Paper No. 4
Presentation Time: 1:30 PM-5:30 PM
SEDIMENTOLOGY & ENVIRONMENTAL MAGNETISM OF CLASTIC SEDIMENTS IN AN ACTIVE KARST GROUNDWATER CONDUIT: SCOTT HOLLOW CAVE, MONROE COUNTY, WEST VIRGINIA
Scott Hollow Cave is located in the Appalachian Plateaus physiographic province, Monroe County, West Virginia. It is developed in the Lower Greenbrier Group by recharge from several surrounding sinkholes in the valley walls east of Flat Top Mountain. In order to evaluate the hydrology and paleohydrology, we investigated the clastic sediments deposited within the cave using sedimentologic and magnetic methods. Nearly all of the gravel found in Scott Hollow Cave is composed of some type of chert, leading to the conclusion that the provenance of detrital sediment is in the Lower Greenbrier Group. One half of the samples were dominated by grave; the other half by clay. Sand-sized material was variable in composition between sample sites, usually dominated by quartz sand derived from the impurities of the Hillsdale Limestone and the Sinks Grove Limestone. Regardless of clast mineralogy, iron oxide stains and possible magnesium oxide stains are present on a large percentage of grains in all sub-samples. Both types of stains occur together, in some cases on the same grain, and also occur separate from each other. The iron oxide stains are a result of high concentrations of magnetic material in the sediment, found at each sampled site in the cave. The magnetic stains are composed of more than 75% magnetite/maghemite in most cases. The one site that contains dominantly hematite/goethite as the primary magnetic carrier is a site down stream from The Spigot, a fountain that has recently started flowing from a wall in the North-South Passage. Grain size of magnetic stain on sediment in tributary passages in general is larger (pseudo-single domain) than in the main passages, possibly because the tributary passages are exposed to higher levels of dissolved iron. Readings from the sediment in the Mystic River indicate that magnetic grain size is smaller, or single domain. This is a Chemical Remnant Magnetization (CRM) deposited by cave waters in a reducing environment. The CRM is deposited on the exposed portion of the grain with higher concentrations located in the main passage of the Mystic River. Clasts that are insulated by other sediment are not as susceptible to the deposition of a CRM. Nearly all of the clastic sediments are autochthonous, containing chert from the limestone of the Lower Greenbrier Group.