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  • Journal article
    Zhang Z, Gora-Marek K, Watson JS, Tian J, Ryder MR, Tarach KA, Lopez-Perez L, Martinez-Triguero J, Melian-Cabrera Iet al., 2019,

    Recovering waste plastics using shape-selective nano-scale reactors as catalysts

    , NATURE SUSTAINABILITY, Vol: 2, Pages: 39-42, ISSN: 2398-9629
  • 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
    Montgomery W, Sephton MA, Watson JS, Lewis JMT, Zeng Het al., 2018,

    The role of minerals in hydrogen sulfide generation during steam-assisted recovery of heavy oil

    , Energy and Fuels, Vol: 32, Pages: 4651-4654, ISSN: 0887-0624

    Heavy oil is recovered from reservoirs using steam-assisted technology, which can lead to H2S generation if the oil is relatively sulfur-rich. We have used laboratory aquathermolysis to simulate the steam-assisted gravity drainage process and have compared free heavy oil to that contained within the mineral matrix. The presence of a mineral matrix was found to affect the amount of H2S produced and the chemical properties of the oil generated. Our findings show that H2S production is initiated by the presence of naturally occurring minerals at specific temperatures and pressures and production techniques that avoid these conditions will minimize H2S production.
  • Journal article
    Zafar R, Watson JS, 2017,

    Adsorption of tetradecanoic acid on kaolinite minerals: Using flash pyrolysis to characterise the catalytic efficiency of clay mineral adsorbed fatty acids

    , Chemical Geology, Vol: 471, Pages: 111-118, ISSN: 0009-2541

    The clay mineral kaolinite is one of the major inorganic constituents of sedimentary rocks. Kaolinite-carboxylic acid interactions are of considerable importance from the geochemical perspective. The two-fold aim of this study was to quantify the adsorption of tetradecanoic acid on kaolinite and then the flash pyrolysis of adsorbed fatty acids-kaolinite samples to understand the transformation of adsorbed fatty acids on kaolinite. Adsorption of tetradecanoic acid on kaolinite results in an s-isotherm which reflects the multilayer adsorption. Adsorption of tetradecanoic acid on kaolinite involves its both functionalities i.e. siloxane (tetrahedral face) and hydroxyl surface (octahedral face) as indicated from the pyrolysis results. Flash pyrolysis of tetradecanoic acid adsorbed kaolinite mainly yielded saturated/unsaturated hydrocarbons, aromatic hydrocarbons, and ketones while pure tetradecanoic acid generated saturated/unsaturated hydrocarbons and a series of unsaturated and saturated low molecular weight fatty acids. We have successively tested an empirical approach to identify organic compounds formed from fatty acid adsorbed kaolinite to the organic compounds obtained from fatty acid adsorbed alumina and silica. Kaolinite mainly reflects the transformation of carboxylic acids into hydrocarbons and ketones via hydroxyl surface (octahedral face). Ketonisation is mainly observed at multilayer adsorption of tetradecanoic acid on kaolinite. The major implication of the work is the understanding of fatty acids adsorption on kaolinite via both surfaces of the mineral which is helpful to understand the fate of fatty acids as they pass into the geosphere during diagenesis.
  • Journal article
    Stucky de Quay G, Roberts GG, Watson J, Jackson CA-Let al., 2017,

    Incipient mantle plume evolution: constraints from ancient landscapes buried beneath the North Sea

    , Geochemistry, Geophysics, Geosystems, Vol: 18, Pages: 973-993, ISSN: 1525-2027

    Geological observations that constrain the history of mantle convection are sparse despite its importance in determining vertical and horizontal plate motions, plate rheology, and magmatism. We use a suite of geological and geophysical observations from the northern North Sea to constrain evolution of the incipient Paleocene-Eocene Icelandic plume. Well data and a three-dimensional seismic survey are used to reconstruct a 58–55 Ma landscape now buried ∼1.5 km beneath the seabed in the Bressay region. Geochemical analyses of cuttings from wells that intersect the landscape indicate the presence of angiosperm debris. These observations, combined with presence of coarse clastic material, interpreted beach ridges, and a large dendritic drainage network, indicate that this landscape formed subaerially. Longitudinal profiles of palaeo-rivers were extracted and inverted for an uplift rate history, indicating three distinct phases of uplift and total cumulative uplift of ∼350 m. Dinoflagellate cysts in the surrounding marine stratigraphy indicate that this terrestrial landscape formed in <3 Ma and was rapidly drowned. This uplift history is similar to that of a slightly older buried landscape in the Faeroe-Shetland basin ∼400 km to the west. These records of vertical motion are consistent with pulses of anomalously hot asthenosphere spreading out from the incipient Icelandic plume. Using simple isostatic calculations we estimate that the maximum thermal anomaly beneath Bressay was 50–100◦C. Our observations suggest that a thermal anomaly departed the Icelandic plume around 57.4±2.2 Ma at the latest, and travelled with a velocity >∼150 km/Ma.
  • Journal article
    Zafar R, Watson JS, Weiss DJ, Sephton MAet al., 2016,

    Organic compound-mineral interactions: using flash pyrolysis to monitor the adsorption of fatty acids on calcite

    , Journal of Analytical and Applied Pyrolysis, Vol: 123, Pages: 184-193, ISSN: 1873-250X

    Fatty acids are near ubiquitous organic compounds in living organisms in the Earth’s biosphere. Following death of an organism in the marine environment its fatty acids may survive descent to the sea bed where they can be juxtaposed with minerals. The aim of this study was to investigate the interaction of fatty acids with the common marine mineral calcite. Adsorption of tetradecanoic acid (C14) on calcite results in a sigmoidal or “s” isotherm. Flash pyrolysis experiments were conducted on samples of fatty acid adsorbed onto calcite and were compared with similar experiments on pure fatty acid and on salts of a fatty acid. Flash pyrolysis of pure tetradecanoic acid generated unsaturated and saturated hydrocarbons and a series of unsaturated and saturated low molecular weight fatty acids. Flash pyrolysis of free tetradecanoic acid salt produced saturated and unsaturated hydrocarbons, an aldehyde and a homologous series of saturated and unsaturated ketones, one of which was a symmetrical mid chain ketone (14-heptacosanone). Flash pyrolysis data from adsorbed tetradecanoic acid samples suggested that adsorption is analogous to the formation of the calcium salt of tetradecanoic acid. A key characteristic of the flash pyrolysis products of adsorbed fatty acids and fatty acid salts was the production of ketones with higher molecular weights than the starting fatty acids. Ketonisation was not observed from the flash pyrolysis of pure acid which implied the catalytic significance of the calcite mineral surface. The abundance of hydrocarbons relative to ketones in the pyrolysates negatively correlated with the proportion of fatty acids adsorbed to the surface of calcite. The ability to use flash pyrolysis to diagnose the nature of fatty acid interactions with mineral surfaces provides a valuable tool for monitoring the fate of these important lipids at the Earth’s surface as they pass into the geosphere and are subjected to diagenetic processes.
  • Journal article
    Henry 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 article
    Montgomery WB, Watson JS, Potiszil C, Sephton MAet al., 2016,

    Sporopollenin, a natural copolymer, is robust under high hydrostatic pressure

    , Macromolecular Chemistry and Physics, Vol: 217, Pages: 2494-2500, ISSN: 1521-3935

    Lycopodium 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.
  • Journal article
    Court RW, Tan J, 2016,

    Insights into secondary reactions occurring during atmospheric ablation of micrometeoroids

    , Meteoritics & Planetary Science, Vol: 51, Pages: 1163-1183, ISSN: 1086-9379

    Ablation of micrometeoroids during atmospheric entry yields volatile gases such as water, carbon dioxide, and sulfur dioxide, capable of altering atmospheric chemistry and hence the climate and habitability of the planetary surface. While laboratory experimentshave revealed the yields of these gases during laboratory simulations of ablation, the reactions responsible for the generation of these gases have remained unclear, with a typical assumption being that species simply undergo thermal decomposition without engaging inmore complex chemistry. Here, pyrolysis–Fourier transform infrared spectroscopy reveals that mixtures of meteorite-relevant materials undergo secondary reactions during simulatedablation, with organic matter capable of taking part in carbothermic reduction of iron oxides and sulfates, resulting in yields of volatile gases that differ from those predicted by simple thermal decomposition. Sulfates are most susceptible to carbothermic reduction, producing greater yields of sulfur dioxide and carbon dioxide at lower temperatures than would be expected from simple thermal decomposition, even when mixed with meteoriticallyrelevant abundances of low-reactivity Type IV kerogen. Iron oxides were less susceptible, with elevated yields of water, carbon dioxide, and carbon monoxide only occurring when mixed with high abundances of more reactive Type III kerogen. We use these insights toreinterpret previous ablation simulation experiments and to predict the reactions capable of occurring during ablation of carbonaceous micrometeoroids in atmospheres of different compositions.
  • Journal article
    Montgomery W, Sephton MA, 2016,

    Pressure effects in polycyclic aromatic nitrogenated heterocycles (PANHs): Diagnostic qualities and cosmobarometry potential

    , The Astrophysical Journal, Vol: 819, ISSN: 0004-637X

    The 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.
  • 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
    Gordon PR, Sephton MA, 2016,

    Rapid habitability assessment of Mars samples by pyrolysis-FTIR

    , Planetary and Space Science, Vol: 121, Pages: 60-75, ISSN: 1873-5088

    Pyrolysis 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.
  • Journal article
    Watson 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: 1557-8070

    The 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.
  • Journal article
    Abubakar R, Muxworthy AR, Southern P, Watson JS, Fraser AJ, Almeida TP, Sephton MAet al., 2015,

    Formation of magnetic minerals in hydrocarbon-generation conditions

    , Marine and Petroleum Geology, ISSN: 1873-4073

    In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (<10 nm), magnetic particles that varied across the rock samples analysed, but more importantly across the pyrolysis temperature range. Magnetic measurements demonstrated the formation of these magnetic minerals peaked at 250 °C for all rock samples and then decreased at 300 °C before rising again at 320 °C. The newly formed magnetic minerals are suggested to be primarily pyrrhotite, though magnetite and greigite are also thought to be present. The sizes of the magnetic minerals formed suggest a propensity to migrate together with oil potentially explaining the magnetic anomalies observed above and within oil fields.
  • Conference paper
    Abubakar R, Muxworthy AR, Sephton M, Fraser A, Heslop D, Paterson G, Southern Pet al., 2015,

    Mapping Petroluem Migration Pathways Using Magnetics and Seismic Interpretations (poster)

    , AGU Fall 2015
  • Journal article
    Mustafa KA, Sephton MA, Watson JS, Spathopoulos F, Krzywiec Pet 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: 1873-4073

    Black 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
  • Journal article
    Wright MC, Court RW, Kafantaris F-CA, Spathopoulos F, Sephton MAet al., 2015,

    A new rapid method for shale oil and shale gas assessment

    , Fuel, Vol: 153, Pages: 231-239, ISSN: 0016-2361
  • Journal article
    Sephton MA, Carter JN, 2015,

    The chances of detecting life on Mars

    , PLANETARY AND SPACE SCIENCE, Vol: 112, Pages: 15-22, ISSN: 0032-0633
  • Journal article
    Luong 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
  • Journal article
    Torokova L, Watson J, Krcma F, Mazankova V, Mason NJ, Horvath G, Matejcik Set 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

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