Shaanxi Binxian Duan Jing River Terraces Is A Preliminary Study

Fluvial geomorphology is an important hotspot in geoseienee. As a major aspect of fluvial geomorphological evolution,river terrace is used to recorver the history of fluvial geomorphological evolution and get related information about tectonic movement and climate change. However, there is no consistent opinion about the process of evolution of Jinghe river, which is the largest tributary of Weihe river.This article study the river terraces of Binxian in the middle of Jinghe river. The conclusions maily are as follows:(1) It develops 5 levels of terraces which named T1,T2,T3,T4,T5 of Jinghe river in Binxian. Base tug-of-war height is 4,10,30,45,and 68m respectively. It's development age is 0.01,0.13,0.65,0.80,1.20 Ma respectively through the terraces sequence contrast of the middle Yellow River water system and the ancient soil dating methods.(2) The high numerical of magnetized susceptibility of T, terrace appeared in the eighth floor and the high numerical of magnetized susceptibility of T2 terrace appeared in So and S1 layer though analysis.The high numerical of magnetized susceptibility reflects the summer monsoon relatively strong, rainfall increases, biological into soil function strongly, climate warm wet environment cause ferromagnetic mineral concentrations increasing. The low numerical of magnetized susceptibility reflects dry climate, sandstorm frequent, extremely weak cause into soil ferromagnetic mineral no enrichment.The first terrace sediments that composed of its size by powder sand primarily, viscous grain content is less. In the second terrace, viscous grain content increased significantly, ancient soil layer of viscous grain content significantly higher than maree soil layer,it because thatclimate warm wet, into soil function strong, viscous grain content high in the development period of ancient soil. However,in the formation period of L0,L1,L2. climate is bad, the number of sandstorm happening is more, coarse sand content increase.(3) The accumulation of Jinghe'firstterraces in Binxian can divide into three stages:fluvial facies; eolian sediments; the wind into loess.Because of tectonic uplift and dry climate, the accumulation process appears depositional period of riverbed gravel layer and the wind into the loess sedimentary period of Jing he T2 terraces in Binxian, It doesn'tappear interactive depositional period.(4)The top of flood develops ancient soil in every terrace except the first terrace of Jinghe in Binxian.Example T5,T4,T3,T2 correspond ancient soil S1-S16,S1-S9,S1-S6,S1respectively, It shows that climate changeplay an important role in terraces forming process, Rivers slice may happen during the periodof glacial changing interglacial. (5) Jinghe slice ratecan divided into three period:(1)Jinghe's area in Binxian uplift 100m since 1.20Ma(T5). When 0.82Ma(T4), Binxian area 's elevating rate is 0.078 mm/a, When 0.62Ma(T3), Binxian area's elevating rate increases to 0.150mm/a. When 0.13Ma(T2), Binxian area's elevating rate reduce 0.040mn/a.It can show that the differences of river's slice rate because of the differences of tectonic activities.