Definition of the Quaternary Qiangtang Paleolake in Qinghai-Tibetan Plateau, China

Since the Quaternary, many lakes have been present in the Qinghai-Tibetan Plateau. As peculiar geological processes in the evolution of the uplifting of Qinghai-Tibetan Plateau, the distributions and evolutions of the Quaternary paleolakes in the Qinghai-Tibetan Plateau have been the focus of interest among the international geosciences circle. Comparisons of the newly obtained and existing data from field surveys, remote sensing images, characteristics of tectonic landforms and distribution of the lacustrine strata, the author have, for the first time, defined a large-sized Quaternary Qiangtang Paleolake. The paleolake starts from the east-westerly direction at Rutog in western Tibet, passing through Gerze, and finally ends at Nagqu in eastern Tibet. Its length is approximately 1,200 kin; it is about 420 km at its widest point （north-southerly）. The Paleolake forms an E-W （or NWW） ellipsoid with an estimated area of 354920 km2. The Paleolake is bordered by the Mts. Gangdise and Nyainqentanglha to the south and the Karakorum Pass-Toze Kangri-Zangbagangri- Tanggula Pass to the north. It generally appears as a basinal landform with low mountains and valleys in the central part （altitudes of 4400 m） and higher altitudes （5000 m） in the peripheries. The formation and development of the Paleolake was controlled by the nearly E-W trending structures. There are three east-westerly extending tectonic sutures inside the Paleolake area, from north to south： （1） the Shuanghu Suture; （2） the Bangong Co-Nujiang River Suture; （3） the Shiquanhe-Lhari Suture. These three sutures have generally controlled the spreading features of the Paleolake and act as the first grade lake-controlling structures. In the southern Paleolake basin, there are a series of south-northerly rift basins, which are controlled by the normal faults and exist as a series of south-northerly grabens and semi-graben faulted basins. The south- northerly rift zones have clearly exerted control over the south margin of the Paleolake as well as the distribution of the residual lake basins after the Paleolake＇s break up. They are the secondary lake- controlling tectonics. Discoveries of the lacustrine strata inside the Plateau, especially the successive discoveries of many high-stand lacustrine strata, are direct evidence supporting the existence of the paleolakes in the Plateau. The dating results of the lake-eroded travertine in the Dong Co in the hinterland of the Quaternary Qiangtang Paleolake have revealed that the lake-eroded travertine is of Late Pleistocene sediments. By considering the analysis of the lacustrine strata as well, the researchers have revealed that the Quaternary Qiangtang Paleolake begins its embryonic form in the Early Pleistocene, successively develops till the Middle Pleistocene, and reaches its full blossom in the middle stage of the Late Pleistocene; it further shrinks and separates by the end of the Late Pleistocene, and finally ceases its whole life as the paleolake. After the Holocene, the huge Late Pleistocene Qiangtang Paleolake no longer exists, leaving a series of widely distributed smaller lakes on the Qiangtang Plateau. These smaller, isolated water systems receive the Holocene lacustrine sediments.