O-18 AND C-13 RECORDS FOR THE LAST 14,000 YEARS FROM LACUSTRINE CARBONATES OF SILING-CO (LAKE) IN THE QINGHAI-TIBETAN PLATEAU

To understand paleoenvironmental changes for the central Qinghai-Tibet an plateau, we analyzed stable isotopes of oxygen and carbon from calc ium carbonates in a bottom sediment core collected from Siling-Co (lak e). Five conventional and two TAMS C-14 dates indicate that the core r ecovered sediments of the last 14,000 years. Calcium carbonates in the sediments seem to be primary carbonates precipitated chemically in th e lake, and not clastic particles from limestones distributed around t he lake, because of large variation of isotopic ratios, isotopic covar iance since 6,000 yr BP and similarity between dates from total calciu m carbonates and organic carbon. Their isotopic composition therefore reflects that of the lake water. We present the following paleoenviron mental history over the last 14,000 years in the central part of the p lateau, from secular variations of deltaO-18, deltaC-13 and CaCO3 cont ent throughout the core: (1) Desiccation was dominant during the latte r part of the Last Glacial stage (14,000 to 11,000 yr BP). (2) The Las t Glacial stage abruptly terminated at 11,000 yr BP. (3) A temperate a nd stable climate was dominant from 11,000 to 5,000 yr BP. (4) Climati c conditions fluctuated from 5,000 to the present, including two stron g desiccation periods (5,000 to 4,000 yr BP and 3,000 to 2,000 yr BP) and an intermediate period of heavy rainfall (4,000 to 3,000 yr BP). T his period is also characterized by a covariant O and C isotopic trend .