Tesis sobre el tema "Geomorphic processes"

Accelerated sea-level rise poses a significant threat to coastal habitats. Salt marshes are critical coastal ecosystems, providing a host of services such as storm protection, food production, and carbon storage. Persistence of salt marshes in the face of rising sea levels relies, in part, on vertical accretion. Current ecogeomorphic models and empirical studies emphasize the importance of the positive relationship between plant production and vertical accretion via sediment trapping by stems aboveground and belowground organic matter production. Thus, changes in plant production influence salt marsh persistence with sea-level rise. However, studies and models of marsh accretion do not consider the effects of animal-mediated changes in plant production. Here, I tested how two co-occurring marsh crustaceans, Uca pugnax (marsh fiddler crab) and Sesarma reticulatum (purple marsh crab), which have contrasting effects on smooth cordgrass (Spartina alterniflora) production, indirectly influence sediment deposition and belowground organic matter contribution, through observational surveys and field manipulation. S. reticulatum feeds directly on S. alterniflora, while U. pugnax facilitates S. alterniflora production through burrowing and biodeposits. I found that U. pugnax facilitated S. alterniflora biomass in some marshes, but not others. However, this facilitation of S. alterniflora biomass did not enhance sediment deposition. U. pugnax had no effect on belowground components of vertical accretion (i.e. root production and decomposition). These results suggest that in isolation, U. pugnax has little impact on saltmarsh geomorphic processes. S. reticulatum reduced S. alterniflora above- and belowground biomass; however, sediment deposition increased as S. alterniflora biomass decreased, contrary to models of ecogeomorphology. This trend was likely due to sediment being resuspended by crab bioturbation, as U. pugnax abundances were higher in S. reticulatum-grazed areas than in non-grazed areas. When U. pugnax occurred in areas of low S. reticulatum grazing, S. alterniflora biomass and sedimentation was similar to areas with only U. pugnax. I suggest that the negative impacts of S. reticulatum are exaggerated when intense grazing results in completely unvegetated areas and subsequent increases in U. pugnax density, where bioturbation erodes sediments. Thus, while S. reticulatum can increase the susceptibility of marsh sediments to physical erosion by removing vegetation, it may also do so by facilitating U. pugnax bioturbation. However, when S. reticulatum grazing intensity is low, facilitation of S. alterniflora growth by U. pugnax can mitigate the negative effect of grazing, which suggests that the net effect of these species may depend on their relative abundance. This study demonstrates that ecological interactions, in addition to physical processes, have significant effects on marsh persistence as sea level rises, and merit incorporation into ecogeomorphic models and empirical studies of marsh accretion.

Coastal wetlands are dynamic ecosystems that are highly susceptible to change due to natural and human factors. The study area, located within the Native Dog Creek sub-catchment of the Logan River - which drains into Moreton Bay, south east Queensland - holds a detailed history of environmental change spanning most of the Holocene epoch. This history is preserved in the estuarine sedimentary record and is a valuable indicator of natural environmental change. More recently, human-induced changes within the study area have been superimposed on the natural process of environmental change. In order to develop a conceptual bio-geomorphic model of the coastal wetlands of Native Dog Creek, this thesis examined - on an integrated catchment basis - the evolution and connectivity of four coastal wetland community types (Melaleuca, Casuarina, saltmarsh and mangroves). The research consisted of four discrete studies within the study area: a geomorphic investigation that provided a framework for understanding how the wetlands evolved during the Holocene epoch; an acid sulfate soil (ASS) study that surveyed the distribution and concentration of sulfides; a palynological study that examined the natural directions of ecosystem change; and an investigation of the impact of specific human activities on these ecosystems. Detailed stratigraphic modelling found that the Logan River system (and its Native Dog Creek sub-catchment) has evolved from an infilling estuary since the peak of the Holocene transgression 6500 years before present. Recognition of the major controls that influenced geomorphic coastal development during the Holocene, provided important insights into the distribution and genesis of estuarine pyritic sediments which strongly influence the soils within the study area. In general, the estuarine central basin and fluvial delta sediments posed the greatest risk to the environment from acidification if disturbed. The major focus of the ASS study was to survey the distribution of ASS and to identify other areas most vulnerable to acidification. A predictive approach that combined chemical and stratigraphic analysis was used. Results showed that these areas are intrinsically related to their environment of deposition. The study found, for example, that the alternation of excessively wet and dry conditions - combined with high organic carbon levels and variations in microtopography - provided ideal conditions for the re-formation of pyrite in the stream channel within the Melaleuca wetlands. The palaeo-environmental study reconstructed the evolution of Holocene coastal wetland vegetation during the marine transgression and subsequent shoreline progradation. Pollen records from the four representative wetland communities (previously mentioned) were examined. The results found the mid-late Holocene vegetation history was controlled by the development of geomorphic features that have affected freshwater input, drainage and salinity. In response to the progradation of the shoreline after sea level stabilised, changes in fossil pollen from mangroves and saltmarsh taxa during the early-mid Holocene, to freshwater taxa during the late Holocene, are estimated to have taken 800 years. Thus, pollen analysis when used in combination with stratigraphic modelling, provided an important point of reference for rates of natural ecological change in response to evolutionary changes to the physical environment. The wetlands within the study area have suffered varying degrees of disturbance since European settlement in the 1820s. The most significant changes occurred during early European settlement, when vast areas of coastal lowlands were cleared for timber, sheep and cattle grazing and for agricultural purposes. A second period of change occurred from 1989 to 1995, when the Melaleuca community suffered dieback in response to hydrological modifications to Native Dog Creek for the development of a golf course. Results indicate that human-induced changes over the past 170 years have occurred at a rate far beyond the ability of the natural ecosystem to adapt or move to a more ecologically sustainable state, at least in the short-term. Hence the current environment is experiencing degradation through both decline in health and loss of indigenous species. The development of a conceptual bio-geomorphic model was based on the integration of results from all four studies, in an effort to provide a holistic understanding of the coastal wetland environment and of the impact of human-induced changes upon that environment. If these vulnerable ecosystems are to be maintained, successful and sustainable coastal management strategies must rely on a sound scientific understanding of the response of a coastal ecosystem to both human and environmental changes.

change due to natural and human factors. The study area, located within the Native Dog Creek sub-catchment of the Logan River - which drains into Moreton Bay, south east Queensland - holds a detailed history of environmental change spanning most of the Holocene epoch. This history is preserved in the estuarine sedimentary record and is a valuable indicator of natural environmental change. More recently, human-induced changes within the study area have been superimposed on the natural process of environmental change. In order to develop a conceptual bio-geomorphic model of the coastal wetlands of Native Dog Creek, this thesis examined - on an integrated catchment basis - the evolution and connectivity of four coastal wetland community types (Melaleuca, Casuarina, saltmarsh and mangroves). The research consisted of four discrete studies within the study area: a geomorphic investigation that provided a framework for understanding how the wetlands evolved during the Holocene epoch; an acid sulfate soil (ASS) study that surveyed the distribution and concentration of sulfides; a palynological study that examined the natural directions of ecosystem change; and an investigation of the impact of specific human activities on these ecosystems. Detailed stratigraphic modelling found that the Logan River system (and its Native Dog Creek sub-catchment) has evolved from an infilling estuary since the peak of the Holocene transgression 6500 years before present. Recognition of the major controls that influenced geomorphic coastal development during the Holocene, provided important insights into the distribution and genesis of estuarine pyritic sediments which strongly influence the soils within the study area. In general, the estuarine central basin and fluvial delta sediments posed the greatest risk to the environment from acidification if disturbed. The major focus of the ASS study was to survey the distribution of ASS and to identify other areas most vulnerable to acidification. A predictive approach that combined chemical and stratigraphic analysis was used. Results showed that these areas are intrinsically related to their environment of deposition. The study found, for example, that the alternation of excessively wet and dry conditions - combined with high organic carbon levels and variations in microtopography - provided ideal conditions for the re-formation of pyrite in the stream channel within the Melaleuca wetlands. The palaeo-environmental study reconstructed the evolution of Holocene coastal wetland vegetation during the marine transgression and subsequent shoreline progradation. Pollen records from the four representative wetland communities (previously mentioned) were examined. The results found the mid-late Holocene vegetation history was controlled by the development of geomorphic features that have affected freshwater input, drainage and salinity. In response to the progradation of the shoreline after sea level stabilised, changes in fossil pollen from mangroves and saltmarsh taxa during the early-mid Holocene, to freshwater taxa during the late Holocene, are estimated to have taken 800 years. Thus, pollen analysis when used in combination with stratigraphic modelling, provided an important point of reference for rates of natural ecological change in response to evolutionary changes to the physical environment. The wetlands within the study area have suffered varying degrees of disturbance since European settlement in the 1820s. The most significant changes occurred during early European settlement, when vast areas of coastal lowlands were cleared for timber, sheep and cattle grazing and for agricultural purposes. A second period of change occurred from 1989 to 1995, when the Melaleuca community suffered dieback in response to hydrological modifications to Native Dog Creek for the development of a golf course. Results indicate that human-induced changes over the past 170 years have occurred at a rate far beyond the ability of the natural ecosystem to adapt or move to a more ecologically sustainable state, at least in the short-term. Hence the current environment is experiencing degradation through both decline in health and loss of indigenous species. The development of a conceptual bio-geomorphic model was based on the integration of results from all four studies, in an effort to provide a holistic understanding of the coastal wetland environment and of the impact of human-induced changes upon that environment. If these vulnerable ecosystems are to be maintained, successful and sustainable coastal management strategies must rely on a sound scientific understanding of the response of a coastal ecosystem to both human and environmental changes.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>Australian School of Environmental Studies<br>Full Text

Weedon Island, a peninsula located on the western inner shoreline of Tampa Bay, Florida, is the location of a collaborative geological and archaeological project that aims to relate the present day geomorphology to natural processes and human occupational activity during the middle to late Holocene. The area is known for extensive archaeological sites, which were originally investigated in the 1920s, although they have received relatively little scientific attention during most of the last century. We hypothesize that activities associated with pre-historic human occupation of Weedon Island at various times during the last ca. 5,000 years influenced the geomorphic evolution of the peninsula. An interdisciplinary approach, including geomorphic mapping, sediment-coring, and archaeological survey and excavation, is being used to test our hypothesis and is expected to reveal the extent to which natural processes and human activities interacted to shape the present-day configuration of the peninsula. More recent human impacts on the peninsula have impeded our efforts in some areas. During the twentieth century, dredging, mosquito ditching, and road construction, have disturbed the surface and portions of the upper sediment record in many locations. Sediments below obvious disturbances or in unimpacted areas of the peninsula, along with radiocarbon dating, have helped reconstruct the mid to late Holocene paleoenvironments and paleolandscape of Weedon Island.

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2008.<br>Title from electronic title page (viewed Oct. 5, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Curriculum in Ecology." Discipline: Ecology; Department/School: Ecology.

Tidal inlets play a significant role in barrier island sustainability along the barrier islands of southern Louisiana. With increasing tidal prism, major changes are taking place within and adjacent to the inlets. The purpose of this thesis is to examine how Caminada Pass, a tidal inlet along the Caminada-Moreau headland, has evolved through time. Fundamental to this effort is evaluating which processes have contributed toward inlet evolution and what is the response of the inlet-bordering barrier island shorelines of Grand Isle and Elmer’s Island. This effort summarizes previous results and utilizes published bathymetric data, aerial photographs, vector shorelines, satellite images, and seafloor grab samples. The intent of this research is to document the variety of data that are available for future studies of Caminada Pass, an evaluation of long and short-term changes to the system, and an overall better understanding of the inlet dynamics of Caminada Pass.

Thesis (Ph. D. )--University of Cincinnati, 2008.<br>Advisors: David Nash PhD (Committee Chair), Lewis Owen PhD (Committee Member), Mark Bowers PhD (Committee Member), Thomas Lowell PhD (Committee Member), David Keefer PhD (Committee Member) Title from electronic thesis title page (viewed Sept. 25, 2008). Includes abstract. Includes bibliographical references.

Aquesta tesis es centra en l’estudi de la transferència d’aigua i sediments des de les àrees font de sediments fins les zones de sedimentació a múltiples escales temporals (des de dades amb una freqüència de cinc minuts fins informació de tot un segle) i espacials (des de vessants fins a conques), i les seves implicacions en la morfologia de la llera de la conca de l’Alt Cinca, una conca de muntanya localitzada al vessant sud dels Pirineus. A escala de micro-conca, les dades d’alta resolució obtingudes durant 5 anys en dos badlands contrastats (0.3 ha cadascun) revelen com la pluja controla els processos erosius associats a l’escolament superficial, m’entre que les baixes temperatures tenen una relació significativa amb els processos de moviments en massa. La morfometria d’aquestes superfícies, conjuntament amb la cobertura vegetal són factors clau que determinen els principals processos geomorfològics i els associats canvis topogràfics. Els principals processos observats han estat seqüències d’Erosió i Sedimentació (Cutting and Filling) i Moviments Gravitacionals (Mass Wasting). Tot i que els badlands tenen un paper important en la producció de sediments, el balanç de sediments de la conca del riu Soto (10 km2) indica que aquestes superfícies no sempre controlen l’exportació de sediments a la sortida de petites conques de muntanya amb caràcter intermitent. Aquest fet és degut a la fluctuació de la connectivitat funcional de la xarxa de drenatge causada per la freqüència i magnitud dels polsos d’aigua i sediments durant crescudes sobtades o flashy. La xarxa de drenatge actua com a font i zona d’emmagatzematge de sediments i es clau per entendre les marcades diferències que hi ha en la proporció del sediment que s’exporta en relació a la producció o també anomenat Sediment Delivery Ratio. Els canvis en els usos de sòl en moltes conques de muntanya constatats des de els anys 50 del segle XX tenen un efecte directe en la generació d’escolament (quantitat i magnitud) i en la producció de sediments. La majoria de la superfície de la conca de l’Alt Cinca (1565 km2) ha sofert aforestació, que ha resultat en una reducció de la connectivitat sedimentaria estructural. La construcció de terrasses afecta la connectivitat molt més que els canvis en la coberta del sòl. Les terrasses generalment redueixen la connectivitat degut a l’establiment de zones planes entre mig de zones en pendent. Contràriament, a una escala més local, les terrasses poden incrementar la connectivitat degut a la convergència de flux produïda per les pròpies estructures, o per la caiguda d’aquestes degut a l’abandonament. La construcció de carreteres modifica el pendent i la xarxa de drenatge, fet que comportarà canvis en la connectivitat estructural, que a la vegada poden afectar els processos erosius en les zones veïnes. Així, els fluxos d’aigua i sediments a la conca de l’Alt Cinca han estat àmpliament modificats durant l’últim segle, amb implicacions directes en la forma de la llera. A més a més, impactes locals derivats de les extraccions d’àrids, construcció d’esculleres i embasaments també han condicionat la dinàmica sedimentaria d’aquest riu, amb un impacte directe sobre la morfologia. Aquesta situació ha generat una metamorfosis de la morfologia del riu en la part baixa de l’Alt Cinca (12 km), canviant d’un patró trenat, molt dinàmic, a un patró més estable amb una tendència cap a canal únic. Els resultats obtinguts indiquen que el tram d’estudi està assolint un nou equilibri morfo-sedimentari imposat pels canvis en els fluxos d’aigua i sediments ocorreguts en el darrer segle, incloent les pertorbacions antròpiques que han modificat la geometria del canal i les característiques morfològiques de la llera. S’han observat un total de tres fases en la seva evolució: abans de l’any 1927, el tram d’estudi es trobava en una situació de quasi-equilibri majoritàriament condicionada per les riuades. Entre l’any 1927 i 2012 el riu s’ha ajustat a les diferents pertorbacions que ha tingut a múltiples escales temporals i espacials. Aquest ajust s’ha portat a terme mitjançant dos canvis contrastats en les característiques morfològiques. Finalment, després de l’any 2012, els resultats indiquen que el riu pot haver assolit de nou un nou equilibri, ajustant-se als fluxos d’aigua i sediment imposats i a la nova configuració del canal. Aquesta tesis presenta innovadors mètodes quantitatius per a l’estudi de la producció de sediments i la transferència entre els diferents compartiments de les conques fluvials. La principal novetat en la majoria dels capítols de la tesis recau en l’elevada resolució, de les dades obtingudes, tant temporal com espacial. Els resultats obtinguts en aquesta tesi permeten entendre millor el funcionament dels sistemes fluvials i la seva evolució, aspectes claus per donar suport en la millora i gestió de conques hidrogràfiques de muntanya.<br>Esta tesis se centra en el estudio de la transferencia de agua y sedimentos desde las áreas fuente de sedimentos hasta las áreas de sedimentación a múltiples escales temporales (desde datos con una frecuencia de cinco minutos hasta información de un siglo) y espaciales (desde laderas hasta cuencas), y sus implicaciones en la morfología del cauce en la Cuenca del Alto Cinca (vertiente sur de los Pirineos). A escala de micro-cuenca, los datos de alta resolución obtenidos durante 5 años en dos badlands contrastados (0.3 ha cada uno) revelan como la lluvia controla los procesos erosivos asociados a la escorrentía superficial, mientras que las bajas temperaturas tienen una relación significativa con los procesos de movimientos en masa. La morfometría de estas superficies, conjuntamente con la cobertura vegetal, son factores clave que determinan los principales procesos geomorfológicos y los cambios topográficos asociados. Los principales procesos observados han sido secuencias de Erosión y Sedimentación (Cutting and Filling) y Movimientos Gravitacionales (Mass Wasting). Pese a que los badlands tienen un papel importante en la producción de sedimentos, el balance de sedimentos de la cuenca del rio Soto (10 km2) indica que estas superficies no siempre controlan la exportación de sedimentos a la salida de pequeñas cuencas de montaña con carácter intermitente. Esto principalmente se debe a la fluctuación de la conectividad funcional de la red de drenaje causada por la frecuencia y magnitud de los pulsos de agua y sedimentos durante las crecidas súbitas o flashy. La red de drenaje actúa como fuente y zona de almacenamiento de sedimentos, y es clave para entender las marcadas diferencias que hay en la proporción de sedimento que se exporta en relación a la producción o Sediment Delivery Ratio. Los cambios en los usos del suelo en muchas cuencas de montaña constatados desde los años 50 del siglo XX tienen un efecto directo en la generación de escorrentía (cantidad y magnitud) y en la producción de sedimentos. La mayoría de la superficie de la cuenca del Alto Cinca (1565 km2) ha sufrido forestación, que ha resultado en una reducción de la conectividad sedimentaria estructural. La construcción de terrazas afecta la conectividad mucho más que los cambios en la cobertura del suelo. A una escala más local, las terrazas pueden incrementar la conectividad debido a la convergencia de flujo producida por las propias estructuras, o por la caída de estas debido a su abandono. La construcción de carreteras modifica la pendiente y la red de drenaje, hecho que comporta cambios en la conectividad estructural, que a su vez pueden afectar a los procesos erosivos en las zonas vecinas. Así, los flujos de agua y sedimento en la cuenca del Alto Cinca han estado ampliamente modificados durante el último siglo, con implicaciones directas en la morfología del canal. Además, impactos locales derivados de las extracciones de áridos, construcción de escolleras y embalses también han condicionado la dinámica sedimentaria de este río, con un impacto directo sobre la morfología. Esta situación ha generado una metamorfosis de la morfología del río en la parte baja del Alto Cinca (12 km), cambiando de un patrón trenzado, muy dinámico, a un patrón más estable con una tendencia hacia el canal único. Los resultados obtenidos indican que el tramo de estudio está alcanzando un nuevo equilibrio morfo-sedimentario impuesto por los cambios en los flujos de agua y sedimentos ocurridos durante el último siglo, incluyendo las perturbaciones antrópicas que han modificado la geometría del canal y las características morfológicas del cauce. Se han observado un total de tres fases en su evolución: antes de 1927, el tramo de estudio se encontraba en una situación de casi-equilibrio, mayoritariamente controlada por las crecidas. Entre el año 1927 y 2012 el río se ha ajustado a las diferentes perturbaciones que ha tenido a múltiples escalas temporales y espaciales. Este ajuste se ha llevado a cabo mediante dos cambios contrastados en las características morfológicas. Finalmente, después del año 2012, los resultados indican que el río puede haber alcanzado un nuevo equilibrio, ajustándose a los flujos de agua y sedimento impuestos y la nueva configuración del canal. Esta tesis presenta innovadores métodos cuantitativos para el estudio de la producción de sedimentos y la transferencia entre los diferentes compartimentos de las cuencas fluviales. La principal novedad en la mayoría de los capítulos de la tesis recae en la elevada resolución de los datos obtenidos, tanto temporal como espacial. Los resultados obtenidos en esta tesis permiten entender mejor el funcionamiento de los sistemas fluviales y su evolución, aspectos clave para dar soporte y apoyo en la mejoría y gestión de cuencas hidrográficas de montaña.<br>This thesis focusses on the study of water and sediment transfer from sources to sinks at multiple temporal (from 5-min data to a century data sets) and spatial (from slope to catchment scales) scales and their implications for channel morphology in the Upper Cinca catchment, a mountain catchment located in the Southern Pyrenees. At the micro-catchment scale, our 5-year High Resolution Data Set of two contrasted badlands (around 0.3 ha each) reveal as rainfall control overland-surface flow processes while low temperatures have a significant relation with mass movement-based processes. Morphometry together with vegetation cover are key factors determining main geomorphic processes and associated topographic changes. Main observed geomorphic processes were Cutting and Filling and Mass Wasting. Although badlands may have an important role on sediment production, the 2-year sediment budget of the Soto catchment (10 km2) indicates that badlands do not always control the export of sediments at the outlet of small intermittent mountain catchments. This is mainly due to the fluctuation of the functional connectivity of the channel network caused by the frequency and magnitude of water and sediment pulses during flashy floods. The channel drainage network acts as sediment source and sink and it is key to understand marked differences in the Sediment Delivery Ration. Land use and cover in many mountain catchments have been modified since the fifties of the 20th century, having a direct effect on runoff and sediment production. Most of the area of the Upper Cinca catchment (1565 km2) has undergone afforestation, which resulted in a decrease of structural sediment connectivity. Terracing affects connectivity much more than changes in land cover. Terraces generally reduce connectivity due to the establishment of flat areas between slopes and, contrarily, locally, may increase connectivity due the convergence produced by the structures or the collapse of terraces due to abandonment. Road construction, however, modify slope and the drainage network, which leads to changes in connectivity that could affect erosional processes in the neighbouring areas. Thus, water and sediment fluxes through the Upper Cinca are spatially and temporal dynamic and have been dramatically modified in the last century, with direct implications on channel morphology. Additionally, localised disturbances such as gravel mining, channel embankments and dams have also impacted on sedimentary dynamics, thus channel morphology. This situation led to a river metamorphosis, changing from a braided pattern to a more static channel towards a wandering pattern. We hypothesise that the lowermost 12-km reach of the Upper Cinca has reaching a new equilibrium imposed by catchment-scale changes of water and sediment fluxes caused by global changes, but also influenced by localised human-disturbances that modify channel geometry and morpho-sedimentary characteristics. Three phases were identified: before 1927, the reach remained in a quasi-equilibrium state imposed, mainly, by water and sediment supply during flood events. During the period 1927-2012 the river adjusted to the disequilibrium imposed by disturbances acting at different temporal and spatial scales, yielding two contrasted channel states. Finally, after 2012, we hypothesise that the river may be reaching again a new equilibrium, adjusting to the imposed water and sediment fluxes and the new channel configuration. This thesis presents some novel quantitative methods for the study of sediment production and transfer between the different compartments of fluvial catchments. The main transversal novelty in all the methods used in each chapter lies in the high resolution of the data obtained. This comprehensive analysis aids at understanding the functioning of the river system and their evolution based on multiple-scale disturbances, which can help to support integrated watershed management practices or plans.

Landscapes evolve in a complex interplay between climate and tectonics. Thus, the geomorphic characteristics of a landscape can only be understood if both, climatic and tectonic signals of past and ongoing processes can be identified. In order to evaluate the impact of both forcing factors it is crucial to quantify the evolution of geomorphic markers in natural environments. The Cenozoic Andes are an ideal setting to evaluate tectonic and climatic aspects of landscape evolution at different time and length scales in different natural compartments. The Andean Cordillera constitutes the type subduction orogen and is associated with the subduction of the oceanic Nazca Plate beneath the South American continent since at least 200 million years. In Chile and the adjacent regions this convergent margin is characterized by active tectonics, volcanism, and mountain building. Importantly, along the coast of Chile megathrust earthquakes occur frequently and influence landscape evolution. In fact, the largest earthquake ever recorded occurred in south-central Chile in 1960 and comprised a rupture zone of ~ 1000 km length. However, on longer time scales beyond historic documentation of seismicity it is not well known, how such seismotectonic segments have behaved and how they influence the geomorphic evolution of the coastal realms. With several semi-independent morphotectonic segments, recurrent megathrust earthquakes, and a plethora of geomorphic features indicating sustained tectonism, the margin of Chile is thus a key area to study relationships between surface processes and tectonics. In this study, I combined geomorphology, geochronology, sedimentology, and morphometry to quantify the Pliocene-Pleistocene landscape evolution of the tectonically active south-central Chile forearc. Thereby, I provide (1) new results about the influence of seismotectonic forearc segmentation on the geomorphic evolution and (2) new insights in the interaction between climate and tectonics with respect to the morphology of the Chilean forearc region. In particular, I show that the forearc is characterized by three long-term segments that are not correlated with short-lived earthquake-rupture zones that may. These segments are the Nahuelbuta, Toltén, and Bueno segments, each recording a distinct geomorphic and tectonic evolution. The Nahuelbuta and Bueno segments are undergoing active tectonic uplift. The long-term behavior of these two segments is manifested in form of two doubly plunging, growing antiforms that constitute an integral part of the Coastal Cordillera and record the uplift of marine and river terraces. In addition, these uplifting areas have caused major changes in flow directions or rivers. In contrast, the Toltén segment, situated between the two other segments, appears to be quasi-stable. In order to further quantify uplift and incision in the actively deforming Nahuelbuta segment, I dated an erosion surface and fluvial terraces in the Coastal Cordillera with cosmogenic 10Be and 26Al and optically stimulated luminescence, respectively. According to my results, late Pleistocene uplift rates corresponding to 0.88 mm a-1 are faster than surface-uplift rates averaging over the last 5 Ma, which are in the range of 0.21 mm a-1. This discrepancy suggests that surface uplift is highly variable in time and space and might preferably concentrate along reverse faults as indicated by a late Pleistocene flow reversal. In addition, the results of exposure dating with cosmogenic 10Be and 26Al indicate that the morphotectonic segmentation of this region of the forearc has been established in Pliocene time, coeval with the initiation of uplift of the Coastal Cordillera about 5 Ma ago, inferred to be related to a shift in subduction mode from erosion to accretion. Finally, I dated volcanic clasts obtained from alluvial surfaces in the Central Depression, a low-relief sector separating the Coastal from the Main Cordillera, with stable cosmogenic 3He and 21Ne, in order to reveal the controls of sediment accumulation in the forearc. My results document that these gently sloping surfaces have been deposited 150 to 300 ka ago. This deposition may be related to changes in the erosional regime during glacial episodes. Taken together, the data indicates that the overall geomorphic expression of the forearc is of post-Miocene age and may be intimately related to a climatic overprint of the tectonic system. This climatic forcing is also reflected in the topography and local relief of the Central and Southern Andes that vary considerably along the margin, determined by the dominant surface process that in turn is eventually controlled by climate. However, relief also partly reflects surface processes that have taken place under past climatic conditions. This emphasizes that due care has to be exercised when interpreting landscapes as mirrors of modern climates.<br>Landschaften entwickeln sich im komplexen Zusammenspiel von Klima und Tektonik. Demzufolge können sie nur verstanden werden, wenn sowohl klimatische als auch tektonische Signale vergangener und rezenter Prozesse identifiziert werden. Um den Einfluss beider Faktoren zu bewerten, ist es deshalb wichtig, die Evolution geomorphologischer Marker in der Natur zu quantifizieren. Die känozoischen Anden sind eine ideale Region, um tektonische und klimatische Aspekte der Landschaftsentwicklung auf verschiedenen Zeit- und Längenskalen zu erforschen. Sie sind das Modell-Subduktionsorogen, assoziiert mit der Subduktion der ozeanischen Nazca-Platte unter den südamerikanischen Kontinent seit ca. 200 Mio Jahren. In Chile ist dieser konvergente Plattenrand geprägt von aktiver Tektonik, Vulkanismus und Gebirgsbildung. Bedeutenderweise ereignen sich entlang der Küste häufig Megaerdbeben, die die Landschaftsentwicklung stark beeinflussen. Tatsächlich ereignete sich das größte jemals aufgezeichnete Erdbeben mit einer Bruchzone von ca. 1000 km Länge 1960 im südlichen Zentralchile. Nichtsdestotrotz ist auf längeren Zeitskalen über historische Dokumentationen hinaus nicht bekannt, wie sich solche seismotektonischen Segmente verhalten und wie sie die geomorphologische Entwicklung der Küstengebiete beeinflussen. Mit semi-unabhängigen morphotektonischen Segmenten, wiederkehrenden Megaerdbeben und einer Fülle geomorphologischer Marker, die aktive Tektonik anzeigen, ist somit der Plattenrand von Chile ein Schlüsselgebiet für das Studium von Zusammenhängen zwischen Oberflächenprozessen und Tektonik. In dieser Arbeit kombiniere ich Geomorphologie, Geochronologie, Sedimentologie und Morphometrie, um die plio-pleistozäne Landschaftsentwicklung des tektonisch aktiven süd-zentralchilenischen Forearcs zu quantifizieren. Mit dieser Analyse liefere ich (1) neue Ergebnisse über den Einfluss seismotektonischer Forearc-Segmentierung auf die geomorphologischen Entwicklung und (2) neue Erkenntnisse über die Interaktion zwischen Klima und Tektonik bezüglich der Gestaltung des chilenischen Forearcs. Ich zeige, dass der Forearc in drei langlebige morphotektonische Segmente gegliedert ist, die nicht mit kurzlebigen Erdbebenbruchzonen korrelieren. Die Segmente heißen Nahuelbuta, Toltén und Bueno Segment, wovon jedes eine andere geomorphologische und tektonische Entwicklung durchläuft. Die Nahuelbuta und Bueno Segmente unterliegen aktiver tektonischer Hebung. Das langfristige Verhalten dieser beiden Segmente manifestiert sich in zwei beidseitig abtauchenden, wachsenden Antiklinalen, die integraler Bestandteil des Küstengebirges sind und die Hebung von marinen und fluvialen Terrassen aufzeichnen. Die Hebung verursachte weitreichende Veränderungen in den Fließrichtungen des Gewässernetzes. Im Gegensatz dazu ist das Toltén Segment, das sich zwischen den beiden anderen Segmenten befindet, quasi-stabil. Um die Hebung und Einschneidung in dem tektonisch aktiven Nahuelbuta Segment zu quantifizieren, habe ich eine Erosionsfläche und fluviale Terrassen in dem Küstengebirge mit kosmogenem 10Be und 26Al bzw. optisch stimulierter Lumineszenz datiert. Meinen Ergebnissen zufolge sind die spätpleistozänen Hebungsraten, die ca. 0,88 mm a-1 betragen, höher als die Oberflächenhebungsraten, die über die letzten 5 Mio Jahre mitteln und ca. 0,21 mm a-1 betragen. Diese Diskrepanz deutet an, dass die Hebung der Oberfläche räumlich und zeitlich sehr stark variiert und sich präferiert an Aufschiebungen konzentriert. Zusätzlich zeigen die Ergebnisse der Expositionsdatierung mit kosmogenem 10Be und 26Al, dass die morphotektonische Segmentierung im Pliozän etabliert wurde, zeitgleich mit dem Beginn der Hebung des Küstengebirges vor ca. 5 Mio Jahren infolge eines Wechsels des Subduktionsmodus von Erosion zu Akkretion. Schließlich habe ich vulkanische Klasten, die aus alluvialen Flächen im Längstal stammen, mit den stabilen kosmogenen Nukliden 3He und 21Ne datiert, um Aufschluss über die Faktoren zu erhalten, die die Sedimentablagerung im Forearc bestimmen. Meine Ergebnisse weisen darauf hin, dass diese flach einfallenden Oberflächen, die vor 150.000 bis 300.000 Jahren abgelagert wurden, in Zusammenhang mit Änderungen des Erosionsregimes in glazialen Episoden entstanden sind. Zusammenfassend zeigen die Daten, dass der heutige geomorphologische Ausdruck des Forearcs post-Miozän und eng mit einer klimatischen Überprägung des tektonischen Systems verknüpft ist. Der klimatische Einfluss spiegelt sich ebenfalls in der Topographie und dem lokalen Relief der Zentral- und Südanden wider. Beide Parameter variieren stark entlang des Plattenrandes, bestimmt durch den jeweils dominierenden Oberflächenprozess, der wiederum letztendlich vom vorherrschenden Klima abhängt. Allerdings reflektiert das Relief teilweise Oberflächenprozesse, die unter vergangenen Klimaten aktiv waren. Das betont die äußerst große Vorsicht, die nötig ist, wenn Landschaften als Spiegel des aktuellen Klimas interpretiert werden.

Wreck Shoal is a subtidal oyster reef area located in the James River, Virginia. Two significantly different types of oyster reefs are found in adjacent areas on Wreck Shoal. Hard-rock reefs are characterized by a relatively thick oyster shell layer, higher densities of live oysters, a coarser interstitial sediment, and a negligible sediment cover. In contrast, mud-shell reefs are characterized by a very thin osyter shell layer, considerably lower densities of live oysters, a finer interstitial sediment, and a 1-2 cm layer of very fine sediments covering the reef. The contemporary sedimentation processes operating on the hard-rock and mud-shell oyster reefs are distinctly different. The hard-rock oyster reefs are in shallower water, experience stronger bottom currents, and present a hydraulically rougher surface to the flow. The mud-shell oyster reefs are in deeper water, experience weaker bottom currents, and present a hydraulically smoother surface to the flow. These factors result in substantially different bottom shear stresses at the fluid-bed interface. The hard-rock oyster reef, with the high bottom shear stress is rarely depositional with respect to fine sediments. In contrast, the mud-shell oyster reef with the low bottom shear stresses is rarely erosional with respect to fine sediments. The James River estuary has evolved, moving upstream and landward in response to a rising sea level. The Wreck Shoal oyster reefs have developed on the ridge and swale topography of a point-bar formed during the late Pliestocene Epoch. From the 1550's to the 1850's the oyster reef developed vertically almost 1.5 m. From the 1850's to present the oyster reefs have lost more than 1.0 m of elevation due to intense harvesting activity. Conceptual models of subtidal oyster reef dynamics and development are proposed and verified based on field observations. The management implications of the results of the study are presented and recommendations are made for the rational exploitation and management of the resource.

O estudo de bacias hidrográficas no meio tropical úmido, tem adquirido grande importância nas últimas décadas, devido a crescente demanda por planejamento de recursos hídricos. Entretanto, muitos desses trabalhos têm confundido o conceito de bacias hidrográficas, acreditando ser esta, uma mera rede de canais interconectados que formam a hidrografia dos terrenos, portanto, tomando-a como simples unidade cartográfica de estudo. Este fato tem banalizado em muito o uso de conceitos relacionados aos estudos de bacias, provocando sérios equívocos nas produções acadêmicas atuais. Partindo do princípio de que as bacias hidrográficas são espaços territoriais de circulação vertical e horizontal dágua, tendo a rede interconectada de canais, como um dos seus principais elementos, que escolhemos a bacia hidrográfica do Rio Benevente para estudo da relação entre a dinâmica fluvial desta e os seus condicionantes estruturais e morfológicos. Fundamentado no método da associação e indeterminação geomorfológica de Leopold e Langbein (1970), e, através de informações oriundas dos procedimentos técnico-operacionais de compartimentação geomorfológica e compilação de dados de parâmetros hidrográficos, foi possível descobrir que os sub-sistemas de drenagem que compõem a hidrografia total da bacia, evoluem condicionados por litoestruturas cristalinas e tectônicas do proterozóico, portanto, de organização antiga, e, que, aparentemente, demonstram não sofrer reativações modernas, a ponto de intervir na evolução dos sub-compartimentos de relevo regionais e na evolução hidrográfica da rede de canais. Chega-se desta forma, à conclusão de que os processos de encaixamento da drenagem, capturas fluviais, seccionamento de litoestruturas, gênese de knickpoints e evolução dos perfis longitudinais fluviais estão associados à dinâmica de processos geomórficos diferenciais, sob litoestruturas de forte natureza anisotrópica e complexa organização geotectônica. Fato que responde pela diversidade de sub-compartimentos de relevo e configuração evolutiva dos sistemas fluviais de dinâmicas diferenciais.<br>The study of watersheds in the humid tropical environment, has acquired great importance in recent decades due to growing demand for water resources planning. However, many studies have confused the concept of watersheds, believing that this was simply a network of interconnected channels that form the hydrography of the land, thus making it as simple cartographic unit of study. This commonplace is the use of concepts related to the studies of basins, causing serious confusion in the current academic productions. Assuming that the basins are territorial spaces of vertical and horizontal movement of water, the interconnected network of channels, as one of its main elements, we chose the basin of Rio Benevente to study the relationship between the dynamics of this river and its structural and morphological constraints. Based on the method of the Association and indeterminacy in geomorphologic Leopold and Langbein (1970), and through information from the technical and operational procedures of geomorphological partitioning and compilation of data from hydrographic parameters, could find that the sub-drainage systems that make up the total of the hydrographic basin, driven by evolving litoestruturas crystal and the tectonic proterozóico, therefore, the old organization, and that, apparently, show not suffer reactivations modern as to intervene in the evolution of sub-compartments of regional importance and the evolution of the network of river channels. Enough is thus concluded that the processes to fit the drainage, catch river, sectioning of litoestruturas, gênesis of knickpoints and evolution of longitudinal river profiles are associated with the dynamic of geomorphic processes differential,under litoestruturas of strong anisotropic nature and complex organization geotectônica. Fact responsible for the diversity of sub-compartments of important configuration and evolutionary dynamics of river systems of differential.

The aim of this study is to understand the extent, depth, magnitude and significance of subglacial sediment deformation. It will examine the role of this deformation in controlling glacier dynamics and landform generation in glaciers in general, and polythermal glaciers in particular. A detailed multi-dimensional approach is used to study recently exposed glacigenic sediments on the forefields of three polyglaciers in the Tarfala Valley, northern Sweden. Overridden fluted moraines and diamicton plains occur in each forefield. These palimpsest landforms consist of multiple subglacial traction tills. Flutes have quasi-regular geometry and about half of those studied have no initiating boulder. It is suggested here that flute formation by forced-mechanisms was superimposed on flute formation related to a topographically-induced flow instability. In each forefield the depth of the deforming-bed averaged between 0.2m and 0.6m thickness. Detailed clast fabric data suggest the diamicton plain is composed of thin layers of traction tills that accreted over time as the zone of deformation moved upwards. Laboratory shear box tests show that subglacial deformation required elevated pore-water pressures, which suggests deforming-bed conditions and flute formation were restricted to the temperate zones of polythermal glaciers. Magnetic fabrics suggest strain magnitudes were moderate (≤10), rather than the very high strain magnitudes (>10²) required by the deforming-bed model. The application of the micro-structural mapping technique demonstrates that subglacial deformation was multi-phase, heterogeneous, and partitioned into the softer and more easily deformed parts of the matrix. Consequently, deformation is controlled by variations in sediment granulometry and pore-water pressure, and is likely to have been spatially and temporally variable, a finding that supports the ice-bed mosaic model. The strain magnitudes and deforming-bed thickness suggest that soft-bed deformation did not exert a major control on glacier dynamics during the Little Ice Age advance.

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2018-03-23T16:50:55Z No. of bitstreams: 1 PGCS15DA035.pdf: 8233837 bytes, checksum: 2bf2d66cbb50bb2bfe83751d86a81f26 (MD5)<br>Made available in DSpace on 2018-03-23T16:50:55Z (GMT). No. of bitstreams: 1 PGCS15DA035.pdf: 8233837 bytes, checksum: 2bf2d66cbb50bb2bfe83751d86a81f26 (MD5) Previous issue date: 2015-09-25<br>Capes<br>The sustainable use of natural resources, with emphasis on soil exploration in conservation base, demand for detailed information on their characteristics and properties, as an indication of its quality, to recommend the correct land use and the best management system. The study aimed to characterization of the nature and properties of the main soils in the southwestern region of the State of Rio Grande do Sul – Brazil, establishing relationships between the physical and chemical attributes with your mineralogical constitution, and researching the causes of the variability of soil classes resultant from the dynamics of the processes considering the lithological variation and modeled of topographic surface. The area studied is situated in the Basin of Santa Maria River in Rosario do Sul County located at latitude 30°15'28" south and longitude 54°54'50" west, with an average altitude of 132 m, humid mesothermal climate, average annual temperature near to 20°C, and a rainfall in the range of 1300 mm. The cartographic base consisted of topographic charts, geological map, satellite imagery, digital elevation models, and support from global positioning system receivers and geographic information system. Geomorphometric variables maps were used for the correlation of the geomorphic surfaces with pedogenesis applying classic models to the compartmentalization of slopes. Topolithosequence were defined as from soil developed with lithology of the Pirambóia, Sanga-of-Cabral and Guará geological formations, choosing to the soil profiles based on types of source material, variations in relief and altitude. It was proceeded a general and morphological description of soil profiles and a horizons sampling collection for chemical, physical, mineralogical and sedimentological analysis, aiming to study the influence of relief forms and the different source materials in the genesis and mineralogical composition of the soil, as well as to understand and describe the main pedogenic processes actants in their evolution. It was observed that soils developed in the same geological formation, in function to lithological variations of the sedimentary package, can have different chemical and mineralogical composition. Furthermore, the differences between the soils also are due to the strong interaction of the source material to the type and intensity of pedogenic processes, influenced by the position they hold in the landscape, conditioned by the flow of water in the soil, as presumably have evolved under the same preterit climatic conditions<br>O uso sustentável dos recursos naturais, com ênfase na exploração do solo em base conservacionista, demanda por informações pormenorizadas das suas características e propriedades, como um indicativo da sua qualidade, para recomendar o uso correto do solo e o melhor sistema de manejo. O estudo teve como objetivo geral a caracterização da natureza e das propriedades dos principais solos da região sudoeste do RS, estabelecendo relações entre os atributos físicos e químicos com sua constituição mineralógica, e investigando as causas da variabilidade das classes de solos decorrentes da dinâmica dos processos, considerando a variação litológica e o modelado da superfície topográfica. A área de estudo está situada na bacia hidrográfica do Rio Santa Maria na cidade de Rosário do Sul-RS localizada a 30° 15′ 28″S e 54° 54′ 50″W, altitude média de 132 m, clima tipo Cfa, temperatura média anual próxima a 20 °C e índice pluviométrico médio de 1300 mm. A base cartográfica básica consistiu de cartas topográficas, mapa geológico, imagens de satélite, modelos digitais de elevação e apoio de receptores GPS e de SIG’s. Mapas de variáveis geomorfométricas foram utilizados para a correlação das superfícies geomórficas com a pedogênese aplicando-se modelos clássicos de compartimentação de vertentes. Foram definidas topolitossequências a partir de solos desenvolvidos de litologias das formações geológicas Pirambóia, Sangado- Cabral e Guará, escolhendo-se os perfis de solos com base em tipos de materiais de origem, variações no relevo e na altitude. Procedeu-se à descrição geral e morfológica dos perfis e a coleta de amostras de solo deformadas em cada um dos horizontes para análises químicas, físicas, mineralógicas e sedimentológicas, visando estudar a influência das formas de relevo e dos diferentes materiais de origem na gênese e na composição mineralógica dos solos, assim como compreender e descrever os principais processos pedogenéticos atuantes na sua evolução. Observou-se que solos desenvolvidos da mesma formação geológica, em função de variações litológicas do pacote sedimentar, apresentam composição química e mineralógica diferente. Além disso, as diferenças entre os solos também se devem à forte interação do material de origem com o tipo e intensidade dos processos pedogênicos, influenciados pela posição que ocupam na paisagem, condicionados pelos fluxos de água no solo, já que supostamente evoluíram sob as mesmas condições climáticas pretéritas

A basin analysis was conducted at the Conway Flat coast (Marlborough Fault Zone, South Island, New Zealand) to investigate the interaction of regional and local structure in a transpressional plate boundary and its control on basin formation. A multi-tiered approach has been employed involving: (i) detailed analysis of sedimentary deposits; (ii) geomorphic mapping of terraces, fault traces and lineaments; (iii) dating of deposits by 14C and OSL and (iv) the integration of data to form a basin-synthesis in a sequence stratigraphy framework. A complex thrust fault zone (the Hawkswood Thrust Fault Zone), originating at the hinge of the thrust-cored Hawkswood anticline, is interpreted to be a result of west-dipping thrust faults joining at depth with the Hundalee Fault and propagating eastwards. The faults uplift and dissect alluvial fans to form terraces along the Conway Flat coast that provide the necessary relief to form the fan deltas. These terrace/fan surfaces are ~9 km long and ~3 km wide, composite features, with their upper parts representing sub-aerial alluvial fans. These grade into delta plains of Quaternary Gilbert-style fan deltas. Uplift and incision have created excellent 3D views of the underlying Gilbert-style fan delta complexes from topsets to prodelta deposits. Erosive contacts between the Medina, Rafa, Ngaroma and modern Conway fan delta deposits, coupled with changes in terrace elevations allow an understanding of the development of multiple inset terraces along the Conway Flat coast. These terraces are divided into five stages of evolution based on variations in sedimentary facies and geomorphic mapping: Stage I involves the uplift of the Hawkswood Range and subsequent increased sedimentation rate such that alluvial fans prograded to the sea to form the Medina fan delta Terrace. Stage II began with a period of incision, from lowering sea level or changes in the uplift and sedimentation rate and continued with the deposition of the Dawn and Upham fan deltas. Stage III starts with the incision of the Rafa Terrace and deposition of aggradational terraces in the upper reaches. Stage IV initiated by a period of incision followed by deposition of estuarine facies at ~8ka and Stage V began with a period of incision and continues today with the infilling of the incised valley by the modern fan delta of the Conway River and its continued progradation. New dates from within the Gilbert-type fan deltas along the Conway Flat coast are presented, using OSL and 14C dating techniques. Faulting at the Conway Flat coast began ~ 94 ka, based on the development of the Medina Terrace fan delta with uplift rates ~1.38~1.42 m/ka. The interplay of tectonics and sea level fluctuations continued as the ~79 ka Rafa Terrace fan deltas were created, with uplift rates calculated at ~1.39 m/ka. Detailed 14C ages from paleoforest (~8.4-~6.4 ka) in the Ngaroma Terrace and from the mouths of smaller streams have established uplift rates during the Holocene ~1-3 m/ka, depending on sea level.

Although the physical characteristics of surfing breaks are well described in the literature, there is little specific research on surfing and coastal management. Such research is required because coastal engineering has had significant impacts to surfing breaks, both positive and negative. Strategic planning and environmental impact assessment methods, a central tenet of integrated coastal zone management (ICZM), are recommended by this thesis to maximise surfing amenities. The research reported here identifies key oceanographic considerations required for ICZM around surfing breaks including: surfing wave parameters; surfing break components; relationship between surfer skill, surfing manoeuvre type and wave parameters; wind effects on waves; currents; geomorphic surfing break categorisation; beach-state and morphology; and offshore wave transformations. Key coastal activities that can have impacts to surfing breaks are identified. Environmental data types to consider during coastal studies around surfing breaks are presented and geographic information systems (GIS) are used to manage and interpret such information. To monitor surfing breaks, a shallow water multibeam echo sounding system was utilised and a RTK GPS water level correction and hydrographic GIS methodology developed. Including surfing in coastal management requires coastal engineering solutions that incorporate surfing. As an example, the efficacy of the artificial surfing reef (ASR) at Mount Maunganui, New Zealand, was evaluated. GIS, multibeam echo soundings, oceanographic measurements, photography, and wave modelling were all applied to monitor sea floor morphology around the reef. Results showed that the beach-state has more cellular circulation since the reef was installed, and a groin effect on the offshore bar was caused by the structure within the monitoring period, trapping sediment updrift and eroding sediment downdrift. No identifiable shoreline salient was observed. Landward of the reef, a scour hole ~3 times the surface area of the reef has formed. The current literature on ASRs has primarily focused on reef shape and its role in creating surfing waves. However, this study suggests that impacts to the offshore bar, beach-state, scour hole and surf zone hydrodynamics should all be included in future surfing reef designs. More real world reef studies, including ongoing monitoring of existing surfing reefs are required to validate theoretical concepts in the published literature.

The term'calcrete' encompasses any secondary carbonate accumulation found within the regolith, irrespective of morphology and degree of induration: Calcretes cover geographically extensive areas of southern Australia as calcareous soils, surficial deposits of carbonate-rich sediment, and calcareous palaeosols. Combined field and laboratory studies of calcretes on the eastern margin of the St Vincent Basin were undertaken to ascertain the mechanisms responsible for calcrete genesis. Geological processes were very important in the development of the Pleistocene carbonate mantle which blankets a variety of substrates in the study area. The unconsolidated carbonate silt in which the calcrete formed contains pellets (10 to 50 pm in diameter) similar to those found in loess. The fine particle size, combined with the regional distribution of the carbonate mantle, indicate that the carbonate silt may have had an aeolian component. During the last glacial maximum when arid climates prevailed in southern Australia and sea level was significantly lowered, conditions were favourable for the formation of carbonate silt. Coastal calcarenites which lacked vegetation and ephemeral carbonate rich lakes, were stranded during the regression and eroded by strong westerly winds. This carbonate was blown inland and mixed with locally reworked acid-insoluble minerals from fluvial/alluvial environments. Deposition of calcareous material occurred in several cycles. Eventually, the deposits formed a blanket of variable thickness over the Pleistocene fluvial landscape. The fluvial nature of the underlying sediments was identified from field observations, granulometric analyses and studies of the surface textures of quartz grains. In the Willunga and Noarlunga Embayments of the St Vincent Basin, the change from fluvial to aeolian depositional environments was gradational and is recorded by compound palaeosols between the Ngaltinga Formation and the carbonate mantle. It has been established that facies variations within the fluvial deposits strongly influenced the form of calcrete. Low rates of fluvial deposition associated with topstratum deposits (Neva Clay Member) allowed the superposition of several carbonate palaeosols and thus the accumulation of thick calcretes. In contrast, where erosion was more rapid associated with channels and, to a lesser extent, crevasse splays of the Snapper Point Sand Member, palaeosols were eroded and rarely preserved. Geomorphic and pedogenic processes had a significant influence on vertical and lateral facies changes in the carbonate mantle. The geomorphic factors which are most important in understanding lateral changes include topography, soil creep, dissolution of hardpans and distance from modern water courses. These factors were identified during mapping of changes in calcrete morphology. The interaction of inorganic and organic pedogenic processes are thought to have controlled the consistent mineralogical changes observed in the carbonate mantle. Typically, low Mg calcite concentrates in nodules, laminae and hardpans at the top of calcrete profiles, declining in abundance with depth as the proportion of calcian dolomite increases. This trend is mimicked by a decline in Ca/Mg ratio (determined from XRF analyses) with depth. It may be explained by the dissolution of both calcite and dolomite from the aeolian deposit, translocation as ions in solution and reprecipitation initially of calcite and then dolomite as the descending solution became progressively Mg enriched. The reprecipitation of calcite may be explained by either the lower solubility of this mineral, or the fact that many of the micro- organisms concentrated in the upper part of the profile biologically control the deposition of calcite within their mucilagenous sheaths and may also influence the inorganic precipitation of micrite by changing pCO2 and moisture levels within the soil. Tubiform calcified filaments of possible fungal and algal origin concentrate in the indurated materials of the calcrete. These filaments, which bind soil macroaggregates and fecal pellets initiated the formation of nodules and are an important component in the coatings on clasts. Two different groups of needle-fibre calcite have been identified. Small microrods are bacterial in origin, whereas larger needle-fibres which may have epitaxial overgrowths to form serrated varieties, grow within mycelial strands associated with plant roots. These calcified micro-organisms, together with rhizoliths and calcareous insect pupal cases, indicate the pedogenic nature of the calcrete. Geological, geomorphic and pedogenic processes interacted during constructional and destructional phases of calcrete genesis. These phases are polycyclic and often coeval. The constructional phase is characterised by the deposition of carbonate silt, followed by the formation of pellets, nodules, platy structure, wedges, rhizoliths, rectangular texture, hardpan and laminae. The macromorphology, mineralogy and micromorphology of each of these calcareous forms helped to identify the mechanisms controlling their formation. During the destructional phase the hardpans were dissolved, brecciated and eroded to liberate clasts which moved downslope and accumulated as colluvial deposits. These deposits were then recemented into rubbly hardpans. Climate and movements in sea level appear to control the timing of major changes from constructional to destructional phases. Thus calcrete genesis is controlled by the polycyclic interaction of climate, geological, geomorphic and pedogenic processes.<br>Thesis (Ph.D.) -- University of Adelaide, Dept. of Soil Science, 1988

Research Doctorate - Doctor of Philosophy (PhD)<br>The main purpose of this research was to determine how river channel functions in the gorge and upland reaches of the highly regulated Snowy River might recover after experimental floods and natural floods from the downstream residual catchment, since Jindabyne Dam closed in 1967. By quantifying the geomorphic effectiveness of various floods at the site, channel unit and cross-section scales, the processes and rates of adjustment with time were determined for channel width, depth, conveyance capacity and surface bed sediment size. This enabled the rates of adjustment and pathways to suitable recovery target endpoints to be quantitatively modelled. Current recovery models are based on few observations and measurements and are lacking well-articulated endpoints. This lack of understanding of channel recovery processes, rates and pathways, limits predictions that could assist in the management of this river. Channel adjustment was spatially and temporally complex. Adjustments were through different processes, at different rates and on different pathways in response to floods with different flood power characteristics. The ‘most geomorphically effective’ floods had high peak stream power (69-77 W/m²), long duration (49-280 days), moderate to large total energy expenditure (78610-128441 Joules x 10³), high peak discharges (126-447 cumecs), and multiple high discharge peaks on the rising and falling limbs of the hydrograph. These floods have disrupted the dynamic equilibrium after nearly 50 years of de-watering. By world standards these floods may seem small, but for the Snowy River, this disequilibrium has returned some river channel functions. Consistent and statistically significant geomorphic adjustment trends occurred in runs, with time but not in riffles, pools and pool-tails. Runs offer the most accurate indicators of channel widening, deepening, increasing conveyance capacity and sediment coarsening. Most run cross-sections selected were predicted to recover to average target endpoints by 2038 ±10 years (allowing for bushfire and flood) if up to 23 ±1 more, ‘most geomorphically effective’ floods are released annually from Jindabyne Dam. A new dynamic equilibrium for most runs might then be reached if adjustment trends in the four geomorphic variables are consistent. Once most run average target endpoints are reached, other ‘moderately’, or ‘less’ geomorphically effective floods can be released for channel maintenance and bank building. Phragmites had the right combination of root-sediment properties to best stabilise the overbank flood deposits that form the new banks of the Snowy River.