Late Viséan coral fringing reef at Tiouinine (Morocco): implications for the role of rugose corals as building organisms in the Mississippian

Abstract

The excellent exposure and preservation of a fringing reef located at Tiouinine, near Khenifra (Central Moroccan Meseta) is a unique case in the Mississippian which allows us to distinguish different facies belts of a classical coral framework reef. The reefal facies rest on thin basal siliciclastic rocks which rest unconformably on Ordovician sandstones. There is a complete zonation from tidal deposits of the inner shelf to reefal talus. Tidal deposits occur in a narrow band and are composed of sandy packstones. There is a transition to reef flat deposits composed of skeletal packstone–grainstone with a patchy distribution of coral colonies. There is also a transitional change to core reef facies that are composed of fasciculate and massive corals reinforced by algal masses around the corals and microbial micropeloidal mudstone to wackestone coating the corals and algae. The spaces between the corals and algal masses are infilled by crinoidal and coral grainstone. The dominant building organisms are rugose corals of the genera Siphonodendron, Lithostrotion, Diphyphyllum and Tizraia, as well as contributions from the tabulate genera Michelinia, Multithecopora and Syringopora. The proximal reef talus is represented by skeletal packstone and rudstone containing highly diverse bioclasts, with corals, crinoids, foraminifers, gastropods and bivalves, as well as large fragments of reworked coral colonies and some coral colonies in growth position. These beds show erosive surfaces and amalgamation of beds. A somewhat more distal reef talus is represented by well-bedded marly limestones containing mainly crinoids and branches of fasciculate corals. The existence of a well-preserved coral reef in the late Viséan in Morocco provides further evidence that rugose and tabulate corals did build reefs after the Late Devonian reef extinction event.