GEOLOGIC MAP OF THE PROVIDENCE FORGE 7.5-MINUTE QUADRANGLE, SOUTHEASTERN VIRGINIA: INSIGHTS INTO THE STRATIGRAPHY AND STRUCTURE OF THE VIRGINIA COASTAL PLAIN

The Providence Forge quadrangle is located on the Middle Atlantic Coastal Plain of southeastern Virginia. This map is part of a larger geologic mapping project for the Richmond Metropolitan Area. The formations exposed in the map area include highly dissected remnants of Tertiary marine plains and their near-shore equivalents as well as a succession of Pleistocene fluvial-estuarine terrace deposits adjacent to the Chickahominy and James rivers. The Eastover (Upper Miocene), Yorktown (Pliocene), and Sedley (Pliocene) Formations were deposited in marine, beach, or estuarine environments. The Bacons Castle (Upper Pliocene) Formation represents widespread fluvial to estuarine deposition during a marine transgression. Pleistocene alloformations, including the Charles City, Chuckatuck, Shirley, and Tabb, typically have a fining-upward sequence; these deposits were delineated largely by their scarp and terrace morphology.

Borehole data in the quadrangle indicate the presence of a buried high-angle fault. The Providence Forge Fault is a north-south oriented fault and appears to be syndepositional with the Yorktown Formation. Down-to-the-east displacement along the fault in this quadrangle, based on abrupt thickening of the Yorktown, exceeds 120 feet. The fault coincides with previously published gravity and magnetic anomalies, aligning with the western margin of a potential buried Mesozoic basin. Future work along strike will help constrain the type of faulting and amount of maximum displacement along the fault.