The variscan front and the midi fault between the channel and the meuse river

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Abstract

The ECORS seismic profile allows a new insight into the deep geology of northern France. Various geological data, such as ancient coal mines, surface mapping and boreholes, are used to interpret the seismic profile. A new cross-section, directly superimposed on the ECORS seismic profile (Cambrai-Dreux), is compared with a previous one, drawn along the Meuse River through the Ardenne Massif. The cylindrism and length-balancing hypotheses are discussed by comparing the two cross-sections. The main geological results are: (a) the emplacement of the Dinant Nappe is later than most of its internal deformation; and (b) major folding and thrusting give an approximate 30–35% shortening, without taking into account the internal deformation (minor folding and cleavage) and the unknown net translation vector of the Dinant Nappe (50 km at least, possibly 150 km).

Résumé

Le profil ECORS du Nord de la France permet un regard renouvelé sur la géologie profonde de cette région. Les données géologiques disponibles, anciennes et récentes (exploitation miniére, cartographie de surface, forages d'exploration), permettent de tenter une interprétation géologique du profil sismique. Ceci est fait á l'aide de deux coupes, l'une le long du profil sismique, l'autre le long de la vallée de la Meuse au travers de l'Ardenne. Leur étude comparative conduit á discuter les hypothéses de construction (cylindrisme et équilibrage). Les principaux résultats géologiques sont l'antériorité de la déformation interne de la Nappe de Dinant sur sa mise en place finale, l'étendue vraisemblablement réduite du bassin houiller, vers le Sud sous la Faille du Midi; l'estimation approximative á 30–35% du raccourcissement par plis et failles, compte non tenu de la déformation interne (plis mineurs et schistosité) ni de la fléche de déplacement de la Nappe de Dinant (50 km au moins, 150 km peut-être).

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Professor Raoult died on 8 February 1987.

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