Nile Delta: Nature and evolution of continental shelf sediments ☆

Abstract The continental shelf off the Nile Delta is covered by terrigenous sands on the shore face, by terrigenous muds on the middle shelf, and by algal carbonates on the outer shelf. As the Holocene transgression began, Nile mud was discharged directly on to the Nile Submarine Fan. About 10,000 years ago, the drainage system was drowned by the transgression. From then on fine sediments were trapped in depressions in the landward-retreating coastal system, deposition of terrigenous mud more or less ceased on the fan, and the waters of the outer shelf became clear enough for the growth of coralline algae. Over the past 5000 years that sealevel has been stable, there have been three phases of sedimentation. During the early, or classical phase, several small distributaries discharged sediment through an arcuate, wave-dominated delta front; westerly currents forced plumes of suspended sediment east along the coast, causing the formation of a middle shelf mud belt, and keeping the outer shelf virtually free of fines. In phase 2, over the past 500 years, discharge became confined to two distributaries, leading to coastal progradation at Rosetta and Damietta. As a result most sediment away from the Rosetta and Damietta Cones is probably relict or palimpsest. In phase 3, after construction of the Aswan High Dam in 1964, the river was dammed near its mouths and wave erosion began to cause serious coastal retreat at Rosetta and Damietta. The shoreline probably will continue to retreat until the delta front becomes once more smooth and arcuate.