FUSION OF LANDSAT-TM, ASTER AND SIR-C/X-SAR REMOTE SENSING DATA: APPLICATION FOR UNDERSTANDING STRUCTURAL CONTROLS ON THE CATARACT NILE, NORTHERN SUDAN

The Nile in northern Sudan and southern Egypt is called the Cataract Nile where it flows across the east-west trending Nubian Swell - a 500-km wide zone of uplifted Neoproterozoic crystalline basement and Cretaceous sediments in the eastern Sahara. The Cataract Nile is in a youthful stage, particularly in northern Sudan where it flows through the Batn el Hajar or "Belly of Stones" as shown by structurally controlled 90° turns, frequent bifurcation of channels through the basement, disruption by several cataracts, and near-absence of flood plains. The absence of vegetation and soil cover outside the Nile channel, coupled with little geologic knowledge of the region and the importance of the Nile's water for regional development make the Batn el Hajr an exciting place to test new remote sensing technologies. Landsat TM and SIR-C/X-SAR data fusion and optimum ASTER band ratio combinations constrained by 2 weeks of field work reveal two distinct structural trends of different ages that control the course of the Cataract Nile: (1) Neoproterozoic (~600 Ma) north-south trending ductile shear zones and folds such as the Kosha and Akasha zones. These shear zones control the course of the Nile in its north-flowing segments and have complex structural histories, involving early sinistral strike-slip displacements followed by normal-slip displacement. (2) Cretaceous and younger east-west and north-south trending faults. The distribution of the east-west faults defines the Nubians Swell, but the role of the younger north-south faults is important in controlling the north and south approaches of the Nile to the Nubian Swell. The relationship between Neoproterozoic and post-Cretaceous north-south faults is unclear. The east-west faults control the Cataract Nile where it makes sharp 90° east and west turns. Recent activity of the post-Cretaceous faults is probably responsible for historic seismicity; there were many earthquakes along one east-west fault, the Kalabsha fault in southern Egypt, in the early 1980's. We conclude that the Nubian Swell is a neotectonic feature with episodic but continuing uplift, and that this affects the course and continuity of the Nile across it.