Northern Western Desert Research Articles

Modes of structural evolution of Abu Gharadig Basin, Western desert of Egypt as deduced from seismic data

The present study, which is mainly devoted to the critical analysis of all available drill hole data and seismic reflection records in the Abu Gharadig Basin area which lies principally to the east of the Qattara Depression in the central portion of the Northern Western Desert of Egypt, indicates that the Abu Gharadig Basin is an elliptical, multicyclic, E-W trending structurally-controlled basin developed originally as a result of the deep crustal extensional tectonics that affected Northern Egypt during the Mesozoic Era. The basin seems to have been initiated by a localized mantle bulge that led to the restricted deep crustal extension in the area under study during the early phases of the Alpine movements which took place in Late Jurassic. The basin was brought to its active maturation phase during the Cretaceous as a result of the large-scale extensional tectonics along two major bounding E-W trending listric growth faults. Tilting of the basin, took place during the Uppermost Cretaceous/Early Tertiary as a result of the compressive stresses (NW-SE) that were associated with the Laramide phase during these times.

Sedimentological studies of neogene evaporites in the northern Western Desert, Egypt

Neogene calcium sulphate deposits at the northern Western Desert, Egypt, are interpreted as shallow photic subaqueous evaporites. Study of the evaporite sequences at Gebel El-Hagif and Dir El-Biraqat areas reveals two principal structures similar to those observed in the Messinian gypsum in and around the Mediterranean Sea. The structures, arranged from base to top are: (1) cryptalgal laminites and stromatolitic structures built up by cyanobacterial (blue-green algal) communities in gypsite and gypsarenite units; and (2) selenite (specchiolino or mirror like gypsum) represented by (a) disordered selenite, and (b) vertically arranged selenite. Cyclic increase and decrease in salinity are represented by interlamination of gypsum and cryptalgal carbonate laminae. General increase of salinity is represented by the general increase in crystals size of gypsum from gypsite to gypsarenite to twinned gypsum crystals more than 5 cm in length at the top of the sequence. A regressive evaporite basin model is suggested for the deposition of the studied evaporite sequence. Dehydration of gypsum into anhydrite through an intermediate bassanite phase, and the subsequent transformation of secondary anhydrite into secondary porphyrotopic gypsum, are the main diagenetic processes affecting the studied Neogene evaporites.

Geological studies of subsurface Paleozoic strata of northern Western Desert, Egypt

The paleozoic rocks encountered in several wells located at the northern part of the Western Desert consist of distinctive series of carbonate and non-carbonate strata representing changes of environmental conditions. The carbonate sequences were deposited during late Cambrian, late Devonian, late Carboniferous and early Permian. The major non-carbonate sequences were deposited during the major span of lower Paleozoic, major span of Devonian, early Carboniferous and early Permina. Five major facies were recognized: quartz arenite, quartz wacke, argillite, biosparite and biomicrite reflecting different environmental conditions. The original sediments were subjected to post depositional changes notably compaction, cementation, overgrowth, neomorphism and micritization.

Paleozoic and Mesozoic Stratigraphy and Oil Potential of Western Desert: ABSTRACT

The depocenter of the Paleozoic basin in western Egypt lies in the northwestern part of the Western Desert. The sediments are primarily terrigenous (with two minor phases of vulcanicity) laid down in an epicontinental sea. The depositional axis of the basin, where thicknesses in excess of 2,800 m (9,200 ft) have been recorded, has a northwesterly trend to the vicinity of the Siwa Oasis. A less well-defined shallower basin with a northerly trend lies to the southwest. The facies show such similarities to those found in the Ghadames and Murzuq basins that the same formational names are applied. Farther east, a possible Paleozoic basin lies in the Abu Gharadig area where 1,300 m (4,265 ft) of sediments were drilled. The limits of this presumed basin are questionable since ba ement was not reached. Following the deposition of the Paleozoic section, there was a marked hiatus; the time of Hercynian movements for Permian and Triassic beds is absent. Uplift and the presence of volcanics dated in Permian-Carboniferous time are indicative of Hercynian tectonic activity. Only in Early Jurassic time did the seas again begin to encroach upon the Western Desert area from the Salum basin in the northwest and the Wadi Natrun basin to the east and northeast. This process continued, until by the time of the Oxfordian transgression maximum there was a relatively uniform carbonate cover to about lat. 29°N over the Western Desert. Further tectonic uplift accompanied by faulting and marine regression is dated from late Kimmeridgian time to the beginning of the Cretaceous, when transgression began once again. The pattern of transgression, however, differs from that of the Jurassic; the two basins, the more westerly Matru basin and the easterly Alamein basin, both have north-northeasterly trends, although by Aptian times they are less clearly distinguishable. The dominant feature, new in the Western Desert, was the development of an east-west extensional basin, the Abu Gharadig basin, in Cretaceous time. It was bounded on the north (30°N) by the Rabat Abu Rivash ridge, which persisted through the Cretaceous. The trough became less distinctive in Cenozoic times when a further trough, the Tiba basin, developed north of the ridge. Production from the northern Western Desert until recently has been disappointing. Exploration results from the Paleozoic Section have yielded little, but the existence of a marine section suggests that the area northeast of Siwa still has potential. The thick deeply buried Jurassic marine sequence in the Western Desert may be the source for at least part of the production from Cretaceous horizons in the Abu Ghradig, Alamein, and Razzak oil and gas fields. End_of_Article - Last_Page 495------------

Evolution of Eocene-Miocene Sedimentation Patterns in Parts of Northern Egypt

An analysis of sedimentologic data of Eocene, Oligocene, and Miocene rocks from northern Egypt has resulted in a synopsis of the depositional systems operative. A complex pattern of dominantly carbonate and minor associated terrigenous facies was deposited during Eocene time in narrow and elongate tectonic basins that were arms of the Tethys sea. The basins were separated by elongate structural ridges that resulted from Late Cretaceous tectonic activity. Infill of the ancestral topography during early and middle Eocene time, as reflected by the distribution of facies, ultimately provided the depositional base for seaward progradation of terrigenous sedimentation beginning in the late Eocene. Progradation during the Oligocene and Miocene was from southwest to northeast, ov r an open shelf of irregular bathymetry. This resulted in deposition of a thick terrigenous section in the western and central parts of the northern Western Desert. Longshore currents aided in the redistribution of sediments in an easterly direction toward the present Nile delta and resulted in an easterly shift of terrigenous depocenters from Oligocene through Miocene time. As the terrigenous clastic depocenters shifted eastward, carbonate environments reappeared in the west and onlapped abandoned parts of the fluvial-delta systems. By the early and middle Miocene, carbonate environments had become extensive and continued to shift eastward with shifting terrigenous clastic deposition. Upper Miocene strata have not been recognized in Egypt by some workers, but terrigenous clastic facies ear and north of Lake Manzala may represent late Miocene deposits. The embryonic Gulf of Suez, which developed as an arm of the Mediterranean during the Oligocene and early Miocene, was the site of deposition of arkosic sands, fanglomerates, and some evaporites, which originated within or from along the edge of the basin. However, fine-grained terrigenous sediments were transported by longshore currents to the Gulf of Suez from ancestral Nile deltas near the present Nile delta. Large volumes of evaporites, contemporaneous with the Nile delta, accumulated in the Gulf of Suez basin during the middle and late Miocene as a consequence of construction of a terrigenous clastic dam at the north end of the gulf.

Petrographic Characteristics of Oil-Bearing Rocks in Alamein Oil Field; Significance in Source-Reservoir Relations in Northern Western Desert, Egypt

In petroleum potential the northern part of the Western Desert of Egypt has become one of the most promising localities of Egypt since the discovery of the Alamein oil field by the Western Desert Operating Petroleum Company (WEPCO). The oil production from the Alamein field comes from Aptian rocks. The Aptian series can be subdivided into two lithostratigraphic units. The lower unit is essentially clastic, whereas the upper one is mainly carbonate rock and commonly is known as the Alamein Dolomite. A petrographic study of the oil-bearing carbonate rocks of the Aptian series in Alamein oil field, the overlying sealing rocks, and the underlying carbonate beds and sandstones of Middle Jurassic age indicated that the dolomites of the Alamein are of syngenetic origin and were subjected to a diagenetic dedolomitization process by volume replacement rather than by molecular replacement. This study revealed that the petrographic characteristics of the Alamein Dolomite are important in the migration and accumulation of petroleum, as well as the source-reservoir relation in the Western Desert of Egypt petroleum province.

A new occurrence of an economic gypsum deposit in the northern Western Desert of Egypt

A new occurrence of an economic gypsum deposit in the northern Western Desert of Egypt

Stratigraphy, Structure, and Origin of Siwa Depression, Western Desert of Egypt

Marine Miocene sedimentation on the broad platform of the northern Western Desert of Egypt was controlled tectonically by slight oscillations and local small undulations and warps of the sea bottom. Sedimentation ceased in post-middle Miocene times when intensified tectonism uplifted the whole platform to form El Diffa Plateau of the present Western Desert. Three lithostratigraphic units--a lower one belonging to the Moghra Formation and two upper units belonging to the Marmarica Formation--are delineated in the Miocene succession exposed across most of the northwestern part of the Western Desert of Egypt. All three units are marine, and generally they are a lower coquina-marlshale member, a middle chalky member, and an upper fossiliferous limestone-chalk member. In the S wa Depression area of the Western Desert, the constant thickness of the middle member helps to define the structural configuration of the depression, which is an elongate asymmetric and irregular basinlike syncline. This gentle syncline has a west-east extension of more than 80 km (50 mi) and forms the middle part of the great geomorphic arc of the Jaghbub-Siwa-Qattara depressions of the northern Western Desert. It is suggested that during post-middle Miocene uplift, hinge faulting and rejuvenation of old faults occurred in the basement underlying the Miocene blanket sediments. This resulted in sags and downwarps of the overlying Miocene beds and finally produced large, tectonically controlled surface depressions like that of Siwa. In the exposed Miocene succession around Siwa Town, along the main trough of the Siwa syncline, the higher beds with relatively lighter overburden are much more deformed than the beds underlying them. This deformation is ascribed to internal stresses generated within a localized core of the irregular Siwa syncline by the squeezing and upward buckling of the freer part of the downwarped sediments, possibly above or along a small decollement. In the wet post-Miocene climate, the morphotectonic depression of Siwa and its associated tectonically induced jointing and other surface fractures immediately captured and localized the surface drainage. Water erosion within the chemically vulnerable Miocene sediments of the initial depression proceeded rapidly and greatly enlarged it. There is conflict of opinion concerning the agents and mechanisms responsible for the creation of the Siwa and other large oasis depressions in the Western Desert; however, this study proves that initial tectonism and subsequent ancient water erosion were the most important factors. Wind deflation had a relatively late and minor role. Exsudation is likewise unimportant except perhaps in the late dry stages.