Geology of the Eastern Prebetic Zone at the Jumilla region (SE Iberia)

This article presents a geological map and cross-sections at 1:50,000 scale covering an area of 609 km2 of the Eastern Prebetic Zone (SE Iberia). The structure of the studied area is characterized by an NW-directed fold-and-thrust belt and inactive salt diapirs that are parallel to the ENE- to NE-regional trend of the eastern Betic Cordillera. This regional trend is locally disrupted by the NW-trending Matamoros Basin, which is flanked by the active Jumilla and La Rosa diapirs. The geological map, the cross-sections and the outcrop observations support the hypothesis that the major Mesozoic rifting phase affecting the Eastern Prebetic Zone occurred during the Upper Jurassic to Santonian times coeval to the development of extensional basins in the Western Tethyan area. The proximal part of this passive margin was subsequently incorporated into the external part of the Betic thin-skinned fold-and-thrust belt. The Upper Cretaceous to Cenozoic tectonic evolution of the study area encompassed the following stages: a Campanian to Aquitanian NW-directed contraction; a Burdigalian to upper Miocene extensional reactivation of the main subsalt faults; and a Serravallian NWdirected contractional reactivation. In this scenario, the combined effect of the previous contractional reactivation of pre-existing salt structures together with the Miocene subsalt extension triggered passive salt extrusion of the La Rosa and Jumilla diapirs

Structural control of inherited salt structures during inversion of a domino basement-fault system from an analogue modelling approach

The geometries of inverted rift systems are different depending on a large variety of factors that include, among others, the presence of decoupling layers, the thickness of the pre- and syn-extension successions, or structural inheritances. Our study focuses on the inversion of an extensional domino-style basement-fault system with a pre-extension salt layer using analogue models to understand the role of pre-existing structural features during inversion. Models investigate how different overburden and salt thicknesses, inherited extensional structures, and salt distributions condition the evolution during inversion. The experimental results show that models with thick salt can partially or totally preserve the extensional ramp-syncline basin geometry independently of the overburden thickness. In contrast, models with a thin salt layer result in a total inversion of the ramp-syncline basins with the development of crestal collapse grabens and extensional faults affecting the overburden. Inversion also triggered the growth or reactivation of salt-related structures such as primary weld reopening and/or obliteration, diapir rejuvenation, salt thickening, or thrust emplacement. The use of analogue modelling allowed us to address the processes that controlled the growth and evolution of these structural elements during the inversion. Experimental results also provide a template of different structural styles resulting from the positive inversion of basins with a pre-extensional salt layer that can help subsurface interpretation in areas with poor seismic imaging

Role of inheritance during tectonic inversion of a rift system in basement-involved to salt-decoupled transition: Analogue modelling and application to the Pyrenean-Biscay system

The reactivation of former rift systems and passive margins during tectonic inversion and their incorporation into fold-and-thrust belts result in significant structural differences not only between internal and external domains, but also along-strike. The Basque-Cantabrian and Asturian systems are among the best examples to address the role of along-strike changes in rift inheritance since they show a transition from salt to basement-inherited structures divided by a transition zone separating thick- from thin-skinned structural domains. While both domains have been widely described in the literature, the transfer system separating the two has not been sufficiently investigated due to poor seismic imaging and the lack of large-scale outcrops. This contribution aims to address the linkage between basement-controlled (i.e. thick-skinned) and salt-decoupled (i.e. thin-skinned) domains and to describe how deformation is accommodated in the transitional zone between these domains. An experimental programme based on analogue models has been designed that was inspired by the transition from the thin-skinned Basque-Cantabrian Pyrenees to the east to the thick-skinned Asturian Massif to the west. As observed in nature, experimental results show that oblique structures (at low angle with the shortening direction) form in the transitional domain, and their location depends on the linkage of the active structures occurring in both surrounding thick- and thin-skinned domains at different positions. Nevertheless, their orientation and evolution are controlled by the underlying decoupling horizon (i.e. salt). The deformation in the thick-skinned domain produces significant topography over a narrow deformation area due to the lack of effective decoupling levels. On the contrary, deformation in the thin-skinned domain is more distributed due to decoupling, resulting in a wider deformation area of less topography. As a result, syn-contractional sedimentation occurs mainly in the foreland basin in front of the thick-skinned domain, whereas it is observed in the foreland but also in piggyback basins in the thin-skinned domain

Influence of fault geometries and mechanical anisotropies on the growth and inversion of hanging-wall synclinal basins: insights from sandbox models and natural examples

Salt is mechanically weaker than other sedimentary rocks in rift basins. It commonly acts as a strain localizer, and decouples supra- and sub-salt deformation. In the rift basins discussed in this paper, sub-salt faults commonly form wide and deep ramp synclines controlled by the thickness and strength of the overlying salt section, as well as by the shapes of the extensional faults, and the magnitudes and slip rates along the faults. Upon inversion of these rift basins, the inherited extensional architectures, and particularly the continuity of the salt section, significantly controls the later contractional deformation. This paper utilizes scaled sandbox models to analyse the interplay between sub-salt structures and supra-salt units during both extension and inversion. Series 1 experiments involved baseline models run using isotropic sand packs for simple and ramp-flat listric faults, as well as for simple planar and kinked planar faults. Series 2 experiments involved the same fault geometries but also included a pre-extension polymer layer to simulate salt in the stratigraphy. In these experiments, the polymer layer decoupled the extensional and contractional strains, and inhibited the upwards propagation of sub-polymer faults. In all Series 2 experiments, the extension produced a synclinal hanging-wall basin above the polymer layer as a result of polymer migration during the deformation. During inversion, the supra-polymer synclinal basin was uplifted, folded and detached above the polymer layer. Changes in thickness of the polymer layer during the inversion produced primary welds and these permitted the sub-polymer deformation to propagate upwards into the supra-salt layers. The experimental results are compared with examples from the Parentis Basin (Bay of Biscay), the Broad Fourteens Basin (southern North Sea), the Feda Graben (central North Sea) and the Cameros Basin (Iberian Range, Spain)

The Merluza Graben: How a failed spreading center influenced margin structure, and salt deposition and tectonics in the Santos Basin, Brazil

The relative timing between crustal extension and salt deposition can vary spatially along passive margin salt basins as continents unzip, or as the locus of extension shifts toward the embryonic ocean spreading center. Determining the relative timing of salt deposition, rifting, and seafloor spreading is often problematic due to the diachronous nature of rifting, the ability of salt to fill pre-existing topography, and the subsequent flow and deformation of that salt. We here use 2D PSDM seismic data and structural restorations to investigate the Merluza Graben, a large rift-related depocentre located in the southern, most proximal part of the Santos Basin, Brazil, along-strike of a failed spreading center, the Abimael Ridge. The graben is defined by up to 3.5km of base-salt relief along its basinward-bounding fault and internal base-salt horsts that are up to 1km high. This compartmentalizes deformation, producing intra-graben extensional and contraction salt structures, ramp-syncline basins, and expulsion rollovers, resulting in a remarkably different salt-tectonic structural style to that seen in the adjacent areas. We also conduct structural restorations to analyze the spatial and temporal evolution of salt-tectonic structural styles and the relationship this has to potential prolonged crustal extension in the Merluza Graben. This approach further constrains local variations in the relative timing of rifting and salt deposition, and the impact this has on salt tectonics along the margin. The results of our study can be applied to better understand the tectono-stratigraphic development of other salt-bearing rifted margins

Evolution of salt structures during extension and inversion of the Offshore Parentis Basin (Eastern Bay of Biscay)

The Late Jurassic-Cretaceous Parentis Basin (Eastern Bay of Biscay) illustrates a complex geological interplay between crustal tectonics and salt tectonics. Salt structures are mainly near the edges of the basin, where Jurassic-Lower Cretaceous overburden is thinner than in the basin centre and allowed salt anticlines and diapirs to form. Salt diapirs and walls began to rise reactively during the Late Jurassic as the North Atlantic Ocean and the Bay of Biscay opened. Some salt-cored drape folds formed above basement faults from the Upper Jurassic to Albian. During Albian-Late Cretaceous times, passive salt diapirs rose in chains of massive salt walls. Many salt diapirs stopped growing in the Mid-Cretaceous when their source layer depleted. During the Pyrenean orogeny (Late Cretaceous-Cenozoic), the basin was mildly shortened. Salt structures absorbed almost all the shortening and were rejuvenated to form squeezed diapirs, salt glaciers and probably subvertical welds, some of which were later reactivated as reverse faults. No new diapirs formed during the Pyrenean compression, and salt tectonics ended with the close of the Pyrenean orogeny in the Middle Miocene. Using reprocessed industrial seismic surveys, we document how salt tectonics affected the structural evolution of this offshore basin largely unknown to the international audience

The role of the Bay of Biscai Mesozoic extensional estructure in the configuration of the Pyrenean orogen: Constraints from the MARCONI deep seismic reflection survey

Seismic interpretation of the MARCONI deepseismic survey enables recognition of the upper crustalstructure of the eastern part of the Bay of Biscay andthe main features of its Alpine geodynamic evolution.The new data denotes that two domains with differentPyrenean and north foreland structures exist in the Bayof Biscay. In the eastern or Basque‐Parentis Domain,the North Pyrenean front is located close to the Spanishcoast, and the northern foreland of the Pyrenees is con-stituted by a continental crust thinned by a north dip-ping fault that induced the formation of the EarlyCretaceous Parentis Basin. In the western or Cantab-rian Domain, the North Pyrenean front is shifted tothe north and deforms a narrower and deeper forelandbasin which lies on the top of a transitional crustformed from the exhumation of lithospheric mantlealong a south dipping extensional low‐angle faultduring the Early Cretaceous. The transition betweenthese two domains corresponds to a soft transfer zonelinking the shifted North Pyrenean fronts and a north‐to WNW‐directed thrust that places the continentalcrust of the Landes Plateau over the transitional crustof the Bay of Biscay abyssal plain. Comparisonbetween this structure and regional data enables char-acterization of the extensional rift system developedbetween Iberia and Eurasia during the Late Jurassicand Cretaceous and recognizes that this rift systemcontrolled not only the location and features of thePyrenean thrust sheets but also the overall structureof this oroge

The MARCONI-3 deep seismic reflection profile: structure of the north Pyrenean foreland at the eastern part of the Bay of Biscay

The MARCONI-3 profile denotes that the structure of the North Pyrenean foreland at the western part of the Parentis Basin consists of a wedge of uppermost Cretaceous to Cenozoic synorogenic sediments lying on the top of a thinned continental crust with a major Mesozoic Basin to the north, the Parentis Basin, and a coeval structural high to the south, the Landes High. The Parentis Basin appears bounded southwards by a major normal fault. It is filled by a thick carbonate succession affected by a salt ridge and diapirs formed during the Albian-Late Cretaceous and squeezed during the late Eocene-middle Miocene. The Landes High includes a thin pre-Upper Cretaceous cover which, together with the synorogenic sediments, is deformed by a thrust wedge that constitutes the north-Pyrenean front. This overall structure evidences that the Mesozoic extension played an important role both in the location and features of the north-Pyrenean contractional deformation. Specially, the Alpine structure in the Parentis Basin denotes that the Landes High acted as a buffer for the north propagation of the Pyrenean deformation until early Miocene and vanished afterwards during the last stages of Pyrenean development when some basement faults reactivated in the Parentis Basin

Inversion of accommodation zones in salt-bearing extensional systems: insights from analog modeling

This work uses sandbox analog models to analyze the formation and subsequent inversion of a decoupled extensional system comprised of two segmented half-grabens separated by a diffuse accommodation zone with thick early syn-rift salt. The segmented half-grabens strike perpendicular to the direction of extension and subsequent shortening. Rifting first created a basement topography that was infilled by model salt, followed by a second phase of extension and sedimentation, followed afterwards by inversion. During the second phase of extension, syn-rift syncline minibasins developed above the basement extensional system and extended beyond the confines of the fault blocks. Sedimentary downbuilding and extension initiated the migration of model salt to the basement highs, forming salt anticlines, reactive diapirs, and salt walls perpendicular to the direction of extension, except for along the intervening accommodation zone where a slightly oblique salt anticline developed. Inversion resulted in decoupled cover and basement thrust systems. Thrusts in the cover system nucleated along squeezed salt structures and along primary welds. New primary welds developed where the cover sequence touched down on basement thrust tips due to uplift, salt extrusion, and syn-contractional downbuilding caused by the loading of syn-contractional sedimentation. Model geometries reveal the control imposed by the basement configuration and distribution of salt in the development of a thrust front from the inversion of a salt-bearing extensional system. In 3D, the interaction of salt migrating from adjacent syn-rift basins can modify the expected salt structure geometry, which may in turn influence the location and style of thrust in the cover sequence upon inversion. Results are compared to the Northern Lusitanian Basin, offshore Portugal, and the Isábena area of the South-Central Pyrenees, Spain

Mesozoic structural inheritance in the Cenozoic evolution of the central Catalan Coastal Ranges (western Mediterranean): Structural and magnetotelluric analysis in the Gaià-Montmell High

The control exerted by the Mesozoic basin configuration on the Cenozoic tectonic evolution of the Catalan Coastal Ranges has been frequently recognized as a key factor to explain its present-day structure. However, details of this structural inheritance and its evolution through geological time is still under discussion. In this work we present two structural cross-sections based on fieldwork, well and magnetotelluric data in order to illustrate the structural styles and tectonic evolution of the Gaià-Montmell High. Here, the Montmell Fault not only constitutes the SW segment of one of the major Neogene faults in the Catalan Coastal Ranges (the Montmell-Vallès Fault System), but also the NW limit of a Late Jurassic-Early Cretaceous extensional basin(the Montmell-Garraf Basin), facts that denote a major role of this fault in the tectonic evolution of the area. The present-day structure of the Gaià-Montmell High resulted, therefore, from two successive episodes of inversion during the Cenozoic. The first one reactivated the Montmell Fault as compressional during the Paleogene. As a result, and among other inversion-related structures, the Gaià-El Camp Thrust developed sa major NW-directed basement footwall shortcut. Later on, the previously formed compressional structure during the Paleogene became reactivated as extensional during the Neogene. During this phase, the reactivation of the Montmell Fault looks limited and, hence, the extension is transmitted to the Baix Penedès Fault. The reactivation of the Gaià-El Camp Thrust is also manifest in the development of an array of extensional faults in the backlimb of the Carme-Cabra Anticline that corresponds to the NE-end of El Camp Fault. This episode of negative inversion developed accommodation zones between the four major faults present in the area ( Vallès-Penedès, Montmell, El Camp and Baix Penedès faults) that are characterized by the presence of relay ramps with breaching faults