mg rich ferric illite in marine transgressive and highstand systems tracts examples from the paleoproterozoic semri group central india this paper focusses upon two glauconitic sandstones in the paleoproterozoic deoland formation and chorhat sandstone both belonging to the semri group central india in both the cases glauconitic minerals occur in sandstones deposited in the marine realm within a transgressive systems tract tst for the former unit and within a highstand systems tract hst for the latter the proportion of glauconitic minerals increases in the paleo offshore direction petrography reveals selective early glauconitization of detrital k feldspars along their fringes cleavages and the fractures created by volume expansion during progressive alteration leading to the generation of peloids with small relics of the precursors xrd and mineral chemistry reveal a structure typical of glauconite and more akin to mg rich ferric illite the mineral chemistry of the glauconitic mineral phases remains the same whether the glauconitization process was incipient or at an advanced

palaeoecology of boreal invertebrate faunas from the upper jurassic of central east greenland abstract the upper jurassic of milne land greenland is a transgressive regressive sequence ranging from offshore shallow sandbar complexes in the late oxfordian to outer shelf muds in the kimmeridgian and early to middle volgian within the middle volgian rapid shoreline progradation led to deposition of inner shelf silts and nearshore sands within this envirobmental framework 22 benthic macroinvertebrate associations and several assemblages occur they are dominated by suspension feeding bivalves less commonly by brachiopods or detritus feeding serpulid polychaetes despite frequently low rates of sedimentation and plenty of suitable substrates surprisingly few shells are bored or encrusted which may reflect biogeographic factors although some inter and intraspecific interactions are recorded the associations are thought to have been largely controlled by environmental parameters low diversity associations are related to low oxygen conditions at the sea floor or unstable shifting substrates but in some cases may have been due to biotic interactions levels with reduced rates of sedimentation and glauconite formation are characterized by epifaunal associations those with higher rates of sedimentation by infaunal or semi infaunal associations the temporal and spatial distribution pattern of the benthic invertebrate fauna is fairly complex due to the interplay of several biotic and abiotic factors the absence of strong environmental gradients in outer shelf areas and diagenetic overprint selectivity removing low density faunas among bivalves species replacement through time was in most cases ecological

geochemistry and correlation of crude oils from reservoirs and source rocks in southern biyang sag nanxiang basin china abstract the paleogene hetaoyuan formation a sequence of gray to dark calcareous mudstone and dolomitic mudstones is the main source rock and reservoir in the biyang sag nanxiang basin eastern china organic geochemical analysis study performed on 57 source rock samples from the hetaoyuan formation demonstrates poor to abundant organic matter content ranging from 0 24 5 4 wt toc content characterized by oil prone type ii kerogen eleven crude oil samples from the hetaoyuan formation in southern biyang sag were analyzed using bulk properties and molecular methods to determine their maturity and origin the results suggest that the crude oils exhibit different maturity and source organic matter three groups of oils were identified by integrated analysis of gas chromatography gas chromatography mass spectrometry stable carbon isotope physical properties and gross composition of crude oil group a oils defined as low mature oil are characterized by high density viscosity sulfur content and low saturated hydrocarbon content this group of oils has relatively high values of ph n c 18 c 24 c 26 and gammacerane index indicating that the original organic matter had more contribution from terrigenous plants and was deposited in saline and stratified water columns under anoxic conditions group b oils defined as normal maturity oil are characterized by moderate density viscosity sulfur content and moderate saturated hydrocarbon content this group of oils has relatively low values of ph n c 18 c 24 c 26 and gammacerane index and displays a slight predominance of c 29 steranes indicating that the original organic matter had more contribution from marine algae and was deposited under sub oxic to anoxic conditions with low salinity group c oils defined as light oil are characterized by low density viscosity and abundant saturated hydrocarbons representative source rock samples were selected for further correlation the results of oil source rock correlation suggest that crude oils from the eh 2 member of hetaoyuan formation are mixture derived from source rocks in the eh 2 member and upper layer of the eh 3 member while oils from the upper and lower layer of the eh 3 member correlate with source rocks in the upper and lower layers of the eh 3 member respectively

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

krill as a central node for iron cycling in the southern ocean 1 in order to establish the potential role of antarctic krill euphausia superba in the recycling of bioactive elements we have quantified the release of iron phosphate and ammonia by these organisms along the antarctic peninsula sector of the southern ocean the experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations as large amounts of this trace element were released by the krill 22 689 nmol fe g dry weight 1 h 1 equivalent to 0 2 to 4 3 nmol fe l 1 d 1 half of this iron release occurred within the first hour of the experiment and differences in iron and phosphate release rates 3 1 to 14 0 mol po43 g dw 1 h 1 seemed to reflect differences in food availability these results identify krill as a major node in iron cycling in the southern ocean potentially influencing iron residence time in the upper water column of this region

multiple stage migration and accumulation of permian lacustrine mixed oils in the central junggar basin nw china abstract the permian lacustrine petroleum system in the central junggar basin northwest china has recently obtained exploration success these accumulations are characterized by mixed oils and multiple stage migration and accumulation this process however has not been well constrained limiting the understanding of the general laws of hydrocarbon migration and accumulation and making it difficult to define exploration strategies here we reconstruct this process mainly based on oil bearing fluid inclusion analyses including petrography homogenization temperature and sequential extraction inclusion petrography shows that petroleum inclusions dominantly display yellow fluorescence while intergranular free oils mostly display strong blue green fluorescence this implies that the reservoirs seem to have experienced at least two stages of hydrocarbon charge from different sources and or maturities the sources maturities are determined through reservoir sequential extraction analyses the free oils are mixed and sourced from the lower permian fengcheng formation p1f and the middle permian lower wuerhe formation p2w while the inclusion oils are also mixed and derived mainly from the p1f source both oils are characterized by moderate maturity homogenization temperature measurements of oil bearing fluid inclusions combined with reconstruction of reservoir burial and thermal history not only further verify multiple hydrocarbon charging events but also characterize the timing which indicates a three stage petroleum charging model during the first stage of the late triassic carboniferous reservoirs were charged by p1f sourced oils which were dysmigrated or remigrated to jurassic reservoirs during the second stage i e the early cretaceous in contrast the third stage from the late cretaceous represents another hydrocarbon charge event that is the primary oil accumulation sourced from the p2w rocks according to this model both primary and secondary oil accumulations contribute to the current region s exploration success and provide future exploration targets

source rock facies distribution predicted from oil geochemistry in the central sumatra basin indonesia the molecular and compound specific isotopic composition of the n alkanes in 30 oil samples from the central sumatra basin were analyzed with the purpose of determining facies variations of the source rock in this basin the oil samples were generated by the eocene oligocene lacustrine brown shale formation biomarkers in the oil samples indicate varying contributions from algal and terrigenous organic matter primarily under oxic or suboxic depositional conditions five source rock facies were identified based on the relative concentrations of n alkanes isoprenoids tricyclic terpanes and steranes the individual facies were also distinguished by the compound specific isotopic composition of the n alkanes source rock depositional environments vary from deep lacustrine shallow lacustrine and lacustrine saline to coal and mixed coal and lacustrine shale deep lacustrine facies predominate in the aman and bengkalis troughs whereas saline and shallow lacustrine facies predominate in the south aman and kiri troughs respectively oils derived from coal and mixed coal and lacustrine shale facies predominate in the northern part of the central sumatra basin in the tanjung medan and north of the balam grabens

tracing migration pathways by integrated geological geophysical and geochemical data a case study from the jx1 1 oil field bohai bay basin china tracing petroleum migration pathways is essential for predicting petroleum occurrence and reducing exploration risks associated with hydrocarbon charge but a difficult task because of rapid lateral and vertical facies changes in lacustrine basins an integration of geological geophysical and geochemical analysis is employed to investigate the origin of crude oil the carrier bed architecture and migration pathways from source to trap in the jx1 1 oil field liaodong bay subbasin bohai bay basin detailed geochemical studies suggest that three potential source rock intervals and exist in the liaodong bay subbasin and crude oil in the jx1 1 field was derived from the and source rocks the carrier beds from and source rocks to the trap were characterized using geophysical data the fan delta sandstone in the member has an immediate contact with source rock and served as dominant conduit for the expulsion and migration of oil generated from source rock the braided delta sandstones overlying the source rock served as dominant conduit for sourced oil the focusing of petroleum migration pathways and the merge of migration pathways in and sandstones account for the accumulation of the jx1 1 field and the mixing of and sourced oil in the field this study suggests that the distribution of permeable sandstones and their stratigraphic contact with the source rocks are key for petroleum migration and occurrence and integration of geophysical geological and geochemical studies provide an effective way to trace petroleum migration pathways

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

distribution controlling factors and oil source correlation of biodegraded oils in the bohai offshore area bohai bay basin china the vast majority of discovered oils in the bohai offshore area have undergone biodegradation varying from 1 to 9 on the pm scale a scale to rank the level of biodegradation proposed by peters and moldowan 1993 the distribution and biodegradation extent of all discovered oils in the bohai offshore area were investigated systematically using geologic and geochemical data to reveal controlling factors of varying levels of biodegraded oils based on the analysis on environment and maternal significances and the resistance to degradation of biomarkers the biomarker parameter assemblage that is suitable for the oil source correlation of severely biodegraded oils higher than pm 6 in the bohai offshore area was determined spatial distribution and biodegradation extent are mainly controlled by current burial depth the duration of biodegradation the area of the oil water contact owc and a late strike slip movement of the tanlu fault almost all biodegraded oils are found in shallow reservoirs above 2000 m the longer the oils are present in these reservoirs or the larger the area of owc the reservoirs show the greater the extent of biodegradation will be the late strong strike slip movement of the tanlu fault may have significantly enhanced the biodegradation extent of several oils in fields located in the tanlu fault zone by introducing oxygenated freshwater from the surface or near surface and creating a more suitable environment for biodegradation c19 tricyclic terpane c23 tricyclic terpane c19 c23 tt c24 tetracyclic c26 tricyclic terpane c24 tet c26 tt and gammacerane c24 tetracyclic gam c24 tet do not seem to be influenced by biodegradation and show obvious differences between the three different source rock intervals such a biomarker parameter assemblage can be used successfully to determined the origin of severely biodegraded oils higher than pm 6 by correlating with extracts of possible source rocks in the bohai offshore area

oil source correlation in the slope of the qikou depression in the bohai bay basin with discriminant analysis abstract the commonly used tools for oil source correlation such as mass chromatograms of biomarkers and bivariate cross plots of geochemical parameters cannot deal with multiple geochemical parameters and plenty of samples simultaneously leading to uncertainties in the results and even failures sometimes in this paper the discriminant analysis da is selected from supervised machine learning algorithms as it is superior to the commonly used tools as well as other multivariate statistical methods with the accumulation of geochemical data of source rocks and oils in the slope of the qikou depression the main source rocks in the third es3 and first members es1 of the paleogene shahejie formation were deposited in similar depositional environments the source rocks cannot be distinguished with the commonly used tools we firstly extended geochemical parameters and then used stepwise da to select informative parameters and to develop a discriminant model for oil source correlation the 22 selected parameters are supported by geochemical characteristics of the source rocks in the study area the da of these parameters for oil source correlation achieved a high correct rate of original validation 96 8 and leave one out cross validation 89 4 indicating a sufficient discriminatory power the oil source correlation results with high posterior probabilities showing strong similarity between the sources and oils coincide with geological conditions and illustrate that there is still much exploration potential in the study area especially for the es3 petroleum system all these illustrate that da is one of the most useful tools for oil source correlation with the accumulation of geochemical data of source rocks and oils

light hydrocarbon gasoline range parameter refinement of biomarker based oil oil correlation studies an example from williston basin abstract we evaluated geochemical compositions of 189 crude oils produced from paleozoic reservoirs across the williston basin emphasis is placed on compositional variations in the gasoline range i c 5 h 12 n c 8 h 18 to verify the biomarker based classification of oil families the oils belong to four distinct compositional oil families a b c and d broadly confined to specific stratigraphic intervals the unique character of each oil family evident from their n alkane and biomarker signatures is supported by distinctive gasoline range characteristics in general and c 7 mango parameters in particular an invariance in the k1 parameter among oils from a single compositional group is observed for most of the oils the k1 ratio although relatively constant within each suite of oils is different for each oil family clearly indicating their compositional distinction other mango parameters n2 p2 p3 show a similar reflection of the oil families however while c 7 parameters provide excellent evidence for distinct familial association of oils from families a b and d family c often overlaps with the latter two families perhaps indicating greater genetic and source heterogeneity in the family c oils nevertheless differences in the gasoline range composition suggest that the existing biomarker based classification of oil families can be more universally applied throughout the entire williston basin moreover because the light hydrocarbon parameters prove very useful in refining oil oil correlations routine gasoline range analysis shows good potential as a supplementary component in geochemical correlation of crude oils especially when high levels of thermal maturity decrease the usefulness of biomarker compounds

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

hydrocarbon generating potential and accumulation contribution of the fourth member of the shahejie formation in the liaodong bay sub basin bohai bay basin abstract the liaodong bay sub basin is one of the most petroliferous sub basins in the bohai bay basin the fourth member of the eocene shahejie formation e 2 s 4 50 5 42 ma which is an important source rock interval in other sub basins was rarely studied in the liaodong bay sub basin the hydrocarbon generating potential biomarker assemblage and accumulation contribution for discovered oil fields of the e 2 s 4 source rock interval in the liaodong bay sub basin were studied using geological and geochemical data the e 2 s 4 source rocks in the liaodong bay sub basin display relatively high total organic carbon contents toc and rock eval hydrogen indices hi and can be considered as a set of excellent oil prone tendency source rocks the source rocks interval is characterized mainly by relatively low pristane phytane pr ph c 19 c 23 tricyclic terpane c 19 c 23 tt c 24 tetracyclic terpane c 26 tricyclic terpane c 24 tet c 26 tt low to medium hopane sterane h s medium 4 methyl steranes c 29 steranes ratio 4 ms c 29 st c 35 22s c 34 22s hopane c 35 c 34 sh and high gammacerane c 30 hopane g h extended tricyclic terpane ratio etr c 28 tt c 29 tt c 28 tt c 29 tt ts and were deposited in anoxic to sub oxic saline water environment with no or minor terrigenous organic matter and medium dinoflagellate input the maturity of e 2 s 4 source rocks in the liaozhong and north liaoxi sags is too high to provide oils for fields the e 2 s 4 source rocks in the south and middle liaoxi sag displayed opportune maturity within the oil window and were proved by oil source correlation having important accumulation contribution for discovered oil fields in this area the e 2 s 4 derived oils should be taken seriously in the future exploration in the south and middle liaoxi sag and on adjacent uplifts

origin and migration pathway of biodegraded oils pooled in multiple reservoirs of the chepaizi uplift junggar basin nw china insights from geochemical characterization and chemometrics methods abstract the chepaizi uplift possesses three sets of oil bearing reservoirs six sets of source intervals multiple episodes of hydrocarbon charging and variable physical properties of crude oils in this study based on geochemical characterization source intervals and the biodegradation rank of the crude oils four oil populations named as group a b c and d d1 d2 were defined the combined results of q cluster analysis qca and discriminant analysis da indicate that group a occurred mainly in lower neogene shawan formation n1s in the western chepaizi uplift and were primarily derived from the middle lower jurassic xishanyao badaowan sangonghe formations j2x j1b j1s and a little of paleogene anjihaihe formation e2 3a of the sikeshu sag group b occurred essentially in upper carboniferous xibeikulasi formation c2x of the western chepaizi and originated mainly from the j1b mudstone of the shawan sag in addition the crude oils of group c occurred mainly in the lower cretaceous tugulu group k1tg of the eastern chepaizi and were primarily derived from carboniferous sourced oil from the chepaizi uplift the crude oils of groups d d1 and d2 are mixed with permian p1f and p2w of shawan sag and carboniferous sourced oil from the chepaizi uplift based on the reconstruction of the migration history the oils of group a in the n1s formation of western chepaizi migrated predominantly from the south sikeshu sag to the north and northeast with wells su1 2 and c27 as the initial filling points the oils of group b in the n1s formation of the western chepaizi travelled predominantly from the southeast shawan sag to the north and northwest the oils of group d1 in the c2x formation of eastern chepaizi migrated mainly from the northeast and southeast shawan sag to the west with well p661 as the initial filling point wells sm011 and c64 are the initial filling points of the k1tg group in the hongche fault belt crude oils of group c in the k1tg group travelled predominantly from the southeast shawan sag and northeast to the west into the eastern chepaizi and from well p68 to the southwest according to the paleo oil preferential filling orientations and paleogeomorphology some favourable targets for petroleum exploration of the chepaizi uplift are forecast in this study

productivity and paleoclimatic controls on source rock character in the aman trough north central sumatra indonesia abstract the central sumatra basin csb is a prolific oil producing basin in indonesia where a single source rock has been identified the brown shale formation of the paleogene pematang group despite the presence of a single source rock the oils in the central sumatra basin and particularly in the aman trough exhibit variable molecular and isotopic compositions previously described as reflective of lateral facies variations within the source rock analyses by gas chromatography gc gas chromatography mass spectrometry gc ms and gas chromatography isotope ratio mass spectrometry gc irms of 15 oil samples from the aman trough allowed identification of vertical and lateral facies changes within the brown shale formation as well as paleoproductivity and paleoclimatic changes that took place during deposition of this prolific source rock the molecular and isotopic data indicate the source rock for these oils was deposited in a fresh to brackish water stratified lake in which co 2 limiting conditions prevailed compound specific isotopic data also indicate that changes in paleoclimatic conditions possibly associated with the eocene oligocene paleoclimatic transition had an effect on the geochemical composition of the source rock in the aman trough

glaucony and carbonate grains as indicators of the condensed section omma formation japan the fifth order depositional sequences of the early pleistocene omma formation exposed along the japan sea coast of central japan were formed by glacial eustasy during oxygen isotope stages 50 to 28 in each depositional sequence two ecostratigraphic datums are always present the appearance and disappearance datums of warm water molluscan species these datums are independent of sequence stratigraphic concepts because the establishment of them is based on immigration events of molluscan species associated with glacio eustatic sea level changes determination of time planes shows that the appearance datum seems to occur near the midpoint of sea level rise on the glacial to interglacial shift in deep sea d 18 o records in order to evaluate the significance of the condensed section in sequence stratigraphy and also to facilitate its recognition this study examines the stratigraphic relationship of the condensed section indicators glaucony and carbonate grains with respect to the position of the ecostratigraphic datums in depositional sequences of the omma formation the results show that the maximum concentration of carbonate grains is a more reliable maximum flooding surface indicator than the concentration of glaucony the combination of indicators of condensed section and ecostratigraphic datums represented by incursion epiboles enables the boundary between transgressive and highstand systems tracts to be recognized in the inner shelf parts of depositional sequences moreover truncation of ecostratigraphic datums during sea level falls demonstrates significant erosion at the sequence boundaries integration of climatic palaeoecology and sequence stratigraphy permits a level of correlational precision of the order of a few thousands of years 1998 elsevier science b v all rights reserved

formation of shallow water glaucony in weakly oxygenated precambrian ocean an example from the mesoproterozoic tieling formation in north china abstract authigenic glaucony precipitation in phanerozoic oceans takes place mostly in middle shelf to upper slope environments with low depositional rate or sediment starvation precambrian glaucony however is more common in stratigraphic successions deposited from shallower water environments with high and variable depositional rates this phenomenon has long been noticed in literature but the controlling factors of shallow water glaucony precipitation in precambrian oceans have not been adequately investigated to better understand the glauconitization processes in precambrian oceans we have conducted an integrated study of the glaucony in stromatolitic carbonates of the mesoproterozoic tieling formation ca 1437 ma in north china using sedimentological mineralogical and geochemical data obtained from field observations petrography xrd sem quantitative eds and icp ms analyses macro and microscopic observations show that the tieling glaucony fills voids of varying sizes and shapes and records different maturation stages of glauconitization geochemical analyses show that the tieling glaucony has high k 2 o avg 8 but low and variable total fe 2 o 3 tfe 2 o 3 contents 1 92 13 65 wt the tfe 2 o 3 contents increase with maturation of glaucony titration results show that the tieling glaucony contains both fe 3 and fe 2 ions but has fe 2 fe 3 ratios much higher than that of the phanerozoic glaucony ree results of glaucony hosting carbonates show weak negative and positive ce anomalies with average ce ce ratio close to 1 0 suggesting carbonate precipitation near the redoxcline of fe mn oxides all these features suggest that the tieling glaucony was precipitated in seawater around the fe redoxcline where both fe 2 and fe 3 were available throughout the glaucony maturation stages high fe 2 fe 3 ratios in the depositional environments led to fe 2 occupation at octahedral sites of glaucony and negative charges on octahedrons which resulted in high k content to balance the negative charges on octahedrons and low tfe 2 o 3 limited by dioctahedral structure the formation of the tieling glaucony and other similar precambrian glauconies is likely controlled by low oxygen concentration in seawater and a shallow redoxcline that controls the availability of fe and k cations during initial precipitation and maturation of glaucony the shift of authigenic glaucony precipitation from shallow water in the precambrian to deep water in the phanerozoic may record the deepening of ocean chemocline in response to increased ocean oxygenation

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

glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

oil shale sedimentology and geochemistry in cenozoic mae sot basin thailand the intermontane mae sot basin thailand contains carbonate rich oil shales in which oil yield mineralogy and major and trace element geochemistry are related to the rock type higher grade oil shale is significantly enriched in silicate minerals quartz feldspars clays and analcite relative to carbonates and in dolomite relative to calcite couplets of organic rich and mineral rich laminae increase in mean thickness from 0 080 mm to 0 670 mm from high to low grade oil shale the organic material consists mainly of lamalginite and yields up to 341 l of oil mt 81 8 gal ton on retorting fish and vascular plant fragments are the main megafossils mappable oil shale sequences 10 m 33 ft thick are interstratified with marlstone sandstone sequences 70 m 230 ft thick markov chain analysis applied to stratigraphic sequences indicates that low grade oil shale passes gradually into high grade oil shale and vice versa the strata are interpreted as the deposits of extensive fresh to brackish lakes with oil shale sequences formed in perennial stratified lakes and marlstone sandstone sequences formed in shallow perennial lakes and subaerially exposed flats dolomite in the oil shales was authigenic the systematic changes in mineralogy and geochemistry between rock types probably reflect a gradient in redox potential from the center to the margins of the lake sandstone and siltstone beds and some carbonate laminae are interpret d as density flow deposits and form a significant proportion of the sequences the episodic deposition of oil shales reflects changes in lake level within the enclosed basin probably due to climatic fluctuations on a 24 000 to 46 000 year scale

constraints on the amplitude of late pliocene eustatic sea level fluctuations new evidence from the new zealand shallow marine sediment record since 2 5 ma global eustatic sea level fluctuations have driven recurrent transgressions and regressions of the shoreline across the world9s continental shelves the resulting shallow marine sedimentary record is cyclothemic each cyclothem corresponding to a single milankovitch climatic or sea level cycle wanganui basin new zealand contains one of the most complete late neogene shallow marine stratigraphic records in the world in the form of a continuous cyclostratigraphy representing every 41 k y and 100 k y sea level cycle since oxygen isotope stage 104 ca 2 6 ma a eustatic sea level curve is derived for oxygen isotope stages 100 74 from high resolution faunal paleobathymetric subsidence and stratigraphic analyses of 12 superposed shallow marine cyclothems in the rangitikei river section wanganui basin between 2 6 and 2 0 ma minimum amplitudes of eustatic sea level fluctuations ranged from 110 20 m stages 100 99 to 25 10 m stages 76 75 these independently derived fluctuations are 20 larger than previous estimates and imply greater climatic variability during the onset of major northern hemisphere ice ages

revised sequence stratigraphic interpretation of the eocene oligocene boundary interval mississippi and alabama gulf coast basin u s a abstract examination of regional stratigraphic relationships and graphic correlation of biostratigraphic data from two important localities has resulted in a new interpretation of the sequence stratigraphy of the eocene oligocene boundary interval in mississippi and alabama the much studied section at st stephens quarry in southwestern alabama does not contain all of the components of the depositional sequence at st stephens the highstand systems tract is missing and is represented by a marine hiatus condensed section at the top of the upper eocene shubuta clay as a consequence the surface of maximum starvation and the overlying sequence boundary are merged lowermost oligocene sediments which were deposited in the lowstand systems tract rest on this maximum flooding surface seque ce boundary these findings agree with those from other parts of the gulf coast where the eocene oligocene boundary has been recognized as a sequence boundary associated with a subaerial unconformity and a downward shift in coastal onlap revision of the sequence stratigraphic interpretation at st stephens quarry alleviates much of the confusion concerning the relationship between the eocene oligocene boundary and the sequence boundary this new interpretation shows that not all sections contain all components of a particular depositional sequence and that caution is warranted when sequence stratigraphic interpretations are used to evaluate observations the sequence stratigraphic interpretation of the section at st stephens has undergone revision as new observations have become available

mixed marine and lacustrine input to an oil cemented sandstone breccia from brora scotland abstract a rounded cobble collected from a beach near brora scotland contains angular brecciated sandstone clasts cemented together by crude oil no oil occurs within the tight dolomite cemented clasts except along fractures provenance of the cobble is uncertain however the lithology and shape of the clasts suggests that they are fault gouge breccia composed of old red sandstone from the nearby helmsdale fault oil emplacement presumably along the fault cemented the breccia prior to transport and weathering of the cobble independent source and biodegradation parameters support mixing of two charges of oil like oil from the nearby beatrice field the oil cement contains 24 n propylcholestanes and carotane that indicate marine and lacustrine source rocks respectively the oil cement also contains pristane phytane residual n alkanes and a complete series of 25 norhopanes which indicate mild and heavy biodegradation respectively the first charge consisted of lacustrine devonian oil that was heavily biodegraded at shallow depth the origin of the second charge is unclear unlike beatrice oil the oil cement contains oleanane and shows a higher 24 24 27 nordiacholestane ratio suggesting input from a cretaceous or younger paralic marine shale source rock although cretaceous and paleocene source rocks are inferred to exist in various depocenters in the northeast atlantic margin subcrops of these rocks offshore brora are thermally immature alternately the second charge could originate from an effective middle jurassic source rock that contains oleanane this hypothesis is supported by mass spectrometric confirmation of oleanane in an extract from the marine equivalent of the middle jurassic brora coal in the nearby ukcs 11 30 2 well oleanane in crude oil is not positive proof of a cretaceous or younger source rock for the oil

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

an integrated sequence stratigraphic geochemical investigation of the jurassic source rocks in the north yellow sea basin eastern china the north yellow sea basin nysb is one of the petroliferous basins in the offshore region of eastern china an integrated sequence stratigraphic geochemical investigation was carried out to identify and assess the effective source rocks of recent oil discoveries in the nysb a total of four third order sequences the first j2sq1 and second j2sq2 third order sequence within the middle jurassic and the first j3sq1 and second j3sq2 third order sequence within the upper jurassic were identified in the jurassic succession in which four types of probable source rocks were distinguished namely lacustrine deep water mudstones lacustrine shallow water mudstones prodeltaic mudstones and deltaic plain mudstones the lacustrine deep water mudstones are widely distributed within the j2sq1 j2sq2 and j3sq2 sequences in the gentle tectonic slope and depression area they are characterized by moderate total organic carbon toc contents 0 79 3 72 wt with an average of 1 71 wt lower hydrocarbon potential indexes the amount of free hydrocarbons before analysis s1 and the amount of hydrocarbons that results from cracking of kerogen s2 i e s1 s2 in a sample during rock eval pyrolysis 0 97 mg hc g rock s1 s2 7 89 mg hc g rock with an average of 3 10 mg hc g rock and predominantly type ii to type iii kerogen in contrast the prodeltaic mudstones in j3sq2 have higher toc contents 1 5 4 0 wt with an average of 2 71 wt higher s1 s2 5 83 25 51 mg hc g rock with an average of 14 89 mg hc g rock and predominantly type i to type ii kerogen the oil source correlation results indicate that the oils discovered in the nysb mainly originated from the prodeltaic j3sq2 mudstones the effective source kitchen is mainly located in the northwestern part of the study area the factors controlling the occurrence of high quality prodeltaic source rocks are a sufficient supply of nutrients and terrigenous organic matter high depositional rates and a suboxic environment

a review of the occurrences and causes of migration contamination in crude oil abstract migration contamination occurs when a migrating or trapped crude oil functions as a solvent dissolving molecular components from the syndepositional organic matter of the migration conduit and or the reservoir rock this review documents the causes and worldwide occurrences of migration contamination and suggests methods of identifying the signatures of this phenomenon within the molecular and isotopic composition of crude oils instances of migration contamination have been identified in oils of australia asia africa and north america and are best identified by the presence of molecular and or isotopic imbalances in the oil such imbalances are most apparent when co occurring molecular suites are incompatible with one another particularly in terms of thermal maturity occurrences of migration contamination in oils of the us gulf of mexico documented by molecular maturity imbalances such as the presence of unsaturated hydrocarbons known to be unstable at petroleum generation temperatures provide the best examples of this phenomenon an attempt is made to quantify the extent and impact of this process in the vermilion 14 field offshore louisiana in the us gulf of mexico here molecular maturity markers in the migrated fluid and in the syndepositional organic matter of the reservoir rocks are compared and the proportion of contamination in each reservoired fluid is estimated examples such as this may assist in explaining maturity anomalies observed in several oils worldwide particularly in tertiary reservoired oils that have migrated through and are trapped in thermally immature sediments it is suggested that the low molecular maturity ratios often observed in tertiary reservoired oils and attributed to unusually high heating rates may be caused at least in part by migration contamination

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

instantaneous movement of krill swarms in the antarctic circumpolar current antarctic krill are known to have strong swimming capabilities but direct observations of the speed and direction of krill swarm movement within their natural environment are rare we identified and examined 4060 swarms within the main flow of the antarctic circumpolar current scotia sea using a combination of an ek60 echosounder a 153 6 khz acoustic doppler current profiler and ground truthing nets net displacement magnitude m and net angle of deviation d were determined by vector subtraction from the background flow immediately below them values were compared against control data sets in which swarms were absent with greater background flow m became increasingly lower than predicted which suggests that drag influences swarm movement the characteristics of the flow regime influenced swarm behavior given that both m and d varied according to the direction of background flow furthermore multiple regression analysis indicated that swarm area the vicinity of the sea ice edge and salinity had a significant influence on m with levels of displacement being greatest in larger swarms and in low salinity regions close to the ice edge the ice edge is a key environment for antarctic krill and swarm behavior may assist in retaining this location only fluorescence was found to have a significant influence on d with deviations being greatest in regions of highest fluorescence this agrees with laboratory observations of krill turning more frequently within food patches we demonstrate that it is possible to measure instantaneous movement patterns in antarctic krill swarms and at large scales these movements are consistent with current understanding of responses of krill to local stimuli such as sea ice and patches of food swarms of antarctic krill form some of the highest concentrations of animal biomass found in any of the world s ocean reaching densities of up to 2 million tons over an area of 100 km2 nowacek et al 2011 krill swarm

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

comprehensive geochemical correlation between surface and subsurface hydrocarbon occurrences in the batman mardin şirnak area se turkey abstract southeast turkey is the main oil producing region of the country located at the northwestern part of the zagros basin in this study we investigated the geochemical characteristics of both surface and subsurface hydrocarbon occurrences in the batman mardin irnak area in southeast turkey to determine whether a genetic relationship exists between the two for this thirty solid bitumens from twenty two different veins along with ten heavy oils and thirteen oil seepage samples from nearby oilfields and seeps were studied using diverse geochemical tools firstly each of the different hydrocarbon types was considered individually with respect to source organofacies level of thermal maturity and degree of biodegradation the results obtained from the source related parameters demonstrate a marine algal source for all investigated samples also lithology determination based on various diasterane tricyclic terpane hopane and homohopane parameters suggests a carbonate source for all samples except for the dadas and iskar seeps clastic thereafter considering the influences caused by thermal and biological alteration processes all heavy oils less mature solid bitumens as well as the less biodegraded seep oils were selected to be correlated using selected additional parameters homohopane distributions reveal that solid bitumens compared to heavy oils and seeps are highly enriched in c31 and depleted in higher homologues possibly due to cracking of high molecular weight homologues to lower ones during and or after solidification processes furthermore the similarities observed for the relative abundances of six series of aromatic hydrocarbons and their alkylated counterparts substantiate strong genetic affinities within the sample set finally compound specific stable carbon isotopes of individual components show that solid bitumens are more enriched in 13c than the heavy oils which is mainly attributed to the preferential removal of light isotopes 12c during solidification our results strongly confirm that turkish solid bitumens are genetically related to the nearby heavy oils thereby providing new information on the petroleum system in this part of the southeast anatolia

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

sulfur rich petroleum derived from lacustrine carbonate source rocks in bohai bay basin east china abstract crude oils produced from the zhanhua depression bohai bay basin are high in sulfur and differ from most lacustrine oils in this basin and elsewhere physical properties biomarker ratios and aromatic hydrocarbon assemblages reveal that they are derived from carbonate source rock horizons representative source rock samples with abundant organic matter toc 1 and s 2 5 mg hc g rock were selected for further correlation and their high bitumen contents indicated their indigenousness to saline or carbonate depositional environments the results of oil source rock correlation suggest that these sulfur rich heavy oils originate from es 3 4 carbonates and marls limited to the bonan sag maturity assessments with burial history showed that they were expelled at the early oil generation window high levels of 20s 5 14 17 and 5 14 17 steranes together with low values for the ts ts tm ratio and two methylated aromatic ratios mdr and mpi 1 were observed in these oils sulfur associated with evaporite and carbonate environments is a significant factor not only in controlling the occurrence of biomarker isomers but also for petroleum formation at abnormally low thermal stress levels

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 2 evidence for significant contribution of mature source rocks to immature oils in the bamianhe field the chemical compositions of 28 representative crude oils and oil sand samples collected from the bamianhe region of the bohai bay basin eastern china were studied in detail in order to understand their genetic relationships biodegradation ranking and thermal maturity level molecular geochemical parameters indicate the presence of one single oil family in the cenozoic reservoirs a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns the extremely low maturity levels of these immature oils as indicated by sterane isomerization ratios were not supported by other maturity parameters the genetic relationship between the oils and the es4 and es3 members of the eocene oligocene shahejie formation present in the deeper part of the niuzhuang sag but not those along the niuzhuang south slope was suggested using a wide range of molecular parameters variation in the sterane concentrations observed from potential source rocks with different maturity levels in the study area suggests a high probability of migration contamination of mature oils by immature bitumens along migration pathways or from intra reservoir shales variation in the level of oil biodegradation could also create anomalies in the use of gross oil compositions as an indicator of oil maturity although the recent rapid subsidence of the bohai bay basin and the saline depositional environment of one of the potential source rocks favor oil generation at relatively low maturity levels most of the economic oils discovered in the bamianhe region appear to have derived from conventionally mature source rocks but contain lower maturity fluids admixed with them

reconstruction of the thickness of the tsushima current in the sea of japan during the quaternary from molluscan fossils abstract the present distribution of the benthic fauna in the sea of japan reveals that the thickness of the warm tsushima current is about 150 m because cold water elements are found in bottom faunas in the underlying cold intermediate water below this depth identification of such cold water taxa from quaternary molluscan assemblages makes it possible to estimate the thickness of the tsushima current in the past in order to determine the depth and nature of the cold water fauna living below the warm surface current molluscan and planktonic faunas were analyzed from the omma formation which comprises at least 14 superposed cyclothems corresponding to oxygen isotope stages 50 to 22 based on faunal analyses one molluscan association that lived below the warm tsushima current was identified from the horizon equivalent to stage 47 about 1 45 ma the depth of the upper limit of the association that is the thickness of the tsushima current was estimated using sedimentary structures and oxygen isotope records from deep sea cores the result show that the thickness of the current was less than two thirds that of today

carbon and hydrogen isotopic compositions of n alkanes as a tool in petroleum exploration compound specific isotope analysis csia of individual organic compounds is a powerful but underutilized tool in petroleum exploration when integrated with other organic geochemical methodologies it can provide evidence of fluid histories including source maturity charge history and reservoir processes that can support field development planning and exploration efforts the purpose of this chapter is to provide a review of the methodologies used for generating carbon and hydrogen isotope data for mid and high molecular weight n alkanes we discuss the factors that control stable carbon and hydrogen isotope compositions of n alkanes and related compounds in sedimentary and petroleum systems and review current and future applications of this methodology for petroleum exploration we discuss basin specific case studies that demonstrate the usefulness of csia either when addressing particular aspects of petroleum exploration e g charge evaluation source rock oil correlation and investigation of maturity and in reservoir processes or when this technique is used to corroborate interpretations from integrated petroleum systems analysis providing unique insights which may not be revealed when using other methods csia of n alkanes and related n alkyl structures can provide independent data to strengthen petroleum systems concepts from generation and expulsion of fluids from source rock to charge history connectivity and in reservoir processes

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

petroleum system analysis of the northwestern part of the persian gulf iranian sector abstract geochemical geological and geophysical data were used to identify and update genetic oil families potential source rocks and hydrocarbon generation kitchen as well as probable migration pathways in the northwestern part of the persian gulf rock eval analysis was performed on 52 cutting samples of prospective cretaceous tertiary source rocks according to the results most of the samples have poor to fair potential for hydrocarbon generation except for the albian formation which possesses good to excellent source rock characteristics in the study area two genetic oil families were identified based on source and age related biomarkers as well as stable carbon isotope ratios for 23 crude oil samples family i occurs in upper jurassic lower cretaceous reservoirs mainly in the surmeh hith basin whereas family ii occurs in lower cretaceous tertiary reservoirs mainly in the garau gotnia basin all attempts to correlate the identified families to prospective source rocks failed due to substantial maturity differences between the oils and rock samples inversion correlation based on detailed isotopic and biomarker analyses however confirms that the carbonates and marls of the neocomian and albian formations are the main oil generating facies for families i and ii respectively the geographical extension and composition of the identified oil families are highly affected by source rock facies distribution and migration pathways 2d cross sections provided in the region indicate the dominance of lateral and vertical migration pathways from the binak depression as the main hydrocarbon generation kitchen toward the structural highs in the study area

the origin of oil in the cretaceous succession from the south pars oil layer of the persian gulf the origin of the oil in barremian hauterivian and albian age source rock samples from two oil wells spo 2 and spo 3 in the south pars oil field has been investigated by analyzing the quantity of total organic carbon toc and thermal maturity of organic matter om the source rocks were found in the interval 1 000 1 044 m for the kazhdumi formation albian and 1 157 1 230 m for the gadvan formation barremian hauterivian elemental analysis was carried out on 36 samples from the source rock candidates gadvan and kazhdumi formations of the cretaceous succession of the south pars oil layer spol this analysis indicated that the om of the barremian hauterivian and albian samples in the spol was composed of kerogen types ii and ii iii respectively the average toc of analyzed samples is less than 1 wt suggesting that the cretaceous source rocks are poor hydrocarbon hc producers thermal maturity and ro values revealed that more than 90 of oil samples are immature the source of the analyzed samples taken from gadvan and kazhdumi formations most likely contained a content high in mixed plant and marine algal om deposited under oxic to suboxic bottom water conditions the pristane nc17 versus phytane nc18 diagram showed type ii iii kerogen of mixture environments for source rock samples from the spol burial history modeling indicates that at the end of the cretaceous time pre permian sediments remained immature in the qatar arch therefore lateral migration of hc from the nearby cretaceous source rock kitchens toward the north and south of the qatar arch is the most probable origin for the significant oils in the spol

the controls on the composition of biodegraded oils in the deep subsurface part ii geological controls on subsurface biodegradation fluxes and constraints on reservoir fluid property prediction the principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry numerical modeling of oil biodegradation in reservoirs and analysis of oil property data sets from a variety of geological settings petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80c in most reservoirs with low concentrations of aqueous sulfate methanogenic degradation is a primary mechanism of petroleum degradation whereas in waters containing abundant sulfate sulfate reduction and sulfide production may dominate net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature the chemical compounds being degraded and relationships between the oil water contact owc area and oil volume the relative volumes of water leg to oil leg prior level of oil biodegradation and reservoir water salinity act as second order controls on the process typically degradation fluxes kilograms of petroleum destroyed per square meter of oil water contact area per year or kg petroleum m2 owc yr1 for fresh petroleum in clastic reservoirs are in the range of 103 104 kg petroleum m2 owc yr1 and increase with decreasing reservoir temperature from zero near 80c to a maximum flux at the owc of less than 103 kg petroleum m2 owc yr1 at a temperature less than 40c at very low reservoir temperatures and with severely degraded oils such as are seen in the near surface canadian tar sands at the present day the net degradation fluxes are much less than maximum values nutrient supply from the aquifer and adjacent shales mostly buffered by mineral dissolution probably provides the ultimate control on the range of degradation flux values oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude oil biodegradation continuous vertical gradients in the oil columns document episodic degradation for many millions of years suggesting that the time scales of oil field degradation and petroleum charging are similar the flux temperature relationship we have derived coupled with typical reservoir charge histories defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge mixing of biodegraded and fresh oils and reservoir temperature history as the primary controls on fluid properties these flux temperature relationships are easily integrated into prospect charge modeling procedures sensitivity analyses show that the limiting factor in fluid property predictions using even this first level approach are ultimately constrained by the accuracy of current oil charge modeling estimates the absence today of any functional geochemical proxies for assessing oil residence time in oil fields and the substantial uncertainty in petroleum charging times estimated by forward basin modeling is a major obstacle to more accurate fluid property predictions that needs to be addressed

reservoir overprinting of crude oils abstract biomarker concentrations are generally low in high api gravity oils and condensates admixture of even small amounts of low maturity biomarker rich bitumen can drastically alter the biomarker profile of such fluids we suggest that a 41 api dst oil from the sunfish 1 well cook inlet alaska is a mixture of jurassic derived oil with approximately 5 wt tertiary input derived from coals interbedded with the reservoir sands reservoir overprinting has significantly altered the biomarker fingerprint of the sunfish 1 oil therefore biomarker patterns or parameters for biomarker lean high api gravity fluids should be scrutinized closely for internal consistency and conformity with bulk properties

gas condensate migration and oil fractionation in deltaic systems abstract the term evaporative fractionation is proposed to describe several phenomena involved in the secondary alteration of reservoired oil firstly it is suggested that oil is frequently partially vaporized in the reservoir secondly that gas bearing substantial portions of the oil in solution is conducted along faults to form independent gas condensate accumulations thirdly that residual oils formed in this fashion bear internal evidence of fractionation in addition to the conspicuous loss of light ends there is an increase in the content of light aromatic and naphthenic hydrocarbons relative to paraffins in the residual oil evaporative fractionation effects are recognized for the first time in the distillation and physical property data of us bureau of mines routine method oil analyses fractionation effects are postulated to be the cause of sigmoid as opposed to normal curvilinear aromatic profiles the effects of evaporative fractionation are widespread in oils throughout the united states they are evident in approximately 75 of oils in the gulf coast region and in a large proportion of the gas condensate accumulations the process is a major and apparently unrecognized means of petroleum alteration and of generation of gas condensates experimental evidence shows that partial vaporization results in enhanced levels of light aromatic hydrocarbons in residual oils oil samples were partially vaporized in excess methane at elevated pressure and temperature followed by removal of the vapour the gas chromatographic features of many gulf coast oils were reproduced various levels of light end depletion and enhancement of aromaticity were brought about

compositional fractionation of petroleum from reservoir to wellhead in the niobrara shale oil play abstract hydraulic fracturing is routinely used to stimulate unconventional reservoirs in the niobrara shale oil play there are several fracking targets but the actual stimulated rock volume is not well constrained this means that allocating produced oil to specific reservoirs in essence oil reservoir correlation is not straightforward the data presented here support that the chalk units are the principal production zones in the niobrara shale oil play several lines of evidence such as the presence of heavy end n alkanes n c31 consistence in composition of gross fractions the distribution of c27 28 29 diasteranes as well as the pristane to phytane ratio all suggest that oils were produced from the a b chalks particularly from the a chalk during production a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur in particular as regards the n alkanes domain and their carbon isotopic compositions regarding the latter a depletion of 13c in the produced oil s n alkanes by more than three per mil relative to all of those core extracts was observed this finding suggests that compound specific isotope analysis in both oil reservoir and oil source rock correlations cannot be taken at face value i e by simple matching of values besides that fractionation appears to result in the enrichment of rather aliphatic nitrogen containing compounds in crude oils

origin and paleoenvironmental reconstruction of phosphorus bearing sandstones of the cambrian xinji formation southwestern margin of the ordos basin china increasing exploration interest in oil and gas hosted by early cambrian strata has focused research efforts on early cambrian sandstones the origin of phosphorus and the paleoenvironment of phosph

geochemical evaluation of oil and gas samples from the upper devonian and mississippian reservoirs southern anadarko basin oklahoma and its implication for the woodford shale unconventional play abstract the woodford shale sycamore and goddard formations have become important liquid rich unconventional resource play targets most petroleum experts believe the mature woodford shale is responsible for much of the southern anadarko conventional and unconventional petroleum production with notable exceptions this paper will focus on the well head oil and gas samples from the south central oklahoma oil province scoop area woodford shale and the younger mississippian reservoirs the purpose of this paper is to characterize the scoop area unconventional resource play using the produced petroleum discrepancies between produced oil and gas geochemistry rock maturity and production characteristics presents an interesting conundrum the produced volatile oils contain lower boiling point compounds c6 c8 that indicate a high maturity product from the woodford shale source whereas the high molecular weight fraction c15 biomarkers suggests a middle mature product from the woodford shale source the produced gas chemistry suggests a low to middle mature product using published gas plots lastly the production gas oil ratio gor and well head fluid gravities are typical of a gas condensate there is no simple unified petroleum system process to explain all these observations there could be a combination of factors resulting in this conundrum such as mixing of multiple charges from both local and off structure sources phase separation as a result of production or well head sampling storage issues at present it may be difficult to fully explain the current results however we do believe the geochemistry and production results demonstrate a significant off structure contribution a simple petroleum systems model based on source rock organic matter type and maturity does not always correctly predict production or ultimate recovery

sedimentology and sequence stratigraphy of a pronounced early ordovician sea level fall on baltica the bjorkasholmen formation in norway and sweden abstract the bjorkasholmen formation consists of interbedded carbonates shales and glauconitic beds and is characterized by heavy bioturbation and few preserved sedimentary structures the unit shows five facies shale glauconitic packstone and three predominantly mud dominated carbonate facies carbonates and shales are arranged in small scale deepening upward cycles a minimum of fourteen of these small scale cycles are recognized in the bjorkasholmen formation they are arranged in stacks of 3 to 5 forming a total of four medium scale cycles separated by decimeter thick shale units based on the predominance of mud rich facies the succession is interpreted to have been deposited in an overall tranquil setting during one mayor sea level fall and subsequent initial rise of third order time estimates suggest that the 14 small scale cycles fall into the milankovitch band of precessional forcing and the overriding medium scale cycles likely represent short eccentricity the sequence stratigraphic interpretation shows that the bjorkasholmen formation is characterized by falling stage lowstand and initial transgressive systems tracts consequently the contact between the bjorkasholmen and the underlying alum shale formation represents the basal surface of forced regression the maximum regressive surface is defined by a hiatus in the oland sections and by shallow marine packstones within mud rich distal ramp carbonates in norway the top of the bjorkasholmen formation represents a flooding surface at the base of the transgressive systems tract a comparison of time equivalent successions worldwide suggests that the bjorkasholmen formation represents a tectonically enhanced lowstand with two overriding short term milankovitch eustatic signals although deposition of the bjorkasholmen formation coincides with the initiation of a foreland basin in the caledonides of norway it remains unclear how these tectonic movements may have lead to the widespread bjorkasholmen lowstand during the early ordovician it is suggested in this study that a combination of compressional forces from avalonia and the caledonian margin may have acted in concert to produce an uplift of larger parts of the baltica plate for a time span of approximately 0 5 myr

acoustically inferred zooplankton distribution in relation to hydrography west of the antarctic peninsula abstract the relationship between the distribution of zooplankton especially euphausiids euphausia and thysanoessa spp and hydrographic regimes of the western antarctic peninsula continental shelf in and around marguerite bay was studied as part of the southern ocean globec program surveys were conducted from the rvib n b palmer in austral fall april june and winter july august of 2001 acoustic video and environmental data were collected along 13 transect lines running across the shelf and perpendicular to the western antarctic peninsula coastline between 65 s and 70 s depth stratified net tows conducted at selected locations provided ground truthing for acoustic observations in fall acoustic volume backscattering strength at 120 khz was greatest in the southern reaches of the survey area and inside marguerite bay suggestive of high zooplankton and micronekton biomass in these regions vertically highest backscattering was in the 150 450 m depth range associated with modified circumpolar deep water cdw the two deep troughs that intersect the shelf break were characterized by reduced backscattering similar to levels observed off shelf and indicative of lower zooplankton biomass in recent intrusions of cdw onto the continental shelf estimates of dynamic height suggested that geostrophic circulation likely caused both along and across shelf transport of zooplankton by winter scattering had decreased by an order of magnitude 10 db in the upper 300 m of the water column in most areas and high backscattering levels were found primarily in a deep 300 m scattering layer present close to the bottom the seasonal decrease is potentially explained by advection of zooplankton vertical and horizontal movements and mortality predictions of expected backscattering levels based on net samples suggested that large euphausiids were the dominant source of backscattering only at very particular locations and depths and that copepods siphonophores and pteropods were more important in many locations

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

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

13c 12c ratio double cyclicity in a miocene browncoal isotopic signals and orbital forcing a detailed stable carbon isotopic profile of a late miocene browncoal seam from the lower rhine embayment germany reveals two clear separate cycles of different frequency this is the first instance of this type of isotopic signature being recognized within coals the ratio of the two frequencies suggests this isotopic signal possibly resulted from climatic or vegetational responses to orbital forcing the cyclicity has been enhanced by the application of conventional filtering methods on the data set an analysis of the seam s palynology indicates a correlation between heavier isotopic compositions and the presence of sequoiapollenites polyformosus whose parent plant is believed to have favoured moist climates and higher groundwater tables

characteristic of source rocks and origin of crude oils in the raoyang sag and baxian sag bohai bay basin china insights from geochemical and geological analyses abstract three potential source rock intervals were evaluated based on the results of rock eval pyrolysis on nearly 700 rock samples and the origin of the twenty two oil fields was studied by the biomarker analysis on 62 source rock samples and 93 oil samples in the raoyang sag and baxian sag bohai bay basin the first member of the shahejie formation es was deposited in an anoxic and salted water column with the dominant contribution of algal organic matters reflected by its rock samples with high gammacerane c30 hopane high etr high c35 c34 hopane high steranes hopanes low pristane phytane low c27 diasterane c27 sterane and low c19 c23 tricyclic terpane characterized by higher c19 c23 tricyclic terpane higher pristane phytane lower steranes hopanes and lower c35 c34 hopane than the es1 rock samples the biomarkers of rocks suggest that the third and forth members of the es were deposited in the sub oxic to anoxic environments with a significant terrestrial organism input further studies suggest that the best source rock interval for oil generation is the es1 source rock interval in the raoyang sag and is the es3 source rock interval in the baxian sag by organic facies analysis of source rocks three source related oil groups have been identified there are two oil groups for the discovered oils in the raoyang sag group i oil dominated by the es1 derived oils has been found in all the oil fields in the raoyang sag and group ii oil mainly derived from the es3 source rock interval only distributes in the north east area and in the south end of the raoyang sag however the three oil groups have been found in the baxian sag but the es3 derived oils are dominant in them and have been found in the major oil fields in the east area and the wen an slope in the west area furthermore the es4 derived oils group iii oil mainly distribute in the baxian sag without any findings in the raoyang sag because of the absence of the es4 source rocks as our studies oils almost accumulate near their source rocks without a long distance migration except the slope areas in the raoyang sag and baxian sag therefore the source rock distribution is a key factor to oil accumulations in the raoyang sag and baxian sag especially the efficient source rock distributions which mainly developed in the organic facies a and b based on the geochemical and geological researches

migration of petroleum into vermilion 14 field gulf coast u s a molecular evidence abstract oils and condensates from vermilion 14 field offshore louisiana u s a are compared using sulfur and nitrogen concentrations whole oil carbon isotope ratios and hydrocarbon distributions all parameters suggest large differences in the organic facies of the source rock s and in thermal maturity of the source at the time of expulsion certain bulk geochemical data including n alkane distributions and whole oil carbon isotope ratios suggest that migration fractionation resulted in oils condensates whose molecular distributions are shifted significantly toward lower molecular weight components migration contamination is supported by the occurrence in the oils of unsaturated and thermally unstable hydrocarbons including oleanenes dammarenes and diasterenes and molecular maturity ratios indicative of immature organic matter molecular maturity ratios of the oils increase with increasing reservoir depth regardless of reservoir lithology or formation for example the 20s 20s 20r 5 h 14 h 17 h 24 ethylcholestane ratio increases from 0 05 to 0 58 over a depth range of 6316 ft to 15 563 ft the same ratio for cuttings extracts from two wells in the vermilion 14 field shows lower values although they also increase with increasing depth it is proposed that the vermilion hydrocarbons were generated from deep source rocks approximately 15 000 ft or more and possibly subjected to migration fractionation during movement to shallower reservoirs during migration and after trapping migration contamination added unsaturated hydrocarbons to the oils condensates resulting in anomalously low molecular maturity ratios we suggest further that the combined effects of migration fractionation and migration contamination resulted in oil in the vermilion 14 field that is compositionally different from that which initially left the deep source rock

organic matter and trace element rich sapropels and black shales a geochemical comparison a distinct pliocene eastern mediterranean sapropel i 282 recovered from three ocean drilling program odp leg 160 sites has been investigated for its organic and inorganic composition this sapropel is characterized by high organic carbon corg and trace element contents and the presence of isorenieratene derivatives the latter suggests that the base of the photic zone was sulphidic during formation of the sapropel combined with evidence of bottom water anoxia preservation of laminae high redox sensitive trace element contents and the abundance and isotopic composition of pyrite this leads to the tentative conclusion that almost the entire water column may have been anoxic this anoxia resulted from high productivity and not from stagnation because an approximation of the trace element budget during sapropel formation shows that water exchange with the western mediterranean is needed entire water column anoxia has been suggested earlier for several black shales with regard to the depositional environment and the corg content however only the cenomanian turonian boundary event ctbe black shales appear to be comparable to this sapropel the proposed trace element removal mechanism of scavenging and co precipitation in an anoxic water column is thought to be similar for both types of deposits the ultimate trace element source for the sapropel however is seawater whereas it is hydrothermal and fluvial input for ctbe black shales because they have a larger temporal and spatial distribution nonetheless the corg rich eastern mediterranean pliocene sapropel discussed here may be considered to be a younger analogue of ctbe black shales

high resolution organic record of bridge creek deposition northwest new mexico abstract organic and inorganic geochemical data are presented and interpreted for a high resolution sample set from the uppermost portion of a transgressive systems tract condensed interval spanning the cenomanian turonian boundary at red wash northwest new mexico source potential toc rock eval yields thermal maturity vr elemental ca th and u in whole rock and molecular n alkanes steranes terpanes data are presented for a 64 sample 12 4 m composite section of limestones marlstones and shales of the bridge creek member of the greenhorn formation vertical sampling resolutions of 1 spl 19 cm spatial and 1 spl 33 ka temporal are used to monitor the progress of the transgression from the uppermost cenomanian up to the beginning of the highstand systems tract the section is thermally immature and maturity fluctuations are absent indicating that organic parameters are a function of organic matter production and preservation including diagenesis the rhythmic lithologic fluctuation within the bridge creek is not reflected in the source potential elemental or molecular data which show either no obvious pattern e g carbonate content toc or a unidirectional trend toward development of anoxia upsection e g hydrogen index sterane distributions homohopane index the distribution of the triaromatic steroid hydrocarbons c 20 21 26 28 according to side chain length also varies significantly despite the absence of maturity differences all of the unidirectional trends in the data are interpreted as related to either productivity differences e g sterane hopane ratios and changes in the relative concentration of r c 28 and r c 30 desmethylsteranes or the development of anoxia in the lower water column e g decreases in the diasterane regular sterane ratio increases in the homohopane index westward movement of the paleoshoreline during bridge creek time is also monitored by upsection decreasing th u ratios at red wash

source characterization of highly mature pyrobitumens using trace and rare earth element geochemistry sinian paleozoic paleo oil reservoirs in south china abstract understanding the relationships between migrated hydrocarbons and source rocks under highly mature conditions i e pyrobitumen source correlation is a critical and challenging issue in the field of petroleum geology and geochemistry based on a case study of three sinian paleozoic paleo oil reservoirs from yunan and guizhou provinces south china we attempt to provide further understanding of this issue using trace and rare earth element ree geochemistry which can characterize the depositional setting organic input and rock provenance of source rocks results show that the bitumens from the three paleo oil reservoirs can be distinguished from each other using post archean australian shale paas normalized trace element distribution patterns ree distribution patterns hierarchal cluster analysis of element concentrations and redox and provenance sensitive elemental ratios e g v ni ni co ni mo zr cr la sc and la co pyrobitumen in the devonian xiaocaoba paleo oil reservoir is derived primarily from devonian source rocks representing a self sourced petroleum system and one stage hydrocarbon charging similarly pyrobitumen in the sinian jinsha yankong paleo reservoir also received a single fluid charge but the source is different and likely generated by contributions from both lower cambrian and sinian sources in contrast the bitumen in ordovician kaili luomian paleo reservoirs are indicated to have contributions from two different hydrocarbon sources and thus experienced two stages of hydrocarbon charging an early charge from lower cambrian source rocks and a later charge from permian source rocks the new trace and rare earth element method used in this study appears to be effective at providing a better understanding of the hydrocarbon source correlation under highly mature conditions the results improve our understanding of the complex hydrocarbon accumulation alteration evolution in the marine strata of south china which is a potential target for petroleum exploration

charging of the neogene penglai 19 3 field bohai bay basin china oil accumulation in a young trap in an active fault zone the penglai 19 3 pl19 3 oil field the largest offshore oil field in china was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl19 3 anticline was not finally formed until about 2 0 ma and is cut by densely distributed faults source rock and crude oil samples from the pl19 3 field were analyzed to determine the origin and formation mechanisms of this large oil field three organic rich oil prone source rock intervals exist in the bozhong subbasin each of which has a distinct biomarker assemblage oil samples from different wells have different biomarker associations and three source related oil classes were identified within the pl19 3 field based on biomarker compositions and multivariate analysis of the data the pl19 3 field displays considerable compositional heterogeneity the compositional heterogeneity within the field and comparison between oil samples from the pl19 3 field and those from nearby structures suggest three field filling directions which is consistent with the results of migration pathway modeling the pl19 3 field was charged in the north by oil generated from dongying formation source rocks in the eastern bozhong depression and bodong depression in the southeast by oil generated from shahejie formation source rocks in the miaoxi depression and in the northwest by oil generated from shahejie formation source rocks in the central bozhong depression oil charge from multiple source rock intervals and multiple generative kitchens and focusing of oil originating from a large area of the bozhong depression into the same trap resulted in rapid oil accumulation in the pl19 3 structure and the formation of this large oil field in a very young trap within an active fault zone

migration induced compositional changes in oils and condensates of a single field thirty one oils and condensates from the vermilion 39 field offshore louisiana u s gulf coast are examined using techniques of elemental isotopic and molecular geochemistry in an effort to determine the causes of compositional differences among them compositional variability in elemental concentration carbon isotope ratios and molecular distributions suggests that at least two sub groups occur in the sample set the sub groups are characterized by differences in n c 15 content relative to n c 15 pristane phytane ratio 13 c sulfur and nitrogen concentration and s n ratio although the separation into these two sub groups is superficially indicative of distinct sources and or variable levels of thermal maturity interpretation of the data set as a whole indicates that source influences maturity differences and biodegradation do not control observed variations in composition reliable source e g r c 27 29 sterane distribution and maturity e g 20s 20s 20r parameters provide clear evidence of a common source and constant maturity level for all 31 oils condensates the remaining geochemical differences including various molecular pristane phytane isotopic 13 c oil and elemental s n parameters correlate with the extent of migration fractionation that each sample has undergone as measured by the relative amount of n c 15 in each sample the migration fractionation process in the vermilion 39 field is facilitated by fault initiated pressure releases within reservoirs that originally contained full range crudes vertical migration of the released saturated hydrocarbon gases has led to a concentration of lighter components in the most fractionated samples this geochemical interpretation is supported by geologic data inasmuch as the extent of fractionation is least in the deepest samples and greatest in the shallowest samples the results presented here indicate the potential for misinterpretation of geochemical parameters previously considered to be influenced solely by source influence or thermal maturity

reducing the risk of finding a working petroleum system using sar imaging sea surface slick sampling and geophysical seafloor characterization an example from the eastern black sea basin offshore georgia abstract as new plays emerge in deepwater settings sea surface slicks are often overlooked as a source of geochemical information to help define potential petroleum systems to demonstrate how sea surface hydrocarbon slicks can be used a case study is presented from the eastern black sea in the rioni basin offshore republic of georgia there source rocks of oligo miocene age maikop are suspected of charging upper miocene deepwater channel levee sands in fold and thrust system traps to reduce exploration risk direct evidence of hydrocarbon generation and migration was sought using sea surface slicks observed there to provide confirmation of charge a collection of diverse data was used first synthetic aperture radar satellite images were utilized to verify the presence of large recurring sea surface slicks over prospective structures these slicks were then sampled for later analysis during the acquisition of 3 d seismic data to verify that the slicks were related to the subsurface expulsion seafloor bathymetric and amplitude data were extracted from the 3 d seismic volume and used to identify potential seafloor features consistent with hydrocarbon seepage some of these seafloor features were found to be coincident with the apparent sea surface origins of the slicks seismic imaging was also used to demonstrate potential migration pathways which may link suspected deep subsurface traps and the seafloor and finally geochemical analysis showed that the compositional characteristics of the slicks hydrocarbons were similar to known maikop sourced oils in the region this combination of data provided a high level of confidence that the seismically imaged traps in offshore republic of georgia are charged suggesting a working petroleum system was present what it cannot tell us is how much petroleum may be in these structures that question can only be answered by the drill bit

recognizing and compensating for interference from the sediment s background organic matter and biodegradation during interpretation of biomarker data from seafloor hydrocarbon seeps an example from the marco polo area seeps gulf of mexico usa abstract a suite of seep samples from the vicinity of the marco polo field in the green canyon area of the gulf of mexico provides an exceptional opportunity to study the impact of interference from sediment background organic matter and alteration by biodegradation on thermogenic hydrocarbons from seafloor seeps these seep samples contain a range in both the concentration of seeped hydrocarbons present and level of biodegradation experienced in addition the subsurface oil that sources the seepage was available for comparison the results of the study show that it is essential to have the biomarker data from the sediment s background organic matter when dealing with low concentration seepage these data provide a means to characterize the contribution of background organic matter to the biomarker distributions this in turn allows the identification of thermogenic hydrocarbons when the concentration of seeped oil in seafloor sediments is low in high concentration seepage the hopanes and regular steranes were found to be more susceptible to near surface microbial alteration while tricylic tetracyclic terpanes diasteranes monoaromatic steroids and triaromatic steroids were more resistant if biodegradation is severe enough all biomarker compounds are vulnerable to alteration and very little information is preserved in an effort to reconstruct the altered distributions low temperature pyrolysis of the seeped oils asphaltenes was done to liberate occluded biomarkers compounds although biomarkers were recovered they did not resemble the parent oil characteristics of some of the recovered biomarker distributions suggest alteration by biodegradation this implies the three dimensional structure of the asphaltenes may not offer complete protection from microbial attack these results demonstrate why interpretation of biomarker data from seafloor seeps can be a difficult task care must be taken to recognize contributions from the sediment s background organic matter as well as identify alteration by biodegradation failure to understand these processes can lead to erroneous interpretations being made about the seep s parent oil and source rock

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

deposition of sedimentary organic matter in black shale facies indicated by the geochemistry and petrography of high resolution samples blake nose western north atlantic

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

change in the thickness of the warm tsushima current at the initiation of its flow into the sea of japan abstract the initiation of flow of the warm tsushima current created significant changes in quaternary paleoceanography and ecosystems in the continental shelf of the japanese islands in the sea of japan in order to understand the behavior of the current at the initiation of its flow we reconstruct the change in the relative thickness of the current during the initiation of flow based on combining planktonic and shallow water molluscan fossil analyses of the early pleistocene omma formation in central japan the result indicates that warm water planktonic foraminifera and cold water molluscs coexisted during about 2300 2400 years just after the initiation of the intrusion of the tsushima current migration of a warm water molluscan fauna to the shelf occurred shortly after the local extinction of cold water molluscs this means that the rate of increase in thickness of the tsushima current during the initiation of flow was faster than that of the sea level rise using deep sea core records and modern biogeographic data the rates of the former and latter are calculated to be 17 2 8 9 m per 1000 years and 1 9 1 1 m per 1000 years respectively because bottom water change might lag behind surface water change during a rapid climatic change in all shallow water combining planktonic and benthic fossil analyses is necessary to reconstruct shallow paleoceanography

mixed oils derived from multiple source rocks in the cainan oilfield junggar basin northwest china part i genetic potential of source rocks features of biomarkers and oil sources of typical crude oils abstract there are four generative hydrocarbon source rocks of carboniferous permian triassic and jurassic age in the east of the junggar basin geochemical study of these has shown that permian source rocks which contain high abundances of organic matter with good genetic potential are the best hydrocarbon source rocks in this area triassic source rocks are shown to be next best in these aspects the abundance of mainly type iii organic matter in jurassic and carboniferous source rocks varies greatly and the genetic potential of these rocks is lower than that of permian and triassic rocks these four source rock units in the fukang sag all reach a mature to highly mature stage of thermal generation and have generated large amounts of oil permian extracts are isotopically light with 13 c ratios generally less than 29 they have low pr ph ratios are rich in carotane tricyclic terpanes gammacerane and c 28 and c 29 steranes contain almost no diasteranes and have a low content of c 27 steranes the carbon isotopic composition of the triassic extracts is similar to that of the permian but they are characteristically rich in ts c 29 ts and diahopanes and have low gammacerane contents the carbon isotopic composition of jurassic extracts is noticeably heavier than that of permian and triassic extracts with 13 c being generally greater than 28 jurassic source rocks have pr ph ratios generally 3 0 and are rich in pentacyclic hopanes and c 29 steranes but poor in tricyclic terpanes gammacerane and c 27 and c 28 steranes using carbon isotopic and biomarker data the crude oils in this area can be divided into five groups the first group of crude oils a is derived from the permian the second group b from the triassic and the third group c from the jurassic source rocks the geochemical properties of the fourth group d of oils are intermediate between the properties of typical permian triassic and jurassic oils and they are interpreted as mixed oils derived from multiple source rocks including the permian triassic and jurassic the fifth group of crude oils e is particularly isotopically heavy and originates from carboniferous source rocks

quaternary time scale for the ontong java plateau milankovitch template for ocean drilling program site 806 a 2 m y oxygen isotope record of globigerinoides sacculifer from the ontong java plateau based on cores from ocean drilling program leg 130 is dated by matching variations to an orbital template the procedure allows us to present the most complete quaternary record available for the western equatorial pacific the template generating algorithm describes a balance between growth and melting of ice following basic milankovitch theory ice growth is taken as constant while melting is taken to depend on summer insolation current ice mass and average past ice mass template settings must be changed once between 1 and 1 2 ma to reflect a major shift in climate template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances one result of template dating is an exact age for the brunhes matuyama magnetic reversal boundary at 790 5 ka as well as several other precise dates 900 ka for the middle pleistocene climate shift 1070 1240 and 1450 ka for isotope stages 31 37 and 47 respectively sedi mentation rates fluctuate between 18 and 28 m m y a ca 400 ka cycle being the most prominent major anomalies arise within the transitional regime 1 2 to 1 ma the origin of the cycles is unknown we propose productivity variations in the western equatorial pacific

cyclic changes in lithofacies and molluscan content in the early pleistocene omma formation central japan related to the 41 000 year orbital obliquity abstract eleven cyclothems based on change in sedimentary facies and molluscan fossil associations are identified in the middle part of the omma formation early pleistocene in kanazawa central japan the systematic change in the molluscan fossil associations within individual cycles indicates that the oceanic conditions changed in parallel with water depth fluctuations such that an increase in water depth corresponds to a marine climatic warming these changes in water depth and oceanic conditions exactly coincides with the oxygen isotope fluctuations reported for deep sea sediments the cyclothems identified here in the omma formation can be explained best as the result of glacio eustasy with a period of the 41 000 years which corresponds to the period of orbital obliquity

mixed oils derived from multiple source rocks in the cainan oilfield junggar basin northwest china part ii artificial mixing experiments on typical crude oils and quantitative oil source correlation abstract there are five groups of crude oils in the east junggar basin four of which are derived from single sources viz permian triassic jurassic and carboniferous the crude oils in the cainan field are of a special type in that they have little correlation with any of the four known source rocks in the basin based on their distribution in the reservoir formations and their carbon isotopic and biomarker compositions it is concluded that these crude oils are mixtures of hydrocarbons from permian triassic and jurassic source rocks a mixing calculation using whole oil stable carbon isotope ratios of typical end member crude oils suggests that the contribution of jurassic source rocks to the cainan crude oils averages 50 65 a second calculation based on absolute concentrations of biomarkers indicates that the jurassic contribution averages 62 while those of the triassic and permian source rocks average 15 and 23 respectively artificial laboratory mixing of three typical permian triassic and jurassic oils indicates that the average contribution of the jurassic source rocks is 65 whereas those of the triassic and permian rocks are around 15 and 20 respectively in summary using whole oil stable carbon isotope ratios and biomarker parameters it can be concluded that the jurassic source makes a contribution of 55 70 while the triassic and permian sources each contribute 10 30 therefore the crude oils in the cainan oilfield are mainly derived from jurassic source rocks in the fukang sag

exposed coasts vs sheltered bays contrast between new zealand and japan in the molluscan record of temperature change in plio pleistocene cyclothems abstract cyclothems in the omma formation on the japan sea coast of central honshu each contains two ecostratigraphic datums the appearance and disappearance datums of warm water molluscs cold water molluscs occur both below in early tst and above in late hst and possibly rst warm water ones which occur in late tst and early hst in contrast no new zealand cyclothems in the main plio pleistocene basins contain both cold and warm water faunas in one cycle cyclothems in the petane group central hawke s bay and in the castlecliff section wanganui basin contain entirely eurythermal and warm water molluscs throughout cyclothems in south wairarapa have entirely eurythermal and cold water molluscs throughout the subantarctic zygochlamys delicatula fauna even in hsts of some cycles this contrast demonstrates the importance of exposure of the deposition site to strong coastal currents for the maximum faunal expression of temperature change the omma formation was deposited in an open site on the japan sea coast where currents transported larvae of a wide variety of molluscs northwards and southwards in response to temperature oscillations the main new zealand cyclothemic successions were deposited in large embayments sheltered from the influence of coastal currents the maximum faunal expression within one cyclothem of plio pleistocene temperature change can be expected in only those few deposition sites that satisfy the optimum requirements deposition of reasonably complete sequences at least tsts hsts and rsts preserved in an exposed coastal site influenced by strong currents from both the north and south on the inner shelf in the temperate regions between ca 30 and 60 north and south near the north south oriented coast of a large continent

a novel approach for recognition and quantification of hydrocarbon migration effects in shale sandstone sequences a detailed organic geochemical study of over 150 samples from two cores with a total combined length of 320 m 1 050 ft through sequences of interbedded source rock type shales 0 84 rm maturity and reservoir sandstones allowed recognition and quantitation of a number of migration effects detailed gas chromatography mass spectrometry of steranes and triterpanes was used to insure that samples being compared to investigate migration effects contain organic matter of a similar type thin shales interbedded in sands and the edges of thick shale units are depleted in petroleum range hydrocarbons to a much higher degree than the centers of thick shale units for the alkanes expulsion occurs with pronounced compositional fractionation effects shorter chain length n alkanes are expelled preferentially and isoprenoid alkanes are expelled to a lesser degree than their straight chain isomers based on material balance calculations expulsion efficiencies were determined and found to be very high in certain instances for thin interbedded shales they decrease from about 80 around c15 to near zero in the c25 region there is no evidence for significant redistribution of steranes and triterpanes in the two sequences compared to c15 to c25 n alkanes they appear relatively immobile the composition of the hydrocarbons impregnating parts of the reservoir sandstones is in agreement with expulsion occurring with pronounced fractionation based on molecular chain length hence consideration of bulk expulsion efficiencies gives an unrealistic picture furthermore the impregnation of a siltstone cap rock from an underlying hydrocarbon accumulation seems to have occurred by bulk oil migration and without significant fractionation the degree of hydrocarbon depletion of some of the shales of both sequences appears to be controlled by compaction and the primary migration process appears to have occurred with chromatographic separation the migration phenomena observed in both sequences lead us to propose that the main phase of expulsion can be preceded by an earlier sta e during which the edges of thick shales and thin interbedded shales appear to be slowly and continuously depleted by the chromatographic processes the composition of the hydrocarbon product accumulating in the reservoirs at this stage appears to be controlled primarily by physical processes rather than by the type and maturity of the organic matter in the generating source rock by this mechanism the origin of accumulations of light oils and gas condensates in low mature sequences bearing predominantly terrestrial derived organic matter can be explained finally the migration effects documented in this study have some consequences for interpretation of geochemical data e g the pristane n c17 ratio a commonly accepted maturity parameter has been shown to be also controlled by the degree of hydrocarbon expulsion

statistical analysis as a tool for assisting geochemical interpretation of the upper triassic yanchang formation ordos basin central china abstract the yanchang formation in the ordos basin is the most important petroleum play not only for conventional oil and gas accumulations but also for newly emerging shale oil and tight gas resources the molecular characterization of the basinwide source rocks predicts three groups of generative petroleum types paraffinic high wax oil mixed base paraffinic naphthenic aromatic low wax oil and gas and condensate supplementary to previous work 68 samples including the crude oils source bitumens and reservoir extracts from the yanchang petroleum play are analyzed the distribution of two terpane classes eight tricyclic terpanes and eight pentacyclic terpanes are determined with subsequent simultaneous rq mode factor analysis for a composite data set of these samples alongside 216 published crude oils worldwide with known facies descriptions thermal maturity has been evaluated as a consistent distribution at first using a combined method of a maturity related biomarker ts ts tm and aromatic parameters methyldibenzothiophene ratios to alleviate the maturity differences effect when discussing geochemical characterization the r mode factor analysis consists of the first two factors that are describing 45 present of the cumulative total variance in the data set and presents a sample grouping pattern in q mode factor analysis which is determined by different contributions of terpane associations i e the tricyclic c21 coupled with pentacyclic c26 c27 c28 and c30 in the same factor space three terpane associations the c26 and c28 terpanes the c21 and c30 terpanes and the c27 pentacyclic terpenes are respectively responsible for discriminating crude oil reservoir extracts and source bitumens in rq mode factor analysis molecular compositions further address more detailed interrelationships among three sample groups that crude oils and reservoir extracts are sharing close genetic relationships both in depositional environment typing and c27 c28 c29 sterane distribution samples from source rocks vary much significantly a mixing process which occurs after oils has been expelled from host source rocks into carrier units during accumulation in addition the migration contamination of c29 sterols when oils are cross through the chang 7 2 unit along migration pathways might also explain this lack of correlation between source rocks and oil reservoir system

controls of oil family distribution and composition in nonmarine petroleum systems a case study from inner mongolia erlian basin northern china abstract the erlian basin is a continental rift basin located in inner mongolia northern china it is a typical representative of cretaceous northeast asian rift system which includes many small petroliferous basins in mongolia republic and northern china although lower cretaceous source rocks are understood to be most important in the erlian petroleum systems the precise identification of these source rock intervals and their determination on oil families distribution and composition are poorly understood in this tectonically complicated nonmarine basin new bulk data have been gathered from source rock intervals oil sands and crude oil samples in eight main oil producing subbasins geochemical analyses indicate that lower cretaceous aershan formation k1ba and tengger 1 formation k1bt1 are two main source intervals in the erlian basin and their source rock facies vary from profundal lacustrine to marginal lacustrine according to biomarker and trace elements calibration the profundal lacustrine facies is characterised by brackish water and anoxic environment which is similar to their correlative oils family 1 oils the marginal lacustrine facies is characterised by freshwater and suboxic environment which sourced the most common family 2 oils meanwhile different maturation processes exercise the second control on oil groups and their compositions the profundal lacustrine source rocks characterised by their sulphur rich kerogens lead to two oil groups group 1 and group 2 oils whose maturity range from low to normal while the marginal lacustrine source rock only lead to normal maturity oils at last biodegradation affected the composition of a certain oils and formed group 4 heavy oils in addition short migration distance in small subbasins made the contamination or fractionation less notable in the erlian basin

application of pyrolysate carbon isotope and biomarker technology to organofacies definition and oil correlation problems in north sea basins abstract detailed sampling of apparently homogeneous potential source rock intervals frequently indicates unsuspected variations in organic facies which may or may not be reflected in the wireline logs carbon isotope analyses of pyrolysates provide a useful technique in these investigations which are essential for valid oil to source correlations in the jurassic of a north sea viking graben well the rich source shales at the top of the draupne formation are significantly depleted in 13 c and correlate with the oils from this area thus suggesting that this interval has acted as the primary source of the viking graben crudes a quite different pattern is evident in a well from the central graben and the data not only explain why the oils of the greater ekofisk area are relatively enriched in 13 c but also demonstrate that the variations within these oils are facies controlled pyrolysate carbon isotopes provide an excellent correlation between the middle devonian upper caithness flagstones of the inner moray firth and the beatrice crude oil this correlation is supported by the biomarker data and there is no need to appeal to a contribution from either an upper or middle jurassic source to achieve a match with the beatrice oil

origin and mechanism of the formation of the low oil saturation moxizhuang field junggar basin china implication for petroleum exploration in basins having complex histories the moxizhuang field is a small oil field in the central junggar basin containing several low saturation low resistivity oil reservoirs which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs biomarker associations of crude oil and grains containing oil inclusions gois of both the present day water bearing zones water zones and the oil and water bearing zones low oil saturation pay zones were analyzed to investigate the mechanisms for the formation of the low saturation low resistivity oil accumulations the biomarker assemblage and hierarchical cluster analysis indicate that oil in the moxizhuang field was mostly generated from permian source rock deposited in brackish to hypersaline anoxic environments the pay zones and several water zones display goi values as much as 38 greater than the generally accepted threshold goi value for an oil column 5 these goi values are similar to those for high saturation oil reservoirs in the bohai bay basin and oil zone samples from australian basins suggesting that both pay zones and water zones were high saturation oil reservoirs in the geologic past geologic history analysis shows that the moxizhuang field was located on the north wing of a paleoanticline during oil charge in the late cretaceous to paleogene this anticline has gradually evolved into a south dipping monocline since the neogene causing northward remigration of accumulated oil differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high goi values completely drained reservoirs and the low saturation low resistivity pay zones partially preserved reservoirs and caused the complex correlation between oil saturation and porosity and permeability compared with other postaccumulation physicochemical alteration processes lateral leakage has rarely been recognized recognizing differential lateral leakage of accumulated petroleum with the existence of high quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories

substrate control on formation and maturation of glauconites in the middle eocene harudi formation western kutch india formation and maturation of glauconites within the early middle eocene harudi formation built up in a lagoon to shelf transition in western kutch india is addressed taking recourse to a combined sedimentological micropalaeontological and mineralogical investigation the glauconite is authigenic and its occurrence coincides with maximum flooding the glauconite is more matured within the fecal pellets and is less matured within the intra particle pores of bioclasts namely foraminifera ostracoda gastropoda and bryozoa sem eds xrd and geochemical studies clearly document that the infilling within the intra particle pores of bioclasts belong to nascent to slightly evolved glauconite 5 wt k2o while the pellet belongs to slightly evolved to evolved glauconite 5 7 wt k2o based on chemical characteristics and sem investigations the glauconitization process can be best explained by the verdissement theory the glauconite possibly formed as initial authigenic glauconitic smectite precipitates while the pellet matured subsequently by addition of k the process was hindered in case of infillings the maturation process also involved addition of si and release of al with or without release of mg the glauconite maturation was facilitated in case of fecal pellets because of higher porosity inter granular nature of pores and availability of necessary elements in semi confined micro environments in contrast the maturation was aborted at an early stage in case of infillings because of the minute closed nature of the pores and prevalent alkaline conditions not allowing dissolution of calcitic tests a low negative cerium anomaly suggests glauconite formation in sub oxic micro environments created by decay of organic matters within the fecal pellets and bioclasts a clear case of substratum control on glauconitization becomes apparent

charging of oil fields surrounding the northern end of liaoxi uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract the liaoxi uplift one of the most petroliferous uplifts in the bohai bay basin is sandwiched by two sags containing multiple mature source rocks the origins of oil located on the northern end of this uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions from 75 source rock extracts and 15 oils two oil families have been identified using 4 biomarker parameters and could be linked to the source rocks of the first and second members of the shehejie formation e 2 s 1 2 and the third member of the dongying formation e 3 d 3 respectively e 2 s 1 2 derived oils were found in the liaoxi sag and on the liaoxi uplift and were interpreted to originate primarily from the liaoxi sag e 3 d 3 derived oils were found in the liaozhong sag and originated from the liaozhong sag the liaoxi uplift have not been charged by e 2 s 3 drived oils from the liaoxi sag mainly because it departed from the dominant migration direction of e 2 s 3 drived oils the liaoxi uplift have not been charged by e 2 s 3 e 2 s 1 2 and e 3 d 3 drived oils from the liaozhong sag mainly because there were no delta sandstones developed on the slope between the liaoxi uplift and the liaozhong sag to serve as migration channels from source rocks to uplift in all three formations the sandstone up dip pinch out traps in e 2 s 3 formation in the liaoxi sag traps within the liaozhong sag and traps on the slope between the liaozhong sag and the liaodong uplift have a better chance to accumulating petroleum

application of new diterpane biomarkers to source biodegradation and mixing effects on central llanos basin oils colombia llanos basin oils have been commonly attributed to the prolific upper cretaceous age source formations outcropping in the eastern cordillera recently however variable oleanane indices have been reported for llanos oils suggesting a contribution from tertiary source sequences largely on the basis of the presence of high relative abundance of oleanane a tertiary age diagnostic biomarker a homologous series of 25 norhopanes in many central llanos basin oils indicates that heavy biodegradation is particularly common to the initial oil charging reservoirs from upper cretaceous marine sources one homologue 20s 25 norhomohopane c30 25 norhopane co elutes with oleanane and may thus contribute to the peak attributed to oleanane also confusing the source identification is the possibility that some cretaceous facies also contain oleanane three plant diterpanes which may be isomers of fichtelite and are common to the central llanos oils have been observed in an eocene source rock sample but not in cretaceous rocks or oils providing additional strong evidence for a tertiary contribution to some llanos basin oils in mixed oils with low to moderate oleanane contents and with a strong co eluting c30 25 norhopane the fichtelite isomers are the more reliable indicators of tertiary source input