Nubian Sandstone

Nubian Sandstone refers to a variety of sedimentary rocks deposited on the Precambrian Basement in the eastern Sahara, north-east Africa and Arabia. It consist of continental sandstones with thin beds of marine limestones, and marls. Nubian sandstone was deposited between the Lower Paleozoic and Upper Cretaceous, with marine beds dating from the Carboniferous to Lower Cretaceous.

Nubian sandstone ranges in age from the Cambrian to Upper Cretaceous eras. Positioning of the paleoequator and paleolatitude at 20° S was derived from paleomagnetic data showing Nubian sandstone was originally deposited in the paleoequatorial to subequatorial zone. These paleomagnetic results corroborated previous studies suggesting there was no polar wandering and continental drift in Africa during 210 to 110 million years and extended this period to 85 million years. Nubian sandstone is deposited under a tropical to subtropical climate and is formed under a variety of continental conditions, excluding eolian merging intermittently into shallow marine.

The Nubian sandstone complex has a thickness varying from under 500 m to over 3000 m, resting on the Precambrian basement. This is complicated by various structural faults and fold axes traversing the region in a north-eastern direction. Maximum development occurs in the Ain Dalla basin, a downthrown structural block south-west of the Bahariya oasis. Basement features present a dominant control on the complex's structural and sedimentological form. Despite many structural complications, Nubian sandstone likely constitutes a single hydrogeological system west of the Suez Gulf. To the east, on the Sinai peninsula, a second system might exist with some connection to the primary western system in the north. The main western system, extending into Libya and Sudan, consists of a multi-layered artesian basin where massive groundwater reserves accumulated, principally during pluvials of the Quaternary. Locally, carbonate rocks overlying the complex display karst features and are recharged by upwards leaks from the underlying major aquifer.Fluvial and structural interpretations from 2007 show the desert in western Egypt was induced by fluvial action, including recently mapped alluvial fans. In central areas, braided channels are spatially aligned to a north-east structural trend, suggesting preferential water flow paths. Alluvial fans and structurally enclosed channels coincided to gentle slopes and optimal recharge conditions between 1 and 5%, indicating high groundwater potential. Synthetic Aperture Radar (SAR) interpretations correlated with anomalies from groundwater in 383 wells, suggesting a connection between the spatial organization of fluvial and structural features with low-salinity groundwater, which exists adjacent to alluvial fans and the south-west reaches of structurally enclosed channels. Wells in the vicinity of structures contained low-salinity water.

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