The geology of Mauritania is built on more than two billion year old Archean crystalline basement rock in the Reguibat Shield of the West African Craton, a section of ancient and stable continental crust.
In the last 251 million years, Mauritania has accumulated additional sedimentary rocks during periods of marine transgression and sea level retreat.
The arid country is 50% covered in sand dunes and has extensive mineral resources, although iron plays the most important role in the economy.
The oldest rocks in Mauritania date to the Archean, over two billion years old in the Reguibat Shield of the West African Craton.
The extremely old crystalline basement rock of the shield is almost entirely Neoarchean age and metamorphosed to hornblende or granulite grade in the metamorphic facies sequence.
They show signs of multiple phases of deformation and intrusion by tectonic and post-tectonic granites, dated at 2.05 billion years, lining up with the Eburnean orogeny.
Geologists have found pebbles within microsyenites and microgranites, in a folded conglomerate, that form part of a metasedimentary unit, which may be the remnants of even older Archean rocks.
[2] Mauritania is part of the Senegal Basin and its Mesozoic sedimentary sequence begins with Late Jurassic dolomite formed in a shallow marine environment.