Pendimoun rock-shelter is among the oldest Neolithic sites known on the French littoral (Impressa culture, since ca. 5700
bce
). It was discontinuously occupied from the Mesolithic to the end of the ...Neolithic. During the Neolithic, it was used for pastoral purposes and domestic activities as well as for pottery production. Agriculture and cereal processing are clearly attested during the Impressa occupation (grains, husk and straw macroremains, grindstones) and become less obvious in the overlying layers. Phytolith analysis concerned 1 Mesolithic sample (Sauveterrian culture) and 16 samples covering most of the 6th millennium
bce
(Impressa, Cardial, and transition to Early Square Mouthed Pottery—SMP cultures). Significant amounts of grass phytoliths and the scarcity of dicot phytoliths suggest that the livestock, whose dung constitutes an important part of the sediment, mainly fed on wild grasses. Inflorescence bract phytoliths are well represented only in the Impressa levels, confirming that cereals were partly processed in situ only during the earliest stages of the Neolithic. Amounts of B
ilobate
short cells proved to be higher than expected in an area where only a few panicoid species can grow. The three candidates for B
ilobate
phytolith producers (
Setaria
spp.,
Digitaria sanguinalis
,
Echinochloa crus
-
galli
) all have a short vegetation cycle that lies entirely between the end of spring and the beginning of autumn, suggesting that the shelter was mainly used during that period. The low amount of inflorescence bract phytoliths (except during the Impressa) seems to restrict that range to the period before the ears become mature, namely the end of spring or early summer.
Oceanic Anoxic Event 2, spanning the Cenomanian-Turonian boundary, was an episode of major perturbations in global biogeochemical cycles, characterized by the widespread burial of organic carbon in ...both oceans and epicontinental basins. In the Vocontian Basin (SE France), this event was expressed by the deposition of the Niveau Thomel, a succession of interbedded dark shales, grey marls and bioturbated carbonates as observed in the Lambruisse section. Analyses of the total organic carbon (TOC) content, combined with the concentrations of redox-sensitive trace elements, revealed that conditions fluctuated from oxic to suboxic-anoxic during the deposition of the Niveau Thomel. Transient periods of deoxygenation were related to perturbations in nutrient cycling reflected by near-zero to negative δ15N signatures indicative of increased diazotrophy.
The development of deoxygenated conditions in the Vocontian Basin was likely preconditioned by hydrographically restricted conditions, as confirmed by Mo vs. U enrichments, reducing bottom-water ventilation associated with water-column stratification. Intervals of reoxygenation were likely linked to climate-induced changes. In particular, a phase of regional or global cooling associated with a drop in pCO2, called the Plenus Cold Event (PCE) resulted in vigorous reoxygenation of the Vocontian Basin.
•The Niveau Thomel presents alternation between oxic and suboxic-anoxic conditions.•Nitrogen isotope compositions reveal diazotrophy in the photic zone.•Deoxygenation is related to the development of a stratified water column.•Climate changes likely controlled bottom waters ventilation in the Vocontian Basin.
The air-sea interface, or sea surface microlayer (1-1000 mu m), is a unique environment with different physical, chemical, and biological properties compared to the underlying water column. It is an ...important, yet often ignored component in the biogeochemical cycling of trace elements in the marine environment due to the lack of trace element clean sampling and analytical methods. A novel technique, a hollow cylinder of ultra-pure SiO2 (quartz glass) with a plastic handle, was developed to sample the microlayer for trace elements. This research also developed and optimized clean trace element techniques to accurately measure nine trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in the dissolved and particulate fractions of the microlayer and underlying water column. Preliminary data from a study in the Western Mediterranean Sea involving a mesocosm (in situ all plastic bag) showed consistent measurements in the trace element concentrations over the course of several days. Microlayer samples that were collected outside the mesocosm showed increased dissolved and particulate trace element concentrations resulting from a wet deposition event.
Turbidites deposited in confined mini-basins may demonstrate extremely complex stratigraphic architectures. We hypothesize that particulate organic matter preserved in turbidites will not be randomly ...distributed and may be used to assist the identification of architectural elements. An integrated sedimentological and palynological study was conducted on confined turbidites in the Peïra Cava sub-basin of the Eocene to Oligocene Grès d'Annot system, SE France; this provides a natural laboratory, where certainty in the stratigraphy allows confidence in sampling of sub-environments. Elements reflect deposits from high and low density flows including: thin-beds that onlap the basin margin and heterolithics spread across the basin; base of slope megabeds; and thick-beds that have a proximal to distal expression from south to north across the basin. One hundred samples were collected from logged sections across the basin, with 10 g of mudstone per sample being processed for a count of three hundred pieces of organic matter. Both allochthonous terrestrial and relatively autochthonous marine matter were recovered, with results showing a progressive fining of material from proximal to distal areas. Base of slope megabeds and proximal ponded thick-beds are dominated by dense humic matter, medial areas become dominated by light plant material, and distal samples are dominated by amorphous matter, interpreted as a result of density sorting of organic matter in turbidity currents. Exploratory ordination analysis and fuzzy cluster analysis were used to examine these results. Based on this study, we provide evidence of density fractionation of organics in turbidity currents, which is implied to be a major control on the distribution of particles in deep-marine depositional systems. This allows a palynofacies classification scheme to be developed to recognise architectural elements, which may be applied to sub-surface samples to assist the characterization of deep-water mini-basin architecture, understanding of which is crucial for hydrocarbon exploration and development.
•Architectural elements of a deep-marine, mini-basin confined turbidite system record proximal to distal sub-environments.•Particulate organic matter preserved in the turbidites displays a mix of terrestrial and marine origins.•Organic matter shows variations across the basin, corresponding with sedimentologically defined sub-environments.•Allows classification of reservoir-type elements based upon their palynofacies, now applicable to sub-surface datasets.
On August 14
th 2015 a large debris flow initiated by the occurrence of two slope failures at the front of the Lou rock glacier flooded part of the town of Lanslevillard, France. The present study ...aims to understand the meteorological and geomorphological context that led to these failures. Investigations were conducted by combining meteorological data, surface movements, and geophysical transects. The analysis indicates that the Lou rock glacier is directly connected to an active torrential channel and has a natural predisposition to frontal failure due to the steepness of its front. The slope failures were triggered after a heat wave followed by a three‐week period of almost continuous rainfall. Water flowing on top of the permafrost table was observed in the two head scarps, suggesting that regressive erosion consecutive to this concentrated subsurface water flow triggered the failures. For one of the slides, traces of previous failures were observable on historical aerial imagery dating back to the 1950's, while the second slide corresponded to a novel event and developed on the frontal slope of a fast‐moving and destabilized rock glacier lobe. We also discuss the increase in local predisposition to failure related to the remarkable morphological modifications such as frontal advance and development of surface cracks associated with the lobe destabilization.
Biogeochemical sulfur cycling has varied widely over geologic time, mainly in response to changes in primary productivity and organic carbon burial, volcanism, weathering, and evaporite deposition. ...Several of these processes are explicitly linked to discreet (<1.2 Ma) intervals of widespread organic carbon burial, termed oceanic anoxic events (OAEs). During the Cretaceous, there is a highly distinctive ~4‰ negative excursion in the sulfur isotope composition of seawater sulfate (δ34SSO4) that is bracketed by the two most prominent OAEs (OAE1a and OAE2). This excursion lasted for ~25 Ma and has been variously attributed to enhanced volcanism, changes in weathering, evaporite burial, and/or changes in modes of organic carbon remineralization. We present new high‐resolution carbon and sulfur isotope records from carbonate‐associated sulfate and pyrite for OAE1a and OAE2. OAE1a is characterized by a monotonic decrease in δ34SSO4 values. Both negative and positive δ34SSO4 excursions are associated with OAE2. To refine hypotheses for the observed changes in biogeochemical sulfur cycling associated with these events, we use a simple sulfur isotope box model. Both empirical and modeling results indicate that δ34SSO4 variability was dominated by input fluxes during OAE1a, whereas enhanced volcanism, weathering, and pyrite burial controlled δ34SSO4 records during OAE2. Our analysis supports the conclusion that Cretaceous marine sulfate concentrations were much lower than modern concentrations and indicates that increases in marine sulfate occurred at the onset of both events. We conclude that increases in marine sulfate from low background concentrations, in conjunction with other environmental characteristics, contributed to the development of OAEs.
Key Points
Cretaceous oceanic anoxic events are linked with a negative excursion in sulfate sulfur isotopes
Pyrite‐sulfur isotopes during OAEs indicate enhanced pyrite burial in oxygen‐depleted environments
Increases in sulfate levels and pyrite burial link volcanism to the development of OAEs
Full-face excavation associated with ground reinforcement is a common technique to build large tunnels in soft rock or hard soil. The phenomenon of the interaction between the excavation process, the ...reinforcements and the ground reaction is a three-dimensional (3D) problem. Currently, software and hardware developments provide the option of a numerical analysis of a 3D tunnel excavation within a reasonable calculation time; however, two-dimensional calculations based on the simplified convergence–confinement method are still the most common approach of engineers in current projects during the design phase.
This study presents the numerical back-analysis of a monitoring section setup in the southern Toulon tunnel in France. The primary goal of this study was to investigate and compare the ability of the two numerical approaches (i.e., 2D and 3D) to reproduce the real behaviour of the tunnel measured in situ. The 3D calculation correctly simulates the in situ data, confirming that this tool can represent the complexity of a tunnel excavation. Fitting the 2D calculations onto the 3D results also enabled the determination of the stress release values corresponding to the real excavation process adopted in the Toulon project. This analysis produces two-dimensional numerical results that are globally satisfactory, considering the ground displacement.
•A monitoring section has permitted to validate numerical simulations.•A 3D model was realized in order to reproduce the real in situ worksteps.•The 3D results showed to fit very well globally with all in situ data.•2D simulations were carried out with the convergence–confinement method.•2D approach able to reproduce well the ground settlements.
Using in-situ LA-ICP-MS, the trace-element composition of hydrothermal quartz from five Sb mineralized Variscan districts, from different parts of France, were compared. Each of these districts is ...characterized by the presence of stibnite, with quartz being a ubiquitous gangue mineral. The resulting dataset was processed using a set of multivariate statistical analyses (i.e. principal component analysis, hierarchical cluster analysis, and permutational multivariate analysis of variance). This approach highlights differences in ore-forming processes (e.g., fluid chemistry), recorded in the trace-element pattern of gangue minerals. Using this methodology, we could distinguish different mineralizing events with intricate paragenesis, such as those in the Sioule nappe, which appear to have recorded two different events of Sb precipitation. Results indicate that Sb incorporation in quartz is weakly correlated to other trace elements, but that its contents increase sharply in quartz from stibnite-bearing veins. In this case, Sb shows values >10 ppm and up to 200 ppm, considerably higher than the values measured in quartz unrelated to Sb mineralization (mainly ≤1 ppm). Intermediate Sb contents in quartz would point to the potential for a fluid to precipitate Sb ore. It is concluded that incorporation of Sb in quartz can be confidentially correlated to its content in the mineralizing fluid. Based on our data from five Sb districts in the French Variscan belt, supplemented by published Sb trace-element data in quartz from a number of other Sb deposits around the world, this study highlights the strong potential of the Sb content of quartz as a proxy for tracing Sb mineralization.
•Sb contents in quartz higher than 10 ppm record deposition of Sb ore.•Sb concentrations from 1 to 10 ppm reflect potential for Sb mineralization.•Quartz signature is a useful tool to untangle polyphase mineralizations.
Many authors focus on the concept of sediment connectivity to predict the sedimentary signal delivered at catchment outlets. In this framework, the sedimentary signal is seen as an emergent ...aggregation of local links and interactions. The challenge is then to open black boxes that remain within a sediment cascade, which requires both accurate geomorphic investigations in the field (reconstruction of sequences of geomorphic evolution and description of sediment routes) and the development of tools dedicated to the modeling of sediment cascades. On the basis of study cases in various environmental regimes (high‐energy mountainous environment and agricultural lowland catchments), in this paper, we (a) exhibit some spatial and temporal paradoxes in terms of sediment delivery and (b) develop various modeling procedures to test some hypothesis of interpretations. These modeling approaches explore different components of sediment connectivity at the catchment scale, including graph theory, agent‐based modeling, and differential equations. Each protocol is chosen according to the scientific objective and how the geomorphological system is simplified. Collectively, the results show that connectivity is an efficient conceptual framework with which to predict how a sediment cascade may transmit (or not) a perturbation throughout the system, including local perturbations (local sediment input, removal of a reservoir, etc.) and perturbations due to external‐boundary forces.
The number and diversity of groundwater bodies (GWBs) in large French administrative regions pose challenges to their monitoring and protection by regional health agencies. To overcome this obstacle, ...we propose, for the Auvergne-Rhône-Alpes region (about 70,000 km2), a grouping of GWBs into homogeneous groups based on the sources of variability within a large dataset of groundwater physico-chemical and bacteriological characteristics (8078 observations and 13 parameters). This grouping involved a dimensional reduction in the data hyperspace by principal component analysis (PCA) and a clustering based on the mean values of each GWB on the factorial axes. The information lost when clustering from the sample point scale to the GWB scale and then to that of the GWB group was quantified by analysis of variance and showed that grouping GWBs is accompanied by a small loss of information. A discriminant analysis confirmed the high spatial and temporal variability within the dataset, as well as the effectiveness of the proposed method for establishing homogeneous sets. Some roadmaps for more targeted monitoring of water resources were briefly proposed.
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