Clay mineral distributions to interpret Nile cell provenance and dispersal: III. Offshore margin between Nile delta and northern Israel

Abstract

Clay assemblages in Holocene sediment on southeast,Mediterranean margins are generally smectite-rich and, in the past, were derived primarily from direct River Nile input to the sea. Depositional patterns in the Nile littoral cell are now undergoing extensive change, largely as a response to closure of the High Dam at Aswan (1964), increased sediment entrapment by canal systems in the Nile delta, and construction of large coastal structures between the Nile delta and Israeli margins. Although information on land-to-sea dispersal by the River Nile and other fluvial and offshore sediment sources to the east remains limited, there appears to be evidence for increased sediment input from erosion of Sinai and Levant shelves and coasts east of the Nile delta. This, the third in a S-part study that focuses on regional clay mineral distributions, was initiated to provide baselines to measure evolving changes of sediment provenance and dispersal patterns on the shelves and upper Nile Cone between the Nile delta and northern Israel. The investigation shows that clay assemblages are not uniformly distributed in the SE Mediterranean, likely a result of several important sediment sources in addition to the Nile. Smectite-rich clay assemblages east of the Nile delta are presently derived from storm wave and coastal current erosion of the Nile delta, reworking of Quaternary deposits along the coast and on the seafloor east of the delta, and from some Israeli rivers between Tel Aviv and Atlit. Kaolinite and illite at offshore sites are supplied in part from erosion of coastal cliff sections, river input between Wadi El Arish in Sinai and the Lebanon-Israel border, and from wind-borne dust from African and Middle East deserts released seaward of the coast. The diverse source terrains that back coastal plains provide laterally variable clay assemblages along the southeastern Mediterranean coast. Presently evolving changes in the volume and mineralogy of sediment transported from the distal Nile region in Egypt, versus those from more proximal coastal sources on Sinai and Levant margins, are likely to be subtle. Post-Aswan High Dam changes of fine-sediment load, composition and dispersal in the eastern Mediterranean should now be determined from water samples and sediment traps set above the seafloor between the coast and upper Nile Cone. Improved quality of information can be derived from clay mineral assemblages in suspended sediment samples in conjunction with geochemical tracers. Moreover, detailed morphologic surveys will provide essential information on altered sediment transport patterns as related to sectors undergoing accelerated coastal erosion.