The facies patterns of lower Givetian rocks (Trois-Fontaines, Terres d'Haurs and Mont d'Haurs Formations) at Resteigne quarry (southern border of Dinant Basin, Belgium) reveal a transition from mixed siliciclastic carbonate ramp to gently sloping carbonate platform without any true reefal barrier. Depositional conditions on the ramp were open marine, well circulated, well lit and very near or within wave base. The ramp evolved through a very shallow-subtidal to supratidal, restricted to semi-restricted, quiet stable platform during early Givetian times. A sedimentological model for this succession enables recognition of 12 major microfacies, ranging from open marine, below wave action zone, to reefal complexes, lagoons and supratidal mats. These microfacies define three principal facies belts. Four ecozones belonging to the "Eifeler ökotyp" are recognized in the Givetian of Resteigne quarry. Ecozone 0 is characterized by Leperditicopida in the middle and upper parts of the Trois-Fontaines Formation and indicates a restricted lagoonal environment; three ostracod sub-assemblages can be recorded in term of salinity. Ecozone I is characterized by a few species of Platycopina, Palaeocopina or Eridostraca, each present in large numbers; it indicates an open lagoonal environment in the Terre d'Haurs Formation and, exceptionally, in the middle and upper parts of the Trois-Fontaines Formation. Ecozone II, dominated by large, thick shelled Podocopina, indicates water turbulence at the base of the Trois-Fontaines Formation and in the Mont d'Haurs Formation. Ecozone III is rich in species of Podocopina, Platycopina, Metacopina, Palaeocopina and Eridostraca; it indicates a shallow open marine environment in the Mont d'Haurs Formation and, exceptionally, in the Terres d'Haurs Formation. Water movement and salinity are the principal ecological factors controlling the composition of the basal Givetian ostracod fauna at Resteigne. Their detailed analysis gives more information about the elementary regressive rhythms that produce ...