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Establishing chronologies of archaeological sites by using a single dating method may not always reliably constrain the age of a deposit or a fossil, as potential biases may naturally arise, particularly in complex sedimentary settings such as caves. In this study, we performed a multi-technique dating approach that targets different materials in two caves from the Cueva Mayor-Cueva del Silo karst system, Sierra de Atapuerca, Spain. Two new fossil teeth from lithostratigraphic unit LU4 (GE-I pit) at Galería de las Estatuas have been dated by combined U-series/ESR and Amino Acid Racemisation (AAR) methods. The former provides ages of 117 ± 13 and 87 ± 9 ka that agree with previous dating studies of this Neandertal site, confirming the assignment of level LU4 to Marine Isotope Stage (MIS) 5. In contrast, AAR analyses produce very scattered ages, pointing to significant post-burial chemical modifications in dentine. A first set of ages is presented for the Cata Litario pit at Sala de los Cíclopes, a palaeontological site formed exclusively of cave bear fossils belonging to the Middle Pleistocene species Ursus deningeri. We provide U-series/ESR and AAR ages for two bear teeth from lithostratigraphic unit LU5, and extended-range luminescence ages for the sediment deposits that host, and immediately underlie and overlie, the bear accumulation. Depositional ages of the sediment were obtained using single-grain thermally-transferred optically stimulated luminescence (TT-OSL) dating of individual quartz grains and post-infrared-infrared stimulated luminescence (pIR-IR) dating of K-feldspars. Several speleothems, both in situ and reworked fragments embedded in the different lithostratigraphic units, have additionally been dated by U-series to constrain the timing of the sequence formation. The results indicate that the sediment originally entered the cave between MIS-12 and MIS-10 (444 ± 28 ka to 367 ± 32 ka). Nevertheless, the AAR and U-series/ESR fossil ages, as well as som, MCIN/AEI/10.13039/501100011033/’ERDF, MCIN/AEI/10.13039/501100011033/FEDER, MCIN/AEI/10.13039/501100011033, Australian Research Council, Junta de Castilla y León, Fundación Atapuerca, Depto. de Geodinámica, Estratigrafía y Paleontología, Fac. de Ciencias Geológicas, TRUE, pub

El método de U/Th permite datar materiales diversos de hasta 600.000 años de antigüedad. En este trabajo se revisan sus fundamentos y las técnicas analíticas disponibles, centrándose en su aplicación más habitual, que es la datación de carbonatos. En concreto, se discuten su potencial y limitaciones en la datación de espeleotemas, travertinos, calcretas, cementos, corales y moluscos aprovechando los ejemplos publicados en España. El cálculo de edades mediante U/Th se basa en la serie de desintegración del 238U e involucra medidas de 238U, 234U y 230Th. Su fundamento radica en el fraccionamiento entre los radionucleidos del uranio y del torio en los sistemas naturales. En el caso de la precipitación de carbonato puro, éste incorpora uranio en el momento de su formación, pero está libre de torio inicial de tal forma que, pasado un tiempo, todo el 230Th medido en la muestra deriva de la desintegración del 234U y esta relación permite calcular la edad de formación del mineral. Teóricamente, por tanto, el carbonato a datar: (1) debe incorporar cierta cantidad de uranio en el momento de su formación, (2) no debe incorporar cantidad significativa de torio y (3) debe comportarse como un sistema cerrado. De estas premisas, la segunda y la tercera no siempre se cumplen por lo que el método se ha adaptado a estos casos añadiendo cálculos y correcciones adicionales. Dada la variedad de carbonatos susceptibles de ser datados, este método es de amplia aplicación en paleoclimatología, paleontología, arqueología, estratigrafía, geomorfología, tectónica y oceanografía, entre otras disciplinas., The U/Th method allows age-dating of various materials up to 600,000 years old. In this work, its fundamentals and the available analytical techniques are reviewed with the focus on its most common application, which is the dating of carbonates. Its potential and limitations in dating speleothems, travertines, tuffs,calcretes, corals and molluscs are discussed reviewing for this purpose some published examples from Spain. The U/Th age calculation is based on the 238U decay series and involves measurements of 238U, 234U, and 230Th. Its foundation lies on the fractionation among uranium and thorium radionuclides in natural systems. In the case of precipitation of pure carbonates, an amount of uranium is incorporated at the time of formation while the mineral remains free of initial thorium in such a way that, after a period of time, all the 230Th measured in the sample derives from the disintegration of 234U and this relationship allows calculating the age of formation of the mineral. Therefore, ideally, the carbonate to be dated: (1) must incorporate a certain amount of uranium at the time of its formation, (2) must not incorporate a significant amount of thorium, and (3) must behave as a closed system. Of these premises, the second and third are not always fulfilled and the method has been adapted to those cases by adding further calculations and corrections. Given the variety of carbonates that can be dated, this method is widely applied in paleoclimatology, paleontology, archaeology, stratigraphy, geomorphology, tectonics and oceanography, among other disciplines., Universidad Complutense de Madrid, Depto. de Geodinámica, Estratigrafía y Paleontología, Fac. de Ciencias Geológicas, TRUE, pub

Silicic magmatic systems are fundamental to the production and evolution of continental crust, the recycling of volatile elements from mantle to atmosphere, and the production of economic deposits. Additionally, silicic systems are responsible for producing some the most catastrophic volcanic eruptions on Earth. The processes and timescales governing the production, evolution, and ultimately eruption of silicic magmatic systems remain poorly constrained but are critical to accurate volcanic hazard assessment. Active debate continues regarding many aspects of silicic magmatic systems, such as: 1) the architecture of the sub-volcanic system (i.e., physical distribution of diverse magmatic components throughout the crust that contribute to erupted magma bodies); 2) the longevity of storage of different magmatic components (i.e. melts, crystals, volatiles) prior to eruption; 3) the timescales over which the erupted magma body (or bodies) assemble prior to eruption; and 4) the predominant thermal (and by proxy physical) state in which silicic magma bodies are stored within the crust. In this dissertation I combine a variety of geochemical tools to explore the thermal the chemical evolution of silicic magmatic systems of different size and eruption magnitude to address this outstanding uncertainty. In detail this dissertation focuses on the two most recent eruptive episodes (1980-86 and 2004-05) from Mount St. Helens (MSH), USA, and six eruptions spanning the last 30 kyrs of activity at the Taupo Volcanic Center (TVC) in New Zealand. In Chapter 1 I use new 238U-230Th-226Ra disequilibria data, in-situ plagioclase trace-element data, and Sr-in-plagioclase diffusion timescales from Mount St. Helens 1980 cryptodome and 2004-2005 dacite domes to evaluate the thermal storage conditions and compositional diversity of recent MSH magmas. Plagioclase trace-element data and U-series characteristics reveal a compositionally heterogenous magmatic system beneath MSH and require multi-s

Silicic magmatic systems are fundamental to the production and evolution of continental crust, the recycling of volatile elements from mantle to atmosphere, and the production of economic deposits. Additionally, silicic systems are responsible for producing some the most catastrophic volcanic eruptions on Earth. The processes and timescales governing the production, evolution, and ultimately eruption of silicic magmatic systems remain poorly constrained but are critical to accurate volcanic hazard assessment. Active debate continues regarding many aspects of silicic magmatic systems, such as: 1) the architecture of the sub-volcanic system (i.e., physical distribution of diverse magmatic components throughout the crust that contribute to erupted magma bodies); 2) the longevity of storage of different magmatic components (i.e. melts, crystals, volatiles) prior to eruption; 3) the timescales over which the erupted magma body (or bodies) assemble prior to eruption; and 4) the predominant thermal (and by proxy physical) state in which silicic magma bodies are stored within the crust. In this dissertation I combine a variety of geochemical tools to explore the thermal the chemical evolution of silicic magmatic systems of different size and eruption magnitude to address this outstanding uncertainty. In detail this dissertation focuses on the two most recent eruptive episodes (1980-86 and 2004-05) from Mount St. Helens (MSH), USA, and six eruptions spanning the last 30 kyrs of activity at the Taupo Volcanic Center (TVC) in New Zealand. In Chapter 1 I use new 238U-230Th-226Ra disequilibria data, in-situ plagioclase trace-element data, and Sr-in-plagioclase diffusion timescales from Mount St. Helens 1980 cryptodome and 2004-2005 dacite domes to evaluate the thermal storage conditions and compositional diversity of recent MSH magmas. Plagioclase trace-element data and U-series characteristics reveal a compositionally heterogenous magmatic system beneath MSH and require multi-s

The application of uranium-thorium dating methods to authigenic carbonates provides unique constraints on the temporal evolution of methane seeps at ocean margins. In this study, we report U-Th isotope measurements for carbonate breccias collected from within a hydrate-bearing pockmark located at the Niger Delta margin. These concretions were extracted from a carbonate-rich layer in the upper two meters of a sediment core (N2-KS-44; ~ 1200 m water depth), well above the present-day sulphate-methane transition zone (about 3 m depth) and the presence of gas hydrates in the sediment. The stratigraphy of core N2-KS-44 was established by tuning its downcore Al/Ti profile to a well-dated nearby reference core, and carbonate 230Th/U ages were calculated using isochron methods. Our results indicate that a major event of aragonite precipitation occurred between about 13 and 2.5 ka at the studied location. Comparison of sediment accumulation rates at both core N2-KS-44 and the nearby reference site suggests that the initial stage of carbonate precipitation, between 13 and 10 ka, was associated with sediment winnowing, probably related to intense fluid seepage. In contrast, our data indicate that sedimentation rates rapidly increased within the pockmark after 7 ka. In agreement with the presence of carbonate breccias exhibiting U-Th ages older than their corresponding stratigraphic age, this observation would suggest that sediment reworking took place after that time, possibly caused by erosion of the surrounding sediment within the pockmark. We hypothesize that the period of carbonate formation between 13 and 2.5 ka was related to an upward migration of gas-hydrate reservoirs to the near seafloor environment. After this pulse of enhanced fluid flow, the diminution of methane fluxes at the base of the local gas-hydrate occurrence zone would have led to hydrate dissolution in sub-surface sediments and pockmark formation, thereby explaining the progressive increase in sedimentat

The application of uranium-thorium dating methods to authigenic carbonates provides unique constraints on the temporal evolution of methane seeps at ocean margins. In this study, we report U-Th isotope measurements for carbonate breccias collected from within a hydrate-bearing pockmark located at the Niger Delta margin. These concretions were extracted from a carbonate-rich layer in the upper two meters of a sediment core (N2-KS-44; ~ 1200 m water depth), well above the present-day sulphate-methane transition zone (about 3 m depth) and the presence of gas hydrates in the sediment. The stratigraphy of core N2-KS-44 was established by tuning its downcore Al/Ti profile to a well-dated nearby reference core, and carbonate 230Th/U ages were calculated using isochron methods. Our results indicate that a major event of aragonite precipitation occurred between about 13 and 2.5 ka at the studied location. Comparison of sediment accumulation rates at both core N2-KS-44 and the nearby reference site suggests that the initial stage of carbonate precipitation, between 13 and 10 ka, was associated with sediment winnowing, probably related to intense fluid seepage. In contrast, our data indicate that sedimentation rates rapidly increased within the pockmark after 7 ka. In agreement with the presence of carbonate breccias exhibiting U-Th ages older than their corresponding stratigraphic age, this observation would suggest that sediment reworking took place after that time, possibly caused by erosion of the surrounding sediment within the pockmark. We hypothesize that the period of carbonate formation between 13 and 2.5 ka was related to an upward migration of gas-hydrate reservoirs to the near seafloor environment. After this pulse of enhanced fluid flow, the diminution of methane fluxes at the base of the local gas-hydrate occurrence zone would have led to hydrate dissolution in sub-surface sediments and pockmark formation, thereby explaining the progressive increase in sedimentat

The application of uranium-thorium dating methods to authigenic carbonates provides unique constraints on the temporal evolution of methane seeps at ocean margins. In this study, we report U-Th isotope measurements for carbonate breccias collected from within a hydrate-bearing pockmark located at the Niger Delta margin. These concretions were extracted from a carbonate-rich layer in the upper two meters of a sediment core (N2-KS-44; ~ 1200 m water depth), well above the present-day sulphate-methane transition zone (about 3 m depth) and the presence of gas hydrates in the sediment. The stratigraphy of core N2-KS-44 was established by tuning its downcore Al/Ti profile to a well-dated nearby reference core, and carbonate 230Th/U ages were calculated using isochron methods. Our results indicate that a major event of aragonite precipitation occurred between about 13 and 2.5 ka at the studied location. Comparison of sediment accumulation rates at both core N2-KS-44 and the nearby reference site suggests that the initial stage of carbonate precipitation, between 13 and 10 ka, was associated with sediment winnowing, probably related to intense fluid seepage. In contrast, our data indicate that sedimentation rates rapidly increased within the pockmark after 7 ka. In agreement with the presence of carbonate breccias exhibiting U-Th ages older than their corresponding stratigraphic age, this observation would suggest that sediment reworking took place after that time, possibly caused by erosion of the surrounding sediment within the pockmark. We hypothesize that the period of carbonate formation between 13 and 2.5 ka was related to an upward migration of gas-hydrate reservoirs to the near seafloor environment. After this pulse of enhanced fluid flow, the diminution of methane fluxes at the base of the local gas-hydrate occurrence zone would have led to hydrate dissolution in sub-surface sediments and pockmark formation, thereby explaining the progressive increase in sedimentat

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 2547–2574, doi:10.1002/ggge.20134., The ridge crest at 9°N–10°N East Pacific Rise (EPR) is dominated by overlapping lava flows that have overflowed the axial summit trough and flowed off-axis, forming a shingle-patterned terrain up to ∼2–4 km on either side of the axial summit trough. In this study, we employ 230Th-226Ra dating methods, in conjunction with geochemistry and seafloor geological observations, in an effort to discern the stratigraphic relationships between adjacent flows. We measured major and trace elements and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, and 238U-230Th-226Ra for lava glass samples collected from several flow units up to ∼2 km away from the axial summit trough on the ridge crest at 9°50′N EPR. Statistical analysis of the 238U-230Th-226Ra data indicates that all but one measured sample from these flows cannot be resolved from the zero-age population; thus, we cannot confidently assign model ages to samples for discerning stratigraphic relationships among flows. However, because groups of samples can be distinguished based on similarities in geochemical compositions, particularly incompatible element abundances with high precision-normalized variability such as U and Th, and because the range of compositions is much greater than that represented by samples from the 1991–1992 and 2005–2006 eruptions, we suggest that the dive samples represent 6–10 eruptive units despite indistinguishable model ages. Geochemical variability between individual flows with similar ages requires relatively rapid changes in parental melt composition over the past ∼2 ka, and this likely reflects variations in the relative mixing proportions of depleted and enriched melts derived from a heterogeneous mantle source., This study was funded by NSF OCE-0623838 to K.W.W. Sims and S.A. Soule and NSF OCE-0527053 to K.W.W. Sims. J. Blichert-Toft acknowledges financial support from the French Agence Nationale de la Recherche (grant M&Ms – Mantle Melting – Measurements, Models, Mechanisms)., 2014-02-01

The ridge crest at 9°N–10°N East Pacific Rise (EPR) is dominated by overlapping lava flows that have overflowed the axial summit trough and flowed off-axis, forming a shingle-patterned terrain up to ∼2–4 km on either side of the axial summit trough. In this study, we employ 230Th-226Ra dating methods, in conjunction with geochemistry and seafloor geological observations, in an effort to discern the stratigraphic relationships between adjacent flows. We measured major and trace elements and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, and 238U-230Th-226Ra for lava glass samples collected from several flow units up to ∼2 km away from the axial summit trough on the ridge crest at 9°50′N EPR. Statistical analysis of the 238U-230Th-226Ra data indicates that all but one measured sample from these flows cannot be resolved from the zero-age population; thus, we cannot confidently assign model ages to samples for discerning stratigraphic relationships among flows. However, because groups of samples can be distinguished based on similarities in geochemical compositions, particularly incompatible element abundances with high precision-normalized variability such as U and Th, and because the range of compositions is much greater than that represented by samples from the 1991–1992 and 2005–2006 eruptions, we suggest that the dive samples represent 6–10 eruptive units despite indistinguishable model ages. Geochemical variability between individual flows with similar ages requires relatively rapid changes in parental melt composition over the past ∼2 ka, and this likely reflects variations in the relative mixing proportions of depleted and enriched melts derived from a heterogeneous mantle source.

The paucity of palaeoclimatic data existing for the Southern Hemisphere and the regional bias of new data from the Northern Hemisphere has meant conclusions regarding the global response to the numerous climatic events of the last 20 kyr is both widely disputed and poorly understood. Despite being one of the Southern Hemisphere’s largest landmasses, Australia in particular displays a limited pool of palaeoclimatic information and the production of a new, robust record providing an insight into the response and timing of key climatic events is paramount to generating a more comprehensive characterisation and improved understanding of palaeoclimate in this region. Speleothems (cave deposits) are valuable archives of palaeoclimate variation, characterised by their extensive growth intervals and large geographic extent. They contain a multitude of ‘proxy’ records both directly and indirectly linked to climatic fluctuations and are typically robust, displaying high preservation potential with no post-depositional alteration. Key to their success is their amenability to radiometric dating, allowing the establishment of robust and reliable chronologies to which their multi-proxy records can be anchored. Consequently speleothems provide a clear opportunity to explore and expand palaeoclimatic knowledge at sites across the globe. This thesis describes and explains the use of state of the art technology to exploit relatively recent advances in U-series dating to construct reliable and detailed records of south east Australia’s response to palaeoclimatic fluctuations over the last 50 kyr using samples collected from cave sites from across the states of Victoria and New South Wales. 28 speleothem samples have been analysed in terms of both their coincident growth intervals and stable isotope variation to provide records with palaeoclimatic implications at a range of time scales. The production of a chronological template of speleothem growth intervals has enabled the assessment

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Silicate weathering acts as a global sink for the greenhouse gas carbon dioxide. In order to understand long‐term climate change and the fluctuations in atmospheric carbon dioxide, it is paramount to investigate the regulators of chemical weathering. The controls of rainfall and uplift have been reported to either enhance or inhibit the extent of chemical weathering, and therefore their relationship is still being highly debated in literature. Investigation of this relationship in the Southern Alps of New Zealand has been modest in comparison to the Himalayas. These studies have either focused on solute geochemistry of rivers, and therefore do not integrate weathering history of the catchment, or have failed to investigate the interplay between the controls of uplift and precipitation. Fluvial sediments record conditions of chemical weathering at the catchment scale, whilst integrating its weathering history. Therefore, this study has been undertaken to improve the understanding of the response of chemical weathering to uplift and precipitation in the Southern Alps, utilising the geochemistry and mineralogy of fluvial sediments. Mineralogical analysis was performed through X‐ray diffraction and optical microscopy, while geochemical techniques included X‐ray fluorescence, uranium‐series isotopes and strontium isotopic analysis. Geochemical results suggest that modern chemical weathering is low to moderate and is predominantly occurring within the weathering profile. In contrast, weathering during transport in the fluvial system appears to be dominated by physical abrasion, which contributes to downstream fining. Furthermore, 238U was shown to be leached with increased residence time in the fluvial system and its depletion enhanced by rainfall. Similarly, rainfall amplified Mg loss, while Na was leached regardless. High uplift rates, on the western coast, increase erosion and therefore reduce sediment residence time in the weathering profile. The extent of chemical we

Determining the timing and source of gas transfer during intermittent intracaldera volcanism can aid in our understanding of degassing in these large systems. Using (210Pb/226Ra) ratios, (parentheses denote activity ratios) as a time-sensitive tracer, injections of 222Rn and the subsequent time scales of gas accumulation and loss can be determined. Variations in (210Pb/226Ra) have been measured for 15 volcanic products erupted at Rabaul Caldera over the period 1994 to 2001. In addition, one basaltic enclave from the 1937 eruption was also analyzed. Water and carbon dioxide contents determined from olivine hosted melt inclusions erupted in 1997 are < 1% and suggest extensive shallow-level degassing. Both 210Pb excesses and deficits are found in andesites and dacites, whereas the basaltic enclave displays an (210Pb/226Ra)0 ratio of 7. Between 1994 and 1997 three samples with (210Pb/226Ra) deficits were erupted which indicate open system gas loss since 1992 and 1994. No correlation exists between (210Pb/226Ra) and lava chemistry, eruptive style or date. 210Pb excesses are more common than deficits in Rabaul samples but cannot be explained by plagioclase feldspar accumulation, Pb sublimate accumulation or differentiation. Instead, a model of intra-magma 222Rn transfer can produce 210Pb excesses of the appropriate magnitude if gas transfer occurs over 1-5 years from an underlying body of magma that is 2-10 times larger than the volume of erupted material and that is consistent with geophysical estimates. Although intermittent gas transfer events can be inferred by the development of 210Pb excess, there is no evidence at Rabaul for a direct link between eruptive style, gas flux and (210Pb/226Ra).

Field observations and U-series ages reveal that Shark Bay, Western Australia (WA) has been inundated by the sea on at least three occasions during the Late Pleistocene/Holocene, resulting in a succession of marine deposits around the Bay. The exact age of these deposits has until now been problematic due to a lack of reliable and accurate age data. This study reports 16 new U-series coral dates from emergent reef deposits around Shark Bay, and point to an extended period of coral reef development during the peak of the last interglacial, marine isotope stage (MIS) 5e. This is attributed to enhancement of marine circulation within the reaches and basins, a result of higher sea levels and an absence of major sill and bank structures. Stromatolites are absent from the geological record within Shark Bay until the late Holocene, suggesting that sea levels and marine sedimentary processes that have operated during the present sea-level highstand are unique to this period. There is little direct evidence of fossil reef development occurring during interglacials of the middle/late Pleistocene (MIS 9/11).

A detailed geomorphologic and morphostratigraphic investigation of raised marine terraces at Cape Cuvier, Western Australia, reveals two morphologically distinct units. A lower, well-developed accretional reef terrace between 3 and 5.5 m above MLWS (mean low-water springs; hereafter denoted as “+”) represents an extended interval of stable sea level. An upper erosional terrace and incipient coralgal rim between + 8.5 to 10.5 m represents a brief sea-level stillstand at this higher elevation. These features suggest the lower and upper terraces developed during discrete sea-level events. In an attempt to better define the timing of emplacement of each marine unit, 20 coral samples collected along vertical and lateral reef growth axis from both terraces were analysed with U-series dating. Unfortunately, all coral samples exhibited elevated d234Uinitial values, suggesting that pervasive uptake of 234U-enriched uranium and 230Th thorium had occurred. Despite the shortcomings of absolute dating, a succession of events can be resolved though morphostratigraphic relationships. Comparison of the facies relationships, coral growth, and morphostratigraphic features between the lower and upper terraces indicates that an early to mid MIS 5e stillstand at + 3 to 5 m was followed by a late rise to + 8.5 to 10.5 m. This agrees with an emerging global view of MIS 5e sea-level history derived from stable carbonate platforms, rejecting the hypothesis that these higher sea-level benchmarks are an artefact of localized tectonic processes.