Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France).

27 pagesInternational audienceSeveral diagenetic models have been proposed for Middle and Upper Jurassic carbonates of the eastern Paris Basin. The paragenetic sequences are compared in both aquifers to propose a diagenetic model for the Middle and Late Jurassic deposits as a whole. Petrographic (optical and cathodoluminescence microscopy), structural (fracture orientations) and geochemical (δ18O, δ13C, REE) studies were conducted to characterize diagenetic cements, with a focus on blocky calcite cements, and their connection with fracturation events. Four generations of blocky calcite (Cal1-Cal4) are identified. Cal1 and Cal2 are widespread in the dominantly grain-supported facies of the Middle Jurassic limestones (about 90% of the cementation), whereas they are limited in the Oxfordian because grain-supported facies are restricted to certain stratigraphic levels. Cal1 and Cal2 blocky spars precipitated during burial in a reducing environment from mixed marine-meteoric waters and/or buffered meteoric waters. The meteoric waters probably entered aquifers during the Late Cimmerian (Jurassic/Cretaceous boundary) and Late Aptian (Early Cretaceous) unconformities. The amount of Cal2 cement is thought to be linked to the intensity of burial pressure dissolution, which in turn was partly controlled by the clay content of the host rocks. Cal3 and Cal4 are associated with telogenetic fracturing phases. The succession of Cal3 and Cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water/rock ratios. These meteoric fluids circulated along Pyrenean, Oligocene and Alpine fractures and generated both dissolution and subsequent cementation in Oxfordian vugs in mud-supported facies and in poorly stylolitized grainstones. However, these cements filled only the residual porosity in Middle Jurassic limestones. In addition to fluorine inputs, fracturation also permitted inputs of sulphur possibly due to weathering of Triassic or Purbeckian evaporites or H2S input during Paleogene times

Non-Invasive Radiation Pattern Measurement of Electrically Small antenna using Fiber Optic Link

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Miniature reconfigurable multi-antenna system for IMT-Advanced band

International audienceThis paper presents a compact reconfigurable multiantenna system addressing the IMT-Advanced band. The antenna system is built using compact antennas whose miniaturization is obtained by limiting instantaneous operating bandwidth. Frequency agility technique it then used to enlarge the operating frequency in accordance with the whole operating band and communication standard waveform. Good decoupling performances are achieved with the multi-antenna device thanks to a particular arrangement of the antennas. This system has been introduced for small mobile terminals, where form factor is very important. The use of two antennas could bring benefits to limit fast fading effects introduced by mobilit

Oxidation kinetics of tailings from the Callovo-Oxfordian argillites: flow-through experiments and modelling at the reactor scale

International audienceThe building of high level waste repository in deep clay formation will lead to large volumes of excavated rocks that will have to be disposed at the surface, where rock samples will be subject to weathering. The impact of these excavated rocks on the surrounding environment must be studied, in particular the eventuality of acid drainage occurrence because of the presence of pyrite in clay rocks. In addition, tailings are envisaged as sealing/backfill material of galleries. The quantitative evaluation of clay rocks transformations during weathering in the presence of atmosphere conditions is thus necessary to study the feasibility of this technical option. Large volumes of excavated Callovo-Oxfordian argillites (COx) have been produced during the construction of the Andra's underground laboratory at Bure, and have been stored on site, at the surface. These weathered samples can thus be studied for the objectives stated above. This study aimed to quantify the chemical effect of rainwater on weathered COx samples in order to obtain a set of kinetic data that are representative of COx clay rock reactivity in the presence of water equilibrated with O 2 and CO 2 at atmospheric partial pressures. Studied material was sampling on the first twenty centimeters of the upper part of 3 years old COx tailings. Flow-through experiments were carried out where outlet-solution chemistry was monitored over time (Fig. 1). Clay suspensions were submitted to aqueous oxidation at various liquid/solid mass ratios (ranging from 8 to 24). Reacting materials was examined prior and after experiments in order to follow mineralogical transformations (XRD, SEM, magnetic measurements). A reactive transport model was then applied to reproduce the data, using PHREEQC3 (Parkhurst and Appelo, 2013), the THERMOCHIMIE database (Giffaut et al., 2014) and reaction kinetic rates published by Marty et al. (2015). Only minor adjustment of reactive surface areas was done to fit outlet concentrations. Following oxidation of the samples, pyrite oxidized and iron oxide-hydroxides mineral precipitated. Reactive transport model captured well the pyrite oxidation kinetics as shown by the good agreement between modeled and measured sulphate concentrations as a function of time (Fig. 1). Pyrite oxidation is responsible for the acidification of water, but flow through experiment data and modeling evinced that this acidification was counterbalanced very efficiently by the reactivity of the carbonate system in our experimental conditions (Fig. 2). Slightly basic pH were obtained due to calcite alteration leaded to the continuously renewing of the reacting solution (i.e. injection of pure water equilibrated under atmospheric condition). The concentrations of other elements in solution as a function of time were also very well reproduced by the model, with the exception of Si, for which only a qualitative agreement could be obtained. These results indicate that the main processes of clay rock reactivity were correctly identified in our experimental conditions. Due to the high carbonates content inside the COx clay-rock (calcite and dolomite ~ 25 % wt.), acid drainage is clearly unlikely. Selected kinetic data would be applicable to the large-scale modelling dealing with the oxidation of COx tailings

A roadmap to a technological platform for integrating nanophotonic structures with micromechanical systems in silicon-on-insulator

On the foundation of joint experience acquired by several research centres there was defined the roadmap to the desired single technological platform for fabrication of a specific class of photonic integrated circuits, which are controlled by mechanical means. In the paper the challenges of fabrication of such photonic circuits are discussed. The main arguments in favour of the Silicon-on-Insulator materials system as the basis for the platform are presented. Options for the mechanics-to-optics arrangement, materials and processes are described and illustrated with the current achievements from the authors' labs. In the roadmap the preference is given to the vertical arrangement in which, the mechanical part is stacked above the waveguiding layer. A flexible trimming routine is designed to complement the process flow if the technologies developed cannot provide the required reproducibility

Weathering of an argillaceous rock in the presence of atmospheric conditions: A flow-through experiment and modelling study

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