The Sandstone Plateaus, SW Western Desert

Abstract

The sandstone plateaus of Gilf Kebir and Abu Ras in SW Egypt have been known as the Gilf Kebir. Recently, this name became restricted to the eastern plateau, while the western is named Abu Ras. They are composed of horizontal beds of Palaeozoic and Mesozoic sandstones, and are covered by a resistant caprock. Volcanic intrusions of different sizes are scattered on the surface of western central part of the Gilf Kebir Plateau, forming black to dark gray sub-circular constructs on its surface, and on floors and wadi walls. Faults of different sizes and directions cut across the Gilf Kebir and Abu Ras Plateaus, and the southern escarpment of Abu Ras and El-Aqaba. Current landforms are due to the interaction of fluvial, mass wasting, and aeolian processes. Therefore, dominant fluvial forms are wadis dissecting both plateaus, and playas restricted to the upper reaches of some wadis in the Gilf plateau, and Dunes are found in Gilf plateau only, covering the N escarpments and the Depression separating the two plateaus, and the falling and climbing dunes in several E-W wadis dissecting the plateau. Geologically and geomorphologically, it can be said that these are the oldest sedimentary plateaus in Egypt and have been exposed to fluvial processes at least from Late Eocene. When climatic conditions became relatively arid at the beginning of the Pleistocene, sand from the Great Sand Sea encroached on the northern slopes of the Gilf and choking some wadis. Only minor change occurred by fluvial action, such as the Holocene playas at the heads of some wadis.