Abstract Critical gravity and magnetic data suggest the presence of a continuous zigzag exhumed mantle body inside the attenuated crust of the north Iberia continental margin. We propose that this body greatly conditioned the structural domains of the Cantabrian–Pyrenean fold-and-thrust belt during their evolution from hyperextension in Early Cretaceous times to shortening and inversion during the Cenozoic. This may be seen as a new line for cross-section construction and balancing, because previous cross-sections do not incorporate comparable volumes of exhumed mantle. Five structural cross-sections, constrained by the results of 3D gravity inversion, feed our discussion of the complexities of the doubly vergent Pyrenean orogen in view of the inversion of a precursor hyperextended rifted margin. In all sections, crustal rocks underthrust the lithospheric mantle in the hyperextended region, supporting that the near-surface exhumed mantle lithosphere acts as a more rigid buttress, allowing weaker continental material to be expelled outwards and upwards by thrusting during the Alpine collision; thus giving rise to two uplifted crustal triangular zones at the boundaries with the exhumed mantle. Contractional slip is localized in lithospheric-scale thrusts, which in turn reactivate parts of the extensional system. The NE–SW transfer zones that offset the rift therefore behave as compartmental faults during the orogenic phase. The amount of shortening increases from 34 km in the Cantabrian Cordillera, where the Basque–Cantabrian Basin partially preserves its original extensional geometry, to 135 km in the nappe stack of the central Pyrenees.

Abstract: Identification of the best sequence of planktonic foraminiferal events that is reproducible across the Coniacian–Santonian boundary interval is determined by comparison of data from three reference sections: the Cantera de Margas section at Olazagutia in northern Spain (Global Boundary Stratotype Section and Point [GSSP] for the base of the Santonian Stage), the Ten Mile Creek section in southern Texas (candidate GSSP stratotype for the base of the Santonian Stage), and Tanzania Drilling Project (TDP) Site 39 drilled in Tanzania. In the stratotype section, the GSSP is marked by the lowest occurrence of the inoceramid Cladoceramus undulatoplicatus (= Platyceramus undulatoplicatus ), which occurs within the planktonic foraminiferal Dicarinella asymetrica Zone, and by secondary microfossil events and a negative 0.3‰ excursion in δ 13 C. The same bio- and chemostratigraphic records have been identified in the Ten Mile Creek section in Texas. In Tanzania, Globotruncana linneiana , a GSSP secondary planktonic foraminiferal marker event, has been used in the absence of Cl. undulatoplicatus and of correlative chemostratigraphic tie points. The planktonic foraminiferal composition in the three stratigraphic sections is similar, although discrepancies are observed in the reproducibility of some bioevents. Similarities between sections include the same order of appearances of the index species Sigalia carpatica , Costellagerina pilula , and G. linneiana in the Cantera de Margas section and TDP Site 39, and the absence of the single-keeled globotruncanids ( Globotruncanita stuartiformis , Globotruncanita elevata ) in the Cantera de Margas and Ten Mile Creek sections. This apparent diachronism mostly pertains to the paleobiogeographic distributions and ecological preferences of species that developed and diversified under specific paleoenvironmental conditions. Overall, the study of the three sections allows derivation of a more accurate and reproducible sequence of planktonic foraminiferal events across the Coniacian–Santonian boundary interval. It demonstrates the reliability of the surface dweller C. pilula as the best proxy for recognition of the base of the Santonian Stage from epicontinental to open-ocean depositional settings and in a wide range of paleolatitudes.

Abstract The Ayoluengo Field, commonly cited as the only onshore oil field in Spain, was discovered in June 1964 by Amospain, a joint venture of Chevron, Texaco and CAMPSA, by then the state-owned company. Ayoluengo is located about 300 km north of Madrid in the southern part of the Basque–Cantabrian Basin, a geological region where natural oil seeps, tar sands and asphalt have been recognized in outcrops since the early twentieth century. Now, 50 years after the first oil in 1967, the field has a cumulated production of 17 million barrels of oil. The 50-year production concession expired at the end of January 2017 and the field is now closed, awaiting a bidding process for a new concession to be awarded. The Ayoluengo Field consists of a NE–SW-orientated salt-cored anticline, related to Triassic salt movements. The field is divided into two large structural blocks by a normal fault. Oil and gas production comes from a series of thin lenticular fluvio-lacustrine sandstone packages of Late Jurassic–Early Cretaceous age. More than 50 separate oil and gas sandstone beds have been identified by drilling. This multilayer reservoir, together with the structural component, means that Ayoluengo is considered to be a grouping of hundreds of small oil and gas fields. After years of intense exploration activity, the Ayoluengo Field still, surprisingly, remains a unique oil discovery and is the only onshore commercial oil field in Spain and also the only one in the entire Iberian Peninsula. This geological singularity has resulted in recurrent discussions between petroleum geologists because it is difficult to explain why a petroleum system is working uniquely at this particular spot and nowhere else within such a vast territory.