Abstract

Early in Couvinian time, a notable change took place in the sedimentary regime of southern Belgium. Reefs developed for the first time and they, together with argillaceous limestones and shales, continued to develop periodically until Frasnian time. Rugose corals are abundant in this Couvinian-Frasnian sequence and occur both in the argillaceous limestones and shales.

It has been found that the distribution of the corals is controlled by the sedimentary facies, and that external and internal characters of the corals such as shape, form of the calyx, septa, septal cones and dissepiments, were strongly influenced by environmental conditions. In the light of these findings, several described species have been interpreted merely as varieties. In considering the stratigraphical ranges of the corals, it is to be noted that the first appearances of many species in the Belgian sequence is not to be correlated with their first appearance in time but rather with the initial establishment of suitable environmental conditions in the region in which they were found.