The Basque-Cantabrian basin of northern Spain was formed by Mesozoic extension of the North Atlantic margins and opening of the Bay of Biscay. The preorogenic history of the basin included two phases of rifting (Early Triassic and Late Jurassic-Early Cretaceous), and two periods of relative quiescence and broad regional subsidence (Middle Triassic-Middle Jurassic and Late Cretaceous-early Tertiary).

The Aptian-Albian interval was characterized by an extensional structural pattern of troughs and highs related to major northwest-southeast fault lineaments. This structural pattern was dominated by a major left-lateral strike-slip system that reactivated Early Triassic structures, and can be related to opening of the Bay of Biscay. The southeastward drift of Iberia with respect to Europe occurred along several such strike-slip systems. Rudistid limestones developed on the highs, mostly during the late Aptian to middle Albian, and a flysch trough formed northeast of the basin in the late Albian. Thicknesses of more than 5,000 m were attained and submarine basaltic volcanism occurred in the Albian. The structural pattern of the basin is believed to have controlled the distribution of e onomic petroleum deposits since the Aptian and during the remainder of the Cretaceous.