A multi-technique provenance study of the Oligocene:recent Nile cone sediments and River Nile hinterland

Abstract

This thesis presents the first detailed multiproxy provenance study of the modern Nile catchment, together with Oligocene-Recent sediments of the offshore Nile cone, and demonstrates for the first time that the palaeodrainage of the Nile has remained relatively stable over the last 30 Ma. Detrital mineral and bulk-rock analyses of modern river, wadi and bedrock samples demonstrate the role of basement lithology, sedimentary recycling, and modern geomorphological features in controlling the composition of sediment reaching the Nile cone. The bulk provenance signature of the modern Nile is dominated by the input of basic detritus from the Cenozoic Ethiopian Large Igneous Province. Detrital zircon signatures are dominated by variations in bedrock lithology, and the availability of easily-eroded Phanerozoic cover sediments. These represent an important source of detritus to the river and are characterised by the presence of strongly negative eHf populations at c. 600 and 1000 Ma, and significant populations of pre-Neoproterozoic grains. Young zircon grains derived from Ethiopian Cenozoic volcanic rocks are also recognised in samples from the Blue Nile, Atbara and Nile trunk. The Sr, Nd and Hf signature of Oligocene Nile cone sediments can only be explained if there is significant input of mafic material being received from the hinterland. The Ethiopian Large Igneous Province represents the only possible source for this detritus, indicating that the Nile has been connected to the Ethiopian Highlands since this time. Zircons with U-Pb ages and hafnium isotope signatures compatible with the Ethiopian LIP have been supplied to the Nile cone since at least the Miocene (16 Ma). Such zircons were not observed in Oligocene 2 delta sediments, but Sr, Nd and Hf isotope data for Oligocene delta muds as old as 31 Ma require significant mafic input. The combined U-Pb and Hf-isotope zircon dataset for Nile catchment and cone sediments represents a significant archive that documents the evolution of the North African crust, in particular highlighting phases in the development of the Arabian Nubian Shield and amalgamation of Gondwana in late Neoproterozoic times.