Matthew Power - Profile on Academia.edu (original) (raw)
Papers by Matthew Power
Two distinct episodes of serpentinisation have been identified within the peridotites of the Liza... more Two distinct episodes of serpentinisation have been identified within the peridotites of the Lizard complex. The first episode (primary serpentinisation) is represented by the complex and pervasive hydration of the Lizard peridotite. The second (later) episode is characterised by a pale to dark green, pseudo-fibrous mixture of lizardite and chrysotile that is restricted to fractures (vein serpentine). Mineralised northnorth-west and east-north-east trending fault zones contain fragments of vein serpentine generated during this second episode. Faults with similar orientations and mineralogy within the gabbro unit contain adularia which have been previously dated by Ar 40 -Ar 39 and K-Ar methods at 210-220 Ma (Triassic). Stable isotope ratios indicate that the mineralisation within the gabbro and peridotite is genetically similar. The primary and secondary serpentinisation episodes are therefore interpreted as pre-Triassic in age. A latest Carboniferous to early Permian age is proposed for the formation of vein serpentine and a late Devonian to Carboniferous age is proposed for the primary serpentinisation episode. This is envisaged to have taken place post-obduction but a pre-obduction initiation of serpentinisation cannot be discounted.
Recycling
Black mass is the industry term applied to end-of-life (EoL) lithium-ion batteries that have been... more Black mass is the industry term applied to end-of-life (EoL) lithium-ion batteries that have been mechanically processed for potential use as a recycled material to recover the valuable metals present, including cobalt, lithium, manganese, nickel and copper. A significant challenge to the effective processing of black mass is the complexity of the feed material. Two samples of black mass from a European source were analysed using a combination of methods including automated SEM-EDS (AMICS) to characterise and quantify the phases present and particle chemistry. Micro X-CT imaging, overlain onto automated mineralogy images, enabled the 3D morphology of the particles to be determined. Micro-XRF was used to map the copper, nickel, manganese and cobalt-bearing phases. Since Li cannot be detected using SEM-EDS, its abundance was semi-quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The integration of these complimentary analytical methods allowed f...
Geological Controls on Reservoir Properties of the Montney Formation in Northeastern BC: An integration of sequence stratigraphy, organic geochemistry, quantitative mineralogy and petrophysical analysis
The Montney-Doig petroleum system is the largest known unconventional play in Canada and the host... more The Montney-Doig petroleum system is the largest known unconventional play in Canada and the host of huge volumes of hydrocarbons in Western Alberta and Northeastern British Columbia. Thanks to horizontal drilling and multistage hydraulic fracturing, the resource production started ramping up in 2006 and has been growing exponentially since then. During the last decade, economic optimization of the development has been largely driven by stimulation design experimentations, increasing the lateral length, the number of fracturing stages and fluid volumes, while focusing on liquid-rich areas of the system. Although all these factors are, and will stay key elements of success, a better understanding of the geological controls on productivity will assume more importance in future development. In Northeastern BC, the Montney formation is typically 200 to 400 m-thick and predicting how reservoir and fluid properties vary throughout this interval will give an edge to companies for landing h...
Previous models for the tectonic-stratigraphy of the Lizard complex ophiolite have proposed three... more Previous models for the tectonic-stratigraphy of the Lizard complex ophiolite have proposed three thrust-bounded units. However, our studies indicate that post-obduction extensional faulting may have exerted a hitherto unrecognised effect on the present distribution of lithologies. Field and previously published geophysical evidence suggest that the uppermost tectonic unit (the Crousa Downs Unit) represents the downfaulted upper levels of the Goonhilly Downs Unit. Deformed lithologies previously thought to be part of the Goonhilly Downs Unit are reassigned to the underlying Basal Unit. A revised model for the tectonic-stratigraphy is presented. The Basal Nappe is underlain by the Basal Thrust and comprises the Traboe schists, the Landewednack schists and the Old Lizard Head Series. The Goonhilly Downs Nappe, underlain by the Goonhilly Downs Thrust, structurally overlies the Basal Nappe and comprises serpentinised peridotite, Trelan and Crousa Gabbro and the Porthoustock Sheeted Dyke Complex. This work highlights the importance of late-to post-Variscan extensional deformation in south Cornwall.
PLOS ONE, 2021
Little is known of the properties of the sarsen stones (or silcretes) that comprise the main arch... more Little is known of the properties of the sarsen stones (or silcretes) that comprise the main architecture of Stonehenge. The only studies of rock struck from the monument date from the 19th century, while 20th century investigations have focussed on excavated debris without demonstrating a link to specific megaliths. Here, we present the first comprehensive analysis of sarsen samples taken directly from a Stonehenge megalith (Stone 58, in the centrally placed trilithon horseshoe). We apply state-of-the-art petrographic, mineralogical and geochemical techniques to two cores drilled from the stone during conservation work in 1958. Petrographic analyses demonstrate that Stone 58 is a highly indurated, grain-supported, structureless and texturally mature groundwater silcrete, comprising fine-to-medium grained quartz sand cemented by optically-continuous syntaxial quartz overgrowths. In addition to detrital quartz, trace quantities of silica-rich rock fragments, Fe-oxides/hydroxides and ...
Marine and Petroleum Geology, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Journal of Archaeological Science: Reports, 2021
Stonehenge is dominated by the large, locally derived sarsen stones which comprise the Outer Sars... more Stonehenge is dominated by the large, locally derived sarsen stones which comprise the Outer Sarsen Circle and the Inner Sarsen Trilithon Circle. Lithologically they are a hard form of sandstone called silcrete. Less obvious are the smaller 'bluestones' which form the Outer Bluestone Circle and Inner Bluestone Horseshoe. The bluestone assemblage is composed of a variety of lithologies, including dolerite (almost all carrying small, cm scale, white to pink 'spots'), rhyolites, volcanic tuffs and two different types of sandstone. The majority of the bluestones have been provenanced to the Mynydd Preseli area in west Wales some 200 km west of Stonehenge, and the distinctive spots in the dolerites were crucial evidence in making that link. However, despite the importance of the spots in that provenancing model, which provides evidence for one of the most remarkable feats of Neolithic time in northwest Europe, they have been little studied and are not fully characterized. One reason for this is the fact that they are difficult to study using standard optical microscopy because of the fine grain size of the component minerals. In order to gain a greater understanding of the mineralogy and origin of the spots we have used a range of alternative optical and analytical techniques, including high resolution photomicrography, 'standard' electron microscopy (SEM-EDS), automated scanning electron microscopy with linked energy dispersive analysis (automated SEM-EDS) and X-ray diffraction. These investigations, based primarily on samples from Carn Goedog and Carn Meini in the Mynydd Preseli, lead us to conclude that the spots result from a two-stage alteration history involving firstly saussuritization of primary igneous calcium-rich plagioclase phenocrysts/glomerocrysts. The saussuritization was probably a late-stage magmatic event, possibly occurring at ca. 400°C, and led to the development of the secondary minerals clinozoisite, zoisite, albite and muscovite. Subsequently, the dolerites were affected by regional low-grade metamorphism at ca. 250-300°C, at the transition from the prehnite-pumpellyite to the greenschist facies. During this metamorphism the background (non-spot) areas of the samples were altered with the development of the secondary minerals chlorite, actinolite, epidote, quartz, titanite and further albite. Interpretation of these data shows that the Carn Goedog sample has a higher percentage of secondary minerals compared to the Carn Meini sample, suggesting that the former shows a higher degree of alteration. Further analyses of dolerite samples from the Mynydd Preseli should provide insight into the potential of the extent of rock alteration in the further refinement of understanding the source or sources of the Stonehenge bluestone dolerites.
Journal of Archaeological Science, 2020
The Altar Stone at Stonehenge is a greenish sandstone thought to be of Late Silurian-Devonian ('O... more The Altar Stone at Stonehenge is a greenish sandstone thought to be of Late Silurian-Devonian ('Old Red Sandstone') age. It is classed as one of the bluestone lithologies which are considered to be exotic to the Salisbury Plain environ, contrasting with the larger sarsen stones, which are a hard, durable silcrete derived from no more than 30km from Stonehenge. It is well established that most of the bluestones are derived from the Mynydd Preseli, in west Wales. However, no Old Red Sandstone rocks crop out in the Preseli; instead a source in the Lower Old Red Sandstone Cosheston Subgroup at Mill Bay, on the shores of Milford Haven, to the south of the Preseli, has been proposed. More recently, on the basis of detailed petrography, a source for the Altar Stone much further to the east, towards the Wales-England border, has been suggested. Quantitative analyses presented here compare data from proposed 2 Stonehenge Altar Stone debris with samples from the Cosheston Subgroup at Mill Bay in west Wales, as well as with a second sandstone type found at Stonehenge which, on palaeontological evidence has been shown to be Lower Palaeozoic in age. The Altar Stone samples have up to 16.7 modal % calcite while the Lower Palaeozoic and Cosheston Subgroup sandstones have less than 0.25 modal %. The Altar Stone also contains up to 3.8 modal % kaolinite and 0.8 modal % barite, minerals that are absent from the other sandstones. Calcite, kaolinite and barite in the Altar Stone samples all occur between the detrital grains and are all thought to be authigenic minerals, which differs markedly with the Cosheston Subgroup and Lower Palaeozoic sandstones. The Cosheston Subgroup sandstone contrasts with the other two sandstone lithologies in having up to 0.7 modal % detrital garnet (<0.08 in both the other two sandstone types). Further differences between the Altar Stone sandstone and the Cosheston Subgroup sandstone are seen when their contained zircons are examined. Not only do they have differing morphologies (size, shape and quality) but U-Pb age dates for the zircons show contrasting populations; the Cosheston Subgroup sample zircon age population is essentially bimodal, with age maxima at 500 and 1500 Ma whilst the Altar Stone zircon population is more diverse, with ages spanning from 472 to 2475 Ma without maxima. Together, all these data confirm that Mill Bay is not the source of the Altar Stone with the abundance of kaolinite in the Altar Stone sample suggesting a source further east than Milford Haven, towards the Wales-England border. The disassociation of the Altar Stone and Milford Haven fully undermines the hypothesis that the bluestones, including the Altar Stone, were transported from west Wales by sea up the Bristol Channel and adds further credence to a totally land-based route, possibly along a natural routeway leading from west Wales to the Severn estuary and beyond. This route, along the valleys followed today by the A40, may well have been significant in prehistory, raising the possibility that the Altar Stone was added en route to the assemblage of Preseli bluestones taken to Stonehenge around or shortly before 3000 BC. Recent strontium isotope analysis of human and animal bones from Stonehenge, dating to the beginning of its first construction stage around 3000 BC, are consistent with having lived in this western region of Britain.
Petroleum Geoscience, 2019
This study focuses on the Lower–Middle Triassic Montney, Sunset Prairie, Doig and Halfway formati... more This study focuses on the Lower–Middle Triassic Montney, Sunset Prairie, Doig and Halfway formations from the foreland basin of the Canadian Cordillera (Alberta and British Columbia). Based on core and outcrop descriptions, the correlation of 400 wells, and on mineralogical analyses, this study interprets the basin-scale, 3D-stratigraphic architecture of these formations and discusses the controls on its evolution.Well correlation highlights four sequences (1–4) interpreted to occur in two second-order cycles (A and B). In this work, the Early Triassic Montney Formation and the early Middle Triassic Sunset Prairie Formation are interpreted to consist of three third-order sequences (1–3) related to the first second-order cycle (cycle A). The Middle Triassic Doig and Halfway formations are interpreted to consist of a fourth sequence (4) related to a second second-order cycle (cycle B). Integration of the stratigraphic surfaces with previously published biostratigraphic analyses emphas...
Distribution of Sedimentary Heterogeneities in Shale Plays: Insight From Sequence Stratigraphy, Multi-Proxies Analysis and Stratigraphic Modeling of the Montney and Doig Formations (Trias, Alberta-British Columbia, Canada)
International Conference and Exhibition, Melbourne, Australia 13-16 September 2015, 2015
A New Solution for the Characterization of Unconventional Shale Resources Based on Analysis of Drill Cuttings
Abu Dhabi International Petroleum Exhibition and Conference, 2015
We introduce a new, cost-effective solution for the characterization of unconventional shale reso... more We introduce a new, cost-effective solution for the characterization of unconventional shale resources based on innovative analysis of drill cuttings. This solution was tested successfully on the Toarcian shales of the Couy-1 well, located in the southern Paris Basin, France. Ten samples of cuttings-sized rock fragments from different depths were subjected to several analytical methods to determine geochemical parameters (LECO and Rock Eval), the mineralogy and texture (QEMSCAN), and the mechanical properties (nanoindentation). Based on the results, the Toarcian shales were subdivided into two mineralogically distinct lithostratigraphic intervals. The Upper Toarcian shales consist of siltstone with a matrix of illitic clays, whereas the Lower Toarcian shales consist mainly of calcareous mudstone with a matrix of finely intermixed calcite and clays. The Young's modulus varies between 12.5 and 25.6 GPa and decreases with increasing TOC content. An interval with high TOC content (&...
First results on sequence stratigraphy, sedimentary architecture, mineralogy and organic content in the Montney and Doig Formations (Alberta / British columbia) The Montney and Doig Formations
In the last decade, rapid increase in the world's hydrocarbon demand has brought the focus on... more In the last decade, rapid increase in the world's hydrocarbon demand has brought the focus on shale resources. Since the 50's, the Lower-Middle Triassic Montney and Doig Formations are well known in the Western Canada for their conventional hydrocarbons resources. In the last five years they became the focus of numerous studies carrying out a spectacular potential for unconventional resources (NEB, 2013). Within these new plays, the knowledge of TOC and mineralogical heterogeneities distribution in sedimentary basins is one of the key elements that will improve hydrocarbons discovery and production. Numerous QEMSCAN analysis, Rock-Eval analysis, palynofacies studies and thin sections analysis had been done on core samples along a 2D section. This study intends to establish links between sequence stratigraphy, sedimentary architecture, mineralogy and organic content the organic rich Montney and Doig Formations.
shown that the PGE-enriched magmatism is a ubiquitous and long-lived feature of the North Atlanti... more shown that the PGE-enriched magmatism is a ubiquitous and long-lived feature of the North Atlantic Igneous Province (NAIP). The British Palaeogene Igneous Province (well-exposed along the north western seaboard of the British Isles) forms the south western expression of the NAIP and is characterised by voluminous flood basalts, extensive dyke swarms and several central intrusive complexes (Figure 1a). Chromitite-hosted PGE References
Journal of Geophysical Research: Atmospheres, 2009
Direct‐sampling and remote‐sensing measurements were made at the crater rim of Masaya volcano (Ni... more Direct‐sampling and remote‐sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d < 10 μm) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d ∼ 1.15 μm. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emi...
Journal of Geophysical Research: Atmospheres, 2008
Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes wer... more Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm < d < 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d < 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearly pure silica; this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent. Measurements of the size, shape and composition of fine silicate particles may potentially offer insights into preemission, synemission, and postemission processes. ...
Geological Society, London, Special Publications, 2013
In the investigation of serious crimes, soil can be, in some cases, a very valuable class of trac... more In the investigation of serious crimes, soil can be, in some cases, a very valuable class of trace evidence. The complexity of soil is part of the reason why it is useful as trace evidence but is also an inherent problem, as there are many different parameters in a soil sample that could potentially be characterized. The inorganic components of soils are dominated by minerals, along with anthropogenic particulate grains; thus, the analysis of soil mineralogy as the main technique for inorganic forensic soil characterization is recommended. Typical methods that allow the bulk mineralogy to be determined, such as X-ray diffraction (XRD), do not allow the texture of the particles to be characterized. However, automated scanning electron microscopy (SEM) provides both modal mineralogy and also allows particle textures to be characterized. A recent advance in this technique has been the ability to report the modal mineralogy of a sample as ‘lithotypes’, which are defined on the basis of ...
Sedimentology, 2003
Estuarine sediments commonly form major sinks for contaminants released during industrial activit... more Estuarine sediments commonly form major sinks for contaminants released during industrial activity. Many industrial processes lead to the release of metals initially in solution, which can then be adsorbed on to, for example, Fe hydroxides or clay minerals. However, in the mining industry, there are two major contaminant waste streams: (1) metals discharged in solution via mine drainage; and (2) particulate grains of the ore‐forming or related minerals released after ore processing. The release of particulate waste can have a major long‐term impact on environmental geochemistry. In this study, we have mapped the distribution of arsenic, copper, tin and zinc within the surficial sediments of the Fal Estuary, Cornwall, UK, an area that drains a historically important polymetallic mining district. There are clear spatial variations in the contaminants, with the highest levels (> 2800 p.p.m. As, > 5000 p.p.m. Cu, > 3000 p.p.m. Sn and > 6000 p.p.m. Zn) within Restronguet Cree...
Assessing the authenticity of a sample taken from the Altar Stone at Stonehenge in 1844 using portable XRF and automated SEM-EDS
Journal of Archaeological Science: Reports
Journal of Geochemical Exploration, 2002
Geochemical analyses of intertidal sediments from the northern part of the Fowey Estuary, Cornwal... more Geochemical analyses of intertidal sediments from the northern part of the Fowey Estuary, Cornwall, UK, reveal a clear pulse in Sn concentration in sediments which predate 1880. Sn concentrations at the base of the cores increase rapidly to peak values of 1200 ppm and then decrease to values of 200 ppm at the present-day sediment surface. The mineralogy of the sediments is consistent with an origin from the release of mine waste from tin streaming and smelt products into the estuary. Further to the south, the down-core geochemistry of the estuary sediments is uniform with values of typically 400 ppm. This is interpreted as due to the natural reworking of the recognised pulse in particulate mine waste seen to the north.
Issues and opportunities in urban forensic geology
Geological Society, London, Special Publications, 2013
Geological trace evidence including, for example, soil, sand and rock dust has been examined usin... more Geological trace evidence including, for example, soil, sand and rock dust has been examined using a wide range of analytical techniques. Whilst such materials are common in rural locations, in urban areas, such geological materials are often perceived to be restricted to parks, recreational areas, gardens and waste ground. However, both geological materials and the wide range of analytical methods used to characterize them are much more applicable to the whole urban environment than is generally realized, with the main differences being the types and amounts of sample analysed and the methods adopted. The range of geological applications can be summarized as those deployed at the broad (decimetres–kilometres) to small (millimetres–decimetres) scale. The broad spatial variation in soil, roadway, water, buildings materials, and wind- or water-borne particles can be contrasted with the variation in urban materials from dwellings to streets or gardens and parks, along with the micro-sp...
Two distinct episodes of serpentinisation have been identified within the peridotites of the Liza... more Two distinct episodes of serpentinisation have been identified within the peridotites of the Lizard complex. The first episode (primary serpentinisation) is represented by the complex and pervasive hydration of the Lizard peridotite. The second (later) episode is characterised by a pale to dark green, pseudo-fibrous mixture of lizardite and chrysotile that is restricted to fractures (vein serpentine). Mineralised northnorth-west and east-north-east trending fault zones contain fragments of vein serpentine generated during this second episode. Faults with similar orientations and mineralogy within the gabbro unit contain adularia which have been previously dated by Ar 40 -Ar 39 and K-Ar methods at 210-220 Ma (Triassic). Stable isotope ratios indicate that the mineralisation within the gabbro and peridotite is genetically similar. The primary and secondary serpentinisation episodes are therefore interpreted as pre-Triassic in age. A latest Carboniferous to early Permian age is proposed for the formation of vein serpentine and a late Devonian to Carboniferous age is proposed for the primary serpentinisation episode. This is envisaged to have taken place post-obduction but a pre-obduction initiation of serpentinisation cannot be discounted.
Recycling
Black mass is the industry term applied to end-of-life (EoL) lithium-ion batteries that have been... more Black mass is the industry term applied to end-of-life (EoL) lithium-ion batteries that have been mechanically processed for potential use as a recycled material to recover the valuable metals present, including cobalt, lithium, manganese, nickel and copper. A significant challenge to the effective processing of black mass is the complexity of the feed material. Two samples of black mass from a European source were analysed using a combination of methods including automated SEM-EDS (AMICS) to characterise and quantify the phases present and particle chemistry. Micro X-CT imaging, overlain onto automated mineralogy images, enabled the 3D morphology of the particles to be determined. Micro-XRF was used to map the copper, nickel, manganese and cobalt-bearing phases. Since Li cannot be detected using SEM-EDS, its abundance was semi-quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The integration of these complimentary analytical methods allowed f...
Geological Controls on Reservoir Properties of the Montney Formation in Northeastern BC: An integration of sequence stratigraphy, organic geochemistry, quantitative mineralogy and petrophysical analysis
The Montney-Doig petroleum system is the largest known unconventional play in Canada and the host... more The Montney-Doig petroleum system is the largest known unconventional play in Canada and the host of huge volumes of hydrocarbons in Western Alberta and Northeastern British Columbia. Thanks to horizontal drilling and multistage hydraulic fracturing, the resource production started ramping up in 2006 and has been growing exponentially since then. During the last decade, economic optimization of the development has been largely driven by stimulation design experimentations, increasing the lateral length, the number of fracturing stages and fluid volumes, while focusing on liquid-rich areas of the system. Although all these factors are, and will stay key elements of success, a better understanding of the geological controls on productivity will assume more importance in future development. In Northeastern BC, the Montney formation is typically 200 to 400 m-thick and predicting how reservoir and fluid properties vary throughout this interval will give an edge to companies for landing h...
Previous models for the tectonic-stratigraphy of the Lizard complex ophiolite have proposed three... more Previous models for the tectonic-stratigraphy of the Lizard complex ophiolite have proposed three thrust-bounded units. However, our studies indicate that post-obduction extensional faulting may have exerted a hitherto unrecognised effect on the present distribution of lithologies. Field and previously published geophysical evidence suggest that the uppermost tectonic unit (the Crousa Downs Unit) represents the downfaulted upper levels of the Goonhilly Downs Unit. Deformed lithologies previously thought to be part of the Goonhilly Downs Unit are reassigned to the underlying Basal Unit. A revised model for the tectonic-stratigraphy is presented. The Basal Nappe is underlain by the Basal Thrust and comprises the Traboe schists, the Landewednack schists and the Old Lizard Head Series. The Goonhilly Downs Nappe, underlain by the Goonhilly Downs Thrust, structurally overlies the Basal Nappe and comprises serpentinised peridotite, Trelan and Crousa Gabbro and the Porthoustock Sheeted Dyke Complex. This work highlights the importance of late-to post-Variscan extensional deformation in south Cornwall.
PLOS ONE, 2021
Little is known of the properties of the sarsen stones (or silcretes) that comprise the main arch... more Little is known of the properties of the sarsen stones (or silcretes) that comprise the main architecture of Stonehenge. The only studies of rock struck from the monument date from the 19th century, while 20th century investigations have focussed on excavated debris without demonstrating a link to specific megaliths. Here, we present the first comprehensive analysis of sarsen samples taken directly from a Stonehenge megalith (Stone 58, in the centrally placed trilithon horseshoe). We apply state-of-the-art petrographic, mineralogical and geochemical techniques to two cores drilled from the stone during conservation work in 1958. Petrographic analyses demonstrate that Stone 58 is a highly indurated, grain-supported, structureless and texturally mature groundwater silcrete, comprising fine-to-medium grained quartz sand cemented by optically-continuous syntaxial quartz overgrowths. In addition to detrital quartz, trace quantities of silica-rich rock fragments, Fe-oxides/hydroxides and ...
Marine and Petroleum Geology, 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Journal of Archaeological Science: Reports, 2021
Stonehenge is dominated by the large, locally derived sarsen stones which comprise the Outer Sars... more Stonehenge is dominated by the large, locally derived sarsen stones which comprise the Outer Sarsen Circle and the Inner Sarsen Trilithon Circle. Lithologically they are a hard form of sandstone called silcrete. Less obvious are the smaller 'bluestones' which form the Outer Bluestone Circle and Inner Bluestone Horseshoe. The bluestone assemblage is composed of a variety of lithologies, including dolerite (almost all carrying small, cm scale, white to pink 'spots'), rhyolites, volcanic tuffs and two different types of sandstone. The majority of the bluestones have been provenanced to the Mynydd Preseli area in west Wales some 200 km west of Stonehenge, and the distinctive spots in the dolerites were crucial evidence in making that link. However, despite the importance of the spots in that provenancing model, which provides evidence for one of the most remarkable feats of Neolithic time in northwest Europe, they have been little studied and are not fully characterized. One reason for this is the fact that they are difficult to study using standard optical microscopy because of the fine grain size of the component minerals. In order to gain a greater understanding of the mineralogy and origin of the spots we have used a range of alternative optical and analytical techniques, including high resolution photomicrography, 'standard' electron microscopy (SEM-EDS), automated scanning electron microscopy with linked energy dispersive analysis (automated SEM-EDS) and X-ray diffraction. These investigations, based primarily on samples from Carn Goedog and Carn Meini in the Mynydd Preseli, lead us to conclude that the spots result from a two-stage alteration history involving firstly saussuritization of primary igneous calcium-rich plagioclase phenocrysts/glomerocrysts. The saussuritization was probably a late-stage magmatic event, possibly occurring at ca. 400°C, and led to the development of the secondary minerals clinozoisite, zoisite, albite and muscovite. Subsequently, the dolerites were affected by regional low-grade metamorphism at ca. 250-300°C, at the transition from the prehnite-pumpellyite to the greenschist facies. During this metamorphism the background (non-spot) areas of the samples were altered with the development of the secondary minerals chlorite, actinolite, epidote, quartz, titanite and further albite. Interpretation of these data shows that the Carn Goedog sample has a higher percentage of secondary minerals compared to the Carn Meini sample, suggesting that the former shows a higher degree of alteration. Further analyses of dolerite samples from the Mynydd Preseli should provide insight into the potential of the extent of rock alteration in the further refinement of understanding the source or sources of the Stonehenge bluestone dolerites.
Journal of Archaeological Science, 2020
The Altar Stone at Stonehenge is a greenish sandstone thought to be of Late Silurian-Devonian ('O... more The Altar Stone at Stonehenge is a greenish sandstone thought to be of Late Silurian-Devonian ('Old Red Sandstone') age. It is classed as one of the bluestone lithologies which are considered to be exotic to the Salisbury Plain environ, contrasting with the larger sarsen stones, which are a hard, durable silcrete derived from no more than 30km from Stonehenge. It is well established that most of the bluestones are derived from the Mynydd Preseli, in west Wales. However, no Old Red Sandstone rocks crop out in the Preseli; instead a source in the Lower Old Red Sandstone Cosheston Subgroup at Mill Bay, on the shores of Milford Haven, to the south of the Preseli, has been proposed. More recently, on the basis of detailed petrography, a source for the Altar Stone much further to the east, towards the Wales-England border, has been suggested. Quantitative analyses presented here compare data from proposed 2 Stonehenge Altar Stone debris with samples from the Cosheston Subgroup at Mill Bay in west Wales, as well as with a second sandstone type found at Stonehenge which, on palaeontological evidence has been shown to be Lower Palaeozoic in age. The Altar Stone samples have up to 16.7 modal % calcite while the Lower Palaeozoic and Cosheston Subgroup sandstones have less than 0.25 modal %. The Altar Stone also contains up to 3.8 modal % kaolinite and 0.8 modal % barite, minerals that are absent from the other sandstones. Calcite, kaolinite and barite in the Altar Stone samples all occur between the detrital grains and are all thought to be authigenic minerals, which differs markedly with the Cosheston Subgroup and Lower Palaeozoic sandstones. The Cosheston Subgroup sandstone contrasts with the other two sandstone lithologies in having up to 0.7 modal % detrital garnet (<0.08 in both the other two sandstone types). Further differences between the Altar Stone sandstone and the Cosheston Subgroup sandstone are seen when their contained zircons are examined. Not only do they have differing morphologies (size, shape and quality) but U-Pb age dates for the zircons show contrasting populations; the Cosheston Subgroup sample zircon age population is essentially bimodal, with age maxima at 500 and 1500 Ma whilst the Altar Stone zircon population is more diverse, with ages spanning from 472 to 2475 Ma without maxima. Together, all these data confirm that Mill Bay is not the source of the Altar Stone with the abundance of kaolinite in the Altar Stone sample suggesting a source further east than Milford Haven, towards the Wales-England border. The disassociation of the Altar Stone and Milford Haven fully undermines the hypothesis that the bluestones, including the Altar Stone, were transported from west Wales by sea up the Bristol Channel and adds further credence to a totally land-based route, possibly along a natural routeway leading from west Wales to the Severn estuary and beyond. This route, along the valleys followed today by the A40, may well have been significant in prehistory, raising the possibility that the Altar Stone was added en route to the assemblage of Preseli bluestones taken to Stonehenge around or shortly before 3000 BC. Recent strontium isotope analysis of human and animal bones from Stonehenge, dating to the beginning of its first construction stage around 3000 BC, are consistent with having lived in this western region of Britain.
Petroleum Geoscience, 2019
This study focuses on the Lower–Middle Triassic Montney, Sunset Prairie, Doig and Halfway formati... more This study focuses on the Lower–Middle Triassic Montney, Sunset Prairie, Doig and Halfway formations from the foreland basin of the Canadian Cordillera (Alberta and British Columbia). Based on core and outcrop descriptions, the correlation of 400 wells, and on mineralogical analyses, this study interprets the basin-scale, 3D-stratigraphic architecture of these formations and discusses the controls on its evolution.Well correlation highlights four sequences (1–4) interpreted to occur in two second-order cycles (A and B). In this work, the Early Triassic Montney Formation and the early Middle Triassic Sunset Prairie Formation are interpreted to consist of three third-order sequences (1–3) related to the first second-order cycle (cycle A). The Middle Triassic Doig and Halfway formations are interpreted to consist of a fourth sequence (4) related to a second second-order cycle (cycle B). Integration of the stratigraphic surfaces with previously published biostratigraphic analyses emphas...
Distribution of Sedimentary Heterogeneities in Shale Plays: Insight From Sequence Stratigraphy, Multi-Proxies Analysis and Stratigraphic Modeling of the Montney and Doig Formations (Trias, Alberta-British Columbia, Canada)
International Conference and Exhibition, Melbourne, Australia 13-16 September 2015, 2015
A New Solution for the Characterization of Unconventional Shale Resources Based on Analysis of Drill Cuttings
Abu Dhabi International Petroleum Exhibition and Conference, 2015
We introduce a new, cost-effective solution for the characterization of unconventional shale reso... more We introduce a new, cost-effective solution for the characterization of unconventional shale resources based on innovative analysis of drill cuttings. This solution was tested successfully on the Toarcian shales of the Couy-1 well, located in the southern Paris Basin, France. Ten samples of cuttings-sized rock fragments from different depths were subjected to several analytical methods to determine geochemical parameters (LECO and Rock Eval), the mineralogy and texture (QEMSCAN), and the mechanical properties (nanoindentation). Based on the results, the Toarcian shales were subdivided into two mineralogically distinct lithostratigraphic intervals. The Upper Toarcian shales consist of siltstone with a matrix of illitic clays, whereas the Lower Toarcian shales consist mainly of calcareous mudstone with a matrix of finely intermixed calcite and clays. The Young's modulus varies between 12.5 and 25.6 GPa and decreases with increasing TOC content. An interval with high TOC content (&...
First results on sequence stratigraphy, sedimentary architecture, mineralogy and organic content in the Montney and Doig Formations (Alberta / British columbia) The Montney and Doig Formations
In the last decade, rapid increase in the world's hydrocarbon demand has brought the focus on... more In the last decade, rapid increase in the world's hydrocarbon demand has brought the focus on shale resources. Since the 50's, the Lower-Middle Triassic Montney and Doig Formations are well known in the Western Canada for their conventional hydrocarbons resources. In the last five years they became the focus of numerous studies carrying out a spectacular potential for unconventional resources (NEB, 2013). Within these new plays, the knowledge of TOC and mineralogical heterogeneities distribution in sedimentary basins is one of the key elements that will improve hydrocarbons discovery and production. Numerous QEMSCAN analysis, Rock-Eval analysis, palynofacies studies and thin sections analysis had been done on core samples along a 2D section. This study intends to establish links between sequence stratigraphy, sedimentary architecture, mineralogy and organic content the organic rich Montney and Doig Formations.
shown that the PGE-enriched magmatism is a ubiquitous and long-lived feature of the North Atlanti... more shown that the PGE-enriched magmatism is a ubiquitous and long-lived feature of the North Atlantic Igneous Province (NAIP). The British Palaeogene Igneous Province (well-exposed along the north western seaboard of the British Isles) forms the south western expression of the NAIP and is characterised by voluminous flood basalts, extensive dyke swarms and several central intrusive complexes (Figure 1a). Chromitite-hosted PGE References
Journal of Geophysical Research: Atmospheres, 2009
Direct‐sampling and remote‐sensing measurements were made at the crater rim of Masaya volcano (Ni... more Direct‐sampling and remote‐sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d < 10 μm) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d ∼ 1.15 μm. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emi...
Journal of Geophysical Research: Atmospheres, 2008
Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes wer... more Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm < d < 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d < 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearly pure silica; this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent. Measurements of the size, shape and composition of fine silicate particles may potentially offer insights into preemission, synemission, and postemission processes. ...
Geological Society, London, Special Publications, 2013
In the investigation of serious crimes, soil can be, in some cases, a very valuable class of trac... more In the investigation of serious crimes, soil can be, in some cases, a very valuable class of trace evidence. The complexity of soil is part of the reason why it is useful as trace evidence but is also an inherent problem, as there are many different parameters in a soil sample that could potentially be characterized. The inorganic components of soils are dominated by minerals, along with anthropogenic particulate grains; thus, the analysis of soil mineralogy as the main technique for inorganic forensic soil characterization is recommended. Typical methods that allow the bulk mineralogy to be determined, such as X-ray diffraction (XRD), do not allow the texture of the particles to be characterized. However, automated scanning electron microscopy (SEM) provides both modal mineralogy and also allows particle textures to be characterized. A recent advance in this technique has been the ability to report the modal mineralogy of a sample as ‘lithotypes’, which are defined on the basis of ...
Sedimentology, 2003
Estuarine sediments commonly form major sinks for contaminants released during industrial activit... more Estuarine sediments commonly form major sinks for contaminants released during industrial activity. Many industrial processes lead to the release of metals initially in solution, which can then be adsorbed on to, for example, Fe hydroxides or clay minerals. However, in the mining industry, there are two major contaminant waste streams: (1) metals discharged in solution via mine drainage; and (2) particulate grains of the ore‐forming or related minerals released after ore processing. The release of particulate waste can have a major long‐term impact on environmental geochemistry. In this study, we have mapped the distribution of arsenic, copper, tin and zinc within the surficial sediments of the Fal Estuary, Cornwall, UK, an area that drains a historically important polymetallic mining district. There are clear spatial variations in the contaminants, with the highest levels (> 2800 p.p.m. As, > 5000 p.p.m. Cu, > 3000 p.p.m. Sn and > 6000 p.p.m. Zn) within Restronguet Cree...
Assessing the authenticity of a sample taken from the Altar Stone at Stonehenge in 1844 using portable XRF and automated SEM-EDS
Journal of Archaeological Science: Reports
Journal of Geochemical Exploration, 2002
Geochemical analyses of intertidal sediments from the northern part of the Fowey Estuary, Cornwal... more Geochemical analyses of intertidal sediments from the northern part of the Fowey Estuary, Cornwall, UK, reveal a clear pulse in Sn concentration in sediments which predate 1880. Sn concentrations at the base of the cores increase rapidly to peak values of 1200 ppm and then decrease to values of 200 ppm at the present-day sediment surface. The mineralogy of the sediments is consistent with an origin from the release of mine waste from tin streaming and smelt products into the estuary. Further to the south, the down-core geochemistry of the estuary sediments is uniform with values of typically 400 ppm. This is interpreted as due to the natural reworking of the recognised pulse in particulate mine waste seen to the north.
Issues and opportunities in urban forensic geology
Geological Society, London, Special Publications, 2013
Geological trace evidence including, for example, soil, sand and rock dust has been examined usin... more Geological trace evidence including, for example, soil, sand and rock dust has been examined using a wide range of analytical techniques. Whilst such materials are common in rural locations, in urban areas, such geological materials are often perceived to be restricted to parks, recreational areas, gardens and waste ground. However, both geological materials and the wide range of analytical methods used to characterize them are much more applicable to the whole urban environment than is generally realized, with the main differences being the types and amounts of sample analysed and the methods adopted. The range of geological applications can be summarized as those deployed at the broad (decimetres–kilometres) to small (millimetres–decimetres) scale. The broad spatial variation in soil, roadway, water, buildings materials, and wind- or water-borne particles can be contrasted with the variation in urban materials from dwellings to streets or gardens and parks, along with the micro-sp...