Bioaccumulation of heavy metals and radionuclides from seawater by encased embryos of the spotted dogfish Scyliorhinus canicula     

Jeffree RA  Warnau M  Oberhansli F  Teyssie JL 《Marine pollution bulletin》2006,52(10):1278-1286

Encased embryos of spotted dogfish Scyliorhinus canicula absorbed six radio-isotopes (241Am, 109Cd, 57Co, 134Cs, 54Mn and 65Zn) directly from seawater during short-term experimental exposure, demonstrating the permeability of the egg-case to these contaminants. Embryo to water concentration factors (CFs) ranged from 0.14 for 134Cs to 7.4 for 65Zn. The 65Zn and 57Co CFs increased exponentially with embryo length, whereas the CF for 109Cd declined with length. Among different components of the encased embryo the egg case was the major repository (69-99%) of all six radio-isotopes that were distributed throughout its wall. Egg-case CFs were as high as 10(3) for 57Co and 65Zn, making it the major source of gamma radiation exposure to the embryo and potentially of radio-isotopes for continued absorption by the embryo, following the uptake phase of the experiment. The patterns of uptake by the egg-case approximated linearity for most isotopes and loss rates were isotope-specific; egg-case biokinetics were not greatly affected by the viability of the contained embryo. Within the embryo initial data on radio isotopic distribution show that the skin is their major site of uptake, as previously demonstrated for juveniles.  相似文献   

Structural control of the distribution of trace elements between silicates and hydrothermal solutions     

Marcel Volfinger  Jean-Louis Robert 《Geochimica et cosmochimica acta》1980,44(10):1455-1461

Over several years many partition coefficients have been measured between framework silicates, sheet silicates and hydrothermal solutions. Only trace alkaline cations are considered in the present work. It is well known that the difference between ionic radii of the trace cation and the major cation is replaces is not satisfactory for a good correlation with the partition coefficients P_X. A structural parameter δ_c is therefore defined, taking into consideration the adaptation of the trace cation to the cavity in which it occurs. This cavity may be the entire site of the major element, or a part of this site in the case of small cations, or a structural cavity located out of the alkali-ion site. The adaptation parameter δ_c is the difference between the ionic radius of the trace cation and the radius of that cavity. This paper shows that the partition coefficient P_X of the trace alkali-ion from the hydrothermal solution is an exponential function of the adaptation parameter δ_c, whatever the silicate may be.  相似文献   

The worldwide character of the 1969–1970 impulse of the secular acceleration rate     

Jean-Louis Le Mouël  Joël Ducruix  Chau Ha Duyen 《Physics of the Earth and Planetary Interiors》1982,28(4):337-350

This paper continues earlier studies to ascertain whether the distribution of the 1969–1970 jump of the secular variation rate has a worldwide character. The geometry of the jump presents some similarities with the geometry of the secular variation itself. We give a new estimation of the westward drift rate and information about spatial and temporal variations of the secular variation field.  相似文献   

Experiments on phase transformations and chemical reactions of mechanically activated minerals by grinding: Petrogenetic implications     

Jean-Louis Dandurand  Robert Gout  Jacques Schott 《Tectonophysics》1982,83(3-4)

Prolonged grinding increases the energy of solids by the production of stored energy in the form of new surfaces and internal defects. Moreover, grinding also generates quasi-hydrostatic pressures which can result in polymorphic transformations and mineral decomposition. Here we demonstrate the solid-state transformation of metastable to stable polymorphs (aragonite → calcite, anatase → rutile); the transformation of low-pressure to high-pressure phases (calcite → aragonite); and the lowering of the dehydration and decarbonation temperatures of minerals (siderite → magnetite or hematite, diaspore → corundum).In the presence of a fluid phase, stored energy from grinding can be released, resulting in accelerated reaction rates and, more importantly, phase transformations. In this paper we demonstrate the following transformations: ground calcite → magnesian calcite (at low Mg²⁺ concentration in solution), ground calcite → aragonite (at high Mg²⁺ concentration), ground magnesite → hydromagnesite, and ground dolomite → aragonite + Mg²⁺.Assuming an analogy between laboratory and natural grinding, tectonic activity may have important consequences on the release of hydrothermal fluids, the solubilization of minerals and on solid-state transformations. As examples the possible role of deformation on the formation of metamorphic aragonite and diaspore-bauxites is discussed.  相似文献   

Osmium isotope geochemistry in the Mackenzie River basin     

Youngsook Huh  Jean-Louis Birck 《Earth and Planetary Science Letters》2004,222(1):115-129

The Cenozoic marine osmium isotope record is largely driven by changes in the continental input. We aid its interpretation by supplying direct measurements of present day riverine Os in known geological and environmental settings. We analyzed Os concentrations and isotopic ratios in the dissolved, suspended, and bed materials of the Mackenzie River in Canada and smaller rivers draining the Western Cordillera into the Pacific Ocean. Rhenium content was measured for suspended and bed materials to provide further constraint. Dissolved ¹⁸⁷Os/¹⁸⁸Os ratios range from 0.74 to 4.5 and are controlled to first order by age and lithology of the bedrock. The rivers draining Jurassic volcanic rocks are unradiogenic, as low as 0.74, and those draining the Precambrian Canadian Shield are radiogenic, as high as 3.5. The headwaters of the Mackenzie left bank tributaries draining metamorphic carbonates in the Eastern Cordillera and Paleozoic black and gray shales in the Transition zone and the Interior Platform are especially radiogenic (3.0-4.5) with relatively high concentrations of Os. These latter rivers are responsible for the Mackenzie being above world average in Os concentration and yield (mol Os/km²/year) as well as in ¹⁸⁷Os/¹⁸⁸Os. The dissolved load is more radiogenic than the suspended or bed loads and constitutes a significant fraction of total fluvial Os.  相似文献   

Tectonic and climatic control of the changes in the sedimentary record of the Karnali River section (Siwaliks of western Nepal)   总被引：1，自引：0，他引：1  

Pascale  Huyghe  Jean-Louis  Mugnier  Ananta Prasad  Gajurel  Bernard  Delcaillau 《Island Arc》2005,14(4):311-327

Abstract A multidisciplinary study was conducted on the section of the Siwalik Group sediments, approximately 5000 m thick, exposed along the Karnali River. Analysis of facies, clay mineralogy and neodymium isotope compositions revealed significant changes in the sedimentary record, allowing discussion of their tectonic or climatic origin. Two major changes within the sedimentary fill were detected: the change from a meandering to a braided river system at ca 9.5 Ma and the change from a deep sandy braided to a shallow sandy braided river system at ca 6.5 Ma. The 9.5‐Ma change in fluvial style is contemporaneous with an abrupt increase of ?_Nd(0) values following a ?_Nd(0) minimum. This evolution indicates a change in source material and erosion of Lesser Himalayan rocks within the Karnali catchment basin between 13 and 10 Ma. The tectonic activity along the Ramgarh thrust caused this local exhumation. By changing the proximity and morphology of relief, the forward propagation of the basal detachment to the main boundary thrust was responsible for the high gradient and sediment load required for the development of the braided river system. The change from a deep sandy braided to a shallow sandy braided river system at approximately 6.5 Ma was contemporaneous with a change in clay mineralogy towards smectite‐/kaolinite‐dominant assemblages. As no source rock change and no burial effect are detected at that time, the change in clay mineralogy is interpreted as resulting from differences in environmental conditions. The facies analysis shows abruptly and frequently increasing discharges by 6.5 Ma, and could be linked to an increase in seasonality, induced by intensification of the monsoon climate. The major fluvial changes deciphered along the Karnali section have been recognized from central to western Nepal, although they are diachronous. The change in clay mineralogy towards smectite‐/kaolinite‐rich assemblages and the slight decrease of ?_Nd(0) have also been detected in the Bengal Fan sedimentary record, showing the extent and importance of the two major events recorded along the Karnali section.  相似文献   

Stony-iron meteorites: History of the metal phase according to tungsten isotopes     

Ghylaine Quitté  Jean-Louis Birck 《Geochimica et cosmochimica acta》2005,69(5):1321-1332

The global composition of the early solar system is thought to be roughly chondritic in terms of refractory components, and this means that metal and silicate should be present together in early planetesimals. To fully understand the metal-silicate differentiation process within the eucrite parent body (EPB), it is important to try and identify the metal reservoir that is complementary to the silicate part. The isotope 182 of tungsten (W), a siderophile element, is partly formed from the decay of ¹⁸²Hf, and W isotopes are useful for examining metal-silicate segregation. The W isotopic composition expected for the metal that is complementary to eucrites falls in the range of iron meteorites. However, mesosiderites seem to be genetically linked to eucrites based on petrologic and oxygen isotopic similarities. Therefore, we undertook the analysis of the metal phase of these stony-irons. Here we present tungsten isotopic data for mesosiderite and pallasite metal to characterize their parent body (bodies) and to assess possible relationships with eucrites.All stony-iron metals are depleted in radiogenic tungsten by −1.3 to −4.2 ε units, relative to the terrestrial standard, while chondrites, for comparison, are depleted by −1.9 ε units. In addition to W isotopic heterogeneity from one stony-iron to another, there is also W isotopic heterogeneity within individual meteorites. A formation model is tentatively proposed, where we show that mesosiderites, pallasites, and eucrites could possibly come from the same parent body. Several hypotheses are discussed to explain the isotopic heterogeneity: the production of cosmogenic tungsten, the in situ decay of hafnium present in inclusions, and tungsten diffusion processes after metal-silicate mixing during the cooling of the meteorites. The two latter hypotheses provide the best explanation of our data.  相似文献   

Late Miocene – Recent exhumation of the central Himalaya and recycling in the foreland basin assessed by apatite fission-track thermochronology of Siwalik sediments, Nepal     

Peter van der Beek  Xavier Robert  Jean-Louis Mugnier  Matthias Bernet  Pascale Huyghe  Erika Labrin 《Basin Research》2006,18(4):413-434

Thermochronological analysis of detrital sediments derived from the erosion of mountain belts and contained in the sedimentary basins surrounding them allows reconstructing the long-term exhumation history of the sediment source areas. The effective closure temperature of the thermochronological system analysed determines the spatial and temporal resolution of the analysis through the duration of the lag time between closure of the system during exhumation and its deposition in the sedimentary basin. Here, we report apatite fission-track (AFT) data from 31 detrital samples collected from Miocene to Pliocene stratigraphic sections of the Siwalik Group in western and central Nepal, as well as three samples from modern river sediments from the same area, that complement detrital zircon fission-track (ZFT) and U–Pb data from the same samples presented in a companion paper. Samples from the upper part of the stratigraphic sections are unreset and retain a signal of source-area exhumation; they show spatial variations in source-area exhumation rates that are not picked up by the higher-temperature systems. More deeply buried samples have been partially reset within the Siwalik basin and provide constraints on the thermal and kinematic history of the fold-and-thrust belt itself. The results suggest that peak source-area exhumation rates have been constant at ∼1.8 km Myr⁻¹ over the last ∼7 Ma in central Nepal, whereas they ranged between 1 and ∼1.5 km Myr⁻¹ in western Nepal over the same time interval; these spatial variations may be explained by either a tectonic or climatic control on exhumation rates, or possibly a combination of the two. Increasing lag times within the uppermost part of the sections suggest an increasing component of apatites that have been recycled within the Siwalik belt and are corroborated by AFT ages of modern river sediment downstream as well as the record of the distal Bengal Fan. The most deeply buried and most strongly annealed samples record onset of exhumation of the frontal Siwaliks along the Himalayan frontal thrust at ∼2 Ma and continuous shortening at rates comparable with the present-day shortening rates from at least 0.3 Ma onward.  相似文献   

Combining Ring Width, Density and Stable Carbon Isotope Proxies to Enhance the Climate Signal in Tree-Rings: An Example from the Southern French Alps   总被引：1，自引：0，他引：1  

Mary Gagen  Danny McCarroll  Jean-Louis Edouard 《Climatic change》2006,78(2-4):363-379

At present the most powerful tree-ring based climate reconstructions use high numbers of growth proxy series (ring width and density) to produce spatially smoothed estimates, such as average Northern Hemisphere summer temperatures. These single parameter reconstructions might be supplemented with regional climate reconstructions capable of capturing variability in more than one climate variable without lower replication compromising statistical quality, if multiple tree ring proxies were used. Pinus sylvestris and Pinus uncinata latewood density, width and δ¹³C series are presented from two sites in the French subalpine zone, east of Briançon. Where two proxies have the same dominant climate control their combination enhances that signal. Where proxies differ in dominant controlling climate variable, combining series allows access to bi-variable calibrations. Using this approach, multi-proxy reconstructions of both temperature and precipitation would better reflect complex synoptic variability in climate on spatially useful scales.  相似文献   

The end of moai quarrying and its effect on Lake Rano Raraku, Easter Island     

Henri J. Dumont  Christine Cocquyt  Michel Fontugne  Maurice Arnold  Jean-Louis Reyss  Jan Bloemendal  Frank Oldfield  Cees L.M. Steenbergen  Henk J. Korthals  Barbara A. Zeeb 《Journal of Paleolimnology》1998,20(4):409-422

We reconstruct aspects of the history of Easter Island over the last 4-5 centuries based on the study of a core from Rano Raraku Lake, situated in the crater that contains the quarry of the island's giant statues or moai. We use microfossils of plants and animals to identify five zones. The last three of these are separated by waves of immigration from South America and from the subantarctic. We argue that the first or South American wave, dated to the second half of the 14th century, may represent a visit by South American Indians. Magnetic information, pollen, diatoms, chrysophyte stomatocysts and fossil plant pigments reveal a synchronism between the South American contact and the cessation of moai quarrying. We therefore suggest that Amerindians contributed to the cultural collapse of the island. The second or subantarctic wave may reflect an early European visit to the island, possibly by Cpt. James Cook in 1774, or by Jacob Roggeveen in 1722.  相似文献