Clay Mineral Distributions to Interpret Nile Cell Provenance and Dispersal: I. Lower River Nile to Delta Sector

Abstract

Clay minerals serve as petrological markers that can he used to measure and interpret ongoing changes in River Nile sedimentation, now largely affected by anthropogenic influences. Closure in 1964 of the High Dam at Aswan, in particular, has entrained marked changes of clay mineral assemblages along the Nile in Egypt. Size-sorting phenomena, for example, arc noted in the Nile delta; reduced grain size of sediment carried by altered Nile water flow patterns across the delta plain in part accounts for increased proportions of smectite in this sector and at the coast. However, most clay assemblage changes between southern Lake Nasser and Cairo are primarily the result of recently altered source terrains and dispersal patterns along this fluvial system rather than textural factors. The new delta forming in southern Lake Nasser contains typical River Nile (smectite-rich) clay mineral assemblages. In contrast, central and northern Lake Nasser contains higher proportions of kaolinite, derived through wave erosion of the lake margin and from wind transported material. The highest proportion of kaolinite in the Nile assemblage is recorded at Aswan. This kaolinite is derived from suspended sediment in Lake Nasser waters dispersed through the High Dam and from scouring of kaolinite-rich pre-Holocene deposits by the river below the dam. These kaolinite assemblages are deposited at least as far as Middle Egypt, about 350 km north of the dam. Relative percentages of kaolinite below Qena likely decrease as a result of progressive downriver input from smectite-rich pre-dam Nile channel and bank deposits; these eroded materials attenuate important amounts of kaolinite transported northward by the Nile. It is predicted that enhanced proportions of kaolinite will be recorded downriver at Cairo within fifty years and to the Mediterranean coast of the Nile delta by the end of the next century.