GEOPHYSICAL ANALYSIS OF THE SCOTTSVILLE MESOZOIC BASIN: IMPLICATIONS FOR DEPOSITIONAL AGE AND BASIN GEOMETRY

The Scottsville basin forms one of the westernmost Mesozoic rift basins in Virginia. The basin lies ~25 km SW of Charlottesville, VA astride the transition zone between the Eastern Blue Ridge and Western Piedmont geologic provinces. The ~110 km² basin is a half-graben bounded by a normal fault to the northwest, and unconformably overlies phyllitic rocks of the Piedmont on its southeast margin. Sedimentary rocks in the basin range from boulder conglomerates to siltstones and are sourced primarily from the Proterozoic units of the Blue Ridge. NNW striking diabase dikes associated with the Central Atlantic Magmatic Pulse (CAMP) crosscut the sedimentary strata. The purpose of this research was to conduct paleomagnetic analysis on rocks in the basin, as well as examine gravity and aeromagnetic data of the region to constrain the depositional age, estimate the 3D geometry of the basin, and to better understand the geologic history of the Scottsville basin and the Atlantic rift margin.

Cores for paleomagnetic analysis were collected from siltstones, diabase, and conglomerates at 16 locations across the Scottsville basin. Although previous paleomagnetic analyses of the Scottsville basin were inconclusive, new measurements yielded consistent results with low error (I: ~350°, D: ~45° and α₉₅ = 5.8-12.6) from siltstones across the extent of the basin, which suggests similar ages of magnetization for those rocks. Low coercivity components of the siltstone magnetic signatures were much stronger than the high coercivity components, suggesting a primary depositional signal as opposed to a remagnetization by chemical weathering. Furthermore, conglomerate test results (random at 95% confidence interval) indicate a depositional magnetic signature as well. Analysis of the diabase yielded mixed results, but additional measurements will be collected. Preliminary data suggest that both the diabase dikes and the siltstones record Jurassic age magnetizations, suggesting that the Scottsville basin may have been formed as late as the Jurassic. Analysis of gravity and magnetic data is ongoing, and future work will include the calculation of the analytic signal of the aeromagnetic data, and the construction of a detailed and retrodeformable cross-section of the Scottsville basin.