Organic contamination identification in sediments from a Mediterranean coastal ecosystem: The case of the Nador lagoon (Eastern Morocco)     

Mohamed Karim Bloundi  Pierre Faure  Joëlle Duplay 《Comptes Rendus Geoscience》2008,340(12):840-849

The Nador lagoon ecosystem (North-East of Morocco) displays a major socioeconomic interest. In fact, it is essential to evaluate consequences of anthropogenic activities in the lagoon especially by organic matter studies (nature and distribution) in the sedimentary compartment. Surface sediments show variable rates in total organic carbon and in sulfur, high in some cases (7.5 and 1.8% respectively). These high contents are recorded in the center of the lagoon. Their distributions are controlled by the hydrodynamism and the anthropogenic degree. The molecular biomarkers analyses and especially n-alkanes distribution reveal: a zone of marine influence; and a zone of continental influence. The occurrence of pentacyclic triterpanes with a typical distribution of a thermally mature organic matter reveals a contamination due to petroleum products in the entire lagoon except for the center. Coprostanol occurrence near cities indicates wastewater effluents inputs and reducing conditions underlined by high values of stanols/sterol ratios. Thus, the organic contamination (petroleum by-products and wastewater effluents) occurs in the vicinity of the cities whereas the littoral edge and center remain weakly affected by these contaminations.  相似文献   

Systematique U-Pb et Evolution du Gisement d'Uranium de Lodève (France)     

Joël R. Lancelot  Bruno de Saint André  Henri de la Boisse 《Mineralium Deposita》1984,19(1):44-53

Résumé Considérée comme syngénétique ou diagénétique précoce, la minéralisation uranifère de la couche 0 de l'Autunien du bassin de Lodève a été étudiée par la méthode U-Pb sur roches totales. Les données U-Pb démontrent l'existence de perte en radon, principalement dans la chaine de désintégration de ²³⁸U, et l'intérêt de l'utilisation du couple ²⁰⁷Pb-²³⁵U pour la détermination des âges de cristallisation des concentrations uranifères. Pour la couche 0, deux phases de remobilisation de l'uranium et du plomb ont pu être déterminées respectivement à 173±6 Ma et 108±5 Ma. La plus ancienne de ces deux phases est la plus marquée dans les échantillons étudiés, dont les systèmes U-Pb ne montrent pas la mémoire d'une concentration uranifère permienne. La première mobilisation de l'uranium et du plomb s'est faite lors d'une phase de distension à 160–170 Ma, affectant la croûte continentale du Sud du Massif Central. Cette phase a provoqué la circulation de fluides minéralisés et est marquée par une recristallisation des illites des pélites permiennes entre 100 et 200 °C (du fait de l'élévation du gradient géothermique) et par la mise en place d'un volcanisme d'origine mantellique daté à 155±6 Ma. La composition isotopique en plomb d'une galène de l'Autunien du Lodévois, est analogue à celles des feldspaths des granitoïdes du Massif Central français et à celles des galènes des minéralisations stratiformes de Pb-Zn des Causses, ce qui fournit un argument pour faire dériver au moins une partie des métaux en traces dans les pélites autuniennes de l'altération de la croûte continentale hercynienne environnante.

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In the Lodeve basin, the uraniferous mineralization associated with the autunian pelitic layer 0 is usually considered as syngenetic or early diagenetic. U-Pb isotopic data performed on U bearing whole rocks demonstrate occurrence of radon losses, mainly in the ²³⁸U decay series; the ²⁰⁷Pb-²³⁵U geochronometer is particularly suitable to date U-Pb systems disturbed by such radon losses. For the autunian layer 0, two U-Pb mobilization phases have been respectively recognized at 173±6 Ma and 108±5 Ma. The oldest phase is the most clearly expressed in the studied samples, no memory of a permian age could be recognized in the U-Pb systems. The first U-Pb mobilization occurred 170 Ma ago, during a distension phase of the continental crust. This phase induced circulations of mineralized fluids, illite recristallization in the permian pelites at temperatures ranging from 100 to 200 °C and emplacement of a mantellic volcanism recently dated at 155±6 Ma. A galena from the Autunian of the Lodeve basin, the feldspars of the surrounding variscan granitoïds and galenas of mesozoïc stratiform deposits in the Causses, present similar Pb isotopic composition, which is in agreement with the hypothesis that some metals of the autunian pelites originated in the surrounding weathered variscan continental crust.

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Luftelektrische Tagesgänge und Massenaustausch im Hochgebirge der Alpen     

H. Israël  H. W. Kasemir  K. Wienert 《Meteorology and Atmospheric Physics》1955,8(1-2):72-94

Zusammenfassung Die luftelektrischen Untersuchungen auf dem Jungfraujoch im Sommer und Herbst 1950, über die vor einiger Zeit in dieser Zeitschrift berichtet worden war, wurden während einer dritten Meßperiode im Winter fortgesetzt und damit zu einer Jahresreihe ergänzt. Trotz ungünstiger Witterung, die den Umfang der Ergebnisse stark einschränkte, konnten die schon früher gezogenen Schlüsse voll bestätigt werden: Die im Sommer starke, im Herbst noch schwach vorhandene systematische Leitfähigkeitsvariation in dieser Alpenhöhe ist im Winter ganz verschwunden; Potentialgefälle und Vertikalstrom verlaufen in ihrem Tagesgang parallel zueinander; im Winter stellt sich somit in der Höhe des Alpenkammes, der jetzt von der Tagesvariation des Massenaustausches offenbar nicht mehr erreicht wird, der ozeanische Typ des luftelektrischen Verhaltens ein.Im Herbst 1950 wurden an einigen Tagen gleichzeitige Registrierungen des Potentialgefälles und des Vertikalstromes auf dem Jungfraujoch und dem 400 km entfernten Sonnblick durchgeführt. Die beiden Elemente zeigen sowohl im mittleren Tagesgang wie auch im einzelnen gute Übereinstimmung. Daraus ist zu entnehmen, daß die auf dem Jungfraujoch gewonnenen Ergebnisse, soweit sie nicht lokal gestört sind, repräsentative Bedeutung für die Kammhöhe der Alpen haben.Eine Studie über Feld und Strom während Niederschlages auf dem Jungfraujoch zeigt, daß trockener Schnee, d. h. Schnee als reines Sublimationsprodukt, stets positiv geladen ist und ein positives Feld (Feld normaler Richtung) erzeugt. Dagegen zeigen feste Niederschlagsteilchen, deren Zustandekommen über den Vergraupelungsprozeß geführt hat (nasser Schnee, Grieseln, Reif- und Frostgraupeln) im allgemeinen negative elektrische Ladung und negative Felder (Feldrichtungsumkehr). Besonders bemerkenswert ist dabei, daß im Sommer in der Regel das Auftreten von Graupeln und Schnee bzw. von Regen und Schnee hintereinander als Zeichen eines sich bildenden Gewitters gewertet werden kann.

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Summary The investigations on atmospheric electricity of summer and autumn 1950 on the Jungfraujoch have been continued with a third recordingperiod in the winter. By these investigations the former results which are already reported in this review are completed to a full-year-research. In spite of bad weather, which strongly limited the extent of the results, the conclusions drawn from earlier investigations could be entirely verified. In this Alpine altitude the systematic variation of the conductivity, that has been found high in summer and scarcely remarkable in autumn, has completely disappeared in winter. The daily variations of the potential gradient and the air-earth-current are essentially parallel; it accounts for that in winter at the ridge of the Alps the oceanic type of atmospheric electricity is predominant. Obviously, the daily variations of the mass exchange do not reach these high levels in the winter months.In autumn 1950 simultaneous records of the potential gradient and the air-earth-current at Jungfraujoch and at Sonnblick, 400 km distant, have been made during some days. The two elements are in good agreement both with regard to the mean daily variations as to particulars. Hence it follows that the results received at Jungfraujoch are representative for the summit of the Alps except for cases with local disturbances.Furthermore an investigation has been carried out at Jungfraujoch on the electric field and the current during precipitation. It resulted that dry snow, i. e. snow originating by sublimation only, always carries a positive charge and generates an electric field of positive direction. On the contrary, the solid precipitation particles which are formed by graupel formation (wet snow, soft hail, granular snow) carry generally a negative charge and generate an electric field of negative direction. In summer the occurence of snow after soft hail or rain can be taken as a remarkable symptom for developing a thunderstorm.

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Résumé Les recherches d'électricité atmosphérique effectuées au Jungfraujoch pendant l'été et l'automne 1950 et dont il a été question précédemment dans cette revue ont été complétées par une série hivernale. Malgré un temps défavorable qui a limité les recherches, les résultats précédents ont pu être confirmés. La variation systématique de la conductibilité observée à haute altitude, forte en été et encore faiblement présente en automne, disparaît complètement en hiver. Le gradient de potentiel et le courant vertical présentent des marches diurnes parallèles, c'est-à-dire qu'en hiver, à l'altitude du faîte alpin qui n'est apparemment plus affecté par la variation diurne de l'échange de masse, s'établit le type océanique de l'état électrique de l'atmosphère.En automne 1950 les enregistrements du gradient de potentiel et du courant vertical furent exécultés pendant quelques jours simultanément au Jungfraujoch et au Sonnblick, distant de 400 km. du premier; il y a bon accord entre les mesures des deux éléments, tant pour la variation diurne moyenne que pour les cas isolés. Il s'ensuit que les résultats obtenus au Jungfraujoch, pour autant qu'ils ne sont pas troublés localement, sont représentatifs de la crête des Alpes.Une étude du champ et du courant au Jungfraujoch pendant des précipitations montre que la neige sèche, c'est à dire comme produit pur de sublimation, est toujours chargée positivement et engendre un champ positif (direction normale). Par contre les particules solides issues du grésil (neige mouillée, neige en grains, grésil) sont en général négativement chargées, dans des champs négatifs (direction inversée). Il est en particulier remarquable qu'en été la neige succédant au grésil ou à la pluie soit dans la règle le signe d'un orage en formation.

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Mit 4 Textabbildungen.  相似文献   

Le Capelinhos (Faïal,Açores) vingt ans après son éruption: le modèle éruptif «surtseyen» et les anneaux de tufs hyaloclastiques     

G. Camus  P. Boivin  A. De Goër De Herve  A. Gourgaud  G. Kieffer  J. Mergoil  P. M. Vincent 《Bulletin of Volcanology》1981,44(1):31-42

Phreatomagmatic structures are of two kinds: maars and tuff-rings. Data given by records of Capelinhos activity (Faïal, Açores, 1957–1958), by structures at west point of Faïal island, and by palagonitic breccias of Velay and Cantal areas (France) lead to relate hyaloclastic tuff-rings and shallow subaquatic («surtseyan») eruptions. It is possible to precise causes, characteristics, and mechanism of formation of tuff-rings.  相似文献   

Identification of a magma chamber in the Ghoubbet-Asal rift (Djibouti) from a magnetotelluric experiment     

Daniele Boyer  Jean-Louis Le Mouël  Vincent Courtillot 《Earth and Planetary Science Letters》1981,52(2):372-380

A very broad band (10^?3 to 10⁴ Hz) magnetotelluric investigation of the axial zone of the Ghoubbet-Asal rift (Djibouti) has revealed a shallow (2–4 km) magma chamber which can be mapped in some detail. The suggested roof of the chamber is shallowest very close to the Ardoukoba volcano which was built during the November 1978 rifting episode.  相似文献   

On the Mátern covariance family: a proposal for modeling temporal correlations based on turbulence theory   总被引：1，自引：1，他引：0  

Gaël Kermarrec  Steffen Schön 《Journal of Geodesy》2014,88(11):1061-1079

Current variance models for GPS carrier phases that take correlation due to tropospheric turbulence into account are mathematically difficult to handle due to numerical integrations. In this paper, a new model for temporal correlations of GPS phase measurements based on turbulence theory is proposed that overcomes this issue. Moreover, we show that the obtained model belongs to the Mátern covariance family with a smoothness of 5/6 as well as a correlation time between 125–175 s. For this purpose, the concept of separation distance between two lines-of-sight introduced by Schön and Brunner (J Geod 1:47–57, 2008a) is extended. The approximations made are highlighted as well as the turbulence parameters that should be taken into account in our modeling. Subsequently, fully populated covariance matrices are easily computed and integrated in the weighted least-squares model. Batch solutions of coordinates are derived to show the impact of fully populated covariance matrices on the least-squares adjustments as well as to study the influence of the smoothness and correlation time. Results for a specially designed network with weak multipath are presented by means of the coordinate scatter and the a posteriori coordinate precision. It is shown that the known overestimation of the coordinate precision is significantly reduced and the coordinate scatter slightly improved in the sub-millimeter level compared to solutions obtained with diagonal, elevation-dependent covariance matrices. Even if the variations are small, turbulence-based values for the smoothness and correlation time yield best results for the coordinate scatter.  相似文献   

PAH transport by sinking particles in the open Mediterranean Sea: a 1 year sediment trap study   总被引：1，自引：0，他引：1  

Bouloubassi I  Méjanelle L  Pete R  Fillaux J  Lorre A  Point V 《Marine pollution bulletin》2006,52(5):560-571

One year time series of sinking particles were collected at two depths in the open Mediterranean Sea and analysed for polycyclic aromatic hydrocarbons (PAH). Average total PAH concentrations were 593+/-284 ng g(-1) at 250 m and 551 +/- 198 ng g(-1) at 2850 m. Total PAH fluxes averaged 73 +/- 58 ng m(-2) d(-1) at 250 m and 53 +/- 39 ng m(-2) d(-1) at 2850 m. Contamination levels and, thus, exposure of marine organisms to PAH are comparable in surface and deep waters. Deep waters appear as a significant, yet overlooked, PAH sink. PAH temporal patterns show noticeable seasonality. This is partly due to varying levels of specific components such as the winter increase of pyrolytic PAH. Downward transport processes and the nature of sinking particles also impact on PAH fluxes, as inferred during periods of increasing productivity. Different phase-associations and interactions with particulate organic carbon for low-MW fossil PAH and high-MW pyrolytic PAH influence their downward transport efficiency.  相似文献   

Review of solutions for 3D hydrodynamic modeling applied to aquaculture in South Pacific atoll lagoons   总被引：1，自引：0，他引：1  

Andréfouët S  Ouillon S  Brinkman R  Falter J  Douillet P  Wolk F  Smith R  Garen P  Martinez E  Laurent V  Lo C  Remoissenet G  Scourzic B  Gilbert A  Deleersnijder E  Steinberg C  Choukroun S  Buestel D 《Marine pollution bulletin》2006,52(10):1138-1155

A workshop organized in French Polynesia in November 2004 allowed reviewing the current methods to model the three-dimensional hydrodynamic circulation in semi-enclosed atoll lagoons for aquaculture applications. Mollusk (e.g. pearl oyster, clam) aquaculture is a major source of income for South Pacific countries such as French Polynesia or Cook Islands. This aquaculture now requires a better understanding of circulation patterns to improve the spatial use of the lagoons, especially to define the best area to set larvae collectors. The pelagic larval duration of the relevant species (<20 days) and the size of the semi-closed lagoons (few hundreds of km2) drive the specifications of the model in terms of the spatial and temporal scale. It is considered that, in contrast with fish, mollusk larvae movements are limited and that their cycle occurs completely in the lagoon, without an oceanic stage. Atolls where aquaculture is productive are generally well-bounded, or semi-closed, without significant large and deep openings to the ocean. Nevertheless part of the lagoon circulation is driven by oceanic water inputs through the rim, ocean swells, tides and winds. Therefore, boundary conditions of the lagoon system are defined by the spatial structure of a very shallow rim (exposition and number of hoas), the deep ocean swell climate, tides and wind regimes. To obtain a realistic 3D numerical model of lagoon circulation with adequate forcing, it is thus necessary to connect in an interdisciplinary way a variety of methods (models, remote sensing and in situ data collection) to accurately represent the different components of the lagoon system and its specific boundary conditions. We review here the current methods and tools used to address these different components for a hypothetical atoll of the Tuamotu Archipelago (French Polynesia), representative of the semi-closed lagoons of the South Pacific Ocean. We hope this paper will serve as a guide for similar studies elsewhere and we provide guidelines in terms of costs for all the different stages involved.  相似文献   

Trace element diffusion and incorporation in quartz during heating experiments     

B.?RottierEmail author  H.?Rezeau  V.?Casanova  K.?Kouzmanov  R.?Moritz  K.?Schl?glova  M.?W?lle  L.?Fontboté 《Contributions to Mineralogy and Petrology》2017,172(4):23

Heating of quartz crystals in order to study melt and high-temperature fluid inclusions is a common practice to constrain major physical and chemical parameters of magmatic and hydrothermal processes. Diffusion and modification of trace element content in quartz and its hosted melt inclusions have been investigated through step-heating experiments of both matrix-free quartz crystals and quartz crystals associated with sulfides and other minerals using a Linkam TS1500 stage. Magmatic and hydrothermal quartz were successively analyzed after each heating step for Cu, Al, and Ti using electron probe micro-analyzer. After the last heating step, quartz crystals and their hosted melt inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry and compared to unheated samples. Heated samples reveal modification of Cu, Li, Na, and B contents in quartz and modification of Cu, Li, Ag, and K concentrations in melt inclusions. Our results show that different mechanisms of Cu, Li, and Na incorporation occur in magmatic and hydrothermal quartz. Heated magmatic quartz records only small, up to a few ppm, enrichment in Cu and Na, mostly substituting for Li. By contrast, heated hydrothermal quartz shows enrichment up to several hundreds of ppm in Cu, Li, and Na, which substitute for originally present H. This study reveals that the composition of both quartz and its hosted melt inclusions may be significantly modified upon heating experiments, leading to erroneous quantification of elemental concentrations. In addition, each quartz crystal also becomes significantly enriched in Cu in the sub-surface layer during heating. We propose that sub-surface Cu enrichment is a direct indication of Cu diffusion in quartz externally sourced from both the surrounding sulfides as well as the copper pins belonging to the heating device. Our study shows that the chemical compositions of both heated quartz and its hosted inclusions must be interpreted with great caution to avoid misleading geological interpretations.  相似文献   

X‐ray tomography of tsunami deposits: Towards a new depositional model of tsunami deposits          下载免费PDF全文

Simon Falvard  Raphaël Paris 《Sedimentology》2017,64(2):453-477

X‐ray computed microtomography is used to obtain high resolution imagery of a historical tsunami deposit in Andalusia, Spain (1755 Lisbon tsunami). The technique allows characterization of grain‐size distribution, structures, component analysis and sedimentary fabric of fine‐grained unconsolidated tsunami deposits at resolutions down to particle scale. The results are validated by comparing to data obtained using other techniques such as laser diffraction, anisotropy of magnetic susceptibility and X‐ray microfluorescence on the same deposits. Specific technical details such as sampling, scanning and image processing methods, and further improvements are addressed. The use of X‐ray computed microtomography provides new insights into the stratigraphy of the deposits and gives access to significantly more detailed view of key sedimentary features such as mudlines, rip‐up clasts, crude laminations, convolutions, floating outsized clasts and contacts between successive units. This analysis of the 1755 tsunami deposits using X‐ray computed microtomography allows the proposal of new hypotheses for the sedimentary processes forming tsunami deposits. Deposition by settling is limited and the section analysed here is dominated by a high shear stress leading to the development of traction carpets, with laminated mudlines corresponding to the basal frictional region of these carpets. The onset of the tsunami backwash is marked by a micro‐vortex resembling Kelvin–Helmoltz instabilities.  相似文献