The vertical succession of the sedimentary formations, which are diachronic with respect to the standard conodont and other microfossils zonation, represents a regressive megasequence in the Belgian Famennian, ranging from relatively deep, offshore open marine, shallow nearshore, to backshore restricted marine environments (THOREZ et al ., 1977). Different associations of platform conodont form genera (Biofacies) reflect different ecological conditions, which are directly or indirectly related to water depth, turbulency, salinity and proximity to the coast ; from offshore to backshore we recognized successively a Palmatolepid, a Palmatolepid-Polygnathid, a Polygnathid-Icriodid, an Icriodid, and a supposed Clydagnathid biofacies. In this way the distribution pattern of conodont biofacies throughout the Famennian, represents a normal response to the oscillating movements of a prograding "coast" in the studied sedimentary basins. The presence moreover of mixed conodont biofacies (or thanatocoenoses) is also related to sedimentological processes, such as storm wave action, turbidity currents and tidal inlets.