inversion of seismic surface wave data to resolve complex profiles for a complex layered site development of a shear wave velocity profile from inversion of seismic surface wave data can yield nonunique results one class of solutions provides depth averaged profiles that are useful but do not detail the local velocity anomalies simulated annealing inversion can be used to establish whether nonuniqueness is a concern for a particular case and if so focus results to allow a solution that is expected based on independent knowledge of site conditions a two step process is recommended whereby the model parameters are first optimized using simulated annealing and then fine tuned by unconstrained linearized inversion the process also yields useful confidence measures one example of a complex layered site where the proposed procedure is helpful is a desert profile with high velocity cemented layers interspersed among uncemented sediments

deep air convection in the firn at a zero accumulation site central antarctica abstract ice cores provide unique archives of past atmospheres and climate but interpretation of trapped gas records and their climatic significance has been hampered by a poor knowledge of the prevalence of air convection in the firn layer on top of polar ice sheets in particular the phasing of greenhouse gases and climate from ice cores has been obscured by a discrepancy between empirical and model based estimates of the age difference between trapped gases and enclosing ice which may be due to air convection here we show that deep air convection 23 m occurs at a windy near zero accumulation rate site in central antarctica known informally as the megadunes site 80 77914 s 124 48796 e deep convection is evident in depth profiles of air withdrawn from the firn layer in the observed pattern of the nitrogen isotope ratio 15 n 14 n the argon isotope ratio 40 ar 36 ar and in the mixing ratios of the anthropogenic halocarbons methyl chloroform ch 3 ccl 3 and hfc 134a ch 2 fcf 3 transport parameters diffusivities were inferred and air was dated using measured carbon dioxide co 2 and methane ch 4 mixing ratios by comparing with the law dome atmospheric record which shows that these are the oldest firn air samples ever recovered co 2 mean age 1863 ad the low accumulation rate and the consequent intense metamorphism of the firn due to prolonged exposure to seasonal temperature cycling likely contribute to deep air convection via large grain size and vertical cracks that act as conduits for vigorous air motion the megadunes site provides a possible modern analog for the glacial conditions in the vostok dome fuji and dome c ice core records and a possible explanation for lower than expected 15 n 14 n ratios in trapped air bubbles at these times a general conclusion is that very low accumulation rate causes deep air convection via its effect on firn structural characteristics

diagenetic history of tight sandstones and gas entrapment in the yulin gas field in the central area of the ordos basin china abstract the ordos basin is a large cratonic basin with an area of 250 000 km2 in central china upper paleozoic coals and shales serve as gas source rocks with peak generation and migration at the end of the early cretaceous recent exploration has verified the huge gas potential in the basin centered gas accumulation system bcgas however the mechanism for the gas accumulation is controversial with an integrated approach of thin section petrography ultra violet fluorescence microscopy fluid inclusion microthermometry raman microspectrometry scanning electron microscopy and x ray diffractometry we identified diagenetic trapping and evaluated the diagenetic history of sandstone reservoirs in the yulin gas field in the central area where structural stratigraphic and or sedimentary lithologic traps have not been found it was revealed that three phases of diagenesis and hydrocarbon charging occurred respectively in the late triassic late jurassic and at the end of the early cretaceous in the first two phases acidic water entered the reservoir and caused dissolution and cementation resulting in porosity increase however further subsidence and diagenesis including compaction and cementation markedly reduced the pore space at the end of the early cretaceous the bulk of the gas migrated into the tight reservoirs and the bcgas trap was formed in the updip portion of this system cementation continued to occur due to low gas saturation and has provided effective seals to retain gas for a longer period of time than water block in the bcgas the mechanism for the gas entrapment was changed from water block by capillary pressure in the bcgas to diagenetic sealing the diagenetic seals in the updip portion of the sand body were formed after gas charging which indicates that there is a large hydrocarbon exploration potential at the basin centered area

sedimentary association of alternated mudstones and tight sandstones in china s oil and gas bearing basins and its natural gas accumulation abstract oil and gas resources are abundant in china s continental sedimentary basins where the main task of exploration has been finding oil for many years in recent years however new discoveries of large scale natural gas have been successively obtained the natural gas mainly exists in the sedimentary association of alternated mudstones and tight sandstones and is dominantly low permeability tight sand gas through the in depth study on gas reservoir analysis diagenetic evolution source rock distribution and hydrocarbon generating behavior natural gas generation and accumulation it is concluded that during the major subsiding stage of large scale lake basins the multicyclic subsiding process of the lake surface controls the development of high quality source rocks the wide distribution of sands and the superimposition of the two types of rocks in the vertical direction the lacustrine muddy source rocks are developed including mud shale carbonaceous mudstone and coal bed which are in the medium high evolution stage and produce mainly gas and the gas generation intensity is high through the analysis of the subsidence evolution processes of the carboniferous permian systems transitional marine continental facies in the ordos basin and the triassic xujiahe formation continental facies in the sichuan basin it is concluded that the widely distributed sandbodies of delta facies although with tight properties are interbedded with source rocks and easy to accumulate natural gases the natural gas is migrated and accumulated within small distance and is characterized by large area accumulation because of the strong hydrocarbon generation capacity big thickness and stable distribution of the underlying mud shale the potential of gas resources should not be underestimated the geocyclicity of china s continental sedimentary basins controls the sedimentary association of alternated mudstones and tight sandstones resulting in superimposed accumulations of shale gas and tight sand gas

gas age ice age differences and the chronology of the vostok ice core 0 100 ka 1 gas is trapped in polar ice at depths of 50 120 m and is therefore significantly younger than the ice in which it is embedded the age difference is not well constrained for slowly accumulating ice on the east antarctic plateau introducing a significant uncertainty into chronologies of the oldest deep ice cores vostok dome fuji and dome c we recorrelate the gas records of vostok and greenland ice sheet project 2 gisp2 cores in part on the basis of new ch4 data and use these records to construct six vostok chronologies that use different assumptions to calculate gas age ice age differences we then evaluate these chronologies by comparing times of climate events at vostok with correlative events in the well dated byrd ice core west antarctica from this evaluation we identify two leading chronologies for the vostok core that are based on recent models of firn temperature firn densification and thinning of upstream ice one chronology involves calculating gas age ice age differences from these models the second new approach involves calculating ice depths in the core that are contemporaneous with depths in the same ice core whose gas ages are well constrained this latter approach circumvents problems associated with highly uncertain accumulation rates in the vostok core the uncertainty in vostok chronologies derived by correlating into the gisp2 gas record remains about 1 kyr and high precision correlations continue to be difficult

atmospheric methane during the last four glacial interglacial cycles rapid changes and their link with antarctic temperature 1 atmospheric methane ch4 recorded in antarctic ice cores represents the closest ice proxy available for greenland temperature changes beyond times when greenland climate records are available the record over four climatic cycles from the vostok ice core offers the opportunity to study the phase relationship between greenland and antarctic climate changes through detailed ch4 profiles combining american and french analytical efforts we have improved the time resolution of the existing ch4 record from petit et al 1999 spectral analyses reveal high and low frequency variability including a strong precessional component the phase relationship between ch4 and the antarctic temperature proxy d shows a systematic lag of ch4 versus temperature by 1100 200 years on long timescales 50 400 kyr and a more complex behavior over shorter timescales i e 25 kyr suggesting that dansgaard oeschger type of climatic variability and associated interhemispheric linkage are robust features of late quaternary climate

reconstructing atmospheric histories from measurements of air composition in firn 1 this paper investigates the use of a numerical model of firn diffusion and bubble trapping in the reconstruction of atmospheric records from firn measurements we describe the concept of mean age and effective age of tracers in firn air and how the growth rate of a tracer in the atmosphere can alter the effective age we discuss an iterative method to assign effective ages to firn measurements for tracers with fairly simple atmospheric histories taking into account atmospheric growth rate variations we then develop a bayesian synthesis inversion calculation for inverting firn concentration measurements this calculation gives estimates of the atmospheric concentration record with uncertainties the dating and inversion techniques are demonstrated here with carbon tetrachloride measurements from a long firn record from law dome antarctica the techniques are then applied to measurements of a range of halocarbons in a companion paper by sturrock et al 2002

δ15n of n2 in air trapped in polar ice a tracer of gas transport in the firn and a possible constraint on ice age gas age differences with respect to gas transport the fim near the surface of an ice sheet can be divided into three zones the uppermost is a convective zone located just below the surface of the ice sheet in which the air is rapidly flushed by convective exchange with the overlying atmosphere below the convective zone there is a diffusive air column in which diffusion is rapid but there is no convection between the bottom of the diffusive air column and the bubble close off region there may be a nondiffusive zone in which diffusion is so slow that negligible gas transport occurs the diffusive air column is characterized by progressive enrichment with depth of 15n in n2 and heavy isotopes of gases in general as predicted using the barometric equation in this paper we present data on the 15n of n2 in recently trapped air samples from 12 ice cores along with numerous downcore samples from byrd vostok and dome c bubble close off depths for these cores calculated from a densification model ranged from 51 to 114 meters below the surface mbs we used these data and the barometric equation to calculate the thickness of the diffusive air column and found that it comprised 46 to 93 of the total firn thickness at our study sites paleo close off depths calculated from the densification model for glacial sections of byrd vostok and dome c are 15 25 m deeper than close off depths today diffusive column heights calculated from 15n varied in a more complex manner the diffusive column height at byrd appears to have decreased from 74 m during the last glacial period to 50 m during the holocene at vostok and dome c the diffusive column height calculated from 15n increase from about 65 m during the last glacial period to about 80 m in the holocene we use records of surface temperature and co2 at byrd and vostok along with their respective chronologies to constrain the ice age gas age difference age throughout the section of the vostok ice core corresponding to the last glacial termination in principle age values calculated from these data can be used to discriminate whether gas in the fim mixes to the bubble close off depth or to a depth equivalent to the diffusive column height in practice however uncertainties in the chronology of byrd and vostok are too great to allow us to distinguish between these two possibilities one can only say that at the time of the last termination age for vostok was between 3 and 10 5 kyr previous estimates fall within this range

reflection waveform inversion using local descent methods estimating attenuation and velocity over a gas sand deposit prestack seismic reflection data contain amplitudes traveltimes and moveout information waveform inversion of such data has the potential to estimate attenuation levels reflector depths and geometry and background velocities however when inverting reflection data strong nonlinearities can cause reflectors to be incorrectly imaged and can prevent background velocities from being updated to successfully recover background velocities previous authors have resorted to nonlinear global search inversion techniques we propose a two step inversion procedure using local descent methods in which we perform alternate inversions for the reflectors and the background velocities for our reflector inversion we exploit the efficiency of the back propagation method when inverting for a large parameter set for our background velocity inversion we use newton inverse methods during the background velocity inversions it is crucial to adaptively depth stretch the model to preserve the vertical traveltimes this reduces nonlinearity by largely decoupling the effects of the background velocities and reflectors on the data nonlinearity is further reduced by choosing to invert for slownesses and by inverting for a sparse parameter set which is partially defined using geological reflector picks applying our approach to shallow seismic data from the north sea collected over a gas sand deposit we demonstrate that the proposed method is able to estimate both the geometry and internal velocity of a significant velocity structure not present in the initial model over successive iterations the use of adaptive depth stretching corrects the pull down of the base of the gas sand vertical background velocity gradients are also resolved for an insignificant extra cost the acoustic attenuation parameter q is included in the inversion scheme the final attenuation tomogram contains realistic values of q for the expected lithologies and for the effect of partial fluid saturation associated with a shallow bright spot the attenuation image may also indicate the presence of fracturing

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

convective mixing of air in firn at four polar sites air withdrawn from the firn at four polar sites dome fuji h72 and ym85 antarctica and north grip greenland was measured for 15 no f n2 and 18 oo f o2 to test for the presence of convective air mixing in the top part of the firn known as the convective zone understanding the convective zone and its possible relationship to surface conditions is important for constructing accurate ice core greenhouse gas chronologies and their phasing with respect to climate change the thickness of the convective zone was inferred from a regression line with barometric slope of the data in the deep firn it is less than a few meters at h72 and ngrip whereas a substantial convective zone is found at dome fuji 8 6 2 6 m and ym85 14 0 1 8 m by matching the outputs of a diffusion model to the data effective eddy diffusivities required to mix the firn air are found at the surface of dome fuji and ym85 these are found to be several times greater than the molecular diffusivity in free air the crossover from dominance of convection to molecular diffusion takes place at 7 2 11 2 and 0 5 0 5 m at dome fuji ym85 and ngrip respectively these depths can be used as an alternative definition of the convective zone thickness the firn permeability at dome fuji is expected to be high because of intense firn metamorphism due to the low accumulation rate and large seasonal air temperature variation at the site the firn layers in the top several meters are exposed to strong temperature gradients for several decades leading to large firn grains and depth hoar that enhance permeability the thick convective zone at ym85 is unexpected because the temperature accumulation rate and near surface density are comparable to ngrip the strong katabatic wind at ym85 is probably responsible for creating the deep convection the largest convective zone found in this study is still only half of the current inconsistency implied from the deep ice core gas isotopes and firn densification models 2006 elsevier b v all rights reserved

multiscale anatomy of a reservoir geological characterization of pembina cardium pool west central alberta canada geological reservoir elements that control a reservoir s conduit system are mineralogy grain size packing pore network lithohydraulic units lithologic continuity fractures and faults and rock fluid interactions all occur at different scales we have focused on four scales typical of a developed reservoir to characterize geological reservoir heterogeneity in the pembina cardium pool 1 megascale the field wide view 2 macroscale the interwell continuity 3 mesoscale the neighborhood of the well and 4 microscale the domain of grains and pores 1 megascale observations the reservoir top is characterized by a ridge and swale topography oriented northwest southeast a similar but more subdued topography is also characteristic of the unconformity between conglomerates and sandstones conglomerates are distributed irregularly and are generally shaly in beds thinner than 1 m thick conglomerates are common on the east and south flanks of underlying ridges and impart northwest southeast fluid production trends and yield zones of reduced pressures in thick conglomerates high flow capacities are detrimental to hydrocarbon recovery as they result in bypassing of injection fluids the conglomerate is a lithohydraulic unit as it is a body of strata distinct from neighboring strata by depositional diagenetic and tectonic imprintin s and by a characteristic set of petrophysical properties 2 macroscale characteristics reservoir lithofacies and lithohydraulic units are laterally discontinuous and form irregular patterns that can possess an irregular northwest southeast orientation fluid production trends oriented northeast southwest in areas of thin shaly conglomerates appear to be the product of fractures in these areas reorientation of injector wells to line drives results in higher oil recoveries 3 mesoscale properties in cores five lithofacies characterize the field they are 1 dark gray mudstone and siltstone 2 bioturbated thin and very thin bedded shale siltstone and very fine and fine grained sandstone 3 thin and very thin bedded shale siltstone and very fine and fine grained sandstone 4 medium to thick bedded very fine and fine grained sandstone and 5 conglomerate as each lithofacies possesses contrasting but partially overlapping petrophysical properties they are lithohydraulic units lithofacies 1 acts as the reservoir seal and restricts flow within the reservoir lithofacies 2 has high porosities low permeabilities and dominates the bottom half of the reservoir lithofacies 2 has a high storage capacity phgrh but its flow capacity kh i low lithofacies 3 reduces cross flow because its vertical permeabilities are very low lithofacies 4 has modest permeabilities and high porosities and is common to the top half of the reservoir this lithofacies flow capacity in t47 r7 w5m is 17 times greater than that of lithofacies 2 lithofacies 5 has modest porosities but very high permeabilities resulting in intervals with very high flow capacities 4 microscale investigations in the sandstones the mineral framework consists predominantly of quartz and chert whereas chert prevails in the conglomerates these mineralogic differences lead to reduced cementation by silica on cherts and result in the preservation of pore spaces resembling original pores in chert rich zones although quartz grains are modified by megaquartz overgrowths chert particles are altered by pressure solution fracturing and crushing in both sandstones and conglomerates framework grains are cemented by siderite calcite kaolinite and illite experiments with reservoir cores flooded with co2 enriched brines and data from waterflooding indicate that siderite and calcite are unstable under reservoir conditions this behavior can result in perm ability losses from release of insoluble fine materials and weakened responses during polymer floods mercury capillary pressure data from 28 measurements of lithofacies 4 sandstones indicate that mercury end page 1233 recovery efficiency increases with decreasing permeability and porosity this behavior if confirmed elsewhere in the field may explain the performance of areas that have reduced permeabilities and porosities but are responding well to waterflooding

the age of the air in the firn and the ice at summit greenland in the framework of the eurocore drilling project 1989 at summit central greenland air samples were collected from a drill hole in the firn at several depth levels the samples have been analyzed for 85kr co2 ch4 cfc s f 11 and f 12 contents and for the isotopic composition of nitrogen and oxygen the measured data are compared with the results of a diffusion model co2 for example takes 12 years with a standard deviation of 7 5 years to diffuse from the surface to the firn ice transition under the present climatic conditions at summit the difference between the age of the ice and the mean age of the occluded air is approximately 210 years an enrichment of the heavier isotopes due to separation by gravity has been observed molecular diffusion alone suffices to explain the observed concentration trends in the firn column we can however not exclude the existence of a convective zone below the surface we have also measured the density and closed porosity along the firn core that has been retrieved when drilling the hole the porosity data reveal that the air is occluded into bubbles mainly between 65 and 80 m corresponding to densities of 790 and 830 kg m3 respectively

ice flow field over lake vostok east antarctica inferred by structure tracking abstract here we present a flow field for the east antarctic ice sheet over lake vostok based on tracking structures across the lake inherited from the western upstream shoreline the structures distinctive peaks and troughs identified in the ice sheet internal layers are imaged in ice penetrating radar data collected in a systematic grid over the lake these structures are resolved in three distinct internal layers at depths between 900 and 3750 m ridges in the internal layers are associated with prominent topographic highs along the western shoreline and troughs are correlated with shoreline topographic lows lake vostok is bisected by a topographic ice divide south of this topographic divide the ice flow is dominantly nnw to sse and north of the divide the ice flow is w to e the flow over the lake is also deflected by the small 0 02 southward lake surface slope accretion ice lake water frozen to the bottom of the ice sheet is preferentially imaged along flowlines emanating from topographic ridges the coincidence of the accretion ice reflector with our flowlines both provides independent support for our new flow field and suggests focused accretion along the western shoreline global positioning system gps data provide additional independent support for our new flow field in the southern lake the new flow field will be crucial for subsequent analyses of mass exchange between the ice sheet and the lake identifying areas of melting above the lake and estimating residence times

the buried shape of an alpine valley from gravity surveys seismic and ambient noise analysis summary it has long been observed that damage due to earthquakes depends greatly on local geological conditions alpine valleys represent a typical populated environment where large amplifications can take place owing to the presence of surface soils with poor mechanical properties combined to complex topography of the rock basin in the framework of the eu interreg iiib sismovalp project seismic hazard and alpine valley response analysis a stretch of the tagliamento river valley trv located in the north western part of the friuli region italy and close to the epicentre of the 1976 mw 6 4 earthquake has been investigated with the aim to define the buried shape of the valley itself two non invasive low cost independent geophysical methods were used i detailed gravity survey and ii h v spectral ratio hvsr of microtremors because of structural geological complexity and active tectonics of the friuli region an irregular valley shape was expected in this area the independent analysis performed by gravity and passive noise and complemented with refraction seismic velocity profiles confirms this hypothesis and leads to two models that were consistent but for some small scale details the maximum depth estimated is about 400 450 m in the southern part of the valley while a mean value of 150 180 m is estimated in the northern part the sediment thickness obtained for this stretch of the trv is quite large if compared to eastern alps plio quaternary rates therefore the valley shape imaged by this study better corresponds to the top of carbonate rocks finally on the basis of the obtained morphology and some direct measurements we conclude that the trv features an overall 1 d seismic response i e the resonance is related only to the sediment thickness rather than to the cross section shape but in its deepest part some limited 2 d effects could take place

chronology of the vostok ice core constrained by o2 n2 ratios of occluded air and its implication for the vostok climate records abstract we present a timescale for the vostok ice core that is derived by orbitally tuning to o 2 n 2 ratios in occluded air for depths deeper than 1550 m 112 ka and by gas correlation to the gisp2 chronology for the section shallower than 1422 m 2 exclusion and hence the o 2 n 2 ratio in trapped gases the newly derived o 2 n 2 chronology is consistent with absolutely dated speleothem records the o 2 n 2 chronology differs from previously published orbital tuning chronologies ch 4 and 18 o atm by up to 6 kyr and from the original gt4 chronology by up to 15 kyr the difference between the o 2 n 2 chronology and the 18 o atm chronology varies in time with strong signals centered at 1 100 and 1 41 kyr 1 the ages for the last four glacial terminations in vostok correspond to high obliquity 23 7 at terminations midpoints they also correspond with decreasing precession index corresponding to increasing boreal summer insolation the vostok temperature record boreal summer insolation and the rate of change of the specmap property reflecting planktonic foram 18 o with respect to time are highly coherent at precession and obliquity periods these three properties vary almost synchronously with the possibility that vostok temperature lags behind the other two our new timescale supports the widespread view that boreal summer insolation played an important role in glacial interglacial cycles

synchronising edml and northgrip ice cores using δ18o of atmospheric oxygen δ18oatm and ch4 measurements over mis5 80 123 kyr abstract water isotope records from the epica dronning maud land edml and the northgrip ice cores have revealed a one to one coupling between antarctic isotope maxima aim and greenland dansgaard oeschger do events back to 50 kyr in order to explore if this north south coupling is persistent over marine isotopic stage 5 mis 5 a common timescale must first be constructed here we present new records of 18o of o2 18oatm and methane ch4 measured in the air trapped in ice from the edml 68 147 kyr and northgrip 70 123 kyr ice cores we demonstrate that through the period of interest ch4 records alone are not sufficient to construct a common gas timescale between the two cores millennial scale variations of 18oatm are evidenced over mis 5 both on the antarctic and greenland ice cores and are coupled to ch4 profiles to synchronise the northgrip and edml records they are shown to be a precious tool for ice core synchronisation with this new dating strategy we produce the first continuous and accurate sequence of the north south climatic dynamics on a common ice timescale for the last glacial inception and the first do events of mis 5 reducing relative dating uncertainties to an accuracy of a few centuries at the onset of do events 24 to 20 this edml northgrip synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period the relationship between antarctic warming amplitudes and their concurrent greenland stadial duration highlights the particularity of do event 21 and its antarctic counterpart our results suggest a smaller southern ocean warming rate for this long do event compared to do events of mis 3

o2 n2 ratios of occluded air in the gisp2 ice core 1 we present and discuss the record of o2 n2 ratios in air occluded in the gisp2 ice core retrieved from summit greenland in this study we examine results for 601 samples from 331 depths measured by 1994 and 92 samples from 46 depths newly measured in 2006 poorly replicated samples samples with no replicates and samples falling more than three standard deviations from the mean of each o2 n2 data set are excluded from the analysis the majority of poorly replicated samples are from the depth zone associated with the transition between gas in bubbles and gas present as clathrate hydrates we found that the o2 n2 ratio of samples is depleted by an average value of 7 3 during 11 years of storage at 35 c o2 n2 ratios measured at various times were corrected for depletion during storage and combined to form a single data set the stacked gisp2 o2 n2 record shows strong spectral power at the orbital frequencies and o2 n2 is in antiphase with local summer insolation this observation is consistent with the earlier findings for the vostok and dome fuji ice cores from east antarctica it validates previous conclusions that fractionation during bubble close off depends on ice grain properties set at the surface by solar insolation in addition the gisp2 o2 n2 record shows millennial duration signals that are in phase with the local temperature record of rapid climate change the exact mechanisms by which local summer insolation induces orbital variability in o2 n2 and by which temperature or related properties induce high frequency signals in o2 n2 remain to be identified

coal quality coal rank variation and its relation to reconstructed overburden upper cretaceous and tertiary plains coals alberta canada near surface coals in the alberta plains occur in upper cretaceous and tertiary sediments the former represented by the belly river group horseshoe canyon formation and wapiti formation and the latter by the scollard member of the paskapoo formation statistical techniques were used to document both the distribution of and the interrelationships among the components of proximate and ultimate analysis and calorific value determinations the coals discussed range in rank from subbituminous c to high volatile bituminous c these coals are variable in ash content and low in sulfur content the relationships among calorific value dry basis in kj kg and ash dry basis in and calorific value moist mineral matter free basis in kj kg and equilibrium moisture meq in were determined to be cvd 29 677 315 17 ashd and cvmmmf 31 816 442 05 meq respectively the maximum depth of coal seam burial dob in m was reconstructed on the basis of previously published graphs relating the equilibrium moisture loss to depth of coal seam burial using the relationship log10meq 1 865 0 000416 dob a least squares regression analysis of calorific value mmmf basis in k kg on the calculated depth of burial dob in m yielded the equation cvmmmf 14 748 6 25 dob indicating a coalification gradient determined on the reconstructed overburden of 6 25 kj kg m 0 82 btu lb ft of depth or overburden near surface coals in the alberta plains increase in rank toward the west southwest toward the foothills and mountains region because of progressively greater amounts of overburden that existed in that direction during the tertiary erosion has since removed between 900 and 1 900 m 3 000 and 6 200 ft of sediment with the greatest amount of removal occurring in a west southwest direction

thermal history of alberta deep basin comparative study of fluid inclusion and vitrinite reflectance data the thermal history of the alberta deep basin the gas saturated westernmost part of the western canadian sedimentary basin has been studied by analyzing aqueous and hydrocarbon fluid inclusions in diagenetic cements and comparing the results with coal maturity data results indicate that most of the diagenetic quartz druse precipitated from low salinity fluids 2 3 wt at a temperature of 170 195 c calcite cement precipitated after quartz druse during uplift and cooling at temperatures of 108 169 c inclusions rich in larger hydrocarbon molecules occur in cements that precipitated at 150 c whereas methane rich inclusions occur in cements that precipitated at 165 c or at lower temperatures after significant uplift and cooling of the b sin maximum burial temperatures tmb calculated from vitrinite reflectance data using the lopatin waples tti ro calibration are significantly lower 150 c than the temperature at which quartz druse precipitated in the same area 190 c an equation directly relating tmb and ro proposed by barker and pawlewicz in 1986 yields maximum burial temperatures 200 210 c only slightly higher than the fluid temperatures the results from this study suggest that hot fluids migrated updip along permeable conglomerates and bedding plane fractures to produce unexpectedly high geothermal gradients 38 c km in the western part of the study area the apparent restriction of hot fluids to the western part of the study area sugge ts that convective heat transfer by fluids may have operated on a scale of only tens of kilometers in lower cretaceous rocks of the alberta deep basin

firn air δ15n in modern polar sites and glacial interglacial ice a model data mismatch during glacial periods in antarctica the phase lag between atmospheric composition air bubbles and temperature water isotopes can be quantified from ice cores provided that the age difference between entrapped air and the surrounding air can be correctly estimated this difference depends on the lock in depth lid when air no longer mixes with the atmosphere the lid can be estimated from firnification models or from the air isotopic composition 15n and 40ar both methods give consistent results for greenland and one coastal site in antarctica byrd new firn measurements in greenland northgrip and antarctica berkner island bas depot dome c confirm that firnification models correctly reproduce the present lid over a large range of surface conditions however a systematic mismatch is observed for the last glacial maximum lgm in east antarctic sites vostok dome c dome f questioning the model s validity here we use new 15n measurements from two coastal antarctic sites kohnen station and law dome providing depth estimates again distinct from firnification model calculations we show that this discrepancy can be resolved by revising the estimate of past accumulation rates 15n measurements can therefore help to constrain past accumulation rate and improve ice core dating

diagenetic traps in sandstones diagenesis may be an important agent in trapping hydrocarbons in sandstones by formation of reservoirs or seals reservoirs are formed by the creation of secondary porosity during burial seals are formed by heavy cementation which may allow sandstones to retain large hydrocarbon columns formation of a diagenetic trap requires that parts of the sandstone unit react differently from each other during burial this can be caused by differences in 1 detrital mineralogy resulting from grain size or depositional environment controls 2 early diagenetic mineralogy largely depositional environment controlled 3 burial history structural movement induced and 4 fluid content hydrocarbon or water saturation each of these factors can lead to differences in porosity and permeability of the sandstone sufficient to form reservoirs and seals in the correct configuration diagenetic traps may be formed basin center gas accumulations result from diagenetic trapping in some instances

impacts of sedimentology and diagenesis on pore structure and reservoir quality in tight oil sandstone reservoirs implications for macroscopic and microscopic heterogeneities abstract integrated analysis of reservoir quality pore structure depositional and petrologic characteristics and types and degree of diagenetic alterations was done in this study by employing petrophysical evaluation thin section observation stable isotope analysis scanning electron microscopy combined with eds x ray computed tomography and high pressure mercury intrusion the purpose was to investigate the macroscopic and microscopic heterogeneities and the effects of depositional factors and diagenetic alterations responsible for them the results indicate that the chang 8 tight oil sandstone of the longdong area in the ordos basin can be divided into three categories namely the type i reservoir with porosity greater than 10 and permeability greater than 1 0 md having sparse lenticular distributions in the mouth bar of the braided delta front the type ii reservoir with porosity of 6 10 and permeability of 0 1 1 0 md mainly distributing in the distributary channel and the type iii reservoir with porosity less than 6 and permeability less than 0 1 md having a reticular distribution in the distributary bay the type i reservoir has an intergranular pore inter p dominant pore system with a greater pore throat radius 1 10 m a larger pore volume and better connectivity the type ii reservoir has a mixed system consisting of intragranular pores intra p and inter p with a pore throat radius of 0 1 1 m smaller pore volume and worse connectivity the type iii reservoir is characterized by an intra p dominated system with a radius between 10 and 500 nm smallest pore volume and worst connectivity the wide range of porosity permeability and pore structure parameters can be attributed to the frequent variations in depositional facies and diagenetic alterations larger grain size higher content of quartz and feldspar and moderate grain coating chlorite content less than 8 are favorable for the preservation of intergranular pores and dominate the formation of the type i reservoir the mesogenetic calcite and ferrocalcite cementation and pore filling kaolinite precipitation obstruct the intergranular space and are the predominant factors tightening the reservoirs in the distributary channel and distributary bay leading to multi scale heterogeneities secondary porosity from dissolution plays a much more important role in contributing to the porosity and permeability of the type ii and iii reservoirs than of the type i reservoir the study provide a comprehensive understanding for the multi scale heterogeneities and can be used to predict the potential high quality zones in tight oil sandstone reservoirs

diagenesis and isotopic evolution of porewaters in the alberta deep basin the falher member and cadomin formation abstract diagenesis and porewater evolution in the alberta deep basin have been studied by combining results from petrologic stable isotope and fluid inclusion analyses of diagenetic minerals four stages of diagenesis and porewater evolution corresponding to burial and subsequent uplift and erosion have been identified in the falher member of the spirit river formation and the cadomin formation stage 1 deposition and burial is marked by early precipitation of hematite siderite or chlorite and the dissolution of unstable detrital grains followed by later albitization precipitation of illite and local calcite cement and pressure solution of chert grains during this stage 18o values of porewaters in the falher member increased from 10 3 to 3 infiltration of saline fluids from pre cretaceous units may have produced porewaters in the cadomin formation with 18o values as high as 4 to 7 stage 2 maximum burial and relief is dominated by precipitation of quartz druse in conglomerates and horizontal fractures porefluids during stage 2 had 18o values of 3 at 190 c 2 3 wt dissolved solids in the falher member and at 150 c in the cadomin formation during stage 3 uplift and erosion precipitation of dickite occurred in both the falher member and the cadomin formation from evolved meteoric water as temperatures and 18o values of the porewater decreased in addition precipitation of ankerite and calcite was initiated in the falher member as the influx of evolved meteoric water continued finally in stage 4 maximum generation of methane from interbedded coals methane saturation of the porespaces marked the end of diagenesis in the down dip gas saturated part of the deep basin

effect of sediment column on weak motion site response for a deep basin fill unique challenges arise when projecting dynamic site response in a deep steep sided irregularly shaped sediment filled basin the influence of shallow sediments on site response was investigated for a 1 km deep alluvial column in the las vegas basin subjected to weak ground motions a one dimensional equivalent linear model was applied response analyses for deep deposits are complicated because dynamic material properties at depth are uncertain to compensate the model half space was placed well above the physical bottom of the sediment column the depth to half space was selected by matching characteristics of projected surface response to measured data or expectations weak ground motion datasets resulting from underground nuclear tests were considered the best match half space depth 375 m greatly exceeded the depth of the threshold shear wave velocity for engineering bedrock the analysis captured site response over the period range 0 3 1 3 s when the parameterization was tested for a weak

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

basic physical principles of conventional and deep basin gas entrapment abstract the model consists of a transparent plexiglass cylinder 2 5 in 6 35 cm in diameter and about 30 in 76 cm high mounted on a support stand the cylinder contains a sand pack made of coarse loose sand separated in the middle by 7 in 17 8 cm of loose fine sand permeability of the coarse sand is in excess of 1 000 darcys while that of the fine sand is several hundred darcys the device was invented by me to study the behavior of gas and water flow through porous media and in particular to investigate the characteristics of conventional and deep basin types of gas traps figure the first demonstration represents the conventional trapping case the second demonstration shows pressure depth graphs for fluid phases to be identical with those found for the elmworth deep basin gas traps i e at the updip contact the gas and water phase pressures are about equal as opposed to the conventional case where the gas pressure was much greater than the water pressure at the contact also the downdip water column beneath the gas column is shown in both cases not to be in pressure continuity with the water column in the upper coarse sand column even though there is a continuous water film wetting the sand grains through the gas saturated coarse sand connecting the water saturated fine sand with the water saturated coarse sand below the gas column the fluid flow process through the depressured gas column from the upper water saturated sands to the base of the gas accumulation will also be discussed end of article last page 572

modeling the densification of polar firn including heat diffusion application to close off characteristics and gas isotopic fractionation for antarctica and greenland sites 1 modeling the densification of polar firn is essential to estimate variations of close off characteristics density close off depth delta age in relation with past climate parameters temperature and accumulation rates furthermore the air composition in the firn is modified by gravitational and thermal fractionation and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations in this work we propose a new model coupling firn densification and heat diffusion in addition to the determination of the firn thickness and gas ice age differences the model allows a reconstruction of the time evolution of the temperature for different sites in antarctica vostok and greenland gisp2 and therefore the evolution of gravitational and thermal isotopic fractionations in firn under present day conditions the modeled profiles are in good agreement with the available temperature measurements in firn for sites with low accumulation rates such as vostok the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur the comparison of the modeled 15n results to measurements allows to better constrain the 18o temperature relationship used to infer the surface temperature history and for gisp2 the model validates the long term borehole based temperature

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

changes in the atmospheric ch4 gradient between greenland and antarctica during the holocene high resolution records of atmospheric methane over the last 11 500 years have been obtained from two antarctic ice cores d47 and byrd and a greenland core greenland ice core project these cores show similar trapping conditions for trace gases in the ice combined with a comparable sampling resolution this together with a good relative chronology provided by unequivocal ch 4 features allows a direct comparison of the synchronized greenland and antarctic records and it reveals significant changes in the interpolar difference of ch 4 mixing ratio with time on the average over the full holocene records we find an interpolar difference of 44 7 ppbv a minimum difference of 33 7 ppbv is observed from 7 to 5 kyr b p whereas the maximum gradient 50 3 ppbv took place from 5 to 2 5 kyr b p a gradient of 44 4 ppbv is observed during the early holocene 11 5 to 9 5 kyr b p we use a three box model to translate the measured differences into quantitative contributions of methane sources in the tropics and the middle to high latitudes of the northern hemisphere the model results support the previous interpretation that past natural ch 4 sources mainly lay in tropical regions but it also suggests that boreal regions provided a significant contribution to the ch 4 hudget especially at the start of the holocene the growing extent of peat bogs in boreal regions would also have counterbalanced the drying of the tropics over the second half of the holocene finally our model results suggest a large source increase in tropical regions from the late holocene to the last millennium which may partly be caused by anthropogenic emissions

development of shoreline shelf sand bodies in a cretaceous epeiric sea deposit abstract the 350 m thick spirit river formation lower cretaceous of west central alberta comprises a clastic wedge which prograded into an epeiric sea within the clastic wedge eight major transgressive and regressive sequences of sedimentation from 30 to 50 m thick have been identified cores from four sequences in the central pan of the study area reveal that the sediments consist of fine grained well sorted sandstone with mostly low angle to horizontal laminations and some palaeophycus burrows conglomerate units up to 10 m thick occur locally the sequences are capped by carbonaceous mudstone and or coal each sequence is interpreted as consisting of shoreface beach deposits with conglomeratic fluvial channel and beach deposits overlain by backswamp lagoon sediments these s quences have sharp sandy bases rather than shaly gradational ones because of a shallow depths and high wave energies and b preservation of basal transgressive deposits on a large scale the shoreline sequences can each be correlated to marine sequences which grade from shale at the bases to fine sandstone at the tops the upper pans of each marine sequence form shoreline attached sheet sandstones each coarsening upward sequence is bounded by marine shale laid down during a transgression when coarser sediment was trapped in nonmarine or marginal marine areas some sequences break up seaward into two coarsening upward units because of minor transgressions within the marine portions of some thicker sequences 5 to 10 m thick coarsening upward units can be defined which are believed to reflect fluctuations in sediment supply the correlation of these units is an application of a technique called event correlation which outlines approximate time surfaces these correlations reveal a series of imbricated seaward sloping surfaces of deposition within each major sequence sedimentation in the epeiric seaway proceeded by seaward accretion of evenly sloping bodies of sediment with no development of a shelf slope basin configuration the gradual slope formed because of a shallow depths controlled by the stable tectonic setting and rapid sediment input and b high wave energy levels which distributed sediment almost uniformly over the ea bottom

the impact of a buried high velocity layer in the seismic site amplification of the city of llolleo chile programa de riesgo sismico prs at the university of chile comision nacional de investigacion cientifica y tecnologica conicyt 2017 21171480 fondo nacional de desarrollo cientifico y tecnologico fondecyt 1170430 advanced mining technology center amtc fb0809 pia conicyt

thermal fractionation of air in polar firn by seasonal temperature gradients 1 air withdrawn from the top 5 15 m of the polar snowpack firn shows anomalous enrichment of heavy gases during summer including inert gases following earlier work we ascribe this to thermal diffusion the tendency of a gas mixture to separate in a temperature gradient with heavier molecules migrating toward colder regions summer warmth creates a temperature gradient in the top few meters of the firn due to the thermal inertia of the underlying firn and causes gas fractionation by thermal diffusion here we explore and quantify this process further in order to 1 correct for bias caused by thermal diffusion in firn air and ice core air isotope records 2 help calibrate a new technique for measuring temperature change in ice core gas records based on thermal diffusion severinghaus et al 1998 and 3 address whether air in polar snow convects during winter and if so whether it creates a rectification of seasonality that could bias the ice core record we sampled air at 2 m depth intervals from the top 15 m of the firn at two antarctic sites siple dome and south pole including a winter sampling at the pole we analyzed 15n 14n 40ar 36ar 40ar 38ar 18o 16o of o2 o2 n2 84kr 36ar and 132xe 36ar the results show the expected pattern of fractionation and match a gas diffusion model based on first principles to within 30 although absolute values of thermal diffusion sensitivities cannot be determined from the data with precision relative values of different gas pairs may at siple dome 40ar 4 is 66 2 as sensitive to thermal diffusion as 15n in agreement with laboratory calibration 18o 2 is 83 3 and 84kr 48 is 33 3 as sensitive as 15n the corresponding figures for summer south pole are 64 2 81 3 and 34 3 accounting for atmospheric change the figure for o2 n2 4 is 90 3 at siple dome winter south pole shows a strong depletion of heavy gases as expected however the data do not fit the model well in the deeper part of the profile and yield a systematic drift with depth in relative thermal diffusion sensitivities except for kr constant at 34 4 suggesting the action of some other process that is not currently understood no evidence for wintertime convection or a rectifier effect is seen

northern hemisphere forcing of climatic cycles in antarctica over the past 360 000 years the milankovitch theory of climate change proposes that glacial interglacial cycles are driven by changes in summer insolation at high northern latitudes the timing of climate change in the southern hemisphere at glacial interglacial transitions which are known as terminations relative to variations in summer insolation in the northern hemisphere is an important test of this hypothesis so far it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined here we present a new chronology of antarctic climate change over the past 360 000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the dome fuji and vostok ice cores this ratio is a proxy for local summer insolation5 and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter the accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation our results indicate that orbital scale antarctic climate change lags northern hemisphere insolation by a few millennia and that the increases in antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of northern hemisphere summer insolation these results support the milankovitch theory that northern hemisphere summer insolation triggered the last four deglaciations

stratigraphic controls on production from a basin centered gas system lower cretaceous cadotte member deep basin alberta canada in this article we examine the controls on gas production from cretaceous clastic strand plain deposits in an area the deep basin of alberta that was instrumental in the development of the basin centered gas concept by integrating core wireline logs three dimensional seismic data petrophysical measurements pressure and production data we show that the best gas production comes from stratigraphic sweet spots consisting of chert rich shoreface and beachface deposits that alternate between tight quartzose sandstone the physical properties of the chert rich and quartzose units are sufficiently different that they can be distinguished seismically seismic modeling and observations show that high amplitude areas correspond to porous and productive chert rich shoreface and beachface deposits a map of seismic amplitudes for the cadotte member shows narrow 0 5 km 0 3 mi width curvilinear high amplitude anomalies corresponding to cherty shoreface and beachface deposits that are parallel to depositional strike east northeast west southwest and correlate precisely with production trends wells drilled outside the high amplitude anomalies do not have sufficient permeability to produce gas at economic rates the shore parallel stratigraphic sweet spots are locally compartmentalized by shale filled channels that cut at high angles through the strand plain like other cretaceous units in this area the cadotte member is wet structurally updip from gas charged rocks the contact between these two phases traversing through our study area and its location is controlled by the interplay of regional structural dip and depositional processes that controlled the lithology and stratigraphic architecture of the rocks

anisotropy and crystalline fabric of whillans ice stream west antarctica inferred from multicomponent seismic data crystal orientation fabric cof describes the intrinsic anisotropic nature of ice and is an important parameter for modeling glacier flow we present the results of three component active source seismic observations from the whillans ice stream wis a fast flowing ice stream in west antarctica surface wave dispersion analysis ray tracing and traveltime inversion of compressional p and shear s waves reveal the presence of transversely isotropic ice with a vertical axis of symmetry vti beneath approximately 65 m of isotropic firn the ice stream is characterized by weak anisotropy involving an average ice thickness of approximately 780 m the analysis indicates that about 95 of the ice mass is anisotropic and the crystalline c axes span within an average broad cone angle of 73 10 with respect to the vertical axis moreover the mean temperature t below the firn estimated from seismic data is 15 5 c these data do not show evidence of englacial seismic reflectivity which indicates the lack of abrupt changes in the cof the presence of azimuthal anisotropy due to transversely compressive flow or fractures aligned along a preferential direction is also excluded we suggest that the observed vti ice structure is typical of large ice streams in regions where basal sliding and bed deformation dominate over internal glacial deformation

lithology dependent diagenetic control of reservoir properties of conglomerates falher member elmworth field alberta conglomerates in the falher member of the lower cretaceous spirit river formation of alberta are the reservoir rocks for the giant 2 3 tcf or 5 8 1010 m3 elmworth gas field three types of conglomerates are present a unimodal granules or pebbles lacking any matrix b bimodal grain supported a framework of pebbles with fine to medium sand in the interstices and c bimodal sand supported pebbles floating in fine to medium sandstone the distribution of these three types is controlled by the original depositional environment the granules and pebbles are composed of chert and silicified sedimentary and volcanic rock fragments the sand grains are dominantly quartz during diagenesis very small 01 0 1 mm drusy quartz crystals form on the cherts and rock fragments whereas quartz grains undergo heavy quartz overgrowth formation because of differences in nucleation and growth of quartz crystals as a consequence most unimodal conglomerates low in quartz have not experienced major reduction of porosity and permeability bimodal conglomerates both sand and pebble supported have lost significant amounts because of cementation of the quartz rich matrix streaks and patches of kaolinite and calcite cements have also reduced porosity and permeability locally gas production from falher wells therefore de ends not only on the amount of conglomerate but also on the proportion of unimodal and bimodal types

firn processes and δ15n potential for a gas phase climate proxy abstract in order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores we must accurately account for the age difference between ice and gas at a given depth this gas age ice age difference depends on the age of the ice at the bottom of the firn layer where the bubbles are closed off firn densification models are used to calculate how this age difference varied in the past but have an uncertainty on the order of 1000 years for central antarctic sites here we explore the possibility that 15 n of n 2 is a gas phase proxy of climate which can be used to synchronize gas and ice records we present the 15 n record from the epica dome c edc ice core covering the last three glacial terminations and five glacial interglacial cycles between 300 and 800 ka previous studies have shown that gravitational settling enriches 15 n as a function of the diffusive column height in the firn if densification models prediction of deeper firn close off under glacial conditions is correct then we would expect heavier 15 n during glacial periods and a negative correlation with temperature instead edc 15 n is positively correlated with the ice deuterium content a proxy for temperature as previously reported at vostok dome fuji and epica dronning maud land we propose a mechanism that links accumulation rate firn permeability and convective mixing in the top meters of the firn to explain this correlation between 15 n and ice deuterium content the tightest correlation is observed over glacial terminations supporting the idea that 15 n is a property in the gas phase that records changes in surface conditions linked to deglacial warming

controls on reservoir quality in fan deltaic conglomerates insight from the lower triassic baikouquan formation junggar basin china abstract fan delta sandy conglomerates form important oil and gas reservoirs recently a new giant oilfield was discovered in the lower triassic baikouquan formation t1b in the mahu sag of the junggar basin northwestern china however the fan delta sandy conglomerate reservoirs are strongly heterogeneous most have poor permeability and host little hydrocarbons while a subset at the delta front exhibit high porosity and permeability forming high quality reservoirs to explain this disparity the sedimentary facies diagenesis and reservoir quality of the sandy conglomerate strata and their interactions were studied detailed logging of 253m cores indicates that the t1b was deposited in a lacustrine fan delta complex comprising ten lithofacies from coarse matrix supported pebbly conglomerate gm to fine massive mudstone fm in four facies associations interpretation of optical microscope backscattered and scanning electron microscope imaging show that these ten lithofacies underwent differential diagenesis especially dissolution of minerals such as orthoclase dissolution was particularly prevalent in the subaqueous distributary channel deposits of sandstones st hyperpycnal flow massive sandstones sm and grain flow deposits of sandy gravelly conglomerates gcs at the delta front forming abundant secondary pores these pores enhanced the reservoir performance and led to high porosity and permeability within these three lithofacies for these reservoirs continuous winnowing at the delta front led to relatively high primary porosities and subsequent mineral dissolution during burial diagenesis closely related to acidic mn rich hydrocarbon bearing fluids significantly improved the porosities further migration of hydrocarbon bearing fluids was facilitated by faults cutting through the reservoir and underlying source rocks this led to the development of belts of high quality reservoir at the delta front near the fault conduits this model for reservoir development and charge suggests that further reservoirs can be expected within the t1b of the mahu sag

what was the surface temperature in central antarctica during the last glacial maximum abstract the temperature increase at vostok antarctica from the last glacial maximum to the present warm period is about 8 c based on the deuterium isotope profile the bore hole temperature temperature profile in the ice sheet indicates that the temperature difference may have been much larger about 15 c the temperature dependent gas occlusion process is the key to evaluate the two scenarios atmospheric air penetrates the porous firn layer of the ice sheet and gets trapped at the firn ice boundary consequently the air is younger than the surrounding ice when it gets enclosed in bubbles this age difference age between ice and enclosed gas is temperature and accumulation rate dependent therefore it is possible to estimate paleotemperatures from a known age we use the linkage between chronologies of ch 4 and water isotopes from byrd station and vostok to obtain an experimental age for vostok this experimental age is then compared to modeled age for the two temperature scenarios our results indicate that the temperature reconstruction deduced from the water isotopic composition is the more probable one

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

new modeling of the vostok ice flow line and implication for the glaciological chronology of the vostok ice core 1 we have used new spaceborne elevation and airborne ice thickness data to constrain a 2d1 2 model of snow accumulation and ice flow along the ridge b vostok station ice flow line east antarctica we show that new evaluations of the ice flow line geometry from the surface elevation ice thickness from low frequency radar data and basal melting and sliding change significantly the chronology of the vostok ice core this new vostok dating model reconciles orbital and glaciological timescales and is in good agreement with the dome fuji glaciological timescale at the same time the new model shows significantly older ages than the previous gt4 timescale for the last glacial part being thus in better agreement with the grip and gisp2 chronologies

origin migration and entrapment of natural gas in alberta deep basin part 2 abstract gas entrapment in the elmworth deep basin occurs under a variety of conditions typical trap types include 1 stratigraphic 2 structural stratigraphic and 3 deep basin the deep basin type of gas trap is the most important in terms of its large size and unconventional trapping conditions the three main physical conditions associated with the deep basin type of gas trap are 1 an updip water gas contact 2 a downdip gas water contact is generally absent and 3 the original reservoir gas pressures are equal to or less than water pressures at the same depth based on extrapolation of water pressure gradients from the updip water saturated region the physical principles underlying this kind of gas entrapment together with the intimate association of mature source rocks constitute a fundamental relationship which is applicable to gas exploration in other sedimentary basins of the world end of article last page 572