During the Cretaceous, the North Pyrenees of southern France suffered complex deformation. The relatively deep marine North Pyrenean Basin formed, a narrow band of rock adjacent to the North Pyrenean fault was metamorphosed, Iherzolite was emplaced, and the Bay of Biscay opened. Compression during the Late Cretaceous and Tertiary Pyrenean orogeny overprinted and partially masked this earlier history.
In order to better understand the regional tectonics off the Cretaceous northern Pyrenees and, specifically, the early history of the North Pyrenean Basin, we compiled and then palinspastically restored a geologic map of the western North Pyrenees. Lithofacies, paleotransport, and isopach maps for the early deposits of the basin, and a pre-Albian palinspastic subcrop map show that the basin was an east-west-elongate, fault-bounded trough at least 300 km long and from 40 to 60 km wide, containing a siliciclastic composite sedimentary package as much as 4,700 m thick.
Detailed structural and stratigraphic studies of the Massif d'Igountze-Mendibelza, which is located along the southern limit of the North Pyrenean Basin in the western Pyrenees, suggest that its Cretaceous cover was deposited against an active, relatively low-angle listric normal fault. This fault is on strike with the North Pyrenean fault zone, a major long-lived zone of deformation in the central and eastern North Pyrenees.