西藏台错盐湖TT-1剖面的沉积特征和年代学研究

Characteristics and Chronology of Saline Sediments along Profile TT-1 of Dahyab Tso(Tai Cuo) in Tibet

台错位于西藏羌塘高原西部 ,这里因环境恶劣而无人类污染和影响。笔者调查了该湖区一级阶地的湖相化学沉积 ,取得了TT 1剖面 (厚度 36 9cm)连续样品 15 6个 ,平均单样厚度 2 .36cm。就台错剖面的年代测定 ,本文分别对同一样品进行了不同方法的测试和相互校验。研究表明 ,14 C方法对有机物质的定年是准确的 ,而在消除盐湖化学沉积建造中碳酸盐的“新碳”、“老碳”的影响方面 ,仍需做进一步的研究。与此同时 ,铀系法测年的全溶样品的等时线技术 ,避免了同位素的分馏问题 ,所有的测试数据在等时线上都有良好的线形关系 ,表明获得的年龄数据是合理的。从而确定了TT 1剖面盐湖沉积的可靠地质时代为 32 .6～ 4 .5kaBP间的晚更新世晚期至全新世中期。

The saline lake Dahyab Tso (Tai Cuo) located in northern Tibetan Plateau was chosen as a study object. Although the environment around Dahyab Tso is very harsh, it has not suffered from human pollution. Field work was carried out in 2001, focusing mainly on the palaeoclimate and palaeoenvironment at the first stage of saline chemical sediments. Sampling was conducted on the 369 cm natural section (TT-1) in a high consistency, and the average thickness of each sample was limited to 2.36 cm. Based on field work and researches, it can be concluded that uranium-series chronology combined with the total-sample-dissolution isochron techniques is a relatively reliable and accurate method for the dating of saline lake sediments. This method has successfully solved the problem of errors caused by later stage carbon isotope fractional distillation. The reliable ages of the profile TT-1 are 32.6～4.5 ka B P, approximately from Late Pleistocene to Middle Holocene.