Earth & Environmental Sciences Theses
https://hdl.handle.net/10023/1942
2024-03-28T22:16:44ZThe co-evolution of Earth's crust and hydrosphere : a silicon isotope perspective
https://hdl.handle.net/10023/29543
The silicon isotope system is a well-established geochemical tool for tracing processes influenced by the interplay of Earth’s present-day crust and hydrosphere. While there is good understanding of stable silicon (Si) isotope systematics for high- and low-temperature processes in the Phanerozoic eon, these are poorly constrained for early Earth processes. Particularly, the Si isotope
composition of Archaean and Proterozoic crustal materials is a scarce record mainly consisting of silica precipitates. However, recent investigations of Si isotopes in Archaean granitoids linked heavy isotopic signatures to seawater-derived sources, invoking the hydrosphere in forming Earth's earliest continental crust.
Motivated by recent research gaps, this thesis aims to explore crust-hydrosphere interactions by establishing the Si isotope compositions of Archaean granitoids, specifically tonalite-trondhjemite-granodiorites (TTGs), and other lithologies representative of more than one-third of Earth history. This thesis presents outcomes from five Si isotope studies on globally diverse, ancient silicates. Here we find Eoarchaean igneous rocks from Greenland were influenced by supracrustal fluids, necessitating a primeval hydrosphere in forming early continents. We explore Si isotope behaviour during ancient partial melting from an Archaean migmatite from Ontario and find that TTG sources were likely seawater-silicified.
This thesis records a secular homogenising of Si isotopes in the ancient upper continental crust from global glacial diamictites, supporting craton stabilisation after ~3.0 Ga. We also show Archaean –Proterozoic Fennoscandian weathering crusts imply no significant Si isotope trends at the Great Oxidation Event and highlight local controls instead. Finally, this thesis explores the Archaean marine silica cycle with a model for the Si isotope evolution of seawater, aligning with data that require a heavy Si isotope signature in the early oceans.
In total, this thesis contributes a more robust temporal Si isotope record of ancient crustal materials and provides a greater understanding of the connection between Earth’s earliest crust and hydrosphere.
2024-06-13T00:00:00ZMurphy, MadeleineThe silicon isotope system is a well-established geochemical tool for tracing processes influenced by the interplay of Earth’s present-day crust and hydrosphere. While there is good understanding of stable silicon (Si) isotope systematics for high- and low-temperature processes in the Phanerozoic eon, these are poorly constrained for early Earth processes. Particularly, the Si isotope
composition of Archaean and Proterozoic crustal materials is a scarce record mainly consisting of silica precipitates. However, recent investigations of Si isotopes in Archaean granitoids linked heavy isotopic signatures to seawater-derived sources, invoking the hydrosphere in forming Earth's earliest continental crust.
Motivated by recent research gaps, this thesis aims to explore crust-hydrosphere interactions by establishing the Si isotope compositions of Archaean granitoids, specifically tonalite-trondhjemite-granodiorites (TTGs), and other lithologies representative of more than one-third of Earth history. This thesis presents outcomes from five Si isotope studies on globally diverse, ancient silicates. Here we find Eoarchaean igneous rocks from Greenland were influenced by supracrustal fluids, necessitating a primeval hydrosphere in forming early continents. We explore Si isotope behaviour during ancient partial melting from an Archaean migmatite from Ontario and find that TTG sources were likely seawater-silicified.
This thesis records a secular homogenising of Si isotopes in the ancient upper continental crust from global glacial diamictites, supporting craton stabilisation after ~3.0 Ga. We also show Archaean –Proterozoic Fennoscandian weathering crusts imply no significant Si isotope trends at the Great Oxidation Event and highlight local controls instead. Finally, this thesis explores the Archaean marine silica cycle with a model for the Si isotope evolution of seawater, aligning with data that require a heavy Si isotope signature in the early oceans.
In total, this thesis contributes a more robust temporal Si isotope record of ancient crustal materials and provides a greater understanding of the connection between Earth’s earliest crust and hydrosphere.Development of a 1-D oxygen isotope photochemical model and its application to atmospheric O₂
https://hdl.handle.net/10023/29486
Oxygen is the second most abundant gas in the Earth’s atmosphere, but this has not always been the case. A suite of geochemical, palaeobiological, and geological proxies have been presented over the last few decades to better constrain the evolution of pO₂ over the history of our planet, but uncertainty remains. Here, we use numerical modelling with the 1-D photochemical model Atmos, firstly by exploring the boundary conditions of the model, and secondly by developing it to predict ∆¹⁷O values – a fairly novel proxy for Proterozoic and Phanerozoic pO₂. Our study of boundary conditions highlights the importance of choosing and describing boundary conditions carefully, as our flux-driven models produce somewhat different results to previous fixed mixing ratio-driven models. Our results provide a potential constraint on pO₂, suggesting that atmospheres with 6×10⁻⁷ < pO₂ < 2×10⁻³ may have been unlikely to exist for long periods of Earth history. We review these conclusions using our newly-developed oxygen isotope model, tuned to predict modern atmospheric ∆¹⁷O. Preliminary results predict the production and preservation of non-zero ∆¹⁷O in the geological record can occur for palaeo-atmospheres with pO₂ > 10⁻⁴, but even the minimum values observed at 1.4 Ga and 635 Ma do not require such low concentrations, especially if pCO₂ is higher than modern. The development of the oxygen isotope model allows the better prediction of ∆¹⁷O under various atmospheric conditions, and will be a useful tool in the interpretation of anomalous oxygen isotope compositions in the geological record.
2021-06-30T00:00:00ZGregory, Bethan SarahOxygen is the second most abundant gas in the Earth’s atmosphere, but this has not always been the case. A suite of geochemical, palaeobiological, and geological proxies have been presented over the last few decades to better constrain the evolution of pO₂ over the history of our planet, but uncertainty remains. Here, we use numerical modelling with the 1-D photochemical model Atmos, firstly by exploring the boundary conditions of the model, and secondly by developing it to predict ∆¹⁷O values – a fairly novel proxy for Proterozoic and Phanerozoic pO₂. Our study of boundary conditions highlights the importance of choosing and describing boundary conditions carefully, as our flux-driven models produce somewhat different results to previous fixed mixing ratio-driven models. Our results provide a potential constraint on pO₂, suggesting that atmospheres with 6×10⁻⁷ < pO₂ < 2×10⁻³ may have been unlikely to exist for long periods of Earth history. We review these conclusions using our newly-developed oxygen isotope model, tuned to predict modern atmospheric ∆¹⁷O. Preliminary results predict the production and preservation of non-zero ∆¹⁷O in the geological record can occur for palaeo-atmospheres with pO₂ > 10⁻⁴, but even the minimum values observed at 1.4 Ga and 635 Ma do not require such low concentrations, especially if pCO₂ is higher than modern. The development of the oxygen isotope model allows the better prediction of ∆¹⁷O under various atmospheric conditions, and will be a useful tool in the interpretation of anomalous oxygen isotope compositions in the geological record.Whodunit? Determining the source and eruptive characteristics of unidentified volcanic eruptions from ice and sediment core archives
https://hdl.handle.net/10023/29279
The most complete records of explosive volcanism from the last 100,000 years are preserved in polar ice cores as deposits of sulfate aerosol and microscopic ash (tephra). These records are essential for reconstructing the history of past eruptions, including their stratospheric sulfur loading, as well as understanding the climatic impact of eruptions. However, few of these deposits have been linked with volcanic sources, leading to assumptions of eruptive source latitude, plume height and stratospheric sulfur loading, which are all essential for interpreting the climate forcing potential of eruptions. A fundamental limitation preventing the correlation of ice core volcanic deposits to eruptive sources is the difficulty of geochemically characterising extremely fine-grained (<10 μm) tephra with conventional analytical methods. This thesis provides a thorough assessment and recommended workflow for analysing <10 μm tephra, increasing potential for characterising cryptotephra from distant eruptions in ice. These tephra method developments are then used alongside sulfur isotope analysis to improve source attributions of major Common Era eruptions recorded in Greenland ice during the 7th century. This allows testing of previous source latitude assumptions for eruptions associated with large climate anomalies and contributes to ongoing efforts to understand climate sensitivity to extra-tropical versus tropical eruptions. Finally, the identification of Atitlán Los Chocoyos supereruption tephra in both Greenland and Antarctic ice ~79,500 years ago suggests even volcanic stratospheric sulfate injection several times greater than any Common Era eruption does not have a long-term (greater than decadal) impact on climate. Grainsize analysis of Los Chocoyos ash in marine sediment cores provides further insights into the physical characteristics of the supereruption, suggesting mechanisms that accelerate fine ash and sulfate fallout from the atmosphere may limit stratospheric sulfur loading. By better constraining source and stratospheric sulfate estimates for both major eruptions of the Common Era and one of the largest supereruptions of the last 100,000 years, this thesis contributes to ongoing efforts to understand the history and global impacts of explosive volcanism.
2024-06-13T00:00:00ZInnes, Helen MaryThe most complete records of explosive volcanism from the last 100,000 years are preserved in polar ice cores as deposits of sulfate aerosol and microscopic ash (tephra). These records are essential for reconstructing the history of past eruptions, including their stratospheric sulfur loading, as well as understanding the climatic impact of eruptions. However, few of these deposits have been linked with volcanic sources, leading to assumptions of eruptive source latitude, plume height and stratospheric sulfur loading, which are all essential for interpreting the climate forcing potential of eruptions. A fundamental limitation preventing the correlation of ice core volcanic deposits to eruptive sources is the difficulty of geochemically characterising extremely fine-grained (<10 μm) tephra with conventional analytical methods. This thesis provides a thorough assessment and recommended workflow for analysing <10 μm tephra, increasing potential for characterising cryptotephra from distant eruptions in ice. These tephra method developments are then used alongside sulfur isotope analysis to improve source attributions of major Common Era eruptions recorded in Greenland ice during the 7th century. This allows testing of previous source latitude assumptions for eruptions associated with large climate anomalies and contributes to ongoing efforts to understand climate sensitivity to extra-tropical versus tropical eruptions. Finally, the identification of Atitlán Los Chocoyos supereruption tephra in both Greenland and Antarctic ice ~79,500 years ago suggests even volcanic stratospheric sulfate injection several times greater than any Common Era eruption does not have a long-term (greater than decadal) impact on climate. Grainsize analysis of Los Chocoyos ash in marine sediment cores provides further insights into the physical characteristics of the supereruption, suggesting mechanisms that accelerate fine ash and sulfate fallout from the atmosphere may limit stratospheric sulfur loading. By better constraining source and stratospheric sulfate estimates for both major eruptions of the Common Era and one of the largest supereruptions of the last 100,000 years, this thesis contributes to ongoing efforts to understand the history and global impacts of explosive volcanism.A quantitative classification tool for porphyry Cu alteration systems
https://hdl.handle.net/10023/28590
Porphyry copper deposits form from upper crustal H₂O saturated magmatic systems, along ancient and active convergent margins. As the world’s major source of copper, gold and molybdenum, along with minor quantities of other base and precious metals, they are an increasingly important source of raw material, essential to the ongoing clean energy transition and in hitting key targets set by global societies today. Driven by the transition to renewable energy sources and electric vehicles, dependent on substantial quantities of iron ore, copper and aluminium, it has been estimated that the demand for copper alone will increase by over 20 times. With current reserves not expected to meet future demand, extensive additional exploration is anticipated. Furthermore, with the depletion of near-surface deposits in mature exploration terranes, there is a clear need for the development of new techniques to identify and unearth deeply buried reserves. Exploration programs rely on many techniques for the identification of the large, distal alteration systems associated with porphyry style mineralisation, which currently focus on pathfinding geochemical indicators. Alongside these techniques, infrared spectroscopy and magnetic susceptibility data is often collected but underutilised, despite providing a rapid and low-cost source of mineralogical information.
Using samples collected form the Aktogay porphyry Cu deposit in the Central Asian Orogenic Belt, an extensive Palaeozoic subduction-accretion complex, the ability of magnetic and infrared spectroscopy to quantifiably define and characterise alteration, when used in conjunction with a specifically developed, unsupervised deep learning algorithm, has been examined. Our findings demonstrate that the resulting subdivision around porphyry mineralisation into twelve discrete domains, can uniquely identify otherwise hidden mineral assemblages. Through examining the consistency of key parameters within each domain such as ore grade and geochemical signatures, their statistical significance has been tested, indicating an increased consistency of between 60 and 70% when compared to traditional alteration zones classified by on-site mining geologists. In addition, detailed petrological and magnetic characterisation independently confirms the validity of the newly defined alteration domains, whilst also demonstrating the importance of magnetic characterisation as a new tool, which can improve our understanding and partial quantification of the magnetic effects during hydrothermal fluid-rock interactions throughout ore deposit formation. Quantifiably defining alteration domains provides a reproducible, rapid and non-destructive method that can be deployed in a wide variety of settings, leading to the consistent separation of domains which can be used as a superior proxy for ore distribution and grade.
2023-11-28T00:00:00ZDixon, Oliver JamesPorphyry copper deposits form from upper crustal H₂O saturated magmatic systems, along ancient and active convergent margins. As the world’s major source of copper, gold and molybdenum, along with minor quantities of other base and precious metals, they are an increasingly important source of raw material, essential to the ongoing clean energy transition and in hitting key targets set by global societies today. Driven by the transition to renewable energy sources and electric vehicles, dependent on substantial quantities of iron ore, copper and aluminium, it has been estimated that the demand for copper alone will increase by over 20 times. With current reserves not expected to meet future demand, extensive additional exploration is anticipated. Furthermore, with the depletion of near-surface deposits in mature exploration terranes, there is a clear need for the development of new techniques to identify and unearth deeply buried reserves. Exploration programs rely on many techniques for the identification of the large, distal alteration systems associated with porphyry style mineralisation, which currently focus on pathfinding geochemical indicators. Alongside these techniques, infrared spectroscopy and magnetic susceptibility data is often collected but underutilised, despite providing a rapid and low-cost source of mineralogical information.
Using samples collected form the Aktogay porphyry Cu deposit in the Central Asian Orogenic Belt, an extensive Palaeozoic subduction-accretion complex, the ability of magnetic and infrared spectroscopy to quantifiably define and characterise alteration, when used in conjunction with a specifically developed, unsupervised deep learning algorithm, has been examined. Our findings demonstrate that the resulting subdivision around porphyry mineralisation into twelve discrete domains, can uniquely identify otherwise hidden mineral assemblages. Through examining the consistency of key parameters within each domain such as ore grade and geochemical signatures, their statistical significance has been tested, indicating an increased consistency of between 60 and 70% when compared to traditional alteration zones classified by on-site mining geologists. In addition, detailed petrological and magnetic characterisation independently confirms the validity of the newly defined alteration domains, whilst also demonstrating the importance of magnetic characterisation as a new tool, which can improve our understanding and partial quantification of the magnetic effects during hydrothermal fluid-rock interactions throughout ore deposit formation. Quantifiably defining alteration domains provides a reproducible, rapid and non-destructive method that can be deployed in a wide variety of settings, leading to the consistent separation of domains which can be used as a superior proxy for ore distribution and grade.A thermodynamic modelling approach to predict the outcome of carbonaceous fluid metasomatism on Earth and Mars
https://hdl.handle.net/10023/28234
The carbon flux between the atmosphere and the geosphere is linked by a broad range of geodynamic and magmatic processes which govern the deep carbon cycles on all telluric planets, asteroids, and moons. On Earth, carbon is introduced into the mantle by subduction. On Mars, deep carbon is mobilised by magmatism and mantle convection, with delamination the only likely mechanism to recycle crustal carbon. The mobilisation and transportation of phases across P-T-X gradients result in the destabilisation of carbon-bearing and hydrated minerals leading to the formation of melts and fluids. Both act as mass-transfer agents, mobilising and transferring carbon. The interaction of fluids and magmas with surrounding rocks results in metasomatism. The role of carbon-rich fluids in the formation of metasomatic minerals and methane reservoirs on Earth and Mars has been studied via thermodynamic modelling. Here I present the results of predictive simulations to express the evolution of metasomatic systems at different P-T-fO₂ conditions.
This study finds that the traditional distinction of diamonds through paragenetic groups cannot be used as a genetic classification because fluid-rock metasomatism can produce the compositional range of garnet and clinopyroxene found as inclusions in diamonds. The amount of carbon in the system – and its speciation – controls the geochemistry of metasomatic silicates, highlighting how carbon is even more influential than previously thought. Furthermore, fluid metasomatism can convert depleted mantle rocks into fertile websterites without championing a mechanism involving partial melting. Fluids have all the rock-forming elements to precipitate anhydrous silicates, and the presence or absence of hydrated minerals is no reliable evidence to distinguish melt and fluid metasomatism. Finally, the reduced conditions of Mars favour the formation of methane, which can be stored in geological reservoirs and then transported to the surface, sustaining the CH₄-based greenhouse required for liquid water on the surface of Early Mars.
2023-11-28T00:00:00ZRinaldi, MicheleThe carbon flux between the atmosphere and the geosphere is linked by a broad range of geodynamic and magmatic processes which govern the deep carbon cycles on all telluric planets, asteroids, and moons. On Earth, carbon is introduced into the mantle by subduction. On Mars, deep carbon is mobilised by magmatism and mantle convection, with delamination the only likely mechanism to recycle crustal carbon. The mobilisation and transportation of phases across P-T-X gradients result in the destabilisation of carbon-bearing and hydrated minerals leading to the formation of melts and fluids. Both act as mass-transfer agents, mobilising and transferring carbon. The interaction of fluids and magmas with surrounding rocks results in metasomatism. The role of carbon-rich fluids in the formation of metasomatic minerals and methane reservoirs on Earth and Mars has been studied via thermodynamic modelling. Here I present the results of predictive simulations to express the evolution of metasomatic systems at different P-T-fO₂ conditions.
This study finds that the traditional distinction of diamonds through paragenetic groups cannot be used as a genetic classification because fluid-rock metasomatism can produce the compositional range of garnet and clinopyroxene found as inclusions in diamonds. The amount of carbon in the system – and its speciation – controls the geochemistry of metasomatic silicates, highlighting how carbon is even more influential than previously thought. Furthermore, fluid metasomatism can convert depleted mantle rocks into fertile websterites without championing a mechanism involving partial melting. Fluids have all the rock-forming elements to precipitate anhydrous silicates, and the presence or absence of hydrated minerals is no reliable evidence to distinguish melt and fluid metasomatism. Finally, the reduced conditions of Mars favour the formation of methane, which can be stored in geological reservoirs and then transported to the surface, sustaining the CH₄-based greenhouse required for liquid water on the surface of Early Mars.New investigations of monsoon depressions using observational data, theory and numerical experiments
https://hdl.handle.net/10023/28207
Monsoon depressions (MDs) are synoptic-scale storms that exist embedded within the planetary-scale summer monsoon circulation.
Their structure and propagation is distinct to other tropical and sub-tropical systems. The last five years have seen particular advances in the understanding of the atmospheric dynamics and growth mechanisms of MDs. This thesis builds upon this recent literature, and then covers the development and results of new analyses of atmospheric reanalysis data and a series of idealised modelling experiments that have been conducted to gain new understanding and insight into MDs.
This work is introduced with a discussion of the global monsoon focusing on the particular background conditions during the South Asian Summer Monsoon that support a high-frequency of MDs. A tracking algorithm for low-pressure events is developed and used to construct composite South Asian MDs in high-resolution ERA5 data. A sensitivity of faster westward MD propagation to the mid-tropospheric meridional temperature gradient is identified.
Such insights then motivate the development of a new idealised moist-thermal quasi-geostrophic (QG) model as a dynamical toolbox to understand the fundamental dynamics of MDs. Linear-modes of this QG model demonstrate a sensitivity to background temperature and precipitation gradients, but fail to organise precipitation and dynamics in a manner similar to that of observed MDs.
A variety of experiments, with large-amplitude MD-analogues, are shown to capture MD-like propagation and sensitivity to background temperature gradients by diabatic-barotropic processes and thermally-modulated beta-drift.
Finally, a set of numerical experiments are conducted in an idealised general circulation model using a series of idealised surface configurations. Results of these experiments demonstrate an idealised configuration that captures South Asian monsoon and MD-like variability, and provide insights into the relationship between MDs and meridional temperature gradients.
2023-11-28T00:00:00ZChaudhri, Alexander KarimMonsoon depressions (MDs) are synoptic-scale storms that exist embedded within the planetary-scale summer monsoon circulation.
Their structure and propagation is distinct to other tropical and sub-tropical systems. The last five years have seen particular advances in the understanding of the atmospheric dynamics and growth mechanisms of MDs. This thesis builds upon this recent literature, and then covers the development and results of new analyses of atmospheric reanalysis data and a series of idealised modelling experiments that have been conducted to gain new understanding and insight into MDs.
This work is introduced with a discussion of the global monsoon focusing on the particular background conditions during the South Asian Summer Monsoon that support a high-frequency of MDs. A tracking algorithm for low-pressure events is developed and used to construct composite South Asian MDs in high-resolution ERA5 data. A sensitivity of faster westward MD propagation to the mid-tropospheric meridional temperature gradient is identified.
Such insights then motivate the development of a new idealised moist-thermal quasi-geostrophic (QG) model as a dynamical toolbox to understand the fundamental dynamics of MDs. Linear-modes of this QG model demonstrate a sensitivity to background temperature and precipitation gradients, but fail to organise precipitation and dynamics in a manner similar to that of observed MDs.
A variety of experiments, with large-amplitude MD-analogues, are shown to capture MD-like propagation and sensitivity to background temperature gradients by diabatic-barotropic processes and thermally-modulated beta-drift.
Finally, a set of numerical experiments are conducted in an idealised general circulation model using a series of idealised surface configurations. Results of these experiments demonstrate an idealised configuration that captures South Asian monsoon and MD-like variability, and provide insights into the relationship between MDs and meridional temperature gradients.The nature of fluids associated with the subvolcanic alkaline magmas and their role in 'hi-tech' metal transport and mineralization
https://hdl.handle.net/10023/27744
Alkaline igneous rocks host many High Field Strength (HFSE) and Rare Earth Element (REE) deposits, which are key for the global low-carbon energy transition. To better target these, a better understanding of alteration associated with silicate-related ore deposits is required. Fluid-rock interaction around syenite forms altered haloes (’fenite’), normally uneconomic, but hosting many of the normally immobile HFSE expelled from the magmatic hearth. The fluid parameters which control the transport and deposition of these elements in the crust, their composition and the element speciation within need to be better constrained.
Here a field study of an exceptionally exposed fenite (Gardar Province, SW Greenland) was followed by major and trace element, and stable isotope (O-H-S) analyses of whole rocks and minerals, and the investigation of fluid inclusion assemblages. The field data show the volcano-sedimentary wall-rocks to the west of Illerfissalik centre were altered by the ejection of metasomatic fluids. Fenitized sediment comprises a skarn-like (garnet-absent) calc-silicate assemblage developed interstitially, often along relict structures, later subjected to short-lived Na– Fe(III) –Ti alteration. Using oxygen isotope equilibria, the temperature of the causal fluid was estimated at ~750°C suggesting a magmatic origin. The differences in O, H and S isotopic data also indicate the system underwent fluid-driven exchange with the country rocks, potentially mixing with externally derived meteoric water. Elements including Ti, Zr, Nb and REE are mobile during alteration, but they precipitate as silicates and phosphates mainly in the late-stage in the basement granite, while rare chevkinite and titanite host much of the early-stage HFSE in the Eriksfjord. An estimated total REE-oxide cargo mobilized from Illerfissalik (~43 Mt) rivals the tonnages of many major ore deposits (i.e. Kringlerne, Ilímaussaq) and underscores how critical fenitization is as a tipping point during evolution of fertile magmas in the upper crust.
2023-06-16T00:00:00ZSokol, KrzysztofAlkaline igneous rocks host many High Field Strength (HFSE) and Rare Earth Element (REE) deposits, which are key for the global low-carbon energy transition. To better target these, a better understanding of alteration associated with silicate-related ore deposits is required. Fluid-rock interaction around syenite forms altered haloes (’fenite’), normally uneconomic, but hosting many of the normally immobile HFSE expelled from the magmatic hearth. The fluid parameters which control the transport and deposition of these elements in the crust, their composition and the element speciation within need to be better constrained.
Here a field study of an exceptionally exposed fenite (Gardar Province, SW Greenland) was followed by major and trace element, and stable isotope (O-H-S) analyses of whole rocks and minerals, and the investigation of fluid inclusion assemblages. The field data show the volcano-sedimentary wall-rocks to the west of Illerfissalik centre were altered by the ejection of metasomatic fluids. Fenitized sediment comprises a skarn-like (garnet-absent) calc-silicate assemblage developed interstitially, often along relict structures, later subjected to short-lived Na– Fe(III) –Ti alteration. Using oxygen isotope equilibria, the temperature of the causal fluid was estimated at ~750°C suggesting a magmatic origin. The differences in O, H and S isotopic data also indicate the system underwent fluid-driven exchange with the country rocks, potentially mixing with externally derived meteoric water. Elements including Ti, Zr, Nb and REE are mobile during alteration, but they precipitate as silicates and phosphates mainly in the late-stage in the basement granite, while rare chevkinite and titanite host much of the early-stage HFSE in the Eriksfjord. An estimated total REE-oxide cargo mobilized from Illerfissalik (~43 Mt) rivals the tonnages of many major ore deposits (i.e. Kringlerne, Ilímaussaq) and underscores how critical fenitization is as a tipping point during evolution of fertile magmas in the upper crust.Fire and ice : understanding volcanic histories from sulfur isotopes in ice cores
https://hdl.handle.net/10023/27568
Reconstructing the history of explosive volcanic eruptions is important for understanding the frequency of eruptions and the climatic forcing of these events. Erupted volcanic SO₂ is oxidised to sulfate aerosols which scatter incoming solar radiation. Aerosols are then deposited at the poles resulting in a peak in sulfate above background concentrations. Therefore, polar ice cores provide an important record of volcanism. The mass-independent fractionation of sulfur isotopes (S-MIF) in ice cores is an indicator of sulfur exposure to ultraviolet radiation via eruption into and above the ozone layer in the stratosphere. Sulfate aerosols from large eruptions that reach the stratosphere have a longer residence time and greater climatic impact than tropospheric aerosols from smaller eruptions. In this thesis I measure sulfur isotopes in volcanic ice core sulfate to investigate the ~74ka Toba supereruption and six unidentified volcanic eruptions from 16ka to 32ka. I found large magnitude S-MIF signals (-4.75‰) for one of the Toba candidates, the timing of which is consistent with independent age estimates for Toba. This places the eruption on the transition into a cool stadial period in Greenland (GS-20). Toba can be excluded as a potential trigger for GS-20, although it could have contributed to the cooling. To help interpret the six eruptions from 16–32ka, I adapted a 1D-diffusion model to simulate the diffusion and thinning of sulfate isotopes in ice cores. I found that the ice core sulfate isotope signatures are consistent with modelled results of sulfate exposed to diffusion and thinning. Finally, I adapted a 1D-photochemical model (Atmos) to model the temporal evolution of sulfur isotope signatures in a volcanic plume. The model predicts S-MIF signatures consistent in timing and shape to those measured in the ice cores for stratospheric eruptions with S-MIF formation primarily via self-shielding due to high SO₂ column densities.
2023-06-16T00:00:00ZCrick, LauraReconstructing the history of explosive volcanic eruptions is important for understanding the frequency of eruptions and the climatic forcing of these events. Erupted volcanic SO₂ is oxidised to sulfate aerosols which scatter incoming solar radiation. Aerosols are then deposited at the poles resulting in a peak in sulfate above background concentrations. Therefore, polar ice cores provide an important record of volcanism. The mass-independent fractionation of sulfur isotopes (S-MIF) in ice cores is an indicator of sulfur exposure to ultraviolet radiation via eruption into and above the ozone layer in the stratosphere. Sulfate aerosols from large eruptions that reach the stratosphere have a longer residence time and greater climatic impact than tropospheric aerosols from smaller eruptions. In this thesis I measure sulfur isotopes in volcanic ice core sulfate to investigate the ~74ka Toba supereruption and six unidentified volcanic eruptions from 16ka to 32ka. I found large magnitude S-MIF signals (-4.75‰) for one of the Toba candidates, the timing of which is consistent with independent age estimates for Toba. This places the eruption on the transition into a cool stadial period in Greenland (GS-20). Toba can be excluded as a potential trigger for GS-20, although it could have contributed to the cooling. To help interpret the six eruptions from 16–32ka, I adapted a 1D-diffusion model to simulate the diffusion and thinning of sulfate isotopes in ice cores. I found that the ice core sulfate isotope signatures are consistent with modelled results of sulfate exposed to diffusion and thinning. Finally, I adapted a 1D-photochemical model (Atmos) to model the temporal evolution of sulfur isotope signatures in a volcanic plume. The model predicts S-MIF signatures consistent in timing and shape to those measured in the ice cores for stratospheric eruptions with S-MIF formation primarily via self-shielding due to high SO₂ column densities.The behaviour of nitrogen during differentiation of Earths igneous continental crust
https://hdl.handle.net/10023/27219
The geological and biological nitrogen cycles are intimately linked. Nitrogen is an essential element in the structure of amino acids, proteins, nucleic acids, and other molecules vital for life, as well as 78% of the Earths atmosphere and present in significant quantities in all of Earths geological reservoirs. Planetary scale processes such as degassing, subduction and differentiation play a key role in generating and supporting a nitrogen rich surface environment suitable for supporting life. However, the fluxes and stores of nitrogen between Earths mantle, crust and atmosphere remain poorly constrained. Constraining the behaviour of nitrogen during these processes is therefore essential. This thesis targets the processing and storage of nitrogen in the Earth’s crust, with a focus on identify fundamental partitioning and isotopic fractionation during magmatic differentiation and assessing what the crustal nitrogen record can inform us about changes in the biogeochemical nitrogen cycle.
Firstly, I utilise two contrasting but well constrained magmatic systems, the aphyric lavas from Hekla volcano, Iceland, and the calc-alkaline Loch Doon zoned pluton, Scotland. These data are to the best of our knowledge the first combined abundance and isotopic ratio measurements for differentiating magmatic suites at a bulk and mineral scale. I show with the Hekla dataset that when undersaturated in a magma, nitrogen behaves more akin to lithophile rather than volatile elements and can be enriched significantly in Earths crust during differentiation. In Loch Doon, at a mineral scale, we find feldspars host 60-90% of the whole rock nitrogen contents in contrast with previous studies suggesting biotite as the main N host phase. Associated with this are significant feldspar-mica isotopic fractionation suggesting magmatic differentiation can impart significant measurable isotopic differences.
Secondly, I assess the ability of the plutonic felsic crust to record changes in the terrestrial sedimentary nitrogen cycle through analysis of a suite of well characterised strongly peraluminous granitoids (SPGs). These data show a significant change in nitrogen biomass burial coincident with sedimentological, pedogenic and biological innovations coincident with the rise of a complex terrestrial biosphere at the onset of the Phanerozoic.
Overall, this thesis improves our understanding of nitrogen in magmatic systems, shows that studying nitrogen in Earths igneous crust is essential for balancing the geobiological nitrogen cycle, and provides a strong basis for more work on igneous systems for future research.
2023-06-16T00:00:00ZBoocock, Toby JamesThe geological and biological nitrogen cycles are intimately linked. Nitrogen is an essential element in the structure of amino acids, proteins, nucleic acids, and other molecules vital for life, as well as 78% of the Earths atmosphere and present in significant quantities in all of Earths geological reservoirs. Planetary scale processes such as degassing, subduction and differentiation play a key role in generating and supporting a nitrogen rich surface environment suitable for supporting life. However, the fluxes and stores of nitrogen between Earths mantle, crust and atmosphere remain poorly constrained. Constraining the behaviour of nitrogen during these processes is therefore essential. This thesis targets the processing and storage of nitrogen in the Earth’s crust, with a focus on identify fundamental partitioning and isotopic fractionation during magmatic differentiation and assessing what the crustal nitrogen record can inform us about changes in the biogeochemical nitrogen cycle.
Firstly, I utilise two contrasting but well constrained magmatic systems, the aphyric lavas from Hekla volcano, Iceland, and the calc-alkaline Loch Doon zoned pluton, Scotland. These data are to the best of our knowledge the first combined abundance and isotopic ratio measurements for differentiating magmatic suites at a bulk and mineral scale. I show with the Hekla dataset that when undersaturated in a magma, nitrogen behaves more akin to lithophile rather than volatile elements and can be enriched significantly in Earths crust during differentiation. In Loch Doon, at a mineral scale, we find feldspars host 60-90% of the whole rock nitrogen contents in contrast with previous studies suggesting biotite as the main N host phase. Associated with this are significant feldspar-mica isotopic fractionation suggesting magmatic differentiation can impart significant measurable isotopic differences.
Secondly, I assess the ability of the plutonic felsic crust to record changes in the terrestrial sedimentary nitrogen cycle through analysis of a suite of well characterised strongly peraluminous granitoids (SPGs). These data show a significant change in nitrogen biomass burial coincident with sedimentological, pedogenic and biological innovations coincident with the rise of a complex terrestrial biosphere at the onset of the Phanerozoic.
Overall, this thesis improves our understanding of nitrogen in magmatic systems, shows that studying nitrogen in Earths igneous crust is essential for balancing the geobiological nitrogen cycle, and provides a strong basis for more work on igneous systems for future research.Reconstructing past coastal change in southeast Scotland : evolution of the Fife coastline
https://hdl.handle.net/10023/27174
The study of past relative sea level (RSL) change is crucial to improve our understanding of how coastlines could be affected by future climate change. This thesis adopts a multidisciplinary approach to explore past coastal change in southeast Scotland, with a focus on the Fife coastline. Development of a RSL model within a geographical information system (GIS) framework allowed for the prediction of RSL over the last ~12 ka at locations around the coast of Fife. Using the created prediction surfaces, palaeo-landscapes were reconstructed for key time periods with palaeoshorelines at 3, 6, 9 and 12 ka. The RSL surfaces show a complex history of fluctuating sea level within the last 12 ka. The models were tested with sedimentological and geophysical field data at the site of Largo Bay. A chronometric framework was measured using optically stimulated luminescence (OSL) and radiocarbon (RC) dating at the site with an age range from ~29 ka to <300 years. A close correlation with the modelled RSL was obtained. Geospatial analysis at the field site of Kincraig Point, utilising LiDAR and unmanned aerial vehicle (UAV) survey, identified five prominent raised rock platforms (P1-P5) with minimum elevations of -1.1, 4.9, 12.3, 23.7 and 35.9 mOD respectively. Platforms P1 and P2 have been inundated and potentially eroded within the last 12 ka. The correlation between field data and modelled data gives a high level of confidence that this combined approach to study of coastal change could be followed in other similar field locations and further that where field evidence of past coastal change is not present the models may be relied upon to give a good indication of past sea level positions and future trends.
2022-06-15T00:00:00ZBoyd, Sarah LouiseThe study of past relative sea level (RSL) change is crucial to improve our understanding of how coastlines could be affected by future climate change. This thesis adopts a multidisciplinary approach to explore past coastal change in southeast Scotland, with a focus on the Fife coastline. Development of a RSL model within a geographical information system (GIS) framework allowed for the prediction of RSL over the last ~12 ka at locations around the coast of Fife. Using the created prediction surfaces, palaeo-landscapes were reconstructed for key time periods with palaeoshorelines at 3, 6, 9 and 12 ka. The RSL surfaces show a complex history of fluctuating sea level within the last 12 ka. The models were tested with sedimentological and geophysical field data at the site of Largo Bay. A chronometric framework was measured using optically stimulated luminescence (OSL) and radiocarbon (RC) dating at the site with an age range from ~29 ka to <300 years. A close correlation with the modelled RSL was obtained. Geospatial analysis at the field site of Kincraig Point, utilising LiDAR and unmanned aerial vehicle (UAV) survey, identified five prominent raised rock platforms (P1-P5) with minimum elevations of -1.1, 4.9, 12.3, 23.7 and 35.9 mOD respectively. Platforms P1 and P2 have been inundated and potentially eroded within the last 12 ka. The correlation between field data and modelled data gives a high level of confidence that this combined approach to study of coastal change could be followed in other similar field locations and further that where field evidence of past coastal change is not present the models may be relied upon to give a good indication of past sea level positions and future trends.Boron based geochemical reconstructions of ocean pH and atmospheric CO₂ in the geological record
https://hdl.handle.net/10023/27101
The boron isotope proxy is a valuable tool for reconstructing ocean pH and atmospheric CO₂ in Earth’s history. Its use on foraminifera in deep sea sediment cores has helped shape our understanding of Cenozoic carbon cycling and climate change, yet most of the extreme examples of biotic and climatic change are in the geological record, where the proxy has seen limited use. The boron isotope proxy’s widespread usage is also hindered by the challenges involved in traditional methods for measuring it: gravity microcolumns require exacting laboratory conditions and are time intensive. Older samples may have more variable matrices which can also be a problem for a gravity column.
In order to expand the boron isotope proxy into a wider variety of matrices, Chapter 3 presents a new batch method for the purification of boron from its sample matrix. Together with methodological improvements for measurement by MC-ICPMS discussed in Chapter 2, these developments allow for measurement of a wide variety of samples with uncertainties roughly half the size, procedural blanks an order of magnitude lower, and sample throughput ~3 times faster than previous methods.
These developments are applied to the geological record in Chapters 4 and 5 for two of the most significant biotic and climatic changes in Earth’s history. Chapter 4 presents boron isotope data from the Triassic-Jurassic boundary, indicating a ≥ 0.34 unit drop in ocean pH coincident with the ‘main’ carbon isotope excursion, suggesting that the carbon isotope excursions associated with the end-Triassic mass extinction event were likely also associated with pulses of ocean acidification. Chapter 5 presents a boron isotope record through the Ordovician into the early Silurian, showing a substantial rise in ocean pH and likely fall in atmospheric CO₂ accompanying the large cooling trend and major radiation in biodiversity though the Ordovician. CO₂-driven cooling thus sets the stage for the glaciation thought to trigger the end-Ordovician extinction event, while rising CO₂ in the early Silurian would have driven climatic recovery.
Together these results highlight the success of the application of the boron isotope proxy to carbon cycle perturbations in the rock record and reveal, for the first time, the changes in the CO₂ system associated with some of the most important events in Earth’s history. In summary, this thesis allows for more accurate and precise boron isotope analysis and a deeper understanding of some of the major environmental events of the Phanerozoic.
2023-06-16T00:00:00ZTrudgill, Molly DianaThe boron isotope proxy is a valuable tool for reconstructing ocean pH and atmospheric CO₂ in Earth’s history. Its use on foraminifera in deep sea sediment cores has helped shape our understanding of Cenozoic carbon cycling and climate change, yet most of the extreme examples of biotic and climatic change are in the geological record, where the proxy has seen limited use. The boron isotope proxy’s widespread usage is also hindered by the challenges involved in traditional methods for measuring it: gravity microcolumns require exacting laboratory conditions and are time intensive. Older samples may have more variable matrices which can also be a problem for a gravity column.
In order to expand the boron isotope proxy into a wider variety of matrices, Chapter 3 presents a new batch method for the purification of boron from its sample matrix. Together with methodological improvements for measurement by MC-ICPMS discussed in Chapter 2, these developments allow for measurement of a wide variety of samples with uncertainties roughly half the size, procedural blanks an order of magnitude lower, and sample throughput ~3 times faster than previous methods.
These developments are applied to the geological record in Chapters 4 and 5 for two of the most significant biotic and climatic changes in Earth’s history. Chapter 4 presents boron isotope data from the Triassic-Jurassic boundary, indicating a ≥ 0.34 unit drop in ocean pH coincident with the ‘main’ carbon isotope excursion, suggesting that the carbon isotope excursions associated with the end-Triassic mass extinction event were likely also associated with pulses of ocean acidification. Chapter 5 presents a boron isotope record through the Ordovician into the early Silurian, showing a substantial rise in ocean pH and likely fall in atmospheric CO₂ accompanying the large cooling trend and major radiation in biodiversity though the Ordovician. CO₂-driven cooling thus sets the stage for the glaciation thought to trigger the end-Ordovician extinction event, while rising CO₂ in the early Silurian would have driven climatic recovery.
Together these results highlight the success of the application of the boron isotope proxy to carbon cycle perturbations in the rock record and reveal, for the first time, the changes in the CO₂ system associated with some of the most important events in Earth’s history. In summary, this thesis allows for more accurate and precise boron isotope analysis and a deeper understanding of some of the major environmental events of the Phanerozoic.The interplay between deformation and magma transport in southeast Iceland
https://hdl.handle.net/10023/27086
Igneous intrusions are of fundamental importance to society's ability to source critical metals, predict major natural hazards and, understand how Earth’s crust evolved. However, the factors that control how magma transits through Earth’s crust and the variables that determine if magma will arrest during the process of ascent or erupt at the surface remains a challenge. This study investigates the interface between key tectonic, host rock and magma parameters to advance our understanding of how these variables influence magma transport processes in sub-volcanic plumbing systems. Specifically, this thesis assesses the interplay of magma flow dynamics and i) deformation structures associated with the ambient extensional stress regime of SE Iceland and ii) host rock deformation processes caused by the process of laccolith intrusion.
The first part of the thesis investigates how surface and overburden deformation (forced folds, faults, and fractures) correlate with the mechanism of magma emplacement. In a case study on the Sandfell Laccoith, eastern Iceland, this chapter presents new palaeomagnetic data and a modified fold test to assess the formation of a forced fold. The results show that the formation of the forced fold occurred in two distinct processes that required the temporal break between the initial injection of magma and the later inflation of the laccolith. An evolutionary model is proposed whereby the continuous forceful emplacement of magma involved initial lateral propagation of a sill-like body preferentially towards the SSW resulting in forced folding with a relatively simple geometry. Continuous addition of magma at the base of the laccolith resulted in subsequent ‘bulldozing’ of magma underlying the cooled, viscously stalled initial magma. Magma that was subsequently injected into the laccolith caused inflation facilitated by further displacement of host rock and the formation of a prominent forced fold that is today observed in outcrop. This study demonstrates the utility of a new modified fold test that provides an effective means to track the style and location of transient shallow-level magma movement associated with forced folding.
Through detailed structural mapping, ²⁰⁶Pb/²³⁸U zircon dating and, anisotropy of magnetic susceptibility (AMS) analyses, the second data chapter of this thesis investigates the relationship between pre-existing fault/fracture networks and magma flow processes in the Reyðarártindur intrusion in southeast Iceland is investigated. The intrusion is interpreted as a sub-volcanic laccolith where magma propagated laterally along a NE-SW primary axis over a timeframe of 10⁴ – 10⁵ years. Pre-existing NNE-striking, faults/fractures in the host rock accommodated intrusive sheets which themselves facilitated upward and outward evacuation of magma from the laccolith. This study elucidates on how the process of magma transport is influenced by pre-existing fault/fracture networks caused by ambient extensional tectonic regimes and shows that lateral offset of eruptive edifices can be controlled by these fracture networks.
The final data chapter uses fracture modelling to provide a revised regional tectonic framework for southeast Iceland. Fracture analysis of fault and joint populations identified within the structural aureole of the Reyðarártindur intrusion and across the southeast Iceland to identify different generations of Riedel shear structures that in turn define a sinistral Riedel shear system. The inferred Riedel shear system is interpreted to have formed within a Neogene WSW-ENE trending transfer zone that linked at least two rift segments. This investigation posits a new interpretation of the contemporaneous stress regime for southeast Iceland and discusses how the associated deformation influenced the transport and storage of magma.
The works of this thesis highlight that investigating the interplay between magma movement and host-rock properties aids in our understanding of magma transport in sub-volcanic systems.
2023-06-16T00:00:00ZTwomey, VincentIgneous intrusions are of fundamental importance to society's ability to source critical metals, predict major natural hazards and, understand how Earth’s crust evolved. However, the factors that control how magma transits through Earth’s crust and the variables that determine if magma will arrest during the process of ascent or erupt at the surface remains a challenge. This study investigates the interface between key tectonic, host rock and magma parameters to advance our understanding of how these variables influence magma transport processes in sub-volcanic plumbing systems. Specifically, this thesis assesses the interplay of magma flow dynamics and i) deformation structures associated with the ambient extensional stress regime of SE Iceland and ii) host rock deformation processes caused by the process of laccolith intrusion.
The first part of the thesis investigates how surface and overburden deformation (forced folds, faults, and fractures) correlate with the mechanism of magma emplacement. In a case study on the Sandfell Laccoith, eastern Iceland, this chapter presents new palaeomagnetic data and a modified fold test to assess the formation of a forced fold. The results show that the formation of the forced fold occurred in two distinct processes that required the temporal break between the initial injection of magma and the later inflation of the laccolith. An evolutionary model is proposed whereby the continuous forceful emplacement of magma involved initial lateral propagation of a sill-like body preferentially towards the SSW resulting in forced folding with a relatively simple geometry. Continuous addition of magma at the base of the laccolith resulted in subsequent ‘bulldozing’ of magma underlying the cooled, viscously stalled initial magma. Magma that was subsequently injected into the laccolith caused inflation facilitated by further displacement of host rock and the formation of a prominent forced fold that is today observed in outcrop. This study demonstrates the utility of a new modified fold test that provides an effective means to track the style and location of transient shallow-level magma movement associated with forced folding.
Through detailed structural mapping, ²⁰⁶Pb/²³⁸U zircon dating and, anisotropy of magnetic susceptibility (AMS) analyses, the second data chapter of this thesis investigates the relationship between pre-existing fault/fracture networks and magma flow processes in the Reyðarártindur intrusion in southeast Iceland is investigated. The intrusion is interpreted as a sub-volcanic laccolith where magma propagated laterally along a NE-SW primary axis over a timeframe of 10⁴ – 10⁵ years. Pre-existing NNE-striking, faults/fractures in the host rock accommodated intrusive sheets which themselves facilitated upward and outward evacuation of magma from the laccolith. This study elucidates on how the process of magma transport is influenced by pre-existing fault/fracture networks caused by ambient extensional tectonic regimes and shows that lateral offset of eruptive edifices can be controlled by these fracture networks.
The final data chapter uses fracture modelling to provide a revised regional tectonic framework for southeast Iceland. Fracture analysis of fault and joint populations identified within the structural aureole of the Reyðarártindur intrusion and across the southeast Iceland to identify different generations of Riedel shear structures that in turn define a sinistral Riedel shear system. The inferred Riedel shear system is interpreted to have formed within a Neogene WSW-ENE trending transfer zone that linked at least two rift segments. This investigation posits a new interpretation of the contemporaneous stress regime for southeast Iceland and discusses how the associated deformation influenced the transport and storage of magma.
The works of this thesis highlight that investigating the interplay between magma movement and host-rock properties aids in our understanding of magma transport in sub-volcanic systems.Negatively charged ions in the deep Earth : quantifying the chemical speciation of F and N in silicate melts and phases
https://hdl.handle.net/10023/26905
Nitrogen and fluorine are essential volatile elements to study in the bulk silicate Earth (BSE) due to their respective influence over the onset of habitability on Earth or over physical and chemical properties of the phases which contain them. Nitrogen is abnormally depleted in the BSE relative to CI chondrite, while fluorine is abnormally enriched, hence questions arise about their chemical speciation and storage mechanisms within planetary reservoirs.
The speciation of nitrogen in high pressure silicate melts was studied using solid-state nuclear magnetic resonance (NMR) and Raman spectroscopy and was found to be heavily influenced by oxygen fugacity. The former technique provided superior results in quantifying the abundance of individual species and higher sensitivity, however it requires ¹⁵N enrichment, low-Fe samples and performs only bulk analysis, while the latter was found to be an efficient in situ technique regardless of sample composition, but it struggled at detecting low-abundance N species.
The speciation of fluorine in silicate melts was studied via NMR spectroscopy at BSE-like concentrations, thanks to this techniques high F sensitivity. F was found to be binding solely with Mg at atmospheric pressure, and this speciation remains predominant until c.a. 8 GPa, where relevant quantities of F start binding with Ca. This is likely due to the changing coordination number of the major components of the melt, but a change in the coordination of fluorine itself might also be occurring.
The ordering of fluoride and hydroxide in the framework of humite group minerals was studied via NMR spectroscopy and computational modelling. The incorporation of one F and one OH anion in neighbouring sites was found to be favoured relative to the incorporation of two identical ions, thanks to the formation of a hydrogen bond. This likely explains the extended stability field of clinohumite when it is F rich.
2022-11-29T00:00:00ZFormoso, FilippoNitrogen and fluorine are essential volatile elements to study in the bulk silicate Earth (BSE) due to their respective influence over the onset of habitability on Earth or over physical and chemical properties of the phases which contain them. Nitrogen is abnormally depleted in the BSE relative to CI chondrite, while fluorine is abnormally enriched, hence questions arise about their chemical speciation and storage mechanisms within planetary reservoirs.
The speciation of nitrogen in high pressure silicate melts was studied using solid-state nuclear magnetic resonance (NMR) and Raman spectroscopy and was found to be heavily influenced by oxygen fugacity. The former technique provided superior results in quantifying the abundance of individual species and higher sensitivity, however it requires ¹⁵N enrichment, low-Fe samples and performs only bulk analysis, while the latter was found to be an efficient in situ technique regardless of sample composition, but it struggled at detecting low-abundance N species.
The speciation of fluorine in silicate melts was studied via NMR spectroscopy at BSE-like concentrations, thanks to this techniques high F sensitivity. F was found to be binding solely with Mg at atmospheric pressure, and this speciation remains predominant until c.a. 8 GPa, where relevant quantities of F start binding with Ca. This is likely due to the changing coordination number of the major components of the melt, but a change in the coordination of fluorine itself might also be occurring.
The ordering of fluoride and hydroxide in the framework of humite group minerals was studied via NMR spectroscopy and computational modelling. The incorporation of one F and one OH anion in neighbouring sites was found to be favoured relative to the incorporation of two identical ions, thanks to the formation of a hydrogen bond. This likely explains the extended stability field of clinohumite when it is F rich.Carbon and sulfur isotope biosignatures in Mars-analogue hydrothermal environments
https://hdl.handle.net/10023/26844
The study of terrestrial environments that bear similarity to Mars provides valuable
information for interpreting data from missions, including how to find evidence of relict
life on the red planet. Stable isotope signatures evidencing microbial metabolic activity
are commonly used as a biosignature tool. Here, an interdisciplinary study investigating
two volcanic hydrothermal systems in Iceland is presented, with additional
contextualisation through a comparison with a non-volcanic hypersaline spring. This
thesis combines mineralogy, geochemistry, microbial community DNA, and stable
isotope systems (carbon and sulfur) to analyse: i) the preservation of isotopic
biosignatures in hydrothermal and hypersaline springs, and ii) the relationships
between the biosignatures and the geochemistry of these environments.
Firstly, a characterisation of two Mars analogue hydrothermal environments in Iceland
(Kerlingarfjöll and Kverkfjöll), reveals deep volcanic processes controlling the
geochemistry of the hydrothermal pools. The volcanic processes create two very distinct
pH environments, with Kerlingarfjöll circum-neutral and Kverkfjöll acidic, with distinct
water geochemistry and mineralogy. The water geochemistry is found to be a key
parameter controlling the microbial communities, based on pH differences and the
different electron donors and acceptors available. Secondly, carbon isotope
fractionations preserved as sedimentary organic carbon, are controlled in Kerlingarfjöll
and Kverkfjöll systems by temperature. Low temperature pools favour carbon CO₂
fixation pathways that produce larger or more variable carbon isotope fractionations.
Lastly, sulfur isotope values (δ³⁴S) recorded in the sediments are not conclusive as
geochemical biosignatures in Kerlingarfjöll and Kverkfjöll sediments. This is due to
abundant H2S with abiotic δ³⁴S values overwhelming biological δ³⁴S values. Conversely,
when combining δ³⁴S with Δ³³S and Δ³⁶S as a Quadruple Sulfur Isotope system (QSI), two
pools in Kerlingarfjöll show complex S-cycling combining biological and volcanic
processes. Importantly, the non-volcanic hypersaline spring preserves larger
fractionations in δ³⁴S and large Δ³³S values, typical of reduction and disproportionation
of sulfur by microorganisms. The main environmental variables causing larger S isotope fractionations in the hypersaline spring are the salinity stress and the limitation of
electron donors and acceptors in the environment.
Overall, this thesis improves the understanding of carbon and sulfur isotopes as
biosignature tools for investigating hydrothermal and hypersaline environments in
Mars, and opens the door for the use of QSI as a more robust biosignature for future
missions.
2022-06-21T00:00:00ZMoreras Martí, ArolaThe study of terrestrial environments that bear similarity to Mars provides valuable
information for interpreting data from missions, including how to find evidence of relict
life on the red planet. Stable isotope signatures evidencing microbial metabolic activity
are commonly used as a biosignature tool. Here, an interdisciplinary study investigating
two volcanic hydrothermal systems in Iceland is presented, with additional
contextualisation through a comparison with a non-volcanic hypersaline spring. This
thesis combines mineralogy, geochemistry, microbial community DNA, and stable
isotope systems (carbon and sulfur) to analyse: i) the preservation of isotopic
biosignatures in hydrothermal and hypersaline springs, and ii) the relationships
between the biosignatures and the geochemistry of these environments.
Firstly, a characterisation of two Mars analogue hydrothermal environments in Iceland
(Kerlingarfjöll and Kverkfjöll), reveals deep volcanic processes controlling the
geochemistry of the hydrothermal pools. The volcanic processes create two very distinct
pH environments, with Kerlingarfjöll circum-neutral and Kverkfjöll acidic, with distinct
water geochemistry and mineralogy. The water geochemistry is found to be a key
parameter controlling the microbial communities, based on pH differences and the
different electron donors and acceptors available. Secondly, carbon isotope
fractionations preserved as sedimentary organic carbon, are controlled in Kerlingarfjöll
and Kverkfjöll systems by temperature. Low temperature pools favour carbon CO₂
fixation pathways that produce larger or more variable carbon isotope fractionations.
Lastly, sulfur isotope values (δ³⁴S) recorded in the sediments are not conclusive as
geochemical biosignatures in Kerlingarfjöll and Kverkfjöll sediments. This is due to
abundant H2S with abiotic δ³⁴S values overwhelming biological δ³⁴S values. Conversely,
when combining δ³⁴S with Δ³³S and Δ³⁶S as a Quadruple Sulfur Isotope system (QSI), two
pools in Kerlingarfjöll show complex S-cycling combining biological and volcanic
processes. Importantly, the non-volcanic hypersaline spring preserves larger
fractionations in δ³⁴S and large Δ³³S values, typical of reduction and disproportionation
of sulfur by microorganisms. The main environmental variables causing larger S isotope fractionations in the hypersaline spring are the salinity stress and the limitation of
electron donors and acceptors in the environment.
Overall, this thesis improves the understanding of carbon and sulfur isotopes as
biosignature tools for investigating hydrothermal and hypersaline environments in
Mars, and opens the door for the use of QSI as a more robust biosignature for future
missions.REE induced defects in minerals : a spectroscopic study
https://hdl.handle.net/10023/24050
This thesis examines the luminescence and mineral physics of Rare Earth Element (REE) bearing
minerals as a precursor to developing smart sorting tools for critical metals used in low-carbon
technologies. I characterise luminescence responses of complex zirconosilicates; eudialyte
(Na₁₅Ca₆(Fe²⁺,Mn²⁺)₃Zr₃[Si₂₅O₇₃](O,OH,H₂O)₃(OH,Cl)₂), wöhlerite (NaCa₂(Zr,Nb)(Si₂O₇)(O,OH,F)₂) and
catapleiite (Na₂Zr(Si₃O₉) · 2H2₂O). Fluorite was included as it is commonly associated with REE ores and
displays strong REE luminescence. Its behaviour provides key insights into REE substitution into ionic
minerals.
X-ray Excited Optical Luminescence (XEOL) and Thermoluminescence (TL) measurements were taken
from 20 to 673 K. Fluorite responses result from a balance of intrinsic luminescence and REE
substituents and evidence for REE and defect coupling. TL indicates the presence of electron traps and
the coupling of these traps to lanthanide emissions, and it shows that the defect and the lanthanide
are clustered in physical space. The absence of changes in TL for different lanthanides shows that
energy is passed efficiently between rare earths, indicating that the REE are clustered.
The zirconosilicates all show increased intensity in XEOL response below 150 K. Cryogenic emissions
are interpreted as originating from the host mineral. There are 3 shared features: UV (~280 nm)
paramagnetic oxygen or oxygen vacancy; blue (440 nm) Al-O⁻-Al /Ti centres; and REE. Wöhlerite and eudialyte show Fe³⁺ band (~708 nm) and wöhlerite displays broad emission attributed to Mn²⁺. Eudialyte shows two additional responses; UV (~320 nm) tentatively assigned to Na migration and
UV/blue (~400 nm) potentially associated with charge balances associated with the coupled
substitution of Al³⁺. Eudialyte shows little emission at room temperature, this is attributed to quenching from Fe²⁺. Emission from eudialyte above room temperature is attributed to alteration
minerals such as catapleiite and potentially to inclusions of luminescent primary mineral phases.
I demonstrate that smart sorting could be a valuable beneficiation tool for REE minerals.
2020-07-29T00:00:00ZHorsburgh, Nicola JaneThis thesis examines the luminescence and mineral physics of Rare Earth Element (REE) bearing
minerals as a precursor to developing smart sorting tools for critical metals used in low-carbon
technologies. I characterise luminescence responses of complex zirconosilicates; eudialyte
(Na₁₅Ca₆(Fe²⁺,Mn²⁺)₃Zr₃[Si₂₅O₇₃](O,OH,H₂O)₃(OH,Cl)₂), wöhlerite (NaCa₂(Zr,Nb)(Si₂O₇)(O,OH,F)₂) and
catapleiite (Na₂Zr(Si₃O₉) · 2H2₂O). Fluorite was included as it is commonly associated with REE ores and
displays strong REE luminescence. Its behaviour provides key insights into REE substitution into ionic
minerals.
X-ray Excited Optical Luminescence (XEOL) and Thermoluminescence (TL) measurements were taken
from 20 to 673 K. Fluorite responses result from a balance of intrinsic luminescence and REE
substituents and evidence for REE and defect coupling. TL indicates the presence of electron traps and
the coupling of these traps to lanthanide emissions, and it shows that the defect and the lanthanide
are clustered in physical space. The absence of changes in TL for different lanthanides shows that
energy is passed efficiently between rare earths, indicating that the REE are clustered.
The zirconosilicates all show increased intensity in XEOL response below 150 K. Cryogenic emissions
are interpreted as originating from the host mineral. There are 3 shared features: UV (~280 nm)
paramagnetic oxygen or oxygen vacancy; blue (440 nm) Al-O⁻-Al /Ti centres; and REE. Wöhlerite and eudialyte show Fe³⁺ band (~708 nm) and wöhlerite displays broad emission attributed to Mn²⁺. Eudialyte shows two additional responses; UV (~320 nm) tentatively assigned to Na migration and
UV/blue (~400 nm) potentially associated with charge balances associated with the coupled
substitution of Al³⁺. Eudialyte shows little emission at room temperature, this is attributed to quenching from Fe²⁺. Emission from eudialyte above room temperature is attributed to alteration
minerals such as catapleiite and potentially to inclusions of luminescent primary mineral phases.
I demonstrate that smart sorting could be a valuable beneficiation tool for REE minerals.Alteration and fluid flow associated with sediment-hosted stratiform copper mineralisation in the 1.1 Ga Midcontinent Rift System, USA
https://hdl.handle.net/10023/23982
The White Pine Cu-Ag deposit is one of the World’s largest examples of a sediment-
hosted copper (SHC) mineral system, with a pre-mining resource of >10 Mt of Cu
metal. The deposit is located on the southern shore of Lake Superior, in Michigan’s
Upper Peninsula. Mineralisation is hosted in the late-Mesoproterozoic Keweenawan
Supergroup of the Midcontinent Rift System (MRS). This succession comprises 20 km
of flood basalts overlain by 10 km of clastic sedimentary rocks. The age, extraordinary
volume of basalt and paucity of evaporite minerals distinguishes the MRS from other
major sediment-hosted Cu basins. Basin formation commenced at c. 1111 Ma, possibly
in response to a mantle plume impacting the base of the lithosphere. The mass of
basalts loaded onto the crust initially drove rapid basin subsidence, forming sag-geometry
basalt
flows
in
the
absence
of
syn-volcanic
faults.
Volcanism
ceased
abruptly
at
c. 1090 Ma and the Oronto Group sediments were deposited at a lower rate of
subsidence. The Copper Harbor and Nonesuch Formations were deposited in a braided
fluvial-marine embayment-sabkha environment. Seawater formed the basis for the
ore-forming fluids. Metals were sourced from the breakdown of basaltic detrital grains
in the Copper Harbor Formation. A Re-Os age of chalcocite mineralisation of 1039 ± 4
Ma corresponds to the early Ottawan phase of the Grenvillian orogenesis, which
caused incipient basin inversion and deposition of the Freda Formation molasse. This
simultaneous burial and mild compression expelled fluids from the Copper Harbor
Formation aquifer. Ore precipitated via reduction of fluids by both in situ organic
matter and liquid petroleum, and thermochemical sulphate reduction, at
temperatures of c. 125˚C. Early Cu-Fe-sulphides nucleated on detrital and authigenic
chlorite. The advancement of the peneconcordant ore zones resulted in their eventual
replacement by chalcocite and native Cu, reflecting the relatively oxidised conditions
and the low sulphur content of late-Mesoproterozoic seawater.
2020-12-01T00:00:00ZJones, Simon MarkThe White Pine Cu-Ag deposit is one of the World’s largest examples of a sediment-
hosted copper (SHC) mineral system, with a pre-mining resource of >10 Mt of Cu
metal. The deposit is located on the southern shore of Lake Superior, in Michigan’s
Upper Peninsula. Mineralisation is hosted in the late-Mesoproterozoic Keweenawan
Supergroup of the Midcontinent Rift System (MRS). This succession comprises 20 km
of flood basalts overlain by 10 km of clastic sedimentary rocks. The age, extraordinary
volume of basalt and paucity of evaporite minerals distinguishes the MRS from other
major sediment-hosted Cu basins. Basin formation commenced at c. 1111 Ma, possibly
in response to a mantle plume impacting the base of the lithosphere. The mass of
basalts loaded onto the crust initially drove rapid basin subsidence, forming sag-geometry
basalt
flows
in
the
absence
of
syn-volcanic
faults.
Volcanism
ceased
abruptly
at
c. 1090 Ma and the Oronto Group sediments were deposited at a lower rate of
subsidence. The Copper Harbor and Nonesuch Formations were deposited in a braided
fluvial-marine embayment-sabkha environment. Seawater formed the basis for the
ore-forming fluids. Metals were sourced from the breakdown of basaltic detrital grains
in the Copper Harbor Formation. A Re-Os age of chalcocite mineralisation of 1039 ± 4
Ma corresponds to the early Ottawan phase of the Grenvillian orogenesis, which
caused incipient basin inversion and deposition of the Freda Formation molasse. This
simultaneous burial and mild compression expelled fluids from the Copper Harbor
Formation aquifer. Ore precipitated via reduction of fluids by both in situ organic
matter and liquid petroleum, and thermochemical sulphate reduction, at
temperatures of c. 125˚C. Early Cu-Fe-sulphides nucleated on detrital and authigenic
chlorite. The advancement of the peneconcordant ore zones resulted in their eventual
replacement by chalcocite and native Cu, reflecting the relatively oxidised conditions
and the low sulphur content of late-Mesoproterozoic seawater.Rapid climate change in the glacial North Atlantic : new insights from geochemical records of temperature, CO₂, redox and circulation
https://hdl.handle.net/10023/23880
Rapid climate change events of the last glacial period are a prime example of the climate system’s ability to flip quickly between different states. These are associated with abrupt shifts in temperature, productivity and CO₂ and are commonly linked with major changes in circulation and sea-ice coverage in the high latitude North Atlantic Ocean. However, despite what is an increasingly well-established paradigm, major questions remain about the links between circulation, temperature, ice-sheet stability and CO₂ storage. This thesis presents a collection of new, high resolution records from Northeast Atlantic core ODP 980, which develop our understanding of the region’s role in rapid climate change.
Analysis of two robust paleo-temperature proxies (percentage abundance and Mg/Ca of Neogloboquadrina pachyderma) reveals the first marine evidence that Heinrich stadials were intervals of extreme seasonality, characterised by very cold winters and increasingly warm summers. These rising temperatures which are attributed to weak Atlantic Meridional Overturning circulation (AMOC), climbing atmospheric CO₂ and the insulating effect of sea ice, support theories for ice-sheet destabilisation in an otherwise cold climate. High resolution boron isotope data also resolve major perturbations of CO₂ in the surface ocean at climate transitions. These show that the North Atlantic CO₂ sink, which persists during stadial periods, weakened dramatically at interstadial onset, likely maintaining elevated atmospheric CO₂ and uncovering a new role for the region in rapid climate change.
Recent studies using authigenic coatings on foraminifera, have employed redox sensitive elements to reconstruct deep water oxygen concentrations. However, data from different oceanic settings, combined with a geochemical model, highlight the sensitivity of element enrichment to changes in surface productivity. The influence of sediment composition is also examined with regards to authigenic Nd/Mn ratios, which show exciting promise as a new indicator of AMOC strength. Together these authigenic data offer new opportunities for paleoclimate reconstruction.
2021-12-01T00:00:00ZLittley, Eloise Frances MargaretRapid climate change events of the last glacial period are a prime example of the climate system’s ability to flip quickly between different states. These are associated with abrupt shifts in temperature, productivity and CO₂ and are commonly linked with major changes in circulation and sea-ice coverage in the high latitude North Atlantic Ocean. However, despite what is an increasingly well-established paradigm, major questions remain about the links between circulation, temperature, ice-sheet stability and CO₂ storage. This thesis presents a collection of new, high resolution records from Northeast Atlantic core ODP 980, which develop our understanding of the region’s role in rapid climate change.
Analysis of two robust paleo-temperature proxies (percentage abundance and Mg/Ca of Neogloboquadrina pachyderma) reveals the first marine evidence that Heinrich stadials were intervals of extreme seasonality, characterised by very cold winters and increasingly warm summers. These rising temperatures which are attributed to weak Atlantic Meridional Overturning circulation (AMOC), climbing atmospheric CO₂ and the insulating effect of sea ice, support theories for ice-sheet destabilisation in an otherwise cold climate. High resolution boron isotope data also resolve major perturbations of CO₂ in the surface ocean at climate transitions. These show that the North Atlantic CO₂ sink, which persists during stadial periods, weakened dramatically at interstadial onset, likely maintaining elevated atmospheric CO₂ and uncovering a new role for the region in rapid climate change.
Recent studies using authigenic coatings on foraminifera, have employed redox sensitive elements to reconstruct deep water oxygen concentrations. However, data from different oceanic settings, combined with a geochemical model, highlight the sensitivity of element enrichment to changes in surface productivity. The influence of sediment composition is also examined with regards to authigenic Nd/Mn ratios, which show exciting promise as a new indicator of AMOC strength. Together these authigenic data offer new opportunities for paleoclimate reconstruction.Title redacted
https://hdl.handle.net/10023/23851
2021-12-01T00:00:00ZShen, JianxunGeochemical reconstructions of Southern Ocean pH and temperature over the last glacial cycle
https://hdl.handle.net/10023/20385
The Southern Ocean is widely thought to play an important role in atmospheric CO₂ change over glacial-interglacial cycles. It has been suggested that as the region that ventilates the majority of the world’s carbon-rich deep waters today, reduced exchange between deep waters and the atmosphere in the Southern Ocean acted to draw down CO₂ over glacial timescales. However, direct evidence of the Southern Ocean’s role in glacial CO₂ drawdown has been lacking thus far.
Here I apply the boron-isotope pH-proxy to foraminifera from the Antarctic Zone sediment core PS1506 over the last glacial cycle. The low boron concentrations in these polar foraminifera makes these samples particularly sensitive to boron blank and so a close examination of the sources of blank, and an assessment of the precision of blank measurements, has been made.
The ratios of trace elements to calcium in foraminiferal shells are widely applied as proxies for palaeoenvironmental parameters such as temperature. As Southern Ocean carbonate sediments are particularly prone to dissolution, which can affect trace element concentrations, an assessment of dissolution has been made. Firstly, dissolution experiments were conducted to constrain the impact of dissolution in a controlled setting, and secondly, shell mass and trace elements were evaluated for the downcore record. Imaging reveals similar etching textures in both experimentally dissolved samples and deglacial intervals, when shell mass is also low and several trace elements exhibit an excursion to lower values.
Boron isotope data for PS1506 show that during the penultimate interglacial, surface water pH was low. At the onset of atmospheric CO₂ drawdown, pH increased, indicating low CO₂ surface waters. This is consistent with the signature predicted for a more stratified Southern Ocean, and is evidence that stratification in the Antarctic Zone acted to contribute to CO₂ drawdown early in the transition to a glacial state.
2020-12-01T00:00:00ZCrumpton-Banks, Jessica Georgina MagdalenThe Southern Ocean is widely thought to play an important role in atmospheric CO₂ change over glacial-interglacial cycles. It has been suggested that as the region that ventilates the majority of the world’s carbon-rich deep waters today, reduced exchange between deep waters and the atmosphere in the Southern Ocean acted to draw down CO₂ over glacial timescales. However, direct evidence of the Southern Ocean’s role in glacial CO₂ drawdown has been lacking thus far.
Here I apply the boron-isotope pH-proxy to foraminifera from the Antarctic Zone sediment core PS1506 over the last glacial cycle. The low boron concentrations in these polar foraminifera makes these samples particularly sensitive to boron blank and so a close examination of the sources of blank, and an assessment of the precision of blank measurements, has been made.
The ratios of trace elements to calcium in foraminiferal shells are widely applied as proxies for palaeoenvironmental parameters such as temperature. As Southern Ocean carbonate sediments are particularly prone to dissolution, which can affect trace element concentrations, an assessment of dissolution has been made. Firstly, dissolution experiments were conducted to constrain the impact of dissolution in a controlled setting, and secondly, shell mass and trace elements were evaluated for the downcore record. Imaging reveals similar etching textures in both experimentally dissolved samples and deglacial intervals, when shell mass is also low and several trace elements exhibit an excursion to lower values.
Boron isotope data for PS1506 show that during the penultimate interglacial, surface water pH was low. At the onset of atmospheric CO₂ drawdown, pH increased, indicating low CO₂ surface waters. This is consistent with the signature predicted for a more stratified Southern Ocean, and is evidence that stratification in the Antarctic Zone acted to contribute to CO₂ drawdown early in the transition to a glacial state.The effect of forest-to-bog restoration on net ecosystem exchange in Flow Country peatlands
https://hdl.handle.net/10023/18563
Northern peatlands play a critical role in the regulation of atmospheric carbon (C) and are
estimated to store approximately 550 Gt C, which is around a quarter of the world soil C pool.
Saturated conditions means aboveground net primary productivity is low, but also results in low
decomposition and subsequently low respiratory losses. The Flow Country of Caithness and
Sutherland, Northern Scotland is the one of the largest areas of contiguous blanket bog in
Europe encompassing an area in excess of 4000 km². However, these peatlands were badly
degraded in the 1970s and 1980s by large-scale forestry plantations with around 17% of the
Flow Country drained and planted with Sitka spruce and Lodgepole pine altering net ecosystem
C functioning. Restoration efforts have been on going since the 1990s to restore these sites to
blanket bog and return them to net C sinks. Using eddy covariance techniques this research
sought to understand C dynamics over two sites restored at different times, assess their C
sink/source status and the key environmental factors driving changes in C dynamics.
Results showed the youngest restoration site (Lonielist; restored in 2003/04) to be a net source
of C to the atmosphere of 80 g C m⁻² yr⁻¹, while the older restoration site (Talaheel; restored in
1997/98) was a net C sink of -71 g C m⁻² yr⁻¹. Partitioning of the net exchange into its
constituent parts of respiration (R[sub](eco)) and photosynthesis (GPP) found significant differences in R[sub](eco) between the two sites, whilst no significant differences were observed in GPP. Soil
temperature and soil moisture were found to be the greatest controls on R[sub](eco), with higher R[sub](eco) associated with drier, warmer conditions. Incident solar radiation controlled GPP, however dry
periods coupled with high vapour pressure deficit resulted in a limitation of photosynthesis.
These results highlight that peatland restoration is successful at returning sites to net C sinks
over multi-decadal timescales.
2016-11-30T00:00:00ZHambley, GrahamNorthern peatlands play a critical role in the regulation of atmospheric carbon (C) and are
estimated to store approximately 550 Gt C, which is around a quarter of the world soil C pool.
Saturated conditions means aboveground net primary productivity is low, but also results in low
decomposition and subsequently low respiratory losses. The Flow Country of Caithness and
Sutherland, Northern Scotland is the one of the largest areas of contiguous blanket bog in
Europe encompassing an area in excess of 4000 km². However, these peatlands were badly
degraded in the 1970s and 1980s by large-scale forestry plantations with around 17% of the
Flow Country drained and planted with Sitka spruce and Lodgepole pine altering net ecosystem
C functioning. Restoration efforts have been on going since the 1990s to restore these sites to
blanket bog and return them to net C sinks. Using eddy covariance techniques this research
sought to understand C dynamics over two sites restored at different times, assess their C
sink/source status and the key environmental factors driving changes in C dynamics.
Results showed the youngest restoration site (Lonielist; restored in 2003/04) to be a net source
of C to the atmosphere of 80 g C m⁻² yr⁻¹, while the older restoration site (Talaheel; restored in
1997/98) was a net C sink of -71 g C m⁻² yr⁻¹. Partitioning of the net exchange into its
constituent parts of respiration (R[sub](eco)) and photosynthesis (GPP) found significant differences in R[sub](eco) between the two sites, whilst no significant differences were observed in GPP. Soil
temperature and soil moisture were found to be the greatest controls on R[sub](eco), with higher R[sub](eco) associated with drier, warmer conditions. Incident solar radiation controlled GPP, however dry
periods coupled with high vapour pressure deficit resulted in a limitation of photosynthesis.
These results highlight that peatland restoration is successful at returning sites to net C sinks
over multi-decadal timescales.Geophysical, geochemical and isotope analysis of the Figueira Branca Suite, Mato Grosso, Brazil
https://hdl.handle.net/10023/18191
The Figueira Branca Suite is a layered mafic-ultramafic complex in the Jauru Terrane,
southwest Amazon Craton. New lithological, geochemical, gamma-ray and potential field data,
integrated with geological, isotope and paleomagnetic data are used to characterize this pulse
of Mesoproterozoic extension-related magmatism. The Figueira Branca Suite formed through
juvenile magma emplacement into the crust at 1425 Ma, coeval with the later stages of the
Santa Helena Orogen. In three papers, this suite was studied from microscopic to continental
scales. First, the Figueira Branca suite was analysed through thin sections to determine the
influence of inaccurate constraints in magnetic and gravity field modelling. Then, the extent of
magmatism within the suite was delimited to four bodies to the north of Indiavaí city, MT -
Brazil, with potential fields and gamma-ray data. Modelling gravity and magnetic field data
indicated that the anomalous sources are close to the surface or outcropping. These intrusions
trend northwest over 8 km, with significant remanent magnetization that is consistent with
published direction obtained through paleomagnetic data. The increasing enrichment of LREE
in the gabbroic bodies of the suite was interpreted as evidence of progressive fractionation of
the magma. The emplacement, mineralogy and geochemical signature point towards a backarc extension tectonic framework in the later stages of the Santa Helena Orogen. The third part of the work consisted on evaluating reconstructions of the Paleo-Mesoproterozoic supercontinent Nuna with magnetic field data. The global magnetic anomaly map, EMAG2, allowed to observe continuity of magnetic lineaments and regimes in domains of similar ages in different cratons (Amazon, Baltica, West Africa and North China). These magnetic features indicated the theory which the magnetic field best supported, and suggested the regional environment where the Jauru Terrane was inserted by the time of the intrusion of the Figueira Branca Suite.
2017-06-21T00:00:00ZLouro, Vinicius Hector AbudThe Figueira Branca Suite is a layered mafic-ultramafic complex in the Jauru Terrane,
southwest Amazon Craton. New lithological, geochemical, gamma-ray and potential field data,
integrated with geological, isotope and paleomagnetic data are used to characterize this pulse
of Mesoproterozoic extension-related magmatism. The Figueira Branca Suite formed through
juvenile magma emplacement into the crust at 1425 Ma, coeval with the later stages of the
Santa Helena Orogen. In three papers, this suite was studied from microscopic to continental
scales. First, the Figueira Branca suite was analysed through thin sections to determine the
influence of inaccurate constraints in magnetic and gravity field modelling. Then, the extent of
magmatism within the suite was delimited to four bodies to the north of Indiavaí city, MT -
Brazil, with potential fields and gamma-ray data. Modelling gravity and magnetic field data
indicated that the anomalous sources are close to the surface or outcropping. These intrusions
trend northwest over 8 km, with significant remanent magnetization that is consistent with
published direction obtained through paleomagnetic data. The increasing enrichment of LREE
in the gabbroic bodies of the suite was interpreted as evidence of progressive fractionation of
the magma. The emplacement, mineralogy and geochemical signature point towards a backarc extension tectonic framework in the later stages of the Santa Helena Orogen. The third part of the work consisted on evaluating reconstructions of the Paleo-Mesoproterozoic supercontinent Nuna with magnetic field data. The global magnetic anomaly map, EMAG2, allowed to observe continuity of magnetic lineaments and regimes in domains of similar ages in different cratons (Amazon, Baltica, West Africa and North China). These magnetic features indicated the theory which the magnetic field best supported, and suggested the regional environment where the Jauru Terrane was inserted by the time of the intrusion of the Figueira Branca Suite.The archaeological potential of windblown sand and its impacts on prehistoric settlements and landscapes in the Orkney Islands, Scotland
https://hdl.handle.net/10023/17889
This thesis comprises an investigation into the nature, chronology, and significance of prehistoric windblown sand deposition on archaeological sites in the Orkney Islands, Scotland. One of the most visible and frequently-encountered forms of evidence for dynamic coastal processes which took place over the last four millennia are horizons of calcareous (shell) and mineral (quartz and feldspar) sands, which were deposited in coastal landscapes and settlements by wind and wave dynamics. Around 20% of the Scottish coastline is made up of sand-based features, with the dune area comprising some 48,000ha (Dargie and Duncan 1999, 143).
Such coastal zones were densely settled in the prehistoric period. As monitoring of the modern coastline for changes affecting known archaeological sites continues, deposits of windblown sand - often interleaved with material evidence for human occupation – are becoming frequently recognised in the archaeological record. One coastal region which has felt the impacts of this coastal process (and continues to do so), is the Orkney archipelago, located off the northern coast of Mainland Scotland. It is this group of islands which form the geographical focus of this thesis. Previous archaeological interpretations of this important coastal process have been concerned with the development of chronologies of deposition in an attempt to tie the deposition of windblown sand to narratives of climatic deterioration. Such approaches fail to recognise the broader social significance of these windblown sand deposits, and how they were encountered by prehistorical inhabitants of the coastline. This thesis synthesises all known occurrences of windblown sand on archaeological sites in Orkney, and suggests additional ways in which their socio-economic significance can be realised.
2019-06-26T00:00:00ZGal, Emily LouiseThis thesis comprises an investigation into the nature, chronology, and significance of prehistoric windblown sand deposition on archaeological sites in the Orkney Islands, Scotland. One of the most visible and frequently-encountered forms of evidence for dynamic coastal processes which took place over the last four millennia are horizons of calcareous (shell) and mineral (quartz and feldspar) sands, which were deposited in coastal landscapes and settlements by wind and wave dynamics. Around 20% of the Scottish coastline is made up of sand-based features, with the dune area comprising some 48,000ha (Dargie and Duncan 1999, 143).
Such coastal zones were densely settled in the prehistoric period. As monitoring of the modern coastline for changes affecting known archaeological sites continues, deposits of windblown sand - often interleaved with material evidence for human occupation – are becoming frequently recognised in the archaeological record. One coastal region which has felt the impacts of this coastal process (and continues to do so), is the Orkney archipelago, located off the northern coast of Mainland Scotland. It is this group of islands which form the geographical focus of this thesis. Previous archaeological interpretations of this important coastal process have been concerned with the development of chronologies of deposition in an attempt to tie the deposition of windblown sand to narratives of climatic deterioration. Such approaches fail to recognise the broader social significance of these windblown sand deposits, and how they were encountered by prehistorical inhabitants of the coastline. This thesis synthesises all known occurrences of windblown sand on archaeological sites in Orkney, and suggests additional ways in which their socio-economic significance can be realised.The North Pacific from glacial to modern : assemblages, isotopes and CO₂
https://hdl.handle.net/10023/17140
Investigating past changes in Earth’s climate can provide useful information for assessing future climate change scenarios. Planktic foraminifera preserved in marine sediment are commonly used as a tool to reconstruct past environmental change. Here I present a combination of modern census and multinet data from the North Pacific, a new compilation of global census data, a new global calibration for Mg/Ca ratios in Neogloboquadrina pachyderma, and foraminifera assemblage, trace element, and boron isotope data from the North Pacific spanning the last deglaciation.
New modern census data from the North Pacific shows that two key sub-polar proxy carrying species, N. pachyderma and Globigerina bulloides, predominantly live between 0-50 m in the water column. Global planktic foraminifera diversity is observed to be driven primarily by sea surface temperature, with upwelling and ocean productivity providing key secondary roles. In the North Pacific, a preservation bias of N. pachyderma over G. bulloides is observed when comparing multinet and core-top samples, highlighting the importance of tracking dissolution during downcore studies. To improve the use of Mg/Ca ratios in N. pachyderma downcore, I produced a new global calibration with a temperature sensitivity of 6 % per °C. This calibration was combined with boron isotope and Mg/Ca data from sediment core MD02-2489 to investigate changes in North Pacific circulation, productivity, and CO₂ during the last deglaciation. Two intervals of high surface CO₂ were observed, the first during Heinrich Stadial 1, where deep ventilation mixed CO₂ and nutrients throughout the water column. The second occurred during the Bølling-Allerød, where stratification pooled nutrients and CO₂ in surface waters, leading to enhanced productivity and CO₂ outgassing. Overall, this thesis improves the use of planktic foraminifera as tools for investigating past climate change and highlights the role of the North Pacific in deglacial CO₂ release.
2019-06-26T00:00:00ZTaylor, Ben JustinInvestigating past changes in Earth’s climate can provide useful information for assessing future climate change scenarios. Planktic foraminifera preserved in marine sediment are commonly used as a tool to reconstruct past environmental change. Here I present a combination of modern census and multinet data from the North Pacific, a new compilation of global census data, a new global calibration for Mg/Ca ratios in Neogloboquadrina pachyderma, and foraminifera assemblage, trace element, and boron isotope data from the North Pacific spanning the last deglaciation.
New modern census data from the North Pacific shows that two key sub-polar proxy carrying species, N. pachyderma and Globigerina bulloides, predominantly live between 0-50 m in the water column. Global planktic foraminifera diversity is observed to be driven primarily by sea surface temperature, with upwelling and ocean productivity providing key secondary roles. In the North Pacific, a preservation bias of N. pachyderma over G. bulloides is observed when comparing multinet and core-top samples, highlighting the importance of tracking dissolution during downcore studies. To improve the use of Mg/Ca ratios in N. pachyderma downcore, I produced a new global calibration with a temperature sensitivity of 6 % per °C. This calibration was combined with boron isotope and Mg/Ca data from sediment core MD02-2489 to investigate changes in North Pacific circulation, productivity, and CO₂ during the last deglaciation. Two intervals of high surface CO₂ were observed, the first during Heinrich Stadial 1, where deep ventilation mixed CO₂ and nutrients throughout the water column. The second occurred during the Bølling-Allerød, where stratification pooled nutrients and CO₂ in surface waters, leading to enhanced productivity and CO₂ outgassing. Overall, this thesis improves the use of planktic foraminifera as tools for investigating past climate change and highlights the role of the North Pacific in deglacial CO₂ release.The application of highly resolved tree-ring isotopes for reconstructing the ecohydrological interactions within riparian forests
https://hdl.handle.net/10023/16672
The research conducted within this thesis aims to advance our understanding of plant-water
interactions, specifically the identification of the source(s) of water available for tree growth
within riparian zones. Through highly resolved tree ring isotopic analyses, it is possible to deconvolve the δ¹⁸O signature of water utilised by a tree during the growing season and relate
this to dynamic hydroclimatic processes. In doing so, this methodology allows for the
reconstruction of the seasonal evolution of tree source water availability for the historical
period. The utility of this method is initially demonstrated for the determination of the isotopic
signature of water utilised by individuals of co-occuring riparian tree species over ten consecutive years. It is found that species-specific seasonal source water variability is indicative of tree rooting depth and the hydroclimatic partitioning of water to each of the floodplain hydrological reservoirs. The technique is then developed in to a methodological ‘toolkit’, comprised of tool groups representing differing levels of data availability. The aim is to enable continued progress in this research area, even under conditions of sub-optimal data availability, whilst also making the suite of methods accessible to other researchers and resource managers. Finally, the hydroclimatic expression of seasonal tree source water avaialbility is characterised across a climate gradient utilising over 800 δ¹⁸O cellulose measurements. The results show that the seasonal progression of tree water availability responds to near- and far-field hydroclimatic processes, but this is mediated by species’ functional type and site lithology. Where near-field processes dominate water availability, there is a potential for increased vulnerability to localised drought conditions and species-specific competition for water resources. Retrodictions of seasonal water source use may prove useful in forest restoration and rehabilitation efforts, assessment of forest vulnerability to future hydroclimatic regimes and for improving agroforestry and sustainable water management practices.
2018-01-15T00:00:00ZSargeant, ChristopherThe research conducted within this thesis aims to advance our understanding of plant-water
interactions, specifically the identification of the source(s) of water available for tree growth
within riparian zones. Through highly resolved tree ring isotopic analyses, it is possible to deconvolve the δ¹⁸O signature of water utilised by a tree during the growing season and relate
this to dynamic hydroclimatic processes. In doing so, this methodology allows for the
reconstruction of the seasonal evolution of tree source water availability for the historical
period. The utility of this method is initially demonstrated for the determination of the isotopic
signature of water utilised by individuals of co-occuring riparian tree species over ten consecutive years. It is found that species-specific seasonal source water variability is indicative of tree rooting depth and the hydroclimatic partitioning of water to each of the floodplain hydrological reservoirs. The technique is then developed in to a methodological ‘toolkit’, comprised of tool groups representing differing levels of data availability. The aim is to enable continued progress in this research area, even under conditions of sub-optimal data availability, whilst also making the suite of methods accessible to other researchers and resource managers. Finally, the hydroclimatic expression of seasonal tree source water avaialbility is characterised across a climate gradient utilising over 800 δ¹⁸O cellulose measurements. The results show that the seasonal progression of tree water availability responds to near- and far-field hydroclimatic processes, but this is mediated by species’ functional type and site lithology. Where near-field processes dominate water availability, there is a potential for increased vulnerability to localised drought conditions and species-specific competition for water resources. Retrodictions of seasonal water source use may prove useful in forest restoration and rehabilitation efforts, assessment of forest vulnerability to future hydroclimatic regimes and for improving agroforestry and sustainable water management practices.Modelling subsurface hydrological processes in riparian zones
https://hdl.handle.net/10023/16337
Soil moisture is a crucial but unseen component of the hydrologic cycle. It provides a hydrologic link
and storage between surface waters and groundwater. This unexposed water sanctuary could be the key to
sustain life during ever-prevalent climatic extremes. To quantify and understand the role of soil moisture in
catchment hydrology, the HaughFlow model has been developed as a new tool to simulate subsurface
hydrology and water flow in floodplain soils. The model is constructed to be flexible, adaptable and
logically composed in order to encourage interaction from the wider scientific community. Model transparency
and parsimony are key; with assumptions clearly explained and only the dominant processes simulated
to limit the number of inputs required and retain efficiency. The dominant processes for hydraulically
connected floodplains comprise lateral saturated flow, driven by river-stage fluctuations, and vertical unsaturated
flow, driven by precipitation and evapotranspiration.
HaughFlow is applied to study sites in Australia and Germany with distinct climate conditions to
exhibit the model’s range of applicability. The lateral and vertical components of the model are calibrated
and evaluated in detail to determine the accuracy of model outputs. Evaluation methods (i.e. graphical
comparison, standard regression, Nash-Sutcliffe efficiency and percentage bias) are used to suggest best
practice for model calibration and the best outputs are then used to establish dominant trends in subsurface
hydrology at each site; including climatic changes and the long-term effects of drought periods.
Oxygen and hydrogen isotope tracers are also incorporated into the model, allowing the user to decouple
the intermixed contributions from lateral and vertical processes in the soil. Observed precipitation and river
isotope inputs can be used to predict actual isotope fractionation and mixing patterns in the soil. Using
artificial isotope inputs, however, can be used to clearly delineate the capillary fringe and water plumes
from individual rainfall events, within the soil. Hence, HaughFlow is a powerful numerical tool that can be
used to establish hydrologic trends and their drivers in the soil, to understand the role of soil moisture in
the hydrologic cycle. Ultimately these outputs can be used to investigate key questions in vegetative water
sourcing and how plants adapt to changes in water availability.
2018-05-30T00:00:00ZEvans, Cristina M.Soil moisture is a crucial but unseen component of the hydrologic cycle. It provides a hydrologic link
and storage between surface waters and groundwater. This unexposed water sanctuary could be the key to
sustain life during ever-prevalent climatic extremes. To quantify and understand the role of soil moisture in
catchment hydrology, the HaughFlow model has been developed as a new tool to simulate subsurface
hydrology and water flow in floodplain soils. The model is constructed to be flexible, adaptable and
logically composed in order to encourage interaction from the wider scientific community. Model transparency
and parsimony are key; with assumptions clearly explained and only the dominant processes simulated
to limit the number of inputs required and retain efficiency. The dominant processes for hydraulically
connected floodplains comprise lateral saturated flow, driven by river-stage fluctuations, and vertical unsaturated
flow, driven by precipitation and evapotranspiration.
HaughFlow is applied to study sites in Australia and Germany with distinct climate conditions to
exhibit the model’s range of applicability. The lateral and vertical components of the model are calibrated
and evaluated in detail to determine the accuracy of model outputs. Evaluation methods (i.e. graphical
comparison, standard regression, Nash-Sutcliffe efficiency and percentage bias) are used to suggest best
practice for model calibration and the best outputs are then used to establish dominant trends in subsurface
hydrology at each site; including climatic changes and the long-term effects of drought periods.
Oxygen and hydrogen isotope tracers are also incorporated into the model, allowing the user to decouple
the intermixed contributions from lateral and vertical processes in the soil. Observed precipitation and river
isotope inputs can be used to predict actual isotope fractionation and mixing patterns in the soil. Using
artificial isotope inputs, however, can be used to clearly delineate the capillary fringe and water plumes
from individual rainfall events, within the soil. Hence, HaughFlow is a powerful numerical tool that can be
used to establish hydrologic trends and their drivers in the soil, to understand the role of soil moisture in
the hydrologic cycle. Ultimately these outputs can be used to investigate key questions in vegetative water
sourcing and how plants adapt to changes in water availability.Nutrient cycling and oxygen availability in ancient oceans : extinction events and evolutionary opportunities
https://hdl.handle.net/10023/16334
2018-05-30T00:00:00ZMettam, ColinBehaviour of zircon and its isotopic systems during intracrustal differentiation
https://hdl.handle.net/10023/16331
2018-06-27T00:00:00ZFischer, SebastianMonitoring environmental change and ecosystem health using seabird guano chemistry
https://hdl.handle.net/10023/15602
One of the first studies to investigate the use of stable isotopes from seabird guano
and extracted uric acid for monitoring environmental changes in diet and trophic
relationships of seabirds and anthropogenic pollutant levels, this study supported the
hypothesis that guano and uric acid offer an alternative non-invasive sampling
technique.
The study found strong evidence of inter- and intra-specific differences in δ¹³ C and
δ¹⁵ N signatures across species and breeding locations, which were primarily
attributed to the feeding ecology of each species. Patterns of intra-and inter-specific
variation were also seen in kittiwakes from the east coast of Scotland where samples
were collected within and between years, with considerable isotopic overlap
observed in the results suggesting that individuals from these colonies were
consuming isotopically similar prey, taken largely from similar regions.
For most species the δ¹³ C and δ¹⁵ N signatures of uric acid were not significantly
different from that of guano (<1‰ for δ¹³ C and 1.2‰ for δ¹⁵ N) with a highly linear
relationship, suggesting that either tissue could be used when studying the short-
term (in the order of days) foraging behaviour of seabirds.
When considering the heavy metal burden of seabirds, the present study showed
that there are both similarities and differences in trace element concentrations both
within and between species that can largely be attributed to dietary variation,
although other factors including anthropogenic activities can potentially contribute to
this variability in specific locations. With knowledge of the sources and controls on
metal variability in diets and bodily accumulation such data derived from seabird
guano can provide a potentially useful bio-monitor of trace element concentrations in
the wider marine environment.
Stable isotope analysis of seabird guano and uric acid can be used to document
changes in diet and trophic relationships that may be associated with environmental
change. Using multiple species and sampling locations, such studies can provide an
alternative monitoring tool at a range of temporal and spatial scales.
2017-01-01T00:00:00ZTait, Elaine M.One of the first studies to investigate the use of stable isotopes from seabird guano
and extracted uric acid for monitoring environmental changes in diet and trophic
relationships of seabirds and anthropogenic pollutant levels, this study supported the
hypothesis that guano and uric acid offer an alternative non-invasive sampling
technique.
The study found strong evidence of inter- and intra-specific differences in δ¹³ C and
δ¹⁵ N signatures across species and breeding locations, which were primarily
attributed to the feeding ecology of each species. Patterns of intra-and inter-specific
variation were also seen in kittiwakes from the east coast of Scotland where samples
were collected within and between years, with considerable isotopic overlap
observed in the results suggesting that individuals from these colonies were
consuming isotopically similar prey, taken largely from similar regions.
For most species the δ¹³ C and δ¹⁵ N signatures of uric acid were not significantly
different from that of guano (<1‰ for δ¹³ C and 1.2‰ for δ¹⁵ N) with a highly linear
relationship, suggesting that either tissue could be used when studying the short-
term (in the order of days) foraging behaviour of seabirds.
When considering the heavy metal burden of seabirds, the present study showed
that there are both similarities and differences in trace element concentrations both
within and between species that can largely be attributed to dietary variation,
although other factors including anthropogenic activities can potentially contribute to
this variability in specific locations. With knowledge of the sources and controls on
metal variability in diets and bodily accumulation such data derived from seabird
guano can provide a potentially useful bio-monitor of trace element concentrations in
the wider marine environment.
Stable isotope analysis of seabird guano and uric acid can be used to document
changes in diet and trophic relationships that may be associated with environmental
change. Using multiple species and sampling locations, such studies can provide an
alternative monitoring tool at a range of temporal and spatial scales.Decrypting the crustal evolution of the Mozambique Belt in Malawi
https://hdl.handle.net/10023/12469
Global paleogeography exerts a first order control on both the deep and surficial components of the Earth system. Temporal and spatial constraints on the Mozambique Belt of Eastern Africa are needed to understand its crustal evolution and its role in assembly of Gondwana. This thesis provides detailed data on the timing, sources and nature of tectono-thermal events responsible for magmatism in the Mozambique Belt in southern Malawi.
An integrated approach of petrography, geochemistry, radiogenic isotopes, and single zircon geochronology has been used to determine spatial and temporal constraints and to better constrain models of the assembly of East and West Gondwana, which occurred along the Mozambique Belt. In particular the thesis attempts to address key unresolved questions about the number and timing of accretionary pulses within the orogen.
LA-ICP-MS single zircon U-Pb results show tectono-thermal events in four periods: Mesoproterozoic from 1128 ± 30 Ma to 1033 ± 20 Ma; Neoproterozoic (956 ± 12 Ma – 594 ± 65 Ma); Cambrian (530 ± 3 Ma – 515 ± 12 Ma); and Cretaceous (118 ± 2 Ma). Metamorphism is dated from a charnockitic gneiss that yielded a lower intercept age of 515 ± 18 Ma.
The granitoids are intermediate to acidic with relative enrichment in LILEs and depletion in HFSEs with moderately negative anomalies in Th, Nb, P, Zr and Ti. REE spider plots show enrichment in LREEs and depleted HREEs with negative Eu anomalies. The meta-granites are largely metaluminous with a few peraluminous, I-type granites belonging to the calc-alkaline series.
Radiogenic isotope data reveals slight differences with older, Mesoproterozoic rocks showing positive ɛNd and ɛHf values signifying derivation from depleted mantle material, whilst the younger rocks display negative epsilon values suggestive of crustal material recycling and mixing for their source and origins.
Granitoids of southern Malawi display characteristics consistent with derivation in a continental Andean type arc with some aspects of the chemistry resembling tonalite-trondhjemite-granite (TTG) suites mapped in the Mozambique Belt in Kenya, Tanzania, Mozambique, and Antarctica although the data are not sufficiently compelling to assign the Malawi rocks to classic TTGs.
2016-06-22T00:00:00ZManda, Blackwell ChawalaGlobal paleogeography exerts a first order control on both the deep and surficial components of the Earth system. Temporal and spatial constraints on the Mozambique Belt of Eastern Africa are needed to understand its crustal evolution and its role in assembly of Gondwana. This thesis provides detailed data on the timing, sources and nature of tectono-thermal events responsible for magmatism in the Mozambique Belt in southern Malawi.
An integrated approach of petrography, geochemistry, radiogenic isotopes, and single zircon geochronology has been used to determine spatial and temporal constraints and to better constrain models of the assembly of East and West Gondwana, which occurred along the Mozambique Belt. In particular the thesis attempts to address key unresolved questions about the number and timing of accretionary pulses within the orogen.
LA-ICP-MS single zircon U-Pb results show tectono-thermal events in four periods: Mesoproterozoic from 1128 ± 30 Ma to 1033 ± 20 Ma; Neoproterozoic (956 ± 12 Ma – 594 ± 65 Ma); Cambrian (530 ± 3 Ma – 515 ± 12 Ma); and Cretaceous (118 ± 2 Ma). Metamorphism is dated from a charnockitic gneiss that yielded a lower intercept age of 515 ± 18 Ma.
The granitoids are intermediate to acidic with relative enrichment in LILEs and depletion in HFSEs with moderately negative anomalies in Th, Nb, P, Zr and Ti. REE spider plots show enrichment in LREEs and depleted HREEs with negative Eu anomalies. The meta-granites are largely metaluminous with a few peraluminous, I-type granites belonging to the calc-alkaline series.
Radiogenic isotope data reveals slight differences with older, Mesoproterozoic rocks showing positive ɛNd and ɛHf values signifying derivation from depleted mantle material, whilst the younger rocks display negative epsilon values suggestive of crustal material recycling and mixing for their source and origins.
Granitoids of southern Malawi display characteristics consistent with derivation in a continental Andean type arc with some aspects of the chemistry resembling tonalite-trondhjemite-granite (TTG) suites mapped in the Mozambique Belt in Kenya, Tanzania, Mozambique, and Antarctica although the data are not sufficiently compelling to assign the Malawi rocks to classic TTGs.Generation and preservation of continental crust in collisional orogenic systems
https://hdl.handle.net/10023/11966
The continental crust is the archive of Earth history. Much of what we know about the development of Earth is learned from the continental crust, and it is within the crust that many natural resources are found. Hence, understanding its formation and evolution is a key aspect to a deeper knowledge of the Earth system.
This thesis is a study of the processes that have formed and shaped the distribution of continental crust, with specific focus on crustal development associated with the Rodinian supercontinent and the Grenville Orogeny spanning ca. 1200 to 900 Ma.
Specifically it addresses an aspect of the incompleteness of the record of continental crust formation. The preserved continental crust is punctuated with periods of lesser and greater frequency of geologic features, e.g., the temporal distribution of the ages of mineral deposits, juvenile granitoids, eclogites, granulites, and the U-Pb crystallization ages of zircons now preserved in modern and ancient sediments (see Gastil, 1960; Barley and Groves, 1992; Condie, 1998; Campbell and Allen, 2008; Brown, 2007; Bradley, 2011). In addition, interpretive features in the geologic record also have an apparent episodic distribution such as passive margins (Bradley, 2011) and supercontinents (Condie, 1998). The episodic nature of these geologic phenomena implies either an episodic formation or preferential preservation of continental crust. These two end member models have been explained through a number of geologic processes such as eruption of superplumes, global disruption of thermal structure of the mantle, assembly of supercontinents, collisional orogenesis. Through the chapters outlined below, this thesis explores the connection of these episodic geologic events with key isotopic signals, principally U-Pb, Hf, and O isotopes in zircon supplemented by sedimentology, structural geology, and igneous geochemistry. It comprises a series of chapters developed around manuscripts prepared for publication.
2013-10-01T00:00:00ZSpencer, Christopher J.The continental crust is the archive of Earth history. Much of what we know about the development of Earth is learned from the continental crust, and it is within the crust that many natural resources are found. Hence, understanding its formation and evolution is a key aspect to a deeper knowledge of the Earth system.
This thesis is a study of the processes that have formed and shaped the distribution of continental crust, with specific focus on crustal development associated with the Rodinian supercontinent and the Grenville Orogeny spanning ca. 1200 to 900 Ma.
Specifically it addresses an aspect of the incompleteness of the record of continental crust formation. The preserved continental crust is punctuated with periods of lesser and greater frequency of geologic features, e.g., the temporal distribution of the ages of mineral deposits, juvenile granitoids, eclogites, granulites, and the U-Pb crystallization ages of zircons now preserved in modern and ancient sediments (see Gastil, 1960; Barley and Groves, 1992; Condie, 1998; Campbell and Allen, 2008; Brown, 2007; Bradley, 2011). In addition, interpretive features in the geologic record also have an apparent episodic distribution such as passive margins (Bradley, 2011) and supercontinents (Condie, 1998). The episodic nature of these geologic phenomena implies either an episodic formation or preferential preservation of continental crust. These two end member models have been explained through a number of geologic processes such as eruption of superplumes, global disruption of thermal structure of the mantle, assembly of supercontinents, collisional orogenesis. Through the chapters outlined below, this thesis explores the connection of these episodic geologic events with key isotopic signals, principally U-Pb, Hf, and O isotopes in zircon supplemented by sedimentology, structural geology, and igneous geochemistry. It comprises a series of chapters developed around manuscripts prepared for publication.Dendroclimatic reconstruction of late Holocene summer temperatures in the Scottish Highlands
https://hdl.handle.net/10023/8418
This thesis focuses on reconstructing past temperatures using Scots pine (Pinus
sylvestris L.) tree-ring chronologies developed from Scotland. The research aims to fill
a spatial and temporal gap in understanding northwest European climate dynamics, thus
providing the context for assessing future climate changes in this region. Development
of both a spatially complete reconstruction from an extensive network of 44 'living'
Scottish tree-ring chronologies for the last few centuries, but also a near-millennium
length chronology from central Scotland using mainly lake-derived 'subfossil' wood
material was undertaken. Before reconstruction development, a combination of treegrowth
modelling and disturbance removal methodologies was utilised in order to
understand the drivers of pine growth in the Scottish Highlands, and to assess and
remove anthropogenic disturbance and other non-climatic influences on growth. The
advantages and limitations of utilising the relatively new 'Blue Intensity' (BI) parameter
was also explored and assessed, particularly in relation to its possible utilization as a
more affordable surrogate for maximum latewood density in the development of
temperature reconstructions and for crossdating validation of undated samples.
Although BI showed much promise for dendroclimatology, elimination of low
frequency biases resulting from sample discolouration still requires further attention.
Chronologies from the Cairngorms in central Scotland were identified as most suitable
for reconstruction development, while reconstructions based on chronologies from other
areas in the west were found to be weaker due to a range of factors including
disturbance. In order to maximise reconstruction strength, BI and ring width (RW) data
were combined to produce composite high-frequency BI / low-frequency RW
chronologies. Although it was possible to develop an ~800 year reconstruction of
temperature from central Scotland, there is substantial potential to further extend this
reconstruction back in time.
2016-06-22T00:00:00ZRydval, MilošThis thesis focuses on reconstructing past temperatures using Scots pine (Pinus
sylvestris L.) tree-ring chronologies developed from Scotland. The research aims to fill
a spatial and temporal gap in understanding northwest European climate dynamics, thus
providing the context for assessing future climate changes in this region. Development
of both a spatially complete reconstruction from an extensive network of 44 'living'
Scottish tree-ring chronologies for the last few centuries, but also a near-millennium
length chronology from central Scotland using mainly lake-derived 'subfossil' wood
material was undertaken. Before reconstruction development, a combination of treegrowth
modelling and disturbance removal methodologies was utilised in order to
understand the drivers of pine growth in the Scottish Highlands, and to assess and
remove anthropogenic disturbance and other non-climatic influences on growth. The
advantages and limitations of utilising the relatively new 'Blue Intensity' (BI) parameter
was also explored and assessed, particularly in relation to its possible utilization as a
more affordable surrogate for maximum latewood density in the development of
temperature reconstructions and for crossdating validation of undated samples.
Although BI showed much promise for dendroclimatology, elimination of low
frequency biases resulting from sample discolouration still requires further attention.
Chronologies from the Cairngorms in central Scotland were identified as most suitable
for reconstruction development, while reconstructions based on chronologies from other
areas in the west were found to be weaker due to a range of factors including
disturbance. In order to maximise reconstruction strength, BI and ring width (RW) data
were combined to produce composite high-frequency BI / low-frequency RW
chronologies. Although it was possible to develop an ~800 year reconstruction of
temperature from central Scotland, there is substantial potential to further extend this
reconstruction back in time.Trends in alluvial channel geometry and streamflow : an investigation of patterns and controls
https://hdl.handle.net/10023/6913
Alluvial river channels are self-formed by the sediment-laden flow that is supplied to them from upstream and the interactions between this flow and the materials forming the channel bed and banks. Thus, any changes in the volumes of solid and liquid discharge or the resistance of the boundary materials can produce adjustments in the form of river channels over time. These shifts may increase or decrease the capacity of a channel to contain flood flows. However, despite a wealth of studies on the average geometry of river channels across different scales and climatic regimes, there has not yet been a systematic assessment of the rates and controls of trends in channel form. Using a combination of USGS data, including manual field measurements and mean daily streamflow data at hundreds of stream gages, this work is the first attempt to quantify how trends in channel geometry develop over decadal timescales and how they contribute to shifts in flood hazard, in comparison with trends in streamflow. Findings reveal that two-thirds of all channel cross-sections studied exhibit significant trends in channel geometry. The majority of the investigated US river channels are eroding, with widening and deepening trends partially offset by decreases in average flow velocity. Rates of change are principally controlled by the channel size. Although large channels develop larger trends, changes are proportionally greater in small channels in percentage terms. A secondary major control is hydrology: rates of change in channel geometry are heightened by the variability and flashiness of flow regimes. Finally, results show that changing flood frequencies can only be accurately quantified when both hydrologic and geomorphic trends are accounted for, and that flood hazard is significantly increasing across the studied sites. These documented trends in channel geometry, hydraulics, and flood hazard have important implications for the management of alluvial channels, navigation, and riverside infrastructure.
2015-06-01T00:00:00ZSlater, Louise J.Alluvial river channels are self-formed by the sediment-laden flow that is supplied to them from upstream and the interactions between this flow and the materials forming the channel bed and banks. Thus, any changes in the volumes of solid and liquid discharge or the resistance of the boundary materials can produce adjustments in the form of river channels over time. These shifts may increase or decrease the capacity of a channel to contain flood flows. However, despite a wealth of studies on the average geometry of river channels across different scales and climatic regimes, there has not yet been a systematic assessment of the rates and controls of trends in channel form. Using a combination of USGS data, including manual field measurements and mean daily streamflow data at hundreds of stream gages, this work is the first attempt to quantify how trends in channel geometry develop over decadal timescales and how they contribute to shifts in flood hazard, in comparison with trends in streamflow. Findings reveal that two-thirds of all channel cross-sections studied exhibit significant trends in channel geometry. The majority of the investigated US river channels are eroding, with widening and deepening trends partially offset by decreases in average flow velocity. Rates of change are principally controlled by the channel size. Although large channels develop larger trends, changes are proportionally greater in small channels in percentage terms. A secondary major control is hydrology: rates of change in channel geometry are heightened by the variability and flashiness of flow regimes. Finally, results show that changing flood frequencies can only be accurately quantified when both hydrologic and geomorphic trends are accounted for, and that flood hazard is significantly increasing across the studied sites. These documented trends in channel geometry, hydraulics, and flood hazard have important implications for the management of alluvial channels, navigation, and riverside infrastructure.Magma chamber dynamics in the peralkaline magmas of the Kakortokite Series, South Greenland
https://hdl.handle.net/10023/6900
Understanding crystallisation in magma chambers is a key challenge for igneous petrology. It is particularly important to understand the origins of layering in peralkaline rocks, e.g. the kakortokite (nepheline syenite), Ilímaussaq Complex, S. Greenland, as these are commonly associated with high value multi-element economic deposits. The kakortokite is a spectacular example of macrorhythmic (>5 m) layering. Each unit consists of three layers comprising arfvedsonite-rich (sodic-amphibole) black kakortokite at the base, grading into eudialyte-rich (sodic-zirconosilicate) red kakortokite, then alkali feldspar- and nepheline-rich white kakortokite. Each unit is numbered -19 to +17 relative to a characteristic well-developed horizon (Unit 0), however there is little consensus on their development.
This project applies a multidisciplinary approach through field observations combined with petrography, crystal size distributions (CSDs), mineral and whole rock chemistries on Units 0, -8 to -11 and a phonolite/micro-nephelinolite (“hybrid”) sequence that crosscuts the layered kakortokite.
Textures and compositions are laterally consistent across outcrop and indicators of current activity are rare. CSDs indicate in situ crystallisation with gravitational settling as a minor process. Chemical discontinuities occur across unit boundaries.
The layering developed through large-scale processes under exceptionally quiescent conditions. The discontinuities reflect open-system behaviour; units were formed by an influx of volatile-rich magma that initiated crystallisation in a bottom layer. Nucleation was initially suppressed by high volatile element concentrations, which decreased to allow for crystallisation of arfvedsonite, followed by eudialyte, then alkali feldspar and nepheline to form each tripartite unit. The chemistry of the hybrid indicates mixing between a primitive (sub-alkaline) magma and kakortokite. Thus injections of magmas of varying compositions occurred, indicating a complex plumbing system below current exposure. The lessons learned at Ilímaussaq, which is extremely well exposed and preserved, are relevant to understanding magma chamber dynamics in the more common instances of pervasively altered peralkaline rocks.
2015-03-30T00:00:00ZHunt, Emma J.Understanding crystallisation in magma chambers is a key challenge for igneous petrology. It is particularly important to understand the origins of layering in peralkaline rocks, e.g. the kakortokite (nepheline syenite), Ilímaussaq Complex, S. Greenland, as these are commonly associated with high value multi-element economic deposits. The kakortokite is a spectacular example of macrorhythmic (>5 m) layering. Each unit consists of three layers comprising arfvedsonite-rich (sodic-amphibole) black kakortokite at the base, grading into eudialyte-rich (sodic-zirconosilicate) red kakortokite, then alkali feldspar- and nepheline-rich white kakortokite. Each unit is numbered -19 to +17 relative to a characteristic well-developed horizon (Unit 0), however there is little consensus on their development.
This project applies a multidisciplinary approach through field observations combined with petrography, crystal size distributions (CSDs), mineral and whole rock chemistries on Units 0, -8 to -11 and a phonolite/micro-nephelinolite (“hybrid”) sequence that crosscuts the layered kakortokite.
Textures and compositions are laterally consistent across outcrop and indicators of current activity are rare. CSDs indicate in situ crystallisation with gravitational settling as a minor process. Chemical discontinuities occur across unit boundaries.
The layering developed through large-scale processes under exceptionally quiescent conditions. The discontinuities reflect open-system behaviour; units were formed by an influx of volatile-rich magma that initiated crystallisation in a bottom layer. Nucleation was initially suppressed by high volatile element concentrations, which decreased to allow for crystallisation of arfvedsonite, followed by eudialyte, then alkali feldspar and nepheline to form each tripartite unit. The chemistry of the hybrid indicates mixing between a primitive (sub-alkaline) magma and kakortokite. Thus injections of magmas of varying compositions occurred, indicating a complex plumbing system below current exposure. The lessons learned at Ilímaussaq, which is extremely well exposed and preserved, are relevant to understanding magma chamber dynamics in the more common instances of pervasively altered peralkaline rocks.The detrital mineral record of Cenozoic sedimentary rocks in the Central Burma Basin : implications for the evolution of the eastern Himalayan orogen and timing of large scale river capture
https://hdl.handle.net/10023/6730
This study contributes to the understanding of major river evolution in Southeast Asia during the Cenozoic. In order to trace the evolution of a hypothesized palaeo-Yarlung Tsangpo-Irrawaddy River, this work undertakes the first systematic provenance study of detrital minerals from Cenozoic synorogenic fluvial and deltaic sedimentary rocks of the Central Burma Basin, employing a combination of high precision geochronology, thermochronology, and geochemistry analytical techniques on single grain detrital zircon and white mica. The dataset is compared to published isotopic data from potential source terranes in order to determine source provenance and exhumation history from source to sink.
A Yarlung Tsangpo-Irrawaddy connection existed as far back as ca. 42 Ma and disconnection occurred at 18–20 Ma, based on provenance changes detected using a combination of U-Pb ages and εHf(t) values on detrital zircons, and ⁴ºAr/³⁹Ar dating on detrital micas. During the Eocene and Oligocene, units are dominated by U-Pb age and high positive εHf(t) values, characteristic of a southern Lhasa Gangdese magmatic arc source. An antecedent Yarlung Tsangpo-Irrawaddy River system formed the major river draining the eastern Himalaya at this time. A significant change in provenance is seen in the early Miocene, where detritus is predominantly derived from bedrock of the eastern Himalayan syntaxis, western Yunnan and Burma, a region drained by the modern Irrawaddy-Chindwin river system characterized by Cenozoic U-Pb ages and negative εHf(t) values. This is attributed to the disconnection of the Yarlung-Irrawaddy River and capture by the proto-Brahmaputra River, re-routing Tibetan Transhimalayan detritus to the eastern Himalayan foreland basin. Re-set zircon fission track ages of 14-8 Ma present in all units is used to infer post-depositional basin evolution related to changes in the stress regime accommodating the continued northward migration of India. The early Miocene initiation of the Jiali-Parlung-Gaoligong-Sagaing dextral shear zone and the continued northward movement of the coupled India-Burma plate aided in focusing deformation inside the syntaxis contributing to the disconnection of the Yarlung Tsangpo-Irrawaddy system, linking surface deformation and denudation with processes occurring at deeper crustal levels.
2015-06-23T00:00:00ZBrezina, Cynthia A.This study contributes to the understanding of major river evolution in Southeast Asia during the Cenozoic. In order to trace the evolution of a hypothesized palaeo-Yarlung Tsangpo-Irrawaddy River, this work undertakes the first systematic provenance study of detrital minerals from Cenozoic synorogenic fluvial and deltaic sedimentary rocks of the Central Burma Basin, employing a combination of high precision geochronology, thermochronology, and geochemistry analytical techniques on single grain detrital zircon and white mica. The dataset is compared to published isotopic data from potential source terranes in order to determine source provenance and exhumation history from source to sink.
A Yarlung Tsangpo-Irrawaddy connection existed as far back as ca. 42 Ma and disconnection occurred at 18–20 Ma, based on provenance changes detected using a combination of U-Pb ages and εHf(t) values on detrital zircons, and ⁴ºAr/³⁹Ar dating on detrital micas. During the Eocene and Oligocene, units are dominated by U-Pb age and high positive εHf(t) values, characteristic of a southern Lhasa Gangdese magmatic arc source. An antecedent Yarlung Tsangpo-Irrawaddy River system formed the major river draining the eastern Himalaya at this time. A significant change in provenance is seen in the early Miocene, where detritus is predominantly derived from bedrock of the eastern Himalayan syntaxis, western Yunnan and Burma, a region drained by the modern Irrawaddy-Chindwin river system characterized by Cenozoic U-Pb ages and negative εHf(t) values. This is attributed to the disconnection of the Yarlung-Irrawaddy River and capture by the proto-Brahmaputra River, re-routing Tibetan Transhimalayan detritus to the eastern Himalayan foreland basin. Re-set zircon fission track ages of 14-8 Ma present in all units is used to infer post-depositional basin evolution related to changes in the stress regime accommodating the continued northward migration of India. The early Miocene initiation of the Jiali-Parlung-Gaoligong-Sagaing dextral shear zone and the continued northward movement of the coupled India-Burma plate aided in focusing deformation inside the syntaxis contributing to the disconnection of the Yarlung Tsangpo-Irrawaddy system, linking surface deformation and denudation with processes occurring at deeper crustal levels.Validating a calcium tracer based tree-ring dating method for tropical wood
https://hdl.handle.net/10023/6389
The tropics are a key part of the global biosphere. Specifically, the woodland environments not only moderate large scale climate dynamics, but are also crucial in the global carbon cycle. Despite this, tropical dendrochronological studies are rare due to the uncertainty in annual dating from the minimal seasonality in most tropic environments. Without distinct annual tree rings, dendrochronological dating methods do not work, therefore other dating methods are required before long term forest growth analyses can be made. Alternatives such as radiocarbon and stable isotope measurements can be expensive and require high resolution measurement in order to identify seasonality. This thesis introduces a novel dating method for tropical trees using calcium as a tracer of annual wood formation. Laser Ablation-ICP-MS provides a fast, high resolution method for measuring mineral elements which could potentially provide a solution to the dating of tropical trees.
Initially, Scots pine provided an excellent testing species for the development of both the methodological and analytical dating methods proposed through this thesis. It’s well defined, annually dated ring structure formed the basis of seasonal signal detection and the development of an objective analysis for dating. This was achieved by the continuous measurement of calcium, and utilising a threshold detection approach to define annual growth cycles with respect to extreme peaks in the tracer data-series.
The initial success of the calcium dating method using pine allowed for testing the technique on a tropical trees species from Cameroon which lacks distinct rings. Along with radiocarbon dating, the robustness of the calcium dating method for this tropical species was assessed. Promising results were initially found however, these could not be replicated and validation of this method proved problematic.
Finally, radiocarbon dates were used to assess the nature of the oxygen and carbon stable isotopic series from the single tree of the same species from the tropical calcium tests. Results showed that despite the clear cyclic signal present in the oxygen isotope record, this did not represent an annual signal. These results reinforce the problems associated with tropical dendro analysis.
2014-04-04T00:00:00ZWood, Cheryl VictoriaThe tropics are a key part of the global biosphere. Specifically, the woodland environments not only moderate large scale climate dynamics, but are also crucial in the global carbon cycle. Despite this, tropical dendrochronological studies are rare due to the uncertainty in annual dating from the minimal seasonality in most tropic environments. Without distinct annual tree rings, dendrochronological dating methods do not work, therefore other dating methods are required before long term forest growth analyses can be made. Alternatives such as radiocarbon and stable isotope measurements can be expensive and require high resolution measurement in order to identify seasonality. This thesis introduces a novel dating method for tropical trees using calcium as a tracer of annual wood formation. Laser Ablation-ICP-MS provides a fast, high resolution method for measuring mineral elements which could potentially provide a solution to the dating of tropical trees.
Initially, Scots pine provided an excellent testing species for the development of both the methodological and analytical dating methods proposed through this thesis. It’s well defined, annually dated ring structure formed the basis of seasonal signal detection and the development of an objective analysis for dating. This was achieved by the continuous measurement of calcium, and utilising a threshold detection approach to define annual growth cycles with respect to extreme peaks in the tracer data-series.
The initial success of the calcium dating method using pine allowed for testing the technique on a tropical trees species from Cameroon which lacks distinct rings. Along with radiocarbon dating, the robustness of the calcium dating method for this tropical species was assessed. Promising results were initially found however, these could not be replicated and validation of this method proved problematic.
Finally, radiocarbon dates were used to assess the nature of the oxygen and carbon stable isotopic series from the single tree of the same species from the tropical calcium tests. Results showed that despite the clear cyclic signal present in the oxygen isotope record, this did not represent an annual signal. These results reinforce the problems associated with tropical dendro analysis.Speciation of metals and metalloids in tobacco and tobacco smoke : implications for health and regulation
https://hdl.handle.net/10023/5728
Some metals and metalloids make significant contributions to the harmful effects of tobacco
consumption although understanding the mechanisms involved in toxicity is hampered by the
lack of information on their chemical and valence species, both in tobacco and in smoke.
This research addresses the speciation of the metals and metalloids most frequently
implicated, particularly those elements that exist in nature in multiple valence states, namely
arsenic (As) and chromium (Cr), there being considerable differences in toxicity with
oxidation state.
A strategy was devised to overcome some of the problems that have thwarted earlier
attempts at speciation. Firstly tobacco plants were cultivated under controlled conditions in
compost burdened with high levels of metals and metalloids resulting in leaf with up to 250 µg g⁻¹
As, although Cr uptake was less successful. Secondly valence speciation even at the
exceptionally low concentrations of As and Cr in smoke from unburdened tobacco was
achieved with XANES analysis using the exceptionally bright Diamond synchrotron source.
This revealed that combustion of tobacco has a marked effect on valence speciation with
As(III), the reduced form of As, dominating (and persisting) in condensate of tobacco smoke
while ash is dominated by the oxidised form, As(V). Chromium also appears to be present in
smoke mainly as reduced Cr(III) species. HPLC-ICPMS analysis of arsenic indicates the
dominance of inorganic over organic species (~4:1). Other metals were investigated in less
detail.
These findings establish that arsenic is present in smoke in its most toxic form and
represents a significant risk to health. Conversely smokers appear to be exposed to the less
harmful species of chromium. These results support a recent WHO report that includes As
but not Cr in a list of four metals and metalloids recommended for regulation in crops and
commercial products in the interests of public health.
Electronic version excludes material for which permission has not been granted by the rights holder
2014-01-01T00:00:00ZCampbell, Robert Charles JamesSome metals and metalloids make significant contributions to the harmful effects of tobacco
consumption although understanding the mechanisms involved in toxicity is hampered by the
lack of information on their chemical and valence species, both in tobacco and in smoke.
This research addresses the speciation of the metals and metalloids most frequently
implicated, particularly those elements that exist in nature in multiple valence states, namely
arsenic (As) and chromium (Cr), there being considerable differences in toxicity with
oxidation state.
A strategy was devised to overcome some of the problems that have thwarted earlier
attempts at speciation. Firstly tobacco plants were cultivated under controlled conditions in
compost burdened with high levels of metals and metalloids resulting in leaf with up to 250 µg g⁻¹
As, although Cr uptake was less successful. Secondly valence speciation even at the
exceptionally low concentrations of As and Cr in smoke from unburdened tobacco was
achieved with XANES analysis using the exceptionally bright Diamond synchrotron source.
This revealed that combustion of tobacco has a marked effect on valence speciation with
As(III), the reduced form of As, dominating (and persisting) in condensate of tobacco smoke
while ash is dominated by the oxidised form, As(V). Chromium also appears to be present in
smoke mainly as reduced Cr(III) species. HPLC-ICPMS analysis of arsenic indicates the
dominance of inorganic over organic species (~4:1). Other metals were investigated in less
detail.
These findings establish that arsenic is present in smoke in its most toxic form and
represents a significant risk to health. Conversely smokers appear to be exposed to the less
harmful species of chromium. These results support a recent WHO report that includes As
but not Cr in a list of four metals and metalloids recommended for regulation in crops and
commercial products in the interests of public health.The impacts of climate change on estuarine ecosystems : a case study on the Eden estuary, Fife, Scotland
https://hdl.handle.net/10023/3625
The Eden Estuary is a small, coastal inlet situated in Fife between the Tay and Forth
Estuaries on the east coast of Scotland. A multidisciplinary case study of the estuary was conducted over a three year period observing the dynamic responses of biotic and abiotic behaviour to long term patterns of climate variability. Historical Trend Analysis (HTA) was combined with autocorrelation and spectral density analysis to identify trends, patterns
and periodicity in natural cycles. River flow and wind direction data were cross-correlated with the North Atlantic Oscillation Index (NAOI) to link local responses to patterns of northern hemisphere circulation, and with Wolfe Sunspot Numbers representing variable solar activity as a potential driving mechanism for climate driven change. Assessment of the current state of ‘estuary health’ used a proxy analysis of ecosystem function, combining Bray-Curtis similarity nMDS of macrofaunal community diversity with species functional traits. The observed estuary responses were subsequently projected onto the forecasted climate change scenarios reported by the IPCCAR4, UKCIP09 and to modelled
projections of solar activity to propose future trajectories of change for the estuary. Autocorrelation analysis of river flow and wind direction data identified significant (95%) correlations corresponding to solar, lunar, planetary and volcanic events. Spectral density analysis similarly identified significant (>95%) frequencies corresponding to known periods of solar activity, lunar cycles and Bruckner climatic cycles. Formal cross -correlation
revealed significant (95%) relationships between both river flow and wind data with the NAOI, and using a longer times series, between river Thames annual flow and Wolfe
sunspot numbers; correlating solar maximums with high flow. Periods consistent to
Schwabe and Hale solar cycles were evident in the wind and river data however the NAOI
only displayed Hale periodicity, inferring the river and wind data are not solely influenced (or potentially driven) by the NAO. No detrimental impact of estuary change was observed in the biotic responses inferring maintenance of estuary health.
This study identifies potential driving mechanisms of estuary perturbation and whilst
causal mechanisms can only be proposed, these observations form a baseline for future
targeted modelling, monitoring and management.
2013-01-01T00:00:00ZChocholek, MelanieThe Eden Estuary is a small, coastal inlet situated in Fife between the Tay and Forth
Estuaries on the east coast of Scotland. A multidisciplinary case study of the estuary was conducted over a three year period observing the dynamic responses of biotic and abiotic behaviour to long term patterns of climate variability. Historical Trend Analysis (HTA) was combined with autocorrelation and spectral density analysis to identify trends, patterns
and periodicity in natural cycles. River flow and wind direction data were cross-correlated with the North Atlantic Oscillation Index (NAOI) to link local responses to patterns of northern hemisphere circulation, and with Wolfe Sunspot Numbers representing variable solar activity as a potential driving mechanism for climate driven change. Assessment of the current state of ‘estuary health’ used a proxy analysis of ecosystem function, combining Bray-Curtis similarity nMDS of macrofaunal community diversity with species functional traits. The observed estuary responses were subsequently projected onto the forecasted climate change scenarios reported by the IPCCAR4, UKCIP09 and to modelled
projections of solar activity to propose future trajectories of change for the estuary. Autocorrelation analysis of river flow and wind direction data identified significant (95%) correlations corresponding to solar, lunar, planetary and volcanic events. Spectral density analysis similarly identified significant (>95%) frequencies corresponding to known periods of solar activity, lunar cycles and Bruckner climatic cycles. Formal cross -correlation
revealed significant (95%) relationships between both river flow and wind data with the NAOI, and using a longer times series, between river Thames annual flow and Wolfe
sunspot numbers; correlating solar maximums with high flow. Periods consistent to
Schwabe and Hale solar cycles were evident in the wind and river data however the NAOI
only displayed Hale periodicity, inferring the river and wind data are not solely influenced (or potentially driven) by the NAO. No detrimental impact of estuary change was observed in the biotic responses inferring maintenance of estuary health.
This study identifies potential driving mechanisms of estuary perturbation and whilst
causal mechanisms can only be proposed, these observations form a baseline for future
targeted modelling, monitoring and management.Fundamental and sedimentological controls on luminescence behaviour in quartz and feldspar
https://hdl.handle.net/10023/2586
The optically stimulated luminescence (OSL) characteristics of a suite of quartz and feldspar samples from a range of modern glaciofluvial sediments have been explored to determine the use of OSL as a depositional pathway tracer. Paraglacial and subglacial source material and various glaciofluvial deposits have been analysed from the glacial catchments of Bergsetbreen, Fåbergstølsbreen, and Nigardsbreen as well as the Fåbergstølsgrandane sandur, Jostedalen, Norway.
The OSL distribution signatures have been characterised through exploration of sample skewness, kurtosis and overdispersion, and dose distributions of the different depositional settings and source materials are distinct for both quartz and feldspar. Residual ages are greatest for feldspar, indicating significant potential age overestimation where feldspar is used to date glaciofluvial deposits. Sample dose distributions and overdispersion characteristics are driven by source sediment properties, whereas residual ages are controlled by transport and depositional processes. Those transport and depositional processes which result in significant light exposure, also influence dose distributions, and processes that sort sediments least effectively have the highest residual doses.
Sample OSL characteristics, transport distance and grain size distributions have been investigated using factor analysis, as a means of predicting sediment source, facies, depositional process and deposit type. Although the depositional processes of the quartz samples can be clearly differentiated based upon OSL characteristics, factor analyses of feldspar and grain size characteristics are inconclusive.
The application of quartz OSL to the Norwegian samples was limited by its very poor luminescence sensitivity. Quartz is the preferred mineral for OSL, however, despite the plethora of successful quartz OSL applications, the precise origin of the UV/blue luminescence emission, measured during OSL, remains unclear. The origins of this emission and controls on its intensity were explored using a variety of spectroscopic techniques including photoluminescence, cathodoluminescence, radioluminescence (RL), ionoluminescence (IL) and x-ray excited optical luminescence (XEOL).
Exciting sample luminescence at a range of energies enables exploration of the different donor centres responsible for the luminescence emission. Cathodoluminescence and RL emission spectra are similar, comprising broad emissions at 1.5, 2.0 and 2.7 eV (detection in the UV part of the spectrum was not possible for these experiments). Ionoluminescence emission spectra were dominated by the ~ 3.3 eV emission, which is a component of the signal conventionally monitored during OSL. This emission depleted as a function of dose, to the benefit of the red emission (1.8-2.0 eV) for all samples throughout IL, and similar observations were made for the 3.4 eV emission observed from the XEOL emission spectra. The XEOL spectra are dominated by an emission at ~ 3.8 eV, not widely reported for quartz, which has tentatively been attributed to peroxy linkages. Differences between the IL and XEOL emission spectra are interpreted as evidence for the presence of multiple excited states.
Electronic version excludes material for which permission has not been granted by the rights holder
2012-06-20T00:00:00ZKing, GeorginaThe optically stimulated luminescence (OSL) characteristics of a suite of quartz and feldspar samples from a range of modern glaciofluvial sediments have been explored to determine the use of OSL as a depositional pathway tracer. Paraglacial and subglacial source material and various glaciofluvial deposits have been analysed from the glacial catchments of Bergsetbreen, Fåbergstølsbreen, and Nigardsbreen as well as the Fåbergstølsgrandane sandur, Jostedalen, Norway.
The OSL distribution signatures have been characterised through exploration of sample skewness, kurtosis and overdispersion, and dose distributions of the different depositional settings and source materials are distinct for both quartz and feldspar. Residual ages are greatest for feldspar, indicating significant potential age overestimation where feldspar is used to date glaciofluvial deposits. Sample dose distributions and overdispersion characteristics are driven by source sediment properties, whereas residual ages are controlled by transport and depositional processes. Those transport and depositional processes which result in significant light exposure, also influence dose distributions, and processes that sort sediments least effectively have the highest residual doses.
Sample OSL characteristics, transport distance and grain size distributions have been investigated using factor analysis, as a means of predicting sediment source, facies, depositional process and deposit type. Although the depositional processes of the quartz samples can be clearly differentiated based upon OSL characteristics, factor analyses of feldspar and grain size characteristics are inconclusive.
The application of quartz OSL to the Norwegian samples was limited by its very poor luminescence sensitivity. Quartz is the preferred mineral for OSL, however, despite the plethora of successful quartz OSL applications, the precise origin of the UV/blue luminescence emission, measured during OSL, remains unclear. The origins of this emission and controls on its intensity were explored using a variety of spectroscopic techniques including photoluminescence, cathodoluminescence, radioluminescence (RL), ionoluminescence (IL) and x-ray excited optical luminescence (XEOL).
Exciting sample luminescence at a range of energies enables exploration of the different donor centres responsible for the luminescence emission. Cathodoluminescence and RL emission spectra are similar, comprising broad emissions at 1.5, 2.0 and 2.7 eV (detection in the UV part of the spectrum was not possible for these experiments). Ionoluminescence emission spectra were dominated by the ~ 3.3 eV emission, which is a component of the signal conventionally monitored during OSL. This emission depleted as a function of dose, to the benefit of the red emission (1.8-2.0 eV) for all samples throughout IL, and similar observations were made for the 3.4 eV emission observed from the XEOL emission spectra. The XEOL spectra are dominated by an emission at ~ 3.8 eV, not widely reported for quartz, which has tentatively been attributed to peroxy linkages. Differences between the IL and XEOL emission spectra are interpreted as evidence for the presence of multiple excited states.