The Republic of Yemen is covered by rocks ranging in age from Precambrian to quaternary.
The Precambrian basement rocks in Yemen comprise metavolcanic, metasedimentary, gne iss and migmatite belts produced in arc environments intruded by post tectonic granites and granodiorites. These are found throughout western Yemen from the northwest (Sa´dah - Al Jawf) and southwest areas (Marib-Al-Bayda), in addition to small outcrops in south of Taiz and west of Mukalla. The oldest known rocks in Yemen occur in the Al Bayda terrane which contains late Archaean aged (Sm-Nd: 2700-2900 Ma) gneisses, amphibolite dykes and granites
These comprise the following:
o Ghabar Group (Infra-Cambrian-Earliest Paleozoic):Sandstone, limestone, silt, gypsum.
o Qinab Group (Infra Cambrian-Lowest Cambrian): Volcano-sedimentary succession consisting of dolerite, sandstone, silty shale and tuff.
o Wajid Formation (Cambrian - Carboniferous): Quartz sandstone.
o Akbarah formation (Late Carboniferous-Permian): Tillite (pebbles & boulders of basement rocks), shales, mudstones, sandstones and siltstones.
o Kuhlan Formation (Lower-Middle Jurassic): Sandstones, thin claystone and siltstone interbeds.
o Amran Group (Middle Jurassic-Lower Cretaceous): Carbonate marl/shale with evaporitic succession.
o Tawilah Group (Cretaceous): Sandstone with siltstone, marl, and shale, often interbedded with sandstone and also forming distinct marl or shale intervals and with generally persistent limestone-marl clasts.
o Mahra Group (Cretaceous): Limestone, marl, and shale, often interbedded with sandstone.
oHadramawt Group (Paleocene-Middle Eocene): Dolomite, shale, limestone with chalk and dolomite, marl, papery shale, bedded gypsum, and alternating sand stone and claystone.
o Majzir Formation (Paleocene-Lower Eocene): A shallow marine-littoral sandstone succession.
oShihr Group (Oligocene-Pliocene): Conglomerate, sandstone, silt, lime tone and gypsumŇ
o Tihamah Group (Middle-Upper Miocene): Sandstone, conglomerate, gypsum, rock salt, shell, mudstone and limestone.
Volcanic and Intrusive Rocks
The was a time of Regional uplift occurred in western Yemen in the Paleocene/Eocene as evidenced by intermittent volcanic activity commencing in the Early Eocene which culminated in Oligocene-Miocene times with extensive extrusive and plateau flood basalt eruptions forming the Yemen Volcanic Group. This comprises an older "trap" series and younger Volcanic Series.
These series include the whole spectrum of basaltic lithologies to silicic ignimbrites and tuffs. Sedimentary units, generally occurring as lenses of limited extent and thickness, occur in many parts of the volcanic sequence between flows (Geukens, 1960, 1966). These are generally composed of lacustrine deposits consisting of calcareous sandstone, mudstone and reworked volcanic clasts. Also observed in inter-trap sedimentary units are fluvio-aeolian sands and palaeo-soils, generally lateritic, often developing along plane surfaces but at times locally cutting across different beds.
The Yemen Volcanic Group is intruded by granitoid rocks along much of the edge of the High Plateau of Yemen, which forms the great eastern escarpment of the Red Sea. Intrusions also occur in the Sana´a and Taiz districts.