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

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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.