The MARCONI-3 profile shows that the western Parentis basin appears as a major half graben bounded southwards by a major N-dipping planar fault (Landes fault). It is filled by a thick sequence of Jurassic-Upper Cretaceous carbonates affected by salt domes and squeezed diapirs. Southwards of the Landes fault, the Landes High acted like a structural high until the Upper Cretaceous. The entire fill of the Parentis basin is overlied by uppermost Cretaceous to lower Miocene synorogenic deposits gently folded upon the diapirs. The features of the basin evidences that the extensional structure resulting from the Bay of Biscay opening played an important role both in the location of the north-Pyrenean front and in the features of the foreland basin. Despite of a thin crust over the Parentis basin, the lack of significant inversion structures denotes that the Landes High acted as an important buffer for the northwards propagation of the Pyrenean contractional deformation. This deformational buffer vanished during the last stages of Pyrenean orogen development when some basement faults reactivated.