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ESR Dating of Glacial Tills at the Headwaters of the rümqi River in the Tianshan Mountains

ZHAO Jing dong 1, ZHOU Shang zhe 1, CUI Jian xin 1, JIAO Ke qin 2, YE Yu guang 3, XU Liu bing 1(1. College of Resources and Environment, Lanzhou University, Lanzhou Gansu 730000, China; 2. Cold and Arid Regions Environmental and Engineering Research Institute, CAS, Lanzhou Gansu 730000, China; 3. Institute of Marine Geology, Ministry of Geology and Mineral Resources, Qingdao Shangdong 266071, China)  
The tills of Shangwangfeng, Xiawangfeng and Gaowangfeng at the headwaters of the Urumqi River were deposited in the Pleistocene. Although many scholars have studied them, there are still controversies over them, especially the ages of the Xiawangfeng till so far. This restricts the further study of the Quaternary Glaciations. In the past two decades, ESR as a new dating determination technique developed rapidly, and this technique could be used to date glacial tills. The studies of the scholars in the past have shown that the Ge center in the quartz is sensitive to the sunlight and grind may bleach it. So the Ge center was chosen as ESR dating signal. Shangwangfeng, Xiawangfeng and Gaowangfeng tills were determined with this technique. The determining shows that the age of Shangwangfeng till was (35±3.5) ka BP, the age of Xiawangfeng till have three ESR values, i.e., (176±18) ka BP, (171.1±17) ka BP, and (184.7±18) ka BP, respectively, and the age of Gaowangfeng was (459.7±46) ka BP. Associated with the available 14 C and ESR ages and the law of geomorphology, the following conclusions could be drawn: The Shangwangfeng till was formed in MIS 2, maybe it included the till deposited by glacier advancing in MIS 3b. The upper part of the Xiawangfeng till was deposited in MIS 4 and the lower part of it was deposited in MIS 6. According to the distribution of it and the erosion rate of the river, it is believed that the Gaowangfeng till is the oldest at the headwaters of the rümqi River, corresponding to MIS 12. The result demonstrates that this segment of the Tianshan Mountains entered the cryosphere around this time and then glaciers began to develop.
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