A very extensively exposed biostromal unit hosting a very diverse reefal assemblage.

One of the best preserved reefal palaeoecosystems of this area is found in the Givetian of Mad`ene el Mrakib (Anti-Atlas, Morocco), exposing a vast, at least ~1.2 km2 area of reef strata.

A surprising feature of this assemblage is the rather subordinate role of stromatoporoids, generally regarded as a main component of the shallow-water Devonian reefs.
Pachyporids and alveolitids dominating, branching forms dominating

The ecological succession is characterised by an upsection increase in the abundance and diversity of the reefbuilding biota, accompanied by a shift in the dominant morphotypes of tabulate corals from platy (pioneering and diversification stages) to branching and massive forms (climax stage).