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  • Journal article
    Fraser WT, Lomax BH, Jardine PE, Gosling WD, Sephton MAet al., 2014,

    Pollen and spores as a passive monitor of ultraviolet radiation

    , Frontiers in Ecology and Evolution, Vol: 2

    Sporopollenin is the primary component of the outer walls of pollen and spores. The chemical composition of sporopollenin is responsive to levels of ultraviolet (UV) radiation exposure, via a concomitant change in the concentration of phenolic compounds. This relationship offers the possibility of using fossil pollen and spore chemistry as a novel proxy for past UV flux. Phenolic compounds in sporopollenin can be quantified using Fourier Transform infrared spectroscopy. The high potential for preservation of pollen and spores in the geologic record, and the conservative nature of sporopollenin chemistry across the land plant phylogeny, means that this new proxy has the potential to reconstruct UV flux over much longer timescales than has previously been possible. This new tool has important implications for understanding the relationship between UV flux, solar insolation and climate in the past, as well as providing a possible means of assessing paleoaltitude, and ozone thickness.

  • Conference paper
    Montgomery W, Sephton MA, Watson J, Zeng Het al., 2014,

    The Effects Of Minerals On Heavy Oil And Bitumen Chemistry When Recovered Using Steam-assisted Methods

    , SPE Heavy Oil Conference-Canada

    The production of gaseous sulfur-containing species during the steam-assisted recovery of heavy oil and bitumen have important consequences for both economics and safety. Factors such as the effects of mineral matrices require laboratory data to produce accurate models. To study mineral effects on gas production we studied a well-characterized oil-containing core and the isolated crude oil from that core. The samples were run at 250-300°C in the continued presence of liquid water for 24 hours. The reaction products of all experiments include gases, oil flotate, oil sinkate, water-soluble products, and water- insoluble residues. All reaction products were studied with a variety of analytical techniques, including FTIR spectroscopy, chromatographic fractionation (SARA analysis), GC-MS, pyrolysis GCMS and GC-FPD/TCD. These techniques were applied to whole oil, maltenes and asphaltene fractions. Physical properties including viscosity and density were also measured. Our data provide insights into the physical and chemical consequences of steam assisted recovery of heavy oils and bituments from sedimentary rock reservoirs and reveal that geological and geochemical context is an essential consideration.

  • Journal article
    Almeida TP, Muxworthy A, Williams W, Kasama T, Dunin-Borkowski Ret al., 2014,

    Magnetic characterization of synthetic titanomagnetites: Quantifying the recording fidelity of ideal synthetic analogues

    , Geochemistry Geophysics Geosystems, Vol: 15, Pages: 161-175
  • Book chapter
    Sephton MA, 2014,

    Organic Geochemistry of Meteorites

    , Treatise on Geochemistry, Editors: Turekian, Publisher: Elsevier Science, Pages: 1-31
  • Journal article
    Neal WD, Appleby-Thomas GJ, Collins GS, 2014,

    Meso-scopic deformation in brittle granular materials

    , 18TH APS-SCCM AND 24TH AIRAPT, PTS 1-19, Vol: 500, ISSN: 1742-6588
  • Journal article
    Ciesla FJ, Davison TM, Collins GS, O'Brien DPet al., 2013,

    Thermal consequences of impacts in the early Solar System.

    , Meteoritics and Planetary Science, Vol: 48, Pages: 2559-2567, ISSN: 1086-9379
  • Conference paper
    Almeida TP, Muxworthy AR, Wiliams W, 2013,

    Oxidation of pseudo-single domain Fe3O4 particles and associated magnetic response examined by environmental TEM and off-axis electron holography (poster)

    , AGU Fall
  • Conference paper
    Mac Niocaill C, Dodd S, McClelland E, Muxworthy AR, Paterson GAet al., 2013,

    Paleomagnetically Determined Emplacement temperatures of the Explosive cycles of Santorini (poster)

    , AGU Fall
  • Journal article
    Martins Z, Price MC, Goldman N, Sephton MA, Burchell MJet al., 2013,

    Shock synthesis of amino acids from impacting cometary and icy planet surface analogues

    , Nature Geoscience, Vol: 6, Pages: 1045-1049, ISSN: 1752-0894
  • Journal article
    Morgan J, Artemieva N, Goldin T, 2013,

    Revisiting wildfires at the K‐Pg boundary

    , Journal of Geophysical Research: Biogeosciences, Vol: 118, Pages: 1508-1520, ISSN: 2169-8953

    <jats:title>Abstract</jats:title><jats:p>The discovery of large amounts of soot in clays deposited at the Cretaceous‐Paleogene (K‐Pg) boundary and linked to the ~65 Ma Chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact. Subsequently, several lines of evidence, including the lack of charcoal in North American sites, were used to argue against global wildfires. Close to the impact site fires are likely to be directly ignited by the impact fireball, whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta. To‐date, models of the latter have yet to take into account that ejection—and thus the emission of thermal radiation—is asymmetric and dependent on impact angle. Here, we model: (1) the impact and ejection of material, (2) the ballistic continuation of ejecta around a spherical Earth, and (3) the thermal pulse delivered to the Earth's surface when ejecta reenters the atmosphere. We find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from Chicxulub, whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter. Our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry, but that the nonuniform distribution of thermal radiation across the surface of the Earth is inconsistent with the ignition of fires globally as a direct and immediate result of the Chicxulub impact. Instead, we propose that the desiccation of flora by ejecta reentry, as well as the effects of postimpact global cooling/darkness, left much of the terrestrial flora prone to fires, and that the volume of soot in the global K‐Pg layer is explained by a combination of syn‐ and postimpact wildfires.</jats:p>

  • Journal article
    Muxworthy AR, Williams W, Roberts AP, Winklhofer M, Chang L, Posfai Met al., 2013,

    Critical single domain grain sizes in chains of interacting greigite particles: Implications for magnetosome crystals

    , GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 14, Pages: 5430-5441, ISSN: 1525-2027
  • Journal article
    Xue Z, Rehkaemper M, Horner TJ, Abouchami W, Middag R, van de Flierdt T, de Baar HJWet al., 2013,

    Cadmium isotope variations in the Southern Ocean

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 382, Pages: 161-172, ISSN: 0012-821X
  • Journal article
    Miljkovic K, Wieczorek MA, Collins GS, Laneuville M, Neumann GA, Melosh HJ, Solomon SC, Phillips RJ, Smith DE, Zuber MTet al., 2013,

    Asymmetric Distribution of Lunar Impact Basins Caused by Variations in Target Properties

    , Science, Vol: 342, Pages: 724-726, ISSN: 0036-8075

    Maps of crustal thickness derived from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission revealed more large impact basins on the nearside hemisphere of the Moon than on its farside. The enrichment in heat-producing elements and prolonged volcanic activity on the lunar nearside hemisphere indicate that the temperature of the nearside crust and upper mantle was hotter than that of the farside at the time of basin formation. Using the iSALE-2D hydrocode to model impact basin formation, we found that impacts on the hotter nearside would have formed basins with up to twice the diameter of similar impacts on the cooler farside hemisphere. The size distribution of lunar impact basins is thus not representative of the earliest inner solar system impact bombardment.

  • Journal article
    Morgan JV, Warner MR, Bell R, Ashley J, Barnes D, Little R, Roele K, Jones Cet al., 2013,

    Next-generation seismic experiments: wide-angle, multi-azimuth,three-dimensional, full-waveform inversion

    , Geophysical Journal International, Vol: in press

    Full-waveform inversion (FWI) is an advanced seismic imaging technique that has recentlybecome computationally feasible in three dimensions, and that is being widely adopted andapplied by the oil and gas industry. Here we explore the potential for 3-D FWI, when combinedwith appropriate marine seismic acquisition, to recover high-resolution high-fidelity P-wavevelocity models for subsedimentary targets within the crystalline crust and uppermost mantle.We demonstrate that FWI is able to recover detailed 3-D structural information within aradially faulted dome using a field data set acquired with a standard 3-D petroleum-industrymarine acquisition system. Acquiring low-frequency seismic data is important for successfulFWI; we show that current acquisition techniques can routinely acquire field data from airgunsat frequencies as low as 2 Hz, and that 1 Hz acquisition is likely to be achievable using oceanbottomhydrophones in deep water. Using existing geological and geophysical models, weconstruct P-wave velocity models over three potential subsedimentary targets: the Soufri`ereHills Volcano on Montserrat and its associated crustal magmatic system, the crust and uppermostmantle across the continent–ocean transition beneath the Campos Basin offshore Brazil,and the oceanic crust and uppermost mantle beneath the East Pacific Rise mid-ocean ridge.Weuse these models to generate realistic multi-azimuth 3-D synthetic seismic data, and attempt toinvert these data to recover the original models.We explore resolution and accuracy, sensitivityto noise and acquisition geometry, ability to invert elastic data using acoustic inversion codes,and the trade-off between low frequencies and starting velocity model accuracy.We show thatFWI applied to multi-azimuth, refracted, wide-angle, low-frequency data can resolve featuresin the deep crust and uppermost mantle on scales that are significantly better than can beachieved by any other geophysical technique, and that these results ca

  • Conference paper
    Almeida TP, Muxworthy AR, Williams W, Dunin-Borkowski Ret al., 2013,

    Visualisation of nano-scale magnetic fields

    , Current Research in Magnetism Meeting
  • Journal article
    Nielsen SG, Wasylenki LE, Rehkaemper M, Peacock CL, Xue Z, Moon EMet al., 2013,

    Towards an understanding of thallium isotope fractionation during adsorption to manganese oxides

    , GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 117, Pages: 252-265, ISSN: 0016-7037
  • Journal article
    Davison TM, O'Brien DP, Ciesla FJ, Collins GSet al., 2013,

    The early impact histories of meteorite parent bodies

    , Meteoritics and Planetary Science, Vol: 48, Pages: 1894-1918, ISSN: 1086-9379

    We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces — compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 -- 5\% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75\% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.

  • Journal article
    Emmerton S, Muxworthy AR, Sephton MA, 2013,

    A magnetic solution to the Mupe Bay mystery

    , Marine and Petroleum Geology, Vol: 46, Pages: 165-172, ISSN: 0264-8172
  • Journal article
    Khan FR, Laycock A, Dybowska A, Larner F, Smith BD, Rainbow PS, Luoma SN, Rehkaemper M, Valsami-Jones Eet al., 2013,

    Stable Isotope Tracer To Determine Uptake and Efflux Dynamics of ZnO Nano- and Bulk Particles and Dissolved Zn to an Estuarine Snail

    , ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 47, Pages: 8532-8539, ISSN: 0013-936X
  • Conference paper
    Muxworthy AR, Evans ME, King JG, 2013,

    A Preisach approach to cooling rate corrections: A case study the late-Archaean Modipe Gabbro, Botswana

    , IAGA

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