Ridge-Depression Landscape Along the Mediterranean NW Coast of the Western Desert

Abstract

The carbonate ridges distinguish the NW coast of Egypt, since they are not repeated elsewhere in Egypt. These ridges form together with the low-lying areas, separating them from each other, a local landscape system called “The Ridge-Depression System.” This system roughly extends parallel to the coastline of the Mediterranean from Alexandria in the east to Sallum city in the extreme west. It is composed of a sequence of low-relief ridges, but with local variations in their number. The height of the ridges varies between 10 and 25 m a.s.l. for the first coastal ridge and 110 m a.s.l. for the inland eighth ridge. The width of the ridges ranges between ~100 and ~10,000 m. Some ridges were found submerged in the Arab Gulf and Maryut Lake or buried by Nile sediments in NW the Nile Delta. A calcareous layer of soils covers Depressions that separate the ridges. These soils are mainly derived from the adjacent ridges. In the first and second Depressions, sabkhas and coastal lagoons were developed either due to connection with the Mediterranean, such as Matruh and Alamain lagoons, or due to seepage of seawater. The ridges are polygenetic, and their age ranges between 0.6–4.3 ka for the first coastal ridge, and 900–950 ka for ridges No. 5–8.