stable carbon and oxygen isotope evidence of cretaceous sea level fluctuations recorded in septarian concretions from pueblo colorado u s a abstract limestone concretions in the blue hill member of the carlile formation middle middle turonian exposed in the lake pueblo state park colorado u s a range in size from 20 cm diameter approximately spherical forms to flattened spheroids 2 m in width and 1 m in height the earliest matrix and septarian calcite cement with 13c and 18o values ranging mostly from 18o oo to 8o oo pdb and 3o oo to 8o oo pdb respectively precipitated from diluted seawater during shallow burial where sulfate reduction largely controlled pore water bicarbonate composition in contrast the latest septarian cements exhibit very depleted 18o values 16o oo with 13c values approaching values of 1o oo to 3o oo reflecting a strong meteoric water component to pore fluids overall 13c and 18o values are inversely covariant concretion matrix calcite and septarian cements precipitated from mixtures of modified marine and meteoric fluids pore water reversals resulted from sea level fluctuations leading up to and associated with the formation of a sequence boundary or possibly the development of parasequences near the top of the blue hill member relative sea level falls caused pore water freshening as the coastal mixing zone migrated seaward similarly modified marine derived pore waters replaced fresher pore fluids accompanying subsequent marine flooding carbonate cements precipitated during this active hydrologic history recorded the isotopic characteristics of their parent fluids negative 18o values of the meteoric end member calcite compositions suggest derivation from high altitude precipitation in the sevier highlands to the west septarian cements in concretions despite their enclosure in relatively impermeable host sediment can act as sensitive indicators of relative sea level fluctuations

the origin of n2 h2 ch4 rich natural gas seepages in ophiolitic context a major and noble gases study of fluid seepages in new caledonia the study of natural gas seepages in new caledonia has shown the occurrence of two gas families one is n2 h2 ch4 rich the other is n2 rich the n2 h2 ch4 rich gases are bubbling in hyperalkaline springs oh rich known in the peridotite massif of the southern part of the island this family of gas shows contents of n2 between 50 and 62 h2 between 26 and 36 and ch4 between 11 and 16 13c values of methane are ranging from 39 to 32 we interpret the origin of h2 as a product of fluid rock interaction between basic ultrabasic rocks and water with oxidation of fe2 and reduction of underground water in the fracture system of the peridotites nappe methane is interpreted as the result of a reduction of dissolved inorganic and or organic carbon in subsurface aquifers the second family of gas emissions was found in thermal springs in the sedimentary units located structurally below the peridotites nappe the gas is composed mostly of n2 between 97 and 98 associated with relatively high concentration of he both gas families show notably high n2 vs fossil noble gas contents 36ar 20ne 84kr suggesting that n2 is not directly issued from gas dissolved in aquifers equilibrated with atmosphere but most likely finds its origin in a deep source probably within metamorphic sediments which are tectonically buried belowthe ophiolitic nappe weinterpret the n2 h2 ch4 rich family of gas as a result of a mixing between two end members 1 a h2 ch4 rich pole issued fromthe weathering of peridotite rocks and 2 a n2 rich pole which would be issued from the metamorphosed sediments buried below the ophiolitic units an unusual inverse correlation between the atmospheric noble gas isotopes 20ne and 36ar is interpreted as the result of a degassing of a relatively shallow confined aquifer related to a bubble flow from depth

diffusive separation of noble gases and noble gas abundance patterns in sedimentary rocks the mechanisms responsible for noble gas concentrations abundance patterns and strong retentivity in sedimentary lithologies remain poorly explained diffusion controlled fractionation of noble gases is modeled and examined as an explanation for the absolute and relative abundances of noble gases observed in sediments since the physical properties of the noble gases are strong functions of atomic mass the individual diffusion coefficients adsorption coefficients and atomic radii combine to impede heavy noble gas xe diffusion relative to light noble gas ne diffusion filling of lithic grains half spaces by diffusive processes thus produces ne enrichments in the early and middle stages of the filling process with f ne values similar to that observed in volcanic glasses emptying lithic grains half spaces produces a xe enriched residual in the late but not final stages of the process producing f xe values similar to that observed in shales exotic but unexceptional shales that exhibit both f ne and f xe enrichments can be produced by incomplete emptying followed by incomplete filling this mechanism is consistent with literature reported noble gas abundance patterns but may still require a separate mechanism for strong retention a system of labyrinths with constrictions and or c si nanotubes when combined with simple adsorption can result in stronger diffusive separation and non steady state enrichments that persist for longer times enhanced adsorption to multiple c atoms inside c nanotubes as well as dangling functional groups closing the ends of nanotubes can provide potential mechanisms for strong retention we need new methods of examining noble gases in rocks to determine the role and function of angstrom scale structures in both the diffusive enrichment process and the strong retention process for noble gas abundances in terrestrial rocks

contrasting styles of shelf sediment transport and deposition in a ramp margin setting related to relative sea level change and basin floor topography turonian cretaceous western interior of central utah usa abstract the turonian lower ferron sandstone and juana lopez members of the mancos shale in the western interior foreland basin form a series of regressive shoreface to shelf depositional complexes sourced from the sevier fold thrust belt to the west continuous dip parallel outcrop exposures around the northern and eastern edges of the tertiary san rafael anticline sra in central utah provide an insight into the origins of anomalous marine mudstone encased sandstones lower ferron strata consist of both coarsening and thickening upward and sharp based shoreface successions interpreted to have been deposited as sequential highstand and falling stage systems tracts overlying these shallow marine deposits is a surface that marks sediment bypass that is correlated down dip into coarse grained cross bedded sandstones interpreted as the deposits of channelised turbidity flows these turbidites are considered to be the products of sustained hyperpycnal flows exiting rejuvenated lowstand rivers based on sustained flow indicators such as dune scale cross bedding absence of genetically related slumps and delta front deposits in up dip areas surfaces of sediment bypass coarser grain sizes than the underlying shoreface deposits and regional palaeogeography the flows are interpreted to have been ignitive in proximal areas down a tectonically induced slope in the uplifted area of the farnham dome the change in depositional style from falling stage to lowstand systems tracts is attributed to increased rates of sediment supply to the shoreline promoting hyperpycnal flows a flooding surface caps the interval and separates the lower ferron sandstone from the overlying juana lopez member this interval in contrast consists only of heterolithic parallel and ripple laminated graded sandstone mudstone couplets interpreted to have been deposited by turbulent storm induced geostrophic flows the couplets are arranged into bundles and are interpreted as parasequences which in turn are arranged into a progradational parasequence set deposited during a period of sea level highstand divergent sole mark and bedform palaeocurrents from both members suggest slight eastward deflection of the turbulent flows off the proto sra further evidence for this topography is inferred from an absence of turbidites along the western side of the structure the inferred influence of local basin floor structures on sedimentation of these units has important implications for structural models for this basin for generalized sequence stratigraphic models applied to ramp type foreland basin sequences and for elucidating the origin of anomalous marine mudstone encased sandstone bodies

determination of crustal fluid residence times using nucleogenic 39ar abstract argon 39 is a radioactive isotope of ar with a half life of 269 years there are two natural sources of 39 ar on earth cosmogenic production in the upper atmosphere and nucleogenic production in rocks cosmogenic 39 ar has been recognized as an ideal tracer for groundwater residence times and oceanic circulation nucleogenic 39 ar has generally been considered problematic for groundwater studies in this work we developed simple models for the evolution of 39 ar 40 ar ratios where 40 ar denotes radiogenic 40 ar produced in the model system in rocks and fluids in rocks both 39 ar and 40 ar are produced and a fraction of the 39 ar and 40 ar is released into the mobile fluid phase in both reservoirs 39 ar reaches production or supply decay equilibrium whereas 40 ar accumulates with time thereby the 39 ar 40 ar ratio in rocks and fluids generally decreases with time our models suggest that the co evolution of these two isotopes in rocks and fluids provides a new chronometer of fluid migration and reaction in the crust this chronometer is relevant to a much wider time range than that limited by radioactive decay of cosmogenic 39 ar i e 1400 years at the current detection limit of 3 modern atmospheric value the 39 ar 40 ar chronometer is applicable to estimating residence times of very old groundwater as well as for studying fluid rock interactions and fluid migration rates such as those occurring during co 2 sequestration and the formation of hydrocarbon reservoirs

depositional and stratigraphic architecture of the santonian emery sandstone of the mancos shale implications for late cretaceous evolution of the western interior foreland basin of central utah u s a abstract the santonian emery sandstone member of the mancos shale is a continental to shallow marine succession that prograded into the cretaceous western interior seaway of western north america sediment sourced from the uplifted sevier orogen to the west fed a shoreline in the adjacent subsiding north south trending foredeep these sandstones are now superbly exposed along a 120 km long strike parallel continuous outcrop in the cliffs of the wasatch plateau of central utah shoreface parasequences are composed of coarsening upward successions of hummocky cross stratified and intensely bioturbated sandstones indicating deposition at a storm dominated shoreline two distinct depositional complexes record eastward and northeastward shoreline progradation at the northern and southernmost extremities of the plateau respectively in the subsurface emery strata comprise a thick succession of coal bearing coastal plain deposits the emery sandstone records a period of long term paralic progradation to aggradation containing at least 17 parasequences arranged into three 600 kyr regressive transgressive cycles that are recognizable in both complexes each cycle comprises only highstand and transgressive systems tracts and erosional sequence boundaries are absent absence of erosional sequence boundaries is attributed to high rates of subsidence in the foreland basin at this time santonian glacio eustatic sea level fluctuations are proposed to account for the high frequency cyclicity whilst longer term aggradation may be a function of organic controls on shoreface stacking patterns by immobile raised coal mires lying landward of the shorefaces when placed in a temporal and spatial context the emery sandstone provides a missing link in the understanding of long term controls on late cretaceous depositional systems in the central utah segment of the foreland basin and allows inferences to be made regarding foreland basin dynamics in particular thrust tectonics is postulated to have played a major role in governing the architecture of late cretaceous strata in central utah marked along strike thickening of the emery sandstone in particular is attributed to long lived elevated rates of subsidence in northern utah and southern wyoming during the late cretaceous that is adjacent to concentrated zones of thrust nappes a north dipping depositional slope is inferred from this subsidence distribution aligned approximately parallel to the structural grain of the hinterland load northeastward progradational directions of successive turonian santonian and early campanian regressive wedges in this part of the western interior basin are attributed to the presence of this tectonically induced regional slope gradient sediment sourced to these late cretaceous shorefaces is likely to have been sourced through structural recesses within the thrust front resulting in a spatial alignment of several successive regressive wedges and implicates an important long lived kinematic control on sediment supply of late cretaceous regressive wedges only the emery sandstone does not temporally coincide with reported periods of active thrusting suggesting that the regression was a consequence of factors other than uplift related elevated rates of sediment supply

on the role of equatorial ocean modes in the enso cycle abstract in order to test certain aspects of the enso mechanism proposed by suarez and schopf and by battisti and hirst we force a shallow water ocean with 28 years of observed fsu winds and decompose both the atmospheric forcing and ocean response into equatorial modes the proposed mechanism was verified in the following sense for each warm phase of the cycle a downwelling kelvin mode directly forced by the weakening of the trade winds in the central pacific was found the same wind anomaly forces an upwelling gravest rossby mode which propagates freely westward and reflects as a freely propagating kelvin mode at the western boundary this kelvin mode returns to the scene of the original warming and acts as a retarded forcing of opposite sign eventually switching the phase of the oscillation from warm to cold the cold phase then proceeds by the same mechanism but with modes of opposite signs to eventually switch to the warm phase the contribution of the higher rossby modes to this process is e

application of sequence stratigraphic concepts to the upper cretaceous tununk shale member of the mancos shale formation south central utah parasequence styles in shelfal mudstone strata

noble gases in crude oils from the paris basin france implications for the origin of fluids and constraints on oil water gas interactions in order to investigate the potential of noble gases to trace the dynamics of oil reservoirs we have analysed the abundance and isotopic composition of all noble gases he ne ar kr and xe in crude oils from the paris basin france using a new extraction and purification procedure the main oil reservoirs are presently located in the jurassic dogger limestone and in the triassic keuper sandstone but hydrocarbons originated from a common source rock formation located in the interbedded liassic sequence despite this common origin the abundance and isotopic ratios of the noble gases differ between the dogger and the keuper the isotopic compositions of kr and xe are indistinguishable from that of air 3he 4he ratios higher than those predicted from radiogenic production in the sediments or in the crust are attributed to the occurrence of mantle derived 3he in the basin each sedimentary sequence is characterised by well defined and homogeneous 21ne 22ne and 40ar 36ar ratios which average 0 0306 0 0008 and 312 10 for the dogger and 0 0367 0 0012 and 664 30 for the keuper respectively the main source of radiogenic noble gases appears to be the continental crust underlying the basin with possible regional contributions of noble gas isotopes produced in the sediments the helium and argon isotopic ratios of the dogger oils are very similar to those observed in geothermal waters flowing in the dogger aquifer throughout the basin demonstrating that noble gases in oils derive from associated groundwaters oil reservoirs in the paris basin therefore accumulate noble gases from wide regions of the continental crust through cross formational flow of groundwaters and subsequent partitioning into oil this observation implies that noble gases cannot be directly used to date oils but can provide time constraints if 1 water oil interactions are quantified and 2 the residence time as well as the noble gas characteristics of associated groundwaters are known oil water gas partitioning processes are well recorded in the fractionation of noble gas elemental abundance two distinct processes have been identified 1 accumulation of atmosphere derived ang and radiogenic noble gases both initially dissolved in groundwaters resulting in a positive correlation between absolute amount of ang and the extent of heavy noble gas fractionation and 2 subsequent fractional degassing resulting in a negative correlation between ang abundance and heavy noble gas fractionation degassing is particularly evident for the keuper oils and might have occurred in the reservoirs following hydrodynamic gas stripping the ang abundance in the dogger reservoirs requires that about one order of magnitude more water than presently observed has interacted with the oil given current estimates of the residence time for groundwaters in the dogger aquifer the duration of oil water interaction is in qualitative agreement with a palaeocene oligocene age for the major episode of secondary oil migration in the paris basin high xenon contents in keuper reservoirs suggest that they have experienced hydrodynamic interactions between flowing waters and oils for long time and that the trias might have reached hydrostatic condition only recently

evolution of coal bed methane in southeast qinshui basin china insights from stable and noble gas isotopes abstract the late carboniferous early permian coal seams of the qinshui basin in shanxi province are the most prolific producer of coalbed methane cbm in china methane formed in the late triassic during deep burial and reheating in late jurassic early cretaceous driven by magmatic underplating basin inversion brought the coal seams to 400 700 m from the surface in the mid late cenozoic here we present results of a study aimed at understanding the origin of the methane and how it was affected by cenozoic exhumation of the basin methane from a 12 km traverse perpendicular to the basin margin in the southeast part of the basin have stable isotope compositions 13c 30 2 to 35 2 and d 155 to 194 indicating a thermogenic origin with limited biogenic input they are however lighter than expected based on coal maturity and c1 c2 c3 1000 are significantly higher than typical thermogenic methane 90 of the radiogenic 4he produced in the coals has been lost prior to equilibrium between gas and water phase in the reservoir this likely occurred in response to gas loss process during rapid exhumation in cenozoic showing that the he and ar content of natural gases is a sensitive indicator of gas loss event caused by recent basin inversion the event may have led to the loss of up to 44 of the methane from the coal seams this study demonstrates the importance of basin inversion on gas preservation in shallow cbm and shows that in contrast to 13cch4 the light noble gases are essential for tracing such a process

gas geochemistry of the macuspana basin mexico thermogenic accumulations in sediments impregnated by bacterial gas a gas survey was performed in the macuspana basin south of mexico two distinct gas families were identified family 1 is represented by homogeneous and purely thermogenic gas associated with condensates expelled at the end of the oil window and family 2 is composed of a mixture of bacterial dry gas and thermogenic gas derived from source rocks at high maturity chemical and isotopic parameters as well as noble gas data provided information about the sources the proportions of mixing and directions of hydrocarbon migration of these two families considering the risk associated with further oil and gas exploration in the basin deeper zones present higher exploratory interest for family 1 gas fields and associated oil accumulations in contrast the bacterial gas fields should be considered a less promising target for future oil and gas exploration

evaluation of undiscovered natural gas in the upper cretaceous ferron coal wasatch plateau total petroleum system wasatch plateau and castle valley utah abstract the total petroleum system approach was used to estimate undiscovered gas potential of the wasatch plateau and castle valley central utah the ferron coal wasatch plateau total petroleum system was geologically defined and subdivided into seven assessment units six of which were formally evaluated geologic data considered in defining the assessment unit boundaries included thermal maturity coal presence and thickness overburden thickness and faulting intensity historical production data were also used to estimate volumes of gas from undrilled areas the one conventional assessment unit includes almost the entire area of the petroleum system and is characterized by known accumulations that occur in structural or combination traps in sandstone reservoirs the estimated undiscovered conventional producible gas that may be added to reserves of this unit ranges from a low f95 of 14 8 billion cubic feet bcfg 419 million cubic meters mm 3 of gas to a high f5 of 82 bcfg 2321 mm 3 and a mean value of 39 9 bcfg 1130 mm 3 continuous gas accumulations are those in which the entire assessment unit is considered to be gas charged within these assessment units there may be wells drilled that are not economic successes but all are expected to contain gas coalbed gas is in this continuous category mean estimates of undiscovered gas for the five continuous assessment units are 1 northern coal fairway drunkards wash 752 3 bcfg 21 323 mm 3 2 central coal fairway buzzard bench 536 7 bcfg 15 194 mm 3 3 southern coal fairway 152 6 bcfg 4320 mm 3 4 deep 6000 feet plus coal and sandstone 59 1 bcfg 1673 mm 3 5 southern coal outcrop 10 6 bcfg 300 mm 3 and joes valley and musinia grabens not assessed the mean estimate of undiscovered gas for the entire tps is 1551 2 bcfg 43 914 mm 3 there is a 95 chance that at least 855 7 bcfg 24 225 mm 3 and a 5 chance that at least 2504 bcfg 70 888 mm 3 of undiscovered producible gas remain in the tps

variation of system openness and geochemical features in overpressured sandstones of the yinggehai basin offshore south china sea abstract hydrocarbon discoveries in recent years in the upper miocene of the yinggehai basin show differences in overpressure magnitude gas and mineral components overpressure close to or reaching the leakage threshold has induced high system openness for one field but the overpressure of another field remains to be safely closed a new vision to investigate the interplay between the system openness and the gas chemical and mineralogical features were conducted the gas components in the high openness system are rich in high maturity hydrocarbons and inorganic co2 which both have heavier carbon isotopes low maturity gases with lighter carbon isotopes are dominant in the low openness system the abnormal carbon isotope ratio between iso butane and n butane in the high openness system confirms that early low maturity leakage has generated abnormal compositional and isotopic fractionation although the sedimentation process was uniform in the two systems the high openness system has rare k feldspar grains and chlorite but it is rich in illite smectite mixed layers i s precipitation is characterized by ankerite and kaolinite in the high openness system whereas the low openness system primarily consists of calcite the strong dissolution of k feldspar grains and chlorite should have released abundant potassium and silicon the high abundances of i s and kaolinite which are both sensitive to potassium and the rarity of quartz overgrowths in the high openness system imply that the leakage of potassium silicon from the sandstones has induced a mass imbalance between dissolution and precipitation even the sandstone porosity was slightly increased by the mass imbalance in the high openness system the risk of hydrocarbon expulsion during brine leakage cannot be ignored

multiple atmospheric noble gas components in hydrocarbon reservoirs a study of the northwest shelf delaware basin se new mexico the northwest shelf of the delaware basin se new mexico is the site of several large and productive oil and gas fields the most productive reservoirs are located in the late pennsylvanian morrow and early permian abo formations production from the latter more important play is predominately from fluvial abo red beds of the pecos slope field the oxidizing conditions implied by the reddish color of the formation require an external hydrocarbon source to test the existing migration model for the region and constrain the location of potential hydrocarbon sources we measured the elemental and isotopic composition of noble gases produced along with the hydrocarbons we found the hydrocarbons to be highly enriched in radiogenic 4he 40 ar and nucleogenic 21 ne f 4he 44 000 250 000 40ar 36ar 400 3145 21ne 22ne 0 044 0 071 the greatest enrichments occur in the pecos slope gas fields the hydrocarbons also contain three independent nonradiogenic noble gas components each with an atmospheric isotopic composition one component is most likely air saturated water asw the second component is enriched in the heavy noble gases f 130xe 8 5 and is derived from the hydrocarbon sources the third component is enriched in ne f 20ne 0 8 that we believe is degassed from sources within the reservoirs this component is correlated with but decoupled from the dominant source of radiogenic 4he and 40 ar very high concentrations of 4he up to 1 by volume in the pecos slope reservoirs require a source external to the reservoirs such as the underlying precambrian basement granites and sedimentary equivalents structural buckles cutting through the pecos field may act as high flux vertical pathways for the radiogenic 4he if the hydrocarbons in the pecos slope fields have migrated northward from the deeper delaware basin as suggested by compositional trends then perhaps the buckles also play an important role in the distribution and filling of the pecos slope reservoirs

the offshore bar revisited a new depositional model for isolated shallow marine sandstones in the cretaceous frontier formation of the northern uinta basin utah u s a abstract shallow marine sandstone bodies isolated within marine mudrock successions are still incompletely understood a robust understanding of such bodies is of interest not only scientifically but also in order to facilitate successful exploration for and production of petroleum and other natural resources such bodies are preserved in the turonian frontier formation of the northern uinta basin in utah and colorado u s a where they have been previously interpreted as the products of offshore bars a reappraisal of these bodies in the uppermost frontier formation herein defined as the turonian ashley valley member reveals three northeast southwest elongate incised highstand forced regressive and lowstand offshore sandstone bodies partially to fully encased in offshore marine mudrock these bodies are herein named the buckskin hills kane hollow and raven ridge sandstones from oldest to youngest five lithofacies were identified from 47 measured outcrop sections located along the western and southern margins of dinosaur national monument they are 1 marine shelf claystones and siltstones 2 lower upper offshore marine admixed siltstone and sandstone 3 lower upper offshore thin bedded sandstones and siltstones 4 distal lower shoreface heavily bioturbated very fine grained sandstone and 5 transgressive lag conglomerate wireline logs from 112 drillhole locations throughout the uinta basin were calibrated with nearby outcrop locations to construct cross sections and net sandstone isochore maps from these regionally traceable horizons flooding surfaces and internal erosion surfaces facilitated an analysis of stacking patterns development of a stratigraphic framework and a depositional environment interpretation overall the ashley valley member preserves a basinward offlapping stacking pattern indicative of shoreline progradation in response to the late turonian greenhorn global eustatic regression that was interrupted by two high frequency transgression regression cycles this nested cyclicity cannot be explained by global eustasy alone and instead is suggestive of a secondary allogenic control likely related to western cordilleran foreland basin wcfb geodynamic driving mechanisms as a result the ashley valley member provides an example of tectonic forcing on stratal stacking patterns highlighting the importance of intrabasinal tectonic processes on dispersal patterns and high frequency relative base level fluctuations within the wcfb stratigraphic record

upper cretaceous vernal delta of utah depositional or paleotectonic feature a conspicuous seaward bulge of the middle to late turonian shoreline of the cretaceous seaway in northeastern utah and southwestern wyoming has been identified by previous authors as the vernal delta strata of the frontier formation and the ferron sandstone member of the mancos shale that form the vernal delta consist largely of fluviodeltaic facies the delta however is not recognizable as a locus of turonian sedimentation there is no isopach thick associated with it the vernal data is a large feature encompassing an area of at least 6250 mi sup 2 16 187 km sup 2 a comparison between the depositional setting and paleogeography of northeastern utah during the late cretaceous and a present day area on the east flank of the andes in colombia indicates strong similarities further comparison suggests that feature the size of the vernal delta could not have been produced by a single river the vernal delta overlies the ancestral uinta mountain uplift an area where cenomanian marine shales were entirely removed by what appears to have been submarine erosion during early turonian time when the shoreline prograded eastward across this area during middle uronian time the sediment load caused the area to subside but at a rate slowermore than rates of subsidence to the north and south this differential subsidence is the cause of the shoreline bulge although it includes deltaic facies the vernal delta is not a delta per se but a feature produced as the result of interaction between sedimentation and gentle tectonic movement of the ancestral uinta mountain uplift less

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

natural gas association with water and oil as depicted by atmospheric noble gases case studies from the southeastern mediterranean coastal plain a model for the equilibrium distribution of atmospheric noble gases ang between natural gas and water phases was extended to include the gas oil relationship the basic assumption is that the ang are introduced into hydrocarbon systems via recharge or seawater theoretical ang patterns of natural gas at equilibrium with water fall between the air pattern and that of air saturated water theoretical ang patterns of natural gas degassed from oil which had previously equilibrated with a water phase cover a wide range including the range calculated for gas water equilibration ang patterns in natural gas which fall outside the overlapping range may thus indicate association of the gas with oil the model was tested in the case of hydrocarbon systems of the southeastern mediterranean coastal plain other geochemical evidence indicates that the ashdod sadot shallow gas wells are not related to oil the relative ang abundances in gas samples from these wells lie within the range predicted for gas water association the relative ang abundances in samples degassed from oils of the helez kokhav oilfield are similar to specific patterns predicted for the degassing of oil which was previously associated with water published and new analyses of methane dominated natural gas samples from california japan and northern israel also reveal ang patterns of the type predicted by the model the results of the case studies support our hypothesis that water is responsible for transport of atmospheric noble gases into subsurface hydrocarbon systems this forms the basis for identification of oil associated natural gases via ang study

quantifying the helium and hydrocarbon accumulation processes using noble gases in the north qaidam basin china abstract limited reserves and insecure resource supply have led to global shortage crises in helium a vital gas for cryogenic engineering and other countless industrial manufacturing processes despite the attention drawn by global supply disruptions the helium accumulation mechanism in natural gas fields remains poorly understood noble gases are excellent tracers for studying migration and accumulation processes of fluids in the subsurface and can be used to investigate the influence of subsurface fluids on helium accumulation we present noble gas isotope and abundance data as well as major gas compositional data from 10 producing wells in three gas fields in the north qaidam basin china helium is more concentrated in the mabei and dongping gas fields 2 06 48 4 10 4 cm3 stp cm3 than in the niudong gas field 1 15 1 42 10 4 cm3 stp cm3 the helium is mainly radiogenic with 3he 4he ratios of 0 01 0 05 ra where ra is the atmospheric value of 3he 4he and lacks significant contribution from the mantle 0 03 0 67 the noble gases derived from air saturated water 20ne 36ar 84kr and 130xe can be explained by an oil modified groundwater exsolution model with excess heavy noble gases the calculated voil vwater and vgas vwater ratios indicate that the mabei region is the most oil rich area and the dongping region has the driest natural gas which is consistent with the geological context these ratios further support the fractionation models the strong linear relationship between 4he and 20ne r2 0 98 suggested that 4he was dissolved into groundwater before migrating into the oil or gas phase the initial 4he concentrations in groundwater can accumulate within 0 31 2 78 myr assuming a 4he flux from the entire crustal section according to the fractionation model helium in groundwater partitions into the gas phase when contacting hydrocarbons the different volume ratios among oil gas and water during the equilibration process cause much greater variability in the helium concentrations in the gas phase e g 6 08 10 4 to 2 01 10 3 cm3 stp cm3 in mabei than those in the groundwater phase e g 9 18 10 3 to 1 39 10 2 cm3 4he stp cm3 h2o in mabei hydrocarbons play a critical role in helium accumulation and dilution helium rich natural gas fields are characterized by old groundwater systems and moderate hydrocarbon abundance this study has succeeded in quantitatively assessing the helium accumulation process in natural gas fields in the north qaidam basin and revealed that both groundwater and hydrocarbon phases control the helium accumulation in the subsurface environment this outcome has broad implications for the prediction of hydrocarbon and helium as resources

the quantification of diffusive hydrocarbon losses through cap rocks of natural gas reservoirs a reevaluation discussion 1 a calculation scheme is presented to estimate the quantities of diffusive gas loss through the water saturated cap rock of natural gas reservoirs over geologic time reexamination of earlier calculations in a 1982 paper by leythaeuser et al revealed that the estimate of the rate of diffusive hydrocarbon losses through the cap rock of the harlingen netherlands natural gas reservoir was based on oversimplified assumptions concerning the boundary conditions at the reservoir cap rock interface according to this recalculation the time required to reduce the present day methane content of the harlingen gas field by one half is approximately 70 m y not the previously published value of 4 5 m y consequently diffusion losses through the cap rock appear to affect the long erm stability of natural gas reservoirs to a lesser extent than suggested by the earlier results

coupled use of carbon isotopes and noble gas isotopes in the potiguar basin brazil fluids migration and mantle influence abstract we used the carbon isotope ratios of hydrocarbons and co 2 and the proportions of noble gas isotopes of associated gases from several geological provinces of the potiguar basin brazil for gas source rock correlation and to determine maturity post genetic processes migration leakage biodegradation and to assess the possible interactions between hydrocarbons and surrounding waters barriers of permeability at the basin scale the amount of water interacting with the accumulated hydrocarbons proportion of meteoric water and contamination of the fluids by the mantle were quantified for the distinct petroleum systems defined in this basin four hydrocarbon provinces have been defined in the potiguar basin the first is located in the southern part of the basin and the other three are in the northern part with offshore pods of generation migration occurred along ne sw horst and grabben structures all gases are mainly thermogenic 13 c of methane between 49 and 34 except for biodegraded gases with isotopically lighter methane generated in the oil window and only two fields from one of the trends seem to have been significantly biodegraded 13 c of propane up to 5 8 per mil the source rocks were lacustrine for the gases from the southwest of the basin and mixed marine lacustrine for two trends the third trend as well as an offshore field appears to have a lacustrine source rock and the hydrocarbon generation and accumulation are older than for the other fields each of the three trends is generally isolated in terms of fluid migration except in one location where noble gas isotopes indicate that the guamare trend is invaded by fluids of the macau trend an important contamination by mantle fluids has been confirmed for all the hydrocarbon fields close to the shore 3 he 4 he ratios up to 1 6 times the atmospheric ratio the mantle contribution as high as 20 of total helium decreases inland the mantle contribution provides some chronological constraints for the hydrocarbon accumulations and may have had an influence in hydrocarbon generation due to an igneous activity associated influence in the hydrocarbon generation pod

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

geochemical characterization of natural gas a physical multivariable approach and its applications in maturity and migration estimates gas geochemistry has recently been shown to enhance information regarding the geological history of hydrocarbons in this paper graphical representations of physico chemical processes affecting the chemical and isotopic signatures of natural gases are exemplified these diagrams are based on experimental studies and the use of basic statistics to extract significant and synthetic parameters from the geochemical data from 11 chemical and isotopic ratios a statistical analysis pca yields two very important parameters the first parameter using mainly the c2 fraction of the gas relates to maturity and the second parameter involving the proportions and d13c values of methane indicates mainly segregative migration positive values of the second parameter indicate that gases accumulated far from their source whereas negative values correspond to residual gas pools after leakage of a part of the fluids a tentative reconstruction of the gas history has been performed in two brazilian basins the espirito santo basin and part of the reconcavo basin the espirito santo basin is located on the passive continental margin of the atlantic ocean and the reconcavo basin corresponds to an intracontinental aborted rift in both cases the source rocks are mainly lacustrine with thermal maturities ranging between the oil window and the beginning of the gas window results show that in the reconcavo basin a major fault the mata catu fault acts as a drain for hydrocarbon migration at the basin scale associating a major isotopic fractionation to the gas migration with a clear correlation between isotope fractionation and the distance of migration in the espirito santo basin this segregation appears in the platform sediments to a lesser extent and is absent in the gas pools located in the paleocanyons filled with turbidites this long distance migration in the platform sediments suggests that a hydrocarbon kitchen is located offshore

detailed facies analysis of the upper cretaceous tununk shale member henry mountains region utah implications for mudstone depositional models in epicontinental seas abstract lower middle turonian strata of the tununk shale member of the greater mancos shale were deposited along the western margin of the cretaceous western interior seaway during the greenhorn second order sea level cycle in order to examine depositional controls on facies development in this mudstone rich succession this study delineates temporal and spatial relationships in a process sedimentologic based approach the 3 dimensional expression of mudstone facies associations and their stratal architecture is assessed through a fully integrative physical and biologic characterization as exposed in outcrops in south central utah sedimentologic characteristics from the millimeter to kilometer scale are documented in order to fully address the complex nature of sediment transport mechanisms observed in this shelf muddy environment the resulting facies model developed from this characterization consists of a stack of four lithofacies packages including 1 carbonate bearing silty and sandy mudstone cssm 2 silt bearing calcareous mudstone scm 3 carbonate bearing silty mudstone to muddy siltstone cms and 4 non calcareous silty and sandy mudstone ssm spatial and temporal variations in lithofacies type and sedimentary facies characteristics indicate that the depositional environments of the tununk shale shifted in response to the 2nd order greenhorn transgressive regressive sea level cycle during this eustatic event the tununk shows a characteristic vertical shift from distal middle shelf to outer shelf cssm to scm facies then from outer shelf to inner shelf environment scm to cms and to ssm facies shifting depositional environments as well as changes in dominant paleocurrent direction throughout this succession indicate multiple source areas and transport mechanisms i e longshore currents offshore directed underflows storm reworking this study provides a rare documentation of the greenhorn cycle as exposed across the entire shelf setting high resolution mapping of genetically related packages facilitate the development of process based depositional models that can be utilized for lateral correlations into the equivalent foredeep strata of the cretaceous interior

formation and migration of hydrocarbons in deeply buried sediments of the gulf of cadiz convergent plate boundary insights from the hydrocarbon and helium isotope geochemistry of mud volcano fluids highlights clay dehydration water expelled from buried sediments drives mud volcanism rise of fluids mediated by crustal scale strike slip faults cross cutting wedge on active accretionary wedge petroleum accumulations were dismantled in neogene 4he enrichment and 13c ch4 50 in fluids reflect an open hydrocarbon system petroleum pools remain on shallow margin microbial gas vented out of active wedge abstract a geochemical study of the composition of hydrocarbon gases and helium isotopes 3he 4he in fluids from mud volcanoes mvs located on and out of the active accretionary wedge of the gulf of cadiz goc provides information on fluid sources and migrations in deeply buried sediments the goc is a tectonically active segment of the africa iberia plate boundary occluded beneath the thick sediments of an accretionary wedge dissected by crustal scale strike slip faults initially built during the miocene gibraltar arc subduction the wedge has since developed toward the w nw in an oblique convergent setting interstitial water expelled from clays undergoing diagenesis in buried sediments drives mud volcanism on the wedge with mvs located along strike slip faults mediating fluid ascent the large excess of radiogenic helium 4he in all goc fluids agrees with a clay mineral dehydration source of water hydrocarbon gases from all deepwater mvs bear methane having similar stable carbon isotope compositions of 50 vpdb whether fluids are highly enriched in methane relative to heavier homologues c2 or not methane ethane propane 10 to 10 000 we suggest that methane with 50 vpdb was largely diffused out of early generating source rocks and became dissolved in the water expelled by the buried sediments consistently low 3he 4he ratios suggest an open hydrocarbon system petroleum accumulations and 3he dissolved in the original sedimentary pore water have mostly escaped into the water column during the major late neogene compressional events at present some mvs vent ch4 rich fluids from dewatering sediments while other structures located on active thrusts additionally vent c2 rich gases generated by active cretaceous source intervals by contrast evaporitic seals preserved petroleum accumulations on the shallow moroccan margin while the westernmost mvs located out of the accretionary wedge vent microbial gas

constraints on fluid origins and migration velocities along the marmara main fault sea of marmara turkey using helium isotopes abstract fluids venting from the submarine portion of the marmara main fault part of the north anatolian fault system turkey were sampled in ti bottles deployed by submersible the fluids consist of mixtures of fault derived gases fault related cold seep fluids and ambient seawater these components can readily be distinguished using the isotopes of he and the he ne ratios 3he 4he ratios range between 0 03 0 1 and 4 9 0 4 ra indicating that both crustal and mantle derived sources of helium are sampled by the fault the dominant gas in all the samples analyzed is methane with the abundance of co2 below detection 2 in the mantle rich high 3he 4he fluids this is in contrast to nearly all mantle derived fluids where the c species are dominated by co2 while high ch4 co2 ratios may reflect organic or inorganic reactions within the crust which reduce mantle derived co2 to methane this is not a priori necessary we show that simple dilution of mantle fluids with methane produced within local sediments could result in the high 3he 4he methane rich gases currently emanating from the fault this observation is supported by an anticorrelation between 3he 4he and c 3he which is consistent with addition of c and 4he simultaneously to the fluids the highest 3he 4he ratios were found in the tekirdag basin at the foot of the escarpment bordering the western sea of marmara where seismic data are consistent with the presence of a fault network at depth which could provide conduits permitting deep seated fluids to rise to the surface the lack of recent volcanism or any evidence of underlying magmatism in the area along with low temperature fluids strongly suggests that the 3he rich helium in these fluids was derived from the mantle itself with the marmara main fault providing a high permeability conduit from the mantle to the surface assuming that the mantle source to the fluids originally had a 3he 4he ratio of 6 ra the minimum fluid velocities considering only vertical transport and no mixing with parentless 4he implied by the high 3he 4he ratios are of the order of 1 100 mm yr 1

foreland basin structural growth recorded in the turonian ferron sandstone of the western interior seaway basin usa tectonic forcing of stratigraphic architecture is likely in foreland basins tectonic driving forces are increasingly being invoked to explain stratigraphic patterns in the cretaceous western interior seaway basin of north america yet the evidence is largely circumstantial and the details of driving forces remain elusive in this paper i show direct stratigraphic evidence for syndepositional growth of a structural arch with at least 50 m of relief during accumulation of the upper turonian ferron sandstone in south central utah united states progressive growth of the arch was superimposed on several high frequency stratal cycles that were driven by a more regionally extensive process geodynamic or eustatic and that produced laterally amalgamated sandstone bodies in a depositional strike parallel orientation north south all of this stratigraphy was then truncated by a more or less planar erosion surface sequence boundary that can be traced physically over at least 67 km north south this surface was later tilted northward such that the upper member of the ferron sandstone thins progressively southward from 50 to 10 m over 67 km the facies juxtapositions revealed by the ferron sandstone could if seen in exposure of limited lateral extent be wrongly interpreted as recording regionally extensive relative sea level drops and potentially used in error as evidence for substantial eustatic sea level falls during the turonian the folding and tilting documented in this study can be clearly attributed to geodynamic and or tectonic driving forces likely related to migration of a forebulge

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

equatorial wave sequence associated with warm pool displacements during the 1986 1989 el nino la nina in the pacific equatorial band the zonal displacement of the eastern edge of the warm pool subject to insignificant seasonal variations is dominated by strong interannual variations almost in phase with the southern oscillation index over the 1971 1973 el nino la nina period gill 1983 suggested that such displacement was caused solely by horizontal advection by zonal current anomaly basin wide geosat derived zonal surface current anomalies are available during the 1986 1989 period and they agree quite well with observed equatorial currents in the western and central pacific within the 4on 4 s equatorial band the cumulative contribution of first baroclinic kelvin and first symmetric m 1 rossby modes to surface zonal equatorial current anomalies account for most of the geosat derived current variability from these geosat derived currents it is demonstrated that the eastward westward displacement of the eastern edge of the warm pool was primarily due to horizontal advection by zonal current anomalies during the 1986 1987 el nino 1988 1989 la nina as a corollary the el nino la nina warm cold sea surface temperature sst anomaly in the central western pacific was the result of anomalous zonal advection the 1986 1989 displacement of the warm pool appeared as a low frequency movement resulting from high frequency forcing i e a succession of local wind forcing and its remote kelvin and m 1 rossby wave responses in the equatorial waveguide in the central western pacific a in 1 downwelling rossby wave issued from the eastern pacific shifted the displacement from eastward to westward and therefore seems to have been the cause for el nino to turn to la nina in boreal fall 1987 in the eastern pacific the simultaneous occurrence of free propagating downwelling upwelling kelvin waves with the seasonal sst warming cooling appeared necessary for the development of local el nino la nina sst anomaly over most of the equatorial pacific slow migration of sst anomalies clearly showed up distinct during el nino and la nina these zonal migrations appeared to result from the delayed association of two phenomena the zonal advection in the central western pacific and the arrival of downwelling upwelling kelvin waves into the eastern pacific synchronous with the seasonal sst warming cooling albeit different in terms of equatorial wave action as compared to the delayed action oscillator theory our results suggest that zonal advection and wave dynamics were both important for the generation and migration of el nino southern oscillation sst anomalies in 1986 1989 finally our observational results about warm pool displacements equatorial wave sequence the shift from el nino to la nina and the slow sst migrations are presented in a schematic form involving sequential ocean atmosphere coupling which appears continuously over the november 1986 to a

gas generation from source rocks aspects of a quantitative treatment abstract quantitative aspects of gas generation in source rocks are discussed first in terms of stoichiometric considerations based on the elemental compositions of different kerogen types i ii iii and coal the maximum amounts of available carbon and hydrogen for the formation of hydrocarbons during maturation were calculated considering a closed source rock system type i kerogen has the highest and coal the lowest specific gas yield the second part discusses the problem whether experimentally derived gross kinetic parameters activation energies and frequency factors can be applied to hydrocarbon generation reactions in the geological environment the third part comprises a detailed case history of gas formation in the upper carboniferous of northern germany for three selected wells in the study area the temperature histories were defined using a computer aided integrated basin modelling approach significantly different temperature histories in those three wells were then used to compute the gas generation from 320 myr ago to present the drastic influence of changes in the kinetic input parameters 50 or 54 kcal mol 1 for the activation energy of oil cracking on timing and duration of gas formation has been demonstrated the results confirmed that accurate knowledge of both the temperature history and the kinetic parameters is of equal importance

the distribution of thermogenic bacterial and inorganic fluid sources in the petroleum systems of the llanos basin colombia insights from the noble gases and carbon stable isotopes abstract the colombian andean foreland is a rich petroleum province where various source rocks and an active circulation of fresh water are present in the subsurface resulting in a complex fluid mixture within the reservoirs moreover some of the traps are shallow and low api gravity oils are found massive meteoric water infiltration and local biodegradation have been proposed to explain these observations but require some in depth investigation to be confirmed in order to provide some new insights into the llanos basin petroleum system we performed a natural gas geochemical survey over different areas of the basin including stable isotopes of hydrocarbon non hydrocarbon and noble gases results show that the influence of meteoric water infiltration is dominant in the shallow area eastward but decreases towards the deepest part of the basin westward a general gas oil phase separation differentiates gas depleted biodegraded shallow reservoirs from deep gas rich less altered reservoirs data suggest that there is a shallow biodegradation associated with meteoric water circulation in the carbonera fm while some of the deeper heavy oils mirador une fms were more likely produced by an early mature source rock however biodegraded oil later mixed with less altered oil and associated gas are plausible this study also indicates a contribution of mantle fluids in the deepest parts of the basin near the contact with the guaycaramo fault system there older rift sequences may have recorded mantle fluid fluxes or alternately the presence of diffuse mantle fluxing along the deep rooted thrust front during the formation of the llanos basin

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

role of diffusion in primary migration of hydrocarbons the following effective diffusion coefficients d cm2 sec were determined for the diffusion of light hydrocarbons through the water saturated pore space of shales methane 2 12 10 6 ethane 1 11 10 6 propane 5 55 10 7 iso butane 3 75 10 7 n butane 3 01 10 7 n pentane 1 57 10 7 n hexane 8 20 10 8 n heptane 4 31 10 8 and n decane 6 08 10 9 on the basis of these new data a deterministic dynamic model was set up to simulate the diffusive transport of light hydrocarbons c1 to c10 from source rocks for eight documented source rock units representing a wid range of geologic conditions maturities of 0 40 to 1 35 mean vitrinite reflectance oil to gas prone kerogens the cumulative amounts of hydrocarbons escaping with time were calculated thus it was shown that diffusion represents an effective process for primary migration of gas but not for oil the rate of mass transport for gas from source rocks with geologic time can be sufficiently high to account for the origin of commercial size gas fields for example a cumulative amount of 109 kg of methane 1 5 109 std m3 or 5 3 1010 scf has escaped by diffusion in 540 000 years from a certain volume 1 000 km2 by 200 m thick of a high mature gas prone mesozoic source rock in western canada the origin of hydrocarbon accumulations with high gas to oil ratios in low mature sediments in geologically young basins early gases and condensates can be explained by an early phase of primary migration predominantly based on diffusion during the initial stages of the accumulation history of those fields extending up to millions of years under certain conditions the reservoir gas changes with geologic time from a methane rich to a wet gas composition at low maturity levels below about 0 6 rm even oil prone source rocks yield methane rich light hydrocarbon mixtures by migration through diffusion compositional trends among reservoir gases of several multiple pay gas fields in louisiana represent evidence for diffusive transport of hydrocarbons the variation in gas composition between the individual pay zones is controlled by increasing distances of diffusive transport of the hydrocarbons from a uniform source rock at depth to their present accumulation sites in the shallow pay zones compounds of high diffusivity are enriched for example in the sligo gas field of louisiana the methane ethane and the iso butane n butane ratios increase from 10 2 to 36 0 and from 0 86 to 1 13 respectively from the deepest to the shallowest of the five productive reservoir sands which are spread over a a depth interval of 5 500 ft 1 676 m diffusion of light hydrocarbons in the subsurface can also have economically adverse effects for example existing gas accumulations can be destroyed by dissipation the rate of this destruction was calculated for the harlingen gas field holland by diffusive loss through 400 m of shale cap rock the initial amount of methane in place of 1 93 109 std m3 6 8 1010 scf is reduced by one half over a period of 4 5 million years this leads us to propose the concept that large gas accumulations can persist through extended periods of geologic time only as dynamic systems reaching some kind of steady state equilibrium between diffusive loss through the cap rock and continuous replenishment from the source rock

isotopic variations of the fixed nitrogen in metamorphic rocks the content and isotopic composition of fixed nitrogen nh 4 n in metasedimentary rocks phyllites mica schists and gneisses from prograde metamorphic zones in the erzgebirge saxon ore mountains g d r were measured and show that the nitrogen content decreases and 15n increases with increasing metamorphic grade the geochemical and isotopic behaviour of nitrogen during contact metamorphism was investigated in a mica schist profile through the contact aureole of a granitic pluton the nitrogen concentrations of the wall rocks decrease towards the contact whereas the 15n values become higher various model experiments were carried out in the laboratory to explain the changes observed in the rock samples the nitrogen isotope fractionation factor was determined for the isotopic exchange in the system ammonium sulphate ammonia at 250 c 1 0143 0 0012 and 350 c 1 0128 0 0006 in accordance with the model experiments the conclusion seems warranted that the change in nitrogen content and its isotopic composition in rocks during metamorphic processes depend mainly on the metamorphic temperature

carbon helium neon and argon isotopes in a po basin northern italy natural gas field the abundance and isotopic composition of he ne and ar have been determined in 19 gas samples taken from the dosso degli angeli hydrocarbon gas field between 3000 and 3750 m depth in the po basin carbon isotope ratios in these samples vary between 13c ch4 67 5 and 73 4 indicating a predominantly biogenic source for the methane c2 c2h6 c3h8 concentrations increase systematically from 0 04 to 0 17 by volume with depth suggesting that there is a small additional thermogenic or diagenetic hydrocarbon contribution to these gases ch4 36ar ratios in the dosso degli angeli gases are in the range predicted for a groundwater which has derived its rare gas by equilibration with the atmosphere and is ch4 saturated under reservoir conditions there is also up to 10 excess of ch4 which is not associated with the groundwater these results are consistent with 90 of the ch4 in the dosso degli angeli reservoir originating from ch4 saturated groundwater measured 20ne 36ar ratios depart from the predicted ratio in air equilibrated groundwater this fractionation is consistent with water gas phase equilibration under reservoir conditions and is similar to that observed in gas reservoirs in the vienna and pannonian basins austria and hungary respectively the he in the dosso degli angeli gases is almost entirely radiogenic and derived from the crust the concentration of 4he in the reservoir gases requires that he is mostly sourced from outside the reservoir volume radiogenic 4he 40ar ratios input into the reservoir gas must be much higher than averaged crustal production ratios as no shift from the atmospheric 40ar 36ar ratio is observed preferential release of 4he over 40ar from the sites of their production is the preferred explanation this observation contrasts with previous studies from active extensional basins in which radiogenic 4he and 40ar appear to have been stored released and transported at near production ratio on a regional scale the most obvious difference between these studies is the comparatively low thermal gradient of the po basin

observed equatorial rossby waves and enso related warm water volume changes in the equatorial pacific ocean 1 modifications of the volume of warm water above the thermocline in the equatorial pacific are thought to be critical for enso el nino southern oscillation preconditioning development and prediction in this paper changes in this warm water volume wwv are first reviewed from the literature and then analyzed within 5 n 5 s in using 1992 2006 altimeter derived sea level anomalies sla and in situ observations we conclude that the 1992 2006 wwv changes in the equatorial band are a residual from the opposite effects of zonally integrated meridional ekman and geostrophic transports of warm water the latter being estimated from sla and validated against in situ observations for the first time with observations we evidence first baroclinic first meridional mode equatorial rossby waves to be responsible for the anomalous meridional geostrophic transports of warm water in changing the basin scale zonal pressure gradient these transports appear in phase opposition and proportional to the anomalous sea surface temperature sst in the region nino3 4 170 w 120 w 5 n 5 s the links between our observational results and the recharge discharge oscillator theory the differences in wwv between enso events and the hint for possible recent changes in the relation between wwv and nino3 4 sst are discussed

air xe enrichments in elk hills oil field gases role of water in migration and storage hydrocarbons from the elk hills naval petroleum reserve npr 1 bakersfield ca are enriched in heavy noble gases the 132xe 36ar ratios are as high as 576 times the ratio in air and represent the largest relative xe enrichments ever observed in terrestrial fluids the xe isotopic composition is indistinguishable from air we show that these samples cannot be explained by equilibration of oil with air saturated water and secondary enrichment via a rayleigh distillation gas stripping process based on laboratory studies of others with potential petroleum source rocks we believe the source of this enriched heavy noble gas component was adsorbed air initially trapped in on the source rocks that was expelled and mixed with the hydrocarbons during expulsion and primary migration kr and xe enrichments decrease with increasing 36ar concentration we propose a model in which an initial kr xe enriched hydrocarbon becomes diluted with noble gases extracted from air saturated groundwater during expulsion migration and storage the model generates an integrated water hydrocarbon ratio for the production fluid which indicates a minimal role for water in hydrocarbon expulsion and migration the results are interpreted to provide time geometrical constraints on the mechanisms by which hydrocarbons can migrate as a separate phase

formation of epithermal sn ag zn vein type mineralization at the pirquitas deposit nw argentina fluid inclusion and noble gas isotopic constraints abstract the pirquitas sn ag zn deposit in northwestern argentina is thought to be an analogue to the miocene polymetallic epithermal sn ag deposits of the southern bolivian tin belt but little is known in detail about the origin and evolution of ore forming fluids at pirquitas this paper reports on a microthermometric study of fluid inclusions in quartz sphalerite ag sn sulfides and ag rich sulfosalts using transmitted near infrared and visible light combined with noble gas isotope analyses of fluids released from mineral separates the study focused on the vein hosted mineralization which formed during two major mineralization events whereby the first event i comprises two stages i 1 and i 2 all studied minerals exclusively contain aqueous two phase inclusions indicating that the ore forming fluids did not undergo two phase phase separation boiling salinity of fluid inclusions in i 1 quartz that precipitated along with pyrite and pyrrhotite ranges between 0 and 7 5 wt nacl equiv and homogenization temperatures th are between 233 and 370 c stage i 2 is characterized by abundant sn ag pb zn sulfides and a variety of ag rich sulfosalts fluid inclusions in stage i 2 ag sn sulfides have salinities up to 10 6 wt nacl equiv and th between 213 and 274 c the deposition of stage i 2 ore is likely related to a new pulse of saline magmatic fluids to the hydrothermal system the mineralization event ii deposited the richest ag ores at pirquitas colloform sphalerite and pyrargyrite deposited during event ii contain two phase aqueous fluid inclusions with homogenization temperatures between 190 and 252 c and salinities between 0 9 and 4 3 wt nacl equiv noble gas concentrations and isotopic compositions of ore hosted fluid inclusions were determined from crushing hand picked ore minerals from both mineralization events with one exception all samples yielded 3he 4he ratios between 1 9 and 4 1 ra which is within the range of published data from the volcanic arc and somewhat higher than typical values of meteoric water derived hot springs in the region this demonstrates a significant contribution of magmatic fluids to the pirquitas mineralization although no intrusive rocks are exposed in the mine region taking the noble gas evidence for a magmatic fluid source we interpret the trends of decreasing th and salinity values in fluid inclusions from events i and ii to represent waning of the magmatic hydrothermal system and or increased admixing of meteoric water to the magmatic fluids

calcite cemented concretions in cretaceous sandstone wyoming and utah u s a abstract spheroidal cannon ball calcite cemented concretions some of gigantic size were studied from three cretaceous shelf sandstone units ferron frontier and second frontier the concretions have diameters between 2 cm and 6 m those larger than 40 cm in diameter in the ferron and frontier have septarian structure rare concretions in the second frontier with cone in cone also have septaria the pattern of carbon and oxygen isotopic data and intergranular volume igv data across concretions indicate that concretion growth was complex not all concretions grew progressively from their centers toward their edges in many concretions displacive fascicular optic high mg calcite foc precipitated simultaneously throughout the concretions pervasive growth pattern although the earliest cementation was concentrated in and near their centers remaining pores were subsequently filled by poikilotopic calcite of lower mg content displacive foc cement in the bodies of concretions and in cone in cone structure and the large igv values indicate that these carbonate phases formed at burial depths no greater than tens of meters igv values indicate that spar cement continued to depths of at least 50 m and possibly deeper the association of organic matter and microbial structures or microbial byproducts with displacive foc and cone in cone calcite raises the possibility that biogenic processes were responsible for the apparently rapid growth of the displacive calcite the oxygen isotope composition of pore waters was fairly uniform in the range of 18o of 4 to 6 smow during 80 of concretion growth but became even more depleted in 18o during the last stage of growth and during septarian fracture filling ranging into values as depleted as 14 smow 13c in calcite is negative 4 to 18 v pdb but variable reflecting a range of microbial processes under both oxidizing and reducing conditions earlier calcites fall mostly in the range of 10 to 16 v pdb relatively later calcite in veins and on concretion margins is more enriched in 13c fe and mn concentrations in calcites have a rough positive correlation with higher 13c values the concentration of mg derived from seawater and altered volcanic rock fragments covaries positively with the degree of meteoric influence lower mg contents correlate positively with relatively depleted 18o values 87sr 86sr values are typical of sr derived from coeval seawater or marine skeletal debris growth of concretions 4 to 6 m in diameter apparently in 5 my requires some spatial localization of growth sites by a self organization process and probably a large supply of carbonate shells in the original sediment elongation of larger concretions in the plane of bedding suggests that advective rather than diffusive supply of cement components dominated late in concretion growth history concretions formed close to the tops of parasequence boundaries

the relationship between he and cl as a criterion for the formation of groundwater composition abstract the analysis of the relationship between 1611 parallel determinations of helium and chloride concentrations in the groundwater of crystalline shields and sedimentary basins was performed the comparison showed that groundwaters have helium and chlorides concentrations in the range of 1 8 10 8 to 6 8 mol m3 and of 5 6 10 3 to 6488 mol m3 respectively and relatively stable he rcl ratios equal to 5 5 10 5 in sedimentary basins and 7 5 10 4 in crystalline shields such behavior of helium and chlorides shows that the formation of the groundwater composition is determined primarily by the processes of mixing fresh meteoric and saline sea waters with ancient brines from great depths during sedimentation sea water penetrates the subsurface and mixes with ancient brines on land fresh meteoric waters dilute the mixtures of seawater and ancient brines most of the radiogenic 4he and chlorides comes from the subsurface ancient brine the radiogenic 4he in the host rocks plays a secondary role therefore the concentration of 4he in saline groundwater reflects the size of the impurities of the ancient brine with a very high content of 4he rather than the residence time within the subsurface

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

noble gas tracing of groundwater coalbed methane interaction in the san juan basin usa the san juan basin natural gas field located in northwestern new mexico and southwestern colorado in the usa is a case type coalbed methane system groundwater is thought to play a key role in both biogenic methane generation and the co2 sequestration potential of coalbed systems we show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas we collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control stable isotope and major species determination clearly characterize the gas in the high production region as dominantly biogenic in origin and the underpressured low producing region as having a significant admix of thermogenic coal gas 3he 4he ratios increase from 0 0836ra at the basin margin to 0 318ra towards the center indicating a clear but small mantle he signature in all gases coherent fractionation of water derived 20ne 36ar and crustal 4he 40ar are explained by a simple rayleigh fractionation model of open system groundwater degassing low 20ne concentrations compared to the model predicted values are accounted for by dilution of the groundwater associated gas by desorbed coalbed methane this rayleigh fractionation and dilution model together with the gas production history allows us to quantify the amount of water involved in gas production at each well the quantified water volumes in both underpressured and overpressured zones range from 1 7 103 m3 to 4 2 105 m3 with no clear distinction between over and underpressured production zones these results conclusively show that the volume of groundwater seen by coal does not play a role in determining the volume of methane produced by secondary biodegradation of these coalbeds there is no requirement of continuous groundwater flow for renewing the microbes or nutrient components we furthermore observe strong mass related isotopic fractionation of 20ne 22ne and 38ar 36ar isotopic ratios this can be explained by a noble gas concentration gradient in the groundwater during gas production which causes diffusive partial re equilibration of the noble gas isotopes it is important for the study of other systems in which extensive groundwater degassing may have occurred to recognize that severe isotopic fractionation of air derived noble gases can occur when such concentration gradients are established during gas production excess air derived xe and kr in our samples are shown to be related to the diluting coalbed methane and can only be accounted for if xe and kr are preferentially and volumetrically trapped within the coal matrix and released during biodegradation to form ch4

geochemical characteristics and origins of noble gases of the kela 2 gas field in the tarim basin china abstract research on noble gases is important which can provide more information on gas origins and sources due to their special chemical inertness and genesis related to nuclear processes however few studies have been carried out on noble gases in the largest un compartmentalized gas field in the tarim basin in this study molecular and isotopic compositions of noble gases and hydrocarbon gases in the kela 2 gas field were analyzed hydrocarbon gases are the dominant gases accompanied by minor n 2 co 2 and extremely low contents of noble gases in the kela 2 gas field he content is generally 1 order of magnitude higher comparing to that of air while ne ar kr and xe contents are 1 3 orders of magnitude lower than corresponding atmospheric values the 13 c 2 value indicates natural gases in the kela 2 gas field are typical coal derived gases noble gases in the kela 2 gas field are typical crustal derived source mainly originating from decay of crustal radioactive elements natural gases in the kela 2 gas field are speculated to be derived from the coal measures source rocks of triassic to jurassic with major contribution from coals and secondary contribution from mudstones

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

evidence for a nitrogen flux directly derived from the european subcontinental mantle in the western eger rift central europe in the czech german border region of the vogtland and nw bohemia western eger rift central europe chemical and isotopic compositions c n he ar of free gas from a thermal water escape fluorite mine schonbrunn two mineral springs eisenquelle bad brambach sprudel iii bad elster and a mofette bublak located along an 40 km long traverse are reported the gases of bublak and bad brambach are co2 rich 99 vol and have 13c values of 1 95 and 4 29 respectively with distance from the center of co2 degassing bublak the 13c values decrease most likely due to physico chemical fractionation of co2 between gaseous and aqueous phases rather than to admixture of organic biogenic co2 the 15n values range between 3 2 and 0 6 compared to an upper mantle value of 4 0 1 0 the four locations are characterized by 3he 4he ratios decreasing from 5 9 ra in the center bublak to 0 8 ra in the periphery schonbrunn and give evidence for mixing of he from a deep seated magmatic source with a crustal source the location with the highest 3he 4he ratio 5 9 ra is accompanied by the highest 40ar 36ar 550 we argue that the nitrogen of the bublak mofette gas is a mixture of predominantly atmospheric and mantle derived components whereas at the other three locations crustal nitrogen may also be present the bublak 15n value of 4 5 1 0 represents the first free gas 15n reference from the european subcontinental mantle escm and indicates that in contrast to the 3he 4he ratios the 15n values are equal for escm and morb respectively

basin wide zonal wind stress and ocean thermal variations in the equatorial pacific ocean wind data obtained from the model results of the european centre for medium range weather forecasts ecmwf for the equatorial pacific ocean from 1985 to 1992 were employed to study the basin wide distributions for various constituents of zonal wind stress forcing the ocean by the individual constituent of zonal wind stress the upper ocean thermal variation was investigated using a linear analytical ocean model the interannual variation of zonal wind stress is largest in amplitude in the west central part of the basin and is dominated by an eastwardly propagating wave the upper layer thickness perturbation h shows an evolving eastward propagation over the region where the interannual wind stress variation occurs while to the east and west the region changes nearly in phase the evolution of h agrees well with the evolution of upper ocean heat content anomaly estimated from the tropical atmosphere ocean tao moored array the annual cycle of zonal wind stress can be described properly by a combination of annual and semiannual variations the annual variation of zonal wind stress was found to propagate westward with relative maxima out of phase to the west and east of the west central pacific the semiannual variation is stationary and is largest in amplitude in the western basin forced by the two components of the annual cycle of zonal wind stress the evolution of h shows a westward propagation this does not correlate well with the pattern of the evolution of the annual cycle of upper ocean heat content which emanates from the east central pacific and shows both eastward and westward propagation the seemingly anomalous eastward propagation is mainly related to the abrupt change during the relaxation intensification period of the easterly wind stress the abrupt change of the annual zonal wind stress variation in both time and space is then critical for the evolution of the pattern of the annual ocean response

structure and evolution of interannual variability of the tropical pacific upper ocean temperature n n yearly in situ temperature anomaly data for the period 1961 1990 are analyzed to reveal the dominant structure and evolution of interannual variability of the tropical pacific upper ocean we use multivariate empirical orthogonal function eof analyses to detect the principal three dimensional structure related to el nino there are well defined subsurface thermal patterns characterized by a prominent sea saw structure with opposite anomaly polarity in the equatorial and off equatorial tropical north pacific regions during an el nino year a positive temperature anomaly is found in the e astern and central tropical upper ocean this is accompanied by a corresponding negative anomaly at subsurface depths in the west with a maximum at 100 150 m off the equator unlike sea surface temperature whose variations are confined largely to the east with one dominant polarity temperature variations at 50 200 m depths have a dipole pattern with out of phase oscillations in the central equatorial pacific and in the western tropical north pacific a reverse pattern of these anomalies is observed during a la nina year evolution between el nino and la nina involves a significant zonal transfer of anomaly phase across the equatorial basin as well as across the off equatorial tropical north pacific showing consistent and coherent variations from west to east from subsurface to sea surface and from on the equator to off the equator this phase propagation is more evident at subsurface depths than that at the sea surface suggesting a continual movement of anomaly pattern in succession eastward along the equator and westward off the equator of the tropical north pacific with spatial inhomogeneities of zonal propagation in longitude our analyses present evidence of the manner in which temperature anomalies evolve at subsurface ocean depths in the tropical pacific thus providing an observational basis for evaluating theoretical studies and model simulations the dynamical implication of these results is also discussed

determination of gross kinetic parameters for petroleum formation from jurassic source rocks of different maturity levels by means of laboratory experiments abstract solvent extracted core samples of lower toarcian carbonate rich shales posidonia shale lias of the hils syncline area lower saxony basin northern germany covering a wide maturity range vitrinite reflectance rr 0 48 0 88 and 1 45 and a kimmeridge mudstone rr 0 45 are pyrolyzed at three different heating rates 0 1 0 7 and 5 0 k min by application of non isothermal first order reaction kinetics to the resulting hydrocarbon evolution curves activation energy distributions between 46 and 70 kcal mol and pre exponential arrhenius factors are obtained by an iteration method hypothetical hydrocarbon generation curves are calculated for the lias assuming three geological heating rates 0 5 5 and 50 k 106a peak hydrocarbon generation temperatures range from 135 to 165 c

noble gas fractionation during subsurface gas migration abstract environmental monitoring of shale gas production and geological carbon dioxide co2 storage requires identification of subsurface gas sources noble gases provide a powerful tool to distinguish different sources if the modifications of the gas composition during transport can be accounted for despite the recognition of compositional changes due to gas migration in the subsurface the interpretation of geochemical data relies largely on zero dimensional mixing and fractionation models here we present two phase flow column experiments that demonstrate these changes water containing a dissolved noble gas is displaced by gas comprised of co2 and argon we observe a characteristic pattern of initial co enrichment of noble gases from both phases in banks at the gas front followed by a depletion of the dissolved noble gas the enrichment of the co injected noble gas is due to the dissolution of the more soluble major gas component while the enrichment of the dissolved noble gas is due to stripping from the groundwater these processes amount to chromatographic separations that occur during two phase flow and can be predicted by the theory of gas injection this theory provides a mechanistic basis for noble gas fractionation during gas migration and improves our ability to identify subsurface gas sources after post genetic modification finally we show that compositional changes due to two phase flow can qualitatively explain the spatial compositional trends observed within the bravo dome natural co2 reservoir and some regional compositional trends observed in drinking water wells overlying the marcellus and barnett shale regions in both cases only the migration of a gas with constant source composition is required rather than multi stage mixing and fractionation models previously proposed

enso simulated by intermediate coupled models and evaluated with observations over 1970 98 part i role of the off equatorial variability enso simulations are investigated in 30 yr integrations of various intermediate coupled models and compared with observed sst wind and thermocline depth anomalies over the tropical pacific the cane and zebiak model simulates warm events with a period close to the observations but with westerlies that are located 30 8 east of them and thermocline anomalies in the western pacific that are much shallower between two warm events the model simulates a series of three weak and short cold sst peaks and hardly ever simulates easterlies the sst in the eastern equatorial pacific is not sensitive to thermocline depth anomalies but to the anomalous downwelling of surface currents induced by ekman shear the model simulates a pair of very strong cyclonic wind stress curl anomalies on both sides of the equator in the eastern off equatorial domain between 78 and 158 lat these are necessary to maintain the oscillatory regime so are the ocean meridional rossby modes higher than 5 the thermocline zonal slopes required to balance the off equatorial curl anomalies are about three times steeper than the ones required to balance the zonal stress along the equator thus the off equator exerts an excess of zonal pressure which by continuity affects the equatorial ocean and plays a crucial role in reversing and triggering the growing events six months after the warm peaks the whole ocean between 158s and 158n is significantly upwelled the equatorial oceanic heat content is recharged from the south prior to a warm event contrary to simulations when the model is driven by observed wind anomalies increasing the friction in the baroclinic ocean does not decrease the off equatorial variability but significantly alters the low frequency oscillations that are no longer enso like introducing the parameterization of subsurface temperature derived from hydrographic profiles in the ocean component does not allow the coupled model to recover cold events as in a forced context introducing the parameterization of convection derived from high cloud temperature measurements is the most effective improvement but results still poorly agree with observations and are in contrast with the simulations driven by observed sst biased toward westerlies in the central pacific upwelled thermocline in the west and warm sst in the east thus modifying the ocean component only or the atmosphere only does not have the same impact on simulations as in a forced context the coupling allows new mechanisms to grow and govern the model behavior one of them is the slow meridional oceanic mass adjusment in quasi sverdrup balance with the winds

thermal constraints on crustal rare gas release and migration evidence from alpine fluid inclusions the palfris marl of the helvetic alpine nappes contains four distinct vein fill generations ch4 rich gas is found in abundant fluid inclusions within these carbonate veins while free ch4 gas has also been produced from exploratory boreholes through this formation the stable isotope and helium neon and argon isotopic composition of these fluids has been determined a constant radiogenic 40ar concentration of 1 25 0 13 1 ppm in these differently sited fluids requires an intimate association between the 40arrad source and the hydrocarbon phase this can only be reasonably explained if the 40arrad was input into the hydrocarbon phase during hydrocarbon generation migration or storage prior to entrapment in the fluid inclusions stable isotope results constrain the maturity of hydrocarbon production while fluid inclusion formation pressures and temperatures record values of up to 2 5 kbars and 250 c these values place limits on the range of thermal conditions in which the hydrocarbon 40arrad relationship was established all fluids within inclusions also contain radiogenic 4he40ar values at predicted crustal production ratios these observations provide the first evidence that both 4herad and 40arrad can be quantitatively released on a regional scale bounded by the thermal conditions required to produce the hydrocarbon phase and the conditions under which the fluid inclusions were formed t 190 250 c these results require that negligible quantities of excess 40arrad decoupled from 4herad have been released into this system given the wide array of mechanisms which can potentially cause decoupling of these two species this result provides an important constraint on the role of these processes within the sedimentary fluid regime in contrast the free borehole gas contains excess radiogenic 4he and 21ne relative to 40arrad in proportions which can be accounted for by local production and subsequent diffusion from the surrounding marl the latter pattern is consistent with rare gas migration in lower temperature environments a conceptual model which considers both diffusional and metamorphic release of helium and argon and the ability of the surrounding fluid regime to transport the rare gases from their respective mineral production sites is consistent with both these results and data from regional rare gas studies

origin of nitrogen rich natural gases in the california great valley evidence from helium carbon and nitrogen isotope ratios abstract dry natural gases produced from the sacramento and northern san joaquin basins contain up to 87 nitrogen 15n measurements for gases with n2 8 vary from 0 9 to 3 5 methane 13c values vary from 61 to 15 3 he 4 he ratios indicate the presence of mantle derived helium in addition to radiogenic crustal helium and suggest that the gases may originate from mixing between three principal components a hydrocarbon rich gas with 3 he 4 he 0 1r a derived from the microbial and thermogenic alteration of sedimentary organic matter a hydrocarbonrich gas with 3 he 4 he 2 75r a derived from the localized pyrolysis of sediments by magmatic volatiles and a nitrogenrich gas with 3 he 4 he 1r a the nitrogen rich component is characterized by methane 13c less negative than 25 and n 2 ar ratios as high as 22 000 nitrogen concentrations tend to increase towards the basement along the shallow eastern margin of the valley suggesting that the nitrogen rich component is derived from metasedimentary rocks deep within the crust the coast ranges fraciscan complex which was thrust well beneath the great valley during late mesozoic and early cenozoic subduction appears to be the most likely source

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

generation of nitrogen and methane from sedimentary organic matter implications on the dynamics of natural gas accumulations nitrogen n2 contents of natural gases in rotliegend and buntsandstein reservoirs of the north german basin regionally approach 100 a review is given of the various hypotheses primordial origin volcanic or magmatic origin radiogenic origin atmospheric origin organic origin inorganic nitrogen in sedimentary rocks presented to account for nitrogen anomalies in this area and other parts of the world the objective of the present study was to investigate sedimentary organic matter in particular coals as a potential source of molecular nitrogen in the subsurface comparison of reservoir sizes and gas generation potentials indicates that carboniferous coal measures which are considered as the source of the natural gas in the north german basin can readily account for the nitrogen quantities found in present day reservoirs laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a fractional generation of methane and nitrogen in natural systems based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates gas containing more than 50 nitrogen is generated under these conditions at temperatures in excess of 300 c nitrogen rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased it is concluded that the amounts of gas encountered in nitrogen rich gas accumulations represent only a small fraction possibly 1 of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere the present day composition of the reservoir gases reflects the composition of only the most recently generated gas on a geologic time scale

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

the noble gas geochemistry of natural co2 gas reservoirs from the colorado plateau and rocky mountain provinces usa identification of the source of co2 in natural reservoirs and development of physical models to account for the migration and interaction of this co2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of co2 in the subsurface we present the results of 57 noble gas determinations in co2 rich fields 82 from three natural reservoirs to the east of the colorado plateau uplift province usa bravo dome nm sheep mountain co and mccallum dome co and from two reservoirs from within the uplift area st john s dome az and mcelmo dome co we demonstrate that all fields have co2 3he ratios consistent with a dominantly magmatic source the most recent volcanics in the province date from 8 to 10 ka and are associated with the bravo dome field the oldest magmatic activity dates from 42 to 70 ma and is associated with the mcelmo dome field located in the tectonically stable centre of the colorado plateau co2 can be stored within the subsurface on a millennia timescale the manner and extent of contact of the co2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic co2 we show that coherent fractionation of groundwater 20ne 36ar with crustal radiogenic noble gases 4he 21ne 40ar is explained by a two stage re dissolution model stage 1 magmatic co2 injection into the groundwater system strips dissolved air derived noble gases asw and accumulated crustal radiogenic noble gas by co2 water phase partitioning the co2 containing the groundwater stripped gases provides the first reservoir fluid charge subsequent charges of co2 provide no more asw or crustal noble gases and serve only to dilute the original asw and crustal noble gas rich co2 reservoir scale preservation of concentration gradients in asw derived noble gases thus provide co2 filling direction this is seen in the bravo dome and st john s dome fields stage 2 the noble gases re dissolve into any available gas stripped groundwater this is modeled as a rayleigh distillation process and enables us to quantify for each sample 1 the volume of groundwater originally stripped on reservoir filling and 2 the volume of groundwater involved in subsequent interaction the original water volume that is gas stripped varies from as low as 0 0005 cm3 groundwater cm3 gas stp in one bravo dome sample to 2 56 cm3 groundwater cm3 gas stp in a st john s dome sample subsequent gas groundwater equilibration varies within all fields each showing a similar range from zero to 100 cm3 water cm3 gas at reservoir pressure and temperature

origin of ore fluids in the muruntau gold system constraints from noble gas carbon isotope and halogen data abstract hydrothermal vein minerals directly associated with native gold mineralization in the muruntau vein system uzbekistan have been studied for noble gas carbon isotope and halogen chemistry of the trapped ore related fluids helium trapped in early arsenopyrite 1 which has preserved the original fluid signature better than associated scheelite and quartz indicates a small input from a mantle source 5 of total he however the overwhelming majority of the he in the fluid 95 is from crustal sources the noble gases ne kr and xe in the sample fluids are dominated by gases of atmospheric origin the carbon isotope 13 c 2 1 to 5 3 and halogen characteristics of the fluids log br cl 2 64 to 3 23 lend further support for the activity of juvenile fluids during the main ore stage the high proportion of crustal components in the ore forming fluids may be explained by intense fluid rock interaction and is also supported by previous nd and sr isotope studies the involvement of a juvenile fluid component during the main stage of hydrothermal activity at muruntau 275 ma can be linked to the emplacement of lamprophyric dikes at muruntau due to apparently overlapping ages for high temperature alteration related ore vein formation and intrusion of the dikes the input of mantle derived fluids possibly related to the hercynian collisional event in the western tien shan stimulated intense fluid rock interaction in the crust in this context the mantle derived fluid should be considered as one possible carrier of metals significant amounts of external meteoric fluids circulating in fracture systems are interpreted to have modified the noble gas signature of fluid in quartz mostly during late low temperature fluid circulation

noble gases fingerprint a metasedimentary fluid source in the macraes orogenic gold deposit new zealand the world class macraes orogenic gold deposit 10 moz resource formed during the late metamorphic uplift of a metasedimentary schist belt in southern new zealand mineralising fluids metals and metalloids were derived from within the metasedimentary host helium and argon extracted from fluid inclusions in sulphide mineral grains three crush extractions from one sample have crustal signatures with no evidence for mantle input r ra 0 03 xenon extracted from mineralised quartz samples provides evidence for extensive interaction between fluid and maturing organic material within the metasedimentary host rocks with 132xe 36ar ratios up to 200 times greater than air similarly i cl ratios for fluids extracted from mineralised quartz are similar to those of brines from marine sediments that have interacted with organic matter and are ten times higher than typical magmatic mantle fluids the macraes mineralising fluids were compositionally variable reflecting either mixing of two different crustal fluids in the metasedimentary pile or a single fluid type that has had varying degrees of interaction with the host metasediments evidence for additional input of meteoric water is equivocal but minor meteoric incursion cannot be discounted the macraes deposit formed in a metasedimentary belt without associated coeval magmatism and therefore represents a purely crustal metamorphogenic end member in a spectrum of orogenic hydrothermal processes that can include magmatic and or mantle fluid input elsewhere in the world there is no evidence for involvement of minor intercalated metabasic rocks in the macraes mineralising system hydrothermal fluids that formed other smaller orogenic deposits in the same metamorphic belt have less pronounced noble gas and halogen evidence for crustal fluid rock interaction than at macraes but these deposits also formed from broadly similar metamorphogenic processes

molecular nitrogen in natural gas accumulations generation from sedimentary organic matter at high temperatures the occurrence of natural gas accumulations with high percentages up to 100 of molecular nitrogen in various hydrocarbon provinces represents a largely unresolved problem and a serious exploration risk in this context a geochemical and basin modeling study was performed to evaluate the potential of sedimentary organic matter to generate molecular nitrogen the masses of nitrogen present in coals if converted into molecular nitrogen are sufficient to fill commercial gas reservoirs a calculation for gas accumulations in northern germany where percentages of molecular nitrogen range from less than 5 to greater than 90 reveals that the molecular nitrogen generated in underlying coal bearing strata is sufficient to account for the nitrogen gas even in the largest fi lds in addition much of the total nitrogen in clay rich rock types such as shales and mudstones is fixed in sedimentary organic matter and may add to the nitrogen generation capacity of the coals a kinetic interpretation of the nitrogen and methane generation characteristics of humic coals during laboratory pyrolysis indicates that nitrogen is generated from organic matter in sedimentary basins at higher temperatures than methane minimum temperatures for preferential nitrogen generation are in excess of 300 c for extremely low heating rates or isothermal conditions lasting over 300 m y thus nitrogen rich gases are mainly formed in the final stage of gas generation when sedimentary rocks grade into metamorphic rocks applications of the kinetic parameters for the generation of nitrogen and methane from coaly organic matter in carboniferous sedimentary rocks are presented for part of the northwest german basin in this area immense volumes of the methane rich gas gener ted during the late paleozoic and mesozoic were lost to the atmosphere the present gas composition mainly reflects the latest cenozoic gas generation this cenozoic gas is nitrogen rich where the carboniferous source rock sequences are highly mature and deeply buried