The depocenter of the Paleozoic basin in western Egypt lies in the northwestern part of the Western Desert. The sediments are primarily terrigenous (with two minor phases of vulcanicity) laid down in an epicontinental sea. The depositional axis of the basin, where thicknesses in excess of 2,800 m (9,200 ft) have been recorded, has a northwesterly trend to the vicinity of the Siwa Oasis. A less well-defined shallower basin with a northerly trend lies to the southwest. The facies show such similarities to those found in the Ghadames and Murzuq basins that the same formational names are applied. Farther east, a possible Paleozoic basin lies in the Abu Gharadig area where 1,300 m (4,265 ft) of sediments were drilled. The limits of this presumed basin are questionable since ba ement was not reached.

Following the deposition of the Paleozoic section, there was a marked hiatus; the time of Hercynian movements for Permian and Triassic beds is absent. Uplift and the presence of volcanics dated in Permian-Carboniferous time are indicative of Hercynian tectonic activity. Only in Early Jurassic time did the seas again begin to encroach upon the Western Desert area from the Salum basin in the northwest and the Wadi Natrun basin to the east and northeast. This process continued, until by the time of the Oxfordian transgression maximum there was a relatively uniform carbonate cover to about lat. 29°N over the Western Desert.

Further tectonic uplift accompanied by faulting and marine regression is dated from late Kimmeridgian time to the beginning of the Cretaceous, when transgression began once again. The pattern of transgression, however, differs from that of the Jurassic; the two basins, the more westerly Matru basin and the easterly Alamein basin, both have north-northeasterly trends, although by Aptian times they are less clearly distinguishable.

The dominant feature, new in the Western Desert, was the development of an east-west extensional basin, the Abu Gharadig basin, in Cretaceous time. It was bounded on the north (30°N) by the Rabat Abu Rivash ridge, which persisted through the Cretaceous. The trough became less distinctive in Cenozoic times when a further trough, the Tiba basin, developed north of the ridge.

Production from the northern Western Desert until recently has been disappointing. Exploration results from the Paleozoic Section have yielded little, but the existence of a marine section suggests that the area northeast of Siwa still has potential. The thick deeply buried Jurassic marine sequence in the Western Desert may be the source for at least part of the production from Cretaceous horizons in the Abu Ghradig, Alamein, and Razzak oil and gas fields.

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