Development Of River Terraces In The Northern Margin Of Ordos And Its Significance For Neotectonics

The evolution of river system is a process of interaction between accumulation and shear,which records a lot of information about tectonic movement and climate change.As an important stratiform landform,river terrace is one of the evidences of neotectonic movement and has a good response to tectonic movement and climate change.Therefore,the study of river terraces is of great scientific significance for the study of regional neotectonic movement and Quaternary paleoclimate change.This paper chooses the northern margin of the Ordos Platform as the research area,and systematically investigates and studies the terraces of the tributaries of the Yellow River through remote sensing interpretation,field investigation and photoluminescence(OSL)dating.Through the study of the history and rate of river accumulation-downcutting,this paper discusses the formation of river terraces on the Quaternary paleoclimate and the northern margin of the Ordos Platform since the Late Pleistocene.In response to tectonic uplift,the results are as follows:1.The order of river terraces on the northern margin of Ordos is determined by the measured cross-section of the valley.The morphological types and development characteristics of terraces are analyzed.There are generally four terraces on the northern margin of Ordos terrace.The main terraces are accumulation terraces and base terraces.The tug-of-war height of the same river terraces in the eastern and western parts of the region is relatively close,and it decreases slowly from east to west to the middle.Trend.2.The chronological framework of river terraces in the northern margin of Ordos since the Late Pleistocene has been established by using the optical luminescence(OSL)dating method.The approximate time of formation of terraces T4,T3,T2 and T1 in the northern margin of Ordos is :78.66±2.58ka-66.45±2.64ka?54.58±1.76-38.20±2.3ka?29.80±2.3-15.22±1.32ka?4.9±0.3ka—now.3.The formation mechanism of river terraces is analyzed based on geomorphology,sedimentology and chronology,The formation of river terraces in the northern margin of Ordos is a combination of tectonic uplift and climate change,butthe degree of tectonic movement and climate is not identical in different periods.The formation of terraces T4 and T3 is mainly controlled by tectonic uplift,while the formation of terraces T2 and T1 is mainly controlled by climate change.The impact is greater.4.The cutting rate of rivers is calculated and the history of accumulation-downcutting of rivers is analyzed based on the elevation difference and age data of terraces.Then the process of tectonic uplift and the difference between eastern and Western uplift since the late Pleistocene in the northern margin of Ordos are discussed.The downcutting rate of Eastern river terraces is higher than that of Western River Terraces in the first stage,and the downcutting rate of eastern and Western River Terraces has converged since the second downcutting stage.From the early stage of late Pleistocene(Qp3-1)to the end of late Pleistocene(Qp3-3),the northern margin of Ordos is characterized by a gradual decline in uplift from east to west to the central part,while since the end of late Pleistocene(Qp3-3),the difference of uplift of northern margin of Ordos has gradually decreased,mainly in the overall uplift.