冰碛物ESR测年与天山乌鲁木齐河源末次冰期系列

ESR Dating on Tills and the Last Glaciation at the Headwaters of the rmqi River, Tianshan Mountains, China

采用ESR方法 ,对天山乌鲁木齐河源末次冰期的冰碛石英砂进行了测年 .下望峰组冰碛层的年代与前人推测的年代不同 ,是 5 0～ 70kaBP末次冰期早阶段形成的 ,分布下限可达海拔 2 30 0m左右的红五月桥附近 .与AMS的测年结果相比 ,末次冰期晚阶段底碛的ESR年代与AMS的年代相当 ,而冰上融出碛ESR年代与AMS的年代相差较大 .认为冰下的压碎和磨蚀作用可能导致冰碛中石英砂的ESR信号归零 。

Using Ge center of quartz grains of size 0.06～0.25 mm, ESR (electron spinning resonance) dating on the glacial quartz sands formed in the Last Glaciation was made at the headwaters of the rümqi River in the Tianshan Mountains, Northwest China. ESR dating on a basal till (subglacial melt-out one) of an end moraine formed in the late stage of the Last Glaciation is consistent with the dating under AMS 14 C method. But dating on the overlying till (supra glacial melt out one) of the same moraine is different from the dating under AMS 14 C method. The underlying till contains much more silt than the overlying till. High content of silt implies a strong subglacial comminution. Based on an experiment, Ge signal in quartz grains decreases by one third after artificial grinding for ten minutes.The till was formed in 50～70 ka BP, the early stage of the Last Glaciation. It was spread in the main valley as low as 2300 m a.s.l. with a length of more than 19 km. Fluvial sandy gravel deposited in the inter glaciation between the early and late stages of the Last Glaciation.