The sequence of quaternary glaciation in the Bayan Har Mountains
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文摘
Four periods of Quaternary glaciation in the Pleistocene have been found 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, glaciers developed only near the mountain ridges of the Bayan Har. In the earlier stage, glaciers expanded down to the piedmont of the Bayan Har Mountains and were as much as 40 km long. In the penultimate ice age, an extensive ice cover developed, depositing an areally widespread till sheet. Erratics were transported 60 km from Bayan Har peak to Qingshuihe 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 km2. Furthermore, evidence including glacial landforms and sediments shows that a larger glaciation existed in this area in an earlier time, possibly during the third most recent (ante-penultimate) glaciation. The scale of this glaciated area is greater than those of the more recent events in the Qinghai-Xizang Plateau, extending over 80,000 km2. This glaciation covered the source area of the Yellow River from Xingsuhai in the west to Duogerangtan in the east, including the areas of Gyaring and Ngoring lakes. Based on the extent and locations of the glaciations, the Bayan Har Stage and Galalahai Stage of the Last Glacial age; the Yematan Ice Age; and the Huanghe Glacial Age can be recognized.