Résumé : The sedimentology and palaeontology of carbonate beds in the lower part of the Fosses Formation (Ashgill of the Condroz area, central Belgium) have been investigated. Two depositional interpretations are suggested: deposition either near a platform-ramp margin as bioclastic turbidites and interbedded shales or on a shelf as a transgressive sequence following a regressive event. Faunal affinities with the Baltic area and Wales are confirmed, and the location of Belgium in the tropics during the Ashgill is supported by the calcareous algae and the coral fauna. © 1993, Cambridge University Press. All rights reserved.