South-central Pyrenees Research Articles

Geometrical characterization of fracture systems using point clouds and SELF-Software: example of the Añisclo anticline carbonate platform, Central Pyrenees

Natural fracture systems contribute significantly to rock mass anisotropies. Characterizing these systems is essential for understanding processes of fluid flow, energy exploration and storage, slope stability or tectonic processes that can affect the permeability or compaction of the material, as well as reflect its temporal evolution. This work presents a set of automatic and supervised algorithms integrated into the open-access software solution SEFL, designed to characterize fracture systems using remote sensing data sets. The software implements various strategies to quantify geometrical parameters with deterministic or stochastic descriptions, facilitating a detailed characterization of the fracture system for numerical simulations. Geological outcrops provide direct access to the rock masses and discontinuities, offering analogies with materials that are otherwise inaccessible for its direct study. The digital acquisition of the terrain using high-resolution techniques, such as Terrestrial Laser Scanner (TLS) or photogrammetry to obtain point clouds, enabled post-field studies, particularly for fracture systems that are complex, inaccessible, or large in scale. Additionally, SEFL offers a tool based on the concept of fracture stratigraphy to identify mechanical units, which are essential frameworks for measuring and calculating fracture properties. This new methodology has been applied to study the fractured Eocene limestone outcrop at the hinge of the Añisclo anticline (South-Central Pyrenees, NE Iberia) which has been digitally acquired and characterized. SEFL output data interpretations revealed an outcrop characterized by over two thousand modelled fractures, five fracture sets, fourteen fracture stratigraphic units, and 1-2 fractures/m.

Inferring on fluvial resilience from multi-temporal high-resolution topography and geomorphic unit diversity

The resilience of a river corridor represents its ability to withstand and recover from disturbances. Quantifying fluvial resilience in the face of various stressors is essential for integrating ecology and geomorphology in a context of river management. Geomorphic unit diversity analysis emerges as a valuable tool for characterizing and quantifying fluvial resilience to disturbances due to its inherent connection with fluvial dynamics. This paper aims to analyse and quantify the fluvial resilience of a wandering gravel-bed river affected by natural (e.g., floods) and human-induced (e.g., instream gravel mining) stressors. To achieve this goal, we use multi-temporal high-resolution topographic surveys of the Upper River Cinca (South-Central Pyrenees) spanning from 2014 to 2020. By employing the Geomorphic Unit Tool (GUT) on these surveys, we can map geomorphic units over time, quantify their diversity, and study geomorphic adjustments through morphodynamic signatures, altogether allowing inferring fluvial resilience.Our findings reveal that topographic changes (i.e., erosion and sedimentation) correlate with the type of stressor: maintenance works and gravel mining lead to degradation, while floods induce aggradation. Geomorphic Unit Diversity decreases following channel disturbances caused by gravel mining but rebounds after periods primarily stressed by floods, returning to pre-impact levels within six years. Geomorphic adjustments, such as channel incision and mid bar development, reflect erosion and sedimentation processes respectively, with channel maintenance works and floods being the main drivers. Despite the recovery of the geomorphic unit diversity within the reach, the deficit resulting from gravel extraction remains unresolved, perpetuating a degrading trend that poses risks in reducing lateral connectivity and could potentially catalyse future vegetation encroachment in bars and floodplains, causing changes on flood conveyance and hydraulics. Monitoring the river's geomorphic diversity provides crucial insights for effective conservation and management decisions regarding land use, development, and conservation along riverbanks, thereby sustaining or enhancing fluvial system resilience.

Decapod crustacean diversity through time and space in a middle-upper Eocene carbonate-siliciclastic platform (southern Jaca Basin, Pyrenees, Spain)

The south-central margin of the Jaca Basin (South-central Pyrenees, Spain) offers well-exposed outcrops ideal for studying the distribution of decapod crustaceans across a mixed carbonate-siliciclastic depositional system during the middle-late Eocene (Bartonian-Priabonian). This study encompasses an area of 1000 km2, featuring environments from siliciclastic coastal plains and deltaic complexes to shallow carbonate and mixed platforms, including coral reefs, extending to prodelta/outer platform deeper conditions. Detailed sampling in four depositional sequences yielded 372 fossil decapod specimens from various lithofacies across 20 localities.Our analysis identifies 39 decapod species within 22 families and demonstrates ecological zonation of decapods in shallow to relatively deep environments. Diversity peaks in siliciclastic shallow proximal prodelta areas and carbonate bryozoan meadows. Species distribution between carbonate and siliciclastic facies is similar, though taxonomically distinct. Articulated specimens predominantly occur in shallow proximal and relatively deep distal siliciclastic areas, linked to sudden sediment input and high sedimentation rates. These findings elucidate the spatial and temporal distribution factors of decapod crustaceans during the middle-late Eocene, contributing to the broader understanding of palaeoecological patterns in mixed depositional systems.

Stratigraphic evolution of a salt-walled basin: the influence of diapirism and compressional tectonics on the sedimentary record of the Estopanyà syncline (South-Central Pyrenees)

This contribution describes the influence of diapirism and compressional tectonics in the sedimentary record of the Estopanyà and Boix synclines (salt-walled basins) in the South-Central Pyrenees (NE Spain). Based on mapping and logging of five stratigraphic sections, two lithostratigraphic units (LU-1 and 2) along the eastern diapir margin of these synclines and five more (LU-3 to 7) in their inner parts are defined. LU-1 and 2 consist of monomictic breccias deposited probably during the Upper Triassic-Oligocene and the Upper Cretaceous, respectively. LU-3 to 7 constitute a marine to fluvial succession of the Tremp Group deposited during the Upper Cretaceous to Paleocene. The stratigraphic and sedimentological record indicates that the topography, position, and accommodation space of the Estopanyà and Boix synclines was actively controlled by the evolution of salt structures from the Late Cretaceous to the Oligocene in response to the advance of the Alpine compression in the South-Central Pyrenees. The growth of salt-inflated ridges with a near parallel orientation to the axis of the studied synclines since the Upper Cretaceous, progressively compartmentalized the Boix syncline until inhibiting sedimentation during the lower Paleocene. In the upper Paleocene, the Alpine compression approached the study area increasing salt evacuation and the subsidence of the Estopanyà and Boix synclines. During the early to middle Ypresian, onset of compression led to salt expulsion by piercing the sedimentary roof of the inherited salt-inflated ridges and forming two salt walls at the eastern margin of the Estopanyà and Boix synclines that were squeezed and welded (possibly through secondary welds) due to tectonic compression during the Oligocene. This contribution provides a new interpretation of the structural and stratigraphic evolution of the Estopanyà and Boix synclines, proposing an evolutionary model that includes the rejuvenation, growth, and extrusion of salt walls as deciphered from the stratigraphy, sedimentology, and petrology of the diapir margin breccias and the sedimentary succession of the adjoining salt-embedded basins. Hence, it provides a new analogue study for understanding the interplay between compressional tectonics, diapirism, and sedimentation to other inverted salt basins with precursor salt walls worldwide.

Salt sheet extrusion and emplacement within the South-Central Pyrenean fold-and-thrust belt: the Les Avellanes Diapir case-of-study

ABSTRACT A detailed geological map of the Les Avellanes salt Diapir (South-Central Pyrenees, Spain) that includes both the diapir body and adjacent areas is presented to understand the diapir evolution and geometry. Structural, stratigraphical, and sedimentary data north and south of the diapir is used to infer the timing of its emplacement. The northern diapir boundary is characterized by a set of extensional faults oblique to the main Pyrenean trend, while the southern boundary is an extrusive salt sheet that overlays the late Eocene-early Oligocene sequence in three adjacent sub-basins. Salt extrusion occurred due to synorogenic folding. The topography created as salt extruded trapped the arrival of external sediments from the north, blocking the transport pathways southward. Low sedimentation rates southwards allowed for the lateral salt extrusion, advancing southwards from the feeder. The salt sheet emplacement was postdated by Oligocene conglomerates, indicating that the salt extrusion was a relatively quick event.

Titanosaurian teeth from the South-central Pyrenees (Upper Cretaceous, Catalonia, Spain)

In Europe, the sauropod record of the uppermost Cretaceous (Campanian–Maastrichtian) concentrates in Spain, France, and Romania with up to eight titanosaurian species erected and a similar number of tooth morphotypes described. Recently, the lower Maastrichtian locality of Els Nerets from the Tremp Basin (Catalonia, Spain) has yielded the largest tooth sample for a Late Cretaceous titanosaur in the continent. A comprehensive description of 18 teeth from this locality shows that they have conical and slender crowns, pronounced development of mesial and distal carinae, a lemon-shaped cross-section, and a coarse enamel wrinkling defined by closely packed longitudinal crenulations that anastomose apically. The teeth are among the largest, slender-most, and most labiolingually compressed teeth from the region. Despite several morphological similarities with some other few titanosaur species described in other localities of SW Europe, the dental material from Els Nerets cannot be referred to any known European species. Finally, by using a rationale based on tooth morphology and wear facets distribution we propose a dental configuration of the new yet to be described taxon.

The kinematics of a salt sheet recorded in an array of distorted intrasalt stringers (Les Avellanes Diapir – South-Central Pyrenees)

Stringers represent fragments of competent, brittle layers, formerly interstratified within a layered evaporite sequence (LES) that are entrained and deformed by viscous flow. To resolve the impact of the stringers on the deformation style of an extrusive salt sheet, an array of decameter-thick, carbonate stringers, preserved in the caprock matrix of the Les Avellanes Diapir (South-Central Pyrenees) was analysed. The diapir exposure was mapped in detail to produce a cross-section that shows the stringer assemblage. To understand the dynamic behaviour of stringers, this natural prototype has been reproduced using scaled analogue models. In the model, stringers were carried into the salt sheet, rotating and deforming while migrating toward the sheet front. The array of stringers can be divided into the following three structural domains: 1) a feeder domain mainly hosting vertical stringers parallel to the stem wall that rotate to a subhorizontal orientation as they approach the allochthonous sheet, 2) a sheet domain containing stack-like sets of subvertical and overturned, to subhorizontal stringers, as well as isoclinally and recumbently folded stringers, and 3) a sheet front domain characterised by stringers dipping toward the salt sheet front. Compartmentalization of the horizontal flow by the transported stringers controlled the deformation in the caprock matrix above. Finally, the similarity between the field observations and the model is evaluated and discussed to shed light on the Les Avellanes Diapir kinematic evolution.

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

Abstract. 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.

Geochemical approach for decoding the paleoenvironmental and depositional evolution of a coastal lacustrine Konservat-Lagerstätte (Early Cretaceous, south-Central Pyrenees)

The lithographic limestone of La Pedrera de Meià (LPM) in south-Central Pyrenees (NE Spain) is considered one of the best preserved lacustrine-coastal successions of the Early Cretaceous in Europe, hosting a taxonomically diverse record of Barremian biota. While this Konservat-Lagerstätte has been extensively surveyed for paleontological purposes, little is known about the paleoenvironmental and depositional conditions prevailing during the formation of this fossil lagerstätte deposit. LPM limestone is made up of a homogeneous, dark gray to pale brown, faintly laminated 50 m-thick succession of micrite-rich intervals. To shed light on the environmental conditions of deposition, 303 rock samples were studied using a multiproxy approach based on different techniques including petrography, SEM-EDX, XRD, ICP-MS, XRF, Rare Earth Element distributions and C and O stable isotope geochemistry. The combination of sedimentological and geochemical data reveals a vertical shift of facies from littoral to profundal environments and then returning to littoral conditions. Profundal facies are made up of filament-rich mudstones originated from in situ precipitation of micrite either through biotically mediated or physico-chemical processes in undisturbed low energy settings, under anoxic conditions, characterized by the presence of transported terrestrial and lacustrine organisms that are exquisitely well-preserved. Littoral areas are characterized by the presence of in situ charophytes, smooth ostracods, and miliolid foraminifera that accumulated in mud-rich facies indicating low/moderate-energy, shallow-water, and relatively oxygenated conditions. Stable isotopic data and elemental geochemistry suggest a hydrologically closed to semi-closed lacustrine system with a restricted water circulation encouraging dysoxic to anoxic conditions in profundal sediments. Paleoproductivity proxies suggest a good correlation between catchment-derived siliciclastic discharge to the lake and primary productivity peaks. Furthermore, a decline in terrigenous input coupled with a reduction of meteoric water entrance to the lake is interpreted based on elemental proxies derived from paleosalinity and paleoredox analysis. Collectively, the strontium/barium (Sr/Ba) ratios, the sparse presence of miliolid foraminifera, and the isotopic signatures indicate an increase in salinity toward the younger intervals of the lake infilling, although their ultimate causes are unclear (i.e., increased evaporation, or a combination of reduced meteoric input and sporadic marine inputs might explain our data). The present work shows the importance of performing detailed multiproxy geochemical-sedimentological studies to better constrain the unique paleoenvironmental and paleohydrological conditions associated with the exceptional preservation of fossil biotas in Konservat-Lagerstätte deposits in analogous depositional settings.

Allochthonous salt advance recorded by the adjacent syn-kinematic sedimentation: Example from the Les Avellanes diapir (South Central Pyrenees)

Allochthonous salt advance recorded by the adjacent syn-kinematic sedimentation: Example from the Les Avellanes diapir (South Central Pyrenees)

Facies distribution along salt walls: The Upper Cretaceous mixed siliciclastic-carbonate deposits of the Cotiella minibasins (Southern Pyrenees, Spain)

To assess the influence of growing salt structures on facies distribution, stratal pattern, and thickness trends, this paper provides the tectonostratigraphic framework of the outstandingly exposed Cotiella minibasins (South-Central Pyrenees, Spain). Based on detailed analysis of field cross-sections, our results showcase the syn-halokinetic upper Coniacian-lower Santonian Cotiella minibasins infill (1.5–3 km thick) records four shallow-marine depositional sequences, made of mixed siliciclastic-carbonate stratigraphic sequences. This infill is subdivided in three tectonostratigraphic units, identified by using large and small-scale halokinetic structures (i.e. wedges, megaflaps) and variations in facies associations, thicknesses, stratal patterns from the salt wall flanks to the central part of the minibasins. The first unit records the onset of salt movement with overlying laterally continuous sheet-like sedimentary layers and progressive facies transitions over distances of kms. The influence of halokinesis on sedimentation patterns was minor, and only impacted thickness trends and depocenters localization. The second unit records salt evacuation at the surface with the presence of salt-wall derived detritus, the rapid downbuilding and a increase of sand-rich facies proportions. The stratal pattern is characterized by sheet like layers, laterally discontinuous over distances of 300–600 m downdip to the salt wall. Topographically elevated salt walls likely amplified tidal currents, implying sand-rich facies accumulation along the salt wall margin. The halokinesis influence on sedimentation, thickness trends and depocenter localization was significant. The third unit records the end of the salt evacuation stage, marking a brutal decrease of sand-rich facies, likely controlled by regional controls such as eustacy and tectonics. The influence of halokinesis on sedimentation patterns, thickness trends, large-scale geometries and depocenter localization was significant. Our work indicates that distinguishing these large-scale tectonostratigraphic units and their characteristics is of prime importance to understand the archetypal facies distribution, thickness and stratal patterns along salt structures margins.

Hydrological characterization of hydropeaks in mountain rivers (examples from Southern Pyrenees)

AbstractStreamflow in the Ésera and Upper Cinca Rivers (South Central Pyrenees) experiences alterations in the form of rapid pulses, commonly referred to as hydropeaks, associated with highly variable on‐demand hydropower production from flowing or stored water. A hydrological characterization of the hydropeaks in these two rivers was carried out to examine their distinct hydropeaking pattern during hydrologically contrasted years. The Ésera demonstrated a hydropeaking regime characterized by a high frequency and magnitude, while the Upper Cinca presented a regime with higher frequency but of lesser magnitude. Additionally, this study classified hydropeaks following the shapes proposed in previous studies and assessed their temporal distribution (frequency), timing, and magnitude. Results indicated that hydropeaks were different in shape and magnitude in both rivers; a Front Step pulse shape dominated in the Ésera whereas a Rectangle pulse shape was the most frequent in the Cinca. The Front Step shape had the highest ramping rates during the rising limb of the hydrograph and the shortest time to the maximum flow; whereas the Rectangle shape had higher duration and a larger volume of water released. Hydropeaks in the Ésera were less frequent (one per day) than in the Cinca (two per day). The river Ésera presented, in general, high‐magnitude hydropeaks, with double volume and duration, and three times larger up‐ramping rates and time between flow pulses. Overall, hydropeak shapes in the Ésera varied depending on the hydrological year and the season, while in the Cinca, shape distribution followed the same temporal pattern regardless of year and season; thus, hydropeaking in the Ésera appeared to be much more dependent on the annual hydrology (whether the year is wet or dry) than in the Cinca. Hydropeaking regimes were characterized based on three categories of variables: magnitude (flow‐based or hydrological variables), timing (duration), and frequency (occurrence). According to the variability of these variables, a total of three statistically significant groups were obtained in the Ésera, while two groups were identified in the Cinca. Hydropeaks can be statistically classified by their hydrological characteristics that in turn may have a direct effect on sediment entrainment and transport with implications to the ecological functioning of rivers. The different shape of the hydropeaks, however, will control the attenuation of the flows downstream and, consequently, the maintenance of the river's competence and capacity. This methodology provides a useful quantification of hydropeaking regimes to assess the potential impacts on physical and biological aspects of river systems.

The early middle Eocene transition at the Esera valley

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 (Nummulitesand 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.

Coralline Algae at the Paleocene/Eocene Thermal Maximum in the Southern Pyrenees (N Spain)

During the Paleocene/Eocene Thermal Maximum, ~55.6 Ma, the Earth experienced the warmest event of the last 66 Ma due to a massive release of CO2. This event lasted for ~100 thousands of years with the consequent ocean acidification (estimated pH = 7.8-7.6). In this paper, we analyze the effects of this global environmental shift on coralline algal assemblages in the Campo and Serraduy sections, in the south-central Pyrenees (Huesca, N Spain), where the PETM is recorded within coastal-to-shallow marine carbonate and siliciclastic deposits. In both sections, coralline algae occur mostly as fragments, although rhodoliths and crusts coating other organisms are also frequent. Rhodoliths occur either dispersed or locally forming dense concentrations (rhodolith beds). Distichoplax biserialis and geniculate forms (mostly Jania nummulitica) of the order Corallinales dominated the algal assemblages followed by Sporolithales and Hapalidiales. Other representatives of Corallinales, namely Spongites, Lithoporella as well as Neogoniolithon, Karpathia, and Hydrolithon, are less abundant. Species composition does not change throughout the Paleocene/Eocene boundary but the relative abundance of coralline algae as components of the carbonate sediments underwent a reduction. They were abundant during the late Thanetian but became rare during the early Ypresian. This abundance decrease is due to a drastic change in the local paleoenvironmental conditions immediately after the boundary. A hardground at the top of the Thanetian carbonates was followed by continental sedimentation. After that, marine sedimentation resumed in shallow, very restricted lagoon and peritidal settings, where muddy carbonates rich in benthic foraminifera, e.g., milioliids (with abundant Alveolina) and soritids, and eventually stromatolites were deposited. These initial restricted conditions were unfavorable for coralline algae. Adverse conditions continued to the end of the study sections although coralline algae reappeared and were locally frequent in some beds, where they occurred associated with corals. In Serraduy, the marine reflooding was also accompanied by significant terrigenous supply, precluding algal development. Therefore, the observed changes in coralline algal assemblages during the PETM in the Pyrenees were most likely related to local paleoenvironmental shifts rather than to global oceanic or atmospheric alterations.

Interpreting the nature of the Aulet and Adons diapirs from sedimentologic and stratigraphic analysis of flanking minibasin strata, Spanish Pyrenees, Catalunya, Spain

ABSTRACT The Aulet and Adons diapirs are exposures of Triassic Keuper evaporites in the Ribagorça Basin in the south-central Pyrenees. The diapirs have been alternatively interpreted from mapped structural relationships as either passive salt diapirs or extensional salt rollers. Correspondingly, the associated diapir-flanking minibasins have been interpreted as either salt-withdrawal or extensional-rollover minibasins, respectively. New field mapping, stratigraphic sections, petrographic analysis, correlation diagrams, and drone photography characterize the depositional facies and stratal architecture of the flanking Sopeira, Sant Gervàs, and Faiada minibasins (upper Albian to lower Santonian synrift to postrift strata), which in turn, constrains the origin and evolution of each salt body and associated minibasins. Each minibasin displays unique facies patterns and stratal thicknesses that reflect depositional systems evolving in response to spatially and temporally variable extension, salt evacuation, and passive diapirism during the Pyrenean rift and postrift phases. The Sopeira minibasin developed in the late Albian with significant localized subsidence, but it remains inconclusive if the bounding Aulet diapir originated as a passive diapir or a salt roller. The Llastarri fault zone, previously interpreted as a salt weld, separates the Sopeira minibasin from the primarily extensional Sant Gervàs minibasin, and is reinterpreted here as a remnant salt ridge, as it lacks evidence for passive diapirism. The Sant Gervàs minibasin remained relatively uplifted until the middle to late Cenomanian, along with the Faiada minibasin. Evidence for passive diapirism in the Faiada minibasin, including diapir-derived detritus and composite halokinetic sequences, indicate salt evacuation into the bounding Adons passive diapir. Integration of detailed sedimentologic and stratigraphic analyses with interpretations of basin formation and structural development provides better resolution of the earlier phases of gravity-driven extension and loading-driven salt movement of the Aulet and Adons diapirs; these insights help constrain structural interpretations and reconstructions of Pyrenean shortening and megaflap development in the Ribagorça Basin. Sedimentological and stratigraphic evidence for or against passive diapirism need to be integrated into structural interpretations, especially when precursor salt structures are obscured by subsequent contraction. This well constrained basin framework demonstrates the effects of inherited extensional structures and passive diapirism on Pyrenean shortening and megaflap rotation.

Faunal composition and paleoenvironmental reconstruction of a Middle–Late Triassic boundary assemblage in the Pyrenean basin (Catalonia, NE Spain)

AbstractThe Ladinian–Carnian transition in the Tethys domain was accompanied by an important environmental change representing a milestone in the climate evolution of the Triassic. However, estimations on paleodiversity composition and paleoenvironmental conditions across this interval are scarce in marine settings due to the lack of fossil-bearing successions. In this work, a refined paleontological and sedimentological study has allowed us to better characterize a well-preserved marine ?Ladinian–Carnian carbonate succession in the South Central Pyrenees (Odèn site, Catalonia, NE Spain). Vertebrate faunas include numerous actinopterygian specimens, forming an assemblage composed of at least four taxa: Peltopleurus cf. P. nuptialis Lombardo, 1999, Saurichthys sp., Colobodus giganteus (Beltan, 1972), and an indeterminate halecomorph. Specimens belonging to the genus Peltopleurus are dominant; the long-snouted Saurichthys, the halecomorph, and the large-bodied Colobodus giganteus are less abundant. Tetrapod remains are scarcely present and are assigned to sauropterygians. Invertebrate faunas include bivalves (Pseudocorbula gregaria [Münster in Goldfuss, 1838]) and brachiopods (Lingula sp.). The fossil assemblage was recovered from organic-rich laminated silty mudstone layers. Sedimentological and textural analyses suggest that fossil biotas were deposited below the fair-weather wave base in shallow subtidal coastal settings. These environments were sporadically sourced by silt/clay. The age of the Odèn site, on the basis of the recovered fauna, is assigned to the ?late Ladinian–middle Carnian (Middle–Late Triassic), which is in agreement with previously published ages based on palynomorph data.The refined integration of paleontological, sedimentological, and biostratigraphic data from the Odèn site and other vertebrate-bearing localities in the Tethys domain can help better constrain the paleoenvironmental conditions and paleogeographical configuration impacting ecosystem diversity during the late Ladinian–Carnian interval.

Effects of glaciation on karst hydrology and sedimentology during the Last Glacial Cycle: The case of Granito cave, Central Pyrenees (Spain)

In Alpine regions, speleothem development on karst systems largely occurs during warm interglacial or interstadial phases due to their limited growth during cold stages. Still, recent attention has been given to the role of clastic sediments in caves, less dependent on temperature conditions. Yet, only a small number of caves worldwide preserve both speleothems and detrital deposits. Here we present an outstanding record of fine-grain laminated sediments and carbonate speleothems from the Granito cave (South Central Pyrenees, Spain) associated with seasonal to annual hydroclimatic pulses through the Last Glacial Cycle (LGC). Analysis of cave clastic facies together with new absolute dates on glacial deposits along the valley has provided new insights into the karst-glacial interactions in relation with long-term landscape evolution, with support of geomorphological, sedimentological, mineralogical, palynological, geochemical and geochronological data (U/Th series, OSL and IRSL).The Granito cave was formed before 153.6±1.2 ky (Marine Isotopic Stage, MIS 6), as indicated by the oldest stalagmites dated in the cave, although speleothem formation occurred preferentially during MIS 5 and the Holocene interglacial stages. A 60 m thick clastic deposit was IRSL dated from 71.8±5.6 ky to after 26.5±2.5 ky corresponding with the maximum ice extent (MIE) during the LGC and subsequent glacial stabilization at 30.3±1.7 – 36.2±2.2 ky. The sediment infill was produced by water ponded in the cave coeval with the presence of glacial ice blocking the cave entrance. The cave clastic sequence includes channel, slackwater and backswamp facies, interpreted to result from pulses of sediment-laden water flow under vadose and phreatic flow regimes. The cave sediment’s mineralogical composition points to an exogenous source associated with glacial till sediments overlying the hillslope above the cave and along the Ara River valley. The palynological results obtained from the cave sediments show the dominance of an open landscape composed of steppe vegetation indicating cold glacial climatic conditions. The opening of the cave occurred before 14.9±1.5 ky, the stabilization age of the innermost Ara glacier moraine, giving rise to scouring and cut-and-fill sequences within the detrital infill. Speleothem growth during the Holocene indicates the return to warm climatic conditions with the development of a soil and vegetation cover above the cave. This study shows how a combined interpretation of clastic and speleothem lithofacies is critical for elucidating landscape evolution and surface-groundwater palaeohydrological changes in northern Iberia during the LGC.

An alternative model for the role of salt depositional configuration and preexisting salt structures in the evolution of the Southern Pyrenees, Spain

Salt depositional configuration exerted a fundamental control on both extensional and contractional deformation in the south-central Pyrenees. We divide the area into three domains and suggest that these domains are inherited from the original configuration of the Triassic Keuper salt basin. The Northern and Southern Domains are salt-diapir provinces with complex Mesozoic growth histories, whereas the Central Domain separating them has no diapirs and simpler Mesozoic isopachs. We use these patterns to interpret the Northern and Southern Domains as transported salt basins that were originally separated by the Central Horst, on which salt was thinner.During Dogger to mid-Cenomanian rifting, the Southern Salt Basin was an interior basin, isolated from deformation in the rift axis, whereas the Northern Salt Basin hosted an extensional breakaway at the updip end of the axial rift. During Pyrenean shortening, regions with preexisting salt structures were preferentially reactivated, whereas the stronger Central Horst remained relatively rigid. Eventually the sedimentary cover of the Southern Pyrenees was translated southwards and the connection with the original basement structure was lost.We tested our hypotheses using physical models. We confirmed that shortening a network of preexisting salt pillows could generate structures like the dome-and-basin pattern observed in the Southern Domain, and that it is possible to shorten salt basins on either side of a central horst while leaving sediments above the horst relatively undeformed.

Middle Eocene calcareous nannofossils in the Jaca transect (South-central Pyrenees Eocene Basin, Aragón river valley, Huesca)

The calcareous nanoplankton is studied from the base of the turbidite systems of the Upper Hecho Group (Jaca Basin, middle Eocene of the South-central Pyrenean Basin) up to the Gracionepel instabilities, within the Larrés slope Marls. This new chronostratigraphic contribution is of crucial importance for the improvement of the detailed temporal and spatial correlation framework of the genetically related depositional systems at basin scale. The calcareous nanofossil assemblage is largely dominated by Coccolithus pelagicus, C. formous as well as different species of Reticulofenestra, accompanied by occasional specimens of several species of Sphenolithus and Chiasmolithus. The results obtained, based on the detailed biostratigraphic study of a composite succession 2,500 m thick, allow us to characterize the main biohorizons of the middle Eocene on the basis of global biostratigraphic standards. The studied succession was deposited during the CNE11-CNE15 or NP15-NP16 biozones, within a time span of ~3.45 Myr, between 43.96 and 40.51 Ma (Lutetian/Bartonian). This age range is compatible with the existing scheme for the South-central Pyrenean Basin. The Upper Hecho Group, between the Roncal-Fiscal megaturbidite (MT-5) and the instability facies of Gracionepel, starts in the uppermost part of Zone NP15 continues into Zone NP16. The proposed biozonation provides new data for a correlation between stratigraphic events of other regional sections and facilitates the understanding of the lateral and temporal evolution of the studied systems, as well as the improvement of the general palaeogeographic framework of the basin.

3D reconstruction of syn-tectonic strata in a salt-related orogen: learnings from the Llert syncline (South-central Pyrenees)

The Llert syncline is located in the South-central Pyrenees, between the eastern termination of the EW-trending Cotiella Basin and the north-western limb of the NS-trending Turbón-Serrado fold system. The Cotiella Basin is an inverted upper Coniacian-lower Santonian salt-floored post-rift extensional basin developed along the northern Iberian rift system. The Turbón-Serrado fold system consists of upper Santonian – Maastrichtian contractional salt-cored anticlines developed along an inverted transfer zone of the Pyrenean rift system. Based on field research, this paper presents a 3D reconstruction of the Llert syncline in order to further constrain the transition between these oblique salt-related structures. Our results suggest that the evolution of the Llert syncline was mainly controlled by tectonic shortening related to the tectonic inversion of the Cotiella Basin synchronously to the growth of the Turbón-Serrado detachment anticline, and by the pre-compressional structural framework of the Pyrenean rift system. Our contribution provides new insight into the geometric and kinematic relationships of structures developed during the inversion of passive margins involving salt.