STRUCTURAL GEOLOGY OF THE SCOTTSVILLE MESOZOIC BASIN, VIRGINIA

The Scottsville Basin in central Virginia is one of the westernmost Mesozoic sedimentary basins formed by continental extension during Pangaean rifting in eastern North America. Structural, stratigraphic, and aeromagnetic data are used to understand the structural geometry of the Scottsville Basin. The basin is developed across the Paleozoic Mountain Run/Bowens Creek fault zones that form the boundary between the Western Piedmont and eastern Blue Ridge. This small basin is a 130 km² half-graben structure bounded in the west by a segmented normal fault. The eastern boundary, previously interpreted as a shallow displacement normal fault, is an unconformable contact with prerift Paleozoic metamorphic rock. The basin is bounded at its northern and southern extent by a distinct “fish mouth” geometry that is likely related to normal faults that cut into the basin. Strata within the basin is estimated to be 2 – 3 km thick and dips perpendicular to the western boundary fault, broadly increasing in dip from west to east. This trend, coupled with a west-to-east fining of sediments, implies synrift deposition. A suite of north-northwest striking Jurassic diabase dikes cross-cut the region and are subparallel to the dominant extensional fracture set that cuts basin sedimentary rocks. En-echelon dikes are consistent with a component of sinistral transtension during emplacement. The orientation of maximum extension appears to have rotated 30˚ to 40˚ in a clockwise direction between basin formation in the Triassic and dike emplacement in the early Jurassic. Although several Mesozoic basins of the central Atlantic margin were tectonically inverted, structural and stratigraphic features in the Scottsville Basin are inconsistent with contractional inversion. It is possible that the magnitude of early Jurassic compressional stress waned from east to west, affecting the Scottsville Basin less than basins further east.