Geography

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	The morphology and present shape of the Shield are mainly the result of relatively recent geologic events linked to the opening of the Red Sea. Cretaceous rifting in the Red Sea led to doming of the Shield area, which uncovered the deep-seated axes of the Nabitah arcs with their dominantly intrusive ridges (Gurayyah-Ranyah, Afif-Miskah, Ha'il). The rifting caused coastel subsidence and the creation of thick laggoonal evaporite deposits during the Late Cretaceous and Tertiary . Alkaline olivine basalt extruded as the result of crustal thinning, creating the enormous lava flows of the tertiary harrats. These eruptions continued until the historic period. Duricrust silcrete and calcrete are found as remains on the Tertiary paleosurface and paleosols exist beneath the recent basalt, witnessing of a humid paleo-climate. At the end of the Tertiary and during the Quaternary, the climatic evolution saw an increasing aridification that caused the great sand sheets with a few periods that were more humid during the interglacial periods.
A Digital Elevation Model of the Shield and Peninsula