Middle Devonian (Givetian) coral-stromatoporoid reefs in West Sahara (Morocco)

Spectacular table reefs, biostromes and patch reefs occur in two areas (Uein Terguet and Gor Loutad) of West Sahara which are part of a narrow belt along the northern margin of the West African Craton (Reguibat Massif) extending for 1500 km from the Zemmour (Mauritania) in the SW to southern Algeria in the E. Six reef cycles can be distinguished in the Givetian which are separated by shales and sandstones. The first cycle is constituted by stromatactis mud mounds which probably also form the nucleus of the 2nd and 3rd reef cycle. The biota of the 2nd to 6th cycles are dominated by large stromatoporoids, associated with tabulate as well as solitary and colonial rugose corals and a great variety of reef-dwelling organisms. The cyclicity may be either a result of relative eustatic sealevel changes or of oscillating siliciclastic input from the West African Craton shelf margin which has repeatedly interrupted reef growth. Isotopic compositions of early cements in the 1st reef cycle indicate a cooler-water setting of about 40° S compared to coeval tropical low latitude reefs in Euramerica and Australia.