INTER-CONDUIT VARIABILITY OF FLUVIAL SEDIMENTARY DEPOSITS WITHIN ORGAN CAVE, WEST VIRGINIA - EFFECTS OF REGIONAL AND LOCALIZED EVENTS

Alluvium preserved in caves is useful for evaluating the timing and characteristics of past hydrologic events. It is often uncertain, however, whether the sediment record reflects regional, or merely localized, events. We studied deposits in major conduits of Organ Cave, West Virginia, a 68 km dendritic/branchwork system developed in Lower Greenbrier Group rocks of the Appalachian Plateaus. There are 10+ sinkholes that provide recharge to the system. Deposits were examined in the Sively, Lipps, and Organ (main stream) segments. The work included calculation of current catchment drainage areas, examination of sedimentary deposits with regard to extent and setting, construction of local stratigraphic columns, bulk sampling for lithologic/grain size analysis, and paleomagnetic sampling.

Catchment areas for the Lipps, Organ, and Sively 3 conduits are 0.038 km², 0.925 km², and 0.027 km². All investigated conduits 1) have evidence of being previously choked with sediments, 2) are presently occupied by streams, and 3) are not currently choked by sediments. This pattern, also seen in other area caves, shows that under present conditions, all (at least in the vadose segments) are undergoing excavation (erosion) of previously deposited sediments. Regional control of sediment supply and/or stream power, suggesting climatic regulation, is therefore likely. There is significant variability, in the sequence and character of deposits between the 3 conduits that were studied. Normal and reverse polarity sediments are found. Sively conduit sediment alternated between poorly sorted gravel and sand, with laminated silt and clay. 1.5 m of diamict comprised the bottom layer. Sediments from 2 Lipps Passage sites contained mostly clay and silt. A 15 cm layer of poorly sorted gravel was observed on a chert shelf at site 1; moist, banded silt and clay with a wide range of coloration was also sampled. Site 2 was comprised mostly of laminated silt with some clay. Silts and clay with traces of sand constitute the Organ conduit sediment. Variability probably results from a variety of factors including: 1) catchment size, 2) catchment lithology, and 3) "random" controls such as occlusion of sinkholes. Therefore, caution should be exercised when drawing regional conclusions based upon sampling in one or a limited number of conduits.