In this work we establish reliable correlations between density and magnetic susceptibility in three paramagnetic granites from the Pyrenees. In total, 128 sites (310 density measurements and >2600 susceptibility ones) were studied in the Mont Louis-Andorra, Maladeta and Marimanha granitic plutons covering the main range of variability of magnetic susceptibility. Regressions were calculated for every granitic body and an integrated linear function was obtained for the entire dataset: ρ (kg/m3) = 2566 (kg/m3) + 0.541κ (10−6 S.I.) (R:0.97). This relationship is only valid in the paramagnetic domain, where iron is mostly fractioned in iron-bearing phyllosilicates and the occurrence of magnetite is negligible (or at least its contribution to the bulk susceptibility). This relationship, likely different in other bodies, allows for transforming magnetic susceptibility data into density data, helping to constrain gravity modelling when density data from rock samples are scarce. Given the large amount of AMS studies worldwide, together with the quickness and cost-effectiveness of susceptibility measurements with portable devices, this methodology allows for densifying and homogenizing the petrophysical data when modelling granite rock volumes based on both magnetic and gravimetric signals., This work was financed by the projects GeoPiri3D (CGL2017-84901-C2-2-P), UKRIA4D (PID2019-104693GB-I00/CTA) and IMAGYN (PID2020-114273GB-C22) from the Spanish Ministry of Science (funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”). This work is methodologically related also with the 3DGeoEU project financed by the European Commission under the ERANET Cofound action GeoERA (Grant No.: 731166). The GeoAp Research group from the Aragonian Government is also acknowledged. We are also in debt to the staff of the Petrophysical Laboratory (IGME, Tres Cantos) and to the Geophysics technicians (José Mª Llorente and Agustín González). The help of the Rock Magnetism Laboratory of the Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement (CEREGE) in Aix en ProvenceMarseille is also acknowledged. P.C. acknowledges funding from PTA2017-14779-I and FJC2019- 041058-I (AEI-Spain) contracts. E.B. thanks the Geomodels Research Institute of the University of Barcelona and GGAC-2017SGR596 (Generalitat de Catalunya)., Peer reviewed

16 Figuras, 29 Páginas, [EN] Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The important difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Pico del Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust., This work was financed by the Sobrarbe County Research fellow-UNESCO Global Geopark (ARP) and by some projects ESS from the Spanish Science National Plan (UKRIA4D-PID2019-104693GB-I00/CTA, DR3AM. CGL2014 54118-C2-2-R and MAGIBER-II. CGL2017-90632-REDT), Peer reviewed

25 Páginas, 15 Figuras, [EN] An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12., AB fieldwork has been supported by the project PGC2018-093903-C1, additional support came from the projects DR3AM (CGL2014-54118-C2-2-R) MAGIBER-II (CGL2017-90632-REDT) and UKRIA4D (PID2019-104693GB-I00/CTA) all of them from the Spanish Science National Plan. The study of calcareous nannofossils was supported by the Research Group of the Basque University System IT-930-16., Peer reviewed

We have carried out a detailed paleomagnetic study of volcanic rocks (18 sites) and red beds (10 sites) from the Late-Carboniferous-Permian series of the Cadí Basin (Eastern Pyrenees). The study provides reliable Late Carboniferous-Permian paleomagnetic directions, in an area where paleomagnetic studies are scarce. The main characteristic component in both rock types shows a SSE direction with a shallow inclination and a dominant reverse polarity. The magnetic carriers, both in the volcanic rocks and the red beds, are magnetite and hematite. The main component is interpreted as a primary magnetization of Permian age in the red beds; in the Late Carboniferous volcanic rocks, the main component likely represents primary magnetization or early remagnetization. These results are consistent with the poles for the Iberian plate during the Permian and indicate an absence of regional vertical axis rotations for the Orri nappe, in whose hanging wall the Cadí Basin was transported southwards during the Pyrenean orogeny., This work was supported by projects grants PID2020-114273GB-C22, PID2019-108753GB-C22, and PID2019-104693GB-I00 funded by MCIN/AEI/10.13039/501100011033, “ERDF Away of making Europe” and grant FPU19/02353 funded by MCIN/AEI/10.13039/501100011033, “ERDF Away of making Europe” and funded by “ESF Investing in your future”. This study represents a contribution from the GeoAp (E01-20R) and the GeoTransfer (E32-20R) Research Groups (Aragón Government). EB thanks the Geomodels Research Institute and AGAUR 2021SGR00076., Peer reviewed

[EN] Palaeomagnetism is a versatile tool in the Earth sciences: it provides critical input to geological timescales and plate tectonic reconstructions. Despite its undeniable perks, palaeomagnetism is not without complications. Remagnetizations overprinting the original magnetic signature of rocks are frequent, especially in orogens which tend to be the areas with better rock exposure. Unraveling the magnetic history of the rocks is a complicated task, especially in areas that underwent several orogenic pulses. In turn, constraining the timing of remagnetization represents an opportunity to solve post-magnetization structural and tectonic kinematics. Here, we evaluate the magnetization history of Silurian-Devonian carbonates from the Axial Zone of the Pyrenees. The Pyrenees are a multi-orogenic mountain belt where Silurian-Devonian rocks have seen the Variscan collision (late Palaeozoic), the opening of the Atlantic/Bay of Biscay (early Cretaceous) and the Alpine orogeny (late Cretaceous to Miocene). Our results show widespread remagnetization(s) carried by magnetite and pyrrhotite in the Silurian-Devonian series of the Pyrenees. The majority of the samples show a post-folding but pre-alpine tilting magnetization. Considering the equatorial inclinations found in such samples, we suggest that they likely acquired their magnetization during the late Carboniferous and early Permian times. Two of the studied sites (located at the western Axial Zone) were subsequently remagnetized at the end of the Alpine orogeny. The palaeomagnetic results constrained that the Variscan orogeny was responsible for the main folding event affecting Palaeozoic rocks in the Axial Zone, whereas the Alpine orogeny produced the large-scale thrusting and antiformal stacking of these units. In addition, we observed a general clockwise rotational pattern which could be related with the formation of the Cantabrian Orocline and/or rotations associated with the Alpine orogeny. The Silurian-Devonian carbonates are thus useful to understand the tectonic evolution of the Pyrenean mountain range after a systematic combination of palaeomagnetism with structural and petrological observations. In contrast, the secondary character of magnetization and complications associated with the Variscan tectonics indicate that a reassessment of Siluro-Devonian poles from the Variscan elsewhere in Europe might be appropriate., This work was funded by postdoctoral (ISES) grant from NWO to DPG and the projects DR3AM, MAGIBER II and UKRIA4D (CGL2014-54118-C2-2, CGL2017-90632-REDT and PID2019-104693GB-I00/CTA) from the Spanish Ministry of Science and Technology., Peer reviewed

[EN] We have carried out a detailed paleomagnetic study of volcanic rocks (18 sites) and red beds (10 sites) from the Late-Carboniferous-Permian series of the Cadí Basin (Eastern Pyrenees). The study provides reliable Late Carboniferous-Permian paleomagnetic directions, in an area where paleomagnetic studies are scarce. The main characteristic component in both rock types shows a SSE direction with a shallow inclination and a dominant reverse polarity. The magnetic carriers, both in the volcanic rocks and the red beds, are magnetite and hematite. The main component is interpreted as a primary magnetization of Permian age in the red beds; in the Late Carboniferous volcanic rocks, the main component likely represents primary magnetization or early remagnetization. These results are consistent with the poles for the Iberian plate during the Permian and indicate an absence of regional vertical axis rotations for the Orri nappe, in whose hanging wall the Cadí Basin was transported southwards during the Pyrenean orogeny., This work was supported by projects grants PID2020-114273GB-C22, PID2019-108753GB-C22, and PID2019-104693GB-I00 funded by MCIN/AEI/10.13039/501100011033, “ERDF Away of making Europe” and grant FPU19/02353 funded by MCIN/AEI/10.13039/501100011033, “ERDF Away of making Europe” and funded by “ESF Investing in your future”. This study represents a contribution from the GeoAp (E01-20R) and the GeoTransfer (E32-20R) Research Groups (Aragón Government). EB thanks the Geomodels Research Institute and AGAUR 2021SGR00076., Peer reviewed

[EN] The North Pyrenean Zone results from the Late Cretaceous-Cenozoic inversion of the Mesozoic rift system extending along the Iberia-Europe plate boundary. The western part of this inverted rift (from the Tardets-Mauléon basin in the West to the Bigorre basin in the East) is strongly decoupled from the basement along Upper Triassic evaporites and slightly, internally overprinted by orogenic processes. These conditions make the area an ideal candidate for the study of rift-related structures and mineral fabrics registering the kinematics of the rifting process. This work focuses on the study of meso and micro-scale rift inheritance through a combination of structural analysis, anisotropy of magnetic susceptibility (AMS) and mineral shape fabrics extracted from X-Ray microtomography analysis. Previous AMS results (Mauléon basin) are integrated with data from 64 new AMS sites, acquired across both the Mesozoic, syn-rift cover and the Paleozoic basement. In syn-rift units, magnetic and mineral fabrics are in agreement and at a great extent inherited from syn- and post-rift stages. The compressional overprint of the Late-Cretaceous-Cenozoic inversion is limited and localizes along the south-western margin of the inverted basin. In the Paleozoic, a partial overprint of Mesozoic extension on AMS occurs in areas where rift-related peak temperatures exceeded ∼350°C. Rift-related mineral and magnetic lineations reveal a regional and constant through time NNW-SSE to NE-SW extension that attests this ample domain of the Pyrenean rift opened under a roughly orthogonal or slightly oblique rifting. Its easternmost part registered a partitioning between N-S and NW-SE extension directions, likely controlled by pre-rift faulting., Authors acknowledge the financial support received from the “Severo Ochoa” extraordinary grants for excellence IGME-CSIC (AECEX2021), the “Ayudas a la Incorporación de Científicos titulares” funded by the Consejo Superior de Investigaciones Científicas (CSIC) and the project UKRIA-4D (PID2019-104693GB-I00) of the Spanish Ministry of Science and Innovation, “ERDF A way of making Europe.” This project has received funding from the European Union's Horizon 2020 research and innovation programme under Grant TNA101005611 for Transnational Access conducted at DMEX-UPPA-FRANCE., Peer reviewed

Comunicación presentada en la LXXVII Sesión Científica / SGE, Boltaña, 29 de noviembre de 2024., [EN] Orogenic zones often exhibit vertical axis rotations (VAR) due to the accommodation of shortening differences along the main structural. In this work, we focus on the central Jaca-Pamplona Basin, where a Bartonian-Priabonian sequence crops out. There two magnetostratigraphic sections, Izaga and Berdún (2800 m), record about 5 Myr of the tectonic and sedimentary evolution of the basin. They have been discretized every 150 m to evaluate the rotational kinematics (spatio-temporal variations of the VAR). In the Izaga section the rotation is non-significant and noisier (dec=003º; inc=39º; a95=18°; k=23) than in the Berdún section, eastern sector, where the clockwise VAR is slightly larger (dec=008º; inc=46º; a95=10°; k=29) although it still overlaps the reference direction. Additional work is needed to refine this paleomagnetic record., [ES] Las zonas orogénicas a menudo exhiben rotaciones de eje ver-tical (VAR) debido a la acomodación de diferencias de acortamiento a lo largo de la tendencia estructural principal. En este trabajo, nos centramos en la parte central de la cuenca de Jaca-Pamplona, don-de aflora una potente secuencia Bartoniense-Priaboniense. Allí dos secciones magnetoestratigráficas, Izaga y Berdún (2800 m), regis-tran unos 5 Ma de la evolución tectónica y sedimentaria de la cuen-ca. Han sido discretizadas cada 150 m para evaluar la cinemática rotacional (variaciones espacio-temporales del VAR). En la sección de Izaga la rotación no es significativa y es más ruidosa (dec=003º; inc=39º; a95=18°; k=23) que en la sección de Berdún, sector orien-tal, donde el valor de VAR en sentido horario es algo mayor (de-c=008º; inc=46º; a95=10°; k=29) aunque todavía se solapa con la dirección de referencia. Serán necesarios trabajos adicionales para precisar este registro paleomagnético., This study was funded by project UKRIA-4D (PID2019-104693GB-I00) of the Spanish Ministry of Science and Innovation, “ERDF A way of making Europe”, which also covered the predoctoral contract of Pablo Sierra-Campos (PRE2020-092425). Pablo Calvín acknowledges funding from FJC2019-041058-I (Ministerio de Ciencia e Innovación Spain) contract., Peer reviewed

37 p., [EN] This study revisits the structural evolution of the Jaca Basin in the Southern Pyrenees through a revision of the works done in the study area combined with a detailed analysis of geological and subsurface data, culminating in a new balanced cross-section. Our findings demonstrate that the propagation of the deformation into the foreland, from the basement to the cover, is heavily influenced by the uneven distribution of the Upper Triassic salt layer, at the base of the deformed Mesozoic-Paleogene succession, and the reactivation of Permian and Triassic extensional faults. This has led to a distinctive non-cylindrical fold-and-thrust belt with frictional and viscous domains displaying different structural styles. In the frictional domains, where Triassic salt is absent, high-angle thrust systems with a short wavelength involve both the basement and overlying strata, resulting in tight folds and related cleavage. In contrast, in the viscous domains where salt is preserved, deformation structures involving the cover succession are decoupled from the basement and propagate further into the foreland. Nevertheless, structures of both domains, independently of their location and geometry, tended to connect and link, resulting into an intricate thrust system with the development of numerous oblique structures. These oblique structures are further accentuated by the reactivation of inherited Permian and Triassic extensional faults, primarily involving basement thrusts. Differences in the topography between the frictional and viscous domains have also influenced the deposition and routing of syntectonic sediments, which in their turn have also determined the thrusting sequence. The evolutionary sequence of thrusting initiated in the late Ypresian and continued into the early Neogene. Contrary to previous models that suggested simply piggy-back propagation, our findings indicate a complex pattern of synchronous and break-back thrusting sequences with continuous forward propagation of the deformation. Detailed field work supports thrusting ages older than previously thought and indicates a greater amount of shortening (approximately 58 km) than earlier estimates. This comprehensive integration of surface and subsurface data challenges traditional interpretations and provides new insights into the structural evolution of the Southern Pyrenees. Our study highlights the importance of considering three-dimensional structural interactions in understanding tectono-sedimentary relationships. These insights into the complex structural geometry of the Jaca Basin enhance our understanding of similar salt-bearing fold-and-thrust belts globally, such as Zagros, Western Alps, Calcareous Alps, among many others, emphasizing the critical role of inherited geological features and uneven salt distribution in shaping orogenic systems., We acknowledge the support of the research projects Structure and Deformation of Salt-bearing Rifted Margins (SABREM), PID2020-117598GB-I00, funded by MCIN/ AEI /10.13039/501100011033 and UKRIA4D (PID2019-104693GB-I00) of the Spanish Ministry of Science and Innovation, “ERDF A way of making Europe”. The Geomodels Research Institute and the Group de Geodinàmica i Anàlisi de Conques (2017SGR-596) are also acknowledged for their financial support., Peer reviewed

We present a new magnetobiostratigraphic study of the Izaga composite section (South Pyrenean foreland basin), performed to investigate the possibility of defining the Bartonian GSSP and to assess the yet unexplored sedimentary expression of the Middle Eocene Climate Optimum (MECO) in the deep palaeoenvironments of the basin. Our results indicate that the section spans from the uppermost part of Chron C19r to the uppermost part of C18n.2n, comprising calcareous nannofossil biozones CNE14 and CNE15. As found in most prospective sections studied previously, the occurrence of delayed magnetizations has prevented precise delineation of the marker of the Bartonian GSSP, the short lived Chron C19n, which reinforces the idea that an alternative biostratigraphic event might need to be chosen as the primary marker of the GSSP. In this regard, we propose the highest occurrence of Sphenolithus furcatolithoides B, whose persistent location close to the top of C19n has been corroborated at the Izaga composite section. If this datum accepted, the Izaga composite section can be regarded as one of the best prospective successions to host the Bartonian GSSP due to its expanded nature and superb outcrop conditions. Our results also reveal an increase in the input of reworked calcareous nannofossils and organic matter of continental origin concurring with a negative shift in the carbonate carbon and oxygen stable isotope record around the C19r/C18n.2n boundary, and hence demonstrate that the enhanced hydrological cycle induced by the MECO is manifested along a complete continental to deep marine transect along the South Pyrenean basin., This study was funded by project UKRIA-4D (PID2019-104693GB-I00) of the Spanish Ministry of Science and Innovation, “ERDF A way of making Europe”, which covered the predoctoral contract of P. Sierra-Campos (PRE2020-092425) and also by the project KINETRANS (PID2024-157800NB-C21). P. Calvín acknowledges funding from FJC2019-041058-I (Ministerio de Ciencia e Innovación Spain) contract. G. Bernaola and A. Payros acknowledges support by the Consolidated Research Group IT602-22 of the Basque Government., Peer reviewed

The anisotropy of the magnetic susceptibility (AMS) in mudrocks has been widely used to study orogenic belts due to their sensitivity to strain, while paleomagnetism remains the most effective method to quantify vertical axis rotations (VARs) resulting from the accommodation of along-strike variations in shortening. However, AMS can be also eventually used as a passive marker to detect VARs and the integration of both techniques offers a powerful approach to understand the tectonic evolution of fold-and-thrusts-belts. In this work, a combined AMS and paleomagnetic study along a stratigraphic section of continental rocks from the Campodarbe Formation in the Jaca-Pamplona Basin, southern Pyrenees, was carried out. This stratigraphic section (Martes section) records the tectonic evolution of this part of the basin from Priabonian to Rupelian times. The magnetic fabrics show the imprint of early stages of deformation, characterized by dominantly oblate ellipsoids and WNW-ESE horizontal magnetic lineations (axes of maximum magnetic susceptibility kmax), parallel to bedding and the main regional structures. In the lower part of the section, kmax axes trend around 290º, gradually rotating to 270º towards the top. The AMS is interpreted as locked under the imprint of the layer parallel shortening (LPS) associated to the activity of the basement thrusts in the northern Jaca-Pamplona Basin. On the other hand, paleomagnetic data indicate clockwise VARs of 6º to 12º in the lower part of the section, and a counterclockwise rotation of 7º to 14º in the upper part. These differential rotations could result from lateral changes in the Biniés basement thrust or the Jaca thrust system that were active during Oligocene times. Both techniques record a net rotation of ca. 25º between the lower and upper part of the section, which support the interpretation that early-locked AMS behaves as a passive marker and validates its use for detecting and quantifying VARs., This study was funded by project UKRIA-4D (PID2019-104693GB-I00) of the Spanish Ministry of Science and Innovation (“ERDF A way of making Europe”), which also covered the predoctoral contract of P. Sierra-Campos (PRE2020-092425), and also by the project KINETRANS (PID2024-157800NB-C21), also from the Spanish Ministry of Science and Innovation., Peer reviewed

This study investigates two burial-related remagnetizations in the Jaca–Pamplona foreland basin (Southern Pyrenees): one with dual polarity and a positive reversals test, and another with only reverse polarity. These components, labeled C3 and C4 based on their mean unblocking temperatures, were identified from a paleomagnetic analysis of 142 sites in Eocene turbidites of the Hecho Group. Component C3 shows unblocking temperatures of 250°C–350°C, systematic reverse polarity, and a predominantly post-folding timing. Component C4 exhibits unblocking temperatures of 250°C–550°C, dual polarity and a mainly syn-to postfolding acquisition. The spatial distribution of C4 polarity defines WNW–ESE bands parallel to structures and younging southward. The acquisition of C4 is interpreted as a chemical remagnetization triggered by progressive burial driven by combined sedimentary and tectonic loading that increased temperatures (up to ∼250°C in the deeper northern sectors, according to previous paleotemperature studies). This thermal evolution promoted authigenic, stable single-domain magnetite growth, beginning during the Lutetian (chron C20) and probably ending in the Rupelian (chrons C11-C10) as uplift and exhumation progressed. In contrast, the reverse polarity and post-folding behavior of component C3 suggest a mixed origin involving both chemical remagnetization and a thermoviscous overprint during the long chron C12r (Rupelian), contemporaneous with the youngest reverse C4 band and preceding the final exhumation of the basin. These findings highlight the complex interplay among tectonics, sedimentation, and chemical remagnetization processes in the South Pyrenean foreland, providing new insight into the timing and kinetics of remagnetization in fold-and-thrust belts., This study was funded by projects UKRIA-4D (PID2019-104693GB-I00) and KINETRANS (PID2024-157800NB-C21) of the Spanish Ministry of Science and Innovation, “ERDF A way of making Europe,” which also covered the predoctoral contract of Pablo Sierra-Campos (PRE2020-092425). Pablo Calvín acknowledges financial support from the postdoctoral contract FJC2019-041058-I of the Spanish Ministry of Science and Innovation, and from the projects EPOS-TNA-MSL 2019-007, which enabled access to the Paleomagnetic Laboratory Fort Hoofddijk (Utrecht University, The Netherlands), and AG2021-1 (CENIEH, Spain) that facilitated paleomagnetic and rock-magnetic analyses at the CENIEH Archaeomagnetism Laboratory (Burgos, Spain)., Peer reviewed

22 p., [EN] The Pamplona Fault at the SE Basque-Cantabrian Basin is one of the most notable and controversial transverse faults of the Pyrenees. Previous studies of this structure have been based on the analysis of single geological and geophysical datasets, which has resulted in a variety of interpretations regarding its origin and role during the Mesozoic rifting and Cenozoic inversion of the Pyrenean orogen. In this study, a 3D model integrating all the geological and geophysical information available for the transition between the Basque-Cantabrian, Jaca-Pamplona and Ebro foreland basins has been built to provide an updated, comprehensive view of the Pamplona Fault. We have found strong conclusive evidence for its presence in the Palaeozoic basement, as part of a widespread NNE-SSW fault network that extends across the study area. Further evidence for the activity of the fault during the Mesozoic rifting derives from the geometry and sedimentary evolution of the overlying, allochthonous Cretaceous sedimentary units. Overall, our results indicate that the Pamplona Fault represented the easternmost boundary of the Basque-Cantabrian basin during Hauterivian-Barremian times, was active during the beginning of the hyperextension process that led to the eastward propagation of the basin across the fault during the Aptian-early Albian and acted as an accommodation structure during the rest of the Cretaceous. By the integration of these results with those from surrounding areas, we identify this fault not as a single structure but as a ~65 km-wide strip labelled Pamplona Transfer Zone that includes the neighbouring Hendaya and Oroz-Betelu faults and represented a diffuse transfer linkage between the Basque-Cantabrian and Mauléon segments of the Pyrenean rift. This wide transfer zone also exerted a clear role during the Cenozoic inversion of the rift, for it had an impact on the style of deformation and the local configuration of the Pyrenean thrust front., This research is a contribution to the Research Group IT1602-22 of the Basque University System and to the UKRIA-4D (PID2019-104693GB-I00) and KINETRANS (PID2024-157800NB-C21) projects funded by the Spanish Ministry of Science and Innovation., Peer reviewed

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12. © A. Rodríguez-Pintó, J. Serra-Kiel, G. Bernaola, A. Barnolas, E.L. Pueyo, J. Tosquella, P. Arbués, R. Scholger, 2022 CC BY-SA.

Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm. can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm. (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The important difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Picodel Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust.

We have carried out a detailed paleomagnetic study of volcanic rocks (18 sites) and red beds (10 sites) from the Late-Carboniferous-Permian series of the Cadí Basin (Eastern Pyrenees). The study provides reliable Late Carboniferous-Permian paleomagnetic directions, in an area where paleomagnetic studies are scarce. The main characteristic component in both rock types shows a SSE direction with a shallow inclination and a dominant reverse polarity. The magnetic carriers, both in the volcanic rocks and the red beds, are magnetite and hematite. The main component is interpreted as a primary magnetization of Permian age in the red beds; in the Late Carboniferous volcanic rocks, the main component likely represents primary magnetization or early remagnetization. These results are consistent with the poles for the Iberian plate during the Permian and indicate an absence of regional vertical axis rotations for the Orri nappe, in whose hanging wall the Cadí Basin was transported southwards during the Pyrenean orogeny.

The North Pyrenean Zone results from the Late Cretaceous‐Cenozoic inversion of the Mesozoic rift system extending along the Iberia‐Europe plate boundary. The western part of this inverted rift (from the Tardets‐Mauléon basin in the West to the Bigorre basin in the East) is strongly decoupled from the basement along Upper Triassic evaporites and slightly, internally overprinted by orogenic processes. These conditions make the area an ideal candidate for the study of rift‐related structures and mineral fabrics registering the kinematics of the rifting process. This work focuses on the study of meso and micro‐scale rift inheritance through a combination of structural analysis, anisotropy of magnetic susceptibility (AMS) and mineral shape fabrics extracted from X‐Ray microtomography analysis. Previous AMS results (Mauléon basin) are integrated with data from 64 new AMS sites, acquired across both the Mesozoic, syn‐rift cover and the Paleozoic basement. In syn‐rift units, magnetic and mineral fabrics are in agreement and at a great extent inherited from syn‐ and post‐rift stages. The compressional overprint of the Late‐Cretaceous‐Cenozoic inversion is limited and localizes along the south‐western margin of the inverted basin. In the Paleozoic, a partial overprint of Mesozoic extension on AMS occurs in areas where rift‐related peak temperatures exceeded ∼350°C. Rift‐related mineral and magnetic lineations reveal a regional and constant through time NNW‐SSE to NE‐SW extension that attests this ample domain of the Pyrenean rift opened under a roughly orthogonal or slightly oblique rifting. Its easternmost part registered a partitioning between N‐S and NW‐SE extension directions, likely controlled by pre‐rift faulting.

Orogenic zones often exhibit vertical axis rotations (VAR) due to the accommodation of shortening differences along the main structural. In this work, we focus on the central Jaca-Pamplona Basin, where a Bartonian-Priabonian sequence crops out. There two magnetostratigraphic sections, Izaga and Berdún (2800 m), record about 5 Myr of the tectonic and sedimentary evolution of the basin. They have been discretized every 150 m to evaluate the rotational kinematics (spatio-temporal variations of the VAR). In the Izaga section the rotation is non-significant and noisier (dec=003º; inc=39º; a95=18°; k=23) than in the Berdún section, eastern sector, where the clockwise VAR is slightly larger (dec=008º; inc=46º; a95=10°; k=29) although it still overlaps the reference direction. Additional work is needed to refine this paleomagnetic record.

Las zonas orogénicas a menudo exhiben rotaciones de eje vertical (VAR) debido a la acomodación de diferencias de acortamiento a lo largo de la tendencia estructural principal. En este trabajo, nos centramos en la parte central de la cuenca de Jaca-Pamplona, donde aflora una potente secuencia Bartoniense-Priaboniense. Allí dos secciones magnetoestratigráficas, Izaga y Berdún (2800 m), registran unos 5 Ma de la evolución tectónica y sedimentaria de la cuenca. Han sido discretizadas cada 150 m para evaluar la cinemática rotacional (variaciones espacio-temporales del VAR). En la sección de Izaga la rotación no es significativa y es más ruidosa (dec=003º; inc=39º; a95=18°; k=23) que en la sección de Berdún, sector oriental, donde el valor de VAR en sentido horario es algo mayor (dec=008º; inc=46º; a95=10°; k=29) aunque todavía se solapa con la dirección de referencia. Serán necesarios trabajos adicionales para precisar este registro paleomagnético.

This study revisits the structural evolution of the Jaca Basin in the Southern Pyrenees through a revision of the works done in the study area combined with a detailed analysis of geological and subsurface data, culminating in a new balanced cross-section. Our findings demonstrate that the propagation of the deformation into the foreland, from the basement to the cover, is heavily influenced by the uneven distribution of the Upper Triassic salt layer, at the base of the deformed Mesozoic-Paleogene succession, and the reactivation of Permian and Triassic extensional faults. This has led to a distinctive non-cylindrical fold-and-thrust belt with frictional and viscous domains displaying different structural styles. In the frictional domains, where Triassic salt is absent, high-angle thrust systems with a short wavelength involve both the basement and overlying strata, resulting in tight folds and related cleavage. In contrast, in the viscous domains where salt is preserved, deformation structures involving the cover succession are decoupled from the basement and propagate further into the foreland. Nevertheless, structures of both domains, independently of their location and geometry, tended to connect and link, resulting into an intricate thrust system with the development of numerous oblique structures. These oblique structures are further accentuated by the reactivation of inherited Permian and Triassic extensional faults, primarily involving basement thrusts. Differences in the topography between the frictional and viscous domains have also influenced the deposition and routing of syntectonic sediments, which in their turn have also determined the thrusting sequence. The evolutionary sequence of thrusting initiated in the late Ypresian and continued into the early Neogene. Contrary to previous models that suggested simply piggy-back propagation, our findings indicate a complex pattern of synchronous and break-back thrusting sequences with continuous forward propagation of the deformation. Detailed field work supports thrusting ages older than previously thought and indicates a greater amount of shortening (approximately 58 km) than earlier estimates. This comprehensive integration of surface and subsurface data challenges traditional interpretations and provides new insights into the structural evolution of the Southern Pyrenees. Our study highlights the importance of considering three-dimensional structural interactions in understanding tectono-sedimentary relationships. These insights into the complex structural geometry of the Jaca Basin enhance our understanding of similar salt-bearing fold-and-thrust belts globally, such as Zagros, Western Alps, Calcareous Alps, among many others, emphasizing the critical role of inherited geological features and uneven salt distribution in shaping orogenic systems.

We present a new magnetobiostratigraphic study of the Izaga composite section (South Pyrenean foreland basin), performed to investigate the possibility of defining the Bartonian GSSP and to assess the yet unexplored sedimentary expression of the Middle Eocene Climate Optimum (MECO) in the deep palaeoenvironments of the basin. Our results indicate that the section spans from the uppermost part of Chron C19r to the uppermost part of C18n.2n, comprising calcareous nannofossil biozones CNE14 and CNE15. As found in most prospective sections studied previously, the occurrence of delayed magnetizations has prevented precise delineation of the marker of the Bartonian GSSP, the short lived Chron C19n, which reinforces the idea that an alternative biostratigraphic event might need to be chosen as the primary marker of the GSSP. In this regard, we propose the highest occurrence of Sphenolithus furcatolithoides B, whose persistent location close to the top of C19n has been corroborated at the Izaga composite section. If this datum accepted, the Izaga composite section can be regarded as one of the best prospective successions to host the Bartonian GSSP due to its expanded nature and superb outcrop conditions. Our results also reveal an increase in the input of reworked calcareous nannofossils and organic matter of continental origin concurring with a negative shift in the carbonate carbon and oxygen stable isotope record around the C19r/C18n.2n boundary, and hence demonstrate that the enhanced hydrological cycle induced by the MECO is manifested along a complete continental to deep marine transect along the South Pyrenean basin.

This study presents a detailed, geometrical characterization of the central-western domain of the Jaca-Pamplona Basin based on a combined interpretation of seismic and surface data and the construction of four serial cross-sections. For the studied portion of the basin, our results highlight that the basement is notably folded and faulted and its overall geometry is strongly controlled by the reactivation and spatial distribution of inherited, Permian-Triassic extensional faults. Basement-involved thrusts define a non-cylindrical thrust system and a prominent thrust salient bounded by NE-SW and NW-SE striking oblique structures to the east and west, respectively. South of the salient, seismic profiles reveal a newly identified basement structure beneath the South Pyrenean frontal thrust, which folds and uplifts outcropping structures in its hanging wall. Across the central-western part of the Jaca-Pamplona Basin, basement thrusts show an upper detachment along Triassic evaporites, transferring displacement forward into the cover succession and deforming previously developed thrust flats along the evaporites. Basement thrusts propagated forward probably from the late Ypresian, although synchronous activity in the southern structural units is documented during the Oligocene. Together with recent studies in the central and eastern Jaca-Pamplona Basin, this study provides a regional- and basin-scale picture of the geometry of basement units and places new constraints on the along-strike variations of main structures, their timing and related shortening and vertical axis rotations.

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12.

Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The significant difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Pico del Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust.

An integrated study including magnetostratigraphy, larger benthic foraminifera and calcareous nannofossil biostratigraphy is presented herein. This work was performed in shallow marine siliciclastics rich in larger foraminifera, around the Ypresian/Lutetian boundary in the Ésera valley (South-Central Pyrenees). Although the calcareous nannofossil content in the studied interval is low, not allowing a precise Y/L boundary to be recognised, the taxa found are enough to support the chronostratigraphic attribution. Data obtained in the Ésera valley section has improved the knowledge of larger benthic foraminifera (Nummulites and Assilina) distribution through chron C21. SBZ 11 to SBZ 12 transition took place at the lowermost C21r, as shown in previous works. SBZ 12 assemblages extend into C21n, where the SBZ 12 to SBZ 13 boundary occurs. These data, obtained in shallow marine siliciclastic facies, with in situ fauna, results in a shift of the SBZ 12/SBZ 13 boundary to the Lower Lutetian, younger than previously believed. Accordingly, the Ypresian/Lutetian boundary occurs in SBZ 12.

Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm. can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm. (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The important difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Picodel Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust.

La anisotropía de la susceptibilidad magnética (ASM) es una técnica que se ha mostrado muy efciente en el estudio de la evolución tectónica de cinturones orogénicos. En rocas débilmente deformadas depositadas en contextos compresivos, la ASM viene marcada por la orientación preferente de flosilicatos paramagnéticos ocurrida durante la diagénesis inicial como respuesta al acortamiento paralelo a las capas (LPS). Estas fábricas asociadas al LPS pueden verse modifcadas con posterioridad como respuesta al cizallamiento en la cercanía de planos de cabalgamiento. En este trabajo se presenta el análisis de la ASM en dos secciones, Izaga y Berdún, que se sitúan en la cuenca de Jaca-Pamplona (Zona Surpirenaica) y registran la evolución tectonosedimentaria de la cuenca desde el Luteciense Superior al Priaboniense Medio. Las partes inferior y superior de la serie de Izaga muestran elipsoides triaxiales/oblatos y oblatos, respectivamente, que indican un decaimiento en la intensidad del LPS asociado a la actividad decreciente del lejano sistema de cabalgamientos de Larra. La sección de Berdún comienza con elipsoides oblatos, que cambian rápidamente a triaxiales y prolatos antes de volver a oblatos hacia la parte media y superior de la serie. Los elipsoides triaxiales y prolatos en la parte baja de la serie marcan, junto con el desarrollo de una guirnalda incipiente entre los ejes mínimos e intermedios de la ASM, el efecto adicional de un cizallamiento que relacionamos con un cabalgamiento no detectado anteriormente y cuya presencia ha sido corroborada por análisis estructural. Aunque el resto de la serie de Berdún refeja el efecto del LPS, no ha sido posible determinar si éste viene condicionado por una estructura cercana o lejana. Los elipsoides prolatos reaparecen en el techo de la serie, circunstancia que relacionamos con un LPS más intenso asociado a la actividad tectónica que condicionó continentalización de la cuenca., The anisotropy of magnetic susceptibility (AMS) is a sensitive marker for studying the spatial and temporal evolution of orogens. In weakly deformed rocks deposited in compressive contexts the AMS signal mostly reflects the preferential alignment and deformation of paramagnetic phyllosilicates during early layer parallel shortening (LPS) related to both near and/or far-field structures. Moreover, localized deformation and post-depositional shearing in the vicinity of thrusts can alter early LPS fabrics. An AMS analysis of 651 samples was conducted along two stratigraphic sections, Izaga and Berdún (2800 m-thick), in the Jaca-Pamplona basin (Southern Pyrenees). The sampled sections record the tectonosedimentary evolution of the basin from the Late Lutetian to the Middle Priabonian. In both sections, the magnetic fabric is controlled by LPS. The lower and upper part of the Izaga section shows triaxial to oblate and oblate ellipsoids, respectively, which are interpreted to indicate a decrease of tectonic activity associated to the Larra thrust system. The Berdún section begins with oblate ellipsoids, which subsequently become triaxial and prolate before returning oblate towards the top of the succession. Ellipsoids in the lower part of the section exhibit an incipient girdle between the minimum and intermediate axes, which signal an undetected thrust, further corroborated, by structural analysis. The remainder of the Berdún section shows a magnetic fabric derived from LPS but it is not possible to associate it to any structure. The uppermost part of the section displays prolate ellipsoids, which we link to enhanced tectonic activity leading to continentalization of the basin., The authors thank Gilen Bernaola and Marcos Marcén for their help during field work, and Francho Gracia-Puzo for the help in the discussion of the results. This study was funded by project UKRIA-4D (PID2019-104693GB-I00) of the Spanish Ministry of Science and Innovation, 'ERDF A way of making Europe', which also covered the predoctoral contract of Pablo Sierra-Campos (PRE2020-092425). Pablo Calvín acknowledges funding from FJC2019-041058-I (Ministerio de Ciencia e Innovación Spain) contract. We acknowledge the two anonymous reviewers for their positive and constructive comments, and also Sameer Ahamed for editorial handling. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.