Démixage lithologique et minéralogique par modélisation du transfert radiatif dans un contexte de mine à ciel ouvert.

La fosse en cours d’exploitation de la mine Canadian Malartic est considérée, dans cette thèse, comme étant un régolithe d’origine anthropique. Les explosions utilisées pour briser la roche conduisent à la formation d’un manteau rocheux non consolidé couvert de poussières, un médium particulaire. Les observations de blocs et de poussières faites directement sur le site confirment que le sol de la fosse rentre dans la définition de régolithe. Le modèle de transfert radiatif de Hapke, habituellement réservé à la planétologie, peut donc être utilisé pour le démixage spectral dans une mine. Une cartographie, réalisée à partir de données spectroscopiques et du modèle de Hapke, apporterait une information spatialement continue en quasi-temps réel aux géologues. Cela les aiderait à prévenir d’éventuels problèmes de drainage minier acide et à mieux discriminer le minerai du stérile. Cependant, les conditions rencontrées dans un contexte de mine à ciel ouvert ne permettent pas d’utiliser le modèle comme habituellement fait en planétologie. En effet, pour le démixage spectral des régolithes planétaires, une valeur de taille de grain générique est entrée dans le modèle et la porosité est souvent ignorée. Ces simplifications permettent de limiter le nombre de solutions possibles lors de l’utilisation du modèle, mais ne peuvent pas être généralisées aux mines à ciel ouvert. La variabilité de la taille de grain et de la porosité rencontrées empêche cette généralisation. Les travaux réalisés dans cette étude montrent que l’inversion du modèle de Hapke est un problème mal posé qui ne peut, sans diverses contraintes a priori, donner une solution unique. Trois lithologies ont été collectées dans la fosse de la mine Canadian Malartic. Les résultats de fluorescence des rayons X montrent qu’une ségrégation chimique significative a lieu durant la fracturation. Cela conduit à une minéralogie différente entre la poussière et la roche mère. Les différentes méthodes d’épandage de poudres de roches broyées, testées dans cette étude, mettent en exergue les incertitudes qui peuvent apparaître si une méthodologie rigoureuse n’est pas suivie. Une méthode qui optimise la répétabilité des mesures spectrales est décrite. Les démixages minéralogiques ont été réalisés à l’aide de pôles purs tirés de la bibliothèque spectrale du « United States Geological Survey ». Ces travaux ont mis en évidence la difficulté de quantifier l’abondance relative des minéraux à cause de la forte quantité de tectosilicates, semi-transparents dans les longueurs d’onde étudiées. Par exemple, un constituant majeur des échantillons, le quartz, peut varier de 20 % à 80 % en abondance sans que cela affecte significativement la modélisation. De plus, l’utilisation de pôles purs minéralogiques pris dans les bibliothèques est délicate tant la variabilité morphologique des spectres est grande pour un même minéral. Le modèle de Hapke utilisant de nombreux paramètres, les solutions permettant un bon accord entre mesures et modélisations peuvent être très différentes de la réalité. Afin de réduire le nombre de variables en entrée du modèle, des pôles lithologiques sont utilisés. De plus, la plupart des particules constituant le médium étant des assemblages minéralogiques, il semble raisonnable de penser le problème en termes de lithologies. Des mélanges binaires de différentes proportions sont utilisés pour contraindre l’inversion du modèle lors du calcul de la partie imaginaire des indices optiques. Cela permet le calcul sur deux pôles à la fois sans nécessiter les spectres de réflectance sur plusieurs granulométries. Les erreurs moyennes d’abondances retrouvées par le modèle dans le cas où les mélanges binaires sont de mêmes tailles de grain n’excèdent jamais 5 %. Les expérimentations en laboratoire de mélanges entre des grains fins et grossiers montrent un comportement spectral qui ne semble pas correspondre aux prédictions faites par le modèle. Une fonction de « taille de grains partagée » est introduite pour rendre compte des observations. Cette fonction permet une amélioration générale des démixages lithologiques en quantifiant plus précisément les abondances relatives massiques des particules fines et grossières. Dans le cas d’un mélange biotite / olivine, cette amélioration atteint 16,5 %. Les tailles de grain calculées, sans être précises, sont suffisamment bonnes pour être classées en fines ou grossières. Enfin, cette étude prouve que les roches, entités constituées de différents minéraux, peuvent être utilisées comme pôles purs d’un mélange constitué de différentes lithologies. Ces travaux ouvrent donc la voie à des cartographies lithologiques qui pourraient être utilisées par les géologues dans un contexte de mine à ciel ouvert

Reactivity of shape-controlled crystals and metadynamics simulations locate the weak spots of alumina in water

International audienceThe kinetic stability of any material in water relies on the presence of surface weak spots responsible for chemical weathering by hydrolysis. Being able to identify the atomistic nature of these sites and the first steps of transformation is therefore critical to master the decomposition processes. This is the challenge that we tackle here: combining experimental and modeling studies we investigate the stability of alumina in water. Exploring the reactivity of shape-controlled crystals, we identify experimentally a specific facet as the location of the weak spots. Using biased ab initio molecular dynamics, we recognize this weak spot as a surface exposed tetra-coordinated Al atom and further provide a detailed mechanism of the first steps of hydrolysis. This understanding is of great importance to heterogeneous catalysis where alumina is a major support. Furthermore, it paves the way to atomistic understanding of interfacial reactions, at the crossroad of a variety of fields of research

Apport de l’approche systémique et pluridisciplinaire dans l’étude du domaine littoral et marin de la Seine-Maritime (France)

Quatre levés morpho-sédimentaires, obtenus au moyen du sonar à balayage latéral, ont été réalisés sur le domaine marin côtier Dieppe/Le Tréport (Seine Maritime), entre 1988 et 2000. Les résultats sont intégrés dans une base d’information géographique qui permet d’observer les changements dans la répartition des faciès sédimentaires. Cette analyse montre un ensablement notable des fonds graveleux à l’est de Penly. L’ensablement concomitant de certains estrans rocheux, alors que les apports continentaux sont négligeables, témoigne d’échanges sableux transversaux entre le large et l’estran. L’approche systémique et pluridisciplinaire adoptée permet de définir les relais de processus qui expliquent ces échanges, connus pour les plages de sables, mais rarement identifiés pour les plages de galets.In 1988 and 1992, four morpho-sedimentary maps of the coastal area Dieppe/Le Tréport (Seine-Maritime, France), were made using side scan sonar data. The results were integrated in a geographic information data base, which allows to observe modifications in the sedimentary facies distribution. This study shows that a significant sand enrichment of the gravely sea floor occured east of Penly. The enrichment in sand of some shore platforms, while terrigeneous sand supply is insignificant, is a positive evidence suggesting that cross-shore transport from the shoreface contributes sands to the intertidal zone. The systemic and pluridisciplinary approach adopted in this study allowed us to define the relays of processes which explain these exchanges, known for sandy beaches, but rarely identified for gravel beaches

Insights into the evolution of Darwin's finches from comparative analysis of the Geospiza magnirostris genome sequence

Background: A classical example of repeated speciation coupled with ecological diversification is the evolution of 14 closely related species of Darwin's (Galápagos) finches (Thraupidae, Passeriformes). Their adaptive radiation in the Galápagos archipelago took place in the last 2-3 million years and some of the molecular mechanisms that led to their diversification are now being elucidated. Here we report evolutionary analyses of genome of the large ground finch, Geospiza magnirostris.Results: 13,291 protein-coding genes were predicted from a 991.0 Mb G. magnirostris genome assembly. We then defined gene orthology relationships and constructed whole genome alignments between the G. magnirostris and other vertebrate genomes. We estimate that 15% of genomic sequence is functionally constrained between G. magnirostris and zebra finch. Genic evolutionary rate comparisons indicate that similar selective pressures acted along the G. magnirostris and zebra finch lineages suggesting that historical effective population size values have been similar in both lineages. 21 otherwise highly conserved genes were identified that each show evidence for positive selection on amino acid changes in the Darwin's finch lineage. Two of these genes (Igf2r and Pou1f1) have been implicated in beak morphology changes in Darwin's finches. Five of 47 genes showing evidence of positive selection in early passerine evolution have cilia related functions, and may be examples of adaptively evolving reproductive proteins.Conclusions: These results provide insights into past evolutionary processes that have shaped G. magnirostris genes and its genome, and provide the necessary foundation upon which to build population genomics resources that will shed light on more contemporaneous adaptive and non-adaptive processes that have contributed to the evolution of the Darwin's finches. © 2013 Rands et al.; licensee BioMed Central Ltd

Convergence and divergence in the evolution of cat skulls: temporal and spatial patterns of morphological diversity

Background: Studies of biological shape evolution are greatly enhanced when framed in a phylogenetic perspective. Inclusion of fossils amplifies the scope of macroevolutionary research, offers a deep-time perspective on tempo and mode of radiations, and elucidates life-trait changes. We explore the evolution of skull shape in felids (cats) through morphometric analyses of linear variables, phylogenetic comparative methods, and a new cladistic study of saber-toothed cats. Methodology/Principal Findings: A new phylogenetic analysis supports the monophyly of saber-toothed cats (Machairodontinae) exclusive of Felinae and some basal felids, but does not support the monophyly of various sabertoothed tribes and genera. We quantified skull shape variation in 34 extant and 18 extinct species using size-adjusted linear variables. These distinguish taxonomic group membership with high accuracy. Patterns of morphospace occupation are consistent with previous analyses, for example, in showing a size gradient along the primary axis of shape variation and a separation between large and small-medium cats. By combining the new phylogeny with a molecular tree of extant Felinae, we built a chronophylomorphospace (a phylogeny superimposed onto a two-dimensional morphospace through time). The evolutionary history of cats was characterized by two major episodes of morphological divergence, one marking the separation between saber-toothed and modern cats, the other marking the split between large and small-medium cats. Conclusions/Significance: Ancestors of large cats in the ‘Panthera’ lineage tend to occupy, at a much later stage, morphospace regions previously occupied by saber-toothed cats. The latter radiated out into new morphospace regions peripheral to those of extant large cats. The separation between large and small-medium cats was marked by considerable morphologically divergent trajectories early in feline evolution. A chronophylomorphospace has wider applications in reconstructing temporal transitions across two-dimensional trait spaces, can be used in ecophenotypical and functional diversity studies, and may reveal novel patterns of morphospace occupation

Climate change and Mediterranean seagrass meadows: A synopsis for environmental managers

This synopsis focuses on the effects of climate change on Mediterranean seagrasses, and associated communities, and on the contribution of the main species, Posidonia oceanica, to the mitigation of climate change effects through sequestering carbon dioxide. Whilst the regression of seagrass meadows is well documented, generally linked to anthropogenic pressures, global warming could be a cause of new significant regression, notably linked to the introduction of exotic species, the rise of Sea-Surface Temperature (SST), and relative sea level. Seagrass communities could also be affected by climate change through the replacement of high structural complexity seagrass species by species of lower complexity and even by opportunistic introduced species. Although it is currently very difficult to predict the consequences of these alterations and their cascade effects, two main potential conflicting trends in the functioning of seagrass ecosystems are acceleration of the herbivore pathway or the detritivore pathway. The mean net primary production of the dominant species, Posidonia oceanica, is relatively high and can be estimated to range between 92.5 to 144.7 g C m-2 a-1. Around 27% of the total carbon fixed by this species enters the sedimentary pathway leading to formation, over millennia, of highly organic deposits, rich in refractory carbon. At the Mediterranean scale, the sequestration rate might reach 1.09 Tg C a-1. The amount of this stored carbon is estimated to range from 71 to 273 kg C m-2, which when considered at the Mediterranean scale would represent 11 to 42% of the CO2 emissions produced by Mediterranean countries since the beginning of the Industrial Revolution. The greatest value of the P. oceanica ecosystem, in the context of mitigation of global climate change, is linked to this vast long-term carbon stock accumulated over millennia, and therefore, efforts should be focused on preserving the meadows to keep this reservoir intact

Insights into the evolution of Darwin’s finches from comparative analysis of the Geospiza magnirostris genome sequence

Background: A classical example of repeated speciation coupled with ecological diversification is the evolution of 14 closely related species of Darwin’s (Galápagos) finches (Thraupidae, Passeriformes). Their adaptive radiation in the Galápagos archipelago took place in the last 2–3 million years and some of the molecular mechanisms that led to their diversification are now being elucidated. Here we report evolutionary analyses of genome of the large ground finch, Geospiza magnirostris. Results: 13,291 protein-coding genes were predicted from a 991.0 Mb G. magnirostris genome assembly. We then defined gene orthology relationships and constructed whole genome alignments between the G. magnirostris and other vertebrate genomes. We estimate that 15% of genomic sequence is functionally constrained between G. magnirostris and zebra finch. Genic evolutionary rate comparisons indicate that similar selective pressures acted along the G. magnirostris and zebra finch lineages suggesting that historical effective population size values have been similar in both lineages. 21 otherwise highly conserved genes were identified that each show evidence for positive selection on amino acid changes in the Darwin's finch lineage. Two of these genes (Igf2r and Pou1f1) have been implicated in beak morphology changes in Darwin’s finches. Five of 47 genes showing evidence of positive selection in early passerine evolution have cilia related functions, and may be examples of adaptively evolving reproductive proteins. Conclusions: These results provide insights into past evolutionary processes that have shaped G. magnirostris genes and its genome, and provide the necessary foundation upon which to build population genomics resources that will shed light on more contemporaneous adaptive and non-adaptive processes that have contributed to the evolution of the Darwin’s finches.Organismic and Evolutionary Biolog

Functional morphology of the cranio-mandibular complex of the Guira cuckoo (Aves)

The cranio‐mandibular complex is an important structure involved in food capture and processing. Its morphology is related to the nature of the food item. Jaw muscles enable the motion of this complex and their study is essential for functional and evolutionary analysis. The present study compares available behavioral and dietary data obtained from the literature with novel results from functional morphological analyses of the cranio‐mandibular complex of the Guira cuckoo (Guira guira) to understand its relationship with the zoophagous trophic habit of this species. The bite force was estimated based on muscle dissections, measurements of the physiological cross‐sectional area, and biomechanical modeling of the skull. The results were compared with the available functional morphological data for other birds. The standardized bite force of G. guira is higher than predicted for exclusively zoophagous birds, but lower than for granivorous and/or omnivorous birds. Guira guira possesses the generalized jaw muscular system of neognathous birds, but some features can be related to its trophic habit. The external adductor muscles act mainly during food item processing and multiple aspects of this muscle group are interpreted to increase bite force, that is, their high values of muscle mass, their mechanical advantage (MA), and their perpendicular orientation when the beak is closed. The m. depressor mandibulae and the m. pterygoideus dorsalis et ventralis are interpreted to prioritize speed of action (low MA values), being most important during prey capture. The supposed ecological significance of these traits is the potential to widen the range of prey size that can be processed and the possibility of rapidly capturing agile prey through changes in the leverage of the muscles involved in opening and closing of the bill. This contributes to the trophic versatility of the species and its ability to thrive in different habitats, including urban areas.Fil: Pestoni, Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Degrange, Federico Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Tambussi, Claudia Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Demmel Ferreira, María Manuela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Tirao, German Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin