Morphology and dynamic sedimentology of the eastern Nile delta shelf

Some 13,000 km of bathymetry and overlapping side-scan sonar data were collected over a 4450-km 2 area of the eastern Nile River shelf. These data, coupled with more detailed surveys of selected areas, including bottom sampling and current measurements, contribute to the understanding of shelf morphology, lithofacies relationships, and sediment transport processes. Four morphologic zones were defined: 1. Zone 1. Smooth-bottomed, flocculated clays and silty clays extending from the shoreline 40 km seaward to the 25-m contour. 2. Zone 2. A sand belt (5–20 km wide) extending eastward from the Damietta mouth and curving to ward the coast at the boundary of the study area. Dominant bottom features were migratory bedforms of various dimensions superimposed on linear sand ridges. 3. Zone 3. Smooth clay to silty-clay bottom topography punctuated with distinct algal mounds. The mounds (up to 10 m relief) are composed of living coralline algae, which contribute coarse debris to the surrounding sediments. 4. Zone 4. Mud diapirs and shelf-edge slumps characterize this distal part of the shelf and the upper slope. Sand on the inner shelf is actively migrating and probably does not represent a relict deposit. The Damietta distributary causes a large-scale perturbation in the mean easterly drift along the Egyptian coast. Unusually strong currents, capable of transporting and reworking large volumes of sand, are associated with an eddy trapped behind this feature. The directionality of these currents and the curvature of the eddy axis correspond well to the distribution pattern of sand on the inner shelf.