Deep-penetration multichannel seismic reflection profiles off the southeastern United States reveal widespread seaward-dipping reflectors (SDRs). Similar features have been imaged and sampled on other North Atlantic rifted margins, where voluminous volcanism has accompanied continental breakup. Beneath the Carolina trough are two sets of SDRs, one along a basement hinge zone and another seaward of the East Coast magnetic anomaly axis. The hinge SDRs lie beneath, and apparently developed prior to, a flood basalt that erupted at 184 ± 3 Ma and is marked by a prominent reflector, J. Beneath the northern Blake Plateau basin, only the hinge SDRs are observed, but they developed after J. We suggest that the inferred north-to-south age difference of SDR emplacement implies a heretofore unrecognized time-transgressive breakup of northwest Africa and North America during the early Middle Jurassic.