During the Aptian and Albian thick terrigenous and carbonate successions of sediments up to 5000 m thick, including shallow water rudist limestones (Urgonian facies), were deposited in the Basque– Cantabrian Basin of northern Spain as a result of an intense rift‐related subsidence. Based on criteria from surface and subsurface data, syn‐sedimentary faults, folds, angular unconformities, diapirs and sub‐basins are distinguished within the Urgonian successions. Faults are grouped into N– S, E– W, NW– SE and NE– SW families and most are normal and strike‐slip. Folds are gentle anticlines and synclines related to major faults. The angular unconformities have small hiatuses, poor lateral continuity and they are associated with either folds or tilted blocks. Diapirs are related to the intersection of major basement faults and in at least one instance the diapir was fossilized by Late Albian times. Strong differential subsidence controlled by basement faults determined the division of the basin into many subbasins of different sizes, which acted as depocentres (e.g. Bilbao). Despite the tectonic inversion which affected the basin during the Tertiary and created thrusts in their margins and centre, the present position of the syn‐sedimentary tectonic structures gives approximate clues about the broad structural style and this reveals the original model of basin extension. Features characteristic of strike‐slip identified in different parts of the basin are displaced geological lines, wrench corridors, drag effects, thickness shifts, paired uplifts and basins, vaulting of ‘slabs’, decreasing displacements, horsetail and fault splays, ‘chessboard’, oroflexural bending, pull‐apart geometries, in‐line horst slices, and restraining/releasing bends. Sinistral strike‐slip movements along major NW– SE faults are supposedly responsible for transtension, which characterized the basin particularly during the Albian. In this scenario, the main wrench movements would have concentrated along the Oiz domain (Biscay Tertiary Synclinorium) and is a situation that has more in common with the strike‐slip model proposed by some workers for the western Pyrenees, than with the simple extension models proposed for the northern margin of the Bay of Biscay.

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Backstripping analysis has been carried out on nine outcrop sections of the Basque‐Cantabrian Aptian and Albian of northern Spain which consist of shallow‐water marine deposits up to 7000 m thick. It reveals four main pulses of common accelerated subsidence: I (Early Aptian), II (Early Albian), III (lower Late Albian), and IV (uppermost Late Albian) separated by tectonic quiescent intervals. Tectonic subsidence rates of 70 m Myr–1 for the Aptian and 101 m Myr–1 for the Albian were recorded (Sopuerta section). The calculated stretching factor referred to a pre‐rift continental crust of 35 km is (βs=1.32) and represents approximately 8.5 km of crustal thinning. Points of change towards lesser subsidence rate in the curves are correlated with major unconformities in the sections, in the Basque‐Cantabrian Basin and in Boreal Europe, suggesting geodynamic changes related with the opening of Bay of Biscay. Minor variations of spreading direction and intensity are proposed to explain the subsidence pulses.

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