Genesis of topography and regional distribution of the concealed red karst landform in the adjoining area of Hunan-Hubei-Chongqing-Guizhou
Red karst is a concealed landform that has been newly discovered and is buried beneath soil,characterized by its red color and unique shapes.It is widely distributed in the area of Wuling mountain of Hunan,Hubei,Chongqing and Guizhou in China.Compared with common karst landforms,red karst landforms have four basic characteristics:red color,stratified convex morphology,landform lithology of argillaceous limestone,and different dissolution causes in soil environment.Because of its bright red color and unique appearance,red karst is very ornamental and has great tourism economic value.The morphological origin of red karst has been discussed from the perspective of macroscopic geological conditions and tectonic forces,but its mechanism of microscopic morphological formation and shaping process have not been deeply analyzed.In addition,as a concealed landform,it is difficult to be found on the surface,so determining its distribution is of great significance for the relevant investigation and research.Therefore,this paper discusses the formation mechanism and shaping process of the concealed red karst landform from the microscopical point of view,and determines the distribution range of the red karst in the adjoining area of Hunan,Hubei,Chongqing and Guizhou.It can provide the basis for the future investigation and development of red karst.Material composition differences,joint fissure cutting and differential dissolution are the key factors in the formation of red karst geomorphology.The main reasons are as follows:(1)The content of soluble matter on the convex surface of red karst landform gradually increases from top to bottom,while the content of soluble matter on the concave surface is the highest and that on the convex surface is the lowest.This shows that the difference of soluble material content is the material basis for the formation of convex and convex forms of red karst landform.(2)The joint fissure is a good transport channel for water required by dissolution,which can greatly improve the weathering and denudation efficiency of karst geomorphic area and lays a prototype for the evolution of geomorphic form.(3)When the content of soluble components in the parent rock is high,the dissolution rate is fast and concave,and on the contrary,it is convex,which causes differential dissolution.During the formation of red karst landform,the difference of material composition horizontally leads to differential dissolution,and the decrease of erosion vertically leads to differential dissolution.Therefore,the difference of soluble material content in rock composition and the layered rhythmic layer are the material conditions that lead to the diversity of red karst geomorphology,and the dynamic conditions are the cleavage of structural joints and the differential dissolution of rock mass.The evolution of red karst morphology mainly goes through four basic stages:the formation stage of material conditions for morphological development,the emergence stage of dissolved rock layers,the formation stage of erosive groundwater in weathered soil,and the stage of differential dissolution in soil.The formation of red karst mainly goes through three key geological processes:(1)joint fissure cutting;this effect has mainly shaped the outlines of trapezoids and cylinders.(2)rock and soil interface corrosion;due to the undulating rock surface,the rock and soil interface corrosion makes erosive groundwater with fast dissolution rate accumulate in the low concave of the surface,often forming a conical or sharp rock mass.(3)dissolution of joint fissure surface;vertically,due to the continuous consumption of erosive H+ions,both the dissolution ability and dissolution rate decrease,with the increase of depth,forming an approximate V-shaped grike;at the same time,the erosive groundwater dissolves the rock wall on both sides of the joint fissure surface in the transverse direction,and is controlled by the difference of soluble material composition,forming the concave-convex interlayer.According to the definition of red karst geomorphology and the field investigation by the research team,five factors such as color,morphology,lithology,exposure and geomorphology conditions are selected as the criteria for determining red karst geomorphology.The rock composition of the red karst geomorphology in Hunan,Hubei,Chongqing and Guizhou is more dependent on the stable distribution of purplish red nodular limestone and argillaceous limestone in Dawan Formation,supplemented by the purplish red carbonate rock in Guniutan Formation or the Cross Pu Formation,in which the outcrop area of Dawan Formation is the key development area.According to 1∶200,000 geological map,the potential distribution area of concealed red karst geomorphology in the adjoining area of Hunan-Hubei-Chongqing-Guizhou covers 3,433.83 km2,and it is distributed in a narrow strip or partially distributed in a patch in SW-NE direction.
red karstdifferential dissolutionconcealed landform landscapeconcave-convex interlayer
万方数据
维普
