Salt Diapirs and Minibasins along a Transect across the Basque-Cantabrian Pyrenees: Implications for Cover-Basement Interaction during Rifting and Inversion.

Abstract

The Basque‐Cantabrian Pyrenees experienced Early Cretaceous rifting and latest Cretaceous toCenozoic inversion, with the presence of prerift Upper Triassic Keuper salt influencing how deformation wasaccommodated. Considerable disagreement exists on the degree of decoupling of supra‐ and subsaltdeformation, the amount of thin‐skinned translation of the cover relative to basement, and the dip polarity of theprimary extensional and contractional lithospheric detachment. To address these issues, we use surface andsubsurface data to evaluate six diapirs and associated minibasins along a transect across the Basque‐CantabrianPyrenees. Key findings include: (a) the Burgalesa Platform and the Alavesa Platform to southern limb of theBilbao Anticlinorium are ramp‐syncline basins, with prekinematic rafts, that record Cretaceous thin‐skinnedextension and translation over north‐dipping basement faults; (b) whereas Bakio and Villasana de Mena hadearly extensional triggers and long‐lived passive diapirism, Poza de la Sal and Salinas de Rosío began as saltanticlines, with the onset of steep passive diapirism in the late Albian and Cenozoic, respectively; (c) althoughSopelana and Montorio were squeezed shut to form vertical welds, Villasana de Mena was not noticeablyshortened; (d) the salt layer was still continuous after extension ceased; (e) the salt served as a ramp‐flat thrustfault during inversion; and (f) although the initiation and evolution of diapirs were influenced by basementfaults, they are not located over those faults today. The deformation to the south of the Bilbao Anticlinorium wasthus decoupled above and below a major north‐dipping salt décollement during both extension and contraction.