Éditeur(s) : INRA : Institut National de la Recherche Agronomique Université des Antilles. Service commun de la documentation
Extrait de : 52e congrès annuel de la Société caribéenne des plantes alimentaires / 52nd annual meeting of the Caribbean food crops society (CFCS), du 10 au 16 juillet 2016. INRA, CFCS
Description : In the new context of the agro-ecological transition, present agricultural systems will have to produce more and better in a more constraint world. Mixed crop livestock systems (MCLS) represent sound alternative ways to progressively achieve these goals through crop-livestock integration (CLI). CLI exploits the synergies between cropping and livestock systems through organic fertilization with manure or plant association, use of crop residues to feed livestock, .... It offers many opportunities to improve productivity, as well as to increase resource use efficiency and improve the resilience of the whole farming system. In the scientific literature, authors advocate the interest of MLCS and CLI, based on theoretical considerations, modelling and empirical evidence from local case studies. But these studies do not clearly identify the respective roles of diversity of activities and CLI management practices in improving performances at the level of the whole farming system. Our aim was thus to assess CLI at farm scale in a range of MCLS and to explain farm performances by analyzing the combination of activities and the level of integration. We conducted our analyses in Guadeloupe, (French West Indies), where MCLS and CLI are complex but important challenges for local agricultural. In order to analyze CLI in a holistic and systemic way, we applied a method traditionally used in ecology, ecological network analysis, to study the structure, functioning and performance of agrosystems. This method was implemented on a range of Guadeloupian MCLS where CLI practices where identified. Nitrogen was retained to conduct the analysis due to its central role for both animal and vegetal productions. The ENA method allows an estimation of productivity, resilience, efficiency, productivity and self- sufficiency of the flows network. Our results show that 1/ efficiency and resilience appear correlated to the complexity and intensity of the network of flows; 2/ efficiency and resiliency are positively correlated when we consider them in terms of N flows; 3/ in the Guadeloupian context, CLI concerns mainly specific practices, as feeding pigs with a wide range of crop residues and organic fertilization of small market gardens and plots used to grow tubers. But at whole system level, CLI remains rare and mainly depends on conventional management practices as mineral fertilization and animal complementation of some farming activities as sugar cane, cattle breeding and banana. Moreover, the combination of productions implemented determines the potential of CLI and related performances linked to relative N efficiency of each production. Consequently, performance and especially efficiency and self-sufficiency depend more on the nature of the activity than on CLI management practices. There is still a gap between theoretical studies and CLI in practice, even though CLI is more complicated than simple flows and provides other services and functions. Dans le nouveau contexte de la transition agro-écologique, les systèmes agricoles actuels devront produire plus et les améliorer dans plus de monde de contrainte. Les systèmes mélangés de bétail de culture (MCLS) représentent des manières alternatives saines d'atteindre progressivement ces buts par l'intégration de culture-bétail (CLI). Le CLI exploite les synergies entre l'emblavage et les systèmes de bétail par la fertilisation organique avec l'association d'engrais ou d'usine, utilisation des résidus de culture d'alimenter le bétail,?. Il donne beaucoup d'occasions d'améliorer la productivité, aussi bien que d'augmenter l'efficacité d'utilisation de ressource et d'améliorer la résilience du système d'exploitation agricole entier. Dans la littérature scientifique, les auteurs préconisent l'intérêt de MLCS et de CLI, basé sur des considérations théoriques, modeler et des preuves empiriques des études de cas locales. Mais ces études n'identifient pas clairement les rôles respectifs de la diversité des activités et des pratiques de gestion de CLI en améliorant des interprétations au niveau du système d'exploitation agricole entier. Notre but était ainsi d'évaluer le CLI à l'échelle de ferme dans une gamme de MCLS et d'expliquer des interprétations de ferme en analysant la combinaison des activités et du niveau de l'intégration. Nous avons réalisé nos analyses en Guadeloupe, (des Antilles françaises), où MCLS et le CLI sont des défis complexes mais importants pour agricole local. Afin d'analyser le CLI d'une manière holistique et systémique, nous avons appliqué une méthode traditionnellement employée en écologie, analyse réseau écologique, pour étudier la structure, le fonctionnement et l'interprétation des agrosystems. Cette méthode a été appliquée sur une chaîne de Guadeloupian MCLS où des pratiques en matière de CLI où identifiée. L'azote a été maintenu pour réaliser l'analyse due à son rôle central pour les productions animales et végétales. La méthode d'ENA permet une évaluation de la productivité, de la résilience, de l'efficacité, de la productivité et de l'autosuffisance du réseau d'écoulements. Nos résultats prouvent que 1 efficacités et résiliences semblent corrélées avec la complexité et l'intensité du réseau des écoulements ; 2 efficacité et élasticité sont franchement corrélés quand nous les considérons en termes d'écoulements de N ; 3 dans le contexte de Guadeloupian, CLI concerne principalement des pratiques spécifiques, en tant que les porcs de alimentation par un large éventail de résidus de culture et de fertilisation organique de petits jardins du marché et complots employés pour cultiver des tubercules. Mais à au niveau système entier, le CLI demeure rare et dépend principalement des pratiques de gestion conventionnelles en tant que complémentation minérale de fertilisation et d'animal de quelques activités agricoles comme canne à sucre, élevage et banane. D'ailleurs, la combinaison des productions mises en application détermine le potentiel du CLI et des interprétations relatives liés à l'efficacité relative de N de chaque production. En conséquence, l'interprétation et particulièrement l'efficacité et l'autosuffisance dépendent davantage de la nature de l'activité que sur des pratiques de gestion de CLI. Il y a toujours un espace entre les études et le CLI théoriques dans la pratique, quoique le CLI soit plus compliqué que des écoulements simples et fournisse d'autres services et fonctions.
Siècle(s) traité(s) : 21
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V16247
V16247

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Evidence of a changing environment in the catchment area of a small pond (Lansquenet, Lorraine, France) during the last millennium was provided by coupling palynology data and organic ratios [terrestrial to aquatic ratio: TAR(HC); the C29 vs. C27 sterols, C29/C27(ST); average chain length, ACL and aquatic/macrophytes ratio, Paq]. The depositional and alteration conditions of organic matter (OM) were provided by the 5α(H)-stanols/Δ5-sterols ratio. This study shows that quite simple organic ratios clearly allow identification of the different evolution steps of a watershed, from a swamp to the progressive settlement of a pond. During the swampy period, the C/N(at) (ca. 11.1), TAR(HC) (ca. 36.8), C29/C27(ST) (ca. 8.7) and Paq (<0.3) show a high contribution of allochthonous OM associated with the presence of particular aquatic and mesohygrophilous species. A woody level dated to the XIIIth century reflects the period of the settlement of the pond in a more oxic environment [5α(H)-stanol/Δ5sterol ratio <0.2]. Then, the progressive increase in aquatic input and the development of submerged and floating macrophytes are evidenced by low C/N(at) (<7.6), TAR(HC) (ca. 2.7), C29/C27(ST) (ca. 2) and high Paq (ca. 0.5), suggesting an increase in the water level and eutrophication of the pond. A second oxic event [5α(H)-stanols/Δ5sterols ratio averaging 0.16], associated with extensive OM degradation, corresponds to the most recent dredging in 2002 and reflects an important disturbance of sediments due to pond management.
ISSN: 0146-6380

hal-00758066
https://hal.archives-ouvertes.fr/hal-00758066
DOI : 10.1016/j.orggeochem.2012.06.004

Éditeur(s) : Elsevier
Résumé : A study of organic carbon mineralization from the Congo continental shelf to the abyssal plain through the Congo submarine channel and Angola Margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling. Two measurement techniques were coupled on a single autonomous platform: in situ benthic chambers and microelectrodes, which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters. In addition, sediment trap fluxes, sediment composition (Org-C, Tot-N, CaCO3, porosity) and radionuclide profiles provided measurements of, respectively input fluxes and burial rate of organic and inorganic compounds. The in situ results show that the oxygen consumption on this margin close to the Congo River is high with values of total oxygen uptake (TOU) of 4 +/- 0.6, 3.6 +/- 0.5 mmol m(-2) d(-1) at 1300 and 3100m depth, respectively, and between 1.9 +/- 0.3 and 2.4 +/- 0.2 mmol m(-2) d(-1) at 4000 m depth. Diffusive oxygen uptakes (DOU) were 2.8 +/- 1.1, 2.3 +/- 0.8, 0.8 +/- 0.3 and 1.2 +/- 0.1 mmol m(-2) d(-1), respectively at the same depths. The magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel-levee system, which indicates that cross-slope transport processes are active over the entire margin. Comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5-8 times larger than the vertical flux recorded in traps. Transfer of material from the Congo River occurs through turbidity currents channelled in the Congo valley, which are subsequently deposited in the Lobe zone in the Congo fan below 4800 m. Ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone, which agrees with the high organic carbon content (3%) and the large sedimentation rate (19 mm y(-1)) found on this site. The Lobe region could receive as high as 19 mol C m(-2) y(-1), 1/3 being mineralized and 2/3 being buried and could constitute the largest depocenter of organic carbon in the South Atlantic.
Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2223-2238

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-7316.pdf
DOI:10.1016/j.dsr2.2009.04.005
http://archimer.ifremer.fr/doc/00000/7316/

Éditeur(s) : HAL CCSD
Résumé : This work focus on the characterization of the source and dynamic of compactional fluids during sedimentary burial, through two complementary examples of late orogenic oil‐field half‐grabens: The exhumed Lodève Permian Basin and a deep buried Jurassic basin in the North Viking Graben (North Sea).Constituting the main part of the thesis, a multi‐disciplinary approach was conducted in the Lodève Basin where Ba‐F‐Cu‐Pb polymetallic mineralized systems are trapped into synrift faults and paleokarsts in the carbonate basement at the hinge point of the rollover. The source, timing and P/T conditions of fluid migration were deduced from the analysis of the microfabric, the fluid inclusions microthermometry, and the isotopic (Sr, S, O, H) and Rare Earth Element (REE) signature. Results are then crossed with a structural and thermal modeling that consolidates the sequence and dynamics of fluid during burial.A similar approach was conducted in the North Viking Graben where fluid markers are restricted to 3D seismic and well core data. Comparable Ba‐Pb‐Zn veins are reported in basin margin, plugging one of the most important siliciclastic hydrocarbon reservoir in the substratum. This analysis provides additional constraints on basinal fluid behavior and allows us to propose a global dynamic model for various compositions of fluids and reservoirs.We conclude to a polyphase fluid sequence history including:(a) In the carbonate basement of the Lodève Basin, karstic paleocanyon incisions and associated cavities coupled to synrift fault, act as major drain for fluids. These structures are early affected by hypogen‐sulfuric karstification in response to the interaction between bacterial oxidation of sulfides entrapped within Lower Permian blackshales and the basement oxidizing aquifer.(b) Disequilibrium compaction initiates overpressure‐driven basinal fluid migration towards basin margins, characterized by temperatures around 150‐180°C and salinities between 9 et 18wt%eq.NaCl. Isotopic (Sr, S, O) and REE analyses reveal that Ba‐M+‐rich mineralizing fluids derived mainly from buried blackshales diagenesis. External fluids coming from the lower crust are also identified that play a key role in fluorite precipitation by the leaching of late hercynian granites (mean temperature of 250°C and salinity > 20wt%eq.NaCl).(c) During the synrift period, fluid overpressure is responsible for the periodic reactivation of fault plane according to seismic‐valve process, bedded‐control shearing and hydraulic brecciation at the basement‐seal interface. These mechanisms induce cyclic polymetallic mineralization by the mixing between in‐situ formation water and deep ascending basinal fluids.(d) Thermogenic fluids expulsion starts with last basinal fluids during late burial stage. Hydrocarbons thus migrate along the same regional pathways up to the rollover crest, where they are partly rerouted by the previous mineralized baffle.(e) In the Lodève basin, post‐rift exhumation of the margins led to the remobilization of synrift deposits by subaerial biochemical processes at the sulfate‐methane transition. The latter results from the interaction between the still active hydrocarbon dysmigration with a playa lake sulfate‐rich aquifer. Secondary low‐temperature barite fronts precipitate then within basement meteoric karsts.In addition to the « source to sink » model of basinal fluids, this work provides new insights on the early plugging of hydrocarbon reservoirs and for the metallogenesis of Mississippi Valley‐Type deposits.
Ce travail porte sur la caractérisation de la source et de la dynamique des fluides de bassin au cours de leur chargement à travers deux exemples complémentaires de demi‐grabens tardi‐orogéniques pétroliers : Le Bassin Permien de Lodève, aujourd’hui à l’affleurement et un bassin jurassique enfouis dans le North Viking Graben (Mer du Nord).Le coeur de la thèse concerne le Bassin de Lodève où, à partir d’une approche pluridisciplinaire intégrée, nous avons caractérisé l’architecture des minéralisations (Ba, F, Cu, Pb) piégées dans un réseau paléokarstique alimenté par les failles syn‐rift, dans le substratum carbonaté à l’apex du roll‐over. La source, le calendrier et les conditions de migration des fluides ont été approchés à partir de l’analyse de la micro‐fabrique, la microthermométrie sur inclusions fluides, les analyses isotopiques (Sr, S, O, H) et de Terres Rares. Les résultats analytiques ont été enfin croisés avec un modèle thermique et structural du bassin qui conforte la séquence et la dynamique du système fluide en cours d’enfouissement.Une démarche similaire, mais plus limitée, a été conduite dans le bassin du North Viking Graben où l’accès aux marqueurs fluides est restreint aux données de sismique 3D et de carottes. Comme à Lodève, les minéralisations Ba‐Pb‐Zn colmatent un réservoir dans le substratum à l’apex du roll‐over. Elles se présentent sous forme de ciments dans des grès ou des fractures. Cette analyse apporte des contraintes complémentaires et permet de proposer un modèle dynamique général avec des variantes en fonction de la nature des fluides et des réservoirs.On retiendra donc la séquence fluide suivante :(a) Dans le cas du bassin de Lodève sur substratum carbonaté, les chemins préférentiels de drainage se développent dans des paléocanyons N‐S couplés à un réseau de fractures et d’endokarsts météoriques. Ces derniers sont élargis en début de rifting par la dissolution hypogène sulfurique produite par l’oxydation bactérienne des sulfates et des pyrites des blackshales, au contact de l’aquifère oxydant du Cambrien.(b) Le déséquilibre de compaction initie la migration des fluides interstitiels en surpression vers les marges avec des températures autour de 150‐180°C et des salinités entre 9 et 18wt%eq.NaCl. Les analyses isotopiques (Sr, S, O) révèlent que la majorité des fluides provient de l’altération diagénétique des blackshales riches en métaux. Des interactions sont également mises en évidence avec des fluides profonds (entre 240°C et 260°C ; salinités > à 20wt%eq.NaCl), qui lessivent les granites tardi‐hercyniens.(c) Pendant le syn‐rift, les conditions de surpression de fluide permettent la réactivation cyclique des failles, les décollements stratigraphiques et la formation de brèches hydrauliques, favorisant la mise en connexion avec les réservoirs superficiels à l’apex du rollover. Le modèle de Sibson ajusté aux fluides de bassins est alors le moteur de la migration verticale.(d) Les fluides thermogéniques commencent à être expulsés avec les derniers fluides de compaction au cours d’un stade plus évolué de l’enfouissement en empruntant les mêmes chemins jusqu’à l’apex du roll over. Ils sont alors partiellement freinés et déviés par les colmatages minéralisés antérieurs.(e) A Lodève, la continentalisation des minéralisations antérieures au cours de l’exhumation post‐rift conduit à leur remaniement partiel au niveau de la transition sulfate‐méthane induite par l’interaction entre une playa évaporitique et la dysmigration des hydrocarbures. Des barytines secondaires de basse température, déprimées en Sr sont alors précipitées de manière synsédimentaire dans des karsts météoriques du socle.Outre l’illustration d’un modèle complet (source to sink) de dynamique des fluides dans un bassin, ce travail apporte de nouvelles contraintes dans l’approche du colmatage des réservoirs à hydrocarbures sur les têtes de blocs basculés et sur la genèse des gîtes miniers de type Mississippi Valley‐Type.
https://hal.archives-ouvertes.fr/tel-01457583

tel-01457583
https://hal.archives-ouvertes.fr/tel-01457583
https://hal.archives-ouvertes.fr/tel-01457583/document
https://hal.archives-ouvertes.fr/tel-01457583/file/th%C3%A8seLaurent2015V2.pdf

Éditeur(s) : HAL CCSD
Résumé : The coastal intrusion of brine threatens populations. This is particularly prejudicial in carbonate environments. We have studied the Miocene coral reef of S-E Majorca for better understanding the relation between geological structure and intrusion. For that purpose, we have used multi-scalar and multi-disciplinary methods. The measurements in 25 boreholes over the whole coral platform have allowed defining the stratigraphic structure and some elements of the regional tectonic. The reef progrades in the NE-SW direction, starting from the Aquitanian to terminates at the Messinian. The Messinian Salinity Crisis involves a disappearance of the Mediterranean corals and results in a Terminal Carbonate Complex which overlays a great part of the previously living corals of Majorca. At the experimental site scale, the study of the mineral composition, the texture, and the diagenesis have allowed characterization of the carbonate sequence heterogeneity. Layers of mineralization accompanied by dolomitization and low porosity correspond to postdepositional eustatic levels. The causes for the existence and the orientation of fractures are studied. The permeability to porosity relation is approached. The porosity structure is studied by comparison between primary and secondary porosity. This study contributes to the knowledge of the world best documented site for the evolution of carbonate reef reservoirs, with applications for brine intrusion and for hydrocarbon extraction.
Les intrusions d'eau salée en zone côtière constituent une menace pour la population. Celles-ci sont particulièrement dommageables en contexte carbonaté. Nous avons étudié le récif corallien Miocène du sud-est de Majorque afin de comprendre la relation entre structure géologique et intrusion. Pour cela nous avons utilisé des méthodes multi-scalaires et multi-disciplinaires. Les mesures dans 25 forages sur l'ensemble de la plateforme corallienne ont permis de préciser la structure stratigraphique et certains éléments de la tectonique régionale. Le récif prograde dans la direction NE-SO, en partant de l'Aquitanien pour aboutir au Messinien. La Crise de Salinité Messinienne entraîne une disparition des coraux méditerranéens et se traduit par un Complexe Carbonaté Terminal qui s'étend sur une grande partie des coraux autrefois vivants de Majorque. A l'échelle du site expérimental, l'étude de la composition minérale, de la texture et de la diagenèse ont permis de caractériser l'hétérogénéité de la séquence carbonatée. Des couches de minéralisation accompagnées de dolomitisation et de faible porosité correspondent à différents niveaux eustatiques post-dépositionnels. Les causes de l'existence et de l'orientation des fractures sont étudiées. La relation de perméabilité à porosité est précisée. La structure de porosité est étudiée par comparaison entre la porosité primaire et la porosité secondaire. Cette étude contribue à la connaissance du site le mieux documenté au monde pour l'évolution des réservoirs carbonatés récifaux, avec applications pour les intrusions d'eau salée et l'extraction des hydrocarbures.
https://tel.archives-ouvertes.fr/tel-00440019

tel-00440019
https://tel.archives-ouvertes.fr/tel-00440019
https://tel.archives-ouvertes.fr/tel-00440019/document
https://tel.archives-ouvertes.fr/tel-00440019/file/thesemariasube.pdf

Éditeur(s) : HAL CCSD Springer/Terra Scientific Publishing Company
Résumé : International audience
We report oil the discovery of magnetite nanoparticles ranging in size from 2 to 14 full in the mineralized zones of the Pena Colorada iron-ore deposit, southern Mexico. Micrometric scale magnetite was magnetically reduced and divided into distinct size ranges: 85-56 mu m, 56-30 mu m, 30-22 mu m, 22-15 mu m, 15-10 mu m, 10-7 mu m and 7-2 mu m. Nanometric-scale magnetite in the size range 2-14 nm was identified. The magnetite was characterized by X-ray diffraction, transmitted and reflected light microscope, high-resolution transmission electron microscopy (TEM), high angle annular dark field, Mossbauer spectroscopy and its magnetic properties. Crystallographic identification of nanostructures Was performed using high-resolution TEM. Characteristic changes were observed when the particles make the size transition from micro- to nanometric sizes, as follows: (1) frequency-dependent magnetic Susceptibility percentage (chi FD%) measurements Show high Values (13%) for the 2-14 nm fractions attributed to dominant fractions of superparamagnetic particles; (2) variations of chi FD% < 4.5% in fractions of 56-0.2 mu m occur in association with the presence of microparticles formed by magnetite aggregates of nanoparticles (< 15 nm) embedded in berthierine; (3) Mossbauer spectroscopy results identified a superparamagnetic fraction; (4) nanometric and 0.2-3 mu m grain size magnetite particles require a magnetic field up to 152 mT to reach saturation during the isothermal remanent magnetization experiment; (5) coercivity and remanent magnetization of the magnetite increase when the particle size decreases, probably due to parallel Coupling effects; (6) two-magnetic Susceptibility versus temperature experiments of the same 2-14 nm sample show that the reversibility during the second heating is due to the formation of new magnetite nanoparticles and growth of those already present. during the first heating process.
ISSN: 1343-8832

hal-00413053
https://hal.archives-ouvertes.fr/hal-00413053

Éditeur(s) : Université de Bretagne Occidentale
Résumé : Study of mineral suspended particulate matter (SPM) is essential to understand ecosystem dynamics. SPM influences light penetration which is closely related to primary production and carries pollutants and nutrients within the water masses. This work aims to study near-surface mineral SPM dynamics in the English Channel using two complementary methods: remote-sensing by satellites and numerical modelling. Firstly, MODIS and MERIS satellite images processed by the IFREMER semi-analytical algorithm and describing non-algal SPM, are analysed to build three statistical models which are able to estimate near-surface SPM using simple variables, e.g., tidal coefficient, significant wave height and mean chlorophyll-a concentration. Secondly, the three-dimensional hydrosedimentary model ROMS (Regional Ocean Modeling System) is applied in the English Channel. It considers tidal forcing along open boundaries, wind stress at the sea-surface, wave-current interactions in the bottom boundary layer and realistic heterogeneous bottom sediments. Results of the more sophisticated statistical model is also used to impose SPM concentrations at open boundaries. Sensitivity tests on SPM boundary conditions show the importance of prescribing realistic sediment concentrations to improve the model predictions. Biological influences on mineral SPM are also tested using settling velocity and critical shear stress for erosion which vary with seasons. Both statistical and numerical models highlight and locate respective influences of tide, waves and biology on mineral SPM. Numerical predictions indicate that near-surface SPM is mainly composed of silts (>70%). Near-surface suspended silts come largely from seabed resuspension alongshore in the Eastern Channel and from the open boundaries of our limited-area coastal model at the West of Cotentin Peninsula and offshore. Near-surface SPM variations are investigated at semi-diurnal, neap-spring tidal cycle time scales and during a wave event. Finally, dynamics of sediments in the turbidity maximum zone around the Isle of Wight is examined depending on hydrodynamical conditions in order to distinguish the role played by advection and local erosion/settling processes in this area. Keywords: Suspended particulate matter, satellite, remote-sensing, modelling, English Channel, sediments, turbidity, tide, wave
L'étude des matières en suspension (MES) minérales est essentielle pour comprendre le fonctionnement des écosystèmes en Manche : les MES influencent la pénétration de la lumière dans la colonne d'eau, paramètre clé pour la production biologique, et sont susceptibles de transporter des polluants et nutriments. Lors de ce travail, la dynamique des MES minérales de surface en Manche est étudiée à l'aide de deux méthodes complémentaires : l'observation par satellite et la modélisation numérique tridimensionnelle. Dans un premier temps, les images satellite MODIS et MERIS, traitées par l'algorithme semi-analytique développé par l'IFREMER et représentant les MES non-algales de surface, sont analysées afin d'élaborer trois modèles statistiques permettant d'estimer la MES de surface en fonction de variables basiques telles que le coefficient de marée, la hauteur significative des vagues et la concentration moyenne en chlorophylle-a. Dans un deuxième temps, le modèle hydrosédimentaire multiclasse tridimensionnel ROMS (Regional Ocean Modeling System) est implémenté en Manche. Il prend en considération le forçage par la marée aux frontières ouvertes, la contrainte exercée par le vent à la surface de la mer, l'interaction houle-courant en couche limite de fond et l’hétérogénéité spatiale réaliste du lit sédimentaire. Les résultats du modèle statistique le plus sophistiqué sont également utilisés pour forcer la concentration en MES aux frontières ouvertes du domaine de calcul. Des tests de sensibilité sur les conditions limites montrent l'importance de considérer de manière réaliste les sédiments entrant en Manche par les frontières ouvertes lors de la modélisation numérique. L'influence de la biologie sur les MES minérales est testée en utilisant une formulation de la vitesse de chute et de la contrainte critique d'érosion variant saisonnièrement. Grâce à ces deux outils associés, les influences respectives de la marée, de la houle et de la biologie sur les MES minérales sont mises en avant et localisées en Manche. Le modèle numérique prédit que les MES de surface sont composées principalement de silts (>70%). Les silts en suspension en surface proviennent majoritairement du lit sédimentaire près des côtes en Manche orientale et des frontières ouvertes du domaine de calcul à l'ouest de la presqu'île du Cotentin et au large en Manche centrale et orientale. Les variations des MES de surface sont ensuite étudiées aux échelles des cycles de marée semi-diurnes, vive-eau/morte-eau et autour d'un épisode de houles. Enfin, l'évolution de la concentration de sédiments dans la zone de forte turbidité autour de l'île de Wight peut être analysée suivant les conditions hydrodynamiques afin d'évaluer les rôles respectifs des processus locaux d'érosion/dépot et d'advection dans la génération de ces turbidités remarquables. Mots-clés : Matière en suspension, télédétection, satellite, modélisation, Manche, sédiments, turbidité, marée, houle

Droits : 2013 UBO
http://archimer.ifremer.fr/doc/00157/26783/24884.pdf
http://archimer.ifremer.fr/doc/00157/26783/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
In the Caribbean, Pterocarpus officinalis swamp forest, a coastal freshwater wetland, has been locally transformed by human activities into Colocasia esculenta monoculture (under the swamp forest) or pasture (where deforestation has occurred). The aim of this study was to evaluate the impact of three land uses of this tropical wetland (swamp forest, C. esculenta monoculture and pasture) on soil abiotic and biological features. We hypothesized that increasing the level of ecosystem alteration by agricultural intensification would negatively impact soil chemical characteristics, soil fauna diversity and carbon mineralization. As expected, land use significantly affected soil characteristics and changes followed the increasing intensity of land use. The ‘undisturbed system’, that is swamp forest, was characterized by a large soil organic matter content, a high level of soil moisture, a small phosphorus content and a slightly lower pH. These characteristics were correlated with a small faunal abundance and diversity and slow carbon (C) mineralization. The ‘low disturbance system’, that is C. esculenta monoculture, was the closest to swamp forest characteristics and changes between the both systems principally concerned a very slight decrease in organic matter content and very small increase in C mineralization and Coleoptera diversity. By contrast, all parameters (soil chemical characteristics, C mineralization and faunal abundance and diversity) were impacted in the most intensive land-use, pasture. Our study confirmed that agricultural practices have an influence on soil fauna and C mineralization processes in wetlands. Moreover, our study suggested that a C. esculenta traditional agroecosystem under swamp forest cover could be considered as an ‘eco-friendly’ agricultural practice.
ISSN: 0266-0032

hal-01562423
https://hal.archives-ouvertes.fr/hal-01562423
DOI : 10.1111/sum.12273

Éditeur(s) : HAL CCSD
Résumé : International audience
Tsavorite is exclusively hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). The gemstone mines, widespread between Kalalani (Tanzania) and Mgama Ridge (Kenya), define a continuous corridor over a hundred kilometers in length. The tsavorite is hosted by a metasedimentary sequence defined as the Kurase tsavorite-bearing metasediments (Kurase-TB metasediments) that also hosts rubies. These metasediments underwent amphibolite-facies metamorphism and are surrounded by granulitic gneisses that are also of sedimentary origin (the Kurase high-temperature gneisses). All these rocks lie below the Kasigau Group, a unit dominated by granulite-facies metamagmatic rocks.To constrain the timing of events that led to this peculiar occurrence of tsavorite, we have performed geochronological analyses of thin sections and of separated grains of zircon, monazite, and rutile using LA-ICP-MS and ID-TIMS, as well as 40Ar/39Ar of muscovite and phlogopite from various lithologies. The results show that the different terranes were metamorphosed synchronously between 620–580 Ma but under different P-T strain conditions. The Kurase-HT gneisses and the rocks from the Kasigau Group are highly strained and underwent granulite-facies metamorphism with abundant partial melting and emplacement of felsic melts between 620 and 600 Ma. Textural observations also underlined a late regional water flux controlling the occurrence of V-free muscovite and monazite mineralizations at 585 Ma. The latter event can be related to the activity of the Galana shear zone, in the east. The Kurase-TB metasediments escaped strain and partial melting. They record amphibolite-facies conditions with static heating, since initial sedimentary structures were locally preserved. The age of the tsavorite mineralization was inferred at 600 Ma from metamorphic zircon rims and monazite from the closest host-rocks, sampled in the mines. Hence, tsavorite crystallization occurred statically at the end of the metamorphic event, probably when the temperature and the amount of volatiles were at maximum levels.Conversely, the ruby formed by local metasomatism of felsic dikes and isolated ultramafic bodies. The rubies are older and zircons and monazites from a ruby-bearing felsic dike (plumasite) were dated at 615 Ma. Finally, data from rutile and micas indicate a global cooling below 430 °C of the whole region between 510 and 500 Ma.
The Canadian Mineralogist

hal-01616037
https://hal.archives-ouvertes.fr/hal-01616037
https://hal.archives-ouvertes.fr/hal-01616037/document
https://hal.archives-ouvertes.fr/hal-01616037/file/JEM.pdf
DOI : 10.3749/canmin.1700019

Éditeur(s) : Gauthier-Villars
Résumé : The distribution and behaviour of nutrients (nitrate, nitrite, ammonia, silicate and phosphate) have been examined over the course of a year in two major Scottish estuaries, the Forth and Tay. Maximum concentrations of nitrate and silicate in both estuaries occur in winter, when mixing is conservative. By contrast maximum phosphate, ammonia and nitrite concentrations (notably in the Forth) are observed in summer, these are related to lower oxygen concentrations both within the water column and sediments. Phosphate, ammonia and nitrite concentrations are high in the Forth relative to the Tay. Phosphate behaviour in plots for both estuaries show some common features including removal at low salinity, mid estuary inputs and simple dilution at high salinity. The results are interpreted on the basis of removal onto particles at low salinity followed by desorption at higher salinity together with an input from sediment porewaters. In the Forth the phosphate flux from sediments during the summer is estimated to be 1.98 +/- 1.25 mmol m-2 day-1. At this time the river input of phosphorus is only 10- 14 % of the mid estuary input. Under low river flow conditions in summer a large turbidity maximum (400-500 mg l-1 suspended solids) develops in the Forth estuary and this results in removal of phosphate. Removal is less dramatic in the Tay estuary as the turbidity is wind generated and therefore rarely exceeds 100 mg 1-1. Water quality in the Forth (as defined by the occurrence of low dissolved oxygen concentrations and the presence of species such as ammonia and nitrite) is inferior to that of the Tay. Relative to contaminated estuaries however concentrations in both estuaries are low. By virtue of its high fresh water discharge the Tay is a more significant source of nitrate to the North Sea during the winter than is the Forth. In the Forth bacterial mineralisation and nitrification of organic nitrogen occurs in the upper estuary, this results in an input of nitrate and consumption of dissolved oxygen. Further downstream broad mid estuarine peaks of nitrite and ammonia are observed indicative of a benthic source. Estimates of this source for ammonia and nitrite are 19-44 and 3.9-8.1 mmol m-2 day-1 respectively. In winter the main source of nitrogen to the Forth is from the river but in summer mid estuarine sources dominate. In the outer Tay a peak in dissolved ammonia is estimated to represent an input of 0.5-1.1 tonnes N day-1, this is attributed to sewer inputs from Dundee.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 3 , P. 261-277

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00100/21160/18779.pdf
http://archimer.ifremer.fr/doc/00100/21160/

Éditeur(s) : HAL CCSD
Résumé : International audience
The prevalence of bone deformities, particularly linked with mineral deficiency, is an important issue for fish production. Juvenile triploid rainbow trout (Oncorhynchus mykiss) were fed a low-phosphorus (P) diet for 27 weeks (60 to 630 g body mass). At study termination, 24.9% of the fish fed the low-P diet displayed homogeneous biconcave vertebrae (deformed vertebrae phenotype), while 5.5% displayed normal vertebral phenotypes for the entire experiment. The aim of our study was to characterize the deformed phenotype and identify the putative genes involved in the appearance of P deficiency-induced deformities. Both P status and biomechanical measurements showed that deformed vertebrae were significantly less mineralized (55.0 ± 0.4 and 59.4 ± 0.5,% ash DM, for deformed and normal vertebrae, respectively) resulting in a lower stiffness (80.3 ± 9.0 and 140.2 ± 6.3 N/mm, for deformed and normal phenotypes, respectively). The bone profiles based on μCT observations showed no difference in the osteoclastic resorption while no difference in matrix production was observed between deformed (total bone area 5442.0 ± 110.1 μm2) and normal vertebrae (total bone area 5931.2 ± 249.8 μm2) in this study. Consequently, the lower P content rather results from a reduced degree of mineralization in the deformed phenotype. Finally, we quantified differential gene expression between deformed vertebrae (pronounced biconcave) and normal phenotype by employing deep RNA-sequencing and mapping against a reference bone transcriptome for rainbow trout. In total, 1289 genes were differentially expressed. Among them, in deformed fish we observed that BGLAP, MGP and NOG, an inhibitor of BMP signalling pathway, were up-regulated while COL11a1 was down-regulated. These genes are central actors involved in the reduced degree of mineralization triggering vertebral deformities. These results will further the understanding of P deficiency-induced deformities; hence providing new tools for improved P management in production settings
Journal of Next Generation Sequencing & Applications

hal-01545768
https://hal.archives-ouvertes.fr/hal-01545768
DOI : 10.4172/2469-9853.1000112

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Geochronological, mineralogical, and geochemical analyses have been focussed on the Mont-Loze're- Borne plutonic complex and surrounding rocks (Ce'vennes, French Massif Central) in which B-W-Sn and As-Au-Sb mineralization is encountered. Two main results are highlighted: (1) the existence of a 301-306 Ma magmatohydrothermal event unrelated to the emplacement of the Pont-de-Montvert-Borne plutonic body at 316 Ma; (2) the magmatic and hydrothermal features are strongly associated, both in time and in space, thus demonstrating an intimate connection between mineralizing processes and magmatism in this part of the French Massif Central. We also show that mineralization and associated hydrothermal occurrences do not correspond to a simple and single geochemical signature and that a contamination model must be invoked in order to account for the complexity of isotopic results. This study demonstrates that the application of the O and H isotopic signatures as tracers of the source and nature of fluids in an orogenic context requires some specific care. Finally, a model of the tectonic-magmatic- hydrothermal evolution of the study area is suggested in which we discuss two alternative scenarios. The first one implies the existence of two different hydrothermal/ mineralizing events (Bo-W-Sn and As-Au-Sb ones). The second one suggests the same source for all hydrothermal and mineralized structures.
ISSN: 1437-3254

insu-00576546
https://hal-insu.archives-ouvertes.fr/insu-00576546
https://hal-insu.archives-ouvertes.fr/insu-00576546/document
https://hal-insu.archives-ouvertes.fr/insu-00576546/file/Chauvet-InternationalJournalEarthSciences-2012.pdf
DOI : 10.1007/s00531-011-0639-1

Éditeur(s) : HAL CCSD Society of Economic Geologists
Résumé : International audience
The ~8-Moz Sadiola Hill gold deposit is located in the Kédougou-Kénieba inlier, a window of deformed ca. 2200 to 2050 Ma rocks that crop out in eastern Senegal and western Mali. The geology of the inlier differs from other Paleoproterozoic granite-greenstone belts and sedimentary basins by the abundance of carbonate rocks. The Sadiola Hill gold deposit occurs within 3 km of the Senegal-Mali shear zone, and country rocks in the region have undergone polycyclic deformation. The lithostratigraphy of the open pit consists of impure limestones overlain by younger sequences of detrital sedimentary rocks, which include arenite, wacke, and siltstone. The sedimentary rocks have been subjected to regional greenschist-facies metamorphism and have been intruded by multiple generations of synkinematic, calc-alkaline stocks and dikes. The bulk of the ore is hosted within a N-S- to NNW-trending, 10- to 50-m-wide, brittle-ductile dilational shear zone defined as the Sadiola shear zone. Gold lodes also occur along an array of steep NNE-trending shear zones. Geometric and kinematic analyses indicate that the ore-hosting structures were undergoing sinistral displacement at the time of mineralization, locally defined as the D3s NNW-SSE-shortening event. Hydrothermal alteration is polyphase and includes an early high-temperature calc-silicate phase (i.e., porphyroblastic growth of actinolite-tremolite) followed by a potassic phase (i.e., biotite-calcite-quartz ± K-feldspar-tourmaline-actinolite) that was synchronous with ore mineral deposition. Paragenetic studies reveal a multistage ore development that includes an As-rich sulfide stage, followed by an Au-Sb stage. The ore is associated with a metal enrichment suite of Au-As-Sb ± Cu-Fe-W-Mo-Ag-Bi-Zn-Pb-Te. The Sadiola Hill deposit shares a similar relative timing and structural setting to that of other world-class orogenic gold systems in the West African craton (e.g., Ashanti, Loulo), with gold deposition occurring during a period of transcurrent tectonics, after the cessation of region-wide compressional deformation. The high-temperature paragenesis at Sadiola Hill is atypical of gold mineralization in the craton and indicates that the late Eburnean tectono-magmatic activity between ca. 2080 and 2060 Ma played an important role in the dynamics of hydrothermal fluid circulation along the Senegal-Mali shear zone.
ISSN: 0361-0128

hal-01583358
https://hal.archives-ouvertes.fr/hal-01583358
DOI : 10.2113/econgeo.112.1.23

Éditeur(s) : Elsevier
Résumé : A field survey was conducted on two intensive shrimp farms using similar technical practices: one (DF) historically affected by a vibriosis, the other (HC) in which the pathogen has been observed although no mortality event has occurred. Because historical data suggest that eutrophication process may directly or indirectly play a role in the disease outbreak, we focussed our research on its dynamics. A higher variability of the phytoplanktonic compartment linked to an imbalance in the molar N:P ratio was observed in farm DF compared to farm HC, implying a modification on the linkage between the bacteria and phytoplankton compartments at DF. The beginning of the mortality outbreak at DF followed a shift from picoto nanophytoplankton. The organic matter mineralization process at the water-sediment interface may explain the disturbance observed in the water column during eutrophication. The consequences of this disturbance on shrimps' health status and pathogen ecology are discussed. (C) 2009 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin (0025-326X) (Elsevier), 2010-03 , Vol. 60 , N. 3 , P. 402-411

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00002/11368/8119.pdf
DOI:10.1016/j.marpolbul.2009.10.012
http://archimer.ifremer.fr/doc/00002/11368/

Éditeur(s) : Elsevier
Résumé : The main feature of the Congo-Angola margin in the Gulf of Guinea is the Congo (ex-Zaire) deep-sea fan composed of a submarine canyon directly connected to the Congo River, a channel and a [sediment] lobe area. During the multi-disciplinary programme called BIOZAIRE conducted by Ifremer from 2000 to 2005, two CTD-O2 sections with discrete water column samples were performed (BIOZAIRE3 cruise: 2003-2004) to study the influence of the Congo River discharges, both in the surface layer and in the deep and near-bottom layers. The surface layer water is greatly diluted with river water that has a heavy particle load. The deep layer is affected by episodic turbidity currents that flow in the deep Congo channel and reach deep areas far from the coast. Previous studies revealed deep anomalies in oxygen (deficit) and nutrient (excess) concentrations at not, vert, similar4000 m depth and assumed that they resulted from mineralisation of the particulate organic matter from the Congo River. The BIOZAIRE3 sections were designed to explore these phenomena in more detail near the Congo channel. Oxygen and nutrients were measured as well as additional parameters, including stable isotopes of oxygen and carbon, dissolved inorganic carbon and pH. For the surface layer, the effect of the Congo River was studied with reference to salinity. Deviations from the theoretical dilution of various inorganic solutes suggested the occurrence of mineralisation and consumption processes. For the deep layer, the network of CTD-O2 stations gave a more detailed description of the deep anomalies than in previous studies. From the east-west section, anomalies appeared on the bottom at 4000 m depth and became slightly shallower when they spread to the west. They were also present north and south on the bottom along the 4000 m isobath. In these deep waters, the decrease in the o13C values of dissolved inorganic carbon confirmed that the mineralisation of organic matter plays a role in generating these anomalies. The location of the origin of this deep anomaly is debated. Here, arguments are given in favour of mineralisation of the particulate organic matter input that overflows from the Congo channel at not, vert, similar4000 m depth during turbidity current events. Other authors suggest that this input comes from downslope particle transport. Anomalies of the same origin, but weaker, also occurred deeper on the Congo lobe, where the Congo channel ends, but with a significant pH decrease on the bottom which was not seen at 4000 m depth.
Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2183-2196

Droits : 2009 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6737.pdf
DOI:10.1016/j.dsr2.2009.04.002
http://archimer.ifremer.fr/doc/00000/6737/

Éditeur(s) : HAL CCSD
Résumé : International audience
Tin mineralization in Achmmach deposit (NE of Moroccan Central Massif) is associated with tourmaline-rich alteration halos and faults, within N70 shear zones, hosted in sandstones and metapelites of the Upper Visean-Namurian. Such deposits were reported as late-Variscan in age and related to the emplacement of late orogenic granite not outcropping in the studied area.From field constraints, it appears that the late Variscan phase is marked by a transition from transpression to extension with conditions of deformation evolving from ductile to brittle environments. During the transpressive phase (horizontal shortening direction roughly trending E-W), pervasive tourmaline is deposited under the form of metasomatic halos around fractures in the upper levels relative to the deep batholith. This hydrothermal activity is coeval with ductile shear zones within a large corridors trending N70. Tourmaline-rich alteration appears as a hardening stage contributing to the modification of the tectonic style of rocks. Thereafter, a strong brecciation occurs in response of re-using and re-opening of the strike-slip structure. The result is (1) the formation of dextral (N070, N020) and sinistral (N120) shears, and (2) the circulation of fluids within early tourmalinites and formation of tourmaline-rich breccia. Subsequently, during the late orogenic extensional phase, tourmalinite breccias reopened as normal faults acting as overpressure fluid pathways for developing other breccias and veins. Such event is marked by deposition of tin mineralization i.e., cassiterite followed by sulphides, and then fluorite and carbonates at the end.From analysis of the shear-zone structure and superimposition of tourmalines and tin mineralization in the same structures, it is possible to suggest a structural control continuum. Such control is well expressed during metasomatism and deposition of hydrothermal tourmaline under the transpressive phase. Thereafter, under the extensive phase allowing open-space, tin-mineralization were trapped.This study has been supported by AI MA/09/210
24ème RST
Pau, France

insu-01546927
https://hal-insu.archives-ouvertes.fr/insu-01546927

Éditeur(s) : HAL CCSD Mineralogical Society of America
Résumé : International audience
In situ mineralization of CO2 in ultramafic rock-hosted aquifers is one of the promising solutions for decreasing CO2 concentrations in the atmosphere. Naturally altered ultramafic rocks suggest that carbonation processes are controlled by local heterogeneities in the structure of the rock and fluid transport at the water-rock interfaces. We studied the role of rock crystallographic anisotropy relative to the global fluid flow direction on the mineralization of CO2 by means of electron microscope analyses from the macro- to the micrometer scale (EBSD-FIB). The sample used for the measurements was a hot pressed olivine core percolated by water enriched in CO2 (pCO2 = 10 MPa) at 180 °C. During the percolation experiment, olivine was dissolved and two types of carbonates, dolomite, and magnesite, were precipitated on olivine surfaces. The results showed that the dissolution of olivine is controlled by its crystallographic properties as shown by the development of etch-pits only on the (010)ol planes and with elongated shapes parallel to the [010]ol axes. In contrast, the precipitation of carbonates is governed by hydrodynamic properties. Carbonates are heterogeneously distributed in the percolated rock. They are mainly located along the moderate (for dolomite) and the minor (for magnesite) flow paths, both oriented parallel to the principal fluid flow direction, which allow carbonates to be supplied with divalent cations (e.g., Ca2+, Mg2+, and Fe2+). In these flow paths, carbonate growth is systematically oriented normal to the flow that facilitates the development of chemical gradients with cationic supersaturation conditions for carbonate precipitation near the walls.In natural systems, the (010)ol planes are parallel to the Moho and the (100)ol planes are vertical; our study suggests that flow of CO2-rich fluids will induce precipitation of carbonates localized along, and preferentially clogging, vertical flow paths while favoring olivine dissolution along horizontal fluid pathways. This dual control of structure and fluid flow on carbonation mechanisms could be an important parameter allowing sustainable CO2 storage in peridotites, while limiting the risks of leakage toward the surface.
ISSN: 0003-004X

hal-01143393
https://hal.archives-ouvertes.fr/hal-01143393
DOI : 10.2138/am-2015-4913

Éditeur(s) : HAL CCSD
Résumé : International audience
Hundreds of Paleoproterozoic gold occurrences are known in the Tapajós Gold Province, northern Brazil. However, few deposits have been analysed in detail to understand the genesis of these systems. In this study, we present data concerning the largest deposit presently known in this Province, the Tocantinzinho deposit. A strike-slip fault system controls the emplacement of the mineralized rocks and the development of the brittle fracturing that host the main gold mineralization. Hydrothermal activity played an important role in the mineralization processes.
Mineral Resources in a Sustainable World
Nancy, France

hal-01356009
https://hal.archives-ouvertes.fr/hal-01356009

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Dentin matrix acidic phosphoprotein 1 (DMP1) is an acidic, highly phosphorylated, noncollagenous protein secreted during dentin and bone formation. Previous functional studies of DMP1 have revealed various motifs playing a role in either mineralization or cell differentiation. We performed an evolutionary analysis of DMP1 to identify residues and motifs that were conserved during 220 millions years (Ma) of mammalian evolution, and hence have an important function. In silico search provided us with 41 sequences that were aligned and analyzed using the Hyphy program. We showed that DMP1 contains 55 positions that were kept unchanged for 220 Ma. We also defined in a more precise manner some motifs that were already known (i.e., cleavage sites, RGD motif, ASARM peptide, glycosaminoglycan chain attachment site, nuclear localization signal sites, and dentin sialophosphoprotein-binding site), and we found five, highly conserved, new functional motifs. In the near future, functional studies could be performed to understand the role played by them.
ISSN: 0022-2844

hal-01545482
https://hal.archives-ouvertes.fr/hal-01545482
DOI : 10.1007/s00239-013-9539-2

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Gold mineralisation in the Yatela Main gold mine is hosted in a saprolitic residuum situated above Birimian supracrustal rocks, and at depth. The supracrustal rocks comprise metamorphosed calcitic and dolomitic marbles that were intruded by diorite (2106 ± 10 Ma, 207Pb/206Pb), and sandstone-siltstone-shale sequences (youngest detrital zircon population dated at 2139 ± 6 Ma). In-situ gold-sulphide mineralisation is associated with hydrothermal activity synchronous to emplacement of the diorite and forms a sub-economic resource; however, the overlying saprolitic residuum hosts economic gold mineralisation in friable lateritized palaeosols and aeolian sands (loess).Samples of saprolitic residuum were studied to investigate the morphology and composition of gold grains as a proxy for distance from source (and possible exploration vector) because the deposit hosts both angular and detrital gold suggesting both proximal and distal sources. U–Pb geochronology of detrital zircons also indicated a proximal and distal source, with the age spectra giving Archaean (2.83–3.28 Ga), and Palaeoproterozoic (1.95–2.20 Ga) to Neoproterozoic (1.1–1.8 Ga) zircons in the Yatela depocentre. The 1.1–1.8 Ga age spectrum restricts the maximum age for the first deposition of the sedimentary units in the Neoproterozoic, or during early deposition in the Taoudeni Basin. Models for formation of the residuum include distal and proximal sources for detritus into the depocentre, however, it is more likely that material was sourced locally and included recycled material. The creation of a deep laterite weathering profile and supergene enrichment of the residuum probably took place during the mid-Cretaceous-early Tertiary.
ISSN: 0899-5362

hal-01277679
https://hal.archives-ouvertes.fr/hal-01277679
DOI : 10.1016/j.jafrearsci.2015.07.017