西藏纳木错晚更新世湖滩岩

Late Pleistocene Lacustrine-beach Rock around the Nam Co in Xizang

通过对西藏海拔最高、面积最大的纳木错湖周缘的第四纪环境演变调查研究与1:25万当雄幅区域填图工作,在环纳木错沿岸发现了一种与湖泊演化有关的湖相沉积岩石——湖滩岩。本文首次对纳木错周缘发育的湖滩岩进行了描述。从湖滩岩水准仪测定的保存高度看,它已构成1.5～8.3m、8.3～15.6m、14～19.9m、18.7～25.8m等四级较明显的湖滩岩阶地。湖滩岩由亮晶砂屑藻凝块灰岩、泥晶白云质砾岩和方解石胶结含砾岩屑砂岩等组成,岩石具粗砂状、含砾砂状、角砾状结构,块状构造,基底式胶结。其铀系全溶样品的等时线年龄测定结果表明,湖滩岩形成于18.7±3.8～29.3±2.7ka BP的晚更新世中晚期。本文根据岩矿鉴定,并结合沉积相、岩相组合等特征,探讨了湖滩岩的形成机理。为研究该区湖泊演化、气候变化、古地理变迁及第四系划分等提供了新资料。

The lacustrine-beach rock of the lacustrine sedimentary rock with lake evolution around the Nam Co (Nam Lake), Xizng(Tibet) , finds have been made during the Quaternary period environmental change and 1: 250000 regional geological surveying on the Nam Co of the best area and the highest elevation in Tibet. The lacustrine-beach rock described in this paper for the first time. The four terraces of the lacustrine-beach rock have made up by the lacustrine-beach rock, such as 1. 5-8. 3 m、8. 3-15. 6 m、14-19. 9 m、18. 7-25. 8 m from keeped altitude of the lacustrine-beach rock by the leveling survey. The lacustrine-beach rock have made up by the sparite psammitic algal limestone, the micrite dolomitic conglomerate and the gravel-bearing lithic sandstone by calcite cement. The rock have the coarse sand, the gravel-bearing sand and the brecciform texture, the block structure, the basal cement. The results of the uranium series dating of the lacustrine-beach rock has been determined have made clear that the lacustrine-beach rock formed the minddle and late of the late Pleistocene. The form mechanism of the lacustrine-beach rock has discussed in this paper by distinguishing of rock and mineral, dealing with sedimentary facies and the lithofacies assemblage. The new data have been provided for the lake evolution, the climate change, the paleogeographic changes and the divide Quaternary period.