AMS DATING ON GLACIAL TILLS AT THE SOURCE AREA OF THE URUMQI RIVER INTHE TIANSHAN MOUNTAINS AND ITS IMPLICATIONS

Using accelerating mass spectrometry (AMS) dating method, a dating has been made on the primary calcium carbonate in tills and secondary cal cium carbonate coating on till gravel and the roche moutonnee formed s ince the Last Glaciation at the source area of the Urumqi River valley in the Tianshan Mountains, northwestern China. The results reveal tha t the carbonate content in the tills in this noncarbonate area is high enough to date by AMS, that the carbon in the coatings on the newly e xposed roche moutons and in the modern till is modern carbon and so th e C-14 dating results in the ancient till can represent the actual age s of the till formation, and that the warm period during the Holocene began as early as 6 500 a B. P. and lasted to 1 800 a B. P.