The Discovery of the Mid-Pleistocene Glacial Tills and Its Geological Significance in Taxkorgan Stone Town Region of Xinjiang

The authors first found the three fossil glacial tills at the ancient army service station, stone town and gas station in Taxkorgan County. Geomorphic Types and distribution of the fossil glacial tills were the remaining glacial platform. The platform is about 3 100 m in height, and we can see a lot of glacial syenite boulders on it. The tafonis developed on glacial syenite boulders were classified into side-wall tafoni, basal tafoni, cellular tafoni according to their morphological characteristics and positions. Field geological investigation shows that the gravel cut down into the old moraine, and the OSL age of the gravel layer is (62.07 ± 2.44) Ka. Contrastive study of the fossil glacial tills in stone town region and the glacial moraine in Muztag Ata-Konggur Mountain was carried out, it is showed that the fossil glacial tills formed in late penultimate glacial period of mid-Pleistocene, and derived from the glacier advance of paleo-glacier in the Sidun Mountain. The discovery of the mid-Pleistocene glacial tills has very important geological significance: (1) the authors divided the Quaternary glaciers in the Sidun Mountain into four ice ages, namely late penultimate glacial period of mid-Pleistocene and last glacial period of late Pleistocene, as well as neoglacial period and little Ice Age of Holocene; (2) the Taxkorgan fault are left-lateral strike-slip faults; (3) the clear bounds and limited scales of Pleistocene glaciations in the Sidun mountain and Muztag are incompatible with imagining a successive ice sheet on the Plateau.