Dating of Middle Pleistocene sediments from a large freshwater lake in the Qaidam Basin, NW China to reveal the climatic and environmental differences to the conditions of the last 30 ka

近40年前，中国地质学家在柴达木盆地中部取样了一个以淡水湖沉积物为主的断崖。该剖面的壳化石经ams测年可追溯到28ka BP。在2002年的野外调查中没有发现原始剖面，但采样了50 m厚的层序。令人惊讶的是，对插层风成砂和河流砂的OSL定年得出的最小年龄约为130 ka，由于定年长石的异常褪色，这使得无法建立年代学。从该剖面7米厚的间隔中取出化石壳，使用TIMS技术通过铀系列测量来确定年代。在测年实验室将贝壳样品分成两个大小的分数，得到了可靠的年龄分别为199±4 ka和217±5 ka。现在，我们申请资助对另外10个样本进行TIMS测年，以确定采样序列的年表。第一次TIMS定年结果表明该剖面上部为间冰期（可能为MIS 7a）。良好的时间控制是解决以下问题的先决条件：温度跳跃是否会导致盆地大量融水供应或更高的降水水平，或者与青藏高原隆起和/或集水区面积相关的非气候变化是否触发了淡水湖的形成。

An escarpment consisting of freshwater lake sediments mainly was sampled about 40 years ago by Chinese geologists in the central Qaidam Basin. Fossil shells from this section were AMS-dated to about 28 ka BP a few years ago. The original section was not found during a field survey in 2002 but a sequence of 50 m thickness was sampled. Surprisingly, OSL dat-ing of intercalated aeolian and fluvial sands yielded minimum ages of about 130 ka which did not allow the establishment of a chronology due to anomalous fading of the dated feldspar. Fossil shells from a 7 m thick interval of the section were bulked for dating by uranium-series measurements using the TIMS technique. The shell sample was split into two size fractions at the dating laboratory and reliable ages of about 199 ± 4 ka and 217 ± 5 ka were obtained. Now, we apply for funding of TIMS dating of further 10 samples to establish the chronology of the sampled sequence. The first TIMS dating result indicates an interglacial age of the up-per part of the section (possibly MIS 7a). A good chronological control is a prerequisite to tackle the question whether temperature jumps causing a large meltwater supply to the basin or much higher precipitation levels, or whether non-climatic changes related to the uplift of the Tibetan Plateau and/or the area of the catchment triggered the freshwater lake formation.