Mesozoic rocks outcrop in southern Egypt and in northern Sinai (Fig. 1.7) where an almost complete sequence from the Triassic to the Cretaceous has been described (Kerdany & Cherif, 1990). However, in the northern Western Desert Mesozoic rocks are buried beneath younger Neogene sediments (Fig. 1.7), and are only known from the subsurface (Kerdany & Cherif, 1990).
Figure 1.7. Geological map of Egypt showing the distribution of sedimentary (Mesozoic and Cenozoic) and igneous rocks (after Egyptian Geological
duction Chapter I Intro
Mesozoic rocks are poorly exposed in the Gulf of Suez region. However there are rare exposures, on the western coast: the Permo-Triassic rocks at the Abu Darag area, the Jurassic rocks of the North Galala Plateau, and the Cretaceous rocks of the Gebel Shabrawet and the South Galala Plateau. Mesozoic rocks are also found on the eastern coast: the Cretaceous rocks of Wadi Sudr. Work on exposures on the eastern side of the Gulf of Suez (e.g. Khalil & McClay, 1998) together with the offshore Gulf of Suez boreholes (e.g. Moustafa & Khalil, 1995) has enabled a complete composite stratigraphic sequence of Mesozoic rocks to be established.
The late Jurassic-early Cretaceous eastward movement of the African plate along sinistral strike-slip faults - as a result of the opening of the Atlantic Ocean - resulted in two main tectonic structures in the northern Western Desert: WNW folding associated with thrusting, and ENE trending strike-slip faults with left lateral movement (Meshref, 1990). At the same time Neotethyan rifting and the development of the eastern and southern margins of the Mediterranean Sea resulted in faulting and uplifting with a E-W trend across the northern Gulf of Suez, the development of the NW-SE trending Suez Arc parallel to the present day western margin of the Gulf of Suez, and a reactivation of the Kharga-Aswan-Red Sea High (Van Houten et al., 1984; Patton et al., 1994). The Kharga and Suez arcs intersected in the northern Red Sea and southern Gulf of Suez resulting in a basement uplift, which persisted throughout the Mesozoic and the early Tertiary (Van Houten et al., 1984).
In general the early Cretaceous sedimentation in the northern Western Desert in general indicates a major regressive phase, demonstrated by the deposition of marginal marine sandstones and shales with rare carbonate streaks of the Alam El Bueib Formation (Neocomian-Barremian). Subsequently this formation
1990). In the extreme north western part of Egypt (Fig. 1.8) a dark brown to dark grey shale unit (the Matruh Shale) rests conformably over the Sidi Barrani Formation of late Jurassic age (Hantar, 1990). Aptian rocks were deposited during a transgressive episode that brought the northern Western Desert area under the influence of a shallow sea, where a carbonate unit (made up of light brown dolomite with a few thin shale interbeds), the Alamein Formation, was deposited. The Albian is represented by another regressive phase in which a large part of the Western Desert was occupied by a shallow marine basin that received the fluvial detritus of rivers coming from the eroded elevated massif to the south, resulting in the deposition of fine to coarse-grained sandstones of the Kharita Formation. In the extreme north around the Matruh Basin, carbonates form a dominant part of the sequence (Said, 1990).
Figure 1.8. Composite lithological successions showing variations in different Cretaceous lithostratigraphic units, compiled from reference boreholes for the extreme northern Western Desert section (Mersa Matruh-1 & Siqeifa-1x wells), and for the central northern Western Desert section (Betty-1 & Abu Gharadig-1 wells). (After Said, 1962). See Fig. 2.1 for well locations.
duction Chapter I Intro
In the northern part of the Gulf of Suez area at Abu Darag, the late Jurassic-early Cretaceous uplift resulted in an hiatus in the geological record (Fig. 1.9).
During the Aptian time, sedimentation renewed and alluvial sediments of the Malha Formation (Aptian-Albian) were deposited over rocks ranging in age from the Precambrian to Jurassic (Soliman & Amer, 1972; Garfunkel & Bartov, 1977; Van Houten et al., 1984; Patton et al., 1994).
Figure 1.9. Detailed (Mesozoic-Cenozoic) composite stratigraphic section of the Gulf of Suez (after Darwish & El Araby, 1993; Bosworth & McClay, 2001).
Late Cenomanian time witnessed regional subsidence across the northern African margin related to Neotethyan rifting. By the late Santonian a right lateral movement between Africa and Laurasia (e.g. Meshref, 1990) due to the opening of the North Atlantic resulted in NW-directed compressive forces across the north eastern margin of the African plate. These compressive forces in turn resulted in a series of N-W folds associated with thrust faults, WNW dextral strike-slip faults across the northern Western Desert, and a ENE-WSW fold system across northern Gulf of Suez - the so called the Syrian Arc System (Meshref, 1990; Patton et al., 1994). During the Campanian-Maastrichtian, extension and subsidence dominated northern Eastern African tectonics, for example, the Abu Gharadig Basin in the Western Desert, while local folding and uplifting took place, for example, in the northern Eastern Desert on the western side of the Gulf of Suez at Wadi Araba (Guiraud & Bosworth, 1999; Guiraud et al., 2001).
Upper Cretaceous sediments in the northern Western Desert and the Gulf of Suez region indicate a major transgressive phase. During the late Cenomanian a regional subsidence related to Neotethyan rifting took place across the northern African margin, and a marine transgression covered the entire northern African plate, including the Gulf of Suez. As a result, fluvio-marine deposits of the Bahariya Formation accumulated in the Western Desert (Fig. 1.8). During the Turonian, marine conditions generally persisted across most of the Western Desert, where a thick carbonate succession in the extreme northern Western Desert (e.g. in the Mersa Matruh-1 & the Seqiefa-1 wells) gave way southward (e.g. in the Betty-1 &
the Abu Gharadig-1 wells) to carbonate and shallow marine clastics of the Abu Roash Formation (Said, 1962, 1990). However, the late Turonian Laramide tectonic event caused uplift and basin inversion of the Sidi Barrani Sub-basin, the Qattara Ridge and the Bahariya Arc (Said, 1990). But by Coniacian times most of the northern Western Desert was again covered by another marine transgression,
duction Chapter I Intro
during which another carbonate succession, known as the Khoman “B” Formation was deposited (Said, 1990). During the Santonian yet another regression took place, where continuing carbonate deposition of the lower part of the Khoman “B”
Formation changed southward to marine clastic sedimentation across the Western Desert (Fig. 1.8). During Campanian-Maastrichtian time, most of the Western Desert was again covered by deep marine waters as a result of a major transgressive cycle, resulting in the deposition of a thick sequence of chalky limestone known as the Khoman “A” Formation (Said, 1990).
The Gulf of Suez area also witnessed the Cenomanian transgressive cycle, where shallow marine shale, sandstone and marl of the Raha Formation (Fig. 1.9) was overlain by the Turonian limestones of the Wata Formation (Kerdany & Cherif, 1990; Said, 1990; Guiraud et al., 2001; Bosworth et al., 2005). During the Coniacian-Santonian period regression took place and as a result, the shales and sandstones of the Matulla Formation were deposited (Said, 1990; Guiraud et al., 2001). The major Campanian-Maastrichtian transgressive cycle also resulted in the deposition of thick carbonate successions (Fig. 1.9), comprised of phosphatic cherty limestones and organic-rich brown limestones of the Duwi Formation, and the snow-white chalky limestone of the Sudr Formation, both lying comformably over the Matulla Formation (Said, 1990; Guiraud et al., 2001).