中文摘要：

利用常规^14C、加速器（AMS）和^230Th等测年方法，对位于青藏高原东北部柴达木盆地察尔汗古湖贝壳堤剖面化石贝壳、湖泊沉积（包括现代沉积）样品有机质（包括碱性残留和胡敏酸组分）、碳酸盐（CaCO3）和剖面顶部石盐（NaCl）晶体在不同实验室进行了系统的实验研究，探讨了不同样品测年结果的可靠性和精确性，并通过与已有研究结果的对比，对柴达木盆地贝壳堤剖面记录的察尔汗古湖高湖面演化历史进行了探讨，得出察尔汗古湖高湖面形成于约39．7～17．5^14C kaB．P．；研究证明柴达木盆地沉积物中有机质含量很低，且主要来源于菌藻类等低等藻类和微生物，受老碳和溶解物质影响强烈，因此必须经过多种方法综合测年才能比较可靠地确定所测样品的形成年代；测年结果的不确定性不仅来源于样品自身元素（同位素）的特性和沉积过程中再沉积作用的影响，也可能源自于放射性^14C产生过程的不稳定性；对比发现贝壳化石老于同层位有机质^14C年龄15～18ka，这可能与柴达木盆地所处的特殊地理位置和巨大的古湖泊面积及水体有关；同时，不平衡铀系测年在确定开放体系矿物晶体年代应用中的可靠性尚须进一步深入分析，其机理也还需要探讨和实验研究。

英文摘要：

Shell Bar is one of the most prominent features in the Qaidam Basin. It is composed of abundant fossil shells of Corbicula fluminea MUller and Corbicula largillierti Philippi and located at the southeastern end （ 36°30′N,96°12′E ） of the paleolake Qarhan. This bar is the highest site that fossil shells have been reported in the Late Pleistocene age. A 2.6-m-thick fresh profile, plus a 10-cm-thick overlying crystallized salt （95% NaCl） layer, is manually excavated to address its forming ages and scope of the high paleolake levels. Accelerator mass spectrometry （AMS）, conventional radiocarbon dating, and sector inductively coupled plasma mass spectroscopy ^230Th methods were used to investigate the reliability and accuracy of dating results in different laboratories, such as Lanzhou University in China, Hannover, Kiel in Germany and University of Minnesota in USA. Ages of various components （ e. g. acid residual and humid acid of the organic matter） from the same sample were determined. Age differences of a variety of materials （ e.g. organic matter, fossil shells, and salt crystals） , and age differences at the same sampling position were evaluated. As the content of the organic matter, which was originated from one or two kinds of thermophilous bacteria and/or algae is low, and in influenced by the reworked organic matters from the old deposits and younger ones from the movable under ground waters, multi-methods dating on various materials can provide reliable and accurate ages. It seems that the AMS ages given by alkali residues and humic acids vary separately, e.g., from 124.5cm upwards; the dating results by humic acids were normal. But moving downward, the dating results of humic acids showed a reversed pattern and those of alkali residues, especially in the lower part of the section, showed an unstable pattern. These phenomena imply that organic matter had been influenced by two separate processes. Possible explanations are that for the alkali residual fraction, it most like