Paleolimnología del Holoceno de la localidad La Horqueta, Prov. de Bs.As., Argentina.

ZARATE, MARCELO A., FERRERO, LAURA Y ESPINOSA, MARCELA A.

Santiago de Chile

Taller; Taller Internacional "El Cuaternario de Chile".; 1993

Diatomites are important stratigraphic components of Holocene alluvial records of the Pampa Interserrana, Argentina. An Early to Middle Holocene paleoenvironmental record has been obtained by diatom, ostracod and gastropod analysis of a 2.5 m thick section from the Río Quequén Grande, Pampa Interserrana, Argentina. The stratigraphic interval under study extends back to sometimes before 9000 14C yr BP when a  soil forming interval prevailed in the fluvial environment. This paleosol was  alkaline and slighty brackish. Soon after 9000 14C yr BP, more humid-subhumid conditions  started evidenced by the flooding of floodplain depressions and the development of pond environments. Diatom assemblages, ostracods and gastropod shells along with the occurrence of soil features at some levels indicate a very shallow pond up to 2 m deep with seasonally fluctuating water levels. The high biogenic sedimentation that dominated in the pond between 9000 and circa 5000 14C yr BP is synchronic with the interval of soil formation in the catchment area. Therefore the diatomite deposition is recording an interval of biostasy. A shift to much drier conditions occurred sometime  between 5000 and 4000 14C yr BP when dessication and subaereal exposure took place giving rise to soil formation. This was followed by an interval of greater variability revealing environmental instability in the fluvial basin evidenced by the increased amount of siliciclastic deposition.