Clay plains and geomorphic history of the central Sudan A review

Abstract

The paper presents an analysis of the Sudan clay plain. Total plain area is 500,000 sq. km., but the paper focuses on an area of 90,000 sq. km. In the east-central Sudan an old erosion surface between 600m× 730m above sea level is probably Miocene in age. The main plainlands lie 200 – 300 m below this and date from entertiary times. Evidence of an “African” surface may occur on skeletal volcanoes near Gedaref. Downwarping along NNW-SSE lines formed distinctive basins including the Blue Nile basin. Sediments accumulated in the basins and a sequence of arkose, paludal sandy clay, alluvial sand, silt and clay in the Blue Nile basin is capped by modern silt and clay which has weathered to form a clay soil. The clays on the plain vary in age from upper Pliocene to modern though the weathering seems in balance with a somewhat wetter climate than at present. The clays dominantly on almost level plains are alluvial or lacustrine. The remainder is residual or colluvial weathered material on flat but extremely gently sloping interfluves on higher ground. The clay of the aggradational plains in the Blue Nile basin has been reworked continuously by the rivers and is therefore, much younger than the clay on the degradational plains which is upper Pliocene to Middle Phistocene in age. The present Blue Nile flows in a wide alluvial valley with the channel incised up to 24 m below the general plain.