Lake-level chronology on the southern Bolivian Altiplano (18 degrees-23 degrees S) during late-glacial time and the early Holocene

Stratigraphic analyses of outcrops, shorelines, and diatoms from the southe rn Bolivian Altiplano (Uyuni-Coipasa basin) reveal two major lacustrine pha ses during the late-glacial period and the early Holocene, based on a chron ology established by radiocarbon and U/Th control. A comparison of C-14 and Th-230/U-234 ages shows that during times of high lake level, radiocarbon ages are valid. However, during low-water periods, C-14 ages must be correc ted for a reservoir effect. The lacustrine Tauca phase started a little bef ore 16,000 C-14 yr B.P., and the lake level reached its maximum between 13, 000 and 12,000 C-14 yr B.P. A dry event (Ticana) occurred after ca, 12,000 and before 9500 C-14 yr B.P. A moderate lacustrine oscillation (Coipasa eve nt) occurred between ca, 9500 and 8500 C-14 yr B.P., using a reservoir-corr ected conventional 14C chronology. Comparisons between the lake-level chron ology in the Uyuni-Coipasa basin and data from other southern tropical area s of South America suggest that the lacustrine evolution may reflect large- scale climatic changes, (C) 1999 University of Washington.