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Joint systems in the eastern portion of the Ebro Basin of the eastern Pyrenees enjoy near continuous exposure from the frontal portion of the belt up to the external portion of its associated foredeep. Utilizing orthophoto mosaics of these world-class exposures, we have manually digitized over 30 000 joints within a 16 km ×50 km study area. The mapped traces exhibit orientations that are dominantly perpendicular to the trend of the belt (transverse) and, subordinately, parallel to the belt (longitudinal). In particular, joints systematically orient perpendicular to the trend of the belt both in the frontal folds and in the inner and central portion of the foredeep basin. Longitudinal joints occur rarely with a disordered spatial distribution, exhibiting null difference in abundance between the belt and the foredeep. Joint orientations in the external portion of the foredeep become less clustered, with adjacent areas dominated by either transverse or oblique joints. Our data indicate that joints in the studied area formed in the foredeep in response to a foredeep-parallel stretching, which becomes progressively less intense within the external portion of the foredeep. There, the minimum stress direction becomes more variable, providing evidence of the poor contribution of the forebulge-perpendicular stretching on stress organization. [ABSTRACT FROM AUTHOR]

Abstract In this work we provide a reappraisal of the mid-Cretaceous extensional basins located to the east of the Pyrenean mountain ranges, from the easternmost portion of Iberia to the Briançonnais Domain of the Western Alps fold-and-thrust belt. These features are reviewed and compared with those of the Bay of Biscay-Pyrenean rift, with the aim of defining geometry, kinematics, timing and lateral extent of the eastern termination of the Mesozoic Iberia-Eurasia plate boundary. Timing and direction of extension, as well as the style of structural segmentation in the Bay of Biscay - Pyrenean rift, are similar to those of basins exposed to the east of the Pyrenean mountain ranges. In both areas, the divergent movement between Iberia and Eurasia caused NNE-SSW oriented extension recorded in WNW-ESE elongated Late Jurassic to mid-Cretaceous basins, segmented by NNE-SSW trending transfer zones. In this work we also individuate and introduce the eastern termination of the Iberia-Eurasia plate boundary. This is the Marguareis extensional system of the Briançonnais Domain of the SW Alps. The crustal-scale Marguareis extensional system involves Paleozoic and Mesozoic rocks and includes a tens of km long transfer fault flanking an extensional domino array that accounted for ca. 2 km of extension along 6 km long sections. When post-Cretaceous alpine rotation is removed, the mid-Cretaceous transfer fault and the extension direction of the Marguareis extensional system become oriented parallel to those of the other portions of the plate boundary, indicating its pertinence to the Bay of Biscay-Pyrenean rift system. Reviewed and newly presented data about the mid-Cretaceous tectonics spanning from the easternmost portion of Iberia to the Western Alps indicate that: (i) the Marguareis extensional system and the extensional structures of south France constituted the easternmost portion of the segmented and laterally terminating Bay of Biscay-Pyrenean rift system; (ii) this easternmost portion of the Iberia-Eurasia plate boundary was characterised by a purely divergent Early to mid-Cretaceous movement. Highlights • The mid-Cretaceous Marguareis extensional system of the Western Alps is introduced. • This system forms part of the eastern portion of the Iberia-Eurasia plate boundary. • This eastern portion included structures of the SE France basin. • The Early to mid-Cretaceous plate margin had a purely divergent movement. [ABSTRACT FROM AUTHOR]

We describe conjugate systems of shear-enhanced compaction bands oriented oblique to the maximum compressive stress and developed in Paleocene quartz-rich calcarenites formed by the interplay between shearing, mechanical compaction, and dissolution. These deformation bands are located in the footwall of the Cotiella Thrust (Spanish Pyrenees), and strike perpendicular to the local tectonic transport direction. Conjugate shear-enhanced compaction bands are mutually perpendicular in cross-section, forming an angle of 45° with the shallow-dipping bedding; no macroscopic evidence of shearing is found along them. These shear-enhanced compaction bands occur together with less abundant bedding-perpendicular compaction bands, which strike perpendicular to the local transport direction. The described shear-enhanced compaction bands consist of mm-thick tabular structures showing higher concentrations of quartz grains with reduced sizes in respect to the surrounding undeformed rock. Optical microscope and SEM investigations show that the high concentration of quartz clasts within the bands was caused by pressure-enhanced dissolution of calcite. Quartz grains fragmentation is also observed within the bands, with no significant clasts rotation and translation. All these features indicate that the described shear-enhanced compaction bands are hybrid structures developed during layer-parallel shortening associated with the Cotiella Thrust and are characterized by localized dissolution of calcite grains and fragmentation of quartz grains. [ABSTRACT FROM AUTHOR]

In the Spanish Pyrenees the Sant Corneli-Bóixols thrust-related anticline displays an outstandingly preserved growth strata sequence. These strata lie on top of a major unconformity exposed at the anticline’s forelimb that divides and decouples a lower pre-folding unit from an upper syn-folding one. The former consists of steeply-dipping to overturned strata with widespread bedding-parallel shears indicative of folding by flexural-slip, whereas the syn-folding strata above define a 200-m amplitude S-shaped fold. In the inner and outer sectors of the forelimb, both pre- and syn-folding strata are near-vertical to overturned and the unconformity angle ranges from 10° to 30º. In the central portion of the forelimb, syn-folding layers are shallowly-dipping, whereas the angular unconformity is about 90° and the unconformity surface displays strong S-C shear structures, which provide a top-to-the foreland shear sense. This sheared unconformity is offset by steeply-dipping faults which are at low angles to the underlying layers of the pre-folding unit. Strong shearing along the unconformity surface also occurred in the inner sector of the forelimb with S-C structures providing an opposite, top-to-the hinterland, shear sense. Cross-cutting relationships and shear senses along the pre-folding bedding surfaces and the unconformity indicate that regardless of its orientation, layering in the pre- and syn-folding sequences of the Sant Corneli-Bóixols anticline was continuously sheared. This shearing promoted an intense stress deflection, with the maximum component of the stress tensor remaining at low angles to beds during most of the folding process. [ABSTRACT FROM AUTHOR]

• The Plataforma Burgalesa of northern Spain is not the hanging wall of a low-dipping ramp rooted in the middle/lower crust. • We list 13 critical problems concerning the Mesozoic and Cenozoic framework proposed by Ramos et al. • We criticize a model that neither honors data on the thrust system nor incorporates concepts on salt-bearing rifted margins. [ABSTRACT FROM AUTHOR]

Abstract: A study of macro and mesostructural deformation patterns of the southern margin of the Cantabrian area (Western Pyrenees, Spain) has revealed a complex Cenozoic tectonic framework. Right-lateral tectonics reactivated inherited WNW–ESE striking faults, which developed during Late Paleozoic and Early Triassic events, and Late Jurassic to Early Cretaceous main rifting stage. The Ubierna Fault represents the southern boundary of the Mesozoic basin. During the Oligocene (even Eocene) to present day deformation, this fault and the Ventaniella Fault located to the south in the study area acted as right-lateral slightly transpressive elements forming a 120km long and 15km wide overstep area, here named Ubierna Fault System, where the cumulative right-lateral displacement exceeds 15km. The Cenozoic tectonic framework of the Ubierna Fault System includes reactivation along the WNW–ESE faults, development of negative and, mostly, positive flower structures, branch faults, strike-slip duplexes, and releasing and restraining bends. NE–SW to ENE–WSW striking reverse faults and contractional horsetail terminations, and NNW–SSE striking normal faults and joints are produced by the WNW–ESE right-lateral strike-slip motion. The extensional elements are well developed and deformation progression implied their incorporation in the strike-slip system as right-lateral faults (forming part of strike-slip duplexes). The abundance of flower structures striking WNW–ESE and paralleling the main strike-slip faults, together with the overall uplift of the overstep area, testifies for a slight compressional component. At a regional scale, the Ubierna Fault System represents the most prominent element of a Cenozoic transpressional belt, which incorporates the western portion of the Basque-Cantabrian Basin and the Asturian Massif area. Lateral transition between this transpressive belt and the dip-slip belt located to the east, occurs across an area experiencing along strike-shortening, which developed to accommodate the eastward extrusion of the transpressional belt. [Copyright &y& Elsevier]

Abstract: Understanding the genetic relationships of folding-related deformation structures is of importance for both academic and industrial purposes. We analysed the three-dimensional deformation pattern of the Añisclo anticline, in the southern Pyrenees. The specifically designed statistical method includes sequential steps of statistical and spatial data analysis and classification. Our results indicate that pressure solution cleavage frequency exhibits a spatial distribution that depends on the position within the fold. Conversely, such a dependence does not occur in joints and veins. Consequently, our data suggest that pressure-solution cleavage is the most appropriate deformation structure for unravelling fault-fold kinematics in carbonate multilayer. In particular, we found that the spacing of solution cleavages (S) is related to the corresponding bed thickness (H). This supports the use of H/S value for deformation intensity quantification instead of spacing. In the Añisclo anticline, analysis of H/S indicates the occurrence of three main deformation panels whose restoration suggests that fold evolution progressed from layer-parallel shortening, to décollement folding, up to thrust breakthrough, and fault-propagation folding. Comparison of H/S values with finite strain data indicates that line-length was not preserved during fold evolution. This evidence has important implications for the kinematic interpretation of layer-parallel shortening and cross-section balancing. [Copyright &y& Elsevier]