Andean icefields to Amazonian jungles: a radical new view of the late pleistocene of South America

Resumo

Late Pleistocene glaciation in the Altlplano of the Central Andes was far more extensive than previously recognized, with all of the northern Altiplano being covered by a glacial icecap. Large paleolakes existed in the Altiplano, but their relationship with glacial episodes is unclear. One Altiplano paleolake filled the basin to the 4,100±m contour drained catastrophically through the Achocalla Valley of Bolivia approximately 45,000-40,000 years B.P. The catastrophic floodwaters flowed north and south upon reaching the lowlands of eastern Bolivia, scouring much of lowland Amazônia and depositing the Belterra Clay. Asymmetric ripplemarks on the Amazon Cone record the passing of the floodwaters into the Atlantic Ocean. The Belterra Clay dammed the eastern outlet of the Amazon drainage to an elevation of 260±m, resulting in the formation of a great freshwater lake, Lake Amazonas Lake Amazonas accumulated vast quantities of fine-grained sediments through deposition in basin-wide "birds's foot" deltas before it began draining eastward about 13,500 years B.P. Except for minor drainage system refinements, the Amazon Basin had assumed its current physical parameters by 6,000 years B.P. Paleolakes may have covered the Altiplano up to the 3,950±m contour in the early Holocene, desiccating to form the modern lakes and salares only in the late Holocene. The geological, biological and climatological ramifications of the Altiplano glaciation and paleolakes, the catastrophic flood and the formation, filling and draining of Lake Amazonas are enormous.