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  • Journal article
    Christeson GL, Morgan JV, Warner MR, 2012,

    Shallow oceanic crust: Full waveform tomographic images of the seismic layer 2A/2B boundary

    , Journal of Geophysical Research, Vol: 117

    We present results of full-waveform tomographic inversions of four profiles acquired over young intermediate- and fast spreading rate oceanic crust. The mean velocity-depth functions from our study include a 0.25–0.30 km-thick low-velocity, low-gradient region beneath the seafloor overlying a 0.24–0.28-km-thick high-gradient region; together these regions compose seismic layer 2A. Mean layer 2A interval velocities are 3.0–3.2 km/s. The mean depth to the layer 2A/2B boundary is 0.49–0.54 km, and mean velocities within the upper 0.25 km of layer 2B are 4.7–4.9 km/s. Previous velocity analyses of the study areas using 1-D ray tracing underestimate the thickness of the high-gradient region at the base of layer 2A. We observe differences in the waveform inversion velocity models that correspond to imaging of the layer 2A event; regions with a layer 2A event have higher velocity gradients at the base of layer 2A. Intermittent high velocities, which we interpret as massive flows, are observed in the waveform inversion velocity models at 0.05–0.10 km below the seafloor (bsf) over 10–25% of the intermediate-spreading profiles and 20–45% of the fast spreading profiles. The high-gradient region located 0.25–0.54 km bsf at the base of layer 2A may be associated with an increased prevalence of massive flows, the first appearance of dikes (lava-dike transition zone), or with increased crack sealing by hydrothermal products. The upper portion of layer 2B, which begins at 0.49–0.54 km bsf, may correspond to sheeted dikes or the top of the transition zone of lavas and dikes.

  • Journal article
    Larner F, Rehkaemper M, 2012,

    Evaluation of Stable Isotope Tracing for ZnO Nanomaterials-New Constraints from High Precision Isotope Analyses and Modeling

    , ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 46, Pages: 4149-4158, ISSN: 0013-936X
  • Conference paper
    Harrison RJ, Muxworthy AR, Lappe SCLL, 2012,

    FORCintense: A graphical implementation of the Preisach method of paleointensity estimation within FORCinel

    , EGU
  • Conference paper
    Biggin AJ, Badejo S, Shaw J, Dekkers MJ, Muxworthy ARet al., 2012,

    How does cooling rate affect the intensity of thermoremanent magnetisation in samples containing multidomain and interacting single domain ferrimagnetic grains? (poster)

    , EGU
  • Journal article
    Collins GS, 2012,

    Moonstruck magnetism

    , Science, Vol: 335, Pages: 1176-1177
  • Journal article
    Welten KC, Meier MMM, Caffee MW, Laubenstein M, Nishizumi K, Wieler R, Bland PA, Towner MC, Spurny Pet al., 2012,

    Cosmic-ray exposure age and preatmospheric size of the Bunburra Rockhole achondrite

    , METEORITICS & PLANETARY SCIENCE, Vol: 47, Pages: 186-196, ISSN: 1086-9379
  • Journal article
    Spurny P, Bland PA, Shrbeny L, Borovicka J, Ceplecha Z, Singelton A, Bevan AWR, Vaughan D, Towner MC, McClafferty TP, Toumi R, Deacon Get al., 2012,

    The Bunburra Rockhole meteorite fall in SW Australia: fireball trajectory, luminosity, dynamics, orbit, and impact position from photographic and photoelectric records

    , METEORITICS & PLANETARY SCIENCE, Vol: 47, Pages: 163-185, ISSN: 1086-9379
  • Journal article
    Collins GS, Melosh HJ, Osinski GR, 2012,

    The Impact-Cratering Process

    , ELEMENTS, Vol: 8, Pages: 25-30, ISSN: 1811-5209
  • Conference paper
    Emmerton S, Muxworthy AR, Sephton MA, Williams Wet al., 2012,

    A relationship between biodegradation and magnetisation in oil sands

    , Magnetic Relaxation
  • Conference paper
    Almeida T, Muxworthy AR, Williams W, Dunin-Borkowski Ret al., 2012,

    Dynamic chemical processes examined by in situ TEM and the implications for investigating palaeomagnetism

    , Magnetic Relaxation
  • Conference paper
    Muxworthy AR, Evans ME, 2012,

    How well can “single crystals” record the geomagnetic field?

    , Magnetic Relaxation
  • Journal article
    Xue Z, Rehkaemper M, Schoenbaechler M, Statham PJ, Coles BJet al., 2012,

    A new methodology for precise cadmium isotope analyses of seawater

    , ANALYTICAL AND BIOANALYTICAL CHEMISTRY, Vol: 402, Pages: 883-893, ISSN: 1618-2642
  • Conference paper
    Miljkovic K, Collins GS, Chapman DJ, Patel MR, Proud WGet al., 2012,


    , 7th Biennial Conference of the American-Physical-Society-Topical-Group on Shock Compression of Condensed Matter, Publisher: AMER INST PHYSICS, ISSN: 0094-243X
  • Report
    Beaty DW, Kminek G, Allwood AC, Arvidson R, Borg LE, Farmer JD, Goesmann F, Grant JA, Hauber E, Murchie SL, Ori GG, Ruff SW, Rull F, Sephton MA, Sherwood Lollar B, Smith CL, Westall F, Pacros AE, Wilson MG, Meyer MA, Vago JL, Bass DS, Joudrier L, Laubach S, Feldman S, Trautner R, Milkovich SMet al., 2012,

    Report of the 2018 Joint Mars Rover Mission Joint Science Working Group (JSWG)

    , Publisher: Mars Exploration Analysis Group (MEPAG)
  • Journal article
    Viera da Silva N, Morgan JV, MacGregor L, Warner MRet al., 2012,

    A finite element multifrontal method for 3D CSEM modeling in the frequency domain

    , Geophysics, Vol: 77, Pages: E101-E115

    There has been a recent increase in the use of controlled-source electromagnetic (CSEM) surveys in the exploration for oil and gas. We developed a modeling scheme for 3D CSEM modeling in the frequency domain. The electric field was decomposed in primary and secondary components to eliminate the singularity originated by the source term. The primary field was calculated using a closed form solution, and the secondary field was computed discretizing a second-order partial differential equation for the electric field with the edge finite element. The solution to the linear system of equations was obtained using a massive parallel multifrontal solver, because such solvers are robust for indefinite and ill-conditioned linear systems. Recent trends in parallel computing were investigated for their use in mitigating the computational overburden associated with the use of a direct solver, and of its feasibility for 3D CSEM forward modeling with the edge finite element. The computation of the primary field was parallelized, over the computational domain and the number of sources, using a hybrid model of parallelism. When using a direct solver, the attainment of multisource solutions was only competitive if the same factors are used to achieve a solution for multi right-hand sides. This aspect was also investigated using the presented methodology. We tested our proposed approach using 1D and 3D synthetic models, and they demonstrated that it is robust and suitable for 3D CSEM modeling using a distributed memory system. The codes could thus be used to help design new surveys, as well to estimate subsurface conductivities through the implementation of an appropriate inversion scheme.

  • Book
    Elmore RD, Muxworthy AR, Aldana MM, Mena Met al., 2012,

    Remagnetization and chemical alteration of sedimentary rocks

    , London, Publisher: Geological Society
  • Journal article
    Chan HS, Martins Z, Sephton MA, 2012,

    Amino acid analysis of type 3 chondrites Colony, Ornans, Chainpur and Bishunpur

    , Meteoritics & Planetary Science, Vol: 47, Pages: 1502-1516, ISSN: 1086-9379

    The CO3s Colony and Ornans and LL3s Chainpur and Bishunpur were analyzed for the first time for amino acids using gas chromatography–mass spectrometry (GC-MS). Type 3 chondrites have relatively unaltered metamorphic and petrological histories. Chainpur was the most amino acid rich of the four type 3 chondrites with a total amino acid abundance of 3330 parts per billion (ppb). The other type 3 chondrites had total amino acid abundances that ranged from 660 to 1110 ppb. A d/l ratio of <0.7 for all proteic amino acids suggests at least some amino acid terrestrial contamination. However, a small fraction of indigenous extraterrestrial amino acids cannot be excluded because of the presence of the nonprotein amino acid α-aminoisobutyric acid (α-AIB), and unusually high relative abundances (to glycine) of β-alanine and γ-ABA. The comparisons between the free and total amino acid contents of the samples also indicate a low free/total amino acid ratio (ranging from about 1:4 in CO chondrites to about 1:50 in Chainpur), which indicate that amino acids are present mainly in the bound form and were made detectable after acid hydrolysis.

  • Journal article
    Larner F, Sampson B, Rehkamper M, Weiss D, Dainty J, O'Riodan S, Panetta T, Bain PGet al., 2012,

    High precision isotope measurements show poorer control of copper metabolism in Parkinsonism.

    , Movement Disorders
  • Journal article
    Court RW, Sephton MA, 2012,

    Extrasolar Planets And False Atmospheric Biosignatures: The Role Of Micrometeoroids

    , Planetary and Space Science, Vol: 73, Pages: 233-242, ISSN: 0032-0633

    The coexistence of oxygen and a reduced gas such as methane in the atmosphere of an extrasolar planet is considered to be strong evidence for the presence of a biosphere. Proposed spacecraft such as Darwin or Terrestrial Planet Finder are designed to be capable of spectroscopically characterising the atmospheres of exoplanets, detecting chemical disequilibrium indicative of life. However, methane can be produced by various abiological mechanisms, including the ablation of carbonaceous micrometeoroids upon atmospheric entry, and it is possible that extrasolar planets in dust-rich systems might receive enough micrometeoroidal infall to produce a false atmospheric biosignature. Here, we review the production of methane from carbonaceous meteoroids upon atmospheric ablation in our solar system and discuss its application to extrasolar planets. The current paucity of data regarding dust densities in systems possessing terrestrial planets in the habitable zones of their stars makes firm conclusions difficult. However, the data suggest that only very young systems possessing very dense debris disks, or systems undergoing reorganisation similar to the Late Heavy Bombardment in our early solar system, would be capable of producing sufficient methane to be mistaken for an atmospheric biosignature.

  • Journal article
    Lomax BH, Fraser WT, Harrington G, Blackmore S, Sephton MA, Harris NBWet al., 2012,

    A novel palaeoaltimetry proxy based on spore and pollen wall chemistry

    , Earth and Planetary Science Letters, Vol: 353-354, Pages: 22-28, ISSN: 0012-821X

    Understanding the uplift history and the evolution of high altitude plateaux is of major interest to a wide range of geoscientists and has implications for many disparate fields. Currently the majority of palaeoaltimetry proxies are based on detecting a physical change in climate in response to uplift, making the relationship between uplift and climate difficult to decipher. Furthermore, current palaeoaltimetry proxies have a low degree of precision with errors typically greater than 1 km. This makes the calculation of uplift histories and the identification of the mechanisms responsible for uplift difficult to determine. Here we report on advances in both instrumentation and our understanding of the biogeochemical structure of sporopollenin that are leading to the establishment of a new proxy to track changes in the flux of UV-B radiation over geological time. The UV-B proxy is based on quantifying changes in the concentration of UV-B absorbing compounds (UACs) found in the spores and pollen grains of land plants, with the relative abundances of UACs increasing on exposure to elevated UV-B radiation. Given the physical relationship between altitude and UV-B radiation, we suggest that the analysis of sporopollenin chemistry, specifically changes in the concentration of UACs, may offer the basis for the first climate independent palaeoaltimetry proxy. Owing to the ubiquity of spores and pollen in the fossil record, our proposed proxy has the potential to enable the reconstruction of the uplift history of high altitude plateaux at unprecedented levels of fidelity, both spatially and temporally.

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