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  • Journal article
    Sephton MA, Sims MR, Court RW, Luong D, Cullen DCet al., 2013,

    Searching for biomolecules on Mars: Considerations for Operation of a Life Marker Chip instrument

    , Planetary and Space Science, Vol: 86, Pages: 66-74, ISSN: 0032-0633

    The search for life on Mars requires instruments that detect organic matter and discriminate between potential sources. One such instrument is the Life Marker Chip that recognizes small molecules which are characteristic of particular organic provenances. The use of an antibody-based detection system requires the delivery of small organic compounds in a suitable solvent. Dedicated extraction protocols have been developed partly through the use of a Life Marker Chip breadboard system. Techniques which provide the strong diagnostic potential of the Life Marker Chip necessitate specific extraction protocols and appropriate sample types. Clay mineral-rich rocks are attractive targets owing to their i) association with liquid water, ii) propensity for organic matter and clay mineral co-deposition following transport from a wide hinterland, and iii) relatively large surface area and therefore potential for trapping/adsorption of organic materials. The most appropriate target organic compounds are the hydrocarbon-dominated lipids that can be highly diagnostic and have relatively high preservation potentials. The sample sites on Mars and sample preparation steps that are needed for successful detection require careful consideration. In this paper we explore the scientific results that may be obtained through the operation of a Life Marker Chip instrument on Mars.
  • Journal article
    Goldberg T, Gordon G, Izon G, Archer C, Pearce CR, McManus J, Anbar AD, Rehkaemper Met al., 2013,

    Resolution of inter-laboratory discrepancies in Mo isotope data: an intercalibration

    , JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, Vol: 28, Pages: 724-735, ISSN: 0267-9477
  • Journal article
    Potter RWK, Kring DA, Collins GS, Kiefer WS, McGovern PJet al., 2013,

    Numerical modeling of the formation and structure of the Orientale impact basin

    , Journal of Geophysical Research: Planets, Pages: n/a-n/a, ISSN: 2169-9100
  • Journal article
    Potter RWK, Collins GS, 2013,

    Numerical modeling of asteroid survivability and possible scenarios for the Morokweng crater-forming impact

    , Meteoritics & Planetary Science, Vol: 48, Pages: 744-757, ISSN: 1945-5100
  • 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

    An outcrop of Wealden beds at Mupe Bay (UK) is associated with a key piece of evidence for the timing of hydrocarbon migration in the Wessex Basin. A conglomeratic bed contains oil-stained clasts and matrix that appear different upon superficial observation. Conventional interpretations assign differences to the erosion and transport of oil-cemented clasts by Wealden rivers before their incorporation into a later stained conglomeratic bed. This scenario constrains the onset of oil migration in the basin to the Early Cretaceous; however, arguments have been put forward for single phase staining.Magnetic information may provide new ways to examine the Mupe Bay record of oil migration. Migrating fluids such as hydrocarbons have been shown to cause chemical conditions suitable for the alteration or formation of authigenic magnetite resulting in associated chemical remanent magnetization (CRM). Magnetic characterization reveals both the matrix and clasts contain multi-domain magnetite but abundant hematite only exists within the clasts. Hysteresis parameters show the matrix has more multi-domain and likely larger magnetic grains than the clasts.Magnetic directions are different in the clasts and matrix supporting a two-phase oil-staining event. Moreover, paleomagnetic directions for the clasts after tilt correction (82.6°N and 155.2°E) are consistent with biodegradation processes in the Early Cretaceous. Consistent directions in separate clasts imply the biodegradation and magnetite formation took place following transportation and incorporation of the oil-cemented clasts into the conglomerate bed. Magnetic directions reveal that the Mupe Bay matrix has a remanent magnetization corresponding to today’s magnetic field, confirming the matrix represents an active oil seep.This study represents an unprecedented use of magnetic data to date the onset of oil migration in a basin. The classic two-stage oil-staining scenario, which constrains the onset in the Wesse
  • Report
    Mustard JF, Adler M, Allwood A, Bass DS, Beaty DW, Bell JF, Brinckerhoff WB, Carr M, Des Marais DJ, Drake B, Edgett KS, Eigenbrode J, Elkins-Tanton LT, Grant JA, Milkovich SM, Ming D, Moore C, Murchie S, Onstott TC, Ruff SW, Sephton MA, Steele A, Treiman Aet al., 2013,

    Report of the Mars 2020 Science Definition Team

    , Report of the Mars 2020 Science Definition Team, Publisher: Mars Exploration Analysis Group (MEPAG)
  • Journal article
    Wainipee W, Cuadros J, Sephton MA, Unsworth C, Gill MG, Strekopytov S, Weiss DJet al., 2013,

    The effects of oil on As(V) adsorption on illite, kaolinite, montmorillonite and chlorite

    , Geochimica et Cosmochimica Acta, Vol: 121, Pages: 487-502, ISSN: 0016-7037

    The effect of oil on As(V) adsorption on clay minerals has been investigated using batch experiments at low and high pH, NaCl concentration and oil contents. Four clay minerals were chosen because of their abundance in sediments and their different crystal chemistry: illite, kaolinite, montmorillonite, and chlorite. The values for pH were 4 and 8 and salt concentrations were 0.001 and 0.7 M NaCl to appreciate the effects of changing salinity, e.g from fresh water to seawater conditions. For the coating experiments, a well-characterised oil was used to survey the main effects of complex organic mixtures on adsorption and oil to clay mineral (w/w) ratios were 0.0325 and 0.3250. As(V) adsorption increased with increasing NaCl concentration, suggesting that the mechanisms of As(V) adsorption are related to the formation of inner-sphere complexes in which Na+ ions act as bridges between the clay surface and the As(V) anions. Cation bridging is also indicated by zeta potential measurements which show that higher NaCl concentrations along with the presence of As(V) can cause the clay particles and adsorbed ions to have a more negative overall charge. Adsorption is lower at higher pH due to the reduced number of positively charged sites on the edge of clay mineral layers. Oil coating reduces As(V) adsorption by decreasing the available surface area of clay minerals, except in the case of oil-coated montmorillonite, where surface area following dispersion in water is increased. The main variables controlling As(V) adsorption are surface area and surface charge density, as confirmed by a simplified quantitative model. These findings advance our ability to predict the effects of complex pollution events in various freshwater and marine settings.
  • Journal article
    Howard KT, Bailey MJ, Berhanu D, Bland PA, Cressey G, Howard LE, Jeynes C, Mathewman R, Martins Z, Sephton MA, Stolojan V, Verchovsky Set al., 2013,

    Biomass preservation in impact melt ejecta

    , Nature Geoscience

    Meteorites can have played a role in the delivery of life to Earth only if organic compounds are able to survive the high pressures and temperatures of an impact event. Although experimental impact studies have reported the survival of organics there are uncertainties in scaling experimental conditions to those of a meteorite impact on Earth and organic matter has not been found in highly shocked impact materials in a natural setting. Impact glass linked to the 1.2-km-diameter Darwin crater in western Tasmania is strewn over an area exceeding 400 km2 and is thought to have been ejected by a meteorite impact about 800 kyr ago into terrain consisting of rainforest and swamp. Here we use pyrolysis–gas chromatography–mass spectrometry to show that biomarkers representative of plant species in the local ecosystem—including cellulose, lignin, aliphatic biopolymer and protein remnants—survived the Darwin impact. We find that inside the impact glass the organic components are trapped in porous carbon spheres.We propose that the organic material was captured within impact melt and preserved when the melt quenched to glass, preventing organic decomposition since the impact. We suggest that organic material can survive capture and transport in products of extreme impact processing, at least for a Darwin-sized impact event.
  • Conference paper
    Dodd S, Muxworthy AR, Mac Niocaill C, 2013,

    Taking the pulse of the Parana-Etendeká large igneous province (poster)

    , IAGA
  • Journal article
    Potter RWK, Kring DA, Collins GS, 2013,

    Quantifying the attenuation of structural uplift beneath large lunar craters

    , Geophysical Research Letters, Vol: 40, Pages: 5615–5620-5615–5620, ISSN: 1944-8007

    Terrestrial crater observations and laboratory experiments demonstrate that target material beneath complex impact craters is uplifted relative to its preimpact position. Current estimates suggest maximum uplift is one tenth of the final crater diameter for terrestrial complex craters and one tenth to one fifth for lunar central peak craters. These latter values are derived from an analytical model constrained by observations from small craters and may not be applicable to larger complex craters and basins. Here, using numerical modeling, we produce a set of relatively simple analytical equations that estimate the maximum amount of structural uplift and quantify the attenuation of uplift with depth beneath large lunar craters.
  • Journal article
    Elbeshausen D, Wünnemann K, Collins GS, 2013,

    The transition from circular to elliptical impact craters

    , Journal of Geophysical Research: Planets, Vol: 118, Pages: 2295–2309-2295–2309, ISSN: 2169-9100

    Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces. Nevertheless, a better understanding of the formation of these craters may significantly contribute to our overall understanding of hypervelocity impact cratering. The existence of elliptical craters raises a number of questions: Why do some impacts result in a circular crater whereas others form elliptical shapes? What conditions promote the formation of elliptical craters? How does the formation of elliptical craters differ from those of circular craters? Is the formation process comparable to those of elliptical craters formed at subsonic speeds? How does crater formation work at the transition from circular to elliptical craters? By conducting more than 800 three-dimensional (3-D) hydrocode simulations, we have investigated these questions in a quantitative manner. We show that the threshold angle for elliptical crater generation depends on cratering efficiency. We have analyzed and quantified the influence of projectile size and material strength (cohesion and coefficient of internal friction) independently from each other. We show that elliptical craters are formed by shock-induced excavation, the same process that forms circular craters and reveal that the transition from circular to elliptical craters is characterized by the dominance of two processes: A directed and momentum-controlled energy transfer in the beginning and a subsequent symmetric, nearly instantaneous energy release.
  • Journal article
    Larner F, Dogra Y, Dybowska A, Fabrega J, Stolpe B, Bridgestock LJ, Goodhead R, Weiss DJ, Moger J, Lead JR, Valsami-Jones E, Tyler CR, Galloway TS, Rehkaemper Met al., 2012,

    Tracing Bioavailability of ZnO Nanoparticles Using Stable Isotope Labeling

    , ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 46, Pages: 12137-12145, ISSN: 0013-936X
  • Book chapter
    Elmore RD, Muxworthy AR, Aldana MM, 2012,

    Remagnetization and chemical alteration of sedimentary rocks

    , Remagnetization and Chemical Alteration of Sedimentary Rocks, Editors: Elmore, Muxworthy, Aldana, Mena, London, Publisher: Geological Society
  • Journal article
    Chang L, Roberts AP, Williams W, Fitz Gerald JD, Larrasoana JC, Jovane L, Muxworthy ARet al., 2012,

    Giant magnetofossils and hyperthermal events

    , Earth and Planetary Science Letters, Vol: 351-352, Pages: 258-269
  • Journal article
    Potter RWK, Kring DA, Collins GS, Kiefer WS, McGovern PJet al., 2012,

    Estimating transient crater size using the crustal annular bulge: Insights from numerical modeling of lunar basin-scale impacts

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 39, ISSN: 0094-8276
  • Conference paper
    Almeida TP, Muxworthy AR, Williams W, Dunin-Borkowski Ret al., 2012,

    Dynamic exsolution of titanomagnetites and their associated magnetic response examined by complementary environmental TEM and off-axis electron holography

    , European Microscopy Congress
  • Journal article
    Boyle EA, John S, Abouchami W, Adkins JF, Echegoyen-Sanz Y, Ellwood M, Flegal AR, Fornace K, Gallon C, Galer S, Gault-Ringold M, Lacan F, Radic A, Rehkamper M, Rouxel O, Sohrin Y, Stirling C, Thompson C, Vance D, Xue Z, Zhao Yet al., 2012,

    GEOTRACES IC1 (BATS) contamination-prone trace element isotopes Cd, Fe, Pb, Zn, Cu, and Mo intercalibration

    , LIMNOLOGY AND OCEANOGRAPHY-METHODS, Vol: 10, Pages: 653-665, ISSN: 1541-5856
  • Conference paper
    Giscard MD, Hammond SJ, Bland PA, Benedix GK, Rogers NW, Russell SS, Genge MJ, Rehkaemper Met al., 2012,

    TRACE ELEMENT COMPOSITION OF METAL AND SULPHIDES IN IRON METEORITES DETERMINED USING ICP-MS

    , 75th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A149-A149, ISSN: 1086-9379
  • Conference paper
    Genge MJ, 2012,

    THE ATMOSPHERIC ENTRY AND ABUNDANCE OF BASALTIC MICROMETEORITES

    , 75th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: A145-A145, ISSN: 1086-9379
  • Book chapter
    Emmerton S, Muxworthy AR, Sephton MA, 2012,

    Magnetic characterization of oil sands at Osmington Mills and Mupe Bay, Wessex Basin, UK

    , Remagnetization and Chemical Alteration of Sedimentary Rocks, Editors: Elmore, Muxworthy, Aldana, Mena, Elmore, Muxworthy, Aldana, Mena, London, Publisher: Geological Society, Pages: 189-198

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