Geological structures on the Howar-Uweinat Uplift in the Western Desert (Egypt, Sudan, Libya)

 -- Jebel Uweinat, Gilf Kebir as well as Jabal Asba and Jabal Dalma (Zalmah) --

Norbert Brügge, Germany
Dipl.-Geol.

 

The regional stratigraphy is continuous across North Africa and have been controlled by the tectonic history of individual basins. Deformational events in the region, most of them minor, are recorded by unconformities reflecting basin tilting, uplift, and erosion of intracratonic structural axes at various throughout the Phanerozoic. The main old deformational events occured in the Precambrian to Early Cambrian, Late Silurian to Early Devonian, Carboniferous to Permian.
Throughout most of Paleozoic, North Africa was a single depositional basin on the northern shelf of the African craton. The basin generally deepened northward where deposition and marine influence were greater. In the Late Silurian and Early Devonian, Laurasia separated from Gondwana resulting in minor deformation, uplift, and lokal erosion. Many of the basins and uplifts preserved today were initially developed during this event from ealier structures. Later, in the Middle to Late Devonian, the initial collision of Laurasia and Gondwana began resulting in erosion and further modification of preexisting structures. The Hercynian orogeny (Carboniferous to Permian) marks the collision between Laurasia and Gondwana and caused regional uplift, folding, and erosion. Paleozoic basins that were delineated by earlier tectonic events were modified, resulting in the development of several intracratonic sag and foreland basins.
Several transgressive-regressive cycles occurred throughout the Paleozoic. Two major flooding events, one in the Silurian and other in the Carboniferous. Many of the prograding fluvial, esturine, deltaic, and shallow marine sands that were deposited during these cycles.


The Kufra Basin in southeast Libya forms an elongate depression oriented northeast-southwest, with an aerial extent of about 400,000 km2. The Kufra Basin began in the Early Paleozoic. By marine transgression during the Lower Silurian and Upper Carboniferous, which intercalated the far-reaching continental sedimentation, thick, vastly differentiated predominantly Paleozoic sediments are found here. The basin fill attains a maximum thickness of 3,000 m and comprises a sequence of Paleozoic sediments unconformably overlain by Mesozoic strata and has remained land since the end of Paleozoic times. The centre oft he basin is sand covered and except for a few small isolated hills of Cretaceous Nubian sandstone outcrops are limited to the southeast and southwest of the Kufra oasis. The base of the Paleozoic succession is exposed only in the north, southeast and southwest where it rests unconformably on Precambrian basement. See also International Conference, Cairo 2007

Another basin developed northeast of the Howar-Uweinat uplift in Egypt. This Dakhla Basin is filled with Mesozoic strata. The Dakhla region was probably in the Paleozoic period mostly a highland. A separation of the Kufra Basin from the Dakhla Basin is evident, because the Dakhla Basin is a younger depression filled predominantly with sediments of the Cretaceous age.

During the Paleozoic, most of the area between northwestern Sudan, southeastern Libya and southwestern Egypt was a stable part of the African craton without much structural differentiation. There was, however, a zone of strong subsidence along the eastern edge of the Kufra basin, the Howar-Uweinat uplift. This area became subsidence during the Early Paleozoic and continued until to the Devonian age. The Howar-Uweinat uplift forms the eastern border of the deep Kufra Basin in Libya. The meaning of the Howar-Uweinat uplift documents itself through the enormous difference of the Basement base between uplift and Kufra Basin of up to >3,000 m. At the eastern edge of the uplift is the difference with <500 m essentially lesser. It is evident, that in maximum of two times probably parts on this structure was uplifted and sediments were eroded. The last significant ascent happened by the Bretonian event of the Upper Devonian age.

The origin of an other uplift (Uweinat-Bir Safsaf-Aswan uplift) is not clear. The whole area from directly east of Jebel Uweinat to Aswan formed a regional high from which Paleozoic and older Mesozoic strata were generally not present, or they were eroded and then transported to south (Lakia Formation in Sudan).


The area between the sandstone plateaus of Jebel Uweinat and Gilf Kebir (incl. Jabal Asba) is the central part of the Howar-Uweinat uplift. The Basement reaches an evenly altitude to the earth's surface. The first uplifting of the area resulted probably already in the Early Paleozoic (late Silurian). The second uplifting resulted probably in the Upper Devonian age (Bretonian event). The third uplifting resulted probably in the Carboniferous age (Sudetian event). The Jabel Arkenu, Babein, Baheri and the Jebel Kissu are granitic intrusions; at the edges "stick" not eroded remains of Paleozoic sediments.

Structural-geological development of Gilf Kebir

The whole uplifted sedimentary block over the Basement reaches both in the Gilf Kebir as well as in the Jebel Uweinat a maximum thickness of 400 to 500 m. The Basement outcrop between Uweinat and Gilf Kebir is approximately of + 500 m NN. The Gilf Kebir block has a high of max. +1100 m NN. The striking mountain ridge of the Hassanein plateau in the Jebel Uweinat (+1800 m NN) is built by a tertiary magmatic intrusion and a followed uplift of the sedimentary block of Paleozoic strata. On top of the mountain ridge is placed a striking crater like structure with a basaltic bottom. The Carboniferous strata at the Uweinat and surrounding are a near-shore facies of a transgression from the Kufra basin. The strata overlain unconformably the northeastern to southeastern foothills of the already uplifted mountain range of the Jebel Uweinat. The sediments of the Lower Carboniferous age in the Abdel-Malik Plateau (northern Gilf Kebir), specially in the Wadi Talh, are the result of an advance of the Carboniferous transgression over the eroded side of the plateau, from the Kufra basin coming. Latest findings of plant imprints support the idea that Carboniferous deposits outside of the plateaus occur, which reaching to eastern and southeastern areas.
In the uplifted area, between Gilf Kebir and Jebel Uweinat, deposits of the Lower Cretaceous (Gilf Kebir Formation) occur at the edge as remains. Specially sediments in the Aqaba passage and south of Wadi Wassa represent the most extensive expansion of early sediments of Cretaceous age, from the Abu Ballas area coming*. More complete Cretaceous deposits are found outside the uplift in the eastern Ballas area (Scarp-contour).
* Meanwhile, the existence of the Gilf Kebir Formation is questionable because the found flora indicates a Carboniferous age of the sediments.

The specials here:

 

Sources:

KLITZSCH, E. & LEJAL-NICOL, A. (1984): Flora and fauna from strata in southern Egypt and northern Sudan (Nubia and surrounding areas).
Berliner geowiss. Abh., (A) 50, p. 47-79.
KLITZSCH, E. (1984): Northwestern Sudan and bordering areas: Geological development since Cambrian time.
Berliner geowiss. Abh., (A) 50, p. 23-45.
KLITZSCH, E. & WYCISK, P. (1987): Geology of sedimentary basins of northern Sudan and bordering areas.
Berliner geowiss. Abh., (A) 75.1, p. 97-136.
LEJAL-NICOL, A. (1987): Flores nouvelles du Paleozoique et du Mesozoique d’Egypte et du Soudan septentrional.
Berliner geowiss. Abh., (A) 75.1, p. 151-248.
 

"Geology of Egypt"
A. A. Balkema, Rotterdam, 1990
 

"The Geology of Libya", Volume I
M. J. Salem & M. T. Busrewil, Academic Press, 1980