| As a typical representative of pinnacle karst in the world,Yunnan stone forest has extremely high value for scientific research,and its formation and evolution characteristics have caused the widespread concern among the scholars at home and abroad.Taking Shilin World Geo-park as the research area,this paper studied stone forest from five aspects:spatial distribution,stone forest morphology,formation conditions,development model and evolution process.The satellite remote sensing technology and GIS spatial analysis method were used to study the distribution characteristics and the spatial distribution law of stone forest;The unmanned tilt photogrammetry and quantitative analysis methods were used to measure the morphological parameters and explore the morphological characteristics of stone forest.Guided by the theory of earth science system,this paper analyzed the influence of formation lithology,geological structure,topography,meteorology,hydrology,vegetation,soil and other conditions on the development of stone forest,and discussed the necessary conditions for the formation of stone forest.The development process of stone forest were discussed in the karst dynamic system which was composed of the necessary conditions to form stone forest.After analyzing the regional geological evolution,the background of paleoenvironment change and the relationship between the strata and the paleostone forest and stone bud,the natural history analysis method was adopted to discuss the present and the past,and the development period and time of stone forest were discussed.The main work and findings of this paper are drawn as follows:(1)The spatial distribution law of stone forest:A total of 102 stone forests have been developed in the study area,which are mainly distributed in the three concentrated development areas,including the Sibeihou-Hemocun,Wukeshu-Qingshuitang and Weiboyi-Geyihei stone forest.The distribution direction is obvious,showing a north-south distribution in the front line of Sibeihou-Shilin town-Qingshuitang.From north to south,the distribution of stone forest shows dense-sparse-dense-sparse changing;From west to east,the distribution of stone forest only changes from dense to sparse.The stone forests are distributed at an altitude of1720m-1970m,mainly in the section of 1750m-1850m.With the elevation increases,the number of stone forests tends to decrease.(2)Morphological characteristics of stone forest:The morphologies of stone forest are described by the average morphological parameters of all stone columns such as the height,the length of projection plane,the width,the area,the axis of long axis and the spacing between stone columns in a single stone forest.The height of stone forest in the aerial survey area is about 5m-14m.The changing trend with height of stone forest reflects the process of its rapid development and slow extinction in a relatively stable evolutionary environment.The projection plane length of stone forest is 5.2m-31.0m,with an average of 12.2m;The width is3.0m-11.0m,with an average of 6.19m;The ratio of length to width is 1.66-4.57,with an average of 2.1,with sword-shaped stone forest as the main type;The area is 11.0m~2-280.0m~2,with an average of 69m~2;The axial direction of long axis is generally northwest.The northeast interval of stone forest is 1.3m-13.6m,with an average of 4.3m.The northwest interval was1.5m-7.4m,with an average of 4.9m.The separation degree of stone forest in the northwest direction is higher than that in the northwest direction.There is a strong spatial autocorrelation of the height,the Projection plane form and the interval of stone forest measured by Aerial survey,and Both of them shows the strongest or weakest variability in the north-west and north-east directions,which reflectes the control effect of the north-west and north-east joints on the morphology of the stone forest.There is a general connection among the morphological parameters of aerial survey stone forest,and the morphological parameters correlation between stone column and stone forest show consistency,which reflects the characteristics of"like attracts like".According to the morphometric value of stone forest,the stone forests were divided into five types.Although different types of stone forest are interspersed with each other as a whole,they show the characteristics of echelon and concentrated distribution.(3)Formation conditions of stone forest:The development processes of stone forest are affected by the formation lithology,geological structure,topography,climate,hydrology,vegetation,soil and other conditions in the four circles of lithosphere,hydrosphere,atmosphere and biosphere.In terms of formation lithology:The dip angle of carbonate rocks in Qixia Formation and Maokou Formation in the study area is 3°-10°,the average layer thickness is more than 2.5m,the rock strength is about 113mpa,and the average porosity is 1.79%-3.75%,the content of calcite,dolomite and other soluble minerals account for more than 99%,which makes the strata have good stability and solubility,and is conducive to the development of stone forest.In terms of geological structure:Intermittent structural uplift is the main crustal movement in Shilin area,influenced by the structural movement,two groups of steep dip"chessboard"joint networks with long extension and close to straight intersection were developed.The joint network,which is conducive to the occurrence of vertical dissolution and strictly controls the shape of stone forest and is favorable for stone forest development.In terms of topography and geomorphology:the development of stone forest has obvious selectivity to slope direction,about 82.35%of stone forests are developed in the south slope,and the number of stone forests development decreases with the increase of altitude and the increase of slope.The development of stone forest is restricted by topography and geomorphology.In terms of Climate:the study area belongs to subtropical plateau monsoon climate,with an average annual temperature of 13?-17?,and an average annual rainfall of 904mm-975mm.The warm climate accelerates the dissolution of carbonate rocks and is conducive to the development of stone forest.In terms of Hydrology:The surface water is transformed into groundwater through the vertical seepage system in Shilin and the calcite saturation index is increased from-3.31 to0.32.In this process,the lower seepage and the carbonate rocks along the way have strong dissolution,which is conducive to the development of stone forest.In terms of vegetation:The value of NDVI in stone forest development area is between 0.04 and 0.31.A large number of plants lead to strong biolysis,which is conducive to the development of stone forest.In terms of soil:The soil moisture content in the stone forest development area is between 21%and 49%,and the CO2 concentration is between 30 ppm and 1000 ppm.This kind of soil characteristics is conducive to downward flow of surface wate,at the same time,it also increases the solubility of the underseeflow,which is conducive to the development of stone forest.(4)The development model of stone forest:Under the combined effect of the development conditions and preservation conditions,stone forests are developed from stone buds by the gradual surficial weathering and sub-soil dissolution in the long geological history.The development process of stone forest can be divided into 6 stages:the stage of tectonic uplifting-joint development,the stage of stone bud development,the rudimentary stage,the forming stage,the decline stage,the extinction stage.different stages,from stone bud development to stone forest extinction are existing in the study area.(5)Evolution of stone forest:stone forest in the study area has developed at least 4 times.The first period of stone forest was formed before the Late Permian.The second period of stone forest was formed from the end of late Permian to the late Eocene.The third period of stone forest was formed from the late Eocene to the end of Oligocene.The fourth period of stone forest was formed from the end of Pliocene to the present day.Nowadays,stone forest in the study area are mainly the fourth period,while in a few areas there are still the third period that is residual. |
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