Arabian-Nubian Shield - Red Sea Rifting and Exposure of The Arabian-Nubian Shield

Red Sea Rifting and Exposure of The Arabian-Nubian Shield

The Arabian-Nubian Shield is representative of the continental crust that underlies NE Africa, SW Asia, and Arabia. Geophysical studies inform us that ANS crust is about 40–45 km thick, typical for continental crust elsewhere. Geologists are interested to study this crust because it provides an outstanding opportunity to learn how continental crust forms. Elsewhere in Arabia and NE Africa the crust is buried beneath kilometers of younger, Phanerozoic sediments and can only be reached by scientific drilling.

Glaciers scoured this land during one of the Neoproterozoic Snowball earth episodes (~630 Ma) and the remarkable Arabian-Nubian peneplain is overlain by the greatest sand sheet on Earth, the Cambro-Ordovician Siq/Saq sands. This is exposed in spectacular cliffs like the site of Petra in Jordan. The Arabian sandstones are overlain by thick deposits of younger sediments that dip and thicken eastwards into the Persian Gulf. These sands are missing in most of Egypt and Sudan, instead the ANS is overlain by the late Mesozoic Nubian sandstones. All of these sediments were peeled off by erosion to expose the ANS, and much of this sand was reworked by desert winds to make great sand dunes in western Egypt and the Ar Rub al Khali (Empty Quarter) of Arabia.

The embryonic ocean called the Red Sea has slowly widened by rifting over the past 25 million years. Rifting typically causes uplift of its margins, or 'rift shoulders', and the covering sediments were removed by erosion as the Red Sea widened, allowing us to examine the basement geology of this region. This examination is favored also by the desert climate of the region - there is no soil, little vegetation, and few cities or roads to obscure the geology.