KARST GEOLOGY AT RICKWOOD CAVERNS STATE PARK

As part of ongoing geologic hazards research at the Geological Survey of Alabama, karst mapping was conducted in Rickwood Caverns State Park area in Blount County, central Alabama. Karst features of the park include a topographic basin in the south-central park area, sinkholes, karst pavement, keyhole canyons, and an elongate cave. The great density of these features in the park allows a comprehensive view of surface-to-subsurface karst relationships.

To analyze the interactions of lithology, structural geology, and hydrology, a variety of field and geospatial techniques were employed. Field methods at the surface and subsurface included describing lithology, mapping geologic unit contacts, describing and measuring dissolution features, and measuring orientations of joints. Elevation data at the surface were obtained with GPS and cross-checked with topographic maps and LiDAR data; elevation data in the cave were obtained with laser and transit measurements in cave surveys.

The park area lies at the southwesternmost exposure of the Bangor Limestone in the Sequatchie anticline of the Valley and Ridge physiographic province. While the majority of the park area bedrock is Mississippian age Bangor Limestone, the upper part of this unit is overlain by the Pennington and Pottsville Formations and underlain by the Hartselle Sandstone. Colluvial boulders of maturely weathered Pottsville sandstone cover the slopes surrounding the park.

The majority of the karst features, including the sinkholes, karst pavement, keyhole canyons, and cave, lie in the Bangor Limestone. In the cave, speleothem and speleogen features include (but are not limited to) stalactites, stalagmites, pillars, drapes, soda straws, gypsum flowers, helictites, pendants, bell holes, and anastomotic channels. Structural and structure-related features in the cave include joint sets, roof collapse, and calcite-filled fractures.

Vertical cave data suggest two horizons of cave passage gently dipping in the direction of anticlinal plunge. Strikes of grikes in the karst pavement and keyhole canyons generally parallel the cave passage strike and the direction of the Sequatchie anticline. Evidence of multiple speleogenetic events may relate to local or regional water level changes, or may be connected with Appalachian uplift events.