Lithology Characteristics Of Kongtong Mountain And Development Mechanism Of Danxia Landform

Kongtong Mountain is located in the southwest edge of Ordos,and the transition zone of the Longdong Loess Plateau and Liupan Mountain,a spectacular Danxia landform developed in the giant continental deposition of the Triassic and Cretaceous conglomerate.At present,Danxia landform research in China is focused on the basic aspects of field investigation and experiment,but theoretical research is relatively lacking.Moreover,large number of research work of Danxia landform has been conducted in southern China;however,research on Danxia landform in the northwestern China is basically in the blank stage.The study on the evolution and lithology characteristics of the Danxia landforms in Kongtong Mountain not only provides important information for exploring the regional geological structure activities,revealing the climate and environment changes,but also enriching theoreticl system of the Chinese Danxia landform,providing more basic information for domestic and international comparison.Based on the Digital Elevation Model(DEM)data of Kongtong Mountain,the surface morphological factors of Danxia landform are extracted and analyzed by using geographic information system(GIS)technology,planation surfaces of the Kongtong Mountain area have been discussed in depth combined with regional geological environment of the Liupan Mountain.In addition,combined with detailed field geological survey and laboratory tests such as Equotip hardness test,rebound test,Xray diffraction,X-ray fluorescence spectroscopy,inductively coupled plasma mass spectrometry,M?ssbauer spectroscopy and scanning electron microscopy,we have done systematic analysis on the physico-mechanical properties,geochemical characteristics and microstructure of the Cretaceous mudstone and Cretaceous,Triassic conglomerate.This paper mainly focus on three aspects:(1)topographic features and planation surfaces of Danxia landform in Kongtong Mountain;(2)The weathering process of the Cretaceous and Triassic conglomerates in Kongtong Mountain and its implicaition on the evolution process of Danxia caves;(3)color genesis of Cretaceous mudstone of Banmashan Mountain.The main conclusions are as follows:(1)The distribution and morphological characteristics of Danxia steep slopes can be effectively interpreted by using elevation,topographic slope and relief amplitude,the slope of Danxia cliff is over 44.4°.The spatial analysis of landform factors can provide important information for the identification of the planation surfaces.There are two levels of planation surfaces in Kongtong Mountain.The first level is Fragrant Moutain with elevation of 2123.5m,the second level is the Middle Platform and the altitude is 1894 m.(2)The composition and intensity of the interstitial materials and gravels in the Cretaceous and Triassic conglomerates are different,and the composition distribution of the interstitial material is not uniform,resulting in differentiated weathering within the conglomerate.The internal pores and fractures of conglomerate and well-developed giant joints provide favorable condition for the water infiltration and corrosion.Danxia cave in Kongtong Mountain mainly distributes in the Cretaceous Sanqiao group and above the discordance interface.Different from the formation of the Danxia caves in the Southern China,Danxia cave in Kongtong Mountain is absent of weak intercalated layer,such as sandstone and mudstone.The weathering process of the conglomerate in the cave is the dissolution and migration of calcareous cements such as calcite,and the crushing and refining of the rock mass.(3)The different color strata of Cretaceous mudstone of Banmashan Mountain are parallel to the horizontal band distribution.The color space parameters L,a,b of the CIE Lab color space can effectively represent the mudstone color,which can be divided into green gray,gray and yellow.In the reddish gray-greenish gray mudstone transition zone,the chemical composition migrates,and the color is influenced by the rock components.However,the relationship between the relative content of oxides and elements and the color characterization parameters was not obvious,but customized paramets R is negative related to L,and R is ?(Al2O3 + Fe2O3)/ ?(SiO2 + MgO + CaO + K2 O + Mn),? is the relative content.The occurrence of iron and its compounds has a great influence on the characterization of rock color.However,the ratio of Fe3+ and Fe2+ could not always reflect the mudstone color.The Cretaceous mudstone of Banmashan Mountain is dominated by Fe3+,but the relative content of iron species have little impact on its rock color,as a matter of fact,it is controlled by multiple factors.(4)Microstructure varies with different rock color,greenish gay and reddish gray mudstone is of basal cementing and matrix supported,with developed micro facture and corrosion pores,and the structure is rather broken.The yellow mudstone is of contact cementing,the particle support,the grain roundness is poor,the structure is more stable,and the structure is more uniform and dense.(5)The lithology stratums of Danxia landform in Kongtong Mountain area mainly consist of the Triassic Yanchang group(T3yn)and the Cretaceous Sanqiao group(K1s),which both are thick continental coarse clastic rocks deposited.The main processes of its development are river intrenching and tectonic uplift,joint development and weathered erosion,collapse and erosion transportation,loess attachment and biological deposition.