KARST CONDUITS AND CAVE SEDIMENTS IN PALEOZOIC STRATA, BRANSON AIRPORT ROAD, SOUTHWEST MISSOURI

Road construction in southwest Missouri has recently exposed several karst conduits in Mississippian and Ordovician strata that may help constrain the timing of regional karst development and formation of speleogenic features in the Missouri Ozarks. These conduits contain features developed along unloading fractures that open to the surface, and voids developing along shale-carbonate boundaries. Calcite flowstone formations within the conduits display vadose and phreatic characteristics. Cave sediments include very well-rounded to angular chert clasts from overlying Mississippian strata. The chert clasts have a thin veneer of iron or manganese oxide typically seen in clasts present in modern Ozarks streams, and some have been polished to a high luster. Sediment bodies contain approximately 50-80% gravel to cobble-size Mississippian-age chert clasts, suggesting a high transport velocity. The sediment bodies grade vertically to clays with high angle depositional layers and truncations implying periods of erosion and deposition. In some conduits, Darcian flow along bedding planes appears to have formed new terra rosa clay, contributing to roof separation and conduit enlargement. Mid-grade sediments consist of alternating laminae of terra rosa clay and dolomitic silt, indicating decreased flow velocity or a change in sediment supply from cherty Mississippian limestones to low-chert Ordovician dolomites. The top layers are terra rosa clays interbedded with saprolites derived from the dolomite. Degraded dolomite clasts are observed in some samples. Surficial organic material has not been observed at any depths. The Branson metropolitan area is undergoing extensive commercial development. In addition to providing information on the timing of regional karst development, an understanding of the origin of these features is important in predicting the movement of groundwater contamination, sinkhole formation, and the prevention of other geologic and hydrogeologic hazards.