WOOD SINK - AN UNUSUALLY LONG TRACER TEST WITHIN THE DAVIS SPRING BASIN

The 190 km² Davis Spring Drainage basin in Greenbrier County, West Virginia is one of the largest karst basins in WV. Its resurgence, Davis Spring, is the largest spring in the state by discharge. A mature karst topography has developed in this area. Several large, integrated cave systems feed this spring from as far away as 21km. This area is underlain by the Greenbrier Group, consisting of more than 400m of Mississippian carbonates. The drainage basin is flat to gently dipping to the northwest, except near local structure where dip can increase to nearly vertical. Long north-south folds and reverse faults cross the basin, hindering development of one regional cave system.

Field work in 2008-2009 to further understand the dynamics of the basin uncovered an unusual set of tracer tests. Tests performed at Wood Sink, a small swallet to a perennial stream only 4.8km from Davis Spring took more than 2 months to reach the resurgence. Tracer travel times from the farthest reaches of the basin under similar hydrological conditions took less than a month to reach the resurgence.

While lack of data precludes a definitive answer to this unusually long travel time, evidence points to a combination of stratigraphic and structural conditions which preclude quick tracer movement. Of particular interest is the placement of the Taggard Shale, a 15m layer subdividing the Greenbrier into a nearly equal upper and lower sequence. The Taggard acts as an aquiclude, and is almost never breached by passage development in this region. Reverse faulting in the area also tend to terminate cave development, as evidenced in several nearby caves. Consequently, far from being an anomaly, the long Wood Sink tracer times are a reaffirmation of regional principles of conduit development as seen elsewhere in the region.