LACUSTRINE SEDIMENTATION IN AN ALTITUDE F OREST SITE, CENTRAL ANDES, BOLIVIA - PALEOCLIMATIC IMPLICATIONS

A sedimentological study of a 755 cm length core simpled in the middle of a marshy depression surrounded by a cloud forest in the central An des reveals that this site has recorded important environmental variat ions during the last 50 000 years. For the most part (625 cm) the core is composed of detrital rich sediments deposited during the Upper Ple istocene. The highest amount oi detrital influx underlines the Last Gl acial Maximum which ranges from ca 29,000 yr B.P, to ca 16,000 C-14 yi B.P. (ca 18,500 cal pr B.P.), between two relatively humid phases. Th e sedimentation of the present Interglacial, starting at ca 12,500 C-1 4. yr B.P. (14,500 cal yr B.P.), is mainly organic, as a consequence o f the great development of soils and the forest vegetal cover all over the catchment area. The maximum extension of this vegetal cover rangi ng from 12,500 to ca 10,500 C-14 pr B.P. (14,500 and 12,400 cal yr B.P .) is followed from 10,500 to 8,000 C-14: yr B.P. (12,400 and 8,800 ca l pr B.P.) by a drier period as revealed by the occurrence of micro-ch arcoals in the sediment. Between ca 8,000 and 4.000 C-14 yr B.P. (8,80 0 and 4,500 cal yr B.P.), the sharp increase of micro-charcoals conten t, likely related to palaeofires, underlines an intensification of thi s dry trend.