Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Dec. 9, 2009). Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

Orientador: Archimedes Perez Filho / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-20T23:58:29Z (GMT). No. of bitstreams: 1 Silva_ViniciusdeAmorim_D.pdf: 9553562 bytes, checksum: 9936c995258ae48b043baf2e46be3e76 (MD5) Previous issue date: 2012 / Resumo: As alterações antropogênicas da morfologia dos subsistemas canal fluvial principal e delta permitiram interpretar as diversas dinâmicas que o sistema rio Jequitinhonha, está submetido, em seu baixo curso. A caracterização, identificação e análise no padrão de drenagem no canal principal e Delta foram possíveis investigando os parâmetros: índice de sinuosidade, morfologia do canal, migração de meandros do canal, vazão, datação por luminescência opticamente estimulada, descrição granulométrica, biológica e cromática dos sedimentos no Delta. Os resultados demonstraram que se identificou o aumento da complexidade sistêmica pela intervenção antropogênica no sistema hidrográfico. Dessa forma, sugere-se que a morfologia do delta, pode estar sendo modificada para que o rio estabeleça um novo equilíbrio geomorfológico em resposta à construção da barragem e retificação do canal fluvial principal. Sugere-se que ao passar do tempo a forma do delta vai se alterar como já está acontecendo, abandonando a sua configuração bifurcada e transformando-se em canal único em direção à sua margem esquerda, desaparecendo-se o canal localizado em na sua margem direita / Abstract: The anthropogenic changes of the morphology of the main river channel and delta allowed to interpret the diverse dynamics to which the Rio Jequitinhonha system was submitted, in its lower course. The drainage pattern characterization, identification and analysis in the main channel and Delta were possible investigating the parameters: sinuosity index, channel morphology, channel neighborhood migration, optically stimulated luminescence dating, granulometric, biological and chromatic description of the sediments in the outfall and Delta. The results showed the identification of the rising systemic complexity due to the anthropogenic intervention in the hydrographic system. So, it is suggested that the delta morphology may have been modified in order to the river to establish a new geomorphological balance, to respond to the construction of the barrage and main channel rectification. It is suggested that with time the form of the delta will be altered in the way it is happening now, abandoning its bisected configuration and transforming in a single channel directed to the left margin, with the disappearance of the channel located in its right margin / Doutorado / Análise Ambiental e Dinâmica Territorial / Doutor em Geografia

Thesis advisor: Douglas A. Edmonds / Delta morphology is traditionally explained by differences in fluvial energy and wave and tidal energy. However, deltas influenced by similar ratios of river to marine energy can display strikingly different morphologies. Other variables, such as grain size of the sediment load delivered to the delta, influence delta morphology, but these models are largely qualitative leaving many questions unanswered. To better understand how grain size modifies deltaic processes and morphologies I conducted 33 numerical modeling experiments and quantified the effects produced by different grain sizes. In these 33 runs I change the median (0.01 - 1 mm), standard deviation (0.1 - 3 φ), and skewness (-0.7 - 0.7) of the incoming grain-size distribution. The model setup includes a river carrying constant discharge entering a standing body of water devoid of tides, waves, and sea-level change. The results show that delta morphology undergoes a transition as median grain size and standard deviation increase while changing skewness has little effect. At small median grain size and standard deviation, deltas have elongate planform morphologies with sinuous shorelines characterized by shallow topset gradients ranging from 1 x 10<super>-4</super> to 3 x 10<super>-4</super>, and by 1 - 8 stable active channels. At large median grain size and standard deviation, deltas transition to semi-circular planform morphologies with smooth shorelines characterized by steeper topset gradients ranging from 1 x 10<super>-3</super> to 2 x 10<super>-3</super>, and by 14 - 16 mobile channels. The change in delta morphology can be morphodynamically linked to changes in grain size. As grain size increases delta morphology transitions from elongate to semi-circular because the average topset gradient increases. For a given set of flow conditions, larger grain sizes require a steeper topset gradient to mobilize and transport. The average topset gradient reaches a dynamic equilibrium through time. This requires that, per unit length of seaward progradation, deltas with steeper gradients have higher vertical sedimentation rates. Higher sedimentation rates, in turn, perch the channel above the surrounding floodplain (so-called `super-elevation'), resulting in unstable channels that frequently avulse and create periods of overbank flow. The overbank flow is more erosive because the steeper gradient causes higher shear stresses on the floodplain, which creates more channels. More channels reduce the average water and sediment discharge at a given channel mouth, which creates time scales for mouth bar formation in coarse-grained deltas that are longer than the avulsion time scale. This effectively suppresses the process of bifurcation around river mouth bars in coarse-grained deltas, which in turn creates semi-circular morphologies with smooth shorelines as channels avulse across the topset. On the other hand, the finest-grained (i.e. mud) deltas have low topset gradients and fewer channels. The high water and sediment discharge per channel, coupled with the slow settling velocity of mud, advects the sediment far from channel mouths, which in turn creates mouth bar growth and avulsion time scales that are longer than the delta life. This creates an elongate delta as stable channels prograde basinward. Deltas with intermediate grain sizes have nearly equal avulsion and bifurcation time scales, creating roughly semi-circular shapes but with significant shoreline roughness where mouth bars form. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Magíster en Ciencias, Mención Geología / Los trabajos de terreno y nuevas datación de U-Pb en circón detrítico en la Formación Cura-Mallín alrededor de Lonquimay, Chile sur-central, nos permiten redefinir esta sucesión como Grupo Cura-Mallín, compuesto por la Formación Guapitrío (volcano-sedimentaria), Formación Río Pedregoso (sedimentaria), y la Formación Mitrauquén. La Formación Río Pedregoso se puede subdividir en tres unidades formales, de base a techo Miembro Quilmahue, Miembro Rucañanco y Miembro Bío-Bío. La base del Miembro Quilmahue tiene un contacto lateral interdigitado con la Formación Guapitrío que aflora entre las localidades de paso Caracoles y paso Rahue esta última localidad datada en trabajos anteriores en 22,0±0,9 Ma por el método K-Ar, la cual fue aparentemente descartada por los mismos autores, quienes no la mencionan en publicaciones posteriores. Sin embargo, esta edad es consecuente con la posición estratigráfica del Miembro Quilmahue y nuestras nuevas dataciones de circón detrítico en las unidades suprayacentes, y coincide con el comienzo de una fase extensional en la Cuenca Cura-Mallín. La deposición del Miembro Quilmahue continuó durante todo el Mioceno temprano, como indican una edad de 17,5 Ma obtenida en trabajos previos y una nueva datación de 16,5 Ma en el estudio actual. La deposición del Miembro Rucañanco ocurrió alrededor de 12,6 Ma durante el Serravaliano, y la del Miembro Bío-Bío en el límite entre el Serravaliano y Tortoniano a los 11,6 Ma. Aunque los tres miembros fueron depositados en un ambiente fluvio-lacustre, han sido dominados por lagos, llanuras de inundación con derrames de llanura, márgenes lacustres con barras de desembocadura, deltas tipo Gilbert y ríos entrelazados distales y meándricos. Los restos de un ave fósil (Meganhinga chilensis) y un mamífero (Protypotherium sp.) han sido vinculados a una edad Mamífero Santacrucense (17.5 16.3 Ma), sin embargo nuevos datos geocronológicos e interpretaciones estratigráficas de este estudio indican que son evidentemente más jóvenes (~13 Ma). Adicionalmente datos de permeabilidad y porosidad en capas de arenisca del Miembro Rucañanco y una posición estratigráfica favorable permiten considerarlo como un potencial reservorio geotérmico. / Este trabajo ha sido financiado por Proyecto Fondecyt N° 1130006 "Tertiary Successions in Chile"

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.

In this study we assessed growth laws of sub-delta crevasses in the Mississippi River delta plain, experimental laboratory deltas, and compared them to previously studied river dominated large deltas worldwide. Metrics for channel and delta geometry for each system were obtained using a combination of geospatial tools, bathymetric datasets, sediment size, and hydrodynamic observations. Most crevasses and experimental deltas appear to obey delta growth laws suggesting that they exhibit planform metrics similar to larger deltas. However, some channels within each system, exhibit outlier behavior (e.g. asymmetric growth) where channel length is much larger than channel width. Hydrodynamic observations and morphodynamic modeling results, support the role of confinement in governing this response, through direct lateral confinement of the receiving basin width and depth thus guiding channels, and indirect confinement caused by sediment cohesion, whereby natural levees guide the systems asymmetric channel growth.

In this study the patterns of sediment transport and deposition in the channels and receiving basin of a crevasse splay in the modern Mississippi River delta are examined, with emphasis on the development of a distributary mouth bar. Simultaneous hydroacoustic and optical measurements on the mouth bar show that the bar conforms to the progradational stage of an existing conceptual model of mouth bar development. This is confirmed by cores dated using Beryllium-7, which provides a record of the deposition on the bar over a 90-day period. Stratigraphic data from cores obtained on the bar are used to extend the conceptual model to account for variable riverine inputs. A numerical model, developed and validated using field data is capable of representing the fundamental sedimentary processes responsible for mouth bar progradation. These results will be of interest to coastal geologists, engineers and coastal managers alike.