valle de Tafı́.
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