During Givetian times, the Jebel Rheris area was situated in a transitional zone at the northern margin of Gondwana, between the emerged Ougnate High in the north and the Mader Basin in the south. A facies pattern developed from stacked or amalgamated coral-stromatoporoid biostromes in the northern near-shore area to an alternating biostrome–crinoidal grainstone succession, which passed over a low angle slope setting towards the south to a pure crinoidal grainstone facies with abundant slumping structures. Finally in the south, a basinal turbiditic facies evolved. In the shallow sea, biostromes probably developed due to the lack of a ‘binder guild’ in the fossil community, which hampered the establishment of mound-like structures, stable enough to resist high-energy storm events. Repeated termination of the coral-stromatoporoid growth is attributed to transgressions. During suitable conditions, colonisation of the sea floor proceeded in three phases: a) cluster settlement; pioneer communities, mostly consisting of tabulate corals and domical to bulbous stromatoporoids, started growing in laterally delimited clusters; b) lateral dispersion; from these centres, settlement prograded laterally, until large areas of the sea-floor were covered; c) vertical accretion; the organisms more and more grew on each other, causing a homogeneous vertical expansion. A significant difference of this up to 200 m thick biostrome—crinoidal grainstone succession compared to continuously growing reefs is the fact that communities repeatedly had to start with the colonisation stage, thus could not reach a mature or climax stage.