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Journal articleHenry DG, Watson JS, John CM, 2016,
Assessing and calibrating the ATR-FTIR approach as a carbonate rock characterization tool
, SEDIMENTARY GEOLOGY, Vol: 347, Pages: 36-52, ISSN: 0037-0738 -
Journal articleMontgomery WB, Watson JS, Potiszil C, et al., 2016,
Sporopollenin, a natural copolymer, is robust under high hydrostatic pressure
, Macromolecular Chemistry and Physics, Vol: 217, Pages: 2494-2500, ISSN: 1521-3935Lycopodium sporopollenin, a natural copolymer, shows exceptional stability underhigh hydrostatic pressures (10 GPa) as determined by in situ high pressuresynchrotron source FTIR spectroscopy. This stability is evaluated in terms of thecomponent compounds of the sporopollenin: p-coumaric acid, phloretic acid, ferulicacid, and palmitic and sebacic acids, which represent the additional n-acid and ndiacidcomponents. This high stability is attributed to interactions between thesecomponents, rather than the exceptional stability of any one molecular component.We propose a biomimetic solution for the creation of polymer materials that canwithstand high pressures for a multitude of uses in aeronautics, vascular autografts,ballistics and light-weight protective materials.
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Journal articleMontgomery W, Sephton MA, 2016,
Pressure effects in polycyclic aromatic nitrogenated heterocycles (PANHs): Diagnostic qualities and cosmobarometry potential
, The Astrophysical Journal, Vol: 819, ISSN: 0004-637XThe influence of polycyclic aromatic nitrogen heterocycles (PANHs), which have been suggested as contributors to the interstellar IR emission bands, on interstellar emission features is difficult to constrain because their infrared characteristics are strongly similar to those for polycyclic aromatic hydrocarbons (PAHs). One possible solution is to seek a means of visualising the presence of PANHs that provides information which is distinct from that for PAHs. Although PANHs and PAHs have similar infrared characteristics in many settings, this relationship may not be universally maintained. We have used in-situ high pressure synchrotron-source Fourier transform infrared (FTIR) spectroscopy to determine that the responses of two representative molecules, acridine and anthracene, differ at high pressures (> ca. 1 GPa). Because there are a number of high pressure environments that can be remotely observed by infrared spectroscopy they represent a potential to glimpse the distribution of PANHs across the Cosmos.
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Journal articleNajorka J, Lewis JMT, Spratt J, et al., 2016,
Single-crystal X-ray diffraction study of synthetic sodium-hydronium jarosite
, Physics and Chemistry of Minerals, Vol: 43, Pages: 377-386, ISSN: 1432-2021Na–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.
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Journal articleGordon PR, Sephton MA, 2016,
Rapid habitability assessment of Mars samples by pyrolysis-FTIR
, Planetary and Space Science, Vol: 121, Pages: 60-75, ISSN: 1873-5088Pyrolysis Fourier transform infrared spectroscopy (pyrolysis FTIR) is a potential sample selection method for Mars Sample Return missions. FTIR spectroscopy can be performed on solid and liquid samples but also on gases following preliminary thermal extraction, pyrolysis or gasification steps. The detection of hydrocarbon and non-hydrocarbon gases can reveal information on sample mineralogy and past habitability of the environment in which the sample was created. The absorption of IR radiation at specific wavenumbers by organic functional groups can indicate the presence and type of any organic matter present. Here we assess the utility of pyrolysis-FTIR to release water, carbon dioxide, sulphur dioxide and organic matter from Mars relevant materials to enable a rapid habitability assessment of target rocks for sample return. For our assessment a range of minerals were analysed by attenuated total reflectance FTIR. Subsequently, the mineral samples were subjected to single step pyrolysis and multi step pyrolysis and the products characterised by gas phase FTIR.Data from both single step and multi step pyrolysis-FTIR provide the ability to identify minerals that reflect habitable environments through their water and carbon dioxide responses. Multi step pyrolysis-FTIR can be used to gain more detailed information on the sources of the liberated water and carbon dioxide owing to the characteristic decomposition temperatures of different mineral phases. Habitation can be suggested when pyrolysis-FTIR indicates the presence of organic matter within the sample. Pyrolysis-FTIR, therefore, represents an effective method to assess whether Mars Sample Return target rocks represent habitable conditions and potential records of habitation and can play an important role in sample triage operations.
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Journal articleAbubakar R, Muxworthy AR, Sephton MA, et al., 2015,
Formation of magnetic minerals at hydrocarbon-generation conditions
, Marine and Petroleum Geology, Vol: 68, Pages: 509-519, ISSN: 0264-8172 -
Journal articleWatson JS, Sephton MA, 2015,
Heat, clay and aromatic units: a mechanism for making macromolecules in the early solar system
, Astrobiology, Vol: 15, Pages: 787-792, ISSN: 1557-8070The major organic component in carbonaceous chondrites is ahighly aromatic macromolecular material. Aromatic organic matter andphyllosilicates are co-located in these meteorites and it is possible that thephysical association represents a synthetic chemical relationship. To explore thepotential reactions that could take place to produce the aromatic macromolecularmaterial we heated various simple aromatic units in the presence ofmontmorillonite with different exchanged cations. The majority of cationexchanged montmorillonites tested, sodium-, aluminium-, iron-, nickel- andcobalt-rich montmorillonites, do not produce polymerisation products. By contrastFe3+ cation exchanged montmorillonite readily facilitates addition reactionsbetween aromatic hydrocarbons. A feasible mechanism for the process isoxidative coupling which involves a corresponding reduction of the Fe3+ cation to its Fe2+ counterpart. A similar reduction process for the other metal cations does not take place highlighting the importance of iron. This simple process is a feasible mechanism for the addition to the aromatic macromolecules such as thosefound in carbonaceous chondrites. The search for a relationship between Fe3+-richphyllosilicates and aromatic organic structures (particularly dimers, trimers and more polymerised forms) in carbonaceous chondrites would represent an effective test for constraining the role of clay catalysis in the early solar system.
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Conference paperAbubakar R, Muxworthy AR, Sephton M, et al., 2015,
Mapping Petroluem Migration Pathways Using Magnetics and Seismic Interpretations (poster)
, AGU Fall 2015 -
Journal articleMustafa KA, Sephton MA, Watson JS, et al., 2015,
Organic geochemical characteristics of black shales across the Ordovician-Silurian boundary in the Holy Cross Mountains, Central Poland
, Marine and Petroleum Geology, Vol: 66, Pages: 1042-1055, ISSN: 1873-4073Black shales in the Holy Cross Mountains area of Poland provide a record of environmental change across the Ordovician-Silurian boundary. The changing depositional conditions have generated a variation in organic matter contents above and below the boundary. Investigating the organic constitution of these black shales has the potential to reveal how their organic matter contents were generated and how suitable these rocks and their lateral equivalents may be for exploitation as shale gas reservoirs. One outcrop at the Holy Cross Mountains with a continuous section across the Ordovician-Silurian boundary occurs near the village of Bardo Stawy in the Kielce region, and contains sandy-silty mudstones, as well as grey and black shales. Organic geochemical analyses of samples at Bardo Stawy reveals low Total Organic Carbon (TOC) contents for Ordovician samples and higher TOC values for Silurian samples. Organic biomarkers indicate that the Ordovician rocks were deposited in a shallow-marine shelf setting, while the Silurian rocks were deposited in a deeper marine environment. The progressive increase in TOC from the uppermost Ordovician to the lowermost Silurian rocks reflects increasingly oxygen-poor depositional conditions during the post-glacial transgression. Following the deposition and preservation of organic matter in the Ordovician and Silurian rocks, these rocks were buried and subjected to thermal maturation. Rock Eval and biomarker thermal maturity parameters all indicate that the organic matter is mature and lies within the oil window. The Ordovician and Silurian shales have direct relevance to recent attempts to discover and exploit shale gas reservoirs in Poland. Our data and interpretations suggest that the relatively low TOC values (<2%) and low maturities for gas generation render these rocks unsuitable for commercial shale gas production. The progressive improvement in conditions for preserving organic matter across the Ordovician-Silurian boundary d
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Journal articleWright MC, Court RW, Kafantaris F-CA, et al., 2015,
A new rapid method for shale oil and shale gas assessment
, Fuel, Vol: 153, Pages: 231-239, ISSN: 0016-2361 -
Journal articleSephton MA, Carter JN, 2015,
The chances of detecting life on Mars
, PLANETARY AND SPACE SCIENCE, Vol: 112, Pages: 15-22, ISSN: 0032-0633- Author Web Link
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- Citations: 13
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Journal articleLuong D, Sephton MA, Watson JS, 2015,
Subcritical water extraction of organic matter from sedimentary rocks
, ANALYTICA CHIMICA ACTA, Vol: 879, Pages: 48-57, ISSN: 0003-2670- Author Web Link
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- Citations: 34
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Journal articleTorokova L, Watson J, Krcma F, et al., 2015,
Gas Chromatography Analysis of Discharge Products in N2-CH4 Gas Mixture at Atmospheric Pressure: Study of Mimic Titan's Atmosphere
, Contributions to Plasma Physics, Vol: 55, Pages: 470-480, ISSN: 0863-1042 -
Journal articleMatthewman R, Court RW, Crawford IA, et al., 2015,
The Moon as a Recorder of Organic Evolution in the Early Solar System: A Lunar Regolith Analog Study
, Astrobiology, Vol: 15, Pages: 154-168, ISSN: 1531-1074<jats:p>The organic record of Earth older than ∼3.8 Ga has been effectively erased. Some insight is provided to us by meteorites as well as remote and direct observations of asteroids and comets left over from the formation of the Solar System. These primitive objects provide a record of early chemical evolution and a sample of material that has been delivered to Earth's surface throughout the past 4.5 billion years. Yet an effective chronicle of organic evolution on all Solar System objects, including that on planetary surfaces, is more difficult to find. Fortunately, early Earth would not have been the only recipient of organic matter–containing objects in the early Solar System. For example, a recently proposed model suggests the possibility that volatiles, including organic material, remain archived in buried paleoregolith deposits intercalated with lava flows on the Moon. Where asteroids and comets allow the study of processes before planet formation, the lunar record could extend that chronicle to early biological evolution on the planets. In this study, we use selected free and polymeric organic materials to assess the hypothesis that organic matter can survive the effects of heating in the lunar regolith by overlying lava flows. Results indicate that the presence of lunar regolith simulant appears to promote polymerization and, therefore, preservation of organic matter. Once polymerized, the mineral-hosted newly formed organic network is relatively protected from further thermal degradation. Our findings reveal the thermal conditions under which preservation of organic matter on the Moon is viable. Key Words: Moon—Regolith—Organic preservation—Biomarkers. Astrobiology 15, 154–168.</jats:p>
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Journal articleSephton MA, Jiao D, Engel MH, et al., 2015,
Terrestrial acidification during the end-Permian biosphere crisis?
, Geology, Vol: 43, Pages: 159-162, ISSN: 1943-2682Excessive acid rainfall associated with emplacement of the Siberian Traps magmatic province is increasingly accepted as a major contributing factor to the end-Permian biosphere crisis. However, direct proxy evidence of terrestrial acidification is so far not available. In this paper, we seek to determine the probability that relative proportions of extractable monophenolic components from soil-derived organic matter in marine sediments provide a molecular proxy for estimating soil acidity. Intermittently low and high ratios of vanillic acid to vanillin detected in latest Permian and earliest Triassic deposits of the southern Alps, Italy, support concepts of pulses of severe acidification (pH <4) during the main phase of the biosphere crisis.
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Journal articleMontgomery WB, Sephton MA, Watson JS, et al., 2015,
Minimising hydrogen sulphide generation during steam assisted production of heavy oil
, Scientific Reports, Vol: 5, ISSN: 2045-2322The majority of global petroleum is in the form of highly viscous heavy oil. Traditionally heavy oil in sands at shallow depths is accessed by large scale mining activities. Recently steam has been used to allow heavy oil extraction with greatly reduced surface disturbance. However, in situ thermal recovery processes can generate hydrogen sulphide, high levels of which are toxic to humans and corrosive to equipment. Avoiding hydrogen sulphide production is the best possible mitigation strategy. Here we use laboratory aquathermolysis to reproduce conditions that may be experienced during thermal extraction. The results indicate that hydrogen sulphide generation occurs within a specific temperature and pressure window and corresponds to chemical and physical changes in the oil. Asphaltenes are identified as the major source of sulphur. Our findings reveal that for high sulphur heavy oils, the generation of hydrogen sulphide during steam assisted thermal recovery is minimal if temperature and pressure are maintained within specific criteria. This strict pressure and temperature dependence of hydrogen sulphide release can allow access to the world’s most voluminous oil deposits without generating excessive amounts of this unwanted gas product.
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Journal articleSephton MA, Watson JS, Meredith W, et al., 2015,
Multiple cosmic sources for meteorite macromolecular materials?
, Astrobiology, Vol: 15, ISSN: 1557-8070 -
Journal articleLewis JMT, Watson JS, Najorka J, et al., 2015,
Sulfate Minerals: A Problem for the Detection of Organic Compounds on Mars?
, Astrobiology, Vol: 15, ISSN: 1557-8070The search for in situ organic matter on Mars involves encounters with minerals and requires an understanding of their influence on lander and rover experiments. Inorganic host materials can be helpful by aiding the preservation of organic compounds or unhelpful by causing the destruction of organic matter during thermal extraction steps. Perchlorates are recognized as confounding minerals for thermal degradation studies. On heating, perchlorates can decompose to produce oxygen, which then oxidizes organic matter. Other common minerals on Mars, such as sulfates, may also produce oxygen upon thermal decay, presenting an additional complication. Different sulfate species decompose within a large range of temperatures. We performed a series of experiments on a sample containing the ferric sulfate jarosite. The sulfate ions within jarosite break down from 500 °C. Carbon dioxide detected during heating of the sample was attributed to oxidation of organic matter. A laboratory standard of ferric sulfate hydrate released sulfur dioxide from 550 °C, and an oxygen peak was detected in the products. Calcium sulfate did not decompose below 1000 ° C. Oxygen released from sulfate minerals may have already affected organic compound detection during in situ thermal experiments on Mars missions. A combination of preliminary mineralogical analyses and suitably selected pyrolysis temperatures may increase future success in the search for past or present life on Mars.
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Journal articleSephton MA, Lewis JMT, Watson JS, et al., 2014,
Perchlorate-induced combustion of organic matter with variable molecular weights: implications for Mars missions
, Geophysical Research Letters, Vol: 41, Pages: 7453-7460, ISSN: 1944-8007Instruments on the Viking landers and Curiosity rover analysed samples of Mars and detected carbon dioxide and organic compounds of uncertain origin. Mineral assisted reactions are leading to uncertainty, particularly those involving perchlorate minerals which thermally decompose to produce chlorine and oxygen which can then react with organic matter. Mineral assisted reactions produce organochlorine compounds and carbon dioxide. Although generally considered a problem for interpretation, the release profiles of generated gases can indicate the type of organic matter present. We have performed a set of experiments with perchlorate and organic matter of variable molecular weights. Results indicate that organic susceptibility to thermal degradation and mineral-assisted reactions is related to molecular weight. The natural occurrence and association of organic matter with differing molecular weights helps to discriminate between contamination (usually low molecular weight organic matter only) and indigenous carbon (commonly low and high molecular weight organic matter together). Our results can be used to provide insights into data returning from Mars.
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Journal articleCourt RW, Sephton MA, 2014,
New estimates of the production of volatile gases from ablating carbonaceous micrometeoroids at Earth and Mars during an E-belt-type Late Heavy Bombardment
, Geochimica et Cosmochimica Acta, Vol: 145, Pages: 175-205, ISSN: 0016-7037
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