Continental rifting and crustal thinning took place between North America and Africa during the Triassic and Early Jurassic, and sea floor spreading began in the Early to Middle Jurassic. Very rapid and variable subsidence along the continental margin off the eastern United States during the Jurassic was controlled by transverse fracture zones, which segmented the margin into four major sedimentary basins - the Georges Bank Basin, the Baltimore Canyon Trough, the Carolina Trough, and the Blake Plateau Basin. Upper Triassic to Lower Jurassic evaporite deposits (including salt) have been drilled in Georges Bank Basin, and linear chains of salt (?) diapirs have been found along the East Coast Magnetic Anomaly in the Carolina and Baltimore Canyon Troughs. The maximum thicknesses of undeformed postrift sedimentary units in these basins are 7, 13, 11, and 12 km respectively. The thickness of deformed synrift sedimentary units (sediments deposited during active rifting) within faulted Triassic grabens beneath these basins probably exceeds 5 km in some places. Gravity models across the three northern basins indicate that 8 to 15 km of transitional crust underlie the basins.