LIMNOGEOLOGY OF LAGUNA MISCANTI - EVIDENCE FOR MID TO LATE HOLOCENE MOISTURE CHANGES IN THE ATACAMA ALTIPLANO (NORTHERN CHILE)

Sedimentological, mineralogical and geochemical analyses of sediment c ores from 9 m-deep, saline Laguna Miscanti, Chile (23 degrees 44'S, 67 degrees 46'W, 4140 m a.s.l.) together with high-resolution seismic pr ofiles provide a mid to late Holocene time series of regional environm ental change in the Atacama Altiplano constrained by (210)pb and conve ntional C-14 dating. The mid Holocene was the most arid interval since the last glacial maximum, as documented by subaerial exposure and for mation of hardgrounds on a playa surface. Extremely low lake levels du ring the mid Holocene appear consistent with lower effective moisture recorded at other sites along the Altiplano and in the Amazon Basin. T ermination of this arid period represented a major shift in the region al environmental dynamics and inaugurated modern atmospheric condition s. The cores show a progressive upward increase in effective moisture interrupted by numerous century-scale drier periods of various intensi ties and durations that characterize a fluctuating late Holocene clima te. In spite of chronological uncertainties, the major environmental c hanges seem to correlate with the available paleorecords from the regi on providing a coherent account of effective moisture variability in t he tropical highlands of South America.