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

中国地质学家于40年前在柴达木盆地中部采集了一个主要由淡水湖沉积物组成的陡崖样品。该剖面的化石壳经AMS测年，年代约为28 ka BP。在2002年的一次实地调查中没有发现原始剖面，但对一个50 m厚的序列进行了取样。令人惊讶的是，OSL测年的夹层风成砂和河流砂产生的最小年龄约130 ka，这并不允许建立一个年表，由于异常褪色的定年长石。从7米厚的间隔部分的化石壳散装铀系列测量使用TIMS技术的年龄。在测年实验室将贝壳样品分成两个粒度级，获得了约199 ± 4ka和217 ± 5 ka的可靠年龄。现在，我们申请资助对另外10个样本进行TIMS测年，以建立采样序列的年代学。第一次TIMS测年结果表明，剖面上部（可能为MIS 7a）为间冰期。一个良好的时序控制是一个先决条件，以解决这个问题，是否温度跳跃导致大量的融水供应到盆地或更高的降水水平，或是否与青藏高原和/或集水区的隆起非气候变化引发的淡水湖形成。

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.