To the genesis of the purple and white sandstones
in the western part of the Gilf Kebir (Egypt/Libya)

Norbert Brügge, Germany

Revised: 13.01.2015

In the western part of the Gilf Kebir and its foothills at the Libyan side is observe widespread conspicuous red discolored areas on the satellite image. This area, beyond the Egyptian border, is an intensively influenced by hydro-volcanic activities during the Oligocene age (Gilf Kebir crater field, Regenfeld pipes, Libyan desert glass etc.). A striking feature is the "Red Spot". Here are the strata complete impregnated by iron-containing hot solutions. Locally it should be noted that these surfaces are covered with hardened ferruginous sandstone plates or detritus on alluvial plains.

In the geological profiles of the hills and mountains in this region is also to observe a several changes of these red layers with white sandstones. Such a change is not necessarily coupled to the bedding planes in the sediments.White sandstones also occur as clusters which break the stratification.

This is a clear indication of the predicted hydrovolcanic processes that have led to a bleaching of the sandstones. The possible chemical and mechanical processes are not explored.

The red and white sandstones occur in principle everywhere, regardless of its stratigraphic position, but regionally dependent. It is striking that mostly the lower parts of the plateau are affected by the phenomenon of bleaching. Except the Abu Ras passage east of Jabal Asa, and also near Wadi Sura, in the lower parts of the Ordovician/Silurian sandstones, are changed white sandstone to observe. Often they are covered with very ferruginous sandstone.
Also upper parts of the plateau are affected by the phenomenon of bleaching (Wadi Abdel Malik). In principle, are the whole Gilf Kebir (inclusive the southern part) and also the Abu Ballas scarp-contour in the GKCF more or less affected by this phenomenon. Locally are to seen again and again white parts in the sandstones. To this belongs also the pushed zone of white erratic blocks in the northern part of the Gilf Kebir (the so-called glaciogenic series).

Note: Another speciality are red clayey layers within Carboniferous strata in the Wadi Talh (western plateau along the Wadi Abdel Malik) and in the western foreland at the Libyan side, which are also partially exposed. These deposits are not formed secondarily. They document marine floodings in the Carboniferous period.

Photo documentation

Abu Ras passage
Photos: Ursula Steiner, Switzerland

 Inside Abu Ras passage

 Striking hydro-volcanic spot

 Northern Abu Ras exit

Western Gilf Kebir (Wadi Talh area)
Photos: Ursula Steiner, Switzerland

Western foreland of Gilf Kebir (Libyan side)

Wadi Sura area

Southern Gilf Kebir & Gilf Kebir Crater Field (GKCF)

Cliff south of Aqaba

Cliff north of Aqaba

 GKCF (Abu Ballas area)