The Age And Significance Of The Ancient Barrier Lake In The Middle And Lower Reaches Of The Yarlung Zangbo River

The Yarlung Zangbo River originated in the Himalayas and flows from the west to the east through the southern part of the Qinghai-Tibet Plateau.It crosses the Himalayas east around at an altitude of 7782 m Namcha Barwa north protruding bends,forming the world's first grand canyon.In the valley of the Yarlung Zangbo river and its tributaries,there have been many events in the river due to glacier activities,collapse,landslide,mud-rock flow and the influence of transverse tectonic activities.A series of ancient dams have been formed,the form of lacustrine terraces are preserved on both sides of the river.Many scholars have carried out a lot of research on the ancient barrier lake in the Yarlung Zangbo River Basin.But so far,there is still controversy over the distribution,age and period of the lake in the ancient lake.The structure and Climatic factors have not been systematically studied.This paper focuses on the deposition of the ancient barrier lake in the middle and lower reaches of the Yarlung Zangbo River,focusing on the middle reaches of the town of Renbu County,Jiacha County,Miling County,Linzhi County,and the tributaries–Guxiang of Parlung Zangbo'sseveral typical sedimentary facies of the lake and lake are observed.Optically Stimulated Luminescence(OSL)and Radiocarbon dating(¹⁴C)dating in the ancient barrier lake,the approximate age of the sedimentary section of the ancient barrier lake is obtained,and the spatial distribution of the sediments of the ancient barrier lake is identified.Multi-period developmental characteristics of three ancient.The main findings are as follows:(1)The formation of the Renbu ancient barrier lake group in the middle of late Pleistocene(76?48 ka B.P.).It is presumed by the Yarlung Zangbo River tectonic belt caused by the tectonic activity of Dangxiong-Yangbajin tectonic belt near the north-south of the collapse,landslides,debris flow and other activities formed by blocking the river barrier.The distribution range is from Rikaze to the area of Renbu,and includes this segment of the Yarlung Zangbo river tributary area.(2)The Gega barrier lake group is formed in the last glacial period(186 ka B.P.,75?40 ka B.P.),which is related to the event of the glacier activity caused by glacier activity since the last glacial period.The distribution range is from the downstream area of Zhongda to Dalin,at the same time,including the segment part tributary of the Yarlung Zangbo river area.Now it also preserves secondary sedimentation in the last glacial(35 ka B.P.,27?8 ka B.P.),and forms two lacustrine terraces.The sedimentary time of T1-lacustrine sediments is 7?4 ka B.P.,T2-lacustrine sediments is 33?19 ka B.P..(3)Parlung Zangbo ancient lake group formed in the late pleistocene the last glacial period(75?10 ka B.P.),it is by the dragon get glaciers caused by the river,the distribution range is from Guxiang to the river intersection of Parlung Zangbo and Yigong Zangbo.There are also two deposition in the late last glacial period and middle of the Holocene,the formation time is 42 ka B.P.and 7 ka B.P..(4)The sedimentary age of the ancient barrier lake is related to the last glacial period and the early ice age of the Holocene.The development of the ancient barrier lake is associated with the glacier activity caused by glacial activity(or ice).