Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Lewis JMT, Najorka J, Watson JS, Sephton MAet al., 2018,

    The search for Hesperian organic matter on Mars: Pyrolysis studies of sediments rich in sulfur and iron

    , Astrobiology, Vol: 18, Pages: 454-464, ISSN: 1531-1074

    Jarosite on Mars is of significant geological and astrobiological interest as it forms in acidic aqueous conditions that are potentially habitable for acidophilic organisms. Jarosite can provide environmental context and may host organic matter. The most common analytical technique used to search for organic molecules on the surface of Mars is pyrolysis. However, thermal decomposition of jarosite produces oxygen, which degrades organic signals. At pH values greater than 3 and high water to rock ratios jarosite has a close association with goethite. Hematite can form by dehydration of goethite or directly from jarosite under certain aqueous conditions. Goethite and hematite are significantly more amenable for pyrolysis experiments searching for organic matter than jarosite. Analysis of the mineralogy and organic chemistry of samples from a natural acidic stream revealed a diverse response for organic compounds during pyrolysis of goethite-rich layers but a poor response for jarosite-rich or mixed jarosite-goethite units. Goethite units that are associated with jarosite but do not contain jarosite themselves should be targeted for organic detection pyrolysis experiments on Mars. These findings are extremely timely as future exploration targets for Mars Science Laboratory include Hematite Ridge, which may have formed from goethite precursors.

  • Journal article
    Najorka J, Lewis JMT, Spratt J, Sephton MAet al., 2016,

    Single-crystal X-ray diffraction study of synthetic sodium-hydronium jarosite

    , Physics and Chemistry of Minerals, Vol: 43, Pages: 377-386, ISSN: 1432-2021

    Na–H3O jarosite was synthesized hydrothermally at 413 K for 8 days and investigated using single-crystal X-ray diffraction (XRD) and electron microprobe analysis (EMPA). The chemical composition of the studied crystal is [Na0.57(3) (H3O)0.36 (H2O)0.07]A Fe2.93(3) (SO4)2 (OH)5.70 (H2O)0.30, and Fe deficiency was confirmed by both EMPA and XRD analysis. The single-crystal XRD data were collected at 298 and 102 K, and crystal structures were refined in space group R3¯¯¯mR3¯m . The room-temperature data match structural trends of the jarosite group, which vary linearly with the c axis. The low-temperature structure at 102 K shows an anisotropic decrease in the unit cell parameters, with c and a decreasing by 0.45 and 0.03 %, respectively. Structural changes are mainly confined to the A site environment. Only minor changes occur in FeO6 and SO4 polyhedra. The structure responds upon cooling by increasing bond length distortion and by decreasing quadratic elongation of the large AO12 polyhedra. The structural parameters at low temperature follow very similar patterns to structural changes that correspond to compositional variation in the jarosite group, which is characterised by the flexibility of AO12 polyhedra and rigidity of Fe(OH)4O2–SO4 layers. The most flexible areas in the jarosite structure are localized at AO12 edges that are not shared with neighbouring FeO6 octahedra. Importantly, for the application of XRD in planetary settings, the temperature-related changes in jarosite can mimic compositional change.

  • Journal article
    Luong D, Court RW, Sims MR, Cullen DC, Sephton MAet al., 2014,

    Extracting organic matter on Mars: A comparison of methods involving subcritical water, surfactant solutions and organic solvents

    , Planetary and Space Science, Vol: 99, Pages: 19-27, ISSN: 0032-0633
  • Journal article
    Montgomery W, Lerch P, Sephton MA, 2014,

    In-situ vibrational optical rotatory dispersion of molecular organic crystals at high pressures

    , Analytica Chimica Acta, Vol: 842, Pages: 51-56, ISSN: 0003-2670
  • Journal article
    Court RW, Sims MR, Cullen DC, Sephton MAet al., 2014,

    Searching for Life on Mars: Degradation of Surfactant Solutions Used in Organic Extraction Experiments

    , Astrobiology, Vol: 14, Pages: 733-752, ISSN: 1531-1074
  • Journal article
    Sephton MA, 2014,

    Astrobiology can help space science, education and the economy

    , Space Policy, Vol: 30, Pages: 146-148, ISSN: 0265-9646
  • Journal article
    Sephton MA, Carter JN, 2014,

    Statistics Provide Guidance for Indigenous Organic Carbon Detection on Mars Missions

    , Astrobiology, Vol: 14, Pages: 706-713, ISSN: 1531-1074
  • Journal article
    Montgomery W, Watson JS, Sephton MA, 2014,

    An organic cosmo-barometer: Distinct pressure and temperature effects for methyl substituted polycyclic aromatic hydrocarbons

    , Astrophysical Journal, Vol: 784, ISSN: 0004-637X

    There are a number of key structures that can be used to reveal the formation and modification history of organic matter in the cosmos. For instance, the susceptibility of organic matter to heat is well documented and the relative thermal stabilities of different isomers can be used as cosmothermometers. Yet despite being an important variable, no previously recognized organic marker of pressure exists. The absence of a pressure marker is unfortunate considering our ability to effectively recognize extraterrestrial organic structures both remotely and in the laboratory. There are a wide variety of pressures in cosmic settings that could potentially be reflected by organic structures. Therefore, to develop an organic cosmic pressure marker, we have used state-of-the-art diamond anvil cell (DAC) and synchrotron-source Fourier transform infrared (FTIR) spectroscopy to reveal the effects of pressure on the substitution patterns for representatives of the commonly encountered methyl substituted naphthalenes, specifically the dimethylnaphthalenes. Interestingly, although temperature and pressure effects are concordant for many isomers, pressure appears to have the opposite effect to heat on the final molecular architecture of the 1,5-dimethylnaphthalene isomer. Our data suggest the possibility of the first pressure parameter or "cosmo-barometer" (1,5-dimethylnaphthalene/total dimethylnaphthalenes) that can distinguish pressure from thermal effects. Information can be obtained from the new pressure marker either remotely by instrumentation on landers or rovers or directly by laboratory measurement, and its use has relevance for all cases where organic matter, temperature, and pressure interplay in the cosmos. © 2014. The American Astronomical Society. All rights reserved.

  • Journal article
    Fraser WT, Watson JS, Sephton MA, Lomax BH, Harrington G, Gosling WD, Self Set al., 2014,

    Changes in spore chemistry and appearance with increasing maturity

    , Review of Palaeobotany and Palynology, Vol: 201, Pages: 41-46, ISSN: 0034-6667
  • 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.

  • Book chapter
    Sephton MA, 2014,

    Organic Geochemistry of Meteorites

    , Treatise on Geochemistry, Editors: Turekian, Publisher: Elsevier Science, Pages: 1-31
  • 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
    Howard K, Bailey MJ, Berhanu D, Bland PA, Cressey G, Howard LE, Jeynes C, Matthewman R, Martins Z, Sephton MA, Stolojan V, Verchovsky Set al., 2013,

    Biomass preservation in impact melt ejecta

    , Nature Geoscience
  • Journal article
    Olsson-Francis K, Watson JS, Cockell CS, 2013,

    Cyanobacteria isolated from the high-intertidal zone: a model for studying the physiological prerequisites for survival in low Earth orbit

    , International Journal of Astrobiology, Vol: 12, Pages: 292-303, ISSN: 1473-5504

    <jats:title>Abstract</jats:title><jats:p>Cyanobacteria are capable of surviving the adverse conditions of low Earth orbit (LEO). We have previously demonstrated that <jats:italic>Gloeocapsa</jats:italic> strain OU_20, <jats:italic>Chroococcidiopsis</jats:italic> and akinetes of <jats:italic>Anabaena cylindrica</jats:italic> were able to survive 548 days of exposure to LEO. Motivated by an interest to understand how cyanobacteria can survive in LEO, we studied the strategies that <jats:italic>Gloeocapsa</jats:italic> strain OU_20 employs to survive in its natural environment, the upper region of the intertidal zone. Here, cyanobacteria are exposed to fluctuations in temperature, UV radiation, desiccation and salinity. We demonstrated that an increase in salinity from 6.5‰ (BG-11 medium) to 35.7‰ (similar to that of seawater), resulted in increased resistance to UV radiation (254 nm), vacuum (0.7×10<jats:sup>−3</jats:sup>±0.01 kPa) and cold temperatures (–20 °C). Concomitantly, biochemical analyses demonstrated that the amount of fatty acids and mycosporine-like amino acids (a UV absorbing pigment) were higher in the stressed cells. Morphological analysis demonstrated that the electron density and thickness of the mucilaginous sheath were also greater than in the control cells. Yet, the control and stressed cells both formed aggregates. As a result of studying the physiological adaptation of <jats:italic>Gloeocapsa</jats:italic> strain OU_20 in response to salinity, we postulate that survival in the high-intertidal zone and LEO involves a dense extracellular mucilaginous sheath and the formation of aggregates. We conclude that studying the physiological adaptation of cyanobacteria in the intertidal zone provides insight into understanding survival in LEO.</jats:p>

  • 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
    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
  • 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
  • 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
  • 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.

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=419&limit=20&respub-action=search.html Current Millis: 1573682202373 Current Time: Wed Nov 13 21:56:42 GMT 2019