Nile Sediment Budget and Partitioning from the Ethiopian Plateau Source to the Nile Deep-Sea Fan Sink since Messinian Salinity Crisis 6 Ma Ago
Sediment budget from source to sink is a crucial component in successful modeling of clastic depositional systems. However, estimate and timing of eroded sediment volume from a source region is often associated with large uncertainties. This study combats this challenge in a GIS-based quantitative analysis using DEM and isotopic age data.
3D mapping of the Blue Nile incision on the Ethiopian Plateau allowed us to calculate that ~100,000 km3 of rocks were removed from the plateau since ~30 Ma. Using isotopic ages of various volcanic beds, we partitioned sediment production, associated with three phases of incision, in time: ~30,000 km3 of sediments were produced between 30 Ma to 10 Ma, ~15,000 km3 between 10 Ma to 6 Ma, and ~50,000 km3 during the last 6 Ma. As the Ethiopian Plateau supplies ~96% of the Nile sediment load through the Blue Nile and Tekeze drainage systems, the calculated sediment volumes would significantly control the sediment partitioning down the Nile system up to the Nile deep-sea fan. Although the existence of a north-flowing, continental-scale Nile system in the geologic past has been controversial, many workers agree the appearance of such a Nile system since at least the Messinian salinity crisis. Hence, the past 6 Ma sediment-yield from the Ethiopian Plateau is more relevant for the evolution of the Nile delta and Nile deep-sea fan depositional systems.
Based on published data of depositional area and sediment-thickness, we estimated sediment volumes, distributed by the Nile system, for various depositional systems. Over the past 6 Ma and from south to north, ~5,000 km3, ~150,000 km3, and ~200,000 km3 of sediments were deposited in alluvial fans of Sudan, Nile Delta, and in the Nile deep-sea fan, respectively. ~50,000 km3 of sediment-production from the Ethiopian Plateau source over the past 6 Ma is seven times lower than the total of ~355,000 km3 of sediments deposited during the same time in various sinks. As far as the conventional knowledge goes, the additional sediments coming from the White Nile and the excavation of the Eonile during Mediterranean sea-level fall linked to Messinian salinity crisis are unlikely to fill this sediment budget-deficit. This mismatch of source to sink sediment budget remains a challenge for future workers.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009