Conditions and mechanism for the formation of iron-rich Montmorillonite in deep sea sediments (Costa Rica margin): Coupling high resolution mineralogical characterization and geochemical modeling     

D. Charpentier  M.D. Buatier  A. Gaudin 《Geochimica et cosmochimica acta》2011,75(6):1397-1410

Iron-rich smectite is commonly described in the diagenetic fraction of deep-sea sediment, as millimeter to centimeter aggregates dispersed in the sediment, or as a coating on sedimentary particles or nodules. This study examines several factors to elucidate formation mechanisms of a particular iron-rich smectite and its potential transformation to glauconite. The study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways.Transmission electron microscopy (TEM) observations and analytical electron microscopy (TEM-AEM) analyses were conducted on microtomed samples of millimeter- to centimeter-long green grains. These grains are widespread in pelagic calcareous sediment from the Costa Rica margin. They are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron-rich particles. Iron-rich montmorillonite grows from an amorphous precursor and its formation requires the input of Si, O, Mg, K, Na and Ca; our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses, siliceous fossils and silicates.Thermodynamic modeling of fluid-sediment interactions was conducted with the geochemical computer code PhreeqC, using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code. Simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions. The extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration. The absence of aluminum in the Costa Rica margin system explains the formation of an iron-rich montmorillonite instead of glauconite, whereas the presence of calcite that buffers the system explains the formation of an iron-rich montmorillonite instead of iron oxides.  相似文献   

Late Weichselian to Holocene paleoenvironments in the Barents Sea     

Elena V. Ivanova  Ivar O. Murdmaa  Jean-Claude Duplessy  Martine Paterne   《Global and Planetary Change》2002,34(3-4)

Paleoceanographic changes since the Late Weichselian have been studied in three sediment cores raised from shelf depressions along a north–south transect across the central Barents Sea. AMS radiocarbon dating offers a resolution of several hundred years for the Holocene. The results of lithological and micropaleontological study reveal the response of the Barents Sea to global climatic changes and Atlantic water inflow. Four evolutionary stages were distinguished. The older sediments are moraine deposits. The destruction of the Barents Sea ice sheet during the beginning of the deglaciation in response to climate warming and sea level rise resulted in proximal glaciomarine sedimentation. Then, the retreat of the glacier front to archipelagoes during the main phase of deglaciation caused meltwater discharge and restricted iceberg calving. Fine-grained distal glaciomarine sediments were deposited from periodic near-bottom nepheloid flows and the area was almost permanently covered with sea ice. The dramatic change in paleoenvironment occurred near the Pleistocene/Holocene boundary when normal marine conditions ultimately established resulting in a sharp increase of biological productivity. This event was diachronous and started prior to 10 ¹⁴C ka BP in the southern and about 9.2 ¹⁴C ka in the northern Barents Sea. Variations in sediment supply, paleoproductivity, sea-ice conditions, and Atlantic water inflow controlled paleoenvironmental changes during the Holocene.  相似文献   

Occurrence of phthalate diesters in rivers of the Paris district (France)     

Marie‐Jeanne Teil  Martine Blanchard  Cendrine Dargnat  Karen Larcher‐Tiphagne  Marc Chevreuil 《水文研究》2007,21(18):2515-2525

The occurrence and fate of six phthalate esters were investigated in the River Seine and two tributaries in the Paris area, at six sites from upstream to downstream, throughout different seasons, with special attention given to a flood episode. At all sites, except the River Marne, whatever the period, diethylhexyl phthalate (DEHP) displayed the highest concentration (0·323–0·779 µg l^?1 as mean values), followed by di‐n‐butyl phthalate (DnBP; 0·211–0·526 µg l^?1 as mean values), which is consistent with the production pattern. High phthalate concentrations appeared to be related to population density and industrial distribution. The strongest values were located downstream from wastewater treatment plant effluent inputs. Seasonal variations were closely related to river flow and air and water temperature. The annual evolution of phthalates was linked to the hydrological conditions. During the flood episode at Paris, the DEHP concentration displayed a sharp increase (260 to 1123 ng l^?1) occurring 9 days before the flood peak. The simultaneous fluctuations of NH₄, typical of domestic origin, and of DEHP suggests a similar origin from combined sewer overflows for both compounds. Other elevated values corresponded to the highest precipitation amounts, and demonstrated the contribution of non‐point‐source runoff and wastewater overflow to DEHP inputs. The DEHP concentration relationship with river flow displayed a clockwise hysteresis loop, corresponding to a ‘first‐flush’ effect in which the finite supplies are swept along in the early stage of the flood. Annual fluxes for 2004 at Paris were 2257 kg of DEHP and 1613 kg of DnBP. The flood period seemed to have a minor impact on annual phthalate transport (29·5% and 41% of the total for DEHP and for DnBP, respectively), which is contrary to annual suspended solids transport (69%). Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

A correlation between earthquakes and eruptive phases at Mt Etna: an example and past occurrences     

Alexandre Nercessian  Alfred Hirn  Martine Sapin 《Geophysical Journal International》1991,105(1):131-138

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Seismic heterogeneity of Mt Etna: structure and activity   总被引：3，自引：0，他引：3  

Alfred Hirn  Alexandre Nercessian  Martine Sapin  Fabrizio Ferrucci  Gérard Wittlinger 《Geophysical Journal International》1991,105(1):139-153

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High to low velocity succession in the upper crust related to tectonic emplacement: Tras os Montes-Galicia (Iberia), Brittany and Limousin (France)     

Alfred Hirn  Luisa Senos  Martine Sapin  Luis Mendes Victor 《Geophysical Journal International》1982,70(1):1-10

Summary. Seismic probing of the upper crust in a catazonal massif in Tras os Montes, Hercynian Iberia, demonstrates the absence of a root towards the lower crust and favours a mechanism of thrust and nappe emplacement. Similar high to low velocity successions in the upper crust are evidenced in particular segments of the Hercynian domain of France. All these occurrences are related to a type region to which a particular meaning has been given in a recent plate tectonics interpretation of the Hercynian orogenesis. This model, implying large-scale nappe displacement and intracrustal thrusts furnishes in turn a general mechanism for the tectonic formation of upper crustal high and low velocity layers of limited extent in orogenic cycles.  相似文献   

Phillipsite formation in nephelinitic rocks in response to hydrothermal alteration at Mount Etinde,Cameroon     

Jacques Etame  Che Emmanuel Suh  Martine Gerard  Paul Bilong 《Chemie der Erde / Geochemistry》2012,72(1):31-37

Fresh nephelinitic rocks and hydrothermally altered rocks at Mount Etinde (Cameroon Volcanic Line, West Africa) have been studied by combined whole rock geochemistry (ICP-MS), mineralogy and mineral chemistry (SEM-EDS, WDS, XRD) techniques. The nephelinites have feldspathoids, clinopyroxene, perovskite and titanomagnetite as the principal minerals in the mode with subsidiary apatite and sphene. The mineralogy of their hydrothermally altered counterparts includes phillipsite, calcite and analcime which are secondary phases developed in response to hydrothermal fluid events. Correspondingly, the bulk rock geochemical data show elevated SiO₂, CaO, Na₂O and K₂O concentrations with increasing alteration and Al₂O₃ and Fe₂O₃ depletion while MgO, MnO and TiO₂ concentrations are largely unaffected. The nephelinites also have high concentrations of LILLE, HFSE and REE and upon hydrothermal alteration they show an enrichment of LREE and MREE over HREE. Phillipsite is the principal alteration mineral in the rocks and it occurs along cracks, vesicles and also forms alteromorphs after feldspathoids. The Ce content of these categories of phillipsite varies. Phillipsite along cracks is richer in Ce while phillipsite associated with calcite has lower Ce concentration and the phillipsite alteromorphs very little or no Ce. Various stages of fluid circulation are proposed hereby to explain the variations in phillipsite generation and composition.  相似文献   

Raman spectroscopic properties and Raman identification of CaS‐MgS‐MnS‐FeS‐Cr2FeS4 sulfides in meteorites and reduced sulfur‐rich systems     

Caroline Avril  Valérie Malavergne  Razvan Caracas  Brigitte Zanda  Bruno Reynard  Emeline Charon  Ema Bobocioiu  Fabrice Brunet  Stephan Borensztajn  Sylvain Pont  Martine Tarrida  François Guyot 《Meteoritics & planetary science》2013,48(8):1415-1426

Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr₂FeS₄). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470 cm^?1 for the Mg‐rich sulfides; at 185, 205, and 285 cm^?1 for the Ca‐rich sulfides; at 250, 370, and 580 cm^?1 for the Mn‐rich sulfides; at 255, 290, and 365 cm^?1 for the Cr‐rich sulfides; and at 290 and 335 cm^?1 for troilite with, occasionally, an extra peak at 240 cm^?1. A peak at 160 cm^?1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first‐order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first‐principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides.  相似文献   

Impact of gamma densitometry on the luminescence signal of quartz grains     

Martine J. J. Couapel  Christopher J. Bowles 《Geo-Marine Letters》2006,26(1):1-5

Most of the marine sediment cores collected in the past 10 years by the ODP and IMAGES programs have been processed using a multi-sensor core logger (MSCL, Geotek). This system estimates the density of sediment using the γ-ray attenuation of a ¹³⁷Cs source. To date, optically stimulated luminescence (OSL) dating has not been applied to sediments from cores treated in this way, because of the possible impact of this exposure on the existing luminescence signal. We have investigated the effect of such γ-ray irradiation by test exposure, measurement and estimation, and conclude that the usual ¹³⁷Cs exposure from γ-ray attenuation densitometry has no impact on the luminescence signal of quartz grains in sediment cores. For longer exposure to the ¹³⁷Cs source, a formula is provided to calculate the received dose. This result will permit the OSL dating technique to be applied to the voluminous body of marine cores already collected and processed by MSCL.  相似文献   

Export flux of particles at the equator in the western and central Pacific ocean     

Martine Rodier  Robert Le Borgne 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

Export of particles was studied at the equator during an El Nin˜o warm event (October 1994) as part of the French ORSTOM/FLUPAC program. Particulate mass, carbon (organic and inorganic) (C), nitrogen (N), and phosphorus (P) export fluxes were measured at the equator in the western and central Pacific during two 6–7 day-long time-series stations located in the warm pool (TS-I at 0°, 167°E) and in the equatorial HNLC situation (TS-II at 0°, 150°W), using drifting sediment traps deployed for 48 h at four depths (between, approximately, 100 and 300 m).The particulate organic carbon (POC) fluxes at the base of the euphotic zone (0.1 % light level), were approximately four times lower at TS-I than at TS-11 (4.1 vs. 17.0 mmol C m^-2 day^-1). Conversely, fluxes measured at 300 m were similar at both sites (3.6vs. 3.7 mmol C m⁻² day⁻¹ at TS-I and TS-11, respectively). This change in export fluxes was in good agreement with food-web dynamics in the euphotic zone characterized by an increase in plankton biomasses and metabolic rates and a shift towards larger size from TS-1 to TS-II. The POC flux profiles indicated high remineralization (up to 78%) of the exported particles at TS-II, between 100 and 200 m in the Equatorial Undercurrent. According to zooplankton ingestion estimates from 100 – 300 m, 60% of this POC loss could be accounted for by zooplankton grazing. At TS-I, no marked increase of flux with depth was observed, and we assume that loss of particles was compensated by in-situ particle production by zooplankton. Fluxes of particulate nitrogen and phosphorus followed the same general patterns as the POC fluxes. The elemental and pigment composition of the exported particles was not very different between the two stations. In particular, the POCYN flux molar ratio at the base of the euphotic zone was low, 6.9 and 6.2 at TS-1 and TS-II, respectively.For particulate inorganic carbon (mainly carbonate) flux, values at the base of the euphotic zone averaged 0.9 mmol C m-2 day-1 at TS-I and 2.3 mmol C m-2 day-1 at TS-11 (corresponding to a 2.6-fold increase) and showed low depth changes at both stations.POC export flux (including active flux associated with the interzonal migrants) at the 0.1 % light level depth represented only 8% of primary production (1°C uptake) measured at TS-1 and 19% at TS-II. For the time and space scales considered in the present study, new primary production, as measured by the 15N method, was in good agreement with the total export flux in the HNLC situation, thus leading to negligible dissolved organic carbon (DOC) or nitrogen (DON) losses from the photic zone. Conversely, export flux was found to be only 50% (C units) and 60% (N) of new production in the oligotrophic system, either because of an overestimation by the 15N method or of a significant export of DOC and DON.Comparison with other oceanic regions shows that export flux in the warm pool was within the same range as in the central gyres. On the other hand, comparison with EgPac data in the central Pacific suggests that there is no straightforward relation between the magnitude of the export and surface nitrate concentrations.  相似文献