Tertiary compressional overprint on Aptian–Albian extensional magnetic fabrics, North-Pyrenean Zone

The Mauléon Basin constitutes part of the North-Pyrenean Mesozoic extensional basins inverted during Pyrenean (Late Cretaceous–Tertiary) orogeny. A structural and magnetic fabric study of the Aptian–Albian black marls of the Mauléon Basin (North-Pyrenean Zone) provides new data indicating that when there is an intense deformation associated with the compressional stage (formation of a pervasive foliation) the magnetic lineation is strongly controlled by the latter tectonic deformation recorded in the basin. However, some areas of the sedimentary basin can still preserve the primary extensional event, depending on its position with respect to basin margin faults and heterogeneous deformation areas. Structural and AMS data define a fabric transition from extensional fabrics indicating an approximate N–S extension in the central (inner) domain of the basin, where compressional deformation was moderate to NE–SW compressional fabrics in boundary domains close to the inverted faults, where compressional deformation was more important (kmax becomes nearly parallel to the main Pyrenean direction NW–SE). Consequently, fabrics in the Mauléon Basin can be interpreted as the result of the overprint of compressional deformation onto a primary extensional fabric, which in turn endures in the central domain of the basin. In spite of its complicated pattern, AMS is revealed useful when considering the long-term history of sedimentary basins undergoing several deformation events.