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1.
Biominerals are natural composite materials comprising organic and inorganic components. Detailed knowledge of the nature and distribution of both components is a crucial requirement in order to advance our understanding of biomineral formation, their material properties and preservation potential as well as the interpretation of environmental data. Detailed chemical data are essential for our understanding of the nature and distribution of such components. Micro-XANES mapping at the sulphur K-edge reveals that, in the brachiopod Terebratulina retusa, the sulphate concentration is higher in the outer (primary) layer than in the calcite fibres of the secondary layer. This is co-incident with a higher magnesium concentration. In contrast, the sheaths surrounding the calcite fibres contain sulphur as thiol, confirming the presence of protein while, the sulphur within the fibres themselves, occurs as sulphate. Micro-XANES analysis of the insoluble organic extract from T. retusa indicates the presence of organic sulphate while Micro-Raman spectroscopy confirms that structurally substituted sulphate (SSS) is also present although semi-quantitative Raman spectroscopy carried out in this spectral region (wavenumbers 900–1200) indicates that the sulphate present is at the threshold of detection by Raman spectroscopy. The distribution of phosphorus in the shell of T. retusa correlates well with that of protein indicating the presence of phosphorylated proteins in the periostracum, the sheaths surrounding the calcite fibres and the interface between the primary and secondary layer.  相似文献   
2.
The presence and localization of organic sulfate within coral skeletons are studied by using X-ray absorption near edge structure spectroscopy (XANES) fluorescence. XANES spectra are recorded from four reference sulfur-bearing organic molecules: three amino acids (H-S-C bonds in cysteine; C-S-C bonds in methionine; one disulfide bond C-S-S-C bonds in cystine) and a sulfated sugar (C-SO4 bonds in chondroitin sulfate). Spectral responses of three coral skeletons show that the sulfated form is extremely dominant in coral aragonite, and practically exclusive within both centres of calcification and the surrounding fibrous tissues of coral septa. Mapping of S-sulfate concentrations in centres and fibres gives us direct evidence of high concentration of organic sulfate in centres of calcification. Additionally, a banding pattern of S-sulfate is visible in fibrous part of the coral septa, evidencing a biochemical zonation that corresponds to the step-by-step growth of fibres.  相似文献   
3.
This work provides five new U–Pb zircon dating and the corresponding Nd isotope data for felsic granulites from the south Itabuna-Salvador-Curaçá Block (ISCB), in the São Francisco Craton, Brazil. Three major sets of felsic granulites can be recognised. The oldest set is tonalitic in composition and of TTG affinity. It is Archaean in age with magmatic zircon cores dated at 2675 ± 11 Ma by LA-ICPMS and up to ca 2.7–2.9 Ga by SHRIMP on an other sample. It exhibits epsilon Nd values between ?8 and ?11 at 2.1 Ga. This Nd signature is similar to that of granulites found in the western Archaean Jequié Block. Cartographically, this set of Archaean terrains represents at least 50% of the granulites in the studied area. The second set corresponds to a Palaeoproterozoic calc-alkaline tonalitic suite with zircon ages from 2019 ± 19 Ma to 2191 ± 10 Ma and epsilon Nd values between ?3 and ?4 at 2.1 Ga, corresponding partially to a newly formed crust. The third set of granulites is also Palaeoproterozoic. It is shoshonitic to monzonitic in composition and synchronous with the high grade metamorphism dated by metamorphic zircons at 2086 ± 7 Ma (average of five samples). The Nd isotope signature for this alkaline set is similar to that of the Palaeoproterozoic calc-alkaline one. Nd isotopes appear to be a very efficient tool to distinguish Archaean from Palaeoproterozoic felsic protoliths in granulitic suites of the Itabuna-Salvador-Curaçá Block (ISCB). Finally, the southern part of the ISCB is composed of a mixture of Archaean and Palaeoproterozoic protoliths, in similar amounts, suggesting that it was probably an active margin between 2.1 and 2.2 Ga located on the eastern border of the Archaean Jequié Block. A major crustal thickening process occurred at ca 2.09 Ga in the ISCB and seems significantly younger towards the west, in the Jequié granulites, where an average of 2056 ± 9 Ma is determined for the high grade event.  相似文献   
4.
In the context of the potential confinement of high-level radioactive wastes (HLW) within the clay engineered barrier system (EBS) in deep geological formations, the evolution of the retention properties of smectite when interacting with Fe(0) needs to be assessed. If some potential natural analogues describing iron-clay reactivity are easily found, metallic iron-clay interactions are poorly described in studies regarding the Earth. Therefore, experimental investigations are needed. Several parameters influence Fe(0)-clay interactions, such as temperature, the interlayer composition of swelling clays, and the presence of octahedral Fe3+, etc. From a geometrical point of view, it is thought that clay destabilization is mainly controlled by phenomena starting at the edge faces of the particles. In the present work, the rates of the smectite-Fe(0) reaction at 80 °C were assessed by XRD, Mössbauer, and CEC analyses for three smectites. The investigations show marked differences in the degree of stability, which cannot be explained by the crystal-chemistry rules established in previous studies. Therefore, the Fe(0)-smectite interactions were studied in view of textural and energetic surface quantitative analyses. The studied smectites have equivalent nitrogen BET-specific surface areas, equivalent argon edge surface areas and slightly different basal surface areas. This similarity in particle shape indicates that the edge surface area cannot be accounted for when explaining the observed differences in reactivity. However, a correlation is obtained between smectite reactivity and the energetic heterogeneity of its edge faces. This is interpreted in terms of a multiplication of the number of sites on the edge faces, where the electron transfer between Fe(0) and the smectite structure can occur.  相似文献   
5.
The studied tonalitic and trondhjemitic granulites are located in the SSE granulitic domain of the São Francisco craton, Bahia, Brazil, where they represent most of the southern part of the Archean and Paleoproterozoic Itabuna-Salvador-Curaçá Block (ISCB). Chemically, the tonalitic and trondhjemitic granulites belong to a low-K calc-alkaline suite; their REE patterns are steep with strong LREE/HREE fractionation and no significant Eu anomaly. Garnet-bearing mafic granulites that occur as enclaves in the tonalitic and trondhjemitic granulites were derived from basalts and/or gabbros of tholeiitic affinity. Geochemical modelling showed that the tonalitic and trondhjemitic granulites were produced by moderate fractional crystallization of an assemblage of hornblende and plagioclase, with subordinate amounts of magnetite, apatite, allanite and zircon. The garnet-bearing mafic granulites would be the source of the magmas that generated these rocks. Partial melting left a residue made up of plagioclase, garnet, orthopyroxene and hornblende.  相似文献   
6.
Coastal cities in East Africa are growing rapidly and consequently there is a rapid increase in urban sewage production, putting added pressure on already strained treatment systems. As a result, peri-urban mangroves are receiving extensive amounts of sewage but very little is know as to the ecological and societal consequences of this. However, UNEP among others advocate the use of low-cost, natural sewage treatment technology whenever possible and mangroves have been suggested as useful second stage biofilters. Because of the high resource dependency in many peri-urban coastal communities in East Africa, it is imperative to investigate potential societal impacts on local communities using sewage impacted peri-urban mangroves. Consequently this paper aims to characterize stakeholder groups currently affected by sewage impacted mangroves and thus also map vulnerabilities across local users in relation to future initiatives to use mangroves as biofilters along the East African coast. As risk perception is an important part of vulnerability, and risk perception related to sewage and pollution in an African setting has been little studied, we also aim to contribute baseline data on risk perception related to pollution across peri-urban populations in Kenya, Tanzania and Mozambique.  相似文献   
7.
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8.
Owing to the delicate nature of fossil microorganisms and inherent difficulties for discriminating true fossils from artifacts, an important challenge is to extract unequivocal biogenic information from individual microfossils using high-resolution, nondestructive and sensitive techniques. Here, we use combined synchrotron (X-ray microfluorescence, X-ray absorption near-edge structure and infrared microspectroscopies) and particle-induced X-ray emission analyses to image the spatial distribution at a μm-scale of a variety of potential biogenic markers (major and trace elements, C-H bonds, and sulfur-oxidation states) in individual prokaryotic microfossils. In particular, we analyzed iron-oxide fossil filaments of putative biogenic origin encapsulated with amorphous silica from a fragment of an inactive hydrothermal chimney of the East Pacific Rise. In order to test the biogenic origin of the markers studied, we performed the same analyses on filamentous bacteria corresponding most likely to the ?-Proteobacteria, and collected from substrates exposed to a hydrothermal fluid vent at the Mid-Atlantic Ridge. In both types of fossil and contemporary filaments, the occurrence of CH2 groups and of three sulfur species (sulfate, sulfite, organic S) showing heterogeneous distribution that underline the cytoplasm of individual cells in the case of the present-day filament, suggests that the original microorganisms were actively metabolizing sulfur. These results show the large potential of combining high-resolution synchrotron techniques to analyze individual microfossils for extracting unequivocal biogenic information. Furthermore, they also suggest that cooccurrence of different sulfur oxidation states within single microfossils could constitute a biogenic metabolic marker indicating S-metabolizing activities.  相似文献   
9.
 Temporal and spatial variability of particulate metal concentrations (Cu, Cr, Zn, Mn and Fe) were investigated in the lower drainage basin of the Paraíba do Sul River. The results showed that the spatial variability was not important for all the studied metals, however, temporal variations seems to be considerable. In general, two distinct behaviors were observed for particulate heavy metals: (1) metal concentration increase together with water flow (Fe and Cu) and (2) concentration decrease with increasing water flux (Zn, Cr and Mn). The Fe and Cu behavior is probably due to the strong association of these metals with surface runoff, although their sources seem to be distinct. Iron probably originates from the regional soils rich in iron oxides, and Cu is possibly associated to the large-scale use of copper fungicides in the sugar cane plantations. The opposite trend observed for Zn, Cr and Mn probably reflects the importance of the industrial and urban effluents as a secondary source of these elements for the system. Their behavior is probably associated with the dilution effect caused by the input of a suspended matter poor in these metals originated from the surface runoff during the rainy season. Received: 4 March 1998 · Accepted: 30 June 1998  相似文献   
10.
For ages, links between environment, climate and their impacts on human health have been observed and studied. Research to improve our understanding of environmental key determinants of infectious diseases can provide innovative information for adaptation strategies and lead to new tools optimizing surveillance, vector control measures, and disease prevention. As earth observation satellites can measure meteorological and environmental parameters, NASA and CNES have separately engaged in an innovative use of their earth observation infrastructure development programs: space tools addressing public health. As NASA and CNES have fruitful cooperation for satellite development missions for years, both health programs have proposed to explore a new area of collaboration: satellites addressing health issues. As members of international organizations, NASA and CNES could promote their common views towards the Group on Earth Observations (GEO) Community of Practice for Health & Environment and the Committee on Earth Observation Satellites (CEOS) Societal Benefit Area on Health.  相似文献   
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