Study On The River Terrace And The New Tectonic Movement From Middle Pleistocene Of River Xilamulun, Hexigten Town, Inner Mongolia, China

Located in the east of Inner Mongolia，Hexigten lies at the interjunction of theDaxinganling Mountains and Yanshan Mountains, which is a typical research areas ofthe Quaternary environment change. This paper is from Hexigten Global Geoparkplanning and construction of the special fund projects.Through the field detailed study of Xilamulun River, especially through thestudy of the river terrace and the analysis of the remote sensing of planar graphs, weestablish the age framework of the river development by TL dating. At the same time,we do a further study on the new tectonic movement sine late Q_p~2of this river basin,invert the process of the river formation and evolution, construct the relation betweenthis development process and the new tectonic movement&ancient climate. The mainresults include:1. Through the field detailed study of river terrace of Xilamulun River, we findout its divisions. The highest river terrace of the river is5. Generally there is3to5river terrace in the upper and middle reaches of Xilamulun River. The relativedispersion in the upper is more than in the middle.2. By analysis of the cross sections of Xilamulun River, we differentiate the riverterraces types as its shape and cause. There are3types of river terrace in XilamulunRiver, which includes accumulation terrace, base terrace and erosion terrace. Theformer two gives priority to the latter one. The main cause of formation of the riverterrace is3, including of new tectonic movement, change of ancient climate andhuman activity. We think the formation of T3to T1is controlled by the climatechange, which corresponds to3phase of the climate change----warm-cold-warm.3. By comprehensive analysis of the age dating results and the other study, weconstruct the river’s development process. the formation of Xilamulun River ispreliminarily formed around160Ka B.P, completely formed around78Ka B.P. Itsdevelopment process can be divided into6phases. No.1, Q_p~2, lake phase, the Riverdoes not take shape, the big lake is linked with small river. No.2, late Q_p~2to early Q_p~3, strong uplifting of the new tectonic movement, the River takes shape initially andpartially reserves T5river terrace. No.3, early Q_p~3to middle Q_p~3, strong uplifting ofthe new tectonic movement, the River takes shape completely and the T4river terraceforms. No.4, late Q_p~3to final phase Q_p~3,T3river terrace forms. No5, final phase Q_p~3toQ_h,T2forms. No.6, Q_hto now, T1forms.4. By analysis of the river terrace and types of the different sectors of this area,we discuss the characters of the new tectonic movement, which shows several phasesand ways in time and space. The new tectonic movement give first place to faultactivity, which includes vertical promotion and demotion movement, horizontaltwisting and tilted lifting.