a carbon isotope reference curve for ca 1700 1575 ma mcarthur and mount isa basins northern australia abstract shallow marine paleo and mesoproterozoic sedimentary successions are widely distributed in several major basins across northern australia the successions are only gently deformed and their stratigraphy is relatively continuous thus offering an ideal opportunity to document secular variations in carbon isotopes marine carbonate intervals from two of these major basins the mcarthur and mount isa basins have been sampled to document secular variation in 13ccarb from approximately 1700 to 1575 ma in all cases the samples have been tied to a well established sequence stratigraphy which along with u pb shrimp zircon dates provides a time resolution of the order of 1 m y the data presented here thus provide the most comprehensive and best dated 13ccarb stratigraphy yet obtained from such ancient rocks diagenesis occurred early in the carbonate rocks from both basins with the result that fluid movements were restricted and primary carbon isotopic signatures were retained the 13ccarb values from both basins vary within a very narrow range around a mean of 0 6 with extreme values seldom lying further than 1 from the mean that is the curves are essentially flat the results of this study combined with earlier studies on younger rocks imply that the global ocean reached a state of equilibrium in the mid paleoproterozoic and remained stable for much of the following billion years current models of the ocean suggest that to maintain the carbon mass balance relatively low levels of tectonic activity would be required which in turn suggests that the availability of nutrients such as phosphorus was stable and low prolonged nutrient stability may therefore have exerted a major influence upon the evolution of the biosphere over this time interval

the influence of fracturing process on microseismic propagation in the hydraulic fracturing process the velocity model for microseismic location is usually constructed by well logs seismic data or calibration shots which ignore the influence of the fracturing process in this work we examine its influence by simulating microseismic events and pore pressure variation in the fracturing process besides the microseismicity produced by hydraulic fracture extension we also simulate the microseismicity caused by fluid leakage by means of the critical pore pressure criterion the coates schoenberg method and fracture compliances are then applied to calculate the real time velocity in the fracturing process and 3d ray tracing method is applied to compare the microseismic propagation variation in the different stages of the fracturing process the results of the simulation show that the deviation caused by the fracturing process varies considerably between different receiver locations and the overall deviation increases with the fracturing process finally a new method is constructed to evaluate the travel time deviation in real data

loess and life out of earth abstract loess is a homogeneous typically nonstratified porous friable slightly coherent often calcareous fine grained silty pale yellow wind blown aeolian and often by water reworked sediment that is distributed on continents world wide recent studies have highlighted the importance of biological loess crusts in trapping and transforming aeolian material into loess and also in prevention from wind and water erosion of deposited material some planets and satellites in our solar system are characterized by conditions comparable to those related to loess formation in terrestrial environments given the requirements for loess deposition on earth this study aims to ask the following questions 1 if loess like sediment formation is possible outside earth what are the mechanisms of sediment deposition and preservation 2 could the possible loess like sediments be stabilized through the activity of extraterrestrial equivalents of biological loess crusts found on earth as loess formation on earth is related to biological activity we propose a new direction in the search for extraterrestrial life evidence about extraterrestrial loess might indicate extraterrestrial life connected to loess formation on the basis of comparative analysis of some astrophysical conditions of seven celestial bodies we propose mars and titan and possibly venus and io to be assessed for evidence of loess deposition and the possible presence of related life forms and their biomarkers following recent advances in our understanding of terrestrial loess deposition we propose new indicators of extraterrestrial life research biomarkers in loess cyanobacterial and other microbial

dual simulations of fluid flow and seismic wave propagation in a fractured network effects of pore pressure on seismic signature summary fluid flow in the earth s crust plays an important role in a number of geological processes in relatively tight rock formations such flow is usually controlled by open macrofractures with significant implications for ground water flow and hydrocarbon reservoir management the movement of fluids in the fractured media will result in changes in the pore pressure and consequently will cause changes to the effective stress traction and elastic properties the main purpose of this study is to numerically examine the effect of pore pressure changes on seismic wave propagation i e the effects of pore pressures on amplitude arrival time frequency content this is achieved by using dual simulations of fluid flow and seismic propagation in a common 2 d fracture network note that the dual simulations are performed separately as the coupled simulations of fluid flow and seismic wave propagations in such fracture network is not possible because the timescales of fluid flow and wave propagation are considerably different typically fluid flows in hours whereas wave propagation in seconds the flow simulation updates the pore pressure at consecutive time steps and thus the elastic properties of the rock for the seismic modelling in other words during each time step of the flow simulations we compute the elastic response corresponding to the pore pressure distribution the relationship between pore pressure and fractures is linked via an empirical relationship given by schoenberg and the elastic response of fractures is computed using the equivalent medium theory described by hudson and liu therefore we can evaluate the possibility of inferring the changes of fluid properties directly from seismic data our results indicate that p waves are not as sensitive to pore pressure changes as s and coda or scattered waves the increase in pore pressure causes a shift of the energy towards lower frequencies as shown from the spectrum as a result of scattering attenuation another important observation is that the fluid effects on the wavefield vary significantly with the source receiver direction that is the azimuth relative to the fracture orientation these results have significant implications for the characterization of naturally fractured reservoirs using seismic methods and may impact on experimental design to infer such attributes in a real reservoir situation particularly in acquiring time lapse seismic data

recognition of a novel precambrian petroleum system based on isotopic and biomarker evidence in yangtze platform south china abstract the precambrian doushantuo formation is regarded as a possible petroleum source rock horizon with toc values of 0 85 1 85 and type i kerogen in northwestern sichuan basin yangtze platform south china while showing high to post mature thermal maturity a set of outcropping bitumen and oil sands from various reservoirs display overall depleted values of 13 c from 36 to 32 average 35 typical of a precambrian source in addition the sterane distributions in these bitumens and oils are unusual compared to marine phanerozoic oils with a predominance of c 29 members as well as their triaromatic counterparts high amounts of 20 n alkylpregnane with very low diasteranes indicate restricted sulfur rich conditions typical of an anoxic carbonate source rock this interpretation is supported by some other specific biomarkers such as abundant 30 norhopane and c 24 tetracyclicterpane and elevated c 35 hopane furthermore the presence of gammacerane indicates a saline stratified water column hydrocarbons extracted from the solid bitumen and oil sands have many compositional characteristics in common with other oils derived from precambrian carbonate source rocks from elsewhere this implies the existence of a precambrian marine petroleum system in the yangtze platform with the doushantuo carbonate as the likely source it is supposed that the reduction of temperature and pressure following basin uplift resulted in petroleum fractionation deasphalting in lower paleozoic reservoirs with the fractionated oils having migrated along the faults becoming trapped in stratigraphically younger reservoirs where the petroleum underwent heavy biodegradation

organic geochemical characteristics of the mesoproterozoic hongshuizhuang formation from northern china implications for thermal maturity and biological sources abstract the mesoproterozoic hongshuizhuang formation 1 4 ga from northern china consists of organic rich sediments which record important environmental and biological information from that time organic and element geochemistry techniques were used to assess the syngeneity and indigeneity of hydrocarbons and the thermal maturity and biological sources of the organic matter in the hongshuizhuang formation results from a slice extraction experiment indicate that the exterior of the core was subjected to contamination from drilling sampling and storage whereas the organic matter in the interior shale core slices was indigenous the organic matter in the interior argillaceous dolomite core slices might have been affected by the migration of oil it is important to remove the outside of the core prior to solvent extraction as this increases the possibility of analysis of indigenous hydrocarbons the source rocks of the oil are the black shales of the hongshuizhuang formation aliphatic and aromatic hydrocarbon distributions indicate that the hongshuizhuang formation samples have a low thermal maturity in the early to middle oil window 0 6 0 8 ro equivalent based on comparison with middle velkerri formation rocks of about the same age in the mcarthur basin northern australia these data are consistent with results based on the values of tmax and protobitumen reflectance and suggest that the samples contain well preserved organic matter that has not been thermally destroyed the redox conditions indicated by the pristane phytane pr ph ratios are not consistent with other evidence the correlations between n c20 n c21 major elements and pr ph indicate that the pr ph ratios are influenced by biological sources and mineralogy rather than by redox conditions pr and ph may have been derived not only from chlorophyll a but also from archaea the short and long chain n alkanes in the hongshuizhuang formation were derived from anoxic clay rich environments and oxic carbonate rich environments respectively the biomarkers observed in the hongshuizhuang formation indicate that the organic matter was primarily derived from prokaryotes

biomarker composition of some asphaltic coastal bitumens from tasmania australia abstract ten bitumen samples collected between 1880 and 1915 from the west and southwest coasts of tasmania three from flinders and king islands in bass strait and one each from preolenna in northwestern tasmania cape jaffa in south australia and a beach in the south of western australia were analysed as part of a study to re evaluate the petroleum prospectivity of tasmania and adjacent areas in southeastern australia the bitumens dissolved completely in chloroform and contained aliphatic hydrocarbons 12 3 17 3 aromatic hydrocarbons 4 4 10 6 and uncharacterized asphaltenes 75 6 82 9 the distributions of aliphatic and aromatic biomarkers were remarkably similar in all of the bitumens indicating that they were derived from a common or very similar source biomarker data confirmed that the bitumens are not related to land plant derived oils presently recovered from the nearby bass otway and gippsland basins of southern australia the high proportions of c 27 steranes and presence of c 30 steranes including dinosterane suggested that the bitumens were derived from a marine source rock containing mainly marine organic matter biomarker maturity parameters were also very similar in all bitumens and consistent with those found in crude oils generated at an equivalent vitrinite reflectance of about 0 75 hopanes showed a high proportion of c 29 and c 30 17 h 21 h hopanes with very minor amounts of the corresponding moretanes the unusual absence of 2 methylhopanes and low abundance of tricyclic alkanes ruled out carbonates or the tasmanite oil shales respectively as sources if the source of the bitumens can be related to local geological features these new findings could be significant for future oil exploration in tasmania and adjacent offshore areas

isotopic evolution of the biogeochemical carbon cycle during the proterozoic eon abstract time related changes in the proterozoic sedimentary isotopic record of organic carbon and carbonates are consistent with the following 1 an increase in the oxidation state of the environment 2 a transition towards microbial populations dominated by producers and utilizers of o 2 and so 4 2 and 3 a relatively minor increase in organic 13 c during postdepositional thermal alteration 13 c increased 3 as h c declined from 0 8 to 0 1 the progressive oxidation of the environment was episodic for example between 2 2 and 1 9 ga crustal and atmospheric reservoirs of o 2 fe 3 and so 4 2 increased relatively rapidly and this increase was too large to be attributed solely to the declining rate of oxidant consumption by volcanic and hydrothermal fluxes of reduced species additional fundamental changes seem to be required in the tectonic style of organic sedimentation and preservation episodic changes in both the biogeochemical c cycle and atmospheric o 2 levels during the proterozoic eon likely influenced the evolution of eukarya

biomarker signatures of the ediacaran early cambrian origin petroleum from the central sichuan basin south china implications for source rock characteristics abstract hydrocarbons with an ediacaran early cambrian origin from the central sichuan basin south china were investigated for biomarker compositions they were obtained by solvent extraction from the upper ediacaran reservoir core samples which contain abundant solid bitumen the solid bitumen is widely believed to be formed by thermal cracking of early charged oils in the reservoirs which have presumed source rocks of an ediacaran early cambrian age thermal maturity parameters based on phenanthrenes and aromatic steroids suggest a very high thermal maturity for the extracted hydrocarbons which is consistent with the severe maturation undergone by their host reservoirs age diagnostic biomarkers including c30 24 isopropylcholestanes and mid chain monomethyl alkanes support source rocks of an ediacaran early cambrian age the extracted hydrocarbons have very similar biomarker signatures which include high relative abundance of acyclic isoprenoids and pristane phytane 1 and the presence of c26 norcholestanes methyl and ethylsteranes the presence of hopanoids including extended series and methylhopanes indicates contributions from prokaryotic bacteria while the presence of various steroids including regular steranes and methylsteranes indicates contributions from the eukaryotic algae parameters based on tricyclic terpane and hopane dibenzothiophene phenanthrene ratios and c27 diasteranes diasteranes regular steranes ratios suggest a major shale source but a mixed shale carbonate source cannot be completely excluded presence of c30 demethylsteranes low pristane phytane ratios high gammacerane index and presence of 28 30 dinorhopane and 2 methyhopanes indicate that the source rocks were deposited in a stratified anoxic marine depositional environment with enhanced salinity conditions

comparative microbial diversity and redox environments of black shale and stromatolite facies in the mesoproterozoic xiamaling formation abstract the composition of microbial communities and their relationship to ocean redox structure in the precambrian are topics of continuing interest in geobiology our knowledge of organismic diversity and environmental conditions during this time are mostly based on fragmentary paleontological and geochemical records and might be skewed accordingly in north china the xiamaling formation 1 37 ga is characterized by black shales of relatively low thermal maturity t max is 445 c and has been identified as a potential petroleum source rock to date however the biological sources of the organic matter and the environmental conditions prevalent during the deposition of these sediments remain unclear in this study we analyzed the hydrocarbon biomarker compositions of the xiamaling formation shales and a superjacent stromatolitic carbonate in order to shed light on the microbial diversity in the sedimentary environments they represent the hydrocarbons extracted from both sediments are dominated by low molecular weight n alkanes with a maximum at c 15 18 suggesting that bacteria and or algae were primary biotic precursors our inability to detect steranes in bitumen i and only traces of rearranged steranes in bitumen ii of black shales indicates that modern eukaryotic algae were either ecologically insignificant or not preserved due to a taphonomic bias the high relative concentration of hopanes and diahopanes ranging from c 27 to c 35 as well as monomethylalkanes suggests that cyanobacteria may have been the dominant primary producers and could have contributed to the biologically available nitrogen pool through n 2 fixation this observation is supported by the low nitrogen isotopic composition of the kerogens even though all facies zones appear to have been anoxic but not sulfidic on the basis of biomarker ratios and trace metals subtle but distinct molecular differences are observed between the stromatolite and the black shales which can be attributed to both lithologically controlled diagenetic rearrangements and differential biotic input the discrepancy between the presence of a large ucm and high abundances of alkyl lipids on one hand yet the absence of a stable carbon isotopic offset between lipids and kerogen on the other suggests that strong heterotrophic reworking might not be the sole source of the biodegraded fingerprint that is so typical for proterozoic bitumens and demands alternative explanations

focal spot imaging based on zero lag cross correlation amplitude fields application to dense array data at the san jacinto fault zone we image the subsurface below a dense seismic array straddling the clark branch of the san jacinto fault zone in southern california the analysis is based on focal spots of surface waves associated with the zero lag amplitudes of noise cross correlations computed between all stations of the dense array local medium properties are inferred from the spatially variable focal spot size and shape based on the first zero crossing of amplitude versus distance distributions the method provides simultaneous estimates of wave speed apparent attenuation and anisotropy without solving a tomographic inverse problem the obtained images of the frequency dependent seismic velocity distributions are consistent with independent estimates from a far field rayleigh wave tomography we observe an anticorrelation between our apparent attenuation coefficient and seismic velocity and a fault parallel alignment of fast propagation directions with greater structural complexity to the southwest of the fault the results imply a complex fault zone structure including a waveguide to the northeast of the fault that is continuous across the observed depth range and a low velocity structure to the southwest associated with a shallow sedimentary basin

biological sources of sedimentary organic matter in neoproterozoic lower cambrian shales in the sichuan basin sw china evidence from biomarkers and microfossils abstract study of the occurrence and formation of sedimentary organic matter in the sichuan basin southern china provides valuable insights into the biological sources and compositions of neoproterozoic to lower cambrian shales rock samples from two sets of shales in the sichuan basin and adjacent areas including the ediacaran doushantuo shale and the lower cambrian qiongzhusi shale in the gaoshiti moxi and ziyang weiyuan areas were collected and geochemically analyzed in this study the distribution of biomarkers stable carbon isotope compositions and microfossil characteristics reveal that eukaryotic algae including chlorophytes pelagophyceae dinoflagellates diatoms or their ancestors and sponges proliferated widely during the late neoproterozoic to early cambrian in the sichuan basin cyanobacteria some proteobacteria rhizobiales and aerobic methanotrophs also made a contribution to organic matter in the studied shales aerobic methanotrophs that utilize 13c depleted substrates such as ch4 as carbon sources may have been the cause of anomalous 13c depleted kerogen in the study area

complex patterns of steroidal biomarkers in tertiary lacustrine sediments of the biyang basin china gas chromatography gc gas chromatography mass spectrometry gc ms and gas chromatography mass spectrometry mass spectrometry gc ms ms with co injected synthetic standards were used to analyse the biomarker patterns of some tertiary lacustrine clayey dolomites from the biyang basin china the lithology low pr ph ratio and high gammacerane content of these sediments indicated that high salinity prevailed during their deposition the distributions of steroidal hydrocarbons were particularly unusual and several pseudohomologous series including regular steranes c27 c29 4 methyl steranes c28 c30 including dinosteranes 3b ethyl steranes c29 c31 lanostanes c30 c32 and a variety of other 3b alkylated steranes were identified 3b n propylcholestane 3b n propylstigmastane and 4 4 dimethylcholestane were identified using authentic standards and this is the first time these compounds have been unambiguously characterised in sediments crown copyright 2001 published by elsevier science ltd all rights reserved

molecular and isotopic characterization of biomarkers in the frick swiss jura sediments a palaeoenvironmental reconstruction on the northern tethys margin abstract molecular and stable carbon isotope compositions of source specific hydrocarbons have been used to reconstruct palaeoenvironmental conditions during deposition of the middle hettangian to upper sinemurian sediments on the northern epicontinental tethys margin frick swiss jura increasing algal cyanobacterial and phytoplanktonic i e dinoflagellate contributions associated with the 13 c enrichment of cyanobacteria derivatives i e hopanes and monomethylalkanes suggest enhanced primary productivity upsection this is related to the 13 c enrichment of dissolved co 2 in the upper layers and the progressive increase of depth and oxygenation of the water column in the middle hettangian shallow water environments lagoon the occurrence of green sulfur bacteria chlorobiaceae derivatives indicates that the lower part of the water column was strictly anoxic and rich in h 2 s since these bacteria require very low light intensity to grow these euxinic conditions may be extended up to the photic zone allowing for anaerobic photosynthesis light penetration depth is most likely reduced by high productivity and or turbidity in the photic zone in these sediments 13 c depleted hopanoids 39 5 are most likely associated with phototrophic purple sulfur bacteria utilizing isotopically light organic carbon at the base of the aerobic zone these purple sulfur bacteria may have consumed the h 2 s used by chlorobiaceae in the deeper layers and thus sustained the algae and cyanobacteria productivity in the upper layers the 13 c depleted carbonate 13 3 may be partially related to the anaerobic oxidation of the organic matter during bacterial sulfate reduction

evidence for ancient halophiles testing biomarker syngeneity of evaporites from neoproterozoic and cambrian strata molecular fossils from evaporites can provide significant insights into the biotic composition of ancient hypersaline ecosystems however hydrocarbon contamination can mask the true nature of this composition and potentially result in misleading interpretations in this study drill core samples of neoproterozoic and cambrian age dolomite anhydrite and halite from the amadeus basin in central australia contain distinctive and varied hydrocarbon signatures the results are consistent with previous studies of ancient hypersaline settings and include elevated concentrations of heptadecane n c17 docosane n c22 a diverse range of acyclic isoprenoids hopanes and steranes including high concentrations of pregnanes furthermore several samples yielded hydrocarbon signatures with high concentrations of mono and dimethylalkanes relative to n alkanes which is characteristic of many cambrian and precambrian bitumens by quantifying the exterior interior concentration differences of biomarkers in these evaporites considerable insight into the syngeneity of these molecules was obtained in most samples the majority of biomarkers were only detected in the exterior demonstrating that they are contaminants and not indigenous to the evaporites these include biomarkers typically assigned to hypersaline environments demonstrating in this case that their presence is not necessarily an indicator of syngeneity we show that even in combination these molecules can have a wide variety of sources that are not necessarily indigenous to the host rocks nevertheless some neoproterozoic evaporites while also marred by contamination contain demonstrably indigenous biomarkers with equal concentrations on the rock exterior and interior we show that the ability to discern biomarker syngeneity in a complex mix of contaminated and indigenous hydrocarbons requires the need for each compound in every sample to be separately evaluated this study provides an example of how to unravel such a complex series of contamination and obtain more accurate insights into biomarkers of ancient evaporites the approach outlined herein can be readily applied to biomarker studies of other ancient settings

geochemical characterization of the devonian mississippian woodford shale from the mcalister cemetery quarry criner hills uplift ardmore basin oklahoma abstract it has been estimated that technically recoverable reserves from shales in the continental u s are believed to be approximately 24 billion barrels of oil bbo and 750 trillion cubic feet tcf of gas in oklahoma the most important hydrocarbon source rock is the woodford shale proposed to be the source of some 70 of the state s liquid hydrocarbon reserves such a regionally widespread source rock provides potential for both academic study and industrial opportunities in this study representative samples of the woodford shale from the mcalister quarry outcrop have been characterized by a variety of geochemical techniques toc values range from 0 07 to 15 6 wt and based on rock eval pyrolysis most of the samples plot within the type i ii kerogen range with several low toc samples plotting in the type iii kerogen range toc and biomarker parameters suggests that two sections of the upper woodford are immature paleosols having been subaerially exposed due to abrupt episodes of sea level fall during the late devonian evidence for these zones of paleoweathering includes highly depleted toc increased oxygen index oi values loss of n alkanes decreases in the aryl isoprenoid ratio air sesquiterpenoids cheilanthanes hopanoids and decreases in many of the polycyclic aromatic hydrocarbons pahs the values of several paleoenvironmental proxies for samples immediately following the frasnian famennian f f stage extinction boundary within the upper woodford suggests that a large influx of weathered terrigenous material occurred at that time the presence of pyrogenic compounds implies that paleowildfires were widespread throughout the middle and late devonian in the north american midcontinent it is possible that these influxes of weathered terrestrial organic material stimulated algal blooms that led to the anoxic water column conditions often attributed to the f f stage extinction event investigation of the stratigraphic framework of these source rocks assists in evaluating their potential as hydrocarbon producers and or unconventional reservoirs integration of geochemical data adds another powerful dimension to this approach it has been proposed that the woodford shale was deposited during a 2nd order depositional sequence the lower member represented the transgressive systems tract tst the upper member the highstand systems tract hst and the middle member bridging the transition between the two numerous 3rd order parasequences were also identified as being part of the overall 2nd order sequence and could be correlated to the devonian sea level curve the major objectives of the study were while this study focuses locally on the mcalister quarry samples it is also of regional importance the woodford is a prolific source rock throughout the anadarko basin and has been the subject of extensive exploration and production efforts particularly in the past decade with the development of horizontal drilling and hydrofracturing techniques continued investigation of the heterogeneity of the shale will greatly enhance the ability to predict more productive facies within the formation throughout the basin

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

geochemistry of oil in fluid inclusions in a middle proterozoic igneous intrusion implications for the source of hydrocarbons in crystalline rocks abstract the ca 1280 ma dolerite sill within the mesoproterozoic roper group in the roper superbasin australia contains evidence for at least two episodes of hydrocarbon migration represented respectively by solid bitumen with a ketone rich extract and a mixture of a high maturity gas condensate and a lower maturity oil within oil bearing fluid inclusions the ketone isomers are formed by flash pyrolysis of kerogen during the intrusion of the dolerite sill org geochem 21 1994 829 and represent the first and oldest phase of hydrocarbon migration the gas condensate and oil were subsequently trapped as a mixture within fluid inclusions at diagenetic temperatures and pressures of around 110 c and 250 bars significantly after cooling of the sill and likely during the neoproterozoic reactivation of the roper superbasin either 1 these fluids migrated together and mixed in the reservoir or 2 an earlier oil charge was flushed by a later condensate charge and the oil condensate mixture was trapped within single fluid inclusions oil inclusions occur chiefly within albitised zones of labradorite laths within the dolerite matrix and within transcrystalline microfractures cutting vein calcite and rarely vein quartz oil inclusions trapped in the vein calcite are accompanied by hypersaline ca mg brines gas chromatography mass spectrometry of oil extracted from inclusions within the dolerite matrix shows that the oil is non biodegraded and was therefore trapped relatively quickly within the host minerals trace amounts of biomarkers indicate that the inclusion oil is of a biogenic origin and excludes any abiotic processes that are apparent sources of hydrocarbons in many crystalline rocks monomethylalkanes pentacyclic terpanes chiefly comprising hopanes and diahopanes and very low concentrations of steranes and diasteranes indicate input from cyanobacterial organic matter with a minor contribution from eukaryotes the hydrocarbons are likely derived from proterozoic source rocks such as the directly overlying velkerri formation and or the underlying barney creek formation from the mcarthur group the study has implications for the source of hydrocarbons in non sedimentary rocks and suggests that fluid inclusions can be used not only to distinguish between biogenic and abiogenic sources of hydrocarbons but also to provide critical information about the composition of the biomass fluid migration events and conditions under which hydrocarbons in different geological settings are trapped

paleobiology of the mesoproterozoic neoproterozoic transition the sukhaya tunguska formation turukhansk uplift siberia silicified carbonates of the latest mesoproterozoic sukhaya tunguska formation northwestern siberia contain abundant and diverse permineralized microfossils peritidal environments are dominated by microbial mats built by filamentous cyanobacteria comparable to modern species of lyngbya and phormidium in subtidal to lower intertidal settings mat dwelling microbenthos and possible coastal microplankton are abundant in contrast densely woven mat populations with few associated taxa characterize more restricted parts of tidal flats the preservation of vertically oriented sheath bundles and primary fenestrae indicates that in these mats carbonate cementation was commonly penecontemporaneous with mat growth eoentophysalis mats are limited to restricted environments where microlaminated carbonate precipitates formed on or just beneath the sediment surface most microbenthic populations are cyanobacterial although eukaryotic microfossils may occur among the simple spheroidal cells interpreted as coastal plankton protists are more securely represented by large up to 320 micrometers in diameter but poorly preserved acritarchs in basinal facies the sukhaya tunguska assemblage contains 27 species in 18 genera by virtue of their stratigraphic longevity and their close and predictable association with specific paleoenvironmental conditions including substrates proterozoic cyanobacteria support a model of bacterial evolution in which populations adapt rapidly to novel environments and thereafter resist competitive replacement the resulting evolutionary pattern is one of accumulation and stasis rather than the turnover and replacement characteristic of phanerozoic plants and animals

composition and syngeneity of molecular fossils from the 2 78 to 2 45 billion year old mount bruce supergroup pilbara craton western australia shales of very low metamorphic grade from the 2 78 to 2 45 billion year old ga mount bruce supergroup pilbara craton western australia were analyzed for solvent extractable hydrocarbons samples were collected from ten drill cores and two mines in a sampling area centered in the hamersley basin near wittenoom and ranging 200 km to the southeast 100 km to the southwest and 70 km to the northwest almost all analyzed kerogenous sedimentary rocks yielded solvent extractable organic matter concentrations of total saturated hydrocarbons were commonly in the range of 1 to 20 ppm g g rock but reached maximum values of 1000 ppm the abundance of aromatic hydrocarbons was 1 to 30 ppm analysis of the extracts by gas chromatography mass spectrometry gc ms and gc ms metastable reaction monitoring mrm revealed the presence of n alkanes mid and end branched monomethylalkanes cyclohexylalkanes acyclic isopre noids diamondoids tri to pentacyclic terpanes steranes aromatic steroids and polyaromatic hydrocarbons neither plant biomarkers nor hydrocarbon distributions indicative of phanerozoic contamination were de tected the host kerogens of the hydrocarbons were depleted in 13 c by 2 to 21 relative to n alkanes a pattern typical of although more extreme than other precambrian samples acyclic isoprenoids showed carbon isotopic depletion relative to n alkanes and concentrations of 2 methylhopanes were relatively high features rarely observed in the phanerozoic but characteristic of many other precambrian bitumens molecular parameters including sterane and hopane ratios at their apparent thermal maxima condensate like alkane profiles high mono and triaromatic steroid maturity parameters high methyladamantane and methyldiaman tane indices and high methylphenanthrene maturity ratios indicate thermal maturities in the wet gas gener ation zone additionally extracts from shales associated with iron ore deposits at tom price and newman have unusual polyaromatic hydrocarbon patterns indicative of pyrolytic dealkylation the saturated hydrocarbons and biomarkers in bitumens from the fortescue and hamersley groups are characterized as probably syngenetic with their archean host rock based on their typical precambrian molecular and isotopic composition extreme maturities that appear consistent with the thermal history of the host sediments the absence of biomarkers diagnostic of phanerozoic age the absence of younger petroleum source rocks in the basin and the wide geographic distribution of the samples aromatic hydrocarbons detected in shales associated with iron ore deposits at mt tom price and mt whaleback are characterized as clearly archean based on their hypermature composition and covalent bonding to kerogen copyright 2003 elsevier ltd

acoustic emission induced by pore pressure changes in sandstone samples an understanding of microseismicity induced by pore pressure changes in stressed rocks is important for applications in geothermal and hydrocarbon reservoirs as well as for co 2 sequestrations we have studied the triggering mechanisms of microseismicity or acoustic emission in the laboratory as a function of triaxial stress conditions and pore pressure changes in investigating the spatiotemporal distribution of acoustic emission activity in water saturated triaxially stressed flechtingen sandstone samples subjected to changes in pore pressure we assumed that acoustic events were triggered by pore pressure increase to estimate pore pressure changes in the sample we used an analytical solution of the 1d diffusion equation a theoretical analysis of the spatiotemporal distribution suggested that for initially insignificantly stressed samples acoustic events were triggered by the migration of a critical pore pressure level through the sample the critical level was controlled by the applied pore press

fast location of seismicity a migration type approach with application to hydraulic fracturing data we propose a new approach for the location of seismic sources using a technique inspired by gaussian beam migration of three component data this approach requires only the preliminary picking of time intervals around a detected event and is much less sensitive to the picking precision than standard location procedures furthermore this approach is characterized by a high degree of automation the polarization information of three component data is estimated and used to perform initial value ray tracing by weighting the energy of the signal using gaussian beams around these rays the stacking is restricted to physically relevant regions only event locations correspond to regions of maximum energy in the resulting image we have successfully applied the method to synthetic data examples with 20 30 white noise and to real data of a hydraulic fracturing experiment where events with comparatively small magnitudes 0 were recorded

biomarker signatures from neoproterozoic early cambrian oil western india abstract the neoproterozoic early cambrian time is the cradle of multicellular eukaryotic life and thereafter metazoan life started populating the planet biomarkers which record the chronicles of biotic events on earth have been investigated using gas chromatography mass spectrometry from a suite of nine oil samples extracted from oil stained sediments and a crude oil of neoproterozoic early cambrian age from bikaner nagaur basin western india the biomarker distribution is characterized by high concentration of both tricyclic terpanes and pentacyclic hopanes the predominance of c 29 regular sterane over c 27 and c 28 steranes indicates green algal contribution and may imply the prominence and diversification of the same algal group the low pristane phytane ratio and occurrence of substantial quantity of gammacerane monomethyl 2 methyl 2 2 4 8 trimethyltridecyl chroman and 1 1 7 8 tetramethyl 1 2 3 4 tetrahydrophenanthrene are indicative of stratified water column as well as anoxic and enhanced salinity condition of the environment of deposition this paper reports for the first time the presence of methyltrimethyltridecyl chromans mttcs from neoproterozoic early cambrian time putative c 19 norsteranes probably indicative of sponge input are recorded in the studied samples and also reported from other infracambrian oils and sediments normal alkanes n c 17 and n c 18 and isoprenoids pristane and phytane are highly depleted in 13 c the overall biomarker distribution and carbon isotope data of oils from bikaner nagaur basin show similarities with those of other infracambrian oils like huqf oils from oman and baykit high oils from eastern siberia

secular and environmental constraints on the occurrence of dinosterane in sediments abstract the distribution patterns of sedimentary a ring methylated steranes have changed markedly over geological time although dinosterane and its isomer 24 ethyl 4 methylcholestane have been tentatively identified in three proterozoic rock units they are either not detectable or occur in low abundance relative to 3 methyl steranes throughout most of the palaeozoic between permian and middle triassic times 260 220 ma ago 4 methyl sterane abundances in marine sediments increased markedly the presence of dinosterane in some middle triassic marine sediments is contemporaneous with the appearance of fossil cysts of uncontested dinoflagellate affinity 4 methyl steranes including dinosterane or their precursor sterenes and sterols then show a continuous presence often in high abundance in marine sediments from the late triassic through to the present day assemblages of 4 methyl steranes and their precursors but with dinosterane absent or in low relative abundance are often the predominant steroids in lacustrine sediments in the cainozoic dinosterane appears to arise predominantly from marine dinoflagellates and as a consequence is a useful biological marker for mesozoic and cainozoic marine organic matter the isomer 24 ethyl 4 methylcholestane is likely to have multiple origins although its very high abundance in tertiary lacustrine sediments and oils compared to older materials suggests that dinoflagellates could also be the source in these cases

a molecular and isotopic geochemical study of meso to neoproterozoic 1 73 0 85 ga sediments from the jixian section yanshan basin north china abstract this paper systematically describes the molecular and isotopic characteristics of meso to neoproterozoic 1 73 0 85 ga sediments from the jixian section yanshan basin north china a correlation is made between molecular fingerprints and paleoenvironmental and paleontologic data acquired from these strata the agreement between these parameters suggest that the biomarkers preserved in these proterozoic sediments are good indicators of the evolution of the paleoenvironment and early life in the yanshan basin the fact that extended regular isoprenoids c20 were detected in most of the studied samples suggest a sustained lipid input to sedimentary organic matter from halophiles and other possible archaebacteria through meso to neoproterozoic two dehydroabietin isomers i e 18 and 19 norabieta 8 11 13 trienes were unexpectedly present in these samples which provides evidence suggesting that the compounds with abieta structure could be derived from primitive organisms such as algae the stable carbon isotope characteristics of kerogen and coexisting carbonate show a rapid decline in atmospheric co2 concentration from 1 73 to1 58 ga and a stable concentration afterwards the difference c in isotopic composition between carbonate and associated kerogen lies in zonal variations along the stratigraphic sequence which can be attributed to the alternations of marine transgressions and regressions that occurred in the yanshan basin during the proterozoic the carbon isotope relationships between kerogen and alkanes from these strata are consistent with the hypothesis that before 1 4 ga both n alkanes and isoprenoids had been derived mainly from heterotrophic halophiles and other archaebacteria but after that only isoprenoids originated from archaebacteria whereas n alkanes were possibly derived from photosynthetic organisms changes in the source of n alkanes around 1 4 ga may suggest a decline of heterotrophic reworking to primary lipids which can be related to the formation of a quiet shallow water environment of an epicontinental sea at this stage in the yanshan basin

biogeochemistry of the 1640 ma mcarthur river hyc lead zinc ore and host sediments northern territory australia abstract the formation of the mcarthur river lead zinc deposit involves thermogenic or biologic oxidation of sedimentary organic matter the products of which generated a massive stratiform sulfide ore body and secondary carbonate and silica precipitates formed within the sediment pile down the flow pathway and above the reaction zone the fine grained texture of the mineralization indicates that primary ore texture is preserved and coupled with the regional thermal maturity indicate that this deposit is an ideal location to study organic matter signals related to ore formation and the sedimentary environment biomarker data point to a marine environment of deposition and are consistent with data previously collected from the host barney creek formation in the adjacent glyde subbasin an unusual biomarker distribution found in some samples from within two orebody is considered to be related to the presence of sulfide oxidizing bacteria these organisms flourished after turbidite deposition when oxygen in the upper part of the water column was mixed down to the sediment water interface the biomarker data are supported by micropalaeontologic observations from the same samples and are consistent with intermittent oxygenation of the water column to the sediment water interface this observation suggests an extension of the known occurrence of sulfide oxidizing bacteria back in time by 800 million years to 1640 ma

an isotopic biogeochemical study of neoproterozoic and early cambrian sediments from the centralian superbasin australia abstract organic matter from neoproterozoic and early cambrian sediments of the amadeus and officer basins of the centralian superbasin australia has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons these sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the cambrian hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially dominated ocean to the early stages of metazoan radiation in particular carbon isotopic data for n alkyl and isoprenoid lipids presented here and in earlier studies showed a reversal in carbon isotopic ordering between the proterozoic and phanerozoic by comparison with the 13c of kerogen n alkyl lipids from deep water proterozoic sediments were enriched in 13c and appear to be derived mainly from heterotrophs whilst open marine phanerozoic counterparts are 13c depleted and evidently derived mainly from autotrophs data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean possibly aided by the innovation of faecal pellets

the formation of microbial metazoan bioherms and biostromes following the latest permian mass extinction abstract after the latest permian mass extinction event microbial mats filled the ecological niche previously occupied by metazoan reefs resulting in widespread microbialites this study focuses on the lipid biomarker molecular fossil and invertebrate fossil records from neotethyan platform margin sections to understand microbial metazoan bioherm formation here we find that early griesbachian thrombolitic and stromatolitic microbialites from curuk dag turkey and kuh e surmeh iran contain abundant lipid biomarkers representing input from cyanobacteria anoxygenic phototrophic bacteria sulfate reducing bacteria and halophilic archaea the biomarker inventory suggests that the microbialites were constructed by cyanobacteria dominated microbial mats biomarkers of halophilic archaea are interpreted to reflect input from the water column suggesting that the neotethys experienced at least episodically hypersaline conditions we also demonstrate that bacteria possible keratose sponges up to 50 of the carbonate is represented by the possible sponges and microconchids lived synergistically to form microbial metazoan bioherms in the immediate aftermath of the extinction along the western margin of the neotethys abundant fossils of oxygen dependent invertebrates i e microconchids bivalves gastropods brachiopods and ostracods and foraminifers were also found within these bioherms the presence of invertebrates in conjunction with abundant molecular fossils of cyanobacteria indicates an oxygenated water column even though the presence of the biomarker isorenieratane in microbialites may considered as evidence for euxinic conditions in the water column its absence in the background sediments rather points to a source organism belonging to the mat community the new finding of bioherms built in part by metazoans suggests that reef ecosystems underwent a major turnover across the extinction event and shortens the metazoan reef gap to just the uppermost changhsingian during the early triassic therefore reefal ecosystems were able to recover in oxygenated settings since the earliest griesbachian albeit in an impoverished state

biomarker geochemistry of crude oils and lower paleozoic source rocks in the tarim basin western china an oil source rock correlation study abstract in order to select biomarker parameters that have potential to quantitatively distinguish between the cambrian lower ordovician and upper ordovician source rocks in the tarim basin with a total organic carbon content 0 5 42 lower paleozoic shale samples were collected from a number of wells and outcrops in the tarim basin northwestern china the biomarkers in the extracts of the source rocks were analyzed by gas chromatography mass spectrometry the results show that c23 and c30 were dominant in the tricyclic terpanes and pentacyclic triterpanes respectively and c27 and c29 were both dominant in c27 29 steranes of the source rock samples the distribution of n alkanes isoprenoids and terpanes indicate that the source rock samples have been slightly to moderately biodegraded and they originated from a reducing depositional environment with considerable marine algal input in comparatively upper ordovician source rock samples presented lower values of c28 c29 regular steranes and higher values of c29 20s 20s 20r and c29 abnormally lower values of c29 20s 20s 20r and c29 were observed in the cambrian lower ordovician strata the set of data in this study show that homohopane index including c31homohopane c30hopane c31 35homohopanes c30hopane and the ratios related to the triaromatic steroids including c26 20s c28 20s tas c27 20r c28 20r c26 20r c27 20s c28 20s and c28 c26 c27 tas could serve as potential biomarker parameters to distinguish between the two groups of source rocks in the tarim basin the values of those parameters in above order in cambrian lower ordovician source rocks were 0 3 0 5 0 85 and 0 8 1 9 1 2 respectively the correlation between the source rock samples and 19 oils obtained from the tadong tabei and tazhong uplifts in the tarim basin show that most of the oils in tabei uplift are probably from upper ordovician source rocks the oils in tadong uplift are more likely from cambrian lower ordovician source rocks and the tazhong uplift is more like a mixed oil region with oils from both of the two groups of source rocks

finite difference modeling of faults and fractures for the purposes of seismic propagation a slip fault may be regarded as a surface across which the displacement caused by a seismic wave is discontinuous while the stress traction remains continuous the simplest assumption is that this slip and the stress traction are linearly related such a linear slip interface condition is easily modeled when the fault is parallel to the finite difference grid but is more difficult to do for arbitrary nonplanar fault surfaces to handle such situations we introduce equivalent medium theory to model material behavior in the cells of the finite difference grid intersected by the fault virtually identical results were obtained from modeling the fault by 1 an explicit slip interface condition fault parallel to the grid and 2 using the equivalent medium theory when the finite difference grid was rotated relative to the fault and receiver array no additional computation time is needed except for the preprocessing required to find the relevant cells and their associated moduli the formulation is sufficiently general to include faults in and between arbitrary anisotropic materials with slip properties that vary as a function of position

contrasting sterane signatures in neoproterozoic marine rocks of australia before and after the acraman asteroid impact abstract organic matter preserved in marine mudstones from three late neoproterozoic depocentres the officer and amadeus basins and the adelaide fold belt was examined using standard microscopic and geochemical methods including gas chromatography mass spectrometry gc ms total organic carbon toc contents of these sediments are typically low

modification of the petroleum system concept origins of alkanes and isoprenoids in crude oils kerogen the source material for petroleum can have a long history of alteration and diagenesis before crude oil forms a common assumption is that the bulk composition of the expressed oil reflects so much of these progressive alterations that most of the primary biological information of the original fixed carbon has been lost exceptions are trace constituents the biomarkers that comprise only a fraction of the organic material in most pristine crude oils analysis of the alkane acyclic isoprenoid fraction of a large number of crude oils and rock extracts from the timan pechora basin russia suggest that this fraction the main constituent of most crude oils is a direct product of liquefaction of biological debris that was preserved essentially unaltered to the point of oil generation therefore the primary biological provenance of this fraction is preserved in the oil fraction a set of gas chromatographic analyses of 242 crude oils as well as 83 solvent extracts from upper to middle paleozoic putative source rocks from the timan pechora basin russia were analyzed by a multivariate data analytical procedure new to organic geochemistry the distributions of n alkanes and acyclic isoprenoids 24 in all in the 325 samples could be reproduced by linear combinations of six end member compositions attributed to distinct biological inputs four of the six are assigned to primary producers waxes from higher plants cyanobacteria microalgae and the microorganism gloeocapsomorpha prisca these end members account for most of the n alkanes and acyclic isoprenoids in our samples the other two represent the products of secondary bacterial alteration of primary organics during sedimentation and low level bacterial alteration in the reservoir biodegradation each end member is composed of a spectrum of analytes whose abundances are related to one another by fixed ratios we surmise that each primary end member represents the breakdown of a resistant biopolymer that forms cell walls and partitions of a given biological group the n alkanes and acyclic isoprenoids in crude oils represent the weighted signatures of their various ancestors i e their primary organic inputs if the precursors of most oils are the products of a small set of chemically simple biopolymers then many of our assumptions concerning the importance of total organic carbon and the nature of the oil window must be reexamined

investigation of injection induced seismicity using a coupled fluid flow and rate state friction model we describe a numerical investigation of seismicity induced by injection into a single isolated fracture injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems egs during which water is injected into fractured low permeability rock triggering slip on preexisting large scale fracture zones a model was developed and used that couples 1 fluid flow 2 rate and state friction and 3 mechanical stress interaction between fracture elements based on the results of this model we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation which we refer to as the sequential stimulation ss mechanism if the ss mechanism is realistic it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity we investigated the effect of injection pressure on induced seismicity for injection at constant pressure there was not a signifi

polymeric substances and biofilms as biomarkers in terrestrial materials implications for extraterrestrial samples organic polymeric substances are a fundamental component of microbial biofilms microorganisms especially bacteria secrete extracellular polymeric substances eps to form slime layers in which they reproduce in the sedimentary environment biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components they are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps biofilms are almost ubiquitous wherever there is an interface and moisture liquid liquid liquid solid liquid gas solid gas in sedimentary rocks they are commonly recognized as stromatolites we also discuss the distinction between bacterial biofilms and prebiotic films the eps and cell components of the microbial biofilms contain many cation chelation sites which are implicated in the mineralization of the films eps biofilms and their related components thus have strong preservation potential in the rock record fossilized microbial polymeric substances fps and biofilms appear to retain the same morphological characteristics as the unfossilized material and have been recognized in rock formations dating back to the early archaean 3 5 b y we describe fps and biofilms from hot spring deep sea volcanic lake and shallow marine littoral environments ranging up to 3 5 b y in age fps and biofilms are more commonly observed than fossil bacteria themselves especially in the older part of the terrestrial record the widespread distribution of microbial biofilms and their great survival potential makes their fossilized remains a useful biomarker as a proxy for life with obvious application to the search for life in extraterrestrial materials

tricyclic terpanes in precambrian bituminous sandstone from the eastern yanshan region north china a bituminous sandstone at the base of the xiamaling formation precambrian is a fossil oil pool which was thermally altered into reservoir bitumen 760 ma ago this reservoir bitumen was extracted fractionated and analyzed for biomarkers a novel series of extended tricyclic terpanes c18 c23 with a 13 n alkyl side chain configuration was identified by co injection of two standards c18 c20 and gc ms analysis some bicyclic sesquiterpanes c18 norditerpanes regular extended tricyclic terpanes c18 c24 no c22 and alkylcyclohexanes were also detected the source of the organic matter its alteration in the sandstone reservoir and the origin of its novel tricyclic terpanes are all inferred to be microbial

oil preserved in fluid inclusions in archaean sandstones oil is generally thought to be geologically young as it is thermodynamically unstable when subjected to elevated temperatures over long periods in open systems1 2 indeed almost all petroleum production comes from rocks younger than 400 million years ref 3 although the oldest known oil occurs in rocks 1 650 myr old4 suitable source rocks were abundant in older geological successions5 and circumstantial evidence suggests that some of these generated hydrocarbons early in their history6 here we report the discovery of oil preserved in fluid inclusions in sandstones dating back 3 000 myr most inclusions lie within healed microfractures confined to individual detrital quartz grains indicating that their oil was emplaced before archaean or palaeoproterozoic metamorphism sealed all voids and thus came from older in some cases archaean sources the fluid inclusions apparently acted as inert pressure vessels that protected the oil from subsequent degradation by circulating fluids and mineral catalysts because of its great age this oil can potentially yield valuable information about the size and diversity of the early biosphere particularly if it contains molecular fossils biomarkers of the primordial organisms from which it was derived

structure and distribution of branched aliphatic alkanes with quaternary carbon atoms in cenomanian and turonian black shales of pasquia hills saskatchewan canada abstract twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms baqcs c14 c33 range are present in the extractable organic matter of cenomanian and turonian black shales of pasquia hills saskatchewan canada five of these pseudohomologous series are also observed in a holocene sample from the russian arctic three of the pseudohomologous series were identified by kenig et al pnas 100 2003 12554 12558 as 3 3 and 5 5 diethylalkanes deas and 2 2 dimethylalkanes dmas the nine other pseudohomologous series of baqcs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3 3 dimethylalkanes dmas 3 ethyl 3 methyl and 5 ethyl 5 methylalkanes 9 9 7 7 and 6 6 diethylalkanes deas 3 3 3 3 and 5 5 5 5 tetraethylalkanes and 5 butyl 5 ethylalkanes pseudohomologous series of branched alkanes with tertiary carbon atoms such as monomethyl and monoethylalkanes are also present in the same carbon number range all these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers clearly indicating a biosynthetic origin baqcs such as 5 5 deas 3 3 deas and 3 ethyl 3 methylalkanes seem to be widespread in sediments and sedimentary rocks ranging from modern to 2 1 billion years a xenobiotic source for baqcs can be excluded at this point baqcs seem to have a very low biodegradability in part explaining their widespread occurrence in ancient sediments

marine biodiversification in response to evolving phytoplankton stoichiometry abstract diversification of the marine biosphere is intimately linked to the evolution of the biogeochemical cycles of carbon nutrients and primary productivity a meta analysis of the ratio of carbon to phosphorus buried in sedimentary rocks during the past 3 billion years indicates that both food quantity and critically food quality increased through time as a result of the evolving stoichiometry nutrient content of eukaryotic phytoplankton evolving food quantity and quality was primarily a function of broad tectonic cycles that influenced not just carbon burial but also nutrient availability and primary productivity increasing nutrient availability during the middle to late proterozoic culminated in the production of food phytoplankton biomass and fresh dead organic matter with c p redfield ratios sufficient to finally promote geologically rapid biodiversification during the proterozoic phanerozoic transition this resulted in further massive nutrient sequestration into biomass that triggered positive feedback via nutrient recycling bioturbation mesozooplankton grazing on phytoplankton productivity increasing rates and depths of bioturbation through the phanerozoic suggest that nutrient recycling continued to increase increasing bioturbation and nutrient cycling appear to have been necessary to sustain the primary productivity and energetics biomass metabolic rates and physical activity such as predation of the marine biosphere because of the geologically slow input of macronutrients like phosphorus from land and the continued sequestration of nutrients into marine and terrestrial biomass

petroleum reservoir characterization using downhole microseismic monitoring imaging of microseismic data is the process by which we use information about the source locations timing and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir a few key projects were instrumental in the development of downhole microseismic imaging most recent microseismic projects involve imaging hydraulic fracture stimulations which has grown into a widespread fracture diagnostic technology this growth in the application of the technology is attributed to the success of imaging the fracture complexity of the barnett shale in the fort worth basin texas and the commercial value of the information obtained to improvecompletions and ultimately production in the field the use of commercial imaging in the barnett is traced back to earlier investigations to prove the technology with the cotton valley imaging project and earlier experiments at the m site in the piceance

micro ablation a new technique to remove drilling fluids and other contaminants from fragmented and fissile rock material abstract we present a new methodology micro ablation that can remove sub millimeter layers of contaminated surfaces from pieces of sedimentary rock that are too small or irregularly shaped to be trimmed using a saw recognizing traces of contaminants is crucial when analyzing samples with low indigenous bitumen content or interpreting trace biomarker components in hydrocarbon rich samples quantitative analysis of individual hydrocarbons in the interior and exterior of these rock fragments can then help to distinguish between autochthonous and allochthonous hydrocarbons

fractured reservoirs an analysis of coupled elastodynamic and permeability changes from pore pressure variation equivalent medium theories can describe the elastic compliance and fluid permeability tensors of a layer containing closely spaced parallel fractures embedded in an isotropic background we propose a relationship between effective stress background or lithostatic stress minus pore pressure and both permeability and elastic constants this relationship uses an exponential decay function that captures the expected asymptotic behavior i e low effective stress gives high elastic compliance and high fluid permeability while high effective stress gives low elastic compliance and low fluid permeability the exponential decay constants are estimated for physically realistic conditions with relationships coupling pore pressure to permeability and elastic constants we are able to couple hydromechanical and elastodynamic modeling codes a specific coupled simulation is demonstrated where fluid injection in a fractured reservoir causes spatially and temporally varying changes in pore pressure permeability and elastic constants these elastic constants are used in a 3d finite difference code to demonstrate time lapse seismic monitoring with different acquisition geometries changes in amplitude and traveltime are seen in surface seismic p to s reflections as a function of offset and azimuth as well as in vertical seismic profile p to s reflections and in crosswell converted s waves these observed changes in the seismic response demonstrate seismic monitoring of fluid injection in the fractured reservoir

abundance and geochemical significance of c2n dialkylalkanes and highly branched c3n alkanes in diverse meso and neoproterozoic sediments several series of branched alkanes with quaternary carbon centers have been detected by gc ms in the saturated hydrocarbon fractions of neoproterozoic sedimentary rocks associated with fossilised microbial mats officer basin south australia and of shallow water carbonates spitsbergen east greenland and baffin island canada a series of 5 5 diethylalkanes was predominant in most of these sediments and was typically accompanied by related series in lower abundance which based on mass spectral characteristics are tentatively assigned as 6 6 diethylalkanes 5 butyl 5 ethylalkanes and 6 butyl 6 ethylalkanes each series displays strong odd or even carbon number preferences several of the sediments contained additional series of structurally undefined c3n alkanes notable for very negative retention time factors which become more negative with increasing molecular weight indicating that branching increases with each c3 addition the strongly sequential carbon preference of the respective c2n and c3n branched alkane series and a predominantly light 13c signature of the 5 5 diethylalkanes cf co occurring n alkanes are consistent with an origin from organisms with a distinct physiology and or carbon source the relatively wide occurrence and high abundance of these branched alkanes in proterozoic sediments containing benthic microbial mats suggests a relationship with specific paleoenvironmental conditions for example strong water column redox gradients that may have been more prevalent than in the phanerozoic