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361.
Recognizing extinction events and determining their cause at the Triassic/Jurassic (T/J) transition and near the Pliensbachian–Toarcian (Lower Jurassic) boundary is a field of growing interest. We provide arguments for these events through a literature based new evaluation of coral diversity from Triassic to Dogger and a new palaeobiogeographical map. The T/J extinction of corals is clearly related to the breakdown of reef environments. Origination curves show that Hettangian (the lowest Jurassic stage) was not only a survival phase but already rather a recovery phase. Post-extinction evolution of reefs and their survival only in the northernmost margin of the Tethys support the hothouse hypothesis for the T/J extinction event. During Pliensbachian, many new taxa appear, but mostly solitary corals, not really framebuilders. Many of these taxa do not occur anymore during the following stages. The new increase in diversity is related to the development of Bajocian (Middle Jurassic) reefs. 相似文献
362.
da Silva DA Buzitis J Krahn MM Bícego MC Pires-Vanin AM 《Marine pollution bulletin》2006,52(2):175-183
This study reports the analysis of polycyclic aromatic compound (PAC) metabolites, as biomarkers of exposure to PACs in marine environment. PAC metabolites were measured in bile samples from 14 species of demersal fish caught in the São Sebastião Channel (SSC), SE Brazilian coastline. Naphthalene (NPH) equivalents, phenanthrene (PHN) equivalents, and benzo[a]pyrene (BaP) equivalents were quantified using a reverse-phase high-performance liquid chromatography coupled with fluorescence detection method. For all samples, the means (±standard deviation, n = 37) of concentrations obtained for NPH, PHN, and BaP equivalents were, respectively, 290,000 ± 200,000 ng/g, 18,000 ± 14,000 ng/g, and 970 ± 1900 ng/g. These results indicate recent exposure of these fish to PACs in their environment. In addition, two species (Cyclichthys spinosus and Prionotus nudigula) of fish were analyzed in order to investigate local sources of PAC contamination in the SSC and the influence of the petroleum terminal in fish caught in remote areas. The results showed that these fish species potentially migrate along the channel, especially P. nudigula. Correlations among groups of PAC metabolites indicate the same petrogenic source for NPH and PHN equivalents and a combustion source (e.g., automobile, ships) for BaP equivalents. The ratio BaP/PHN equivalents (0.05 ± 0.07, n = 37) confirms the predominance of petrogenic PACs for contamination by these chemicals in this region. 相似文献
363.
We present hereafter the formulation of a Timoshenko finite element straight beam with internal degrees of freedom, suitable for nonlinear material problems in geomechanics (e.g., beam type structures and deep pile foundations). Cubic shape functions are used for the transverse displacements and quadratic for the rotations. The element is free of shear locking, and we prove that one element is able to predict the exact tip displacements for any complex distributed loadings and any suitable boundary conditions. After the presentation of the virtual power and the weak form formulations, the construction of the elementary stiffness matrix is detailed. The analytical results of the static condensation method are provided. It is also proven that the element introduced by Friedman and Kosmatka in 1 , with shape functions depending on material properties, is derived from the new beam element. Validation is provided using linear and material nonlinear applications (reinforced concrete column under cyclic loading) in the context of a multifiber beam formulation. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
364.
Praca E Laran S Lepoint G Thomé JP Quetglas A Belcari P Sartor P Dhermain F Ody D Tapie N Budzinski H Das K 《Marine pollution bulletin》2011,62(5):1058-1065
Risso’s dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Risso’s dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (δ13C, δ15N) and organochlorines. Significantly different δ15N values were obtained in Risso’s dolphins (11.7 ± 0.7‰), sperm whales (10.8 ± 0.3‰) and pilot whales (9.8 ± 0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whale’s diet. Similar δ13C contents between species indicated long-term habitat superposition or corroborated important seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 μg.g−1 lw) and higher tDDT/tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Risso’s dolphins and may indicate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns. 相似文献
365.
3D stochastic inversion of magnetic data 总被引:1,自引:0,他引:1
366.
Denis Yu. Zezin Artashes A. Migdisov Anthony E. Williams-Jones 《Geochimica et cosmochimica acta》2011,75(18):5140-5495
This experimental study sheds light on the complexation of gold in reduced sulphur-bearing vapour, specifically, in H2O-H2S gas mixtures. The solubility of gold was determined in experiments at temperatures of 300, 350 and 365 °C and reached 2.2, 6.6 and 6.3 μg/kg, respectively. The density of the vapour varied from 0.02 to 0.22 g/cm3, the mole fraction of H2S varied from 0.03 to 0.96, and the pressure in the cell reached 263 bar. Statistically significant correlations of the amount of gold dissolved in the fluid with the fugacity of H2O and H2S permit the experimental data to be fitted to a solvation/hydration model. According to this model, the solubility of gold in H2O-H2S gas mixtures is controlled by the formation of sulphide or bisulphide species solvated by H2S or H2O molecules. Formation of gold sulphide species is favoured statistically over gold bisulphide species and thus the gold is interpreted to dissolve according to reactions of the form:
(A1) 相似文献
367.
Ulrike Rantzsch Christoph D. K. Gauert Willem A. Van der Westhuizen Isabelle Duhamel Michel Cuney Gerhard J. Beukes 《Mineralium Deposita》2011,46(2):187-196
The Neo-Archean Dominion Reefs (~3.06 Ga) are thin meta-conglomerate layers with concentrations of U- and Th-bearing heavy
minerals higher than in the overlying Witwatersrand Reefs. Ore samples from Uranium One Africa’s Rietkuil and Dominion exploration
areas near Klerksdorp, South Africa, were investigated for their mineral paragenesis, texture and mineral chemical composition.
The ore and heavy mineral assemblages consist of uraninite, other uraniferous minerals, Fe sulphides, Ni–Co sulfarsenides,
garnet, pyrite, pyrrhotite, monazite, zircon, chromite, magnetite and minor gold. Sub-rounded uraninite grains occur associated
with the primary detrital heavy mineral paragenesis. U–Ti, U–Th minerals, pitchblende (colloform uraninite) and coffinite
are of secondary, re-mobilised origin as evidenced by crystal shape and texture. Most of the uranium mineralisation is represented
by detrital uraninite with up to 70.2 wt.% UO2 and up to 9.3 wt.% ThO2. Re-crystallised phases such as secondary pitchblende (without Th), coffinite, U–Ti and U–Th phases are related to hydrothermal
overprint during low-grade metamorphism and are of minor abundance. 相似文献
368.
Guillaume Morard Denis Andrault Nicolas Guignot Julien Siebert Gaston Garbarino Daniele Antonangeli 《Physics and Chemistry of Minerals》2011,38(10):767-776
High pressure melting behavior of three Fe-alloys containing 5 wt% Ni and (1) 10 wt% Si, (2) 15 wt% Si or (3) 12 wt% S was
investigated up to megabar pressures by in situ X-ray diffraction and laser-heated diamond anvil cell techniques. We observe
a decrease in melting temperature with increasing Si content over the entire investigated pressure range. This trend is used
to discuss the melting curve of pure Fe. Moreover, our measurements of eutectic melting in the Fe–Fe3S system show a change in slope around 50 GPa concomitant with the fcc–hcp phase transition in pure solid iron. Extrapolations
of our melting curve up to the core–mantle boundary pressure yield values of 3,600–3,750 K for the freezing temperature of
plausible outer core compositions. 相似文献
369.
Jérôme Aléon Marc Chaussidon Michel Champenois Denis Mangin 《Geostandards and Geoanalytical Research》2001,25(2-3):417-429
A new analytical procedure has been developed to measure oxygen isotopic ratios and, more generally, stable isotopic ratios in microparticles with a few % precision. This procedure uses ion microprobe quantitative imaging with a scanning microbeam. In this mode, ion images are acquired on the electron multiplier. Image processing allows extraction of areas of interest from the whole image and computation of isotopic ratios in the selected areas. The accuracy of this method has been tested for the analysis of the 18O/16O ratio in quartz and magnetite reference samples powdered to a grain size of 2-5 μm. A detailed study of the instrumental mass fractionation allowed an understanding of differences between classical spot analysis and scanning ion imaging, and showed that fractionation effects were related to grain topography for microparticle analysis, and to image processing or to secondary optical settings for ion imaging. The precision obtained for the measurement of ä18O was 3% for grains having a diameter of 2 μm. 相似文献
370.
Michael Denis Higgins 《Contributions to Mineralogy and Petrology》1991,106(3):340-354
Well-laminated plagioclase-rich rocks (‘anorthosite’) occur as layers in mineralogically similar but massive rocks in the
Sept Iles intrusion. Several phases of crystallization of poikilitic clinopyroxene have preserved the intermediate stages
in the production of these rocks. Plagioclase nucleated and initially grew in random orientations in the stationary part of
the boundary layer. There, in the absence of other events, crystallization produced the massive anorthosite. The laminated
anorthosite may have been produced by episodic increases in the velocity of the magma adjacent to the boundarylayer induced
by magmatic density-currents. Such currents would have caused the zone of simple shear of the boundary-layer to migrate outwards
into the previously stationary part. This simple shear would then have rotated the existing plagioclase crystals, as well
as crystals that nucleated at that time, towards the shear-plane. Some rocks show evidence of several periods of enhanced
flow-velocities. The production of the lamination may have weakened the crystal-mush and enabled slumping to occur, producing
folds and contorted layers. Finally, compaction liberated large quantities of intercumulus magma of which some was trapped
as granophyric segregations and some escaped by overturing and churning the crystal-pile. Earlier-formed granophyric segregations
and laminated layers were disrupted during this process to produce a range of more-complex rocks including igneous breccias. 相似文献