Master of Science

M.S.

The Spruce Run Mountain area embraces about 45 square miles in the south-central portion of Giles County. It lies wholly within the Appalachian Valley and Ridge Province. The rocks exposed in the Spruce Run Mountain area range in age from Middle Cambrian to Lower Devonian. All the rocks are sedimentary rocks deposited in a marine environment and have an aggregate thickness of approximately 6,500 feet. An important disconformity separates rocks of Lower Ordovician age from those of Middle Ordovician age. The Saltville thrust, a southeast dipping thrust fault, crosses the Spruce Run Mountain area trending northeast. The thrust separates Middle Cambrian dolomite from Ordovician formations on the southeast flank of the Spruce Run Mountain syncline. The Spruce Run Mountain syncline is a northeast trending overturned syncline with a southeast dipping axial surface. The Clover Hollow anticline and the Bane anticline border the northwest flank of the Spruce Run Mountain syncline. The geomorphology and geologic history of the area are briefly discussed. / Master of Science

The Bouguer gravity field, deterrmined from 395 measurements in Giles County, Virginia exhibits a broad positive anomaly approximately 12 mgal in amplitude situated over the Bane Dome, and several smaller anomalies of a few milligals amplitude. For the most part they are produced by the distribution of relatively high density carbonate rocks and lower density clastic rocks within the dome. These anomalies can be explained by two contrasting interpretations of the structure of the Bane Dome. One interpretation, represented by the geologic cross sections of Woodward and Gray (Woodward, 1985) and Bartholomew (personal communications, 1987) suggests that the dome is cored by a relative abundance of high density carbonate rocks transported by overthrusting within the Narrows thrust sheet. Because the gravity anomalies can be entirely explained by sources confined to the Narrows thrust sheet, this interpolation precludes the existence of significant lateral density contrasts associated with deeper structure beneath the decollement zone in the Rome Formation. The contrasting interpretation represented by the cross section of Gresko (1985), suggests a smaller proportion of carbonate rocks in the core of the dome due to duplex structures in the lower density clastic rocks. This interpretation proposes high angle faults with associated lateral density contrasts in the deeper rocks underlying the decollement. Because sources within the Narrows thrust sheet are insufficient to completely account for the gravity anomalies, the density contrasts associated with deeper structure are required. The Bouguer gravity field can be separated into regional and residual parts. The regional field is caused by changes in crustal thickness known independently from the seismic measurements of James, Smith, and Steinhart (1968). The remaining residual field can be explained in terms of anomaly sources within the upper 10 km of the crust. / Master of Science

The Poplar Hill area lies in the southwest corner of Giles County, Virginia and contains marine sedimentary rocks that range in age from Middle Cambrian to Middle Bilurian. The formations trend northeast in narrow outcrop belts. The summit of Walker Mountain is the southeastern boundary of the area and the southern slopes of Brushy and Buckeye Mountains form the northwestern boundary. Nineteen different rock formations are recognized and are mapped, measured, and described in detail. The geologic structure of the area is described and includes a major thrust fault, a homocline, two synclines, and two anticlines, all illustrated on the geologic map (P1. 1). The geologic history of the area is briefly discussed and several possible localities for limestone and dolomite quarries are described. / Master of Science