Geologic and Geomorphic Controls on Karst Conduit Development and Drainage Rearrangement in Burnsville Cove, Bath County, Virginia

The Burnsville Cove is a significant region of cave and karst development in Bath County, Virginia and contains >100 km of explored cave passages in systems developed primarily within the Silurian-Devonian Keyser Limestone of the Helderberg Group. Patterns of cave development are the result of geologic controls on paleo-conduit systems and geomorphic development of modern drainage. Cave passages within the cove follow a combination of joints, minor faults, small and large folds. At present, many of the caves are dominantly vadose/near-surface hydrologic systems that drain north to the Bullpasture River, which flows south into the James River. However, the caves have several solutional and sedimentary features that are indicative of former phreatic conditions and substantially different paleo-drainage characteristics.

Incision of the Bullpasture River Gorge, which continues today, has caused regional karstic drainage patterns to rearrange, and significant portions of the system have either reversed their flow direction or been pirated by new discharge points along the Bullpasture River. This change from phreatic to vadose conditions may have been caused by tectonic uplift, nick point migration, and (or) a change in climate that resulted in relatively rapid incision and lowering the base-level of the Bullpasture River.

In addition, the caves contain mineralogical evidence that is suggestive of hydrothermal fluid migration. In the Butler Cave-Sinking Creek Cave System, for example, one or more of the following minerals are generally exposed in faults, sheared bedding planes, tension gashes, and tight fold axes: (1) calcite, (2) singly and doubly-terminated quartz crystals, (3) milky quartz and (4) lithiophorite [(Al,Li)MnO2(OH)2]. These observations suggest that many early conduits may have developed along proto-conduits from early hydrothermal fluid migration.