FACIES MODELS FOR CLASTIC CAVE SEDIMENTS: EVENT DEPOSITS STRONGLY INFLUENCED BY SOURCE AREA DYNAMICS, SEDIMENT TRANSPORT MECHANICS, AND ACCOMMODATION SPACE

Clastic cave deposits are typically given significantly less attention than speleothems, yet both represent the continuum of particles and dissolved chemicals flowing through cave passageways, and both are important indicators of land surface conditions overlying caves, climatic and hydrologic processes implicit in redistribution of geologic materials, and cave evolution processes such as enlarging and filling volumes of open space in the cave system. This study utilized exhumed paleocaves in the Carboniferous Leadville, Madison, and Pahasapa limestones of western North America to apply facies analysis concepts to clastic cave deposits. Most clastic cave sediments are mass flows (event deposits) classified as debrites, inundites, and jointites. Debrites formed from subaqueous debris flows in phreatic tubes, and incorporate clasts from karst breccias, chert nodules, and resedimented speleothems such as flowstone clasts. Inundites are flood deposits in phreatic tubes with characteristic upper flow regime plane bed, climbing ripples, normal grading, and may include mud drapes or even mudcracks (from subsequent phreatic tube dewatering). Jointites are the results of episodic sheetflow events on the land surface that infilled open fractures or joints. These vadose zone deposits often show time lags between successive events, such as capping weathered surfaces or paleosols. There are significant differences between these clastic cave deposits and surface analogs. First, the morphology of these event deposits is significantly affected by the geometry of available depositional space, such as changes in cross-sectional shape and area within cave passageways. Second, flow dynamics varies between partial to complete pipeflow for even individual events. Third, there is a strong potential for reworking under conditions of subsequent high-energy flows in confined spaces. Fourth, accommodation space can be created (e.g., falling water tables result in new cave passageways) or destroyed (e.g., infilled by sediment or cave collapse) over relatively short time spans. Fifth, cave depositional systems ultimately have higher preservation potential than deposits in surficial terrestrial environments, thus clastic cave deposits are important geological archives of the overlying land surface environment.