THE SEQUENCE OF QUATERNARY GLACIATION IN THE BAYAN-HAR MOUNTAINS

Four periods of Quatemary glaciation in the Pleistocene have been foun d in the area of the Bayan Har Mountains. They represent, respectively , the two stages of the Last Glacial age; the penultimate ice age, and an earlier ice age. During the late stage of the Last Glacial age, gl aciers developed only near the mountain ridges of the Bayan Har. In th e earlier stage, glaciers expanded down to the piedmont of the Bayan H ar Mountains and were as much as 40 km long. In the penultimate ice ag e, an extensive ice cover developed, depositing an areally widespread till sheet. Erratics were transported 60 km from Bayan Har peak to Qin gshuihe town to the south, and to Yematan land to the north. Granitic erratics are also distributed over elevated geomorphological positions , such as Chalaping Ridge. The area of ice cover encompassed up to 50, 000 km(2). Furthermore, evidence including glacial landforms and sedim ents shows that a larger glaciation existed in this area in an earlier time, possibly during the third most recent (ante-penultimate) glacia tion. The scale of this glaciated area is greater than those of the mo re recent events in the Qinghai-Xizang Plateau, extending over 80,000 km(2). This glaciation covered the source area of the Yellow River fro m Xingsuhai in the west to Duogerangtan in the east, including the are as of Gyaring and Ngoring lakes. Based on the extent and locations of the glaciations, the Bayan Har Stage and Galalahai Stage of the Last G lacial age; the Yematan Ice Age; and the Huanghe Glacial Age can be re cognized. (C) 1997 INQUA/Elsevier Science Ltd.