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21.
The detection and identification of carbonates on Mars are of prime importance to establish the evolution of its atmosphere, correlated to the history of the liquid water, or even to determine the existence of a possible ancient biological activity. Till date, no large deposits of carbonates have been found. In fact, their detection is specific to local areas and in very low amounts. The absence of such deposits is commonly attributed to the harsh environmental conditions at the surface of Mars. Additionally, the presence of UV radiation has been proposed to explain their photodecomposition and hence their absence. However, contradictory results from laboratory experiments mimicking Mars’ surface UV radiation did not resolve the behaviour of carbonates in such an environment, which is why we exposed, in low Earth orbit and in laboratory experiments, both abiotic and biotic calcium carbonates to UV radiation of wavelength above 200 nm, the same spectral distribution as the one reaching the surface of Mars. For low Earth orbit (LEO) exposure, this was done for the UVolution experiment on board the BIOPAN ESA module, which was set outside a Russian Foton automated capsule, and exposed to space conditions for 12 days in September 2007. The targeted carbonates are biominerals and abiotic samples. Our laboratory results mainly show that the exposed carbonates appear to be stable to UV radiation if directly exposed to it. The LEO experiment results tend to the same conclusion, but the integrated exposition time to Solar UV during the experiment is not sufficient to be conclusive. However, the stability of the biominerals derived from the laboratory experiment could strengthen the interest to explore deeper their potential as life records at Mars. Hence, they should be considered as primary targets for in situ analyses during future missions.  相似文献   
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Near-critical angle and refraction studies were performed at IFP as piggyback studies during a wider programme of crustal imagery operated by WesternGeco on behalf of the Ministry of Energy of the United Arab Emirates. The main objective is to illuminate the base of the Semail Ophiolite along part of a regional transect (D1) crossing the Northern Emirates from the Gulf of Oman in the east up to the Arabian Gulf in the west. Results confirm that the sole thrust of the ophiolite has been folded during the Miocene stacking of the underlying Arabian Platform. The thickness of the ophiolite grades from zero in the core of the Masafi tectonic window, up to a maximum of 1.7 km below the axial part of a successor basin which has been preserved on top of the serpentinite west of the current exposure of the main ultramafic bodies. Apatite grains extracted from plagiogranites of the Semail ophiolite also provide evidences for an early unroofing of the gabbros and plagiogranites during the Late Cretaceous, with cooling ages of 72–76 Ma at the top of the ophiolite in the east (not far from the Fujairah coast line), which are coeval and also consistent with the occurrence of Late Cretaceous paleo-soils, rudists and paleo-reef deposits on top of serpentinized ultramafics in the west. Younger cooling ages of 20 Ma have been also found at the base of the ophiolite near Masafi, in the core of the nappe anticline, thus providing a Neogene age for the refolding of the allochthon and stacking of underlying parautochthonous platform carbonate units. These results, together with the occurrence of a thick sedimentary pile illuminated below the metamorphic sole along the north-trending, strike-profile D2 running parallel to the axis of the Masafi window, should stimulate a renewal of the exploration in the central part of the Emirate foothills, where the ophiolite thickness is currently limited, and was already drastically reduced by the end of its Late Cretaceous obduction.  相似文献   
24.
Fluxgate vector magnetometers can be powerful instruments in magnetic mapping and in the detection of unexploded ordnance (UXO). Being lightweight and having low power requirements, they allow the development of multi-sensor use. The main problems in using fluxgate magnetometers arise from calibration errors and drift but these can be overcome using a quick and simple method of calibration in the field. This method also has the advantage of compensating permanent and induced magnetic fields generated by magnetized objects carried with the sensors. Measurement accuracy is similar to that obtained with scalar magnetometers. Multi-magnetometer profiling allows direct inversion of raw magnetic data along profiles in order to locate and characterize dipoles typically generated by UXO. The method used is a non-linear inverse procedure that estimates the three coordinates and magnetization vector of the dipole. Application of the technique to both a synthetic case and a field example illustrates the advantages of the method compared with the use of the analytic signal.  相似文献   
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The crest of the Absheron anticline in the South Caspian Basin at a few hundred meters below the present seafloor shows a subcircular depression about 8 km in diameter and 200 m deep, bounded by steep edges dipping 15° to 45° into it. The depression and the surrounding series are respectively filled and overlain by a regional mass-transport deposit (MTD) 150 m thick outside the depression and 300 m thick inside, composed mostly of extensional blocks. Geometric and stratigraphic analyses indicate that 150 m of initially deposited sediment were removed from a closed area after burial. Seismic evidence of shallow gas accumulations below the crater-like feature suggests that gas likely played a significant role in its development. The model proposed for the emplacement of the crater is that the gas-bearing cover of a shallow gas reservoir underwent exsolution when its overburden thinned during an episode of extensional slope failure. This resulted in loss of resistance to shear and evacuation of the gas-bearing sediment, likely at the shearing base of the failed mass. This evacuation feature is considered an example where the presence of gas locally governs the morphology of an MTD. The interpreted process shows a positive feedback between slope failure and loss of strength at the base of the resulting MTD.
Graphical Abstract
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27.
This Introduction presents an overview of selected contributions from the 11th Gas in Marine Sediments International Conference held on the 4–7 September 2012 in Nice, France, and published in this special issue of Geo-Marine Letters under the guest editorship of Catherine Pierre, Patrice Imbert and Jean Mascle. These cover fluid seepage dynamics at widely varying spatiotemporal scales in a giant buried caldera of the Caspian Sea, mud volcanoes and pockmarks in the Mediterranean and adjoining Gulf of Cadiz, as well as Lake Baikal, pockmarks of shallower waters along the Atlantic French coast and in Baltic Sea lagoons, deepwater pockmarks and cold seeps on the Norwegian margin and the Hikurangi Margin of New Zealand, asphalt seepage sites offshore southern California, and the tectonically controlled southern Chile forearc. We look forward to meeting all again at the 12th Gas in Marine Sediments conference scheduled for 1–6 September 2014 in Taipei, Taiwan.  相似文献   
28.
In the Norwegian North Sea, the Sleipner field produces gas with a high CO2 content. For environmental reasons, since 1996, more than 11 Mt of this carbon dioxide (CO2) have been injected in the Utsira Sand saline aquifer located above the hydrocarbon reservoir. A series of seven 3D seismic surveys were recorded to monitor the CO2 plume evolution. With this case study, time‐lapse seismics have been shown to be successful in mapping the spread of CO2 over the past decade and to ensure the integrity of the overburden. Stratigraphic inversion of seismic data is currently used in the petroleum industry for quantitative reservoir characterization and enhanced oil recovery. Now it may also be used to evaluate the expansion of a CO2 plume in an underground reservoir. The aim of this study is to estimate the P‐wave impedances via a Bayesian model‐based stratigraphic inversion. We have focused our study on the 1994 vintage before CO2 injection and the 2006 vintage carried out after a CO2 injection of 8.4 Mt. In spite of some difficulties due to the lack of time‐lapse well log data on the interest area, the full application of our inversion workflow allowed us to obtain, for the first time to our knowledge, 3D impedance cubes including the Utsira Sand. These results can be used to better characterize the spreading of CO2 in a reservoir. With the post‐stack inversion workflow applied to CO2 storage, we point out the importance of the a priori model and the issue to obtain coherent results between sequential inversions of different seismic vintages. The stacking velocity workflow that yields the migration model and the a priori model, specific to each vintage, can induce a slight inconsistency in the results.  相似文献   
29.
Abstract

Data unavailability is the main reason for limited applications of hydrodynamic models for predicting inundation in the developing world. This paper aims to generate moderately high-resolution hybrid terrain data by merging height information from low-cost Indian Remote Sensing satellite (IRS) Cartosat-1 stereo satellite images, freely-available Shuttle Radar Topograph Mission (SRTM) digital elevation model (DEM) data, and limited surveyed channel cross-sections. The study reach is characterized by anabranching channels that are associated with channel bifurcation, loops and river islands. We compared the performance of a simple 1D–2D coupled LISFLOOD-FP model and a complex fully 2D finite element TELEMAC-2D model with the hybrid terrain data. The results show that TELEMAC-2D produced significantly improved simulated inundation with the hybrid terrain data, as compared to the SRTM DEM. LISFLOOD-FP was found unsuitable to work with the hybrid DEM in a complicated fluvial environment, as it failed to efficiently divert water in the branches from the main channel.
Editor D. Koutsoyiannis; Associate editor A. Viglione  相似文献   
30.
In common‐reflection‐surface imaging the reflection arrival time field is parameterized by operators that are of higher dimension or order than in conventional methods. Using the common‐reflection‐surface approach locally in the unmigrated prestack data domain opens a potential for trace regularization and interpolation. In most data interpolation methods based on local coherency estimation, a single operator is designed for a target sample and the output amplitude is defined as a weighted average along the operator. This approach may fail in presence of interfering events or strong amplitude and phase variations. In this paper we introduce an alternative scheme in which there is no need for an operator to be defined at the target sample itself. Instead, the amplitude at a target sample is constructed from multiple operators estimated at different positions. In this case one operator may contribute to the construction of several target samples. Vice versa, a target sample might receive contributions from different operators. Operators are determined on a grid which can be sparser than the output grid. This allows to dramatically decrease the computational costs. In addition, the use of multiple operators for a single target sample stabilizes the interpolation results and implicitly allows several contributions in case of interfering events. Due to the considerable computational expense, common‐reflection‐surface interpolation is limited to work in subsets of the prestack data. We present the general workflow of a common‐reflection‐surface‐based regularization/interpolation for 3D data volumes. This workflow has been applied to an OBC common‐receiver volume and binned common‐offset subsets of a 3D marine data set. The impact of a common‐reflection‐surface regularization is demonstrated by means of a subsequent time migration. In comparison to the time migrations of the original and DMO‐interpolated data, the results show particular improvements in view of the continuity of reflections events. This gain is confirmed by an automatic picking of a horizon in the stacked time migrations.  相似文献   
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