directional borehole logging configurations using dc and telluric methods for detecting deep conductors not intersected by wells herewith two borehole directional geoelectrical configurations have been introduced for the detection of deep conductors not intersected by the well the first one is a hole to surface configuration hsc using the dc current and the second one is a telluric configuration tc characterized by a deeper penetration depth and a directional effect both configurations have superiority comparable with other traditional geoelectrical configurations basically a directional natural induced polarization methodology termed dnip has been developed and proposed by benefiting from borehole telluric measurements taken at two sufficiently low frequencies these configurations have been tested in the rouez mine bretagne france where sulphide mineralization is known to occur several anomalies have been isolated in field data and interpreted by different interpretative techniques the results obtained by applying these configurations are in good agreement and the detected conductors are confirmed by morphological and lithological description

organic geochemistry of oils and condensates in the kekeya field southwest depression of the tarim basin china this study shows that the oils and condensates in the kekeya field in the tarim basin nw china belong to a single family most likely derived from marine shale source rocks deposited under oxic suboxic conditions with mixed terrigenous and algal bacterial organic inputs the maturity data clearly indicate that the paraffinic condensates were not formed by thermal cracking of oil during late catagenesis ro 1 2 both the oils and condensates were generated within the normal oil window whereas addition of gaseous hydrocarbons from a separate source resulted in migration fractionation and hence spuriously high heptane indices age specific biomarkers show that the oils and condensates were not generated from the mesozoic cenozoic strata but from the carboniferous permian sections 1d basin modeling results are consistent with this interpretation suggesting that the mesozoic eocene strata are currently immature with respect to hydrocarbon generation and expulsion deep seated faults may have provided routes for upward fluid migration at the time of active deformation during several pulses of the himalayan orogeny the favored targets for further petroleum exploration in front of the kunlun mountains include the deep structures within the carboniferous permian strata for indigenous petroleum accumulations and anticlines and stratigraphic traps within the mesozoic cenozoic sections that are cut by deep seated thrust faults where secondary petroleum accumulations most likely occurred

the stability of gypsum in marine sediments using the entire odp iodp porewater composition database abstract the stability of gypsum in marine sediments has been investigated through the calculation of its saturation index at the sediment in situ temperature and pressure using the entire odp iodp porewater composition database 14416 samples recovered from sediments collected during 95 odp and iodp legs saturation is reached in sediment porewaters of 26 boreholes drilled at 23 different sites during 12 odp iodp legs as ocean bottom seawater is largely undersaturated with respect to gypsum the porewater ca content or its so4 concentration or both must increase in order to reach equilibrium at several sites equilibrium is reached either through the presence of evaporitic gypsum layers found in the sedimentary sequence and or through a salinity increase due to the presence of evaporitic brines with high concentrations of ca and so4 saturation can also be reached in porewaters of seawater like salinity 35 provided sulfate reduction is limited in this case saturation is due to the alteration of volcanogenic material which releases large amounts of ca to the porewaters where the ca concentration can reach 55 times its seawater value as for example at odp leg 134 site 833 at a few sites saturation is reached in hydrothermal environments or as a consequence of the alteration of the basaltic basement in addition to the well known influence of brines on the formation of gypsum these results indicate that the alteration of sediments rich in volcanogenic material is a major process leading to gypsum saturation in marine sediment porewaters therefore the presence of gypsum in ancient and recent marine sediments should not be systematically interpreted as due to hypersaline waters especially if volcanogenic material is present

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

on sensitivity of surface to borehole resistivity measurements to the attitude and the depth to center of a three dimensional spheroid borehole to surface and surface to borehole resistivity measurements are versatile but not totally tested methods for detecting anomalies in the vicinity of a borehole the former method has been discussed by several authors alfano 1962 merkel 1971 merkel and alexander 1971 barnett 1972 snyder and merkel 1973 snyder 1976 daniels 1977 1978 and 1983 but the latter has not received much attention morrison 1971 and daniels 1977 are among the few who have addressed the problem each method has its own advantages surface to borehole resistivity measurements are made by placing a current source on the surface and measuring the apparent resistivity in a borehole in which the measuring electrodes are closer to the body than in the borehole to surface case pilot studies presented here suggest that the surface to borehole method can provide indicators of the attitude and the depth to the center of a body this paper illustrates a simple method for qualitatively determining the attitude and t

hole to surface resistivity measurements hole to surface resistivity measurements over a layered volcanic tuff sequence illustrate procedures for gathering reducing and interpreting hole to surface resistivity data the magnitude and direction of the total surface electric field resulting from a buried current source is calculated from orthogonal potential difference measurements for a grid of closely spaced stations a contour map of these data provides a detailed map of the distribution of the electric field away from the drill hole resistivity anomalies can be enhanced by calculating the difference between apparent resistivities calculated from the total surface electric field and apparent resistivities for a layered earth model lateral discontinutities in the geoelectric section are verified by repeating the surface field measurments for current sources in several drill holes a qualitative interpretation of the anomalous bodies within a layered earth can be made by using a three dimensional 3 d resistivity model in a homogeneous half

the character and origin of lacustrine source rocks in the lower cretaceous synrift section congo basin west africa lower cretaceous synrift lacustrine shales from the congo basin west africa have been analyzed with sedimentological and geochemical techniques to characterize source rock quality and identify triggers for deposition of intervals richest in organic carbon the sequence includes a lower active rift section deposited during active faulting and subsidence overlain by an upper late rift section deposited during reduced faulting and subsidence total organic carbon toc averages 2 3 wt throughout the active rift siliciclastic shale section 6 in marls in the lower part of the late rift section and 1 2 in deltaic shales in the upper part of the late rift section organic matter consists of mixed types i and iii kerogen in the active rift shales pure type i kerogen in the late rift marls and a type i and iii mixture in the late rift deltaic shales redox proxies indicate that the deep lake was relatively reducing throughout deposition of the active rift and lower late rift sections therefore enhanced anoxia did not trigger deposition of the richest source rocks decreased sedimentation rates in the late rift do not account for the full increase in toc nor the shift on organic matter type the richest source rocks are associated with high rates of organic productivity and chemical sedimentation indicating that flux of dissolved components to the rift lake including nutrients for algae growth was critical we propose that reduced topography associated with the late rift was necessary for efficient cycling of plant derived carbon into soil carbonate and ultimately the rift lake and for enhancing chemical weathering and nutrient flux

chemistry of interstitial waters and sediments in the norwegian greenland sea deep sea drilling project leg 38 interstitial waters of several sites drilled during the deep sea drilling project in the norwegian greenland sea during leg 38 have revealed substantial changes in dissolved constituents and in the 18o16o composition of interstitial waters studies of the chemical composition of the bulk sediments and their 1 m fraction indicate the presence of large amounts of volcanic ash especially in sites close to iceland the presence of authigenic clay minerals illite smectite suggests that alteration of this volcanic ash is an important process a study of site 348 reveals that dissolved ca gradients are caused mainly by transport from the underlying basalts but that decreases in mg and 18o h2o are largely due to reactions involving alteration of volcanic ash in the sediments studies of 87sr86sr distributions of dissolved sr confirm this process in those sites with high contents of volcanic matter on the other hand in sites where the chemical composition of dissolved constituents has been little influenced by alteration reactions 87sr86sr ratios reveal complete diffusive exchange with present day seawater

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

oil source rock correlations limitations and recommendations a rigorous defensible and causal oil source rock correlation definitively ties an individual source rock sample to an individual crude oil using genetically based internally consistent parameter matches such a correlation is a relationship established between the two components which is consistent with all known chemical geochemical and geological information and meets three criteria a the relationship must be causal the oil must arise at least in part from the specified source rock s b chemical data used in the correlation must be comparable the elemental molecular and isotopic data derived from the source rock must be of the same type as that derived from the oil and c all available geological data must be supportive clear geological evidence must exist which allows the proposed source rock to have sourced the oil the three points of this definition are satisfied and the correlation is successful if we solve one analytical and three geological problems natural extraction of crude oil from its source rock i e expulsion differs mechanically and temporally from laboratory extraction leading to a correlation problem referred to as extraction differences and representing the single greatest analytical uncertainty in correlation efforts geologically three aspects confound oil source correlations occurrence of multiple source units and or source units at differing maturity levels lateral and vertical depositional variations in source unit s organic matter and lateral and vertical variation in reservoir unit s organic matter these concerns are overcome by taking five actions for each oil source correlation effort 1 select representative samples using statistically defensible methods 2 establish the inherent compositional variability laterally and temporally due to depositional and maturation processes in each prospective source unit 3 assess the extent of migration induced changes in oil composition including post migration changes such as in reservoir alteration 4 support each correlation with migration histories derived from 4d models 5 iterate correlation results with new data gathered from ongoing exploration efforts these five actions will a allow correlation success to be measured more objectively b establish risking parameters for direct use in basin assessment and c provide baseline criteria for use in assessing the reliability of oil source rock correlations although these approaches will improve conventional oil source rock correlation efforts ultimately they may not be needed if inversion methods become more reliable the ability to invert compositional data for crude oil i e predict the age lithology maturity and other characteristics of a source rock solely through chemical analysis of its expelled oil could eventually result in successful oil source rock correlations in which source rock analysis for oil source rock correlation purposes is less critical

organic geochemistry as an aid in the interpretation of the history of oil migration into different reservoirs at the hibernia k 18 and ben nevis i 45 wells jeanne d arc basin offshore eastern canada abstract the jeanne d arc basin is situated in the northeastern part of the grand banks off the east coast of newfoundland several large oil and gas fields have been discovered in this basin the largest of which is the giant hibernia field the principal source rock of most of the oils in the jeanne d arc basin is the kimmeridgian aged egret member of the rankin formation a characteristic feature of the biomarker distributions of both the oils and the egret member extracts is the very high abundance of 4 methyl steranes the high concentration of these compounds prevents the accurate measurement of maturity and other parameters based on 4 desmethyl steranes using gc ms sim the use of collision activated decomposition cad gc ms ms is demonstrated as a method of overcoming the problem of chromatographically co eluting compounds to obtain reliable biomarker data biomarker and other geochemical data are then used to help elucidate the history of oil migration into stacked reservoirs in two wells in the jeanne d arc basin all the hibernia k 18 oils are sourced from the egret member we interpret our data to indicate that all the reservoirs over a 1570 m depth interval were originally filled by a single pulse of oil that migrated vertically via faults in the lowermost hibernia reservoirs this event is being overprinted by more mature hydrocarbons leaking from the underlying overpressured zone with increasing depth at ben nevis i 45 oils show an increase in maturity and in the proportion of hydrocarbons that are derived from a source rock other than the egret member this second source is dominated by terrestrially derived organic matter oils are found in other wells in the jean d arc basin with similar characteristics all these wells are located in one small area of the basin and are in close proximity to the trinity fault

cyclic terpenoids of contemporary resinous plant detritus and of fossil woods ambers and coals abstract cyclic terpenoids present in the solvent extractable material of fossil woods ambers and brown coals have been analyzed the sample series chosen consisted of wood remains preserved in holocene to jurassic sediments and a set of of ambers from the philippines copalite israel canada and dominican republic the brown coals selected were from the fortuna garsdorf mine and miocene formations on fiji the fossil wood extracts contained dominant diterpenoid or sesquiterpenoid skeletons and aromatized species were present at high concentrations with a major amount of two ring aromatic compounds tricyclic diterpenoids were the predominant compounds in the ambers aromatized derivatives were the major components consisting of one or two aromatic ring species with the abietane and occasionally pimarane skeletons the saturated structures were comprised primarily of the abietane and pimarane skeletons having from three to five carbon c1 c2 etc substituents kaurane and phyllocladane isomers were present in only minor amounts bicyclic sesquiterpenoids as saturated and partial or fully aromatized forms were also common in these samples but only traces of sesterterpenoids and triterpenoid derivatives were found the brown coal extracts were composed of major amounts of one and two ring aromatized terpenoids with a greater proportion of triterpenoid derivatives than in the case of the woods and ambers this was especially noticeable for the german coal where the triterpenoids were predominant open c ring aromatized structures were also present in this coal steroid compounds were not detectable but some hopanes were found as minor components in the german brown coal an overview of the skeletal structure classes identified in each sample as well as the general mass spectrometric characteristics of the unknown compounds are included in the present paper it can be concluded from these structural distributions that aromatization is the main process for the transformation of terrestrial cyclic terpenoids during diagenesis constituting a general pathway for all terpenoids

hydrogeochemistry of the northern barbados accretionary complex transect ocean drilling project leg 110 detailed studies of the major element geochemistry oxygen and hydrogen isotope ratios of pore fluids and the 87sr 86sr ratio of dissolved strontium have made it possible to unravel physical and chemical processes that affect the pore fluid chemistry in a transect of drill holes across the northern barbados accretionary complex these processes include 1 alteration of volcanic ash buried in the pleistocene pliocene sediment column 2 alteration of underlying basalts of layer 2 of the oceanic crust 3 movement of fluids from deep in the accretionary complex along fault zones particularly the decollement and minor permeable layers these fluids from deeper in the complex are characterized by low chloride concentrations and increased 18o h2o values presumably as a result of dehydration of smectite interlayers and 4 mixing processes involving the migrating fluids cause incongruities in the geochemical anomalies of these fluids

recent advances in petroleum isotope geochemistry abstract organic matter is isotopically heterogeneous lipids tend to be depleted in the heavy carbon and hydrogen isotopes as compared to carbohydrates and lignite the c and h isotopic composition of kerogens is determined by many factors such as environmental conditions during formation and deposition and variability of sources of organic matter stable isotope concentrations in mature kerogens are not significantly altered during maturation and hence reflect the variability of the organic matter during deposition isotope variations in kerogens therefore reflect to some extent the paleogeographic situation and can be used for paleoreconstruction a basin facies with anoxia and a marginal facies with detrital input can be differentiated isotopically in the toarcian of central europe coals are isotopically heterogeneous due to different isotopic composition of macerals inertinite and vitrinite tends to be enriched in deuterium as compared to exinite also boghead coals tend to be depleted in dueterium which possibly reflects various lipid contents of respective precursor materials petroleums can be genetically classified through the patterns of covariance of their compound classes carbonate and shale sourced petroleums may be additionally differentiated through their deuterium content the general world wide applicability of such genetic differentiations needs still to be proved carbon and hydrogen isotope variations in methane are genetically controlled bacterial methane in freshwater environments is characteristically depleted in deuterium even complex origins of natural gases can be unraveled using compositional and isotopic variations new analytical developments led to the application of carbon isotope analyses of gaseous hydrocarbons desorbed from sediments for geochemical surface exploration a discussion reveals that processes such as isotope effects during degassing and bacterial oxidation as well as indigenous formation of hydrocarbons may completely obscure the results

origin of nama basin bitumen seeps petroleum derived from a permian lacustrine source rock traversing southwestern gondwana abstract biodegraded bitumens associated with quartz and calcite veins in the cambrian fish river subgroup sediments of the nama group of southern namibia have a geochemical signature diagnostic for organic matter that was deposited in a saline lacustrine palaeoenvironment in particular they contain abundant gammacerane carotane and 3 methylhopanes while 24 isopropyl cholestanes and dinosteroids are not detectable sealed tube hydrous pyrolysis of asphaltene and polar fractions yielded saturated hydrocarbons amenable to c isotopic analysis and these analyses show unusually low 13 c values these combined characteristics are also present in immature bitumens from the permian irati formation of brazil and a saline lacustrine facies of the whitehill formation in the karoo basin south africa we conclude that the bitumens originated from whitehill equivalent strata of the kalahari basin deposited in what was an extensive saline lacustrine basin in southwestern gondwana during the early permian in southern africa source rocks of the whitehill formation are generally immature for petroleum generation and it is therefore likely that the nama bitumens were expelled by contact metamorphism during emplacement of karoo dolerite sills and dykes in the jurassic

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

charging history of paleogene deep gas in the qibei sag bohai bay basin china abstract the qibei sag qs at the western region of the bohai bay basin bbb eastern china has made significant progress in the deep gas exploration recently indicating that the deep gas reservoirs have good exploration prospects the deep gas reservoirs within the second member of the shahejie formation of the paleogene e2s2 are buried at approximately 5000 m the sources and hydrocarbon accumulation mechanisms were investigated by analyzing the regional structure integrating geologic and geochemical parameters of source rocks and natural gas analyzing results show that in the qs and adjacent areas qsaa three sets of source rocks e2s1 e2s2 e2s3 were developed which differ in organic chemical characters but have abundant organic matters in fair good standard affected by burial history e2s3 source rocks have entered into the high mature over mature stage and e2s1 source rocks are mainly in mature stage the methane content of natural gas 78 91 the methane carbon isotope value 41 3 34 6 and the positive carbon isotope sequence 13c1

impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern hikurangi margin abstract we present geochemical data collected from volcanic ash bearing sediments on the upper slope of the northern hikurangi margin during the rv sonne so247 expedition in 2016 gravity coring and seafloor drilling with the marum mebo200 allowed for collection of sediments down to 105 meters below seafloor mbsf release of dissolved sr2 with isotopic composition enriched in 86sr 87sr 86sr minimum 0 708461 at 83 5 mbsf is indicative of ash alteration this reaction releases other cations in the 30 70 mbsf depth interval as reflected by maxima in pore water ca2 and ba2 concentrations in addition we posit that fe iii in volcanogenic glass serves as an electron acceptor for methane oxidation a reaction that releases fe2 measured in the pore fluids to a maximum concentration of 184 m several lines of evidence support our proposed coupling of ash alteration with fe mediated anaerobic oxidation of methane fe aom beneath the sulfate methane transition smt which lies at 7 mbsf at this site in the 30 70 mbsf interval we observe a concurrent increase in fe2 and a depletion of ch4 with a well defined decrease in 13 c ch4 values indicative of microbial fractionation of carbon the negative excursions in 13 c values of both dic and ch4 are similar to that observed by sulfate driven aom at low so 4 2 concentrations and can only be explained by the microbially mediated carbon isotope equilibration between ch4 and dic mass balance considerations reveal that the iron cycled through the coupled ash alteration and aom reactions is consumed as authigenic fe bearing minerals this iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals as estimated from sequential extraction analyses using a numerical modeling approach we estimate the rate of fe aom to be on the order of 0 4 mol cm 2 yr 1 which accounts for 12 of total ch4 removal in the sediments although not without uncertainties the results presented reveal that fe aom in ash bearing sediments is significantly lower than the sulfate driven ch4 consumption which at this site is 3 0 mol cm 2 yr 1 we highlight that fe iii in ash can potentially serve as an electron acceptor for methane oxidation in sulfate depleted settings this is relevant to our understanding of c fe cycling in the methanic zone that typically underlies the smt and could be important in supporting the deep biosphere

distinguishing gases derived from oil cracking and kerogen maturation insights from laboratory pyrolysis experiments kerogen separated from an immature type i mudstone from the third section of the tertiary shahejie formation es 3 3 in the dongying depression of bohai bay basin was subjected to stepwise isothermal pyrolysis products were extracted fractionated into chemical groups and re mixed to obtain a synthetic oil with a group composition similar to reservoir oil and a pseudo kerogen composed of 83 kerogen and 17 residual soluble organic matter referred as s oil and p kerogen respectively to distinguish them from a produced reservoir oil and a real kerogen the two samples were pyrolyzed in sealed gold tubes under constant pressure 50 mpa and non isothermal heating 300 600 c conditions and their generated gases were analyzed the two gases are quite different in their chemical and isotopic composition compared with the gas derived from the p kerogen the s oil derived gas is enriched in c2 c5 hydrocarbons in its early cracking stages and c1 c3 hydrocarbons are depleted in d 13 c throughout the cracking stages the maximum wetness c2 5 c1 5 of the s oil gas and the p kerogen gas is 0 62 and 0 35 respectively and the carbon isotopic ratio differences between the two type gases can reach 10 d 13 c1 14

strontium and its isotopic composition in interstitial waters of marine carbonate sediments abstract the concentrations and isotopic compositions of strontium in interstitial waters from several dsdp sites where sediments consist chiefly of carbonate oozes and chalks are used as indicators of carbonate diagenesis by reference to a recently produced curve showing detailed variations in the87sr 86sr ratio of seawater with time carbonate sediments of the walvis ridge show increases in interstitial sr2 concentrations in the upper carbonate ooze sections with the highest concentrations near the ooze chalk boundary where maximum rates of carbonate recrystallization occur below this in situ production of sr2 diminishes and there is a diffusive flux of sr to an underlying sink presumably volcanogenic sediments or basalts leading to sr isotopic disequilibrium between carbonates and interstitial waters in some other sites however there is no apparent sr sink at depth and isotopic equilibrium is retained overall diffusive smoothing of profiles exerts an important control on the87sr 86sr ratios although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of mg2 loss and reflect a combination of a flux of sr2 from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter

origin and occurrence of 25 norhopanes a statistical study abstract the alkane fraction of more than 200 rocks biodegraded oils and non biodegraded oils have been analysed by means of computerized gc ms in order to investigate the effect of natural biodegradation on the occurrence of demethylated hopanes i e 17 25 norhopanes the results obtained indicate that 25 norhopanes are preexisting biomarkers the concentration of which is enhanced by selective biodegradation of more readily degradable homologs i e regular hopanes rather than by demethylation of hopanes in reservoirs however the use of 25 norhopane enrichment as a palaebiodegradation indicator in apparently non biodegraded oils is still valuable providing the initial background content in the corresponding source rocks is known furthermore 25 norhopanes appear to be diagnostic of specific environmental conditions marine and lacustrine source rocks dysoxic and not very hypersaline lastly one other novel bacterially resistant rearranged hopanoic compound namely a c29 neohopane is applicable for both biodegradation and maturation evaluation

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

organic geochemistry and reservoir characterization of the organic matter rich calcilutite in the shulu sag bohai bay basin north china abstract although extensive studies have been conducted on unconventional mudstone shales reservoirs in recent years little work has been performed on unconventional tight organic matter rich fine grained carbonate reservoirs the shulu sag is located in the southwestern corner of the jizhong depression in the bohai bay basin and filled with 400 1000 m of eocene lacustrine organic matter rich carbonates the study of the organic matter rich calcilutite in the shulu sag will provide a good opportunity to improve our knowledge of unconventional tight oil in north china the dominant minerals of calcilutite rocks in the shulu sag are carbonates including calcite and dolomite with an average of 61 5 wt the carbonate particles are predominantly in the clay to silt size range three lithofacies were identified laminated calcilutite massive calcilutite and calcisiltite calcilutite the calcilutite rocks including all the three lithofacies in the third unit of the shahejie formation in the eocene es3 have total organic carbon toc values ranging from 0 12 to 7 97 wt with an average of 1 66 wt most of the analyzed samples have good very good or excellent hydrocarbon potential the organic matter in the shulu samples is predominantly of type i to type ii kerogen with minor amounts of type iii kerogen the temperature of maximum yield of pyrolysate tmax values range from 424 to 452 c with an average of 444 c indicating most of samples are thermally mature with respect to oil generation the calcilutite samples have the free hydrocarbons s1 values from 0 03 to 2 32 mg hc g rock with an average of 0 5 mg hc g rock the hydrocarbons cracked from kerogen s2 yield values in the range of 0 08 57 08 mg hc g rock with an average of 9 06 mg hc g rock and hydrogen index hi values in the range of 55 749 mg hc g toc with an average of 464 mg hc g toc the organic rich calcilutite of the shulu sag has very good source rock generative potential and have obtained thermal maturity levels equivalent to the oil window the pores in the shulu calcilutite are of various types and sizes and were divided into three types 1 pores within organic matter 2 interparticle pores between detrital or authigenic particles and 3 intraparticle pores within detrital grains or crystals fractures in the shulu calcilutite are parallel to bedding high angle and vertical having a significant effect on hydrocarbon migration and production the organic matter and dolomite contents are the main factors that control calcilutite reservoir quality in the shulu sag

petrographic and geochemical characterization of microfacies in a lacustrine shale oil system in the dongying sag jiyang depression bohai bay basin eastern china abstract petrology and rock eval analyses have been conducted in the lower third and upper fourth members lower es3 and upper es4 of the shahejie fm source rock intervals in well fanye1 in the dongying sag jiyang depression bohai bay basin eastern china the organic matter in rocks intersected by this well is dominated by lamalginite and bituminite and most samples contain type i or ii kerogen microfacies a h has been identified according to their organic mineral composition and structure using polished thin sections under microscopy the form and location of hydrocarbon residue occurrences mainly as solid bitumen with fluorescence are different in those microfacies microfacies a which is dominant in well fanye 1 is calcareous mudstone without lamination and the hydrocarbon residue is dispersed through the rock with some being present in subtle microfractures microfacies b and f are mostly composed of shale with adsorbed hydrocarbon indicated by fluorescence along mineral grains microfacies c is laminated argillaceous carbonate with hydrocarbon residue mainly occurring in thin microfractures along the bedding plane microfacies d and e are mainly carbonate and microfacies d is laminated with micrite and sparite and hydrocarbon residue occurrence is not only in the microfractures along the bedding but also in the micropores among the grains in the sparite layers which is the main place for hydrocarbon residue occurrence in microfacies type e without lamination microfacies g and h are both micrite microfacies g shows bioturbation and hydrocarbon residue occurs within small irregular microfractures along the bedding planes and pores only a little solid bitumen without fluorescence has been observed in microfacies h the rock eval oil saturation index osi s1 100 toc value is variable because of the different characteristics of these hydrocarbon residue occurrences osi values in microfacies a are normally high 74 8 242 8 mg hc g toc average of 117 2 mg hc g toc and likely much higher if microfractures develop 200 mg hc g toc osi values averaging 43 7 mg hc g toc are lowest in microfacies f because of adsorption on the shales and osi values are the highest in microfacies d 371 3 mg hc g toc and e 199 9 mg hc g toc since the hydrocarbon residues are stored both in microfractures and pores between the grains both osi values are high in microfacies g and h because of low toc content the combination of petrographic and osi analysis appear to be a promising tool for characterizing shale oil systems

carbon isotope composition of marine crude oils 1 a histogram of isotope 13 c values of 621 post ordovician marine oils shows a trimodal distribution within this distribution four groups of oils can be recognized on the basis of isotope 13 c values in conjunction with pristane phytane ratios and sulfur contents oils with isotope 13 c values of 32 0 to 28 0 o oo are mainly marine shale oils older than oligocene oils with isotope 13 c values of 28 0 to 23 5 o oo are mainly deltaic oils of varying geologic age or mesozoic carbonate oils and oils with isotope 13 c values heavier than 23 5 o oo are mainly marine shale oils of miocene age the isotope 13 c variation among oil groups is explained primarily by different factors that control the fractionation of carbon isotopes during primary production of rganic carbon miocene and younger marine shale oils are isotopically heavier than older marine shale oils because of decreased atmospheric co 2 concentration since 25 ma which has resulted in decreased isotope fractionation by marine plankton during photosynthesis deltaic oils are mostly derived from terrestrial organic matter and their isotope 13 c values reflect the time invariant average isotope 13 c value of land plant carbon at about 25 o oo mesozoic carbonate oils are isotopically heavy due mainly to salinity and temperature effects during primary production in restricted environments from which terrestrial organic matter is excluded processes that occur after oil generation generally have smaller effects on isotope 13 c values of oils as a result isotope 13 c val es of oils are useful for determining oil oil and oil source rock relationships and in conjunction with other geochemical properties can indicate the possible age and depositional environment of source rocks

the effects of composition laminar structure and burial depth on connected pore characteristics in a shale oil reservoir the raoyang sag of the bohai bay basin china abstract to evaluate the effects of the composition laminar structure and burial depth on pore volumes connected by pore throats of different sizes in a shale oil reservoir the es1x formation in the raoyang sag of the bohai bay basin was selected as an example the effects of component contents laminar structure and burial depth on pore volumes connected by pore throats with widths of

multiple oil families in the west siberian basin two major oil families are identified in the west siberian basin twenty six of 32 analyzed oils occur in jurassic and cretaceous reservoirs and are derived from anoxic marine upper jurassic bazhenov source rock based on geochemical comparison of oils and source rock extracts these oils are widely distributed both north and immediately south of the ob river and their biomarker ratios indicate a wide range of source rock thermal maturity from early to middle oil window van egan russkoye samotlor sovninsko sovyet olyenye ozynornoye and kogolym to peak oil window srednekhulym yem yegov vostochno surgut khokhryakov fedorov and urengoi to late oil window salym some of these oils have been mildly e g fedorov 75 to heavily e g russkoye biodegraded n the reservoir the bazhenov sourced oils show different compositions that support regional variations of organic facies in the source rock for example the anoxic marine bazhenov facies which generated the oils in the samotlor fedorov and nearby fields was particularly clay poor and sulfur rich six nonbiodegraded highly mature oils show geochemical characteristics that suggest they were derived from clastic rich lacustrine or nearshore marine source rocks dominated by terrigenous higher plant input like those in the lower to middle jurassic tyumen formation although no correlation was observed between the oils and a single rock sample yem yegov 15 from the formation the six oils occur in the tyumen taitym geologiche and cheremshan and fractured basement paleozoic gerasimov yagyl yakh and verchnekombar reservoirs in positions readily accessible to any oil migrating from the tyumen source rock for example at the gerasimov location the tyumen formation lies unconformably on weathered basement paleozoic reservoir rocks most of the probable tyumen sourced oils ar from south of the ob river but the occurrence of geologiche oil to the north suggests that related oils may be widespread in the basin

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

new methodology for computation of the earth s polarizability from telluric borehole logging measurements taken at different frequencies an important approach for computation of the earth s polarizability is achieved by developing a novel method with new parameters called natural percent frequency effect npfe and natural metal factor nmf resulting from telluric logging data taken at different frequencies the essential advantage of the developed approach relies on using natural electrical currents instead of an artificial electrical source usually needed in the standard frequency domain applied in the induced polarization method furthermore a good qualitative correlation has been found between the new parameters and those of the traditional induced polarization method obtained in time and frequency domains the new method has been tested in well 32 in the rouez mine in france where sulphide mineralization is well known to occur

tetrahymanol its widespread occurrence and geochemical significance abstract the occurrence of tetrahymanol gammaceran 3 ol in sediments from various marine depositional environments such as the santa monica basin and palos verdes shelf southern california bight the santa barbara basin off the northern california borderland the atlantic shelf slope and rise and the antarctic region as well as in bacterial algal mats from the santa barbara basin and baja california together with its detection in sediments from the peru upwelling region odp leg 112 and baffin bay odp leg 105 suggests that tetrahymanol occurs ubiquitously in marine samples tetrahymanol is the only known likely biological precursor of gammacerane which is found in many petroleums and shales the common occurrence of tetrahymanol in marine environments implies that primitive organisms similar to tetrahymena or organisms other than tetrahymena other protozoa bacteria are also likely to contain this compound its isomer diplopterol has also been detected in several sediment sections

diagenesis in tephra rich sediments from the lesser antilles volcanic arc pore fluid constraints we present sediment pore fluid and sediment solid phase results obtained during iodp expedition 340 from seven sites located within the grenada basin of the southern lesser antilles volcanic arc region these sites are generally characterized as being low in organic carbon content and rich in calcium carbonate and volcanogenic material in addition to the typical reactions related to organic matter diagenesis pore fluid chemistry indicates that the diagenetic reactions fall within two broad categories 1 reactions related to chemical exchange with volcanogenic material and 2 reactions related to carbonate dissolution precipitation or recrystallization for locations dominated by reaction with volcanogenic material these sites exhibit increases in dissolved ca with coeval decreases in mg we interpret this behavior as being driven by sediment water exchange reactions from the alteration of volcanic material that is dispersed throughout the sediment package which likely result in formation of mg rich secondary authigenic clays in contrast to this behavior sediment sequences that exhibit decreases in ca mg mn and sr with depth suggest that carbonate precipitation is an active diagenetic process affecting solute distributions the distributions of pore fluid 87sr 86sr reflect these competitive diagenetic reactions between volcanic material and carbonate which are inferred by the major cation distributions from one site where we have solid phase 87sr 86sr site u1396 the carbonate fraction is found to be generally consistent with the contemporaneous seawater isotope values however the 87sr 86sr of the non carbonate fraction ranges from 0 7074 to 0 7052 and these values likely represent a mixture of local arc volcanic sources and trans atlantic eolian sources even at this site where there is clear evidence for diagenesis of volcanogenic material carbonate diagenesis appears to buffer pore fluid 87sr 86sr from the larger changes that might be expected given the high abundance of tephra in these sediments part of this carbonate buffering at this site as well as throughout the region derives from the fact that the sr concentration in the non carbonate fraction is generally low 200 ppm whereas the carbonate fraction has sr concentrations approaching 1000 ppm

charging of oil fields surrounding the shaleitian uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract this paper discusses origin and charging directions of oil fields on the shaleitian uplift bohai bay basin the shaleitian uplift is a footwall uplift surrounded by three sags containing mature source rocks the origins of the four oil fields on the shaleitian uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions for 61 source rock samples and 27 oil samples hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and or depositional conditions allowed the identification of six oil types or classes these six oil classes could then be linked to three distinct source rock intervals ranging in age from 43 0 ma to 30 3 ma the third member 43 0 38 0 ma in age and first member 35 8 32 8 ma of the eocene shahejie formation and the third member of the oligocene dongying formation 32 8 30 3 ma each sourced one class of oil the other three classes represent mixtures of oil generated from multiple source rock intervals traps on the shaleitian uplift were charged in the east by oil generated from the eocene shahejie formation in the bozhong sag in the southeast by oil generated from the eocene shahejie and then oligocene dongying formations in the southwestern part of the bozhong sag and or in the eastern part of the shanan sag and in the southwest by oil generated from the eocene shahejie formation in the western part of the shanan sag the estimated migration distances range from less than 5 km to about 20 km the compositional heterogeneity within fields and multiple parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist

improved understanding of the petroleum systems of the niger delta basin nigeria biomarker and n alkane compound specific stable carbon isotope analyses csia were carried out on 58 crude oil samples from shallow water and deepwater fields of the niger delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks using a source organofacies prediction approach from oil geochemistry the presence in the western deepwater oils relatively abundant c27 steranes c30 24 n propyl cholestane low oleanane index relatively low pr ph ratios gammacerane and positive to nearly flat c12 c30 n alkane compound specific stable carbon isotope profiles suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub oxic and stratified water column conditions this contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water niger delta oils oils in the shallow water accumulations can be separated into terrigenous and mixed marine terrigenous families the terrigenous family indicates expulsion from source rock s containing overwhelmingly higher plant source organic matter average oleanane index 0 48 high c29 steranes as well as having negative sloping n alkane isotope profiles oxic source depositional conditions pr ph 2 5 and non stratified conditions absence to low gammacerane content are inferred for the terrigenous family the mixed marine terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils bitumen extracts of the sub delta late cretaceous araromi formation shale in the dahomey basin are comparable both molecularly and isotopically to the studied western deepwater oil set but with an over all poor geochemical correlation this poor geochemical match between araromi shale and the western deepwater oils does not downgrade the potential of sub delta cretaceous source rock contribution to the regional oil charge in the deepwater niger delta

sr isotopes in interstitial waters of marine sediments from deep sea drilling project cores sr isotopic compositions of interstitial sea waters have been documented in detail with cores from 37 deep sea drilling project sites the 87sr 86sr ratios are sensitive indicators of diagenetic reactions involving alteration of volcanic matter dispersed in sediments and recrystallization of carbonates effects of basalt alteration reactions except possibly for hydrothermal signals and of alteration of continental debris are minimal carbonate recrystallization has a significant effect on the geochemical mass balance of sr but diffusion of unradiogenic strontium from interstitial waters has only a small effect on the 87sr 86sr ratio of ocean water

major cation gradients in dsdp interstitial waters the role of diffusive exchange between seawater and upper oceanic crust abstract interstitial water analyses from dsdp legs 1 53 were surveyed to identify sites at which the dominant process supporting gradients of major seawater cations is alteration of the underlying oceanic crust sites with thin sediment cover are generally without gradients sites with appreciable sediment accumulation are generally with gradients the transition is probably the result of cessation of convective circulation within the sediments a model is developed for the diffusive flux through an accumulating unreactive sedimentary layer supported by continued reaction within the crust the model is consistent with the observations provided that convection within the crust extends to depths 1 km and that convective flow within the sediments ends once 100 150 m of sediment accumulates the model suggests a steady state gradient inversely proportional to the sedimentation rate this dependence is apparent in the data however some variation in the reaction rate is also required fluxes of mg and na are systematically related to the flux of ca which because of its mobility serves as a tracer of hydrolysis of the basalt when the ca flux is low the mg flux serves as the principal sink for alkalinity produced during basalt hydrolysis when the ca flux is high the mg flux becomes diffusion limited and nabearing alteration phases must form the fluxes resulting from these alteration reactions exert little influence on either the chemistry of seawater or that of the upper crust

pressure retardation of organic maturation in clastic reservoirs a case study from the banqiao sag eastern china abstract three depth related pressure systems are developed in the banqiao sag eastern china as indicated by well logs and direct pressure measurements there are hydropressure mild overpressure and high overpressure within the overpressured sediments the organic maturation profile is nonlinear with five nonparallel segments segments 1 and 3 have abnormally low r o gradients such an organic maturity anomaly is distinctly different from those caused by variation in activation energies thermal conductivity contrasts and hydrologic effects and is believed to result from overpressure retardation the division criteria of diagenetic stages published by china national petroleum corporation cnpc most widely used in china cannot be applied to overpressured clastic reservoirs in the banqiao sag improved division criteria of diagenetic stages are established according to vitrinite reflectance spore pollen colour tai alteration of clay minerals and geotemperature overpressure retardation of maturation is suggested to be important for clearly understanding deep exploration in overpressured sedimentary basins

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

geochemistry and correlation of oils and source rocks in banqiao sag huanghua depression northern china abstract located in the western part of huanghua depression s central segment in the bohai bay basin the banqiao sag is a significant sedimentary basin the crude oil produced has low density low viscosity low sulfur and high wax content crude oil types include conventional crude as well as condensate oil gas light oil and low maturity oil four possible source rocks are present within the banqiao sag however at present the oil source is not very clear rock eval pyrolysis stable carbon isotope composition and biomarker analysis were conducted on 26 source rock core samples in the banqiao sag to evaluate their characteristics results indicate that the shahejie formation 43 32 8 ma has source rocks that can be graded between poor to excellent quality they were deposited in a marine based reducing environment and rich in organic matter sha 1 member es1 and sha 3 member es3 are considered thermally immature to mature based on various maturity indicators 17 crude oil samples from the banqiao sag were compared with these rocks biomarkers and stable carbon isotope parameters the analyzed crude oils were divided into 4 groups based on carbon isotope composition and q type cluster analysis qca there are two sets of effective hydrocarbon source rocks in the study area s shahejie group i e es1x and es3 contributing to the oil found in the structural belts oil and source rock correlation results indicate that group b1 oil is probably derived from highly mature es3 group b2 oil is most likely derived from a mixed mature es3 and early mature es1 group b3 oil is derived from es3 in tanggu xingang buried hill structural belts and from es1 in immature or low mature stage in banqiao sag group b4 oil is derived from mature es3 in banqiao sag with little early mature es1 this study can highly benefit future oil and gas exploration work in the banqiao sag

hopanoid hydrocarbon maturation by an igneous intrusion abstract the thermal effects of an igneous intrusion 0 9 m thick dyke upon the abundance and composition of hopanes and hopenes are reported for a suite of samples within a single sedimentary horizon a carbonate concretion 1 6 m in diameter from the jurassic dun caan shale member bearreraig bay isle of skye scotland the conventional hopane maturity parameters show normal trends towards the dyke and through the oil window approximately 22 45 cm from the dyke i e 25 50 dyke thickness with the exception of the ts ts tm parameter which shows a progressive fall with increasing maturity until the middle of the oil window when it increases markedly molecular abundances demonstrate that the observed changes in the hopane maturity parameters result from the combined effects of generation presumed to be from kerogen and degradation of individual compounds with isomerization in the free phase being minimal or unimportant the unexpected behaviour of ts ts tm results from the minimal generation of ts compared with tm our data indicate that the ts skeleton is not present in the kerogen and at least under the elevated heating associated with an igneous intrusion may be derived from 18 h 22 29 30 trisnorneohop 13 18 ene in the bitumen thermally induced modifications to hopane carbon number distributions are also reported and show that oil source rock correlations between samples of different maturity must consider the effects of generation degradation of kerogen bound hopanes

lithium isotope geochemistry of pore waters from ocean drilling program sites 918 and 919 irminger basin the distribution of li isotopes in pore waters to a depth of 1157 m below seafloor is presented for odp sites 918 and 919 in the irminger basin offshore greenland lithium isotope data are accompanied by strontium isotope ratios to decipher diagenetic reactions in the sediments which are characterized by the pervasive presence of volcanic material as well as by very high accumulation rates in the upper section the lowering of the 87sr 86sr ratio below contemporaneous seawater values indicates several zones of volcanic material alteration the li isotope profiles are complex suggesting a variety of exchange reactions with the solid phases these include cation exchange with nh4 and mobilization from sediments at depth in addition to the alteration of volcanic matter lithium isotopes are therefore a sensitive indicator of sediment water interaction 6li values of pore waters at these two sites vary between 42 and 25 at shallow depths 100 mbsf rapid decreases in the li concentration accompanied by a shift to heavier isotopic compositions indicate uptake of li into alteration products a positive anomaly of 6li observed at both sites is coincident with the nh4 maximum produced by organic matter decomposition and may be related to ion exchange of li from the sediments by nh4 in the lower sediment column at site 918 dissolved li increases with depth and is characterized by enrichment of 6li the li isotopic compositions of both the waters and the solid phase suggest that the enrichment of li in deep interstitial waters is a result of release from pelagic sediments the significance of sediment diagenesis and adsorption as sinks of oceanic li is evaluated the maximum diffusive flux into the sediment due to volcanic matter alteration can be no more than 5 of the combined inputs from rivers and submarine hydrothermal solutions adsorption on to sediments can only account for 5 10 of the total inputs from rivers and submarine hot springs