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Sohag Basin (Upper Egypt)
Geological setting and stratigraphy
The name of Sohag Basin refers to a Neogene phase that is developed during the Nile evolution in which diferent intermontane basins were created in the Upper Egypt (Philobbos et al. 2015). The Sohag Basin is formed and evolved as a NW–SE-trending local graben that is approximately 30 km wide and 75 km long. Sohag Basin in is bounded mainly by the Early Eocene sequence which is classifed into two formations (Thebes and Drunka formations, Said 1990). Thebes Formation forms mainly the foot of the bounding scarps and is characterized by thinly bedded and laminated limestones with chert bands. Whereas, Drunka Formation conformably overlies Thebes Formation and is diferentiated by its snow white massive-bedded limestones. Sohag Basin shows two main sedimentary stages during its evolution (Mahran and Hassan 2019). The older stage is dominated by fuvial sediments lasting from Late Miocene to Pliocene age, while the younger one is composed of mixed fuvial and lacustrine carbonates of Pleistocene age. The post-Eocene rock units of Sohag Basin can be summarized in the followings (Figs. 1 and 2)v/o
Fig. 1 Geological map of Sohag Basin, Upper Egypt (after Mahran et al. 2013; Abu Seif 2015b).
Fig. 2 SW-NE cross section showing the main stratigraphic rock units in Sohag Basin, Upper Egypt (based on Said 1960, 1971, 1981, 1983; Mahran et al., 2013; Abu Seif 2015b).
Katkut Formation
In Sohag Basin, Katkut Formation is unconformably overlying the Early Eocene sequence and consisting mainly of gravel sequence. Katkut Gravels are flling the NW grabens of Early Eocene sequence. Katkut Formation is avoiding of fauna content and basement pebbles. Thus, based on its feld relations and mineral content, Katkut Formation is assigned to Late Oligocene age (Issawi et al. 1999; Issawi 2005; Mahran et al. 2013; Abu Seif 2015b). Katkut Gravels were derived from Lower Eocene sequence as a result of karstifcation processes (Mahran and Hassan 2019).
Abu Retag Formation
Abu Retag Formation forms the lower part of the basinfll succession, and represents the initial fuvial sedimentation stage of the Sohag basin flling (Mahran et al. 2013). It unconformably overlies the Lower Eocene sequence tilted blocks. It belongs to the Late Miocene age and attains up to 50 m thickness. Abu Retag Formation is composed of gravels and gravelly sands enriched with basement pebbles (Said 1983; Mahran et al. 2013; Abu Seif 2015b).
Madmoud Formation
Madmoud Formation (Pliocene, Said 1975, 1981) represents the Paleonile stage which began with the transgression of the Mediterranean Sea and flling the Nile canyon. It is mainly composed of chocolate brown claystone intercalated with siltstones and fne sandstones near its upper part.
Armant Formation
Armant Formation (Said 1975, 1981) consists of mixed clastic–carbonate sequence (10 m–30 m thick). Clastics of Armant Formation are started by cross-bedded sandstones followed upwards by massive reddish brown and grayish mudstones. Its carbonates are characterized by meter-scale lacustrine–palustrine and tufa cycles, in which the pedogenic modifcation increases upward.
Issawia Formation
Issawia Formation (Said 1981) is represented by wellcemented red breccias that crop out along the eastern and western margins of the basin (up to 10 m thick). Issawia Formation unconformably overlies the clastic part of Armant Formation and is stratigraphically equivalent with carbonate part of Armant Formation (Mahran and El-Haddad 1992). In some places, Issawia Formation unconformably overlies Madmoud Formation.
Qena Formation
The Middle Pleistocene Qena Formation (Said 1981) exhibits low topographic hills with rounded surfaces and low scarps extending in NW–SE direction close to the cultivated land. The sequence of Qena Formation is started at the base with cycles of cross-bedded coarse-grained sandstones, followed upwards by even to cross-laminated fne sandstones and siltstones (up to 30 m thick).
Abbassia Formation
Abbassia Formation (Said 1975, 1981) is represented by 10 m thick and unconformably overlies and and cut-through the Qena and Armant formations. It easily distinguished in the feld by its yellowish gray to grayish white color. It is reaching maximum thickness in the areas which face the major wadis draining the Eocene plateaus. Abbassia Formation consists of yellowish white well-rounded sandy gravel sequence that is derived mainly from Lower Eocene limestone.
Dandara Formation
Dandara Formation (Said 1975, 1981) is generally closer to the cultivated land and is represented by sand and silt intercalations along the eastern bank of the Nile. A thickest section of Dandara Formation occurred in the eastern margin of Sohag Basin, where it starts by 4 m massive siltstone and fne grained sandstone and is graded upward into gypsiferous claystone with lenticles of hard sandstone (3 m thick). This section is topped by 5-m-thick gray and even laminated claystone enriched with nodular to thin laminar calcrete crusts (El-Haddad 2014).
Holocene Sequence
The Holocene sequence in the study area can be subdivided into the following three units; Flood Plain Deposits are well developed along two banks of the modern Nile River and are consisting mainly of silts, clays and fne sands with thickness varying from 2 to 10 m. Sand Dunes and shadows are representing an intensive geo-hazard owing their environmental harmful impacts that lead to desertifcation (Abu Seif and El-Khashab 2019). Wadi Deposits are accumulated by temporary streams that derived reworked materials from the pre-existing sediments.
Data source: Geotechnical study on the utilization of Pleistocene Sands in Sohag Basin (Upper Egypt) as a construction raw material. A. Abdel‑Hamed El‑Shater, T. M. Mahran,· El‑Sayed Sedek Abu Seif, Khaleed Mahmoud. 2020
Следующий Бассейн: Rukwa Rift