• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 186
  • 135
  • 45
  • 19
  • 5
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 470
  • 133
  • 106
  • 99
  • 88
  • 81
  • 58
  • 49
  • 47
  • 43
  • 42
  • 41
  • 41
  • 40
  • 35
  • 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.
281

Estrutura trófica da comunidade de peixes de riachos da bacia do rio Itanhaém, litoral sul do estado de São Paulo, Brasil /

Silva, André Teixeira da. January 2009 (has links)
Orientador: Roberto Goitein / Banca: Norma Segatti Hahn / Banca: Francisco Manoel de Souza Braga / Resumo: Este estudo foi organizado de maneira a compreender as relações tróficas da ictiofauna estabelecida em diferentes riachos da Bacia do rio Itanhaém, considerando as particularidades em relação às características morfológicas e físico-químicas de cada um destes. Foram considerados nove riachos presentes na zona de planície da bacia do rio Itanhaém, que foram amostrados em duas campanhas (maio e novembro de 2006). Foi determinado um trecho de 50 metros em cada riacho, que foi percorrido no sentido jusante-montante utilizando-se de um aparelho de pesca elétrica. Neste mesmo trecho foram obtidos os dados abióticos: largura, profundidade, velocidade de corrente, substrato predominante, oxigênio, pH, condutividade, turbidez, temperatura da água, tipo de vegetação adjacente, estado de preservação da vegetação ciliar e cobertura da vegetação. Os itens preferenciais foram determinados a partir do Índice de Kawakami & Vazzoler, e a comparação entre os diferentes riachos e campanhas (quando o número de estômagos com alimento permitiu essas comparações) foi realizada com uma Análise de Agrupamento utilizando-se do Índice de Morisita e o método de ligação adotado foi o UPGMA. A amplitude de nicho de cada espécie foi calculada a partir do índice de Levins. As espécies foram distribuídas em grupos tróficos a parti dos itens predominantes, como segue: Carnívoros Predadores, Insetívoros, Herbívoros, Perifitívoros, Detritívoros, Onívoros Bentônicos e Onívoros. Os riachos foram ordenados utilizando-se da Análise de Escalonamento Multidimensional Não Métrica (NMDS) e as distâncias utilizadas para as ordenações foram: Índice de Morisita, para verificar a proporção em biomassa de cada grupo trófico; Índice de Bray-Curtis, para ordenar os riachos em relação às características abióticas. A relação entre as variáveis consideradas e as dimensões... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The purpose of this study was to understand the trophic relationships which have been established for the fish species at distinct streams of the Itanhaém river basin. For this purpose the morphologic and physic-chemical properties of distinct streams were also considered. Nine distinct streams at the low flooding part of the system were sampled during two distinct field campaigns (march and november, 2006). In each of them a 50 m segment was sampled, by sampling in the sense direction from the river mouth to the water source. An electric fishing device was used to catch the fish. At the same places where fish were caught, abiotic data were also obtained: stream width, depth, current flow speed, main substrate composition, dissolved oxygen, water pH, conductivity, turbidity, water temperature, marginal vegetation, its preservation state, vegetation cover. The fish food preferential items were determined by using the Kawakami-Vazzoler Index, and the comparison for different streams and campaigns (when the stomach numbers contents were sufficient to permit analyses) was calculated by the use of the Grouping Analysis using the Simpson Index and the connection method adopted by the UPGMA. The species width niche, for each one of them was calculated using the Levins Index. The fish species were distributed at distinct trophic groups by the inspection of the predominant items, as follows: carnivorous-predator, insectivorous, herbivorous, perifitivorous, detritivorous, benthonic omnivorous and omnivorous species. The streams were classified at distinct by the use of the Non-Metric Multidimentional Scaling analysis (NMDS). The distances used for the ordenations were: Morisita Index, to verify the streams ordenation related to the proportion of the fish mass of each trophic group; the Euclidian distance to ordenate the streams in relation to the abiotic properties... (Complete abstract, click electronic access below) / Mestre
282

Estudo do balanço hídrico e da dinâmica do nitrogênio em uma microbacia com plantação florestal de eucalipto no litoral norte do Estado de São Paulo / Study of the hydric balance and nitrogen dynamics in a micro-basin with forest plantation of eucalyptus in the northern coast of São Paulo state

Rodrigo Trevisan 28 August 2009 (has links)
A conversão da Mata Atlântica original, em áreas de agricultura, florestas plantadas, pecuária e outras atividades, têm causado impactos ambientais cujas conseqüências ainda não foram completamente avaliadas do ponto de vista científico, incluindo estudos hidrológicos em locais onde houve a implantação de florestas de eucalipto. Dentro desse contexto, o objetivo principal do presente trabalho foi o de realizar um estudo integrado da hidrologia e da dinâmica do nitrogênio ( N-NH4 + e N-NO3 -) , em uma bacia com cobertura florestal de eucalipto, localizada na Fazenda Sertãozinho II, pertencente a Votorantim Papel e Celulose , próximo ao Parque Estadual da Serra do Mar, núcleo de Santa Virgínia. O estudo realizado no período de janeiro a dezembro de 2008, mostrou que a área de estudo apresentou uma precipitação de aproximadamente de 1300 mm, 14% de interceptação, 38% de deflúvio e uma evapotranspiração de aproximadamente de 800 mm para o período de estudo. O escoamento superfícial foi pouco expressivo, devido a baixa intensidade da precipitação. Em termos de nitrogênio, a microbacia apresenta concentrações muitos baixas desse composto, em sua maioria abaixo do limite de detecção (0,71 \'mü\'M para N-NO3 - e 1,43 \'mü\'M para N-NH4 +). O aporte atmosférico de nitrogenio inorgânico no período de estudo foi de 2,35kg. ha-1, e a saída via deflúvio foi de 0,14 kg.ha-1 / The conversion of the original Mata Atlântica, into areas of agriculture, planted forests, cattle and other activities have caused environmental impacts which consequences havent been completely evaluated yet by the scientific point of view, including hydrological studies in places where there had been an implantation eucalyptus forests. In this context, the main objective of the present paper was to carry out an integrated study of the hydrology and the nitrogen dynamics (N-NH4+ e N-NO3-), in a basin covered with eucalyptus forest, located in a farm called Fazenda Sertãozinho II, wich is a property of Votorantim Papel e Celulose, near Parque Estadual da Serra do Mar, nucleus of Santa Virginia. The study carried out from January to December of 2008, showed that the studied area presented a precipitation of aproximately of 1300 mm, 14% of interception, 38% of runoff and evapotranspiration of aproximately of 800 mm in the period of study. The superficial draining was of little significance, due to a low intensity of the precipitation. In terms of nitrogen, the microbasin presents very low concentrations of this compound, in its majority below detention limit (0.71 \'mü\'M for N-NO3 - and 1.43 \'mü\'M for N-NH4 +). The atmosphere input of inorganic nitrogen during the period of study was 2.35 kg.ha-1, and the exit through runoff was 0.14 kg. ha-1
283

Avaliação ambiental do rio Pardo, Brasil: ênfase para Áreas de Preservação Permanente, ecossistemas aquáticos superficiais e condições físico-químicas da água / Environmental assessment of the Pardo river, Brazil: emphasis on Permanent Preservation Areas, aquatic ecosystems and surface water physicochemical conditions

Carolina de Freitas Sampaio 24 January 2013 (has links)
O rio Pardo é o principal e fluente da Bacia do Pardo nos estado de Minas Gerias e São Paulo, Brasil, sendo considerado um importante corpo hídrico na região. Esse estudo teve como objetivo realizar uma avaliação ambiental no rio Pardo, integrando a caracterização da situação das Áreas de Preservação Permanente (APP); a integridade dos habitats a partir de um Protocolo de Avaliação Rápida (PAR) e o monitoramento de parâmetros físico-químicos da água. Também, foi objetivo deste estudo avaliar se existe algum grau de concordância estatística entre os resultados do PAR e dos parâmetros físico3químicos da água. Foram avaliados 12 trechos no rio Pardo, desde a nascente até a foz, totalizando 550 km, em quatro campanhas de coleta de dados, sendo duas no período chuvoso e duas no período seco. Em cada trecho, foi caracterizada a condição da APP e qualificados os seguintes parâmetros do PAR: Substratos e/ou habitats disponíveis, Regimes de velocidade/profundidade, Deposição de sedimentos, Condições de escoamento do canal, Alterações no canal, Sinuosidade do canal, Estabilidade das margens, Proteção das margens pela vegetação, Estado de conservação da vegetação do entorno, Materiais sólidos flutuantes. Também em cada trecho foram analisados pH, temperatura, turbidez, oxigênio dissolvido, condutividade elétrica da água. Os resultados das condições das APPs indicam em nenhum dos trechos avaliados houve respeito aos limites estabelecidos pela legislação (BRASIL, 2012). Os resultados da avaliação pelo PAR revelaram que a maioria dos trechos foi classificada como em \"Boas\" condições. A diferença encontrada nas avaliações das condições das APPs com os resultados do PAR podem ser devidas ao fato de que o PAR permite verificar desde a existência de substratos para a colonização da fauna até a composição da mata ciliar. Os resultados dos parâmetros físico-químicos revelaram que o pH dos trechos 1 e 2 estavam abaixo dos limites estabelecidos pela legislação (BRASIL, 2005); as temperaturas mais baixas foram verificadas nos trechos 1 e 2; os resultados de oxigênio dissolvido na água apontam que o trecho 12 estava abaixo dos limites estabelecidos pela legislação (BRASIL, 2005). A comparação entre os resultados dos parâmetros físico-químicos durante os períodos chuvosos e secos demonstram que houve diferença entre os resultados de temperatura, oxigênio dissolvido e turbidez. Os resultados da avaliação de concordância estatística entre os resultados do PAR e os parâmetros físico-químicos apontaram baixa reprodutibilidade (k<0,35), indicando que não foi encontrada concordância estatisticamente significante entre os resultados obtidos do PAR e da análise físico-química da água. Esse resultado indica que o PAR, mesmo sendo uma ferramenta importante para as avaliações ambientais em rios, não deve ser considerado substituto aos métodos de avaliação físico-químicos da água, e sim um complemento para avaliação integrada do ecossistema. Recomendamos o reflorestamento da mata ciliar e o tratamento adequado dos efluentes de indústrias antes do lançamento no rio Pardo. Cabe destacar que o nosso grupo de pesquisa está propondo, perante agências de fomento, a realização de um estudo de avaliação de risco para a população frente à exposição a pesticidas e fertilizantes presentes nesse corpo hídrico, considerando as extensivas culturas agrícolas da região. / The Pardo river is the main river of Pardo basin in the states of Minas Gerais and São Paulo, Brazil and is considered an important water body in the region. This study aimed to conduct an environmental assessment in the Pardo river, integrating the characterization of the status of Permanent Preservation Areas (PPA), the integrity of habitats from a Rapid Assessment Protocol (RAP) and monitoring of physico-chemical parameters of water. Also, an objective of this study was to assess whether there is any degree of statistical correlation between the results of the RAP and the physico-chemical parameters of the water. Twelve stretches were evaluated in the Pardo river, from its source to its mouth, completing 550 km in four data collection campaigns, two in the rainy season and two in the dry season. In each stretch, was characterized the condition of PPA and qualified the following parameters RAP: Substrates and/or habitats available, Speed/depth regimes, Sediment deposition, Channel flow conditions, Channel changes, Channel sinuosity, Margins stability, Margins protection by vegetation, Conservation status of the surrounding vegetation, Solid materials floating. Also in each stretch were analyzed pH, temperature, turbidity, dissolved oxygen, water electrical conductivity. The results of PPAs conditions indicates that none of the evaluated stretch had the limits established by law respect (BRASIL, 2012). The evaluation results for the PAR revealed that most of the sections was classified as in \"Good\" conditions. The difference in assessments of the conditions of the PPAs with the results of PAR may be due to the fact that the check from PAR allows the existence of substrates for colonization by fauna composition of riparian vegetation. The results of physicochemical parameters revealed that the pH of stretches 1 and 2 were below the limits established by law (BRASIL, 2005), the lowest temperatures were recorded in sections 1 and 2, the results of dissolved oxygen in the water indicate that the stretch 12 was below the limits established by law (BRASIL, 2005). The comparison between the results of physicochemical parameters during the wet and dry periods show that were difference between the results of temperature, dissolved oxygen and turbidity. The results of the statistical evaluation of agreement between the results of the PAR and the physico-chemical parameters showed poor reproducibility (k<0.35), indicating no statistically significant correlation was found between the results of the RAP and physicochemical analysis of water. This result indicates that the RAP, despite being an important tool for environmental assessments in rivers should not be considered as an alternative to methods of physico-chemical assessment of water, but a complement to integrated assessment of ecosystem. We recommend the riparian vegetation reforestation and industry effluent proper treatment before launching into the Pardo river. It is worth noting that our research group is proposing to carry out an evaluating risk to the population about exposure to pesticides and fertilizers in this river, considering the extensive agricultural crops in the region.
284

Estudo do balanço hídrico e da dinâmica do nitrogênio em uma microbacia com plantação florestal de eucalipto no litoral norte do Estado de São Paulo / Study of the hydric balance and nitrogen dynamics in a micro-basin with forest plantation of eucalyptus in the northern coast of São Paulo state

Trevisan, Rodrigo 28 August 2009 (has links)
A conversão da Mata Atlântica original, em áreas de agricultura, florestas plantadas, pecuária e outras atividades, têm causado impactos ambientais cujas conseqüências ainda não foram completamente avaliadas do ponto de vista científico, incluindo estudos hidrológicos em locais onde houve a implantação de florestas de eucalipto. Dentro desse contexto, o objetivo principal do presente trabalho foi o de realizar um estudo integrado da hidrologia e da dinâmica do nitrogênio ( N-NH4 + e N-NO3 -) , em uma bacia com cobertura florestal de eucalipto, localizada na Fazenda Sertãozinho II, pertencente a Votorantim Papel e Celulose , próximo ao Parque Estadual da Serra do Mar, núcleo de Santa Virgínia. O estudo realizado no período de janeiro a dezembro de 2008, mostrou que a área de estudo apresentou uma precipitação de aproximadamente de 1300 mm, 14% de interceptação, 38% de deflúvio e uma evapotranspiração de aproximadamente de 800 mm para o período de estudo. O escoamento superfícial foi pouco expressivo, devido a baixa intensidade da precipitação. Em termos de nitrogênio, a microbacia apresenta concentrações muitos baixas desse composto, em sua maioria abaixo do limite de detecção (0,71 \'mü\'M para N-NO3 - e 1,43 \'mü\'M para N-NH4 +). O aporte atmosférico de nitrogenio inorgânico no período de estudo foi de 2,35kg. ha-1, e a saída via deflúvio foi de 0,14 kg.ha-1 / The conversion of the original Mata Atlântica, into areas of agriculture, planted forests, cattle and other activities have caused environmental impacts which consequences havent been completely evaluated yet by the scientific point of view, including hydrological studies in places where there had been an implantation eucalyptus forests. In this context, the main objective of the present paper was to carry out an integrated study of the hydrology and the nitrogen dynamics (N-NH4+ e N-NO3-), in a basin covered with eucalyptus forest, located in a farm called Fazenda Sertãozinho II, wich is a property of Votorantim Papel e Celulose, near Parque Estadual da Serra do Mar, nucleus of Santa Virginia. The study carried out from January to December of 2008, showed that the studied area presented a precipitation of aproximately of 1300 mm, 14% of interception, 38% of runoff and evapotranspiration of aproximately of 800 mm in the period of study. The superficial draining was of little significance, due to a low intensity of the precipitation. In terms of nitrogen, the microbasin presents very low concentrations of this compound, in its majority below detention limit (0.71 \'mü\'M for N-NO3 - and 1.43 \'mü\'M for N-NH4 +). The atmosphere input of inorganic nitrogen during the period of study was 2.35 kg.ha-1, and the exit through runoff was 0.14 kg. ha-1
285

Root-enhanced Infiltration in Stormwater Bioretention Facilities in Portland, Oregon

Hart, Ted David 03 March 2017 (has links)
I evaluated the effectiveness of plant roots to increase infiltration rates within stormwater bioretention facilities (SBFs), roadside planter compartments that filter stormwater. SBFs attenuate harmful effects of stormwater by reducing peak flow and retaining pollutants, with increased infiltration that improves both these functions. Researchers have shown that roots can increase infiltration within greenhouse, lab, field, and test SBF settings. However, no researchers have yet measured either the extent to which different root characteristics can increase infiltration or the variation in root characteristics and their effect on infiltration rates among plant assemblages within currently functioning SBFs. To determine if root-enhanced infiltration was occurring within SBFs, I hypothesized 1) there is a relationship between root characteristics and infiltration during late spring, and 2) seasonal root growth increases infiltration rates. Within Portland, OR, I measured infiltration rate from January 2014 to February 2015 and root characteristics from January-February (J-F) and May-June (M-J) 2014 in ten SBFs with "Elk Blue" rush (Juncus patens) and 1 or 2 trees of less than 8.4 cm stem diameter. During M-J, four root characteristics showed a positive relationship with infiltration rate, and two root characteristics showed a strong positive relationship with infiltration rate within the topsoil. Also, a relationship was shown between the increase (J-F to M-J 2014) in three root characteristics and the increase in infiltration rate. To determine if root morphology and infiltration rates differed among SBFs with two different dominant vegetation taxa (small and large root biomass), I hypothesized 3) Juncus patens and tree dominant assemblage (greater root biomass) exhibits greater infiltration compared to the Carex dominant assemblage, 4) the increase in infiltration rate and root characteristics from J-F to M-J is greater in the Juncus compared to the Carex assemblage, and 5) root surface area density (RSAD) within Juncus SBFs shows a positive relationship with infiltration rate in late spring. I measured infiltration rate from January 2014 to February 2015 and root characteristics from January-February (J-F) and May-June (M-J) 2014 among five large-root (Juncus and tree) and five small-root biomass (Carex sp) SBFs. Juncus SBFs showed greater values for three root characteristics during J-F and five root characteristics during M-J 2014 compared to Carex SBFs. Also, Juncus SBFs showed an increase from J-F to M-J 2014 for five root characteristics while Carex SBFs showed no root increase. Juncus SBFs showed a relationship with four root characteristics and Carex SBFs a showed relationship with one root characteristic and infiltration rate. This work strongly suggests plant roots increase infiltration, and thus the primary functions of SBFs. Different root characteristics appear to increase infiltration rate at different depths. Data also show larger-root biomass plants increase infiltration rate to a greater degree than smaller-root biomass plants. I recommend considering several site and facility characteristics when determining the potential for root-enhanced infiltration. When selecting plant species to enhance infiltration, I recommend using several criteria, determining root characteristic values at certain depths, considering installation approaches, and accounting for regional climate changes.
286

Evaluation and Prediction of Unconventional Gas Resources in Underexplored Basins Worldwide

Cheng, Kun 2012 May 1900 (has links)
As gas production from conventional gas reservoirs in the United States decreases, industry is turning more attention to the exploration and development of unconventional gas resources (UGR). This trend is expanding quickly worldwide. Unlike North America where development of UGRs and technology is now mature and routine, many countries are just beginning to develop unconventional gas resources. Rogner (1996) estimated that the unconventional gas in place, including coalbed methane, shale gas and tight-sand gas, exceeds 30,000 Tcf worldwide. As part of a research team, I helped to develop a software package called Unconventional Gas Resource Advisory (UGRA) System which includes the Formation Analog Selection Tool (FAST) and Basin Analog Investigations (BASIN) to objectively and rapidly identify and rank mature North American formations and basins that may be analogous to nascent international target basins. Based on BASIN and FAST results, the relationship between mature and underexplored basins is easily accessed. To quantify the unconventional resource potential in typical gas basins, I revised and used a computer model called the Petroleum Resources Investigation Summary and Evaluation (PRISE) (Old, 2008). This research is based on the resource triangle concept, which implies that all natural resources, including oil and gas, are distributed log-normally. In this work, I describe a methodology to estimate values of technically recoverable resources (TRR) for unconventional gas reservoirs by combining estimates of production, reserves, reserves growth, and undiscovered resources from a variety of sources into a logical distribution. I have also investigated mature North American unconventional gas resources, and predict unconventional resources in underexplored basins worldwide for case study. Based on the results of testing BASIN and PRISE, we conclude that our evaluation of 24 North American basins supports the premise that basins analysis can be used to estimate UGRs.
287

A hydroeconomic model for water resources assessments with application to the apalachicola chattahoochee flint river basin

Kimaite, Frederick Masolo 28 June 2011 (has links)
Several river basins in the world are faced with growing water scarcity and water use conflicts attributed to increasing water demand and competition among users, climate change and variability, and environmental degradation. Addressing these challenges necessitates shifting from the traditional uncoordinated sectoral approach to more integrated and fully participatory approaches supported by credible information generated by reliable and robust technical tools. Combining engineering, economics and hydroclimatological science, hydro-economic tools are well suited to provide reliable and impartial technical information that can support multi stakeholder negotiation and decision making processes in a river basin. This research develops and applies a detailed hydro-economic model to support multi-objective water resources assessments. The model supports integrated assessments of physical and economic impacts of changes in water demand, climate conditions, water resources management objectives and policies, and other system constraints on a basin's water resources. The main contribution of this research is the systematic coupling of detailed water resources and economic assessment models that are capable of (a) representing complex physical system characteristics and constraints; (b) simulating system operation at diverse temporal and spatial scales; and (c) representing water-based economic production processes at a basin scale. The research integrates a wide range of potential climate change impacts into the hydro-economic modeling framework through consideration of multiple future climate change scenarios from 13 Global Circulation Models under the medium and high emission projection scenarios. Economic uncertainty is characterized through conjunctive use of Monte Carlo simulation and Geometric Brownian Motion techniques to generate multiple forecast traces of important economic parameters. The model is applied to the Apalachicola-Chattahoochee-Flint River basin in the southeast USA as a case study.
288

Offshore mapping and modeling of Miocene-Recent extensional basins adjacent to metamorphic gneiss domes of the D'Entrecasteaux Islands, eastern Papua New Guinea

Fitz, Guy Gregory 15 February 2012 (has links)
The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded domes with ~2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites exhumed in an Oligocene-Miocene arc-continent collision and subduction zone subject to Late Miocene to Recent continental extension. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, a grid of 1,518 km of 2-D multi-channel seismic (MCS) reflection data and well data is interpreted from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. The offshore study is combined with onshore geologic information to constrain the area's Oligocene to Recent basinal and tectonic evolution. MCS and well data show the Trobriand basin formed as a forearc basin caused by southward Miocene subduction at the Trobriand trench. Late Miocene basin inversion uplifted the southern and northern basin margins. Subduction slowed at ~8 Ma as the margin transitioned to an extensional tectonic environment. Since then, the Trobriand basin has subsided 1-2.5 km as a broad sag basin with few normal faults deforming the basin fill. South of the DEI, the Goodenough rift basin developed after extension began (~8 Ma) as the hanging-wall of the north-dipping Owen-Stanley normal fault bounding the southern margin of the basin. Rapid uplift of the adjacent footwall of the Owen-Stanley fault zone in the Papuan Peninsula accompanied the formation of the Goodenough submarine rift basin. The lack of upper crustal extension accompanying subsidence in the Trobriand and Goodenough basins suggests depth-dependent lithospheric extension from 8-0 Ma has accompanied uplift of the DEI gneiss domes. Structural reconstructions of seismic profiles show 2.3 to 13.4 km of basin extension in the upper crust, while syn-rift basin subsidence values indicate at least 20.7 to 23.6 km of extension occurred in the lower crust since ~8 Ma. Results indicating thinning is preferentially accommodated in the lower crust surrounding the DEI are used to constrain a schematic model of uplift of the DEI domes involving vertical exhumation of buoyant, post-orogenic lower crust, far-field extension from slab rollback, and an inverted two-layer crustal density structure. / text
289

Water storage contributions to the excitation of polar motion

Kuehne, John William, 1960- 05 February 2013 (has links)
The goal of this research was to investigate further the role of air redistribution and continental water storage changes in the excitation of both the annual and Chandler wobbles for the period 1900-85. The annual and Chandler excitations from air redistribution have been studied by Wilson and Haubrich (1976), Wahr (1982), and Hinnov and Wilson (1985). Annual excitation from water storage was estimated by Van Hylckama (1970), Hinnov and Wilson (1985), and Chao and O'Connor (1988). Chandler wobble excitation from water storage changes has been addressed only by Hinnov and Wilson (1985). This study was undertaken as a refinement to their encouraging but preliminary results. / text
290

Constraining the age of the Noumea Basin : isotope ages and paleomagnetic data from New Caledonia

Orton, Kristopher T. 21 July 2012 (has links)
Geological evidence suggests large-scale continental extension during the breakup of the eastern Gondwana margin was the predominant force controlling rifting of New Caledonia from the eastern Gondwana margin and formation of the Tasman Sea in the Late Cretaceous. Tectonic models suggest slab-rollback forces elongated and thinned the crustal lithosphere detaching crustal fragments from the Gondwana margin. Current tectonic models lack detailed timing and placement of this crustal detachment with respect to New Caledonia based on lack of evidence (rocks). An isotope and paleomagnetic study was carried out on a bi-modal assemblage of volcanic rock exposed on the southwest side of New Caledonia in the Nouméa Basin. U/Pb isotope ages of zircon grains found within siliceous volcanic rock in the Nouméa Basin provide temporal evidence that volcanism persisted both before and after the breakup of the eastern Gondwana Continent (100-90 Ma) in the Late Cretaceous. Four isotope ages >97 Ma and a series (11 samples) ranging from 91-76 Ma constrain the siliceous volcanism of the Nouméa Basin to the Late Cretaceous. A paleomagnetic inquiry utilizing statistics of both McFadden/Reid and Fisher carried out on 16 Nouméa Basin siliceous and mafic in situ formations place the oldest volcanic units found within the Nouméa Basin at 650 S latitude as New Caledonia began to separate from Gondwana (~100 Ma). The data suggests a well-developed arc signature in the region, which persisted for at least 15 Ma in the Late Cretaceous. Compared to current tectonic models of the southwest Pacific Region from the Late Cretaceous to Eocene, our data suggests New Caledonia was further south on the eastern Gondwana supercontinent prior to rifting in the Late Cretaceous than current models. / Geologic background -- Tectonic setting -- Methods -- Sampling -- Results -- Discussion. / Department of Geological Sciences

Page generated in 0.6557 seconds