River Terrace Sequence Of The Middle And Lower Reaches Of Dadu River And Its Response To Mountain Uplift

River terraces are an important part of the river's geomorphic system and can reflect the geological structure and climate change of the terraces in a certain period of time.The middle and lower reaches of the Dadu River are located at the junction of the western Sichuan Plateau and Panxi Plateau,The river valley spreads along the "Y"-shaped junction of Xianshuihe fault,Longmenshan fault,and Daduhe ductile fracture zone,special location.It has certain reference significance for studying the uplifting history of the mountain in the region.This paper conducts field investigation and indoor chronological analysis of river terraces in the asbestos-Jinkou River area in the middle and lower reaches of the Dadu River.In-depth study on types,distribution,sequence division of river terraces and characteristics of terrace sediments in the study area,At the same time,combining the development characteristics of river terraces in the study area,Preliminary discussion on the response of river terraces to the uplift of mountain tectonics,The main results are as follows:(1)Comprehensive analysis of the heights of the tug-of-war,terrace systems,and section features at all levels of terraces,Preliminary determination of the distribution and sequence of terraces in the study area.The results show that there are 6 terraces developed in the middle and lower reaches of the Dadu River.The terrace types are mainly erosion terraces,base terrace and stacked terraces.Where T1 and T2 are stacked terraces,T3,T4,T6 are base terraces and T5 is erosion terraces.Tall heights of T1-T6 terraces are 21-25m?47-49m?79-94m?145-175m?403m?502m,The terraces of T3-T6 reflect the lower cuts and tectonic uplift of the rivers in different periods.(2)Estimation of T1-T6 terraces in the middle and lower reaches of Dadu River using OSL and ESR geochronology,The formation age of T1-T6 terraces is 16.8-18.5ka ?35.1-42.6ka?94.8-110.6ka?389.8-418.5ka?656±99.2ka?722.5-795.3ka.Through the analysis of terrace types,distribution patterns of terraces within the river basin,and analysis of the characteristics of terrace sedimentary cycles,The origin of river terraces in the study area is dominated by structural uplift and formed by the joint action of climate participation.(3)The results of the river terraces types,altitude to river bed and different heights between two adjacent terraces sensitively indicates that the tectonic uplift in study area since the end of the early Pleistocene.