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  • Journal article
    Emmerton S, Muxworthy AR, Sephton MA, Aldana M, Costanzo-Alvarez V, Bayona G, Williams Wet al., 2013,

    Correlating biodegradation to magnetization in oil bearing sedimentary rocks

    , GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 112, Pages: 146-165, ISSN: 0016-7037
  • Conference paper
    Martins Z, Modica P, Sephton MA, Zanda B, d'Hendecourt Let al., 2013,


    , 76th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: A236-A236, ISSN: 1086-9379
  • Journal article
    Carter JN, Sephton MA, 2013,

    A Bayesian statistical assessment of representative samples for asteroidal or meteoritical material

    , Meteoritics & Planetary Science, Vol: 48, Pages: 976-996, ISSN: 1086-9379

    <jats:title>Abstract</jats:title><jats:p>Primitive substances in asteroid and meteorite materials represent a record of early solar system evolution. To allow the study of these materials, they must be collected and transferred to the laboratory. Collection during sample return missions requires an assessment of the size of samples needed. Meteorite falls or finds must be subdivided into appropriate subsamples for analysis by successive generations of scientists. It is essential, therefore, to determine a representative mass or volume at which the collected or allocated sample is representative of the whole. For the first time, we have used a Bayesian statistical approach and a selected meteorite sample, Murchison, to identify a recommended smallest sample mass that can be used without interferences from sampling bias. Enhancing background knowledge to inform sample selection and analysis is an effective means of increasing the probability of obtaining a positive scientific outcome. The influence of the subdivision mechanism when preparing samples for distribution has also been examined. Assuming a similar size distribution of fragments to that of the Murchison meteorite, cubes can be similarly representative as fragments, but at orders of magnitude smaller sizes. We find that: (1) at all defined probabilities (90%, 95%, and 99%), nanometer‐sized particles (where the axes of a three‐dimensional sample are less that a nanometer in length) are never representative of the whole; (2) at the intermediate and highest defined probabilities (95% and 99%), micrometer‐sized particles are never representative of the whole; and (3) for micrometer‐sized samples, the only sample that is representative of the whole is a cube and then only at a 90% probability. The difference between cubes and fragments becomes less important as sample size increases and any &gt;0.5 mm‐sized sample will be representative of the whole with a probability of 99.9%. The resul

  • Journal article
    Gilmour I, Gilmour M, Jolley D, Kelley S, Kemp D, Daly R, Watson Jet al., 2013,

    A high-resolution nonmarine record of an early Danian hyperthermal event, Boltysh crater, Ukraine

    , Geology
  • Journal article
    Sephton MA, 2013,

    Aromatic units from the macromolecular material in meteorites: Molecular probes of cosmic environments

    , Geochimica et Cosmochimica Acta, Vol: 107, Pages: 231-241, ISSN: 0016-7037
  • Conference paper
    Montgomery W, Sephton MA, Court RW, Watson JS, Zeng H, Rees Aet al., 2013,

    Quantitative Laboratory Assessment Of Aquathermolysis Chemistry During Steam-assisted Recovery Of Heavy Oils And Bitumen, With A Focus On Sulfur

    , SPE Heavy Oil Conference, Publisher: Society of Petroleum Engineers

    The production of gaseous sulfur-containing species during the steam-assisted recovery of heavy oil and bitumen presents problems owing to their toxicity, corrosion properties and odor. In order to quantitatively study aquathermolysis sulfur chemistry during the thermal (steam-assisted) recovery of heavy oils we have subjected a well-characterized and sulfur-rich bitumen core sample to 150 - 325°C and 70 - 1740 psia (0.48 - 12 MPa) conditions in the continued presence of liquid water for 24 hours. The reaction products include gases, oil flotate, oil sinkate, water-soluble products, and water- insoluble residues. All have been studied with a variety of analytical techniques, including FTIR spectroscopy, chromatographic fractionation (SARA analysis), GC-FPD and GC-MS. Moreover, these techniques have been extended to analysis of the asphaltene fractions. Results suggest that some in-situ upgrading of the oil occurs under these conditions; additionally, gaseous hydrogen sulfide is released at temperatures at and above 250 °C. Variations in the relative abundances of solubility classes and chemical fractions imply that the source of sulfur is via the thermal degradation of resins and/or asphaltenes. The experimental methods, results and quantification approach discussed herein will be useful to support the development of models for engineering design of facilities for the steam-assisted recovery of heavy oils and bitumen.

  • 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
    Sephton MA, James RH, Fehr MA, Bland PA, Gounelle Met al., 2013,

    Lithium isotopes as indicators of meteorite parent body alteration

    , Meteoritics & Planetary Science, Vol: 48, Pages: 872-878, ISSN: 1086-9379

    Hydrothermal processing on planetesimals in the early solar system produced new mineral phases, including those generated by the transformation of anhydrous silicates into their hydrated counterparts. Carbonaceous chondrites represent tangible remnants of such alteration products. Lithium isotopes are known to be responsive to aqueous alteration, yet previously recognized variability within whole rock samples from the same meteorite appears to complicate the use of these isotopes as indicators of processing by water. We demonstrate a new way to use lithium isotopes that reflects aqueous alteration in carbonaceous chondrites. Temperature appears to exert a control on the production of acetic acid-soluble phases, such as carbonates and poorly crystalline Fe-oxyhydroxides. Temperature and degree of water-rock interaction determines the amount of lithium isotope fractionation expressed as the difference between whole rock and acetic acid-leachable fractions. Using these features, the type 1 chondrite Orgueil (d7Li(whole rock) = 4.3&; D7Li(acetic-whole) = 1.2&) can be distinguished from the type 2 chondrites Murchison (d7Li(whole rock) = 3.8; D7Li(acetic whole) = 8.8&) and carbonate-poor Tagish Lake (d7Li(whole rock) = 4.3; D7Li(acetic-whole) = 9.4&). This initial study suggests that lithium isotopes have the potential to reveal the role of liquid water in the early solar system.

  • Journal article
    Sephton MA, 2013,

    Pyrolysis, spectroscopy and extraterrestrial organic matter

    , SpectroscopyEurope, Vol: 25, Pages: 6-11, ISSN: 0966-0941
  • Journal article
    Montgomery W, Court RW, Rees AC, Sephton MAet al., 2013,

    High temperature reactions of water with heavy oil and bitumen: insights into aquathermolysis chemistry during steam-assisted recovery

    , Fuel, Vol: 113, Pages: 426-426, ISSN: 0016-2361

    To better understand the hot water-mediated organic transformation process (aquathermolysis) that occurs during the steam-assisted recovery of heavy oils and bitumen we have performed a series of experiments that subject a heavy oil to progressively higher temperatures and pressures in the presence of liquid water. As temperature and pressure increases, from ambient conditions to 300 °C and 1250 psig (8.6 MPa), a floating oil (flotate) is generated and is composed of mostly aliphatic hydrocarbons that appear to be generated at the expense of polars and asphaltenes. Analyses of hopane maturity parameters for the flotate indicate lower temperatures than the starting material suggesting the liberation of hopanes and, therefore, other hydrocarbons, from asphaltenes. Infrared spectra confirm changes in overall organic constitution as the relative abundance of hydrocarbons to oxygen-containing functional groups increases in the flotate. At the highest temperatures and pressures (325 °C, 1750 psig (13.8 MPa)) the flotate is at a maximum relative amount, the untransformed heavy oil is at a minimum and significant amounts of methane are generated indicating the onset of cracking. Steam-assisted recovery of heavy oil, therefore, leads to changes in the chemical constitution of a number of chemical fractions generating a lighter oil and gases that must be taken into account when planning field operations for production.

  • Journal article
    Matthewman R, Martins Z, Sephton MA, 2013,

    Type IV kerogens as analogues for organic macromolecular materials in aqueously altered carbonaceous chondrites

    , Astrobiology, Vol: 13, Pages: 324-333, ISSN: 1531-1074
  • 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
    Sephton MA, Court RW, Lewis JM, Wright MC, Gordon PRet al., 2013,

    Selecting samples for Mars sample return: Triage by pyrolysis-FTIR

    , Planetary and Space Science, Vol: 78, Pages: 45-51, ISSN: 0032-0633

    A future Mars Sample Return mission will deliver samples of the red planet to Earth laboratories for detailed analysis. A successful mission will require selection of the best samples that can be used to address the highest priority science objectives including assessment of past habitability and evidence of life. Pyrolysis is a commonly used method for extracting organic information from rocks but is most often coupled with complex analytical steps such as gas chromatography and mass spectrometry. Pyrolysis-Fourier transform infrared spectroscopy is a less resource demanding method that still allows sample characterization. Here we demonstrate how pyrolysis-Fourier transform infrared spectroscopy could be used to triage samples destined to return to Earth, thereby maximising the scientific return from future sample return missions.

  • 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.

  • Journal article
    Sephton MA, Hazen RM, 2013,

    On the origins of deep hydrocarbons

    , Reviews in Mineralogy & Geochemistry, Vol: 75, Pages: 449-465, ISSN: 1529-6466

    Deep deposits of hydrocarbons, including varied reservoirs of petroleum and natural gas,represent the most economically important component of the deep carbon cycle. Yet despitetheir intensive study and exploitation for more than a century, details of the origins of somedeep hydrocarbons remain a matter of vocal debate in some scientific circles. This long andcontinuing history of controversy may surprise some readers, for the biogenic origins of “fossilfuels”—a principle buttressed by a vast primary scientific literature and established as textbookorthodoxy in North America and many other parts of the world—might appear to be settled fact.Nevertheless, conventional wisdom continues to be challenged by some scientists.The principal objectives of this chapter are: (1) to review the overwhelming evidence for thebiogenic origins of most known deep hydrocarbon reservoirs; (2) to present equally persuasiveexperimental, theoretical, and field evidence that components of some deep hydrocarbondeposits appear to have an abiotic origin; and (3) to suggest future studies that might help toachieve a more nuanced resolution of this sometimes polarized topic.

  • 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

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

    295 A novel palaeoaltimetry proxy based on spore and pollen wall chemistry

    , 日本花粉学会会誌, Vol: 58, Pages: 133-134, ISSN: 0387-1851
  • 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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