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A compilation of new and previously published vitrinite reflectance (R0) data from Carboniferous coals constitutes the most comprehensive map of reflectance across Great Britain. Values of R0 range from 0.38 to 3.29%, recording an ambient thermal maturity in the early oil window (standard reference point for reflectance studies), modified by elevated heat flow in northern England and along the Variscan orogenic front. The map provides a context for other geological datasets. Supplementary material: A statistical summary of vitrinite reflectance data is available at https://doi.org/10.6084/m9.figshare.c.4529969

Sandstone uranium (U) roll-front deposits of Wyoming and Colorado (USA) are important U resources, and may provide a terrestrial source for critical accessory elements, such as selenium (Se), molybdenum (Mo), and tellurium (Te). Due to their associated toxicity, Mo Se Te occurrences in roll-fronts should also be carefully monitored during U leaching and ore processing. While elevated Mo Se concentrations in roll-fronts are well established, very little is known about Te occurrence in such deposits. This study aims to establish Mo Se Te concentrations in Wyoming and Colorado roll-fronts, and assess the significance of these deposits in an environmental and mineral exploration context. Sampled roll-front deposits, produced by oxidized groundwater transportation through a sandstone, show high Mo Se content in specific redox zones, and low Te, relative to crustal means. High Se concentrations (up to 168 ppm) are restricted to a narrow band of alteration at the redox front. High Mo content (up to 115 ppm) is typically associated with the reduced mineralized nose and seepage zones of the roll-front, ahead of the U orebody. Elevated trace element concentrations are likely sourced from proximal granitic intrusions, tuffaceous deposits, and local pyritic mudstones. Elevated Mo Se content in the sampled roll fronts may be regarded as a contaminant in U in-situ recovery and leaching processing, and may pose an environmental threat in groundwaters and soils, so extraction should be carefully monitored. The identification of peak concentrations of Mo Se can also act as a pathfinder for the redox front of a roll-front, and help to isolate the U orebody, particularly in the absence of gamma signatures.

We gratefully acknowledge two anonymous reviewers for their constructive comments on an earlier version of this manuscript. Earth System Evolution and Early Life: a Celebration of the Work of Martin Brasier. ed. / A. T. Brasier; D. McIlroy; N. McLoughlin. 978-1-78620-279-6

There is very little understanding of tellurium (Te) distribution and behaviour in sedimentary rocks. A suite of 15 samples of reduction spheroids (centimetre-scale pale spheroids in otherwise red rock), including samples from eight localities in Triassic red beds across the British Isles, were mapped for Te using Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry. Almost all showed enrichment in Te in the cores of the spheroids relative to background red bed concentrations, by up to four orders of magnitude. Some were also enriched over background in gold and/or mercury. In one case, discrete telluride minerals were recorded. The data show that Te is mobile and can be concentrated in low-temperature sedimentary environments, controlled by redox variations. The consistency in enrichment across widely separate localities implies that the enrichment is a normal aspect of red bed diagenesis and so likely to be controlled by a ubiquitous process, such as microbial activity.

The interaction of microbes and metals is widely assumed to have occurred in surface or very shallow subsurface environments. However new evidence suggests that much microbial activity occurs in the deep subsurface. Fluvial, lacustrine and aeolian ‘red beds’ contain widespread centimetre-scale reduction spheroids in which a pale reduced spheroid in otherwise red rocks contains a metalliferous core. Most of the reduction of Fe (III) in sediments is caused by Fe (III) reducing bacteria. They have the potential to reduce a range of metals and metalloids, including V, Cu, Mo, U and Se, by substituting them for Fe (III) as electron acceptors, which are all elements common in reduction spheroids. The spheroidal morphology indicates that they were formed at depth, after compaction, which is consistent with a microbial formation. Given that the consequences of Fe (III) reduction have a visual expression, they are potential biosignatures during exploration of the terrestrial and extraterrestrial geological record. There is debate about the energy available from Fe (III) reduction on Mars, but the abundance of iron in Martian soils makes it one of the most valuable prospects for life there. Entrapment of the microbes themselves as fossils is possible, but a more realistic target during the exploration of Mars would be the colour contrasts reflecting selective reduction or oxidation. This can be achieved by analysing quartz grains across a reduction spheroid using Raman spectroscopy, which demonstrates its suitability for life detection in subsurface environments. Microbial action is the most suitable explanation for the formation of reduction spheroids and may act as metalliferous biosignatures for deep subsurface microbial activity.

The exploration for selenium (Se) and tellurium (Te) will become intensified as the technological demand for these elements grows. It is known that they are enriched in organic-rich sedimentary rocks over crustal mean values. LA-ICP-MS measurement of pyrite in two biodegraded palaeo-oil reservoirs in central England shows that Se and Te are enriched in them, but not in other sulfide samples from the region and elsewhere. The Carboniferous source rock shales in the region are Se-rich, implying that this enrichment was conferred to the oil generated from them. The Se and Te are located in pyrite precipitated in the palaeo-reservoirs by microbial activity. Exhumed oil reservoirs merit further investigation for concentrations of these elements.

Mid-Jurassic pyritic coals exposed at the village of Brora, northern Scotland, UK, contain a marked enrichment of tellurium (Te) relative to crustal mean, average world coal compositions and British Isles Carboniferous coals. The Te content of Brora coal pyrite is more than one order of magnitude higher than in sampled pyrite of Carboniferous coals. The Te enrichment coincides with selenium (Se) and mercury (Hg) enrichment in the rims of pyrite, and Se/Te is much lower than in pyrites of Carboniferous coals. Initial pyrite formation is attributed to early burial (syn-diagenesis), with incorporation of Te, Se, Hg and lead (Pb) during later pyrite formation. The source of Te may have been a local hydrothermal system which was responsible for alluvial gold (Au) in the region, with some Au in Brora headwaters occurring as tellurides. Anomalous Te is not ubiquitous in coal, but may occur locally, and is detectable by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS).

The ESA/Roscosmos ExoMars rover will be launched in 2018. The primary aim of the mission will be to find evidence of extinct or extant life by extracting samples from the subsurface of Mars. The rover will incorporate a drill that is capable of extracting cores from depths of up to 2 m, a Sample Preparation and Distribution System (SPDS) that will crush the core into small grains and a suite of analytical instruments. A key component of the analytical suite will be the Raman Laser Spectrometer (RLS) that will be used to probe the molecular and mineralogical composition of the samples. In this work we consider the capability of the proposed Raman spectrometer to detect reduced carbon (possibly associated with evidence for extinct life) and to identify the level of thermal alteration/maturity. The Raman analysis of 21 natural samples of shale (originating from regions exhibiting different levels of thermal maturity) is described and it is shown that reduced carbon levels as low as 0.08% can be readily detected. It is also demonstrated that the Raman spectra obtained with the instrument can be used to distinguish between samples exhibiting high and low levels of thermal maturity and that reduced carbon can be detected in samples exposed to significant levels of oxidation (as expected on the surface of Mars).

The quantity of methane in Mars' atmosphere, and the potential mechanism(s) responsible for its production, are still unknown. In order to test viable, abiotic, methangenic processes, we experimentally investigated two possible impact mechanisms for generating methane. In the first suite of experiments, basaltic rocks were impacted at 5 km s−1 and the quantity of gases (CH4, H2, He, N2, O2, Ar and CO2) released by the impacts was measured. In the second suite of experiments, a mixture of water ice, CO2 ice and anhydrous olivine grains was impacted to see if the shock induced rapid serpentinization of the olivine, and thus production of methane. The results of both suites of experiments demonstrate that impacts (at scales achievable in the laboratory) do not give rise to detectably enhanced quantities of methane release above background levels. Supporting hydrocode modelling was also performed to gain insight into the pressures and temperatures occurring during the impact events.

The analysis of sulphur isotopic compositions in three sets of surface sulphate samples from the soil zone in the Haughton impact structure shows that they are distinct. They include surface gypsum crusts remobilized from the pre-impact gypsum bedrock (mean δ34S +31‰), efflorescent copiapite and fibroferrite associated with hydrothermal marcasite (mean δ34S −37‰), and gypsum-iron oxide crusts representing weathering of pyritic crater-fill sediments (mean δ34S +7‰). Their different compositions reflect different histories of sulphur cycling. Two of the three sulphates have isotopically light (low δ34S) compositions compared with the gypsum bedrock (mean δ34S +31‰), reflecting derivation by weathering of sulphides (three sets of pyrite/marcasite samples with mean δ34S of −41, −20 and −8‰), which had in turn been precipitated by microbial sulphate reduction. Thus, even in the absence of the parent sulphides due to surface oxidation, evidence of life would be preserved. This indicates that on Mars, where surface oxidation may rule out sampling of sulphides during robotic exploration, but where sulphates are widespread, sulphur isotope analysis is a valuable tool that could be sensitive to any near-surface microbial activity. Other causes of sulphur isotopic fractionation on the surface of Mars are feasible, but any anomalous fractionation would indicate the desirability of further analysis.

Meteorite impacts are among the very few processes common to all planetary bodies with solid surfaces. Among the effects of impact on water-bearing targets is the formation of post-impact hydrothermal systems and associated mineral deposits. The Haughton impact structure (Devon Island, Nunavut, Canada, 75.2 °N, 89.5 °W) hosts a variety of hydrothermal mineral deposits that preserve assemblages of primary hydrothermal minerals commonly associated with secondary oxidative/hydrous weathering products. Hydrothermal mineral deposits at Haughton include intra-breccia calcite-marcasite vugs, small intra-breccia calcite or quartz vugs, intra-breccia gypsum megacryst vugs, hydrothermal pipe structures and associated surface "gossans," banded Fe-oxyhydroxide deposits, and calcite and quartz veins and coatings in shattered target rocks. Of particular importance are sulfide-rich deposits and their associated assemblage of weathering products. Hydrothermal mineral assemblages were characterized structurally, texturally, and geochemically with X-ray diffraction, micro X-ray diffraction, optical and electron microscopy, and inductively coupled plasma atomic emission spectroscopy. Primary sulfides (marcasite and pyrite) are commonly associated with alteration minerals, including jarosite (K,Na,H(3)O)Fe(3)(SO(4))(2)(OH)(6), rozenite FeSO(4)·4(H(2)O), copiapite (Fe,Mg)Fe(4)(SO(4))(6)(OH)(2)·20(H(2)O), fibroferrite Fe(SO(4))(OH)·5(H(2)O), melanterite FeSO(4)·7(H(2)O), szomolnokite FeSO(4)·H(2)O, goethite α-FeO(OH), lepidocrocite γ-FeO(OH) and ferrihydrite Fe(2)O(3)·0.5(H(2)O). These alteration assemblages are consistent with geochemical conditions that were locally very different from the predominantly circumneutral, carbonate-buffered environment at Haughton. Mineral assemblages associated with primary hydrothermal activity, and the weathering products of such deposits, provide constraints on possible microbial activity in the post-impact environment. The initial period of active hydrothermal circulation produced primary mineral assemblages, including Fe sulfides, and was succeeded by a period dominated by oxidation and low-temperature hydration of primary minerals by surface waters. Active hydrothermal circulation can enable the rapid delivery of nutrients to microbes. Nutrient availability following the cessation of hydrothermal circulation is likely more restricted; therefore, the biological importance of chemical energy from hydrothermal mineral deposits increases with time. Weathering of primary hydrothermal deposits and dissolution and reprecipitation of mobile weathering products also create many potential habitats for endolithic microbes. They also provide a mechanism that may preserve biological materials, potentially over geological timescales.

The Mesoproterozoic Stoer Group of the ‘Torridonian9 has been dated at 1177 ± 5 Ma (2σ), based on 40 Ar/ 39 Ar dating of authigenic K-feldspars precipitated in degassing structures within the Stac Fada Member, interpreted previously as an impact ejecta deposit. Fluid inclusion analysis of the K-feldspar shows that it precipitated from hot fluids, and so must immediately post-date emplacement of the ejecta blanket. The oxygen isotopic composition of K-feldspar is remarkably constant at 9.7 ± 0.2‰ (V-SMOW) and is consistent with derivation from evaporated lake water. The new age supports previous determinations of 1199 ± 70 Ma from Pb–Pb dating of limestone and 1180 Ma from palaeomagnetic data, but provides much higher precision. Supplementary material: The raw 40 Ar/ 39 Ar data, J-parameters, correction factors, air calibrations and blank data are available at http://www.geolsoc.org.uk/SUP18453.

Raman spectroscopy is a versatile analytical technique capable of characterizing the composition of both inorganic and organic materials. Consequently, it is frequently suggested as a payload on many planetary landers. Only approximately 1 in every 10(6) photons are Raman scattered; therefore, the detection of trace quantities of an analyte dispersed in a sample matrix can be much harder to achieve. To overcome this, surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) both provide greatly enhanced signals (enhancements between 10(5) and 10(9)) through the analyte's interaction with the locally generated surface plasmons, which occur at a "roughened" or nanostructured metallic surface (e.g., Cu, Au, and Ag). Both SERS and SERRS may therefore provide a viable technique for trace analysis of samples. In this paper, we describe the development of SERS assays for analyzing trace amounts of compounds present in the solvent extracts of sedimentary deposits. These assays were used to detect biological pigments present in an Arctic microoasis (a small locale of elevated biological productivity) and its detrital regolith, characterize the pigmentation of microbial mats around hydrothermal springs, and detect fossil organic matter in hydrothermal deposits. These field study examples demonstrate that SERS technology is sufficiently mature to be applied to many astrobiological analog studies on Earth. Many current and proposed imaging systems intended for remote deployment already posses the instrumental components needed for SERS. The addition of wet chemistry sample processing facilities to these instruments could yield field-deployable analytical instruments with a broadened analytical window for detecting organic compounds with a biological or geological origin.

New measurements of permeability from 14 samples of impact breccia in meteorite impact craters all indicate values of 1 mD or lower. These values are low and suggest that fluid flow through impact craters, evidenced by hydrothermal systems in numerous craters, is predominantly through fracture systems. Mineral precipitation by circulating fluids would eventually seal the fractures. The focussing of hydrothermal fluid flow in fractures emphasizes their importance as potential sites for microbial colonization, and suggests that the sealing minerals are good targets to search for evidence of life.

In the 23-km-diameter Haughton impact structure, Canadian High Arctic, in sulfate-rich bedrock, widespread hydrothermal sulfide mineralization occurred in breccias formed during the impact. The sulfides exhibit extreme sulfur isotopic fractionation relative to the original sulfate, requiring microbial sulfate reduction by thermophiles throughout the crater. This evidence of widespread microbial activity demonstrates that colonization could occur within the lifetime of a moderately sized, impact-induced hydrothermal system. The pyrite was subsequently oxidized to jarosite, which may also have been microbially mediated. The successful detection of evidence for microbial life suggests that it would be a valuable technique to deploy in sulfate-rich impact terrain on Mars.

The formation of Sudbury's economically important magmatic Ni–Cu–PGE sulphide deposits is attributed to superheating of crustal rocks, following meteorite impact at 1.85 Ga. Crustal contamination of magmatic sulphide deposits is thought to be important in the mineralization process and this paper documents the first occurrence of sedimentary carbon in the Sudbury Ni–Cu–PGE sulphides near the base of the Sudbury Igneous Complex (SIC). Spherules of graphitic and more disordered carbon inclusions were found in chalcopyrite crystals, suggesting that carbon has behaved as a chalcophilic element in the impact melt. Samples from the impact structure have been subjected to carbon isotopic analysis and Raman microspectroscopy in order to investigate the relationship between carbonaceous strata of the Huronian basement, the crater-fill impact breccias, and the mineral deposits associated with the Sudbury impact. Carbonaceous material occurs in the impact breccias of the Onaping Formation and this study presents stratigraphically constrained carbon isotopic analysis of the impact breccias. Sulphides from the hydrothermal Zn–Pb–Cu Vermilion–Errington deposits 1.5 km above the SIC were found to contain both carbon spherules and larger irregular carbonaceous flakes, suggesting a genetic link between the Ni–Cu–PGE deposits and the hydrothermal Zn–Pb–Cu mineralization. A shared source of carbon for the Vermilion–Errington mineralization and the cross-cutting anthraxolite veins 100m above the deposits in post-impact carbonaceous shales of the Onwatin Formation is indicated by the similarity in their Raman spectra. This is considered to be carbon remobilized by metamorphic hydrothermal fluids preferentially scavenging disordered carbon from within the Onaping Formation breccias. The occurrence of carbon in the Sudbury Ni–Cu–PGE massive sulphide deposits indicates that carbon from the target rocks played a role in the mineralization process, hitherto unrecognized.

The 39 +/- 2 Ma Haughton impact structure on Devon Island comprises a thick target succession of sedimentary rocks, mainly carbonates. The carbonates contain pre-impact organic matter, including fossil biological markers. Haughton is located in an area where no major thermal event has affected the sedimentary succession after heating caused by impact. This makes Haughton uniquely suitable for studies concerning the preservation of fossil biological markers following an impact event. Melt breccia is the most common impactite at Haughton. It is composed of clasts of the target, mainly carbonates, embedded in a fine groundmass. The groundmass is composed of material that was melted during impact. In this study, fossil biological marker maturity parameters (tricyclic terpane-hopane ratio and pregnane-sterane ratio) and an aromatic maturity parameter [methylphenanthrene ratio (MPR)] were used to compare the degree of thermal alteration in different size fractions of carbonate clasts (

A petrographic and fluid inclusion microthermometric study was performed on sandstones from the Devonian-Carboniferous reservoir rocks of the Clair Field, west of Shetland. Fluid inclusion petrographic and microthermometric observations were collected from quartz, K-feldspar and calcite cements and veins. Vein and cement minerals host both aqueous and hydrocarbon two-phase (liquid and vapor-filled) fluid inclusions indicating that cementation occurred during oil charging. The location of hydrocarbon fluid inclusions in the paragenetic sequence of the reservoir rocks indicates that hydrocarbon migration during early-stage diagenesis occurred via intergranular pores as well as fractures, whereas towards the later stages of diagenesis, as porosities were occluded, hydrocarbon migration was predominantly fracture controlled. The microthermometric characteristics of primary and secondary aqueous fluid inclusions in association with hydrocarbon fluid inclusions indicates that cementation and veining during oil charging occurred at temperatures up to 180 °C. Salinity values are variable (0–10.9 wt% NaCl eq.) indicating that fluid mixing occurred during veining and cementation. Basin modeling and vitrinite reflectance data indicate that temperatures of up to 180 °C could not have been attained through burial alone. The high temperatures attained during late-stage diagenesis are interpreted to be caused by high temperature, short-lived fluids circulating within the Devonian-Carboniferous reservoir rocks in association with late Cretaceous and Paleocene magmatism. These high temperature fluid flow events were not recorded in the vitrinite reflectance data because of their short duration.

Graphitic carbon is a widespread precipitate in terrestrial and extraterrestrial samples. However it has a range of possible origins, which can be difficult to distinguish, including the in situ alteration of organic matter, thermal alteration of hydrocarbons, and precipitation from C–O–H fluids. Petrographic characteristics help to understand the origin of the graphite, including relationships with rock fabric, paragenetic sequences and evidence for fluid mobility. Characterization of a range of terrestrial samples will allow better interpretation of the petrography of carbon in extraterrestrial samples. In particular, improved petrographic data from carbonaceous chondrites and ureilite meteorites should help to distinguish the origin of carbon in their parent bodies.

Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data.

Organic geochemistry applied to samples of bedrock and surface sediment from the Haughton impact structure detects a range of signatures representing the impact event and the transfer of organic matter from the crater bedrock to its erosion products. The bedrock dolomite contains hydrocarbon-bearing fluid inclusions which were incorporated before the impact event. Comparison of biomarker data from the hydrocarbons in samples inside and outside of the crater show the thermal signature of an impact. The occurrence of hydrocarbon inclusions in hydrothermal mineral samples shows that organic matter was mobilized and migrated in the immediate aftermath of the impact. The hydrocarbon signature was then transferred from bedrock to the crater-fill lacustrine deposits and present-day sediments in the crater, including wind-blown detritus in snow/ice. Separate signatures are detected from modern microbial life in crater rock and sediment samples. Signatures in Haughton crater samples are readily detectable because they include hydrocarbons generated by the burial of organic matter. This type of organic matter is not expected in crater samples on other planets, but the Haughton data show that, using very high resolution detection of organic compounds, any signature of primitive life in the crater rocks could be transferred to surface detritus and so extend the sampling medium.

Authigenic carbonate crusts, nodules and chemoherms were sampled from pockmarks and mud diapirs on the southern part of the Voring Plateau during the TTR-8 and TTR-10 marine expeditions. A petrographic and geochemical study was carried out to investigate their possible relationship with the seepage of hydrocarbon fluids. All authigenic carbonates are depleted in 13 C (−31.6‰ δ 13 C δ 18 O 18 O (4.6‰ δ 18 O 18 O-rich fluid. The occurrence of different carbonate mineral phases (aragonite, calcite, dolomite) is possibly related to varying dissolved sulphate concentrations in the diagenetic environment. Fluid inclusion microthermometry and Raman spectroscopy indicate the presence of an aqueous + hydrocarbon mixture inside the inclusions. This seepage mixture was almost certainly immiscible, resulting in heterogeneous trapping.

The measurement of organic matter in carbonates and evaporites is of value to both the petroleum and minerals industries and has future potential during planetary exploration. Bulk analyses provide basic information on thermal maturity and hydrocarbon prospectivity. Specific analysis of hydrocarbon gases is also related to thermal maturity and has been shown to exhibit patterns related to the distribution of ore mineralization. More advanced analyses rely on extracting hydrocarbons from oil fluid inclusions, which allows the integration of geochemical data with petrography, especially where individual inclusions can be analysed. Data from distinct populations of inclusions can highlight changes in geochemistry with time from a single sample. The extraction of organic molecules from aqueous inclusion fluids will be much more difficult technically but, if achieved, could help to obtain biomolecular data from early Earth samples and from samples retrieved from other planets. This will require very high resolution techniques, including the application of biotechnology to geological samples.

The hydrocarbon potential of sandstone reservoirs may be significantly affected by postdepositional compartmentation by grain-scale deformation mechanisms such as pressure solution, dislocation creep, microfracturing, and small-scale faulting. Deformation bands, sub 1-mm-thick elongate layers characterized by intense localized brittle fracturing, are important small-scale structural features controlling fluid flow in reservoir sands. They can act as fluid pathways or as barriers to fluid flow, depending on the timing relationship between hydrocarbon charge and deformation. Characterization of deformation-band scale, distribution, and timing of deformation relative to hydrocarbon charge is therefore critical in a full assessment of reservoir history. Integrated CL and UV studies of fluid inclusions from the Jeanne d'Arc Basin, Newfoundland, demonstrate that hydrocarbon charge predated deformation-band formation because oil-trapping quartz overgrowths are clearly cut by deformation bands. In contrast, porous, bitumen-rich sandstones from the Upper Old Red Sandstone of Caithness, NE Scotland, contain hydrocarbon inclusions trapped in quartz overgrowths that formed after deformation. Detailed petrographic work and CL imaging of these Old Red Sandstone samples demonstrates that hydrocarbons are absent in cemented deformation bands and occur only in undeformed sandstone pores and late quartz overgrowths. Post-deformation hydrocarbon migration pathways were thus constrained by effectively sealed deformation bands. In a third example, from the Jurassic of Skye, there is evidence for hydrocarbons in early (pre-band) cements, entrainment of hydrocarbons during band development, and a later pore-filling oil charge, indicating a complex relationship between the migration history and the bands.

In addition to the accepted roles of plate tectonics in regulating planetary habitability through the composition of the atmosphere and temperature, and creating continents to enhance land-based evolution and biodiversity, it has a hitherto unexplored role in influencing surface mineralogy with possible implications for early evolution. Plate tectonics creates continents through the accretion of buoyant granitic crust. Erosion of the granites yields specific minerals including quartz, radioactive (uranium-, thorium-bearing) phases and phosphates, which could play a role in early evolution. Radioactive grains could help to concentrate carbon and increase its complexity through irradiation-induced polymerization at the prebiotic stage, and possibly influence mutation rates once life was established. Weathering of phosphate minerals was an important source of phosphorus for the biochemistry that is essential to life. Quartz-rich sands provide a translucent refuge for early photosynthesizers below the harmful effects of ultra-violet irradiation at the surface. Uranium is also important to the development of nuclear power in an advanced civilization. The mineralogy that engenders these processes is distinct from that to be expected on a planet without plate tectonics, where volcanogenic sediments would predominate, and further emphasizes the importance of plate tectonics to the evolution of life.

Petroleum fluids escape from hydrocarbon reservoirs through permeable networks of fractures, injected sands and by seepage through low permeability host rocks. Carbon stable isotope analysis of carbonate cement associated with such structures shows that the escaping petroleum fluid is intimately involved in precipitating carbonate cement. Within fractures and injected sands, oxidation of chained hydrocarbons supplies bicarbonate to the co-existing aqueous solution from which carbonate precipitates (y 13 C around 20xV-PDB). y 13 C values within carbonate crusts associated with seeps are lower (as low as 50xV-PDB) suggesting a component of carbon derived from methane within these structures. This suggests a separation within the escaping petroleum fluids, with chained hydrocarbons remaining trapped within sand injectites and fractures, whereas more buoyant fluids (methane) continue to escape through low permeability host rocks. The abundance of fluorescing (chained) hydrocarbon inclusions within cement associated with fractures and injected sands versus the scarce occurrence of fluorescing inclusions within carbonate crusts associated with seeps is in agreement with results from stable isotope analysis. Oxygen stable isotope ratios indicate that carbonate cement within fractures and sand injectites precipitates at temperatures between 30 and 50 jC in the subsurface, whereas carbonate cement associated with seeps at the seafloor precipitates at temperatures around 0 jC. D 2003 Elsevier Science B.V. All rights reserved.

Transmitted light and ultraviolet (UV) light microscopy combined with microthermometry of fluid inclusions in sandstonesfrom 10 wells in the Irish Porcupine Basin reveal the presence of aqueous and oil-bearing fluids in cements and detrital quartz grains. Jurassic sandstone samples contain two-phase oil inclusions trapped during syn- and post-cementation and homogenise to the liquid state at ∼50 to 125 °C. Furthermore, early trapping in cement of less mature relatively heavy oil (°API gravity∼25–35) followed by ingress of lighter more mature oil (°API gravity∼45–50) is indicated. Primary two-phase aqueous fluid inclusions trapped in cements are generally of low salinity (

Petroleum fluid inclusions from the Paleogene Shahejie Formation in Bohai Basin, Eastern China, were characterized usingMicro-Fourier transform-infrared (Micro-FT-IR) and fluorescence microscopy, and Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS). Primary and secondary populations of organic inclusions were recognized. The primary petroleum inclusions contain organic compounds with relatively long alkyl chains, whereas the secondary petroleum inclusions contain organic materials with relatively short alkyl chains and also some H 2 S. The homogenization temperature ( T h ) of the primary inclusions is lower (coeval petroleum and aqueous inclusions both mean 87 °C) than that of the secondary inclusions (coeval aqueous mean 106 °C), suggesting that the primary petroleum inclusions experienced a lower degree of thermal evolution than that of the secondary inclusions. This inference is consistent with the fluorescence characteristics of the inclusions. The Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) analysis successfully distinguished the compositions of the two populations of petroleum inclusions, and also detected traces of saline aqueous fluid present in the primary inclusions.

Veins of bitumen occur in the Jurassic-Cretaceous of northern Cuba in the vicinity of oil fields dominated by extra-heavy crude. Some bitumen veins are associated with hydrothermal mineralization. Calcite vein rock at Soroa contains evidence for three phases of hydrocarbon migration: fresh oil fluid inclusions, followed by thermally altered oil (coeval aqueous fluid inclusions at up to 221 °C), then less altered oil. In addition to demonstrating a mechanism for producing altered oil other than by biodegradation, these observations support a model of multi-episodic hydrocarbon migration, which may be related to thrusting of the source beds.

Recent fluvial sediments of the Rio Neuquen, Argentina, contain variable amounts of placer gold. In addition to rounded, detrital placer gold, the sediments also contain pristine crystalline gold (type 1 gold), which occurs as overgrowths on detrital placer gold cores. Type 1 gold is locally rimmed by gold with a wormlike or crystalline texture (type 2 gold). The chemistry of the primary cores indicates variable intragrain and intergrain compositional heterogeneity. This is interpreted to indicate a multisource origin. Type 1 gold is composed of virtually pure gold (>98 at. % Au) and type 2 gold is an Au-Hg amalgam (4–9 at. % Hg). Both varieties are authigenic in origin. The formation of the virtually pure type 1 gold is interpreted to be due to the addition of Au from an external source, rather than by the removal of Ag and other metals. The AuHgAg type 2 gold is interpreted to be due to Hg contamination from historic mining. Type 1 gold is interpreted to be analogous to the Ag-poor rims present on many placer gold grains. The evidence presented in this study supports the view that the Ag-poor rims on placer gold grains are the result of Au addition and not Ag removal. This study also has implications for both quantitative morphological and paragenetic studies of placer gold grains.

Fluid inclusions in minerals hold the potential to provide important data on the chemistry of the ambient fluids during mineral precipitation. Especially interesting to astrobiologists are inclusions in low-temperature minerals that may have been precipitated in the presence of microorganisms. We demonstrate that it is possible to obtain data from inclusions in chemosynthetic carbonates that precipitated by the oxidation of organic carbon around methane-bearing seepages. Chemosynthetic carbonates have been identified as a target rock for astrobiological exploration. Other surficial rock types identified as targets for astrobiological exploration include hydrothermal deposits, speleothems, stromatolites, tufas, and evaporites, each of which can contain fluid inclusions. Fracture systems below impact craters would also contain precipitates of minerals with fluid inclusions. As fluid inclusions are sealed microchambers, they preserve fluids in regions where water is now absent, such as regions of the martian surface. Although most inclusions are < 5 microns, the possibility to obtain data from the fluids, including biosignatures and physical remains of life, underscores the advantages of technological advances in the study of fluid inclusions. The crushing of bulk samples could release inclusion waters for analysis, which could be undertaken in situ on Mars.

A suite of Permian sylvite samples from Boulby potash mine, Yorkshire, UK, consistently yield traces of hydrogen upon analysis by a cold crush technique for liberating volatiles from entrapped fluid inclusions. In contrast, accompanying halite samples do not yield hydrogen. These data suggest the formation of hydrogen by radiolysis of water due to irradiation from potassium in the sylvite. The data indicate radiolysis as a mechanism for subsurface hydrogen generation, where it is available as an electron donor for a deep biosphere.

A demonstration study of the application of fluid inclusion data from the Jeanne d'Arc Basin shows that it provides valuable information about the oil charge history and reservoir compartmentation. Oil inclusions occur within both cements and annealed microfractures, indicating that diagenesis continued after or during oil emplacement, and that fractures were involved in oil migration. The oil inclusions occur in cements subsequently deformed in granulation seams, showing that the earliest oil charge pre-dated the end of deformation. Oil inclusions are sufficiently abundant to measure oil geochemistry. In a comparison between adjacent barren and oil-bearing wells in the Terra Nova Field, oil inclusions in the barren well testify to the breaching of a trap. Bulk volatile data (fluid inclusion stratigraphy, FIS) record the occurrence of hydrocarbon inclusions throughout sandstone reservoir sections, and also give indications of seepage to shallower levels.

There are a large number of solid bitumen veins in Central Peru which are known to be ubiquitously enriched in vanadium. The bitumen was emplaced as a viscous fluid under pressure, directly influenced by the igneous and tectonic activity in the Western Cordillera. The close association of the bitumen veins with the bituminous Pariatambo Formation suggests that a genetic relationship exists, i.e. the bitumen was sourced from the shale. Organic geochemical and elemental data from bitumen samples are characteristic of a fairly high maturity oil. Preliminary investigations suggest that the vanadium presence within the bitumen may be attributed to syn-sedimentary vanadium accumulation and subsequent transport within the migrating bitumen

Much gold in the Witwatersrand conglomerates is directly associated with seams of carbon that are generally parallel with bedding. Some seams locally crosscut bedding and form anastomosing fracture patterns, showing that emplacement of liquid hydrocarbons in those seams was postdepositional and infilled fractures that are generally parallel to bedding. Seams that are not observed to crosscut bedding are nonetheless petrographically identical and are believed to have a common, postdepositional origin. Carbon also occurs along sets of bedding-parallel microfractures through individual quartz pebbles in mineralized conglomerates. Planes of fluid inclusions parallel to the microfractures in pebbles show further evidence for the importance of bedding-parallel fluid flow. The occurrence of carbon seams on sedimentary discontinuity surfaces may reflect preferential emplacement of carbon along planes of weakness. Brittle extensional fracturing in pebbles indicates high fluid pressures, which may relate to hydrocarbon generation. Bedding-parallel minealization by quartz, clays, metamorphic chlorite/pyrophyllite, and gold, which reflect a complex multistage paragenesis, indicate repeated reactivation of bedding-plane permeability. Previous arguments against a hydrocarbon origin for the carbon seams have been based upon the low intergranular permeability of the rocks; however, the present study shows that this condition actually caused focusing of hydrocarbon fluid flow along discontinuity surfaces and facies boundaries. Interaction with uranium could have caused fixation of fluid hydrocarbon by radiolytic polymerization. The columnar nature of carbon in many of the seams, interpreted by others as a biogenic structure, could instead reflect polymer swelling normal to bedding in the direction of least confining stress.

Previous studies on naturally radioactive materials suggested that they can have a mutagenic effect on plants (growing in sands in Kerala, South West India), and on bats (dwelling in an abandoned underground mine of primary monazite ore in Namaqualand, Western Cape, South Africa). We hypothesised, based on previous theoretical work, that radioactive sands would not induce mutants in microorganisms over time scales typical of doubling times in the natural environment. The potential of exceptionally monazite (Th)-rich mineral sands collected from the coast of Espirito Santo, Brazil to induce single-point reversion in Escherichia coli cultures (both repair-competent and repair-deficient strains) was tested using the tryptophan reverse mutation assay. The results show that at least on a short-term scale (1–7 days), the monazite-rich sands did not cause an increase in reversion above background.

In a series of experiments the pyrolytic effects of the heating induced during the hypervelocity impact (HVI) of small projectiles of high TOC mudrock were observed. Impacts at these high speeds (km s−1) release sufficient energy to vaporise metal projectiles, and the temperatures created greatly exceed the pyrolysis temperatures typically employed during laboratory studies of the thermal alteration of sedimentary organic matter. Despite this the organic geochemical analyses of projectiles of Orcadian Laminite impacted into targets of sand and water at hypervelocities provides evidence that the structural backbone of biomarkers has remained intact and that only a comparatively low degree of thermal alteration (pre-oil window) has occurred. While further studies are necessary, it appears that the organic component of a projectile captured at hypervelocity will be a slightly thermally altered sample of its precursor.

An important process in the evolution of life is the precipitation and concentration of organic species. There are several examples of minerals acting as templates for the accumulation and concentration of organic matter. These include for instance clays (e.g. Cairns-Smith and Hartman, 1986), radioactive minerals (e.g. Rasmussen, et al. 1993), zeolites and feldspars (e.g. Smith, et al. 1999) and the sulphide mineral pyrite (FeS2) (e.g. Wachtershauser, 1988). Wachtershauser (1988) suggested that prebiotic chemistry and eventually life itself could have started on the surface of pyrite. Pyrite carries a slight positive electrical charge, and can attract negatively charged organic molecules, bringing them close enough to interact. Pyrite is also oil-wet in some circumstances (Yusupova, 2002). This means that if the mineral is exposed to a mix of oil and water, the oil will preferentially adhere to the surface of pyrite. We have studied migrated organic matter in the Irish Carboniferous, including in sulphide deposits, to assess whether sulphides in fact do act as templates for organics. Here, pyrite was found acting as a template for carbon fixation in hydrothermal calcite veins, cutting through limestone. The pyrite crystals are ca. 1 mm in diameter and scattered throughout the vein matrix. The organic matter is migrated bitumen, and appears as smooth and rounded solid droplets, concentrated around the pyrite crystals. Scanning electron microscope analyses show the organics occurring as a ca. 150 µm thick and even coating around the pyrite crystals. Sulphide templates could be important for carbon fixation on Mars. There is widespread evidence of that sulphur species are prominent in Martian surface environments, assumed to have been introduced to the surface through volcanic activity. Currently, the Martian surface is highly oxidizing and therefore sulphates predominate, but early in the planet’s history reducing conditions pertained. Accordingly it has been suggested that sulphides occurs on Mars (Burns and Fisher, 1990), now preserved at depth. Sulphides are also known to be present on Mars from Martian meteorites (e.g. Greenwood, et al. 2000). Sulphides are sources of fuel for micro-organisms that oxidize sulphides on Earth, and the same could have been the case on Mars (Bishop, et al. 2004). The carbon coated pyrite in this study, is one example from the geological record showing that terrestrial sulphides can have a high potential for the preservation of organic materials. This could also be possible on Mars, and therefore Martian sulphides are good targets for seeking evidence of putative Martian life.

Solid bitumens in fracture systems commonly contain microscopic crystals of authigenic quartz which were precipitated coevally with the bitumen early in the paragenesis of the fracture-fillings. The quartz contains primary fluid inclusions (both aqueous and hydrocarbon), yielding homogenization temperatures particularly in the range 95–130°C, indicating minimum temperatures of entrapment during petroleum migration. Volumes of up to 50% entrained quartz, and a predominance of aqueous inclusions, indicate that the petroleum fluid had a substantial aqueous component.

The global trend in environmental awareness and search for low carbon energy sources has led to an increasing interest in certain strategic elements, including Selenium (Se) and Tellurium (Te), whi...

Solid bitumen vein deposits were mined until recently in Shuitian, Hunan Province, China. The Shuitian bitumen veins occur in Lower Cambrian black siltstones beneath the pre-Cretaceous unconformity. The H/C ratio of the bitumen is very low, suggesting that the bitumen is very mature and can be classified as impsonite. The carbon in both the bitumen and the host rock is completely aromatic. The minerals associated with the bitumen are quartz, calcite, pyrite and barite. Two kinds of vanadium-bearing mineral inclusions, montroseite and roscoelite, occur within the bitumen. It can be deduced that the vein must have formed within the interval from Caledonian Orogeny to Cretaceous sedimentation, although there is not enough evidence to indicate the exact timing of the vein formation.

The occurrence of a potash salt cement in halite is a newly recognized feature of early (syndepositional) diagenesis of halite. The potash salt cement has been recognized in modern halite of the Qarhan salt lake playa of the Qaidam Basin, NW China, and in ancient halite of the Permian Teesside Group from Boulby, NE England. Syndepositional textures in ancient halite are normally very difficult to determine. The potash salt cement consists of carnallite and sylvite precipitated in dissolution cavities and fractures in halite. In the Boulby deposits, there is evidence for the incongruent dissolution of carnallite to form sylvite, a process which ultimately leads to the complete replacement of carnallite. In the Qarhan salt lake playa, the potash salt cement may have been precipitated through both the cooling of a surfacial residual brine and mixing of calcium chloride brine from deep fault/oil field with the interstitial brine in the halite.

One of the key-principles of the iron-sulphur world theory is to bring organic molecules close enough to interact with each other, using the surface of pyrite as a substrate in a hydrothermal setting. The present paper explores the relationship of pyrite and organic matter in a hydrothermal setting from the geological record; in hydrothermal calcite veins from Carboniferous limestones in central Ireland. Here, the organic matter is accumulated as coatings around, and through, pyrite grains. Most of the pyrite grains are euhedral-subhedral crystals, ranging in size from ca 0.1-0.5 mm in diameter, and they are scattered throughout the matrix of the vein calcite. The organic matter was deposited from a hydrothermal fluid at a temperature of at least 200°C, and gives a Raman signature of disordered carbon. This study points to an example from a hydrothermal setting in the geological record, demonstrating that pyrite can have a high potential for the concentration and accumulation of organic materials.

A 1 cm thick sandstone disk exposed to atmospheric re-entry on the heat shield of a spacecraft (the STONE 5 experiment) shows alteration of fluid inclusions compared to a control sample. The sandstone contained inclusions in quartz grains, feldspar grains and calcite cement before flight. After flight, inclusions in the feldspar were all decrepitated, few inclusions in calcite survived intact and they yielded widely varying microthermometric data, and the quartz inclusions also yielded disturbed microthermometric data. The quartz becomes less affected with depth below the surface, and extrapolation suggests would be unaffected at a depth of about 2 cm. These data show that fluid inclusion data from meteorites must be treated with caution, but that a genuine fluid record may survive in the interior portions. The possibility of thermal sterilization to 2 cm depth also implies that small meteorites may be unsuitable vehicles for the transfer of microbial life from one planetary body to another. As the interiors of larger meteorites tend to have very low porosity and permeability, microbial colonization would be difficult, and the potential for panspermia is accordingly low.

International audience; If life ever appeared on Mars, could we find traces of primitive life embedded in sedimentary meteorites? To answer this question, a 3.5 billion-year-old volcanic sediment containing microfossils was embedded in the heat shield of a space capsule in order to test survival of the rock and the microfossils during entry into the Earth's atmosphere (the STONE 6 experiment). The silicified volcanic sediment from the Kitty's Gap Chert (Pilbara, Australia) is considered to be an excellent analogue for Noachian-age volcanic sediments. The microfossils in the chert are also analogues for potential martian life. An additional goal was to investigate the survival of living microorganisms (Chroococcidiopsis) protected by a 2 cm thick layer of rock in order to test whether living endolithic organisms could survive atmospheric entry when protected by a rocky coating. Mineralogical alteration of the sediment due to shock heating was manifested by the formation of a fusion crust, cracks in the chert due to prograde and retrograde changes of α quartz to β quartz, increase in the size of the fluid inclusions, and dewatering of the hydromuscovite-replaced volcanic protoliths. The carbonaceous microfossils embedded in the chert matrix survived in the rock away from the fusion crust but there was an increase in the maturity index of the kerogen towards the crust. We conclude that this kind of sediment can survive atmospheric entry and, if it contains microfossils, they could also survive. The living microorganisms were, however, completely carbonised by flame leakage to the back of the sample and therefore non-viable. However, using an analytical model to estimate the temperature reached within the sample thickness, we conclude that, even without flame leakage, the living organisms probably need to be protected by at least 5 cm of rock in order to be shielded from the intense heat of entry.

SOME of the Precambrian natural fission reactors at Oklo in Gabon contain abundant organic matter1,2, part of which was liquefied at the time of criticality and subsequently converted to a graphitic solid3,4. The liquid organic matter helps to reduce U(VI) to U(IV) from aqueous solutions, resulting in the precipitation of uraninite5. It is known that in the prevailing reactor environments, precipitated uraninite grains incorporated fission products. We report here observations which show that these uraninite crystals were held immobile within the resolidified, graphitic bitumen. Unlike water-soluble (humic) organic matter, the graphitic bituminous organics at Oklo thus enhanced radionu-clide containment. Uraninite encased in solid graphitic matter in the organic-rich reactor zones lost virtually no fissiogenic lan-thanide isotopes. The first major episode of uranium and lead migration was caused by the intrusion of a swarm of adjacent dolerite dykes about 1,100 Myr after the reactors went critical. Our results from Oklo imply that the use of organic, hydrophobic solids such as graphitic bitumen as a means of immobilizing radionuclides in pretreated nuclear waste warrants further investigation.

We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon.\ud \ud The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar–Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian.\ud \ud Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono–thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar–Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar–Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention.

Ambient inclusion trails (AIT) are enigmatic microtubular structures created by the migration of mineral crystals through a lithified substrate. The decomposition of organic material has been suggested as the driving force for the crystal migration, but has yet to be rigorously tested. AIT may hold potential as a biosignature for investigating early life on Earth if the associated organic material can be shown to be biological. This paper attempts to test the formation mechanism and biogenicity of AIT from the c . 3400 Ma Strelley Pool sandstone of Western Australia using NanoSIMS technology. In doing so, we demonstrate the unique ability of the NanoSIMS to combine sub-micron scale imaging with in situ chemical and isotopic data, thereby enhancing our ability to evaluate the biogenicity criteria for Archaean microstructures. Enrichments of a suite of major elements (C, N, P, S) and trace elements (Co, Fe, Ni, Zn), often associated with biological processes, are found within several AIT in this sandstone. C and N enrichments are most common along AIT margins, and correlate with depletions of Si, O, Ca and Mg, indicating that this material is indeed organic in nature. δ 13 C values of this carbonaceous material average −26‰. Petrographic observations show that some of the AIT occur in the centre of detrital sandstone grains where they were sealed from later fluid flow and therefore preserve primary Archaean (bio)geochemistry. In contrast, AIT found around the outer edges of sandstone grains may contain more recent organic material introduced by later fluid migration and are an unreliable biosignature. Using the petrographic and geochemical data a multi-stage model for AIT formation and subsequent diagenetic modification is proposed. The possible sources of the primary organic material are discussed and we conclude that the data are consistent with a biological origin for these AIT. An abiogenic origin is more difficult to sustain but cannot yet be completely excluded for AIT in general.

Nodules of thorium-rich hydrocarbon are recorded in sandstone sequences from several basins. The hydrocarbon nodules contain mineral inclusions, particularly of thorite or monazite. There is evidence both for accretion of hydrocarbons around detrital heavy mineral grains and for epigenetic growth by interaction of hydrocarbons with thorium-bearing fluids. Both mechanisms depend upon the precipitation of solid hydrocarbons induced by irradiation from thorium. The nodules exhibit aggressive replacement of other grains, a characteristic of radioanomalous hydrocarbons. The occurrence of the nodules is dependent upon an appropriate (plutonic) source for the thorium, but given this constraint they are important evidence for hydrocarbon migration pathways.