Research on Main Controlling Factors of Ordovician Karst Development in Lu'an Coal Field

The main controlling factor of Ordovician Karst development were studied based on field investigation,in-door experiment,and drilling data.The results show that: 1) The Caledonian-Hercynian karsts were developed within the Fengfeng formation of the Ordovician roof while new karsts were formed only in the bedrock exposed area,shallowly buried area,and newly formed fault zone during neotectonic movement,forming some multi-layer horizontal karsts;2) There are three sedimentary rhythmic structures in the middle the Ordovician,making the newly formed karsts in shallow zones have a strata bound phenomenon,forming 3 zones of gypsum breccia zone,cataclastic rock zone,and fracture zone because of the gypsum swelling and solution of gypsum,which is the major casue for the marlite layer to become the fractured karst aquifer;3) The joint action of shallow-along-strike strong runoff zone and the deep-reversed-inclination weak runoff zone makes the CaCO3 and MgCO3 corrosion area quite limited and so the superposition of the newly developed karst zone with the old one can be seen only in shallow area,making the deep old karst or collapse column be filled up;and 4) The neotectonic fault zone is the leaking recharge channel through which the ground karst water in the west mining area is recharged.