The Controlling Effects Of Structures On Supergene Karst

Miaoqian area is located in the middle section of the South China fold belt and the Yangtze block,which is significantly controlled by tectonics,forming various karst types with typical characteristics.Based on the geological field investigation,measurement and sampling of karst outcrops in the studied Miaoqian area,combining the techniques of laser ranging,drone shooting and microscopic observation,this research studied the basic development conditions,types,and characteristics of epigenetic karst of Menggongao Formation of the Lower Carboniferous,as well as the controlling effects of different structures on the epigenetic karst and various epigenetic karst models.From the morphological analysis of karst landforms,the karst in Miaoqian area mainly consists of cave,karren,lapis,grike,stone teeth,stone forest,sinkhole,karst pit,doline,karst depression,collapse doline,karst valley,stalactites,stalagmites,etc.From the perspective of karst genesis,combined with the relationship between karst and structures,it is classified into structure-controlled karst and non-structural-controlled karst.The structure-controlled karst could be further classified according to hydrodynamic type to structure-controlled erosional karst which develops river or subterranean stream,and structure-controlled dissolved karst which doesn't develop river or subterranean stream.The structure-controlled karst dominates in Miaoqian area of the Carboniferous.The controlling effects of structures on Karst are respectively analyzed in the relationships between faults,structural fissures,folds and tectonic movements with supergene karst.The folds on the side of active wall of tensional faults,tension-torsion faults and compressive faults are most favorable for the development of supergene karst;the occurrence of structural fractures controls the dominant direction of karst development,and the karst strength increases with the increase of fracture density.Compared with low-angle fractures,high-angle fractures are more conducive to the vertical seepage of atmospheric precipitation and develop stronger karstification.The karstification of large vertical tensional fractures developed in thick or massive limestone is intense.The influence of tectonic movements on karst is mainly reflected in the inheritance and transformation of existing structures;the neotectonic movement mainly affects the vertical strength zoning of karst and controls the karst cycle times.On the basis of fully understanding the controlling factors of karst in Miaoqian area,the supergene karst model was established.According to the structural types controlling karst development,the karst models are categorized into four types: tensional fault karst model,torsional fault karst model,shear fracture karst model and tensional fracture karst model.The shear fracture karst model can be further categorized into conjugate shear fracture karst model and high angle shear fracture model.The tensional fracture karst model can be further categorized into small tensional fracture karst model and tensional fracture karst model of syncline axis.Finally,the comprehensive karst model of Miaoqian area is established by synthesizing the main supergene karst types and development characteristics of the Menggongao Formation of the Carboniferous.The model shows that the karst distribution characteristics in Miaoqian area are mainly controlled by the pre-existing fractures and faults produced by Yanshan and Indosinian tectonic movements.There are four sets of shear fractures along NWW,NNW,NNE and NEE,and nearly NS compressive-torsional faults.The episodic uplift of Himalayan movement controlled the vertical cycles of supergene karst in Menggongao Formation.According to the development characteristics and altitude of supergene karst in Shima mountain,the karstification stages of the studied outcrop can be divided into three stages: the first stage is Moyanli canyon(278m),the second stage is Xijin Cave-Moonlight Cave System(210-233m),and the third stage is underground river-cave system connected with Qingyu spring(200m).