Nubia Formation of Central Eastern Desert, Egypt--Major Subdivisions and Depositional Setting

Abstract

The Nubia Formation of the central Eastern Desert is a record of predominantly nonmarine sedimentation in response to local and regional structural movements during the Late Cretaceous. The Nubia section of the Eastern Desert can be divided into five major lithologic units, in ascending order: (1) basal unit of fluvial trough-cross-bedded conglomeratic sandstone (absent near Safaga); (2) coastal and marginal-marine gray and red shale and thin sandstone (restricted to Aswan area); (3) fluvial tabular-cross-bedded sandstone; (4) coastal fluvial-plain and delta-plain ripple-laminated siltstone and lenticular fine-grained sandstone; and (5) coastal and marginal-marine clay-shale and siltstone. Facies relations and cross-bed directions in the lower Nubia suggest that, during the middle Cretaceous (Cenomanian?), fluvial sediments were transported westward from highlands in the area of the present Red Sea and southward from uplifted areas north of Aswan and near Safaga. The Cenomanian transgression from the northwest reached the vicinity of Aswan, where marginal-marine sediments interfingered with fluvial deposits from the east. Later, uplift in the area south of the Eastern Desert and subsidence of the northern margin of the African shield caused the streams to flow northward, spreading a blanket of sandy fluvial sediment over the entire area now between the Red Sea and the Nile Valley. As the supply of sediment from the south continued, progressively finer terrigenous materi l reached the region that is now the Eastern Desert. During the Campanian, fine-grained coastal fluvial-plain and delta-plain sediment interfingered to the north with coastal muds. Continued subsidence of the northern flank of the Egyptian shield and the Late Cretaceous eustatic rise in sea level brought deposition of coastal mud progressively farther south.