Enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in Mesozoic limestones and shales   总被引：1，自引：0，他引：1  

Nicolas Tribovillard  Armelle Riboulleau  François Baudin 《Chemical Geology》2004,213(4):385-401

There have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition. Among them, molybdenum (Mo) is frequently cited as an effective proxy for sediments and sedimentary rocks. Recently, Helz et al. (Helz, G.R., Miller, C.V., Charnock, J.M., Mosselmans, J.L.W., Pattrick, R.A.D., Garner, C.D., Vaughan, D.J., 1996. Mechanisms of molybdenum removal from the sea and its concentration in black shales: EXAFS evidences. Geochim. Cosmochim. Acta, 60, 3631-3642) and Adelson et al. (Adelson, J. M., Helz, G. R., Miller, C. V., 2001. Reconstructing the rise of recent coastal anoxia; molybdenum in Chesapeake Bay sediments. Geochim. Cosmochim. Acta, 65, 237-252.) suggested that Mo does not behave conservatively in the water column when H₂S reaches a threshold concentration. Above this concentration, a “switch” operates, and Mo is scavenged by forming bonds with metal-rich (notably iron) particles, sulfur-rich organic molecules and pyrite. In this paper, Mo-trapping by sulfur-rich organic matter (OM) in ancient marine deposits is emphasized. The following Mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized OM: the Akkuyu Formation (Turkey), the Calcaires d'Orbagnoux (France) and Kimmeridge Clay (UK) and its timeequivalent in Boulonnais (France), the Kashpir oil shales (Russia), and the La Luna Formation (Venezuela). The sulfur-rich OM is identified by either measured organic-S abundance or kerogen microscope observation. Our results show that Mo is systematically more enriched relative to the other redox-sensitive/sulfide-forming elements studied (U, V, Ni, Cu, Zn, Cr), and Mo enrichment is positively correlated with the amount of sulfurized OM but not with pyrite abundance. These results illuminate the role played by sulfurized OM in geologic-scale Mo capture and retention, but they also underline the role played by reactive iron. Significant OM sulfurization is only possible when reactive iron is limited. Nevertheless, pyrite formation, though limited, could act as an initial Mo trap, prior to Mo uptake by OM that is sulfurized after the pyritization step. In future paleoenvironmental reconstructions, attention must be paid to this enhanced Mo enrichment in the presence of sulfurized organic matter. In such cases, the use of Mo could lead to overestimation of the reducing conditions of the depositional environment.  相似文献   

From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin   总被引：1，自引：0，他引：1  

Sylvie Leroy  Pascal Gente  Marc Fournier  Elia d'Acremont  Philippe Patriat  Marie-Odile Beslier  Nicolas Bellahsen  Marcia Maia  Angelina Blais  Julie Perrot  Ali Al-Kathiri  Serge Merkouriev  Jean-Marc Fleury  Pierre-Yves Ruellan  Claude Lepvrier  Philippe Huchon 《地学学报》2004,16(4):185-192

A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present‐day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago.  相似文献   

Nouvelles données sur la genèse des bauxites à mur karstique du sud-est de la France     

J. Nicolas 《Mineralium Deposita》1968,3(1):18-33

Résumé En de nombreux secteurs du Sud-Est de la France, des brèches séparant la bauxite de son mur, des fossiles et des figures de sédimentation ont été découverts, au sein même de la bauxite: ces éléments prouvent que le minerai ne s'est pas formé au lieu même où on le trouve aujourd'hui. C'est un sédiment qui s'est déposé en milieu aqueux, sous forme de bauxite déjà constituée, après avoir subi un transport, en milieu aqueux également. Une étude pétrographique détaillée montre que ce transport s'est effectué par étapes au cours desquelles la bauxite a continué à subir le phenomène de latéritisation. Les bauxites sont le vestige d'anciens profils de latérite-bauxitique, ferrugineux et alumineux, cuirassés, qui ont été démantelés. La répartition verticale des différents niveaux de bauxite montre qu'ils peuvent, souvent, constituer des profils inversés de latérites primaires dont on peut interpréter le dépôt à la faveur de la théorie de la bio-rhéxistasie de H. Erhart. Les bauxites ont été piégées par des sédiments de nature lithologique et d'âges divers, qui constituent leurs toits et auxquels elles passent progressivement, ce qui confirme leur caractère sédimentaire.

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In numerous areas of the South East of France breccias separating bauxite from its wall, fossiles and sedimentation textures have been discovered right in the bauxite, which prove that the ore has not been formed in the site where found now. It is a sediment which was deposited in aqueous flow. A detailed petrographic study demonstrates that this transportation has been made in different stages, the bauxite continuing to undergo the process of lateritization. The bauxites are the remnants of former profiles of ferruginous and aluminous laterites-bauxites which have been crustified and destroyed. These profiles are former laterite profiles which have been inverted. Their formation may be interpreted through the bio-rhexistasie theory of H. Erhart. The bauxites have been buried by sediments of different ages and composition which form their roofs and into which they pass progressively. This confirms their sedimentary nature.

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Structures in podiform chromite from the Maqsad district (Sumail ophiolite,Oman)     

G. Ceuleneer  A. Nicolas 《Mineralium Deposita》1985,20(3):177-184

About 15 chromite bodies have been recognized in the Maqsad area of the Oman ophiolite. The occurrence in this area of three chromite bodies within the cumulate sequence must be integrated into the classification of Cassard et al. (1981) which presently explains only those pods lying in the uppermost mantle sequence (plastically deformed harzburgites and dunites). The occurrence of chromite bodies within the cumulates and the abundance of chromite in the Maqsad area are related to the exceptional magmatic activity and the unusual plastic-flow pattern particular to this area. It was probably a feeding zone along the oceanic spreading center sitting on top of a mantle diapir.  相似文献   

Kinematic interpretation of folds in alpine-type peridotites     

A. Nicolas  F. Boudier 《Tectonophysics》1975,25(3-4)

From a general understanding of the flow mechanisms in alpine-type peridotites, it is possible to describe without ambiguity the general flow regime and its directions in a massif. This result provides the means for an investigation of the origin of the folding in pyroxenitic layers independent of any preconceived theory on folding.The folds are usually isoclinal and of the flexural-flow type as demonstrated by petrofabric studies in hinges. Their axes are always parallel or subparallel to a mineral lineation which in turn is parallel or close to the orientation of the fabric elements defining the flow line. Their axial plane, which usually coincides with the foliation, is parallel to or close to the flow plane. This conclusion, also supported by paragenetic observations, shows that the folds were formed or transposed during the plastic flow responsible for the development of structures (foliation and lineation), textures and preferred mineral orientations. In the case of the Lanzo Massif and a few other Iherzolite massifs, the flow occurred during the intrusion from the mantle. The mapping in Lanzo yields evidence of a large-scale U-shaped fold with a remarkable pattern of mesoscopic folds attached to it: the tight isoclinal folds are restricted to the limbs of the largescale structure, and the open folds locally refolding former isoclinal ones to the hinge area where the angle between the folded pyroxenitic layering and the axial-plane foliation is large. Stereograms of the field structures in this hinge area clearly illustrate the geometric relations mentioned above.This folding, characterized by its axis and axial plane respectively close to the flow line and flow plane, can be explained either by rotation towards the flow line of non-cylindrical-fold axes or by direct formation in a non-plane flow when the flow line is initially contained in the layering or close to it. In this respect, the folding may bring information on the minor flow component, complementary to that given on the major flow component by considering the textures and fabrics. Finally this folding is shown to be ubiquitous in plastically deformed peridotites. It is proposed that these conclusions be extended to other domains submitted to intense non-plane flow.  相似文献   

Thrusting of young lithosphere in subduction zones with special reference to structures in ophiolitic peridotites     

Adolphe Nicolas  Xavier Le Pichon 《Earth and Planetary Science Letters》1980,46(3):397-406

Two contrasted types of structures have been recognized in peridotites from ophiolites and from the oceanic environment. The first one, typical of high-temperature/moderate-stress conditions, is observed in the upper part of ophiolitic peridotites and has been ascribed to plastic flow in an oceanic ridge environment. The second one, typical of moderate-temperature/high-stress conditions, is more specially dealt with here. It is printed in the peridotites above the basal metamorphic aureole found in many ophiolites. The strain increases downward over 1–2 km to produce peridotite mylonites at the contact with the metamorphic aureole. Similarities with rocks from trench and island arc environments suggest ascribing this deformation in ophiolites to a trench environment. We propose that shear fracturing in a young oceanic lithosphere is initiated by the compressive elastic stress in its lower part which is produced by bending of the subducted plate. An externally applied compressive stress is responsible for subsequent overthrusting of the fractured lithosphere. This interpretation is in good agreement with the available geophysical data on young subducted plates and with the physical data on ophiolitic peridotites.  相似文献   

K-Ar ages from Tertiary lavas of the northernmost Chilean Andes     

Dr. Cedric Mortimer  Dr. Edward Farrar  Ing. Nicolas Saric 《International Journal of Earth Sciences》1974,63(2):484-490

Radiometric ages for lava flows of northern Chile indicate that a regional Oligocene erosion surface was faulted when the Cordillera de la Costa was uplifted at the end of the Paleogene. Uplift of the coastal mountains caused the longitudinal depression to infil with sediment until aggradation virtually ceased in the Middle Miocene. Ignimbrites of the Rhyolite Formation were deposited in the Pampa del Tamarugal and across the Cordillera de la Costa in the earliest Miocene, whereas volcanoes of the “Andesite” Formation were locally active at least as early as the Middle Miocene.  相似文献   

Reviewing the discoverability and accessibility to data and information products linked to Essential Climate Variables     

Maria Teresa Miranda Espinosa  Gregory Giuliani  Nicolas Ray 《International Journal of Digital Earth》2020,13(2):236-252

ABSTRACT

Essential Climate Variables (ECVs) are geophysical records generated from systematic Earth Observations associated with climate variations, changes, and impacts. ECVs products support the data and information needs of international frameworks and policies such as the work of the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC). We map the main networks and initiatives publishing ECVs, by presenting an overview of existing satellite-based ECVs, their general data creation characteristics, discoverability and accessibility methods from an end-user perspective. We investigate key initiatives providing or coordinating access to ECV data records, such as the Global Climate Observing System (GCOS), the Committee on Earth Observation Satellites (CEOS), the Coordination Group for Meteorological Satellites (CGMS), Joint Working Group on Climate (WGClimate), the Remote Sensing Systems (REMSS), and the European Space Agency Climate Change Initiative (ESA CCI). We find that ECV data discovery and access is difficult and time consuming due to the lack of common data and metadata catalogues. In addition, the selection of fit-for-purpose data records by end-users requires the implementation of interoperable standards and scalable data infrastructures to allow the generation of tailored applications and data-driven information products in support of decision-making processes.  相似文献   

The AAT/WFI survey of the Monoceros Ring and Canis Major dwarf galaxy – I. From l= (193–276)°     

Blair C. Conn  Richard R. Lane  Geraint F. Lewis  Rodrigo Gil-Merino  Mike J. Irwin  Rodrigo A. Ibata  Nicolas F. Martin  Michele Bellazzini  Robert Sharp  Artem V. Tuntsov  Annette M. N. Ferguson 《Monthly notices of the Royal Astronomical Society》2007,376(3):939-959

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Stable isotopes reveal food web modifications along the upstream–downstream gradient of a temperate stream     

Nicolas Hette-Tronquart  Jérôme Belliard  Evelyne Tales  Thierry Oberdorff 《Aquatic Sciences - Research Across Boundaries》2016,78(2):255-265

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