Provenance Analysis Of The Late Cenozoic Sediment Of The Upper Yellow River And Its Evolution

The Yellow River is the mother river of the Chinse nation,the birthplace of Chinse civilization.She plays a pivotal role in the modern economic and social development,and the environmental protection.The Yellow River is a very large river system,connectting the largest plateau(the Qinghai-Tibet Plateau)and the largest ocean(the Pacific)all over the world.Its formation and evolution has important scientific significance and practical value,which long attracted a lot of attention of geogical scientists.We select the Upper Yellow River as a major study area,discuss the tectonic geomorphologic evolution and the formation of the Yellow River in the late Cenozoic,combined with structural geomorphology,sedimentological and chronological analyses.The main work of this paper includes three aspects: Firstly,look for the ancient Yellow River remains(terrace,ancient gravel bed),determinate the stratigraphic ages by the method of geochronology,build up their framework of space-time;Secondly,samples(U-Pb and heavy mineral)are collected in the location of key strata,obtain the provenance characteristics;Thirdly,systematically collect published source data of the different sections and times,compare the data with ourselves,discuss the provenance characteristic of the Late Cenozoic sediment of the Upper Yellow River and its evolution.The main conclusion is as follows:(1)Based on the contrastive analysis of the detrital zircon U-Pb ages,the sediment from the nineth terrace foundation in the Hetao Basin,Inner Mongolia Autonomous Region,the gravel bed of Ganhegou Formation in the Zhongning area,Ningxia Hui Autonomous Region,and the gravel bed of Qunaihai Formation in the Longyangxia Gorge area,Qinghai Province,show have similar characteristics,which provides some evidence for the evolution of the Upper Yellow River in its early stage.(2)The heavy-mineral assemblages of the sediment from the nineth terrace foundation in the Hetao Basin,Inner Mongolia Autonomous Region,the gravel bed of Ganhegou Formation in the Zhongning area,Ningxia Hui Autonomous Region,are dominated by unstable mineral amphibole followed by epidote,and some zircon,apatite,rutile,tourmaline,titanite,resemble the sediment of the modern Upper Yellow River,the typital terrace and ancient gravel bed in the Lanzhou City,and the ancient gravel bed of the drill hole in the Yinchuan Basin,supporting the result from the similar detrital zircon U-Pb age spectrum.(3)Combined with field observations of fluvial terraces and ancient sediment of the Yellow River,age spectrum of detrital zircon,heavy mineral assemblage,it can be concluded that the Upper Yellow River was initially formed at least by the Early Pliocene,whose location and pattern resembling the modern Yellow River.