The Young Nile

Abstract

Views on when the Nile System (henceforth the Nile) connected from its sources in the Ethiopian and East Africa plateaus to its sink in the eastern Mediterranean have been vastly different. These include the ones advocating for it to be as old as early Oligocene (~30 Ma) to those which consider it to be as young as Pleistocene (~2.5 Ma). This work presents geoscientific observations supporting the notion that the emergence of the Nile System as a major trans-continental drainage system with its present-day drainage pattern, as it was assembled from several drainage sub-systems, is as recent as Pleistocene in age. Geomorphological observations show that the two sources of the Nile are separated by the ~300 km wide Turkana Depression, a feature that pre-dates the development of the dynamic topography of the two sources of the Nile. This indicates that there was no connectivity between drainage systems of the two sources of the Nile other than at its downstream in Khartoum, Sudan. Geochronological studies of samples from Precambrian crystalline basement rocks and morpho-tectonic analyses using Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) indicate that the evolutionary paths of the dynamic topography of the two sources of the Nile were independent and have evolved through separate volcanic and tectonic uplift histories since the early Oligocene. These studies also indicate that the major tectonic uplift phase in the two sources of the Nile is much younger than early Oligocene, and that it has occurred during the Pliocene (~5.4 Ma). Geomorphological observations from eastern and northern Sudan (Gezira alluvium fan and the Great Bend of the Nile) and southern Egypt (the Tortonian (~11 Ma–~7 Ma) rivers of Egypt) do not support the existence of an integrated Nile drainage system since the early Oligocene. Rather, these observations show the youthful nature of the Nile, and that the integrated Nile was only established after the Messinian (~5.6 Ma). Records of the sedimentary rocks that fill the Messinian Eo-Nile canyon show that only the top part of the canyon is filled with sediment sourced from the Ethiopian plateau. Sediment budget considerations point to that building of the Oligocene to Pliocene sedimentary section of the submerged Nile delta cone requires sediment sources other than the Ethiopian plateau. Mineralogical, paleontological, and geochemical sediment provenance studies show that the contribution of sediment transported from the Ethiopian plateau by the Blue Nile and the Tekeze River to the submerged Nile delta cone might have only commenced at the beginning of the Pleistocene.