petroleum formation by fischer tropsch synthesis in plate tectonics a somewhat speculative hypothesis of petroleum genesis in the upper lithosphere is proposed based on fischer tropsch synthesis this hypothesis is distinct from both the organic biogenic model and the inorganic model of hydrocarbon degassing from the earth s interior fischer tropsch synthesis is a well known industrial process whereby millions of tons of hydrocarbon oil resembling petroleum are produced annually from carbon monoxide or carbon dioxide and hydrogen gases reacting on a metallic iron or iron oxide catalyst like natural petroleum this synthetic oil consists of gas gasoline diesel oil and wax fractions all rich in saturated aliphatic hydrocarbons and enriched in the light 12c isotope the hypothesis presented in this paper proposes that petroleum liquids form by fischer tropsch synthesis on magnetite and hematite catalysts when carbon dioxide derived by massive metamorphic or igneous decarbonation of subducted sedimentary carbonates reacts with hydrogen generated by the serpentinization in the absence of air of shallow mantle lithosphere and ophiolite thrust sheets oblique plate movements may favor hydrocarbon formation by creating deep faults that aid fluid flow and serpentinization the world s richest oil provinces including those of the middle east may be tentatively interpreted to have formed by this mechanism

a conceptual model for glaciogenic reservoirs from landsystems to reservoir architecture abstract glaciogenic sediments are present in many hydrocarbon producing basins across the globe but their complex nature makes it difficult to characterise the reservoir quality sedimentary units despite this ordovician glacial deposits in north africa and carboniferous permian glaciogenic sequences in the middle east have been proven to host significant economical hydrocarbon accumulations additionally discoveries have been made in the shallow

light hydrocarbon gases in guaymas basin hydrothermal fluids thermogenic versus abiogenic origin light hydrocarbon gases methane through pentane in high temperature hydrothermal fluids of the guaymas basin gulf of california are predominantly derived from thermocatalysis of organic carbon in sediments intruded by mid ocean ridge volcanic rocks the spectrum of c1 c5 gases in guaymas basin hydrothermal fluids is characterized by a preponderance of alkanes with essentially no alkenes present comparison with high temperature fluids from 21 n on the east pacific rise where geochemical evidence indicates a distinct lack of thermogenic gas and where methane is derived abiogenically from the basalts shows that the 21 n hydrocarbon gases are characterized by a prominent ethylene signature stable isotope compositions of guaymas basin m thane differ from 21 n gas guaymas basin has dgr13c values of 43 to 51 pmil vs pdb compared to 21 n where values as high as 15 pmil have been measured these differences reflect the different origins of light hydrocarbon gases in the two systems with guaymas methane being overwhelmingly of an organic thermogenic derivation and showing no evidence of the abiogenic basalt derived gas that characterizes the 21 n environment carbon isotope analyses of dissolved inorganic carbon in guaymas basin hydrothermal fluids indicate that high temperature hydrocarbon oxidation may be an important process acting in conjunction with high temperature thermocatalytic hydrocarbon generation

fluid inclusion and stable isotope c o and s constraints on the genesis of the high grade langdu cu skarn deposit in yunnan sw china abstract the langdu cu skarn deposit is the highest grade cu deposit average 6 49 cu in the zhongdian polymetallic district in sw china skarns and ore bodies occur primarily in the contact zone of upper triassic qugasi formation fm and late triassic ca 217 ma intrusions disseminated massive stockwork and vein like sulfide ores occur in the skarn quartz calcite veins porphyry and marble skarn minerals include pyroxene garnet actinolite and epidote four types six subtypes of fluid inclusions fis are identified in the sulfide bearing quartz veins type i liquid rich two phase fis have varying vapor liquid ratios and yielded homogenization temperatures of 110 338 c and salinities of 1 7 29 5 wt nacl eqv type ii vapor rich fis contain ch4 n2 bubbles and homogenized to vapor at 262 425 c type iii fis are single phase at room temperature 20 c a vapor phase is present at below 120 c and the fis homogenized at 117 to 114 c type iv daughter mineral bearing fis homogenized by halite disappearance at 295 392 c and have salinities of 37 8 46 6 wt nacl eqv such characteristics suggest that fis were trapped by fluid immiscibility and phase separation the 34scdt values of chalcopyrite and pyrrhotite are of 5 3 to 0 7 on the 34s histogram all langdu data show a cluster of 32s rich 34scdt 5 3 to 4 6 and a cluster of 34s rich 34scdt 1 1 to 0 7 type i calcite in skarn and type ii calcite in quartz sulfide vein have 13cpdb and 18osmow values of 8 4 to 7 8 6 3 to 6 1 and 10 1 to 12 3 and 12 0 to 13 0 respectively type iii calcite from calcite sulfide veins has 13cpdb 5 6 to 0 2 and 18osmow 12 5 to 16 3 biotite garnet and pyroxene syn ore quartz and chlorite yielded 18osmow values of 6 9 4 1 5 13 2 15 3 and 6 8 respectively sulfur carbon and oxygen isotopic features of these hydrothermal minerals and the fis microthermometric data suggest that the ore forming fluids were magmatic sourced and contaminated by meteoric formation water during ascent and or fluid wallrock interactions low 34s 5 3 to 4 6 in sulfides and the ch4 in the fis are interpreted to reflect the reaction between the magmatic fluids and the carbonaceous slate in qugasi fm the methane likely expanded the vapor liquid immiscibility field and reduced the sulfates so42 to sulfides s2 and extensive water rock reaction and fluid mixing may have occurred leading to the high grade cu mineralization at langdu

methane flux and origin in the othrys ophiolite hyperalkaline springs greece abstract the occurrence and origin of methane ch4 generated by serpentinization of ultramafic rocks is of current timely interest in planetary geology astrobiology and energy resource exploration as it may contribute in particular to decipher the source of methane on mars the origin of life and the potential of abiotic hydrocarbon synthesis methane of dominant abiotic origin in serpentinized peridotites on continents ophiolites or igneous intrusions has been documented so far with complete carbon and hydrogen isotope composition in six countries in the philippines turkey oman new zealand japan and italy we report the discovery of two new sites in greece at archani and ekkara located in the othrys ophiolite massif portable sensors based on fourier transform infrared spectrometry ftir and tunable diode laser absorption spectroscopy tdlas allowed to realize that out of 21 ophiolitic springs methane is released only by four hyperalkaline ph from 10 7 to 11 3 and calcium hydroxide ca oh type waters all other 17 springs with ph

bitumen biomarkers in the mid proterozoic ilimaussaq intrusion southwest greenland a challenge to the mantle gas theory abstract gc and gc ms ms analysis on rock extracts has shown that the bitumen in the peralkaline ilimaussaq intrusion previously assumed to be abiogenic is biotic in origin a biotic origin is in accordance with previously published stable carbon isotopic data on bituminous matter in the rocks the biomarker distribution in the bitumen including the less common bicadinanes resembles that of oil seeps on the central west greenland coast 2200 km farther north whose source rocks and migration history are relatively well established we use a recent re construction of the subsidence and later exhumation of the west greenland coastal region during the mesozoic cenozoic japsen et al 2006a b to anticipate that hydrocarbons migrated from deeper parts of the basin offshore west of greenland the rocks of ilimaussaq were probably more deeply invaded than the surrounding granites due to their higher proportion of corroded minerals which may explain why bitumen has not been observed elsewhere in the area hydrocarbon gases c1 c5 present in fluid inclusions were also analysed after having been released by treatment with hydrochloric acid that resulted in an almost complete disintegration of the ilimaussaq intrusion rocks the acid extraction method proved generally more efficient than the crushing procedure applied by others but gave similar results for the chemical composition of the gas ch4 88 97 and isotopic ratios 13 c ch 4 1 6 to 5 0 13 c c 2 h 6 9 2 to 12 5 with the exception of hydrocarbons hosted in quartz which showed significantly lower isotopic values for methane graser et al 2008 previous researchers have suggested an abiotic origin for these hydrocarbon gases but we suggest a biotic origin for the majority of them not just those in quartz assuming that the isotopic ratio of the constituents have changed due to loss of gas by diffusion the assumption of gas loss via diffusion is supported by published studies on micro fissures in minerals typical of the ilimaussaq and field investigations showing diffusive loss of gas from the peralkaline khibina and lovozero massifs on the kola peninsula russia which are in many respects of mineralogy and hydrocarbon content similar to the ilimaussaq intrusion both the hydrocarbon gases and bitumen in the khibina and lovozero massifs have been cited as prime examples of a deep mantle source although the carbon isotopic ratio of the bitumen clearly pointed to an organic origin the trends in carbon isotopic ratio of methane released with time from freshly exposed rocks also supports our hypothesis of 13c enrichment of the methane remaining within the rock thus there is good evidence that the hydrocarbons in the kola alkaline massifs are mostly biotic in origin in which case the probability of finding economic hydrocarbon accumulations from a deep mantle source seems exceedingly small

natural fracking and the genesis of five element veins hydrothermal ag co ni bi as five element vein type ore deposits show very conspicuous textures of the native elements silver bismuth and arsenic indicating formation from a rapid far from equilibrium process such textures include up to dm large tree and wire like aggregates overgrown by co ni fe arsenides and mostly carbonates despite the historical and contemporary importance of five element vein type deposits as sources of silver bismuth and cobalt and despite of spectacular museum specimens their process of formation is not yet understood and has been a matter of debate since centuries we propose based on observations from a number of classical european five element vein deposits and carbon isotope analyses that natural fracking i e liberation of hydrocarbons or hydrocarbon bearing fluids during break up of rocks in the vicinity of an active hydrothermal system and mixing between these hydrocarbons e g methane and or methane bearing fluids and a metal rich hydrothermal fluid is responsible for ore precipitation and the formation of the unusual ore textures and assemblages thermodynamic and isotope mixing calculations show that the textural chemical and isotopic features of the investigated deposits can entirely be explained by this mechanism

methane derived hydrocarbons produced under upper mantle conditions there is widespread evidence that petroleum originates from biological processes 1 3 whether hydrocarbons can also be produced from abiogenic precursor molecules under the high pressure high tem

reappraisal of the fossil methane budget and related emission from geologic sources converging evidence from new top down and bottom up estimates of fossil radiocarbon free methane emissions indicates that natural geologic sources account for a substantial component of the atmospheric methane budget comparing emission estimates based on atmospheric 14 ch 4 radiomethane with geologic emissions from seepage including terrestrial macroseeps microseepage marine seeps and geothermal volcanic emissions from the earth s crust shows that such geo ch 4 sources can be conservatively estimated at 53 11 tg yr 1 globally this makes geo ch 4 second in importance to wetlands as a natural methane source such a new appraisal can easily be accommodated within the uncertainty of the global methane budget as recently compiled and recognizes the importance of geophysical out gassing of methane generated within the lithosphere we propose a new coherent contemporary budget in which 30 5 based on atmospheric radiomethane measurements of the global source of 582 87 tg yr 1 has fossil origin both natural and anthropogenic

chemical and isotopic equilibrium between co2 and ch4 in fumarolic gas discharges generation of ch4 in arc magmatic hydrothermal systems the chemical and isotopic composition of fumarolic gases emitted from nisyros volcano greece and of a single gas sample from vesuvio italy was investigated in order to determine the origin of methane ch4 within two subduction related magmatic hydrothermal environments apparent temperatures derived from carbon isotope partitioning between ch4 and co2 of around 340 c for nisyros and 470 c for vesuvio correlate well with aquifer temperatures as measured directly and or inferred from compositional data using the h2o h2 co2 co ch4 geothermometer thermodynamic modeling reveals chemical equilibrium between ch4 co2 and h2o implying that carbon isotope partitioning between co2 and ch4 in both systems is controlled by aquifer temperature n2 3he and ch4 3he ratios of nisyros fumarolic gases are unusually low for subduction zone gases and correspond to those of midoceanic ridge environments accordingly ch4 may have been primarily generated through the reduction of co2 by h2 in the absence of any organic matter following a fischer tropsch type reaction however primary occurrence of minor amounts of thermogenic ch4 and subsequent re equilibration with co existing co2 cannot be ruled out entirely co2 3he ratios and 13cco2 values imply that the evolved co2 either derives from a metasomatized mantle or is a mixture between two components one outgassing from an unaltered mantle and the other released by thermal breakdown of marine carbonates the latter may contain traces of organic matter possibly decomposing to ch4 during thermometamorphism

abiotic methane in continental ultramafic rock systems towards a genetic model abstract methane ch4 often in substantial quantities is reported for numerous surface manifestations seeps springs and aquifers in continental serpentinized ultramafic rocks in ophiolites peridotite massifs and intrusions frequently this gas is considered to have a dominant abiotic origin with variable though generally minor components of biotic gas thermogenic or microbial abiotic ch4 production through low temperature fischer tropsch type reactions ftt between a carbon c compound and h2 is endorsed by most of scholars but direct derivation from olivine hydration serpentinization magmatic sources and fluid inclusions have also been suggested here we review the application of ftt in geology discussing the appropriateness of several c compounds co2 co formic acid formate or elemental c as ch4 precursors and of aqueous versus gas phase reactions we examine published gas geochemical and flux data that provide clear constraints on the methane origins in the analysis we add new isotopic and gas seepage data acquired in surface gas manifestations at acquasanta in the voltri ophiolite genova italy multiple lines of evidence including a stable isotope compositions of ch4 co2 and helium b radiocarbon free ch4 c isotopic disequilibrium between ch4 and h2o d low temperatures of ch4 production based on clumped isotopes and heat flow data and e methane seepage forms and intensities suggest that ch4 is not formed directly in water or from magmatic sources or fluid inclusions rather all the lines of evidence taken together are compatible with the hypothesis of low temperature

natural emissions of methane from geothermal and volcanic sources in europe it has recently been demonstrated that methane emission from lithosphere degassing is an important component of the natural greenhouse gas atmospheric budget globally the geological sources are mainly due to seepage from hydrocarbon prone sedimentary basins and subordinately from geothermal volcanic fluxes this work provides a first estimate of methane emission from the geothermal volcanic component at european level in europe 28 countries have geothermal systems and at least 10 countries host surface geothermal manifestations hot springs mofettes gas vents even if direct methane flux measurements are available only for a few small areas in italy a fair number of data on co2 ch4 and steam composition and flux from geothermal manifestations are today available for 6 countries czech republic germany greece iceland italy spain following the emission factor and area based approach the available data have been analyzed and have led to an early and conservative estimate of methane emission into the atmosphere around 10 000 ton yr 4000 16 000 ton yr basically from an area smaller than 4000 km2 with a speculative upper limit in the order of 105 ton yr only 4 18 of the conservative estimate about 720 ton yr is due to 12 european volcanoes where methane concentration in volcanic gases is generally in the order of a few tens of ppmv volcanoes are thus not a significant methane source while the largest emission is due to geothermal areas which may be situated next to volcanoes or independent here inorganic synthesis thermometamorphism and thermal breakdown of organic matter are substantial methane flux can reach hundreds of ton yr from small individual vents geothermal methane is mainly released in three countries located in the main high heat flow regions italy greece and iceland turkey is likely a fourth important contributor but the absolute lack of data prevents any emission estimate therefore the actual european geothermal volcanic methane emission could be easily projected to the 105 ton yr levels reaching the magnitude of some other natural sources such as forest fires or wild animals

methane rich fluids in the oceanic crust analyses of fluid inclusions in plutonic rocks recovered from the slow spreading southwest indian ridge swir record ch4 concentrations of 15 40 times those of hydrothermal vent fluids and of basalt hosted volcanic gases and provide the first direct sampling of co2 ch4 h2o h2 c bearing fluids in the oceanic crust compositional thermal and spatial analyses of these fluids are used to model the evolution of volatiles during the crystallization and cooling of mid ocean ridge magma chambers and to assess the potential importance of carbon bearing fluids in geochemical processes in the lower crustal component of hydrothermal systems results from these analyses show that the earliest fluids to be exsolved from the melts are dominated by co2 rich vapors which with progressive fractionation evolved to more h2o rich compositions these later fluids were most likely exsolved under immiscible conditions and involved the development of co2 h2o rich vapors and co2 h2o nacl brines that were trapped during mineral growth as well as during later high temperature fracturing events co2 ch4 h2o rich fluids in olivine and plagioclase minerals that contain up to 30 50 mol co2 and 33 mol ch4 may reflect respeciation of magmatic co2 during cooling and attendant graphite precipitation phase equilibria suggest that these fluids reequilibrated at 500 600 c and at fo2 s 3 log units below to close to qfm conditions alternatively the inclusions may record respeciation of magmatic fluids attendant with the inward diffusion of h2 into the inclusions and reduction of entrapped co2 during degassing and cooling of the gabbros throughout the subsolidus regime subsequent seawater reaction at minimum temperatures of 400 c with mafic rich layers within the gabbroic rocks or with ultramafic material that underlies the plutonic sequence resulted in the formation of ch4 h2o fluids that contain up to 40 mol ch4 molecular h2 and graphite daughter minerals these data provide strong evidence that the ch4 h2o rich fluids produced during serpentinization reactions were trapped under equilibrium conditions in the presence of graphite at very near to qfm conditions the ubiquitous occurrence of ch4 rich fluids in oceanic crustal layer 3 rocks from the swir indicates that these fluids may be a significant and previously unrecognized source for these volatile species in some hydrothermal systems venting on the seafloor and that the deep seated fluids most likely play an important role in the transfer of carbon from the lithosphere to the hydrosphere

linking serpentinization hyperalkaline mineral waters and abiotic methane production in continental peridotites an integrated hydrogeological bio geochemical model from the cabeco de vide ch4 rich aquifer portugal abstract continental active serpentinization of ultramafic rocks is today recognized as a key process triggering a sequence of phenomena involving the passage from inorganic to organic and metabolic reactions these may have a role in the origin of life and may explain the occurrence of abiotic hydrocarbons on earth and other planets production of hyperalkaline waters and abiotic methane ch4 are two critical steps in this sequence they were described independently by specific hydrogeological and geochemical models here we update and combine these models into a unified scheme using and integrating geological hydrogeological hydrogeochemical gas geochemical and microbial analyses acquired from 2002 to 2014 in the cabeco de vide cdv study site portugal the hyperalkaline ph 10 5 na cl ca oh mineral water of cdv evolve from groundwater peridotite interaction serpentinization generating hydrogen h2 which according to multiple theoretical laboratory and field evidence likely reacted with co2 within metal catalyst rich rocks abiotically producing ch4 up to 1 2 mg l 24 4 oo

the origin of ch4 rich fluids in reduced porphyry skarn cu mo au systems abstract although most of the methane on earth is of biogenic origin significant abiogenic methane has been identified in a variety of geological environments moreover the presence of methane has been reported recently in fluid inclusions from a number of reduced porphyry deposits the genesis of this methane however remains poorly understood here we present results of a study of magma exsolved ch4 rich aqueous fluid inclusions in the seleteguole reduced porphyry skarn cu mo au deposit nw china four types of fluid inclusions namely intermediate density two phase aqueous inclusions low density vapor inclusions brine inclusions and aqueous liquid inclusions have been distinguished on the basis of the phases present at room temperature the intermediate density inclusions were trapped as a single phase and contain 3 8 10 4 mol kg ch4 corresponding to an oxygen fugacity between fmq 1 and fmq 0 5 this attests to the remarkably reduced nature of the fluid the 13c value of the ch4 hosted fluid inclusions ranges from 29 4 to 19 1 pdb which distinguishes this methane from biogenic methane indeed the high homogenization temperature of the ch4 rich inclusions 400 c implies that the ch4 was exsolved directly from the magma given the environment in which the magma was likely generated i e at or immediately above a subducting plate we propose that the methane was produced by reactions involving organic matter bearing carbonate rocks in the subduction zone although cu mo and au in most porphyry systems are interpreted to have been transported under oxidizing conditions our results indicate that reduced aqueous liquids and vapors are also capable of transporting appreciable concentrations of these metals

the utility of methane clumped isotopes to constrain the origins of methane in natural gas accumulations methane clumped isotope compositions provide a new approach to understanding the formational conditions of methane from both biogenic and thermogenic sources under some conditions these compositions can be used to reconstruct the formational temperatures of the gas and this capability can be applied to common subsets of both biogenic and thermogenic systems additionally there are examples in which clumped isotope compositions do not reflect gas formation temperatures but instead mixing effects and kinetic phenomena such kinetic effects also occur in common and recognizable subtypes of biogenic and thermogenic gases here we review the use of methane clumped isotope measurements for understanding the origin of methane in the subsurface we review methane clumped isotope measurements from numerous biogenic and thermogenic natural gas reservoirs we then place these measurements in the context of common frameworks for identifying the formational conditions of methane including the use of methane 13 c and d values and c 1 c 2 3 ratios finally we propose a framework for how methane clumped isotopes can be used to identify the origin of methane accumulations

combined raman microprobe spectrometry and microthermometry of fluid inclusions in minerals from igneous rocks of the gardar province south greenland abstract raman microprobe spectrometry has been applied to analysis of the gaseous phase in individual fluid inclusions in minerals from alkalic igneous rock types and associated hydrothermal veins from the gardar province south greenland quantitative analyses are given for co2 ch4 c2h6 h2 and h2s traces of co were observed in one co2 inclusion in conjunction with data from microthermometry the results permit calculation of the bulk chemical composition of entrapped fluids and evaluation of the possible pressure temperature oxygen fugacity and sulphur fugacity during entrapment of the individual fluid inclusions calculated oxygen fugacity values correspond to those of the nno and qfm buffer reactions at temperatures of 300 400 c and pressures of 0 5 1 0 kbar calculated sulphur fugacity values are within the range of normal ore forming solutions log fs2 6 to 10

a reassessment of models for hydrocarbon generation in the khibiny nepheline syenite complex kola peninsula russia although hydrocarbon bearing fluids have been known from the alkaline igneous rocks of the khibiny intrusion for many years their origin remains enigmatic a recently proposed model of post magmatic hc generation through fischer tropsch type reactions suggests a primary co2 fluid this hypothesis is based upon textural data gas bulk and isotopic composition and low entrapment temperature of fluid inclusions that indicate an abiogenic origin for the hc gases however new petrographic microthermometric laser raman bulk gas and isotope data are presented and discussed in the context of previously published work in order to reassess models of hc generation the gas phase is dominated by ch4 with only minor proportions of higher hydrocarbons no remnants of the proposed primary co2 rich fluid are found anywhere in the complex primary and secondary fluid inclusions show similar compositions and entrapment conditions the majority of the fluid inclusions are of secondary nature and trapped in healed microfractures this indicates a high fluid flux after magma crystallisation entrapment condtions for primary fluid inclusions are 450 550 c at 2 8 4 5 kbar these temperatures are too high for hc gas generation through the ft reaction chemical analyses of rims of fe rich phases suggest that they are not the result of alteration but instead represent changes in magma composition during crystallisation furthermore there is no clear relationship between the presence of fe rich minerals and fluid inclusion abundance as reported elsewhere fluid inclusion planes generally start and terminate at mineral boundaries 13c values for methane range from 22 4 to 5 4 confirming also an abiogenic origin for the gas these data support an abiogenic hc origin but are not consistent with a post magmatic ft type reaction the presence of primary ch4 dominated fluid and melt inclusions which contain a methane rich gas phase indicate that a magmatic origin is more likely an increase in methane content together with a decrease in 13c isotope values towards the intrusion margin suggest that magmatically derived abiogenic hydrocarbons may have mixed with biogenic hydrocarbons derived from the surrounding country rocks

geochemical and isotopic approach to maturity source mixing estimations for natural gas and associated condensates in the thrace basin nw turkey abstract the tertiary thrace basin located in nw turkey comprises 9 km of clastic sedimentary column ranging in age from early eocene to recent in age fifteen natural gas and 10 associated condensate samples collected from the 11 different gas fields along the nw se extending zone of the northern portion of the basin were evaluated on the basis of their chemical and individual c isotopic compositions for the purpose of the study the genesis of ch4 thermogenic c2 gases and associated condensates were evaluated separately methane appears to have 3 origins group 1 ch4 is bacteriogenic calculated 13cc1 c 61 48 silivri field and found in oligocene reservoirs and mixed with the thermogenic group 2 ch4 they probably formed in the upper oligocene coal and shales deposited in a marshy swamp environment of fluvio deltaic settings group 2 13cc1 c 35 80 hamitabat field and group 3 13c1 c 49 10 degirmenkoy field methanes are thermogenic and share the same origin with the group 2 and group 3 c2 gases the group 2 c2 gases include 63 of the gas fields they are produced from both eocene overwhelmingly and oligocene reservoirs these gases were almost certainly generated from isotopically heavy terrestrial kerogen 13c 21 present in the eocene deltaic hamitabat shales the group 3 c2 gases produced from one field were generated from isotopically light marine kerogen 13c 29 lower oligoce ne mezardere shales deposited in pro deltaic settings are believed to be the source of these gases the bulk and individual n alkane isotopic relationships between the rock extracts gases condensates and oils from the basin differentiated two groups of condensates which can be genetically linked to the group 2 and 3 thermogenic c2 gases however it is crucial to note that condensates do not necessarily correlate to their associated gases maturity assessments on the group 1 and 2 thermogenic gases based on their estimated initial kerogen isotope values 13c 21 29 and on the biomarkers present in the associated condensates reveal that all the hydrocarbons including gases condensates and oils are the products of primary cracking at the early mature st age req 0 55 0 81 it is demonstrated that the open system source conditions required for such an early mature hydrocarbon expulsion exist and are supported by fault systems of the basin

production of carbonic fluids during metamorphism of graphitic pelites in a collisional orogen an assessment from fluid inclusions abstract fluid inclusions in quartz veins within proterozoic metamorphic rocks in the black hills south dakota were examined by microthermometry and raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic rich shales and late orogenic magmatism both of which were related to the collision of the wyoming and superior crustal blocks fluid inclusions occur in veins that began to be generated before or during regional compression and metamorphism that reached at least garnet grade conditions and in veins within the aureole of the harney peak granite hpg where temperatures reached second sillimanite grade conditions early veins in the schists have undergone recrystallization during heating and deformation that modified the composition of early ch4 or co2 and n2 dominated inclusions these fluids were apparently trapped under conditions of immiscibility with a saline aqueous fluid phase they are interpreted to represent components generated during maturation of organic matter and dehydration of phyllosilicates during incipient metamorphism at reducing fo2 conditions most inclusions in the quartz veins are however secondary co2 bearing they imply a transition to higher fo2 conditions with increasing temperature of regional metamorphism the fo2 conditions may have been controlled by the mineral assemblage in the host metapelites the prevalence of bimodal distributions of trapped co2 n2 and aqueous endmembers in the biotite and garnet zones also suggests that two immiscible fluid phases existed during the regional metamorphism in the aureole of the hpg graphite was evidently consumed by influx of magmatic fluids co2 h2o fluid inclusions dominate but they have significantly less n2 than inclusions at lower metamorphic grades all inclusions define secondary trails in mostly unstrained quartz the bimodality of inclusion compositions is not as well defined as at lower grades with many inclusions containing intermediate co2 h2o compositions this suggests that a single fluid phase existed at the high temperatures in the granite aureole but then unmixed during cooling a set of late quartz veins with graphitized and tourmalinized selvages in the granite aureole contains ch4 bearing inclusions with little n2 the existence of ch4 in these inclusions is attributed to complexing of magmatic b with hydroxyl anions taken from the co2 h2o fluid phase effectively causing reduction in fo2 and promoting precipitation of graphite

shallow submarine seep of abiotic methane from serpentinized peridotite off the island of elba italy abstract abiotic methane ch4 is today widely reported in gas seeps and hyperalkaline springs in ophiolites and peridotite massifs characterized by low temperature continental serpentinization origin and distribution of this gas have far reaching implications in microbiology astrobiology and carbon cycle we report an in depth study of a recently described abiotic ch4 seep occurring in shallow seafloor along the western coast of elba island tyrrhenian sea italy the gas is characterized by stable c and h isotopic compositions of ch4 13c 18 2h 141 and a very low co2 content that are typical of abiotic gas in continental ultramafic rock systems based on local geothermal gradients the temperature of methane production is estimated to be below 100 c the isotope signature of methane is similar to that occurring in the liguria region about 200 km north of elba island where the same ophiolite unit exposed a mantle co2 component suggested by relatively high 3he 4he ratios has likely acted as ch4 precursor the reconstruction of the geological structural setting of elba ophiolite sequence highlighted that the seep occurs in correspondence with a faulted reverse limb of the antiform of the ophiolite unit the gas bearing fault forms a contact between mafic and ultramafic serpentinized rocks as typically observed in other continental seeps and springs related to ophiolites magmatic intrusions in the island may have contributed to the c feedstock of methane

the early earth geochemical and isotope record of serpentinizing environments from archean stichtite mg6cr2 oh 16 co3 4h2o abstract a record of the conditions and duration of archean serpentinization is preserved as chemical isotopic and textural properties of the magnesium chromium hydroxycarbonate mineral stichtite this provides a window into the conditions associated with a potentially habitable environment on early earth and mars stichtite is associated with archean chromite rich serpentinite rocks of south africa western australia and southern india stichtite compositions range within the cr fe al hydrotalcite group with trends unique to each discrete serpentinite host body elemental and textural analysis of stichtite associated chromite indicates that stichtite forms in fore arc layered intrusive boninite setting rocks through interaction of chromite and methane rich serpentinizing fluids the degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the stichtite window carbon stable isotope values of archean stichtite suggest carbon sourcing from marine kerogen with minor marine dissolved inorganic carbonate in most samples as opposed to the strongly kerogen dominated phanerozoic stichtite the carbon and hydrogen stable isotope profile of archean stichtite ranges from the methane fields of active serpentinizing zones to geothermal with trends suggestive of methane oxidation rather than the substrate depletion noted in phanerozoic stichtite thus isotope values of stichtite appear to record oceanic oxygenation levels the association of the stichtite 2h polytype nee barbertonite with aragonite antigorite suggests this is a higher pressure temperature polytype of stichtite reaction textures isotopic values and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization in a methane h2 rich environment within fluid conduits ranging from near the surface to depths where pressure is up to 2 8 gpa and temperature is up to 300 c

hydrothermal gases offshore milos island greece hydrothermal fluids emerge from the seafloor of paleohori bay on milos the gases in these fluids contain mostly co2 but ch4 concentrations up to 2 are present the stable carbon isotopic composition of the co2 near 0 indicates an inorganic carbon source dissociation of underlying marine carbonates the carbon and hydrogen isotopes of most ch4 samples are enriched in the heavy species delta 13c 9 4 to 17 8 per mille sign delta d 102 to 189 per mille sign which is believed to be characteristic for an abiogenic production of ch4 by co2 reduction fischer tropsch reactions depletions in the deuterium content of three ch4 samples to 377 are probably caused by unknown subsurface rock alteration processes secondary hydrogen isotope exchange processes between methane hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures we show that excess helium slightly enriched in 3he is present in the hydrothermal fluids emerging the seafloor of paleohori bay when the isotopic ratio of the excess component is calculated a 3he 4heexcess of 3 6 10 6 is obtained this indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium we infer that the mantle derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface

methane bursts as a trigger for intermittent lake forming climates on post noachian mars lakes existed on mars later than 3 6 billion years ago according to sedimentary evidence for deltaic deposition the observed fluviolacustrine deposits suggest that individual lake forming climates persisted for at least several thousand years assuming dilute flow but the lake watersheds little weathered soils indicate a largely dry climate history with intermittent runoff events here we show that these observational constraints although inconsistent with many previously proposed triggers for lake forming climates are consistent with a methane burst scenario in this scenario chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate using numerical simulations we find that outgassed methane can build up to atmospheric levels sufficient for lake forming climates if methane clathrate initially occupies more than 4 of the total volume in which it is thermodynamically stable such occupancy fractions are consistent with methane production by water rock reactions due to hydrothermal circulation on early mars we further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake forming climates to less than a million years consistent with observations we conclude that methane bursts represent a potential pathway for intermittent excursions to a warm wet climate state on early mars

neon identifies two billion year old fluid component in kaapvaal craton abstract the deep gold mines of the witwatersrand basin south africa have gained recent attention not only because of investigations of the deep fracture water and associated ch4 and h2 rich gases found there but because of recent reports of deep microbial communities persisting to depths of almost 3 km an exotic outpost of the earth s deep biosphere while shallower fluids in the basin to approximately 1 km were found to contain abundant populations of methanogens and sulphate reducing bacteria the deepest oldest most saline fracture waters in the basin hosted hitherto unrecognised low biomass and low biodiversity chemoautotrophic ecosystems independent from the photosphere shallow and deep fluids also show distinct differences in gas and fluid geochemistry paleometeoric waters are dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilising the co2 reduction pathway in contrast the deepest most saline fracture waters contain gases that are dominated by high concentrations of h2 gas and ch4 and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water rock reaction the high salinities up to hundreds of g l highly altered 18o and 2h signatures and both 36cl and measurements of co occurring nucleogenic noble gases for these fracture waters are consistent with extensive water rock interaction over geologically long time scales in these high rock water ratio environments while the ultimate origin of these fluids has been attributed alternately to saline waters that penetrated the crystalline basement formation water or hydrothermal fluids in some cases their 18o and 2h isotopic signatures have typically been so profoundly overprinted by the effects of long term water rock interaction that for the most saline end members little evidence of their primary composition remains the key objective of the present study is to further investigate the origin of these fluids by integrating for the first time detailed neon isotope analyses on the dissolved gases helium isotopic analysis confirmed that there is no significant mantle derived component associated with these fluids and gases neon isotope results show distinct differences in neon composition that correspond to the different fluid geochemical end members previously identified typical crustal neon signatures type a are identified in the paleometeoric waters populated with abundant methanogens in contrast the deep more saline fracture waters contain an enriched nucleogenic neon signature unlike any previously reported in crustal fluids these samples show the highest 21ne 22ne ratios 0 160 0 003 ever reported in groundwater fluid inclusions in these rocks yield even higher 21ne 22ne ratios between 0 219 and 0 515 consistent with an extrapolated 21ne 22ne value of 3 3 0 2 at 20ne 22ne 0 we show that this enriched nucleogenic neon end member represents a fluid component that was produced in the fluorine depleted archaean formations and trapped in fluid inclusions 2 ga ago the observation of enriched nucleogenic neon signatures in deep fracture water implies the release of this billion year old neon component from the fluid inclusions and its accumulation in exceptionally isolated fracture water systems the observed association of this archean neon signature with h2 hydrocarbon rich geogases of proposed abiogenic origin dissolved in the same deep groundwater suggests that the fracture systems have also allowed for the accumulation of various products of water rock reactions throughout geologic times one of these fracture systems contained the deepest characterised microbial ecosystems on earth chemolithotrophs eking out an existence at maintenance levels independent from sunlight consequently the enriched nucleogenic neon isotope signature may indicate regions in the archaean crust where investigations of the deep biosphere might be focused

abiotic methane formation during experimental serpentinization of olivine fluids circulating through actively serpentinizing systems are often highly enriched in methane ch4 in many cases the ch4 in these fluids is thought to derive from abiotic reduction of inorganic carbon but the conditions under which this process can occur in natural systems remain unclear in recent years several studies have reported abiotic formation of ch4 during experimental serpentinization of olivine at temperatures at or below 200 c however these results seem to contradict studies conducted at higher temperatures 300 c to 400 c where substantial kinetic barriers to ch4 synthesis have been observed here the potential for abiotic formation of ch4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 c to 320 c a 13c labeled inorganic carbon source was used to unambiguously determine the origin of ch4 generated in the experiments consistent with previous high temperature studies the results indicate that abiotic formation of ch4 from reduction of dissolved inorganic carbon during the experiments is extremely limited with nearly all of the observed ch4 derived from background sources the results indicate that the potential for abiotic synthesis of ch4 in low temperature serpentinizing environments may be much more limited than some recent studies have suggested however more extensive production of ch4 was observed in one experiment performed under conditions that allowed an h2 rich vapor phase to form suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of ch4

c o h n salt fluids associated with contact metamorphism mcgerrigle mountains quebec a raman spectroscopic study abstract contact metamorphism and metasomatism of a sequence of cambro ordovician pelitic calcareous and psammitic metasediments in the thermal aureole of the devonian mcgerrigle pluton has resulted in the generation of a wide variety of fluid compositions which can be described by the system c o h n salt microthermometric and raman spectroscopic data on fluid inclusions trapped in quartzsulfide veins adjacent to the intrusive contact indicate that three fluid types existed in the aureole 1 h 2 o 2 h 2 o co 2 and 3 ch 2 n 2 co 2 the aqueous fluids have salinities which range from 0 to 50 eq wt nacl cacl 2 this range in fluid compositions resulted from the progressive devolatilization of a variety of lithologies and the release of waters from the intrusion the range in salinity of the aqueous fluids is attributed to variable contributions of high salinity waters from the intrusions and lower salinity dehydration and formation waters some of the co 2 may be orthomagmatic however most of it probably came from decarbonation of calcareous and possibly carbonaceous lithologies ch 4 and n 2 were generated in pelitic units during thermal metamorphism ch 4 from reactions involving bitumen and graphite and n 2 from nh 2 in silicate minerals and possibly from bitumen the restriction of high mole fractions of ch 4 and n 2 to water free fluid inclusions can be explained by fluid immiscibility within the fracture system the partitioning of co 2 between water poor and water rich fluids was less extreme and in some cases co 2 and h 2 o may have been completely miscible

formation of meteorite hydrocarbons from thermal decomposition of siderite feco3 thermal decomposition of siderite has been proposed as a source of magnetite in martian meteorites laboratory experiments were conducted to evaluate the possibility that this process might also result in abiotic synthesis of organic compounds siderite decomposition in the presence of water vapor at 300 c generated a variety of organic products dominated by alkylated and hydroxylated aromatic compounds the results suggest that formation of magnetite by thermal decomposition of siderite on the precursor rock of the martian meteorite alh84001 would have been accompanied by formation of organic compounds and may represent a source of extraterrestrial organic matter in the meteorite and on mars the results also suggest that thermal decomposition of siderite during metamorphism could account for some of the reduced carbon observed in metasedimentary rocks from the early earth

significance of microbial processes in gases of the south caspian basin abstract the south caspian basin has been a major petroleum producing province for more than a century while the basin s oil has been the focus of a number of studies the region s gas has been largely understudied this study examines 31 gas samples from 14 fields with the primary purpose of determining their mode s of formation and the role that microbial activity has had in their formation and alteration the basin s natural gas accumulations display significant differences in both molecular and isotopic composition gas wetness ranges from less than 1 at absheron to greater than 12 at guneshli methane carbon isotopic composition ranges from 57 to 37 relative to the pdb standard the stable carbon isotopic composition of the wet gas c 2 components also displays a very broad range e g c 2 ranges from 37 to 20 c 3 ranges from 31 to 10 and n c 4 ranges from 30 to 11 no strong depth related trends were observed in any of the geochemical attributes the absence of a trend implies that the gases have not been generated in situ but have migrated vertically been altered or represent a mixed product mixing is also suggested by the differences in the calculated thermal maturity levels between the c 2 components and methane in some accumulations e g karabagly as much as 55 of the methane may have a biogenic origin these data further indicate that among the gas samples studied those from bakhar appear to be the most mature with thermal maturity values consistent with the condensate window in several fields including guneshli and neftchala the wet gas components display evidence for microbial alteration this is largely manifested in anomalously heavy isotopic compositions of propane n butane and n pentane

hydrocarbon gases in the crystalline rocks of the gravberg 1 well swedish deep gas project abstract desorbed gas analyses of cuttings from the gravberg 1 well the culmination of the swedish deep gas project were undertaken every 100 m from 219 to 5907 m a sample at 6517 m from sidetrack 2 was also included the desorbed gas method performed by hot acid treatment in an evacuated system was superior to both ball mill crushing and thermodesorption methods two types of hydrocarbon gases were found in trace quantities one type associated with the dolerite sills was an isotopically heavy 13 c 1 11 to 15 dry gas with a methane content up to 98 the other type occurring throughout the granitic rocks was an isotopically lighter gas 13 c 1 21 to 39 containing 30 45 of c 2 c 4 olefins and paraffins were present in almost equal amounts in the second type of gas the dry gas observed in the dolerites is assumed to be abiogenic gas existing in inclusions of basic minerals which react with acid during the analytical procedure the other type of hydrocarbon gas is thought to be formed from h 2 and co 2 by a catalytic reaction since it is mainly associated with the magnetic fraction of the rock a fischer tropsch reaction over a magnetite catalyst is the most likely reaction since it produces both paraffins and olefins studies on thin sections of cores and coarse cuttings suggest that the wet gas is not isolated in inclusions and the changes with time observed for a few thin sections indicate that it diffuses quite freely the potential risks of contamination from drilling fluids and bit metamorphism were examined by comparing the hydrocarbon results with changes in the mud system rate of penetration and bit life hydrocarbon analyses of a few mud additives were included as well the result of these examinations plus the results of hydrocarbon analyses of cores from pilot core holes in the siljan crater suggest that the hydrocarbons observed in the cuttings are indigeneous comparing the results of the present study with other hydrocarbon occurrences outside of the siljan crater indicates that the hydrocarbons found in the gravberg 1 well occur widespread in crustal rocks

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

unravelling abiogenic and biogenic sources of methane in the earth s deep subsurface at four underground sites in precambrian shield rocks in canada and south africa hydrocarbon and hydrogen gases exsolving from saline fracture waters are analyzed for compositional and isotopic signatures dominated by reduced gases such as ch4 h 2 and higher hydrocarbons ethane propane butane the most 13 c enriched methane end members at all four sites show a pattern of carbon and hydrogen isotopic values similar to abiogenic gases produced by water rock interaction that have been identified previously at one site on the precambrian shield in canada the abiogenic nature of these gases was not previously recognized due to mixing with a second methane component produced by microbial processes the microbial methane end member is identified based on carbon and hydrogen isotopic signatures and dna gene amplification pcr data that indicate the presence of methanogens a framework is presented to estimate the relative contribution of abiogenic versus microbial hydrocarbon gases at these sites this approach has important implications for evaluation of potential abiogenic hydrocarbon reservoirs in a wide range of geologic settings including the longstanding controversy concerning the possible contribution of abiogenic gases to economic petroleum hydrocarbon reservoirs the association of high concentrations of h2 with 13 c enriched ch4 end members and h2 depletion in the 13 c depleted methanogenic end members further suggests the possibility that abiogenic gases may support h2 autotrophy linked to methanogenesis in the deep subsurface d 2005 elsevier b v all rights reserved

geochemical characteristics and origins of natural gas in the zhu iii sub basin pearl river mouth basin china abstract the zhu iii sub basin is an important petroliferous region in the south china sea where hydrocarbon distribution shows strong heterogeneity with oil primary produced from the wenchang b depression and gases from the wenchang a depression however a mixture of oil and gases are produced from the surrounding qionghai and shenhu uplifts the origin generation history and migration pathway of oil have been intensively studied but no study have been done directly on the gas which restricts future petroleum exploration in this study natural gas molecular compositions were measured on 46 samples stable carbon isotopic composition were measured on 39 samples and light hydrocarbon composition were measured on 30 samples results indicate that natural gases in the zhu iii sub basin are mainly composed of hydrocarbon gases with abundant co2 and n2 the hydrocarbon gases are all thermogenic gases which are mainly derived from the oligocene enping formation e3e 35 30 ma the contribution of the eocene wenchang formation e2w 56 35 ma to natural gases increases from the wenchang a depression to the south boundary fault sbf and surrounding uplifts this is caused by the early generated natural gases with more contribution from the e2w and dissolved in oils that migrated to the surrounding qionghai and shenhu uplifts natural gases and oil in the surrounding uplifts and near the sbf therefore avoided secondary cracking due to the high gas migration rate through the sbf and lateral sandstone carrier beds whereas natural gases in the wenchang a depression mainly originated from the secondary cracking of oil the equivalent vitrinite reflectance values of source rocks when the natural gases were generated varied from 0 6 to 1 5 based on carbon isotope differences between hydrocarbons indicating mature to high mature stage co2 with abundance less than 10 mainly originated from organic matter decomposition co2 with abundance more than 15 was sourced from the deep mantle and crust and mainly concentrated in the deep layers near the sbf which cuts into the basement n2 is probably the product of in situ reservoir alteration such as biodegradation in shallower layers our study on the geochemical characteristics and origins of the natural gas will enable a better understanding of petroleum system in the zhu iii sub basin and provide theoretical basis for optimizing future petroleum exploration strategy detailed study on shallow layers in the qionghai and shenhu uplifts and deep layers near the sbf are needed because exploration risks are relatively high in these plays

deep seated abiogenic origin of petroleum from geological assessment to physical theory the theory of the abyssal abiogenic origin of petroleum is a significant part of the modern scientific theories dealing with the formation of hydrocarbons these theories include the identification of natural hydrocarbon systems the physical processes leading to their terrestrial concentration and the dynamic processes controlling the migration of that material into geological reservoirs of petroleum the theory of the abyssal abiogenic origin of petroleum recognizes that natural gas and petroleum are primordial materials of deep origin which have migrated into the earth s crust experimental results and geological investigations presented in this article convincingly confirm the main postulates of the theory and allow us to reexamine the structure size and locality distributions of the world s hydrocarbon reserves

origin of hydrogen nitrogen gas seeps oman six gas samples were collected from five thermal springs in the semail nappe ophiolite and the calcareous calcite and dolomite hajar formation northern oman the3he 4he 4he 20ne 40ar 36ar and38ar 36ar ratios chemical compositions h2 n2 co2 ch4 o2 ar and he and stable isotope compositions dh2 dh2o 13cco2 13cch4 and 15nn2 are reported samples from the ophiolite region are significantly anoxic with major constituents of h2 ch4 and n2 while those from calcite and dolomite regions are ordinary gas seeps consisting of n2 co2 and or o2 the former h2 rich gas is characterized by relatively high3he 4he ratio 0 4 0 8 ratm with low he content 300 ppm slight radiogenic40ar 36ar ratio high n2 ar ratio 77 97 and low 15nn2 value 0 observed dh2 value of 536 in h2 rich gas is distinguished from the literature value of 699 in the ophiolite region giving discrepant isotope formation temperatures

carbon isotope composition of organic compounds produced by abiotic synthesis under hydrothermal conditions although it is widely believed that production of organic compounds by fischer tropsch synthesis and related processes occurs in many geologic environments unambiguous identification of compounds with an abiotic origin in natural samples has been hampered by a lack of means to discriminate between abiotic compounds and organic matter from biological sources while isotopic compositions might provide a means to discriminate between biologic and non biologic sources of organic matter there are few data presently available to constrain the isotopic composition of compounds produced by abiotic processes in geologic systems here we report results of laboratory experiments conducted to evaluate the isotopic composition of organic compounds synthesized abiotically under hydrothermal conditions we find the organic products are depleted in 13c to a degree typically ascribed to biological processes indicating that carbon isotopic composition may not be a particularly effective diagnostic means to differentiate between biologic and non biologic sources furthermore our results suggest that the isotopic compositions of reduced carbon compounds found in many ancient rocks that have heretofore been attributed to biological sources could be consistent with an abiotic origin in a hydrothermal setting

early mars serpentinization derived ch4 reservoirs h2 induced warming and paleopressure evolution ch4 has been observed on mars both by remote sensing and in situ during the past 15 yr it could have been produced by early mars serpentinization processes that could also explain the observed martian remanent magnetic field assuming a cold early mars a cryosphere could trap such ch4 as clathrates in stable form at depth the maximum storage capacity of such a clathrate cryosphere has been recently estimated to be 2 x 10 19 to 2 x 10 20 moles of methane we estimate how large amounts of serpentinization derived ch4 stored in the cryosphere have been released into the atmosphere during the noachian and the early hesperian due to rapid clathrate dissociation and photochemical conversion of ch4 to h 2 these episodes of massive ch4 release may have resulted in transient h 2 rich atmospheres at typical levels of 10 20 in a background 1 2 bar co2 atmosphere the collision induced heating effect of h 2 present in such an atmosphere has been shown to raise the surface temperature above the water freezing point we show how local and rapid destabilization of the cryosphere can be induced by large events such as the hellas basin or tharsis bulge formation and lead to such releases our results show that the early mars cryosphere had a sufficient ch4 storage capacity to have maintained h 2 rich transient atmospheres during a total time period up to several million years or tens of million years having potentially contributed to the formation of valley networks during the noachian early hesperian

abiogenic methanogenesis in crystalline rocks isotopically anomalous ch4 rich gas deposits are found in mining sites on both the canadian and fennoscandian shields with 13cch4 values from 22 4 to 48 5 and dch4 values from 133 to 372 these methane deposits cannot be accounted for by conventional processes of bacterial or thermogenic methanogenesis compositionally the gases are similar to other ch4 rich gas occurrences found in canadian and fennoscandian shield rocks sherwood lollar et al 1993 however the isotopically anomalous gases of this study are characterized by unexpectedly high concentrations of h2 gas ranging from several volume percent up to 30 vol the h2 gases are consistently depleted in the heavy isotope with dh2 values of 619 to 659 3h 4he ratios in the range of 0 4 10 8 to 4 4 sx 10 8 indicate that there is no resolvable component of mantle derived he in these deposits based on these results a mantle derived source for the c bearing gases is unlikely several lines of evidence support an alternative abiogenic origin for the gases from sudbury canada and juuka and pori finland the d depleted h2 gas and calculated d ch4 h2 equilibration temperatures of 110 170 c at all three sites are in good agreement with results obtained for abiogenically produced ch4 and h2 in ophiolite sequences in oman and the philippines serpentinization and the hydration of ultramafic rocks are the proposed mechanisms for ch4 and h2 production in these ophiolite sequences the widespread occurrence of serpentinized and altered ultramafic rocks at juuka and at a number of other sites in both canada and finland implies that similar mechanisms may be involved in gas production at at least three sites on the shields the origin of the gases at the remaining shield sites is discussed alternative hypothesis include 1 production of the rest of the shield gases by mixing between abiogenic endmembers and bacterially generated hydrocarbon gas such as identified elsewhere on the canadian and fennoscandian shields sherwood lollar et al 1993 and 2 production of a series of isotopically distinct abiogenic ch4 endmembers at each site due to variability in the isotopic composition of available carbon sources we cannot conclusively distinguish between the alternative scenarios based on existing data however the evidence for an abiogenic ch4 endmember at at least three sites emphasizes the need for substantial revision of current theories of methanogenesis abiogenic processes of ch4 production may be considerably more widespread than previously anticipated

abiotic methane on earth 1 over the last 30 years geochemical research has demonstrated that abiotic methane ch4 formed by chemical reactions which do not directly involve organic matter occurs on earth in several specific geologic environments it can be produced by either high temperature magmatic processes in volcanic and geothermal areas or via low temperature 100 c gas water rock reactions in continental settings even at shallow depths the isotopic composition of c and h is a first step in distinguishing abiotic from biotic including either microbial or thermogenic ch4 herein we demonstrate that integrated geochemical diagnostic techniques based on molecular composition of associated gases noble gas isotopes mixing models and a detailed knowledge of the geologic and hydrogeologic context are necessary to confirm the occurrence of abiotic ch4 in natural gases which are frequently mixtures of multiple sources although it has been traditionally assumed that abiotic ch4 is mainly related to mantle derived or magmatic processes a new generation of data is showing that low temperature synthesis related to gas water rock reactions is more common than previously thought this paper reviews the major sources of abiotic ch4 and the primary approaches for differentiating abiotic from biotic ch4 including novel potential tools such as clumped isotope geochemistry a diagnostic approach for differentiation is proposed

chemical and isotopic analyses of hydrocarbon bearing fluid inclusions in olivine rich rocks we examined the mineralogical chemical and isotopic compositions of secondary fluid inclusions in olivine rich rocks from two active serpentinization systems the von damm hydrothermal field mid

abiotic methane flux from the chimaera seep and tekirova ophiolites turkey understanding gas exhalation from low temperature serpentinization and implications for mars abstract the emission of abiotic methane ch 4 into the atmosphere from low temperature serpentinization in ophiolitic rocks is documented to date only in four countries the philippines oman new zealand and turkey serpentinization produces large amounts of hydrogen h 2 which in theory may react with co 2 or co to form hydrocarbons fischer tropsch type synthesis ftt similar mechanisms have been invoked to explain the ch 4 detected on mars so that understanding flux and exhalation modality of ophiolitic gas on earth may contribute to decipher the potential degassing on mars this work reports the first direct measurements of gas ch 4 co 2 flux ever done on onshore ophiolites with present day serpentinization we investigated the tekirova ophiolites at cirali in turkey hosting the chimaera seep a system of gas vents issuing from fractures in a 5000 m 2 wide ophiolite outcrop at this site at least 150 190 t of ch 4 is annually released into the atmosphere the molecular and isotopic compositions of c 1 c 5 alkanes co 2 and n 2 combined with source rock maturity data and thermogenic gas formation modelling suggested a dominant abiotic component 80 90 mixed with thermogenic gas abiotic h 2 rich gas is likely formed at temperatures below 50 c suggested by the low deuterium hydrogen isotopic ratio of h 2 d h2 720 consistent with the low geothermal gradient of the area abiotic gas synthesis must be very fast and effective in continuously producing an amount of gas equivalent to the long lasting 2 millennia emission of 100 t ch 4 yr 1 otherwise pressurised gas accumulation must exist over the same ophiolitic formation 3 km away from chimaera we detected an invisible microseepage of abiotic ch 4 with fluxes from 0 07 to 1 g m 2 d 1 on mars similar fluxes could be able to sustain the ch 4 plume apparently recognised in the northern summer 2003 10 4 or 10 5 t yr 1 over the wide olivine bedrock and outcrops of hydrated silicates in the syrtis major and nili fossae just one seep like chimaera or more realistically a weak spatially sporadic microseepage would be sufficient to maintain the atmospheric ch 4 level on mars

geochemistry of natural gases in deep strata of the songliao basin ne china chemical composition and stable carbon isotopic studies were undertaken for 27 gas samples from deep strata of the xujiaweizi depression in the songliao basin to investigate their origin gas molecular and carbon isotopic compositions show great variety methane is the main component for all studied samples and its content ranges from 57 4 to 98 2 with an average of 90 1 gas wetness ranges from 0 8 to 16 7 with an average of 2 7 the main non hydrocarbon gases are carbon dioxide and nitrogen with an average of 4 0 and 3 2 respectively carbon isotope data suggest that these deep strata gases are mainly coal type gases mixed with minor amounts of associated oil type gases coal type gases are characterized by heavier carbon isotopic values and drier chemical compositions these gases were generated from the lower cretaceous shahezi formation coals interbedded shales with type iii kerogen during the postmature stage of hydrocarbon generation oil type gases are characterized by lighter carbon isotope and higher wetness which were generated from the lower cretaceous shales with type ii kerogen in the shallow strata during the early mature stage of hydrocarbon generation mixing of two different gases causes unusual carbon isotopic distribution patterns with lighter isotopic values in higher numbered carbons in most gases the discovery of coal type gases in the songliao basin provides new prospects for the exploration in this region

evidence and age estimation of mass wasting at the distal lobe of the congo deep sea fan on continental margins sulfate reduction occurs within the sedimentary column it is coupled with the degradation of organic matter and the anaerobic oxidation of methane these processes may be significantly disturbed by sedimentary events leading to transient state profiles for the involved chemical species yet little is known about the impact of turbidity currents and mass wasting on the migration of chemical species and the redox reactions in which they are involved due to its connection to the river the congo deep sea fan continuously receives huge amount of organic matter rich sediments primarily transported by turbidity currents which impact on the development of the associated ecosystems rabouille et al 2016 thus it is well suited to better understand causal relationships between sedimentary events and fluid flow path with consequences on the zonation of early diagenesis sequences here we combined sedimentological observations with geochemical analyses of pore water and sediment samples to explore how sedimentary instabilities affected the migration of methane and the distribution of organic matter within the sedimentary column the results unveiled mass wasting processes affecting recent turbiditic and pelagic deposits and are interpreted as being slides slumps and debrites two slides were responsible for the exhumation of an organic matter rich sedimentary block of more than 5 m thick and the movement of a methane rich sedimentary block while turbidity currents enable the intercalation of sandy intervals within a pelagic clay layer the youngest slide promoted the development of two sulfate methane transition zones smtz and may have possibly triggered a lateral migration of methane numerical simulation of the sulfate profile indicates that the youngest sedimentary event has occurred around a century ago our study emphasizes that turbidity currents and sedimentary instabilities can significantly affect the transport paths and the distribution of both methane and organic matter in the terminal lobe complex with consequences on geochemical zonation of the sequential early diagenetic processes within the sedimentary column

baseflow recession and recharge as nonlinear storage processes discharge in many rivers is often fed by outflow from a shallow groundwater reservoir it is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow q and storage s for which the equation s aqb was adopted values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0 5 which is in accordance with the findings of other studies and theoretical approaches yielding b 0 5 for unconfined aquifers and relating the coefficient a to catchment properties primarily area and shape of basin pore volume and transmissivity this non linear reservoir function is proposed as a more realistic alternative to the linear reservoir function the relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of old pre event water into the river bed as fissure and pore volumes communicate hydraulically it appears physically reasonable to model the system by one non linear reservoir for catchments or parts of them instead of applying independent parallel linear reservoirs the non linear reservoir algorithms are supported by an analytical derivation they are extended for the automatic separation of baseflow from a time series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing the time series obtained allow the identification and quantification of long term changes to the water balance relationships between computed groundwater storage and observed groundwater level can also be established copyright 1999 john wiley sons ltd

evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes abstract the assessment of gas origin in mud volcanoes and related petroleum systems must consider post genetic processes which may alter the original molecular and isotopic composition of reservoir gas beyond eventual molecular and isotopic fractionation due to gas migration and microbial oxidation investigated in previous studies we now demonstrate that mud volcanoes can show signals of anaerobic biodegradation of natural gas and oil in the subsurface a large set of gas geochemical data from more than 150 terrestrial mud volcanoes worldwide has been examined due to the very low amount of c 2 in mud volcanoes isotopic ratios of ethane propane and butane generally the best tracers of anaerobic biodegradation are only available in a few cases however it is observed that 13 c enriched propane is always associated with positive 13 c co2 values which are known indicators of secondary methanogenesis following anaerobic biodegradation of petroleum data from carbon isotopic ratio of co 2 are available for 134 onshore mud volcanoes from 9 countries azerbaijan georgia ukraine russia turkmenistan trinidad italy japan and taiwan exactly 50 of mud volcanoes all releasing thermogenic or mixed methane show at least one sample with 13 c co2 5 pdb thermogenic ch 4 associated with positive carbon isotopic ratio of co 2 generally maintains its 13 c enriched signature which is therefore not perturbed by the lighter secondary microbial gas there is however high variability in the 13 c co2 values within the same mud volcanoes so that positive 13 c co2 values can be found in some vents and not in others or not continuously in the same vent this can be due to high sensitivity of 13 c co2 to gas water rock interactions or to the presence of differently biodegraded seepage systems in the same mud volcano however finding a positive 13 c co2 value should be considered highly indicative of anaerobic biodegradation and further analyses should be made especially if mud volcanoes are to be used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas

microbial hydrocarbon gases in the witwatersrand basin south africa implications for the deep biosphere in this study compositions and 13c and 2h isotopic values of hydrocarbon gases from 5 mines in the witwatersrand basin south africa support the widespread occurrence of microbially produced methane in millions of years old fissure waters the presence of microbial methane is to a large extent controlled by the geologic formations in which the gases are found samples from the witwatersand supergroup have the largest microbial component based on 13c and 2h signatures and ch4 c2 values based on mixing between a microbial ch4 component and a more 13c enriched and 2h depleted c2 rich end member conservative estimates of the contribution of microbial ch4 to the gas samples range from 90 microbial ch4 at beatrix masimong and merriespruit to between 5 and 80 microbial ch4 at evander and 18 microbial ch4 at kloof the witwatersrand basin s history of thermal alteration of organic rich ancient sedimentary units suggests a thermogenic origin for this 13c enriched end member alternatively the potential for an abiogenic origin similar to hydrocarbon gases produced by water rock interaction at other precambrian shield mines is discussed microbial methane is predominantly found in paleo meteoric fissure waters with 18o and 2h values that fall on the meteoric waterline and have temperatures between 30 to 40 c in contrast fissure waters with a larger component of nonmicrobial hydrocarbon gases show a trend towards more enriched 18o and 2h values that fall well above the meteoric waterline and temperatures of 45 to 60 c the enrichment in 18o and 2h in these samples and their high salinity are similar to the isotopic and compositional characteristics of saline groundwaters and brines produced by water rock interaction at precambrian shield sites elsewhere the reported 100 ma ages of fissure waters from the witwatersrand and ventersdorp formations suggest that these microbial hydrocarbon gases are the product of in situ methanogenic communities in the deep subsurface of the witswaterand basin small subunit ribosomal rna genes were amplified using archaeal specific primer sets from dna extracts derived from several of these waters fissure waters with a high proportion of microbial methane also contained sequences resembling those of known methanogens

dual stable isotopes of ch 4 from yellowstone hot springs suggest hydrothermal processes involving magmatic co 2 abstract volcanism and post magmatism contribute significant annual methane ch 4 fluxes to the atmosphere on par with other natural sources such as forest fire and wild animal emissions and have been implicated in past climate change events the yellowstone hot spot is one of the largest volcanic systems on earth and is known to emit ch 4 as well as carbon dioxide co 2 and other gases but the ultimate sources of this ch 4 flux have not been elucidated here we use dual stable isotope analysis 2 h and 13 c of ch 4 sampled from ten high temperature geothermal pools in yellowstone national park along with other isotopic and gas analyses to evaluate potential sources of methane the average 13 c and 2 h values of ch 4 emitted from hot springs 26 7 2 4 and 236 9 12 0 respectively are inconsistent with microbial methanogenesis but do not allow distinction between thermogenic and abiotic sources correlation between 13 c ch4 and 13 c of dissolved inorganic c dic is consistent with dic as the parent c source for the observed ch 4 or with equilibration of ch 4 and dic methane formation temperatures estimated by isotopic geothermometry based on 13 c ch4 and 13 c co2 ranged from 250 350 c which is just below previous temperature estimates for the hydrothermal reservoir further the 2 h h2o of the thermal springs and the measured 2 h ch4 values are consistent with equilibration between the source water and the ch 4 at the formation temperatures though the ultimate origin of the ch 4 could be attributed to either abiotic of themorgenic processes with subsequent isotopic equilibration the c 1 c 2 composition of the gases is more consistent with abiotic origins for most of the samples thus our data support the hypothesis that subsurface rock water interactions are responsible for at least a significant fraction of the ch 4 flux from the yellowstone national park volcanic system

geochemistry and geobiology of a present day serpentinization site in california the cedars ultra basic ph 11 12 reducing 656 to 585 mv groundwater springs discharging from serpentinized peridotite of the cedars ca were investigated for their geochemistry and geobiology the spring waters investigated were of meteoric origin however geochemical modeling suggests that there were two sources of groundwater a shallow source with sufficient contact with the cedars peridotite body to be altered geochemically by serpentinization and a deeper groundwater source that not only flows through the peridotite body but was also in contact with the marine sediments of the franciscan subduction complex fsc below the peridotite body we propose that the groundwater discharging from lower elevations gps1 and cs1 reflect the geochemistry of the deeper groundwater in contact with fsc while groundwaters discharging from springs at higher elevations ns1 and bsc were a mixture of the shallow peridotite only groundwater and the deeper groundwater that has been in contact with the fsc cell densities of suspended microbes within these waters were extremely low in the ns1 and bsc spring fluids cell densities ranged from 10 2 to 10 3 cells ml while suspended cells at gps were lower than 10 cells ml however glass slides incubated in the bsc and gps1 springs for 2 3 weeks were colonized by cells with densities ranging from 10 6 to 10 7 cells cm 2 attached to their surfaces all of the springs were very low 1 m in several essential elements and electron acceptors e g nitrate ammonium sulfate and phosphate required for microbial growth which is not uncommon at sites of continental serpentinization gases rich in n 2 h 2 and ch 4 were exsolving from the springs the stable carbon isotope value 13 c ch4 68 0 6 and the ch 4 c 2 10 3 of methane and other gaseous hydrocarbons exsolving from ns1 were typical of microbially sourced methane whereas the isotope values and the ch 4 c 2 of bsc and cs1 springs were more enriched in 13 c and had ch 4 c 2 10 3 suggesting a mixture of microbial and non microbial methane the concentrations of aromatic compounds and ethane propane iso and n butane were well described by simple physical mixing between the aromatic and alkane poor shallow groundwater and the relatively aromatic and alkane rich groundwater that flows through both the peridotite and the fsc suggesting that these aromatic and alkane compounds originated in the deeper fsc groundwater and are not produced in the shallow peridotite only groundwater the aromatic compounds most probably originated from the diagenesis degradation of organic matter in the marine sediments below the peridotite body while the gaseous alkanes may have multiple sources including thermal degradation of the organic matter in the marine sediments below the peridotite body and possibly by abiogenic reactions occurring within the peridotite body this geochemical study demonstrates the complexity of the cedars and the possible sources of hydrocarbons at continental sites of serpentinization

hydrogen generation from mantle source rocks in oman hydrogen gas associated with ca2 oh rich alkaline groundwaters ph 10 12 is at present emanating from ultramafic rocks of the oman ophiolite isotopic and chemical evidence indicates that hydrogen is formed by low temperature redox reactions in a closed groundwater environment this is normally a cryptic process in the hydrosphere but is fortuitously revealed by the unusual hydrogeological conditions in oman where atmospheric oxygen is totally assimilated it is suggested that hydrogen generation in mantle source rocks at depth and in the early archaean surface environment may be more widespread than has hitherto been realised

limited role for methane in the mid proterozoic greenhouse abstract pervasive anoxia in the subsurface ocean during the proterozoic may have allowed large fluxes of biogenic ch4 to the atmosphere enhancing the climatic significance of ch4 early in earth s history indeed the assumption of elevated pch4 during the proterozoic underlies most models for both anomalous climatic stasis during the mid proterozoic and extreme climate perturbation during the neoproterozoic however the geologic record cannot directly constrain atmospheric ch4 levels and attendant radiative forcing here we revisit the role of ch4 in earth s climate system during proterozoic time we use an earth system model to quantify ch4 fluxes from the marine biosphere and to examine the capacity of biogenic ch4 to compensate for the faint young sun during the boring billion years before the emergence of metazoan life our calculations demonstrate that anaerobic oxidation of ch4 coupled to so42 reduction is a highly effective obstacle to ch4 accumulation in the atmosphere possibly limiting atmospheric pch4 to less than 10 ppm by volume for the second half of earth history regardless of atmospheric po2 if recent po2 constraints from cr isotopes are correct we predict that reduced uv shielding by o3 should further limit pch4 to very low levels similar to those seen today thus our model results likely limit the potential climate warming by ch4 for the majority of earth history possibly reviving the faint young sun paradox during proterozoic time and challenging existing models for the initiation of low latitude glaciation that depend on the oxidative collapse of a steady state ch4 greenhouse

origin of methane in serpentinite hosted hydrothermal systems the ch4 h2 h2o hydrogen isotope systematics of the hakuba happo hot spring abstract serpentinite hosted hydrothermal systems have attracted considerable attention as sites of abiotic organic synthesis and as habitats for the earliest microbial communities here we report a systematic isotopic study of a new serpentinite hosted system the hakuba happo hot spring in the shiroumadake area japan 36 42 n 137 48 e we collected water directly from the hot spring from two drilling wells more than 500 m deep all water samples were strongly alkaline ph 10 and rich in h2 201 664 mol l and ch4 124 201 mol l despite the relatively low temperatures 50 60 c thermodynamic calculations suggest that the h2 was likely derived from serpentinization reactions hydrogen isotope compositions for happo 1 happo 3 were found to be as follows d h 2 700 710 d ch 4 210 300 and d h 2 o 85 84 the carbon isotope compositions of methane from happo 1 and 3 were found to be c 13 34 5 and 33 9 respectively the ch4 h2 h2o hydrogen isotope systematics indicate that at least two different mechanisms were responsible for methane formation happo 1 has a similar hydrogen isotope compositions to other serpentinite hosted systems reported previously the elevated d ch 4 with respect to the equilibrium relationship suggests that the hydrogen of the happo 1 methane was not sourced from molecular hydrogen but was derived directly from water this implies that the methane may not have been produced via the fischer tropsch type ftt synthesis but possibly by the hydration of olivine conversely the depleted d ch 4 with respect to the equilibrium relationship in happo 3 suggests the incorporation of biological methane based on a comparison of the hydrogen isotope systematics of our results with those of other serpentinite hosted hydrothermal systems we suggest that abiotic ch4 production directly from h2o without mediation by h2 may be more common in serpentinite hosted systems hydration of olivine may play a more significant role in abiotic methane production than previously thought

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

evidence from fluid inclusions for microbial methanogenesis in the early archaean era methanogenic microbes may be one of the most primitive organisms although it is uncertain when methanogens first appeared on earth during the archaean era before 2 5 gyr ago methanogens may have been important in regulating climate because they could have provided sufficient amounts of the greenhouse gas methane to mitigate a severely frozen condition that could have resulted from lower solar luminosity during these times nevertheless no direct geological evidence has hitherto been available in support of the existence of methanogens in the archaean period although circumstantial evidence is available in the form of approximately 2 8 gyr old carbon isotope depleted kerogen here we report crushing extraction and carbon isotope analysis of methane bearing fluid inclusions in approximately 3 5 gyr old hydrothermal precipitates from pilbara craton australia our results indicate that the extracted fluids contain microbial methane with carbon isotopic compositions of less than 56 per thousand included within original precipitates this provides the oldest evidence of methanogen 3 46 gyr ago pre dating previous geochemical evidence by about 700 million years

origins of methane discharging from volcanic hydrothermal geothermal and cold emissions in italy abstract we have addressed the origins of methane in fumarolic thermal and cold emissions discharging from a diversity of geological settings spread all over the italian peninsula and at panarea and pantelleria islands fluid discharges from the main geothermal systems of the peri tyrrhenian area including mt amiata larderello latera and manziana show 13c ch4 and d ch4 values 28 v pdb and 160 v smow respectively and c1 c2 concentration ratios 1000 these patterns suggest that ch4 discharged from these systems is primarily generated by abiogenic reduction of co2 and or co methane seems to have at least partially a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or alternatively to methane polymerization fumaroles from the volcanic systems of solfatara vesuvio panarea and pantelleria have c1 c2 concentration ratios in a wide range from 17 to 4300 but 13c ch4 and d ch4 values 21 v pdb and 120 v smow respectively such isotopic values are very similar to those reported for ch4 discharging from ultramafic hydrothermal systems in agreement with recent evidence provided for solfatara and pantelleria we therefore infer that the ch4 in the volcanic fumaroles is mainly abiogenic too the 13c ch4 from 21 6 to 36 9 v pdb and d ch4 from 113 to 164 v smow values as well as the c1 c2 concentration ratios from 19 to 2240 in the co2 rich fluid discharges located between the geothermal volcanic systems and the apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish suggesting that the ch4 production is mainly related to thermogenic processes according to this general trend the ch4 dominated fluids from mud volcanoes located eastwards of the co2 rich emissions are fed by an almost pure thermogenic source the easternmost fluid discharges from the po valley and the adriatic coast where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient record the lowest 13c ch4 and d ch4 values i e as low as 69 v pdb and

have olivine will gas serpentinization and the abiogenic production of methane on mars 1 spatial variability of methane ch4 on mars suggests the presence of localized subsurface sources here we show that olivine hydration in the martian regolith and crust may be a major ch4 source which contributed significantly to the warming of early mars methane production is kinetically and thermodynamically favored during low t aqueous alteration of olivine rich rocks sustained release of ch4 on present day mars may come through the breakdown of ancient ch4 hydrates and from springs driven by geothermal heat

hydrogen isotope fractionation in land based serpentinization systems comment on origin of methane in serpentinite hosted hydrothermal systems the ch4 h2 h2o hydrogen isotope systematics of the hakuba happo hot spring by suda et al earth planet sci lett 386 2014 112 125

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

origin and formation of methane in groundwater of glacial origin from the cambrian vendian aquifer system in estonia abstract groundwater in the cambrian vendian aquifer system in estonia is characterised by the most depleted isotopic composition known in europe 18o down to 23 the water most likely originates from glacial meltwater recharge from the fennoscandian ice sheet in the pleistocene the aquifer system is characterised by relative high methane concentrations up to 50 of dissolved gases estimated absolute concentration up to 1600 mol l 1 the origin of which has so far remained unclear in this paper we focus on the origin of methane the factors controlling its spatial distribution and its isotope geochemistry in the aquifer system the data reveal a large spatial variability in methane concentration 13cch4 and 2hch4 values from 6 to 105 and from 220 to 420 respectively we show that local oxidation processes rather than different pathways of methane formation have affected the initial isotopic composition of methane using the least modified 13cch4 values from 85 to 105 we conclude that methane most likely originates from the organic material overridden by the fennoscandian ice shield during the late weichselian glaciation that was carried into the aquifer system with infiltrating glacial meltwater the estimated 18o values of the water where the methane was formed are 17 1 5 supporting the inference that the methane was formed during the middle weichselian interstadial the study shows that groundwater of glacial origin in the cambrian vendian aquifer system can serve as an alternative palaeoenvironmental archive to be used for studying the variations in climatic and environmental conditions in northern europe during glacial interglacial cycles of the pleistocene

methane clumped isotopes in the songliao basin china new insights into abiotic vs biotic hydrocarbon formation abiotic hydrocarbon gas typically generated in serpentinized ultramafic rocks and crystalline shields has important implications for the deep biosphere petroleum systems the carbon cycle and astrobiology distinguishing abiotic gas produced by chemical reactions like sabatier synthesis from biotic gas produced from degradation of organic matter or microbial activity is sometimes challenging because their isotopic and molecular composition may overlap abiotic gas has been recognized in numerous locations on the earth although there are no confirmed instances where it is the dominant source of commercially valuable quantities in reservoir rocks the deep hydrocarbon reservoirs of the xujiaweizi depression in the songliao basin china have been considered to host significant amounts of abiotic methane here we report methane clumped isotope values 18 and the isotopic composition of c 1 c 3 alkanes co 2 and helium of five gas samples collected from those xujiaweizi deep reservoirs some geochemical features of these samples resemble previously suggested identifiers of abiotic gas 13 c enriched ch 4 decrease in 13 c 12 c ratio with increasing carbon number for the c1 c4 alkanes abundant apparently non biogenic co 2 and mantle derived helium however combining these constraints with new measurements of the clumped isotope composition of methane and careful consideration of the geological context suggests that the xujiaweizi depression gas is dominantly if not exclusively thermogenic and derived from over mature source rocks i e from catagenesis of buried organic matter at high temperatures methane formation temperatures suggested by clumped isotopes 167 213 c are lower than magmatic gas generation processes and consistent with the maturity of local source rocks also there are no geological conditions e g serpentinized ultramafic rocks that may lead to high production of h 2 and thus abiotic production of ch 4 via co 2 reduction we propose that the songliao gas is representative of an atypical type of thermogenic gas that can be mistaken for abiotic gas such gases may be encountered more frequently in future exploration of deep or over mature petroleum systems

microstructure specific carbon isotopic signatures of organic matter from 3 5 ga cherts of the pilbara craton support a biologic origin the 3 5 ga dresser formation from the north pole dome of the pilbara craton western australia contains some of the oldest evidence for life on earth here we present a detailed study of microstructure specific carbon isotopic composition of organic matter om preserved in dresser formation bedded cherts and hydrothermal chert vein using in situ secondary ion mass spectrometry sims the om in these rocks occurs mainly as clots that together with minor fine om layers and laminae are considered primary textures formed prior to host rock lithification other than rare om rich stylolites no evidence was found for later om migration beyond the micrometer scale average 13c om values in specific microstructural types range between 33 6 and 25 7 no correlation is seen between measured 13c values and h c ratios in the studied om microstructures this lack of correlation and the low metamorphic grade of the rocks studied argue against significant modification of om isotopic composition by later metamorphic alteration it is thus concluded that the range of 13c values found in the samples represents primary om isotopic variability within some individual samples variable 13c om values are correlated with specific microstructural types this observation is not consistent with solely abiotic om formation via fisher tropsch type reactions when compared with associated 13c ankerite values average 13c om values indicate c isotopic fractionation 13c ank om of 25 33 which translates to dissolved co2 om isotopic fractionation 13c co2 om of 20 30 this range of 13c co2 om is consistent with enzymatic c fixation via the calvin cycle utilized by photoautotrophs and the reductive acetyl coa pathway utilized by chemolithoautotrophs photosynthetic om formation is supported by the relatively shallow water depth inferred for the dresser environment and the restricted occurrence of stromatolites to shallow water deposits in this unit whereas chemolithosynthesis is supported by the abundance of om in sub seafloor hydrothermal chert veins the range of 13c om values observed in the samples may therefore represent the remains of different organisms utilizing different c fixation pathways other biologic effects such as the growth rate and density of microbial communities and further heterotrophic overprinting of the autotrophic biomass may have also contributed to the observed range of 13c om values

large compositional differences in the gases released from the kizildag ophiolitic body turkey evidences of prevailingly abiogenic origin abstract we investigated the geochemical features of the gases released from the kizildag ophiolitic complex hatay turkey twenty three samples both dissolved in hyperalkaline waters and free gases bubbling gases and dry seeps were collected samples were analysed for their chemical he h 2 o 2 n 2 ch 4 and co 2 and isotopic he 13 c ch 4 2 h ch 4 2 h h 2 composition including the content and c isotopic composition of c 2 to c 5 alkanes in free gases analytical results evidence h 2 production through low temperature 4 production through fischer tropsch type reactions in some sample small additions of methane either of microbial or of thermogenic origin can be hypothesized at one of the sites kisecik a clear fractionation pattern due to microbial methane oxidation leading to strongly enriched isotopic values 13 c 15 and 2 h 68 and depletion in methane concentrations has been evidenced at the dry gas seep of kurtbagi methane flux measurements have been made and a preliminary output estimation of about 1000 kg per year has been obtained

consumption of atmospheric methane in a limestone cave in indiana usa abstract recent observations suggest that karst landscapes may be an unaccounted sink for atmospheric ch4 but questions remain about the processes contributing to sub atmospheric ch4 mole fractions in caves the ch4 dynamics associated with karst environments were studied over 18 months at 6 locations in buckner cave southern indiana by measuring the mole fractions and stable isotopic composition of ch4 and carbon dioxide co2 co2 mole fractions were used to infer seasonal changes in airflow samples were obtained on a monthly basis ch4 mole fractions ranged from 1 9 0 1 ppm near the cave entrance to 0 1 0 1 ppm in the more remote parts of the cave the carbon and hydrogen stable isotopic compositions of ch4 in the cave ranged from 58 7 to 7 vpdb and 170 to 10 vsmow respectively the isotopic data suggest that the ch4 dynamics of buckner cave can be described by a seasonally variable mixing system in which atmospheric ch4 enters primarily through the main entrance and is subsequently consumed by methanotrophs additionally at least two smaller ch4 sources are evident when air has been stagnant the results suggest that subterranean karst cavities are an important sink for atmospheric ch4

geochemistry and occurrence of inorganic gas accumulations in chinese sedimentary basins abstract inorganic gases are commonly seen in eastern china and occasionally in southern china from the shallow water columns above hot and cold springs the gases contain 68 to nearly 100 co2 with 13 c co 2 and 13c1 values in the range of 1 18 to 6 00 and 19 48 to 24 94 respectively all of the 34 large inorganic co2 and one inorganic methane accumulations discovered in china are distributed in eastern parts of the country from both onshore and continental shelf basins no commercial inorganic gas accumulation has been found in central and western china this is a review of the occurrence and geochemical characteristics of inorganic gas accumulations in chinese sedimentary basins a detailed study of gas samples collected from four representative inorganic co2 pools and one possible inorganic methane pool indicates that inorganic alkane gases typically show 13c1 values greater than 10 versus pdb mostly 30 with a positive stable carbon isotope sequence of 13c1 13c2 13c3 13c4 inorganic gases also tend to show less negative 13 c co 2 values 10 than biogenic gases

thermodynamic constraints on the formation of condensed carbon from serpentinization fluids abstract recent studies have identified carbonaceous material in serpentinite bodies but whether these deposits have a biologic or abiotic origin remains uncertain in this work thermodynamic calculations were performed to examine the potential for abiotic condensed carbonaceous material to be produced from serpentinization derived fluids under hydrothermal conditions calculation of reaction pathways during serpentinization of olivine showed that fluid compositions should equilibrate with condensed carbonaceous material which controls the h 2 and co 2 activities fluids from laboratory serpentinization experiments and from the lost city and the rainbow hydrothermal field are shown to be consistent with this model the predictions indicate that carbonaceous material should be the dominant carbon product of co 2 reduction in these hydrothermal settings which would have significant implications for a number of processes including the deep earth carbon cycle by creating a pool of relatively immobile reduced carbon the extent of h 2 production in ultrabasic environments and mechanisms leading to abiotic reduced carbon compounds

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

fluid geochemistry of the cuopu high temperature geothermal system in the eastern himalayan syntaxis with implication on its genesis abstract high temperature geothermal fluids dissolve constituents pertinent to water rock interaction and magmatic volatile absorption resulting in high total dissolved solid tds values however this study focuses on the hydrochemical evolution of the low salinity hco3 na type high temperature geothermal fluid in cuopu eastern himalayas the geothermal water is recharged by local precipitation and glacier water from surrounding mountains the tds values are below 834 mg l and the constituents are mainly products of the water carbon dioxide rock interactions lacking magmatic volatile dissolved in the fluid the geothermal water reaches an almost complete chemical equilibrium with the feldspar or plagioclase enriched reservoir rock in a reducing condition the reservoir temperature is between 175 c 200 c while the temperature could reach up to 400 c in the deep crustas indicated by the carbon isotopic exchange equilibrium between co2 and ch4 the infiltrated glacier water was heated during its circulation within the hot thickened crust and continued dissolving the crustal metamorphic gas such as radiogenic helium and limestone metamorphic co2 until the junction of the two sets of faults provided an ascending channel for it upon rising along the conduit the geothermal water mixed with cold groundwater to different degrees approximately 0 015 mol l co2 escaped from the geothermal fluid when it scattered as bubbling hot springs on the surface of the anisotropic porous quaternary sediments such kind ofhydrochemical evolution of lowsalinity alkaline hco3 na type water represents a typical formation mechanism of the high temperature geothermal systems along the himalayas

graphite ch4 h2o co2 equilibria at low grade metamorphic conditions equilibrium calculations and published phase equilibria are used to show that at temperatures below 400 c and pressures above 300 bar the fluids coexisting with graphite in the c o h system consist either of co2 h2o mixtures or ch4 h2o mixtures bulk fluid compositions consisting of ch4 h2o will unmix to methane rich fluid and h2o rich liquid at temperatures below about 325 c compositions on the co2 h2o join will unmix only at temperatures below about 275 c oxygen fugacity in the ch4 h2o graphite three phase region is fixed at constant p and t and approximately equal to that of the quartz magnetite fayalite assemblage in the co2 h2o graphite three phase region oxygen fugacity is about three orders of magnitude greater from the end stages of diagenesis to temperatures of 300 c and possibly 400 c in salt rich systems many metamorphic rocks may contain ch4 h2o fluids rather than co2 h2o mixtures thus metamorphic reactions involving carbonate minerals would involve ch4 graphite and h2o rather than co2 the immiscibility between ch4 and h2o could result in the common occurrence of methane natural gas in low grade metamorphic terrains

fischer tropsch synthesis of hydrocarbons during sub solidus alteration of the strange lake peralkaline granite quebec labrador canada abstract the composition of the carbonic phase s of fluid inclusions in pegmatite quartz from the strange lake peralkaline complex has been analysed by gas chromatography using online extraction of inclusion contents and a poraplot q capillary column the measured gas species are in order of abundance ch 4 h 2 c 2 h 6 co 2 n 2 ca n c 4 h 10 n c 5 h 12 c 2 h 2 i c 4 h 10 and c 2 h 4 minor amounts of i c 5 h 12 n c 6 h 14 i c 6 h 14 and neo c 6 h 14 were also detected but not quantified in some samples a suite of quartz samples from ca metasomatised pegmatites contains fluid inclusions with a similar distribution of hydrocarbons but much higher proportions of c0 2 the carbonic fluid coexisted immiscibly with a brine salvi and williams jones 1992 which on the basis of field and petrographic evidence was interpreted to have originated from the magma however thermodynamic calculations indicate that the above gas species specifically the hydrocarbons could not have coexisted at equilibrium in the proportions measured at any geologically reasonable conditions either prior to or post entrapment we propose instead that the gas compositions measured in the strange lake inclusions and in inclusions from other alkalic complexes resulted from the production of h 2 during the alteration of arfvedsonite to aegirine and the subsequent reaction of this h 2 with orthomagmatic c0 2 and co to form hydrocarbons in a magnetite catalysed fischer tropsch synthesis locally influx of an oxidised calcic brine derived externally from the pluton altered the original composition of the fluid by converting hydrocarbons to c0 2

abiogenic fischer tropsch synthesis of hydrocarbons in alkaline igneous rocks fluid inclusion textural and isotopic evidence from the lovozero complex n w russia a detailed fluid inclusion study has been carried out on the hydrocarbon bearing fluids found in the peralkaline complex lovozero petrographic microthermometric laser raman and bulk gas data are presented and discussed in context with previously published data from lovozero and similar hydrocarbon bearing alkaline complexes in order to further understand the processes which have generated these hydrocarbons ch4 dominated inclusions have been identified in all lovozero samples they occur predominantly as secondary inclusions trapped along cleavage planes and healed fractures together with rare h2o dominant inclusions they are consistently observed in close association with either arfvedsonite crystals partially replaced by aegirine aegirine crystals or areas of zeolitization the majority of inclusions consist of a low density fluid with ch4 homogenisation temperatures between 25 and 120 c those in near surface hand specimens contain ch4 h2 up to 40 mol higher hydrocarbons however inclusions in borehole samples contain ch4 higher hydrocarbons h2 indicating that at depth higher hydrocarbons are more likely to form estimated entrapment temperatures and pressures for these inclusions are 350 c and 0 2 0 7 kbar a population of high density liquid ch4 dominant inclusions have also been recorded mainly in the borehole samples homogenising between 78 and 99 c these consist of pure ch4 trapped between 1 2 and 2 1 kbar and may represent an early ch4 bearing fluid overprinted by the low density population the microthermometric and laser raman data are in agreement with bulk gas data which have recorded significant concentrations of h2 and higher hydrocarbons up to c6h12 in these samples these data combined with published isotopic data for the gases ch4 c2h6 h2 he and ar indicate that these hydrocarbons have an abiogenic crustal origin and were generated during postmagmatic low temperature alteration reactions of the mineral assemblage this would suggest that these data favour a model for formation of hydrocarbons through fischer tropsch type reactions involving an early co2 rich fluid and h2 derived from alteration reactions this is in contrast to the late magmatic model suggested for the formation of hydrocarbons in the similar peralkaline intrusion ilimaussaq at temperatures between 400 and 500 c

conditions of stichtite mg 6 cr 2 oh 16 co 3 4h 2 o formation and its geochemical and isotope record of early phanerozoic serpentinizing environments abstract stichtite is a magnesium chromium hydroxycarbonate mineral found in association with early phanerozoic chromite rich serpentinite rocks of tasmania australia and tehuitzingo mexico elemental analysis of stichtite shows a range of compositions within the cr fe al hydrotalcite group with compositional trends associated with each discrete serpentinite host body elemental and textural analysis of stichtite associated chromite indicates that stichtite forms in fore arc setting rocks through interaction of chromite and methane rich serpentinizing fluids the degree to which chromite is replaced by stichtite is inferred to correlate with the length of time that the host rocks spent within the stichtite window carbon stable isotope analyses of stichtite suggest carbon sourcing from marine kerogen with a minor marine carbonate component in some samples the carbon and hydrogen stable isotope profile of stichtite ranges from the field of methane from active serpentinizing zones to organic thermogenic methane the association of the stichtite 2h polytype nee barbertonite with aragonite antigorite suggests this is a higher pressure temperature polytype of stichtite reaction completion textures isotopic values and qualitative mineral thermobarometric indicators indicate that stichtite forms during serpentinization of fore arc setting rocks in a methane h2 rich environment within fluid conduits ranging from low temperatures and pressures near the surface to depths where pressure is up to 0 8 1 2 gpa and temperature is up to 300 c these unique chemical isotopic and textural properties of stichtite from distinct serpentinite bodies likely record the duration of serpentinization at specific thermobarometric conditions and provide a window into the conditions associated with a potentially habitable environment on early earth and other bodies of the solar system

extreme methane deuterium nitrogen and helium enrichment in natural gas from the homorod seep romania abstract methane ch 4 in terrestrial environments whether microbial thermogenic or abiogenic exhibits a large variance in c and h stable isotope ratios due to primary processes of formation isotopic variability can be broadened through secondary post genetic processes such as mixing and isotopic fractionation by oxidation the highest and lowest 13 c and 2 h or d deuterium concentrations in ch 4 found in various geologic environments to date are defined as natural terrestrial extremes we have discovered a new extreme in a natural gas seep with values of deuterium concentrations d ch4 up to 124 that far exceed those reported for any terrestrial gas the gas seeping from the small homorod mud volcano in transylvania romania also has extremely high concentrations of nitrogen 92 vol and helium up to 1 4 vol carbon isotopes in ch 4 c 2 h 6 and co 2 and nitrogen isotopes in n 2 indicate a primary organic sedimentary origin for the gas a minor mantle component is suggested by the 3 he 4 he ratio r ra 0 39 both thermogenic gas formation modeling and rayleigh fractionation modeling suggest that the extreme deuterium enrichment could be explained by an oxidation process characterised by a d ch4 and 13 c ch4 enrichment ratio h c of about 20 and may be accounted for by abiogenic oxidation mediated by metal oxides all favourable conditions for such a process exist in the homorod area where increased heat flow during pliocene quaternary volcanism may have played a key role finally we observed rapid variations within 1 h in c and h isotope ratios of ch 4 and in the h 2 s concentrations which are likely caused by mixing of the deep oxidized ch 4 n 2 h 2 s he rich gas with a microbial methane generated in the mud pool of one of the seeps we hypothesize that the unusual features of homorod gas can be the result of a rare combination of factors induced by the proximity of sedimentary organic matter mafic metal rich volcanic rocks and salt diapirs leading to the following processes a primary thermogenic generation of gas at temperatures between 130 and 175 c b secondary alteration through abiogenic oxidation likely triggered by the neogene quaternary volcanism of the eastern transylvanian margin and c mixing at the surface with microbial methane that formed through fermentation in the mud volcano water pool the homorod gas seep is a rare example that demonstrates how post genetic processes can produce extreme gas isotope signatures thus far only theorized and that extremely positive d ch4 values cannot be used to unambiguously distinguish between biotic and abiotic origin

abiotic methane seepage in the ronda peridotite massif southern spain abstract abiotic methane in serpentinized peridotites msp has implications for energy resource exploration planetary geology subsurface microbiology and astrobiology once considered a rare occurrence on earth reports of msp are increasing for numerous localities worldwide in low temperature land based springs and seeps we report the discovery of six methane rich water springs and two ponds with active gas bubbling in the ronda peridotite massif in southern spain water is hyperalkaline with typical hydrochemical features of active serpentinization ph 10 7 to 11 7 t 17 1 to 21 5 c ca oh facies dissolved ch4 concentrations range from 0 1 to 3 2 mg l the methane stable c and h isotope ratios in the natural spring and bubbling sites 13cch4 12 3 to 37 vpdb 2hch4 280 to 333 vsmow indicate a predominant abiotic origin in contrast springs with manmade water systems i e pipes or fountains appear to have mixed biotic abiotic origin 13cch4 44 to 69 2hch4 180 to 319 radiocarbon 14c analyses show that methane c in a natural spring is older than ca 50 000 y bp whereas dissolved inorganic carbon dic analysed in all springs has an apparent 14c age ranging from modern to 2334 y bp therefore most if not all of the ch4 is allochthonous i e not generated from the carbon in the hyperalkaline water methane is also released as bubbles in natural ponds and as diffuse seepages 101 102 mg ch4 m 2d 1 from the ground up to several tens of metres from the seeps and springs albeit with no overt visual evidence these data suggest that the gas follows independent migration pathways potentially along faults or fracture systems physically isolated from the hyperalkaline springs methane does not seem to be genetically related to the hyperalkaline water which may only act as a carrier of the gas gas bearing springs vents and invisible microseepage in land based peridotites are more common than previously thought in addition to other geological sources msp is potentially a natural source of methane for the troposphere and requires more worldwide flux measurements

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

implications of present day abiogenic methane fluxes for the early archean atmosphere 1 during earth s early history greenhouse warming by atmospheric methane helped to maintain elevated surface temperatures here we estimate the present day abiogenic ch4 flux generated by mineral alteration serpentinization at mid ocean ridges volcanic emissions and geothermal sources in addition we assess the impact that abiogenic methane may have had on greenhouse warming during the early prebiotic archean based on estimates of the rate of seafloor spreading and the degree of serpentinization within the oceanic crust the flux of methane generated by serpentinized lithosphere is calculated to be 1 35 mt ch4 y 1 while volcanic and geothermal sources are estimated to contribute 0 1 and 0 9 mt ch4 y 1 respectively furthermore it is shown that if atmospheric co2 partial pressures were above 0 01 bar the present day level of abiogenic methane production could have been sufficient to maintain above freezing surface temperatures during the archean the very high temperatures 70 c that have been suggested for the early archean however would have required extremely high methane fluxes or more likely greatly elevated atmospheric co2 levels

methane and hydrogen in hyperalkaline groundwaters of the serpentinized dinaride ophiolite belt bosnia and herzegovina abstract methane ch 4 in continental serpentinized peridotites msp has been documented in numerous hyperalkaline ph 9 springs and gas seeps worldwide with a dominantly abiotic origin msp is often associated with considerable amounts of hydrogen h 2 produced by serpentinization both gases may fuel microbial activity in igneous rocks and may have played roles in the origin of life msp is also a natural ch 4 source for the atmosphere not included in the global greenhouse gas budget yet here we document a new and major case of msp in the dinaride ophiolite belt in bosnia and herzegovina ch 4 is dissolved 83 2706 m in low temperature 13 30 c hyperalkaline ph 10 to 12 8 waters in six sites sampled through springs and boreholes four sites slanac vlajici kulasi and ljesljani show ch 4 isotopic signatures typical of abiotic msp 13 c 18 5 to 35 7 2 h 221 to 335 4 two sites vaiceva and kiseljak show a dominantly biotic signature 13 c 58 8 and 65 1 2 h 310 8 and 226 8 probably due to mixing with gas from coal beds adjacent to the ultramafic rocks h 2 concentration is highly variable up to 348 m ethane propane and butane reach 0 13 vol in total and helium isotopic composition r ra 0 12 to 0 48 reflects a dominant crustal signature the ljesljani site features the highest ph 12 8 and ch 4 emission 9 ton y 1 in peridotite hosted hyperalkaline groundwater documented so far geological and geochemical data converge towards the hypothesis that as proposed in similar cases ch 4 was mainly generated by sabatier reaction between h 2 from serpentinization and co 2 from c bearing rocks in tectonic contact with the ophiolite or other co 2 sources ch 4 h 2 h 2 o disequilibria and sabatier reaction constraints suggest that ch 4 is not formed in the hyperalkaline water but in water free or unsaturated rocks hosting opportune metal catalysts e g chromitites the amount of methane released to the atmosphere from individual springs is comparable to that of conventional biotic gas seeps springs in sedimentary basins

dissolved hydrogen and methane in the oceanic basaltic biosphere abstract the oceanic basaltic crust is the largest aquifer on earth and has the potential to harbor substantial subsurface microbial ecosystems which hitherto remains largely uncharacterized and is analogous to extraterrestrial subsurface habitats within the sediment buried 3 5 myr old basaltic crust of the eastern juan de fuca ridge flank the circulating basement fluids have moderate temperature 65 c and low to undetectable dissolved oxygen and nitrate concentrations sulfate present in high concentrations is therefore expected to serve as the major electron acceptor in this subsurface environment this study focused on the availability and potential sources of two important electron donors methane ch4 and hydrogen h2 for the subseafloor biosphere high integrity basement fluids were collected via fluid delivery lines associated with integrated ocean drilling program iodp circulation obviation retrofit kits corks that extend from basement depths to outlet ports at the seafloor two new corks installed during iodp 327 in 2010 1362a and 1362b were sampled in 2011 and 2013 the two corks are superior than earlier style corks in that they are equipped with coated casing and polytetrafluoroethylene fluid delivery lines reducing the interaction between casing materials with the environment additional samples were collected from an earlier style cork at borehole 1301a the basement fluids are enriched in h2 0 05 1 8 mol kg suggesting that the ocean basaltic aquifer can support h2 driven metabolism the basement fluids also contain significant amount of ch4 5 32 mol kg revealing ch4 as an available substrate for subseafloor basaltic habitats the 13c values of ch4 from the three boreholes ranged from 22 5 to 58 while the 2h values ranged from 316 to 57 the isotopic compositions of ch4 and the molecular compositions of hydrocarbons suggest that ch4 in the basement fluids is of both biogenic and abiotic origins varying among sites and sampling times the 2h values of ch4 in cork 1301a fluid samples are much more positive than found in all other marine environments investigated to date and are best explained by the partial microbial oxidation of biogenic ch4 in conclusion our study shows that ch4 and h2 are persistently available to fuel the deep biosphere and that ch4 is both produced and potentially consumed by microorganisms in the oceanic basement