Revista de la Asociación Geológica Argentina
versión impresa ISSN 0004-4822
We present numerical ages of lacustrine deposits associated with the San Juan River, which emerge in the depression of Zonda. Four different Quaternary units were identified from downstream bajada deposits, ancient fluvial deposits, lacustrine deposits and present fluvial terrace deposits. The lacustrine sediments were dated on both sides of the valley in the outcrops located in the distal portion of the eastern slope of the sierra de Zonda and the western slope of the Marquesado range. According to the dating and stratigraphic relationships, this lake-swamp episode would have occurred in the late Holocene (2,840 ± 80 BP), remaining around 1,000 years. Towards the eastern side of the valley, the dating yields an age of (1,890 ± 80 AP). The area of the cold and freshwater body would have been around 750 km2 covering a great part of the Zonda and Ullum valley.
Palabras llave : Lacustrine basins; Late Holocene; San Juan River; Central Andes.