The initiation and evolution of the River Nile

Laura Fielding,Yani Najman,Ian Millar,Peter Butterworth,Eduardo Garzanti,Giovanni Vezzoli,Dan Barfod,Ben Kneller

doi:10.1016/j.epsl.2018.02.031

Abstract

The Nile is generally regarded as the longest river in the world. Knowledge of the timing of the Nile's initiation as a major river is important to a number of research questions. For example, the timing of the river's establishment as a catchment of continental proportions can be used to document surface uplift of its Ethiopian upland drainage, with implications for constraining rift tectonics. Furthermore, the time of major freshwater input to the Mediterranean is considered to be an important factor in the development of sapropels. Yet the river's initiation as a major drainage is currently constrained no more precisely than Eocene to Pleistocene.Within the modern Nile catchment, voluminous Cenozoic Continental Flood Basalts (CFBs) are unique to the Ethiopian Highlands; thus first detection of their presence in the Nile delta record indicates establishment of the river's drainage at continental proportions at that time. We present the first detailed multiproxy provenance study of Oligocene–Recent Nile delta cone sediments. We demonstrate the presence of Ethiopian CFB detritus in the Nile delta from the start of our studied record (c. 31 Ma) by (1) documenting the presence of zircons with U–Pb ages unique, within the Nile catchment, to the Ethiopian CFBs and (2) using Sr–Nd data to construct a mixing model which indicates a contribution from the CFBs. We thereby show that the Nile river was established as a river of continental proportions by Oligocene times. We use petrography and heavy mineral data to show that previous petrographic provenance studies which proposed a Pleistocene age for first arrival of Ethiopian CFBs in the Nile delta did not take into account the strong diagenetic influence on the samples.We use a range of techniques to show that sediments were derived from Phanerozoic sedimentary rocks that blanket North Africa, Arabian–Nubian Shield basement terranes, and Ethiopian CFB's. We see no significant input from Archaean cratons supplied directly via the White Nile in any of our samples. Whilst there are subtle differences between our Nile delta samples from the Oligocene and Pliocene compared to those from the Miocene and Pleistocene, the overall stability of our signal throughout the delta record, and its similarity to the modern Nile signature, indicates no major change in the Nile's drainage from Oligocene to present day.

Highlights

The Nile is generally regarded as the longest river in the world, stretching >6800 km across the length of north-eastern Africa
All Nile delta cone sand samples from Oligocene to Pleistocene are dominated by a c. 600 Ma Pan-African peak in zircon age distributions (Fig. 2, Appendix 3)
Sparse Archaean and Palaeoproterozoic grains are present in each sample in different proportions, with Oligocene and Pliocene samples containing a higher proportion of grains >1500 Ma compared to the Miocene and Pleistocene samples

Summary

Introduction

The Nile is generally regarded as the longest river in the world, stretching >6800 km across the length of north-eastern Africa. Its evolution has been used to date the timing of the region’s surface uplift and constrain continental break-up tectonics Its runoff is proposed to have had a major influence on sapropel development in the Mediterranean Krom et al, 2002; Meijer and Tuenter, 2007) and its delta plays host to a major hydrocarbon producing region. Despite its clear importance, little is known of the river’s evolution through time. The present-day Nile has three main tributaries: the White Nile, the Blue Nile and the Atbara (Fig. 1). Sediment supplied to the Nile trunk in Egypt is dominated by contributions from the Blue Nile (50–61%) and Atbara (30–42%) (Padoan et al, 2011).

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Conclusion