biological markers and carbon isotope composition of organic matter in the upper cretaceous coals and carbonaceous shale succession jiza qamar basin yemen origin type and preservation abstract bituminous coals and carbonaceous shales located in the jiza qamar basin on the eastern yemen were analysed based on a combined investigation of organic geochemistry and petrology to define the palaeodepositional environment condition organic matter inputs and their thermal maturity carbon isotope compositions and various biomarkers were performed on coals and carbonaceous shales within the upper cretaceous mukalla formation in the jiza qamar basin the 13 c values range from 29 2 to 24 5 with average values around 26 7 whereas the organic carbon contents in most sediment samples are consistently high 3 indicating that the organic matter in the mukalla coal and carbonaceous shale sediments has a predominantly terrigenous origin with slightly marine influence during burial this has also been identified from kerogen microscopy which is characterized by dominance of vitrinite and liptinite organic matter the investigated biomarkers indicated that the mukalla coals and carbonaceous shales contain high contribution of land plants with a minor aquatic organic matter input that was deposited in a fluvial to deltaic environments and preserved under relatively oxic conditions this has been achieved from acyclic isoprenoids terpane and sterane biomarkers of a saturated hydrocarbon and dibenzothiophene alkylnaphthalene and methylphenanthrene biomarkers of an aromatic hydrocarbon based on the analysed biomarker thermal maturity indicators it may be deduced that the mukalla coals and carbonaceous shales in the jiza qamar basin have entered an early mature to mature stages for hydrocarbon generation this is also supported by vitrinite reflectance values of 0 63 0 83 ro indicative that these sediments have reached oil window maturity

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

secondary migration of hydrocarbons in the zhujiang formation in the huixi half graben pearl river mouth basin south china sea the process and mechanisms of secondary hydrocarbon migration in the huixi half graben pearl river mouth basin were investigated on the basis of geological analysis of the strata and study of the porosity and permeability of the reservoir rocks fluid potential oil properties and geochemistry of oil source correlation the results suggest that the hydrocarbons of the zhujiang formation in the huixi half graben were derived from source rocks of the eocene wenchang formation and the eocene oligocene enping formation in the huizhou sag the hydrocarbons migrated laterally from northeast to southwest the sandstone in the upper member of the zhujiang formation exhibited superior physical properties porosity and permeability and connectivity than the lower member thin sandstone beds with good physical properties and stable distribution in the upper member of the zhujiang formation were the main carrier beds for lateral hydrocarbon migration

structure and significance of c30 4 methyl steranes in lacustrine shales and oils abstract the structure of the abundant c 30 4 methyl steranes of ancient freshwater lacustrine sediments and derived oils is of interest as their precursors the 4 methyl and in particular 4 23 24 trimethyl sterols dinosterols are reported to be specific to dinoflagellates this study employs a novel liquid crystal gc phase combined with gc ms and gc ms ms to separate and characterise mixtures of c 30 4 methyl sterane standards not resolvable on non polar phases this technique is then applied to identify the c 30 4 methyl steranes in an ancient freshwater sediment a freshwater lacustrine and a marine derived oil a comparison is also made with the 4 methyl steranes in marine sediments containing varying amounts of dinoflagellate cysts the c 30 4 methyl steranes of the freshwater lacustrine samples have been shown to possess a 4 methyl 24 ethylcholestane structure while both 4 methyl 24 ethylcholestanes and 4 23 24 trimethyl 5 h cholestanes dinosteranes were found in the marine dinoflagellate rich sediments while still indicative of dinoflagellates 4 methyl 24 ethyl sterols are generally not the major dinoflagellate sterol and alternative explanations for the abundance of 4 methyl 24 ethylcholestanes in ancient lacustrine sediments should be considered possibly ancient freshwater dinoflagellates synthesised principally the 4 methyl 24 ethyl form alternatively a source from an unrecognized algal class is possible while a source from bacteria which are known to synthesise certain 4 methylsterols is discussed

identification and significance of 3β ethyl steranes in sediments and petroleum abstract 3 ethyl steranes 5a c occur in ancient sediments and petroleum particularly those of paleozoic and proterozoic age this newly recognised modification to the sterane ring system has no known direct counterpart in the steroid metabolism of extant organisms when they are present in a sample the pattern of side chain substitution and some aspects of the isomer distributions of co occurring 3 ethyl steranes 5a c 3 methyl steranes 3a c 2 methyl steranes 2a c and desmethyl steranes 1a c are similar this suggests that these ring a alkylated steranes are not synthesised de novo by their source organism s but arise via microbial modifications to sedimentary sterenes during the early stages of diagenesis

hydrocarbon generation potential of upper eocene enping formation mudstones in the huilu area northern pearl river mouth basin south china sea upper eocene enping formation mudstones in the pearl river mouth basin south china sea which formed during a lake flooding event are one of the most important sets of cap rocks in the basin however the generation potential gp of enping formation mudstones remains poorly understood and controversial despite a lack of documentation these mudstones are presumed to have the potential to generate hydrocarbons in this study new organic geochemical data for these mudstones are provided based on several new wells drilled into eocene strata in the huilu area northern pearl river mouth basin which illustrate their hydrocarbon gp total organic carbon content ranges from 0 55 to 3 3 wt mean 1 31 wt with kerogens dominated by type iii organic matter om derived from terrigenous plant material the zhuqiong ii movement a rifting episode that occurred during the late eocene ca 38 ma was associated with the introduction of a large quantity of terrigeneous higher plants by rivers that led to type iii om accumulation and preservation of enping formation mudstones rapid transverse facies changes led to the geochemical heterogeneity of the source rocks the om in these rocks reached an early midmature stage in uplifted areas vitrinite reflectance ro e 0 5 1 0 and a late mature stage in sags ro e 1 0 1 3 stages wherein hydrocarbons can be generated therefore the enping formation mudstones may have had the potential to generate hydrocarbons especially gas and hence deserve attention in future exploration

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

sedimentary organic matter sources and depositional environment in the yegua formation brazos county texas abstract the complex depositional environment of the eocene yegua formation brazos county texas can be better understood by integrating organic matter om geochemistry with stratigraphy yegua sediments represent parasequences separated by exposure surfaces organic petrography and geochemistry biomarkers c n ratios and carbon isotopes indicate the presence of both terrestrial and marine om in transgressive sediments in contrast regressive sediments contain only terrestrial om these differences relate to contrasting om sources and depositional styles on the shelf om in the sediments is immature and the potential for generating hydrocarbons is poor the study suggests that organic geochemical data can help in distinguishing transgressive and regressive environments in sedimentary formations

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

abundant and diverse early paleozoic infauna indicated by the stratigraphic record marine benthic animals have lived within the sediment since the late precambrian an abundant early paleozoic infauna is indicated by bioturbated zones and diversity of deposit feeder and suspension feeder trace fossil genera burrow depths extended tens of centimetres below the sediment water interface trace fossil evidence of an abundant early paleozoic infauna conflicts with evidence from the shelled fauna which lacks infauna this requires reinterpretation of early paleozoic community structure and raises new questions about interactions between early paleozoic soft bodied and skeletonized animals

application of 24 norcholestanes for constraining source age of petroleum abstract two c26 sterane ratios the 24 nordiacholestane ratio ndr and the 24 norcholestane ratio ncr are useful for assessing petroleum source age values for these parameters generally increase in the cretaceous when diatoms were rapidly radiating and further in the oligo miocene due to widespread high latitude deposition of diatomaceous sediments sources with shale lithologies tend to exhibit the highest ratios while carbonate and terrigenous rich lithologies generally show lower ratios on the north slope of alaska elevated ratios are observed for cretaceous hrz oils and mixed oils containing cretaceous input compared to older triassic and jurassic derived oils tertiary sourced oils from romania and bulgaria have much higher ratios relative to jurassic sourced oils in the black sea region oleanane was observed in comparable levels in some black sea tertiary and jurassic oils and source rocks ndr and ncr coupled with other age diagnostic indicators such as oleanane and dinosterane provide powerful tools for differentiating age of source and organic facies for oils from the black sea and sub andean basins of peru and ecuador respectively oils derived from sources deposited in low tropical latitudes tend to have little diatom input and as a consequence do not display high values regardless of age

the origin and fate of 4 methyl steroids ii dehydration of stanols and occurrence of c30 4 methyl steranes abstract certain features of the distributions of sedimentary 4 methyl steroid hydrocarbons have been investigated i competitive dehydration experiments with stanols adsorbed on a shale suggests a possible explanation for the low abundance of 4 methyl sterenes relative to their desmethyl counterparts in immature sediments ii a 4 methyl spirostene which is a minor product of the backbone rearrangement of 4 methylcholest 4 ene in the laboratory has been tentatively assigned its presence in a toarcian black shale with a second isomer provides further evidence that the sedimentary backbone rearrangement of 4 methyl sterenes is analogous to that of their desmethyl counterparts and iii the major c30 4 methyl steranes in semecourt shale toarcian paris basin differ from those in an eocene lacustrine shale from china this indicates the potential complexity of c30 steroidal alkanes both 4 methyl and desmethyl which can occur in sedimentary organic matter and shows that care must be taken in using m z 217 mass chromatograms alone for routine input and maturity assessment using steroidal alkanes

dinoflagellate origin for sedimentary 4α methylsteroids and 5α h stanols biological marker compounds provide useful tools for evaluating the depositional environments of recent and ancient sediments and petroleums1 largely through established relationships between the organic matter of sediments and source organisms1 2 such relationships are best tested and explored by investigating the lipid components of natural populations of autochthonous biota that can be clearly recognized as contributors to underlying bottom sediments in this context we have studied the lipids of the freshwater dinoflagellate peridinlum lomnickii woloszynska order peridiniales class dinophyceae collected from the waters of priest pot3 a eutrophic lake in the english lake district its distributions of both 4 methylsterols and 4 methylstanones closely resemble those of the underlying bottom sediments demonstrating that dinoflagellates are important contributors of these sedimentary compounds the 4 methylsteroidal hydrocarbons found in ancient sediments and petroleums4 6 are presumably diagenetic products of such 4 methylsteroids and therefore reflect dino flagellate inputs to the original depositional environments furthermore the prominence of 5 h cholestan 3 ol in p lomnickii suggests that dinoflagellates may be the long sought direct biological source of sedimentary 5 h stanols

sources and preservation of organic matter in the cretaceous toolebuc formation eastern australia abstract the organic matter rich toolebuc formation of eastern australia was deposited in a lower cretaceous epicontinental sea parameters from biological marker studies indicate that the organic matter is immature to marginally mature for hydrocarbon generation the occurrence of abundant coccoliths and the distribution of alkane biomarkers suggest that the organic matter type ii is largely of planktonic origin and only in the southeastern part of the depositional area can a terrestrial influence be discerned variations in kerogen composition can be attributed to the extent of the oxidation of the source materials and the degree of incorporation of sulphur the atomic h c ratios c 1 1 are remarkably constant for most of the toolebuc formation atomic o c ratios vary from 0 1 and 0 4 and can be related both to depth and paleogeographic position kerogen sulphur contents range up to 7 and the highest values occur in the most carbonate rich sediments total sulphur inorganic organic to carbon ratios in the sediments vary from 1 to

role of seepage forces on seismicity triggering 1 borehole fluid injection is commonly used for geological sequestration of carbon dioxide underground storage of natural gas waste injections and during stimulations and development of geothermal and hydrocarbon reservoirs typically the injection process induces significant seismicity with some earthquakes as large as magnitude four induced seismicity has also been observed around producing hydrocarbon boreholes recently it has been argued that some induced seismicity data can be explained by a highly nonlinear fluid diffusion mechanism or by the propagation of fluid pressure pulses the nature of the nonlinearity and the mechanisms by which a pressure pulse can trigger seismicity are still uncertain in this paper i show that the same spatiotemporal variation of seismicity can be explained and predicted by linear diffusion coupled to deformation of a linear poroelastic medium by calculating the propagation of coulomb yielding stress cys perturbation with time it is demonstrated that seismicity can be triggered by this perturbation the change of cys along the diffusion front is caused by seepage forces which are body forces generated by fluid pressure gradients and can explain induced seismicity during borehole fluid injection and extraction using published experimental data i demonstrate how the spatiotemporal distribution of fluid induced seismic events can be used for reservoir modeling and characterization

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

the distribution of molecular fossils derived from dinoflagellates in paleogene lacustrine sediments bohai bay basin china steroids with unconventional side chains in ancient sediments and petroleum have been increasingly used as age diagnostic markers triaromatic dinosteroids and dinosteranes occur widely throughout the eocene oligocene shahejie formation in the southeastern bohai bay basin china consistent with its abundant fossil dinoflagellate assemblages in addition 24 norcholestane biomarkers which commonly appear in marine oils have been found in this lacustrine formation although a firm link has not been established between 24 norcholestane and specific modern taxa both diatoms and dinoflagellates are shown to be likely sources of 24 norcholestanes although the shahejie strata lack intact diatom frustules they do exhibit a good relationship between 24 norcholestane other molecular fossils of dinoflagellates and dinocysts dinoflagellates are important precursor taxa of 24 norcholestanes and the various species identified in eocene oligocene lacustrine shales and mudstones of the shahejie formation are all potential sources of the 24 norcholestanes

a molecular and carbon isotope biogeochemical study of biomarkers and kerogen pyrolysates of the kimmeridge clay facies palaeoenvironmental implications abstract structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite a bituminous shale and an oil shale of the kimmeridge clay formation kcf in dorset were studied in order to gain insight into i the type and extent of water column anoxia and ii changes in the concentration and isotopic composition of dissolved inorganic carbon dic in the palaeowater column the samples studied fit into the curve of increasing 13 c of the kerogen 13 c toc with increasing toc reported by huc et al 1992 their hypothesis that the positive correlation between toc and 13 c toc is the result of differing degrees of organic matter om mineralisation in the water column was tested by measuring the 13 c values of primary production markers these 13 c values were found to differ on average by only 1 among the samples implying that differences in the extent of om mineralisation cannot fully account for the 3 difference in 13 c toc the extractable om in the oil shale differs from that in the other sediments due to both differences in maturity and differences in the planktonic community these differences however are not likely to have significantly influenced 13 c toc either all three sediments contain abundant derivatives of isorenieratene indicating that periodically euxinia was extending into the photic zone the sediments are rich in organic sulfur as revealed by the abundant sulfur compounds in the pyrolysates the prominence of c 1 c 3 alkylated thiophenes over n alkanes and n alkenes is most pronounced in the pyrolysate of the sediment richest in toc this suggests that sulfurisation of om may have played an important role in determining the toc 13 c toc relationship reported by huc et al 1992

origin of hydrocarbons in triassic serpiano oil shales hopanoids abstract the hydrocarbons in the sapropelic serpiano oil shales have been examined the hopanoids are the most predominant hydrocarbons present in the bitumen with hopanes hopenes benzohopanes and monoaromatic secohopanoids being detected the novelty of the serpiano hopanoid assemblages lies in the occurrence of high concentrations of methylhopanoids the distributions of the hopanoids and of their corresponding methylhopanoids are remarkably similar this similarity was also observed for the hopanes and methylhopanes which were generated from the asphaltene and kerogen by hydrous pyrolysis and is indicative of a common biosynthetic pathway

geochemical and petrographic characterization of organic matter in the upper jurassic madbi shale succession masila basin yemen origin type and preservation the upper jurassic madbi formation located in the masila basin eastern yemen represents the major source rock in this basin organic rich shales from two oilfields kharir and wadi taribah were analysed to evaluate the type and origin of the organic matter and to determine the factors controlling its deposition this study is based on geochemical analyses of whole rock total organic carbon content rock eval pyrolysis and carbon isotope data and petrographic analyses on organic matter kerogen maceral composition and palynofacies by optical and scanning electron microscopy organic petrographic composition of kerogen shows that the madbi shale is characterized by high amounts of organic matter consisting predominantly of yellow fluorescing amorphous organic matter and alginite of marine origin terrigenous organic materials such as vitrinite spores and pollen are present in low quantities the predominance of marine plankton as indicated by visual kerogen analysis is consistent with reported carbon isotopic values it appears that the high amounts of organic matter in the madbi shale succession might be mainly due to good preservation under suboxic anoxic conditions consequently the madbi shales possess very good petroleum generative potential owing to high content of hydrogen rich type ii and i oil prone kerogen

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

geochemistry and origin of heavy oils in the south part of zhanhua depression east china abstract the sanhecun sag located in the south of the zhanhua depression has yielded a significant amount of heavy oil in recent years and is becoming a new exploration focus in the jiyang sub basin surprisingly oils in the deep shahejie formation have higher densities and viscosities than those in the shallow guantao formation in this study geochemical and fluid inclusion analyses of oils from different depths were carried out to clarify their source and the cause of the high densities oils in the shahejie formation with high contents of resins and asphaltenes 47 56 are generated from the es4 carbonate source rocks that were deposited in a hypersaline environment with a relatively high terrigenous organic matter contribution maturity parameters and fluid inclusions show that the oils with low saturated hydrocarbon contents and high resin and asphaltene contents were charged to the shahejie formation from 29 ma to 27 ma when the source rocks were in the early oil generation window although subsequent biodegradation further increased oil density the main control on the high densities of oils in the shahejie formation is the nature of the source kerogen oils in the shallow guantao formation can be divided into two groups a group from es3 source rocks in the gunan sag and a second from es3 and es4 source rocks in the bonan sag they were expelled within the oil generation window and charged the reservoirs between 3 ma and the present day oils in the guantao formation have undergone light to heavy biodegradation ranging from pm levels 2 to 5 with the increase of biodegradation level saturated hydrocarbon contents gradually decrease from 50 to 22 while the contents of resins and asphaltenes increase from 28 to 43 biodegradation is the primary cause of oil densification in the guantao formation although oils in the guantao formation suffered more severe biodegradation they still have higher contents of saturated hydrocarbons than those in the shahejie formation source type maturity and biodegradation thus combine in different ways to control the density of heavy oils in the sanhecun sag this study also indicates that low mature oils from es4 carbonate source rocks can charge reservoirs in the southern part of zhanhua depression before late oligocene uplift and low mature oil may be a potential future target in this area

sterane and triterpane biomarkers in the precambrian nonesuch formation north american midcontinent rift abstract molecular fossils and organic matter from microbial communities living around 1 1 ga ago are well preserved in the nonesuch formation of the us midcontinent rift system although some compound classes of biological markers have been recognized repeatedly in previous studies of nonesuch rocks and associated petroleums steranes and triterpanes have not been detected failure to detect these compounds was due primarily to instrumental limitations and the relatively high thermal maturity of samples collected within zones of copper mineralization our analyses of nonesuch samples from the white pine mine and nonmineralized localities in michigan and wisconsin reveal suites of c 26 c 30 steranes and c 27 c 35 pentacyclic triterpanes similar to those found in phanerozoic oils and sedimentary rocks of marine origin stereoisomeric distributions in the nonesuch samples are consistent with moderate thermal maturity except in the mineralized zone near white pine

the significance of 24 norcholestanes 4 methylsteranes and dinosteranes in oils and source rocks from east sirte basin libya abstract the present paper involves a detailed evaluation of specific steroid biomarkers by gas chromatography mass spectrometry gc ms and gc metastable reaction monitoring mrm analyses of several crude oils and source rocks from the east sirte basin 24 norcholestanes dinosteranes 4 methyl 24 ethylcholestanes and triaromatic steroids have been identified in both source rocks and crude oils of the east sirte basin diatoms dinoflagellates including those potentially associated with corals and or their direct ancestors are amongst the proposed sources of these biomarkers these biomarker parameters have been used to establish a mesozoic oil source correlation of the east sirte basin hydropyrolysis of an extant coral extract revealed a similar distribution although immature of dinosteranes and 4 methyl 24 ethylcholestanes also observed in the sirte oils and source rocks this is consistent with the presence of dinoflagellates present during the deposition of the mesozoic aged east sirte basin formations a good data correlation for the rock extracts revealed a similar distribution of 3 24 dimethyl triaromatic steroids 3 methyl 24 ethylcholestanes 4 methyl 24 ethylcholestanes and 2 methyl 24 ethylcholestanes observed in one of the oil families and associated source rocks for the east sirte basin

biological marker compounds as indicators of the depositions history of the maoming oil shale abstract the eocene maoming oil shale from guangdong province occurs as a laterally uniform stratigraphic section typically 20 25 m thick from which the aliphatic hydrocarbon constituents of six representative samples were investigated using gc and c gc ms the sediments evaluated included the basal lignite a vitrinite lens from the overlying claystone and four intervals from the massive oil shale bed as expected the lignite and vitrinite differ markedly from the oil shales the lignite is dominated by bacterial hopanoids and components of higher plant origin including c 29 steroids and triterpenoids such as oleanenes visually the oil shale samples show corroded and degraded phytoclasts spores wispy particles of fluorescent organic material attributable to dinoflagellates and especially in the uppermost sample colonial algal bodies the distributions of biological markers in the oil shales show many features in common notably a dominance of dinoflagellate derived 4 methylsteroids and a significant proportion of higher plant derived n alkanes with marked odd over even carbon number predominance overall they exhibit several features that resemble characteristics of the messel shale the hydrocarbons of the lowest shale horizon suggest that there may have been a gradual transition between deposition of the original peat and the subsequent oil shales the aliphatic hydrocarbons of the uppermost shale are dominated by a number of c 31 and c 33 botryococcane homologues and other unusual branched alkanes possibly derived from green algae all of the samples are immature overall molecular and microscopic examination of the stratigraphic succession of the maoming oil shale suggests a shallow lacustrine environment within which peats were deposited this lake subsequently deepened to support abundant algal populations especially dinoflagellates culminating in a dominance of botryococcoid algae

thiophenic biomarkers for palaeoenvironmental assessment and molecular stratigraphy reconstruction of ancient depositional environments is an important objective in the earth sciences the complex assemblages of organic molecules in sediments include compounds that can be related to known biochemicals produced by specific biota from well defined habitats1 3 and these chemical fossils are applied frequently to reconstruct palaeoenvironments especially in studies of organic and petroleum geochemistry and in chemical oceanography most of the compounds used in this way are hydro carbons2 4 although oxygenated for example alcohols acids and ketones and nitrogen containing for example porphyrins compounds have also been applied successfully1 2 here we report on the use of organic sulphur compounds as geochemical tools for palaeoenvironmental and stratigraphic assessment depth profiles of specific sulphur compounds related to certain organisms show significant variations reflecting changes both in sources of organic matter and in physical conditions such as salinity of the depositional environment in a number of cases these variations are not otherwise revealed by changes in lithology geochemical bulk data and or absolute and relative amounts of hydrocarbon biological markers moreover several organic sulphur compounds reveal the presence of unprecedented biochemicals in these palaeoenvironments

organic geochemistry and basin modeling of late cretaceous harshiyat formation in the onshore and offshore basins in yemen implications for effective source rock potential and hydrocarbon generation abstract the purpose of this study is to present the source rock characteristics of late cretaceous harshiyat formation source rock in the onshore and offshore basins of yemen i e mukalla sayhut sayun masilah and jiza qamar source rock geochemical characterizations were completed and integrated to perform 1 d basin modeling to back predict source rock thermal maturation oil generation and expulsion the geochemical findings revealed that mudstone intervals within the harshiyat formation comprised favorable source rocks with total organic carbon toc content between 0 50 and 35 10 wt the organic matter intervals in the harshiyat mudstones are mainly types ii iii and iii kerogens with certain amount of type ii and i kerogens based on rock eval hi values ranging from 40 to 923 mg hc g toc mixed kerogen types were consistent with vitrinite and sapropelic organic matters as observed by visual kerogen examination and the distribution of biomarker fingerprints the existence of mixed types i ii and iii organic matter suggests that the harshiyat mudstones could contribute to oil and gas at sufficient thermal maturity levels the biomarker data of the organic matter in the harshiyat mudstones show that the source rock contains a mix marine phytoplanktonic bacteria terrestrial land plant enthronement and were deposited in suboxic anoxic conditions results of chemical and optical maturity indicators led to the conclusion of varying maturity stages from immature to late oil window levels for the mudstones of the harshiyat formation thermal maturation distributions inferred from the analyzed samples indicate that mudstone intervals in the offshore mukalla sayhut basin are extremely mature compatible with the late mature oil window and may have generated significant amounts of oil this interpretation was supported by strong geochemical similarity between the organic matter in the mudstones and those of the oils found in the offshore mukalla sayhut basin and demonstrated by the concentrations of n alkanes and isoprenoids as well as carbon isotopes in the offshore ras ghashwah 1x well burial and thermal models were constructed and used to address the effect of tectonic events in triggering oil generation and expulsion from mature harshiyat source rock in the offshore area kinetic database models for type ii and iii kerogen mixtures indicate that the initial conversion of kerogen to oil occurred since the late oligocene with transformation ratios tr that span between 10 and 50 furthermore the oil was expelled from organic matter intervals in the harshiyat source rock starting from late oligocene and continuing until late miocene with trs of 50 72 from that period up to the present the retained oil was cracked into wet gas in the gas window with an easy ro greater than 1 30 and with peak tr ratios greater than 72

dinosteranes 4 23 24 trimethylsteranes and other biological markers in dinoglagellate rich marine sediments of rhaetian age abstract alkane biological marker distributions and concentrations have been determined in 18 samples from a section of rhaetian age from the bristol trough and a quantitative micropalaeontological analysis carried out taking into account previous geological investigations of the sequence three end member depositional settings have been recognised from changes in total organic carbon content the biological markers and the micropalaeontological composition these depositional environments are attributed as follows the first which occurs in the lower part of the section corresponds to deposition in a supratidal sabkha type setting with the major organic input being of allochthonous origin the second also in the lower part of the section indicates the occurrence of periods of marine incursion with enhanced salinity resulting from evaporation in the upper part of the section marginal marine conditions are apparent with higher organic carbon biological marker and amorphous organic matter contents at the top suggesting the establishment of more stable conditions of oxygen depletion some sediments in the sequence are notable for containing an abundance of cysts of rhaetogonyaulax rhaetica one of the oldest marine dinoflagellates comparison of microfossil abundances with hydrocarbon abundances extends the circumstantial evidence for the dinophyceae being the major biological source of dinosteranes 4 23 24 trimethylcholestanes and some other 4 methyl steranes in marine sediments the presence of dinosteranes and their 24 ethyl counterparts extends the stratigraphic range of occurrence of such components back to the rhaetian c 31 methyl steranes in the sediments from the second depositional setting are tentatively assigned a 4 22 23 24 tetramethyl sterane skeleton and a dinoflagellate origin