Дисертації з теми "Marginal structure model"
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Sekhi, Ikram. "Développement d'un alphabet structural intégrant la flexibilité des structures protéiques." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC084/document.
Повний текст джерелаThe purpose of this PhD is to provide a Structural Alphabet (SA) for more accurate characterization of protein three-dimensional (3D) structures as well as integrating the increasing protein 3D structure information currently available in the Protein Data Bank (PDB). The SA also takes into consideration the logic behind the structural fragments sequence by using the hidden Markov Model (HMM). In this PhD, we describe a new structural alphabet, improving the existing HMM-SA27 structural alphabet, called SAFlex (Structural Alphabet Flexibility), in order to take into account the uncertainty of data (missing data in PDB files) and the redundancy of protein structures. The new SAFlex structural alphabet obtained therefore offers a new, rigorous and robust encoding model. This encoding takes into account the encoding uncertainty by providing three encoding options: the maximum a posteriori (MAP), the marginal posterior distribution (POST), and the effective number of letters at each given position (NEFF). SAFlex also provides and builds a consensus encoding from different replicates (multiple chains, monomers and several homomers) of a single protein. It thus allows the detection of structural variability between different chains. The methodological advances and the achievement of the SAFlex alphabet are the main contributions of this PhD. We also present the new PDB parser(SAFlex-PDB) and we demonstrate that our parser is therefore interesting both qualitative (detection of various errors) and quantitative terms (program optimization and parallelization) by comparing it with two other parsers well-known in the area of Bioinformatics (Biopython and BioJava). The SAFlex structural alphabet is being made available to the scientific community by providing a website. The SAFlex web server represents the concrete contribution of this PhD while the SAFlex-PDB parser represents an important contribution to the proper function of the proposed website. Here, we describe the functions and the interfaces of the SAFlex web server. The SAFlex can be used in various fashions for a protein tertiary structure of a given PDB format file; it can be used for encoding the 3D structure, identifying and predicting missing data. Hence, it is the only alphabet able to encode and predict the missing data in a 3D protein structure to date. Finally, these improvements; are promising to explore increasing protein redundancy data and obtain useful quantification of their flexibility
Xiao, Yongling. "Flexible marginal structural models for survival analysis." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107571.
Повний текст джерелаDans les études longitudinales, aussi bien les covariables que les traitements peuvent varier au cours de la période de suivi. Les modèles de Cox à effets proportionnels avec variables dépendantes du temps peuvent être utilisés pour modéliser l'effet de traitement variant au cours du temps. Cependant, deux défis apparaissent pour ce type de modélisation. Tout d'abord, une modélisation précise des effets des traitements dépendants du temps sur le risque nécessite de résoudre l'incertitude quant à l'importance étiologique des traitements pris a différentes périodes de temps. Ensuite, un second défi se pose dans le cas de la présence d'une variable de confusion qui dépend du temps et qui est également un médiateur de l'effet du traitement sur le risque. Deux différentes méthodologies ont récemment été suggérées pour répondre, séparément, à chacun de ces deux défis, respectivement l'exposition cumulée pondérée et les modèles structuraux marginaux (MSM). Dans cette thèse, j'ai proposé la combinaison de ces méthodologies de façon à répondre aux deux défis simultanément, étant donné qu'ils peuvent tous les deux fréquemment se poser en même temps dans des études longitudinales. Dans le premier article, j'ai proposé et validé une nouvelle approche pour mettre en œuvre le Cox MSM avec la pondération par l'inverse de probabilité de traitement (PIPT) directement à partir d'un modèle de Cox a effets proportionnels pondéré et avec variables dépendantes du temps plutôt que par une approximation par régression logistique sur données agrégées. Les simulations montrent que l'estimateur PIPT donne des estimations consistantes de l'effet causal du traitement alors qu'il serait associé à une grande variabilité dans les estimations, à cause d'inverses de probabilités de traitement extrêmement élevés. La simple troncature de poids a été proposée et couramment utilisée dans la pratique comme une autre solution pour réduire la grande variabilité des estimateurs PIPT. Cependant, les niveaux de troncature sont généralement choisis en fonction de critères ad hoc, qui n'ont pas été systématiquement évalués. Ainsi, dans le deuxième article, j'ai proposé une approche systématique adaptative aux données systématique pour sélectionner le niveau de troncature optimal qui minimise l'erreur quadratique moyenne des estimations PIPT. Dans le troisième article, j'ai proposé un nouveau modèle flexible afin d'estimer l'effet cumulatif de traitements qui varient dans le temps en présence de facteurs de confusion/médiateurs dépendant du temps. Le modèle intègre la modélisation de l'exposition cumulative pondérée dans un Cox MSM. Plus précisément, l'exposition cumulée pondérée a été utilisée pour résumer l'histoire du traitement, qui a été définie comme la somme pondérée des traitements antérieurs. La fonction qui assigne des poids différents aux traitements reçus à différents moments a été modélisée avec des régressions par B-splines cubiques, en utilisant différentes covariables dépendantes du temps artificielles. Les poids IPT stabilisés pour chaque personne à chaque visite ont été calculés afin de tenir compte des variables de confusion et des médiateurs qui dépendent du temps. Le modèle structurel marginal de Cox à effets proportionnel et avec des covariables dépendantes du temps pondéré, qui utilise des poids stabilisés pondérés, a été ajusté pour estimer l'effet cumulatif causal total des traitements sur le risque. Les simulations montrent que le nouveau modèle proposé permet d'estimer l'effet cumulatif causal total, c'est à dire qu'il permet de capturer à la fois les effets direct et indirect.Dans le dernier article, j'ai appliqué le modèle structural marginal avec exposition cumulée pondérée à une étude de cohorte suisse sur le VIH afin de réévaluer si l'exposition cumulée à la thérapie abacavir augmentait le risque potentiel d'événements cardiovasculaires, tels que l'infarctus du myocarde ou le décès lié a un événement cardiovasculaire.
Havercroft, William G. "Exploration of marginal structural models for survival outcomes." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.684750.
Повний текст джерелаYang, Shibing. "Application of Marginal Structural Models in Pharmacoepidemiologic Studies." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3471.
Повний текст джерелаLusivika, Nzinga Clovis. "Estimation d’effets individuels de traitements pris en combinaison dans les études observationnelles." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS218.
Повний текст джерелаRandomized controlled trials cannot be implemented in all situations for estimating effects of therapeutic strategies. Observational studies would then constitute an alternative for evaluating treatment effects. We have a specified interest in four types of methodological difficulties for such studies: 1) confounding by indication ; 2) presence of time-dependent confounding ; 3) The relationship between a given time-dependent treatment and its effect may vary over time ; 4) In real life, patients often receive multiple treatments, sequentially or simultaneously. In this context, the evaluation of individual effects of treatment is a methodological challenge. The overall objective of this thesis was to propose a methodological framework in which these methodological difficulties are accommodated, allowing the individual effects of treatments to be correctly estimated within the context of multi-treatments in an observational study. We evaluated the performance of the marginal structural Cox model when estimating the individual and joint effects of two treatments and showed that it performed well in the presence of three different scenarios of time-dependent confounding. We also showed the importance of estimating the interaction term when exploring the treatment effect from combination therapy. We compared the performance of weighted cumulative exposure marginal structural Cox model with that of a conventional TD WCE Cox model for estimating time-varying effects of treatments without bias in the presence of TD confounding. Our results showed that the WCE Cox MSM performed better and can be applied to real data whatever the strength of time dependent confounding
Hage, Fabio Sismotto El. "A estrutura tarifária de uso das redes de distribuição de energia elétrica no Brasil: análise crítica do modelo vigente e nova proposta metodológica." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-04042011-122312/.
Повний текст джерелаThe present work discusses the question of efficient pricing on electric power distribution systems. The subject is approached from the discussion of the classical economic theory applied to energy production and transport models, passing through a critical evaluation of the current rate structure used in Brazil, to the description of a consistent and simplified proposal for the electric power distribution rate design. The theory of natural monopolies is the background of an integrated discussion on classical rate design models concerning the electric energy transportation activity. By the classical problem analysis, some theories commonly approached are linear pricing, non linear pricing and peak load pricing. The current Brazilian methodology used for the rate design of the usage of distribution networks, applied by the National Regulatory Agency (ANEEL), is revisited under a critical technical vision. As a result, some concepts are reassessed due to the observed excessive operational complexity allied to the lack of economical and statistical foundation. Finally, a simplified methodology for the rate structure of the usage of electrical distribution networks is proposed. The methodology aims, at the same time, greater economic efficiency, simpler operational application and a solid theoretical foundation, thereby reducing arbitrariness and subjectivity found in the current methodology.
Mojaverian, Nassim. "Effects of sparse follow-up on marginal structural models for time-to-event data." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110690.
Повний текст джерелаContexte : Le temps de survie est un paramètre d'intérêt commun qui peut être évalué en faisant appel aux modèles à risques proportionnels de Cox lorsqu'il mesuré en continu. Un autre moyen d'estimer des risques relatifs est de diviser le temps en intervalles égaux et d'assigner une valeur de 0 ou de 1 à chaque intervalle selon que l'individu y est vivant ou non. Dans cette approximation à temps discret, on doit avoir recours à une régression logistique regroupée plutôt qu'à un modèle de Cox pour obtenir une estimation sans biais du temps de survie sous l'hypothèse que le taux de décès par intervalle est bas. Cette hypothèse est raisonnable lorsque les intervalles sont suffisamment courts pour éviter les événements multiples mais ce faisant, des problèmes de valeurs manquantes ou autres peuvent subvenir car les visites effectives ont lieu moins fréquemment dans un contexte de survie et la possibilité que des valeurs soient manquantes est bien réelle.Objectif : Nous examinons l'effet de deux méthodes d'imputation de valeurs manquantes, à savoir la reconduction de la dernière observation (RDO) et l'imputation multiple (IM), de même que la technique d'études des cas disponibles. Nous comparons ces trois approches en prenant comme point de référence l'analyse des cas complets.Méthodes : La régression logistique regroupée pondérée est utilisée afin d'estimer l'effet de traitement causal marginal. Des données complètes ont été générées au moyen de l'algorithme de Young afin d'obtenir des informations mensuelles au sujet de tous les individus ; des observations ont ensuite été sélectionnées à partir des données complètes en supposant que des visites de suivi aient lieu tous les trois ou six mois. Ainsi, en vue d'analyser les données observées sur une base mensuelle, on a effectué la reconduction de la dernière observation (RDO) et l'imputation multiple (IM) pour remplacer les données manquantes et comparer les résultats à ceux d'une analyse de données entièrement observables. On a également effectué une analyse des données observées avant imputation. On a ensuite appliqué ces techniques à la cohorte de co-infection canadienne afin d'évaluer l'impact de la consommation d'alcool sur la fibrose du foie. Résultats: Dans la plupart des simulations, les estimations fondées sur l'imputation multiple se sont avérées moins biaisées et moins variables que les autres, surpassant même celles fondées sur l'observation de données complètes. En présence d'effets confondants, les estimations fondées sur l'imputation multiple ont présenté un biais accru mais ont été moins variables que celles fondées sur les données entièrement observables.Conclusion : L'imputation multiple est supérieure à la reconduction de la dernière observation et à l'analyse des données brutes lorsque des modèles structuraux marginaux sont utilisés pour ajuster l'exposition temporelle et les variables dans un contexte d'analyses de survie où les données sont mesurées à basse fréquence ou incomplètes.
Fujii, Tomoko. "Human Atrial Natriuretic Peptide for Acute Kidney Injury in Adult Critically III Patients: A Multicenter Prospective Observational Study." Kyoto University, 2019. http://hdl.handle.net/2433/242410.
Повний текст джерелаPang, Menglan. "A study of non-collapsibility of the odds ratio via marginal structural and logistic regression models." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110697.
Повний текст джерелаContexte : Il a été observé en épidémiologie et en biostatistique que lorsque le "odds ratio" (OR) est utilisé pour mesurer l'effet causal d'un traitement ou d'une exposition, il y a une différence entre l'OR marginal et l'OR conditionnel et ce, même s'il y a absence de biais de confusion. Ceci est décrit comme le non-collapsibilité de l'OR. Il est parfois incorrectement décrit comme un biais dans l'effet estimé du traitement à partir d'un modèle de régression logistique, si une covariante importante est exclue.Objectifs : Distinguer le biais provenant du biais de confusion du non-collapsibilité et mesurer l'effet du non-collapsibilité sur l'OR dans plusieurs scénarios.Méthode : On a utilisé des modèles structuraux marginaux et la régression logistique ajustée pour mesurer l'effet du non-collapsibilité dans une étude d'exposition par points. Cette approche peut être utilisée pour vérifier les conditions de l'absence de non-collapsibilité et pour examiner le phénomène de biais de confusion sans non-collapsibilité. Une approche graphique est employée pour démontrer la relation entre le non-collapsibilité et le risque de base ou la probabilité du résultat marginal; ceci révèle le comportement de non-collapsibilité avec une étendue d'effets d'exposition et de covariance différents. De manière à explorer l'effet de non-collapsibilité de l'OR en présence de biais de confusion variant en fonction du temps, une étude d'observation de cohorte a été simulée.Résultats et Conclusion : La différence entre les effets conditionnels et bruts peut être décomposée dans la somme de l'effet de non-collapsibilité et du biais de confusion. Nous suggérons une formule générale pour exprimer l'effet du non-collapsibilité dans plusieurs scénarios différents. Notre approche analytique expose des résultats similaires à d'autres étant trouvés avec des formules présentes dans la littérature. Plusieurs observations intéressantes sur le non-collapsibilité peuvent être faites à partir de différents scénarios, avec ou sans biais de confusion, en utilisant notre approche graphique. De manière surprenante, l'effet d'une covariable joue un plus grand rôle dans le non-collapsibilité que l'effet de l'exposition. En présence de biais de confusion reliée au temps, l'effet du non-collapsibilité est comparable à l'effet de l'étude d'exposition par point.
Börsum, Jakob. "Estimating Causal Effects Of Relapse Treatment On The Risk For Acute Myocardial Infarction Among Patients With Diffuse Large B-Cell Lymphoma." Thesis, Uppsala universitet, Statistiska institutionen, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447241.
Повний текст джерелаEwings, F. M. "Practical and theoretical considerations of the application of marginal structural models to estimate causal effects of treatment in HIV infection." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1346448/.
Повний текст джерелаBailly, Sébastien. "Utilisation des antifongiques chez le patient non neutropénique en réanimation." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAS013/document.
Повний текст джерелаCandida species are among the main pathogens isolated from patients in intensive care units (ICUs) and are responsible for a serious systemic infection: invasive candidiasis. A late and unreliable diagnosis of invasive candidiasis aggravates the patient's status and increases the risk of short-term death. The current guidelines recommend an early treatment of patients with high risks of invasive candidiasis, even in absence of documented fungal infection. However, increased antifungal drug consumption is correlated with increased costs and the emergence of drug resistance whereas there is yet no consensus about the benefits of the probabilistic antifungal treatment.The present work used modern statistical methods on longitudinal observational data. It investigated the impact of systemic antifungal treatment (SAT) on the distribution of the four Candida species most frequently isolated from ICU patients', their susceptibilities to SATs, the diagnosis of candidemia, and the prognosis of ICU patients. The use of autoregressive integrated moving average (ARIMA) models for time series confirmed the negative impact of SAT use on the susceptibilities of the four Candida species and on their relative distribution over a ten-year period. Hierarchical models for repeated measures showed that SAT has a negative impact on the diagnosis of candidemia: it decreases the rate of positive blood cultures and increases the time to positivity of these cultures. Finally, the use of causal inference models showed that early SAT has no impact on non-neutropenic, non-transplanted patient prognosis and that SAT de-escalation within 5 days after its initiation in critically ill patients is safe and does not influence the prognosis
Chen, I.-Chen. "Improved Methods and Selecting Classification Types for Time-Dependent Covariates in the Marginal Analysis of Longitudinal Data." UKnowledge, 2018. https://uknowledge.uky.edu/epb_etds/19.
Повний текст джерелаOba, Koji. "How to use marginal structural models in randomized trials to estimate the natural direct and indirect effects of therapies mediated by causal intermediates." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/152045.
Повний текст джерелаPedley, Katherine Louise. "Modelling Submarine Landscape Evolution in Response to Subduction Processes, Northern Hikurangi Margin, New Zealand." Thesis, University of Canterbury. Geological Sciences, 2010. http://hdl.handle.net/10092/4648.
Повний текст джерелаFarmer, R. E. "Application of marginal structural models with inverse probability of treatment weighting in electronic health records to investigate the benefits and risks of first line type II diabetes treatments." Thesis, London School of Hygiene and Tropical Medicine (University of London), 2017. http://researchonline.lshtm.ac.uk/4646129/.
Повний текст джерелаHirsch, Katja K. "Integrating structural and sedimentological observations with numerical lithospheric models to assess the 3D evolution of the South African continental passive margin." Potsdam GFZ, 2008. http://d-nb.info/993223532/34.
Повний текст джерелаHirsch, Katja K. [Verfasser]. "Integrating structural and sedimentological observations with numerical lithospheric models to assess the 3D evolution of the South African continental passive margin / Katja K. Hirsch." Potsdam : GFZ, 2008. http://d-nb.info/993223532/34.
Повний текст джерелаHirsch, Katja K. [Verfasser]. "Integrating structural and sedimentological observations with numerical lithospheric models to assess the 3D evolution of the South African continental passive margin / Katja K. Hirsch." Berlin : Freie Universität Berlin, 2009. http://d-nb.info/1023464497/34.
Повний текст джерелаEmpinotti, Luiz Carlos Lucena. "Arcabouço crustal profundo da parte Centro-Norte da margem de Angola: modelo de afinamento e contato de crostas." Universidade do Estado do Rio de Janeiro, 2011. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=9471.
Повний текст джерелаThe main objectives of this study are to identify features on seismic data that allow (1) the building of a deep crustal framework and of the upper portion of the mantle, in part of the Angolan margin; (2) to compare this framework with the adjacent outcropping basement of the African continent and; (3) to try to fit these results to the published continental breakup models. In order to achieve these objectives, five deep reflection seismic lines (25 km of depth) situated in the in Kwanza and Lower Congo Basins on the passive margin of Angola were interpreted. The features identified on seismic were useful to recognize the tripartite division that caracterize the oceanic crust and in defining the Mohorovicic Discontinuity (that represents the limit between crust and mantle). The seismic interpretation associated with the data obtained from the scientific literature (that provided density values for the packages identified on seismic interpretation) allowed the establishment of a gravity modeling that was compared to the gravity data acquired during the seismic acquisition. The gravity model was useful to validate the seismic interpretation, acting as a quality control of the latter. In case of the gravity anomaly generated by the modeling not being in accordance with the measured anomaly, the seismic interpretation was revised in order to obtain a better adjustment between the modeled and the measured result. This adjustment, however, was always done honoring the reflectors that were clearly positioned on seismic. In addition, the magnetic data acquired on the field was used to help on interpretation. The crustal framework obtained by the methodology described above was compared with the passive margin evolution models found on scientific literature, showing some points in common with the models that postulate the occurrence of exhumed mantle in magma-poor passive margins. The final interpretation of these data showed the existence of a proximal domain characterized by a thick continental crust slightly thinned in contact with a distal domain marked by a hyper-extended continental crust. Oceanwards there is a region where the exhumation of the mantle took place. The passage of the proximal to the distal domain is abrupt, here termed as a Necking Zone. Oceanic crust is identified to the west of exhumed mantle. The comparison of the results obtained in this study with data from the outcropping basement on the African continent suggests a basement control on the vales of continental crust thinning attained under the basins and on the regions of exhumed mantle. Recent works done on the Angolan and Brazilian margins show features similar to the ones identified on this dissertation.
Krishna, Rao Sree Vidya. "Epidemiology of oral cancer in India: a life course study." Thesis, 2014. http://hdl.handle.net/2440/91305.
Повний текст джерелаThesis (Ph.D.) -- University of Adelaide, School of Dentistry, 2014
Found, Adam. "Essays in Municipal Finance." Thesis, 2014. http://hdl.handle.net/1807/65660.
Повний текст джерелаJiang, Tammy. "Suicide and non-fatal suicide attempts among persons with depression in the population of Denmark." Thesis, 2021. https://hdl.handle.net/2144/42580.
Повний текст джерелаRobitaille-Grou, Marie-Christine. "Biais écologique de la méta-analyse avec modificateur d'effet sous le paradigme de l'inférence causale." Thèse, 2017. http://hdl.handle.net/1866/20209.
Повний текст джерелаFoley, Christine Marie. "Comparison And Application Of Methods To Address Confounding By Indication In Non-Randomized Clinical Studies." 2013. https://scholarworks.umass.edu/theses/1121.
Повний текст джерелаRodrigues, Sara Morgado. "Seismostratigraphic model of the Sines contourite drift (SW portuguese margin) - depositional evolution, structural control and paleoceanographic implications." Master's thesis, 2017. http://hdl.handle.net/10451/27603.
Повний текст джерелаThe Sines Contourite Drift, located in the Southwest Portuguese margin, is a distal drift of the Contourite Depositional System of the Gulf of Cadiz, built by the influence of the Mediterranean Outflow Water (MOW). This drift is located between 1000 and 2000 m water depth on the Alentejo margin continental slope. The Sines Drift is bounded by four major morphologic features: the 1.4 km high Pereira de Sousa Fault escarpment to the west, the upper continental slope to the east and the Setúbal and São Vicente canyons to the north and south, respectively. This work presents a seismic stratigraphic analysis and proposes an evolutionary model for the Sines Drift, as well as the identification of its main driving mechanisms and constraints. In pursuing such objectives, the following dataset was used: i) new and unpublished seismic reflection profiles acquired during the MOWER/CONDRIBER cruise in September-October 2014; ii) pre-existent multichannel seismic profiles BIGSETS, STEAM and GSI; iii) SWIM multibeam bathymetry; iv) lithostratigraphic and chronological data from Site U1391 of IODP (Integrated Ocean Drilling Program) Expedition 339 carried out in 2011-2012. Three evolutionary phases are identified for the Sines Drift development: 1) a sheeted-contourite-drift phase (<5.3-3.2 Ma) built since the Late Miocene by an initially weak flowing MOW; 2) a mounded-contourite-drift phase (3.2-0.7 Ma) from Late Pliocene to Early Quaternary times characterized by a mounded drift in the south and sheeted in the north, with a succession of sinuous N-S paleomoats in the east built as a result of a MOW enhancement; and 3) a plastered-contourite-drift phase from Mid-Pleistocene (0.7 Ma) till the present-day, characterized by the present depositional (sandy-muddy drifts) and erosional (moats) contourite features associated with two major events of MOW intensification. The growth of the Sines Drift was constrained by seafloor paleomorphologies that resulted from the rifting processes of the Southwest Portuguese margin, inherited from the Mesozoic rifting phases. The paleomorphologies provided accommodation space for drift growth and conditioned its overall architecture. The N-S horsts and grabens built during the Mesozoic rifting confined drift deposition and did not allow its lateral migration. The formation of the Sines Drift has also been influenced by climatic fluctuations and sea-level changes especially during the Quaternary. The succession of sinuous paleomoats beneath the present-day moat suggests a persistent and northward flowing MOW with several phases of enhancement. It was also perceived that the São Vicente and Setúbal canyons took most of the downslope sediment supply, as well as the occurrence of mass-movement processes in the west associated with the steep gradient of the Pereira de Sousa escarpment. All these results suggest the Sines Drift had a complex evolution controlled by several factors at different scales.
Contornitos são corpos sedimentares depositados ou retrabalhados por correntes de fundo que circulam paralelamente aos contornos batimétricos da margem. A formação dos contornitos é afetada, a longo e curto prazo, por fatores externos e/ou internos que podem modificar o padrão de circulação das correntes. Os depósitos contorníticos podem atingir dimensões consideráveis com vários quilómetros de largura e comprimento, os quais conservam informação paleoclimática e paleoceanográfica. Os contornitos também desempenham um papel importante no estudo dos riscos naturais submarinos, associados à ocorrência de deslizamentos, e na indústria de exploração petrolífera, como potenciais reservatórios e selantes. Um extenso Sistema Deposicional Contornítico (CDS, Contourite Depositional System) formou-se no Golfo de Cádis, desde o fim do Miocénico Superior (5.33 Ma), pela ação da Água de Saída Mediterrânica (MOW, Mediterranean Outflow Water). Este CDS abrange vários depósitos contorníticos e outras formas sedimentares, deposicionais e erosivas, ao longo da margem continental Sul e Sudoeste Ibérica. O Contornito de Sines, localizado na margem Sudoeste Portuguesa, é um contornito distal do CDS do Golfo de Cádis. Este corpo situa-se entre 1000 e 2000 m de profundidade na Bacia do Alentejo, com aproximadamente 70 km de comprimento, 40 km de largura, 1 km de espessura, morfologia assimétrica e configuração agradante com inclinação para oeste. O Contornito de Sines está limitado por quatro morfoestruturas: a escarpa da Falha Pereira de Sousa com 1.4 km de altura a oeste, a plataforma continental a este e os canhões de Setúbal e São Vicente a norte e sul, respetivamente. Este trabalho apresenta uma análise sismostratigráfica e propõe um modelo evolutivo para o Contornito de Sines, além da identificação dos principais mecanismos e constrangimentos que controlaram a sua evolução. Para atingir estes objetivos, recorreu-se ao seguinte conjunto de dados: i) linhas de reflexão sísmica multicanal não publicadas, adquiridas durante a campanha MOWER/CONDRIBER em setembro-outubro de 2014; ii) linhas de reflexão sísmica multicanal, pré-existentes, dos projetos BIGSETS, STEAM e GSI; iii) batimetria multifeixe SWIM e iv) dados litostratigráficos e cronológicos da sondagem U1391 da Expedição 339 do IODP (Integrated Ocean Drilling Program), realizada em 2011-2012. A metodologia utilizada durante este trabalho consistiu em interpretação de estratigrafia sísmica, análise batimétrica, calibração e correlação cronostratigráfica dos horizontes e unidades sísmicas com a sondagem U1391 e representação gráfica das propriedades litológicas e físicas da sondagem referida. A interpretação sismostratigráfica dos dados apresentados permitiu identificar seis unidades sísmicas (U1 a U6), com idades compreendidas entre o Miocénico Superior e o Presente. Estas unidades foram depositadas sobre uma superfície basal erosiva (B) e estão separadas por cinco horizontes sísmicos (H2 a H6), que marcam descontinuidades na sucessão sísmica. As unidades sísmicas apresentam fácies transparente a maior profundidade, com configuração em cunha, que transita para uma fácies estratificada de elevada amplitude e configuração lobular a menor profundidade. A análise litostratigráfica da sondagem U1391 permitiu a calibração cronostratigráfica das unidades sísmicas interpretadas, bem como a caracterização da sua litologia. As unidades U2 (onde a sondagem U1391 atingiu a sua máxima profundidade) e U3, situadas entre os 671.5 e 566.1 m de profundidade, têm idades compreendidas entre o Pliocénico Superior e o Quaternário Inferior (3.2-2.5 Ma). Estas unidades são constituídas por vasa carbonatada, de composição dolomítica (~0.87 m) aos 632 m de profundidade e um debrito (~0.35 m) aos 604 m de profundidade. Às unidades U4 e U5, recuperadas entre 566.1 e 196.1 m de profundidade, foram atribuídas idades entre o Pleistocénico Inferior a Médio (2.5-0.7 Ma) e são constituídas por contornitos finos intercalados por sucessões de vasa carbonatada. A unidade sedimentar mais recente, U6, depositou-se desde o Pleistocénico Médio (0.7 Ma) até ao Presente. A unidade U6 é composta por alternância de depósitos contorníticos finos e grosseiros recuperados entre 196.1 m de profundidade e o fundo oceânico. Estes depósitos apresentam sucessões com bigradação, gradação normal e inversa (separadas por contactos gradacionais, bioturbados e, mais raramente, descontinuidades). Esta unidade contém seis intervalos contorníticos arenosos, areias finas a grosseiras, a 2, 50, 83, 96, 115 e 150 m de profundidade. Foram identificadas três fases na evolução deposicional do Contornito de Sines: 1) uma primeira fase de contornito com configuração em camada (sheeted drift) (<5.3-3.2 Ma), construída desde o final do Miocénico Superior, por uma corrente MOW de fraca intensidade; 2) uma fase de contornito monticular (mounded drift) (3.2-0.7 Ma), desde o Pliocénico Superior ao Quaternário Inferior, caracterizada por uma morfologia monticular a sul e agradante a norte, com uma sucessão de paleo-fossas sinuosas ao longo da margem continental a este, que atestam a ocorrência de uma intensificação moderada a elevada da MOW e 3) uma fase final de contornito agradante (plastered drift), desde o Pleistocénico Médio (0.7 Ma) até ao Presente, caracterizada pelas atuais formas deposicionais (contornitos argilosos a arenosos) e erosivas (fossas), associadas a dois eventos de intensificação da MOW. A formação do Contornito de Sines terá tido início no Miocénico Superior, possivelmente após o final da Crise de Salinidade do Messiniano, que afetou a região Mediterrânica entre 5.33 e 5.96 Ma, a qual teve repercussões drásticas para a circulação oceânica entre o Mediterrâneo e o Atlântico. Após a Crise de Salinidade do Messiniano e o restabelecimento da circulação através do Estreito de Gibraltar, a MOW possuía fraca intensidade. A sucessão de paleo-fossas subjacentes à fossa atual sugere uma corrente semipermanente e persistente ao longo da margem Sudoeste Portuguesa, em direção a norte, com vários eventos de intensificação. A edificação do Contornito de Sines foi constrangida pelas paleo-morfologias do fundo do mar que resultaram dos processos de rifting, herdados das fases de rifting Mesozóicas na margem Sudoeste Portuguesa. Estas paleo-morfologias forneceram espaço de acomodação para o crescimento do contornito e condicionaram a sua arquitetura deposicional. Os horsts e grabens, com orientação aproximada N-S, resultantes do rifting Mesozóico, confinaram a formação do contornito impedindo a sua migração lateral. A edificação do Contornito de Sines foi também influenciada por variações climáticas e eustáticas, especialmente durante a sua última fase de desenvolvimento. Durante o Quaternário, os eventos de intensificação da MOW correlacionam-se com dois eventos climáticos do Pleistocénico, registados na região Mediterrânica e nos depósitos contorníticos do Golfo de Cádis: o Middle Pleistocene Revolution (0.7-0.78 Ma) e o Late Quaternary Discontinuity (0.4 Ma). Os sedimentos que constituem o Contornito de Sines são maioritariamente sucessões contorníticas de composição carbonatada, com uma maior componente biogénica na primeira fase de desenvolvimento (sheeted drift), e uma maior componente siliciclástica (contornitos arenosos), na última fase de desenvolvimento (plastered drift). A componente biogénica na primeira fase provavelmente indica a ocorrência de fenómenos de afloramento costeiro e deposição hemipelágica ao longo da margem Oeste Portuguesa, enquanto que a maior contribuição siliciclástica na última fase está associada a eventos de intensificação da MOW. O Contornito de Sines evoluiu de um sistema deposicional inicialmente carbonatado para siliciclástico na última fase de desenvolvimento, testemunhando variações de intensidade da MOW. Os sedimentos carreados para a margem do Alentejo são maioritariamente fornecidos por deposição hemipelágica, fenómenos de afloramento costeiro e resultante de erosão da margem continental pela circulação da MOW. O Contornito de Sines não é significativamente afetado por processos gravíticos, sendo registado apenas uma ocorrência no Pliocénico (debrito de ~0.35 m). A baixa incidência de processos gravíticos resulta, provavelmente, da morfologia da margem e da existência dos canhões de Setúbal e São Vicente, que canalizam grande parte do material deslocado. No entanto, existem depósitos de movimento de massa que afetam o sector ocidental do Contornito de Sines, que estão associados ao elevado declive da escarpa da Falha Pereira de Sousa. A formação destes depósitos poderá estar associada a vários fatores intrínsecos e extrínsecos à área em estudo. No que se refere aos fatores intrínsecos, destaca-se a potencial geração de planos de descolamento nas interfaces entre sedimentos contorníticos arenosos e vasosos caso se encontrem sobre pressão, com excesso de fluídos e/ou intercalados por sedimentos menos porosos. No que respeita aos fatores extrínsecos, a atividade sísmica registada na margem Sudoeste Ibérica poderá espoletar a ocorrência de deslizamentos submarinos no Contornito de Sines. Os resultados obtidos sugerem que o Contornito de Sines teve uma evolução complexa, controlada por vários fatores, a diferentes escalas.
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