Abstract:

A geologic framework is required to understand the environmental impact of proposed mining of lead and zinc on large springs in the karst area of south-central Missouri. Information about lithologies, faults, joints, and karst features (sinkholes, caves, and springs) contributes to the development of a conceptual model of karst hydrogeology. Conduits and caves along bedding planes and joints provide avenues for ground-water recharge, movement, and discharge. The trend of joints was studied to determine if they controlled the orientation of cave passages and conduits. The data show that cave passages are curvilinear and do no correlate well with measured joint trends. Instead, stratigraphy, bedding-plane dip, and local base level affect conduit and cave development. The majority of caves in south-central Missouri have developed within stromatolitic dolomite horizons beneath sandstone beds. It is thought that the sandstone beds act as confining units allowing artesian conditions and mixing to occur beneath them, thus, enhancing dissolution. Joints and the high primary porosity of the stromatolitic dolomite beds form openings in the bedrock that initiate solution. Where a solution-widened joint intersects a bedding plane, lateral movement of ground water is controlled by the bedding plane.