Western Pyrenees Research Articles

Normal Faulting in the 1923 Berdún Earthquake and Postorogenic Extension in the Pyrenees

AbstractThe 10 July 1923 earthquake near Berdún (Spain) is the largest instrumentally recorded event in the Pyrenees. We recover old analog seismograms and use 20 hand‐digitized waveforms for regional moment tensor inversion. We estimate moment magnitude Mw 5.4, centroid depth of 8 km, and a pure normal faulting source with strike parallel to the mountain chain (N292°E), dip of 66° and rake of −88°. The new mechanism fits into the general predominance of normal faulting in the Pyrenees and extension inferred from Global Positioning System data. The unique location of the 1923 earthquake, near the south Pyrenean thrust front, shows that the extensional regime is not confined to the axial zone where high topography and the crustal root are located. Together with seismicity near the northern mountain front, this indicates that gravitational potential energy in the western Pyrenees is not extracted locally but induces a wide distribution of postorogenic deformation.

Rapid age assessment of glacial landforms in the Pyrenees using Schmidt hammer exposure dating (SHED)

AbstractSchmidt hammer (SH) sampling of 54 10Be-dated granite surfaces from the Pyrenees reveals a clear relationship between exposure and weathering through time (n=52, R2=0.96, P<0.01) and permits the use of the SH as a numerical dating tool. To test this 10Be-SH calibration curve, 100 surfaces were sampled from five ice-front positions in the Têt catchment, eastern Pyrenees, with results verified against independent 10Be and 14C ages. Gaussian modelling differentiates Holocene (9.4±0.6 ka), Younger Dryas (12.6±0.9 ka), Oldest Dryas (16.1±0.5 ka), last glacial maximum (LGM; 24.8±0.9 ka) and Würmian maximum ice extent stages (MIE; 40.9±1.1 ka). These data confirm comparable glacier lengths during the LGM and MIE (~300 m difference), in contrast to evidence from the western Pyrenees (≥15 km), reflecting the relative influence of Atlantic and Mediterranean climates. Moreover, Pyrenean glaciers advanced significantly during the LGM, with a local maximum at ~25 ka, driven by growth of the Laurentide Ice Sheet, southward advection of the polar front, and a solar radiation minimum in the Northern Hemisphere. This calibration curve is available online (http://shed.earth) to enable wider application of this method throughout the Pyrenees.

Genomic selection signatures in sheep from the Western Pyrenees

BackgroundThe current large spectrum of sheep phenotypic diversity results from the combined product of sheep selection for different production traits such as wool, milk and meat, and its natural adaptation to new environments. In this study, we scanned the genome of 25 Sasi Ardi and 75 Latxa sheep from the Western Pyrenees for three types of regions under selection: (1) regions underlying local adaptation of Sasi Ardi semi-feral sheep, (2) regions related to a long traditional dairy selection pressure in Latxa sheep, and (3) regions experiencing the specific effect of the modern genetic improvement program established for the Latxa breed during the last three decades.ResultsThirty-two selected candidate regions including 147 annotated genes were detected by using three statistical parameters: pooled heterozygosity H, Tajima’s D, and Wright’s fixation index Fst. For Sasi Ardi sheep, chromosomes Ovis aries (OAR)4, 6, and 22 showed the strongest signals and harbored several candidate genes related to energy metabolism and morphology (BBS9, ELOVL3 and LDB1), immunity (NFKB2), and reproduction (H2AFZ). The major genomic difference between Sasi Ardi and Latxa sheep was on OAR6, which is known to affect milk production, with highly selected regions around the ABCG2, SPP1, LAP3, NCAPG, LCORL, and MEPE genes in Latxa sheep. The effect of the modern genetic improvement program on Latxa sheep was also evident on OAR15, on which several olfactory genes are located. We also detected several genes involved in reproduction such as ESR1 and ZNF366 that were affected by this selection program.ConclusionsNatural and artificial selection have shaped the genome of both Sasi Ardi and Latxa sheep. Our results suggest that Sasi Ardi traits related to energy metabolism, morphological, reproductive, and immunological features have been under positive selection to adapt this semi-feral sheep to its particular environment. The highly selected Latxa sheep for dairy production showed clear signatures of selection in genomic regions related to milk production. Furthermore, our data indicate that the selection criteria applied in the modern genetic improvement program affect immunity and reproduction traits.

Fluid circulations in response to mantle exhumation at the passive margin setting in the north Pyrenean zone, France

Sub-continental lithospheric mantle rocks are exhumed in the distal part of magma-poor passive margins. Remnants of the North Iberian paleo-passive margin are now exposed in the North–Pyrenean Zone (NPZ) and offers a field analogue to study the processes of continental crust thinning, subcontinental mantle exhumation and associated fluid circulations. The Saraille Massif which belongs to the ‘Chainons Bearnais’ range (Western Pyrenees), displays field, petrographic and stable isotopic evidence of syn-kinematic fluid circulations. Using electron probe micro-analyses on minerals, O, C, Sr isotopes compositions and micro thermometry/Raman spectrometry of fluid inclusions, we investigate the history of fluid circulations along and in the surroundings of the Saraille detachment fault. The tectonic interface between the pre-rift Mesozoic sedimentary cover and the mantle rocks is marked by a metasomatic talc-chlorite layer. This layer formed through the infiltration of a fluid enriched in chemical elements like Cr leached from the exhuming serpentinized mantle rocks. In the overlying sediments (dolomitic and calcitic marbles of Jurassic to Aptian age), a network of calcitic veins, locally with quartz, formed as a consequence of the infiltration of aqueous saline fluids (salinities up to 34 wt% NaCl are recorded in quartz-hosted fluid inclusions) at moderate temperatures (~ 220 °C). These brines likely derived from the dissolution of the local Triassic evaporites. In the upper part of the metasomatic system, upward movement of fluids is limited by the Albian metasediments, which likely acted as an impermeable layer. The model of fluid circulation in the Saraille Massif sheds light onto other synchronous metasomatic systems in the Pyrenean realm.

Rift-margin extensional forced folds and salt tectonics in the eastern Basque-Cantabrian rift basin (western Pyrenees)

Abstract In this paper we present and discuss Cretaceous extensional folds of the eastern Basque-Cantabrian Basin (Northern Spain). Geometry and kinematics of folds is constrained by means of structural and sedimentological fieldwork integrated with geological mapping, revealing an intimate link between coeval folding, extensional faulting, and salt mobilization. In detail, the Mesozoic succession of the northwestern and southern borders of the Palaeozoic Bortziriak-Cinco Villas massif (eastern margin of the BCB) host late Albian–early Cenomanian syn-rift forced folds. The studied forced fold axes trend parallel and are located above main and inferred Cretaceous syn-sedimentary basement faults. Structural data indicate that these folds formed during the late Albian − early Cenomanian interval. The presence of Upper Triassic clay and evaporite outcrops along and/or close to the axes of folds and their stratigraphic relationship with Upper Cretaceous strata indicate their halokinetic origin and extrusion during folding. The trigger of salt tectonics is attributed to a basement extensional pulse during the Bay of Biscay – Pyrenean rifting. Related high subsidence-rates allowed salt to flow towards faults, forming salt walls and causing the inflation and folding of the overburden.

La ressource génétique locale sous tensions : Trajectoires d’évolution des races ovines laitières Corse et Pyrénéennes, entre modèles d’élevage et valorisation collective des fromages de terroir

EnglishThe evolving nature of a local breed can disrupt its relationships with its home territory. We explore such relationships through the case of dairy sheep breeds of Corsica island and French Western Pyrenees. We analyze the trajectory of evolution of these breeds according to the evolving patterns of breeding and the valorization of cheeses (PDO Brocciu and PDO Ossau-Iraty). The local breeds and their selection settings are put in tension between choices of cheese qualification (proof of origin), and the choice of breeding, which can be contradictory processes: intensification of farming systems and re-anchorage of products. In Western Pyrenees, recent appropriation of local breeds leads to renewing their selection settings. There are no such noticeable processes in Corsica. Thus, territorialization of agriculture challenges the territoriality of the local breeds francaisLe caractere evolutif d’une race locale peut perturber ses relations avec son territoire d’origine. Nous les explorons a travers le cas des races ovines laitieres de Corse et des Pyrenees-Atlantiques. Nous analysons la trajectoire de ces races en regard de l’evolution des modeles d’elevage et de la valorisation des fromages de terroir (AOP Brocciu et AOP Ossau-Iraty). Les races locales et leurs referentiels de selection sont mis en tension entre des choix de qualification des fromages, et des choix d’elevage, deux processus parfois contradictoires : intensification des systemes d’elevage et re-ancrage des produits. Alors qu’en Pyrenees-Atlantiques, l’enjeu de durabilite locale des elevages pousse a une nouvelle appropriation des races locales et a renover les referentiels de selection, on n’observe pas de tel phenomene en Corse. La reterritorialisation de l’agriculture interroge ainsi la territorialite des races locales.

Importance of artificial stopover sites through avian migration flyways: a landfill‐based assessment with the White Stork Ciconia ciconia

Open landfills seem to be playing an increasing role as target feeding areas for several species, not only in their breeding areas or during the winter, but also during the migration period. Evaluating the extent to which landfill sites are used by migrants is crucial to understanding their role in driving stopover decisions during migration, and in the potential health risks linked to feeding on refuse. The aim of this study was to evaluate the role of two open landfills located just before (France) and after (Spain) the East‐Atlantic flyway enters Iberia through the western Pyrenees as potentially important stopover sites for the White Stork populations moving along this route. Overall, we detected that these sites were used by storks that had been ringed from many western European breeding populations, mainly during the migration period, but also in winter. The mean distance between the stork breeding/ringing origin and the landfill sites increased from summer to winter, suggesting that storks breeding further away pass through Iberia later in the season, reflecting population‐specific timing of migration. During the autumn migration period (August–September), the first encountered landfill in France was estimated to be used by c. 1200 storks, and the other in Spain by 4000 storks. Our study hence contributes to a better understanding of the current and potentially hazardous role played by landfill sites in White Stork ecology, which is essential in order to provide management recommendations, and to evaluate the consequences of proposed open landfill closures in Europe.

El otro lado de los Pirineos: Aquitania en la Edad del Hierro

The work that we’re about to present deals with the current state of archaeological knowledge of the Region of Aquitaine, France, during Iron Age. Firstly, we will lay out the main historical lines of research of Archaeology of Late Prehistory of this territory. This will include what has been researched, as well as the deficiencies that persist to this day. Using the available archaeological information, we will talk about its palaeogeography, with special attention to its climate and environment, the cultural evolution of the different human groups, and the development of different territories and their connections during the last millennium BC. We will also explain the current state of research regarding the different ethnicities that populated this area during Iron Age II. Lastly, we will cover the impact of the arrival of Rome in the context of the occupation of the Garonne Valley, The Western Pyrenees, Ebro Valley, and The Cantabrian Region.

Living with the Enemy: German Occupation, Collaboration and Justice in the Western Pyrenees, 1940–1948 by Sandra Ott

Living with the Enemy: German Occupation, Collaboration and Justice in the Western Pyrenees, 1940–1948 by Sandra Ott

La ocupación ganadera de los Pirineos occidentales de Catalunya en época romana e inicios de la Edad Media

Las investigaciones recientes sobre el poblamiento de las zonas altas de los Pirineos occidentales de Catalunya, concretamente en el actual Parque Nacional de Aigüestortes i Estany de Sant Maurici han permitido documentar una extensa secuencia de poblamiento humano y de explotación y modificación del medio físico. El presente trabajo detalla la evolución de este poblamiento desde el final de la prehistoria hasta entrados los primeros siglos de la Edad Media; un poblamiento que intensifica a partir de época imperial, especialmente durante el Bajo Imperio. La descripción de la información arqueológica se combina con la exposición resumida de los indicios de afectación de esta ocupación en el medio vegetal principalmente, como resultado de diversas actividades llevadas a cabo: la ganadería, la agricultura, la minería y la producción metalúrgica.

Intensive forest management affects bryophyte diversity in the western Pyrenean silver fir-beech forests

Understanding how bryophytes respond to management gradients in temperate forests is an important issue for their conservation and has major implications for forest management. This is especially true for western Pyrenean silver fir-beech forests, where high bryophyte turnover, as well as species loss, has been reported in the last 30years. This study is the first to explore bryophyte diversity patterns across western Pyrenean silver fir-beech forests with different management intensities. Our specific aims were to determine the main drivers of bryophyte richness and turnover and explore which bryophyte species can be used as indicators of management intensity. The effect of management was assessed on the overall bryophyte diversity as well as on the bryophyte groups based on taxonomy, life cycle strategy, sensitivity to forest management intensity and habitat preference. Bryophyte diversity was analyzed by generalized linear mixed models and multiple regression analysis on distance matrices. The results suggest that bryophyte richness in the Pyrenean forests is decreasing with intensive forest management. The bryophyte richness decrease on highly disturbed stands can be attributed to a loss of suitable microhabitats, such as large trees. Elevational gradient, as a proxy of climatic factors, is also an important driver of bryophyte species richness in the studied area. Long-lived and epiphytic bryophytes decreased on steep slopes. Turnover was driven by elevation and percentage of large gaps, which might be linked with forest management. The results also suggest that Dierssen's classification of bryophytes regarding sensitivity to forest management is not suitable for the evaluation of the effects of forest management in the studied region. Our main recommendation for bryophyte conservation is to avoid intensive forest management and to minimize the forest practices in steep slopes which are prone to soil erosion.

Variations to calcareous nannofossil CaCO3 content during the middle Eocene C21r-H6 hyperthermal event (~ 47.4 Ma) in the Gorrondatxe section (Bay of Biscay, western Pyrenees)

The carbonate content of calcareous nannofossils is dependent on seawater composition. One of the factors that affect seawater chemistry and consequently the degree of calcification in coccolithophores is temperature, as seen in present day warming oceans. The depth at which carbonates are dissolved (Calcite Compensation depth, CCD) can rise due to an increase in HCO3– and decrease in pH, leading to a major dissolution on the seabed and burndown. Similar processes have also been deduced for Eocene hyperthermal events, such as the PETM and ETM2. This study reports changes in coccolith carbonate mass from a hemipelagic setting (Gorrondatxe, at 1500m paleodepth) during the core of a minor Eocene hyperthermal event, namely the C21r-H6 event (47.44–47.32Ma). Image analysis techniques were used to determine differences in the carbonate mass of selected calcareous nannofossil taxa, revealing species-specific patterns. The CaCO3 mass of Chiasmolithus solitus decreased by 50% over the course of the C21r-H6 event, and many specimens also lost their crossed central bars, an additional indication of mass loss; Reticulofenestra sp. (3–5μm) showed a similar trend, but the percentage of mass lost was lower; Toweius pertusus, interpreted as being reworked, mirrored the behaviour of Chiasmolithus solitus, suggesting that the CaCO3 mass loss may have occurred on the seabed, rather than in the water column. In general, it can be concluded that the lysocline rose to 1500m paleobathymetry in the Bay of Biscay during the C21r-H6 event. Formation of corrosive bottom water in the North Atlantic Ocean is regarded as being responsible for the rise in the lysocline.

Thermal evolution of a hyperextended rift basin, Mauléon Basin, western Pyrenees

AbstractOnshore and offshore geological and geophysical observations and numerical modeling have greatly improved the conceptual understanding of magma‐poor rifted margins. However, critical questions remain concerning the thermal evolution of the prerift to synrift phases of thinning ending with the formation of hyperextended crust and mantle exhumation. In the western Pyrenees, the Mauléon Basin preserves the structural and stratigraphic record of Cretaceous extension, exhumation, and sedimentation of the proximal‐to‐distal margin development. Pyrenean shortening uplifted basement and overlying sedimentary basins without pervasive shortening or reheating, making the Mauléon Basin an ideal locality to study the temporal and thermal evolution of magma‐poor hyperextended rift systems through coupling bedrock and detrital zircon (U‐Th)/He thermochronometric data from transects characterizing different structural rifting domains. These new data indicate that the basin was heated during early rifting to >180°C with geothermal gradients of ~80–100°C/km. The proximal margin recorded rift‐related exhumation/cooling at circa 98 Ma, whereas the distal margin remained >180°C until the onset of Paleocene Pyrenean shortening. Lithospheric‐scale numerical modeling shows that high geothermal gradients, >80°C/km, and synrift sediments >180°C, can be reached early in rift evolution via heat advection by lithospheric depth‐dependent thinning and blanketing caused by the lower thermal conductivity of synrift sediments. Mauléon Basin thermochronometric data and numerical modeling illustrate that reheating of basement and synrift strata might play an important role and should be considered in the future development of conceptual and numerical models for hyperextended magma‐poor continental rifted margins.

Changes to sea-surface characteristics during the middle Eocene (47.4 Ma) C21r-H6 event: evidence from calcareous nannofossil assemblages of the Gorrondatxe section (western Pyrenees)

Changes to sea-surface characteristics during the middle Eocene (47.4 Ma) C21r-H6 event: evidence from calcareous nannofossil assemblages of the Gorrondatxe section (western Pyrenees)

Architecture, growth patterns, and early diagenetic modifications of a greenhouse ramp to rimmed shelf system: Danian of the Urbasa–Andia plateau, western Pyrenees, North Spain

The Danian carbonates exposed in the Urbasa–Andia plateau (western Pyrenees, North Spain) provide the opportunity to examine at different scales the facies types and architecture of a greenhouse ramp to rimmed shelf from the slope to coralgal reefal margin through to the highly restricted evaporitic inner shelf areas, integrated with a range of porosity-forming, early diagenetic phases associated with third-order highstands and lowstands. The detailed nature of the stratal architecture of this greenhouse system provides an understanding of potential reservoir layering, lateral facies and facies cycle changes, and widespread early dolomitization but significantly allows a whole paleokarst macroporosity system related to a third-order lowstand to be accessed, illustrating how eogenetic karstic porosity can vary drastically from margins to shelf interiors. The outcrops serve as potential analogs for fields in Paleocene carbonates in North Africa and the Middle East and also offer valuable depositional and digenetic models for greenhouse platforms of other ages.

Diatreme-forming volcanism in a deep-water faulted basin margin: Lower Cretaceous outcrops from the Basque-Cantabrian Basin, western Pyrenees

Deep-water diatremes and related eruption products are rare and they have been mainly interpreted from seismic-based data. We present lithofacies and geochemistry analysis of two Lower Cretaceous (Albian) deep-water diatremes and associated extra-diatreme volcaniclastic deposits at a well-exposed outcrop of the northern margin of the Basque-Cantabrian Basin (north Iberia). The studied diatremes are located along a N-S trending Albian fault and present sub-circular to elongate sections, inward-dipping steep walls and smooth to very irregular contacts with the host rocks. They are filled by un-bedded mixed breccias constituted by juvenile and lithic (sedimentary, igneous and metamorphic) clasts. Their textural and structural characteristics indicate that they represent lower diatreme and root zones of the volcanic system. Mapping, geochemical and petrologic data from diatreme-fills support their genetic relationship with the extra-diatreme volcaniclastic beds, which would be generated by the eruption of an incipiently vesicular trachytic magma. Studied diatremes result from multiple explosions that lasted over an estimated period of 65k.y. during the Late Albian (H. varicosum ammonite Zone, pro parte), and reached up to a maximum subsurface depth of ca. 370m, whereas extra-diatreme volcaniclastic beds were formed by eruption-fed gravity-driven flows on the deep-water (200–500m) paleoseabed. Petrological features suggest that these diatremes and related extra-diatreme deposits resulted mainly from phreatomagmatic explosions. In addition, organic geochemistry data indicate that the thermal effect of the trachytic melts on the sedimentary host caused the conversion of the abundant organic matter to methane and CO2 gases, which could also contribute significantly to the overpressure necessary for the explosive fragmentation of the magma and the host rocks. Considering the inferred confining pressures (ca. 8–11MPa) and the possible participation of unvesiculated (or degassed) melts, our results stress the importance of active hydraulic structures (e.g. faults) and the supplementary driving forces (e.g. thermogenic gases) in the formation of deep-water marine diatremes.

A high-order 3D spectral-element method for the forward modelling and inversion of gravimetric data - Application to the western Pyrenees

A high-order 3D spectral-element method for the forward modelling and inversion of gravimetric data - Application to the western Pyrenees

Mesozoic and Cenozoic decapod crustaceans from the Basque-Cantabrian basin (Western Pyrenees): new occurrences and faunal turnovers in the context of basin evolution

Twenty-nine new identifications of fossil decapod crustacean remains in the Basque-Cantabrian Basin (Western Pyrenees) spanning from the Jurassic to the Miocene and coming from twenty-four new and five yet known localities are described here for the first time. These remains represent a substantial advance in the knowledge of these faunas and their diversity in this basin, giving an accurate image of the decapod faunal succession. The study includes a taxonomical description and discussion with reference to the known occurrences. Their accurate dating and the environmental ascription have been possible after the analysis of the stratigraphic occurrence in the context of a well-known basinal stratigraphy. This has ultimately permitted a brief analysis of the decapod palaeoecology and faunal turnovers in the context of basin evolution.

Multi-Criteria Optimization for Fleet Size with Environmental Aspects

Abstract This research concerns multi-criteria vehicle routing problems. Mathematical models are formulated with mixed-integer programming. We consider maximization of capacity of truck vs. minimization of utilization of fuel, carbon emission and production of noise. The problems deal with green logistics for routes crossing the Western Pyrenees in Navarre, Basque Country and La Rioja, Spain. We consider heterogeneous fleet of trucks. Different types of trucks have not only different capacities, but also require different amounts of fuel for operations. Consequently, the amount of carbon emission and noise vary as well. Companies planning delivery routes must consider the trade-off between the financial and environmental aspects of transportation. Efficiency of delivery routes is impacted by truck size and the possibility of dividing long delivery routes into smaller ones. The results of computational experiments modeled after real data from a Spanish food distribution company are reported. Computational results based on formulated optimization models show some balance between fleet size, truck types, utilization of fuel, carbon emission and production of noise. As a result, the company could consider a mixture of trucks sizes and divided routes for smaller trucks. Analyses of obtained results could help logistics managers lead the initiative in environmental conservation by saving fuel and consequently minimizing pollution.

Herb layer in silver fir – beech forests in the western Pyrenees: Does management affect species diversity?

Silver fir-beech forests form ecologically important ecosystems in European mountains, where they have been intensively managed due to timber harvesting. Forest management effects can be evaluated using herb layer diversity as an indicator of environmental changes. Therefore, revealing the patterns of herb layer diversity is necessary for developing strategies for sustainable management. Knowledge on management history of fir-beech forests in the western Pyrenees is still limited. In this study we aim to disentangle the environmental drivers of species richness and species composition of these forests emphasizing the role of forest management. We sampled the herb layer vascular plants in 68 plots distributed among 14 silver fir-beech stands of the association Scillo lilio-hyacinthi-Fagetum sylvaticae and related diversity patterns with management histories, light conditions and topographic and climatic variables. Four management categories were established: recently managed, long managed, recently abandoned and long abandoned. Species richness was analysed by GLMM and species composition by partial CCA and PCNM. Multivariate dispersion analysis was used to assess differences in beta diversity among management categories. Management, continentality and slope had in general a weak effect on species richness, continentality with a positive effect whilst slope and management, in category of recently abandoned stands, with a negative effect. In addition, the percentage of large gaps had a moderate effect on open area species richness. Species composition was related to slope, ombrothermic index, forest management and spatial effects in terms of neutral processes. Long managed forests showed differences in beta diversity with recently abandoned and long abandoned forests. Our study suggests that environmental variables in combination with spatial effects are the main drivers of species diversity at small sampling scale, highlighting that management plays an important role in these western Pyrenean silver fir-beech forests.