Abstract

An analysis of sedimentologic data of Eocene, Oligocene, and Miocene rocks from northern Egypt has resulted in a synopsis of the depositional systems operative. A complex pattern of dominantly carbonate and minor associated terrigenous facies was deposited during Eocene time in narrow and elongate tectonic basins that were arms of the Tethys sea. The basins were separated by elongate structural ridges that resulted from Late Cretaceous tectonic activity. Infill of the ancestral topography during early and middle Eocene time, as reflected by the distribution of facies, ultimately provided the depositional base for seaward progradation of terrigenous sedimentation beginning in the late Eocene. Progradation during the Oligocene and Miocene was from southwest to northeast, over an open shelf of irregular bathymetry. This resulted in deposition of a thick terrigenous section in the western and central parts of the northern Western Desert. Longshore currents aided in the redistribution of sediments in an easterly direction toward the present Nile delta and resulted in an easterly shift of terrigenous depocenters from Oligocene through Miocene time. As the terrigenous clastic depocenters shifted eastward, carbonate environments reappeared in the west and onlapped abandoned parts of the fluvial-delta systems. By the early and middle Miocene, carbonate environments had become extensive and continued to shift eastward with shifting terrigenous clastic deposition. Upper Miocene strata have not been recognized in Egypt by some workers, but terrigenous clastic facies near and north of Lake Manzala may represent late Miocene deposits.

The embryonic Gulf of Suez, which developed as an arm of the Mediterranean during the Oligocene and early Miocene, was the site of deposition of arkosic sands, fanglomerates, and some evaporites, which originated within or from along the edge of the basin. However, fine-grained terrigenous sediments were transported by longshore currents to the Gulf of Suez from ancestral Nile deltas near the present Nile delta. Large volumes of evaporites, contemporaneous with the Nile delta, accumulated in the Gulf of Suez basin during the middle and late Miocene as a consequence of construction of a terrigenous clastic dam at the north end of the gulf.

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