The Pleistocene sediments of the Palaeoatbara in eastern Sudan as an archive for the evolution of the Nile river system

Geological evidence and geodynamic modelling suggest that the Nile river system has been largely stable since its origins ~30 Ma. The Nile could have provided a long-term migration route for vertebrates including hominins between Eastern and Northern Africa. However, other geological data contradict such an old stabilisation of the course of the Nile. Fieldwork along the middle stretches of the Atbara River, the last tributary to the Nile before it crosses the Sahara, provides evidence for a complex fluvial history during the last 450 ka, with several periods of fluvial re-establishment that differ markedly in their fluvial style and hydrodynamics. While some rivers were dominated by gravelly and sandy braid bars, others had prominent fine-grained point bars, and some were perennial, while others showed high discharge variance, with significantly varying catchment areas. The fine-grained floodplain deposits contain different types of paleosols, but predominantly evidence seasonal and semi-arid conditions. The changes in river style, discharge dynamics and catchments can be attributed to Pleistocene climatic changes and to tectonic processes. The riverine landscapes of the Palaeoatbara were colonised by a diverse fauna including hominins which are represented by fossils and stone tool remains. The study of the sediments, fossils and archaeology along the middle Atbara, together with high-resolution age dating, provide new insights into the history of the Nile river system, and has implications for our understanding of early hominin migrations and the formation of modern ecosystems in Africa.