Mesozoic rifting in the Basque-Cantabrian Basin (Spain): Inherited faults, transversal structures and stress perturbation

In the BasqueCantabrian Basin (Northern Iberian Margin), inherited WNWESE-striking faults were reactivated during the Mesozoic extensional stage associated with the opening of the Bay of Biscay. Syn-rift structures in the area include different sets, apparently indicating multiple extensional stages. In particular, abundant NESW-striking extensional elements have been interpreted in the past as having developed during a late rifting, left-lateral transtensional stage. However, the development of these structures also fits well with an analytical model of ridge-perpendicular extension. Along-strike stretching imposed by displacement variations along inherited faults locally produced an additional stress field oriented obliquely to the regional one. This caused rotation of the local minimum stress and development of anomalously oriented transversal structures. A single extensional stage is thus inferred during Mesozoic rifting, with a stretching direction oriented approximately perpendicular to the trend of the Bay of Biscay oceanic ridge.