NERC Open Research Archive

    Variscan sourcing of Westphalian (Pennsylvanian) sandstones in the Canobie Coalfield, UK

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    The zircon age spectrum in a sample from the Canonbie Bridge Sandstone Formation (Asturian) of southern Scotland contains two main peaks. One is Early Carboniferous in age (348– 318 Ma), and corresponds to the age of igneous activity during the Variscan Orogeny. The other is of late Neoproterozoic to early Cambrian age (693–523 Ma), corresponding to the Cadomian. Together, these two groups comprise 70 % of the zircon population. The presence of these two peaks shows unequivocally that a significant proportion of the sediment was derived from the Variscides of western or central Europe. The zircon population also contains a range of older Proterozoic zircons and a small Devonian component. These could have been derived from the Variscides, but it is possible that some were locally derived through recycling of northerly derived sandstones of Devonian–Carboniferous age. The zircon age data confirm previous suggestions of Variscide sourcing to the Canonbie area, made on the basis of petrographical, heavy mineral and palaeocurrent evidence, and extend the known northward distribution of Variscan-derived Westphalian sediment in the UK

    Petrographic analysis of igneous and metamorphic rocks from the Fishguard 1:50000 sheet, south Wales

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    This report presents the results of petrographic analysis of samples of igneous and metamorphic rocks collected as part of a mapping survey of the Fishguard 1:50000 sheet, south Wales. The objective of the report is to provide petrographic descriptions of the rocks and to discuss the origin of the fabrics present

    A feasibility study on the use of isotope dilution as a tool for quantifying uranium isotopic concentrations by quadrupole ICP-MS

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    The determination of uranium elemental concentrations and isotope ratios has been a major task for the BGS inductively coupled plasma mass spectrometry (ICP-MS) laboratory over the last five years. UK government departments and the nuclear industry have ongoing environmental monitoring programmes which require high quality data. The need for a greater understanding of chemical pathways, sinks and sources has been a driver for BGS to continue to improve analytical performance but with a minimal increase in costs. This study seeks to identify whether isotope dilution could provide a significant increase in analytical performance with minimal cost implications. This report reviews the fundamental concepts of isotope dilution and its advantages over related techniques such as internal standardisation. It considers the potential benefits of quadrupole ICPMS (ICP-QMS) over other techniques where high productivity is an issue, such as for environmental monitoring. The optimisation of the ICP-MS acquisition parameters including peak dwell times, detector dead-times, spike concentrations and operating conditions are examined. Isotope dilution (ID) relies heavily on the accurate calibration of the 233U spike and the process of reverse isotope dilution is used and discussed as part of this study. A series of experiments was conducted to ascertain the degree of chemical preparation required for accurate isotope dilution determination. These included comparing the effectiveness of using the 233U spike with internal standardisation by a proxy element, to overcome ICP-MS matrix effects and changes in sensitivity. Finally, the proposed methodology was tested using a range of natural rock reference materials with known uranium concentrations covering various common igneous and metasedimentary types. This project established that the use of 233U, a by-product of nuclear fuel processing, provided superior precision when used as an internal standard for measurements of other uranium isotope concentrations, compared to indium, rhenium or bismuth. The data suggest that the within sample precision is better when full ID quantification is performed, regardless of the matrix, than when using the spike as an internal standard. The IDMS technique could potentially eliminate the current column separation procedure, which would achieve significant savings in staff time and consumables. A small systematic bias has been observed in the data. It is thought that one of the most likely factors is the assumption made about the density of the 233U spike solution, which would affect the IDMS calculations but have no influence when 233U is used as an internal standard. It will not always be appropriate to use this method for the determination of uranium isotope concentrations and a decision tree needs to be devised to determine the appropriate method to be used for each potential application. The investigation has proved the value and potential of this methodology for isotope concentration analysis by quadrupole ICP-MS. Once a robust, fit for purpose methodology can be applied routinely, the possibility of the use of IDMS for other stable isotopes should be considered

    Ascension Observatory Monthly Magnetic Bulletin: August 2010

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    This bulletin contains the monthly preliminary observatory results, published to meet the needs of all users of geomagnetic data. Magnetic observatory data are presented as a series of plots of one-minute, hourly and daily values, followed by a table of monthly values. The operation of the observatory and presentation of data are described in the introduction

    Porosity of the Bunter sandstone in the Southern North Sea basin based on selected borehole neutron logs

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    This report presents the results of a porosity study of the Bunter Sandstone (BNS) in the Southern North Sea Basin based primarily on the analysis of neutron logs. The Bunter Sandstone is a Triassic fluvial sandstone (Cameron et al 1992). It contains layers or lenses of varying thickness of shale and/or siltstone. The Prizm module from the GeoGraphix interpretation software suite (v. 2004.1), was used to display the borehole logs. Neutron logs were plotted alongside gamma, sonic and density logs. The gamma log was used to identify shales in the Bunter Sandstone to assist in averaging the neutron porosity over the sandy intervals only. Most porosities in the BNS had values in the interval of 10-22% but some extremes as low as 1% and as high as 27% were identified. Gas effect and salt cementation were also noted in some boreholes. Maps of the neutron and core porosities, depth to, and thickness of the sandstone, were produced in GeoAtlas, also from the GeoGraphix Interpretation suite 2004.1. In general the lowest porosities not linked with salt cementation coincided with the Sole Pit Trough, a major depocentre for the BNS

    The internal layering of Pine Island Glacier, West Antarctica, from airborne radar-sounding data

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    This paper presents an overview of internal layering across Pine Island Glacier, West Antarctica, as measured from airborne-radar data acquired during a survey conducted by the British Antarctic Survey and the University of Texas in the 2004/05 season. Internal layering is classified according to type (continuous/discontinuous/missing) and the results compared with InSAR velocities. Several areas exhibit disruption of internal layers that is most likely caused by large basal shear stresses. Signs of changes in flow were identified in a few inter-tributary areas, but overall the layering classification and distribution of layers indicate that only minor changes in ice-flow regime have taken place. This is supported by bed-topography data that show the main trunk of the glacier, as well as some of the tributaries, are topographically controlled and located in deep basins

    Estimating the location of the open-closed magnetic field line boundary from auroral images

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    The open-closed magnetic field line boundary (OCB) delimits the region of open magnetic flux forming the polar cap in the Earth’s ionosphere. We present a reliable, automated method for determining the location of the poleward auroral luminosity boundary (PALB) from far ultraviolet (FUV) images of the aurora, which we use as a proxy for the OCB. This technique models latitudinal profiles of auroral luminosity as both a single and double Gaussian function with a quadratic background to produce estimates of the PALB without prior knowledge of the level of auroral activity or of the presence of bifurcation in the auroral oval. We have applied this technique to FUV images recorded by the IMAGE satellite from May 2000 until August 2002 to produce a database of over a million PALB location estimates, which is freely available to download. From this database, we assess and illustrate the accuracy and reliability of this technique during varying geomagnetic conditions. We find that up to 35% of our PALB estimates are made from double Gaussian fits to latitudinal intensity profiles, in preference to single Gaussian fits, in nightside magnetic local time (MLT) sectors. The accuracy of our PALBs as a proxy for the location of the OCB is evaluated by comparison with particle precipitation boundary (PPB) proxies from the DMSP satellites. We demonstrate the value of this technique in estimating the total rate of magnetic reconnection from the time variation of the polar cap area calculated from our OCB estimates

    Eskdalemuir Observatory Monthly Magnetic Bulletin: August 2010

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    This bulletin contains the monthly preliminary observatory results, published to meet the needs of all users of geomagnetic data. Magnetic observatory data are presented as a series of plots of one-minute, hourly and daily values, followed by tabulations of monthly values, geomagnetic activity indices and reports of rapid variations. The operation of the observatory and presentation of data are described in the introduction

    High genetic diversity at the extreme range edge: nucleotide variation at nuclear loci in Scots pine (Pinus sylvestris L.) in Scotland

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    Nucleotide polymorphism at 12 nuclear loci was studied in Scots pine populations across an environmental gradient in Scotland, to evaluate the impacts of demographic history and selection on genetic diversity. At eight loci, diversity patterns were compared between Scottish and continental European populations. At these loci, a similar level of diversity (θsil=~0.01) was found in Scottish vs mainland European populations, contrary to expectations for recent colonization, however, less rapid decay of linkage disequilibrium was observed in the former (ρ=0.0086±0.0009, ρ=0.0245±0.0022, respectively). Scottish populations also showed a deficit of rare nucleotide variants (multi-locus Tajima's D=0.316 vs D=−0.379) and differed significantly from mainland populations in allelic frequency and/or haplotype structure at several loci. Within Scotland, western populations showed slightly reduced nucleotide diversity (πtot=0.0068) compared with those from the south and east (0.0079 and 0.0083, respectively) and about three times higher recombination to diversity ratio (ρ/θ=0.71 vs 0.15 and 0.18, respectively). By comparison with results from coalescent simulations, the observed allelic frequency spectrum in the western populations was compatible with a relatively recent bottleneck (0.00175 × 4Ne generations) that reduced the population to about 2% of the present size. However, heterogeneity in the allelic frequency distribution among geographical regions in Scotland suggests that subsequent admixture of populations with different demographic histories may also have played a role

    IMF clock angle control of multifractality in ionospheric velocity fluctuations

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    We present an analysis of 8 years of meridional line-of-sight ionospheric plasma velocity measurements from the Halley SuperDARN radar which investigates the effect of the interplanetary magnetic field (IMF) clock angle on the scaling exponents of the first three order velocity structure functions. We only use velocity measurements made poleward of the open/closed magnetic field line boundary in the nightside ionosphere. The measured scaling exponents are consistent with multifractal Kraichnan-Iroshnikov turbulence for all clock angles but with varying intermittency that decreases to zero during purely northward IMF conditions. We thus propose that intermittency is inherited from the solar wind but also discuss other possible reasons for this relationship. Citation: Abel, G. A., M. P. Freeman, and G. Chisham (2009), IMF clock angle control of multifractality in ionospheric velocity fluctuations, Geophys. Res. Lett., 36, L19102, doi:10.1029/2009GL040336
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