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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
151

Estruturas transversais às bacias de Taubaté e Resende: natureza e possível continuidade na bacia de Santos, Brasil / Transverse structures in Taubaté and Santos basins: nature and possible continuity in Santos Basin, Brazil

Moura, Thais Trevisani 23 September 2015 (has links)
As bacias de Taubaté e Resende são bacias continentais paleógenas do tipo rift, orientadas segundo a direção NE a ENE e fazem parte do segmento central do Rift Continental do Sudeste do Brasil. Ambas foram instaladas durante o Eoceno, resultantes de um campo de esforços distensivo de direção NW-SE. Este campo reativou zonas de cisalhamento de direção NE do embasamento pré-cambriano como falhas normais, importantes durante a instalação e evolução da bacia. Há também inúmeras estruturas transversais ao eixo da bacia, de direções N-S, NE-SW e NW-SE, as quais compreendem falhas e dobras que estiveram ativas durante diferentes intervalos de tempo, embora seus papeis na evolução da bacia ainda sejam pouco conhecidos. A fim de reconhecer estas estruturas em subsuperfície na Bacia de Taubaté, cinco perfis sísmicos longitudinais ao eixo da bacia foram interpretados, demonstrando o caráter distinto dessas estruturas como falhas normais e inversas, que interceptam diferentes unidades sísmicas, indicando uma deformação tectônica polifásica. A presença de altos estruturais transversais, distinguíveis em perfis sísmicos, ativos durante a abertura da bacia, pode estar relacionada com anticlinais formados na capa das falhas, durante uma evolução relacionada ao crescimento das falhas principais de borda em um regime distensivo de direção NW-SE. Ainda, foram descritas em afloramentos falhas sinsedimentares de componente normal, de direção NW-SE e transversais à Bacia de Resende, dispostas em um alto ângulo com relação à orientação ENE das falhas principais de borda. Estas estruturas foram interpretadas como falhas de alívio formadas no mesmo contexto distensivo. As relações estratigráficas e a análise de paleotensões das populações de falhas indicaram que as estruturas transversais estão relacionadas a quatro eventos deformacionais: compressão NE-SW, provavelmente durante o Mioceno; compressão NW-SE, durante o Pleistoceno Superior; distensão E-W a NW-SE durante o Holoceno; e por fim compressão E-W relacionada ao campo de esforços atual. A evolução da Bacia de Santos na porção adjacente offshore durante o Cenozoico pode estar diretamente relacionada à presença de estruturas transversais, mudanças de campo de estresse e a geração e eventos deformacionais nas bacias continentais do tipo rift. / The Taubaté and Resende are NE-to-ENE-oriented Paleogene continental rift basins of the central segment of the Continental Rift of Southeastern Brazil. Both basins were installed during the Eocene as a result of a NW-SE-oriented extensional stress field. This stress field reactivated NE-trending shear zones of the Precambrian basement as normal faults, which played a major role during the basin installation and evolution. There are also numerous N-S, NE-SW and NW-SE-oriented structures transverse to the NE-trending basin axis. These structures comprise faults and folds that were active at different time intervals, but their role in the basin evolution is poorly understood yet. In order to recognize these structures in the subsurface in Taubaté Basin, five longitudinal seismic profiles were interpreted showing their distinctive character as normal and reverse faults, which intersect different seismic units and indicate a polyphasic tectonic deformation. The presence of transverse structural highs, recognizable in the seismic profiles, which were active during the opening of the basin, can be related to anticlines formed in the hangingwall during an evolution related to the growing of the border master faults in a NW-SE-trending extensional regime. Moreover, syn-sedimentary NW-SE-oriented transverse normal faults oblique to the ENE-orientation of the border master faults were described in outcrops in the Resende Basin. These structures are interpreted as release faults and thus formed in the same extensional context. Stratigraphic relationships and paleostress analysis of fault populations indicate that transverse structures are related to four deformational events: a NE-SW-oriented compression probably during the Miocene, a NW-SE-oriented compression in the Late Pleistocene to Holocene, an E-W-to-NW-SE-oriented extension in the Holocene and lastly, an E-W-oriented compression related to the present-day stress field. The evolution of the adjoining offshore Santos Basin during the Cenozoic has a narrow correlation with the formation and evolution of Taubaté and Resende basins. The migration of depocenters in the Santos Basin during the Cenozoic can be associated with the presence of NW-SE-oriented transverse structures, changes in the stress fields, and generation and deformation events in the continental rift basins
152

On the complexity of energy landscapes : algorithms and a direct test of the Edwards conjecture

Martiniani, Stefano January 2017 (has links)
When the states of a system can be described by the extrema of a high-dimensional function, the characterisation of its complexity, i.e. the enumeration of the accessible stable states, can be reduced to a sampling problem. In this thesis a robust numerical protocol is established, capable of producing numerical estimates of the total number of stable states for a broad class of systems, and of computing the a-priori probability of observing any given state. The approach is demonstrated within the context of the computation of the configurational entropy of two and three-dimensional jammed packings. By means of numerical simulation we show the extensivity of the granular entropy as proposed by S.F. Edwards for three-dimensional jammed soft-sphere packings and produce a direct test of the Edwards conjecture for the equivalent two dimensional systems. We find that Edwards’ hypothesis of equiprobability of all jammed states holds only at the (un)jamming density, that is precisely the point of practical significance for many granular systems. Furthermore, two new recipes for the computation of high-dimensional volumes are presented, that improve on the established approach by either providing more statistically robust estimates of the volume or by exploiting the trajectories of the paths of steepest descent. Both methods also produce as a natural by-product unprecedented details on the structures of high-dimensional basins of attraction. Finally, we present a novel Monte Carlo algorithm to tackle problems with fluctuating weight functions. The method is shown to improve accuracy in the computation of the ‘volume’ of high dimensional ‘fluctuating’ basins of attraction and to be able to identify transition states along known reaction coordinates. We argue that the approach can be extended to the optimisation of the experimental conditions for observing certain phenomena, for which individual measurements are stochastic and provide little guidance.
153

Previsão de níveis fluviais em tempo atual com modelo de regressão adaptativo: aplicação na bacia do rio Uruguai

Moreira, Giuliana Chaves January 2016 (has links)
Este trabalho avaliou o potencial da aplicação da técnica recursiva dos mínimos quadrados (MQR) para o ajuste em tempo atual dos parâmetros de modelos autorregressivos com variáveis exógenas (ARX), as quais são constituídas pelos níveis de montante para melhorar o desempenho das previsões de níveis fluviais em tempo atual. Três aspectos foram estudados em conjunto: variação do alcance escolhido para a previsão, variação da proporção da área controlada em bacias a montante e variação da área da bacia da seção de previsão. A pesquisa foi realizada em três dimensões principais: a) metodológica (sem recursividade; com recursividade; com recursividade e fator de esquecimento); b) temporal (6 alcances diferentes: 10, 24, 34, 48, 58 e 72 horas); e c) espacial (variação da área controlada da bacia e da área da bacia definida pela seção de previsão). A área de estudo escolhida para essa pesquisa foi a bacia do rio Uruguai com exutório no posto fluviométrico de Uruguaiana (190.000 km²) e as suas sub-bacias embutidas de Itaqui (131.000 km²), Passo São Borja (125.000km²), Garruchos (116.000 km²), Porto Lucena (95.200 km²), Alto Uruguai (82.300 km²) e Iraí (61.900 km²). Os dados de níveis fluviométricos, com leituras diárias às 07:00 e às 17:00 horas, foram fornecidos pela Companhia de Pesquisa de Recursos Minerais (CPRM), sendo utilizados os dados de 1/1/1991 a 30/6/2015. Para a análise de desempenho dos modelos, foi aplicado como estatística de qualidade o coeficiente de Nash-Sutcliffe (NS) e o quantil 0,95 dos erros absolutos (EA(0,95): erro que não foi ultrapassado com a frequência de 0,95). Observou-se que os erros EA(0,95) dos melhores modelos obtidos para cada bacia sempre aumentam com a redução da área controlada, ou seja, a qualidade das previsões diminui com o deslocamento da seção de controle de jusante para montante. O ganho na qualidade das previsões com a utilização dos recursos adaptativos torna-se mais evidente, especialmente quando observam-se os valores de EA(0,95), pois esta estatística é mais sensível, com diferenças maiores em relação ao coeficiente NS. Além disso, este é mais representativo para os erros maiores, que ocorrem justamente durante os eventos de inundações. De modo geral, foi observado que, à medida que diminui a área da bacia, é possível obter previsões com alcances cada vez menores. Porém a influência do tamanho da área controlada de bacias a montante melhora o desempenho de bacias menores quando se observam principalmente os erros EA(0,95). Por outro lado, se a proporção da bacia controlada de montante já é bastante grande, como é o caso das alternativas 1 e 2 utilizadas para previsão em Itaqui (entre 88,5% e 95,4 %, respectivamente), os recursos adaptativos não fazem muita diferença na obtenção de melhores resultados. Todavia, quando se observam bacias com menores áreas de montante controladas, como é o caso de Porto Lucena para a alternativa 2 (65% de área controlada), o ganho no desempenho dos modelos com a utilização dos recursos adaptativos completos (MQR+f.e: mínimos quadrados recursivos com fator de esquecimento) torna-se relevante. / This study evaluated the potential of the application of the recursive least squares technique (RLS) to adjust in real time the model parameters of the autoregressive models with exogenous variables (ARX), which consists of the upstream levels, to improve the performance of the forecasts of river levels in real time. Three aspects were studied jointly: the variation of the lead time chosen for the forecast, the variation in the proportion of controlled area in upstream basins and variation in the area of forecasting section of the basin. The research was conducted in three main dimensions: a) methodological (without recursion; with recursion; with recursion and forgetting factor); b) temporal (6 different lead times: 10, 24, 34, 48, 58 and 72 hours); and c) spatial (variation in the controlled area of the basin and the area of the basin defined by the forecast section). The study area chosen for this research was the Uruguay River basin with its outflow at the river gage station of Uruguaiana (190,000 km²) and its entrenched sub-basins in Itaqui (131,000 km²), Passo São Borja (125,000 km²), Garruchos (116,000 km²), Porto Lucena (95,200 km²), Alto Uruguai (82,300 km²), and Iraí (61,900 km²). The river levels data, with daily readings at 7am and 5pm, were provided by the Company of Mineral Resources Research (CPRM), with the data used from January 1, 1991 to June 30, 2015. We applied the Nash-Sutcliffe coefficient (NS) and the quantile 0.95 of absolute errors (EA(0,95): error has not been exceeded at the rate of 0.95) for the analysis of models performances. We observed that the errors EA(0.95) of the best models obtained for each basin always increase with the reduction of the controlled area then the quality of the forecasts decreases with displacement of the downstream control section upstream. The gain in quality of the forecasts with the use of adaptive resources becomes more evident especially when the observed values of EA(0.95) as this statistic is more sensitive with greater differences in relation to the Nash-Sutcliffe Coefficient (NS). Moreover, this is most representative for larger errors which occur precisely during flooding events. In general, we observed that, as much as the area of the basin decreases, it is possible to obtain forecasts with smaller lead times, but the influence of the size of the area controlled upstream basins improves the performance of smaller basins when observing, especially the errors EA (0.95). However, if the proportion of the upstream of controlled basin is already quite large - as in the case of the alternatives 1 and 2 used for forecast in Itaqui (between 88.5% and 95.4%, respectively) - the adaptive resources do not differ too much in getting better results. However, when observing basins with smaller areas controlled upstream - as is the case of Porto Lucena to alternative 2 (65% controlled area) - the performance gain of the models with the use of the complete adaptive resources (MQR+f.e.) becomes relevant.
154

Reconstrução dos paleoventos do Gonduana no Juro-cretáceo

Mello, Raquel Gewehr de January 2018 (has links)
A passagem de um padrão monsoonal para um padrão de circulação atmosférica zonal ocorreu durante o Cretáceo devido à fragmentação do Supercontinente Gonduana. Essa mudança na direção dos paleoventos é registrada no mergulho de estratos cruzados de dunas eólicas acumuladas em várias bacias de Gonduana. Três mapas de reconstrução de paleoventos foram construídos com a integração de dados paleocorrentes compilados de bacias Fanerozoicas brasileiras, Bacia de Neuquén na Argentina e bacias do Congo e Huab na África. O Gonduana foi dominado por ventos do nordeste ao norte e ventos do sudoeste ao sul, deslocando, assim, a Zona de Convergência Intertropical para 15º a 20 sul do equador durante o Jurássico Tardio até o início do Cretáceo. Por sua vez, os ventos apresentaram uma tendência geral para o oeste-noroeste em latitudes baixas e médias no Gonduana no final do Cretáceo Inical. Esses resultados apontam para a existência de um padrão monsoonal durante o Jurássico Tardio até o início do Cretáceo Inicial e a entrada do padrão zonal no final do Cretáceo Inicial, associado à fragmentação de Gonduana. / The passage of a monsoonal pattern to a zonal atmospheric circulation pattern occurred during the Cretaceous due to fragmentation of Gondwana Supercontinent. This change in the paleowind direction is recorded in crossstrata dip directions of eolian dunes accumulated in various basins of Gondwana. Three maps of paleowind reconstruction were built with integration of compiled paleocurrent data from Phanerozoic basins in Brazil, Neuquén Basin in Argentina and Congo Basin and Huab Basin in Africa. Gondwana was dominated by northeast winds to the north and southwest winds to the south, thus shifting the Intertropical Convergence Zone to 15º to 20⁰ south of the equator during Late Jurassic to the beginning of the Cretaceous. In turn, winds had a general tendency towards west-northwest at low and mid-latitudes in Gondwana at the end of Early Cretaceous. These results point to the existence of a monsoonal pattern during the Late Jurassic to the beginning of Early Cretaceous and the entry of zonal pattern at the end of Early Cretaceous, associated with fragmentation of Gondwana.
155

Caracterização genética do pintado Pseudoplatystoma corruscans (Siluriformes: Pimelodidae), da Bacia Paraná-Paraguai, por marcadores moleculares do tipo microssatélite /

Benites, Celso. January 2008 (has links)
Orientador: Fausto Foresti / Banca: Claudio de Oliveira / Banca: Luiz Edivaldo Pezzato / Banca: Alexandre Wagner Silva Hilsdorf / Banca: Newton Castagnolli / Resumo: O gênero Pseudoplatystoma pode ser encontrado nas principais bacias hidrográficas da América do Sul e é formado por algumas das espécies de maior porte da família Pimelodidae. O "pintado", Pseuplatystoma corruscans, tem função ecológica muito importante em seu habitat, agindo como predador voraz. É espécie muito apreciada na pesca esportiva e atinge alto valor comercial, pela qualidade de sua carne, o que leva ao desenvolvimento de grandes esforços na elaboração de programas de reprodução em cultivo intensivo em escala industrial. Considerando que os microssatélites constituem um dos marcadores moleculares mais importantes e apropriados para o estudo de populações e visando a avaliação e preservação da variabilidade genética da espécie, o presente trabalho teve como objetivos testar esses marcadores moleculares e avaliar a estrutura e os níveis de diversidade genética das populações naturais do pintado. Foram coletadas nove populações de pintado pertencentes a rios tributários da Bacia do Paraguai, no Pantanal Mato-grossense e mais três populações da Bacia do Alto paraná. As amostras tiveram seu DNA total extraído usando a resina Chelex@. Sete primers microssatélites desenvolvidos para a espécie foram testados e utilizados nas análises. Os locos foram amplificados por PCR e submetidos à eletroforese em gel de poliacrilamida a 6%. Posteriormente foram corados com nitrato de prata e fotodocumentados. O tamanho dos fragmentos foi estimado por comparação com o marcador Ladder de 10 bp (Invitrogen) por meio do programa computacional Kodak Digital Science lD. As análises populacionais foram realizadas através dos programas PopGen 1.32, Arlequin 3.11, GeneClass2.0 e Structure 2.2. Os locos microssatélites mostraram-se...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The genus Pseudoplatystoma can be found in ali major river basins of South America and is composed by some of the largest species of fish of the Pimelodidae. family The "pintado", P. corruscans, has a very important ecological role in their habitat acting mainly as a voracious predator. This species is highly appreciated in sport fishing reaching high commercial value due the quality of their meat, which leads to the development of huge efforts in the preparation and development of breeding programs for enhancing juvenile production to meet the demand of the industrial scale. Whereas the microsatellites are one of the most usefull molecular markers for populations studies in order to evaluate and conserve the genetic variability of the species, this work aimed to use these molecular markers in evaluating the structure and levels of genetic diversity of natural populations of the pintado. Nine sample belonging to tributaries of the Paraguay River Basin in the Pantanal Region Mato Grosso and three from Parana River Basin were coleted. Total DNA was extracted using the resin Chelex @. Seven microsatellites primers developed for the species were used in the analyses. The loci were amplified by PCR and submitted to the 6% polyacrylamide gel electrophoresis. Subsequently the gels were stained with silver nitrate and fotodocumented. The size of the fragments were estimated by comparison with the label Ladder of 10 bp (Invitrogen) by the computer program Kodak Digital Science 1D. The analyses were performed with softwares PopGen 1.32, Arlequin 3.11, GeneClass2.0 and Structure 2.2. The microsatellites locis have proved highly polymorphics with the identification of 119 allels (average of 17 per site). The observed heterozygosity (HO) ranged from 0.0370 to 0.9231. The populations showed significant deviation from Hardy-Weinberg equilibrium (HWE) for most of the loci, ...(Complete abstract click electronic access below) / Doutor
156

Análise do impacto do Sistema Cantareira sobre o regime de vazões na bacia do rio Piracicaba / Analysis of the Cantareira System impact on the flow regime in Piracicaba river basin

Frederice, Aline 02 October 2014 (has links)
Neste trabalho, buscou-se caracterizar o regime natural de vazões dos principais rios da bacia do rio Piracicaba e identificar as alterações ocorridas nesse regime, principalmente em decorrência da implantação dos reservatórios do Sistema Cantareira. As análises foram feitas com base nas séries de vazões médias diárias de seis postos fluviométricos situados na bacia (prefixo DAEE: 3D-001, 3D-002, 3D- 006, 3D-009, 4D-001 e 4D-007). Foi utilizado o software IHA (Indicators of Hydrologic Alteration), o qual calcula 33 parâmetros hidrológicos relevantes ecologicamente, que caracterizam a magnitude, o tempo, a frequência, a duração e a taxa de flutuações das vazões, além de dividir a vazão ambiental em cinco componentes: vazões extremas baixas, vazões baixas, pulsos de vazão alta, pequenas cheias e grandes cheias. As séries foram divididas em dois períodos, pré e pós impacto, sendo considerado como ano do impacto o ano correspondente a data da ruptura da homogeneidade das séries de vazões, verificada por meio do teste não paramétrico de Pettitt. Foram determinados pelo software IHA, para o período pós impacto, os fatores de alteração hidrológica de cada um dos 33 parâmetros hidrológicos e as mudanças ocorridas nos componentes da vazão ambiental. Para os rios influenciados pelo Sistema Cantareira, foi constatado que no período pós impacto (a partir das décadas de 1970/80), no geral, houve uma diminuição nas vazões médias de aproximadamente 24% (posto 3D-006) no rio Atibaia, 50% (posto 3D-009) e 34% (posto 4D-001) no rio Jaguari, e 14% (posto 4D- 007) no rio Piracicaba, principalmente no período seco (abril a setembro). Verificou-se também uma redução no valor da mediana das vazões mínimas anuais de 7 dias consecutivos igual a 25% (posto 3D-006), 56% (posto 3D-009), 43% (posto 4D-001) e 15% (posto 4D-007) e aumento na duração e na frequência de ocorrência das vazões mais baixas. Foi também constatado, nesses postos, a diminuição na duração das vazões altas, bem como o aumento nas taxas de ascensão e recessão dessas vazões. As mudanças mais significativas ocorreram no rio Jaguari, seguido pelo rio Atibaia e foram menos significativas no rio Piracicaba, o qual se encontra mais distante dos reservatórios. Já para o rio Camanducaia (sem influência do Sistema Cantareira), após a década de 1970, não houve mudança no valor da mediana das vazões mínimas anuais de 7 dias consecutivos e constatou-se, no geral, um aumento nas vazões médias de aproximadamente 21% (posto 3D-001) e 14% (posto 3D-002), assim como o aumento na frequência de ocorrência das vazões máximas, porém, as mudanças não foram tão significativas como nos demais rios. / The aim in this paper was to characterize the natural flow regime of the main rivers of Piracicaba River basin and identify the alterations in this regime, mainly due to the implementation of Cantareira System reservoirs. The analyzes were based on the average daily flow series from six fluviometric stations in the basin (DAEE prefix: 3D- 001, 3D-002, 3D-006, 3D-009, 4D-001 and 4D-007). The IHA (Indicators of Hydrologic Alteration) software was used to calculate 33 hydrological parameters ecologically relevant, that characterizes the magnitude, timing, frequency, duration and rate of flow changes, besides spliting the environmental flow into five components: extreme low flows, low flows, high flow pulses, small floods and large floods. The daily flow series were divided into two periods, pre and post impact, and it was considered as the year of the impact the year that corresponding to the breaking of homogeneity date from the flow series, verified by the nonparametric Pettitt test. It was determined by the IHA software, for post impact period, the Hydrological Alteration factors of the 33 hydrologic parameters and the changes in the environmental flow components. For the rivers influenced by Cantareira System, it was observed that in the post impact period (from 1970/80s), overall, there was a decrease in the mean flow, approximately 24% (3D-006 station) in Atibaia River, 50% (3D-009 station) and 34% (4D-001 station) in Jaguari River, and 14% (4D-007 station) in Piracicaba River, mainly in the dry season (April to September). There was also a decrease in the median of the annual seven days minimum flows by 25% (3D- 006 station), 56% (3D-009 station), 43% (4D-001 station) and 15% (4D-007 station), and an increase in the frequency and duration of the lower flows. It was also found for these stations a decrease in the duration of high flows as well as an increase in the rise rates and the fall rates of these flows. The most significant changes occurred in Jaguari River, followed by the Atibaia River and were less significant in the Piracicaba River, which is the farthest from the reservoirs. For the Camanducaia River (without influence from Cantareira System), after the 1970s, there was no change in the median of the annual seven days minimum flows and it was observed, overall, an increase in the mean flow by 21% (3D-001 station) and 14% (3D-002 station), as well as an increase in the frequency of the maximum flows, however, the changes were not as significant as in the other rivers.
157

Soil Phosphorus Characterization and Vulnerability to Release in Urban Stormwater Bioretention Facilities

Shetterly, Benjamin James 26 March 2018 (has links)
Modern urban stormwater infrastructure includes vegetated bioretention facilities (BRFs) that are designed to detain water and pollutants. Phosphorus (P) is a pollutant in stormwater which can be retained in BRF soils in mineral, plant, and microbial pools. We explored soil properties and phosphorus forms in the soils of 16 operational BRFs in Portland, OR. Since soil hydrology can significantly impact P retention, we selected BRFs along an infiltration rate (IR) gradient. We conducted sequential fractionation and tests of P pools and measured P release in a subset of soils after drying and flooding samples for ten days. We hypothesized that mineral or organic soil P forms would be correlated with IR, and that vulnerability to P release would depend on the interaction of drying and flooding treatments with P forms and pools. IR did not significantly explain differences in P forms. Soil TP was elevated across all sites, compared with TP in agriculturally-impacted wetlands and was substantially composed of soil organic matter (OM)-associated P. Phosphorus sorbed to mineral Fe and Al oxides- was variable but positively correlated with water-extractable P. The concentration gradient of water-extractable P was primarily controlled by overall P pools. Experimentally induced P releases were seen in 5 of 6 soils exposed to drying conditions, presumably released through microbial mineralization of OM. Only one site showed significant P release following the flooding treatment. Our measurements supported the idea that Fe and Al oxides provide P sorption capacity in these BRF soils. Variable inputs of P to BRFs through stormwater and litterfall may contribute to variability in P profiles and P release vulnerability across sites. Design specifications and management decisions relating to bioretention soils (e.g. establishment of acceptable soil test P levels, focusing on P forms known to influence vulnerability of P release) may benefit from detailed biogeochemical investigations.
158

Tectonique et architecture des bassins intracratoniques Paléozoïques : impact sur l’enregistrement sédimentaire et la géométrie des réservoirs associés : exemple de la marge Nord Gondwanienne / Architecture and tectonic of Paleozoic intracratonic Basins : impact on the sedimentary record and associated geometries : example of peri-Hoggar Basins (North Gondwana marge)

Perron, Paul 27 June 2019 (has links)
La plate-forme Saharienne paléozoïque, comprenant les bassins péri-Hoggar (Murzuq, Illizi, Mouydir, Ahnet, Reggane et Tim Mersoï) sont définies comme des bassins intracratoniques. Ils ont été dominés par des mouvements verticaux lents et à grande longueur d'onde, conduisant à une subsidence globale à faible vitesse (i.e. ca. 10 m/Ma à 50 m/Ma) et à l'accumulation d'une couverture sédimentaire étendue de type plate-forme (environnements de dépôts peu profonds), rythmée par des périodes pulsatiles d’augmentation et de diminution du taux de subsidence probablement déclenchées par des événements géodynamiques régionaux. Les mouvements verticaux de la plate-forme ont créé plusieurs arches également appelés dômes, paléo-topographies (e.g. les arches de la Tihemboka, d’Amguid El Biod, d’Arak-Foum Belrem et de l’Azzel Matti) et des bassins (en forme de synclinal) de différentes longueurs d'onde allant de plusieurs centaines à plus de milliers kilomètres. La persistance d’un ensemble assez uniforme de mouvements verticaux semble contrôler l’architecture des bassins, ce qui semble indiquer un contrôle à grande échelle (i.e. lithosphérique). Ce dernier contrôle spatialement et temporellement la dynamique sédimentaire de dépôt et d'érosion. Plusieurs périodes d'érosion majeures ont considérablement tronqué les sédiments préexistants sur de vastes zones, produisant des discordances régionales, restreintes et amalgamées sur les arches, qui séparent la couverture sédimentaire de la plateforme. À travers une approche intégrée multidisciplinaire originale allant d’une analyse géologique de bassin, associant le substrat et l’architecture de bassin à une modélisation thermomécanique numérique de la lithosphère, cette étude a permis de décrypter les facteurs de forçage des bassins intracratoniques de la plate-forme saharienne (bassins péri-Hoggar).L'architecture en Arches-Bassins est mise en évidence par l'identification de structures tectono-sédimentaires (onlap divergents, troncatures…). Cette architecture se caractérise par des variations d'épaisseur et des partitionnements de faciès, organisés par des failles normales planes sub-verticales formant des systèmes d'horst-graben souvent associés à des plis forcés dans la couverture. Connectés et nucléés aux grandes zones de méga-cisaillement, les systèmes d'horst-graben sont inversés (inversion positive) ou réactivés (plis forcés) au cours d'événements géodynamiques successifs (par exemple : extension cambro-ordovicienne, rebond glaciaire ordo-silurien, extension/ compression Siluro-Dévonien «Calédonienne», extension/compression du dévonien tardif et compression «hercynienne»).Formée sous une lithosphère précambrienne de type accrétionnaire héritées de plusieurs paléo-orogénèses (e.g. Eburnéenne, Panafricaine), une zonation des substrats sous l’architecture en Arches-Basins est observée : Les terranes Archéen à Paléoprotérozoïque se situent sous les hauts structuraux et les terranes méso-néo-protérozoïques sous les dépressions.Sur la base de ces observations géologiques et de l’hypothèse de densités différentielles conservées (impliquant un potentiel isostatique) entre les différents terranes accrétées héritées (i.e. les terranes archéennes et protérozoïques) dans la lithosphère, un modèle numérique thermo-mécanique 2D est proposé. Les facteurs de forçage du premier et du second ordre, respectivement caractérisés par de faible taux de subsidence et par leurs déviations cycliques pendant de longues durées (250 Ma), sont bien contraint par le modèle réconciliant aussi l’architecture tectono-stratigraphique singulière en Arches-Basins. Les différentes simulations ont montré l’importance des anomalies thermiques, de la tectonique (faible taux de déformation) et de l’apport externes en sédiments sur la dynamique de ces bassins intracratoniques. Le flux sédimentaire contrôle la vitesse et la durée de remplissage du bassin jusqu'à l'équilibre isostatique (…). / The Paleozoic Saharan platform including the peri-Hoggar Basins (i.e. Murzuq, Illizi, Mouydir, Ahnet, Reggane and Tim Mersoï basins) are defined as intracraonic basins. Their histories have been dominated by slow long-wavelength vertical motions leading to overall low subsidence rate (i.e ca. 10 m/Ma to 50 m/Ma) and accumulation of an extensive cover of platformal sediments (i.e. shallow deposits environments), rhythmed by pulsatile periods of increasing and decreasing rate probably triggered by regional geodynamic events. The vertical motions of the platform produced several arches also called domes, swells, highs, ridges (e.g. the Tihemboka, Amguid El Biod, Arak-Foum Belrem and Azzel Matti Arches) and basins (syncline-shaped) with different wavelengths going from several hundred to more than a thousand kilometres. The persistence of a rather uniform pattern of vertical motions seems to control the architecture of the basins indicating a large-scale control (i.e. lithospheric). This latter controls spatially and temporally the deposition and the erosion dynamics. Several major erosion events significantly truncated the pre-existing sediments over wide areas, producing regional unconformities, especially restricted and amalgamated on arches, which separate the platformal cover into divisions. Through an original multidisciplinary integrated approach going from a geological basin analysis, coupling the substrate and the basin architecture to a numerical thermo-mechanical modelling of the lithosphere, this study has led to decipher the forcing factors of the intracratonic basins of the Saharan platform.The Arches-Basins architecture is highlighted through the identification of tectono-sedimentary structures (growth strata, truncatures…). This architecture is featured by thickness variation and facies portioning, organized by sub-vertical planar normal faults (sometimes blind faults) forming horst-graben systems associated with forced folding in the cover. Connected and nucleated to major mega-shear zones, horst-graben systems are inverted (positive inversion) or reactivated (forced folds) during successive geodynamic events (e.g. Cambro-Ordovician extension, Ordo-Silurian glacial rebound, Siluro-Devonian “Caledonian” extension/compression, late Devonian extension/compression and “Hercynian” compression).Formed under a Precambrian lithosphere of accretionary type, inherited during several paleo-orogenies (e.g. Eburnean, Pan-African), a substrates zonation of the Arches-Basins framework is described, where the Archean to Paleoproterozoic terranes are forming the structural highs and the Meso-Neoproterozoic terranes the structural lows.Based on these geological observations and the hypothesis of conserved differential densities (implying an isostatic potential) between the inherited different accreted terranes in the lithosphere (i.e. archean and proterozoic terranes), a 2D thermo-mechanical numerical model is proposed. The first and second order forcing factors, respectively recorded in the subsidence rate pattern by the low long-lived and by their cyclic deviations, are well constrained reconciling the singular Arches-Basins tectono-stratigraphic architecture. The different simulations have shown the importance of thermal anomaly, tectonics (weak strain rate) and external sediment supply on the dynamic of these intracratonic basins. Where, sediment flux controls the speed and the duration of basin infill until achievement of the isostatic equilibrium. The thermal anomaly and the tectonics compel the tectono-stratigraphic complexification such as the arches framework (intra-arches, boundary secondary arches…) and the stratigraphy architecture (wedges, diachronic unconformities) (…).
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Characterizing Ecologically Relevant Variations in Streamflow Regimes

Chinnayakanahalli, Kiran J. 01 May 2010 (has links)
Maintaining the ecological health of streams is vital for sustainable water resources management. Streamflow is a primary factor influencing the structure and function of ecological communities. A quantitative understanding of how stream biota respond to variation in streamflow is required for stream bioassessment. This dissertation focuses on quantifying relationships between streamflow regime and stream macroinvertebrate richness and composition. The contribution comprises statistical models that predict stream macroinvertebrate class from streamflow regime and predict streamflow regime from watershed attributes, and a tool that helps derive watershed attribute variables used in these models. The dissertation is a collection of three papers. In the first paper 12 variables were used to represent streamflow regime at 543 sites in the western US. Principal component analysis (PCA) and K-means clustering were used to obtain statistically independent factors and streamflow regime classes. We examined the relationship between these characterizations of streamflow and macroinvertebrate richness and composition at 63 of the 543 sites where there was also biological data. This analysis identified specific aspects of the streamflow regime that were useful in predicting macroinvertebrate richness and composition and that have potential application in classification-based bioassessment and management. A regional-scale study such as this requires tools for efficiently delineating watersheds and deriving their attributes. Paper two presents a multiple watershed delineation tool that addresses issues such as a) incorrectly positioned outlets and b) large Digital Elevation Models. This tool has capabilities to delineate stream networks with the threshold that determines drainage density being objectively determined so that the resulting networks adhere to geomorphological stream network laws. It also derives a suite of geomorphological watershed attributes that were used in prediction models in paper three. In paper three, we developed statistical models to predict streamflow regime class from watershed attributes. Four popular statistical methods were used and the uncertainty associated with class predictions for each method was quantified. Paper three also identified the watershed attributes that were most important for discriminating streamflow regime classes.
160

Subduction rollback, arc formation and back-arc extension

Schellart, Wouter Pieter January 2003 (has links)
Abstract not available

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