Dinantian lithostratigraphic units (Belgium)

Abstract

Six paleogeographic sedimentation areas (s. a.) are recognized in the Namur-Dinant Basin: (1) the Hainaut s. a., (2) the Namur s. a., (3) the Condroz s. a., (4) the Dinant s. a., (5) the Visé-Maastricht s. a., and (6) the southern Avesnois s. a. (only in northern France). Together with the sea-level variations (third-order sequences), local controls influenced the nature of the sedimentary deposits, so the lithostratigraphic successions in each sedimentation area are distinctive. The depositional setting was that of a carbonate platform which evolved from a ramp in the early Tournaisian to a rimmed shelf during the early Viséan and then to a regionally extensive shelf during the middle and late Viséan. Before the Livian, open marine fades were developed to the south, but from the Livian onwards open marine facies were restricted to the north while evaporites developed in the south. This inversion of the normal pattern was probably related to an early phase of Variscan shortening. Dinantian biostratigraphy is mainly based upon foraminifera, rugose corals and conodonts. Fifty formations (including members), 3 groups and 2 informal lithostratigraphic units are briefly described.