peer reviewed ; This work details for the first time the sedimentology of Les Monts de Baileux section. This section, located in a quarry between Chimay and Couvin, exposes a remarkable succession of strata from the top of the Jemelle Formation to the base of the Mont d’Haurs Formation. It therefore offers the opportunity to investigate the entire Hanonet, Trois- Fontaines and Terres d’Haurs formations, biostratigraphically from Polygnathus ensensis to P. timorensis conodont zones. This large lithostratigraphic thickness of clayley and argillaceous, and also pure limestones encompasses the Eifelian/ Givetian boundary in the lower part of Hanonet Formation, allowing a better understanding of the transition between the Eifelian which corresponds to a mixed siliciclastic-carbonate detrital ramp and the lower Givetian dominated by a carbonate rimmed shelf-related sedimentation. Petrographic study leads to the definition of 21 microfacies integrated into two palaeogeographical models. The first model (13 microfacies) is proposed for the Jemelle, Hanonet and Trois-Fontaines formations, i.e. P. ensensis Zone and almost entire P. hemiansatus Zone. In this platform model, the fore-reef environment is characterized by a high influence of storm events and carbonate input coming from proximal settings. The reef is mainly composed of an accumulation of stromatoporoids, crinoids, tabulate corals and rugose corals with a peloidal matrix. The back-reef area is dominated by agitated environments and calmer lagoons. Locally, less agitated conditions allow growth of massive and laminar organisms. The second model (6 microfacies) concerns the Terres d’Haurs Formation with the end of P. hemianstus Zone and significant part of the P. timorensis Zone. This ramp model is divided into a mid-ramp characterized by open-marine sedimentation interrupted by storm-related events and an inner ramp composed of ooidal shoals, back-shoal sedimentation and storm related deposits. Two other microfacies are fragmentarily defined for the Mont d’Haurs ...