Large sand accumulation preserved on the continental shelf during and after a marine transgression. The massifs represent former estuary-mouth sand bars (inlet-associated shoals) or former zones of longshore-drift convergence (cape-associated shoals). In the Middle Atlantic Bight of the east coast of the USA the massifs are up to 70 km long by 20 km wide and can be found offshore from the present Hudson, Delaware, and Chesapeake estuaries, and longshore-drift convergence zones such as Cape Hatteras.