Development Characteristics Of The Qianhe River Terrace And Its Tectonic Significance

The river landscape has always been a product of the interaction of neotectonic movement and paleoclimate chang.By research on terrace which is one of the basic shape of the basin's landforms not only can restore the revolutionary history of river landscape,but also can extract the information which have relations with neotectonic movement and climate change.This paper based on a special geological and geomorphological mapping project “ Caobi Town of Shaanxi Province,etc.,with six 1:50000 loess cover map pilot sites ”,on the basic of comprehensive insight into tectonic geomorphic features in this region.Though use the method of field investigation combined with indoor research,the distribution features and composition of QianheRiver and the loess and paleosol on the river terrace had been invastigated in detail,also determined the series of river terraces.In addition,by comparing loess paleosol sequence with standard profile and the sequence of terraces with the river system in the middle reaches of the Yellow River,the age of its formation was obtained,and its genesis and development patterns were further explored.The main understanding of this paper is as follows:1.The detailed study of profiles of the upper QingheRiver terraces shows that QingheRiver mainly developed 5 river terraces,the types of terraces are all accumulation terraces.Qianhe River covered by loess and paleosol,and T1,T2,T3,T4,and T5 correspond to paleosol layers S0,S0~S1,S0~S5,S0~S8,and S0~S14,respectively.The loess paleosol layers at the bottom of the terrace are S0,S1,S5,S8 and L15,respectively.2.Through the comparison of the loss or paleosol of the lowest level of each terrace in Qianhe River and the Baoji standard loess profile,we can infer the age of the river terraces,and combined with the age of regional river terraces,the ages of T1,T2,T3,T4,and T5 in Qianhe five terraces were defined as 0.01 Ma,0.13 Ma,0.60 Ma,0.80 Ma,and 1.2Ma,respectively.3.Through the research on the relationship between the morphological types,forming ages,and climatic stages of the QianheRiver terrace,it was found that the stream trenching may occur during the transition from the glacial period to the interglacial period,while the asymmetrical distribution on both sides of the Qianhe terrace is related to the regional tectonic activity.The difference in uplifting structural background coincides.Therefore,it is inferred that the river terraces in the upper reaches of the Qianhe River are mainly driven by tectonic uplift while the effects of climate change are complementary.4.Through analysis,it is believed that the formation of the terraces at the Qianhe River T5,T4,and T3 correspond to the Kunlun-YellowRiver movement in which the Qinghai-Tibet Plateau rose up.The formation of the T2 terraces corresponds to the Republican Movement.The formation of the Qianhe 5th terrace is a response to the extended NE effect of the Qinglong-Tibet Plateau uplift.