THE YOUNG NILE

Views on when the Nile System connected from its sources in the Ethiopian and East Africa plateaus to its sink in the Mediterranean has been vastly different from the ones advocating for it to be as old as early Oligocene (~30 Ma) to it being as young as Pleistocene (~2.5 Ma). This work presents geoscientific observations indicative of the young age of the timing of emergence of the Nile System as a major trans-continental drainage system with its present-day drainage pattern as it assembled from several drainage sub-systems. Geomorphological observations show that the two sources of the Nile System are separated by the ~500 wide Turkana Depression, a feature that pre-dates the development of the dynamic topography of the two sources of the Nile System. This indicates that there was no connectivity between drainage systems of the two sources of the Nile System other than in its downstream in 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 path of the dynamic topography of the two sources of the Nile was independent and has evolved through separate volcanic and tectonic uplift history since ~30 Ma. These studies also indicate that the major tectonic uplifting event in the two sources of the Nile System is much younger than ~30 Ma occurring during the Pliocene ~5.4 Ma. Geomorphological observations from eastern and northern Sudan (Gazira Alluvial Fan and the Great Bend of the Nile) and southern Egypt (Tortonian (11 Ma – 7 Ma) rivers of Egypt) do not support the existence of an integrated Nile drainage system since ~30. Rather, these observations suggest a youthful nature of the drainage system that was established after the Messinian (~5.6 Ma). Records of the sedimentary rocks that fill the Messinian Eonile Canyon show that only the top part of it 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 Nile delta cones requires sediment sources other than the Ethiopian plateau. Contribution of sediment transported from the Ethiopian plateau by the Blue Nile and the Tekeze river to the Nile delta cones might have commenced only at the Pleistocene ~2.5 Ma.