AMS radiocarbon dating of late Quaternary glacial landforms, source of the Urumqi River, Tien Shan―a pilot study of ~(14)C dating on inorganic carbon

摘要

Carbonate coatings on roche moutonnees and till clasts and calcite in the fine matrix of late Quaternary glacial landforms were dated by using accelerating mass spectrometry (AMS) radiocarbon dating, at the source area of the Urumqi River, Tien Shan. The values of ~(13)C and the sedimentary properties of tills and coatings show that the precipitation of inorganic carbon in calcite in the till matrix is synchronous with till formation. The carbon dating of the fine matrix of till and the coatings on till clasts can be used to determine or estimate the ages of glacial moraines, as the inorganic carbon in fine matrix and coatings may preserve well with no or little fractionation. The largest-scaled moraine near Wangfeng road maintenance station was dated to be 19-23 ka. The age of the local Last Glaciation Maximum was, therefore, coincident with the global Last Glaciation Maximum. The moraine at Glacier Observatory, which was formerly believed to be the product of Neoglaciation, seems to be the relics of a lateral moraine, also formed during the Last Glaciation.