Geochemical evaluation of mineralization potential of the Somie-Ntem area within the Tikar plain,Cameroon: implication on petrogenesis

Acta Geochimica - Somie-Ntem area of the Tikar plain belongs to the western Cameroon Domain. The lithology of the plain has been characterized, and the mineral potential is still unclear despite...     

Improving hydrogeological understanding through well-test interpretation by diagnostic plot and modelling: a case study in an alluvial aquifer in France

Hydrogeology Journal - The study of groundwater resources using pumping test data is usually carried out with the Theis solution, which enables the hydraulic parameters of porous aquifers such as...     

Evaluating the genetic effects of the invasive Ocenebra inornata on the native oyster drill Ocenebra erinacea

Studies focusing on the effect of invasive species on the genetic diversity of native marine invertebrates remain scant. Here we report diversity among French populations of the intertidal gastropod Ocenebra erinacea (Linnaeus, 1758) sampled in the presence and absence of the invasive Ocenebra inornata (Recluz, 1851). Between 1999 and 2004, a total of 352 individuals of O. erinacea was collected from 15 sites (five of which had the invasive present) and was genotyped at the mitochondrial locus Cytochrome Oxidase 1 (cox1). No statistical difference was observed between polymorphism levels recorded within native populations exposed to the invasive, compared with populations sampled in the absence of O. inornata. No sign of native population decline was detected in response to the invader. While significant shifts in native O. erinacea population sizes have previously been reported in the literature, genetic effects may take longer to accumulate, or may be undetectable without a larger panel of genetic markers. By contrast, large genetic distances and significant population differentiation were recorded between Atlantic and Mediterranean O. erinacea samples, suggesting that these populations have distinct evolutionary histories. Comparison of genetic divergence within the closely related genus Nucella suggests that the Atlantic populations of O. erinacea and those from Thau Lagoon in the Mediterranean may belong to different species or subspecies.     

Pyroxene structures,cathodoluminescence and the thermal history of the enstatite chondrites

Abstract— In order to explore the thermal history of enstatite chondrites, we examined the cathodoluminescence (CL) and thermoluminescence (TL) properties of 15 EH chondrites and 21 EL chondrites, including all available petrographic types, both textural types 3–6 and mineralogical types α–δ. The CL properties of EL3α and EH3α chondrites are similar. Enstatite grains high in Mn and other transition metals display red CL, while enstatite with low concentrations of these elements show blue CL. A few enstatite grains with >5 wt% FeO display no CL. In contrast, the luminescent properties of the metamorphosed EH chondrites are very different from those of metamorphosed EL chondrites. While the enstatites in metamorphosed EH chondrites display predominantly blue CL, the enstatites in metamorphosed EL chondrites display a distinctive magenta CL with blue and red peaks of approximately equal intensity in their spectra. The TL sensitivities of the enstatite chondrites correlate with the intensity of the blue CL and, unlike other meteorite classes, are not simply related to metamorphism. The different luminescent properties of metamorphosed EH and EL chondrites cannot readily be attributed to compositional differences. But x-ray diffraction data suggests that the enstatite in EH5γ,δ chondrites is predominantly disordered orthopyroxene, while enstatite in EL6β chondrites is predominantly ordered orthopyroxene. The difference in thermal history of metamorphosed EL and EH chondrites is so marked that the use of single “petrographic” types is misleading, and separate textural and mineralogical types are preferable. Our data confirm earlier suggestions that metamorphosed EH chondrites underwent relatively rapid cooling, and the metamorphosed EL chondrites cooled more slowly and experienced prolonged heating in the orthopyroxene field.     

Multi-Beam Echo Sounders–INS Automatic Latency Calibration

Abstract

This paper presents an automatic, rigorous, and robust method to determine a Multi-Beam Echo Sounder (MBES) and Inertial Measurement Unit/Inertial Navigation System (IMU/INS) latency calibration. The latency may be due to the IMU/INS itself, but also to the time-tagging configuration, which is generally left to the survey systems user. One survey strip over a flat seafloor is the required configuration of line for using this approach, called Multibeam IMU/INS Latency Automatic Calibration (MILAC), standing for MBES to IMU/INS Latency Automatic Calibration. The algorithm considers only data with maximum latency effects and integrates an automatic data selection for this purpose. The latency estimation procedure is based on an iterative Least Square adjustment method followed by a statistical analysis. Our process can deal with beam acoustic refraction caused by the speed of sound in sea water. The accuracy of MILAC is about 2?ms (millisecond) and its average precision of 0.15?ms. MILAC is able to determine the latency with an average resolution of 5?ms. However, the morphology of the survey line is restricted to smooth and regular seafloor and the survey platform should have a relatively high attitude rate.     

High-temperature infrared properties of forsterite

Polarized emittance measurements were acquired for synthetic forsterite, the pure magnesium end member of the olivines group, on the whole infrared spectral range and up to the melting point by using CO₂ laser heating. The experimental data, fitted with a semi-quantum dielectric function model, allowed the retrieval of the temperature dependence of the absorption coefficient of forsterite both in the opaque and semi-transparent regions. The analysis of the phonon parameters indicates that the lattice dynamics evolve drastically with increasing temperature. The normal modes involving motions of the magnesium cations located in site 1 are the more impacted, and some of them vanish around 1,200 K. The results confirm that the enhancement of the lattice anharmonicity and the increasing mobility of the magnesium cations are closely linked and are at the origin of the anomalies observed in the evolution of the thermophysical properties. This complete set of spectroscopic data may be a step toward a more precise evaluation of the impact of thermal radiation heat transfer inside systems involving forsterite and quantification of their heat budget.     

Penetrative convection in the upper ocean due to surface cooling

Abstract

A new non-linear model of mixing and convection based on a modelling of two buoyant interacting fluids is applied to penetrative convection in the upper ocean due to surface cooling. In view of simple algebra, the model is one-dimensional. Dissipation is included, but no mean shear is present. A non-similar analytical solution is found in the case of a well-mixed layer bounded below by a sharp thermocline treated as a boundary layer. This solution is valid if the Richardson number, R _i , defined as the ratio of the total mixed-layer buoyancy to a characteristic rms vertical velocity, is much greater than unity. The model predicts a deepening rate proportional to R _i ^?3/4. The thermocline remains of constant thickness, and the ratio thermocline thickness to mixed-layer depth decreases as R _i ^?3/4 as the mixed layer deepens. If the surface flux is constant, the mixed-layer depth increases with time as t ^½. The vertical structure throughout the mixed layer and thermocline is given by the analytical solution, and vertical profiles of mean temperature and vertical fluxes are plotted. Computed profiles and available laboratory data agree remarkably well. Moreover, the accuracy of the simple analytical results presented here is comparable to that of sophisticated turbulence numerical models.     

Relationships between hydraulic conductivity distribution and synsedimentary faults,Rharb-Mamora basin,Morocco; Hydrogeological,geostatistical and modeling approaches

This paper deals with the relationship between the physical characteristics of the Rharb-Mamora basin (Northern Morocco) and the distribution of hydraulic conductivity values in the Plio-Quaternary aquifer. A steady state groundwater model has been calibrated using these values. The distribution of hydraulic conductivity corresponds to a hydrodynamic partition with permeabilities of 2×10^–3 to 5×10^–2 ms^–1 (in the coastal part). A numerical modeling process shows a relative error map between calculated and measured piezometric surfaces, in order to facilitate calibration in steady state.The distribution of hydraulic conductivity values, and the lateral variation of sequences (deduced from engineering geology methods e.g. hydrogeological drilling data, seismic reflection interpretation, and geostatistical analysis), are controlled by synsedimentary fault activity, which deepened the Mio-Pliocene basement resulting in a thickening of overlying permeable rocks.

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Resumen Esta nota trata la relación existente entre las características físicas y la distribución de la conductividad hidráulica de los acuíferos subyacentes de la cuenca del Rharb-Mamora (norte de Marruecos). Para la simulación del flujo del agua subterránea se ha establecido un modelo en régimen permanente. La distribución de la conductividad hidráulica corresponde a un reparto hidrodinámico cuyo grado de permeabilidad es generalmente alto: desde 2×10^–3 hasta 5×10^–2 ms^–1 (zona costera). Con el objetivo de facilitar la calibración del modelo en régimen permanente, el proceso numérico realizado mostró errores relativos entre la piezometría calculada y medida. La distribución de los valores de permeabilidad y la variación lateral de las unidades permeables ha sido deducida a partir de métodos de geología aplicada (análisis de los sondeos hidrogeológicos, interpretación de los perfiles de sísmica de reflexión y aplicación de métodos geoestadísticos), y están controlados por la actividad de las fallas sinsedimentarias que influyen sobre la topografía del basamento mio-plioceno y el grosor de las unidades acuíferas.

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Résumé Cette note traite la relation entre les caractéristiques physique du bassin Rharb-Mamora (Nord du Maroc) et la répartition de la conductivité hydraulique du réseau aquifère. Le modèle de simulation des écoulements souterrains a été établi en régime permanent. La distribution de la conductivité hydraulique correspond à un découpage hydrodynamique dont le degré de perméabilité est généralement bon entre 2×10^–3 to 5×10^–2 ms^–1 (zone côtière). Afin de faciliter le calage en régime permanent, le code numérique établi permet de mettre en évidence les erreurs relatives entre la piézométrie calculée et mesurée.La distribution des valeurs de perméabilité et la variation latérale des unités perméables, déduites des méthodes de la géologie appliquée (analyse des forages hydrogéologiques, interprétation des profils sismique réflexion et analyse géostatistique), sont contrôlées par lactivité des failles synsédimentaires qui influencent lapprofondissement du substratum hydrogéologique mio-pliocène et lépaississement des corps perméables.

     

顽辉石陨石中A,B矿的微量元素化学意义

运用电子探针和中子活化分析方法测定了清镇和Ｂｕｓｔｅｅ顽辉石无球粒陨石中含铬硫化物相的组成和微量元素含量。正如早期的报告结果，电子探针分析结果不足１００％，表明有相当含量的轻元素（ｚ〈１０）存在。     

A novel method to infer historical DDT use on Cape Cod,Massachusetts (USA), based on ΣDDT degradation and <Superscript>210</Superscript>Pb dating in lake sediment cores

Glacier shrinkage and melting of snow patches caused by the current phase of warming is having a profound impact on lake ecosystems located in glacierized environments at high altitude and/or latitude because it alters the hydrology and the physico-chemistry of the river discharges and catchment runoff. These changes, in turn, have a major impact on the biota of these lakes. In this study, we combined geochemical and diatom analyses of a sediment core retrieved from Lake Kanas (N.W. China) to assess how climate change has affected this ecosystem over the past ~ 100 years. Our results show that the aquatic ecosystem of Lake Kanas was sensitive to changes in the regional climate over that period of time. The lake has been affected by change in hydrology (e.g. influx of glacier meltwater, variations in precipitation) and change in hydrodynamics (water column stability). The variations in abundance and composition of the diatom assemblages observed in the sedimentary record have been subtle and are complex to interpret. The principal changes in the diatom community were: (1) a rise in diatom accumulation rates starting in the AD 1970s that is coeval with changes observed in temperate lakes of the Northern Hemisphere and (2) an increase in species diversity and assemblage turnover and a faster rate-of-change since ~ AD 2000. The diatom community is expected to change further with the projected melting of the Kanas glacier throughout the twenty-first century.