Processus géologiques de formation du site moustérien du Roc de Marsal (Dordogne, France)

Le gisement du Roc de Marsal a livré le squelette d’un enfant néandertalien. Il présente, par ailleurs, une séquence archéologique importante pour la compréhension des industries moustériennes. Cette étude se propose d’établir la litho-stratigraphie du site et d’appréhender l’impact des processus dynamiques et diagénétiques sur les ensembles archéologiques. Les travaux réalisés montrent que le remplissage de la cavité s’est formé essentiellement par ruissellement. L’éboulisation et la sédimentation d’origine anthropique jouent un rôle d’importance variable. Ruissellement et bioturbation, en particulier, laissent envisager des perturbations notables des ensembles archéologiques. Enfin, la lecture des processus sédimentaires permet de discuter le caractère intentionnel du creusement de la fosse néandertalienne.Roc de Marsal site has yielded a Neandertal child skeleton. It presents an important archaeological sequence for the comprehension of Mousterian industries. This study establishes the Roc de Marsal litho-stratigraphy and explains the impact of both dynamic and diagenetic processes on the archaeological assemblages. The results of the study show that sedimentation occurred primarily as a result of deposition by run-off. Rockfall and anthropogenic sedimentation played a role of variable importance. The mechanisms identified here (run-off and bioturbation in particular) let us evaluate notable disturbances of the archaeological assemblages. Finally, understanding the site-formation processes allows us to discuss the intentional nature of Neandertal pit-digging

Les isotopes stables de l’oxygène et du carbone dans les spéléothèmes : des archives paléoenvironnementales

Les spéléothèmes constituent des archives majeures des paléoclimats et paléoenvironnements terrestres notamment grâce à leurs enregistrements des variations isotopiques de l’oxygène et du carbone, situés dans un cadre chronologique fiable à l’aide de datations U-Th. De plus en plus étudiés au cours des dernières années, ces signaux isotopiques n’en demeurent pas moins complexes et leur interprétation doit s’appuyer sur une bonne connaissance des conditions de fractionnement isotopique lors de la précipitation et du contexte de formation des spéléothèmes. Cet article propose une revue bibliographique de l’utilisation des isotopes stables de l’oxygène et du carbone des spéléothèmes pour les reconstructions paléoclimatiques et paléoenvironnementales. Les processus physico-chimiques qui agissent de concert pour déterminer la composition isotopique de la calcite précipitée sont d’abord présentés. Puis les limites et incertitudes propres à l’interprétation de ces signaux isotopiques sont discutées ainsi que les moyens d’identification des perturbations du signal isotopique.Speleothems are regarded as major palaeoclimate and palaeoenvironmental archives, notably because of their records of oxygen and carbon isotopic variations, which are constrained in a reliable chronological framework with U-series dating. Increasingly studied, these isotopic signals are, however, complex and their interpretation must be based on a good knowledge of the isotopic fractionation conditions during calcite precipitation and of the context of speleothem formation. This paper presents a bibliographic review of the use of speleothem stable isotopes in palaeoclimate and palaeoenvironmental reconstruction. The physico-chemical processes that combine to determine the isotopic composition of the precipitated calcite are first presented. Then, the limits and uncertainties associated with the interpretation of these isotopic signals are discussed, along with the means by which to identify isotope signal disturbances

Les spéléothèmes, archives des variations paléoenvironnementales

Les spéléothèmes font l’objet d’un intérêt grandissant de la part des climatologues en raison de leur fort potentiel en tant qu’archives paléoclimatiques. Le plus souvent étudiés pour leurs enregistrements isotopiques de l’oxygène et du carbone, ils n’en offrent pas moins de nombreux autres vecteurs d’information paléoenvironnementale à différentes échelles et résolutions. Cet article propose une revue de ces propriétés. La distribution spatiale des spéléothèmes et leurs modalités de précipitation sont d’abord rappelées. Puis, les différentes méthodes de datation applicables à ces archives sont rapidement exposées. Les datations offrent un cadre chronologique fiable aux fluctuations climatiques et environnementales enregistrées à travers les variations de propriétés particulières, dont les diverses natures sont ensuite détaillées : 1) survenance et vitesse de croissance (i.e. présence/absence des phases de croissance, fréquence et intensité) ; 2) propriétés physico-chimiques (pétrographie, éléments traces, isotopes de l’uranium et du strontium) ; et 3) inclusions, telles que matière organique et pollens. Enfin, d’autres types d’informations fournis de manière plus occasionnelle sont abordés, liés à des événements anthropiques ou naturels sporadiques.Speleothems have attracted increasing interest from climate-change researchers because of their strong potential as palaeoclimatic archives. Whilst most often studied for their oxygen and carbon isotopic records, speleothems host many other properties that are capable of yielding independent palaeoenvironmental information, at different scales and resolutions. This paper provides a review of these properties. The spatial distribution of speleothems and their modes of formation are first examined. Then, the different dating methods applicable to these archives are briefly discussed. Dating provides a reliable chronological framework for speleothem records of climate and environmental change, which are preserved through variations in specific properties. The natures of these properties are then examined in detail: (i) incidence and growth rates (i.e. presence/absence of growth phases, growth frequency and intensity); (ii) physico-chemical attributes, such as petrography, trace elements, and uranium and strontium isotopes; and (iii) inclusions, such as organic matter and pollen. Finally, less common features providing information on sporadic natural or anthropic events are addressed

La grotte de Gargas (Aventignan, Hautes-Pyrénées) : nouvelles perspectives de recherche et premiers résultats sur les occupations gravettiennes.

International audienceIn this paper, we present the first results of new excavations of Gargas Cave from 2004 to 2005. These excavations were undertaken 90 years after the interruption of archaeological research by É. Cartailhac and H. Breuil (1911 and 1913). The current excavation concerns a zone that corresponds to a debris cone that naturally closed the cave. It contains two loci, separated by 20 metres. The first one (GES) is at the base of the cone near the former Cartailhac-Breuil excavations. The second one (GPO), which has not yet been excavated, is at the top of the cone near the prehistoric entrance. In the GES sector, we have identified the upper part of the stratigraphic sequence described during the Cartailhac-Breuil excavations and which corresponds to the Gravettian occupations. In the GPO sector, the deposit shows some sedimentological differences, but the Gravettian ensemble is also represented there. Our study of the newly excavated materials integrates information contributed by the old collections. According to the results of C14 dating, the Gravettian occupations occurred between 27,000 and 25,000 BP. The lithic industry is attributed to the Middle Gravettian with Noailles burins and shows a clear microlithic trend. The bone industry is principally composed of “mattocks” made on herbivore ribs, smoothers, awls and retouchers. The antler waste products show that longitudinal grooving was used for the fabrication of tools. Though no Isturitz Points have yet been found during the new excavations, this characteristic Gravettian point type is present in the old collections. The personal ornaments consist mainly of pierced Atlantic shells and perforated Cervid, Bovin, Izard and Carnivore teeth. In terms of their meat diet, the Gravettian groups at this site consumed mostly Reindeer, Bovinae and Izard. A zooarchaeological analysis has also demonstrated that the cave was occupied during all seasons and that butchery and consumption activities were performed there.Nous présentons ici les premiers résultats obtenus au cours de la reprise des fouilles dans la grotte de Gargas (campagnes 2004-2005). Celles-ci interviennent 90 ans après l'interruption des recherches archéologiques d'É. Cartailhac et H. Breuil (1911 et 1913). La fouille actuelle concerne la zone correspondant au cône d'éboulis qui a fermé naturellement la grotte. Elle se déroule sur deux locus distant d'une vingtaine de mètres : le premier (GES) à la base du cône, à proximité des anciennes fouilles Cartailhac- Breuil, le second (GPO) en amont du cône, proche de l'entrée préhistorique ; cette dernière zone n'avait pas été fouillée jusqu'à ce jour. Dans le secteur GES, nous avons retrouvé la partie supérieure du profil stratigraphique, décrit lors des fouilles Cartailhac-Breuil et qui correspond aux occupations gravettiennes. Dans le secteur GPO, le remplissage présente quelques différences sédimentologiques, mais l'ensemble gravettien est également présent. L'étude du matériel récent est réalisée en intégrant l'apport documentaire des anciennes collections. D'après les résultats des datations14C, les occupations gravettiennes s'échelonnent entre 27 000 et 25 000 BP. L'industrie lithique se rapporte au Gravettien moyen à burins de Noailles, avec une nette tendance à la microlithisation. L'industrie en matières dures d'origine animale se compose principalement de côtes d'herbivores utilisées, de lissoirs, de poinçons et de retouchoirs. Les déchets de débitage en bois de Cervidés témoignent de l'utilisation du rainurage longitudinal pour la fabrication de l'outillage. Si aucune « sagaie d'Isturitz » n'a été découverte au cours des campagnes récentes, ce type caractéristique du Gravettien fait néanmoins partie des anciennes collections. Les éléments de parure sont principalement constitués de coquillages perforés de provenance atlantique et de dents percées de Cervidés, de Bovinés et de Carnivores. Le régime carné des Gravettiens était principalement basé sur le Renne, les Bovinés et l'Isard. L'analyse archéozoologique a également permis d'établir que la grotte a été fréquentée à toutes les périodes de l'année et qu'elle fut le lieu d'activités de boucherie et de consommation

Seeking cyclonic activity records in speleothems from central Pacific: preliminary sample screening

PosterInternational audienceIdeal cyclone-sensitive speleothems would have the following properties: active at the time of sampling and recording the past few millenia, with fast growth rate, made of clean primary calcite, precipitated without kinetic fractionation, and fed by water with a short residence time allowing for the isotopic signal of short events like cyclones to be transferred but long enough for the drip water to be supersaturated. The screening for this type of speleothem is still in progress and the results presented here are very preliminary. U-Th dating: low U concentration (9-40ng/g; host rock is reef limestone) ; significant detrital content, involving large corrections and large final age uncertainties. Growth rate is highly variable, from ~0.12 mm/yr to ~0.03mm/yr. Tau12A: δ 18 O profile shows some quite large variations (~3‰), with several abrupt events that we will try to identify in other archives. δ 13 C signal amplitude is very large (~-4 to ~-14‰) suggesting the effect of prior calcite precipitation. The δ 18 O signal gets heavier when the δ 13 C does, which could reflect the rainfall amount in this context. Var12C: δ 18 O profile shows values between-3.1 and-6.3‰, with decadal or centennial fluctuations, superimposed on a general trend which is consistent with the one of the δ 13 C profile without being correlated, which implies that calcite precipitation could occur in conditions close to isotopic equilibrium. Once properly dated, this record should provide interesting information about past rainfall regimes on the island

Speleothem growth intervals reflect New Zealand montane vegetation response to temperature change over the last glacial cycle

Flowstone speleothem growth beneath Mount Arthur, New Zealand shows a clear relationship to vegetation density and soil development on the surface above. Flowstone does not currently form beneath sub-alpine Nothofagus forest above ca. 1000–1100 m altitude but U-Th dating shows it has formed there during past intervals of warmer-than-present conditions including an early–mid Holocene optimum and the last interglacial from ca. 131–119 ka. Some flowstones growing beneath ca. 600 m surface altitude, currently mantled with dense broadleaf-podocarp forest, grew during full glacial conditions, indicating that local tree line was never below this altitude. This implies that Last Glacial Maximum annual temperature was no more than ca. 4 °C cooler than today. Flowstone growth appears to be a robust indicator of dense surface vegetation and well-developed soil cover in this setting, and indicates that past interglacial climates of MIS 7e, 5e, the early–mid Holocene and possibly MIS 5a were more conducive to growth of trees than was the late Holocene, reflecting regional temperature changes similar in timing to Antarctic temperature changes. Here, flowstone speleothem growth is a sensitive indicator of vegetation density at high altitude, but may respond to other factors at lower altitudes

Synchronous timing of abrupt climate changes during the last glacial period.

Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude-to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies

Synchronous timing of abrupt climate changes during the last glacial period

Many geographically dispersed records from across the globe reveal the occurrence of abrupt climate changes, called interstadial events, during the last glacial period. These events appear to have happened at the same time, but the difficulty of determining absolute dates in many of the records have made that proposition difficult to prove. Corrick et al. present results from 63 precisely dated speleothems that confirm the synchrony of those interstadial events. Their results also provide a tool with which to validate model simulations of abrupt climate change and calibrate other time series such as ice-core chronologies.Science, this issue p. 963Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies

Magnesium in subaqueous speleothems as a potential palaeotemperature proxy

Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles

Social Deprivation Is Associated With Lower Access to Pre-emptive Kidney Transplantation and More Urgent-Start Dialysis in the Pediatric Population

Introduction Socioeconomic status (SES) is recognized as an important determinant of kidney health. We aimed to evaluate the association of social deprivation with different indicators at kidney replacement therapy (KRT) initiation in the French pediatric metropolitan population. Methods All patients with end-stage kidney disease (ESKD) who started KRT before 20 years old in France between 2002 and 2015 were included. We investigated different indicators at KRT initiation, which are as follows: KRT modality (dialysis vs. pre-emptive transplantation), late referral to a nephrologist, and dialysis modality (hemodialysis [HD] vs. peritoneal dialysis [PD], urgent vs. planned start of dialysis, use of catheter vs. use of fistula for HD vascular access). An ecological index (European Deprivation Index [EDI]) was used as a proxy for social deprivation. Results A total of 1115 patients were included (males 59%, median age at dialysis 14.4 years, glomerular/vascular diseases 36.8%). The most deprived group represented 38.7% of the patients, suggesting pediatric patients with ESKD come from a more socially deprived background. The most deprived group was more likely to initiate KRT with dialysis versus kidney transplantation. Among patients on HD, the odds of starting treatment in emergency with a catheter was >2-fold higher for the most deprived compared with the least deprived children (adjusted odds ratio [aOR] 2.35, 95% CI 1.16–4.78). Conclusion Children from the most deprived area have lower access to pre-emptive transplantation, have lower access to PD, tend to be late referred to a nephrologist, and have more urgent initiation of HD with a catheter