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Some Characteristics of Stratigraphic Sequences and Lacustrine Sediments of Main Quaternary Lakes on the Qinghai-Tibet Plateau

ZHENG Mianping1,2,3) LIU Xifang1,2,3) YUAN Heran1,2,3)ZHANG Chengjun1,2,3) WANG Hailei1,2,3)1) Key Laboratory of Saline Lake Resources and Environment,Ministry of Land and Resources,Beijing 1000372) Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 1000373) R & D Center for Saline Lake and Epithermal Deposit,Chinese Academy of Geological Sciences,Beijing 100037  
In this study an extensive investigation of representative Quaternary lacustrine sedimentary areas was carried out on the Qinghai-Tibet Plateau.The investigated region extends from the Kunteyi Lake of Qaidam and Kunlun Pass southward to Jiangbu-Nyingchi,and eastward from Tianshuihai to Dêqên. According to the geological structure,sedimentary sequences and geomorphology of the plateau,the Quaternary stratigraphic region of the plateau is divided into six stratigraphic areas: southern Tibet lake basin area(I);Qiangtang plateau lake basin area(II)(southern Qiangtang lake basin sub-area(II-1) and northern Qiangtang lake basin sub-area(II-2)),Sanjiang high mountain-river valley area(III);Kunlun high mountain area(IV);Qaidam-Qinghai Lake basin area(V);and Altyn Tagh-Qilian high mountain area(VI).We have made a detailed division and correlation of the Quaternary lacustrine stratigraphic sequences for the above-mentioned I-V stratigraphic areas and thus pointed out the following characteristics of the Quaternary lacustrine sediments on the Qinghai-Tibet Plateau: ①Except for the Qaidam-Qinghai lake basin area,the lacustrine detrital sediments of the lake-lakeshore sections of other areas are coarser,which coincides with the fact that the Qinghai-Tibet Plateau belongs to the Quaternary youngest uplift over the globe.②Lacustrine sediments in the lake basins tend to be superimposed on or associated with alluvial-proluvial,eolian and till or fluvio-glacial sediment,mudflow sediments,chemical sediments and hydrothermal deposits.They reflect that cold phases occurred frequently in the lake-basin sedimentary environment after the Qinghai-Tibet Plateau was uplifted and entered the cryosphere in the Quaternary,and also show that: in the plateau uplift setting landslides and mudflows induced in the flood season dammed water flows to form lakes or that flooding resulted in bank bursting of internal lakes and disappearance of lakes on margins of the plateau(e.g.areas III and IV) and salt precipitation in the plateau lakes was closely related to deep processes and strong neotectonic movement.③Most Quaternary lacustrine sediments in these areas were not deposited continuously except the Qaidam-Qinghai Lake area(V) and part of large lake basins in the Qiangtang Plateau lake basin area where Quaternary continuous lacustrine sediments are found.④As the Qinghai-Tibet Plateau becomes arid gradually during the Holocene,quite a number of lakes have dried up except some modern catchments,so lacustrine sediments are lacking at the top.In summary,in order to acquire continuous records of the Quaternary sedimentary environment on the Qinghai-Tibet Plateau,it is necessary to select a few Cenozoic basins with continuous sediments in the interior or on margins of the plateau.This paper demonstrates that the Qaidam basin is a fairly ideal area for the study of Late Cenozoic lacustrine sediments of the plateau.We suggest that a Late Cenozoic resource and environment scientific drilling project be implemented in the Qaidam basin.
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