青藏高原第四纪冰川的早期记录及其构造与气候含义

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

综合青藏高原第四纪冰川早期记录的研究进展和典型盆地地层、沉积、古生物、古环境研究的系统成果,扎达盆地香孜组上部冻融层的出现代表了区域的古海拔达到了高原冰缘的高度,即3500m以上。这一段地层的时代可能从2.3Ma前后开始,并与贡巴砾石层下部冰水沉积层的时代基本一致。卓奥友冰期和希夏邦马冰期的时代与扎达盆地沉积结束后,直接覆盖其上的终碛垄和冰碛垄的时代大致相当,展现了这一时期喜马拉雅山脉的山岳冰川进一步发育,也说明喜马拉雅山脉作为青藏高原海拔最高的地区开始冰冻圈的环境很可能在早更新世早中期。川西地区的早更新世的冰川沉积说明东喜马拉雅构造结附近地区这一时期已经抬升至冰冻圈高度,但是,海拨高度与气候环境与喜马拉雅山脉应有不同。具体的时代仍需要深入工作。青藏高原普遍开始冰冻圈记录是在中更新世早期。伴随着全球冰期的到来,这一时期的冰川作用在青藏高原最为发育和广泛。这些暗示着青藏高原在中更新世早期整体性地较快速抬升进入冰冻圈,即海拔3500m以上。详细的过程仍有待深入研究。

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.