A 3500 C-14 YR HIGH-RESOLUTION RECORD OF WATER-LEVEL CHANGES IN LAKE-TITICACA, BOLIVIA PERU/

Sediment cores collected from the southern basin of Lake Titicaca (Bol ivia/Peru) on a transect from 4.6 m above overflow level to 15.1 m bel ow overflow level are used to identify a new century-scale chronology of Holocene lake-level variations. The results indicate that lithologi c and geochemical analyses on a transect of cores can be used to ident ify and date century-scale lake-level changes. Detailed sedimentary an alyses of subfacies and radiocarbon dating were conducted on four repr esentative cores. A chronology based on 60 accelerator mass spectromet er radiocarbon measurements constrains the timing of water-level fluct uations. Two methods were used to estimate the C-14 reservoir age. Bot h indicate that it has remained nearly constant at similar to 250 C-14 yr during the late Holocene. Core studies based on lithology and geoc hemistry establish the timing and magnitude of five periods of low lak e level, implying negative moisture balance for the northern Andean al tiplano over the last 3500 cal yr. Between 3500 and 3350 cal yr B.P., a transition from massive, inorganic-clay facies to laminated organic- matter-rich silts in each of the four cores signals a water-level rise after a prolonged mid-Holocene dry phase. Evidence of other significa nt low lake levels occurs 2900-2800, 2400-2200, 2000-1700, and 900-500 cal yr B.P. Several of the low lake levels coincided with cultural ch anges in the region, including the collapse of the Tiwanaku civilizati on. (C) 1997 University of Washington.