No abstract

We examine the evolution of the northwestern Red Sea, Egypt, by study of the Quseir-Umm Gheig subbasin. The subbasin records two main tectonic events. The fi rst event is related to development of Late Cretaceous synclinal basins due to sinistral movement along the reactivated Najd fault system. Evidence for this includes: (1) the Cretaceous basins are concentrated mainly in the central Eastern Desert, which represents the main infl uence zone of the Najd fault system, (2) folds are not everywhere parallel to the faults and their axes are curvilinear, (3) the faults dislocated the axial plane of the synclines, (4) the Cretaceous basins occur in an en-echelon arrangement, (5) there is a difference of 20° between the orientation of the sinistral strike-slip shear zones and the associated en-echelon synclinal folds, (6) principal stress directions are delineated by subhorizontal σ 1 and σ 3 and subvertical σ 2 , (7) sheared conglomerate is detected in the Nubia Formation, (8) minor overturned folds and minor NE-vergent thrusts occur in the Duwi and Dakhla Formations, and (9) there is a predominance of NE-SW normal faults in Cretaceous-Eocene sequences. The second event is related to the sinistral movement along the NNE-SSW Aqaba-Dead Sea transform and dextral movement along Queih and Hamrawin shear zones. This movement was synchronous with northeast extension of the Red Sea. The structures developed during this movement include: (1) NW-trending extensional faults, (2) extensional fault-related folds in Miocene-Pliocene deposits, and (3) buckle folds in Pliocene and post-Pliocene sequences. Buckle folds were developed during NW compression associated with sinistral movement along NNE-SSW strike-slip faults. Gypsiferous shale-rich beds in Miocene-Pliocene rocks played the main role in development of fault-related folds and buckle folds in the Quseir-Umm Gheig subbasin.

Transpressional deformation has played an important role in the late Neoproterozoic evolution of the Arabian‐Nubian Shield including the Central Eastern Desert of Egypt. The Ghadir Shear Belt is a 35 km‐long, NW‐oriented brittle‐ductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic. Within this shear belt, strain is highly partitioned into shortening, oblique, extensional and strike‐slip structures at multiple scales. Moreover, strain partitioning is heterogeneous along‐strike giving rise to three distinct structural domains. In the East Ghadir and Ambaut shear belts, the strain is pure‐shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple‐shear dominated. These domains are comparable to splay‐dominated and thrust‐dominated strike‐slip shear zones. The kinematic transition along the Ghadir shear belt is consistent with separate strike‐slip and thrust‐sense shear zones. The earlier fabric (S1), is locally recognized in low strain areas and SW‐ward thrusts. S2 is associated with a shallowly plunging stretching lineation (L2), and defines ∼NW‐SE major upright macroscopic folds in the East Ghadir shear belt. F2 folds are superimposed by ∼NNW–SSE tight‐minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation. F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt. The sub‐parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear‐dominant deformation in fold zones. Dextral ENE‐striking shear zones were subsequently active at ca. 595 Ma, coeval with sinistral shearing along NW‐ to NNW‐striking shear zones. The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt. Oblique convergence may have been provoked by the buckling of the Hafafit gneiss‐cored domes and relative rotations between its segments. Upright folds, fold with vertical axes and sinistral strike‐slip shear zones developed in response to strain partitioning. The West Ghadir Shear Zone contains thrusts and strike‐slip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian‐Nubian Shield during agglutination of East and West Gondwana.

The Bahariya Oasis is an example of an extremely hyperarid environment and it is characterized by an extensive nonrenewable Nubian Sandstone Aquifer System (NSAS), which is deemed the crucial provenance for agrarian and national development ventures. The present work aimed to assess the groundwater occurrences in the NSAS, and to document the main factors that control the geochemistry of the groundwater in the Bahariya Oasis. Groundwater samples were collected from 52 locations in April 2019 and were analyzed for a total of 13 water-quality physicochemical parameters. A diverse geological and structural setup has greatly impacted the groundwater flow pattern and has diverted it towards the NE by the great Bahariya anticline structure, the ENE-oriented Bahariya mid dextral strike-slip fault, and NE-striking normal faults, while NW-oriented normal faults cause the groundwater to diverge perpendicular to the groundwater flow lines. The groundwater is highly contaminated by trace metals (Fe2+ and Mn2+), which exceed the permissible limit for different purposes. Conventional graphical plots and geochemical modeling integrated with multivariate factor analysis (FA) revealed that the chemical composition of the groundwater is strongly affected by its interaction with the lithologies of the NSAS. The dissolution of aquifer host rocks (carbonates and iron oxides) and chloride salts through the infiltration of groundwater, and the incorporation of cations by the ionic exchange of Na+ by Ca2+ in clay minerals, emerged as worthy mechanisms for the groundwater development. Furthermore, the region’s rapidly increasing population, agricultural expansion, and the associated anthropogenic practices have generated a need for groundwater-quality assurance as a prime source of the water supply. Consequently, reducing the effects of the NSAS’s unsustainable extraction requires long-term monitoring and the ongoing evaluation of the groundwater.

The drainage network of Wadi Ghadir watershed, southeastern Desert, Egypt was extracted from topographic maps (1:50. 000), and from the 30 m digital elevation data (DEM) of the Shuttle Radar Topography Mapping Mission (SRTM). Four topographic sheets were digitized and used for extraction. Archydro function in ArcGIS 10x was utilized for network extraction and for morphometric analysis. Networks derived from topographic sheets and DEM were considerably coincident. Different morphometric parameters from both sources were evaluated to examine the accuracy of DEM for hydrologic applications. Results clarified 6 th order streams for both drainage networks with moderate to high drainage density (D) of 2.51 km.km 2 (topographic) and 2.54 km.km 2 (DEM) reflecting that W. Ghadir drainage basin is impermeable with considerable surface runoff. DEM showed higher stream frequency (F) of 4.49 than those derived from topographic maps (4.38). Calculated bifurcation ratio (Rb) of streams derived from topographic sheets reached about 3.47 and about 4.60 for those derived from DEM. DEM-derived morphometric parameters provided good and satisfactory information about the catchment characteristics and revealed accurate watershed delineation confirming high potential of surface runoff of the W. Ghadir drainage basin. Finally, SRTM DEM proved advantageous over the topographic sheets for drainage delineation and basin morphometry for hydrologic analysis underpinned with the finer spatial resolution and the vertical accuracy.