Semi-automatic determination of the carbon and oxygen stable isotope compositions of calcite and dolomite in natural mixtures     

M. Baudrand  G. Aloisi  C. Lécuyer  F. Martineau  F. Fourel  G. Escarguel  M.-M. Blanc-Valleron  J.-M. Rouchy  V. Grossi 《Applied Geochemistry》2012

A semi-automatic, on-line method was developed to determine the δ¹³C and δ¹⁸O values of coexisting calcite and dolomite. An isotopic mass balance is used to calculate the compositions of dolomite after having measured that of calcite and of the “bulk” sample. The limit of validity of this method is established by performing isotopic measurements of artificial mixtures made of precisely weighted and isotopically-characterised dolomite and calcite. The accuracy and repeatability of the calculation of dolomite δ¹³C and δ¹⁸O are statistically determined with a Monte-Carlo procedure of error propagation. Stable isotope ratios are determined by using an automated MultiPrep™ system on-line with an isotope-ratio mass-spectrometer (IRMS). The reaction time and the temperature of reaction were optimised by comparing the results with the isotopic composition of known mixtures. The best results were obtained by phosphoric acid digestion after 20 min at 40 °C for calcite and 45 min at 90 °C for dolomite. This procedure allows an accurate determination of the isotopic ratios from small samples (300 μg). Application of this protocol to natural mixtures of calcite and dolomite requires the accurate determination of the relative abundance of calcite and dolomite by combining Mélières manocalcimetry (MMC) and X-ray diffractometry (XRD).  相似文献   

CH₄-consuming microorganisms and the formation of carbonate crusts at cold seeps     

Giovanni Aloisi  Ioanna BouloubassiSander K. Heijs  Richard D. Pancost  Catherine PierreJaap S. Sinninghe Damsté  Jan C. GottschalLarry J. Forney  Jean-Marie Rouchy 《Earth and Planetary Science Letters》2002,203(1):195-203

To understand the role played by microorganisms in the formation of cold seep carbonates, we conducted an integrated microbial, mineralogical and organic geochemical study of methane-related authigenic carbonate crusts formed on eastern Mediterranean mud volcanoes. We show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane. Combined lipid biomarker analysis and 16S rRNA gene surveys identified a highly diversified methane-consuming archaeal community possibly comprising novel species, implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation. Moreover, pore-water sulphate gradients produced by co-occurring methane-based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation. We propose that this may be the dominant mode of carbonate crust formation at cold seeps world-wide, in agreement with aquatic chemistry predictions and explaining carbonate mineralogy.  相似文献   

The end of the Messinian Salinity Crisis in the western Mediterranean: Insights from the carbonate platforms of south-eastern Spain   总被引：1，自引：0，他引：1  

Raphaël Bourillot  Emmanuelle Vennin  Jean-Marie Rouchy  Marie-Madeleine Blanc-Valleron  Antonio Caruso 《Sedimentary Geology》2010,229(4):224-485

How the Messinian Salinity Crisis (MSC) ended is still a matter of intense debate. The Terminal Carbonate Complex (TCC) is a late Messinian carbonate platform system that recorded western Mediterranean hydrological changes from the final stages of evaporite deposition till the advent of Lago-Mare fresh- to brackish water conditions at the very end of Messinian times. A multidisciplinary study has been carried out in three localities in south-eastern Spain to reconstruct the history of TCC platforms and elucidate their significance in the MSC. Overall, this study provides evidence that the TCC formed following a regional 4th order water level rise and fall concomitant with an opening-restriction trend. It can be subdivided into four 5th order depositional sequences (DS1 to DS4) recording two phases: (1) from DS1 to DS3, a tide-dominated ooidic to oobioclastic system with stenohaline faunas developed as a result of a 70 m water level rise. During this period, the TCC developed in a shallow sea with close to normal marine salinity; (2) in depositional sequence 4, a microbialite-dominated platform system developed. This is indicative of a significant environmental change and is attributed to a 30 to 40 m water level fall in the basins under study. These restricted conditions were coeval with intense evaporite deformation and brine recycling. The syn-sedimentary deformation of evaporites had a major impact on platform architecture and carbonate production, affecting the Messinian series throughout south-eastern Spain at the end of the TCC history. At that time, the TCC developed in a lake with fluctuating, brackish- to hypersaline water. These findings suggest a temporary restoration of marine conditions in the western Mediterranean marginal basins due to Atlantic water influxes prompted by a global sea level rise around 5.6 Ma. Whether marine conditions extended to the entire western Mediterranean still needs to be investigated.  相似文献   

Unusual twinning features in large primary gypsum crystals formed in salt lake conditions, Middle Miocene, Madrid Basin, Spain: palaeoenvironmental implications—reply     

J. P. Rodríguez-Aranda  J. M. Rouchy  J. P. Calvo  S. Ordez  M. A. García del Cura 《Sedimentary Geology》1995,100(1-4)

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Découverte d''une frayère de poissons téléosteens dans des diatomites messiniennes du Djebel Murdjadjo (environs d''Oran, Algérie)     

Jean Gaudant  Jean-Paul Saint-Martin  Mostefa Bessedik  Bouhameur Mansour  Pierre Moissette  Jean-Marie Rouchy 《Journal of African Earth Sciences》1997,24(4):511-529

A new locality of Messinian fossil fish has been found in the diatomite outcropping in the surroundings of the former “Ferme Giraud”, in the Murdjadjo Massif (near Oran, Algeria). It has yielded an oligospecific fish fauna, including five species indicative of a littoral marine environment that may have occurred in a gulf bottom. This was probably linked to a brackish lagoon, as indicated by the diatom flora.  相似文献