Paleolimnology of Laguna Cerrillo del Medio, Monte, Buenos Aires Province

Abstract

The regional physical environment was characterized, describing the physiographic and geomorphic features, the hydrologic regime and the origin of the shallow lake basin. The surficial geology is defined by ten stratigraphic units (seven lithostratigraphic units and three geosols); the oldest one, Ensenada Formation of Middle Pleistocene, makes up the regional substrate, in which the lake basin was excavated. It is overlain by the loess of the Buenos Aires Formation of Late Pleistocene, which is topped by a geosol. The four overlying units are constituted by aeolian deposits (clay dunes and loessic sediments) and two paleosols, ascribed to La Postrera I, II, III and IV Formation from Late Pleistocene to Upper Late Holocene age and the Puesto Callejón Viejo and Puesto Berrondo Geosols. In the lakes infilling sediments, six stratigraphic units were recognized. Five of them are aquatic deposits of decreasing age: Luján Formation, La Chumbiada, Lobos and Río Salado Members from Late Pleistocene to Early to Middle Holocene age; suballuvial formation of Late Holocene and the recent alluvial formation, The sixth unit is a Late Pleistocene intrabasinal clay dune deposit. The sequence of geologic events is registred in the infilling sediments and those of the lake surroundings, which encompass a span much more than 64 ky, represented by five dry climate episodes, from the Buenos Aires Formation loess of Late Pleistocene to La Postrera IV Formation loess, assigned to the little ice age, i.e: IS4, IS2, D3-L3, D2-L2, D1-L1 and five humid, i.e: IS3, S3, IS1, S1 and the present alluvial sediments.