Stratiform manganese mineralisation near Inverness,Scotland: A Devonian sublacustrine hot-spring deposit?     

K. Nicholson 《Mineralium Deposita》1990,25(2):126-131

A stratiform manganiferous horizon, up to 4 m thick but localised in aerial extent, occurs 10 km south-east of Inverness in north-east Scotland. It overlies Precambrian Grampian Group schists and is itself overlain by Middle Old Red Sandstone (Devonian) conglomerate, which elsewhere rests unconformably on the schists. The deposit was mined briefly in the early 1920s and is composed principally of fine-grained braunite with minor bustamite. Lower sections of the deposit contain cavities, infilled by late baryte, calcite and rhodochrosite, which resemble stromatactis. This horizon is underlain by a hematite-quartz layer, thought to represent a laterite formed by pre-MORS weathering of the underlying schists. The mineralogy and geochemistry of the manganese ore (enriched in Ag, As, Ba, Bi, Pb, Sb, Sr and Zn) are characteristic of a hydrothermal origin. Such an origin, when considered in conjunction with the outcrop, textures, mineralogy and stratigraphy of the deposit together with the palaeogeography of the region, can only be explained by deposition from hot-springs in a sublacustrine environment. Nearby baryte mineralisation may also have been deposited from the same geothermal system, which had the Caledonian 407 Ma Moy granitoid as heat source. The managanese ore is enriched in gold pathfinder elements and minor detrital gold has been found in the area. Gold mineralisation may therefore have also been deposited in the upper sections of this Devonian geothermal system.  相似文献   

Application of 3D empirical travel times to routine event location     

T. Nicholson 《Physics of the Earth and Planetary Interiors》2006,158(1):67-74

The unmodeled effects of lateral heterogeneity are a primary cause of event mislocation in routine methods. Approaches that account for the effect of lateral heterogeneity on travel times are commonly used in specialized studies, but some methods have recently been developed that are suitable for routine location. A variety of changes to the routine procedures have been suggested by other authors. These proposed changes are shown to be compatible to with the use of 3D travel time predictions. 3D empirical travel times are discussed in a routine context. This one step approach, based on direct use of a database of the most reliable previous observations, is shown to be suitable as an additional final step in routine procedures to give a supplementary high accuracy location. The empirical travel time approach is tested on a reference dataset of 155 ground truth events and shown to reduce epicentral mislocation by 45%. The approach is found to be particularly effective at reducing large mislocations. Improvement is demonstrated for every region represented in the dataset but particularly large improvements are shown for events in Europe, USA and Japan.  相似文献   

Chlorine stable isotope studies of old groundwater,southwestern Great Artesian Basin,Australia     

Min Zhang  Shaun K. Frape  Andrew J. Love  Andrew L. Herczeg  B.E. Lehmann  U. Beyerle  R. Purtschert 《Applied Geochemistry》2007

Stable Cl isotope ratios (³⁷Cl/³⁵Cl) were measured in groundwater samples from the southwestern flow system of the Great Artesian Basin, Australia to gain a better understanding of the Cl⁻ sources and transport mechanisms. δ³⁷Cl values range from 0‰ to −2.5‰ (SMOC), and are inversely correlated with Cl⁻ concentration along the inferred flow direction. The Cl isotopic compositions, in conjunction with other geochemical parameters, suggest that Cl⁻ in groundwaters is not derived from salt dissolution. Mixing of the recharge water with saline groundwater cannot explain the relationship between δ³⁷Cl and Cl⁻ concentration measured. Marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the Cl⁻ concentrations observed in wells that are close to the recharge area, and in groundwaters sampled along the southern transect. δ³⁷Cl values measured in the leachate of the Bulldog shale suggest that the aquitard is the subsurface source of Cl⁻ for the majority of groundwater samples studied. Diffusion is likely the mechanism through which Cl⁻ is transported from the pore water of the Bulldog shale to the aquifer. However, a more detailed study of the aquitard rocks is required to verify this hypothesis.  相似文献   

Modelling the hydrodynamics of offshore sandbanks     

S. Pan  N. MacDonald  J. Williams  B.A. O’Connor  J. Nicholson  A.M. Davies 《Continental Shelf Research》2007

This paper describes the details of a quasi-three-dimensional model (3DBANK), which has been developed to investigate medium and long-term morphological evolution and development of offshore sandbanks. The model is based on a three-dimensional tidal module using the Galerkin-eigenfunction method, but also includes four sub-modules to compute: the instantaneous bedform characteristics from which the temporal and spatial variations of the shear stresses at the sea bed can be derived; the suspended sediment concentration through the water column; the bed-load and suspended sediment fluxes at a point-in-plan; and the resulting morphological changes, respectively. The model also includes the effects of the wind and waves at the sea surface, as well as the wave–current interaction (WCI), and operates with full hydrodynamic and morphodynamic interaction. The components of the model were tested against laboratory and field data, and the complete model was then applied to Middlekerke Bank off the Flemish coast where extensive field measurements were taken during the European Community (EC) funded Circulation and Sediment Transport Around Banks (CSTAB) Project using various advanced instrumentation including STABLE and HF OSCR. Comparisons of the model results with the field measurements and observations show that the model is capable of reproducing the current and wave-induced bedforms, bed roughness, tidal currents and tidal residuals around the sandbank satisfactorily, and can be used to study the long-term sandbank evolution under various offshore conditions. This paper, however, focuses on the hydrodynamic aspects of the model, while the details of the morphological components will be given in a companion paper.  相似文献   

Automatic Detection of Magnetic δ in Sunspot Groups     

Sreejith Padinhatteeri  Paul A. Higgins  D. Shaun Bloomfield  Peter T. Gallagher 《Solar physics》2016,291(1):41-53

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Multivariate trends in phytoplankton species groups in the southern North Sea     

Nicholson  Mike; Fryer  Rob; Maxwell  David 《ICES Journal of Marine Science》1998,55(4):581-586

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A Case Study of Soil-Gas Sampling in Silt and Clay-Rich (Low-Permeability) Soils     

Todd A. McAlary  Paul Nicholson  Hester Groenevelt  David Bertrand 《Ground Water Monitoring & Remediation》2009,29(1):144-152

Soil-gas sampling and analysis is a common tool used in vapor intrusion assessments; however, sample collection becomes more difficult in fine-grained, low-permeability soils because of limitations on the flow rate that can be sustained during purging and sampling. This affects the time required to extract sufficient volume to satisfy purging and sampling requirements. The soil-gas probe tubing or pipe and sandpack around the probe screen should generally be purged prior to sampling. After purging, additional soil gas must be extracted for chemical analysis, which may include field screening, laboratory analysis, occasional duplicate samples, or analysis for more than one analytical method (e.g., volatile organic compounds and semivolatile organic compounds). At present, most regulatory guidance documents do not distinguish between soil-gas sampling methods that are appropriate for high- or low-permeability soils. This paper discusses permeability influences on soil-gas sample collection and reports data from a case study involving soil-gas sampling from silt and clay-rich soils with moderate to extremely low gas permeability to identify a sampling approach that yields reproducible samples with data quality appropriate for vapor intrusion investigations for a wide range of gas-permeability conditions.  相似文献   

Using structure‐from‐motion to create glacier DEMs and orthoimagery from historical terrestrial and oblique aerial imagery          下载免费PDF全文

Jordan R. Mertes  Jason D. Gulley  Douglas I. Benn  Sarah S. Thompson  Lindsey I. Nicholson 《地球表面变化过程与地形》2017,42(14):2350-2364

Increased resolution and availability of remote sensing products, and advancements in small‐scale aerial drone systems, allows observations of glacial changes at unprecedented levels of detail. Software developments, such as structure‐from‐motion (SfM), now allow users an easy and efficient method to generate three‐dimensional (3D) models and orthoimages from aerial or terrestrial datasets. While these advancements show promise for current and future glacier monitoring, many regions still suffer a lack of observations from earlier time periods. We report on the use of SfM to extract spatial information from various historic imagery sources. We focus on three geographic regions, the European Alps, high Arctic Norway and the Nepal Himalayas. We used terrestrial field photographs from 1896, high oblique aerial photographs from 1936 and aerial handheld photographs from 1978 to generate digital elevation models (DEMs) and orthophotos of the Rhone glacier, Brøggerhalvøya and the lower Khumbu glacier, respectively. Our analysis shows that applying SfM to historic imagery can generate high quality models using only ground control points. Limited camera/orientation information was largely reproduced using self‐calibrated model data. Using these data, we calculated mean ground sampling distances across each site which demonstrates the high potential resolution of resulting models. Vertical errors for our models are ±5.4 m, ±5.2 m and ±3.3 m. Differencing shows similar patterns of thinning at lower Rhone (European Alps) and Brøggerhalvøya (Norway) glaciers, which have mean thinning rates of 0.31 m a^?1 (1896–2010) to 0.86 m a^?1 (1936–2010) respectively. On these clean ice glaciers thinning is highest in the terminus region and decreasing up‐glacier. In contrast to these glaciers, uneven topography, exposed ice‐cliffs and debris cover on the Khumbu glacier create a highly variable spatial distribution of thinning. The mean thinning rate for the Khumbu study area was found to be 0.54 ± 0.9 m a^?1 (1978–2015). Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Forecasting Solar Flares Using Magnetogram-based Predictors and Machine Learning     

Kostas Florios  Ioannis Kontogiannis  Sung-Hong Park  Jordan A. Guerra  Federico Benvenuto  D. Shaun Bloomfield  Manolis K. Georgoulis 《Solar physics》2018,293(2):28

We propose a forecasting approach for solar flares based on data from Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) mission. In particular, we use the Space-weather HMI Active Region Patches (SHARP) product that facilitates cut-out magnetograms of solar active regions (AR) in the Sun in near-realtime (NRT), taken over a five-year interval (2012?–?2016). Our approach utilizes a set of thirteen predictors, which are not included in the SHARP metadata, extracted from line-of-sight and vector photospheric magnetograms. We exploit several machine learning (ML) and conventional statistics techniques to predict flares of peak magnitude \({>}\,\mbox{M1}\) and \({>}\,\mbox{C1}\) within a 24 h forecast window. The ML methods used are multi-layer perceptrons (MLP), support vector machines (SVM), and random forests (RF). We conclude that random forests could be the prediction technique of choice for our sample, with the second-best method being multi-layer perceptrons, subject to an entropy objective function. A Monte Carlo simulation showed that the best-performing method gives accuracy \(\mathrm{ACC}=0.93(0.00)\), true skill statistic \(\mathrm{TSS}=0.74(0.02)\), and Heidke skill score \(\mathrm{HSS}=0.49(0.01)\) for \({>}\,\mbox{M1}\) flare prediction with probability threshold 15% and \(\mathrm{ACC}=0.84(0.00)\), \(\mathrm{TSS}=0.60(0.01)\), and \(\mathrm{HSS}=0.59(0.01)\) for \({>}\,\mbox{C1}\) flare prediction with probability threshold 35%.  相似文献   

Cytological and Physiological Biomarker Responses from Green Mussels, Perna viridis (L.) Transplanted to Contaminated Sites in Hong Kong Coastal Waters   总被引：2，自引：0，他引：2  

Shaun Nicholson 《Marine pollution bulletin》1999,39(1-12):261-268

Biological monitoring of marine contaminants often involves the analysis of metals accumulated in mussel tissues. Critiques of this type of monitoring suggest that although relatively good indications of ambient metal concentrations are determined, actual biological harm is not elucidated. Biomarkers, techniques originally developed in medicine, have recently been employed in an attempt to ascertain the health of marine mussels. Biomarkers have been used with good effect in temperate marine pollution monitoring programmes. The use of biomarkers in the toxicological evaluation of tropical and subtropical waters is, however, generally lacking, which is somewhat surprising, as considerable industrialisation and environmental degradation is taking place in the Pacific-rim countries of Southeast Asia. In the present study, a suite of cytological and physiological biomarkers have been measured from mussels (Perna viridis: Mytilidae) transplanted within the coastal waters of Hong Kong. Mussels from contaminated sites, had labile lysosomal membranes, whereas animals from a cleaner reference site had more stable membranes. These cytological responses have been related to metal-induced stress and are simple, cost-effective markers of pollution. Cardiac activity from mussels transplanted to polluted sites was generally similar to that of individuals from the reference site, although a mild tachycardia was associated with one site. The cause of the tachycardia and the use of heart rate in mussels as a biomarker is discussed. Integrated physiological responses to stress, condition indices, revealed mussels from a clean reference site had higher indices than animals from contaminated sites. The relative sensitivities of the cytological and physiological biomarkers deployed in this study and their application to pollution monitoring is discussed.  相似文献