GEOLOGIC MAP AND COMPOSITE AEROMAGNETIC/GRAVITY ANOMALY MAP OF PRE-CRETACEOUS ROCKS BENEATH THE ATLANTIC COASTAL PLAIN, VA TO SOUTHERN NJ

The geologic map shows the interpreted distribution of buried crystalline rocks, faults, and early Mesozoic rift basins beneath the Atlantic Coastal Plain (ACP) from VA to southern NJ. Data sources include borehole records, borehole basement rock samples (many new), and geophysical (seismic, magnetic, gravity) surveys. Buried extensions of Piedmont terranes and early Mesozoic rift basins are identified by available borehole data and geophysical character, and are useful for constructing the inner ACP basement map. The inner ACP is flanked successively eastward by rocks of the concave-east Salisbury gravity anomaly and Sussex mafic complex, Neoproterozoic and Paleozoic rocks of the Chesapeake zone (mostly greenschist facies), and epidote-amphibolite-facies to amphibolite-facies rocks of the Hatteras (Neoproterozoic) and Cape May (Mesoproterozoic?) zones. Circular to elliptical gravity lows commonly coincide with Paleozoic granites. The bedrock surface slopes eastward across NJ-DE-MD and northeastward in VA beneath the inner ACP, and much steeper eastward beneath the outer ACP.

Boreholes near the Fall Line reveal buried extensions of Piedmont geologic units such as the Baltimore Complex and Petersburg Granite, whereas borehole samples from basement near the Atlantic coast provide insights into deeply buried rock units that have no surface exposures. The borehole data and sample descriptions provide a lithologic basis for interpreting the geology and identifying the sources of aeromagnetic and gravity anomalies. The aeromagnetic/gravity map and derivative maps provide structural grain and regional context to image the geographic extent and help define contacts between basement geologic source units. The integrated results on the map contribute insights into kinematics of buried faults, basement-rooted ACP faults, and the influence of Paleozoic fault systems on Mesozoic rift structures. The map also provides a foundation for further investigations of upper crustal structure across terranes, sutures, failed rift basins, the Chesapeake Bay impact structure, Cenozoic faulting, and intraplate seismicity. The map and geodatabase, awaiting edit and approval, can serve as a prototype for maps of pre-Cretaceous basement beneath the entire Atlantic and Gulf Coastal Plains.