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.

Accumulations of fine sediments in deep-ocean contourites form a sedimentary record that has been hypothesized to be directly related to bottom-current behavior. This is known as the 'sortable silt' hypothesis and states that the non-cohesive, coarse silt in the 10 to 63 µm size range within a deposit can be used as a proxy for paleocurrent velocity. Slow deposition rates on contourites (2−10 cm/kyr) make it difficult to test this hypothesis in the field and few laboratory studies have been conducted. To test the 'sortable silt' hypothesis in the laboratory, a non-recirculating flume was constructed in which silt and clay could be deposited under a variety of velocities, sediment concentrations, and silt to clay ratios. Samples of the deposited material from each experiment were analyzed to determine the grain-size distribution using a Micromeritics Sedigraph 5120 particle size analyzer. The results of these experiments were used to evaluate the following two hypotheses: 1. The proportion of sortable silt (SS%) compared to the proportion of clay is a better indicator of current velocity than the mean size of the sortable silt (SS). 2. The presence of clay will impact the movement and sorting of silt in the bed. Results show that increased velocity correlates with increased (SS), and that (SS) generally decreases downstream of the sediment source. (SS) was found to be more representative of velocity than (SS%) and, counter to the original hypothesis, clay did not have a significant effect on silt deposition. / Master of Science / The ’sortable silt’ hypothesis states that there is a relationship between the velocity of an ocean current and the size of the sediment that deposits on the bottom of the ocean. These deep-ocean deposits consist of material smaller than sand such as clay and silt. Smaller particles require less force than larger particles to remain suspended, and higher current velocities produce larger forces. For this reason larger current velocities are thought to be associated with the deposition of coarser sediments. It is challenging to test this hypothesis in the field because of the cost and the slow rates at which change occurs. Laboratory studies can help to overcome these challenged by test scenarios otherwise impossible in the field. For this research, a flume was constructed and used to examine how different sediment types sort under flowing water. Most laboratory flumes recirculate water using pumps, but this flume does not. A mixture of dry material and water flows through the flume, depositing a bed over time. This deposited material can then be tested for its size parameters. These size parameters are compared to the material type and the velocity of the current in the flume to help answer two main questions: 1. Is the amount of silt in a sample a better indication of the current velocity than the average size of the material deposited? 2. Will the addition of clay will change the way silt deposits in the system?. Results show that silt does sort with increasing velocity and that the mean sortable silt size is good indicator of current velocity.

Atlantic Meridional Overturning Circulation (AMOC) is a vital process that transfers heat and nutrients throughout the world's oceans, helping to regulate global climate and support marine ecosystems. The timing and nature of the shift to modern AMOC, and especially to deep-water formation in the North Atlantic, has been a topic of ongoing study, with the Eocene-Oligocene Transition (EOT, ~34 Ma) as a potential focal point of this shift. However, the role played by abrupt EOT cooling and Antarctic glaciation in North Atlantic circulation remains unclear. Improved constraints on Paleogene circulation will provide insight into the sensitivity of AMOC to perturbations in global climate, which is particularly relevant in light of contemporary climate change. To examine deep North Atlantic circulation response to the EOT we obtained grain-size data from the terrigenous fraction of the mud-dominated sediments of the Southeast Newfoundland Ridge contourite drift complex at IODP Site U1411, which is interpreted to have formed under the influence of the Deep Western Boundary Current. We analyzed 195 samples that span 150 m of stratigraphy from 36-26 Ma. The main objective was to use the 'sortable silt' fraction (10-63 µm) to generate a record of relative change in bottom-current intensity. These data are complemented with a record of the abundance and size of lithogenic sand (>63 µm). Here we present the first physical proxy record of abyssal current intensity in the North Atlantic, from late Eocene to mid Oligocene. Invigoration of North Atlantic deep circulation occurred gradually (over Myr timescales), with no significant changes linked temporally to the EOT. We infer that deep circulation in the North Atlantic was not sensitive to the abrupt global cooling and Antarctic glaciation associated with the EOT. Rather, our data suggest that changes in North Atlantic circulation were likely governed by longer-term processes related to the opening of key tectonic gateways, such as the Greenland-Scotland Ridge in the North Atlantic, and the Drake and Tasman Passages in the Southern Ocean. Additionally, we identify a significant mid-Oligocene invigoration of North Atlantic abyssal circulation, which climaxes around 27.9 Ma, and is coeval with a decrease in atmospheric CO2. / Master of Science / Atlantic Meridional Overturning Circulation (AMOC) is a vital process that transfers heat and nutrients throughout the world’s oceans, helping to regulate global climate and support marine ecosystems. However, AMOC has not always existed as we know it, and different modes of ocean circulation have operated in Earth’s past. The timing and nature of the shift to the modern form of AMOC/global ocean circulation has been a topic of ongoing study. The Eocene-Oligocene Transition (EOT, ~34 million years ago), a period of intense global cooling and Antarctic ice sheet growth, is thought to be a potential focal point of this shift to modern ocean circulation. However, the role played by abrupt EOT cooling and Antarctic glaciation in the evolution of ocean circulation remains unclear, especially in the North Atlantic. Understanding how and why ocean circulation has changed in more recent geologic time (within the past 65 million years), and ultimately evolved into its modern state, will help us understand the processes which led to, and now maintain, Earth’s modern climate state, as well as provide insight into the sensitivity of AMOC to perturbations in global climate, which is particularly relevant in light of contemporary climate change. To examine the response of ocean circulation in the North Atlantic to climate changes at the EOT, we obtained grain-size data from the mud-dominated sediments of the Southeast Newfoundland Ridge contourite drift complex at IODP Site U1411, which is interpreted to have formed under the influence of the Deep Western Boundary Current. Contourite drifts are massive sediment build-ups on the ocean floor, which are formed due to bottom-currents depositing large amounts of sediment in one area. Therefore, contourite drift deposits can hold valuable records of bottom-current activity over millions of years. We analyzed 195 samples that span 150 m of stratigraphy from 36-26 Ma (Ma = millions of years ago). The main objective was to use the ‘sortable silt’ fraction (10-63 µm) to generate a record of relative change in bottom-current intensity. These data are complemented with a record of the abundance and size of sand (>63 µm). Here we present the first physical proxy record of abyssal current intensity in the North Atlantic, from late Eocene to mid Oligocene. We find that invigoration of North Atlantic deep circulation occurred gradually (over million-year timescales), with no significant changes linked temporally to the EOT. We infer that deep circulation in the North Atlantic was not sensitive to the abrupt global cooling and Antarctic glaciation associated with the EOT. Rather, our data suggest that changes in North Atlantic circulation were likely governed by longer-term processes related to the opening of key tectonic gateways, such as the Greenland-Scotland Ridge in the North Atlantic, and the Drake and Tasman Passages in the Southern Ocean. Additionally, we identify a significant midOligocene invigoration of North Atlantic abyssal circulation, which climaxes around 27.9 Ma, and coincides with a decrease in atmospheric CO₂.

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.