Abstract
The general tectonic framework of Egypt can be described in simple terms as comprising three units that have controlled the sedimentological history and the structural make up of the country; These are the Arabian-Nubian massif, the stable shelf and the unstable shelf. The stable shelf covers a large part of Egypt surrounding the Arabo-Nubian massif. It reflects relative tectonic stability towards the south. Much of northern Egypt belongs to the unstable shelf that suffered intense rock deformations. Four fault systems oriented at : 55°, 70°, 80° and 150° represent major transcontinental and regional fracture zones. These originated during different Proterozoic episodes of crustal deformation. Phanerozoic intraplate deformation and related processes of erosion and sedimentation were generally controlled by structural trends which were frequently reactivated along existing fault systems. During the Paleozoic, the 150° fault trend dominated the paleogeographic situation. Magmatic and tectonic activity in Egypt at the end of the Paleozoic continued into the Triassic. Over a kilometer of Nubia Sandstone strata were deposited in southern Egypt from Jurassic to Late Cretaceous or Early Cenozoic. Tectonic and magmatic activity increased again towards the end of the Cretaceous Period. The Cretaceous tectonics were so severe that in many parts of Egypt they account for the present day geomorphology. ENE to E-W master wrench faults control the Cretaceous-related structures all over the country. In the central and southern parts of Egypt the sedimentary units of the Jurassic-Nubian interval are capped by younger formations. The base of the Nubia Sandstone forms swell-like uplifts separated by troughs. Restricted tectonic basins are now characterized by a thick accumulation of Mesozoic— Cenozoic sediments. Old fractures inherited from the basement were used after vertical propagation as shear zones along which the whole sedimentary cover would deform. Geological observations made in southern Egypt support the tectonic origin of the Nile Valley. The most complicated area in the Egyptian course of the Nile is the Qena bend, believed to be the result of rejuvenation of the NE fault system superimposed on NW and N-S trends.
