The North Pyrenean front and related foreland basin along the Bay of Biscay: constrains from the MARCONI deep seismic reflection survey

Abstract

Profile interpretation of MARCONI seismic profiles show that two domains exist in the Bay of Biscay with a different Pyrenean and north-foreland structure: the eastern, Basque-Parentis and the western, Cantabrian domains. In the eastern one, the North Pyrenean front is located close to the Spanish coast and the northern foreland of the Pyrenees is constituted by a continental crust thinned by Early Cretaceous extensional structures. In the western, Cantabrian domain, the North Pyrenean front is shifted to the north and belongs to a thrust imbricated stack deforming a foreland basin which lies on the top of the Lower Cretaceous oceanic or transitional crust that floors the Bay of Biscay abyssal plain. The coincidence of the transition between these two domains with the eastern border of this abyssal plain denotes that differences along strike of the Pyrenean structure are related to a dramatic change in the nature of the subducted crust from continental to the east, to oceanic or transitional westwards. Thus, the rift system developed between Iberia and Eurasia during the Early Cretaceous appears as a major factor controlling not only the location and features of most of the Pyrenean thrust sheets but also the overall structure of the chain.