Water-resisting characteristics and distribution rule of carbonate strata in the top of Ordovician in North China

Presented a viewpoint that increasing the whole thickness and strength of aquifuge by taking advantage of the water-resisting characteristics of carbonate rock in the top of Ordovician,which proved by using several methods.Carbonate rock of Ordovician remaining in the middle of North China Plain is thick,whose residual position is high(new),while getting smaller in the margin,with lower residual position(old).Filling-type aquifuge only exist in the top of Ordovician where carbonate rock dominate,as well as in areas such as old Karst platform and old Karst slope of caledonian,while both filling-type and nondevelopment-type aquifuge,with large thickness,exist in the top of Ordovician where dolomite rock is the main composition,as well as in area of old Karst basin.Reconstruction in later period caused some damages to carbonate aquifuge in the top of Ordovician,including collapse pillar,fractures,outcrop zones in shallow part and new Karst in strata,which are also the most important parts of water protection and conservation.