Facies and architecture of a coarse-grained alluvial-dominated incised valley fill: a case study from the Oligocene Gebel Ahmar Formation,Southern Tethyan-shelf (northern Egypt)

Exposures of multistorey, alluvial deposits from the Oligocene Gebel Ahmar Formation in the Cairo-Suez province (north Eastern Desert, Egypt) show the architecture of an up to 35 m thick continuously prograding fluvial/alluvial filling of an incised valley. The Oligocene base level fall resulted in cannibalization of the Eocene bedrock. Subsequent baselevel rise created accommodation space that was filled by deposition of four stacked storeys: lower storeys (1-2) of low sinuosity sandy braid plains and upper storeys (3-4) of gravelly braid plain. These braid plains were sourced from exposed Upper Cretaceous-Eocene and Paleozoic-Lower Cretaceous siliciclastic successions to the south. These successions dominate the Galala-Araba inverted structures. The sandy braid plain channel belts mainly downstream accretion (DA), downstream oblique accretion(DLA), lateral accretion (LA), sandy bedforms (SB), channel (CH), and Hollow (HO) elements, while the gravelly braid plain consists mainly of gravel bars and sheets (GB), gravel-sandstone foresets (GSF), gravel-sand couplets (GSC), and scour pool filling (SPF) architectures. Incised valley incision is potentially linked to a global drop of sea level caused by glaciation, although hinterland tectonism (i.e. Late Cretaceous-Paleogene tectonic inversion and Late Eocene-Oligocene crustal updoming in the source terrains) as well as Late Oligocene-Miocene rifting play a significant role in the subsequent filling. The hinterland tectonism as well as the climate controls the sediment supply. The understanding of the nature of the Oligocene incised valley fill helps in the constrain potential down depositional dip hydrocarbon reservoirs in Nile Delta, East Mediterranean basins, and similar settings in passive continental margins.     

Structural architecture and tectonic evolution of the Maghara inverted basin,Northern Sinai,Egypt

Large NE–SW oriented asymmetric inversion anticlines bounded on their southeastern sides by reverse faults affect the exposed Mesozoic and Cenozoic sedimentary rocks of the Maghara area (northern Sinai). Seismic data indicate an earlier Jurassic rifting phase and surface structures indicate Late Cretaceous-Early Tertiary inversion phase. The geometry of the early extensional fault system clearly affected the sense of slip of the inverted faults and the geometry of the inversion anticlines. Rift-parallel fault segments were reactivated by reverse slip whereas rift-oblique fault segments were reactivated as oblique-slip faults or lateral/oblique ramps. New syn-inversion faults include two short conjugate strike-slip sets dissecting the forelimbs of inversion anticlines and the inverted faults as well as a set of transverse normal faults dissecting the backlimbs. Small anticline–syncline fold pairs ornamenting the steep flanks of the inversion anticlines are located at the transfer zones between en echelon segments of the inverted faults.     

Maastrichtian carbon cycle changes and planktonic foraminiferal bioevents at Gebel Matulla,west-central Sinai,Egypt

Comparison between the planktonic foraminiferal bioevents from different palaeolatitudes suggests that the biostratigraphic criteria used to identify the Maastrichtian stage boundaries are problematic. A new high-resolution calibration of planktonic foraminiferal biostratigraphic, carbon-isotope, and sequence-stratigraphic criteria has been recorded for the first time from the Maastrichtian Sudr Formation at Gebel Matulla, west-central Sinai. The sedimentary successions allow the identification of prominent long-term carbon isotope events in the Maastrichtian, namely the negative excursion of the Campanian–Maastrichtian Boundary Event (CMBE), the positive excursion of the mid-Maastrichtian Event (MME), and the decline towards the Cretaceous-Palaeogene transition (KPgE). Termination of these well known δ¹³C events is associated with unconformities, created by eustatic sea-level changes, although the long duration argues for superimposed local tectonic control.     

A New Hiatus within the Lutetian of the El Basatin Section,Gebel Mokattam,Egypt:Field and Sedimentological Observations,with Special Emphasis on Nummulites

The Eocene succession of the El Basatin Section in Gebel Mokattam, east of Cairo, consists, from base to top, of two main units; the Mokattam and Maadi Formations. The Mokattam Formation consists of two Members, the Building Stone Member and the Giushi Member. The Upper Building Stone Member yielded six species of Nummulites belonging to the Upper Lutetian. These species are: Nummulites farisi Hussein et al., 2004; Nummulites cf. praegizehensis Boukhary and Hussein-Kamel, 1993; Nummulites cf. gizehensis(Forsk?l, 1775); Nummulites discorbinus(Schlotheim 1820) and Arxina schwageri(Silvestri, 1928) emended by Boukhary et al. 2012 and Nummulites crassichordatus Boukhary et al., 2010. The Giushi Member yielded three species that indicate a Bartonian age. These species, which continued from their first appearance in the Upper Building Stone Members, are N. discorbinus, A. schwageri and N. crassichordatus. The Maadi Formation, which has been previously considered to be of Bartonian–Priabonian age, is devoid of fossils in the study section. The two members of the Mokattam Formation represent a carbonate platform facies. The deposition of the Upper Building Stone Member was disturbed during the Lutetian by slumping and a convolute-bedding interval, indicating a short hiatus. The subsequent regression resulted in a very shallow marine to near-shore facies in the above Maadi Formation.     

Structural architecture and tectonic evolution of the Yelleg inverted half graben,northern Sinai,Egypt

The Gebel Yelleg area includes a number of folds belonging to the northern Sinai Syrian Arc structures. Detailed surface structural mapping and subsurface (seismic and borehole) data show that the Gebel Yelleg structures are related to Late Cretaceous-Early Tertiary inversion of a Jurassic asymmetric (or half) graben formed during the opening of Neotethys. The inversion structures include a large (45-km long) asymmetric fold (Yelleg Anticline) with a steep flank overlying the southeastern (main) bounding fault of the inverted half graben as well as some right-stepped en echelon folds overlying the northwestern bounding fault of the half graben. The large inversion anticline is dissected by a large number of long, nearly orthogonal normal faults whereas the en echelon folds are dissected by transverse normal faults and two sets of oblique-slip faults. Inversion of the northern Sinai extensional basins is related to Africa-Eurasia convergence and was probably transpressional with a small component of dextral slip. This study shows that the magnitude of inversion in the northern Sinai fold belt decreases toward the southern boundary of the Jurassic extensional province.     

Structural regime and its impact on the mechanism and migration pathways of hydrocarbon seepage in the southern Gulf of Suez rift: An approach for finding new unexplored fault blocks

A Natural active oil seepage occurs at the intersection of the NW-oriented rift coastal fault and a NE-oriented cross fault which bound the southwest dipping Little Zeit tilted fault block at the southwestern side of the Gulf of Suez, Egypt. Detailed surface geological mapping followed by subsurface mapping using aeromagnetic, seismic and borehole data of Ras El Ush oilfield (the nearest oil field to the seepage) provide a reliable hydrocarbon migration pathway model of the area.The proposed model suggests that hydrocarbons migrated upward at the intersection of a NE-oriented and the NW-oriented rift coastal faults where they found their way to the surface. The Nubia Sandstone occurs south of Ras El Ush oilfield in a trap door structure and probably entrapped some of the migrating hydrocarbons while a probable oil-water-contact at −1000 m which resulted into the migration of hydrocarbon through the damage zone of the northeast fault.The original oil in place of the predicted reservoir is estimated to be more than 47.5 MMBO which encourages the design makers for more investigation of this reservoir to increase its certainty and putting it in the plan of the future investments.