The role of the Bay of Biscai Mesozoic extensional estructure in the configuration of the Pyrenean orogen: Constraints from the MARCONI deep seismic reflection survey

Abstract

Seismic interpretation of the MARCONI deepseismic survey enables recognition of the upper crustalstructure of the eastern part of the Bay of Biscay andthe main features of its Alpine geodynamic evolution.The new data denotes that two domains with differentPyrenean and north foreland structures exist in the Bayof Biscay. In the eastern or Basque‐Parentis Domain,the North Pyrenean front is located close to the Spanishcoast, and the northern foreland of the Pyrenees is con-stituted by a continental crust thinned by a north dip-ping fault that induced the formation of the EarlyCretaceous Parentis Basin. In the western or Cantab-rian Domain, the North Pyrenean front is shifted tothe north and deforms a narrower and deeper forelandbasin which lies on the top of a transitional crustformed from the exhumation of lithospheric mantlealong a south dipping extensional low‐angle faultduring the Early Cretaceous. The transition betweenthese two domains corresponds to a soft transfer zonelinking the shifted North Pyrenean fronts and a north‐to WNW‐directed thrust that places the continentalcrust of the Landes Plateau over the transitional crustof the Bay of Biscay abyssal plain. Comparisonbetween this structure and regional data enables char-acterization of the extensional rift system developedbetween Iberia and Eurasia during the Late Jurassicand Cretaceous and recognizes that this rift systemcontrolled not only the location and features of thePyrenean thrust sheets but also the overall structureof this orogen