LATE QUATERNARY SPATIOTEMPORAL LIMNOLOGICAL VARIATIONS IN THE ALTIPLANO OF BOLIVIA AND PERU

Between the western and eastern Andean cordilleras in Peru and Bolivia, there are three main lacustrine basins: Lake Titicaca, Lake Poopo, and the group of Coipasa-Uyuni. For the past few millennia, highly variable environmental conditions have been recorded in their sediments. Today a latitudinal meteorological gradient influences the lakes' status, leading to specific deposits and ostracod communities. Lake Titicaca in the north is oligohaline, whereas Lake Poopo further south is polyhaline. In the south, the Coipasa-Uyuni depression is characterized by a 12,000-km(2) surficial salt crust. During the Late Pleistocene (ca. 40,000 to 25,000 yr B.P.), the water depth and salinity in paleolake Poopo fluctuated widely and paleolake Titicaca was slightly larger than at present. Sedimentation was mostly biocarbonate in the shallower areas and it was detrital-organic in the deepest zones. During the Holocene, a dry period transformed Lake Poopo into a ''salar'' with evaporite precipitation. Lake Titicaca registered a large decline in water leve1 (8100-3600 yr B.P.) initially inducing gypsum precipitation followed by short influxes of water, with an ostracod faunal composition similar to that of the modern brines of Lake Poopo. Lake Titicacas' present condition only appeared between 2200 and 1500 yr B.P. (C) 1995 University of Washington.