Late Pleistocene and Late Holocene environment and climate in the campos region of southeastern South America inferred from phytolith, diatom and geochemical data

A paleolimnological study was undertaken for a sediment core from Laguna Formosa, a subtropical lake in the northern campos inland region of Uruguay. The record encompasses a Late Pleistocene and Late Holocene interval, interrupted by a hiatus. We analyzed (1) opal phytoliths and diatoms to infer the regional environment, climate, and changes in lake trophic state, and (2) total carbon and nitrogen (TC and TN) and stable isotope data (delta C-13 and delta N-15) to infer organic matter sources and composition. Findings indicate that, in Late Pleistocene times, a cool, semi-arid or highly seasonal climate existed, with a dominance of C3 grasslands and riparian hydrophilous shrublands while the shallow freshwater environment was characterized by benthic diatoms and littoral macrophytes. Late Holocene times were initially characterized by a temperate and humid or sub-humid climate, and dominance of grasslands and bunch grasses, while Laguna Formosa was dominated by phytoplankton. The abundance and diversity of littoral hydrophilic vegetation, and riparian forest vegetation, increased progressively over time, as a result of increased rainfall, from ca. 1800 cal yr BP and the onset of a subtropical (temperate and humid) climate by ca. 1300 cal yr BP. Such inferences are in close agreement with an earlier palynological study of Laguna Formosa, and support the paleoclimatic models for the Late Pleistocene and Late Holocene of southeastern South America.