Imperial College London


Faculty of EngineeringDepartment of Earth Science & Engineering

Research Officer in Organic Geochemistry and Mineralogy



+44 (0)20 7594 6399jonathan.watson




2.54Royal School of MinesSouth Kensington Campus





Publication Type

63 results found

Royle S, Watson JS, Sephton M, 2021, Transformation of cyanobacterial biomolecules by iron oxides during flash pyrolysis: Implications for Mars life detection missions, Astrobiology, ISSN: 1531-1074

Answering the question of whether life ever existed on Mars is a key goal of both NASA’s and ESA’s imminent Mars rover missions. The obfuscatory effects of oxidising salts, such as perchlorates and sulfates, on organic matter during thermal decomposition analysis techniques are well established. Less well studied are the transformative effects of iron oxides and (oxy)hydroxides, which are present in great abundances in the martian regolith. We examined the products of flash pyrolysis GC-MS, a technique analogous to the thermal techniques employed by past, current and future landed Mars missions, formed when the cyanobacteria Arthrospira platensis was heated in the presence of a variety of Mars-relevant 16iron bearing minerals. We found that iron oxides/(oxy)hydroxides have transformative effects on the pyrolytic products of cyanobacterial biomolecules. Both the abundance and variety of molecular species detected were decreased as iron substrates transformed biomolecules, by both oxidative and reductive processes, into lower fidelity alkanes, aromatic and aryl-bonded hydrocarbons. Despite the loss of fidelity, a suite containing mid-length alkanes and PAHs and/or aryl-bonded molecules in iron-rich samples subjected to pyrolysis, may allude to the transformation of cyanobacterially-derived mid-long chain length fatty acids (particularly unsaturated fatty acids) originally present in the sample. Haematite was found to be the iron-oxide with the lowest transformation potential and so, because this iron oxide has a high affinity forco-deposition of organic matter and preservation over geological timescales, sampling at Mars should target sediments/strata which have undergone a diagenetic history encouraging the dehydration, dehydroxylation and oxidation of more reactive iron-bearing phases to haematite by looking for (mineralogical) evidence of the activity of oxidising, acidic/neutral and either hot or long-lived fluids.

Journal article

Royle SH, Tan J, Watson JS, Sephton MAet al., 2021, Pyrolysis of carboxylic acids in the presence of iron oxides: implications for life detection on missions to Mars, Astrobiology, Pages: 1-19, ISSN: 1531-1074

The search for, and characterization of, organic matter on Mars is central to efforts in identifying habitable environments and detecting evidence of life in the martian surface and near surface. Iron oxides are ubiquitous in the martian regolith and are known to be associated with the deposition and preservation of organic matter in certain terrestrial environments, thus iron oxide-rich sediments are potential targets for life-detection missions. The most frequently used protocol for martian organic matter characterization (also planned for use on ExoMars) has been thermal extraction for the transfer of organic matter to gas chromatography-mass spectrometry (GC-MS) detectors. For the effective use of thermal extraction for martian samples, it is necessary to explore how potential biomarker organic molecules evolve during this process in the presence of iron oxides. We have thermally decomposed iron oxides simultaneously with (z)-octadec-9-enoic and n-octadecanoic acids and analyzed the products through pyrolysis-GC-MS. We found that the thermally driven dehydration, reduction, and recrystallization of iron oxides transformed fatty acids. Overall detectability of products greatly reduced, molecular diversity decreased, unsaturated products decreased, and aromatization increased. The severity of this effect increased as reduction potential of the iron oxide and inferred free radical formation increased. Of the iron oxides tested hematite showed the least transformative effects, followed by magnetite, goethite, then ferrihydrite. It was possible to identify the saturation state of the parent carboxylic acid at high (0.5 wt %) concentrations by the distribution of n-alkylbenzenes in the pyrolysis products. When selecting life-detection targets on Mars, localities where hematite is the dominant iron oxide could be targeted preferentially, otherwise thermal analysis of carboxylic acids, or similar biomarker molecules, will lead to enhanced polymerization, aromatiz

Journal article

Kirby M, Sonnenberg JL, Watson JS, Weiss Det al., 2020, Prevention of UVI precipitation in alkaline aqueous solutions by the siderophore desferrioxamine B, Publisher: American Chemical Society (ACS)

In alkaline and saline solutions, uranium VI (UVI) forms uranyl salts, limiting its mobility in leachates released from nuclear waste repositories into groundwater. However, recent experimental and computational work suggested that natural organic molecules widely present in groundwater such as siderophores could potentially prevent solid precipitation because of the formation of stable UVI-siderophore complexes. It is important we assess the impact of siderophores on aqueous UVI chemistry as they could mobilise UVI from contaminated land and radioactive waste storage and disposal sites. Here we test this hypothesis by combining for the first time experimental studies on uranium precipitation in alkaline pH in the presence of desferrioxamine B (DFOB) and electron structure method calculation of uranyl – hydroxamate complexes to assess their stability. Stirred batch experiments containing 0 to 420 µM DFOB, 42 µM UVI and 0.1 M NaCl were conducted at pH 11.5. DFT was employed to explore the relative stability of different UVI-hydroxamate complexes, representative of the local binding mode of DFOB. During the stirred batch experiments, 5%, 11-12%, 41-53%, 95-96% and 100% of UVI passes through the filter membranes (0.2-1 µm pore diameter) after 24 hours when 0, 4.2, 42, 130 and 420 µM DFOB was added to solution. The DFT results suggest one hydroxamate functional group is most likely to complex with UVI with ∆rG calculated as +3 kJ/mol and -9 kJ/mol for [UO2(OH)3(Lmono)]2- and [UO2(OH)2(L)]- respectively. Conversion of the experimentally derived log β (-1.2 ± 0.3) through the equation ∆rG = -2.303RTlogβ provides ∆rG of +7 kJ/mol, similar to the ∆rG of these two complexes. The results of our study confirm that UVI precipitation could be hindered by the formation of a DFOB complex with UVI complexation through a single hydroxamate functional group as a likely mechanism. These results highlight the mobilising effect siderophores

Working paper

Bullen JC, Torres-Huerta A, Salaün P, Watson JS, Majumdar S, Vilar R, Weiss DJet al., 2020, Portable and rapid arsenic speciation in synthetic and natural waters by an As(V)-selective chemisorbent, validated against anodic stripping voltammetry, Water Research, Vol: 175, Pages: 1-11, ISSN: 0043-1354

Inorganic arsenic speciation, i.e. the differentiation between arsenite and arsenate, is an important step for any program aiming to address the global issue of arsenic contaminated groundwater, whether for monitoring purposes or the development of new water treatment regimes. Reliable speciation by easy-to-use, portable and cost-effective analytical techniques is still challenging for both synthetic and natural waters. Here we demonstrate the first application of an As(V)-selective chemisorbent material for simple and portable speciation of arsenic using handheld syringes, enabling high sample throughput with minimal set-up costs. We first show that ImpAs efficiently removes As(V) from a variety of synthetic groundwaters with a single treatment, whilst As(III) is not retained. We then exemplify the potential of ImpAs for simple and fast speciation by determining rate constants for the photooxidation of As(III) in presence of a TiO2 photocatalyst. Finally, we successfully speciate natural waters spiked with a mix of As(III) and As(V) in both Indian and UK groundwaters with less than 5 mg L−1 dissolved iron. Experimental results using ImpAs agreed with anodic stripping voltammetry (ASV), a benchmark portable technique, with analysis conditions optimised here for the groundwaters of South Asia. This new analytical tool is simple, portable and fast and should find applications within the overall multi-disciplinary remediation effort that is taking place to tackle this worldwide arsenic problem.

Journal article

Kirby ME, Watson JS, Najorka J, Louvane Kenney JP, Krevor S, Weiss DJet al., 2020, Experimental study of pH effect on uranium (UVI) particle formation and transport through quartz sand in alkaline 0.1 M sodium chloride solutions, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 592, Pages: 1-11, ISSN: 0927-7757

A thorough understanding of the aqueous uranium VI (UVI) chemistry in alkaline, sodium containing solutions is imperative to address a wide range of critical challenges in environmental engineering, including nuclear waste management. The aim of the present study was to characterise experimentally in more detail the control of pH on the removal of UVI from aqueous alkaline solutions through particle formation and on subsequent transport through porous media. We conducted first static batch experiments in the pH range between 10.5 and 12.5 containing 10 ppm UVI in 0.1 M NaCl solutions and examined the particles formed using filtration, dynamic light scattering, transition electron microscopy and X-ray powder diffraction. We found that at pH 10.5 and 11.5, between 75 and 96 % of UVI was removed from the solutions as clarkeite and studtite over a period of 48 h, forming particles with hydrodynamic diameters of 640 ± 111 nm and 837 ± 142 nm, respectively and representing aggregates of 10′s nm sized crystals randomly orientated. At pH 12.5, the formation of particles >0.2 μm became insignificant and no UVI was removed from solution. The mobility of UVI in these solutions was further studied using column experiments through quartz sand. We found that at pH 10.5 and 11.5, UVI containing particles were immobilised near the column inlet, likely due physical immobilisation of the particles (particle straining). At pH 12.5, however, UVI quantitatively eluted from the columns in the filter fraction <0.2 μm. The findings of our study reinforce a strong control of solution pH on particle size and U removal in alkaline solutions and subsequently on mobility of U through quartz porous media.

Journal article

Abubakar R, Muxworthy A, Fraser A, Sephton MA, Watson JS, Heslop D, Paterson G, Southern Pet al., 2020, Mapping hydrocarbon charge-points in the Wessex Basin using seismic, geochemistry and mineral magnetics, Marine and Petroleum Geology, Vol: 111, Pages: 510-528, ISSN: 1873-4073

This study reports a multidisciplinary approach to determining hydrocarbon charge-points and migration in the Wessex Basin, southern England. Geochemical analysis of reservoir core material (Bridport Sandstone and Inferior Oolite) using gas chromatography-mass spectrometry (GC-MS), suggests that the oil in the Wessex Basin is from a single source, and that small variations in environmentally sensitive biomarkers are likely due to small differences in maturity or depositional conditions during the formation of the oil over millions of years. Using seismic data, basin modelling revealed two potential hydrocarbon migration pathways from the hanging wall of the Purbeck fault into the Sherwood Sandstone reservoir at Wytch Farm. One of these potential pathways is represented by cores termed Creech and the other Bushey Farm. To try to distinguish between the two potential pathways, cores were studied using mineral magnetic techniques. The magnetic signature was characterised using low-temperature (<50 K) magnetic measurements; this is because much of the magnetic signature was dominated by nanoparticles < 30 nm, which are thermally activated at room temperature and magnetically “transparent”. Wells that contained considerable amounts of hydrocarbons were dominated by nanometric magnetite (<30 nm). Such particles are small enough to migrate with the oil, through pore spaces, which are of the order ~100 nm. Wells located at the fringes of large hydrocarbon accumulation had enhanced pyrrhotite-dominated magnetic signals. Of the two potential migration pathways, the mineral magnetic results suggest that the oil migrated through Creech rather than through Bushey Farm.

Journal article

Royle S, Watson J, Zhang Y, Chatzitheoklitos G, Sephton Met al., 2019, Solid Phase Micro Extraction: Potential for Organic Contamination Control for Planetary Protection of Life-Detection Missions to the Icy Moons of the Outer Solar System, Astrobiology, Vol: 19, Pages: 1153-1166, ISSN: 1531-1074

Conclusively detecting, or ruling out the possibility of, life on the icy moons of the outer solar system will require spacecraft missions to undergo rigorous planetary protection and contamination control procedures to achieve extremely low levels of organic terrestrial contamination. Contamination control is necessary to avoid forward contamination of the body of interest and to avoid the detection of false positive signals which could either mask indigenous organic chemistry of interest or cause an astrobiological false alarm. Here we test a new method for rapidly and inexpensively assessing the organic cleanliness of spaceflight hardware surfaces using solid phase micro extraction (SPME) fibres to directly swab surfaces. The results suggest that the method is both time and cost efficient. The SPME-gas chromatography mass spectrometry (GC-MS) method is sensitive to common mid-weight, non-polar contaminant compounds, e.g. aliphatic and aromatic hydrocarbons, which are common contaminants in laboratory settings. While we demonstrate the potential of SPME for surface sampling, the GC-MS instrumentation restricts the SPME-GC-MS technique’s sensitivity to larger polar and non-volatile compounds. Although not used in this study, to increase the potential range of detectable compounds, SPME can also be used in conjunction with high performance liquid chromatography/liquid chromatography-mass spectrometry systems suitable for polar analytes [Kataoka et al., 2000]. Thus, our SPME method presents an opportunity to monitor organic contamination in a relatively rapid and routine way that produces information-rich data sets.

Journal article

Georgieva MN, Little CTS, Watson JS, Sephton MA, Ball AD, Glover AGet al., 2019, Identification of fossil worm tubes from Phanerozoic hydrothermal vents and cold seeps, Journal of Systematic Palaeontology, Vol: 17, Pages: 287-329, ISSN: 1477-2019

One of the main limitations to understanding the evolutionary history of hydrothermal vent and cold seep communities is the identification of tube fossils from ancient deposits. Tube-dwelling annelids are some of the most conspicuous inhabitants of modern vent and seep ecosystems, and ancient vent and seep tubular fossils are usually considered to have been made by annelids. However, the taxonomic affinities of many tube fossils from vents and seeps are contentious, or have remained largely undetermined due to difficulties in identification. In this study, we make a detailed chemical (Fourier-transform infrared spectroscopy and pyrolysis gas-chromatography mass-spectrometry) and morphological assessment of modern annelid tubes from six families, and fossil tubes (seven tube types from the Cenozoic, 12 Mesozoic and four Palaeozoic) from hydrothermal vent and cold seep environments. Characters identified from these investigations were used to explore for the first time the systematics of ancient vent and seep tubes within a cladistic framework. Results reveal details of the compositions and ultrastructures of modern tubes, and also suggest that two types of tubes from ancient vent localities were made by the annelid family Siboglinidae, which often dominates modern vents and seeps. Our results also highlight that several vent and seep tube fossils formerly thought to have been made by annelids cannot be assigned an annelid affiliation with any certainty. The findings overall improve the level of quality control with regard to interpretations of fossil tubes, and, most importantly, suggest that siboglinids likely occupied Mesozoic vents and seeps, greatly increasing the minimum age of the clade relative to earlier molecular estimates.

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

Royle SH, Oberlin E, Watson JS, Montgomery W, Kounaves SP, Sephton MAet al., 2018, Perchlorate‐driven combustion of organic matter during pyrolysis‐gas chromatography‐mass spectrometry: implications for organic matter detection on earth and mars, Journal of Geophysical Research: Planets, Vol: 123, Pages: 1901-1909, ISSN: 2169-9097

The search for life on Mars targets the detection of organic matter from extant or extinct organisms. Current protocols use thermal extraction procedures to transfer organic matter to mass spectrometer detectors. Oxidizing minerals on Mars, such as perchlorate, interfere with organic detection by thermal extraction. Thermal decomposition of perchlorate releases oxygen which promotes combustion of organic carbon. We have assessed the minimum mass ratio of organic carbon to perchlorate required to detect organic matter by thermal extraction and mass spectrometry. Locations on Mars with organic carbon to perchlorate ratios above 4.7-9.6 should be targeted. Because habitability is enhanced by the presence of liquid water and because perchlorate is a water soluble salt, locations on Mars with evidence of past or recent liquid water are high priority targets.

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

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.

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

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

Journal article

Luong D, Sephton M, Watson J, 2015, Subcritical water extraction of organic matter from sedimentary rocks, Analytica Chimica Acta, ISSN: 1873-4324

Subcritical water extraction of organic matter containing sedimentary rocks at 300 °C and 1500 psi produces extracts comparable to conventional solvent extraction. Subcritical water extraction of previously solvent extracted samples confirms that high molecular weight organic matter (kerogen) degradation is not occurring and that only low molecular weight organic matter (free compounds) are being accessed in analogy to solvent extraction procedures. The sedimentary rocks chosen for extraction span the classic geochemical organic matter types. Type I organic matter-containing sedimentary rock produces n-alkanes and isoprenoidal hydrocarbons at 300 °C and 1500 psi that indicate an algal source for the organic matter. Extraction of a rock containing type II organic matter at the same temperature and pressure produces aliphatic hydrocarbons but also aromatic compounds reflecting the increased contributions from terrestrial organic matter in this sample. A type III organic matter-containing sample produces a range of non-polar and polar compounds including polycyclic aromatic hydrocarbons and oxygenated aromatic compounds at 300 °C and 1500 psi reflecting a dominantly terrestrial origin for the organic materials. Although extraction at 300 °C and 1500 psi produces extracts that are comparable to solvent extraction, lower temperature steps display differences related to organic solubility. The type I organic matter produces no products below 300 °C and 1500 psi, reflecting its dominantly aliphatic character, while type II and type III organic matter contribute some polar components to the lower temperature steps, reflecting the chemical heterogeneity of their organic inventory. The separation of polar and non-polar organic compounds by using different temperatures provides the potential for selective extraction that may obviate the need for subsequent preparative chromatography steps. Our results indicate that subcritical water extraction can act as a

Journal article

Montgomery WB, Sephton MA, Watson JS, Zeng H, Rees Aet al., 2015, Minimising hydrogen sulphide generation during steam assisted production of heavy oil, Scientific Reports, Vol: 5, ISSN: 2045-2322

The 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.

Journal article

Lewis JMT, Watson JS, Najorka J, Luong D, Sephton MAet al., 2015, Sulfate Minerals: A Problem for the Detection of Organic Compounds on Mars?, Astrobiology, Vol: 15, ISSN: 1557-8070

The 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.

Journal article

Sephton MA, Watson JS, Meredith W, Love GD, Gilmour I, Snape CEet al., 2015, Multiple cosmic sources for meteorite macromolecular materials?, Astrobiology, Vol: 15, ISSN: 1557-8070

Journal article

Sephton MA, Lewis JMT, Watson JS, Montgomery W, Garnier Cet 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: 1944-8007

Instruments 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.

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

Montgomery W, Sephton MA, Watson J, Zeng Het al., 2014, The Effects Of Minerals On Heavy Oil And Bitumen Chemistry When Recovered Using Steam-assisted Methods, SPE Heavy Oil Conference-Canada

The production of gaseous sulfur-containing species during the steam-assisted recovery of heavy oil and bitumen have important consequences for both economics and safety. Factors such as the effects of mineral matrices require laboratory data to produce accurate models. To study mineral effects on gas production we studied a well-characterized oil-containing core and the isolated crude oil from that core. The samples were run at 250-300°C in the continued presence of liquid water for 24 hours. The reaction products of all experiments include gases, oil flotate, oil sinkate, water-soluble products, and water- insoluble residues. All reaction products were studied with a variety of analytical techniques, including FTIR spectroscopy, chromatographic fractionation (SARA analysis), GC-MS, pyrolysis GCMS and GC-FPD/TCD. These techniques were applied to whole oil, maltenes and asphaltene fractions. Physical properties including viscosity and density were also measured. Our data provide insights into the physical and chemical consequences of steam assisted recovery of heavy oils and bituments from sedimentary rock reservoirs and reveal that geological and geochemical context is an essential consideration.

Conference paper

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

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