Origin, Evolution, and Distribution of Shoreface Sand Ridges, Atlantic Inner Shelf, U.S.A.
A computer mapping system was employed to document the location of 259 shoreface-attached and detached sand ridges in water < 20 m deep and the temporal and spatial distribution of 309 historical and active tidal inlets along the U.S. Atlantic Coast (Montauk Point, New York, to Miami Beach, Florida). This database was compiled through the analysis of over 600 historical maps, 50 bathymetric charts, and other published data. A genetic relationship between the location of certain historical and active tidal inlets and shoreface-attached sand ridges is documented. It is inferred that ebb-tidal deltas provided the initial sand source for the development of many shoreface-attached sand ridges. Although shoreface-attached sand ridges appear to have several different modes of formation, a two- step process for the development of most shoreface-attached and detached sand ridges along U.S. Atlantic barrier island and cape coastlines is proposed: (1) sand is deposited as ebb-tidal deltas or river deltas along the lower shoreface and/or inner continental shelf prior to or during transgression, followed by (2) further transgression, which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes. The best-developed shoreface sand ridge fields along the U.S. Atlantic shelf lie adjacent to shorelines characterized by all of the following: (1) transgression, (2) mixed energy, wave-dominated barrier islands, and (3) laterally migrating tidal inlet systems. Tidal inlet systems are natural sediment sinks that capture sand carried by longshore sedimen