Sainte-Luce – Roches gravées de Montravail

Les roches gravées de Montravail sont situées sur le territoire de la ville de Sainte-Luce. Cette commune qui en est le propriétaire, est également chargée de leur gestion et de leur mise en valeur. Les blocs gravés sont situés sur les parcelles D 882 et D 883, localisées proche de la forêt domaniale de Montravail, gérée par l’Office National des Forêts (ONF). La plupart des parcelles ont été nettoyées et déboisées. Les roches gravées, qui sont au nombre de 5 (Blocs A, B, C, D et E) sont enva..

Exposure to negative socio-emotional events induces sustained alteration of resting-state brain networks in older adults

Basic emotional functions seem well preserved in older adults. However, their reactivity to and recovery from socially negative events remain poorly characterized. To address this, we designed a ‘task–rest’ paradigm in which 182 participants from two independent experiments underwent functional magnetic resonance imaging while exposed to socio-emotional videos. Experiment 1 (N = 55) validated the task in young and older participants and unveiled age-dependent effects on brain activity and connectivity that predominated in resting periods after (rather than during) negative social scenes. Crucially, emotional elicitation potentiated subsequent resting-state connectivity between default mode network and amygdala exclusively in older adults. Experiment 2 replicated these results in a large older adult cohort (N = 127) and additionally showed that emotion-driven changes in posterior default mode network–amygdala connectivity were associated with anxiety, rumination and negative thoughts. These findings uncover the neural dynamics of empathy-related functions in older adults and help understand its relationship to poor social stress recovery

MATOBART : étude internationale et pluridisciplinaire, conservation et mise en valeur d'un patrimoine rupestre d'exception

National audienc

On Byers Peninsula, the largest summer ice-free area in the South Shetland Islands, a thick Upper Jurassic-Lower Cretaceous sedimentary sequence and penecontemporaneous igneous activity records the progressive emersion of a volcanic arc. The oldest rocks are represented by voluminous basaltic flows intercalated within late Jurassic shallow marine sediments. Following the emersion, Lower Cretaceous strata were deposited. Welded and nonwelded dacitic to rhyolitic ignimbrites are exposed locally at the base of the continental succession. However, the majority of the Outcrops consists of Lower Cretaceous basaltic to basaltic andesite plugs and dykes, representing the roots of a volcanic arc, which form most of the topographic highs of the peninsula. Byers Peninsula lavas are porphyritic with mineralogical associations typical of orogenic series. Major, trace and rare-earth element data show that all the rocks are relatively poor in K2O, enriched in large ion lithophile elements and that they have a clear subduction imprint (Nb-Ta anomaly). Furthermore, a tholeiitic tendency is shown by the REE patterns of some basaltic lavas. Sr- Nd- and Pb isotopic data support an origin from the sub-arc asthenosphere. Byers lavas have isotope signatures similar to that of the South Sandwich intra-oceanic arc. The enriched nature of most of the samples, revealed by Pb isotope ratios and Th/Yb enrichment, indicates that the MORB-like mantle source has been modified by fluids and sediments derived from the subducting slab. No clear temporal chemical change is observed during the evolution of this near-trench volcanic arc.

International audienc

Seasonal pressurization of a coastal karst: the paleolithic decorated Cosquer cave (SE France)

International audienceThe Cosquer cave is a paleolithic decorated cave, in a coastal karst linked to the sea. Stability of climatic parameters in caves is known to be one main condition for conservation of art. Hydroclimate data are measured since several years at a 5 minutes time step: karst air pressure, water level in the karst, atmospheric pressure and sea level. Data shows an unusual behaviour for a karst: the karst air pressure is nearly always higher than the atmospheric pressure. As a result, water level in the karst is below the sea level. Some rock art figures present on walls near water level undergo wash out and fading but limited thanks to the karst pressurization. A stop of this mechanism due to rising sea-level, an increase of the massif permeability or changes in climatic conditions would lead to the loss of arts near water bodies.The cave air overpressure is related to the rock permeability that should be low. The pressure time series show that three main processes drive the cave pressure. The daily variations of the sea tide provide an assessment of the cave air volume above the pools water level. Although the cave air is confined by the rock and the seawater, there are external air inflows during short pressurization events, that can be deduced from pressure data. Then, the low cave air pressure decrease over the summer season is explained by air outflow through the rock. A bulk permeability is then calculated using Darcy law, assuming a gas permeability in a non-saturated medium. Three theoretical cases are evaluated: an equivalent porous medium, a single fracture, and a single karst conduit. The time series give an observation database to assess future changes in the pressure behaviour of this decorated paleolithic cave, and to detect water level increase and adjust conservation choices

Mesoscale permeability variations estimated from natural airflows in the decorated Cosquer Cave (SE France)

International audienceAbstract. Conservation of decorated caves is highly dependent on airflows in the karst network and through the surrounding host rock. Airflows are driven by pressure gradient and influenced by the shape of the karst conduits and the permeability of the carbonate rock massif. The Cosquer cave is an Upper Paleolithic decorated cave, half drowned in a coastal karst, where conservation is also dependent on the cave’s pools connected to the sea. Hydroclimatic data, such as air pressure and temperature and water level inside and outside the cave have been measured for several years to identify the main processes governing the water level variations, the airflows and the air renewal. Data show an unusual behavior for a karst: the karst air pressure is nearly always higher than the atmospheric pressure. As a result, the water level in the cave is below the sea level. The daily variations of the sea tide provide an assessment of the cave volume above the pools water level. Although the cave air is confined by the rock and the seawater, there are also external air inflows during short pressurization events. Moreover, the carbonate rocks effective permeability to air at the massif scale is inferred from the cave air pressure decrease over the summer season, by applying Darcy’s law in a partially-saturated medium. Six years of data show that permeability varies from year to year, and according to the cumulated rainfalls during the spring and summer. The driest years are correlated with a higher permeability, a faster air pressure decrease in the cave and a faster rise of the pools water level. In the future, in the context of climate change, a perturbation of the rock permeability is then expected in the near surface caves, which will impact airflows in decorated caves and may alter their fragile hydroclimatic stability

Geochemical fingerprints of mantle metasomatism beneath the Massif Central, France

The geological history of the Massif Central is complex, starting at the Hercynian time, continuing during the Cenozoic time with a mantle upwelling until Tertiary-Quaternary times with volcanic provinces emplacement. These processes can be observed in xenoliths. Peridotites from Devès and Velay Oriental display a large range of microstructure, modal compositions and can contain volatile bearing-phases, carbonated phase and glass, providing evidence for percolation and interaction between fluids and peridotites. They display large variations in trace-element contents within a same locality, even within a single sample. These variations cannot be correlated with microstructures, nor with the lithospheric depth of origin from about 27 to 54 km as estimated from equilibrium temperatures (800 to 1050C). Amphibole shows an increasing enrichment in trace elements with their modal content. The calculated liquids in equilibrium with trace-element host minerals showed that the xenoliths are in equilibrium with alkali type magmas different from alkali host lavas. The depleted samples would require less than 5 % melting to be compatible with partial melting model. Isotopic compositions in O of silicates indicate disequilibria within a single sample, suggesting percolation of one or more fluids with a heavier O isotopic composition than the host peridotites. The isotopic compositions in Sr, Nd and Hf of cpx and amp show that the metasomatism affecting the peridotites is characterized by mixing between two sources: a depleted mantle type (DM) and an enriched mantle type (HIMU, EAR). The plume beneath the Massif Central is heterogeneous, explained by its complex geological historyL'histoire géologique du Massif Central est complexe, débutant à l'Hercynien, se poursuit au Cénozoïque par la remontée d'une intumescence thermique jusqu'au Tertiaire-Quaternaire par la mise en place de provinces volcaniques. Ces phénomènes ont été observés dans les péridotites. Les xénolites du Devès et du Velay Oriental montrent une grande variabilité texturale et modale pouvant ou non contenir des indices d'intéraction, entre des fluides externes et les péridotites, caractérisés par la présence de phases hydroxylées, carbonatées et des verres. Les péridotites présentent une grande variation des teneurs en éléments traces au sein même d'une seule localité voire au sein d'un seul échantillon. Ceci n'est pas lié à la microstructure, ni à la profondeur lithosphérique de provenance (de 27 à 54 km pour des temperatures de 800 à 1050C). Les amphiboles montrent un enrichissement croissant avec leur teneur modale. Les liquides en équilibre recalculés à partir des minéraux porteurs d'éléments traces montrent que ces roches sont en équilibre avec des magmas alcalins différents des laves hôtes. Les péridotites appauvries en LREE sont compatibles avec un modèle de fusion (< 5 % de taux de fusion). Les compositions isotopiques en O des silicates montrent des déséquilibres au sein même d'un échantillon. Ceci suggère la percolation d'un ou plusieurs fluides avec une plus lourde valeur isotopique. Les rapports isotopiques du Sr, Nd et Hf des cpx et amp suggèrent que le métasomatisme est caractérisé par l'existence de mélanges entre une source type manteau appauvri (DM) et une plus enrichie (type HIMU, EAR), indiquant que la composition du panache n'est pas homogène.ST ETIENNE-BU Sciences (422182103) / SudocSudocFranceAustraliaFRA

Geochemical fingerprints of mantle metasomatism beneath the Massif Central, France

The geological history of the Massif Central is complex, starting at the Hercynian time, continuing during the Cenozoic time with a mantle upwelling until Tertiary-Quaternary times with volcanic provinces emplacement. These processes can be observed in xenoliths. Peridotites from Devès and Velay Oriental display a large range of microstructure, modal compositions and can contain volatile bearing-phases, carbonated phase and glass, providing evidence for percolation and interaction between fluids and peridotites. They display large variations in trace-element contents within a same locality, even within a single sample. These variations cannot be correlated with microstructures, nor with the lithospheric depth of origin from about 27 to 54 km as estimated from equilibrium temperatures (800 to 1050C). Amphibole shows an increasing enrichment in trace elements with their modal content. The calculated liquids in equilibrium with trace-element host minerals showed that the xenoliths are in equilibrium with alkali type magmas different from alkali host lavas. The depleted samples would require less than 5 % melting to be compatible with partial melting model. Isotopic compositions in O of silicates indicate disequilibria within a single sample, suggesting percolation of one or more fluids with a heavier O isotopic composition than the host peridotites. The isotopic compositions in Sr, Nd and Hf of cpx and amp show that the metasomatism affecting the peridotites is characterized by mixing between two sources: a depleted mantle type (DM) and an enriched mantle type (HIMU, EAR). The plume beneath the Massif Central is heterogeneous, explained by its complex geological historyL'histoire géologique du Massif Central est complexe, débutant à l'Hercynien, se poursuit au Cénozoïque par la remontée d'une intumescence thermique jusqu'au Tertiaire-Quaternaire par la mise en place de provinces volcaniques. Ces phénomènes ont été observés dans les péridotites. Les xénolites du Devès et du Velay Oriental montrent une grande variabilité texturale et modale pouvant ou non contenir des indices d'intéraction, entre des fluides externes et les péridotites, caractérisés par la présence de phases hydroxylées, carbonatées et des verres. Les péridotites présentent une grande variation des teneurs en éléments traces au sein même d'une seule localité voire au sein d'un seul échantillon. Ceci n'est pas lié à la microstructure, ni à la profondeur lithosphérique de provenance (de 27 à 54 km pour des temperatures de 800 à 1050C). Les amphiboles montrent un enrichissement croissant avec leur teneur modale. Les liquides en équilibre recalculés à partir des minéraux porteurs d'éléments traces montrent que ces roches sont en équilibre avec des magmas alcalins différents des laves hôtes. Les péridotites appauvries en LREE sont compatibles avec un modèle de fusion (< 5 % de taux de fusion). Les compositions isotopiques en O des silicates montrent des déséquilibres au sein même d'un échantillon. Ceci suggère la percolation d'un ou plusieurs fluides avec une plus lourde valeur isotopique. Les rapports isotopiques du Sr, Nd et Hf des cpx et amp suggèrent que le métasomatisme est caractérisé par l'existence de mélanges entre une source type manteau appauvri (DM) et une plus enrichie (type HIMU, EAR), indiquant que la composition du panache n'est pas homogène.ST ETIENNE-BU Sciences (422182103) / SudocSudocFranceAustraliaFRA

Bacterial diversity associated with saline efflorescences damaging the walls of a French decorated prehistoric cave registered as a World Cultural Heritage Site

International audienc