Continuation of the Appalachian Piedmont under the New Jersey coastal plain investigated using geophysical and drilling data

Analysis of gravity and magnetic data, seismic reflection profiles, and drill hole data reveals the New Jersey Coastal Plain basement structure, lithology, and age. These factors yield an interpretation of basement terranes and geologic history which is critical to the understanding of the exposed Piedmont in the Mid-Atlantic region. Laurentian crust of Grenville age is interpreted to subcrop under the New Jersey Coastal Plain as far southeast as Cape May. This requires an interpretation of the uplift of large-scale nappes in the Alleghanian orogeny which uplifted and transported the allochthonous supracrustal Carolina (Avalon) terrane rocks and the Taconic suture rocks. The Taconic suture rocks are preserved as rootless, infolded and fault-bounded synforms under the Piedmont and Salisbury gravity and magnetic anomalies. The greatest uplift of the Appalachian core was in the area of the Mid-Atlantic Coastal Plain; unroofing of the strongly uplifted autochthonous Grenville basement by erosion removed much of the Carolina (Avalon) terrane rocks. Excessive uplift in the Mid-Atlantic part of the Appalachians may be related to uplift of an Alleghanian dextral transpressional shear-duplex between the Virginia and New York promontories.; The interpreted basement structural framework for seismic reflection profile TXC-10 across southern Delaware and eastern Maryland reduces the non-uniqueness of the interpreted structural framework for the outer Coastal Plain (the Chesapeake terrane). Beneath a major detachment thrust identified along profile TXC-10 a stratified sequence of rocks is interpreted to be remnants of the parautochthonous Lower Paleozoic Laurentian margin drift-stage sedimentary rocks. The stratified rocks within the basement of the Chesapeake terrane are interpreted to be sedimentary layering. This requires approximately 200 km of overthrusting in the Taconic orogeny and further transpression in the Alleghanian orogeny.; A Mesozoic rift basin, the “Sandy Hook Basin”, and associated east bounding fault is identified, based upon gravity modeling, in the vicinity of Sandy Hook, New Jersey. The thickness of the rift-basin sedimentary rocks contained within the “Sandy Hook Basin” is approximately 4.7 km, with the basin extending offshore to the east of the New Jersey coast. Gravity modeling indicates a deep rift basin and the magnetic data indicates a shallow magnetic basement caused by magnetic diabase sills and/or basalt flows contained within the rift-basin sedimentary rocks. The igneous sills and/or flows might be the eastward continuation of the Watchung and Palisades bodies.