Bryant and Eastern Canyon systems are located on the northwest Gulf of Mexico, and they are characterized by a very complex sedimentological history related to glacioeustatic cycles, river discharges, and interactions of depositional and halokinetic processes. Both canyon systems were active during the low sea-level stand of Oxygen Isotope Stage 6, and provided the pathways for the transport of enormous amounts of sediments on the continental slope and abyssal plain of the northwest Gulf of Mexico. Right after their abandonment, at the beginning of Stage 5, salt diapirs encroached into the canyons, and resulted in their transformation into a network of intraslope basins. The transformation of the canyons resulted in the generation of massive sediment failures. The mid-shelf (Stages 4 and 3) to shelf edge (Stage 2) lowering of the sea-level during the last glacial episode resulted in: 1) extensive river-sourced deposits on the outer shelf and/or upper continental slope that contributed in a seaward mobilization of the underlying salt masses, and 2) the generation of numerous gravity flows and turbidity currents on the outer shelf/upper continental slope. The seaward mobilization of the salt masses resulted in the oversteepening of the flanks of the basins, and consequently in the generation of numerous and massive sediment failures. The turbidity currents were confined on the intraslope basins of the upper continental slope, depositing their coarsest material. However, their most diluted upper and end members were able to continue their downslope propagation depositing characteristic fine-grained turbidites. The frequency of the turbidity currents was highly increased during the last glacial maximum (Stage 2), and three short melt-water pulses centered at 30.5, 36, and 52 ky B.P. The last deglaciation event is characterized by the development of a major melt water event that resulted in the deposition of distinct organic rich sediments, similar to the sapropels of the Eastern Mediterranean. At about 11 ky B.P. the melt water discharges of the North America switched from Mississippi River to St Lawrence Seaway, causing the domination of hemipelagic sedimentation on the continental slope of the northwest Gulf of Mexico.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23017号 / 理博第4694号 / 新制||理||1673(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 成瀬 元, 准教授 堤 昭人, 教授 生形 貴男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Continental slope channels, which serve as the primary conduits for sediment transport into the deep marine, occasionally become sites of sediment deposition with excellent reservoir potential. Increasingly reported in the literature are subsurface channel fills exhibiting shingled seismic reflectors that are interpreted to have formed by lateral channel migration. In lower Isaac Formation channels inclined strata are observed but at a lateral scale that is far below industry-seismic detection. Distinctively these flat-based channels are filled with coarse-grained sandstone that transitions abruptly and obliquely upwards into thin, fine grained turbidites. Like rivers, lateral accretion in Isaac channels is interpreted to be the result of the interaction of inertial and pressure forces, but in highly turbulent, highly density-stratified turbidity currents. This resulted in the formation of two superimposed secondary circulation cells that caused enhanced erosion on the outer bank and preferential deposition of coarse-grained sediment along the inner bank.

Thesis (S.M.)--Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 77-79). / This study describes the spatial distribution of sediment deposition in the wake of a circular patch of model vegetation and the effect of the patch on turbulence and mean flow. Two difference types pf vegetation were used along with two different stem densities totaling four different case studies. The spatial location of enhanced deposition correlated with the steady wake zone, which has length, L1. The steady wake zone only occurred downstream of the rigid emergent patches of vegetation and was not seen downstream of the flexible submerged patches of vegetation. The enhanced deposition occurred when both turbulence and mean velocity was below the upstream, initial values. The enhanced deposition occurred when the mean velocity was less than or equal to half of the initial velocity. For the four cases studied, theses parameters of low velocity and low turbulence were primarily met within the steady wake region immediately downstram of the two rigid emergent patches of vegetation. In all four cases, large coherent structures are created in the flow due to the patch. Lateral vortices are formed downstream of the patch in a von-Karman vortex street that meets at the center of the flow a distance, Lw, downstream of the patch. For the flexible submerged cases, streamlines reattach to the bed of the flume a distance, Lv, downstream of the patch. In addition, for the flexible submerged cases, a secondary circulation is generated with flow moving laterally away from the patch at the surface and toward the centerline of the patch at the bed. / by Alejandra C. Ortiz. / S.M.

<p> Sedimentary structures, textures and fabric were studied in detail in eight turbidite greywacke beds from the Cloridorme Formation (Middle Ordovician), Gaspe, Quebec. The beds are exposed on the wave-cut platform near Grande Vallee and were traced for about two miles along the strike (276 degrees), which is parallel to the average current direction (274 degrees) as indicated by sole mark directions. </p> <p> The beds under study show the following systematic downcurrent changes along the strike from east to west: (i) Sole mark types show the following changes: (1) tool marks such as grooves, prod marks and isolated flute marks, to (2) longitudinal ridges, longitudinal ridges with overlapping flute, closely spaced flutes, to (3) poorly developed, shallow longitudinal ridges with occasional cuspate crossing bars, to (4) smooth bottom with occasional grooves. (ii) There is an increase in variance of sole mark directions without a large change in the mean direction in most beds, but the sole mark direction changes by nearly 90° as one of the beds is traced from east to west along the strike. (iii) Most of the beds are massive and are divided into two parts by a bedding joint. However, in the proximal region, if a bed is unusually thin, the bedding joint is absent and the bed shows slightly wavy, plane-laminated structure at places. (iv) Grain orientations are generally statistically non-significant in the upper massive part of the bed in the proximal region and significant in the rest of the bed. Significant grain orientations and graptolite orientations show large deviations from the sole in the distal region. Deviations increase towards the top of the bed. (v) The beds show a change from good grading to poor grading or slight reverse grading from the proximal to distal region. It is considered that the beds were deposited by low concentration, highly turbulent currents. Deposition of the beds took place in two distinct phases. First a 'quick' bed separated from the current was sheared extensively by the overflowing current and on consolidation formed the lower part of the bed. Later deposition in the proximal region from the upper part of the current and the part close to the tail was by settling of individual particles from the suspension. Separation and consolidation of another 'quick' bed in some cases formed the upper part of the beds in the distal region. </p> <p> The depositing currents produced a good vertical and lateral grain size grading in the proximal region, but poor vertical grading in the distal region due to the loss of coarse grains and possibly increased concentration of flocculated clay. Also, the turbidity currents tended to "meander" greatly on slowing down in the distal region. </p> / Thesis / Doctor of Philosophy (PhD)

Turbidity currents are one of the primary means of transport of sediment in the ocean. They are fast-moving, destructive fluid flows which are able to entrain sediment from the seabed and accelerate downslope in a process known as `ignition'. In this thesis, we investigate one particular model for turbidity currents; the `Parker model' of Parker, Pantin and Fukushima (1986), which models the current as a continuous sediment stream and consists of four equations for the depth, velocity, sediment concentration and turbulent kinetic energy of the flow. We propose two reduced forms of the model; a one-equation velocity model and a two-equation shallow-water model. Both these models give an insight into the dynamics of a turbidity current propagating downstream and we find the slope profile to be particularly influential. Regions of supercritical and subcritical flow are identified and the model is solved through a combination of asymptotic approximations and numerical solutions. We next consider the dynamics of the four-equation model, which provides a particular focus on Parker's turbulent kinetic energy equation. This equation is found to fail catastrophically and predict complex-valued solutions when the sediment-induced stratification of the current becomes large. We propose a new `transition' model for turbulent kinetic energy which features a switch from an erosional, turbulent regime to a depositional, stably stratified regime. Finally, the transition model is solved for a series of case studies and a numerical parameter study is conducted in an attempt to answer the question `when does a turbidity current become extinct?'.

[pt] A combinação de modelos numéricos com modelos computacionais tem contribuido muito para o melhor entendimento matemático de fluxos gravitacionais, porém esses modelos não podem substituir a análise através de trabalhos experimentais. O uso de modelos físicos em escala provou ser essencial na validação de equações para modelagem de correntes de turbidez. Com o objetivo de diminuir o nível de dificuldade em modelar numericamente essas correntes e de gerar modelos computacionais de alto desempenho, algumas simplificações foram feitas durante o desenvolvimento das equações de velocidade. Dessa forma, para provar que tais simplificações não iriam alterar os resultados numéricos do modelo, foram realizados inúmeros experimentos, coletando informações sobre a evolução espaço- temporal de velocidades das correntes de turbidez não- confinadas com e sem partículas. Comparando os resultados do modelo numérico com os do modelo físico, foi concluído que, infelizmente, as aproximações influenciaram os resultados. Contudo, os dados e a comparação visual entre as simulações também revelaram alguns resultados encorajadores, os quais estimularão pesquisas futuras para se melhorar a precisão da equação de velocidade utilizada no modelo numérico. / [en] The combination between numerical and computer models has improved dramatically the mathematical understanding of gravity currents; however, these models can not replace the analysis by experimental work. The use of scaled analogue models, or physical models, proved to be essential in validating velocity equations for turbidity currents. In order to reduce the level of difficulty to model mathematically these currents, some approximations were applied during the development of the velocity equation. Therefore, willing to prove that these approximations would not compromise the numerical results, innumerous experiments were performed to acquire a spatio-temporal velocity evolution database for both unconfined particle free and particulate turbidity flows. Comparing the results from the numerical and physical simulations, it was concluded that, unfortunately, the approximations have influenced the numerical results. Nevertheless, the data and visual comparisons between the simulations also revealed some encouraging results, which will stimulate some future research to improve the accuracy of the depth-averaging velocity equation.

Στην παρούσα διπλωματική εργασία εξετάζονται τα χαρακτηριστικά των υποθαλάσσιων αποθέσεων της ερυθράς ιλύος που καλύπτουν τεράστια έκταση του πυθμένα του κεντρικού Κορινθιακού κόλπου και προκύπτουν ως μεταλλευτικό κατάλοιπο της επεξεργασίας βωξιτών για την παραγωγή αλουμινίου. / In the present diplomatic work are examined the characteristics of submarine red mud tailings that cover enormous extent of seabed of central corinthian gulf and result as mining residue of treatment of bauxites for the production of aluminium.

Les courants de gravité, écoulements issus de la présence d’un contraste de densité dans un fluide ou de la présence de fluides de densités différentes, sont rencontrés dans de nombreuses situations naturelles ou industrielles. Quelques exemples de courants de gravité sont les avalanches, les marées noires et les courants de turbidité. Certains courants de gravité peuvent représenter un danger pour l’homme ou l’environnement, il est donc nécessaire de comprendre et de prédire leur dynamique. Cette thèse a pour objectif d’étudier l’évolution de courants de gravité de masse fixée, et notamment l’influence d’une forme initiale non-axisymétrique sur la dynamique, effet jusque-là peu abordé dans la littérature. Pour cela, une large gamme de paramètres est couverte, incluant le rapport de masse volumique entre le fluide ambiant et le fluide dans le courant, le rapport de forme initiale, la forme de la section horizontale de la colonne de fluide (circulaire, rectangulaire ou en forme de croix), le nombre de Reynolds (couvrant jusqu’à 4 ordres de grandeur) et la nature du fluide lourd (salin ou chargé en particules). Deux campagnes d’expériences ont été menées et complétées par des simulations numériques hautement résolues. Le résultat majeur est que la propagation du courant et le dépôt de particules (lorsque particules il y a) sont fortement influencés par la forme initiale de la colonne de fluide. Dans le cas de la colonne initialement rectangulaire le courant se propage plus vite et dépose plus de particules dans la direction initialement de plus courte dimension. Ce comportement non-axisymétrique est observé dans une large gamme des paramètres étudiés ici. Pourtant les modèles analytiques existants et notamment le modèle dit de boîte (box model) qui prédit avec succès le comportement des courants de gravité/turbidité dans les cas plan et axisymétrique ne sont pas capables de reproduire ce phénomène. C’est pourquoi une extension du box model a été développée ici, et est en mesure de décrire la dynamique de courants de gravité de masse fixée dont la forme initiale est arbitraire. Le cas plus général d'un courant de gravité évoluant sur un plan incliné a été abordé et une dynamique intéressante a été observée. / Gravity currents are buoyancy driven flows that appear in a variety of situations in nature as well as industrial applications. Typical examples include avalanches, oil spills, and turbidity currents. Most naturally occurring gravity currents are catastrophic in nature, and therefore there is a need to understand how these currents advance, the speeds they can attain, and the range they might cover. This dissertation will focus on the short and long term evolution of gravity currents initiated from a finite release. In particular, we will focus attention to hitherto unaddressed effect of the initial shape on the dynamics of gravity currents. A range of parameters is considered, which include the density ratio between the current and the ambient (heavy, light, and Boussinesq currents), the initial height aspect ratio (height/radius), different initial cross-sectional geometries (circular, rectangular, plus-shaped), a wide range of Reynolds numbers covering 4 orders of magnitude, as well as conservative scalar and non-conservative (particle-driven) currents. A large number of experiments have been conducted with the abovementioned parameters, some of these experiments were complemented with highly-resolved direct numerical simulations. The major outcome is that the shape of the spreading current, the speed of propagation, and the final deposition profile (for particle-driven currents) are significantly influenced by the initial geometry, displaying substantial azimuthal variation. Especially for the rectangular cases, the current propagates farther and deposits more particles along the initial minor axis of the rectangular cross section. This behavior pertaining to non-axisymmetric release is robust, in the sense that it is observed for the aforementioned range of parameters, but nonetheless cannot be predicted by current theoretical models such as the box model, which has been proven to work in the context of planar and axisymmetric releases. To that end, we put forth a simple analytical model (an extension to the classical box model), well suited for accurately capturing the evolution of finite volume gravity current releases with arbitrary initial shapes. We further investigate the dynamics of a gravity current resulting from a finite volume release on a sloping boundary where we observe some surprising features.

[pt] Correntes de turbidez ocorrem tanto na natureza como em situações criadas pelo homem. Segundo alguns pesquisadores, grande parte das reservas de petróleo conhecidas no mundo estão armazenadas nos reservatórios de hidrocarbonetos formados a partir dos sistemas turbidíticos. Tendo em vista a importância dessas correntes, este trabalho pretende propor um modelo numérico consistente e com baixo custo computacional, capaz de auxiliar na previsão de sedimentação de bacias nos processos de modelagem estratigráfica no contexto do simulador numérico de sedimentação tridimensional com ênfase nos processos deposicionais em ambientes de talude plataforma e bacia, chamado Steno, e validar o modelo numérico proposto através de simulações físicas conduzidas no Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul. O modelo numérico proposto é baseado nas equações de Navier-Stokes, que são resolvidas tirando-se a média na profundidade do perfil de velocidades característico. Além disso, uma aplicação gráfica tridimensional para simulação numérica de correntes de turbidez, chamada Turb3D, foi desenvolvida com base nas equações propostas. O programa possui uma interface gráfica amigável para o usuário no que diz respeito à entrada de dados, solução e visualização dos resultados. Os resultados obtidos mostraram que apesar do modelo numérico possuir um bom desempenho computacional, se comparado com os complexos modelos numéricos existentes, não foi possível reproduzir com precisão a evolução das correntes de turbidez e seus depósitos. Contudo, acredita-se que a abordagem dada ao problema de simulação numérica de correntes de turbidez apresentada neste trabalho pode fornecer bons resultados. Entretanto, é fundamental que seja dada continuidade a pesquisa, de modo que ajustes e melhorias ao modelo proposto possam ser realizadas. / [en] Turbidity currents occur in both natural and man-made situations. In agreement with some researchers, most of the world’s oil reserves are stored in hydrocarbon reservoir built by turbidity systems. Because of the importance of these currents, this work proposes a consistent and efficient numerical method for simulations of turbidity currents for basin sedimentations predictions in the stratigraphic modelling process, which will be incorporated to the numerical simulator of sedimentation 3D called Steno. In order to validate the proposed numerical model experiments were conducted at the Hydraulics Research Institute of Federal University of Rio Grande do Sul. The proposed numerical model is based on Navier-Stokes equations that are solved in the depth-average. Moreover, a three-dimensional graphic application for numerical simulations of turbidity currents called Turb3D was developed. The application user interface provides a common, user-friendly, graphical environment for pre-processing, solution and post-processing. Despite the good computational performance achieved by using this approach, the method presented did not reproduce accurately the evolution of turbidity current and their deposits. However, it is believed that the approach to the numeric simulation of the turbidity current problem given in this work can provide better results, although this research should continue and improvements should be made.