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Early records of Quaternary glaciation in Qinghai-Tibet plateau and their tectonic and climatic implications

ZHAO Yue,QIAN Fang,ZHU Da-gang,ZHANGYong-shuang,SHAO Zhao-gang,HE Zhe-feng(Institute of Geomechanics,CAGS,Beijing 100081,China)  
This paper gives a review of early records of Quaternary glaciation in Qinghai-Tibet plateau,based upon recent progress in the study of ages of Early Quaternary glaciation as well as the related stratigraphy,sedimentology,paleontology and paleo-environment in this plateau,especially in its typical basins.The existence of freeze-thaw layers in the upper part of the Xiangzi Formation of Zada basin within western Himalayas represents,regionally,an ice margin paleo-environment of the plateau around 3500m a.s.l.The freeze-thaw layers in the upper part of the Xiangzi Formation in Zada basin are Early Pleistocene in age,similar to the age of aqueoglacial deposits in the lower part of Gongba Conglomerate in Mount Qomolangma region,around ca.2.3 Ma.The age of moraines at the top of the Xiangzi Formation can be correlated to the Cho Oyo ice age and the Shisha Pangma ice age of Mount Qomolangma region,showing the further development of mountain glaciers in the region.This suggests that the Himalayas,the highest region in Qinghai-Tibet plateau,began its cryosphere environment in sometime of early and middle Early Pleistocene.Early Pleistocene moraines in western Sichuan area adjacent to the eastern Himalayan tectonic syntaxis demonstrate that peaks of the region had reached to cryosphere during that time.However,their elevation and climate may be different from those of the Himalayas.Most of the surface of the plateau rose above the cryosphere in early Middle Pleistocene with intense deformation taking place in the plateau region during global ice ages.The glaciation in early Middle Pleistocene in Qinghai-Tibet plateau is the most developed and extensive glaciation,which suggests that the surface of Qinghai-Tibet plateau rose entirely and rapidly into cryosphere in earliy Middle Pleistocene,that is,above 3500m a.s.l.The detailed processes still need a deepgoing investigation in future.
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