Western Pyrenees Research Articles

Crustal imaging and characterization of active faults with a large-N nodal deployment - Application to the Chaînons Béarnais region (western Pyrenees foothills, France)

Understanding the driving forces and nature of intraplate seismicity remains a major unsolved problem in seismology. In the western Pyrénées, seismicity is concentrated in a narrow region that follows the boundary between the Axial Zone and the North Pyrenean Zone. Despite the presence of a permanent network in the region, the geometry of active faults, and their relationship with crustal structures, remain elusive, owing to significant earthquake location uncertainties. Here, we exploit data recorded by a large-N nodal array deployed in the Chaînons Béarnais region during four weeks of 2022 in order to image crustal structures and characterize active faults. We automatically detected and picked P and S waves with PhaseNet, resulting in a catalog of over 500 events, half of which are located beneath the temporary deployment. Tomographic images obtained from the inversion of P and S arrival times provide detailed insight into the geometry of folds and thrusts in the sedimentary cover, as well as the presence of a main fault in the basement which dips northward with an angle of 65° (Chaînons Béarnais normal fault). Seismicity relocation within the 3D model obtained by tomography shows that earthquakes are concentrated along this main active fault, extending from the top of the basement to a depth of approximately 16 km. These results demonstrate that passive imaging approaches can offer cost-effective alternatives to traditional controlled source imaging for seismotectonic studies and natural resource exploration in regions with active seismicity.

Festive Leisure and Rural Sport in the Basque Mugak: Sare and Extalar Cases

ABSTRACT This paper describes and analyses two cross-border sports festivals in the western Pyrenees: the Day of the Smugglers of Sare and the Festival of the Tradition of the wood pigeons hunt of Lizaieta (Etxalar-Sare). The selected examples show how border communities use rural sports in festive contexts to bring together people from both sides of the border (emic limit) and to express their thoughts about the state border. To address this research, an ethnographic methodology based on the observation of festive events and interviews with participants has been employed. The article addresses the identity of this border area whose inhabitants do not consider themselves entirely French, Spanish, or Basque, but all at once under the self-designation of fronterako jendea (the people of the border). In short, our study examines the role that local culture plays in defining and shaping border areas.

The middle‐upper Eocene Loza‐Portilla Formation (Western Pyrenees, North Spain): Palustrine‐lacustrine carbonate‐dominated sequences in a piggy‐back basin under compressional tectonic stress

The middle‐upper Eocene Loza‐Portilla Formation (Western Pyrenees, North Spain): Palustrine‐lacustrine carbonate‐dominated sequences in a piggy‐back basin under compressional tectonic stress

Geologically constrained geometry inversion and null-space navigation to explore alternative geological scenarios: a case study in the Western Pyrenees

SUMMARY Reducing the gap between geophysical inversion and geological interpretation can be achieved by integrating geological modelling into geophysical inversion. For this, we use a generalized, iterative level-set gravity inversion scheme in which geological units are deformed automatically. During the inversion process, a regularization term is defined using automated geological modelling to account for geological data and principles. This provides model-dependent geological constraints and encourages geological realism throughout inversion. To alleviate the dependence on the starting model and consider the possibility of features unseen by direct observations, an automated geophysical data-driven method is proposed to insert new rock units in the model. Uncertainty quantification is achieved through the null-space shuttle algorithm, which is used to generate a series of alternative models that are consistent with geophysical data. This methodology is applied to assess the uncertainties of a pre-existing 3-D crustal-scale geological model of the Western Pyrenean orogeny (France, Spain). The area is characterized by a positive gravity anomaly generally attributed to the presence of a shallow mantle body. The impact of variations in shape and density of key crustal and mantle features is investigated. Different scenarios are explored in 3-D space to produce a range of viable, relatively simple crustal-scale models of the area. This application demonstrates the capability and potential of this approach to evaluate alternative interpretations of geophysical data. The results show the plausibility of scenarios with a shorter subducted Iberian lower crust and a denser Axial Zone than in the pre-existing model.

Environmental Constraints and Human Agency in Early Medieval Village Formation: A Geoarchaeological Approach in the Western Pyrenees (Navarre, Spain)

ABSTRACT The interaction between human agency and environmental factors is a key topic in the archaeological study of early medieval village formation. Such interactions are particularly visible in the construction and maintenance of agrarian landscapes, which often become central to the local socio-economic development. This article explores these processes in a local context of the western Pyrenees (Navarre, Spain) through a combined analysis of documentary sources, toponymy, field survey, and core sampling for geochemical analysis. The foundations of the local landscape were laid down in the Early Middle Ages, closely related to the establishment of a village settlement and the collective appropriation of agrarian resources. The local geological and soil features, marked by the presence of thick and soft, mineral nutrient-rich soils derived from the weathered volcanic rock substrate, permitted the construction and maintenance of a terraced field system. This fact has been key for later landscape evolution at the local and regional scales, including the formation of a supra-local valley community during the Late Middle Ages, or the deep agrarian and demographic transformations that followed the introduction of New World crops during the Early Modern period.

Separation of source, attenuation and site parameters of 2 moderate earthquakes in France: an elastic radiative transfer approach

Summary An accurate magnitude estimation is necessary to properly evaluate seismic hazard, especially in low to moderate seismicity areas such as Metropolitan France. However, magnitudes of small earthquakes are subject to large uncertainties caused by major high-frequency propagation effects which are generally not properly considered. To address this issue, we developed a method to separate source, attenuation and site parameters from the elastic radiative transfer modeling of the full energy envelopes of seismograms. The key feature of our approach is the treatment of attenuation -both scattering and absorption- in a simple but realistic velocity model of the Earth’s lithosphere, including a velocity discontinuity at the Moho. To reach this goal, we developed a 2-step inversion procedure, allowing first to extract attenuation parameters for each source-station path from the whole observed energy envelope using the Levenberg-Marquardt and grid-search algorithms, then to determine site amplification and the source displacement spectrum from which the moment magnitude Mw is extracted. In the first step, we use the forward modeling procedure of Heller et al. (2022) in order to simulate energy envelopes by taking into account the full treatment of wave polarization, the focal mechanism of the source and the scattering anisotropy. The inversion procedure is then applied to the 2019 ML 5.2 Le Teil and 2014 ML 4.5 Lourdes earthquakes which both occurred in southern France. Data from 6 stations are selected for each event. The inversion results confirm a significant variability in the attenuation parameters (scattering and absorption) at regional scale and a strong frequency dependence. Scattering appears to be stronger towards the French Alps and Western Pyrenees. Absorption is stronger as frequency increases. Although not very resolvable, the mechanism of scattering appears to be forward or very forward. By inverting the source spectrum, we determine moment magnitudes Mw of 5.02 ± 0.17 for the Le Teil earthquake and 4.17 ± 0.15 for the Lourdes earthquake.

The social-ecological landscape of herding on the high mountain commons of Larrau in the western Pyrenees (France)

IntroductionMuch has been written about herding, pastoralism and the ethos of the commons that persists in Soule and the valley republics of the western Pyrenees. However, more has been written about the idealized norms of the practice than the social dynamics of alliance formation on which cooperation in herding on the high mountain commons in Soule has depended for centuries. We use empirical evidence from the parish-commune of Larrau to analyze the emergence, social alliance, and landscape placement of Cayolar, a syndicate of herders associated with a named inholding within the high mountain commons, to inform our understanding of the process of settling down in the western Pyrenees.MethodsWe abstract the institutional features of herding in the Soule Valley then proceed with a (1) Bayesian analysis of calibrated radiocarbon dates from herding sites across the commons, (2) a Bayesian social network analysis of herders and other alliance-relevant information, and (3) a landscape analysis of the placement of Cayolar inholdings.ResultsA syndicate of herders organized as a Cayolar succeed by following mutually agreed upon rules, making credible commitments to each other, and monitoring members' conformance to the rules. The organizational performance of a Cayolar depends on the articulation of herders to the members of the Soule community of interest through nested levels of institutional decision-making. Archaeological, historical and ethnographic results provide direct evidence for use of Cayolar structures and inholdings by c. 1000 CE and the institutional and organizational aspects of decision-making by c. 1100 CE.DiscussionThe Cayolar is an enduring place-based organization with an average use-span of c. 850 years. Members have a regulatory interest in enforcing the collaboration of others in collective herding and little incentive to defect since unlike Hardin's herders, Cayolar members share a past and expect to share a future as members of the Soule community of interest. Íñigo Arista established the Basque kingdom of Navarra in 824 CE, and his donations contributed to the founding of the Benedictine monastery of Leyre that established a pastoral enterprise at Betzula within the Soule Valley. Other monastic orders soon turned their attention to the western Pyrenees responding to attempts by the Catholic Church to counter civil unrest in southern France. The real turning point for collective herding on the high mountain commons was the introduction of primordial fueros on the Iberian side of the Pyrenees. These direct royal agreements with freemen encouraged resettlement and repopulation of the western Pyrenees and provided the means for local communities of interest to coalesce and develop institutions to organize the collective effort of individuals for the benefit of a group.

Mortoniceratinae (Ammonoidea) from the lower upper Albian of the Basque-Cantabrian basin (Western Pyrenees): New records, new taxa and their taxonomic and biostratigraphical value

The subfamily Mortoniceratinae comprises Albian to early Cenomanian ammonoids whose phylogeny forms the basis of a biozonation for the upper Albian due to their highly evolving nature and worldwide distribution. However, both morphological plasticity of the group and the known common occurrences in many condensed successions call for accurate taxonomy and stratigraphy in order to ascertain the phylogeny and temporal/spatial relationships. Here, early late Albian Mortoniceratinae from mostly uncondensed successions, with a continuous record, are described from a hyperextended pericratonic rift basin in the Western Pyrenees. Although quite rare in the study area, we can here provide a detailed taxonomic study of 55 specimens, representing 19 species, with a single new genus and five new subspecies, all recovered over a period of 30 years from upper Albian strata in eight sedimentary areas covering nearly 1000 square kilometres and more than 4000 m of measured logs. Most of these mortoniceratines show morphologies that are in agreement with their known and accepted phyletic lineage in which tuberculation stages are key; however, we also record tri- and quadrituberculate forms that depart from the main and represent unsuccessful offshoots. A reassessment of Mortoniceras (M.) fallax is presented, inclusive of a more complete, emended diagnosis, and referral of the eponymous biozone to the lower upper Albian. The palaeobiogeographical distribution of species studied corresponds to the western Mediterranean area, part of the central Tethyan Realm, in the Basque-Cantabrian Basin (Western Pyrenees) which faces the northern European basins of the Boreal Realm. This strategic location is interpreted to be a nexus between worldwide basins, as the striking cosmopolitan character of most species studied suggests. The ammonoid fauna studied is proposed as support of the western Mediterranean biozonation; it is tentatively correlated interregionally as well.

Power and alterity: Depictions of the Vascones from antiquity to the middle ages

AbstractThis article undertakes an examination of the origins and evolution of a discourse of alterity against the Vascones –the alleged forefathers of the Basques – and other Western Pyrenean peoples from Antiquity to the Middle Ages. The methodology employed involves the study of literary references made to these peoples, which are then compared to recent scholarly and archeological evidence. Through this analysis, it becomes possible to evaluate the accuracy of these mentions and interpret them within their specific historical context. The results of this research indicate that mentions of the Vascones during this timeframe were mainly polemic in nature and lacked substantial grounding in empirical reality. Instead, it seems that the underlying objective of these narratives of alterity was twofold: to enhance the social and political standing of their authors and to support their claims to political control over the Western Pyrenees. The abandonment of these interpretative repertoires during the tenth century, coinciding with the emergence of the kingdom of Pamplona and the county-duchy of Wasconia, further emphasizes the connection between the display of these tropes and imbalances in political power between the region and its neighbors. The conclusions of this article directly challenge the underpinnings of discourses that depict the ancient Vascones as entirely alien to the political and religious paradigms derived from the Roman and Christian traditions. In so doing, it thus confront narratives about these “ancient Basques” that are prevalent in contemporary Basque cultural production.

Albitization evidences of Mesozoic carbonates: petrological study of authigenic albites in the northwest of the Bortziriak Cinco Villas Massif, eastern Basque-Cantabrian Basin

The presence of authigenic Na-feldspars in sedimentary carbonate rocks is unusual and its origin is controversial in terms of genesis and timing. The use of optical microscopy, cathodoluminescence and in situ semi-quantitative EDX analysis techniques, has allowed the identification and characterization of authigenic albite crystals in the Mesozoic pre- and syn-rift carbonates of the northwestern margin of the Bortziriak-Cinco Villas Massif, in the northeastern Basque-Cantabrian Basin (western Pyrenees). The euhedral habit, crystal size, spatial distribution and crosscutting relationships, together with the pure albitic composition, suggest a relatively early replacement origin. Compaction of sediments during burial, besides possible fluid migration linked to the intense syn-rift halokinetic activity, may have been decisive for the mobilisation of cations, and hence, for the albitization of the carbonate rocks.

Assessment of determinants of high nature value (HNV) farmland at plot scale in Western Pyrenees

The concept of High Nature Value (HNV) farming hinges on the causality between agroecosystems with low intensity of management and the corresponding environmental outcomes, including high levels of biodiversity and the presence of semi-natural habitats. Although European strategies for rural development and biodiversity conservation have long recognized the importance of HNV farmlands, many of those areas are currently threatened by intensification and land abandonment. A variety of approaches have been developed for identifying HNV areas and measuring changes in their distribution and extent at landscape scales. In contrast, quantitative approaches for evaluating differences in HNV among the most basic units of management (farms and farm plots) are scarce and almost exclusively based on biodiversity indicators. This gap limits our ability to derive existing gradients of HNV at fine scale and the underlying cause conducive to HNV. Hence, we implemented an index to capture multiple facets of HNV based on expert knowledge criteria and field surveys performed at the finest scale of management (plot). First, we computed this index for hundreds of grasslands located across the Western Pyrenees. Then, we analysed the relationship between the nature value of plots and environmental, management and socio-economic variables. Our results evidence a gradient between low diversity and intensively used agricultural plots and HNV grasslands in the Western Pyrenees. Highest nature values were significantly related to the occurrence of plots in meadows located in steep areas within the Natura 2000 network, whereas lowest values were related to recently opened areas and the number of treatments per year. Importantly, this index, which could be adapted to other farming areas, provides quantitative information to support the implementation of result-based schemes, including eco-schemes and agri-environment-climate interventions of the new CAP (2023–2027).

The Quaternary activity of the Estella diapir from the uplift record of fluvial terraces, pediments and cave sediments in the Western Pyrenees, Spain

This work analyses the Quaternary landforms, geomorphic changes and stratigraphic evidences of evaporite dissolution and halokinesis in the Estella salt diapir (Basque-Cantabrian Basin). The mapping of Quaternary deposits demonstrates that karstic subsidence and diapirism happen at the same time. The diapir geometry is characterised by a prominent 4.5 km-long fault scarp attributed to the uplift of the diapir and a fluvial gypsum escarpment along the northern and eastern diapir edges. The dissolution of the gypsiferous caprock is responsible for the development of a large number of collapse sinkholes, the local thickening of terrace deposits and a network of endokarstic conduits connected to saline springs that cause a notable increase in the salinity of the Ega river across the diapir (70% electrical conductivity increase). The 40 m vertical displacement of T4 terrace and P5 pediment deposits, the anomalous longitudinal profile of the old terraces, the deflection of infilled-valleys at the base of the fault scarp, the occurrence of wind gaps and the continuous lateral migration of the Ega river away from the diapir support salt upwelling since 644 ± 81 ka ago at a long-term, average uplift rate of 0.05–0.07 mm/yr. The 12 m offset of T8 terrace, the steepening of the Ega river floodplain and the tilting of the upper level and the antigravitative erosion genesis of the Longinos cave point to a faster diapir rising rate of 0.23–0.57 mm/yr in the last 36 ± 15 ka coinciding with a period of increasing river incision. The lack of tectonic activity in the region suggests that diapirism is enhanced by erosional unloading related to fluvial entrenchment. The thickening of pediment P5 supports the north-northeast flow of salt towards the river valley.

Pleistocene river diversions caused by large landslides in the western Pyrenees (Oria River drainage basin, N Spain)

AbstractRiver‐blocking landslides exert a deep impact on mountain range landscapes and the organization of catchments. A blocked river diverted to another watershed modifies both original and transferred drainage networks both up‐ and downstream. Using western Pyrenees examples, a geological and geomorphic framework with diagnostic criteria to detect river diversion by landslides is presented, including the identification of elbows of diversion, eroded divides, beheaded underfit rivers, diverted overfit rivers, reversed river segments and the landslides at fault. Some landslides caused the formation of lakes that overflowed upstream at catchment divide segments with elevations lower than those of blocking landslide tops. Unravelling the presence of fan deltas at distinct sites/elevations of palaeolake shores contributed as well to identification of river damming and later diversion episodes. Reconstruction of the sedimentary organization of river palaeovalleys and of their associated fluvial terraces and palaeoriver channels (some currently submerged by the Cantabrian Sea), along with the reconstruction of river profiles, analysis of bedrock and morphology of watershed divides, identify seven river diversions caused by landslides and 14 additional slides that variably constrained river basin dynamics in the area studied. The diverting slides have current areas between 0.06 and 12.3 km2 (thus including giant examples), thicknesses up to 300 m and translational–rotational rupture surfaces usually with low dip angles (3.5–12.3°). A combination of relative dating methods and published absolute ages suggests that diversion events occurred during the Quaternary. This study shows that river diversion by landslides can be significant in mountainous areas of moderate relief.

Pyric herbivory increases soil microbial diversity but has a site-dependent effect on soil mesofauna in the mid-term

Woody plant encroachment threatens grassland biomes at a global scale. Pyric herbivory combines prescribed burnings and targeted grazing to restore open habitats and has proved to be successful in promoting landscape and plant community diversity. However, less is known on the effects of pyric herbivory practices on belowground biodiversity. We evaluated the midterm effect on mesofauna, bacteria and fungi of prescribed burns and targeted horse grazing regimes implemented to restore a grassland encroached by gorse (Ulex gallii Planch.). We hypothesized that 1) low-intensity shrub-to shrub burnings had no effect or had a transient effect of low magnitude on soil microbial diversity, and that 2) targeted horse grazing after burning increased soil mesofauna and microbial diversity in the midterm. We established an experiment in two shrub-encroached grasslands in western Pyrenees with three treatments (no burning and no grazing as control, burning but no grazing, and burning and grazing). We measured soil properties and soil diversity of fungi and bacteria (DNA-metabarcoding) just after fire, and vegetation structure, soil properties and soil diversity of fungi, bacteria and mesofauna after two periods of targeted grazing (a year and a half after the burning). The response to pyric herbivory differed among soil organisms. Fungi were more sensitive to burning than bacteria, but both recovered a year and a half after burning –fungi only recovered in the presence of grazing–. Grazing increased soil fungi and bacteria diversity indexes (∼20 % and ∼5 % increase, respectively) at the two sites. A year and a half after burning, burned and ungrazed areas had a 30 % more mesofauna diversity than control areas whereas grazing of the burned areas decreased mesofauna diversity by 30 % at one of the sites compared to the control. Since the responses to pyric herbivory vary among soil organisms, a wide range of management intensities across space and time are recommended for maximizing soil biodiversity.

Spatiotemporal Behavior of an Extremely Small Seismic Swarm in Pyrenean Foreland, France

ABSTRACT During the large-N MAUPASACQ passive seismic experiment in the foreland of the western Pyrenees (southwest France), an unusual swarm-type seismic sequence was serendipitously recorded in a normally quiet area. Thanks to the density of the deployment and the proximity of all events, it was possible to relocate the hypocenters with a very good relative accuracy through template matching, cross-correlation phase picks, and double-difference algorithm. The four-month seismic activity consists of more than 600 events with local magnitudes ranging between −1.4 and 2.1, clustered in an extremely small volume, and rooted at 4 km depth. The sequence can be divided in two phases of similar durations and event occurrence rates, but of different magnitude–frequency distributions. The presence of an asperity is suggested by the relative abundance of stronger events during the second phase. Fine mapping suggests a small but clear geographic offset of a few tens of meters between the events of the two phases and a very slow migration suggesting a process involving fluids. Changes in the correlation matrices and waveforms of late arrivals at a specific station are also observed, arguing either (and again) for migration of the hypocenters or for changes in the propagation medium between the two phases. The geographical coincidence with the repeated observation of hydrogen leaks on the surface, almost above the swarm, suggests a connection through channels that could carry fluids.

Delineating vulnerability to drought using a process-based growth model in Pyrenean silver fir forests

Assessing tree growth patterns and deviations from expected climate baselines across wide environmental gradients is fundamental to determine forest vulnerability to drought. This need is particularly compelling for the southernmost limit of the tree species distribution where hot droughts often trigger forest dieback processes. This is the case of some silver fir (Abies alba) populations located in southwestern Europe (Spanish Pyrenees) which present ongoing dieback processes since the 1980s. We sampled 21 silver fir stands showing different dieback intensity, assessed using defoliation levels, quantified their growth patterns and characterized their responses to climate. Then, we assessed growth deviations from climatic predictions using the process-based Vaganov-Shashkin (VS) growth model. The forests showing most intense dieback, i.e. highest defoliation levels, were mainly located in low-elevation sites of the western Pyrenees. Trees in these stands displayed the lowest growth rates and the highest year-to-year variability in growth and their growth was limited by late-summer evaporative demand. In eastern and central Pyrenees, we detected a mild growth limitation by low soil moisture during the late growing season and positive growth recovery in recent years with respect to a climate baseline. Decreasing growth trajectories were the most common pattern, while rising trends were common in stands with low dieback in eastern and central Pyrenees. Our results portend systematic spatial variability of growth trends across the Pyrenean silver fir populations forming the south-western distribution limit of the species in Europe. Decoupling of growth between eastern and western populations observed in the recent decades suggests contrasting vulnerability to climate change, and more importantly, the decoupling of growth patterns in western clusters could be used as an early-warning signal of impending dieback. Consequently, we foresee future dieback events to have more detrimental effects in the western compared with the eastern Pyrenees.

Pyrenean Silver Fir Forests Retain Legacies of Past Disturbances and Climate Change in Their Growth, Structure and Composition

Recent drought-induced dieback alters forest dynamics, which are also shaped by past management. In western Pyrenean silver fir (Abies alba) stands, dieback concurs in space and time with the legacies of past management, but the impacts on forest growth, structure and composition are unknown. We aim to disentangle how dieback interacts with the legacies of past human use and modulates the recent dynamics of silver fir forests. To this end, we sampled eleven silver fir forests across wide climatic gradients and included declining and non-declining sites. We measured radial growth, structure, composition, understory cover and type and amount of deadwood. Silver fir growth declines in response to late-summer drought. In declining sites, most defoliated stands showed the lowest silver fir density and were those where growth depended more on water availability. Tree death enhanced the cover of dominant understory plants such as Buxus sempervirens. Past management activities leave an imprint in the growth of silver fir, such as releases due to past logging, but also affect the number of stumps and snags and the current tree density. A more extensive monitoring will be required to fully disentangle the multiple influences of past management legacies and current climate change on forest dynamics.

Grazing intensity drives a trophic shift in the diet of common alpine birds

Large mammalian herbivores (LMH) shape vertebrate communities and structure food webs in many terrestrial ecosystems. However, the mechanisms that underlie the effects of LMH on other vertebrates are poorly understood. In France, domestic LMH have grazed alpine and mountain grasslands for thousands of years, profoundly influencing landscapes and wildlife. As LMH modify habitat structure, favour coprophagous insects and compete with herbivorous insects, the diet of insectivorous alpine birds may be deeply influenced by LMH grazing intensity. To investigate this, we sampled common insectivorous birds faeces (water pipit Anthus spinoletta and wheatear Oenanthe oenanthe) in sites characterized by different levels of grazing intensity by domestic and wild herbivores, in the open landscapes of the southern French Alps and the western Pyrenees. We used isotopic discrimination based on nitrogen stable isotope ratios as an indicator of the trophic level of the arthropods found in bird faeces. From isotopic ratios, we found that bird diets shift from mainly herbivorous arthropods at sites of low grazing intensity, to one mainly composed of other groups, such as predatory, detritivorous or coprophagous arthropods, at sites of higher grazing intensity. This result highlights the strong trophic link between LMH and insectivorous birds in open landscapes, contributing to a better understanding of interactions between domestic grazing, an activity that has historically modelled European landscapes, and biodiversity, with particular relevance for landscape management and bird conservation.

Neanderthal teeth from Lezetxiki (Arrasate, Iberian Peninsula): New insights and reassessment

AbstractObjectivesWe reassess the taxonomic assignment and stratigraphic context of a permanent upper first molar and a permanent lower third premolar recovered from the archeological site of Lezetxiki in the North of the Iberian Peninsula.Materials and MethodsWe assessed the external and internal morphology of the teeth using qualitative descriptions, crown diameters, dental tissue proportions, and geometric morphometrics. The teeth from Lezetxiki were compared with Middle Pleistocene specimens, Neanderthals, Upper Paleolithic modern humans, and recent modern humans.ResultsBoth teeth were consistent with a Neanderthal classification. The upper first molar shows taurodontism, and its cusp proportions and overall morphology match those of Neanderthals. Geometric morphometric analyses of occlusal anatomy classify this molar as a Neanderthal with a posterior probability of 76%. The lower third premolar, which was originally classified as a lower fourth premolar, also shows a Neanderthal morphology. This premolar is classified as a Neanderthal with a posterior probability of 60%.DiscussionThese teeth represent the only adult Neanderthal teeth from the Western Pyrenees region found to date. The teeth were found at a stratigraphic level (designated Level III) that marks the transition level from Mousterian to Aurignacian, and are among the most recent Neanderthal remains from the north of the Iberian Peninsula.

High-resolution cyclochronology of the lowermost Ypresian Arnakatxa section (Basque-Cantabrian basin, western Pyrenees)

High-resolution cyclochronology of the lowermost Ypresian Arnakatxa section (Basque-Cantabrian basin, western Pyrenees)