resolving volatile sources along the western sunda arc indonesia we present the chemical and isotope hecn characterization of active fumaroles and hydrothermal gases and waters from the summits and flanks of 19 volcanic centers along the western sunda arc indonesia samples were collected over two field expeditions 1991 and 2010 and cover 13 volcanic centers in sumatra 5 in java and one in bali in addition we present data from three geothermal sites in sumatra associated with active fault systems in between volcanic centers ibvc the overall aim is to resolve volatiles associated with the sub arc mantle subducting slab and mantle wedge from inputs derived from the over riding arc crust the western sunda arc is a prime locality to assess controls on volatile provenance at subduction zones due to changes in composition and thickness of over riding crust and variations in sediment input rates along the strike of the arc the dry gas chemistry of the majority of volcanic samples is dominated by co2 with inert gas variations hearn2 typical of subduction zone gases however there is a strong crustal control on the heco2 isotope and relative abundance systematics on a number of volcanic centers this effect is most clearly observed at flank localities and in water phase samples filtering the entire database for modifications due to air contamination degassing induced fractionation c isotopes and co2 3he ratios and crustal contamination associated with volatile transport within shallow level hydrothermal systems allows recognition of the magmatic volatile signature of individual volcanoes along the arc helium isotopes at all but two volcanic centers talang and dempo on sumatra range from 5 3 ra to 8 1 ra ra air 3he 4he pointing to the mantle wedge as the principal source of he but with a small input of crustal radiogenic he at some localities samples from java and bali span an even more limited range 6 6 to 7 9 ra implying a relatively smaller input of crustal he carbon isotope and co2 3he ratios vary from 1 4 to 6 4 and 4 38 to 150 109 respectively with higher and more variable values to the north of sumatra this latitudinal effect is not apparent in air corrected n isotope values 15nc 3 91 to 5 92 or various elemental ratios such as n2 ar and n2 he the three ibvc sites all located in sumatra have significantly lower 3he 4he ratios 3 6 ra with co2 3he values both higher and lower than volcanic centers their 13c 15nc and gas ratios overlap with the volcanic centers the elemental and isotopic characteristics of carbon and helium have been modified at ibvc sites due to crustal processes however based upon relationships between ch4 and 3he as well as co variations between hecn isotopes the over riding crust and associated sediments add minimal volatiles to volcanic centers throughout the western sunda arc in turn subducted sediment particularly the nicobar fan which supplies himalayan derived sediment to the slab off sumatra exerts a strong control on the magmatic co2 characteristics although it is less influential for n2 in spite of large sections of incoming sedimentary material being off scraped during subduction our data suggest that a significant fraction must enter the trench enhancing fluid melt production in the mantle wedge we propose that subduction related source contamination plays the dominant role over thick old crustal basement in supplying the major volatile output budget of the western sunda arc

geochemistry characteristics and genetic types of natural gas in central part of the tarim basin nw china abstract according to the chemical carbon isotopic and hydrogen isotopic compositions and 3 he 4 he ratios of 127 natural gas samples the natural gas in the tarim basin is mainly composed of gaseous alkanes dominated by methane the contents of the gaseous alkanes decrease with the increase of their carbon numbers the 13 c values of ch 4 c 2 h 6 and c 3 h 8 in the platform area of the tarim basin vary in the range of 54 4 24 4 an average value of 39 2 43 1 26 7 an average value of 36 1 and 37 9 21 6 an average value of 31 8 respectively the overall carbon isotopic composition of the alkanes follows the trend of 13 c 1 13 c 2 13 c 3 13 c 4 and in some cases varies with 13 c 1 13 c 2 or 13 c 3 13 c 4 the lower carbon isotope values of methane 13 c 1 13 c 2 may be attributed to thermal sulfate reduction tsr and the higher propane value 13 c 3 13 c 4 was caused by the mixing of the natural gases of the same genetic type formed at different stages the methane hydrogen isotopes 2 h c 1 of the natural gases in the tarim basin are in the range of 195 122 with an average value of 156 the 3 he 4 he ratios of the natural gases are in the range of 2 3 10 8 66 8 10 8 suggesting that there is no deep mantle derived gas in the platform area of the tarim basin the carbon isotope fractionation of alkane gases 13 c 2 13 c 3 1 c 2 vs lnc 2 c 3 and c 2 c 3 vs 13 c 2 13 c 3 of the natural gases indicate that the oil type gas in the tarim basin has different predominant formation processes including kerogen cracking oil cracking oil and gas cracking secondary gas cracking and mixing of the kerogen cracking and oil cracking gases the gas evolved from gas cracking gas to oil and gas cracking gas and oil cracking gas along the direction from the west side of the manjar sag to the central tarim basin the natural gases in some areas of tazhong are the mixtures of the kerogen cracking and oil cracking gases

hydrocarbons and inorganic gases in the gravberg 1 well siljan ring sweden abstract hydrocarbons and inorganic gases have been analyzed in the drilling fluid of the gravberg 1 well siljan ring sweden which represents the first commercial exploration for mantle derived methane hydrocarbons detected to a depth of 6 6 km have been in trace amounts dissolved in the drilling fluid low concentrations of hydrocarbons from granite intervals are rich in unsaturated hydrocarbons and may result from abiogenic synthesis from inorganic carbon species in the granite or may be synthesized during drilling operations from organic precursors in the drilling fluid below 5 km higher hydrocarbon concentrations in granite intervals are correlated with two different lubricants added to the drilling fluid these gases are characterized by distinctive suites of hydrocarbons especially in the c4 c6 range the effects of hydrocarbon production from these and other additives are particularly pronounced in this well due to the low concentration of indigenous hydrocarbons the highest concentrations of methane were enriched in 13c 13 c 26 and were associated with several dolerite intrusions in the granite rocks this methane was present in both a core and cuttings and is similar to methane isolated from dolerite in a well recently drilled in massachusetts u s a the methane may have a deep upper mantle origin or may be a product of abiogenic synthesis in crustal rocks significant quantities of h2 and he occurring deeper than 6 km appear to have a low temperature crustal origin there is no evidence of significant amounts of upper mantle he in the gravberg 1 gases

the siljan deep well helium isotope results the siljan ring impact structure in sweden is the scene of current deep drilling exploration for methane trapped in a crustal reservoir the initial hole drilled to a depth of 6100 m through precambrian granite has been augmented by three branching side track holes beginning at 4700 m that have extended the drilled depth to 6957 m forty four gas samples extracted from the circulating drilling fluid have been analyzed for he ne and 3he4he ratios granite chips recovered from the well and eight natural gas seeps from the siljan ring and other localities in sweden have also been analyzed to provide ambient helium comparisons the 3he4he ratios in the well gases are mixtures of three components 1 atmospheric helium dissolved in recirculated drilling fluid 2 carrier he used for well site gas chromatography that contaminated some of the samples taken for he isotope analysis and 3 a crustal radiogenic component from the granite with a 3he4he ratio of 0 015 times the atmospheric ratio 1 40 10 6 although helium concentrations are generally low throughout the hole up to 4800 ppm hydrofracturing at the termination of drilling in side track hole 3 yielded gas with 23 100 ppm of helium and the crustal isotope ratio for siljan granite fluids isotope ratios in the gas seeps are in agreement with the deep crustal value but the granite itself has lower 3he4he ratios due to preferential extraction of 3he from li bearing micas no evidence of a mantle helium component is observed in the isotopic data an upper limit calculation based on the difference between he isotope ratios in the granite and in the formation waters gives a maximum of 0 15 of more helium in the well gas helium

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

origin of methane rich natural gas in japan formation of gas fields due to large scale submarine volcanism eighty seven samples of ch4 rich natural gas were collected from commercial gas and oil wells in japan the3he 4he and4he 20ne ratios chemical composition of major minor and trace components ch4 c2h6 c3h8 co2 n2 o2 ar he ne and h2 and the c isotope composition of ch4 are reported most3he 4he ratios of natural gases in the forearc regions are as low as 1 4 10 7 and are comparable to those from large gas reservoirs in other parts of the world suggesting that the ch4 has a biogenic origin in contrast the3he 4he ratios of samples from gas reservoirs in the green tuff region along the japan sea vary considerably high ratios are observed for gases from volcaniclastic reservoirs in the deeper zone and low ratios are found in shallow reservoirs of sedimentary rocks the highest3he 4he ratio 9 37 0 34 10 6 is equivalent to the highest value in the subduction zone the high4he 20ne ratios observed in most samples suggest that there is no significant atmospheric contamination an overall regularity between3he 4he ratios and 13cch4 values is observed for japanese natural gases the 13cch4 value of gas with a high3he 4he ratio reaches about 35 and that of gas with a low ratio is about 75 total c to3he ratios c 3he vary over a wide range 6 108 9 1012 but those of gases in volcaniclastic reservoirs are in a rather narrow range with a value of 2 109 coinciding with that of a mantle reservoir the relation between the observed3he 4he ratios and 13cch4 values of gases together with their c 3he ratios suggests that ch4 rich gases in volcaniclastic reservoirs are a mixture of gases from two sources magmatic and biogenic the formation of gas reservoirs with high3he 4he ratios may be attributed to large scale submarine volcanism that occurred in the middle miocene gas separation from volcaniclastic rocks is expected to have occurred during the process of sea water rock interaction at a high temperature over a long period in a submarine environment the middle miocene volcanic episode which occurred under extensional stress was quite different from the present arc volcanism and is thought to have been closely related to the opening of the japan sea

origin of natural gas in sacramento basin california the remnant of a late mesozoic early cenozoic fore arch basin the sacramento valley is principally a dry gas province complex stratigraphic relations widespread deformation and faulting and the presence of igneous intrusives testify to an active tectonic history sediments are organically immature down to an average of 10 000 ft 3 000 m and are geopressured throughout much of the basin small fields with nitrogen concentrations as high as 88 are found along the shallow eastern margin gases were sampled from 94 producing wells methane dgr13c and dgrd values range from 61 to 15 pmil and 200 to 96 pmil respectively indicating a wide range of source rock maturities wet gases in the western delta area sgrc2 c5 sgrc1 c5 12 5 have ethane dgr13c values between 31 and 20 pmil and propane dgr13c values between 27 and 12 pmil dry gases elsewhere in the basin sgrc2 c5 sgrc1 c5 1 6 have ethane dgr13c values as light as 58 pmil the chemical and stable isotope data are consistent with four principal sources gases in the western delta area were generated from mature source rocks within the oil and condensate window gases in the northern and southeastern basin are mixtures of indigenous gas mostly microbial methane with small quantities of diagenetic ethane dry thermogenic gas migrated from post mature source rocks in the basin deep and nitrogen rich gases thought to originate in metasedimentary rocks deep beneath the sediment these results place logical constraints on the location of productive traps with high btu gas and suggest caution in the interpretation of stable isotope data from other tectonically active basins due to dynamic migration and mixing processes

fingerprinting coal derived gases from the uk abstract the large scale extraction of unconventional hydrocarbons in the united states has led to fears of methane contamination of shallow groundwaters differentiating between the deep gas released during extraction shale gas coal bed methane and underground coal gasification and natural shallow sourced methane is imperative for the monitoring and managing of environmental risks related to the extraction process here for the first time we present measurements of the major gas and stable and noble gas isotope composition of coal bed methane cbm from central scotland and coal mine methane cmm from central england uk the molecular c1 c2 c3 21 to 121 and stable isotope compositions 13cch4 39 5 to 51 1 dch4 163 to 238 indicate a thermogenic origin for the methane they are distinct from the majority of shallow sourced gases in uk both sample suites exhibit high he concentrations 338 to 2980 ppmv that are considerably above atmospheric and groundwater levels simple modelling shows that these high 4he concentrations cannot be solely derived from in situ production since coal deposition and hence the majority is derived from the surrounding crust the scottish cbm contains a resolvable mantle he ne and ar contribution that may originate from melts in the deep crust demonstrating the uk coals have acted as a store for deep volatiles for 10s of millions of years the high 4he in the coal derived gases has the potential to be used as a novel diagnostic fingerprint to track fugitive release of deep methane from future unconventional gas extraction operations in the uk

magmatic fluids play a role in the development of active gas chimneys and massive gas hydrates in the japan sea abstract the earth s marine continental margins hold significant amount of carbon in the form of gas hydrate which can interact dynamically with seawater and the atmosphere and potentially influence global climate it is generally assumed that degradation of organic matter through either biogenic or thermogenic processes is responsible for the majority of the gas hydrate presently found in these deposits we present stable isotope and noble gas results from gas hydrates in the eastern margin of the japan sea and compare them with previously published data regarding gases which are found nearby in deep hydrocarbon wells associated with early miocene igneous and sedimentary rocks our results show that most of the gases which accumulate in the hydrate can be described as a mixture between a deeply sourced methane rich thermogenic crustal source tc a methane rich admixture of biogenic gases with relatively shallow air saturated seawater basw and a methane poor magmatic mantle source mm the presence of hydrate with a mantle 3he 4he signatures indicates that fluids enriched in mantle gases are responsible for the mobilization of thermogenic gas within active japan sea chimney structures the growth of primary hydrate at shallow marine sediment depths is ongoing as is the cycling of gas to hydrate which is eventually buried and dissociated at the base of the gas hydrate stability zone leading to large pockmark structures

the fate of mantle derived carbon in a continental sedimentary basin integration of c he relationships and stable isotope signatures abstract the isotopic composition and abundances of the rare gases he ne and ar and active gases co2 ch4 have been determined in a series of commercial gas reservoirs in the pannonian and vienna basins of hungary and austria respectively in these zones of continental extension significant components of mantle derived 4he up to 39 8 and 21ne up to 58 are identified the results of this study indicate a major component of mantle derived carbon in these systems as well ranging in composition from close to 100 co2 to ch4 dominated reservoirs with trace concentrations ppm of co2 these gas reservoirs provide a unique opportunity to examine the relationship of the conservative rare gases to the active gas components and to examine the sources and sinks for mantle and crustal derived carbon phases with the exception of kismarja gas field which shows evidence of addition of 3he depleted crustal co2 all gas fields exhibit a trend whereby the most co2 rich samples approach co 2 3 he mntl values similar to morb 2 109 to 7 109 while co2 depleted samples extend to co 2 3 he mntl values as low as 105 the lack of any correlation of co 2 3 he mntl ratios with r ra values indicates the observed trends are not a function of mixing between crustal and mantle derived endmembers but instead reflect progressive loss of the mantle derived co2 carrier phase during volatile transport and emplacement in the continental crust based on stable isotopic signatures from the kismarja field a crustal co2 endmember with an isotopic composition of 6 8 and a mantle co2 endmember with an isotopic composition no more depleted in 13c than 5 0 can be identified one of the few instances where the isotopic signatures of mantle and crustal derived co2 can be reliably distinguished in a continental setting covariation in 13cco2 and 13cch4 values in the gas fields is used to place constraints on two alternative models whereby the trends in percent co2 and co 2 3 he mntl ratios can be accounted for by 1 loss of the mantle derived co2 carrier phase 2 addition of crustal derived co2 3 addition of crustal derived thermogenic ch4 and potentially 4 conversion of the co2mntl carrier phase to mantle derived ch4 based on an estimated total mantle 4he flux for the pannonian basin of 4 2 108 atoms m 2 s 1 mantle carbon flux estimates for this basin alone range from 3 108 g c yr to 1 109 g c yr which over the lifetime of the basin is only 4 5 orders of magnitude less than flux estimates based on the total area of the spreading ridges clearly the addition of mantle derived carbon to the crust in areas of continental extension is significant and may have been previously underestimated we demonstrate here that integration of 13c data with rare gas isotopic tracers provides an important tool in constraining models of mantle carbon sources and sinks in continental settings

normal and reverse unroofing sequences in syntectonic conglomerates as evidence of progressive basinward deformation when a new mountain belt is generated by tectonics the denudation of the mountain front may cause the development of alluvial fans at its base the retreat of the mountain front by denudation processes and a widening of the drainage network in the source area create adjacent alluvial fan conglomerates with an inverted vertical clast distribution this vertical clast distribution represents a normal unroofing sequence renewed uplift of a previous inverted vertical clast distribution can produce a reverse unroofing sequence if continued shortening occurs in the same area a rejuvenation of the source area and basin margin may produce a new generation of clasts from the source area and a partial or total reworking of previously deposited conglomerates to supply second generation clasts if this type of reworking process is repeated as fault uplift steps basinward several new inverted and stratigraphic vertical clast distributions may arise

spatial variations of local magnitude in earthquakes recorded in northeastern spain since 1984 a seismic surveillance of the baix ebre region ne of the iberian peninsula and the la cerdanya valley eastern pyrenees has been performed by the institut d estudis catalans and the universitat de barcelona by means of four digital stations an investigation of the apparent magnitude has been carried out to explain the observed anomalous differences between the amplitude of the recorded events and their associated magnitude as given by the different agencies calculating the local magnitude with independent attenuation parameters and comparing the obtained results using the different stations we obtain differences up to 1 0 these differences are interpreted in terms of very local effects and point out the uselessness of some stations to assign magnitudes of local events results emphasize that the effectiveness of the trigger algorithms in digital stations rarely depends on the apparent local magnitude as expected the magnitude sensitivity is related to the values of the station correction terms meaning that extra information is required for an optimum surveillance of a local area a 2 d analysis of the distribution of the differences between the computed and reported magnitude shows no significant azimuthal dependence this indicates that the obtention of a local magnitude scale with an appropriate station correction term related to epicentral distance results in an important factor to provide magnitude to local events the obtained results corroborate previous works done at the same area and emphasis is placed on further analysis directed to obtain a better characterization of the local site influence

helium isotope compositions in sedimentary basins in china abstract the abundance and isotopic composition of he have been determined for a variety of natural gases oil field gases in sedimentary basins in the continent of china the 3 he 4 he and 4 he 20 ne ratios range from 0 004 to 4 99 ra where ra denotes atmospheric 3 he 4 he ratio 1 4 10 6 and from 100 39 000 respectively helium in the gas sample is composed of mantle derived he and crustal radiogenic he the high 3 he 4 he ratios were observed in the sedimentary basins which underwent cenozoic extension in the eastern domain such as the songliao liaohe north china subei sanshui and south china sea basins the basins where mantle derived he is recognized are characterized by the presence of surface and subsurface volcanic rocks high terrestrial heat flow deep faults and thinned crust on the other hand regions which underwent pre tertiary extension such as the jungar tarim tuba caidam and yumen basins in the nw and tectonic loading such as the ordos and sichuan basins in the central domain are marked by almost pure radiogenic 4 he of crustal origin and thus by an apparent absence of mantle derived he which coincides with complete lack of cenozoic volcanics low terrestrial heat flow and thickened crust such a 3 he 4 he distribution pattern clearly indicates that tectonic environment control the distribution of he isotopes in the continent of china

lateral variations of the local magnitude at ebre station northeastern iberian peninsula since 1984 a seismic surveillance at the baix ebre region ne of the iberian peninsula has been carried out from a seismic network consisting of two digital and one analog stations large discrepancies between the recorded amplitudes and the magnitude estimates given by different agencies have been observed to explain these discrepancies that consist of a large reduction of amplitude and a strong dependence of the azimuth a local magnitude formula for the area has been computed using the analog records obtained at ebr short period station global results show an average station correction factor between the computed local magnitude and the reported magnitude of the order of 1 presenting large variations around the mean value with a clear dependence on the azimuth a detailed analysis of this variation around the mean value reveals that earthquakes can be classified according to their location in different geological units thus obtaining for each zone a distinct station correction factor that can fluctuate as much as 0 6 around the average these large lateral variations of the magnitude are in good agreement with previous studies of coda q attenuation

geochemical characteristics of gases from the largest tight sand gas field sulige and shale gas field fuling in china abstract this study performed a detailed geochemical analyses of the components stable carbon isotopes of alkane gas and co2 stable hydrogen isotopes of alkane gas and helium isotopes of reproducing gas from the largest tight gas field sulige and shale gas fuling field in china the comparative study shows that tight gas from the sulige gas field in the ordos basin is of coal derived origin which is characterized by a positive carbon and hydrogen isotopic distribution pattern 13c1 13c2 13c3 13c4 2h1 2h2 2h3 i e the carbon and hydrogen isotopes increase with increasing carbon numbers carbon dioxide from this field are of biogenic origin and the helium is crust derived shale gas from the fuling shale gas field belongs to oil derived gas which has complete carbon and hydrogen isotopic reversal of secondary alteration origin 13c1

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

geochemical characteristics of he and co 2 from the ordos cratonic and bohaibay rift basins in china abstract according to the compositional and isotopic analyses of he co 2 and ch 4 of 95 gas samples from the ordos basin and 76 gas samples from the bohaibay basin in china this study carried out a detailed investigation on the geochemical characteristics of helium and co 2 from the cratonic and rift basins especially the cratonic ordos basin and rift bohaibai basin in china compared to the rift bohaibay basin the cratonic ordos basin has lower level of helium and co 2 lower r ra ratio and lower 13 c co2 maximum value when the content of co 2 is 2 associated with the hydrocarbon generation process and inorganic co 2 from the thermal decomposition of carbonates or dissolution of organic acid rift basin can also have co 2 20 and 13 c co2 of 6 2 or 4 9 which is of volcanic magmatic or mantle derived origin while cratonic basin has no such type of co 2 the cratonic basins ordos sichuan have co 2 13 c co2 i e 25 6 0 8 26 4 the rift basins have higher level of co 2 r ra ratios and 13 c co2 values the content of co 2 can reach 100 the r ra ratio can be up to 6 45 and the variation range of 13 c co2 is 34 7 27 bigger variation range of 13 c co2 implies stronger tectonic activities which is not favorable for the gas accumulation while smaller variation range means more stable structure which is favorable for the discovery of large gas fields sample in the cratonic basin in china generally has ch 4 3 he of 10 9 10 12 and r ra 4 3 he of 10 5 10 13 and r ra of 0 1 6 45 it is concluded that methane with ch 4 3 he 10 8 is of inorganic origin and methane with ch 4 3 he 10 11 is of organic origin the regression equation for the ch 4 3 he r ra in the cratonic basin is y 3e 11e 46 28x and it is y 4e 10e 1 791x in the rift basin both ordos and bohaibay basins found gas wells with he 0 05 which has significant commercial values and provides a clue for the exploration of helium rich gas fields traps with r ra 2 is a favorable clue for the discovery of co 2 gas fields seven co 2 gas fields have been found in the bohaibay basin but no systematic development has been carried out and only some liquid co 2 has been injected for tight oil from the huagou co 2 gas field

comparative study of stable carbon and hydrogen isotopes of alkane gases sourced from the longtan and xujiahe coal bearing measures in the sichuan basin china abstract two sets of coal bearing measures the upper triassic xujiahe formation t 3 x and the upper permian longtan formation p 2 l have been extensively developed in the sichuan basin sw china and some large gas fields related to these coal bearing measures have been discovered the stable carbon and hydrogen isotopic composition of alkane gases sourced from the two sets of coal bearing measures t 3 x and p 2 l gases have been investigated in this study the main controls on the gas composition and isotopic abundances of gases in the sichuan basin have been identified and distinguished on the basis of their molecular and isotopic composition the carbon and hydrogen isotopic compositions of methane 13 c c1 42 5 to 26 8 d c1 173 to 107 vary widely and show a positive correlation with the thermal maturity of the source rocks the 13 c c2 value of the t 3 x and p 2 l gases in the sichuan basin ranged from 28 2 to 21 3 and showed less variations with increasing maturity from r o values of 1 2 to 2 8 however these 13 c c2 values differ greatly from that of oil associated gas in the sichuan basin thus we provide further evidence that the value of 13 c c2 is a useful parameter to distinguish coal derived and oil associated gases the hydrocarbon gases in the xujiahe and jurassic reservoirs in contrast showed little isotopic difference indicating that secondary migration has little influence on their carbon and hydrogen isotope compositions in addition the 13 c values of p 2 l co 2 2 6 to 3 3 may reflect an origin from dissolution of the carbonates in the reservoir by acidic fluids containing h 2 s

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

origin and carbon isotope fractionation of co2 in marine sour gas reservoirs in the eastern sichuan basin abstract according to gas chemical and carbon isotopic compositions for 75 gas samples from the eastern sichuan basin c 1 c 3 gaseous hydrocarbons are dominant with high dryness coefficient c 1 c 1 3 0 99 1 0 despite the presence of various contents of h 2 s and co 2 a reasonably good positive correlation is exhibited when both contents are 5 the carbon dioxide in the natural gas in the eastern sichuan basin mainly originated from carbonate dissolution by acid gases and thermochemical sulfate reduction tsr the content of co 2 produced at the early stage of acid gas dissolution is commonly 13 c co2 value 2 content exceeds 5 the 13 c co2 values range from 8 to 2 and the co 2 and h 2 s contents demonstrated a positive correlation the majority of co 2 is generated via tsr as well as acid gas dissolution during the late uplift of the basin particularly the co 2 with 13 c co2 value 2 generated via the tsr after it was partially precipitated to form calcite while the co 2 with 13 c co2 value 3 is a mixture of the co 2 produced early via tsr and the co 2 produced by the subsequent carbonate rock dissolution by acid gases

helium and neon isotope systematics in carbon dioxide rich and hydrocarbon rich gas reservoirs the isotopic compositions and elemental abundances of helium and neon were measured in three natural gas reservoirs in the pannonian sedimentary basin of hungary kismarja a co2 rich reservoir and szeghalom south and szeghalom north both ch4 dominated reservoirs are located on topographic basement highs close to the derecske sub basin in eastern hungary mantle derived neon has been identified in mixed ch4 co2 reservoirs in the vienna basin austria this study establishes that mantle derived neon and helium are a characteristic feature of gas reservoirs throughout the neogene extensional basins of hungary and austria regardless of the dominant active gas composition 3he4he ratios within these samples are attributable to a two component mixing between mantlederived and crustal radiogenic helium the percent contribution of mantle derived 4he varies from 2 3 to 17 in contrast neon isotopic ratios indicate that the gases contain a significant component of atmosphere derived neon in addition to the mantle and crustal derived components 20ne 21ne and 22ne abundances can be corrected for this atmospheric contribution calculated contributions of mantle and crustal derived 21ne are between 3 6 21 and 1 37 respectively 20ne22nec and 21ne22nec ratios derived for these atmosphere corrected components correlate with measured r ra values and plot along a single two component mixing line between crustal and mantle isotopic endmembers this is consistent with a model in which simple mixing occurs between crustal and mantle endmembers with fixed he ne ratios the mixing line is defined by a hyperbolic constant k where k 4he22ne rad 4 he22ne mntl with a mean value of 67 3 11 8 based on estimated values of 0 47 for 21ne22nerad and 1 62 0 03 107 for 4he21ne rad kennedy et al 1990 values of 7 61 106 for he22ne rad and 11 3 104 for 4he22ne mntl can be calculated for the pannonian basin gases this 4he22ne mntl value is indistinguishable within error from the value of 8 04 104 calculated for rare gases in natural gases from the vienna basin these results clearly establish that the continental expression of mantle derived rare gases in continental extensional systems in austria and hungary is distinct and consistently different from that of gases discharging at the spreading ridges where best estimates of 4he22ne mntl are 8 1 11 3 times higher 9 10 105 staudacher et al 1989 given the remarkable agreement in the continental expression of mantle derived gases throughout the pannonian and vienna basins it is difficult to attribute the observed neon enrichment helium depletion with respect to morb gases to fractionation related to lithospheric transport processes kinetic fraction ation processes involved in transport through the crust might be expected to produce a much wider variation in the observed he ne elemental ratios the consistent order of magnitude neon enrichment observed throughout these gas fields instead implies that mantle derived fluids in these continental extensional systems may be sourced in a region of the mantle distinct from that supplying the mid ocean spreading ridges

effects of deep co 2 on petroleum and thermal alteration the case of the huangqiao oil and gas field abstract the co2 rich natural gas from the huangqiao oil and gas field of the subei basin is produced along with crude oil the co2 content ranging from 80 56 to 99 30 and the 3he 4he ratio of 0 94 10 6 to 4 67 10 6 indicates that this includes a substantial fraction of mantle derived co2 in the huangqiao region although the positive carbon isotopic series of alkane gases i e 13c1 the crude oil of the huangqiao region is light or condensate oil with low densities of 0 7933 0 8255 g cm3 saturated hydrocarbons comprise 90 06 97 37 the crude oil while the aromatic non hydrocarbon and asphaltene fractions are very small the n alkanes range from c13 to c34 with highest abundances at c16 and c17 the gas chromatogram of the crude oil shows an unresolved hump or unresolved complex mixture ucm distribution of a complete n alkane series non odd even predominance and major n alkane peaks on the highest positions of the ucm distribution this may indicate that deep mantle derived co2 fluid extracted and accumulated the oil now found in the reservoirs or source rocks

basin scale natural gas source migration and trapping traced by noble gases and major elements the pakistan indus basin he ne and ar concentrations he and ar isotopic ratios carbon isotopic ratios and chemical compositions of hydrocarbon gases were measured in natural gas samples from gas producing wells in the indus basin pakistan where no oil has ever been found 3he 4he ratios are in the range 0 01 0 06 ra ra is the atmospheric value of 1 38 10 6 indicating the absence of mantle derived helium despite the trias extension 40ar 36ar ratios range from 296 to 800 consistent with variable additions of radiogenic argon to atmospheric groundwater derived argon rare gas concentrations show large variations from 6 10 5 to 1 10 3 mol mol for 4he and from 3 10 7 to 3 10 5 mol mol for 36ar in general 36ar concentrations are high compared to literature data for natural gas co2 and n2 concentrations are variable ranging up to 70 and 20 respectively mantle derived he is not observed therefore co2 and n2 are not mantle derived either hydrocarbon gas maturity is high but accumulation efficiency is small suggesting that early produced hydrocarbons including oil were lost as well as mantle helium this is consistent with the generally late pliocene trap formation and explains the high n2 concentrations since n2 is the final species generated at the end of organic matter maturation based on 13c data co2 originates from carbonate decomposition very elevated 20ne 36ar ratios are found reaching a maximum of 1 3 compared to 0 1 0 2 for air saturated water and 0 5 for air and these high values are related to the lowest rare gas concentrations we suggest that this highly fractionated signature is the trace of the past presence of oil in the basin and appeared in groundwater we propose a model where oil water contact is followed by gas water contact both with rayleigh distillation for rare gas abundance ratios thereby generating the fractionated 20ne 36ar signature in groundwater first and transferring it to gas later assuming the gas water contact occurred shallower than present reservoir depths this model explains the generally high 36ar concentrations and low ch4 36ar ratios compared to other studies on younger basins it thus provides a historical perspective on fluid transfer in a sedimentary basin where a gas accumulation may have been buried to greater depth since formation rare gas and major element data point to mixing between two gas pulses produced successively the very co2 n2 rich gases are terminal products of organic matter maturation which have been trapped after important migration this gas was followed by a more typical thermogenic gas which mixed with it

3 he 4 he ratios in ch 4 rich natural gases suggest magmatic origin natural gas and oil fields commercially exploited since the 1950s are distributed in the zonal area facing the sea of japan in north east japan we report here measurements of the 3he 4he ratios in 27 ch4 rich natural gases obtained from commercial oil and gas wells in the area we observed extraordinarily high 3he 4he ratios up to 8 65 10 6 in gases from wells drilled into deep reservoirs in volcaniclastic rock formations the so called green tuff fig 1 these values are almost identical to those of volcanic fumaroles in the japanese islands in contrast gases in shallower sedimentary rock reservoirs have low 3he 4he ratios with a minimum value of 0 3 10 6 these low values are similar to those of natural gases originating from biological materials this suggests that the formation of natural gas reservoirs in the volcaniclastic rock may be attributed to large scale magmatic activities which occurred in the middle miocene

a magnus opus helium neon and argon isotopes in a north sea oilfield this study of the magnus oilfield located in the east shetland basin northern north sea represents the most detailed investigation of noble gas isotope systematics in a liquid hydrocarbon reservoir yet undertaken samples from nine producing wells across this middle jurassic field were taken and the helium neon and argon isotopic ratios and abundances in the oil were determined both the helium and the neon isotope systematics require a contribution from a mantle source if the mantle endmember is modeled using mid ocean ridge mor values 2 3 4 5 of the 4he and 4 3 6 2 of the 21ne is mantle derived the remainder of the 4he and 9 0 12 0 of the 21ne is crustal radiogenic and the remaining 21ne is atmosphere derived the resolved mantle derived he ne ratio is quite distinct from upper mantle values estimated from mor samples but indistinguishable from values resolved in other regions of continental extension this result provides strong evidence that the subcontinental lithospheric mantle not only has a different noble gas inventory to the convecting mantle under mors but also has a near uniform composition the quantity of radiogenic noble gas associated with the magnus oil groundwater system can only be accounted for by production predominantly from outside the volume of the magnus sandstone aquifer reservoir drainage area and the associated kimmeridge clay source rock formation and together with the mantle derived noble gases provides strong evidence for cross formational communication with deeper regions of the crust the 20ne and 36ar must have been input into the oil phase by interaction with an air equilibrated groundwater noble gas partitioning between a seawater derived groundwater and the oil phase at the average magnus sandstone aquifer temperature requires a subsurface seawater oil volume ratio of 110 40 to account for both the 20ne and 36ar concentrations in the central and southern magnus samples the volume of groundwater which has equilibrated with the magnus oil is indistinguishable from the static volume of water estimated to be in the down dip magnus aquifer reservoir drainage volume this suggests that the magnus oil has obtained complete equilibrium with the groundwater in the reservoir drainage volume probably during secondary migration and further suggests that concurrent cementation of the magnus sandstone aquifer has occurred with little or no large scale movement of air equilibrated groundwater through the aquifer system higher concentrations of 20ne and 36ar in the n magnus oil cannot be accounted for by equilibration with a seawater derived groundwater this is qualitatively consistent with the earlier and more mature oil in this section equilibrating with freshwater which is known to have been trapped in the crest of the reservoir structure

on the dependence of hindcast skill on ocean thermodynamics in a coupled ocean atmosphere model abstract three different mechanisms for the generation of enso sst anomalies within a simplified tropical pacific ocean model are examined thermocline depth changes ekman induced upwelling anomalies and zonal advection changes the effect of varying the relative influence of these terms on the realism of tropical pacific coupled models is analyzed the principal tool used to assess such realism is hindcast skill with forced ocean and oscillatory behavior also being examined of the mechanisms considered thermocline perturbations are shown to be crucially important for high coupled model hindcast skill furthermore it is concluded that the realism of the model as measured by hindcast skill deteriorates markedly when the influence on sst of ekman upwelling becomes greater than a small fraction of the thermocline influence this provides strong evidence for the hypothesis that ekman upwelling anomalies which are essentially a local response to wind stress anomalies have only a small influence on th

carbon isotopes of hydrocarbons and carbon dioxide in natural gases in china abstract 130 natural gases in the continent of china were determined for the abundance and carbon isotopes of hydrocarbons and carbon dioxide the 13c pdb values of methane range from 68 to 24 4 and the largest isotopic variability for hydrocarbons is of 13c1 there is no direct evidence for the presence of abiogenic hydrocarbon in natural gases in china one sample from songliao basin shows a heavier 13c1 24 and reverse isotopic distribution pattern 13c1 13c2 13c3 concerning the occurrence of mantle derived he ne ar and xe in the south songliao basin we propose that the methane mantle derived and heavy hydrocarbons ethane propane butane etc formed from polymerization of the mantle derived methane the 13c values for carbon dioxide range from 13 9 to 13 5 suggesting the multiple origins gases with co2 concentrations greater than 10 have a narrow range of 13c values from 8 to 2 and show higher 1he 4he ratios 0 1 times the atmospheric value suggesting that a mantle derived component is diluted by co2 derived from carbonate and or organic matter positive 13c values 4 14 indicate co2 reduction to ch2 co2 with trace concentration in ch4 rich gases can be attributed to microbial decomposition of organic matter in sedimentary rocks

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

mantle helium in sacramento basin natural gas wells abstract helium isotope ratios in sacramento basin natural gas wells show a strong mantle signal the3he 4he ratios range from 0 11 times the atmospheric ratio 0 11 ra in the rio vista field to 2 75 ra in the moon bend field indicating that 1 to 34 of the helium is mantle derived 3he 4he versus ch4 4he ratios provide evidence of two component mixing between crustal and magmatic end members extrapolation of the linear regression line to ch4 4he 0 gives a hypothetical magmatic end member 3he 4he ratio of 3 84 ra half the typical mantle ratio this indicates that the magmatic end member may actually represent a mixture of mantle and crustal helium gases which deviate from the simple two component mixture can be explained by addition of pure methane radiogenic 4he or a high n2 he component with 3he 4he 0 6 ra to 1 0 ra the ch4 3he ratio of the magmatic end member remains poorly constrained 0 to 3 109 and one cannot rule out the possibility that a significant proportion of the methane in some fields may be of deep earth origin however fields with the highest 3he 4he ratios are associated with buried plio pleistocene intrusives which have up arched sediments to form hydrocarbon traps the methane in these fields may have been produced by rapid thermal alteration of the intruded sediment elsewhere the methane appears either to have migrated from deeply buried sediments in the western basin or to have been produced by local microbial activity

helium isotopes in north sea gas fields and the rhine rift the popular assumption that all natural hydrocarbon accumulations are biogenic in origin has recently been questioned1 2 with the suggestion that deep source mantle derived hydrocarbons may contribute to accumulated biogenically produced hydrocarbons and also give rise to hydrocarbon deposits in unexpected parts of the crust the possibility that deep source volatiles are present in significant quantities in the hydrocarbon bearing parts of the crust of western europe is assessed here using analyses of 3he abundances in groundwaters and natural gas accumulations within the uk mainland and continental shelf for comparative purposes analyses are also presented for groundwaters from the southern part of the rhine graben a region that has been relatively active tectonically and the site of tertiary and quaternary volcanic activity in contrast the north sea sedimentary basins and central graben have no recorded tertiary or younger volcanic activity helium associated with north sea gas fields and groundwaters on the uk mainland is dominantly radiogenic produced by decay of u and th in the continental crust even where heat flow exceeds 100 mw m 2 a minor component 15 in groundwater samples fault structures seem to be important for the transport of mantle helium through the brittle upper crust the results are entirely consistent with a biogenic origin for north sea hydrocarbons

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

western pacific sst prediction with an intermediate el nino prediction model abstract to improve forecasting skills in the western pacific sea surface temperature sst the authors utilized and modified an intermediate el nino prediction model the original model does not have the major sst thermodynamics for western pacific sst variability so it cannot simulate interannual variation in the western pacific correctly therefore the authors have introduced some modifications such as heat flux and vertical mixing into the dynamical model in order to capture sst thermodynamics more realistically the modified model has better forecast skill than the original one not only for the western pacific but also for the eastern central pacific the model has predictive skill up to 6 months lead time as judged by a correlation exceeding 0 5

geochemistry of artificially heated humic and sapropelic sediments ii oil and gas generation simulated maturation experiments on recent sediments from different source environments give quantitative and kinetic information on the production of petroleum and natural gas starting material temperature and time of heating play critical roles in determining quantities and types of reaction products sediment samples from recent peaty deltaic and algal mat lagoonal deposits were heated separately in closed systems for 1 15 000 hr at 35 550 c 95 1 022 f reaction products were monitored for both quantity and isotopic composition the products monitored were hydrogen carbon dioxide natural gas range volatile hydrocarbons c1 c5 and oil range hydrocarbons and nonhydrocarbons c15 three stages of petroleum formation have been documented the immature stage is characterized by production of c1 c5 hydrocarbons but essentially no new c15 components carbon isotope values for the initial volatile products formed through kerogen and humic acid rearrangements display marked kinetic effects in the mature stage catagenetically derived products are added to the original biologically related c15 hydrocarbon fraction methane formed in this stage is produced by cleavage of methyl groups from the bitumen and is characterized by stable carbon isotope values 15 ppt lighter than the starting material the post mature stage shows conversion of c2 c5 components to isotopically heavy methane the quantity of oil and gas range products formed per gram of total organic carbon is approximately the same for the peat and algal pyrolysis experiments but the organic source facies affects the rate of generation and the product distribution peaty deltaic organic matter generates hydrocarbon and nonhydrocarbon gases and extractable bitumen at lower levels of thermal stress than does algal material the most notable product variation is that the c2 c5 component constitutes a greater proportion of the algal generated volatiles

he n and c isotopes and fluxes in aira caldera comparative study of hydrothermal activity in sakurajima volcano and wakamiko crater kyushu japan abstract we investigate the degassing activity of an active submarine crater wakamiko and an active sub aerial volcano sakurajima both located in aira caldera southern kyushu japan we provide 3he 4he 13c co2 and 15n data for 15 hot springs wells and bubbling gas from sakurajima volcano along with 3he 4he from seawater at four different sites for both kagoshima bay and wakamiko crater we find a common magmatic 3he 4he ratio for sakurajima and wakamiko 7 2 0 8 ra which is consistent with 1 a mixing between air saturated water asw and morb type he and 2 a common magmatic source located in the center of aira caldera corrected 3he 4he 13c co2 and ch4 3he data for sakurajima are correlated with the distance from the volcanic vent showa crater which we attribute to crustal contamination and biogenic reaction the low 13c co2 values 10 1 0 2 to 13 7 0 3 observed at sakurajima may result from the addition of carbon from organic matter from basement rocks in magmatic source after correction for air derived nitrogen we find 15nc values range between 1 7 and 4 3 which indicates that magmatic n is dominated by a sedimentary derived component up to 65 8 we calculate wakamiko fluxes of 4he 975 228 mol y 3he 0 011 0 003 mol y co2 184 43 t d and heat 195 22 mw our helium and heat fluxes are the first in situ fluxes ever reported for wakamiko crater all these wakamiko fluxes are at least one order of magnitude lower than those observed for sakurajima co2 1800 t d 3he 0 71 mol y heat 2100 mw degassing at sakurajima volcano is much stronger than that at wakamiko crater the variation of sakurajima co2 flux with time source minamidake or showa crater and eruptive activity appears not to significantly affect the co2 flux at wakamiko crater which is much more stable 132 307 t d during the last 30 years this indicates that there is no link between sakurajima and wakamiko degassing activity despite having the same magmatic source