Etude de la sedimentation lacustre d'un site de foret d'altitude des Andes centrales (Bolivie). Implications paleoclimatiques

A sedimentological study of a 755 cm length core sampled in the marshy depression surrounded by a cloud forest in the central Andes reveals that this site has recorded important environmental variations during the last 50 000 years. For the most part (625 cm) the core is composed of detrital rich sediments deposited during the Upper Pleistocene. The highest amount of detrital influx underlines the Last Glacial Maximum which ranges from ca 29 000 ¹⁴C yr B.P. to ca 16 000 ¹⁴C yr B.P. (ca 18 500 cal yr B.P.), between two relatively humid phases. The sedimentation of the present Interglacial, starting at ca 12 500 ¹⁴C yr B.P. (14 500 cal yr B.P.), is mainly organic, as a consequence of the great development of soils and the forest vegetal cover all over the catchment area. The maximum extension of this vegetal cover ranging from 12 500 to ca 10 500 ¹⁴C yr B.P. (14 500 and 12 400 cal yr B.P.) is followed from 10 500 to 8000 ¹⁴C yr B.P. (12 400 and 8800 cal yr B.P.) by a drier period as revealed by the occurrence of micro-charcoals in the sediment. Between ca 8000 and 4000 ¹⁴C yr B.P. (8800 and 4500 cal yr B.P.), the sharp increase of micro-charcoals content, likely related to palaeofires, underlines an intensification of this dry trend.