SEDIMENTS FROM AN ABANDONED KARST GROUNDWATER CONDUIT: WINDY MOUTH CAVE, GREENBRIER COUNTY, WEST VIRGINIA

The Big Levels of West Virginia is a karstified upland formed near the eastern edge of the Appalachian Plateaus physiographic province. The Greenbrier River, with a mean daily discharge of 60 cubic meters per second, serves as regional base level for the hydrologic system. The river is incised 115 meters below the upland surface. Windy Mouth Cave is an 11 km long, North-South oriented, abandoned groundwater conduit formed in the southern wall of the Greenbrier River gorge, 30 meters above the present river level. The cave supplied a now-abandoned spring on the river.

Clastic (fluvial) sediment samples were collected throughout the cave from gravel bars and floor deposits in domes and the main trunk passages. The deposits were coated black by manganese oxide, stained from rich iron oxide waters after deposition, or both. Particle size distributions revealed 2 end members. Samples contained: a high percentage of gravel, lacking mud and sand, or a high percentage of mud, with no gravel or sand. Four of the sixteen samples were intermediate between the two.

A surprisingly high percentage of chert dominated the samples, with the gravel size fractions averaging 75%. Quartz (as determined by XRD) dominated the clay fraction lithology. Three samples varied in grain size, and contained a broader distribution of lithology than the others. Where chert percentage decreased, the percentage of shale and siltstone increased.

Grain shape percentage among size fractions >2.00 mm and >1.00mm both contained high amounts of sub-rounded to sub-angular grains. The latter had a greater distribution of grain shapes, containing higher percentages of rounded and sub-rounded than 2.00mm.

The vast majority of clastic sediments found in the cave appear to have been locally derived from rocks of the Greenbrier Group. Sinkhole inputs to the surface feed different branches of the conduit. Due to spatial variation of water and clast input, a complex pattern of sediment distribution in the cave has resulted. Chaotic gravel deposits indicate periods of intense, probably pipe-full, water flow. Fine grained deposits relate to low flow conditions caused either by lack of recharge, or obstruction of the conduit outlet.