Neste estudo, o tamanho médio do Sortable Silt da fração ‹ 63 micra dos sedimentos terrígenos foi medido em um testemunho para os últimos 800 ka na Bacia de Santos. Os estágios isotópicos marinhos (MIS) foram identificados até MIS o 19. Investigamos as variações oceanográficas passadas para obter uma melhor compreensão sobre a intensidade do fluxo de corrente de fundo durante os períodos glaciais / interglaciais. Os registros contínuos do Sortable Silt, isótopos de oxigênio e carbono, susceptibilidade magnética, taxa de sedimentação, fluxos de massa e conteúdo de carbonato foram obtidos e mostraram uma forte modulação com a intensidade do fluxo de corrente de fundo em resposta a ciclos glaciais e interglaciais. Em geral, para os períodos glaciais, foi possível observar uma dominância do deslocamento da água do fundo em direção ao norte. Uma comparação entre diferentes métodos de análise granulométrica (laser e técnica de pipetagem), revelou que ambos caracterizam os períodos interglacial e glacial. As análises espectrais mostraram um forte sinal no Sortable Silt para os ciclos da excentricidade (∼ 100 ka), o que foi confirmado pelos isótopos de oxigênio e susceptibilidade magnética, que apresentaram um sinal similar. Variações concomitantes no Sortable Silt e nos diferentes traçadores confirmam o potencial do primeiro como um proxy para a intensidade do fluxo de corrente de fundo. / In this study, the Sortable Silt mean size of the ‹ 63micra terrigenous sediment fraction were measured in a core for the last 800kyrs in Santos Basin. Marine Isotopic Stages (MIS) down to MIS 19 were identified. We investigate the past oceanographic variations to obtain a better understanding about bottom-current flow intensity during glacial/interglacial periods. Continuous records of Sortable Silt, oxygen and carbon isotopes, magnetic susceptibility, sedimentation rate, mass fluxes and carbonate content were obtained and show a strong modulation of bottom-current flux intensity in response to glacial and interglacial cycles. In general, for glacial periods it was possible to observe a dominance of northward bottom water. A comparison between different methods of grain-size analysis (laser and the pipetting technique), revealed that both characterize the interglacial and glacial periods. The spectral analyzes showed a strong signal in the Sortable Silt for the cycles of the eccentricity (~ 100 ka), which was confirmed by the oxygen isotopes and magnetic susceptibility, which presented a similar signal. Concomitant variations in the sortable silt and in the different tracers confirms the potential of the first as a proxy for bottom-current flow intensity.

Neste estudo, o tamanho médio do Sortable Silt da fração ‹ 63 micra dos sedimentos terrígenos foi medido em um testemunho para os últimos 800 ka na Bacia de Santos. Os estágios isotópicos marinhos (MIS) foram identificados até MIS o 19. Investigamos as variações oceanográficas passadas para obter uma melhor compreensão sobre a intensidade do fluxo de corrente de fundo durante os períodos glaciais / interglaciais. Os registros contínuos do Sortable Silt, isótopos de oxigênio e carbono, susceptibilidade magnética, taxa de sedimentação, fluxos de massa e conteúdo de carbonato foram obtidos e mostraram uma forte modulação com a intensidade do fluxo de corrente de fundo em resposta a ciclos glaciais e interglaciais. Em geral, para os períodos glaciais, foi possível observar uma dominância do deslocamento da água do fundo em direção ao norte. Uma comparação entre diferentes métodos de análise granulométrica (laser e técnica de pipetagem), revelou que ambos caracterizam os períodos interglacial e glacial. As análises espectrais mostraram um forte sinal no Sortable Silt para os ciclos da excentricidade (∼ 100 ka), o que foi confirmado pelos isótopos de oxigênio e susceptibilidade magnética, que apresentaram um sinal similar. Variações concomitantes no Sortable Silt e nos diferentes traçadores confirmam o potencial do primeiro como um proxy para a intensidade do fluxo de corrente de fundo. / In this study, the Sortable Silt mean size of the ‹ 63micra terrigenous sediment fraction were measured in a core for the last 800kyrs in Santos Basin. Marine Isotopic Stages (MIS) down to MIS 19 were identified. We investigate the past oceanographic variations to obtain a better understanding about bottom-current flow intensity during glacial/interglacial periods. Continuous records of Sortable Silt, oxygen and carbon isotopes, magnetic susceptibility, sedimentation rate, mass fluxes and carbonate content were obtained and show a strong modulation of bottom-current flux intensity in response to glacial and interglacial cycles. In general, for glacial periods it was possible to observe a dominance of northward bottom water. A comparison between different methods of grain-size analysis (laser and the pipetting technique), revealed that both characterize the interglacial and glacial periods. The spectral analyzes showed a strong signal in the Sortable Silt for the cycles of the eccentricity (~ 100 ka), which was confirmed by the oxygen isotopes and magnetic susceptibility, which presented a similar signal. Concomitant variations in the sortable silt and in the different tracers confirms the potential of the first as a proxy for bottom-current flow intensity.

The Understen-Märket trench is located in the Southern Quark and is the only deep-water connection between the Baltic Propper and the Gulf of Bothnia. Bathymetric mapping reveals a number of eroded channels and drift deposits exists on the seafloor, indicating that the area is heavily affected by current activity. Bottom current behavior in the area is not thoroughly understood, but generally in the BalticBasin, there is southward flowing fresh surface waters compensated by denser northward-flowing more saline bottom waters. The dominant direction of flow for bottom waters in the Southern Quark is northward. Northward speeds often exceed the threshold required to erode fine material on the seafloor. Using geophysical data and marine sediment cores, this study shows that current eroded channels and drift deposits in the Understen-Märket trench were initially formed in the late Holocene between 3 – 4kyr BP, during the transition from the Littorina to the Post Littorina stages of the Baltic Sea. Application of the sortable silt (SS) proxy for current sorting show three distinct regimes that closely match the assigned lithologic units (LU) based on core descriptions. Downcore grain size analysis of three marine sediment cores reveals a gradual boundary to sandy sediments that caps two of the cores recovered from an eroded channel. The third core was recovered from the drift deposit which mostly consists of silt. The progressive coarsening suggests that the current activity has increased during the late Holocene. A simplified model is presented that shows how moderate (20-50 m) shallowing of the sill, which has occurred in response to isostatic rebound between 8 and 4 kyr BP, could have generated the higher current speeds seen today. However, this should be explored using more advanced paleo-circulation models.

Stratigraphic successions of sedimentary rocks represent an important repository for signals pertaining to the history and evolution of Earth. Whereas the specific processes reflected by the stratigraphic record differ with respect to a given depositional environment, deposits in deep-marine settings, particularly passive margins, provide a unique, long-term record of paleoclimate, paleoceanography, and tectonics affecting the basin in question. Whereas deep-marine strata may be used to answer myriad of questions regarding the evolution and development of Earth systems, this dissertation narrowly targets two distinct aspects of sedimentation in deep-sea settings. The first two chapters focus on the utility of sortable silt in reconstructing bottom-current intensity linked to major shifts in climate. First, the relationship of sortable silt to flow velocity was tested under controlled conditions in a flow-through flume. This chapter investigates the correlation of sortable silt metrics across several experimental parameters, which is found here to dispute longstanding assumptions that multiple metrics must correlate to infer sediment sorting by deep currents. Additionally, the results are compared to calibrations from natural settings, where the correlation between the two datasets is remarkably similar, validating the relationship of sortable silt with current velocity in the deep ocean. Chapter two leverages sortable silt to investigate the long-term evolution of the Deep Western Boundary Current in the North Atlantic, targeting contourite drifts offshore Newfoundland to investigate the Eocene-Oligocene Transition (EOT), the most recent global greenhouse-to-icehouse transition. Results suggest that the Deep Western Boundary Current intensified gradually from 35-26 Ma, not abruptly at the EOT, and change consistent with deepening of the Greenland-Scotland Ridge and enhanced overflow of deep water into the North Atlantic. Chapter three utilizes detrital zircon U-Pb dating to characterize source-to-sink pathways and linkages during the rift-to-drift transition, in the Early Cretaceous, along the U.S. mid-Atlantic passive margin. This work shows that onshore and offshore system segments were initially disconnected, and progressively integrated over the course of ~45 Myr. Taken together, this work demonstrates a focused yet powerful example of how deep-marine sedimentary systems can be leveraged to robustly model major changes throughout Earth history. / Doctor of Philosophy / Sediments and sedimentary rocks deposited in the deep ocean house long-term signals pertaining to important Earth processes and properties. The nature of a given deposit, for example, can be the direct result of climatic conditions or tectonic development in adjacent mountainous and coastal environments. While the range of questions that can be answered using the sedimentary record is vast, this dissertation narrowly focuses on 1) how deep-ocean currents change over long periods of time, and 2) how onshore and offshore depositional environments correlate during the early phases of supercontinent break-up. To address the reconstruction of deep-ocean currents, laboratory experiments were performed to test how the sortable silt proxy – the 10-63 um fraction of a deposit – correlates with current velocity, the first controlled test of the proxy since its inception by paleoceanographers nearly three decades ago. Sortable silt is then applied to sediments of Eocene-Oligocene age, recovered from contourites offshore Newfoundland, Canada, to assess the long-term behavior of the Deep Western Boundary Current in the North Atlantic across the Eocene-Oligocene Transition (EOT). While the EOT, a major global cooling that occurred ~33.7 Ma, is well-studied with respect to Antarctica and its surrounding ocean basins, little is known about the paleoceanographic response of the North Atlantic. Grain-size records show a gradual increase in sortable silt before, during, and after the EOT, through entirety of the 9 Myr record. This trend is interpreted to reflect a long-term invigoration of the Deep Western Boundary Current in North Atlantic, likely due to progressive deepening of the Greenland-Scotland Ridge. The final chapter leverages detrital zircon U-Pb geochronology to compare sediment provenance of Early Cretaceous fluvial sandstones with coeval, distal turbidite sands. Results suggest that coastal rivers were fed by a single source terrane during the earliest Cretaceous, disconnected from the regional catchment feeding the submarine fan. By the Aptian-Albian, coastal rivers share a detrital zircon signature with turbidite strata, suggesting that rivers were progressively integrated into the sediment-routing system feeding the offshore margin.

Le Canal de Corse est un bassin confiné asymétrique localisé entre l’Île de Corse et l’Archipel de la Toscane, dont le flanc ouest est dominé par des processus turbiditiques et hémipélagiques et le flanc est par des mouvements en masse et des processus contouritiques. Le présent projet de doctorat a pour objectif de comprendre plus précisément les mécanismes contrôlant la formation des glissements sous-marins dans les contourites vaseuses (dépôts sédimentaires formés par les courants) pendant la période Plio-Quaternaire. Le vaste jeu de données disponible pour ce projet de doctorat inclut : la bathymétrie multifaisceaux, la sismique réflexion, les mesures géotechniques in situ, les mesures de vitesse de courant et les résultats d’un modèle hydrodynamique.Les contourites du Canal de Corse sont principalement composées de vase avec la présence de couches de sable formées par de forts courants de fond pendant les périodes de baisse du niveau marin. La croissance des dépôts contouritiques dépend de la disponibilité de sédiment fourni par le système turbiditique. Ainsi, cette croissance est lente pendant les périodes interglaciaires de haut niveau marin et rapide pendant les bas niveaux marins. Les courants contrôlent la morphologie du fond et génèrent les plastered drifts de forme convexe avec des pentes plus raides dans la partie avale, limités par une incision créée par les courants (moat). Le Pianosa Slump a été initié dans cette partie basse du plastered drift. Les moats pourraient être érodés préférentiellement pendant les périodes froides passées déclenchant ainsi certains glissements observés. Un autre facteur prédisposant l’instabilité de pente sur la Ride de Pianosa est la faiblesse d’une couche dont le comportement mécanique se caractérise par du radoucissement (perte de résistance avec le cisaillement). Cette propriété particulière est due à la présence de zéolites (produit de l’altération des roches volcaniques). Cette couche a formé la surface basale de rupture du Pianosa Slump. En conclusion, les deux principaux facteurs prédisposant la formation de glissements sous-marins sur la Ride de Pianosa sont : la morphologie du plastered drift avec une pente plus raide en aval et la couche faible composée de sédiment vaseux riche en zéolites. Le principal facteur déclenchant semble être l’érosion basale. / The Corsica Trough is an asymmetric confined basin located between the Corsica Island and the Tuscan Ar-chipelago, with the western flank dominated by turbiditic and hemipelagic processes and the eastern flank by mass transport and contouritic processes. The present PhD project aims to develop our understanding of the mechanisms that control the formation of submarine landslides within muddy contourites (sediment deposits related to bottom currents) during the Plio-Quaternary. The broad data set available for this PhD project includes: multibeam bathymetry, seismic reflection data, sediment cores, in situ geotechnical measurements, current ADCP measurements and results of a hydrodynamic model.The contourites of the Corsica Trough are mainly composed of mud with sandy layers formed by enhanced bottom currents during periods of sea level fall. The contourite drifts grow slowly during sea level high-stands and rapidly during sea level low-stands due to the high sediment availability provided by an active turbidite sys¬tem. Bottom currents control the seafloor morphology and generate plastered drifts on the slope. This is a con¬vex-shaped contourite with steep slope gradients in the lower part limited by a moat (incision created by bottom currents). The Pianosa Slump was initiated in this lower part of the plastered drift. The occurrence of continuous erosive processes during cold periods could undercut the slope and trigger submarine landslides. Another predis¬posing factor for slope instability identified is the presence of a potential weak layer with a post-peak strain soften¬ing behaviour (strength loss with increasing strain). This particular property is caused by the presence of zeolites (product of the alteration of volcanic rocks). This layer originated the basal failure surface of the Pianosa Slump.In summary, the two main factors predispose the formation of submarine landslides in the Pianosa Ridge are: the morphology of the plastered drift with steep slopes in the lower part and a potential weak layer composed of zeolitic muddy sediment. The main triggering factor seems to be undercutting by bottom currents.

Near-bottom current data was collected over a period of 8 years at the U.S. Army Corps of Engineers Field Research Facility in Duck, North Carolina. This data set consisted of currents measured up to three elevations above the bottom at deployment depths of 5 meters, 8 meters and 13 meters, as well as continuous real-time wind and wave data collected at the pier. The data was collated, quality checked and analyzed to define a climatology of near bottom currents along the study area using current moments. This data set had previously never been available for analysis due to the large amount of effort required to take old computer files and subject them to rigorous processing and quality control. The analyses conducted in this thesis represent the first ever attempt to analyze this type of data on this scale. An initial monthly investigation was conducted at the 8-meter site to determine driving forces of mean currents, and a more in depth seasonal investigation was subsequently completed to quantify the relationships between the cross-shore currents and different forcing mechanisms. Once seasonal trends were established relating mean current to incident wave height, wave steepness and wind speed, an examination of some significant historical events within the study was completed to help link cross-shore current behavior to storm events. Three separate nor’easter events and three significant hurricanes (Bonnie, Dennis and Floyd) were found to produce significant cross-shore currents at the study site. Similar to previous nearshore studies, it was found that the occurrence of onshore winds and wave heights greater than about 1.5 meters produce near-bottom mean currents moving in the offshore direction. Alternatively, when winds are blowing in the offshore direction, waves are still propagating onshore, but mean near-bottom currents tend to be directed in the onshore direction. The importance of vertical current structure within the water column was apparent, even though the instruments’ measurement elevations were all located within the bottom boundary layer. In contrast to the assumption of zero cross-shore velocity at near-coast sites implicit in two-dimensional depth averaged models used in most coastal engineering studies today, it was found that cross-shore near-bottom currents are rarely ever zero. Depth-averaged models inherently assume that currents move as a single block of water throughout the water column. The physical impacts of this misrepresentation of nearshore currents become very significant in predictions of many coastal phenomena, such as storm surge, sediment transport and wave conditions at the coast. When wave heights exceed 2 meters, mean currents tend to be between 0.2-0.5 meters per second in both the onshore and offshore direction, in the opposite direction of the primary forcing at the surface. In some instances, wave heights are low with strong mean currents while wind speeds are high, indicating the driving force in this situation is wind speed. However, there are cases where wave heights are large and mean current values are relatively low, which requires further investigation. Future work will include investigating phenomena that are related to higher-order odd moments of the current statistics, since they are expected to play a critical role in improved understanding of the physics within the nearshore and are very much needed for predictions of coastal evolution under future sea level rise and potential climate change.