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101.
102.
Flow dynamics at the origin of thin clayey sand lacustrine turbidites: Examples from Lake Hazar,Turkey 下载免费PDF全文
Sophie Hage Aurélia Hubert‐Ferrari Laura Lamair Ulaş Avşar Meriam El Ouahabi Maarten Van Daele Frédéric Boulvain Mohamed Ali Bahri Alain Seret Alain Plenevaux 《Sedimentology》2017,64(7):1929-1956
Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focused on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X‐ray, thin sections and CT scan imagery combined with grain‐size, geochemical and mineralogical measurements on the cores allow characterization of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence‐dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence‐dominated mechanism despite their high clay content. This divergence may in part relate to input variables, such as water chemistry and clay mineralogy, that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field‐scale basin made of a complex physiography that cannot be tackled by flume experiments. 相似文献
103.
The vibratory driving technique is used for driving piles, sheet piles, tubes and rods into the ground by imparting to the element a longitudinal periodic motion. The small amplitude vibrations induced by the equipment reduce the ground resistance which allows penetration under the action of a relatively small axial force. The technique offers an alternative to impact driving due to lower installation costs and reduced environmental disturbance (noise, vibration, etc.) especially in sensitive environments, such as industrial and urban sites or offshore wind farm sites. The vibratory technique is also preferred when the maximum stress levels imparted to the driven element are of concern. Despite the advantages of the vibratory driving technique, its application remains however mainly driven by pragmatic aspects. Within that context, the access to experience databases and full-scale field test results is of valuable interest. The aim of this paper is to review the Hypervib1 model developed by (Holeyman 1993) for assessing the vibratory drivability of piles and sheet piles, based on the analysis of such experimental results. New findings and developments brought to the model are discussed. Conclusions in terms of reliability of the method are finally drawn. 相似文献
104.
105.
The Ereendavaa Range (north-eastern Mongolia): an additional argument for Mesozoic extension throughout eastern Asia 总被引:3,自引:0,他引:3
Yannick Daoudene Denis Gapais Patrick Ledru Alain Cocherie Sébastien Hocquet Tatiana V. Donskaya 《International Journal of Earth Sciences》2009,98(6):1381-1393
Mesozoic rift basins locally bounding metamorphic core complexes have been recognized in Transbaikalia and northern China.
Numerous basement outcrops located between these two regions, in eastern Mongolia, are considered as pre-Palaeozoic in age.
One of these, the Ereendavaa Range, appears as a gneissic core marked by amphibolite-facies metamorphic conditions. The range
is overlain to the NW by the unmetamorphosed Mesozoic Onon Basin. Below the basin, the upper part of the range consists of
a gently NW-dipping shear zone associated with top-to-the-NW motion. The structural pattern is consistent with syn-extensional
exhumation of the range. Preliminary geochronological data indicate that the shear zone is late Jurassic to early Cretaceous
in age, coeval with the Onon Basin. These new data from eastern Mongolia constitute a link between Transbaikalia and northern
China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region. 相似文献
106.
Bernard Marandat Sylvain Adnet Laurent Marivaux Alain Martinez Monique Vianey-Liaud Rodolphe Tabuce 《Swiss Journal of Geoscience》2012,105(3):417-434
A new mammal fauna from the earliest Eocene of Le Clot (Corbières, Southern France) is described. Some taxa identified there, such as Corbarimys hottingeri and Paschatherium plaziati, allow a correlation with the previously described Corbières fauna of Fordones. Moreover, the presence at Le Clot of Lessnessina praecipuus, which is defined in Palette (Provence, Southern France) allows correlating both localities. All three of these localities are referred to the MP7 reference level, even if a direct correlation with the type locality of MP7 (Dormaal, Belgium) is not ascertained. A Southern Europe biochronological sequence is proposed for the beginning of the Eocene: Silveirinha, Fordones/Palette/Le Clot, Rians/Fournes. The diagnosis of a new species of a neoplagiaulacid multituberculate (?Ectypodus riansensis nov. sp.) is proposed. From a compilation of data concerning the earliest Eocene faunas from both Northern Europe and Southern Europe, we conclude that two faunas corresponding to two distinct palaeobiogeographical provinces existed in Western Europe. This faunal disparity, probably related to climatic differences, makes correlations particularly difficult between the two provinces. 相似文献
107.
Nicolas Fritier Nicolas MasseiBenoit Laignel Alain DurandBastien Dieppois Julien Deloffre 《Comptes Rendus Geoscience》2012,344(8):396-405
The inter-annual to multi-decadal winter variability (DJFM) of precipitation on the Seine River watershed (France) was analysed using continuous wavelet transform analysis and compared to the winter North Atlantic Oscillation Index (NAOI). Nine weather stations were used over the 1951 to 2004 period and confirmed the homogeneity of inter-annual fluctuations for all stations but one. Wavelet coherence between SLP over the Icelandic and Azores regions and precipitation highlighted coherence for different scales of variability according to the centre of action considered. Segmentation and wavelet analysis and coherence between precipitation and NAOI over a long period of time (1873–2004) showed: i) increasing variability across the last century at most time scales, especially for NAOI; ii) the existence of change points for the mean and variance of both signals; iii) overall discontinuity of the coherence whatever the scale considered, especially between ∼1910 and ∼1955 for inter-decennial to pluri-decennial scales. 相似文献
108.
Pierre Boszczuk Li Zhen Cheng Hanafi Hammouche Patrice Roy Sylvain Lacroix Alain Cheilletz 《Journal of Applied Geophysics》2011,75(1):77-86
Two inversions, unconstrained and constrained, of a gravity survey of the Matagami mining camp (Abitibi Archaean Subprovince, Canada) have been performed in order to identify the downward extension of a rhyolitic horizon hosting VMS-type base metals deposit and the morphologies of the major felsic plutons. A comparative study exhibits the similarities between measured and calculated densities from chemical compositions of the Matagami lithologies. This allows building an initial 3D geodensity model which integrates densities and available structural and geological surface mapping data. This model is integrated during the iteration process of the constrained inversion in the objective function. The resulting true density model and two derived cross-sections upgrade the 3D imaging of this area. Also, the model gives new insight for regional geological interpretation exposing possible shapes of the main geological units at depth and suggests the potential existence of deep fertile geological bodies. 相似文献
109.
Daniele L. Pinti Catherine Béland-Otis Alain Tremblay Chris M. Hall Jean-Yves Lavoie 《Geochimica et cosmochimica acta》2011,75(15):4228-4243
Brines in Cambrian sandstones and Ordovician dolostones of the St-Lawrence Lowlands at Bécancour, Québec, Canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path, in addition to quantifying their residence time. Major ion chemistry indicates that the brines are of Na-Ca-Cl type, possibly derived from halite dissolution. 87Sr/86Sr ratios and Ca excess indicate prolonged interactions with silicate rocks of the Proterozoic Grenville basement or the Cambrian Potsdam sandstone. The brines constrain a 2-3% contribution of mantle 3He and large amounts of nucleogenic 21Ne∗ and 38Ar∗ and radiogenic 4He and 40Ar∗. 4He/40Ar∗ and 21Ne∗/40Ar∗ ratios, corrected for mass fractionation during incomplete brine degassing, are identical to their production ratios in rocks. The source of salinity (halite dissolution), plus the occurrence of large amounts of 40Ar∗ in brines constrain the residence time of Bécancour brines as being older than the Cretaceous. Evaporites in the St-Lawrence Lowlands likely existed only during Devonian-Silurian time. Brines might result from infiltration of Devonian water leaching halite, penetrating into or below the deeper Cambrian-Ordovician aquifers. During the Devonian, the basin reached temperatures higher than 250 °C, allowing for thermal maturation of local gas-prone source rocks (Utica shales) and possibly facilitating the release of radiogenic 40Ar∗ into the brines. The last thermal event that could have facilitated the liberation of 40Ar∗ into fluids and contributed to mantle 3He is the Cretaceous Monteregian Hills magmatic episode. For residence times younger than the Cretaceous, it is difficult to find an appropriate source of salinity and of nucleogenic/radiogenic gases to the Bécancour brines. 相似文献
110.
Alain Genty Christophe Le Potier Stéphane Gounand 《Geotechnical and Geological Engineering》2011,29(4):537-554
Numerical simulations of the transport of radionuclide from high-level radioactive waste stored in geological repositories
often do not take into account construction defects in the repository. The potential impact of drilling and excavation deviation
from the engineer planned design is a priori considered negligible. We conducted computations on repository geometries that
contain deviations from horizontal of a few degrees. The analysis of the results shows that the impact of deviation defects
varies from 9 to 16%. A perfect control of the galleries and waste repository cell orientations is then of concern for radioactive
waste repository construction, failing which numerical simulations must be conducted on the worst geometric configuration
or margin errors added. On the other hand, if the orientation control is precise enough, a modification of the repository
design including controlled deviations from the horizontal may be of interest. 相似文献