SUR LES DIFFICULTÉS D'INTERPRÉTATION DES HIATUS STRATIGRAPHIQUES (EXEMPLE TIRÉ DE LA TRANSITION DÉVONO-CARBONIFÈRE, BASSIN DE DINANT)
Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement, CP160/02, 50 av FD Roosevelt, B-1050, Bruxelles
Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement, CP160/02, 50 av FD Roosevelt, B-1050, Bruxelles
Abstract
ABSTRACT. On the difficulties of stratigraphic hiatus interpretation (an example derived from the Devono-Carboniferous transition, Dinant basin). Carbonate sequences crossing the Devonian-Carboniferous boundary are well exposed in the Bocahut quarry (Avesnes-sur-Helpe). This is geologically important as these successions are, at the time being, poorly exposed in the Avesnois region. Microfacies analysis enables recognition of 10 local levels ranging through the Epinette, Etroeungt, Avesnelles and Hastière formations. The 'bathymetric' sequences (eustatism, subsidence, salinity) range from open marine spiculite, below the storm wave base to semi-restricted lagoon. Nearby and in the same basin, similar facies are observed at Anseremme. If correlations for same sequences are easy on sedimentological and microfaunal arguments, other sequences 'disappear' completely, indicating undetected hiatuses. The time intervals involved and an estimation of the chronostratigraphie value is difficult and depends on the sedimentological model used. But half of the geological time is apparently missing at Anseremme. In the Avesnois, the variability of the sequences does not match a continuous highstand hypothesis. Even in the same basin and for small distances, correlations remain difficult and cannot be oversimplified by hypothetical highstand successions.