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1
Cossu, Matteo. „Genomic evolution of archaea thermococcales“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS028.
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L'objectif principal de mon projet de doctorat est d'étudier l'évolution génomique de l'ordre des Archaea Thermococcales. Je me suis intéressé à comprendre les mécanismes des éléments mobiles génétiques (MGE) pouvant influencer l'évolution des génomes. En utilisant une approche multidisciplinaire, nous avons pu explorer les différents aspects de ce phénomène in silico, in vitro et in vivo. Grâce à des analyses in silico de tous les génomes de Thermococcales complètement séquencés disponibles, nous avons montré que cet ordre affiche un niveau élevé de réarrangements pouvant perturber les modèles d'expression génique. Dans une première approche, nous avons étudié l'existence de l'organisation chromosomique. L'inefficacité dans la prédiction de l'origine et de la terminaison de la réplication sur la seule base de la composition de l'ADN chromosomique ou skew, nous a motivé à utiliser une approche différente basée sur des séquences biologiquement pertinentes. Nous avons donc déterminé la position de l'origine de la réplication (oriC) dans tous les 21 génomes séquencés Thermococcales. La position potentielle de la terminaison a été prédite dans 19 génomes à ou près du site dif, où les dimères chromosomiques sont résolus avant la ségrégation de l'ADN. Le calcul du génome central a révélé un certain nombre de grappes de gènes essentiels avec une position chromosomique remarquablement stable à travers les espèces, en utilisant oriC comme référence. D'autre part, les régions core-free semblent correspondre à des éléments mobiles intégrés putatifs. Ces observations indiquent qu'un degré remarquable d ' «ordre» a été maintenu à travers les Thermococcales, même s'ils présentent des chromosomes fortement brouillés, les inversions étant particulièrement fréquentes. La découverte et la caractérisation d'un nouvel organisme, Thermococcus nautili nous ont permis de mieux comprendre le mécanisme sous-jacent causant ces inversions. En effet, le séquençage et l'analyse in silico de son génome ont fortement suggéré l'implication d'une nouvelle classe de tyrosine recombinases dans la plasticité génomique. Le plasmide pTN3 de T. nautili, qui est intégré dans le chromosome et auto-réplicable, code une intégrase appartenant à la classe des tyrosine recombinases. Des plasmides similaires ont également été trouvés intégrés dans le chromosome d'autres séquences de Thermococcales (par exemple TKV4 dans T. kodakarensis). Afin de tester son activité enzymatique, l’integrase codée par le plasmide pTN3 a été surproduite et purifiée. Les expériences in vitro ont d'abord permis de déterminer le segment de séquence minimal requis pour l'activité de l'intégrase et optimisé la réaction enzymatique in vitro. Ces résultats nous ont permis, en suite, de démontrer la réaction d'excision / d'intégration observée avec d'autres recombinases de tyrosine. De plus, l'excision in vivo d'un élément intégré apparenté (TKV4 de T. kodakarensis) par l'intégrase pTN3 a été réalisée au cours de cette étude. Pour cela, le gène IntpTN3 a été clone dans un vecteur de la bactérie E. coli / Thermococcus pour la transformation et l'expression dans T. kodakarensis. Après incubation, les cellules ont montré la présence de l'élément TKV4-intégré dans la forme circulaire libre. Enfin, nous avons pu imiter l'inversion chromosomique in vitro en utilisant des substrats synthétiques contenant des séquences cibles d'intégration. Nous avons également pu montrer que l'intégrase pTN3 possède une activité qui peut intervenir sur des inversions génomiques à grande échelle en utilisant différents sites et donc expliquer les réarrangements observés dans Thermococcales (Cossu et al, in prep)The main goal of my PhD project is to investigate the genomic evolution of the Archaea Thermococcales order. I am interested in understanding how mobile genetic elements (MGE) can influence the evolution of genomes. Using a multidisciplinary approach, we were able to explore the different aspects of this phenomenon in silico, in vitro and in vivo. Through in silico analyses of all available completely sequenced Thermococcales genomes, we showed that this order displays a characteristic high level of rearrangements potentially disrupting gene expression patterns. In a first approach, we investigated the existence of chromosomal organization. The inefficiency in predicting origin and termination of replication on the sole basis of chromosomal DNA composition or skew, motivated us to use a different approach based on biologically relevant sequences. We determined the position of the origin of replication (oriC) in all 21 sequenced Thermococcales genomes. The potential position of the termination was predicted in 19 genomes at or near the dif site, where chromosome dimers are resolved before DNA segregation. Computation of the core genome uncovered a number of essential gene clusters with a remarkably stable chromosomal position across species, using oriC as reference. On the other hand, core-free regions appear to correspond to putative integrated mobile elements. These observations indicate that a remarkable degree of “order” has been maintained across Thermococcales even if they display highly scrambled chromosomes, with inversions being especially frequent. The discovery and characterization of a new organism, Thermococcus nautili allowed us to better understand the underlying mechanism causing these inversions. The sequencing and in silico analysis of its genome strongly suggested the involvement of a new class of tyrosine recombinases in genomic plasticity. T. nautili pTN3 plasmid, which is found integrated into the chromosome and also self-replicating encodes an integrase belonging to this class. Similar plasmids have also been found integrated in the chromosome of other sequenced Thermococcales (e.g. TKV4 in T. kodakarensis). In order to test its enzymatic activity, we overproduced and purified the integrase encoded by pTN3. In vitro experiments first determined the minimal sequence segment required for integrase activity and optimized the enzymatic reaction in vitro. Due to this early results, we were able to demonstrate the excision/integration reaction observed with other tyrosine recombinases. Additionally, the in vivo excision of a related integrated element (TKV4 from T. kodakarensis) by the pTN3 integrase was performed during this study. The IntpTN3 gene has been cloned into an E. coli/Thermococcus shuttle vector for transformation and expression in T. kodakarensis. After incubation, cells showed the presence of the TKV4-integrated element in free circular form. Finally, we were able to mimic in vitro chromosomal inversion using synthetic substrates containing integration target sequences. We were also able to show that pTN3 integrase possesses an activity which can mediate large scale genomic inversions using different sites and therefore explain the rearrangements observed in Thermococcales)
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Aouad, Monique. „Phylogenomic study of the evolutionary history of the Archaea and their link with eukaryogenesis“. Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1246.
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L'explosion des données de séquençage a permis de résoudre la plupart des relations phylogénétiques chez les archées. Néanmoins, de nombreuses questions restent à résoudre à l'échelle du domaine des archées et à l'échelle des trois domaines du vivant. Parmi elles, les relations phylogénétiques au sein du cluster II, notamment la position des archées halophiles extrêmes qui ont été placées à différentes positions dans l'arbre en fonction des marqueurs et des modèles de reconstruction utilisés, ainsi que la position de la racine des archées et la position des eucaryotes à la lumière des lignées d'archées nouvellement séquencées. Au cours de ma thèse, j'ai contribué à (i) affiner la phylogénie du domaine des Archaea en se concentrant sur les relations phylogénétiques au sein du cluster II, en particulier les positions des lignées halophiles extrêmes par rapport aux méthanogènes à travers des analyses dédiées à cette partie spécifique de l'arbre, et (ii) établir une phylogénie globale des archées afin de comprendre leur histoire évolutive ancienne et leur lien avec les eucaryotes à travers une analyse phylogénomique en deux étapes à l'échelle des trois domaines du vivant. D'abord, en utilisant des approches de génomique comparée sur 155 génomes complets appartenant aux Halobacteria, Nanohaloarchaea, méthanogènes de classe II, Archaeoglobales et Diaforarchaea, j'ai identifié 258 protéines portant un signal phylogénétique fiable pour étudier les relations de parente au sein du cluster II. En combinant différentes approches limitant l'impact du signal non phylogénétique sur l'inférence phylogénétique (comme la méthode Slow-Fast et le recodage des acides aminés), j'ai montré que les Nanohaloarchaea branchent avec les Methanocellales et les Halobacteria branchent avec les Methanomicrobiales. Ce jeu de données a ensuite été utilisé pour étudier la position d'une troisième lignée halophile extrême, les Methanonatronarchaeia, qui se positionnent entre les Archaeoglobales et les Diaforarchaea. Ces résultats suggèrent que l'adaptation à la salinité extrême serait apparue au moins trois fois de manière indépendante chez les archées et que les similitudes phénotypiques observées chez les Nanohaloarchaea, Halobacteria et Methanonatronarchaeia résulteraient d'une convergence évolutive, éventuellement accompagnée de transferts de gènes horizontaux. Enfin, ces résultats suggèrent que le groupement basal des Nanohaloarchaea avec d'autres lignées des DPANN serait la conséquence d'un artefact de reconstruction. Pour la deuxième partie de ma thèse, j'ai appliqué une stratégie consistant à analyser séparément les trois domaines du vivant considérés deux à deux, en mettant à jour 72 familles protéiques précédemment identifiées par Raymann et ses collègues (2015) pour inclure toutes les nouvelles lignées d'archées séquencées depuis la publication de cette étude comme les Asgard, les DPANN, les Stygia, les Acherontia, etc. Au total, mon échantillonnage taxonomique comprend 435 archées, 18 eucaryotes et 67 bactéries. Les résultats des analyses par la méthode Slow-Fast soutiennent une racine des Archaea située entre le superphylum basal des DPANN et le reste des archées séparées en deux groupes monophylétiques : les cluster I et cluster II, comme décrits par Raymann et ses collègues (2015), et montrent que la monophylie des Euryarchaeota est liée aux positions évoluant vite. Mes résultats placent les eucaryotes en tant que groupe frère du superphylum des TACK et montrent que leur regroupement avec les Asgard est lié aux positions évoluant vite. Ces résultats ont des implications majeures sur les inférences de la nature du dernier ancêtre commun des archées et sur l'histoire évolutive de ce domaine qui a conduit à l'apparition de la première cellule eucaryoteThe burst of sequencing data has helped disentangling most of the phylogenetic relationships in Archaea. Nevertheless, many questions remain to be addressed both at the level of the archaeal domain and at the level of the three domains of life. Among them, the phylogenetic relationships inside the cluster II, in particular the position of extreme halophilic archaeal lineages relatively to the methanogens which have been placed at different positions in the tree based on the different markers and reconstruction models used, as well as the position of the root of the Archaea and the position of the eukaryotes in the light of the newly sequenced archaeal lineages. During my thesis, I have contributed to (i) refine the phylogeny of the archaeal domain by focusing on the phylogenetic relationships among the cluster II Archaea, in particular the positions of the extreme halophilic lineages through dedicated analyses focusing on this specific part of the archaeal tree, and (ii) establish a global phylogeny of the Archaea to understand their early evolutionary history and their link with the eukaryotes through a large-scale two-step phylogenomic analysis at the level of the three domains of life. First, using comparative genomics approaches on 155 complete genomes belonging to the Halobacteria, Nanohaloarchaea, methanogens class II, Archaeoglobales, and Diaforarchaea, I have identified 258 proteins carrying a reliable phylogenetic signal to investigate the position of the extreme halophilic lineages in Archaea. By combining different approaches limiting the impact of non-phylogenetic signal on phylogenetic inference (like the Slow Fast method and the recoding of amino acids), I showed that the Nanohaloarchaea branch with Methanocellales, and Halobacteria branch with Methanomicrobiales. This dataset has been subsequently used to investigate the position of a third extreme halophilic lineage, the Methanonatronarchaeia, which I showed to branch in between the Archaeoglobales and Diaforarchaea. These results suggest that adaption to high salinity emerged at least three times independently in Archaea, and that the phenotypic similarities observed in Nanohaloarchaea, Halobacteria, and Methanonatronarchaeia likely result from convergent evolution, possibly accompanied by horizontal gene transfers. Finally, these results suggest that the basal grouping of Nanohaloarchaea with other DPANN lineages is likely the consequence of a tree reconstruction artefact. For the second part of my thesis, I have applied a strategy consisting in separately analyzing the three domains of life two by two, by updating 72 protein families previously identified by Raymann and colleagues (2015) to include all novel archaeal lineages that were sequenced since the publication of this study like the Asgard, the DPANN, the Stygia, the Acherontia, etc. In total, my taxonomic sampling includes 435 archaea, 18 eukaryotes, and 67 bacteria. The results of the Slow-Fast method supported a root of the Archaea lying between a basal DPANN superphylum and the rest of the Archaea separated into two monophyletic groups: the cluster I and cluster II as described by Raymann and colleagues (2015), and showed that the monophyly of the Euryarchaeota is supported only by the fast-evolving sites. My results also placed the eukaryotes as the sister group to the TACK superphylum and showed that their sister grouping with the Asgard is linked to the fast-evolving sites. These results have major implications on the inferences of the nature of the last common archaeal ancestor and the subsequent evolutionary history of this domain that led to the rise of the first eukaryotic cell
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Berthon, Jonathan. „Etude de la réplication de l'ADN chez les Archaea“. Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00344124.
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Les organismes cellulaires appartiennent à l'un des trois domaines du vivant : Archaea, Bacteria, Eucarya. Les Archaea sont des organismes unicellulaires avec un phénotype bactérien mais qui possèdent de nombreux caractères moléculaires eucaryotes. En particulier, la machinerie de réplication archéenne est une version homologue et simplifiée de celle des eucaryotes. Au cours de cette thèse, j'ai étudié la réplication de l'ADN chez les Archaea en combinant des approches in vitro et in silico.Premièrement, j'ai essayé de purifier la protéine initiatrice de la réplication Cdc6/Orc1, sous une forme native, dans l'espoir de mettre au point le premier système de réplication de l'ADN in vitro chez les Archaea. Malheureusement, cette approche a été infructueuse en raison de l'instabilité et des propriétés d'agrégation de la protéine.
Deuxièmement, j'ai réalisé une analyse comparative du contexte génomique des gènes de réplication dans les génomes d'Archaea. Cette analyse nous a permis d'identifier une association très conservée entre des gènes de la réplication et des gènes liés au ribosome. Cette organisation suggère l'existence d'un mécanisme de couplage entre la réplication de l'ADN et la traduction. De manière remarquable, des données expérimentales obtenues chez des modèles bactériens et eucaryotes appuient cette idée. J'ai ensuite mis au point des outils expérimentaux qui permettront d'éprouver la pertinence biologique de certaines des prédictions effectuées.
Finalement, j'ai examiné la distribution taxonomique des gènes de la réplication dans les génomes d'Archaea afin de prédire la composition probable de la machinerie de réplication de l'ADN chez le dernier ancêtre commun des Archaea. Dans leur ensemble, les profils phylétiques des gènes de la réplication suggèrent que la machinerie ancestrale était plus complexe que celle des organismes archéens contemporains.
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Petitjean, Celine. „Phylogénie et évolution des Archaea, une approche phylogénomique“. Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-01070633.
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En 1977, Carl Woese sépare les procaryotes en deux grands groupes en proposant une nouvelle classification basée sur des critères phylogénétiques. Les Archaea deviennent ainsi un domaine à part entière aux cotés des Bacteria et des Eucarya. Depuis, la compréhension de ce nouveau groupe et de ses relations avec les deux autres domaines, essentielles pour comprendre l'évolution ancienne du vivant, est largement passée par l'étude de leur phylogénie. Presque 40 ans de recherche sur les archées ont permis de faire évoluer leur image : de bactéries vivant dans des milieux spécialisés, souvent extrêmes, on est passé à un domaine indépendant, très diversifié aussi bien génétiquement, métaboliquement ou encore écologiquement. Ces dernières années la barre symbolique de cent génomes complets d'archées séquencés a été franchie et, parallèlement, les projets génomiques et métagénomiques sur des groupes peu caractérisés ou de nouvelles lignées de haut rang taxonomique (e.g. Nanohaloarchaea, Thaumarchaeota, ARMAN, Aigarchaeota, groupe MGC, groupe II des Euryarchaeota, etc.) se sont multipliés. Tout ceci apporte un matériel sans précédent pour l'étude de l'histoire évolutive et de la diversité des Archaea. Les protéines ribosomiques ont été utilisées de façon courante pour inférer la position phylogénétique des nouvelles lignées d'Archaea. Néanmoins, les phylogénies résultantes ne sont pas complètement résolues, laissant des interrogations concernant d'importantes relations de parenté. La recherche de nouveaux marqueurs est donc cruciale et c'est dans ce contexte que mon projet de thèse s'inscrit. À partir de l'analyse des génomes de deux Thaumarchaeota et d'une Aigarchaeota, nous avons identifié 200 protéines conservées et bien représentées dans les différents phyla d'archées. Ces protéines sont impliquées dans de nombreux processus cellulaires, ce qui peut apporter un signal phylogénétique complémentaire à celui des marqueurs de type informationnel utilisés par le passé. En plus de confirmer la plupart des relations phylogénétiques inférées à partir de ces derniers (i.e., protéines ribosomiques et sous unités de l'ARN polymérase), l'analyse phylogénétique de ces nouveaux marqueurs apporte un signal permettant une meilleure résolution de la phylogénie des archées et la clarification de certaines relations jusqu'ici confuses. Un certain nombre de ces nouveaux marqueurs sont aussi présents chez les bactéries. Les relations entre les grands phyla d'archées restant encore non résolues, nous avons utilisé ces protéines pour essayer de placer la racine de l'arbre des Archaea en utilisant comme groupe extérieur les bactéries. Nous avons ainsi pu identifier 38 protéines, parmi les 200 sélectionnées précédemment, ayant un signal phylogénétique suffisamment fiable pour cette étude, auxquelles nous avons ajouté 32 protéines ribosomiques universelles. L'utilisation conjointe de ces données nous a permis de placer la racine entre les Euryarchaeota, d'une part, et un groupe rassemblant les Thaumarchaeota, les Aigarchaeota, les Korarchaeota et les Crenarchaeota, d'autre part. Ce nouvel éclairage sur l'évolution ancienne des archées nous a amené à proposer une révision de leur taxonomie avec, principalement, la création du nouveau phylum "Proteoarchaeota" contenant les quatre phyla actuels que nous proposons de rétrograder en classes : Thaumarchaea, Aigarchaea, Korarchaea et Crenarchaea.Finalement, l'analyse des protéines codées dans les trois génomes qui ont servi de point de départ de ma thèse nous a permis de générer une masse considérable de données qui ont révélé des traits particuliers ou encore des histoires évolutives inattendues. Un exemple est l'histoire du complexe formé par la chaperonne DnaK et de ses co-chaperonnes GrpE, DnaJ, et DnaJ-Fer chez les Thaumarchaeota, impliquant plusieurs transferts horizontaux entre les trois domaines du vivant.
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Hepp, Benjamin. „Characterization of IntpTN3 : A suicidal integrase capable of in vitro homologous recombination“. Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASL151.
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Les organismes hyperthermophiles sont des microorganismes qui prospèrent de manière optimale à des températures de 85 °C ou plus. On les trouve couramment dans des environnements extrêmes tels que les sources chaudes, les puits de pétrole et les fosses océaniques près des évents hydrothermaux, tels que les fumeurs noirs. Ces organismes sont devenus des ressources précieuses pour les applications biotechnologiques en raison de leur production d'enzymes thermostables, notamment les polymérases utilisées dans la PCR (réaction de polymérase en chaîne) et les enzymes utilisées dans l'industrie des détergents pour dégrader les biomolécules à haute température. Au sein de l'archée hyperthermophile Thermococcus nautili, nous avons découvert une enzyme capable de catalyser la recombinaison de l'ADN avec pratiquement n'importe quelle molécule d'ADN. Cette enzyme présente un immense potentiel en tant qu'outil biotechnologique robuste pour les chercheurs, permettant l'assemblage in vitro de molécules d'ADN et facilitant les processus de modification de l'ADN. Ces découvertes prometteuses nous ont conduits à déposer une déclaration d'invention pour notre enzyme, reconnaissant sa valeur significative dans l'avancement de la biologie moléculaire et de l'ingénierie génétiqueHyperthermophilic organisms are microorganisms that thrive optimally at temperatures of 85°C or higher. They are commonly found in extreme environments such as hot springs, oil wells, and oceanic trenches near hydrothermal vents, such as black smokers. These organisms have emerged as valuable resources for biotechnological applications due to their production of thermostable enzymes, including polymerases used in PCR (Polymerase Chain Reaction) and enzymes employed in the detergent industry for breaking down biomolecules at high temperatures. Within the hyperthermophilic archaea Thermococcus nautili, we have discovered an enzyme capable of catalyzing DNA recombination with virtually any DNA molecule. This enzyme holds immense potential as a robust biotechnological tool for researchers, enabling the in vitro assembly of DNA molecules and facilitating DNA modification processes. These promising findings have led us to file an invention disclosure statement for our enzyme, recognizing its significant value in advancing molecular biology and genetic engineering
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Li, Jun, und 李俊. „Molecular evolution and phylogeny of methanogenic archael genomes“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208152.
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Methane (CH4) is the major chemical component of natural gas, as well as a particularly potent greenhouse gas. Methanogens are the archaeal organisms that produce methane and play a key role in biological methanogenesis. A total of six taxonomic orders of archaeal methanogens have been discovered and almost all previous phylogenetics studies have confirmed that these methanogens are genetically diversified and do not belong to a phylogenetically monophyletic group. To date, the relationships between methanogens and closely related non-methanogen species at the taxonomic order level remain unresolved and different studies have often produced contradictory results based on different gene markers. These studies suggest the complicated and distinct evolutionary histories between different genes in these genomes.
In this thesis, 74 fully sequenced archaeal genomes, including 41 methanogens, were collected and used in a comprehensive comparative genomics and evolutionary analysis. First, numerous phylogenomic trees were reconstructed based on various datasets using several methods and the results show that Methanopyrales is close to Methanobacteriales (or Methanopyrales) in the statistically best species tree. In addition, Methnocellales and Methanosarcinales, and as well as Methanomicrobiales and Halobacteriales are sister clades in the best species tree, but the confidence level is low. Further incongruence tests among the phylogenetic forest, which is composed of 3,694 ortholog gene families, reveal that the archaeal core genes have much stronger consistent vertical evolutionary signals than other genes, but these core genes are not topologically fully congruent with each other.
Secondly, a series of weighted network analyses were implemented to decompose the hierarchical structure and to reveal the co-evolved gene modules, global and local features in the archaeal methanogen phylogenetic forest. The results show that this co-evolution network contains 7 statistical robust modules, and the module with the highest average node strength includes the majority of the core genes located in the central position of the network. Further in-depth evolutionary analysis reveals that the modularized evolution in the archaeal phylogenetic forest is closely related to the time of origin, HGT rate and ubiquitous vertical inheritance in gene families.
Lastly, to investigate the causes for and factors related to the pervasive topology incongruence in the phylogenetic forest, in-depth clanistics analysis and HGT detection were carried out. These results show that (1) about 63% of gene families experienced at least 1 HGT event in their whole history; (2) core genes are not immune to HGT but they do have much lower HGT rates than other genes; (3) methanogens have distinct trends of HGTs from non-methanogen species; and (4) highly frequent inter-order HGTs, even for core genes, in methanogen genomes lead to their scrambled phylogenetic relationships. Further clanistics analysis screened out 119 candidate genes related to methanogenic pathways adaptation and most of these gene families have experienced at least one HGT.
In conclusion, a complex evolutionary scenario for methanogenic archaeal species was described in this thesis as a combination of complicated vertical and non-vertical evolutionary processes in a modularized phylogenetic forest.published_or_final_version
Biological Sciences
Doctoral
Doctor of Philosophy
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Archibald, John M. „Studies on the evolution of archaeal and eukaryotic chaperonins“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ66656.pdf.
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Robertson, S. „Late Archaean crustal evolution in the Ivisartoq region, southern west Greenland“. Thesis, University of Exeter, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353048.
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Dougherty-Page, Jon Stanley. „The evolution of the Archaean continental crust of Northern Zimbabwe“. Thesis, Open University, 1994. http://oro.open.ac.uk/54877/.
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Granitoid clasts preserved in Late Archaean conglomerates indicate the presence of continental crust in Northern Zimbabwe prior to the ≈ 2.7 to ≈ 2.6Ga "event" which terminated with the stabilisation of the Zimbabwe Craton. The "Kober Technique" (Kober, 1986, 1987) of direct thermal ionisation of zircons has been set up in order to investigate the geochronological record preserved in such clasts. Conglomerates were sampled from two localities, Shamva, within the central part of Northern Zimbabwe, and Chinhoyi, at the north-western boundary of the craton. The results from both localities demonstrate the presence of continental crust in Northern Zimbabwe with a long and complex history prior to the Late Archaean "event". The minimum age of continental crust in the Shamva region is 3.34 Ga (Sm-Nd model age),with further episodes of granitiod intrusion indicated by zircon crystallisation at 3/197 ± 10 Ma, 2,925 ± 10 Ma, and 2,800 ± 20 Ma (Pb-Pb zircon). The Chinhoyi region has a shorter, simpler history, with the earliest recorded continental crust at 2,875 ± 3 Ma and later intrusions of granitoids at 2/800 ± 20 Ma, and2,720 ± 6 Ma (Pb-Pb zircon). Chemically, the early crust was dominated by sodic, Tonalite Trondhjemite-Granodiorite granitoids, whose formation may be modelled by the partial melting of metabasalts with residual hornblende and/or garnet. By contrast, the granitoids formed during the Late Archaean "event" which culminated in the stabilisation of the craton, dominantly follow calc-alkalinetrends, and their formation may be modelled by the fractionation of basaltic magmas (combined with assimilation- of pre-existing continental material) or intra-crustal remelting. This major switch in the origins (and hence chemistry) of granitoids may be attributed to mantle plume activity, the onset of which is recorded by the presence of greens tone belt volcanics derived from anomalously hot mantle, dated at' 2,713 ± 15 Ma (U-Pb zircon Jelsma, 1993).
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Ticak, Tomislav. „Anoxic quaternary amine utilization by archaea and bacteria through a non-L-pyrrolysine methyltransferase; insights into global ecology, human health, and evolution of anaerobic systems“. Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1429897518.
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Megrian, Nuñez Daniela. „Phylogenomic approaches to uncover the diversity and evolution of the bacterial cell envelope“. Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS349.
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L’enveloppe bactérienne est l’une des structures cellulaires les plus anciennes et les plus fondamentales. Toutefois, de nombreux aspects concernant sa diversité et son histoire évolutive sont encore inconnus. Dans cette thèse, j’ai profité du nombre croissant de génomes disponibles dans les bases de données publiques, afin de mener une analyse de phylogénomique et de génomique comparative à une large échelle évolutive. Les deux objectifs de ce travail doctoral étaient (i) d’identifier de nouvelles lignées didermes au sein des Firmicutes pour éclairer la transition monoderme/diderme, et (ii) d’élucider l’histoire évolutive de l’enveloppe cellulaire chez les bactéries et d’en déduire la nature chez le LBCA.En résumé, les résultats que j'ai obtenus au cours de cette thèse fournissent une avancée significative dans notre compréhension de la diversité et de l'évolution de l'enveloppe cellulaire, et sur l'une des transitions majeures de l'histoire des bactéries, celle entre les monodermes et les didermesThe bacterial envelope is one of the oldest and most fundamental cellular structures. Yet, many aspects of its diversity and evolutionary history are unknown. In this thesis I have taken advantage of the large available genomic data to investigate the issue through a large-scale phylogenomic and comparative genomic analyses at the level of Bacteria. The two goals of this doctoral work were (i) to identify putative new diderm lineages in the Firmicutes to illuminate the monoderm/diderm transition, and (ii) to elucidate the evolutionary history of the cell envelope in Bacteria and infer its nature in the LBCA. To sum up, the results I obtained during this thesis provide a timely and significant advancement to our understanding of the diversity and evolution of the cell envelope, and on one of the major transitions in the history of Bacteria, that between monoderms and diderms
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Lombard, Jonathan. „Origines et évolution des voies de synthèse des phospholipides dans les trois domaines du vivant. Implications pour la nature des membranes du cenancêtre“. Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00819686.
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Les bases fondamentales de la biologie suggèrent que tous les organismes actuels partagent un dernier ancêtre commun, le cenancêtre. Dès que la comparaison moléculaire des organismes des trois domaines du vivant (archées, bactéries et eucaryotes) est devenue possible, d'importants débats ont émergé sur l'habitat du cenancêtre, son rapprochement des origines de la vie, sa nature unique ou communautaire et ses relations avec les trois domaines du vivant. Cependant, jusqu'à il y a peu les informations disponibles sur les organismes modernes n'étaient pas suffisantes pour décrire précisément sa biologie. Notamment, la découverte chez les archées de membranes dont les composants principaux, les phospholipides, sont synthétisés par des mécanismes très différents de ceux des bactéries et les eucaryotes a conduit à proposer que chaque mécanisme de synthèse des phospholipides soit apparu indépendamment dans les lignées modernes. Dans ces hypothèses le cenancêtre aurait été dépourvu de phospholipides et, donc, de membranes. Cela met en cause la nature cellulaire du cenancêtre, qui semblait pourtant soutenue par d'autres indices indirects. Ces contradictions posent la question de l'existence de traces dans les organismes modernes d'une synthèse des phospholipides chez le cenancêtre. Dans cette thèse j'ai profité de l'explosion récente des données génomiques pour répondre à cette question. Il avait déjà montré que des membres de deux superfamilles protéiques universelles pouvaient avoir synthétisé de façon non spécifique chez le cenancêtre les énantiomères de glycérol phosphate servant d'ossature aux phospholipides. Les phospholipides archéens sont composés d'isoprénoïdes et les bactériens et eucaryotes d'acides gras. J'ai donc étudié l'évolution des voies de synthèse de ces molécules ainsi que celle de l'assemblage de tous les composants dans des phospholipides. Mes résultats montrent que la voie de synthèse des isoprénoïdes des eucaryotes et une voie hypothétique de synthèse des acides gras chez les archées avaient probablement des ancêtres moins spécifiques chez le cenancêtre. Une partie au moins de la machinerie d'assemblage des phospholipides semble aussi avoir été présente chez le cenancêtre.Ceci suggère que le cenancêtre avait probablement des mécanismes peu spécifiques de synthèse des phospholipides et que les différences entre les membranes actuelles sont dues à la spécialisation de la machinerie ancestrale dans chaque lignée. Mes observations soulignent aussi l'importance d'étudier le cenancêtre à partir des informations issues des organismes actuels pour éviter toute confusion avec les origines de la vie.
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De, Angelis Franco. „The evolution of two archaic Sicilian poleis : Megara Hyblaia and Selinous“. Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:f2347179-5efc-4cbe-881b-8bd5579c5849.
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This study attempts to revive T.J. Dunbabin's multi-dimensional approach to the history of Early Iron Age Sicily in The Western Greeks (Oxford 1948). Dunbabin recognised that archaic Sicily had no real history, and that any historical account involved combining the very scant documentary record with the fuller and ever-growing body of archaeological evidence to produce a framework for writing social and economic history. These innovative methods ended with Dunbabin, however: today the field is dominated by scholars impeded artificially by disciplinary boundaries, which discourage the productive combination of historical and archaeological sources, leaving a number of important questions in a sort of academic no man's land. In the introduction an overview of the study of Sicily since Dunbabin is given, and Dunbabin's own weaknesses are explored: Dunbabin modelled Greek colonisation in Sicily on modern British colonisation; such a decision strait-jacketed his image of the past, causing him to draw conclusions unacceptable today. The increase in the quantity of archaeological evidence since Dunbabin means that it is no longer possible to make an in-depth study of the whole of Sicily in a single volume. Consequently, the focus has to be considerably more restricted than Dunbabin's; specific questions need to be selected. Megara Hyblaia and Selinous offer two particular advantages for studying the evolution of Greek settlement in Sicily: besides being Megarian, both are sufficiently well explored archaeologically to make historical investigation profitable, but they were founded a century apart on different sides of the island, in different environmental and socio-political contexts. The study itself is divided into two main parts, the first focusing on Megara Hyblaia and the second on Selinous; each of these two parts consists of five chapters, in which the same questions are asked of the evidence from the two sites, for comparative purposes. Chapters I and VI explore the background to settlement, with such subjects as the native world encountered by the settlers at the time of colonisation, pre- and proto-colonial activity, and the respective foundations of the colonies examined. Settlement development is the subject of chapters II and VII; the emphasis here is to monitor the successive stages of the physical growth of the colonies, and also to study the size and nature of the settlement itself. Chapters III and VIII deal with demography (particularly population size). The following chapters (IV and IX) use archaeological and written evidence to reconstruct socio-political history. Chapters V and X investigate environment and economy. In the closing chapter, after a review of the conclusions reached, the question of why Selinous evolved so differently from it mother-city is addressed. The thesis ends with brief consideration of the (Megarian) Sicilian contribution to the study of the polis.
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Fernández, Guerra Antonio. „Ecology and evolution of microbial nitrifiers / Ecología y evolución de los microorganismos nitrificantes“. Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/108001.
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Ammonia oxidation, the first and the rate-limiting step in nitrification, is one of the cornerstones of the cycle. Members from the bacterial and archaeal domains are key players in ammonia oxidation in many different environ- ments. Usually these organisms are found coexisting but the most recent studies suggests that archaeal ammonia oxidizers show an incredible ability to adapt and oxidize ammonia under different environmental conditions and have displaced their bacterial counterparts in terms of importance in the global biogeochemical cycle, providing an avalanche of AOA molecular data (16S rDNA and amoA gene sequences) from very diverse environments worldwide. As far as we don’t have enough genomic data to perform an holistic approach using population genomics and reverse ecology to unveil the ecological and evolutionary mechanisms driving the adaptation; we focused our experiments on the amoA gene sequence. Because ammonia monooxygenase is supposed to be the key enzyme in the ammonia oxidation, we applied a combination of community ecology and molecular evolution methods to understand the mechanisms of the diversification patterns observed in the amoA gene. Another unsolved question in the archaeal ammonia oxidation is the unusual biochemistry found in the genome sequences from cultured archaeal ammonia oxidizers. In archaea, all the elements of the bacterial ammonia oxidizing pathway are missing but the genes coding for the presumptive AMO. To unveil missing pathways in this process, we have developed a powerful approach based on graphical models to capture all the functional associations present in metagenomes based in their ecological co-ocurrence.
The results of the analyses revealed for the first time a global picture of the phylogenetic community structure of ammonia- oxidizing assemblages. Our study unveiled larger phylogenetic richness in AOA with more dissimilar communities and clear monophyletic groups for the different habitats. The rates of diversification in AOA were higher than in AOB and the archaeal diversification dynamics showed an unusual feature, with an initial diversification process followed by a long period of stasis and a final burst of diversification. The variations observed between AOB and AOA in terms of community structure, phylogenetic diversity, diversification patterns, and habitat dispersion were unexpected just a very few years ago, and the community phylogenetics approach has nicely captured these differences.
Understand the diversification processes observed in AOA and their successful performance under a myriad of different environmental conditions such as low pH, different ammonia concentrations, high hydrostatic pressures, high light exposure, low oxygen availability among others, needs however of a deeper insight adding the evolutionary processes. Individual changes at the level of nucleotides were translated to the global diversification patterns of archaeal ammonia oxidizers. Thus, this resulted in a step further from the results obtained after applying community phylogenetics methods providing precise evolutionary information behind the phylogenetic patterns observed within an ecological context. We will gain the full picture once the results can be integrated in a comparative genomics framework.
After applying methods of reverse engineering of regulatory the associations between the known and the unknown fraction were reconstructed offering a pioneering fresh view for microbial ecology. One especially relevant result obtained from this approach on AOA was the reconstruction of the association network of the different AMO subunits to the other proteins previously reported in the marine AOA Nitrosopumilus. The information recovered from metagenomics combined with available genomes fuels hypothesis for the particular and yet unknown biochemistry of ammonia oxidation in Archaea.La oxidación del amonio es una de las piezas clave del ciclo del Nitrógeno. Tanto las bacterias como las arqueas oxidadoras del amonio se pueden encontrar coexistiendo a lo largo de diferentes ambientes. Pero cuando la primera arquea oxidadora del amonio fue aislada, se puso en relevancia la importancia de estas en comparación con las bacterias en los ciclos biogeoquímicos globales. Desde entonces hemos sido inundados por una avalancha de secuencias génicas de estas arqueas, mostrando una gran capacidad de diversificación y adaptación a ambientes diferentes. Al no disponer de suficientes datos para realizar una aproximación holistica utilizando genómica de poblaciones y de ecología inversa para poder discernir los mecanismos ecológicos y evolutivos relacionados con la adaptación; nos hemos centrado en estudiar la secuencia del amoA. La amonio monooxigenasa es la enzima responsable de la oxidación del amonio, para su estudio hemos aplicado una combinación de técnicas de ecología de comunidades y de evolución molecular con el objetivo de entender los mecanismos de los patrones de diversificación observados. Por otra banda, otro de los misterios asociados a la oxidación del amonio por parte de las arqueas, es su inusual bioquímica para realizar la oxidación del amonio. En arqueas faltan todos los elementos necesarios para llevar a cabo la oxidación del amonio a excepción del AMO. Para poder aportar algo de luz a este misterio hemos desarrollado un potente método basado en modelos gráficos para capturar todas las asociaciones funcionales presentes en los metagenomas basado en sus co-ocurrencias ecológicas.
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Hapugoda, Hapugoda Udage Sarath. „Late Archaean and Early Proterozoic crustal evolution of the Georgetown Block, Northeast Queensland, Australia /“. St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16503.pdf.
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Alwadain, Ayed Said A. „A model of enterprise architecture evolution“. Thesis, Queensland University of Technology, 2014. https://eprints.qut.edu.au/71204/1/Ayed%20Said%20A_Alwadain_Thesis.pdf.
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Enterprise architectures are exposed to fast emerging business and information technology capabilities. A prominent example is the paradigm of service-orientation, which leads to its own architectural requirements and impacts the design and ongoing evolution of Enterprise Architectures. This thesis develops the first theoretical model describing enterprise architecture evolution and outcomes in light of a changing IT landscape such as service-oriented architectures. The developed theoretical model explains enterprise architecture evolution, its main stages and related capabilities. This model can be used to derive theoretical, sound guidelines to manage enterprise architectures in a changing environment.
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Heather, Kevin B. „The geological evolution of the Archean Swayze Greenstone Belt, Superior Province, Canada“. Thesis, Keele University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341304.
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Wolff, Christopher B. „A study of the evolution of Maritime Archaic households in northern Labrador“. Ann Arbor, Mich. : ProQuest, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3336811.
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Thesis (Ph.D. in Anthropology)--S.M.U.Title from PDF title page (viewed Mar. 16, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: A. Advisers: David Meltzer; Torben Rick. Includes bibliographical references.
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Yearron, Lorraine M. „Archaean granite petrogenesis and implications for the evolution of the Barberton mountain land, South Africa“. Thesis, Kingston University, 2003. http://eprints.kingston.ac.uk/20723/.
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This research covers the granitoid rocks associated with the Archaean Barberton Greenstone Belt, Kaapvaal Craton, South Africa. The granitoid rocks were emplaced over a 500 Myr interval and can be divided into two suites. The TTG suite (emplaced ea 3.5 - 3.2 Ga) contains tonalites, trondhjemites and granodiorites, and the GMS suite (emplaced ca 3.2 - 3.1 Ga) includes granodiorites, monzogranites and a small syenite-granite complex. These rocks are important as they hold insights into the source rocks from which they were derived, the restitic materials that must have been produced as a result of magma generation, and the tectonic processes that operated during the Archaean. Geochemically, the TTGs are typically low- to medium-K, metaluminous I-type granitoids. Their chondrite-normalised rare-earth-element (REE) patterns show two trends. The majority of plutons are LREE-enriched and HREE-depleted (indicating the presence of garnet during magma genesis), with small or no Eu anomalies. The Steynsdorp and Doornhoek plutons, however, are relatively HREE-undepleted and have significant Eu anomalies. Highly scattered major- and trace-element trends against SiO[sub]2 imply that the TTG magmas were derived from heterogeneous sources. Nd isotope analyses show that the 3.4 Ga TTGs have positive [epsilon][sub]Nd values (O to +3.7), similar to the oldest greenstone belt formations of the Onverwacht. This indicates a juvenile crustal source for these oldest granitoids. In contrast, the 3.2 Ga TTGs have negative [epsilon][sub]Nd (O to -2.48), suggesting input from a more evolved crust. Partial melting experiments on greenstone amphibolite have been used to constrain the source-rocks of the TTGs. The results showed that granodioritic melts can be produced at 1.6 GPa, and 1000 °C, coexisting with eclogitic mineral assemblages of Grt + Opx + Cpx. Furthermore, the minimum pressure for the appearance of garnet has been constrained to 1.52 ± 0.05 GPa, corresponding to a depth of 52 ± 2 km. This has important implications, because it suggests that the majority of the TTG rocks were derived from greenstone amphibolite material at depths that correspond to greatly thickened mafic crust. The GMS rocks are medium- and high-K, metaluminous to slightly-peraluminous, I-type granitoids. They display two different groups of REE patterns. Medium-K GMS rocks (the Dalmein and Heerenveen monzogranite) are LREE-enriched and HREE-depleted, with no Eu-anomalies, whereas the high-K GMS rocks (Heerenveen granodiorites, Mpuluzi and Boesmanskop) are relatively HREE-enriched, with negative Eu anomalies. These indicate that the majority of the GMS magmas were derived at shallower crustal depths than the TTGs, after a period of post-orogenic, crustal thinning. Scattered major- and trace-element trends against SiO[sub]2, particularly in the Dalmein, Heerenveen and Mpuluzi plutons, suggest that their sources were heterogeneous. The Boesmanskop syenite has both positive and negative [epsilon][sub]Nd values (-4.4 to +4.8) implying that its source was mixed, containing both depleted-mantle and crustal components. Material such as alkali basalt magma and TTG-rich crust are considered to be likely source components. Contemporaneous emplacement of the Mpuluzi batholith and the Boesmanskop syenite suggests that the more potassic batholithic granitic magmas must have formed in the same tectonomagmatic setting as the syenite-granite complex. Zircon morphological and geochemical studies were undertaken to determine whether the TTG rocks were involved in the formation of the GMS rocks. However, the results were inconclusive. The local TTG rocks (or materials similar to them) may have been present in the source of the GMS magmas, but this cannot be demonstrated presently. Petrogenetic models for the magmas strongly suggest the operation of subduction in the Archaean, particularly as a driving force for collision and crustal thickening. The generation of TTG magmas is known to have occurred during periods of terrane collision or accretion (at ~3.50 and 3.23 Ga). Additionally, the results of the experimental studies show that the crust must have reached thicknesses of ~ 52 km to produce TTG magmas. The fact that there is strong evidence that mafic greenstone amphibolite rocks are the source-rocks of the TTG magmas implies that the TTG rocks were only derived from mafic oceanic crust. The petrogenesis of GMS rocks is more difficult to constrain. They were generated during periods of crustal thinning and strike-slip activity. The proposed petrogenetic model involves upwelling alkali basaltic magma, which induced partial melting of the TTG crust. Mixing of the crustal and mantle-derived magmas produced hybrids, and subsequent fractional crystallisation generated the monzogranitic/granodioritic magmas, as well as residual syenitic liquids.
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Wiemer, Daniel. „Tectonic evolution of the Early Archaean Doolena Gap Greenstone Belt, East Pilbara Terrane, Western Australia“. Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/102985/1/Daniel_Wiemer_Thesis.pdf.
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This thesis examined how the oldest core of the Australian continent formed more than 3.5 billion years ago. Unraveling the complex tectonic and petrologic history of ancient rocks of the East Pilbara in Western Australia provided important new insights into how and why continents developed on our hot, young planet. A multifaceted methodology of field-based structural geology, uranium-lead (U-Pb) dating of zircon, whole-rock geochemistry, and petrology improved our understanding of early Archaean mass and heat transfer, including the history of the associated planetary surface environment, which hosted some of the earliest life on Earth.
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Rivard, Benoit. „Petrochemistry of a layered Archean magma chamber and its relation to models of basalt evolution“. Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66046.
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Guevara, Victor Emmanuel. „How Hot, How Deep, How Long: Constraints on the Tectono-Metamorphic Evolution of Granulite Terranes“. Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77915.
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Granulites are the dense, strong metamorphic rocks that are produced during high- (HT) to ultrahigh-temperature metamorphism (UHT) and partial melting of Earth's crust. Granulites are ubiquitous in exhumed Archean cratons and are thought to comprise much of Earth's stable lower crust. Understanding the mechanisms responsible for crustal heating in Archean terranes is thus paramount to understanding the stabilisation of early continental crust, and whether such mechanisms resemble modern tectonic processes. It is therefore important to quantify the pressure–temperature–time (P–T–t) paths of Archean granulites, as such paths can be diagnostic of heating mechanism. This dissertation explores: 1) novel approaches to reconstructing the P–T–t paths of granulites, and 2) what the deciphered P–T–t paths of rocks from two Archean granulite terranes reveal about Archean crustal heating. The first chapter shows how petrologic modelling at multiple scales from a texturally heterogeneous granulite can provide "snapshots" of the P–T path, which would be difficult to reconstruct otherwise. The remaining chapters are focused on reconstructing the P–T–t paths of two Archean granulite terranes: the Beartooth Mountains, and the Pikwitonei granulite domain (PGD). The second and third chapters present evidence for cryptic HT metamorphism of the Beartooth granulites at ~2.7 Ga characterized by rapid (< 1 Ma) exhumation at HT and fast cooling (~10-100 C/Ma) in the middle crust. This suggests advective/conductive heating over short length-scales. In the fourth chapter, thermobarometric data suggest the western PGD experienced UHT decompression followed by cooling in the lower crust. High-precision zircon and monazite dates reveal apparently episodic crystallization over at least ~24 Ma. This episodicity could reflect multiple thermal cycles or the control of local reactions on zircon/monazite crystallization during cooling. High-spatial resolution petrochronology provides temporal constraints on prograde metamorphism. These data suggest metamorphism in the PGD was driven by a long-lived heat source over large length-scales near the base of the lithosphere. Disparities in the timescales, length-scales, and the depth and amount of heating between the terranes may suggest different crustal heating mechanisms in each, and that the late Archean Earth may have been tectonically diverse.Ph. D.
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Shannon, Andrew J. „Volcanic framework and geochemical evolution of the Archean Hope Bay Greenstone Belt, Nunavut, Canada“. Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/741.
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Part of the Slave Structural Province, the Hope Bay Greenstone Belt is a 82 km long north-striking sequence of supracrustal rocks dominated by mafic volcanic rocks with lesser felsic volcanic and sedimentary rocks. Mapping of two transects in the southern section and two transects in the northern section have contributed to a robust stratigraphic framework the belt. Three recently discovered Archean lode gold deposits in the Hope Bay Greenstone belt have associations with major structures and specific lithologies (Fe-Ti enriched basalts).
The Flake Lake and the Clover Transects are in the southern part of the belt and the Wolverine and Doris-Discovery Transects are in the northern part of the belt. This work subdivides the volcanic rocks into distinct suites based upon field, petrologic, geochemical, and geochronologic criteria. Some of the suites are stratigraphically continuous and can be correlated tens of kilometres along strike thereby linking the two parts of the Hope Bay Greenstone Belt.
U-Pb geochronology supports work by Hebel (1999) concluded that virtually all the supracrustal rocks in the Hope Bay Greenstone Belt were deposited over at least 53 m.y. (2716-2663 Ma), with the majority of the volcanism occurring after 2700 Ma.
A number of basalt groups are identified and include the normal basalt, the LREE-enriched basalt, the Ti-enriched basalt and the Ti-enriched Al-depleted basalt groups. They have chemical signatures that vary in trace elements particularly HFSE and REE’s, and can be easily be distinguished by geochemical screening. The felsic volcanic suites are also divided into three main groups, tholeiitic rhyolite, calc-alkaline dacite and calc-alkaline rhyolite groups. Nd and Hf isotope signatures are consistent with trace element signatures in identifying mafic and felsic volcanic groups, with the tholeiitic rhyolite showing highly variable signature.
The Hope Bay Greenstone Belt has been show to have a number of felsic and volcanic cycles. An early construction phase of the belt is made up of primarily mafic volcanics which is followed by felsic volcanism equalled mafic volcanism which lacks basalts enriched in Ti. The geodynamic environment that created the Hope Bay Greenstone Belt can be explained by plume influenced subduction zone.
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Bouhallier, Hugues. „Evolution structurale et métamorphique de la croûte continentale archéenne (craton de Dharwar, Inde du sud)“. Rennes 1, 1994. https://tel.archives-ouvertes.fr/tel-00619323.
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Sperber, Steven M. „Regulation, function and evolution of the Distal-less-related genes in the pharyngeal arches“. Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/29169.
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The vertebrate Dlx homeodomain-containing genes are generally organized as three convergently transcribed bigene clusters. Paired genes share highly conserved overlapping expression patterns in the forebrain, the pharyngeal arches, sensory placodes and limb/fin buds. Little is known about how the Dlx genes are targeted to their sites of expression, or what particular roles individual genes play in development. In the pharyngeal arches, Dlx genes are expressed in a nested manner, which defines proximodistal identity. We identified two distinct cis-acting enhancers, I12a and I56i situated between Dlx1/2 and Dlx5/6 pairs respectively that regulate expression in the mandibular arch. In transgenic animals, the two enhancers targeted reporter gene expression to distinct populations of mesenchymal cells in the mandibular arch. Both enhancers responded to epithelial signaling cues, such as FGF8 and BMP4, similar to endogenous Dlx genes. Therefore, the combinatorial arch expression is achieved through interaction between signaling factors and intrinsic cellular factors. To investigate the individual roles of the paired Dlx1/2 gene in patterning the pharyngeal arches, we silenced zebrafish dlx1a and dlx2a using morpholino antisense oligonucleotides. Loss of dlx2a function in zebrafish embryos resulted in reductions of arch neural crest markers as well as perturbation of neurogenic and chondrogenic derivatives. Loss of dlx1a resulted in malformations of cartilage elements indicating a role in arch patterning. To explore further the evolution of the Dlx gene family, we characterized the Distal-less homologue, Odidll, in the protochordate species, Oikopleura dioica. Odidll is not part of a bigene cluster suggesting either that a paralogue was lost or that the tandem duplication event occurred subsequent to the species' divergence. Odidll, was expressed in ectodermally-derived tissues suggesting a role that may have been observed in a common chordate ancestor. These results contribute to our understanding of Dlx regulation, function and evolution.
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Yamashita, Katsuyuki. „Origin and evolution of mid- to late-Archean crust in the western Slave province, Canada“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/NQ29128.pdf.
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Fedo, Christopher M. „Geologic evolution of the Archean Buhwa Greenstone Belt and surrounding granite-gneiss terrane, southcentral Zimbabwe“. Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164845/.
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Jansson, Anna Maria, und Anna Maria Jansson. „Stratigraphy, Landscape Evolution, and Past Environments at the Billy Big Spring Site, Montana“. Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/626384.
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This thesis reconstructs the landscape evolution of the Billy Big Spring site (24GL304, Glacier County, north-central Montana) from the last glacial maximum to present through the analysis of sediment and soil samples collected from a transect of auger tests that bisected the site and surrounding landforms. Interpretations were drawn from stratigraphy, pedologic data, sedimentologic analysis and radiocarbon dating. The site landscape came into being in the late-Pleistocene, after Wisconsin-age glaciers retreated. Glacial retreat left a meltdown depression on the land that filled with water to form a pond, which persisted through the early-Holocene. The onset of the mid-Holocene (Altithermal) occurred before ~8,415 cal. yrs. BP, when increasingly arid conditions caused the water level to drop. The first radiocarbon dated human occupation of this site occurred during the Altithermal, ~7,030 cal. yrs. BP, after the eruption of Mount Mazama (~7,633 cal. yrs. BP). Arid conditions continued until ~7,000 cal. yrs. BP, when pond water re-expanded across the basin, marking the transition to the cooler late-Holocene. Sometime before 2,100 cal. yrs. BP, dry conditions returned, and the extent of the pond water decreased again. Since this time, overland alluvial processes have deposited sediments in the basin. Many hypotheses on how the Altithermal impacted the people of the Northwestern Plains have been proposed since the 1950s, but little agreement has been reached. This is due to the fact that there was great variation in how the Altithermal expressed itself throughout the Northwestern Plains. The human reactions to this phenomena cannot be explained simplistically for the region as a whole. This study shows that the Billy Big Spring site experienced drying during the Altithermal, but despite this, people continued to occupy this site. This evidence adds to the argument that the Altithermal climate of the Northwestern Plains did not have severe enough impacts to impose much hardship on its occupants.
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Rich, Benjamin H. „An investigation of the Archaean Wangary Gneiss and its relevance to the evolution of the southern Gawler Craton /“. Title page, abstract and contents only, 2000. http://web4.library.adelaide.edu.au/theses/09SB/09sbr498.pdf.
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Green, Michael Godfrey. „Early Archaean crustal evolution: evidence from ~3.5million year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia“. Thesis, The University of Sydney, 2001. http://hdl.handle.net/2123/505.
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In the Pilgangoora Belt of the Pilbara Craton, Australia, the 3517 Ma Coonterunah Group and 3484-3468 Ma Carlindi granitoids underlie the 3458 Ma Warrawoona Group beneath an erosional unconformity, thus providing evidence for ancient emergent continental crust. The basalts either side of the unconformity are remarkably similar, with N-MORB-normalised enrichment factors for LILE, Th, U and LREE greater than those for Ta, Nb, P, Zr, Ti, Y and M-HREE, and initial e(Nd, Hf) compositions which systematically vary with Sm/Nd, Nb/U and Nb/La ratios. Geological and geochemical evidence shows that the Warrawoona Group was erupted onto continental basement, and that these basalts assimilated small amounts of Carlindi granitoid. As the Coonterunah basalts have similar compositions, they probably formed likewise, although they were deposited >60 myr before. Indeed, such a model may be applicable to most other early Pilbara greenstone successions, and so an older continental basement was probably critical for early Pilbara evolution. The geochemical, geological and geophysical characteristics of the Pilbara greenstone successions can be best explained as flood basalt successions deposited onto thin, submerged continental basement. This magmatism was induced by thermal upwelling in the mantle, although the basalts themselves do not have compositions which reflect derivation from an anomalously hot mantle. The Carlindi granitoids probably formed by fusion of young garnet-hornblende-rich sialic crust induced by basaltic volcanism. Early Archaean rocks have Nd-Hf isotope compositions which indicate that the young mantle had differentiated into distinct isotopic domains before 4.0 Ga. Such ancient depletion was associated with an increase of mantle Nb/U ratios to modern values, and hence this event probably reflects the extraction of an amount of continental crust equivalent to its modern mass from the primitive mantle before 3.5 Ga. Thus, a steady-state model of crustal growth is favoured whereby post ~4.0 Ga continental additions have been balanced by recycling back into the mantle, with no net global flux of continental crust at modern subduction zones. It is also proposed that the decoupling of initial e(Nd) and e(Hf) from its typical covariant behaviour was related to the formation of continental crust, perhaps by widespread formation of TTG magmas.
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Green, Michael Godfrey. „Early Archaean crustal evolution: evidence from ~3.5million year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia“. University of Sydney. Geosciences, 2001. http://hdl.handle.net/2123/505.
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In the Pilgangoora Belt of the Pilbara Craton, Australia, the 3517 Ma Coonterunah Group and 3484-3468 Ma Carlindi granitoids underlie the 3458 Ma Warrawoona Group beneath an erosional unconformity, thus providing evidence for ancient emergent continental crust. The basalts either side of the unconformity are remarkably similar, with N-MORB-normalised enrichment factors for LILE, Th, U and LREE greater than those for Ta, Nb, P, Zr, Ti, Y and M-HREE, and initial e(Nd, Hf) compositions which systematically vary with Sm/Nd, Nb/U and Nb/La ratios. Geological and geochemical evidence shows that the Warrawoona Group was erupted onto continental basement, and that these basalts assimilated small amounts of Carlindi granitoid. As the Coonterunah basalts have similar compositions, they probably formed likewise, although they were deposited >60 myr before. Indeed, such a model may be applicable to most other early Pilbara greenstone successions, and so an older continental basement was probably critical for early Pilbara evolution. The geochemical, geological and geophysical characteristics of the Pilbara greenstone successions can be best explained as flood basalt successions deposited onto thin, submerged continental basement. This magmatism was induced by thermal upwelling in the mantle, although the basalts themselves do not have compositions which reflect derivation from an anomalously hot mantle. The Carlindi granitoids probably formed by fusion of young garnet-hornblende-rich sialic crust induced by basaltic volcanism. Early Archaean rocks have Nd-Hf isotope compositions which indicate that the young mantle had differentiated into distinct isotopic domains before 4.0 Ga. Such ancient depletion was associated with an increase of mantle Nb/U ratios to modern values, and hence this event probably reflects the extraction of an amount of continental crust equivalent to its modern mass from the primitive mantle before 3.5 Ga. Thus, a steady-state model of crustal growth is favoured whereby post ~4.0 Ga continental additions have been balanced by recycling back into the mantle, with no net global flux of continental crust at modern subduction zones. It is also proposed that the decoupling of initial e(Nd) and e(Hf) from its typical covariant behaviour was related to the formation of continental crust, perhaps by widespread formation of TTG magmas.
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Skulski, Thomas. „The tectonic and magmatic evolution of the central segment of the Archean La Grande greenstone belt, central Québec /“. Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65986.
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Ghassemi, Mohammad Reza. „Tectonic evolution of the Late Archean Pontiac Subprovince, Superior Province, Canada: Structural, metamorphic, and geochronological studies“. Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/9932.
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The Pontiac Subprovince is a Late Archean (ca. 2.7 Ga) metasedimentary-metavolanic-granitoid-gneiss terrane situated along the southeastern margin of the Superior Province in Quebec. Detailed structural study of the northwestern part of this amphibolite facies metasedimentary belt has revealed a protracted history of deformation in Late Archean and Early Proterozoic time. An early contractional event (D$\sb1$) resulted in development of steep foliations now preserved as folded or straight relics within microlithons of S$\sb2$ foliation. During this stage, the Cadillac-Larder Lake fault zone acted as a major fault zone along which greenstones for the Abitibi Subprovince were thrust over the Pontiac Subprovince. Regional metamorphism resulted from both thickening of the crust, and intrusion of voluminous I-type graintes. D$\sb2$ structures record peak metamorphic high-temperature deformation of the crustal rocks during which large-scale D$\sb2$ nappes moved towards the south-southeast. The basal thrust faults of these nappes are preserved as high-strain shear zones within the study area. Second order east-trending recumbent F$\sb2$ folds, a penetrative S$\sb2$ crenulation foliation, and a north-northwest-trending L$\sb2$ elongation lineation are other important structures of this deformational event. A later D$\sb3$ contractional event superimposed east-trending upright folds on all earlier structures. Extensional D$\sb4$ structures are associated with reactivation of the Cadillac-Larder Lake fault zone as a normal fault zone, and are only recorded in or close to normal faults within this fault zone. Finally, brittle D$\sb5$ thrust faults and kink structures are superimposed on all older structures in the northwestern Pontiac Subprovince. Gneisses of the Lac Opasatica area record pre-D$\sb1$ penetrative structures that are not present within the other rock types of the study area. Increasing metamorphic grade from biotite zone to sillimanite zone is evident from north (the Cadillac-Larder Lake fault zone) to south in the study area, close to outcrops of the S-type granites. Thermobarometry of samples from the study area indicates that regional metamorphism of the rocks in the northwestern Pontiac Subprovince occurred at about 590$\sp\circ$C and 6.2 kbar. Investigation of the metamorphic and structural history of these Late Archean rocks suggests a clockwise PT path similar to that of Phanerozoic collisional belts. $\sp{40}$Ar/$\sp{39}$Ar age constraints from this study combined with other geochronologic indicate a slow cooling rate of about 2$\sp\circ$ to 6$\sp\circ$C/Ma, and reveal that temperatures as high as 350$\sp\circ$C and 280$\sp\circ$C were persistent in crustal rocks of the area until ca. 150 Ma after attainment of peak metamorphic conditions. (Abstract shortened by UMI.)
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Green, Michael Godfrey. „Early archaean crustal evolution evidence from 3̃.5 billion year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia /“. Connect to full text, 2001. http://hdl.handle.net/2123/505.
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Thesis (Ph. D.)--University of Sydney, 2002.Title from title screen (viewed Apr. 23, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Geosciences, Division of Geology and Geophysics. Degree awarded 2002; thesis submitted 2001. Includes bibliography. Also available in print form.
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Evins, Paul M. „Structural evolution of the Twilight-Mystery Lakes gneiss domes in the Archean Winnipeg River Subprovince, northwest Ontario“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0017/MQ53461.pdf.
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Stevenson, Ross Kelley. „Implications for the evolution of continental crust from hafnium isotope systematics of detrital zircons in Archean sandstones“. Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184895.
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The fractionation of zircons by sedimentary processes into continental margin sandstone deposits results in a biased preservation of pre-existing continental crust in the form of zircon in those sequences. This provides a unique opportunity to distinguish between the contrasting theories of episodic growth versus constant volume of continental crust over geologic time through Hf isotope ratios of detrital zircons. ¹⁷⁶Hf/¹⁷⁷Hf ratios were determined for detrital zircon fractions from 2.6-3.0 Ga old sedimentary sequences from the Canadian Shield, North Atlantic, Wyoming, and Kaapvaal Cratons. Hf T(CHUR) ages are less than 3.0 Ga and ε(Hf) values are positive or slightly negative at the time of deposition for most of the Malene, Canadian Shield, Wyoming and upper portions of the Kaapvaal sediments. Notable exceptions are basal samples of the Pongola (3.32 Ga), Dominion (3.11 Ga) and Witwatersrand (3.13 Ga), an arkose from Michigan (3.20 Ga) and one Malene sample (2.97 Ga), all of which either unconformably overlie or are closely associated with pre-3.0 Ga crust. Nd data for shales from the same sequences in the Canadian Shield and Kaapvaal sequences mimic the Hf results. The late Archean sequences appear to be dominated by zircon populations of late Archean age. Hf model ages, from pre-3.0 Ga strata (Upernavik of Labrador and quartzites from Montana), range from 3.1 to 3.6 Ga and are broadly consistent with ages of coexisting volcanics or intrusives, suggesting little inheritance of significantly older material. 2.0-2.5 Ga old quartzites from the Canadian Shield, Wyoming and South Africa have 2.58 to 2.84 Ga model Hf ages indicative of a large expanse of late Archean crust exposed at the time of deposition. The data strongly suggest inheritance of pre-3.0 Ga zircons only in areas where pre-3.0 Ga old crust exists today, and imply that the quantity of continental crust prior to 3.0 Ga ago was not much greater in extent than the pre-3.0 Ga crust exposed today. Small amounts of continental crust prior to 3.0 Ga ago and rapid addition of continental crust between 2.5 and 3.0 Ga ago are consistent with the episodic growth theory of crustal evolution.
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TUCCI, Serena. „Lost worlds: tales of archaic hominin admixture in Southeast Asia and Oceania“. Doctoral thesis, Università degli studi di Ferrara, 2016. http://hdl.handle.net/11392/2403221.
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Sebbene studi recenti abbiano contribuito a far luce su alcuni aspetti dell’interazione tra uomo anatomicamente moderno e forme umane arcaiche, come Neandertal e Denisova, sappiamo ancora ben poco riguardo all’interazione tra popolazioni di nostri antenati e altre forme umane oggi estinte – come ad esempio l’enigmatico Homo floresiensis – con cui siamo convissuti per migliaia di anni. In questo progetto abbiamo analizzato il genoma completo (coverage ~40x) di 10 individui appartenenti ad una popolazione pigmea dell’isola di Flores, in Indonesia orientale. Il villaggio abitato da questa popolazione si trova nelle vicinanze della grotta di Liang Bua dove i fossili di H.floresiensis sono stati rinvenuti, e i suoi abitanti presentano delle caratteristiche morfologiche in comune con H. floresiensis. Abbiamo analizzato questi dati - che rappresentano anche i primi dati di genomi complete dell’Indonesia ottenuti finora - utilizzando un approccio recentemente sviluppato che consente di identificare DNA ereditato a seguito di ibridazione con specie umane arcaiche, senza la necessita’ di conoscere il genome della specie arcaica. Le nostre analisi hanno rivelato la presenza nei pigmei di Flores, di regioni genomiche divergenti, che potrebbero derivare da ibridazione con H. floresiensis e che potrebbero quindi contribuire a fornire una nuova visione della nostra interazione con specie estinte, in questa regione del mondo che e’ stata cruciale per la nostra evoluzione – e dove non e’ possibile, al momento, ottenere DNA da resti fossili. Infine, abbiamo applicato lo stesso approccio a dati di genomi completi di 1,523 individui di diverse popolazioni mondiali, che includono 35 nuovi genomi Melanesiani da noi prodotti, con lo scopo di identificare sequenze ereditate dall’ibridazione con Neandertal e Denisova. Abbiamo mostrato che l’ibridazione con i Neandertal sarebbe avvenuta numerose volte in diverse popolazioni non-Africane, abbiamo caratterizzato regioni genomiche che appaiono significativamente impoverite di sequenze arcaiche, ed infine abbiamo identificato la presenza di introgressione adattativa in questi genomi.Although recent genetic findings have contribuited to shed light on some aspects of the interaction between anatomically modern humans and archaic hominin forms, such as Neandertals and Denisovans, very little is known about the interaction between our ancestors and other extinct species - such as the enigmatic Homo floresiensis - with which they co-existed for thousands of years. Here we analyzed 10 new high coverage genomes (~40x) from a pygmy population in the Island of Flores (Eastern Indonesia). This village is near where remains of H. floresiensis were found and its people have been reported to have morphological similarities to Homo florensiensis. We used a newly developed approach to identify DNA inherited from archaic hominin ancestor, which does not rely on ancient genomes. Moreover, our data represent to date the first complete genomes from Indonesia. Our analysis revealed the presence of highly divergent genomic regions in the Flores pygmies, that might result from past admixture with H. floresiensis, and contribuited to provide new insights on the landscape of hominin interactions in this part of the world crucial for our evolutionary history – where ancient DNA work may not be tractable. Finally, we applied the same approach to whole-genome sequences from 1,523 geographically diverse individuals, including 35 new Island Melanesian genomes with the goal of identifying sequences inherited from Neandertals and Denisovans. We showed that Neandertal admixture occurred multiple times in different non-African populations, we characterized genomic regions that are significantly depleted of archaic sequence, and identified signatures of adaptive introgression.
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Groussin, Mathieu. „Résurrection du passé à l’aide de modèles hétérogènes d’évolution des séquences protéiques“. Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10201/document.
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La reconstruction et la résurrection moléculaire de protéines ancestrales est au coeur de cette thèse. Alors que les données moléculaires fossiles sont quasi inexistantes, il est possible d'estimer quelles étaient les séquences ancestrales les plus probables le long d'un arbre phylogénétique décrivant les relations de parentés entre séquences actuelles. Avoir accès à ces séquences ancestrales permet alors de tester de nombreuses hypothèses biologiques, de la fonction des protéines ancestrales à l'adaptation des organismes à leur environnement. Cependant, ces inférences probabilistes de séquences ancestrales sont dépendantes de modèles de substitution fournissant les probabilités de changements entre acides aminés. Ces dernières années ont vu le développement de nouveaux modèles de substitutions d'acides aminés, permettant de mieux prendre en compte les phénomènes biologiques agissant sur l'évolution des séquences protéiques. Classiquement, les modèles supposent que le processus évolutif est à la fois le même pour tous les sites d'un alignement protéique et qu'il est resté constant au cours du temps lors de l'évolution des lignées. On parle alors de modèle homogène en temps et en sites. Les modèles récents, dits hétérogènes, ont alors permis de lever ces contraintes en permettant aux sites et/ou aux lignées d'évoluer selon différents processus. Durant cette thèse, de nouveaux modèles hétérogènes en temps et sites ont été développés en Maximum de Vraisemblance. Il a notamment été montré qu'ils permettent d'améliorer considérablement l'ajustement aux données et donc de mieux prendre en compte les phénomènes régissant l'évolution des séquences protéiques afin d'estimer de meilleurs séquences ancestrales. A l'aide de ces modèles et de reconstruction ou résurrection de protéines ancestrales en laboratoire, il a été montré que l'adaptation à la température est un déterminant majeur de la variation des taux évolutifs entre lignées d'Archées. De même, en appliquant ces modèles hétérogènes le long de l'arbre universel du vivant, il a été possible de mieux comprendre la nature du signal évolutif informant de manière non-parcimonieuse un ancêtre universel vivant à plus basse température que ses deux descendants, à savoir les ancêtres bactériens et archéens. Enfin, il a été montré que l'utilisation de tels modèles pouvait permettre d'améliorer la fonctionnalité des protéines ancestrales ressuscitées en laboratoire, ouvrant la voie à une meilleure compréhension des mécanismes évolutifs agissant sur les séquences biologiquesThe molecular reconstruction and resurrection of ancestral proteins is the major issue tackled in this thesis manuscript. While fossil molecular data are almost nonexistent, phylogenetic methods allow to estimate what were the most likely ancestral protein sequences along a phylogenetic tree describing the relationships between extant sequences. With these ancestral sequences, several biological hypotheses can be tested, from the evolution of protein function to the inference of ancient environments in which the ancestors were adatapted. These probabilistic estimations of ancestral sequences depend on substitution models giving the different probabilities of substitution between all pairs of amino acids. Classicaly, substitution models assume in a simplistic way that the evolutionary process remains homogeneous (constant) among sites of the multiple sequence alignment or between lineages. During the last decade, several methodological improvements were realised, with the description of substitution models allowing to account for the heterogeneity of the process among sites and in time. During my thesis, I developed new heterogeneous substitution models in Maximum Likelihood that were proved to better fit the data than any other homogeneous or heterogeneous models. I also demonstrated their better performance regarding the accuracy of ancestral sequence reconstruction. With the use of these models to reconstruct or resurrect ancestral proteins, my coworkers and I showed the adapation to temperature is a major determinant of evolutionary rates in Archaea. Furthermore, we also deciphed the nature of the phylogenetic signal informing substitution models to infer a non-parsimonious scenario for the adaptation to temperature during early Life on Earth, with a non-hyperthermophilic last universal common ancestor living at lower temperatures than its two descendants. Finally, we showed that the use of heterogeneous models allow to improve the functionality of resurrected proteins, opening the way to a better understanding of evolutionary mechanisms acting on biological sequences
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Bouhallier, Hughes. „Evolution structurale et métamorphique de la croûte continentale archéenne ( craton de Dherwar, Inde du Sud)“. Phd thesis, Université Rennes 1, 1994. http://tel.archives-ouvertes.fr/tel-00619323.
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Le but de cette thèse est de caractériser l'évoiution tectono-métamorphique d'un segment de croûte continentale drchéenne (> 2.5 Ga). L'objet étudié est le craton de Oharwar (Inde du Sud) qui présente, du Nord vers le Sud, une transition continue de niveaux structuraux de plus en plus profonds. Cette région n'est affectée par aucune déformation post-archéenne. Nous montrons que les champs de déformation mis en évidence résultent de l'interférence entre le développement d'instabilités gravitaires diapiriques et un raccourcissement régional. Toutes les structures d'échelle crustale résultantes (diapirs et décrochements) sont générées au cours d'un seul et même événement que nous avons daté aux environs de 2.5 Ga. Elles sont contemporaines (i) d'un épisode de formation de croûte continentale juvénile (batholite du Closepet), (ii) d'un métamorphisme régional parfois intense (migmatisation, granulitisation). La cartographie des champs de déformation nous permet d'infirmer la présence de structures chevauchantes ou d'un empilement caractéristique des zones de collision continentale modernes. L'étude pétrographique révèle que seules certaines zones diapiriques dont la * subsidence a été la plus rapide ont enregistré une évolution prograde avec une augmentation de pression de 3 à 7-8 kbar. De plus, ces régions montlent une hétérogénéité dans la composition de la phase fluide qui semble être associée à une différence de perméabilité induite par la nature et l'orientatiôn des textures des roches métamorphiques. En conclusion, la croûte continentale archéenne du craton de Dharwar ne montre pas de structure tectonique susceptible d'avoir généré un épaississement crusta: important. Sa déformation est due principalement à des forces de volume (diapirisme) et, dans une moindre mesure, à des forces de surface (décrochements). Le développement d'instabilités gravitaires diapiriques, parce qu'il affecte des volumes de croûte considérables et qu'il ne peut être rapporté à aucune évidence structurale d'épaississement crustal, constitue une particularité de la tectonique de l'Archéen.
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Xie, Qianli. „Trace element systematics of mafic-ultramafic volcanic rocks from the Archean Abitibi greenstone belt, Canada, implications for chemical evolution of the mantle and archean greenstone belt development“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24020.pdf.
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Oliver, Hazel S. „The geochemical and tectono-magmatic evolution of the volcanic and intrusive rocks of the Archaean Shining Tree greenstone belt, Abitibi subprovince, Ontario, Canada“. Thesis, University of Portsmouth, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271459.
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Papineau, Dominic. „The rise of atmospheric oxygen and the evolution of the sulfur and nitrogen cycles on the Archean and Paleoproterozoic Earth“. Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3207686.
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Wasilewski, Benjamin. „Geochronology, Petrogenesis and Crustal Evolution of the Saglek-Hebron Complex (Northern Labrador): Over One Billion Years of Archean Geological History“. Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39617.
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The Saglek-Hebron Complex (SHC) in Northern Labrador represents one of the oldest terrains on Earth and it is closely related to the Archean Itsaq Gneiss Complex (IGC) in Greenland. The SHC is a typical granite-greenstone terrain that recorded over one billion years of magmatic history between ~3900 Ma and ~2700 Ma. Our geochronological and geochemical study shows that the SHC includes five generations of trondhjemite-tonalite-granodiorite suites (TTG): the ~3870 Ma Iqaluk gneiss, the ~3750 Ma Uivak I gneiss, the ~3600 Ma Uivak II gneiss, the newly described ~3300 Ma Iluilik gneiss, and the ~3220 Ma Lister gneiss. These granitoid units are mostly consist of trondhjemite and tonalite with only rare granodiorites that appear to define a distinct unit formed at ~3330 Ma and newly defined as the Iluilik gneiss. The Iluilik granodiorite appears to be derived from a Hadean mafic crust as supported by its combined whole-rock geochemical composition, its positive µ142Nd value of +6, and its low εHf= -6 and εNd= -3, at 3300 Ma. SHC granites were emplaced throughout the Archean, from 3800 to 2700 Ma, but are predominant in the Neoarchean. They appear to have been mainly formed from the reworking of the SHC TTG, as supported by their low εHf and εNd initial values of respectively -16 and -11 at 2700 Ma. The granitoids include numerous enclaves of supracrustal rocks from various size, up to a few kilometers in scale, consisting of metavolcanic metasedimentary rocks. Previous work has suggested that they were formed at two different ages, with the younger Upernavik supracrustal unit deposited around 3400 Ma and the older Nulliak supracrustal assemblage deposited at around 3750 Ma. We show that both units are comparatively geochemically homogeneous with no distinction between the mafic and ultramafic rocks from both supracrustal assemblages. They mainly consist of mafic metavolcanic amphibolites with tholeiitic affinities, consistent with more depleted mafic and more enriched compositions produced by magmatic differentiation. Their complementary Eu anomaly and whole-rock geochemistry suggest that they formed from fractional crystallization of gabbroic assemblage that derived from similar if not the same parental magma. The mafic metavolcanic rocks are also often associated with ultramafic rocks that we divided into two distinct units, respectively referred as the high-Fe and the low-Fe ultramafic rocks, characterized by different FeO contents and Al/Ti ratio. They both represent olivine-rich cumulative rocks derived from distinct parental komatiitic basalt magmas. Our interpretation contrasts with previous work suggesting that the SHC ultramafic rocks were komatiites and slivers of residual lithospheric mantle. Most SHC TTG exhibit a positive 142Nd anomaly, as high as µ142Nd = +15, suggesting a source formed by differentiation in the Hadean. This 142Nd isotopic composition is similar to the Nulliak supracrustal rocks that exhibit on average a µ142Nd of +10. TTG is generally considered to derive from a mafic precursor. This study therefore shows that mafic crustal source of the SHC Eoarchean TTG, potentially the Nulliak metabasalts, derives from an ancient highly depleted mantle, described as the Saglek mantle, sharing a similar early history as the mantle reservoir involved in the formation of the ancient Itsaq terrane of southwest Greenland. The Saglek depleted mantle is interpreted to have formed at ~4400 Ma, exhibit highly depleted signature with a 147Sm/144Nd ratio of 0.221-0.240.
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SESSA, GIANLUCA. „GEOCHEMISTRY OF AMPHIBOLE FROM ARCHEAN AND EARLY PROTEROZOIC ULTRAMAFIC ROCKS: IMPLICATIONS FOR THE SECULAR EVOLUTION OF THE EARTH¿S MANTLE“. Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/609805.
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Since its formation at 4.5 Ga, the Earth underwent a complex evolution that progressively differentiated its original composition into the reservoirs that we presently know. Our knowledge on the composition and differentiation mechanisms active in the Early and Ancient Earth are still fragmentary for the paucity of suitable preserved rock records. The poor knowledge on the Archean mantle composition arises a series of problems spanning from the effective chondritic composition of the Earth to how volatile elements (hydrogen, oxygen, chlorine and fluorine) were added to the Earth. For the unavailability of mantle sectors preserving the Archean geochemical signature, valuable information on the Archean mantle composition can be exclusively extracted from Archean mantle-derived igneous rocks. In the Archean greenstone belts, different products of mantle melting are found as lavas and sills spanning in composition from tholeiites through Fe-picrites to komatiites. All these rocks are generally affected by extensive alteration which prevent the bulk rocks to be fully informative on the primary mantle melt composition and particularly on its volatile element contents. However, in some of these rocks primary igneous mineral phases such as amphibole are preserved that may be useful to constrain the primary melt composition including its volatile budgets.
In this thesis amphibole-bearing ultramafic rocks of late Archean and Early Proterozoic age (Stone et al., 2003; Fiorentini et al., 2004; Fiorentini et al., 2008) were selected. For comparison amphibole-bearing ultramafic rocks from different tectonic settings of the Phanerozoic were also considered. The Archean and Early Proterozoic rocks share many petrographic and textural similarities with hornblendites and amphibole-bearing pyroxenites from Phanerozoic orogenic settings. In all studied rocks the crystallisation of amphibole follows that of the early crystallising minerals: olivine + spinel ± orthopyroxene + clinopyroxene. The chemical composition of Archean and Early Proterozoic amphiboles is more similar to that of amphibole from alkaline lavas than that of amphibole in orogenic settings. The geobarometric calculations on Archean and Early Proterozoic rocks yield large uncertainty on the pressure of crystallisation with values between 0 and >3 Kbar, which are not conclusive about the deep or shallow origin of amphibole. In the Archean and Early Proterozoic rocks amphibole is in clear disequilibrium with the early crystallizing clinopyroxene. Modelling of melt differentiation suggests that amphibole crystallized from a melt percolating the cumulate pile. Such melt evolved by crystallization of olivine and pyroxene and subsequently modified its composition in response to olivine assimilation.
A major problem in the studied Archean and Early Proterozoic rocks is about the origin of the H2O necessary to stabilize amphibole. The H2O concentrations in the Archean and early Proterozoic amphiboles are comparable to those of either subduction-related or amphibole megacrysts from alkaline lavas, thus suggesting that melts in equilibrium with amphiboles possessed almost the same water contents irrespective of age. According to the composition of amphibole in fluid-mobile elements (e.g., F, Cl, B and Sr) a contribution of seawater-derived fluid in the Archean and Early Proterozoic rocks is unlikely. The range of δD values of the Archean and Paleoproterozoic amphiboles is between -99.5 ‰ and -129.8 ‰, that is slightly lower than the mantle range but still consistent with a magmatic origin for water. The hypothesis of a crustal contribution in the origin of the amphiboles (and in turn a crustal origin of water) contrasts with the oxygen isotope signature of amphibole showing δ18O values lighter than those of the mantle. Because the involvement of recycled crustal materials, able to provide the required seawater-like geochemical anomalies, is unlikely for the genesis of the studied amphiboles, the light δ18O signature is interpreted as a primary feature of the mantle source.
In order to monitor possible changes marked by amphibole in the secular evolution of the Earth’s mantle, the trace element composition of the melt in equilibrium with amphibole from Archean and Early Proterozoic rocks was calculated and compared with that of melts produced nowadays at the different geodynamic settings. Equilibrium melts show increasing Nb/Y ratios from komatiites through tholeiites to Fe-picrites that are in agreement with the increased alkalinity of the parental melt as inferred from the literature. All calculated melts share an incompatible trace element pattern paralleling that of present-day OIB. The comparison of the water content in primary melts calculated from Archean-early Proterozoic amphiboles and present-day primary mantle melts reveals that the mantle source of the Archean komatiites had a much higher water content than that characterizing present day OIB. The highly variable water contents in Fe-picrites however suggest a large heterogeneity in the composition of the mantle source. The comparison between the Archean-early Proterozoic amphiboles and those from the Phanerozoic has also revealed heterogeneities in the Nb/Ta ratios of the mantle through the Earth’s history. Some of the calculated melts (since early Proterozoic) show an enriched Nb/Ta signature that is independent from space (geological setting) and time and that was interpreted as a primary feature of the different mantle sources. The observed heterogeneous Nb/Ta signature of the Earth’s mantle was interpreted as related to the addition of extra-terrestrial material after the mantle-core equilibration prior to 4.4 Ga and to an incomplete equilibration of these domains during the Earth’s evolution.
In conclusion, the data of this thesis suggest that the Earth’s mantle is much more heterogeneous than commonly assumed. The occurrence in the Archean and Early Proterozoic of mantle domains enriched in volatile elements but unrelated to subduction processes has been documented. An extra-terrestrial signature for some mantle domains was also reported and I do not exclude that the light oxygen isotope signature of the Archean and Early Proterozoic rocks is also a reminiscence of extra-terrestrial inputs possibly related to the meteoritic Late Veneer.
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Adam, Panagiotis. „Life before oxygen : linking phylogenomics and paleogeochemistry to unravel the nature and function of microbiota in the early Archean“. Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC153.
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Les premières formes de vie sur Terre seraient apparues durant l’Archéen, il y a 4 à 2,5 milliards d’années. Durant cette période, les océans et l’atmosphère étaient anoxiques. Vers la fin de cet éon, la concentration en dioxygène a brusquement augmenté grâce à la photosynthèse, contribuant à la Grande Oxygénation de la Terre. Toutefois, en raison de la rareté des microorganismes fossiles connus, les métabolismes actifs à cette époque restent mal compris. Le fractionnement des isotopes stables du carbone est souvent utilisé comme un critère de biogénicité et pour l’appréciation des voies métaboliques présentes. Ces fractionnements peuvent être le résultat d’au moins six à huit voies de fixation du carbone. Pour étudier l’histoire évolutive des voies de fixation du carbone et de déterminer leur ordre d’émergence, j’ai appliqué une approche phylogénomique sur l’importante diversité microbienne récemment découverte. Le but était d’identifier les voies responsables des signatures isotopiques du carbone datant de l’éon Archéen inférieur (>3,2 milliards d’années). Le premier chapitre constitue une revue récente sur la diversité, l’écologie et l’évolution des Archaea. J’ai construit une phylogénie de référence des Archaea, robuste et incluant un nombre important de nouveaux génomes. Cette phylogénie m’a permis de mettre en évidence de nouveaux clades d’Archaea pour lesquels j’ai proposé des nouveaux noms. De plus, j’ai examiné la distribution des gènes marqueurs classiquement utilisés dans la taxonomie des Archaea. Dans le chapitre 2, j’ai assemblé différents jeux de données pour construire des phylogénies de référence pour les bactéries. Ceci m’a permis de discuter la classification au sein de ce domaine et la position de quelques groupes proches de la racine. Ces phylogénies des Archaea et Bacteria m’ont servi de cadre pour retracer l’évolution des voies de fixation du carbone. J’ai ensuite étudié la voie de Wood-Ljungdahl (WL) qui est considérée comme la forme la plus ancienne de fixation du carbone mais dont les origines restent encore controversées. J’ai assemblé des banques de données locales englobant 6400 génomes et couvrant toute la diversité connue des archées et des bactéries. Ces banques ont été utilisées pour des recherches exhaustives des homologues des enzymes de la branche carbonyle (chapitre 3) et méthyle basée sur la tétrahydrométhanoptérine (H4MPT; chapitre 4) de la voie de WL. Ces analyses m’ont permis d’inférer la présence d’une forme fonctionnelle de la branche carbonyle chez LUCA (Last Universal Common Ancestor). Cette voie a ensuite été héritée verticalement chez les archées et bactéries en gardant la co-localisation de ses gènes, à l’exception de quelques rares transferts intra et inter-domaines. La branche méthyle-H4MPT semble être apparue chez les archées puis transférée aux bactéries chez lesquelles elle serait impliquée dans la syntrophie ou l’assimilation du carbone. A la suite de gains et de pertes de gènes au sein de cette branche, elle a ensuite été successivement adaptée pour la méthylotrophie anaérobie, la détoxification du formaldéhyde, et la méthylotrophie aérobie. Ces résultats indiquant l’origine de la voie de WL à l’Archéen m’ont permis d’interpréter les signatures isotopiques du carbone et d’apporter des éléments sur la composition de l’atmosphère à la fin de cet éon. Enfin, dans le chapitre 5, j’ai étudié l’histoire évolutive des autres voies de fixation du carbone (Calvin-Benson-Bassham, Reductive Hexulose Phosphate, reverse Krebs, 3-hydroxypropionate bicycle, 3-hydroxypropionate/4-hydroxybutyrate, dicarboxylate/4-hydroxybutyrate). Mes résultats préliminaires m’ont permis de discuter la présence possible de ces voies pendant l’ArchéenLife on Earth emerged during the Archean Eon (4-2.5 billion years ago). At the time the oceans and atmosphere were anoxic, and oxygen rose at the end of the Eon as a result of oxygenic photosynthesis, in what is known as the Great Oxygenation Event. Anaerobic microorganisms and metabolisms are expected to have operated at the time. However, the specifics are poorly understood, since the fossil record is scarce. The fractionation of stable carbon isotopes is often used as a criterion of biogenicity but also to interpret possible metabolic processes. Such fractionations can arise from at least six to eight different carbon fixation pathways. I took advantage of the newly available microbial diversity, and applied a phylogenomic approach to elucidate the evolutionary history of carbon fixation pathways, and determine their relative order of emergence. The aim was to deduce which ones would have been responsible for the isotopic signatures in the lower Archean (before 3.2 billion years). In the first Chapter, I reviewed the recent literature on the diversity, ecology, and evolution of Archaea. I constructed a well-resolved reference phylogeny taking into account all the novel lineages, for which genomic information has recently become available. I assigned names to some of them, as well as to some of the taxonomic units that were recovered from the phylogeny. Then I examined the distribution of genes that have been used in the past as taxonomic markers for the Archaea. Similarly, in Chapter 2, I constructed well-resolved bacterial phylogenies using different datasets, and used them to map the distribution of potential marker genes. I then discussed the taxonomic classification of Bacteria above phylum level, and the position of some possibly deep-branching phyla. From these endeavors, I gleaned highly resolved phylogenies of Bacteria and Archaea which were then used to map the evolution of carbon fixation pathways. Next, I analyzed the evolution of the Wood-Ljungdahl pathway. It is believed to be the most ancient form of carbon fixation but its origins have been controversial. I assembled local databanks of over 6400 genomes of Bacteria and Archaea encompassing all their known diversity. These were used to perform exhaustive homology searches for the components of the carbonyl (Chapter 3) and tetrahydromethanoperin (H4MPT; Chapter 4) methyl branches. A functional form of the carbonyl branch was found to date back to the Last Universal Common Ancestor. It was then inherited mostly vertically across Bacteria and Archaea with its genes remaining co-localized, except for a few rare intra and interdomain transfers. The H4MPT branch seems to have originated in Archaea and was subsequently transferred to Bacteria where its original role was probably related with hydrogen syntrophy or as a carbon assimilation electron sink. Afterward, through gene gains and losses linking the branch with other pathways, it came to be used in anaerobic methylotrophy and formaldehyde detoxification, and finally in aerobic methylotrophy. These results highlight a presence of the Wood-Ljungdahl pathway throughout the Archean, and also allow me to discuss possible inferences on the composition of the atmosphere and the interpretation of some late Archean carbon isotopic signatures.Finally, in Chapter 5, I attempt to determine the earliest possible origin for the remaining carbon fixation pathways (Calvin-Benson-Bassham, Reductive Hexulose Phosphate, reverse Krebs, 3-hydroxypropionate bicycle, 3-hydroxypropionate/4-hydroxybutyrate, dicarboxylate/4-hydroxybutyrate), by studying the evolution of their marker genes. I managed to deduce some possible constraints about the presence of these pathways in the Archean. My results contribute to expanding our knowledge on early life, the Last Universal Common Ancestor, and the evolution of carbon fixation. They also shed light on the processes on the Archean Earth from the perspective of microbial evolution
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Flageole, Janick. „Sm-Nd Isotopic Composition of Mantle-Derived Rocks from the Saglek-Hebron Gneiss Complex, Northern Labrador“. Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39208.
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The Saglek-Hebron Gneiss Complex (SHC) is located in Northern Labrador within the Nain Province. It has recorded multiple magmatic events over more than 1 billion years, making it ideal to study the evolution of mantle-derived rocks through time. Here we present a 147Sm-143Nd isotopic study focussing on the different generations of mantle-derived rocks in the SHC. A total of 83 samples have been analysed, including: 1) mafic metavolcanic rocks; 2) ultramafic rocks divided into two distinct groups (a Fe-rich group enriched in incompatible elements and more depleted ultramafic rocks with lower Fe contents); 3) mafic metamorphosed dikes called the Saglek dikes; and 4) undeformed mafic dikes. Some samples exhibit evidence of post-magmatic geochemical and isotopic disturbance but only the least disturbed samples have been considered to constrain the timing of formation of the different lithologies and the isotopic composition of their mantle source. The mafic metavolcanic rocks combined with the co-genetic low-Fe ultramafic rocks yield an isochron age of 3819 ± 190 Ma (MSWD=34, n=25) with an initial εNd value of +2.3 ± 0.6. The high-Fe enriched ultramafic rocks yield a younger age of 3433 ± 220 Ma (MSWD=10.4, n=10) with an initial εNd= +1.8 ± 0.5. The two generations of mafic dikes appear to have been emplaced in the Mesoarchean and the Neoarchean. The Saglek dikes yield an isochron age of 3565 ±120 Ma (MSWD=1.17, n=10) with an initial εNd value of +1.7 ± 0.1, while the Sm-Nd isochron age for the undeformed mafic dikes is 2694 ±79 Ma (MSWD=3.2, n=21) with an initial εNd value of +1.7 ± 0.1. All generations of mantle-derived rocks yield positive initial εNd values, where only the Eoarchean rocks display an initial Nd isotopic composition similar to the depleted mantle. The Mesoarchean ultramafic rocks, Saglek dikes and Neoarchean mafic dikes display almost identical initial εNd values, despite an age difference of ~800 Ma. This could suggest the contribution of distinct mantle sources or, if all generations of mantle-derived rocks in the SHC were produced from the same mantle source, it implies that this source evolved with a nearly chondritic Sm/Nd ratio for almost the whole Archean Eon. The fact that the initial isotopic compositions of the mantle-derived rocks appear to deviate from the depleted mantle with time, could also suggest an increasing interaction with older evolved crust.
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McCuaig, Thompson Campbell. „The genesis and evolution of lode gold mineralization and mafic host lithologies in the late-Archean Norseman Terrane, Yilgarn Block, western Australia“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24001.pdf.
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Moloto-A-Kenguemba, Gaétan Roch. „Evolution géotectonique paléoprotérozoi͏̈que à néoprotérozoi͏̈que de la couverture du craton archéen du Congo aux confins du Congo, du Cameroun et de Centrafrique“. Orléans, 2002. http://www.theses.fr/2002ORLE2034.
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Aux confins du Cameroun, du Congo et de Centrafrique, affleurent des terrains protérozoi͏̈ques mal connus qui recouvrent la bordure septentrionale du craton archéen du Congo. 1/ Ces terrains sont constitués de dépôts détritiques terrigènes interstratifiés par des métavolcanites à composition de tholéiites continentales et de tholéiites de rift initial. L'ensemble est plissé et affecté de décrochement senestre N-S. Le plissement correspond à des plis droits à axe N30ʿ qui décrivent une virgation sub-méridienne le long du grands décrochements. Ces terrains sont attribués au Paléoprotérozoi͏̈que et comparés au Francevillien. 2/ Des petites intrusions de granites calco-alcalins protomylonitiques sont alignés le long du décrochement N-S de la Sangha et de petits pointements de syénite alcaline traversent la couverture. Ces granites ont été datés par Rb/Sr au Mésoprotérozoi͏̈que. La syénite donne un âge modèle TDM (Sm-Nd) à 1,54 Ga. De ce fait, le décrochement de la Sangha est kibarien (ca. 1,3 Ga). 3/ Des dykes de dolérites orientés N130ʿ à N-S recoupent la couverture plissées et les granitoi͏̈des. Elles ont une composition intermédiaire entre les tholéiites continentales et les tholéiites de rift initial et sont rattachées à la phase d'extension pré-pan-africaine d'Afrique centrale, vers 1 Ga. Un isochrone Nd/Sm nous donne : 1213,5±76 Ma. 4/ Des dépôts tillitiques cryogéniens (ca. 720 Ma) sont discordants sur la couverture plissée et les intrusions. Ils sont surmontés par des formations carbonatées néoprotérozoi͏̈ques (650-630 Ma). 5/ Tout cet ensemble est chevauché, vers 630 Ma par la nappe pan-africaine de Yokadouma à semelle d'ultramylonites quartzitiques à séricite-chlorite. L'ensemble de ces résultats et les corrélations régionales permettent de proposer un modèle d'évolution géotectonique du Paléoprotérozoi͏̈que au Néoprotérozoi͏̈que. Nous attribuons le plissement et l'essentiel de la structuration des formations de couverture paléoprotérozoi͏̈que à l'événement Kibarien.
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Lacarce, Eva. „Evolution structurale, minéralogique et géochimique d'une séquence Vertisol - Alfisol : étude dans la zone de transition climatique du sud de l'Inde sur socle Archéen“. Paris 6, 2006. http://www.theses.fr/2006PA066283.
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Dans la zone de transition climatique du sud de l'Inde, des Vertisols noirs et des Alfisols rouges sont associés au sein de petits bassins versants. Quels sont les déterminismes et les mécanismes à l'origine de leur différenciation ? La roche, ici un complexe métamorphique, mais aussi l'eau par les transports de particules ou de solutés et l'ambiance chimique qu'elle induit, peuvent être des facteurs clef. Pour répondre à cette question, une étude multi-scalaire des structures et des constituants du sol, depuis le bassin versant jusqu'au minéral, a été menée sur le bassin versant de Mule Hole. La chimie et la minéralogie des constituants ont été déterminées, finement pour les argiles et les oxydes de fer qui sont respectivement les principaux responsables de la formation d'horizons vertiques et de la couleur des sols. Dans l'altérite, une roche felsique produit des kaolinites et une roche mafique produit des smectites. Ces 2 roches ont contribué à la formation des horizons pédologiques. Néanmoins une forte influence felsique engendre plus de sables de quartz et moins d'argile et gène la formation d'horizons vertiques. Par contre dans les horizons superficiels et vertiques, les smectites subissent une transformation en kaolinite via un interstratifié K/S du fait d'une acidification du sol et de l'épuisement de l'alcalinité que constituent les minéraux primaires altérables. A terme ce processus pourrait aussi induire la transformation des Vertisols. Parallèlement, du fer est libéré des silicates et produit de l'hématite rouge à l'amont qui est drainé et des hydroxydes et des formes amorphes à l'aval
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Mendez, Fernando Luis. „Archaic Introgression And Natural Selection in yhe Evolution Of Modern Humans: A Study of Genetic Variation at the Loci Containing the Immune Genes OAS1 and STAT2“. Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/216971.
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Human populations evolved throughout the Old World for over 1 million years. However, anatomical characteristics of modern humans are thought to have evolved only in Africa in the last 200 thousand years. To this day, the extent to which archaic human populations contributed to the modern human gene pool is largely unknown. This work explores the evidence of genetic contribution from archaic populations at two loci in chromosome 12. Two different archaic humans, Neandertal and Denisova, living respectively in West Eurasia and in East Asia, have been indicated as potential contributors to anatomically modern human populations outside of Africa. This research shows the presence in non-Africans of two distinct introgressive alleles from archaic populations at the immune genes OAS1 and STAT2. In addition to the detection of patterns of genetic variation previously proposed as indicators of genetic introgression from archaic populations, it was possible to use the sequence of archaic individuals to infer a recent common ancestry between the introgressive modern allele and the archaic sequences. The analysis of genetic variation at the genomic region containing the gene STAT2 shows the presence of introgressive Neandertal-like and Denisova-like haplotypes. The elevated frequency in Melanesian populations of the haplotype introgressive from Neandertals suggests that this haplotype has been adaptive in Melanesians (APPENDIX B). A haplotype of the gene OAS1, nearly restricted to Melanesian populations, provides evidence of introgression from a population with genetic affinities to Denisova. The introgressive haplotype carries non-synonymous variants predicted to have functional significance and a block of very deep divergence with the remaining modern sequences (APPENDIX A). A second haplotype, observed mostly in Eurasian populations, shows evidence of having introgressed recently from Neandertals. The Neandertal-like haplotype also contains a block with very deep divergence with the remaining modern sequences (APPENDIX C). Blocks of very deep divergence within introgressive haplotypes suggest an important role of ancient population structure in the evolution of humans.