On the problem of Quaternary glaciations, and the extent and patterns of Pleistocene ice cover in the Qinghai-Xizang (Tibet) Plateau

Abstract

Data accumulated during investigations since the 1960s indicate that up to four Pleistocene glaciations can be recognized in the Qinghai-Xizang (Tibet) Plateau and the adjacent Himalaya Mountains. In order of decreasing age, these are the Xixabangma, Nyanyaxungla, Guxiang, and Baiyu glacial episodes. The history of Pleistocene glacial evolution in various areas throughout the plateau differs, and the pattern is very complex. Throughout the Early Pleistocene, the elevation of the Qinghai-Xizang Plateau was approximately 2000 m above sea level. During the Xixabangma glacial episode recorded at higher elevations, the climate and topographical conditions on the plateau were largely unfavourable for the development of glaciers. Present investigations have revealed that the oldest till is only found at isolated localities on the plateau. Glaciofluvial or alluvial deposits, such as the Gongba Conglomerate (dating from 2.4 to 0.73 Ma BP), and the fluvial-lacustrine deposits of the Qiantang Group (dating from 2.4 to 1.7 Ma BP), are present, rather than glacial till. Therefore, the postulate of a large Early Pleistocene ice sheet proposed previously has been disproves. During the most recent glaciation, uplift of the plateau and the Himalayas continued. The majority of the Qinghai-Xizang Plateau reached 4000 m a.s.l., and the Great Himalaya were approximately 6000 m a.s.l. The mountains formed a barrier against the incursion of the Indian monsoon, so that precipitation decreased sharply on the northern flank of the Himalayas, and the climate to the north became cold and dry. All of the glaciers on the Qinghai-Xizang Plateau underwent extensive retreat. Thus, during the Pleistocene, no unified glacial cover existed over the Qinghai-Xizang Plateau. Similarly, the source area of the Hwang He (Yellow River) did not support a local ice sheet.