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Rift Shoulder Source to Prodelta Sink: The Cenozoic Development of the Nile Drainage System

Macgregor, Duncan 1
(1)Surestream Petroleum, Reading, United Kingdom.

The reconstruction of source to sink relationships for the Oligocene to Recent Nile system relies on integrating evidence and data on past sedimentation rates and volumes, seismic facies, quantification of denudation (AFTA), topographic features and past climatic change. Such a compilation is presented here within GIS that enables the past history of the river to be reconstructed in a manner that honours estimations for volumes eroded and deposited.

The Present Day Nile river system demonstrates strong climatic and topographic controls, with 80% of current sediment originating from the seasonally wet Ethiopian rift shoulders. This pattern is however only indicative of the current unusual dry conditions affecting the hinterland and during frequent wetter interglacial phases, more sediment was derived from the Red Sea rift shoulders and to a lesser extent from the Nubian and Darfur swells. This ‘wet phase’ sediment was more sand prone with more granitic material being eroded than during dry periods. Sands thus preferentially entered the Nile shelf during highstands and were later reworked as deep water turbidites during lowstands.

The course of the drainage system has changed, particularly within Egypt, where a more westerly course is apparent in pre-Messinian times. However, evidence from sedimentation rates and volumes in the offshore Nile, together with denudation studies, suggest the origin and outlet of the river have remained in much the same locations, at least for the Blue Nile. The sediment volumes measured in the Nile Cone are inconsistent with previously published histories of the river that do not include contributions from Sudanese and Ethiopian rift shoulders until relatively recent times.

Sedimentation rate changes and seismic facies indicators also suggest the prodelta sediment thick may have periodically switched between the Herodotus and Levantine Basins with distal turbidite reservoirs likely to extent well beyond Egyptian waters.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.