Lithological Characteristics Of The Red Beds And Genesis Of Danxia Landform In Zhangye

Zhangye Danxia is representative of Danxia landform in the arid regions of northwest China,the window-like and palace-like Danxia landform and colorful hilly landform are the first in China,the rest of Danxia landform is unique.Moreover,the red beds of Zhangye Danxia is located in the northeastern margin of the Tibetan Plateau,special studies on the red beds in this area are rare.The paper takes Zhangye Danxia as the main research object,conducts field geological survey on the geological environment and the red-beded landform in research area;explores the lithological characteristics of the red beds by the measurement of magnetic susceptibility and strength,conglomerate statistics and analysis,polarizing microscope observation,XRD,SEM,soluble salt experiments and other means;extracts the river system and explores neotectonic movement and climatic characteristics,analyzes the genesis of Zhangye Danxia.The main conclusions are as follows:(1)Zhangye Danxia is located in the special geological environment,spanning three geological units of the North Qilian Mountains-Hexi Corridor Basin-Alashan.It is divided into the North-South Danxia landform group.There are many types with strange shape of Danxia landform,window-like and palace-like landform,forest-like landform,laminated landform,canyon-like landform,steeply inclined landform,honeycomb landform,mud landform and pictographic rocks.(2)The red beds of Triassic and Cretaceous are selected for research in the study area.The conglomerate size along the Liyuan River in the North Qilian Mountains and Hexi Corridor decreases gradually,the sortability improves gradually,and the structural maturity decreases gradually.The different cementing types of the Xiagou Formation and Zhonggou Formation are the key factor for the different landforms;in contrast,the metamorphic mineral content of conglomerate increases in the Alashan section.The mudstone that has different color in the Cretaceous has commen mineral composition basically,different microstructures slightly,and its color parameters show certain regularity.The content of gypsum salt ions in the mud Danxia landform is an important factor that affectes morphological characteristics,and its constituent materials are derived from weathered debris of Danxia landform.(3)The valleys of the river system that are formed by tectonic activities promote the formation of Danxia landform;the neotectonic movement accelerates the formation process of Danxia landform;due to the unique climate pattern,Danxia landform are carved by external conditions such as weathering erosion,frost heaving,hydraulic erosion.Under the coupling of tectonic activity(neotectonic movement),lithological characteristics of red beds,and external conditions,Zhangye Danxia is able to show various landscape features.