South America

Abstract

The loess record of southern South America covers a vast region of the heterogeneous Chaco-Pampean plain and the mountain valleys of Sierras Pampeanas. Loess deposits have also been reported from the Altiplano of Perú and Bolivia, NE Brazil, the Llanos de Orinoco and Ecuador. The Pampean record extending from the late Miocene to the Holocene is dominantly composed of loessoid (loess-like) deposits resulting from the reworking of primary loess deposits. Loess becomes regionally important during the last glacial cycle. The successions are characterized by the occurrence of carbonate accumulations, a rich vertebrate fossil content, pedogenic features throughout the sections and commonly welded paleosols. Impact glasses (escorias) are a remarkable feature of the southern Pampas successions. The loess–paleosol sequence of Tucuman mountain valleys constitutes the most continuous continental record of high resolution. It extends back to around 1.15Ma. Loess from the Chaco region is known in general but detailed studies remain to be done. The last glacial loess record reveals a heterogeneous composition across the region. The Andes Cordillera has been the main source area of loess deposits. Sierras Pampeanas, the Paraná basin, and some other local sources have also contributed as secondary source areas. Inferred westerly and southwesterly wind directions, as dominant carriers of the eolian deposits, are in agreement with westerly paleowind simulations using climate models.