early diagenetic transformation of higher plant triterpenoids in deep sea sediments from baffin bay abstract a sediment sequence of early miocene to holocene from ocean drilling program site 645 in central baffin bay was found to contain abundant triterpenoids of higher plant origin including monodesmethyl derivatives and other oxidative degradation products 24 nor triterpenoids of the oleanene ursene and lupane series were found in the nonaromatic hydrocarbon and alcohol fractions of the sediment extracts other diagenetic transformation products included 24 28 dinor olean 17 ene and 24 nor urs 12 en 1 1 one as well as their tentatively identified des a counterparts the identification of these novel degradation products was confirmed by synthesis of a suite of reference compounds the simple reaction sequence applied to obtain 24 nor urs 12 ene from 3 acetoxyurs 12 en 24 oic acid is likely to happen in a similar manner during early diagenesis of organic matter in nature these results have implications for the understanding of the diagenetic reaction sequence leading to the formation of other demethylated triterpenoids of terrigenous origin e g 24 28 dinor lupanes 28 30 dinor 17 hopane is sometimes the dominant hydrocarbon in the most deeply buried samples its co occurrence with higher plant triterpenoids and the low abundance of other regular hopanoids is not considered an indication however that 28 30 dinor 17 hopane is derived from a higher plant precursor molecule it is suggested that two independent sedimentary processes are responsible for the presence of the two types of demethylated triterpenoids observed in baffin bay sediments

organic geochemistry of the sedimentary basins of new zealand part iv a biomarker study of the petroleum seepage and some well core bitumens from the geothermal region of ngawha springs abstract the crude oil which seeps to the surface at ngawha springs was mature but the oil biomarker parameters indicated that its unlocated source rocks had not reached the peak of oil generation the oil had a mixed marine and terrigenous origin and had not undergone secondary migration except to the surface the oil was distinguished from diesel oil which might have polluted thermal springs in the area by several parameters specifically those which relate to the source of an oil the seep oil was concluded to have arisen from accelerated diagenesis of organic material in tertiary rocks which cap the geothermal system at ngawha a surface asphalt which had formed from the oil was lightly degraded it had absorbed hydrocarbons from immature organic matter near the surface and its hydrocarbon composition was characterised by an abundance of a 22r homohopane this triterpane was also present in rock bitumens together with appreciable proportions of hopanes bitumens extracted from potential source rocks were largely of terrigenous origin they had characteristics of sedimentary organic material which had not reached the oil generation threshold these rocks did not prove to be the source of the seep oil one of the bitumens contained a c 28 triterpane the presence of which suggested that the sedimentary organic material had been reworked by bacteria such a view was consistent with the geological history of ngawha springs

comparison of covalently bound aliphatic biomarkers released via hydropyrolysis with their solvent extractable counterparts for a suite of kimmeridge clays abstract fixed bed hydropyrolysis at pressures greater than 10 mpa has the unique ability to maximise the yields of covalently bound alkanes without adversely affecting their stereochemistries in order to compare the yields and compositions of the solvent extractable and kerogen bound hopanes and steranes for source rocks of varying maturity six kimmeridge clay samples jurassic type ii kerogen have been subjected to successive dichloromethane extraction and hydropyrolysis the ratios of free to kerogen bound aliphatic biomarkers increase markedly at relatively low vitrinite reflectance ca 0 45 0 50 with large reductions occurring in the concentrations of bound hopanes and steranes however the fact that the total concentrations of observable hopanes and steranes i e free plus kerogen bound do not decrease until the vitrinite reflectance is greater than ca 0 50 provides evidence that neither oil migration nor aromatisation has begun to occur to a significant extent below this maturity level to the authors knowledge this represents the first study to observe a systematic change in epimer ratios with increasing maturity for hopanes and steranes covalently bound in kerogens indeed the kerogen bound hopanes and steranes undergo the same epimerisation reaction pathways as their free counterparts in the bitumen but they are generally less mature in terms of isomerisation at both ring and side chain chiral centres indeed the range of the moretane hopane index for the hydropyrolysis oils is much larger than that for the bitumens ca 5 times indicating a much greater sensitivity to relatively small changes in maturity the covalently bound hopanes and steranes released via hydropyrolysis have enabled the maturity of a contaminated core from the north sea central graben maturity to be assessed and have showed that it is compatible with the kimmeridge formation

biological marker distribution in coexisting kerogen bitumen and asphaltenes in monterey formation diatomite california organic rich 18 2 monterey formation diatomite from california was studied the organic matter consist of 94 bitumen and 6 kerogen biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter while 17 alpha h 18 alpha h 21 alpha h 28 30 bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes it was not detected in the pyrolysates of the kerogen a c40 isoprenoid with head to head linkage however was present in pyrolysates of both kerogen and asphaltenes but not in the bitumen from the diatomite the maturation level of the bitumen based on the extent of isomerization of steranes and hopanes was that of a mature oil whereas the pyrolysate from the kerogen showed a considerably lower maturation level these relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock we consider the possibility however that some of the 28 30 bisnorhopane rich monterey formation oils have not been generated through thermal degradation of kerogen but have been expelled from the source rock at an early stage of diagenesis

a geochemical reconstruction of oil generation in the barrow sub basin of western australia abstract a suite of crude oils and petroleum source rock extracts from the barrow sub basin of western australia have been analysed for biological marker compounds by capillary gc ms and for volatile hydrocarbons by whole oil capillary gc these analyses were used to calculate values for twenty three biomarker parameters in order to assess aspects of source type maturity migration and biodegradation of the hydrocarbons the crude oils had a source in the upper jurassic dingo claystone formation these hydrocarbons accumulated in the reservoir sands and in some cases were biodegraded several accumulation and biodegradation episodes have been recognised while the basin continued to subside which resulted in a suite of oils showing marked differences in composition

gc ms identification of biomarkers in road asphalts and in their parent crude oils relationships between crude oil maturity and asphalt reactivity towards weathering abstract asphalt cements vacuum residues of petroleum used as binders for road construction can undergo weathering phenomena or natural oxidation to various degrees depending on their chemical structures and on their origin the first aim of this study was to determine the characteristics of the source rocks generating the parent crude oils the second aim was to correlate the chemical structures of recovered asphalt cements to the genesis data of their parent crude oils in order to predict their sensitivity towards weathering towards these ends saturated fractions of sixteen asphalt cements and their parent crude oils have been analysed by gc ms sir many linear branched and naphthenic compounds from the saturated hydrocarbon fraction have been identified hopanes m z 191 norhopanes m z 177 163 and steranes m z 217 and 218 have been selected to characterize original and weathered asphalts as well as their parent crude oils using geochemical indices t s t s t m c29 steranes etc aliphatic structures of the asphalts and corresponding crude oils could be differentiated through principal component analysis pca the selected variables involve geochemical indices and asphalt rheological characteristics results are in good agreement with the classification obtained from ftir indices linear alkanes branched aliphatics aliphatics versus aromatic structures etc moreover good correlations in geochemical indices have been found between asphalts and their parent crude oils finally it was also possible to predict some rheological properties e g stiffness at low temperature using a multilinear regression which involves geochemical indices of parent crude oils before any physical transformation distillation etc and ftir indices of corresponding asphalt cements

geochemical characterization of solid bitumen in the chesterian mississippian sandstone reservoir of the hitch field southwest kansas solid bitumen was identified within the mississippian chester sandstone reservoir in the hitch field southwest kansas the adjacent etzold field has similar reservoir properties but lacks solid bitumen although the hitch and etzold fields were thought to be in pressure communication and have common source rocks hitch and etzold crude oils and core extracts were characterized geochemically to gain a better understanding of the reservoir filling history and geological and geochemical controls on solid bitumen formation in the hitch reservoir based on a variety of geochemical characteristics we propose that the hitch and etzold oils are mixtures derived from ordovician and late devonian early mississippian woodford shale source rocks the solid bitumen in the hitch reservoir probably results from mixing of oils having different geochemical compositions which filled the reservoir over an extended period no evidence of severe biodegradation or thermal alteration is observed a reservoir filling scenario is proposed in an effort to explain why the hitch oils are geochemically more heterogeneous than etzold oils furthermore gas de asphalting and regional pressure drops as a result of post laramide orogeny may have contributed to a phase change in the reservoir fluid and deposition of solid materials by disturbance of thermodynamic equilibrium the major significance of this study is related to improving our knowledge on the occurrence of the presence of solid bitumen in reservoirs that can introduce barriers into the reservoir complicating waterflood operations and leading to erroneous oil in place calculations and subsequently lower than expected oil recovery

hydrocarbon compositions of bitumens associated with igneous intrusions and hydrothermal deposits in britain abstract the possible modes of formation and thermal history of various palaeozoic and precambrian bitumens associated with hydrothermal deposits and igneous intrusions have been evaluated by molecular organic geochemistry the aliphatic hydrocarbon compositions of extracts of such bitumens from a number of localities have been determined by gc and gc ms procedures the stereochemical configurations and low abundance of their steranes hopanes and degraded hopanes resemble those characteristic of various mature weathered and biodegraded crude oils comparisons of the distributions of tricyclic terpanes hopanes demethylated hopanes 8 14 secohopanes and steranes reveals a close correspondence between all the bitumens from the welsh borderlands correlations suggestive of a common source rock the occurrence and abundance of 8 14 secohopanes in the bitumens is consistent with their generation as thermal degradation products of hopanes a similar mode of formation is proposed for the other unidentified secohopane in a bitumen from the midland valley of scotland overall the hydrocarbon compositions of the bitumens are compatible with their ultimate biological origins and subsequent thermal experience

lower tertiary and upper cretaceous source rocks in louisiana and mississippi implications to gulf of mexico crude oil the lower tertiary sparta formation wilcox group and the midway group in southern louisiana include organic rich source facies that generate crude oil at relatively high thermal maturities the wilcox group is an important source of wilcox crude oil and regional kerogen variations explain two crude oil subfamilies wilcox crude oils in downdip areas of southern louisiana migrated short distances but long range lateral migration about 150 km best explains wilcox crude oils far updip from mature source rocks crude oils in oligocene and younger reservoirs in southern louisiana migrated vertically from deep lower tertiary source rocks some crude oils in upper cretaceous tuscaloosa reservoirs were emplaced by long range lateral migration from tuscaloosa source rocks g ven little evidence of upper tertiary source rocks and the overmaturity problems of mesozoic source rocks most crude oils in upper tertiary and pleistocene reservoirs of the gulf continental shelf are best explained by vertical migration from deep lower tertiary source rocks even so it is simplistic to assume an exclusive lower tertiary origin many tertiary and pleistocene crude oils of this study probably include an overprint of high maturity hydrocarbons from mesozoic sources

possible origin of 25 norhopanes in jurassic organic poor mudstones from the northern qaidam basin nw china 25 norhopanes have been found for the first time in jurassic organic poor mudstones in the northern qaidam basin northwestern china the carbon number distribution in the m z 177 mass chromatograms does not consist of the full suite from c 28 to c 34 although this is a well known feature generally ascribed to 25 norhopanes in source rocks the ranges of c 29 25 norhopane c 29 30 norhopane and c 29 25 norhopane c 30 hopane are 0 07 0 08 and 0 03 0 04 respectively these values are within the recognized global background level for 25 norhopane concentrations in source rocks blanc p l connan j 1992 origin and occurrence of 25 norhopanes a statistical study organic geochemistry 18 813 828 here we provide additional evidence for the existence of 25 norhopanes in mudstones source rocks they were not detected in organic rich mudstones implying that the accumulation or diagenesis of the organic poor mudstones may have provided the right conditions for the formation of 25 norhopanes the depositional setting is suggested to be anaerobic and distant from the lacustrine lakeshore based on biomarker and petrological features and previous sedimentary environment studies in such a nutrient limited environment with relatively low source organic matter microbial reworking of biomass occurred microbial consortia scavenged the existing hopanoids contributing biomass and releasing nutrients to perform 25 norhopane forming reactions

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

families of miocene monterey crude oil seep and tarball samples coastal california biomarker and stable carbon isotope ratios were used to infer the age lithology organic matter input and depositional environment of the source rocks for 388 samples of produced crude oil seep oil and tarballs to better assess their origins and distributions in coastal california these samples were used to construct a chemometric multivariate statistical decision tree to classify 288 additional samples the results identify three tribes of 13c rich oil samples inferred to originate from thermally mature equivalents of the clayey siliceous carbonaceous marl and lower calcareous siliceous members of the monterey formation at naples beach near santa barbara an attempt to correlate these families to rock extracts from these members in the nearby cost continental offshore stratigraphic test ocs cal 78 164 well failed at least in part because the rocks are thermally immature geochemical similarities among the oil tribes and their widespread distribution support the prograding margin model or the banktop slope basin model instead of the ridge and basin model for the deposition of the monterey formation tribe 1 contains four oil families having geochemical traits of clay rich marine shale source rock deposited under suboxic conditions with substantial higher plant input tribe 2 contains four oil families with traits intermediate between tribes 1 and 3 except for abundant 28 30 bisnorhopane indicating suboxic to anoxic marine marl source rock with hemipelagic input tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher plant input tribes 1 and 2 occur mainly south of point conception in paleogeographic settings where deep burial of the monterey source rock favored petroleum generation from all three members or their equivalents in this area oil from the clayey siliceous and carbonaceous marl members tribes 1 and 2 may overwhelm that from the lower calcareous siliceous member tribe 3 because the latter is thinner and less oil prone than the overlying members tribe 3 occurs mainly north of point conception where shallow burial caused preferential generation from the underlying lower calcareous siliceous member or another unit with similar characteristics in a test of the decision tree 10 tarball samples collected from beaches in monterey and san mateo counties in early 2007 were found to originate from natural seeps representing different organofacies of monterey formation source rock instead from one anthropogenic pollution event the seeps apparently became more active because of increased storm activity

on the nonlinear versus linearized lower boundary conditions for topographically forced stationary long waves abstract for quasi geostrophic stationary long waves forced by topography the nonlinear lower boundary condition is derived in terms of the geopotential height and compared with the linearized version the common practice of replacing terms describing the flow over and around a mountain by upstream zonal flow over the mountain and evaluating the resulting condition at sea level is found to be a good approximation for the cases considered and does not need to be modified as sometimes suggested specifically it is found that this approximation does not affect for most cases the lower boundary condition expressed in terms of the geopotential height provided that the stationary wave is not near resonance at resonance the eddy advection terms may become important for large amplitude waves when dissipation and surface diabatic heating are taken into account

organic geochemistry of dsdp site 467 offshore california middle miocene to lower pliocene strata abstract results of the analyses of twenty three samples from the middle miocene to lower pliocene strata from dsdp site 467 offshore california are presented the analyses were performed with the aim of determining the origin of the organic matter the stratigraphic section s hydrocarbon generation potential and extent of organic diagenesis organic carbon contents are an order of magnitude greater than those typically found in deep sea sediments suggesting an anoxic depositional environment and elevated levels of primary productivity hydrocarbon generation potentials are above average for most samples the results of elemental analyses indicate that the kerogens are primarily composed of type ii organic matter and are thermally immature analysis of the bitumen fractions confirms that the samples are immature in cores from 541 to 614 meters the gas chromatograms of the c 15 non aromatic hydrocarbon fractions are dominated by a single peak which was identified as 17 h 18 h 21 h 28 30 bisnorhopane this interval is the same area in which the highest degrees of anoxia are observed as reflected by the lowest pristane phytane ratios this correlation may have some implications with regard to the origin of the bisnorhopane and its possible use as an indicator of anoxic depositional conditions within thermally immature sediments

the use of bisnorhopane as a stratigraphic marker in the oseberg back basin north viking graben norwegian north sea abstract this paper discusses the occurrence of 28 30 dinor 17 18 21 hopane bisnorhopane in stratigraphically fairly well preserved viking group sections from wells in local depressions in the north viking graben area the results show the presence of high relative amounts of bisnorhopane in the syn rift sections whilst the post rift sections contain little or no bisnorhopane since most exploration wells are drilled on structural highs primarily penetrating the post rift draupne this may explain why many analyzed source rock sections in this area contain little bisnorhopane as a correlation of draupne sections using the vertical relative bisnorhopane distributions it is suggested to be a potential stratigraphic marker for the area indicating the presence of syn rift draupne sediments the relative bisnorhopane amounts follow a logarithmic reduction with depth and thermal maturity the bisnorhopane signal is nearly extinguished at 3700 m depth at a maturity of r o 0 9 1 0

short term biomarker variability in the monterey formation santa maria basin abstract forty eight samples of a 370 ft miocene monterey formation core from the union leroy 51 18 well santa maria basin california are examined for source rock potential and molecular distributions total organic carbon content rock eval pyrolytic yield vitrinite reflectance and distribution of regular steranes tricyclic and pentacyclic terpanes and aromatic steroids are measured the present day temperature range through the sampled interval is estimated to be less than 5 c maturity differences among samples are negligible source rock potential and molecular distribution differences are considered to arise entirely from the effects of source input diagenesis including lithologic effects and migration the sampled section is comprised of siliceous and phosphatic carbonate lithofacies and covariances between geochemical parameters source potential and biomarker distribution and lithofacies are recognized several molecular parameters change systematically with depth lithology including ethylcholestane ratios and c 20 and c 22 sterane and hopane epimer ratios the siliceous lithofacies possesses higher moretane hopane tricyclic pentacyclic terpane and sterane terpane ratios and lower mono mono tri aromatic steroid ratios bisnorhopane hopane ratios are up to 40 times higher in the phosphatic carbonate lithofacies than in the siliceous lithofacies increased relative concentrations of aromatic steroids are attributed to sulfur sterol reactions during very early diagenesis whereas increased relative bisnorhopane amounts are considered to result from massive input of specific anaerobic biota although kerogen elemental ratios change abruptly at the lithofacies boundary molecular distributions within the extractable organic matter change gradually beginning about 30 ft 9m above this interface this gradual change is tentatively attributed to upward migration of hydrocarbons originating in the phosphatic carbonate lithofacies probably through fractures within the lower part of the siliceous lithofacies interval

the petroleum geochemistry of canadian beaufort tertiary non marine oils abstract molecular isotopic and elemental data for a set of 28 paleogene and 3 cretaceous oils from the mackenzie delta and offshore canadian beaufort sea have been evaluated the depositional environment and organic matter characteristics of the source units for these oils have been predicted the paleogene oils of the canadian beaufort are molecularly distinctive and clearly contain a major land plant component oleanane and the 17 h and 17 h 24 28 bisnorlupanes are present as well as the following compound types 24 norlupanes and possibly higher homologues de a lupane noroleanenes norursene dehydroabietane 28 30 bisnorhopanes several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils the cretaceous oils are separately sourced from the paleogene oils the latter oils comprise two distinct land plant derived genetic families distinguished by the presence absence of 24 28 bisnorlupanes 24 norursene 24 norlupane and 24 noroleanenes the kugmallit richards family contains each of these compound types and is considered to originate from the eocene richards formation in contrast lupanoids and noroleanenes are absent in oils of the reindeer moose channel family the occurrence of 28 30 bisnorhopane and or oleanane in these oils suggests a paleocene origin although these source rock predictions are supported by the available data they must be considered speculative until detailed molecular isotopic and elemental compositional data are available regionally for potential source rocks of the eocene and paleocene source units in the canadian beaufort

compound specific isotope analysis as a tool for characterizing mixed oils an example from the west of shetlands area abstract the origin of an oil accumulation can be difficult to establish when the oil is a mixture from multiple sources or when multiple episodes of charging are involved in this study oils from the clair field west of shetland islands which are mixtures of nonbiodegraded oil added to biodegraded oil are characterized by comparing the carbon isotope ratios of the gasoline range hydrocarbons grh of the oil to the grh released from the pyrolysis of the asphaltenes in the oil this comparison allows characterization of the source of the first versus the second pulse of oil into the reservoir information useful in assessing the source potential of the basin

reworked triterpenoid and steroid hydrocarbons in a recent sediment abstract the distributions of steranes pentacyclic triterpanes and aromatic steroid hydrocarbons in core sections of a recent intertidal sediment bridgwater bay severn estuary u k have been examined by gas chromatography mass spectrometry depending on sample depth the distributions are explicable in terms of 1 i a reworked origin for these compounds from a geological source probably as a result of erosion of nearby organic rich sediments of lower liassic age or 2 ii a dual origin from both i and a more mature source probably an anthropogenic input of petroleum origin these results show that not all of these steroid and triterpenoid hydrocarbons in surface sediments necessarily result from fossil fuel pollution they indicate also that attention should be paid to the possibility of contributions from reworked components when using the distributions of these compounds in geochemical studies of sediments that are low in extractable organic matter

internal tide dissipation mixing and vertical nitrate flux at the shelf edge of ne new zealand an internal tide on the ne shelf of new zealand was observed with a combination of moored temperature loggers and current meters and vertical profiling with a microstructure probe internal tide energy flux across the shelf edge was calculated to be 400 w m with considerable variability driven by the passage of a storm through the region energy associated with the internal tide was significantly greater than the energy of the barotropic tide or of inertial shear dissipation of the internal tide calculated from the energy loss between two of the moorings was estimated to be 15 10 mw m 2 the associated vertical eddy diffusivity was 4 3 x 10 4 m 2 s 1 the microstructure observations indicated internal tide driven vertical diffusivities at the nitracline of 7 x 10 4 m 2 s 1 the observations of vertical eddy diffusivities are combined with measurements of the vertical nitrate gradient to suggest that mixing driven by the internal tide is the dominant mechanism for driving diapycnal nutrient supply during summer the calculated flux of about 12 mmol n m 2 d 1 into the photic zone is suggested to drive significant new subsurface production throughout the summer amounting to a possible contribution to annual new production on the shelf of 100 g c m 2

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

effects of thermal maturity on biomarker distributions in gondwana coals from the satpura and damodar valley basins india abstract organic geochemistry of gondwana coals especially the distribution of molecular fossils or biomarkers is not well constrained throughout the world in this study we have therefore evaluated biomarker signatures along with bulk organic matter and petrographic characteristics in coal samples collected from two gondwana basins in india satpura basin kanhan coalfield and damodar valley basin jharia coalfield from both coalfields the samples were collected from the lower permian barakar formation which is one of the major coal bearing strata in india a significant variation in thermal maturity levels in the samples is indicated by rock eval pyrolysis and petrographic analysis with the kanhan samples generally belonging to immature to early mature stage while the jharia samples display characteristics of overmature coals this variation in the thermal maturity strongly affects the biomarker distributions especially the terpenoids hopanes and steranes were considerably degraded due to thermal maturation and were below detection limit in the overmature samples presence of aliphatic diterpanes ent 16 h kaurane 16 h phyllocladane as well as aromatic diterpanes retene methylretenes tetrahydroretene simonellite and bisnorsimonellite in low maturity samples indicate terrestrial input possibly from the primitive conifers however the aliphatic and aromatic diterpanes were below detection limit in overmature samples making it difficult to infer their source distributions of polycyclic aromatic hydrocarbons pahs are also controlled by thermal maturity levels as evident from difference in pah ratios in the low and high maturity samples

unusual biological marker geochemistry of oils and possible source rocks offshore beaufort mackenzie delta canada abstract tertiary oils and source rocks from the offshore beaufort mackenzie delta have been examined for their biological marker content the triterpane and sterane distributions suggest a predominant land plant contribution to the oils the oils range in maturity from extremely immature to moderately mature 18 h oleanne is a major triterpane of the oils together with probable bisnorlupanes and an excellent correlation is observed in the concentration of these components in individual oils an excellent correlation is also observed between the concentration of bisnorlupanes and oil maturity based on sterna and triterpane maturation parameters suggesting that the decrease in relative concentration of these components with increasing maturity is a result of progressive dilution by hydrocarbons generated by the cracking of kerogen only one formation in cores taken from the delta has been found to contain bisnorlupanes and were present they are the dominant hydrocarbons of the branched cyclic fraction

mineralogical and geochemical evidence for coupled bacterial uranium mineralization and hydrocarbon oxidation in the shashagetai deposit nw china unusual mineral structures have recently been found in a sandstone hosted roll type uranium deposit in the middle jurassic zhiluo formation in the shashagetai deposit the northern ordos basin nw china the structures possess a chemical composition and crystal structure characteristic of mineral coffinite usio4 1 x oh 4x which occurs as nanoparticles with size ranging from 5 to 25 nm these structures are interpreted to be fossilized microorganisms based on mineralogical biosignatures including morphology size occurrence of biogenic coffinite as nano crystals and biological elements such as p the intimate intergrowth of coffinite with secondary pyrite of bacterial origin as defined by low 34 s values and calcite cements with petroleum derived carbon supports its biogenic origin oil inclusions in the host sandstone are characterized by abundant n alkanes slightly increased pr nc17 and ph nc18 ratios significant amounts of demethylated hopanes and tricyclic terpanes and the existence of unresolved complex mixtures these characteristics are interpreted to be a result of mixing of an earlier heavily degraded oil with a later charged fresh oil subsequently the oils were slightly degraded these lines of evidence lead to the proposal that the reduction of sulfate and oxidization of petroleum are likely synchronous with reduction of hexavalent u vi to tetravalent u iv uranium by sulfate reducing bacteria srb the discovery of a natural association of microorganism like structures a uranium mineral and biodegraded petroleum has implications for uranium biomineralization and fossil fuel exploration

micropalaeontological and geochemical evidence of mid cretaceous dysoxic anoxic palaeoenvironments in the sergipe basin northeastern brazil

the occurrence of 19 28 bisnorlanostane derivatives in a plant fossil a novel geochemical degradation process of triterpenoids abstract four novel triterpene ketones bearing 24 methyl 28 nor and 24 methyl 19 28 bisnor 5 lanostane skeletons were identified in a fossil of a stem of a plant belonging to the lauraceae family the structures of these compounds have been determined by comparison of their spectral data with those of authentic specimens derived from lanosterol and 24 methylenecycloartanol this is the first finding of compounds bearing a 19 28 bisnorlanostane skeleton which implies a novel possible microbiological pathway of degradation of lanostanes in the sedimentary environment

origin of petroleum in the neoproterozoic cambrian south oman salt basin abstract the south oman salt basin sosb is host to the world s oldest known commercial deposits most of the south oman oils have been proven to be associated with the source rocks of the neoproterozoic to cambrian huqf supergroup but the assignment of oils to specific huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire huqf sequence possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition this study was conducted to establish improved correlations between organic rich rock units and reservoir fluids in the sosb through detailed molecular and isotopic analysis of the huqf supergroup with special emphasis directed towards understanding the ara carbonate stringer play unusual biomarkers tentatively identified as a norsteranes show distinctive patterns among carbonate stringer oils and rocks different from those observed in nafun sediments and ara rocks from the athel basin these putative a norsteranes form the basis for new oil source correlations in the sosb and provide for the first time geochemical evidence of a self charging mechanism for the carbonate stringer play the paucity of markers specific to the nafun group shuram buah and masirah bay formations confounds attempts to quantify their respective contributions to huqf oil accumulations nafun inputs can only be determined on the basis of subtle differences between nafun and ara biomarker ratios the most useful geochemical characteristics delineating nafun group organic matter from ara group intra salt source rocks included low relative abundance of mid chain monomethyl alkanes x compounds low relative abundance of gammacerane 28 30 dinorhopane 25 28 30 trinorhopane and 2 methylhopanes low c 22 t c 21 t and high c 23 t c 24 t cheilanthanes ratio values based on these parameters molecular evidence for major contributions of liquid hydrocarbons from nafun group sediments shuram buah and masirah bay formations is lacking our results suggest that the majority of sosb hydrocarbon accumulations originate from within the ara group either from the carbonate stringers or from the package of sediments that comprises the thuleilat athel silicilyte and u shale formations subtle aspects of the composition of some carbonate stringer and post salt huqf oils could suggest some degree of sourcing from the nafun rocks but stronger evidence is needed to confirm this

biomarker characterisation and hydrous pyrolysis of bitumens from tertiary volcanics queen charlotte islands british columbia canada abstract a number of bitumen samples have been recovered from vugs and fractures in outcropping tertiary basalts of the queen charlotte islands off the west coast of british columbia canada n alkanes and acyclic isoprenoids are not present and the polycyclic biomarker distribution of the four samples analyzed by gc and gc ms has been altered one sample contains no remaining recognizable biomarkers two bitumens were also obtained from lower jurassic potential source rocks including one from the sandilands formation which was considered previously to be the most likely source of the tertiary bitumens although these two bitumens were also taken from outcrops they are considerably less biodegraded the sandilands formation bitumen contains 28 30 bisnorhopanes and since these compounds were not detected in the tertiary bitumens there is no evidence from the initial results for a sandilands formation contribution to the hydrocarbons in the tertiary basalts the presence of 18 h oleanane in the saturate fraction of two of the tertiary bitumens from widely separated locations indicates that they are at least partially sourced from tertiary organic matter because the distribution of biomarkers in some samples has been severely affected by biodegradation the asphaltenes of the bitumens were hydrously pyrolysed and the saturate fractions of the resulting pyrolysates analysed for possible additional information on the origin of the bitumens the pyrolysates from the more degraded samples contain compounds not detected in the saturate fractions of the original bitumen and show some of the expected characteristics of the original non degraded bitumen however the compounds most useful for correlation are not present in the pyrolysates apparently due to their non incorporation into the kerogen macromolecule our results suggest that hydrous pyrolysis of asphaltenes is of limited use in the correlation of biodegraded samples and in determining their origins

the occurrence of bisnorhopane trisnorhopane and 25 norhopanes as free hydrocarbons in some australian shales abstract the triterpenoid hydrocarbons of some west australian shales have been examined by gc ms in addition to the common 17 h 21 h hopanes 17 h 21 h hopanes and 17 h 21 h moretanes 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes were identified in the organic extracts in contrast pyrolysates of the solvent extracted sediments contained only the common hopane and moretane series indicating that 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes are not bonded to kerogen but rather are present in the sediments as free hydrocarbons

gc ms characterisation of c27 and c28 triterpanes in sediments and petroleum abstract earlier studies have shown that an unusual c 27 triterpane is abundant in sediments from the norwegian continental shelf and the north sea this compound was assigned the tentative structures 24 28 30 trisnormoretane or 25 28 30 trisnormoretane but we have now shown from detailed retention time measurements and a reinterpretation of the mass spectral data that its correct structure is 17 h 18 h 21 h 25 28 30 trisnorhopane two other triterpanes 25 28 30 trisnormoretane and 28 30 bisnormoretane have also been identified as minor constituents of extracts of sediments from the north sea possible origins for these compounds are discussed

mineralogical and geochemical evidence for biogenic and petroleum related uranium mineralization in the qianjiadian deposit ne china abstract the sandstone hosted qianjiadian uranium deposit hosted in the upper cretaceous yaojia formation in the qianjiadian area songliao basin ne china has been studied for over twenty years however there exists debate on whether mineralization fluid is low temperature groundwater in favor of biogenic mineralization or diabase related magmatic hydrothermal fluid for this deposit and other adjacent geologically linked sandstone hosted uranium deposits baixingtu baolongshan and huitianzhao deposits in the north china this study provided new data from petrographic and geochemical analyses geochronology of uranium minerals the empa chemical dating method and petroleum hydrocarbon biomarkers in host sandstones two types of host sandstone were recognized in calcareous sandstones pitchblende coexists with colloform pyrite and poikilitic calcite cement while quartz and feldspars were extensively corroded in non calcareous sandstones coffinite coexists with colloform pyrite and only feldspars were slightly corroded this suggests that pitchblende formed in high ph ph 9 fluid while the ph of ore forming fluid for coffinite was lower ph 7 9 besides empa chemical dating revealed two stages of uranium mineralization stage a occurred in 43 28 ma with pitchblende as the only uranium mineral species stage b occurred in 19 3 ma with the formation of both pitchblende and coffinite the uranium mineralization was biogenic under low temperature groundwater condition and thus not from a diabase related mafic magmatic hydrothermal fluid based on the following lines of evidence i some coffinite occurs as phosphorus rich microorganism like microspherules structure ii pyrite aggregates were generated from bacterial sulfate reduction as indicated by the 34s values as low as 41 4 iii calcite cement in calcareous sandstone contains only single phase aqueous inclusions and have 13c values as low as 11 2 indicating that part of the carbon was derived from organic matter oxidation iv the organic matter oxidation is further supported by hydrocarbons extracted from petroleum inclusions within calcite cement showing occurrence of c26 c31 17 21 25 norhopanes typically resulting from heavy biodegradation

fluid inclusion evidence for an early marine sourced oil charge prior to gas condensate migration bayu 1 timor sea australia the distribution of oil bearing fluid inclusions fi in currently gas bearing jurassic reservoir sandstones from bayu 1 northern bonaparte basin timor sea is consistent with the bayu gas condensate field originally containing a palaeo oil column beneath a thick palaeo gas cap in order to assess the origin of the oil trapped in the fis and its relationship if any to the gas condensate a detailed molecular geochemical study was carried out on a fi oil extract and a condensate sample recovered from a similar interval by modular formation dynamics tester mdt compared to the condensate the fi oil was generated from a more marine influenced less clay rich source rock or source facies which was deposited in a less oxic environment with greater eukaryotic input the source rock of the condensate was more terrigenous and had greater microbial input the bayu fi oil contains a greater amount of c28 and c29 tricyclic terpanes than the bayu condensate and particularly compared to the elang plover sourced oils from further to the northwest e g corallina and laminaria which are more terrestrially dominated the bayu condensate has previously been attributed to either the marine cretaceous echuca shoals formation or mixed sourcing from the less terrestrially influenced facies of the jurassic elang and plover formations together with the marine flamingo group analysis of the fi oil confirms a more marine influenced source facies of the palaeo oil with the echuca shoals formation being the most likely source based on oil oil and oil source correlations the fi oil appears to represent a marine source end member and it is likely that mixing of this oil sourced from the echuca shoals formation with hydrocarbons sourced from the more terrestrially dominated plover elang source facies could account for the intermediate composition of the currently reservoired condensate a discrete flamingo group is not required and this oil family may not be present in the bayu area the differences are nevertheless subtle and a contribution from the flamingo group cannot be completely discounted the fi oil has a mid oil window maturity 0 75 vitrinite reflectance equivalent vre whereas the currently reservoired condensate has a higher maturity 0 9 vre these maturity data are consistent with early expulsion from the more labile marine derived organic matter in the echuca shoals formation followed by expulsion of large amounts of condensate from the more terrestrially dominated elang and plover formations three possible transition mechanisms from gas over oil to condensate are consistent with the fi petrographical and geochemical data the first charge may have 1 been lost by breaching of the seal 2 been displaced by the condensate or 3 been partly dissolved in the later condensate charge a combination of factors 2 and 3 is considered most likely but further investigation is required to assess these options the fi oil at bayu 1 predominantly represents a different hydrocarbon charge compared to the condensate liquid and so by analogy the large residual oil columns that are observed elsewhere in the northern bonaparte basin are unlikely to be due to water washing of a pre existing gas condensate column similar to bayu undan

identification and geochemical significance of demethylated highly cyclized regular polyprenoids in oils and source rocks abstract polycyclic polyprenoid hydrocarbons and related demethylated compounds have been identified in severely altered bitumen from oil stained rocks of upper jurassic lower cretaceous age they occur as three series one homologue of which has been isolated and structurally characterized from nuclear magnetic resonance nmr studies they comprise hydrocarbons demethylated at the a b ring junction compounds demethylated at rings e f g and a novel series of compounds demethylated at both the ring a b junction and the ring e f g junction identified for the first time the occurrence in a number of unaltered and biodegraded oils and source rocks of upper jurassic lower cretaceous age of non demethylated hydrocarbons together with related series demethylated at rings e f g indicates that the demethylation process is unlikely to be related to a late degradation process but rather results from the early transformation of precursors bearing functionalised methyl groups on rings e f g in contrast polycyclic polyprenoid hydrocarbons demethylated at the a b ring junction occur only in the most biodegraded samples suggesting that this demethylated series is formed at later stages of alteration by further demethylation of both non demethylated compounds and compounds demethylated at rings e f g in addition a novel series of carboxylic acids related to the polycyclic polyprenoids has been tentatively identified using gas chromatography mass spectrometry gc ms and comprises both non demethylated and demethylated structures at rings e f g it is proposed that the acids represent alteration products of polyprenoids bound to aromatic sub units from macromolecular material that have been released upon severe oxidation during exposure to biodegradation weathering

chemical molecular and isotopic differentiation of organic facies in the tertiary lacustrine duaringa oil shale deposit queensland australia abstract total organic matter extractable organic matter bitumen and pyrolysates released on low temperature sealed tube pyrolysis of kerogen were analysed chemically and isotopically based on bulk bitumen and biomarker parameters the sediments are immature to a depth of approx 1300 m within the terrestrial and lacustrine depositional environments of the tertiary duaringa basin various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land plant and algal sources the latter derived mainly from pediastrum and with a varying botryococcus content the lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community relative contributions from allochthonous land plants and for the lower lamosite a slightly more saline and restricted lake environment the lower lamosite is associated with the highest concentrations of c 28 c 30 4 methylsteranes and 13 c depletion in toc in the upper lamosite there is a strong positive correlation between botryococcus content and 13 c enrichment the organically lean claystones have sources nearly identical to the lamosites but the organic matter is diluted due to rapid influx of siliciclastics the terrestrial facies the cannel coal and carbonaceous shales are mainly distinguished from the lacustrine facies by higher relative proportions of c 29 steranes c 30 4 methylsteranes and 13 c values for the pyrolysed hydrocarbons intermediate between the two lamosite facies the carbonaceous oil shale has a composite geochemical signature intermediate between the two end members lamosite and cannel coal oleanane and ring a degraded triterpanes derived from lupane arborane and oleanane skeletons are distributed throughout all organic facies representing both autochthonous and allochthonous higher plant inputs higher concentrations of oleanane and des a lupane are associated with the terrestrial facies hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies for the lamosites the aliphatic biopolymer algaenan is implicated as the dominant source for n alkanes from analysis of their yields homologue abundances and individual 13 c values in the terrestrial facies resinites are paraffinic and are a major source for the n alkanes released on pyrolysis compound specific analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen for the lamosites low molecular weight n alkanes in the bitumen are derived mainly from a pediastrum source while botryococcus is associated with waxy n alkanes however the situation is reversed in the kerogen pediastrum algeanan has a longer average alkyl chain length than botryococcus algaenan the magnitude of the isotopic differences between single n alkanes released at different temperatures is useful in determining multiplicity of sources

geochemical characterization and source investigation of oils discovered in khoraghat nambar structures of the assam arakan basin india abstract we examined the geochemical compositions of the newly discovered bokabil and sylhet oils and of the extracts of potential source rock samples from the khoraghat nambar area of the assam arakan basin india stable carbon isotopic compositions and a number of biomarkers indicate that oils in the bokabil formation early to middle miocene can be correlated across the khoraghat and nambar fields however oil from the sylhet formation middle to late eocene is distinct from those in the bokabil formation late eocene to early oligocene barail coal shale and middle to late eocene kopili shale sequences are identified as potential source rocks both strata contain organic matter predominantly derived from higher land plants however different organofacies exist for barail coal shale and kopili shale sequences that can be distinguished by the stable carbon isotopic compositions and biomarker distributions an oil source correlation study shows that barail rock extracts are genetically correlatable with the bokabil oils whereas kopili rock extracts have similar source specific parameters to those of the sylhet oil thus the study suggests the presence of two petroleum systems in the khoraghat nambar area the barail bokabil and the kopili sylhet petroleum systems barail and kopili sediments from the study area are of lower maturity than the oils suggesting that the actual source strata are more mature equivalents likely to be present in the naga schuppen zone therefore areas in and around the naga schuppen zone where better reservoir facies are expected are favoured targets for further exploration