NUMERICAL DATING OF QUATERNARY GLACIATION IN THE SOURCE AREA OF THE URUMQI RIVER, TIEN SHAN, NORTHWESTERN CHINA

Quaternary glaciations were studied by many researchers in details at the source area of the Urumqi river, northwestern China. However, numerical dating data were lack until recent years. We used the AMS (accelerating mass spectrometry) techniques and ESR (electron spinning resonance) techniques to date the glacial tills. Carbonate coatings on roche moutonnees and till gravels and calcite in the fine matrix of modern and ancient glacial tills were collected for radiocarbon dating. The values of stable isotope carbon 13 and the sedimentary properties of tills and coatings show that the inorganic carbon in calcite in till matrix is synchronous with the till formation. The carbon dating of the fine matrix of till and the coatings on till gravels can be used to determine or estimate the ages of glacial moraines since the inorganic carbon in fine matrix and coatings may preserve well with no or little fractionation. Quartz grains with the size range from 0.032 to 0.25mm in modern and ancient glacial tills were selected for ESR dating. Subglacial comminution and sunshine might make the ESR signal reset, particularly in smaller sizes, and thus makes the ESR dating on basal till possible. Based on the dating results, the largest-scaled moraine near Wangfeng road maintenance station was coincident with the global Last Glaciation Maximum in this region. The moraine at Glacier Observotary, which was formerly believed to be the product of the neoglaciation seems to be the relics of lateral moraine, also formed during the Last Glaciation. Lower Wangfeng Group that has been controversial over its age was formed in 50-70ka, the early stage of the Last Glaciation.