An ostracod-inferred large Middle Pleistocene freshwater lake in the presently hyper-arid Qaidam Basin (NW China)
An ostracod-inferred large Middle Pleistocene freshwater lake in the presently hyper-arid Qaidam Basin (NW China)
复制标题
DOI：
10.1016/j.quaint.2009.03.002
复制
发表时间：
2010-05
影响因子：
2.2
通讯作者：
S. Mischke;Zhencheng Sun;U. Herzschuh;Zizhen Qiao;Naida Sun
中科院分区：
文献类型：
--
作者：
S. Mischke;Zhencheng Sun;U. Herzschuh;Zizhen Qiao;Naida Sun
对青藏高原北缘12万km2柴达木盆地50m厚的裸露沉积物进行了调查。细粒粉质沉积物构成了该剖面的大部分，并堆积在一个湖泊中。风沙夹层和河流或滨海成因表明，该湖在剖面处经历了干燥期和浅水期。湖泊沉积物提供了令人惊讶的丰富的介形类组合，几乎所有的物种都指示淡水到低盐条件。物种丰富，该剖面位于柴达木盆地地形隆起的南部邻近地区，以及河流和风成砂的夹层，表明整个层序的大部分区域都存在相对边缘的滨海湖泊环境。最大水深可能达到几十米，至少在该剖面的某些部分，从我们的数据可以推断出一个覆盖大约一半柴达木盆地大小的大湖。这一推断与柴达木盆地最低凹陷现今风状地貌形成鲜明对比，那里有盐滩和浅盐湖。通过光学激发发光和铀系列测量进行年代测定，不能确定所调查部分的确切年代学。根据从长石上获得的120-140ka左右的红外激发发光年龄和散布在100-400ka之间的230Th/U年龄，推测该湖形成的中更新世年龄为120-400ka。
Exposed sediments of 50m thickness were investigated in the 120,000km2Qaidam Basin at the northern margin of the Tibetan Plateau. Fine-grained silty sediments constitute most of the section and were accumulated in a lake. Intercalated beds of aeolian sand, and of fluvial or littoral origin, show that the lake experienced periods of desiccation and shallow water levels at the section site. The lake sediments provided surprisingly species-rich ostracod assemblages with almost all species indicating freshwater to oligohaline conditions. The species richness, the position of the section in the southern neighbourhood of a topographic rise in the Qaidam Basin and intercalated layers of fluvial and aeolian sands suggest that a relatively marginal, littoral lake setting existed throughout most of the sequence. A maximum water depth of several tens of metres may be assumed at least for some parts of the section, and a large lake covering about half the size of the Qaidam Basin may be inferred from our data. This inference is in clear contrast to the present-day wind-shaped topography with salt playas and shallow saline lakes in the lowermost depressions of the Qaidam Basin. Dating by optically stimulated luminescence and uranium-series measurements did not allow the establishment of a firm chronology for the investigated section. However, based on infrared stimulated luminescence dates of around 120–140ka obtained on feldspars and regarded as minimum ages; and230Th/U ages scattering between 100 and 400ka, a Middle Pleistocene age between 120 and 400ka is assumed for the lake formation.