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

对中国西北柴达木盆地一个大型淡水湖的中更新世沉积物进行年代测定，以揭示过去 30ka 条件下的气候和环境差异

• 批准号: 24920288
• 负责人: Professor Dr. Steffen Mischke
• 金额: --
• 依托单位: Faculty of Earth Sciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2006
• 资助国家: 德国
• 起止时间: 2005-12-31 至 2006-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/24920288?language=en
• 关键词: Dating; Middle; Pleistocene; sediments; large

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.

大约40年前，中国地质学家在柴达木盆地中部采集了一个以淡水湖沉积为主的悬崖。这一部分的贝壳化石被AMS测得大约在28 ka BP前。在2002年的一次野外调查中没有发现原始剖面，但对50米厚的序列进行了采样。令人惊讶的是，对夹层风沙和河流沙的OSL测年得出的最小年龄约为130ka，由于年代长石的异常褪色，无法建立年代学。该区段7米厚的化石贝壳被放大，以便通过使用TIMS技术的铀系测量进行测年。贝壳样品在测年实验室中被分成两个大小的组分，获得了199±4ka和217±5ka的可靠年龄。现在，我们申请资助另外10个样品的TIMS测年，以建立样本序列的年代学。第一个TIMS测年结果表明，该剖面上部(可能是MIS7a)处于间冰期。一个良好的时间控制是解决这个问题的先决条件，这个问题是温度跃升是否导致盆地大量融化水供应或更高的降雨量，或者与青藏高原和/或集水区地区隆起有关的非气候变化是否触发了淡水湖的形成。