Connexion porphyre cuprifère–épithermaux de type low-sulfidation : analyse structurale et représentation 3D du secteur de Bolcana,monts Apuseni,Roumanie

The AuPbZn low-sulfidation epithermal ore deposits of Troita, Trestia, and Magura (Apuseni Mountains, Romania) are spatially related to the Bolcana Cu-porphyry. In an attempt to demonstrate the connection between these mineralizations, a geometric study was made based on structural measurements and GOCAD^© geomodeller 3D representation of deposits. This study indicates that a specific spatial distribution of the different Au and PbZn veins of the epithermal deposits occurs around the Cu-porphyry, which cannot result from telescoped systems. To cite this article: O. Cardon et al., C. R. Geoscience 337 (2005).     

Identification of groundwater quality trends in a chalk aquifer threatened by intensive agriculture in Belgium

The European Union (EU) has adopted directives requiring that Member States take measures to reach a “good” chemical status of water resources by the year 2015 (Water Framework Directive: WFD). In order to achieve the environmental objectives for groundwater, the identification and reversal of significant upward trends in pollutant concentrations are required. A very detailed dataset available for the Hesbaye chalk aquifer in Belgium is used to evaluate tools and to propose efficient methodologies for identifying and quantifying nitrate trends in groundwater. Results indicate that the parametric linear regression and the non-parametric Mann-Kendall tests are robust; however, the latter test seems more adequate as it does not require verification of the normality of the dataset and it provides calculated nitrate trends very comparable to those obtained using linear regression. From a hydrogeological point of view, results highlight a general upward trend in the whole groundwater basin. The extrapolation of the trend analysis results indicates that measures have to be taken urgently in order to avoid further major degradation of groundwater quality within the next 10–70 years. However, a good groundwater quality status cannot be expected in the Hesbaye aquifer for the 2015 EU WFD deadline.     

Isotopic exchange of Zn with stable Zn adsorbed on reference clay minerals

For reference clays of low organic content, Zn adsorbed on the clay minerals is in kinetic equilibrium with ⁶⁵Zn in solution. Thus the specific activity approach applied to the transport of ⁶⁵Zn(II) at the water-reference clay interface is intrinsically valid.     

Rate of Convergence of the Gibbs Sampler in the Gaussian Case

We show that the Gibbs Sampler in the Gaussian case is closely linked to linear fixed point iterations. In fact stochastic linear iterations converge toward a stationary distribution under the same conditions as the classical linear fixed point one. Furthermore the covariance matrices are shown to satisify a related fixed point iteration, and consequently the Gibbs Sampler in the gaussian case corresponds to the classical Gauss-Seidel iterations on the inverse of the covariance matrix, and the stochastic over-relaxed Gauss-Seidel has the same limiting distribution as the Gibbs Sampler. Then an efficient method to simulate a gaussian vector is proposed. Finally numerical investigations are performed to understand the effect of the different strategies such as the initial ordering, the blocking and the updating order for iterations. The results show that in a geostatistical context the rate of convergence can be improved significantly compared to the standard case.     

Effect of diurnal and seasonal temperature variation on Cussac cave ventilation using co2 assessment

Cussac cave was investigated to assess the cave air temperature variations and to understand its ventilation regime. This cave is located in an active karst system in the south west part of France. It has a single entrance and is considered as a cold air trap. In this study, air mass exchanges were probed. Measurements of temperature and Pco₂ with a 30-min frequency were made in several locations close to the cave entrance. Speed of the air flow was also measured at the door of cave entrance. Results show that cave air Pco₂ varies from 0.18 to 3.33 %. This cave appears to be a CO₂ source with a net mass of 2319 tons blown in 2009. Carbon-stable isotope of CO₂ (¹³Cco₂) ranges from −20.6 ‰ in cold season to −23.8 ‰ in warm season. Cave air is interpreted as a result of a mix between external air and an isotopically depleted air, coming from the rock environment. The isotopic value of the light member varies through time, from −23.9 to −22.5 ‰. Furthermore, this study ascertains that the cave never stops in communicating with the external air. The ventilation regime is identified. (1) In cold season, the cave inhales at night and blows a little at the warmest hours. However, in warm season, (2) cave blows at night, but (3) during the day, a convection loop takes place in the entrance area and prevents the external air from entering the cave, confirming the cold air trap.

     

Measuring complexity in OGC web services XML schemas: pragmatic use and solutions

The use of standards in the geospatial domain, such as those defined by the Open Geospatial Consortium (OGC), for exchanging data has brought a great deal of interoperability upon which systems can be built in a reliable way. Unfortunately, these standards are becoming increasingly complex, making their implementation an arduous task. The use of appropriate software metrics can be very useful to quantify different properties of the standards that ultimately may suggest different solutions to deal with problems related to their complexity. In this regard, we present in this article an attempt to measure the complexity of the schemas associated with the OGC implementation specifications. We use a comprehensive set of metrics to provide a multidimensional view of this complexity. These metrics can be used to evaluate the impact of design decisions, study the evolution of schemas, and so on. We also present and evaluate different solutions that could be applied to overcome some of the problems associated with the complexity of the schemas.     

Recent vertical movements from precise levelling in the vicinity of the city of Basel, Switzerland

The southern end of the Upper Rhine Graben is one of the zones in Switzerland where recent crustal movements can be expected because of ongoing seismotectonic processes as witnessed by seismicity clusters occurring in this region. Therefore, in 1973 a control network with levelling profiles across the eastern Rhine Graben fault was installed and measured in the vicinity of the city of Basel in order to measure relative vertical movements and investigate their relationship with seismic events. As a contribution to EUCOR-URGENT, the profiles were observed a third time in the years 2002 and 2003 and connected to the Swiss national levelling network. The results of these local measurements are discussed in terms of accuracy and significance. Furthermore, they are combined and interpreted together with the extensive data set of recent vertical movements in Switzerland (Jura Mountains, Central Plateau and the Alps). In order to be able to prove height changes with precise levelling, their values should amount to at least 3–4 mm (1). The present investigations, however, have not shown any significant vertical movements over the past 30 years.     

Direct detection and characterization of extrasolar planets: The Mariotti space interferometer

Space infrared nulling interferometry has been identified as one of the most promising techniques for direct detection of Earthlike extrasolar planets and spectroscopic analysis of their atmospheres in the near future. After a review of various nulling interferometer schemes, we introduce the concept of internal modulation. As an illustration, we describe a two-dimensional array of telescopes that provides full internal modulation capabilities: the Mariotti space interferometer. It consists of six free-flying telescopes positioned on the sides of an equilateral triangle and grouped into three nulling interferometers. Their nulled outputs are suitably phase-shifted with respect to each other, coherently recombined, and detected. The phase shifts applied between the nullers are periodically changed, providing signal modulation at a frequency that can be selected to minimize instrumental and background noise. The frequency upper limit is set by the read-out noise of the detectors, and turns out to be ¹⁰⁻¹-¹⁰⁻² Hz for currently available Si:As BIB devices. This “fast” signal modulation allows much better monitoring of the background and detector drifts than when one relies solely on the external modulation provided by the slow rotation of the whole interferometer (at typical frequencies of 3×¹⁰⁻⁴-3×¹⁰⁻⁵ Hz). Mariotti internal modulation, also known as “phase chopping,” thus appears as a major step toward the feasibility of the Darwin and TPF space missions.     

Organic petrology and geochemistry of the Carboniferous coal seams from the Central Asturian Coal Basin (NW Spain)

This paper presents for the first time a petrological and geochemical study of coals from the Central Asturian Coal Basin (North Spain) of Carboniferous (Pennsylvanian), mainly of Moscovian, age. A paleoenvironmental approach was used, taking into account both petrographic and organic geochemical studies. Vitrinite reflectance (R_r) ranges from 0.5% to 2.5%, which indicates a high volatile bituminous to semianthracite and anthracite coal rank. The coal samples selected for paleoenvironmental reconstruction are located inside the oil–gas-prone phase, corresponding to the interval between the onset of oil generation and first gas generation and efficient expulsion of oil. This phase is represented by coals that have retained their hydrocarbon potential and also preserved biomarker information. Paleodepositional reconstruction based on maceral and petrographic indices points to a swamp environment with vitrinite-rich coal facies and variable mineral matter content. The gelification index (GI) and groundwater influence index (GWI) indicate strong gelification and wet conditions. The biomarkers exhibit a high pristane/phytane ratio, suggesting an increase in this ratio from diagenetic processes, and a high diterpanes ratio. This, in turn, would seem to indicate a high swamp water table and a humid climate. The maximum point of coal accumulation occurred during the regressive part of the Late Moscovian sequence and in the most humid climate described for this period of time in the well-known coal basins of Europe and North America.     

The growth of point source plumes at Rayleigh numbers up to 108 and Prandtl numbers up to 1000

Two-dimensional numerical simulations were conducted of the growth of thermal plumes from a point heat source at Rayleigh numbers up to 108 and Prandtl numbers up to 1000. Scaling the convection equations by the free fall velocity rather than the thermal diffusivity, increased the Prandtl number range available to numerical simulation by one order of magnitude from Prandtl number 100 to 1000. We present animations showing how the plumes grow with time for different Prandtl numbers. Plumes with Prandtl numbers around 7 (water) were found to be unstable to sinuous instabilities; whereas those at Prandtl numbers of 1000 had straight stems and fewer sinuous instabilities. Wavelet analysis was used to analyze the scales at which plumes initiated, and the scales at which sinuous instabilities occurred. The scale of both the plume structures and instabilities was found to decrease with Prandtl number.