Deep Seismic Investigation in the Parentis Basin (Southwestern France)

The 300 km ECORS Bay of Biscay deep seis­ mic profile was recorded to provide a better understanding of the development of the offshore part of the Paren­ tis Basin. This basin appears in the seismic profile as a 100 km wide depression. Up to 15 km of Tertiary, Meso­ zoic, and possibly Paleozoic sediments rest on a very at­ tenuated crust overlying a 15 km Moho uplift. After a gentle sagging of the basement in the Triassic-Jurassic, the basin was rifted in the early Cretaceous, essentially along the main Ibis Fault. Tectonic inversions in the early Albian and middle Eocene reactivated the faults and created anticlines and flexural depressions. After a li­ thospheric stretching in the early Cretaceous, further crustal thinning seems to have occurred beneath the ba­ sin through deep-seated processes involving metamorphism, magmatism, and/or delamination in the deep crust. Reflections occurring beneath the present Moho may be interpreted as the trace of a former lower crustal layering or a layered lower crust partly restored beneath the basin. Discrepancy between crustal stretching and at­ tenuation and indications of crust-mantle interaction have also been found in deep seismic profiles shot across Fig. 1Location map: main structural features in France and adjacent areas and location of deep seismic profilesFig. 2Bay of Biscay deep seismic survey. 1 Armorican shelf; 2 Parentis Basin boundary; 3 Landes High; 4 Pyrénées belt; 5 oil exploration well; 6 deep seismic profile; heavy line reflection recording; R1–R6 Expanding Spread Profiles; 7 Expanding Spread Profile mid-point; 8 water depth other basins. The formation and evolution of sedimentary basins may often have resulted from a combination of several geodynamic processes e.g., lithospheric stretching, active mantle upwelling, and flexural sagging of the basement.