Study On Karst Development And Water-bearing Characteristics Of Limestone Of Maokou Formation In Western Guizhou

The western part of Guizhou is located in the eastern slope of the Wumeng Mountains.The mountains are high and steep,the terrain is strongly cut,and the conditions for the occurrence and enrichment of shallow groundwater are poor.The area is rich in coal resources,and the mining and processing of coal resources seriously pollute the water environment.The problems of engineering water shortage and water quality shortage are serious.The limestone strata of the Maokou Formation are widely distributed,with strong karst development and abundant karst groundwater.In addition,the presence of the overlying tight rock layer Emeishan basalt blocks the hydraulic connection between the Longtan Formation coal seam and the Maokou Formation,so its water quality is good and it is an ideal water source in the area.Therefore,this article takes the west of the Weining-Shuicheng-Guanling-Zhenfeng line in western Guizhou as the research area.The characteristics of karst development are discussed from the macro and micro aspects by means of field profile measurement,sampling,and indoor testing,in addition to single-factor analysis of variance,multivariate discrimination,mathematical statistics and other methods.And the.controlled factors of karst development are analyzed.The characteristics of water-bearing capacity are discussed from the types of karst groundwater system,the circulation characteristics of groundwater,the uniformity of groundwater occurrence,and the water richness of groundwater.Through systematic analysis and research,the main results are as follows:(1)The macroscopic karst development rate is 3.8%-33.7%,and the density of individual karst landforms is 0.0068-0.0789/km~2.The degree of structural development and borehole karst development is the strongest in the middle,followed by the north and south,and the order of macro karst development intensity is:central>north>south,>west>east.The effective depth of limestone karst development in the vertical Maokou Formation is 50 m from the top of the Maokou Formation.Dissolution fissures,dissolved pores and caves are developed.And the degree of karst development near the faulted structural zone is higher than that in other areas.(2)The limestone of the Maokou Formation in the study area is dominated by grain-clastic structure.The interstitials are mainly sprite and micrite calcite.The average grain-to-base ratio is 0.92-3.55,the average porosity is 0.88%-1.08%,and the average permeability is 0.009-0.016m D;The microscopic corrosion forms are mainly intragranular dissolved pores,intergranular dissolved pores,corrosion cavities,and corrosion cracks.The microscopic surface karst development rate is between 1.85%and 4.01%,and the order of the microscopic karst development intensity is:central>north>southern,west>east.(3)The key geochemical elements that affect chemical corrosion and their degree of influence are in the order of Ca>Si>Fe>Al>Mg>O>C.The construct ed chemical corrosion index to determine the degree of limestone karstification in the Maokou Formation is CHI=-16.937×ln(Ca)-5.675×ln(Mg)-4.925×ln(Si)+3.025×ln(Al)+1240×ln(Fe)-43.308.(4)The geological structure types of the groundwater system in the study area are mainly divided into three types of combinations:karst zone+basalt caprock,karst zone+siliceous rock caprock,and karst zone+clastic rock caprock.Groundwater systems are mainly divided into"karst zone-like layered groundwater systems"and"structural water-controlling groundwater systems".The characteristics of groundwater system compensation and uniformity are analyzed.(5)By counting the flow of springs,underground rivers and wells outcropping in the Maokou Formation,the water-rich distribution map was drawn using the Kriging interpolation method.Through the evaluation,it is concluded that the water richness in the middle of the study area is good,the north is normal,and the south is poor;the water richness in the west is good,and the east is normal.The water richness in the region is spatially uneven.According to the characteristics of karst development and water richness,The study area is divided into the favorable area to the north of the Qinglong-Xingren line and the unfavorable area to the south of the Qinglong-Xingren line.