湖相自生沉积作用与环境──兼论西藏色林错沉积物记录

LACUSTRINE AUTHIGENIC DEPOSITION EXPRESSIVEOF ENVIRONMENT AND THE SEDIMENT RECORDFROM SILING CO, XIZANG (TIBET), CHINA

内陆封闭湖泊自生沉积作用与当地的气候、环境密切相关，自生沉积速率主要受湖水蒸发量和补给水的化学成分控制，并受湖面变化影响。西藏色林错沉积物岩芯地球化学和矿物组成的变化揭示了当地１２０００年以来的气候和湖面变化，其中１２０００—１００００ａＢ．Ｐ．干旱、低湖面，１００００—４２００ａＢ．Ｐ．温湿、湖面上升，４２００年以来的干旱、湖面波动下降的趋势。

Lacustrine sediments are the archives of paleoclimatic and paleoenvironmental variations.How the information about the variations is extracted from the archives is now a branch ofearch science with exciting opportunities for reasearch.In this paper, the relationship betweenlake authigenic deposition and its environment is discussed in a comprehensive syntheses.Thedeposit rates (or flux) of the alkaline matal elements or their compounds in a closed lake increase with evaporation and contents of the elements of inflow water and are related with thelake-level fluctuations. The ratio between alkaline elements of the sediments, for example,Mg/Ca raltio can be used as an indicator of paleoclimatic and paleohydrological changes.Chemical and mineralogical analyses have been carried out on the sediment core CH8803 from the lake Siting CO, the central Qinghai-Xizang (Tibetan) Plateau. The chemical composition are characterized by CaO, MgO and CO2 rich. The carbonates are mainly composedof authigenic calcite, aragonite, dolomite and hydromagnesite. The records of carbonate composition, Ca and Mg deposit rates, and Ma/Ca ratio from the core show the conditions thatthey are cold-dry and low lake-level during terminal Pleistocene (12 000─10 000 a B. P.),warm-wet and high lake-level durinig the early-middle Holocene (10 000─4 200 a B. P.), andwarm dabing (and/or cooling) and lowering lake level trends since 4 200 a B. P. The changes inclimate and lake-level of the lake Siling Co during the last 12 000 a B. P. agree generally faiththe records from the lake Qinghai in the northeastern margin of the Qinghai-Xizang Plateau andSumxi Co in the western plateau. These results indicate that there was a strong summermonsoon in the Qinghai-Xizang Plateau in the early-middle Holocene, and confirm the modelpredictions of an intensified monsoon over the Northern Hemisphere during about 9000─6 000 a. B. P., owing to an orbitals induced increase in summer insolation.