The Palaeocene/Eocene boundary section at Zumaia (Basque‐Cantabric Basin) revisited: new insights from high‐resolution magnetic susceptibility and carbon isotope chemostratigraphy on organic matter (δ13Corg)     

Jean‐Yves Storme  Xavier Devleeschouwer  Johann Schnyder  Geoffrey Cambier  Juan Ignacio Baceta  Victoriano Pujalte  Antonietta Di Matteo  Paola Iacumin  Johan Yans 《地学学报》2012,24(4):310-317

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Wave disturbance behind low-crested structures: Diffraction and overtopping effects     

Diego Vicinanza  Iván Cáceres  Mariano Buccino  Xavier Gironella  Mario Calabrese 《Coastal Engineering》2009,56(11-12):1173-1185

In recent years the hydraulic performance of low-crested structures has been widely studied both theoretically and through experimental analyses, but only a few studies have been focused on the combined diffraction-overtopping effects on wave transmission and induced wave currents.In this paper hydraulic model tests conducted at the 3D wave basin of Delft University of Technology (Cáceres et al., 2008) were used to obtain and discuss two simple methods for predicting the wave height at the lee of a single detached breakwater of finite length and the related current regime. For the first time diffraction effects are expressly accounted for. The agreement with experimental data is encouraging.The main objective of the paper is to aid engineers in the first stage of the design process, when using a mathematical model could be unnecessarily excessive.  相似文献   

Construction of an evolutionary deglaciation model for the Irish midlands based on the integration of morphostratigraphic and geophysical data analyses     

Xavier M. Pellicer  William P. Warren  Paul Gibson  Rogelio Linares 《第四纪科学杂志》2012,27(8):807-818

Alternative, established models for the deglaciation of the midlands of Ireland are tested against an interpretation of a suite of deglacial sediments covering an area of 600 km² in the east central midland area. Interpretation of the sediments is based on geomorphological mapping, lithostratigraphic characterization of exposures and geotechnical data supported by electrical resistivity tomography (ERT) and ground penetrating radar (GPR). GPR depicted small‐scale sedimentological and deformational structures within low‐conductivity soft sediments, such as cross‐bedding, planar bedding, channel‐like features and faulting planes, and revealed the internal architecture of eskers, glaciodeltas, subaqueous fans and raised bogs. ERT data permitted the detection of depth to bedrock and the lithological characterization of unconsolidated sediments. The ten sites presented were surveyed by traditional mapping methods and/or geophysical techniques. This allowed the construction of a local model of the deglaciation of the area which recognized five main stages. An ice sheet covering most of Ireland withdrew as a single body as far as the midlands. At this stage, two main directions of ice retreat are identified from the spatial distribution of meltwater/overflow channels, esker and morainic ridges, and ice‐marginal glaciolacustrine deposits. A pattern of deglacial sedimentation into an expanding ice‐marginal glacial lake is depicted. The glacial lake was dammed to the west by two ice dome fronts, one decaying to the north‐west and another to the south‐west, and by the Shannon Basin watershed to the east. Glacial lake outlets identified along the watershed and the altitude of the topset/foreset interface zone depicted in glaciodeltaic deposits allowed the identification of three lake water levels. The highest level is at 87–89 m Ordnance Datum (OD), the second lake level at 84 m OD and the third at 78 m OD. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Long-term evolution (1988–2008) of Zostera spp. meadows in Arcachon Bay (Bay of Biscay)     

Plus Martin  Dalloyau Sébastien  Trut Gilles  Auby Isabelle  Xavier de Montaudouin  Éric Emery  Noël Claire  Viala Christophe 《Estuarine, Coastal and Shelf Science》2010

The spatial variability of seagrass meadows in Arcachon Bay, was studied between 1988 and 2008 using a combination of mapping techniques based on aerial photographs for intertidal dwarf-grass (Zostera noltii) beds and acoustic sonar for permanently submerged eelgrass (Zostera marina) populations. The results show a severe decline over the period for both species, as well as an acceleration of the decline since 2005 for Z. noltii. The total surface regression over the studied period is estimated to be 22.8 km² for Z. noltii and 2.7 km² for Z. marina, which represent declines of 33 and 74% respectively.  相似文献   

New cranial remains of titanosaurian sauropod dinosaurs from the Late Cretaceous of Fox-Amphoux-Métisson (Var,SE France)     

Verónica Díez Díaz  Géraldine Garcia  Fabien Knoll  Xabier Pereda Suberbiola  Xavier Valentin 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(4):626-637

The Fox-Amphoux Syncline of the Aix Basin (SE France) has yielded a diverse Late Cretaceous vertebrate assemblage, including several taxa of dinosaurs. Here, we report on cranial material of titanosaurian sauropods, which consist of a partial braincase, two fragmentary skull roofs, and nine teeth, from the Métisson locality (Var Department). The braincase differs from those found previously in Europe (i.e., Ampelosaurus atacis, Lirainosaurus astibiae, and an unnamed juvenile skull from Romania) as well as from other titanosaurian braincases in having a groove that extends along the ventral surface of the occipital condyle neck (this feature may be autapomorphic). One of the fragmentary skull roofs may belong to the same taxon, whereas the other suggests the presence of a second titanosaur at Métisson very close to Ampelosaurus. Two dental morphologies are present in the sample; one of them includes teeth of different sizes. We suggest that this could be accounted for by age differences within a single taxon, or be due to different positions in the tooth row. The presence of a new, still unnamed titanosaurian taxon in the Ibero-Armorican Island supports previous works indicating a high titanosaurian diversity during the Campanian-Maastrichtian in southern Europe.  相似文献   

M. Armstrong, A. Galli, H. Beucher, G. Le Loc’h, D. Renard, B. Doligez, R. Eschard, F. Geffroy: Plurigaussian Simulations in Geosciences     

Xavier Emery 《Mathematical Geosciences》2012,44(2):239-240

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Consequences of the Thermal Transient on the Evolution of the Damaged Zone Around a Repository for Heat-Emitting High-Level Radioactive Waste in a Clay Formation: a Performance Assessment Perspective     

Li Yu  Eef Weetjens  Xavier Sillen  Tim Vietor  Xiangling Li  Pierre Delage  Vincent Labiouse  Robert Charlier 《Rock Mechanics and Rock Engineering》2014,47(1):3-19

A proper evaluation of the perturbations of the host rock induced by the excavation and the emplacement of exothermic wastes is essential for the assessment of the long-term safety of high-level radioactive waste disposals in clay formations. The impact of the thermal transient on the evolution of the damaged zone (DZ) has been explored in the European Commission project TIMODAZ (thermal impact on the damaged zone around a radioactive waste disposal in clay host rocks, 2006–2010). This paper integrates the scientific results of the TIMODAZ project from a performance assessment (PA) point of view, showing how these results support and justify key PA assumptions and the values of PA model parameters. This paper also contextualises the significance of the thermal impact on the DZ from a safety case perspective, highlighting how the project outcomes result into an improved understanding of the thermo–hydro–mechanical behaviour of the clay host rocks. The results obtained in the TIMODAZ project strengthen the assessment basis of the safety evaluation of the current repository designs. There was no evidence throughout the TIMODAZ experimental observations of a temperature-induced additional opening of fractures nor of a significant permeability increase of the DZ. Instead, thermally induced plasticity, swelling and creep seem to be beneficial to the sealing of fractures and to the recovery of a very low permeability in the DZ, close to that of an undisturbed clay host rock. Results from the TIMODAZ project indicate that the favourable properties of the clay host rock, which guarantee the effectiveness of the safety functions of the repository system, are expected to be maintained after the heating–cooling cycle. Hence, the basic assumptions usually made in PA calculations so far are expected to remain valid, and the performance of the system should not be affected in a negative way by the thermal evolution of the DZ around a radioactive waste repository in clay host rock.  相似文献   

Plio-Quaternary thin-skinned tectonics along the crustal front flexure of the southern Central Andes: a record of the regional stress regime or of local tectonic-driven gravitational processes?     

Grégoire Messager  Bertrand Nivière  Pierre Lacan  Yves Hervouët  Jean-Paul Xavier 《International Journal of Earth Sciences》2014,103(3):929-951

We present here a record of Plio-Pleistocene deformations above the flexural front of the southern Central Andes of Argentina. We combine a seismic profile with structural and geomorphological observations to show that thin-skinned extension located on top of the crustal front flexure is coeval with thin-skinned shortening at the toe of the topographic bulge. The seismic line shows that a flat zone with no internal deformation separates the stretched and shortened domains. Such features are usually interpreted as the result of strike-slip faulting along basement faults, or tangential longitudinal strain folding in the soft sedimentary cover above crustal bending. We propose an alternative linking extension at the apex of the crustal anticline, to basal contraction by the downslope translation of a rigid thin nappe of sediments (30 × 30 km² in area) above evaporites at a depth of 700–900 m. The size of such a process is unusually large onshore (630–810 km³) but mimics the gravity gliding observed in deltas and passive margins. Since this process disconnects zones with a shallow stress field from deeper crustal levels, it could allow extension above a compressive deformation front and should not be interpreted merely as a record of the crustal stress regime. Large-scale gravity gliding of the cover down the slope of a structural high could also explain some of the extension observed in mountain hinterlands.  相似文献   

Effect of thermal stress,condensation and freezing–thawing action on the degradation of stones on the Castle of Chambord,France     

Asaad Al-Omari  Xavier Brunetaud  Kevin Beck  Muzahim Al-Mukhtar 《Environmental Earth Sciences》2014,71(9):3977-3989

This work consists in estimating the role of climatic conditions in the degradation of two French limestones, tuffeau and Richemont stone, used in the construction and the restoration of the Castle of Chambord, the largest castle in the Loire Valley, France. Meteorological data, air temperature, air relative humidity and rainfall were statistically analysed in combination with stone data from thermal–humidity sensors inserted into the walls. The climatic conditions of the surrounding area were described to assess their role in enhancing the degradation of the stones through three weathering processes: thermal stress, condensation and freezing–thawing. The damage risks due to the weathering processes were taken into account not only through the bulk effects on the stone surfaces, but also their effects were extended to investigate the damage that occurs within the porous structure of the stone. Field observations showed that the main patterns of degradation affecting the stones of the castle are biological colonization and stone detachment in the form of stone spalling and exfoliation. The results of the analysis show that there is no risk of damage to the stones due to thermal stress. Moreover, the two stones experience similar overall trends against freezing–thawing processes. Finally, this study clearly highlights the important role of condensation in the degradation of the stones of the castle.  相似文献   

The occurrence of gypsum in the scaling of stones at the Castle of Chambord (France)     

Sarah Janvier-Badosa  Kévin Beck  Xavier Brunetaud  Muzahim Al-Mukhtar 《Environmental Earth Sciences》2014,71(11):4751-4759

The main cause of degradation in tuffeau, a soft siliceous and clayey limestone extensively used in the construction of the castles of the Loire Valley in France, is scaling. The most damaging form of weathering is spalling. Over time, a plaque several centimetres in thickness gradually forms under the stone surface and eventually falls away, leaving the resulting new surface powdered. Hypotheses regarding the initiation and development of such degradation have not yet met scientific consensus. The objective of the present paper is to improve existing knowledge of scaling degradation by analysing in situ samples representing different stages of the same degradation process. The analysis of the stones at the Castle of Chambord, revealed the presence of gypsum (CaSO₄·2H₂O), mainly located in cracks parallel to the stone surface. This gypsum was then studied in terms of its crystal morphology and distribution with depth. For comparison purposes, another form of scaling identified at the Castle of Chambord but rarely studied, flaking, was also examined. A first attempt at explaining the origin and formation of the observed gypsum in both scaling processes was conducted by interacting and comparing the characterisation results with historical and environmental data.  相似文献