西藏安多的湖泊变化与环境

钻孔和剖面资料表明，西藏安多地区两个较大的现代湖泊，错那湖和兹格塘错湖至迟形成于３５ｋａＢ．Ｐ．。早期两源相连，水位较高。随后因气候变干，湖面下降，但在２０－１７ｋａＢ．Ｐ．期间湖面又重新升高，并保持相对稳定。自１７ｋａＢ．Ｐ．以后，湖面急剧下降，矿化度随这提高，钙质胶结物出现。在此过程中，因湖面阶段性的相对稳定所形成的１０道砂坝堤，反映了该区气候波动的特征。

Fluctuations of Lakes and Their Environments Since Last Glaciation in Amdo Area, Tibet

CoNag Lake and ZigeTangco Lake are two bigger modern lakes in Amdo area, Tibet.The former is an opening lake basin and the later is closed one. The records of lacustrinedepositional stratigraphy,pollen data,hydrochemical analysis and ~(14)C datings from theCoNag Lake and the ZigeTangco Lake cores and from sediments cropping out in the basinsby the Sino-German Joint Expedition to Tibet 1989 give information on major changes inboth regional environments and local hydrology.Both lake basins are tectonic-glaciated basins and the lacustrine deposits are generallythinner and younger. The lakes might have only existed since 35 ka B.P.. The underlying stra-ta is Tertiary fluviallacustrine sediments with glaciated deformational structures. In extensivelake period ofearly stage, two lakes were connected together, the lake level was 130-160 mmore higher than these of present. After that, the unifed lake had been separated and the leveldeclined gradually by a reversal event toward dry. However, a rapid lake-level rises with rela-tive stable level height ocurred in the ZigeTangco Lake at ca.20-17 ka B.P.. After ca, 17 kaB.P., an abrupt dropping of the lakelevels started reappeaing with the long-term trend to-ward dry. The salinity of the ZigeTangco Lake water trended to increase and the sedimentspacked with calcium ocurred. And ten rimsand bars around the ZigeTangco Lake show thateach lakelevel declined event leads to drier conditions than the preceding one, whereas succes-sive humid pluses have lower and lower amplitude.