This study proposes a reappraisal of the role of the basement tectonics in the structuration of the Alpine foreland, across the Castellane fold-and-thrust belt located in southwestern Alps. We ...construct three 30km length N–S balanced cross-sections across the entire fold-and-thrust belt, in order to quantify the amount of horizontal shortening due to the Pyrenean and Alpine deformations. We then assess the role of the basement inherited structures during the compressional phases which resulted in the exhumation of the Argentera–Mercantour External Crystalline Massif and the Barrot Dome. The construction of these balanced cross-sections suggests a dominant thick-skinned deformation style, which includes the reactivation of inherited Permian and Early Cretaceous basement normal faults. We reconstructed three restoration stages: the oldest one highlights the geometry of Permian and Early Cretaceous extensional structures; the intermediate one after the Late Cretaceous evidences a first compressional episode linked to the Pyrenean compression; and the latest one in the Oligocene shows the first Alpine folds resulting from the southward thrusting of the internal units over the external ones along of the Penninic Frontal Thrust. Balanced cross-sections suggest very moderate crystalline basement–sedimentary cover decoupling. On the western and central cross-sections, the estimated amount of shortening ranges from 9.5 to 10km (21%) whereas on the easternmost one shows ~5km of shortening (9%). These shortening values are consistent with previously published estimates in the surrounding foreland subalpine chains. They highlight a decreasing value of Pyrenean shortening toward the east, while the Alpine shortening dominates and amplifies this first phase in a similar direction. We interpret this dominantly thick-skinned structural style as a possible consequence of the Neogene thermal weakening in the European passive margin above the Ligurian slab rollback.
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•Three 30km-balanced geological cross sections are proposed.•Restorations in 3 stages are reconstructed from the Lower Cretaceous.•No or little crystalline basement–sedimentary cover decoupling is proposed.•Prominence of basement (thick-skin) tectonics into the Alpine foreland deformation•Pyrenean compression decreases significantly from W Provence to Castellane Arc.
Bees (Anthophila) are one of the major groups of angiosperm-pollinating insects and accordingly are widely studied in both basic and applied research, for which it is essential to have a clear ...understanding of their phylogeny, and evolutionary history. Direct evidence of bee evolutionary history has been hindered by a dearth of available fossils needed to determine the timing and tempo of their diversification, as well as episodes of extinction. Here we describe four new compression fossils of bees from three different deposits (Miocene of la Cerdanya, Spain; Oligocene of Céreste, France; and Eocene of the Green River Formation, U.S.A.). We assess the similarity of the forewing shape of the new fossils with extant and fossil taxa using geometric morphometrics analyses. Predictive discriminant analyses show that three fossils share similar forewing shapes with the Apidae one of uncertain tribal placement and perhaps near Euglossini, one definitive bumble bee (Bombini), and one digger bee (Anthophorini), while one fossil is more similar to the Andrenidae. The corbiculate fossils are described as Euglossopteryx biesmeijeri De Meulemeester, Michez, & Engel, gen. nov. sp. nov. (type species of Euglossopteryx Dehon & Engel, n. gen.) and Bombus cerdanyensis Dehon, De Meulemeester, & Engel, sp. nov. They provide new information on the distribution and timing of particular corbiculate groups, most notably the extension into North America of possible Eocene-Oligocene cooling-induced extinctions. Protohabropoda pauli De Meulemeester & Michez, gen. nov. sp. nov. (type species of Protohabropoda Dehon & Engel, n. gen.) reinforces previous hypotheses of anthophorine evolution in terms of ecological shifts by the Oligocene from tropical to mesic or xeric habitats. Lastly, a new fossil of the Andreninae, Andrena antoinei Michez & De Meulemeester, sp. nov., further documents the presence of the today widespread genus Andrena Fabricius in the Late Oligocene of France.
The geology of the “Vence” landslide (0.8 million m
3
, south-eastern France) explains the complex hydrology of the site which plays a key role in the destabilization of the slope (water circulation ...within the sliding mass, fluid exchanges between superficial layers and deep karstic aquifer through faults). To understand fluid circulations within the unstable slope, a 9.5-year multi-parametric survey was set up. The survey combines electrical resistivity tomography (daily acquisition), rainfall records since 2006 and boreholes monitoring groundwater level since 2009. The objective of this work is to present an automated clustering analysis applied to the ERT data enabled to locate geological units displaying distinct hydrogeological behaviours. Clustering analysis, based on a hierarchical ascendant classification (HAC), helped to simplify the ERT section isolating three groups of apparent resistivity values. Comparing the variations of these clusters’ behaviours in time to the variations of the groundwater levels on site, we identified hydrogeological units. The role of the faults cutting the substratum is thereby highlighted. It is the simultaneous analysis of such a large real dataset that allowed obtaining robust results characteristic of the long-term behaviour of the natural hydrogeological system. This type of qualitative information on the variability of the slope hydrogeological behaviour both spatially and temporally is crucial to help improving the conversion of resistivity data into hydrologic quantities. Indeed, the definition of petrophysical models to convert ERT measurements into hydrological measurements should be site-specific and take into account the spatial and temporal variability of the medium. In this work, we show a method that can also help to focus on the areas in depth that have different levels of permeability and observe how the saturation degree evolves in time. This can be used to optimize the location of additional instrumentation (such as temperature probes and chemical sampling) and, thus, help in the prevention of the risk in such problematic areas.
The SW Alps are an active orogen undergoing intra-mountainous extension and peripheral compression. We discuss the significance of syn-orogenic extension based on a comparison of paleo-stress derived ...from fault-slip data inversion reflecting the long-term (<12Ma) evolution of SW Alps and the present-day stress state obtained by the inversion of the focal mechanisms of the last 30-years seismicity. The resulting stress states of long-term and active tectonic regimes are in good agreement, showing that extension accompanies strike-slip and reverse faulting in the southern part of the belt. The extensional deformation regime is limited to specific tectonic domains that can be interpreted as ‘transitional’ between pure strike-slip segments where the deformation concentrates on inherited ductile shear zones that were formed between 32° and 20Ma ago. We thus propose that the extensional deformation in the SW Alps can be defined as a local deformation in a pull-apart type domain (High Durance - Jausiers area) or above slowly exhuming internal massifs (Dora Maira - Ivrea Body) along a curved boundary between the slowly rotating Apulian block and the relatively immobile Western Europe. The transcurrent fault system merges into a compressional front along the Mediterranean – Ligurian coast mainly to the east of San Remo.
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•SW Alps undergo neogene-present intra-mountain extension and peripheral compression.•Comparison of Paleo-stress (fault-slip data) and current stress (focal mechanisms)•Results from both techniques are in good agreement.•Extension is limited to specific tectonic domains between pure strike-slip segments.•The transcurrent system merges into a compressional front along the Ligurian coast.
Thermal sources are common manifestations of geothermal energy resources in Alpine regions. The up-flow of the fluid is well-known to be often linked to cross-cutting fault zones providing a ...significant volume of fractures. Since conventional exploration methods are challenging in such areas of high topography and complicated logistics, 3D geological modeling based on structural investigation becomes a useful tool for assessing the overall geology of the investigated sites. Geological modeling alone is, however, less effective if not integrated with deep subsurface investigations that could provide a first order information on geological boundaries and an imaging of geological structures. With this aim, in the present paper the combined use of 3D geological modeling and gravity surveys for geothermal prospection of a hydrothermal area in the western Alps was carried out on two sites located in the Argentera Massif (NW Italy). The geothermal activity of the area is revealed by thermal anomalies with surface evidences, such as hot springs, at temperatures up to 70°C. Integration of gravity measurements and 3D modeling investigates the potential of this approach in the context of geothermal exploration in Alpine regions where a very complex geological and structural setting is expected. The approach used in the present work is based on the comparison between the observed gravity and the gravity effect of the 3D geological models, in order to enhance local effects related to the geothermal system. It is shown that a correct integration of 3D modeling and detailed geophysical survey could allow a better characterization of geological structures involved in geothermal fluids circulation. Particularly, gravity inversions have successfully delineated the continuity in depth of low density structures, such as faults and fractured bands observed at the surface, and have been of great help in improving the overall geological model.
•Integrates gravity and geologic data to compute realistic 3D models•Covers a region where gravity data were previously not available•Emphasizes the importance of 3D modeling for geothermal prospection•Underlines the effectiveness of 2D gravity inversions in delineating fault zones•Provides a method which can be applied in all the geological contexts
Statistical analysis of bed thickness was performed for sampled turbidite successions from well-documented architectural elements of the Grès d' Annot Formation to characterize confined deep-water ...mini-basins of the Tertiary foreland basin of SE France. The purpose was to use advanced statistical processing techniques in order to evaluate whether a discrimination of different architectural elements is feasible through observed statistical signatures of bed thickness. Statistical methods were focused on: i) fitting of widely used non-normal theoretical distribution models using robust non-parametric goodness-of-fit statistical tests, and ii) detecting the possible presence of non-random bed thickness clustering using existing and new clustering estimation methods. Results indicate that the bed thickness data are best characterized by a multi-modal lognormal distribution model which probably reflects a background sedimentological process. Several datasets exhibit power law as well as exponential thick-bedded tails. The data also exhibit non-random clustering of bed thickness. Discrimination of architectural elements in this confined turbidite succession seems to be feasible based on the characteristics of the observed composite lognormal distributions such as number and variability of the detected components. The estimation of the degree of facies clustering has potential for the discrimination of architectural elements in confined basin settings if used in conjunction with alternative estimation methods (such as periodogram estimation). This methodology may now be applied to other confined turbidite successions, be they outcrops with less certain architecture, or subsurface datasets with borehole imaging.
•Characteristic architectural elements of a confined turbidite system were logged in detail.•Bed thickness distribution patterns and possible facies clustering were investigated using advanced statistical techniques.•Discrimination of sampled architectural elements seems to be feasible based on statistical parameters observed.
We have used high resolution seismic imaging to detect and characterize the recent deformation recorded by the Quaternary sediments of Le Bourget Lake. The last glacial episodes (MIS 6a and 2, i.e., ...Riss and Würm) scoured out an elongated over-deepened basin to more than 300m below the present lake level and the basin accumulated 150m of post-LGM to Holocene sediments. The well-stratified character of the infill is locally disturbed by tectonic deformations and gravity reworking. A northern fault zone, in continuation with the left-lateral strike–slip Culoz Fault, is imaged within the Holocene and Late Glacial accumulations. A southern fault zone is also detected, which can be related to the sub-lacustrine continuation of a much smaller fault affecting the Jura alpine foreland: the Col du Chat left lateral strike–slip fault. Different generations of fractures have been identified in the lake, allowing correlation and mapping. In pre-Quaternary substratum, the Culoz Fault has a N 160° orientation. Within the post-LGM sediments, fractures related to the Culoz Fault have an orientation between N135° and 95°. A Cloos model (1932) is thus proposed to explain the observed pattern of lacustrine deformations. The calculated horizontal slip rate for Culoz Fault during Holocene is about 1.3mm·yr−1, and for the Col du Chat Fault is around 0.6mm·yr−1.
•Confirmation of active faulting in Southern Jura•Concentration of this activity along NW–SE strike slip faults•Differential deformation of recent soft sediments above hard basement•Natural example of Cloos model (1932)•Interest of large lacustrine fills for active tectonic investigations
A high resolution mineralogical study (bulk-rock and clay-fraction) was carried out upon the hemipelagic strata of the Angles section (Vocontian Basin, SE France) in which the Valanginian positive ...C-isotope excursion occurs. To investigate sea-level fluctuations and climate change respectively, a Detrital Index (DI: (phyllosilicates and quartz)/calcite) and a Weathering Index (WI: kaolinite/(illite
+
chlorite)) were established and compared to second-order sea-level fluctuations. In addition, the mineralogical data were compared with the High Nutrient Index (HNI, based on calcareous nannofossil taxa) data obtained by Duchamp-Alphonse et al. (2007), in order to assess the link between the hydrolysis conditions recorded on the surrounding continents and the trophic conditions inferred for the Vocontian Basin. It appears that the mineralogical distribution along the northwestern Tethyan margin is mainly influenced by sea-level changes during the Early Valanginian (
Pertransiens to
Stephanophorus ammonite Zones) and by climate variations from the late Early Valanginian to the base of the Hauterivian (top of the
Stephanophorus to the
Radiatus ammonite Zones). The sea-level fall observed in the
Pertransiens ammonite Zone (Early Valanginian) is well expressed by an increase in detrital inputs (an increase in the DI) associated with a more proximal source and a shallower marine environment, whereas the sea-level rise recorded in the
Stephanophorus ammonite Zone corresponds to a decrease in detrital influx (a decrease in the DI) as the source becomes more distal and the environment deeper. Interpretation of both DI and WI, indicates that the positive C-isotope excursion (top of the
Stephanophorus to the
Verrucosum ammonite Zones) is associated with an increase of detrital inputs under a stable, warm and humid climate, probably related to greenhouse conditions, the strongest hydrolysis conditions being reached at the maximum of the positive C-isotope excursion. From the
Verrucosum ammonite Zone to the base of the Hauterivian (
Radiatus ammonite Zone) climatic conditions evolved from weak hydrolysis conditions and, most likely, a cooler climate (resulting in a decrease in detrital inputs) to a seasonal climate in which more humid seasons alternated with more arid ones. The comparison of the WI to the HNI shows that the nutrification recorded at the Angles section from the top of the
Stephanophorus to the
Radiatus ammonite Zones (including the positive C-isotope shift), is associated with climatic changes in the source areas. At that time, increased nutrient inputs were generally triggered by increased weathering processes in the source areas due to acceleration in the hydrological cycle under greenhouse conditions. This scenario accords with the widely questioned palaeoenvironmental model proposed by Lini et al., (1992) and suggests that increasing greenhouse conditions are the main factor that drove the palaeoenvironmental changes observed in the hemipelagic realm of the Vocontian Basin, during the Valanginian positive C-isotope shift. This high-resolution mineralogical study highlights short-term climatic changes during the Valanginian, probably associated to rapid changes in the C-cycle. Coeval Massive Paraña–Etendeka flood basalt eruptions may explain such rapid perturbations.
► Bulk rock and clay mineral indices as sea-level and climate proxis. ► Regression-transgression couplet during the Early Valanginian. ► Rapid climate changes during the Late Valanginian. ► Valanginian positive C-isotope excursion associated with a warm and humid climate. ► Nutrification triggered by hydrolisis conditions.
This paper discusses problems in predicting the mobility of slow-moving landslides. Three case studies are presented here where research has been carried out by the Utrecht University: The La Valette ...landslide complex in the French Alps, the La Mure landslide in the French pre-Alps near Grenoble and the Hau landslide in Switzerland.
To predict field velocities of these slow-moving landslides the viscosity parameters of the material of these landslides were determined by strain-controlled tests in a ring shear apparatus based on Bishop's design at Utrecht University. The viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field. This discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid, wavy slip surface and/or by convergent flow effects. The associated gain in strength results in a higher apparent viscosity.
A more detailed analysis is made for the movements of the La Valette landslide. Observed velocities at the La Valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level. This deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under (partly) undrained conditions. The emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides.
A morphometric multivariate and univariate study involving all the three taxa within the Fritillaria tubaeformis complex was carried out. A total of 86 individuals from 8 populations were studied in ...vivo and complemented by the analysis of 116 individuals from herbarium specimens. According to our results, some morphological characters clearly support the separation among F. burnatii, F. tubaeformis and F. moggridgei. Despite this, some morphological overlapping does exist among F. tubaeformis and F. moggridgei, which show contiguous, partially interdigitated, but not overlapping ranges, and we deem more opportune their separation at subspecies level. On the contrary, Fritillaria burnatii is a clearly distinct species, albeit it can occasionally co-occur in the same site with F. tubaeformis subsp. moggridgei. An identification key for both fresh and dry specimens is provided.
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