Overall view

In 1926, when Prince Kemal el Din Hussein makes the expedition to Jebel Uweinat, he saw a "great plateau", and called it "Gilf Kebir" (Great Barrier). What he could not know that the Gilf Kebir is a vast plateau of Paleozoic sandstones with a length of about 260 km in the NW-SE direction. The more than 500 m thick sandstone sequence lies as that of Jebel Uweinat directly on outcropping Precambrian basement. The entire sequence is part of a between 2000 and 3000 meters uplifted structure on the eastern edge of the Kufra basin, which extends up to Libya and southern Sudan extends (Howar-Uweinat uplift).

Geomorphologically, the Gilf Kebir can be divided into two parts. An offshoot of the Great Sand Sea, Wadi Assib (with the passage Aqaba) separates visually a northwestern part (Abdel-Malik plateau) from a southeastern part (Kemal-el-Din plateau).

The Abdel-Malik plateau extends over 140 kilometers from north to south and about 40 kilometers from west to east. It is cutted by two gigantic wadis, the approximately 100 km long Wadi Abdel Malik and the Wadi Hamra.
On the southwestern edge of the plateau continues to Libya (Jabal Um Ras, Jabal Rukn and Jabal Asba). The morphological separation is effected by the Um-Ras passage. The mountains Um-Ras and Abu-Ras the passage overtop on both sides.

The Kemal-ed-Din plateau extends over 120 km in a north-south direction and 80 km in the east-west direction. Many wadis cuts its east and south sides. It are from north to south the named Wadi Mashi, Dayiq Wadi, Wadi Maftuh, Wadi Bakht, Gazayir Wadi, Wadi Wassa, Wadi Akhdar, Wadi Firaq.

Historical Photo of Wadi Abdel-Malik ( L. Almasy in his Aeroplane in 1933)

The geographical exploration of the Gilf Kebir began in the 30s of the last century. This were the Hungarian Laszlo Almasy and the four Englishman Sir Robert Clayton East, Penderel, Patrick Clayton and Ralph Bangnold.

Despite some meritorious German-French attempts in the 70s and 80s of the last century to decrypt the previously unknown geological structure of the Gilf Kebir (Klitzsch, Lejal-Nicol, Wycisk), there is still no conclusive answers. So could be the official geological map of the Gilf Kebir false. By new finds of plants imprints of the Carboniferous period at the edges of the Gilf Kebir are the postulated Cretaceous sediments within both plateaus put into question.

The Abdel-Malik Plateau is complicated structured and geologically difficult to decode. A special feature are marine Carboniferous deposits with plants imprints, which are widely spread in the so-called Wadi Talh, and probably above a heavily eroded relief of older Paleozoic sandstones lie.

The Kemal-el-Din Plateau has a simple structure, but has a subvolcanic overprint that also spread is in the surrounding ranges (eg Clayton Craters and Gilf Kebir Crater Field).

                   

In the Abdel-Malik plateau, of about 100 km in length, an eponymous Wadi separates two different structural-geological units. The western part, the so-called Wadi Talh area, is dominated by shallow marine Carboniferous deposits (Wadi Malik formation in sense KLITZSCH), which were deposited on a relief of heavily eroded older sediments. The eroded layers include the time of Devon and Silurian. In contrast, the eastern and southern part is by thick, sometimes significantly cross-stratified sandstones dominated, which lie in an unconformity on in varying degrees eroded Ordovician sandstones. This unit includes deposits of Silurian and Devonian.

Separated by the Abu Ras passage is this about structural-geological unit to the SW in the Libyan Jabal Um Ras and Jabal Rukn away. The subsequent Jabal Asba has in its structural-geological development of a special relationship between the Kufra Basin and the Howar-Uweinat Uplift. Striking is a much deeper level of the basement. Here are to find also clearly open marine Silurian deposits. In the Gilf Kebir are this Silurian strata by a fluviale to shallow marine facies replaced.

For a temporal allocation of the sediments in the Gilf Kebir, however, are only the Carboniferous strata secured. Plants prints and brachiopods are available. Without fossils it is difficult to distinguish Ordovician, Silurian and Devonian strata. The presence of trace fossils (Scolithos, Cruziana, Arthrophycus or Harlania) in some sequences is not enough. Characteristic, however, is a Paleosol-layer with rich Scolithos in all structures (Gilf Kebir, Jebel Uweinat and Jabal Asba). This horizon occur in the upper unit of a series of particularly compact sandstones above the basement, and should be used as a marker horizon between the Ordovician and Silurian. It follow Silurian strata with Arthrophycus and Harlania. This sequence corresponds to the so-called Um-Ras formation (KLITZSCH), but without the lower part with the Scolithos-layer. It corresponds to the Ordovician Karkur Talh formation (KLITZSCH) in Jebel Uweinat.

In the official geological map early Cretaceous sediments are widespread in the Gilf Kebir plateau. There are, however, no concrete evidence. This assumption is probably based on an determination of a few poorly preserved plant imprints, not accurately localized by Anni Lejal-Nicol, in the Aqaba passage and in the northern foothills of the plateau were found.. The associated sedimentary sequence is called "Gilf Kebir Formation".

Structural-geological models
 

Plateau escarpment
 

Northern plateau (Wadi Talh area) and foothills with Carboniferous strata
 

Plateau main wadis
 

"Red Spot"
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 hydrothermal processes that have led to a bleaching of the sandstones. The possible chemical and mechanical processes are not explored.

Red layers
White layers

Along the southwestern ridge of the Gilf Kebir Plateau can be studied Paleozoic strata at many places. The Ordovician/Silurian Um-Ras Formation (in sense KLITSCH) reaches a thickness of 100 m between the Um Ras passage area and the southwestern slope of the Abdel-Malik plateau. It consists mainly of fluvial and deltaic sandstone, intercalated with interbeds of shallow marine siltstone, some shale and burrowed sandstone. These beds contain Harlania harlani DESIO, Cruziana cf. acacensis SEILACHER, Scolithos sp. and other trace fossils at several levels. At the type locality, the Um-Ras Formation directly overlies Precambrian basement. South of the Um Ras passage, the trilobite tracks (Cruziana) of Ordovician age occur only some meters above basement. The Um-Ras Formation is overlain by maximal 300 m fluvial sandstone similar to the Devonian Tadrart and Binem Sandstone, are exposed at the escarpments of the plateau as well as in large wadis in the plateau.

Stratigraphical typus (KLITZSCH & WYCISK, 1987)

The Karkur-Talh Formation is represented by 30 meters of shallow marine and tidal sandstone.
"The Formation can be interpreted as deposits of subtidal shoals and tidal channels. The coarsening-upward sequence at the lowermost part of the section is made up of interbedded laminated siltstone and fine-grained sandstone with wavy lamination and ripple cross-lamination. It contains trace fossils. The upper part of this coarsening-upward sequence is made up of fine- to medium-grained destratified sandstone, containing abundant Skolithos-burrows. This Skolithos-sandstone of up to two meters in thickness is erosively overlain by tidal channel-sandstone, consisting of medium- to coarse-grained, trough and planar cross-bedding with intraformational conglomerates at the channel floor.
The uppermost part of this first shallow marine unit is formed by skolithos-baering, medium- to coarse-grained sandstone which is poorly defined cross-bedded and partly conglomeratic. This unit can be up to 18 m thick. The density of the skolithos-burrows increases towards the top. The environment of origin is assumed to have been subtidal shoals, produced during more rapid sedimentation.
The second minor shallow marine intercalation in the upper part of the formation is only up to 5m thick. It is composed of a fining-upward tidal-channel sequence with trough cross-bedde sandstone and fine-grained sandstone to shaly siltstones, with partly intensive bioturbation towards the top. Locally, a subfacies of well-sorted, fine-grained sandstone exhibiting horizontal and low-angle cross-stratification with parting lineation occurs. This subfacies indicates upper-flow conditions within the nearshore environment. The shallow marine intercalations can be traced to the area of Aqaba passage (Gilf Kebir)."
The Um Ras Formation is typical for the interface of fluvial and very shallow marine environment near the edge of the Silurian marine transgression. It has a thickness of approximately 75-80 meters.
"The deposits of the Um-Ras Formation are descrided  as non-cyclic, braided fluvial systems. This sheet-like, medium- to coarse-grained sandstone is moderatly sorted and exhibits small- to large-scale tabular cross-stratification. Grouped sets of omikron crross-stratification alternate with a minor facies of horizontal stratification, and low-angle cross-bedding and single pebbly layers. Deformed cross-bedding is frequent and may occur in successively superimposed sts. The style of deformation ranges from buckled to overturned and convolute foresets. Braided fluvial systems are subject to rapid fluctuations in flow velocity and cause the sediment to be deposited mainly in the form of channel bars. The planar stacked cross-bedded sandstone is attributed to high-stage deposition within transverse bars by straight-crested megaripples. The facies association corresponds to rivers of low sinuosity with linguoid and partly transverse bars. The abundant overturned foresets within this facies are attributed to the action of current drag on a liquefied sand bed. The coarse friable nature of the sandstone make internal fabric conditions an unlikely cause of liquefaction. An external mechanism such as of tectonism  must be sought."
The Devonian strata of the Tadrat and Binem Formation have not been dated until now by fossils. Lithofacies and stratigraphic comparisons with the corresponding sequences in th Kufra basin suggest a stratigraphic connection between the fluviatile deposits in the area of Jebel Uweinat und Gilf Kebir. It has a thickness of approximately 300-400 meters.
"The fluvial sandstone is medium- to coarse-grained, subangular to subrounded, and moderately sorted. Small-scale to large stacked tabular cross-bedding is the most common bedding type. Minor lithofacies are the horizontal bedding, through cross-bedding and the thin-bedded pebble-bearing sandstone layers. The predominantly non-cyclic fluvial sequences can be interpreted as braided river deposits. Unlike the Silurian strata, these contain an increasingly high pebble content. The pebbly sandstone can be seen as deposits fromproximal outwash braidplains, including some shallow channels. The paleocurrent direction indicates a NW to locally NE drainage pattern." Source: KLITZSCH & WYCISK (1987)

Eroded Skolithos paleosol layer: Probably Wadi Talh area

Boulder with Skolithos

 Rippel marks

Silurian sandstone in state of exfoliation

 Foggini/Mestekawi cave

 Wadi Zura (with Bivalves ?)

Stratigraphical typus in sense
KLITZSCH & WYCISK, 1987

Distribution of Carboniferous layers with plant imprints

Pushed zone of white erratic blocks. Source: Klitzsch & Wycisk, 1987: Loc 24�32'25"N / 25�05'30"E

 Rhodea plant imprint

Locations

 Bright sandstone with Sigillaria imprints
Source: A. Barakat

Bioturbation in the Wadi Hamra region
Source: U.Steiner

Lepidosigillaria imprints at eastern edge of plateau
Source: U.Steiner

Structural-geological models

NE-edge; right young fluvial deposits

Wadi Maftuh

 Cross-bedded Silurian sandstone

 Devonian (Aqaba passage)

Distribution of Carboniferous layers

Warve-type

Shallow marine type

Slope with plant imprints

Pecopteridae imprints

Stalks of Cordaites

 Ferruginous Calamites

Silty shallow marine and near shore grained sandstone with Paleoweichselia imprints

 Aqaba: Are this the mysterious Cretaceous strata ?

 ore here ? (Three Castles)

 Southern foothill, secondary (?) deposited Calamites

 Foothills near Kemal-el-Din monument

Many volcanic fissures with erected layers between Wadi Sura and Aqaba

 Hydrovolcano (Um Ras)

Ring intrusion

Basalt hill on top of plateau

Documented Locations (Loc)

Depression outside of Wadi Mashi with Basalt debris and Quartz

Basalt Wadi Mashi (Loc 3)