LAUSR

Abstract Soils of two Nile Valleys (White Nile and Blue Nile) and the neighboring Nubian Sandstone plateaus (Qoz) in Central Sudan were investigated. The White and Blue Niles rise from different areas and are different in their water flow velocity, flood amplitude and flooding time. The results of this study show that sediments of both valleys consist of an allochthonous and a parautochthonous component. The allochthonous part of the White Nile and Blue Nile show different texture and mineralogical composition. It consists of smectite-rich clayey material in the White Nile whereas the Blue Nile sediment contains carbonates, is rich on smectite and is silty-clay. The parauthochthone part in both Nile Valleys is sandy and rich on kaolinite. Its origin is predominantly eolian and fluvio-eolian from Nubian Sandstone. Its amount in the first terraces (youngest terraces) is highest and lowest in the second Terraces. This point out, that the youngest terraces as well as the third terrace on the Blue Nile were developed in a time when the surrounding area was covered with a loose vegetation cover (ergo-dry climate) and the second terraces were developed in a period with a dense vegetation cover (ergo wet climate).