Near bottom variations of turbidity in the St Lawrence estuary     

Bruno d'Anglejan  R. Grant Ingram 《Estuarine, Coastal and Shelf Science》1984,19(6):655-672

Observations of the turbidity and velocity fields in the near-bottom waters of the St Lawrence estuary were obtained with a package which includes a self-recording attenuance meter and a currentmeter. The latter also measures salinity and temperature. Time series varying in length between 26 h and 26 days, and with repetition rates between one and 15 min are discussed for 3 typical open-channel and nearshore stations. A high-frequency sampling mode provides a means to observe the passage of a frontal disturbance over the bottom during the semi-diurnal cycle. With lower frequency records having lengths of one week to one month, contributions to the turbidity fluctuations due to the spring-neap oscillations, seasonal changes in run-off, and the sudden rise in solid discharge of local tributaries following storms, can be resolved. From turbidity polar diagrams, local onshore sources of particulate suspended matter can be identified. Among other advantages, it is possible from such records to time precisely the occurrence of turbidity peaks in relation to the ebb and flow velocities, to assess the importance of resuspension, and to specify exactly the time rate of change of the turbidity. On the whole, self-recording equipments provide a wealth of information unavailable from more traditional hydrocast sampling techniques.  相似文献   

Can the gold coast beaches withstand extreme events?     

Bruno?CastelleEmail author  Yann?Le?Corre  Rodger?Tomlinson 《Geo-Marine Letters》2008,28(1):23-30

The Gold Coast sandy beaches of Queensland (Australia) are exposed to energetic wave conditions. Storms, particularly tropical cyclones, have a high potential of destruction. The Gold Coast has not experienced excessive erosive events over the past 30 years. However, some climate indicators suggest that cyclone frequency is likely to increase in response to global climate change within the near future. Over a 2-month period in early 2006, beach surveys were undertaken with a theodolite total station at four different sites. Offshore wave conditions were provided by SWAN regional wave modelling. During this study, the Gold Coast was exposed to three major storms, the first one being the second most energetic over the past 30 years. Results show a substantial variability of the beach response to these events along the Gold Coast, and that engineering structures do not have marked effects. Easterly swells have the greatest impact on the Gold Coast sub-aerial beach morphology. When low wave-energy conditions prevail, the southern Gold Coast beaches recover more quickly than the northern ones, as they are sheltered from high SE waves and draw advantage from the artificial sand bypassing system. Nevertheless, the data show that the Gold Coast beaches are exceedingly fragile. For instance, the early March decadal event considerably weakened the beaches, which resulted in surprisingly high erosion rates all along the Gold Coast during the two following annual wave events. This study suggests that the Gold Coast beaches would not be able to withstand the impact of an increased frequency of extreme events similar in scale to those of 1967.  相似文献   

Classifying chalk microtextures: Sedimentary versus diagenetic origin (Cenomanian–Santonian,Paris Basin,France)     

Jessica Saïag  Pierre‐Yves Collin  Jean‐Pierre Sizun  Frdric Herbst  Ophlie Faÿ‐Gomord  Carmela Chateau Smith  Bruno Caline  ric Lasseur 《Sedimentology》2019,66(7):2976-3007

Microtexture describes the type of particles and their arrangement in matrix samples at scanning electron microscopy scale. Although a microtexture classification exists for micritic limestone, it cannot be directly applied to chalk. This study therefore proposes a classification of chalk microtextures and discusses the origin of microtexture variability. Chalk was sampled at thirteen spatio‐temporal locations along the coastline of northern France (Cenomanian–Santonian). Four criteria are defined to describe, characterize and determine chalk matrix microtexture: (i) mineralogical content; (ii) biogenic fraction; (iii) micritic fraction; and (iv) cement fraction. From these criteria, two major groups are defined: Pure Chalk Microtexture Group, with seven classes, and Impure Chalk Microtexture Group, divided into two subgroups: Argillaceous Microtexture with four classes and Siliceous Microtexture with two classes. Microtexture variability is related both to initial sedimentation and to diagenesis. Sedimentological conditions (for example, climate and distance from shore) affect chalk composition (carbonate content and type of insoluble particles), thus influencing microtexture. Changes in Pure Chalk Microtexture are the result of increasing diagenetic intensity. This classification can also be used to characterize the microtexture of subsurface chalk reservoirs. Reservoir quality depends on the petrophysical and mechanical properties of reservoir rocks, which can be better understood by exploring their sedimentary and diagenetic history, revealed by the study of chalk microtexture variability.  相似文献   

New aspects of magma storage and transfer     

Bruno Scaillet  Laurent Arbaret  Fabrice Gaillard 《Comptes Rendus Geoscience》2019,351(8):523-524

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Titanite: A potential solidus barometer for granitic magma systems   总被引：1，自引：1，他引：0  

Saskia Erdmann  Rucheng Wang  Fangfang Huang  Bruno Scaillet  Kai Zhao  Hongsheng Liu  Yan Chen  Michel Faure 《Comptes Rendus Geoscience》2019,351(8):551-561

Constraining crystallization pressure and thus intrusion depth of granites in various geodynamic settings remains challenging, yet important to further our understanding of magma system and crustal evolution. We propose that titanite, which is a common accessory in metaluminous and weakly peraluminous granites, can be used as a barometer if it crystallized in magmatic, near-solidus conditions and in equilibrium with amphibole, plagioclase, K-feldspar, quartz, biotite, and magnetite ± ilmenite. Titanite Al₂O₃ increases with pressure (P) according to: P (in MPa) = 101.66 × Al₂O₃ in titanite (in wt%) + 59.013 (R² = 0.83) with estimated uncertainties of ~±60 to ~±100 MPa for crystallization between ~150 and 400 MPa. We highlight that the current calibration dataset is limited, and that systematic experimental studies are needed to rigorously quantify the relation. The most important use of this empirical barometer will be for rocks in which amphibole is present but significantly altered, or in combination with amphibole barometry, as titanite can be easily dated by LA-ICP-MS.  相似文献   

Automatic correction and simplification of geological maps and cross-sections for numerical simulations     

Pierre Anquez  Jeanne Pellerin  Modeste Irakarama  Paul Cupillard  Bruno Lévy  Guillaume Caumon 《Comptes Rendus Geoscience》2019,351(1):48-58

Incorporating prior geological knowledge in geophysical process models often meets practical meshing challenges and raises the question of how much detail is to be included in the geometric model. We introduce a strategy to automatically repair and simplify geological maps, geological cross-sections and the associated meshes while preserving elementary consistency rules. To identify features breaking validity and/or the thin features potentially problematic when generating a mesh, we associate an exclusion zone with each model feature (horizon, fault). When these zones overlap, both the connectivity and the geometry of the geological layers are automatically modified. The output model enforces specific practical quality criteria on the model topology and geometry that facilitates the generation of a mesh with lower bounds on minimum angles and minimum local entity sizes. Our strategy is demonstrated on an invalid geological cross-section from a real-case study in the Lorraine coal basin. We further explore the impacts of the model modifications on wave propagation simulation. We show that the differences on the seismograms due to model simplifications are relatively small if the magnitude of simplifications is adapted to the physical problem parameters.  相似文献   

Rates of generation and growth of the continental crust   总被引：4，自引：1，他引：3  

Chris Hawkesworth  Peter A. Cawood  Bruno Dhuime 《地学前缘(英文版)》2019,10(1):165-173

Models for when and how the continental crust was formed are constrained by estimates in the rates o crustal growth. The record of events preserved in the continental crust is heterogeneous in time with distinctive peaks and troughs of ages for igneous crystallisation, metamorphism, continental margin and mineralisation. For the most part these are global signatures, and the peaks of ages tend to b associated with periods of increased reworking of pre-existing crust, reflected in the Hf isotope ratios o zircons and their elevated oxygen isotope ratios. Increased crustal reworking is attributed to periods o crustal thickening associated with compressional tectonics and the development of supercontinents Magma types similar to those from recent within-plate and subduction related settings appear to hav been generated in different areas at broadly similar times before ~3.0 Ga. It can be difficult to put th results of such detailed case studies into a more global context, but one approach is to consider when plate tectonics became the dominant mechanism involved in the generation of juvenile continental crust The development of crustal growth models for the continental crust are discussed, and a number o models based on different data sets indicate that 65%-70% of the present volume of the continental crus was generated by 3 Ga. Such estimates may represent minimum values, but since ~3 Ga there has been reduction in the rates of growth of the continental crust. This reduction is linked to an increase in th rates at which continental crust is recycled back into the mantle, and not to a reduction in the rates a which continental crust was generated. Plate tectonics results in both the generation of new crust and it destruction along destructive plate margins. Thus, the reduction in the rate of continental crustal growth at ~3 Ga is taken to reflect the period in which plate tectonics became the dominant mechanism b which new continental crust was generated.  相似文献   

前陆褶皱冲断带厚皮缩短盐构造运动的物理模拟   总被引：8，自引：0，他引：8  

戈红星 《高校地质学报》2004,10(1):39-49

尺度物理实验用干石英砂和聚合硅树脂为实验材料,模拟了前陆褶皱冲断带厚皮缩短盐构造,并与薄皮缩短盐构造及无盐层的褶皱冲断带构造模型进行了对比。实验表明,由于塑性盐层的存在,厚皮缩短盐构造呈3层式结构模式。盐上层主要形成敞开褶皱、箱状褶皱、前冲和背冲断层以及冲垒构造,盐下层形成逆冲断层及冲垒构造,断层通常都终止于盐层中。尽管盐层局部变薄或增厚,但不形成刺穿型盐构造。褶皱冲断带不具构造指向特征,其楔形库仑锥剖面呈平台与斜坡两段式形态。模型对比表明,厚皮缩短与薄皮缩短所产生的盐上层构造形态相似,不易区分;但二者的库仑锥剖面有所不同。厚皮前陆褶皱冲断盐构造与无盐层的褶皱冲断构造无论是其几何形态、还是库仑锥剖面都有极大的差别,极易区分：实验结果对解释前陆褶皱冲断构造和寻找盐下油气圈闭都有着重要的指导意义。  相似文献   

Field observations of an evolving rip current on a meso-macrotidal well-developed inner bar and rip morphology   总被引：1，自引：0，他引：1  

Nicolas Bruneau  Bruno Castelle  Philippe Bonneton  Rodrigo Pedreros  Rafael Almar  Natalie Bonneton  Patrice Bretel  Jean-Paul Parisot  Nadia Snchal 《Continental Shelf Research》2009,29(14):1650-1662

The Aquitanian Coast (France) is a high-energy meso-macrotidal environment exhibiting a highly variable double sandbar system. The inner and the outer bar generally exhibit a bar and rip morphology and persistent crescentic patterns, respectively. In June 2007, an intense five-day field experiment was carried out at Biscarrosse Beach. A large array of sensors was deployed on a well-developed southward-oriented bar and rip morphology. Daily topographic surveys were carried out together with video imaging to investigate beach morphodynamic evolution. During the experiment, offshore significant wave height ranged from 0.5 to 3 m, with a persistent shore-normal angle. This paper identifies two types of behavior of an observed rip current: (1) for low-energy waves, the rip current is active only between low and mid tide with maximum mean rip current velocity reaching 0.8 m/s for an offshore significant wave height (H_s) lower than 1 m; (2) for high-energy waves (H_s≈ 2.5–3 m), the rip current was active over the whole tide cycle with the presence of persistent intense offshore-directed flows between mid and high tide. For both low and high-energy waves, very low-frequency pulsations (15–30 min) of the mean currents are observed on both feeder and rip channels.A persistent slow shoreward migration of the sandbar was observed during the experiment while no significant alongshore migration of the system was measured. Onshore migration during the high-energy waves can be explained by different sediment transport processes such as flow velocity skewness, wave asymmetry or bed ventilation. High-frequency local measurements of the bed evolution show the presence of significant (in the order of 10 cm) fluctuations (in the order of 1 h). These fluctuations, observed for both low- and high-energy waves, are thought to be ripples and megaripples, respectively and may play an important but still poorly understood role in the larger scale morphodynamics. The present dataset improves the knowledge of rip dynamics as well as the morphological response of strongly alongshore non-uniform meso-macrotidal beaches.  相似文献   

Alfvénic turbulence in high speed solar wind streams as a driver for auroral activity     

R. D’Amicis  R. Bruno  B. Bavassano 《Journal of Atmospheric and Solar》2009,71(10-11):1014-1022

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