La couverture sédimentaire du bassin Parisien le long du profil ECORS-Nord de la France The Sedimentary Cover of the Paris Basin from the Ecors-Nord de la France Seismic Profile

Abstract

Le profil ECORS-Nord de la France, implanté sur la bordure nord-ouest du bassin Parisien, ne traverse pas celui-ci dans sa région de subsidence maximale. Il apporte néanmoins une vision générale d'un transect et permet de préciser l'histoire du Bassin. Nous retiendrons, parmi les éléments les plus intéressants : - la présence possible de petits bassins stéphaniens ou permiens dans la région de Banthelu et Marville; - la structuration jurassique à éocène le long des grands accidents que sont les failles de la Seine, du Bray et de la Somme; - l'histoire de la subsidence de la bordure nord-ouest du Bassin. The Nord de la Francedeep seismic profile has been shot on the northwestern edge of the Paris Basin, about 100 km away from its main subsiding center. It is, however, the first regional line crossing the basin and some details of its geological history have been emphasized: (a) Stephanian or Permian basins with restricted sizes have been encountered below the Mesozoic cover along some parts of the line. Their location has been made possible by the simultaneous use of seismic refraction and reflection data. (b) 3 major faults have been crossed: the Seine, Bray and Somme faults. All of them had normal displacements in Jurassic and Lower Cretaceous times. This is clearly observed today through differences in sedimentary thicknesses on both sides of the faults. The Seine and Bray faults were reactivated as transcurrent and/or reverse faults in Eocene time during the north-south oriented Pyreneanshortening. This tectonic event has led to slight inversions of the basin between these 2 faults. (c) The subsidence history of the basin has been computed along the seismic line. The total tectonic subsidence was very small in Mesozoic times (500-400 m). A slight increase in subsidence in the Upper Jurassic is correlated with the Cimmerian rifting which is well known in the North Sea.