青海格尔木三岔河组年龄测定与昆仑古湖发育

文章主要研究和讨论青海省格尔木市昆仑河第五级阶地的三岔河组河湖相沉积,特别是其上部的一套典型的湖相沉积。根据野牛沟和纳赤台西北两剖面三岔河组沉积样品的ESR和U系法年龄测定结果,三岔河组堆积于约355～95kaB.P.间,而被称为昆仑古湖的湖相沉积大致开始于约 200～160kaB.P.（ESR）或约150kaB.P.（U系）,结束于约 150～120kaB.P.（ESR）或约95kaB.P.（U系）左右,其中深湖时期约为190kaB.P.（ESR）或约110～100kaB.P.（U系）左右。此外,纳赤台东北昆仑河第三级阶地剖面上部的湖相沉积,则是约90(ESR)/72～25kaB.P.（U系）的末次冰期期间形成,可称为纳赤台古湖。根据昆仑古湖湖相沉积地层中的沉积构造和所发现的介形类化石,讨论了湖泊的沉积环境;根据区域对比,认为三岔河组发育于约355～95kaB.P.,而其中约120～95kaB.P.的末次间冰期的早中期则是昆仑古湖的发育时期与青藏高原的羌塘东湖等古大湖发育早期的最高湖面时期,而40～30kaB.P.的MIS3的后半段只是这些大湖分解过程中的一个阶段。

DATING OF THE SANCHAHE FORMATION AND DEVELOPMENT OF PALEOLAKE KUNLUN IN GOLMUD CITY|QINGHAI PROVINCE

This paper deals with the Sanchahe Formation alluvial lacustrine deposits which constitute the fifth terrace of the Kunlun River and the Yeniu gully in its upper reaches,south of Golmud City,Qinghai Province. The upper part of the Sanchahe Formation is a typical lacustrine deposit. Two profiles of the fifth terrace are described：  one is in the Yeniu gully 9km west of Sanchakou and the other in the Kunlun River 2.5km northwest of Nachitai. From the two localities we collected lacustrine and alluvial samples for dating and palaeontologic study. ESR and U-series dating results show that the Sanchahe Formation was deposited between ca.355kaB.P. and 95kaB.P. The lacustrine deposits named the “Paleolake Kunlun” were probably deposited between ca.200～160kaB.P. and 150～120kaB.P.(ESR dating)or ca.150kaB.P. and 95kaB.P.(U-series dating),while the deep lake stage were in ca.190kaB.P.(ESR dating)or ca.110～100kaB.P.(U-series dating), The Paleolake Kunlun might be a dammed lake. In addition,the lacustrine deposits named the “Paleolake Nachitai” in the upper part of a profile of the third terrace of the Kunlun River about 1.5km northeast of Nachitai might be formed in the Last Glaciation of the Late Pleistocene between 90(ESR)/72kaB.P. and 25kaB.P.(U-series dating). The depositional environments of the paleolakes were analyzed  on the basis of dating results and fossil Ostracoda found in the deposits. Regional correlation of the paleolakes shows that the Sanchahe Formation should develop between ca.355kaB.P.  to 95kaB.P.  The paleolake Kunlun,paleolake East Qiangtang as well as other plaeolakes  in the Qinghai Tibet Plateau reached their highest lake level in the early middle stage of the Last Interglacial Period between ca.120kaB.P. and 95kaB.P. The latter half of the marine isotope stage 3(MIS 3)between 40kaB.P. and 30kaB.P. was the desiccation stage of these paleolakes.
ESR  Dating,U-series dating,Qinghai Tibet Plateau,Sanchahe Formation,“Paleolake Kunlun”