A Proposed Hypogenic Origin of Karst in the Shenandoah Valley, Virginia and West Virginia

Current conceptual models of karst development in the Appalachian Valley and Ridge Province focus on shallow phreatic and vadose zone processes of epigenic karstification. We propose an alternative hypothesis of hypogenic mixing-corrosion karst development for the Shenandoah Valley, Virginia and West Virginia. Features that suggest hypogenic initiation to karst development include 1) the preponderance of cave passage morphologies indicative of ascending fluids, 2) a general absence of cave streams or cave stream deposits, except along ridge flanks or near modern, base level surface streams, 3) reported high yield wells (>400 L/min) in carbonate rocks at depths greater than 300 m (1000 ft) below land surface, 4) dye-traces indicating slow, divergent flowpaths with low dye recovery at springs, 5) springs elevated an average of 25 m above base level streams, some with decades-old ground water as the young component, 6) active warm springs and evidence of ancient warm spring deposits in carbonates, 7) locations of springs in relation to major structural features such as thrust faults and cross-strike faults, 8) ore deposits associated with a regional migration of reactive hydrothermal fluids and solution features in carbonate formations, 9) widespread distribution of travertine-depositing springs, and 10) biological evidence for a once regionally extensive karst system dissected into compartments by uplift and incision. Our examination of larger caves in the region indicates that most initially formed under fully phreatic conditions along fold axes and limbs, and have been subsequently invaded by vadose waters as a result of erosion and exhumation. Such a karst system is distinct from the classic conceptual model of epigenic karst development built around studies in the Interior Low Plateau Province (e.g., Mammoth Cave region).