Structure and Geology of Jebel Uweinat in the three country triangle Egypt-Sudan-Libya
Norbert Brügge, Germany
Dipl.-Geol.

Update:
02.01.2016

Images: Andras Zboray, Gabor Merkl and the author
Many thanks to Andras Zboray, a great connoisseur of the Jebel Uweinat, for the valuable discussions

Overall view

The Jebel (Jabal, Djebel) Uweinat is a mountain range in the area of the Egyptian-Libyan-Sudanese border, far away from any civilization. The Jebel Uweinat was first reported by the Egyptian discoverer Ahmed Pasha Hassanein, who in 1923 passed the Uweinat mountain range.

The mountain is composed of two very different parts. The western part of the massive consists of a collapsed dome of intrusive granite, arranged in a ring shape of some 25 km diameter, separated by three eroded wadis, named Karkur Idriss, Karkur Hamid and Karkur Ibrahim.

The eastern part consists of a large block of paleozoic sandstone, resting upon metamorphic Proterozoic basement rocks, propped against the granite dome to the west.

The sandstone slab forms a large elevated plateau which is topped by four separate units of uplifted sandstone blocks: The split Hassanein plateau, connected by a narrow neck on which is a volcanic structure ("White Spot"), the Italia plateau and an unnamed plateau in the northern direction. The highest point of Uweinat is on top of the Italia plateau (about 1,300 m on ground). The cliffs form a perpendicular wall all around of at least 200 m height.

The high plateaus via four named wadis are accessible: Karkur Talh from the east and Karkur Murr, Wadi Wahesh from the south.

A southern third valley, Wadi Waddan, crosses the contact zone between the granite dome and tectonically tilted sandstones at the edge of the eastern plateau. Here are large parts of the Proterozoic basement exposed.


1-- Hassanein P. SE;  2-- Hassanein P. NW;  3--Italia P.;  4--northern unnamed P.;  5--Mt.Bangnold


A. Structural-geological model of Jebel Uweinat

The Jebel Uweinat is one of several striking sandstone plateaus in the western desert. They crown the several thousand meters uplifted Proterozoic basement at the eastern edge of the Kufra Basin (Howar-Uweinat Uplift). The plateaus consist of remnants of Paleozoic sediments that originally the entire area has filled, but today is greatly reduced by erosion. Two of some structures, Jebel Uweinat and Jabal Arkenu, are in the "slipstream" of granitic ring-intrusions (before 42-46 Ma years in the early Oligocene age) has been preserved from the total erosion.
The age of the Paleozoic sediments is difficult to determine because fossils are rare. Trace fossils (Skolithos, Cruziana, Arthrophycus etc.) indicate Ordovician. The occurrence of Silurian and Devonian deposits is dominant. But Silurian marine sediments with graptolites (as at the margin of the Kufra basin) are missing. In contrast, some fossil plant imprints indicate the Carboniferous age of the uppermost paleozoic layers.
Between the old Paleozoic strata and Carboniferous deposits there are probably a significant time gap. In the northern Gilf Kebir (Wadi Abdel Malik) Carboniferous layers at the same level with probably Devonian strata are encountered. Therefore, we must assume that the Carboniferous strata were deposited on an already eroded and rugged relief of older Paleozoic layers. So were Devonian strata in areas between the plateaus of Uweinat, Gilf Kebir etc mostly or completely eroded. The Carboniferous strata in the Uweinat are terrestrial-fluvial of origin, and were deposited in paleo-valleys; or they are of shallow marine origin in the eastern foothills of the Uweinat.
The Uweinat structure is designed by one of these granitic ring-intrusion and can be divided into four areas today. In the western part (granite dome) are only remnants of the basement and changed sandstones between the dominant granites.
In a transition zone between the granite dome (Mt. Bangnold) and the sandstone slab (Italia plateau), parts of the basement and the entire package of sediments were uplifted by intrusion of granite and tilted to the north.

The eastward subsequent extensive sandstone slab was deposited on an uneven relief of the basement. This is documented by outcrops of the basement in the Wadi Wahesh (+820 m above sea level), Karkur Murr (+750 m above sea level), and in the lower branch of Karkur Talh (+710 m above sea level).

A special feature are four plateaus, which are marked by high cliffs. This plateaus crown the sandstone slab and tower over this partly 200 m. With a maximum height of about +1.900 m SL (Italia plateau) is simulated a total thickness of the sandstone series up to 1,200 m in the Jebel Uweinat.
But the four plateaus are significantly uplifted above the level of the sandstone slab by lateral granite intrusion at the edge of the collapsed granite dome. Such lateral intrusions under the sandstone slab are documented by some penetrations of granite on the slab. The Italia plateau achieved the highest uplift rate and is separated from the other plateaus by a fault (Wadi Wahesh incision).

The original thickness of all paleozoic strata is unknown, because we have below the four plateaus an eroded relief. But, in the comparable Gilf Kebir thicknesses of the layers of about 400 m can be measured. So the entire Paleozoic serie could originally have reached a thickness of maximal 500 m and is partly reduced to less than 50 m. How this discrepancy between the apparent thickness of the sandstone series of 1,200 m and the presumed thickness of 500 m can be dissolved, is explained model-like in the profiles (below).

Structural-geological models
 


Profiles lines


Profile A-A'


Profile B-B'


Profile C-C'


Profile D-D'

      

The mountain ridge of the Hassanein plateau is built by a tertiary magmatic intrusion and a followed uplift of basement as well as the sedimentary block. On top of the mountain ridge is placed a striking crater like structure with a basaltic bottom.
As if to confirm this, in 2007 Mahmoud Marai have found crystals on top the Hassanein plateau. He sent me a photo and I have identified the crystals as quartz crystals (see below). That means, in the underground of the Hassanein Plateau is an uplifted granite !  Into the sandstone plateau is at least one fissure with connection to the granite.
Then wrote Andras Zboray: The crystals are definitely quartz. We have found several quartz crystalls on top of the plateau, including some perfectly formed and transparent. On our ascent we have found a fissure with crystals covering both sides of the fissure.

 

Uplifted high plateaus

 

Tilted sandstone layer area (Wadi Waddan)

Wadi Waddan

View from Italia plateau (3)

View from Mt.Bangnold

View from the Dome site

 Tilted sandstone package

Eroded sandstone slab (with Wadis)

 


B. Sedimentary accumulation and stratigraphy

1.  Proterozoic basement rocks
The area located between Jebel Uweinat and Jebel Kamil is the best area of the basement inlier outcrop. The major rock assemblages were subdivided by Klerkx (1980) and Richter (1986) into three units namely, the Granoblastite Formation, the Anatexite Formation and the Metasedimentary Formation.
The Granoblastite Formation (Karkur Murr Form.) consists mainly of a group of pyroxene ganulites containing charnockitic, noritic, and diopsidic gneisses and metaquartzites.
The Anatexite Formation (Ain Dua Form.) is dominated by migmatites interpreted as anatectic granulites and contains abundant supracrustal intercalations.
The Metasedimentary Formation is a low to medium grade supracrustal sequences with intercalations of bimodal basaltic-rhyolitic rocks believed to be the source of the layered iron quartzite. The tectonic environment of these rocks is interpreted as an intracontinental rift (Richter 1986).

                  Typus locality Jebel Kamil (M. Elkady, 2003)

Kamil basement units

Ultramafic rocks Anatexite Banded Iron Formation (BIF)

High grade granulitic Granoblastite Formation (Ultramafic-Mafic rocks)
The ultramafic-mafic and calc-silicate rocks (UM) are exposed as spots or bands in some localities, especially in the southern area. The rocks are grey to green, fine to medium-grained. The bands consist mainly of high deformed, fine-grained gabbro-norite. To the southwest of the area, the exposures of the UM are represented by bands and spots of highly deformed gabbroic rocks, serpentinite and talc-carbonate.
The presence of olivine and spinel in these ultramafic-mafic rocks indicate that their parent rock was formed at a relatively high temperature and high pressure, and originated in the upper mantle.
Remobilized Anatexite Formation
The characteristic feature of the Anatexite sequence is the predominance of migmatic gneiss, i.e. diatexites, metatexites and metablastites. Whereas the highly mobilized, medium-grained diatexites are of a homogeneous to nebulitic texture, rarely showing foliation, metatexites and metablastites are well-foliated and a two-phase nature - melanosome and leucosome - becomes obvious, arranged in the form of layers or schlieren and patches.
In the area the Anatexite sequence is usually found in the valleys as isolated exposures of low relief, consisting of leucosome and melanosome bands. The leucosome bands with felsic components are buff grey to white, medium to coarse grained, and composed mainly of quartz and alkali-feldspar. The melanosome bands of mafic components are greyish green to dark green, fine to medium-grained, and are composed mainly of amphibole and plagioclase.
Metasedimentary Formation (Banded Iron Formation)
The Banded Iron Formation (BIF) is built up of accumulated clastics of psammitic and subordinate pelitic character. The BIF bands are well-foliated and generally fine-grained. The lower part of the BIF exhibits a frequently cataclastic metamorphism, but some parts still show weak graded bedding. The BIF succession consists of variegated bands with colours of yellow, red, brown, black and grey. The iron-rich bands are composed of black magnetite and dark greyish brown and red hematite alternating with quartz bands, whereas the silica-rich bands consist mainly of quartz or chert and jaspilite.
Generally, the chert bands dominate in the upper parts of the BIF while the quartz bands (metamorphosed chert bands) increase toward the base. Chert and jaspilite bands occupy the top of the formation. The chert contains more hematite and shows remnants of thin layering in contrast to the quartz rich bands in the middle and lower part of the BIF succession.
The BIF differs from base to top as follows:
Metapelitic and volcanosedimentary bands; Fuchsite bearing quartz bands; Well banded iron-silica bands; Lower part of the iron-silica-rich bands

Eroded sandstone slab (with wadis)

Basement outcrops

Mouth of Karkur Talh (loc 1)

Old basement granite: SW-branch of Karkur Talh (loc 2)

Southern edge and dome area

South-Uweinat basement outcrops from space  Mouth of Wadi Wahesh Wadi Wahesh: Outcrop Debris: Southern foreland BIF (Quartzbands) Karkur Idris BIF, dome side


2.  Lower Paleozoic sedimentation

The sediments of the Paleozoic period rest directly on the uplifted Proterozoic basement. In between is a significant time gap, because the sedimentation begins earliest in the Ordovician period. The detection of trace fossils (Skolithos, Arthrophycus, Cruziana, etc.) is an indication of this. Cambrian sediments are missing definitely.

The Ordovician and Silurian strata were described first from the southwestern Gilf Kebir (Abdel-Malik Plateau) by KLITZSCH & WYCISK (1987). Near the Um Ras Passage approximately 100 meters of fluvial, deltaic and nearshore marine sandstone occur, interbedded by rare silt- to fine sand layers, that locally containing abundant burrows of Cruziana/Arthrophycus as well as Harlania and other ichnofossils and beds full of Skolithos.

These sediments are, apart from a marine sequence, are similar to the of BELLINI & MASSA almost simultaneously studied deposits in Jabal Rukn and Jabal Asba. These are an extension the Gilf Kebir towards Libya.

It is believed that the boundary between the Ordovician and Silurian strata is above beds with rich Skolithos therein.
In the area of ​​Gilf Kebir and Jebel Uweinat the Ordovician series is called Karkur Talh Formation (in sense KLITZSCH); the Silurian series is called Um-Ras Formation (in sense KLITZSCH).
In analogy to comparable stratigraphic profiles in the Gilf Kebir and Jebel Asba a similar stratigraphic sequence of Ordovician, Silurian and Devonian is also in the Jebel Uweinat available. The thicknesses of the layer sequence are confirmed: 25-30m Ordovician (Karkur-Talh Fm.); 75-80m Silurian (Um-Ras Fm.); about 300-400m Devonian (Tadrat Fm.).

The Karkur Talh Formation of Ordovician age rest on Precambrian metamorphics, whereas at other locations the Um-Ras Formation rest directly on the Precambrian metamorphics and the Ordovician layers were missing.
The same type of strata, also containing Cruziana/Arthrophycus, Harlania and Skolithos beds, is present in the Egyptian part of Jebel Uweinat at Karkur Talh.

Three horizons with trace fossil have been identified: In the southern and western branch of Karkur Talh at about +715 m SL and +740 m SL, and more recently on the eastern plateau at the higher stratigraphic position (+805 m SL). Some beds with small thickness at the base of this serie contains abundant Skolithos sp.

The upper limit of the Silurian strata in the Uweinat is confirmed by the discovery of the upper Arthrophycus layer, about 100 m above the basement. Carboniferous strata in the Jebel Uweinat and the wider area partly overlap directly Silurian strata or the basement. This means there is a time gap between Carboniferous and Devonian. In this time the Devonian strata by fluvial erosion were mostly or completely reduced across the region. The current high plateaus such as Jebel Uweinat, Gilf Kebir, Jabal Arkenu etc. contain more complete Devonian strata.


The following Devonian strata (Tadrat Formation) are eroded at the edges of Jebel Uweinat usually up to the level of the Silurian and Ordovician strata. Its original thickness is only in the uplifted plateaus preserved.

Carboniferous strata in the Jebel Uweinat and the wider area partly overlap directly Silurian strata or the basement. This means there is a time gap between Carboniferous and Devonian. In this time the Devonian strata by fluvial erosion were mostly or completely reduced across the region. The current high plateaus such as Jebel Uweinat, Gilf Kebir, Jabal Arkenu etc. contain more complete Devonian strata.


Stratigraphical typus profiles


The Karkur-Talh Formation is represented by 25 to 30 meters of well bedded shallow marine sandstone are intercalated with coarse to conglomeratic fluviatile 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 18m 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 shallow marine environment near the edge of the Silurian marine transgression (Kufra basin). 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 Formation have not been dated until now by fossils. Lithofacies and stratigraphic comparisons with the corresponding sequences in th Kufra basin suggest a straigraphic 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)

 

      Trace fossils (marine Silurian layers)

Western branch of Karkur Thal (+740 m SL) Southern  branch of Karkur Thal (+740 m SL) Eastern plateau (+805 m)
Left:
Prasopora (Bryozoa)
Karkur Talh

Source: Jean Pierre Connan
    Above:
Arthrophycus (8x)
     


2.1 Karkur Talh Formation (Ordovician)


    
Fine stratified to conglomeratic compact sandstone

 

 

Southern Uweinat: layer with Skolithos Southern branch of Karkur Talh    

      Silty layer with trace fossils

       

Southern branch of Karkur Talh (+715 m SL)

 

 

       


 

2.2 Um-Ras Formation (Silurian)
 

      Fine stratified compact sandstone

Boundary between Basement and Silurian (Karkur Talh; +710 m SL)

 

 

 

   

      Clearly stratified and partly cross-bedded layer

 

      Silty layer with trace fossils

 

 

Western branch of Karkur Talh (+740 m SL)

 

Southern branch of Karkur Talh (+740 m SL)

 

 Eastern Plateau (+805 m SL)


2.3 Tardrat Formation (Devonian)

      Uplifted plateaus

     Below of high plateaus (Slab)


3. Carboniferous sedimentation

The presence of Carboniferous strata has been known for a long time from Karkur Murr and Karkur Talh at the eastern side of Jebel Uweinat. It was already known, that the so-named Karkur Murr Formation consist of sandy shales and include often numerous plant imprints.

But the type locality of Carboniferous sediments is the region of Wadi Talh (meant is not Karkur Talh)  in the Gilf Kebir (Abdel-Malik Plateau) and is described in detail by KLITZSCH & WYCISK (1987) as Wadi Malik Formation.

"The lowermost part consists of medium- to coarse-grained sandstone with grouped sets of small- to large-scale planar cross-bedding alternating with horizontally bedded medium-grained sandstone. The percentage of horizontally stratified sets increases towards the top. Overturned cross-bedding is less frequent  in this facies. The facies type displays conditions of extensive deposits of braided river.

The second part of the succession shows a fining-upward sequence with a slighlty erosive base made up of medium- to fine-grained sandstone and intercalated thin laminated shaly siltstone. This cross-bedde pointbar sequence is 8 to 12m in thickness and is topped by fine-grained, partly even laminated overbank deposits, which lacally display pedogenetic features. These facies represents deposits of high sinuosity rivers.

The third part consists of fine-grained sandstone with shaly siltstone intercalations and horizontal strata. Main bedding types are ripple cross-lamination, even and wavy lamination and flaser-bedding.  Parting lineation can be observed in the uppermost part of this unit. Ferruginous siltstone layers and reworked shale intraclasts within scour-and-fill structures occur. Asymetrical oscillation ripples are common on the bedding planes. Tadpool nest ripples indicate shallow water conditions in a predominantly low energy wave-generated environment. This facies can thus be considered as a marine influenced sedimentary environment in a transition zone from alluvial to coastal plains.

The uppermost part represents a shallow marine sequence of Late Visean age. The sequence is made up of various increasingly thick layers of tidal channel-filled sandstone with distinct erosive contact which interfinger with the above mentioned facies. Channel-sandstones with a maximum thickness of up to 3 meters are overlain by thin-bedded fine-grained sandstone with interbedded clay-iron-stone layers. Intensive bioturbation, trace fossils such as Bifungites and remains of brachiopods confirm the marine origin of this probably tidal channel to subtidal paleoenvironment." Source: KLITZSCH & WYCISK (1987)

Today, more and more solidified the impression that Carboniferous sediments with abundant plant imprints (Lepidodendron, Sigillaria etc.), suspected more than before, are the youngest Paleozoic deposits in the Jebel Uweinat and surrounding (see right).

The Carboniferous strata of surrounding areas are a near-shore facies of a transgression from the western Kufra basin. The strata overlain unconformably the southern  foothills of the current mountain range the Jebel Uweinat. Remains of strata from the Carboniferous transgression also were found extensive in the Wadi Talh area of Gilf Kebir, at the  Clayton Craters in the northern direction of  Uweinat and approximately 100 kilometers southeast of Jebel Kissu.


Gilf Kebir: Stratigraphical typus in sense
KLITZSCH & WYCISK, 1987

Carboniferous strata in the Jebel Uweinat and the wider area partly overlap directly Silurian strata or the basement. This means there is a time gap between Carboniferous and Devonian. In this time the Devonian strata by fluvial erosion were mostly or completely reduced across the region. The current high plateaus such as Jebel Uweinat, Gilf Kebir, Jabal Arkenu etc. contain more complete Devonian strata.

 In the Jebel Uweinat this sediments mostly consists of fine- to medium grained sandstone and sandy shales (nearshore influation), or coarse-grained sandstone (terrestrial). Warve-type strata within the terrestrial fazies were interpreted as limnisch.

At Karkur Murr these strata rest directly on methamorphic Proterozoic rocks, while at southern Karkur Talh, as well as east of Jebel Uweinat, they rest on Paleozoic strata.

In the current plateau area terrestrial deposits are not consistently horizon. They occure on infra-Devonian level in paleovalleys, because they are products of erosive ablation of older strata. The deposits are not clearly layered and have a medium-  to coarse-grained facies.


Distribution of Carboniferous layers

3.1 Carboniferous layer

     Terrestrial paleovalley sediments

Eastern edge of Uweinat: Warve-type sediment

Eastern plateau: Warve-type sediment with ripple marks

Floor of paleovalley

 Coarse grained sandstone

Plant imprints (Loc 3)

     River and coastal sediments

 

 

 Edge of southern Uweinat: Downfall blocks (Loc 10)

 

 Mouth of Karkur Murr

 

 Foothills at southern Uweinat

 


3.2 Carboniferous plant imprints

Historic finds

At Jebel Uweinat (Karkur Murr and Karkur Talh) the Wadi Malik Formation contains the following flora of Lower Carboniferous age:
Cyclostigma ungeri JONGMANS
Lepidodendropsis aff. rhombiformis DE ROUVRE
Lepidodendropsis cf. vandergrachti JONGMANS
Precyclostigma tadrartense LEJAL-NICOL


Directly east and southeast of Jebel Uweinat as well as approximately 100 kilometers east of Jebel Kissu, both in northwestern Sudan, the following flora was found:
Triphyllopteris cf. rhombifolia DABER.
Lepidodendron veltheimi STERNBERG
Lepidodendropsis vandergrachti JONGMANS
Prelepidodendron aff. lepidodendropsis LEJAL
Lepidosigillaria intermedia LEJAL
Archaeosigillaria vanuxemi KIDSTON
Precyclostigma sp.


Without exact statements to the place of discovery in the Jebel Uweinat and surrounding are finds mentioned of
Rhodea aff. lotzensis STOCKMANS
Cordaites cf. angulostriatus GRAND'EURY
Eskdalia africana LEJAL-NICOL
Eskdalia malikense LEJAL-NICOL
Eremopteris elegans E.L.
Ursodendron aegyptiacum LEJAL-NICOL
Archaeocalamites sp.

 



Eskdalia africana LEJAL-NICOL



Eskdalia malikense LEJAL-NICOL



Cyclostigma sp.



Precyclostigma tadrartense LEJAL-NICOL


Cyclostigma ungeri JONGMANS


Ursodendron aegyptiacum LEJAL-NICOL



Ursodendron aegyptiacum LEJAL-NICOL



Archaeocalamites sp.



Eremopteris elegans E.L.


Lepidodendron veltheimi STERNBERG

New finds by travel participants
In recent years, and especially in 2008, 2009 and 2013 by Andras Zboray, Hungary, and his groups, were found new fossil plant-imprints on the northeastern part of the Uweinat plateau. The plant-remains of the types "Lepidodendron", "Sigillaria", "Stigmaria" and "Calamites"are usually not well preserved. The barely layered deposits have a medium- or coarse-grained facies. It is likely that this deposits are terrestrial, this means, products of the intra-erosion older deposits. This facies differs from the coastal facies on the southeastern side of the Uweinat. The plant-remains are preserved in situ. In contrast, the plant-remains in shallow-marine deposits are allochthon of origin.
Now for the first time are corresponding plant imprints in the sediment by Andras Zboray and group on the tour in 2013 at the eastern edge of the Jebel Uweinat documented (see below).
  



Locations (Loc 1 - 10)



Loc 1 -- Lepidodendron sp.



Loc 2 -- Downfalled terrestrical sandstone remains,
  found on terrace 20 metres above valley floor
 



Loc 2 -- Stigmaria imprint on coarse-grained sandstone



Loc ? -- Sigillaria imprint



Loc ? -- Stigmaria



Loc ? -- Lepidodendron aff. veltheimi



Loc 3 -- Roots aff. Stigmaria



Loc 3 -- Sigillaria



Loc 4  -- Lepidodendron aff. volkmannianum



Loc 5 -- Sigillaria imprint on fine-grained sandstone



Loc 5 -- Sigillaria imprints



Loc 6 -- Lepidodendron imprint



Loc 7 -- Sigillaria aff. cancriformis



Loc 8 -- Sigillaria aff. cancriformis



Loc 10 -- Ledidodendropsis ?



Loc 8 -- Sigillaria imprints


New Loc 9 -- Large Lycophyta (Lepidodendron) and Sphenophyta (Calamites) imprints
(Photos by Gabor Merkl & Andras Zboray)

 


C
. Igneous and tectonic inventory

In the Jebel Uweinat (Libyan part) we can see the unusual circular structure. These structure are the surface expression of a granitic intrusion. This Granite intruded into the Proterozoic metamorphic basement as well as Paleozoic sandstone strata along a ring fracture. Three igneous activities has occured probably in the Early Oligocene age (42-46 Ma).
The composite intrusion of the Jebel Uweinat is roughly circular with a diameter of about 23 km, and is flanked on the northern side by three smaller overlapping intrusive rings which are aligned along a north-northeast-trending axis. The main complex is composed of deeply weathered alkaline rocks, forming very large well-rounded blocks. The outer rim is formed by coarse-grained quartz syenite which steeply slopes toward the surrounding basement. The rock is assembled of quartz up to 12% and major euhedral perthitic alk-feldspar beside minor aegirine. Toward the centre, in the south and west, the outer intrusive ring is followed by a highly complex zone of coarse-grained quartz syenite and coarse to fine-grained alkali granite. This zone forms the outer rim in the north. According to KLERKX & RANDLE (1976), similar to the syenite the alkali granite is essentially composed of subhedral alk-feldspar but with an increased amount of interstitial quartz and aegirine. The central depression of the ring complex is occupied by a reddish, fine-grained quartz syenite with trachytic matrix that encloses rare phenocrysts of K-feldspar. The rock is locally cut by trachytic dykes and sills. A steep inner slope around the central quartz syenite depression is build up by alternating cone-sheets of syenite, consisting largely of perthite with no quartz.

Outside of the granitic dome, on the remaining sandstone slab, are some interesting igneous and tectonic implications to find.

  Outside of the Granite dome

Northern branch of Karkur Talh: Trachyte and Rhyolite intrusiva

 Plug (Karkur Talh)

Trachyte (Karkur Talh)

Quartz crystals
 (Italia plateau)

Sandstone columns (Karkur Talh)

Igneous structure on slab

Lamphrophyre dyke

Igneous penetration on slab

Igneous fissure
 (Wadi Wahesh)

Wahesh fault
 (between high plateaus)

 "Basalt" Wahesh fault

Crater "White Spot" with igneous basalt
(High plateaus)

Plug with splitted sandstone
  (High plateaus)