大布苏湖全新世沉积岩心的碳酸盐含量与湖面波动

CARBONATE CONTENT OF SEDIMENTARY CORE AND HOLOCENE LAKE-LEVEL FLUCTUATION OF DABUSU LAKE

大布苏湖是我国东北地区极为罕见的盐湖 ,通过对该湖现代湖盆碳酸盐沉积相的分析 ,以及钻孔岩心碳酸盐含量和 1 4 C年代的测定 ,探讨了大布苏湖全新世湖面波动与环境演化的过程 ,结果表明 ,大布苏湖有两次高湖面时期 ,分别为 10 45 0～ 72 6 0和 5 40 0～ 36 0 0 a BP,湖泊水位稳定在 12 5 m以上 ,这两个时期也是松嫩沙地古土壤集中发育的时期 ,晚全新世以来 ,大布苏湖明显萎缩 。

The Dabusu Lake is located in the south of Qian’an highland,a tectonic fault lake developed on the terrace plain.The degree of mineralization in the lake water fluctuates from 62 34 to 347 34 g/l and its a very rare salty lake in Northeast China. The modern depositional environment research shows that grain size of sediments becomes gradually coarser and content of carbonate gradually lower from shallow lake facies to muddy flat facies to sandy flat facies and then to lake shore facies.That is to say,the finer the grain size,the higher the carbonate content.The association of grain size and carbonate content provides an important basis for analyzing paleo sedimentary environment. The core dating shows that the Dabusu Lake had both a great sediment thickness and high sedimentation rate in Holocene compared with other lakes in North China,which was caused by climatic fluctuations and also by fault tectonic background.The increasing of the modern sedimentation rate is mainly due to serious soil erosion caused by human activities since Liaojin period. There were two high lake level periods in Holocene,i.e.10 450～7 260 aBP and 5 400～3 600 aBP respectively.Their lake level could reach up to 125 m,with the highest of about 128 m.The palaeosol in Songnen sand land developed just in these two periods.Since late Holocene,Dabusu Lake has shrunk obviously,because the climate began to become dry.