This study works out the sedimentation of upper paleozoic formations of Belgium and northern France.It deals with sequential analysis of calcareous facies, more particularily, the so-called « black marbles »; it is possible to recognize a number of « rythmic patterns » which can be followed laterally from quarry to quarry. These « rhythms » have chronostratigraphic value; coupled with local markers, they enable the building of an extremely precise paleogeography.The petrographic investigation of the strata of « black marbles » leads to a more general classification of limestones in which the type of cement and the proportions of the different calcareous debris (allochems) arc the main variables.Ecologie studies on the relative distribution of macro- and niicrofauna show the faunal assemblage to be dominated by biocenic influences. « Black marbles » are neither characteristically rich in plankton, nor deposited in sulfuric environments; they are characterized by the thinness and uniformity of the calcite grains and by a reducing Eh at the sedimentation time.