linking the geochemistry of crude oils and petroleum inclusions in the ubarana and lorena oilfields potiguar basin brazilian equatorial margin abstract a study of petroleum inclusions based on ultraviolet fluorescence petrography microspectrophotometry and biomarker analyses was carried out on samples from two wells of the onshore lorena and the offshore ubarana oilfields potiguar basin brazil this study aimed to evaluate the contribution and compositional variability of oils associated with different source rocks through the geochemical correlation of petroleum inclusions and crude oils three groups of inclusions were identified i a group from the lorena reservoir pendencia formation ii a second from the ubarana siliciclastic reservoir acu formation and iii a third from the carbonates adjacent to the ubarana reservoir ponta do mel formation pml fluorescence microspectrophotometry shows that the three groups of inclusions have different api gravity oils variable proportion of saturate aromatic resins and asphaltenes and are not biodegraded moreover pendencia and pml inclusions suggest multiple pulses of hydrocarbon migration while acu inclusions record a homogeneous pulse biomarkers indicate that the pendencia and acu inclusion oils correlate with reservoir oil extracts the pendencia inclusion oils are similar to the lacustrine oils of the umbuzeiro graben pendencia formation whereas the acu inclusion oil displays closer biomarker signature to the areia branca trend of mixed oils alagamar formation source rock however the oil from fluid inclusions of the pml has characteristics of the alagamar formation lacustrine organic facies the absence of mixed oils in the pml suggests an earlier lacustrine oil migration through the carbonate fractures prior to the main infill of mixed oils in the ubarana oilfield

hydrocarbon source rock variability within the austin chalk and eagle ford shale upper cretaceous east texas u s a abstract the austin chalk and eagle ford shale are upper cretaceous deposits that extend across texas from the northeast to southwest these formations contain organic carbon enriched mudstones and chalks that were deposited during transgressions of the cretaceous epeiric sea in north america recent workers in petroleum geochemistry have demonstrated that these organic enriched rocks possessed attributes common to oil source rocks the present study of these austin chalk and eagle ford shale rocks is from the perspective of organic petrology and it augments the earlier geochemical work that documented source variability within units of these formations as with the earlier work the results of this study show that both formations contain intervals that are when mature capable of generating commercial quantities of liquid hydrocarbons however this work further revealed that eagle ford rocks not only exhibit greater or ganic carbon contents but also have greater quantities of oil prone kerogen fluorescent amorphinite and exinite when compared with rocks from the austin chalk these source rock differences relate to levels or degrees of organic preservation dysaerobic to oxic depositional settings seem to be more characteristic of the austin chalk than of the eagle ford shale such oxic environments do not consistently favor the preservation of organic matter usually well preserved kerogen forms under more anoxic conditions such as those that occurred during deposition of some eagle ford units these anoxic conditions suggest that the geographically more extensive eagle ford shale is a more important source for oil than is the austin chalk

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

the oleananes origin maturation and limits of occurence in southern nigeria sedimentary basins oleananes occur within well defined age and paleogeographic boundaries in the sedimentary province of southern nigeria thus signifying that the biomarkers may be analogous to index fossils in anambra syncline lower benue trough the biomarkers are found in rocks which are as old as late upper cretaceous in tertiary niger delta the concentration composition and distribution of the oleananes in rocks and oils are determined mainly by palaeodepositional environment and thermal history and are independent of age and geographical location of specific samples oleanane content varies with increasing burial depth with peak concentration coinciding within rm range 0 4 0 6 implying early generation of hydrocarbons from the basin s typically resin rich kerogens it is evident that the oleanane content parameter is superior to the hopane and sterane isomerisation indices for monitoring thermal maturation in the delta and for differentiating paralic from paralic marine source facies as well as early from late generated oils

organic geochemical study of sequences overlying coal seams example from the mansfield formation lower pennsylvanian indiana abstract roof successions above two coal seams from the mansfield formation lower pennsylvanian in the indiana portion of the illinois basin have been studied with regard to sedimentary structures organic petrology and organic geochemistry the succession above the blue creek member of the mansfield formation is typical of the lithologies covering low sulphur coals 2 the transgressive regressive packages above both seams reflect the periodic inundation of coastal mires by tidal flats and creeks as inferred from bioturbation and sedimentary structures such as tidal rhythmites and clay draped ripple bedforms geochemistry and petrology of organic facies above the blue creek coal suggest that tidal flats formed inland in fresh water environments these overlying fresh water sediments prevented saline waters from invading the peat contributing to low sulphur content in the coal above the unnamed coal trace fossils and geochemical and petrological characteristics of organic facies suggest more unrestricted seaward depositional environment the absence of saline or typically marine biomarkers above this coal is interpreted as evidence of very short periods of marine transgression as there was not enough time for establishment of the precursor organisms for marine biomarkers however sufficient time passed to raise so42 concentration in pore waters resulting in the formation of authigenic pyrite and sulphur incorparation into organic matter

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

oil source rock correlation in the tempoku basin of northern hokkaido japan abstract geochemical correlation studies of seven oils and source rocks from the onshore tempoku basin of northern hokkaido were carried out low sulfur high wax and high pristane phytane ratios of the oils suggest that they were generated mainly from nonmarine source rocks source rock evaluation and hydrous pyrolysis data show that coals and coaly shales in the paleogene haboro formation and cretaceous hakobuchi group have oil generating potential these nonmarine source rocks are correlated as the major source of the tempoku oils using sterane and triterpane distributions and carbon isotope compositions correlation studies also suggest a minor contribution from marine source rocks of the neogene onishibetsu or paleogene magaribuchi formations to the oils of the yuchi and wakkanai fields located in the western part of the basin

the west mariana ridge western pacific ocean geomorphology and processes from new multibeam data the western flank of the west mariana ridge and the distal parece vela basin have been mapped for the first time using a modern multibeam echosounder the new data reveal the ridge to be composed of 82 volcanic peaks of which 25 have summits with water depths of 1000 m and 11 have summits with depths of 500 m deep five of the volcanoes have summit craters and two are guyots the remaining 75 seamounts are peaked volcanoes one volcanic peak has a summit water depth of 16 m and two in the central region have summits as shoal as 7 m the erosional character of the volcanoes suggests a younging toward the south the western flank of the west mariana ridge is buried by a sediment apron that merges with the distal parece vela basin the sediment apron is incised by a series of canyon channel systems that head on the upper flank or summit of the west mariana ridge and trend downslope to the west several of the channels are sediment filled with an incised thalweg suggesting a multiphase evolution to the channel systems none of the channels have a pelagic drape whereas the seafloor adjacent to the channels does suggesting recent activity the lack of guyots the apparent younging of the volcanoes to the south and the youth of channel activity suggest the west mariana ridge may be either recently or is presently tectonically active with the evidence suggesting uplift

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

application of organic geochemistry to sequence stratigraphic analysis four corners platform area new mexico u s a abstract the sequence stratigraphic model of sedimentation postulates the existence of a time condensed section deposited at very low sedimentation rates occurring in the uppermost transgressive systems tract and the lowermost highstand systems tract this condensed interval has of often been equated with zones of increased hydrocarbon source potential and invoked as a petroleum source rock often in the absence of supporting geochemical data in this study isotopic molecular lithostratographic and paleontological data are presented for 51 outcrop samples from a cenomanian turonian section at red wash new mexico u s a interpretations are made within a sequence stratigraphic framework ramp model sedimentation rates are estimated in order to define the location of the codensed intervalm for comparison with the zone of best source potential approximately 80 m of section were sampled the interval of maximum flooding and westernmost progression of the cretaceous seaway shoreline as defined by paleontological data is stratigraphically immediately below the occurrence of discontinuities in total organic carbon content hydrogen index and fluoramorphinite concentration in the kerogen the overall transgressive event is accompanied by increases in relative concentrations of 24 n propylcholestane total steranes and rearranged steranes these changes are consistent with a simultaneous decrease in the ratio of terrigenous organic matter to marine algal input as westward flooding proceeded the simultaneous occurrence of discontinuities in kerogen related parameters and continuous trends in bitumen related parameters probably implies mobilization of soluble organic matter across the flooding event boundary sedimentation rate estimates for six intervals in the red wash section show that the best oil source rock potential occurs immediately above the condensed interval and maximum flooding surface within the highstand systems tract previous studies of cretaceous sections in other portions of the western interior basin have located the best source rock potential below the condensed zone we conclude that the equivalence between source rock occurence and condensed sections as applied through the sequence stratigraphic model requires modification before the model may be used to predict the location of oil source rocks in a ramp setting in this respect it is critical that the data in sequence stratigraphic studies be used to define the model and not allow the model to dictate the interpretation of the data

planetary magnetic signature of the storm wind disturbance dynamo currents ddyn 1 during magnetic storms joule heating and ion drag in auroral zones strongly influence the circulation of thermospheric neutral winds joule heating produces equatorward neutral winds at f region heights with return flow at e region altitudes around the equator the so called hadley cell the modified thermospheric circulation produces upwelling of molecule enriched air at high latitudes and global changes in the atmospheric composition the equatorward neutral winds extending from the auroral zone to mid and low latitudes through the coriolis force create westward storm wind which drives an equatorward dynamo current in this paper we detect for the first time in the three longitude sectors the planetary magnetic signature ddyn of ionospheric disturbance dynamo with its main features 1 the decrease of the equatorial electrojet due to a westward electric current flow opposite to the regular eastward current flow and 2 the equatorward ionospheric disturbance dynamo currents at midlatitudes

source and significance of selected polycyclic aromatic hydrocarbons in sediments hovea 3 well perth basin western australia spanning the permian triassic boundary abstract stable carbon isotopic data for polycyclic aromatic hydrocarbons pahs chrysene and triphenylene benzo e pyrene 9 methylphenanthrene in sediments of comparable thermal maturity from a petroleum drill core hovea 3 well perth basin western australia spanning the largest mass extinction event in the past 500 million years permian triassic boundary are consistent with an algal kerogen source in the basal triassic as opposed to a combustion and or higher plant source in the underlying permian sediments the 13c values of extractable pahs are less negative in the permian inertinitic interval 24 7 to 29 2 than the triassic sapropelic interval 30 to 33 3 a strong correlation is evident between 13c of individual pahs 13c of kerogen and rock eval pyrolysis hydrogen index providing unequivocal evidence that pah 13c is mainly controlled by organic matter type abundant algal derived pahs in basal triassic sediments may be a global feature the lack of coal globally in the basal triassic sediments is also consistent with this observation the early triassic coal gap appears to coincide with the global extinction of peat forming plants at the end of the permian coal did not reappear until the middle triassic and permian levels of plant diversity and thick peat deposits did not recover until the late triassic the pah isotopic data support the contention that a global anoxic event at the end of the permian period contributed to the gradual worldwide asphyxiation and ultimate extinction of many marine and terrigenous organisms

evolution of backarc rifting mariana trough 20 24 n the mariana trough is an actively opening backarc basin in the western pacific the trough formed by extension which longitudinally split an earlier arc massif creating a crescent shaped basin between the remnant west mariana ridge and eastern active volcanoes of the mariana arc opening increases southward from the volcano islands near 24 n where the two arcs join at 18 n in the central mariana trough the basin is widest and may be opening primarily by seafloor spreading we present a synthesis of closely spaced shipboard gravity magnetic and bathymetry measurements from the northern basin 20 24 n an area that undergoes a significant progressive southward increase in extension we have identified three stages in the evolution of rifting in this area 1 asymmetric rifting from 24 n to 22 15 n where faulting and magmatism have migrated laterally to remain near the active volcanic arc side of the basin 2 a localization of rifting from 22 15 n to 21 n where the primary zone of rifting separates from the active volcanic arc and 3 a further concentration of rifting from 21 n to 20 n leading to the formation of deep tectonic grabens near the center of the basin this last stage may be a precursor to or incipient seafloor spreading we describe a new type of magnetic lineation resolved in a three dimensional seafloor magnetization inversion of the trough between 20 and 24 n the detailed character of these lineations their association with tectonic structures and other geophysical observations indicate that they are not seafloor spreading lineations but rather result from magnetic intrusions and volcanism emplaced within preexisting less magnetic rifted arc crust the development of these well defined magnetization bands indicates that the zone of magmatism remains relatively narrow at any one time throughout the opening of the trough although tectonic deformation appears to be more widely distributed in addition the geometry of the magnetization bands with respect to the remnant arc border faults indicates that rifting propagated rapidly northward

characterisation of oil and potential source rocks in the northeastern song hong basin vietnam indications of a lacustrine coal sourced petroleum system oil discovered in the b10 stb 1x well in the northeastern song hong basin vietnam has typical lacustrine coaly geochemical features indicating the existence of a principally lacustrine sourced petroleum system with minor contributions from a coal source the presence of lacustrine source rocks in the basin is indicated by distinct high amplitude seismic reflectors in undrilled half grabens and outcrops of oligocene immature mudstones and humic coals at dong ho and on bach long vi island the mudstones from dong ho generally have a toc content of 8 17 wt and hi values 500 mg hc g toc the organic matter is principally composed of fluorescing amorphous organic matter and liptodetrinite alginite with botryococcus morphology is present the organic matter corresponds to type i kerogen the bach long vi island mudstones contain 2 7 wt toc and have hi values from 200 700 mg hc g toc the organic matter is largely similar to that in the dong ho mudstones but in addition may contain some marine organic material the b10 stb 1x oil shows features common to both the dong ho and bach long vi island mudstones but was probably principally generated from a source similar to the dong ho mudstones with contributions from higher land plant organic matter a prominent activation energy peak dominates the activation energy distributions of the mudstones and upon artificial maturation hydrous pyrolysis the mudstones show extensive hydrocarbon generation over a narrow temperature range hydrocarbon expulsion has been estimated to occur at a vitrinite reflectance of 0 75 ro the source of the b10 stb 1x oil may be located in the thuy nguyen graben and maturity modelling shows that the lacustrine mudstones will be thermally mature in this graben

formation and evolution of nonmarine petroleum in songliao basin china in large lake basins source rocks containing sapropelic kerogen have a high transformation ratio and a high potential for petroleum and they offer the material basis for the formation of a large nonmarine oil field on the basis of geologic and geochemical data and the results of thermal simulation of kerogen it is confirmed that the maturation sequence of kerogen is type i type ii and type iii

oleanane or lupane reappraisal of the presence of oleanane in cretaceous tertiary oils and sediments nonpolar gc columns are normally used for gc ms analysis of saturate fractions from crude oils under these conditions lupane coelutes with oleananes and some minor c30 compounds of non terrigenous origin having lupane like mass spectra because any peak eluting fractionally earlier than 17 21 h hopane in the m z 191 mass chromatogram is routinely assigned to oleanane the presence of lupane may sometimes have been overlooked lupane and oleananes are easily separated using reverse phase hplc triterpane concentrates from 10 crude oils known to contain oleananes were hplc separated lupane was unambiguously identified in six of the oils by full scan gc ms analysis of fractions having the hplc retention time of authentic lupane gc separation of lupane and oleananes is possible using polar gc columns having a polyethylene glycol stationary phase organic geochemistry 23 1995 21 allowing estimation of the lupane lupane oleanane ratio high ratios were measured in the marraat oil west greenland 0 8 and the amauligak oil from the beaufort mackenzie delta 0 26 the results suggest that lupane may be more frequently occurring than previously thought and that this compound is preferably associated with high latitude samples high concentrations of 28 nor and 24 28 bisnortriterpanes oleananes lupanes and taraxastanes were detected in the marraat oil

geochemical application of sterane and triterpane biomarkers to a description of oils from the taranaki basin in new zealand abstract the distributions of sterane and terpane biomarkers in a suite of 25 oils from onshore and offshore regions of the taranaki basin of new zealand have been determined by gc ms features of these distributions include the presence of relatively high concentrations of a number of c 24 tetracyclic terpanes the virtual absence of tricyclic terpanes a predominance of c 29 normal iso and dia steranes and the presence of a number of non hopanoid triterpanes in one member of the suite urenui 18 h oleanane is the most abundant component m z 191 ion chromatogram of the terpane class of biomarkers based upon the distributions of 18 h oleanane the mckee and moturoa families of oils can be delineated these terpane distributions are qualitatively similar to those encountered in crude oils from a number of far eastern basins and from the handil field of the mahakam delta indonesia the taranaki oils are of approximately the same thermal maturity maturity parameters calculated from the distributions of c 29 steranes and of 17s h 21 h and 17 h 21s h hopanes confirm recent findings of incomplete nuclear isomerisation in oils derived from tertiary sediments an attempt has been made to correlate the mckee 1 and maui 4 crude oils with potential source rocks from depths of 3708 m and 3825 m respectively the rocks studied have attained insufficient maturity to have been the sources of these oils

extended hopanoids in peat environments abstract detailed results are presented for the distributions of triterpenoid alkanes acids and alcohols of the hopane family in ten samples of peat from three environments and of contributing organisms in the case of lyne of skene scotland extended hopanoids of the and configuration appear at the very earliest stage of diagenesis such environments appear to be characterised by particular distributions of c 32 hopanoid acids and alcohols and a high preponderance of the c 31 hopane

tertiary oils from upper assam basin india a geochemical study using terrigenous biomarkers abstract the upper assam basin in northeast india is a tertiary sub basin of the assam arakan basin hydrocarbons are present in the langpar formation upper palaeocene lakadong member of the sylhet formation lower eocene and the barail oligocene tipam lower miocene and girujan middle miocene formations in the basin a detailed study to understand the nature and origin of the oils from different stratigraphic horizons using terrigenous and other biomarkers has been carried out further the variation in maturities of oils occurring in different stratigraphic horizons has also been studied the study shows that rearranged oleananes oleananes and bicadinanes are present in these oils implying land plant input to their source rocks the oils have been classified into different groups using ratios of rearranged oleananes oleananes bicadinanes and steranes indicating presence of multiple source rocks in the basin with subtle variation in characteristics maturity studies show that oils from younger horizons barail tipam and girujan are more mature than oils from older horizons langpar and lakadong there is an apparent mismatch in maturity of oils as measured by different biomarker maturity parameters this is due to the mixing of two different charges of oils having different maturities and generated from two different source rock kitchens in the same reservoir principal component analysis pca of biomarker data has also been able to classify the oils into various groups a new parameter has been developed using ratios of rearranged oleananes for determining maturity of these oils

comparative organic petrology of interlayered sandstones siltstones mudstones and coals in the upper carboniferous ruhr basin northwest germany and their thermal history and methane generation in the coal mining ruhr area upper carboniferous rocks ca 4000 m consist of interlayered sandstones siltstones mudstones and coals they were deposited in a tropical paralic environment where alternating fluvial sedimentation occasional marine ingressions and swamp growth resulted in an irregular cyclic succession the total sedimentary package contains on an average 6 vol of organic matter about 70 vol of the organic matter occurs in coal seams the rest as dispersed organic matter in clastic rocks the organic matter is autochthonous in the coals and allochthonous in associated sandstones and siltstones it consists of about 70 vitrinite 20 inertinite and 10 liptinite the overall maceral group composition is the same for coals and dispersed organic matter this surprising similarity is caused by a nearly exclusive input of land plant derived organic matter to swamps and fluvial systems and a similar degree of preservation highest average liptinite contents of total macerals were found in unrooted mudstones highest average inertinite contents in coarse grained siltstones and highest average vitrinite percentages in sandstones

saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast alaska abstract dinorlupanes norlupanes olean 12 ene 18 olean 12 ene and urs 12 ene occur in a heavily biodegraded tertiary oil tested from the ocs y 0849 1 well drilled on the hammerhead prospect in the beaufort sea offshore northeast alaska these indicators and other source related characteristics of the hammerhead oil ring a degraded oleanoids ursanoids and lupanoids v and ni less than 2 0 ppm v v ni less than 0 5 indicate a land plant angiospermous character in the source facies the olefins in the hammerhead and canadian oils are considered to be contributed directly from the source rather than extracted from adjacent immature non source sediments during migration as indicated by a the accompanying presence in the oil of saturated angiosperm markers and b the absence of measurable amounts of other olefins characteristic of immature organic matter e g diasterenes and hopenes

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

regional source rock potential of lacustrine oligocene kishenehn formation northwestern montana intermontane basins of the northern united states overthrust belt have received only minor attention from petroleum geologists and geochemists in the modern literature despite the common occurrence of oil shales and thick sediment columns in such basins the present study investigates the petroleum source rock potential of the freshwater lacustrine sediments including mudstones oil shales and lignites of the kishenehn basin of northwestern montana and southeast british columbia outcrop samples of the tertiary kishenehn formation include excellent albeit immature petroleum source rocks average total organic carbon contents and hydrogen indices exceed 6 and 500 mg g respectively and numerous samples contain type i kerogen all samples studied are thermally immat re to marginally mature having vitrinite reflectance values of 0 28 to 0 51 ro organic geochemical and petrographic analyses of the kishenehn sediments allow estimates of detailed depositional setting and specific biological input to the sediment column the southernmost sediments in the basin contain the least land plant organic matter input and possess the richest petroleum source potential although vitrinite reflectance values are not particularly sensitive to maturity differences in this sample set molecular geochemical data were found to be useful in evaluating fine maturity distinctions and are used here to establish the order of kishenehn outcrops on the basis of maturity this use of molecular markers as maturation and depositional setting indicators for freshwater lacustrine environments has widespread application in thrust belts the results of this tudy will be useful in exploration of over two dozen intermontane basins throughout the northern extent of the united states overthrust belt

steroidal hydrocarbons of the kishenehn formation northwest montana abstract the oligocene kishenehn formation of northwest montana and southeast british columbia consists of fluvial and lacustrine sediments marlstones lignites and oil shales deposited in an elongate intermontane half graben the petroleum source rock potential and steroidal hydrocarbon distribution of selected shales of the kishenehn formation were examined several steroidal hydrocarbon series were documented including 4 desmethylsteranes 4 methylsteranes sterenes diasterenes spirosterenes c ring monoaromatic steroids and b ring monoaromatic anthrasteroids non steroid hydrocarbons present include hopenes hopanes moretanes perylene botrycoccane a series of alkylcyclohexanes and a fused ring aromatic tentatively identified as a tetrahydrochrysene source rock analysis indicates that the kishenehn formation possesses excellent petroleum source potential conventional thermal maturity parameters vitrinite reflectance and rock eval tmax values as well as maturity parameters derived from molecular parameers n alkane steroid and hopanoid distributions suggest that much of the kishenehn formation is currently undergoing organic diagenesis typical molecular indicators of thermal immaturity include the occurrence of high relative amounts of a 5 h desmethylsteranes b 14 h b ring monoaromatic anthrasteroids and c 4 ch3 methylsteranes a near shore freshwater lacustrine depositional environment is indicated with some input of terrigenous organic matter high cpi c23 c31 n alkanes and relatively high ethylcholestane content while the presence of 4 methylsteroids and botryococcane indicate significant contributions from dinoflagellates andbotryococcus braunii the occurrence in the kishenehn formation of a diverse selection of 4 methyl and 4 desmethyl aliphatic and aromatic steroids provides a unique opportunity to monitor co variance of molecular maturity indicators in sediments depositedunder relatively constant depositional conditions

age depth correlation of the philippine sea back arc basins and other marginal basins in the world abstract statistical analysis of underway bathymetric profiles of the philippine sea back arc basins the mariana trough the shikoku basin the parece vela basin and the west philippine basin reveals an age depth correlation in the basins the basement depths of the philippine sea range from 3200 to 6000 m with their ages from 0 to 60 ma the age depth curve of the whole philippine sea can be represented by the following equation depth m 3222 366 age ma the equation shows that the basement depth of the philippine sea is about 800 m deeper than that of the major ocean floors of the same age the coefficient of 366 in this equation is close to that for major oceans 350 this suggests that the cooling processes of the lithospheres in the philippine sea and major oceans are similar to each other whereas the structure and composition of the deeper layers of the philippine sea seem to be different from those of major oceans our analysis of etop digital bathymetric data however indicates that this relationship does not hold for some other marginal basins marginal basins other than back arc basins generally follow the age depth curve of major oceans young back arc basins

magnetic signature of the ionospheric disturbance dynamo at equatorial latitudes ddyn 1 during magnetic storms wind disturbances produced by auroral phenomena can affect the whole thermospheric circulation and associated ionospheric dynamo currents for many hours after the end of the storms in this paper we define criteria to select a new simple type of ionospheric disturbance dynamo events that allow a simple interpretation over all longitude sectors these events exhibit a weak auroral activity during at least 24 ut hours on the day after the storm we analyze the magnetic disturbances ddyn observed at equatorial latitudes in the three longitude sectors of such selected events it is found for all the cases that the amplitude of the h component of the earth s magnetic field is reduced on the day after storm at equatorial latitudes in agreement with the ionospheric disturbance dynamo model blanc and richmond 1980 the observation of h component decrease on the day after storm is longitudinally asymmetric the observed signature of the ionospheric disturbance dynamo process in a specific longitude sector is strongly dependent on the magnitude the start time and the duration of the storm

compound specific stable carbon isotope analysis as a tool for correlating coal sourced oils and interbedded shale sourced oils in coal measures an example from turpan basin north western china molecular geochemical methods have shown that it is often diacult to diaerentiate between coal and interbedded shale sourced oils even though coals and interbedded shales may exhibit considerable organic influx variation e g land plant vs algal organic matter due to the changes of depositional setting however compound specific stable carbon isotopic compositions are sensitive to the source input variations typically specific molecules are more depleted in 13 c with increasing content of aqueous biota this hypothesis is examined and exemplified by comparing the stable carbon isotopic ratios of n alkanes from source rock extracts and related oils of the turpan basin northwestern china stable carbon isotopic values of n alkanes extracted from coals and interbedded shales show that d 13 c values of n alkanes with less than 20 carbon atoms vary only slightly however there are dramatic changes in the isotopic compositions of higher molecular weight n alkanes furthermore n alkanes from coal extracts are enriched in 13 c relative to that of interbedded shales with excursions up to 2 3 this comparison enables the diaerentiation of coal and interbedded shale sourced oils and provides information useful in assessing the hydrocarbon system of a basin 2000 elsevier science ltd all rights reserved

submarine eruption fed and resedimented pumice rich facies the dogashima formation izu peninsula japan in the izu peninsula japan the pliocene pumice rich dogashima formation 4 55 0 87 ma displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave base marine setting it includes high concentration density current deposits that contain clasts that were emplaced hot indicating an eruption fed origin the lower part of the dogashima 2 unit consists of a very thick sequence 1 m pumice and ash rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension in dogashima 1 and 2 thick cross and planar bedded facies composed of sub rounded pumice clasts are intercalated with eruption fed facies implying inter eruptive mass wasting on the flank of a submarine volcano and reworking and resedimentation by high energy tractional currents in a below wave base environment

molecular genetic markers and maturity indices in intermontane lacustrine facies kishenehn formation montana abstract molecular markers have considerable promise as thermal maturation indicators in source rocks having a well defined depositional environment this occurs in the kishenehn formation northwest montana and southeast british columbia an oligocene unit comprised of fluvial and lacustrine shales up to 3 km of these non marine sediments were deposited in a 900 sq km elongated half graben atop the precambrian rocks of the lewis thrust sheet specific outcrops of the coal creek member of the kishenehn formation are known to contain excellent potential source rocks including extensive oil shales the source rock potential and molecular marker geochemistry of most of the major kishenehn outcrops have now been investigated and regional results are presented in this paper source rock analysis of a regional suite of kishenehn samples indicates excellent petroleum potential immature type i kerogen throughout the basin several classes of distinctive diagenetic molecular markers occur within the coal creek member of the kishenehn formation including diasterenes spirosterenes methylspirosterenes b ring monoaromatic anthrasteroids hopanes and moretanes molecular markers indicative of non marine deposition include dehydroabietane conifer input and an onocerane recently identified in leaf fossils of miocene lacustrine beds in adjacent idaho triterpane ratios are significantly more sensitive than vitrinite reflectance methods in assessing thermal maturation in the kishenehn and are successfully used in this study to order outcrop locations according to thermal maturity level the systematic variation of specific markers with increasing thermal maturation suggests that molecular correlation is feasible and could provide a method of assessing stratigraphic continuity in the basin

oleananes in oils and sediments evidence of marine influence during early diagenesis abstract the oleananes as markers for the angiosperms provide valuable source and age information when present in an oil nevertheless they are not quantitatively related to the land plant input and indeed their presence reflects only a small leak in diagenetic processes leading primarily to aromatic oleanoids because they are minor products the abundance of oleananes in terrigenous oils and sediments may be highly sensitive to changes in early diagenetic conditions here we present evidence that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil oleananes are absent or present at very low concentrations in samples from the base of an eocene coal seam affected by postdepositional seawater intrusion however their abundance increases toward the top of the seam in correlation with organic sulphur dibenzothiophene phenanthrene and the homohopane index similarly in deltaic sediments from the south sumatra basin oleanane hopane is strongly correlated with indicators of marine influence such as c 27 c 29 steranes and the homohopane index in each case increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and for the south sumatra basin the proportion of a ring contracted oleananes an angiosperm derived miocene coal from the philippines deposited under freshwater conditions shows abundant aromatic oleanoids but no oleananes these results show that oleananes need to be used with caution as age and source markers in fluvio deltaic and lacustrine petroleum systems on the other hand their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems

on the historical origins of the cej dp2 and ddyn current systems and their roles in the predictions of ionospheric responses to geomagnetic storms at equatorial latitudes in this short letter we recall the differences between the counter electrojet cej which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo ddyn which can be observed during and after a geomagnetic storm the cej is well known to occur near the geomagnetic dip equator it can be identified by a reversal in the horizontal component h of the geomagnetic field daily regular variations in contrast to equatorial electrojet eej that flows eastward in the daytime the cej is considered to flow westward the magnetic signatures of the reversed solar quiet sq current at the low latitude during magnetic storms are due to the ddyn this disturbance ddyn is produced by current systems that are driven by thermospheric storm winds originating from the joule heating of enhanced high latitude currents the dp2 is the magnetic effect of current systems at high latitudes these currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines they are associated to the magnetospheric convection during intense magnetic storms these high latitude currents are enhanced and their magnetic effects can extend toward the low latitudes this work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents the use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations prompt penetration of the magnetospheric convection electric field and disturbance dynamo electric field this was performed in the paper nava et al 2016

density and size distribution of seamounts in the eastern pacific inferred from wide beam sounding data theoretical expressions relating the distribution of apparent seamount heights per unit length of ship track to the distribution of actual seamount heights per unit area of seafloor are derived for both narrow beam and wide beam echo sounders the shapes of seamounts are approximated as truncated right circular cones of constant slope e height to radius ratio and flatness f i e a seamount of basal radius r has a height h r a flat top of radius fr and a slope angle of arctan e the set of all seamounts in a given physiographic province is assumed to be a poissonian ensemble specified by a function v r the average number of seamounts per unit area for which r r a simple choice for the size distribution of seamounts and one shown to be consistent with data in the eastern pacific is to specify that it decays exponentially with r v r vo exp r in the case of a profile of length l taken in water of depth d with a wide beam echo sounder half beam width the shallow slope deep water approximation e 1 e d yields that the expected number of seamounts with apparent heights h h is n h l 2 1 ed 2 fh lv0e h we apply this sampling theory to apparent height data measured from 44 020 km of wide beam profiles on pacific crust of post mesozoic age although the spatial distribution of seamounts in the eastern pacific is certainly not poissonian the abundance statistics do not involve spatial correlations and we show they are robust with respect to deviations from the poisson model provided the statistics are interpreted as averages over the area actually sampled by the track lines the observed falloff of apparent heights in the eastern pacific is very nearly exponential justifying our use of an exponential model of seamount size distribution the shape parameters are estimated from multibeam surveys of pacific seamounts an analysis of 30 features in the height range 200 4000 m yields 0 21 0 011 and f 0 21 0 028 using these parameters we obtain vo 4 0 1 1 10 9 m 2 and 6 3 0 8 10 4 m 1 these values imply that per 106 km2 in the eastern pacific there are 1600 400 seamounts with summit heights greater than 300 m and 200 60 greater than 1000 m integrated over the entire size distribution seamounts occupy about 6 of the seafloor area and constitute about 0 4 of the oceanic crustal volume our estimates of seamount abundance are appreciably greater than those of most other authors a discrepancy we attribute primarily to the sampling bias of previous studies which generally used uncorrected map counts this hypothesis is corroborated by a comparison of our statistics with map count data for seamounts of heights exceeding 2000 m compiled for the eastern central pacific from the scripps charts above 3000 m the map counts are consistent with the predictions of the exponential model but below this height they are biased to low values

monitoring tectonically controlled marine to lacustrine transitions using organic facies ridge basin california u s a abstract ridge basin is an elongate intermontane basin filled with upper miocene pliocene clastics located 80 km north northwest of downtown los angeles over 13 km of marine lacustrine and fluvio deltaic sandstones and shales are present because of southeastward depocenter migration throughout basin development no more than 4 5 km of vertical section are present in any one location this has resulted in an ideal situation to study organic facies variability namely a thick thermally immature stratigraphic succession with only minor variations in maturity level in this paper we use molecular isotopic and petrographic data to help identify systematic variability in organic facies in the castaic ridge route and peace valley fms all late miocene and relate these variations to the paleolimnology tectonic history and oil source rock potential of the basin as strike slip movement continued along the san gabriel fault during the late miocene the sedimentation regime changed from a marine dominance to one controlled by lacustrine and fluvio deltaic processes this transition results in changes in the organic facies within the basin as reflected in a a systematic decrease in organic carbon isotope ratios b an increase in relative yields of phenolic and n aliphatic structures in the kerogen pyrolysate c an increasing occurrence of perhydro carotene indicating episodic development of a halocline in the water column and d decreasing pristane phytane and c 29 c 28 sterane ratios unusual patterns of kerogen maceral distribution and a ring sterane methylation are also observed these geochemical data support the existence of a marine embayment in the early late miocene yielding to a lacustrine and fluvio deltaic setting which experienced considerable variation in bathymetry salinity and oxicity low levels of thermal maturity preclude the occurrence of hydrocarbon source rocks although source rock potential is present in sporadic localities optical and molecular maturity indicators show no systematic variation with stratigraphic succession this lack of variation is consistent with the known tectonic development in the basin and the shingled sedimentation pattern resulting from a migrating depocenter internal variability in the sterane and hopane epimer ratios may eventually be useful in estimating the uneven extent of overburden in the peace valley and ridge route fms leading to applications elsewhere in intermontane lacustrine basins with tectonically migrating depocenters

evolution of the mariana convergent plate margin system the mariana convergent plate margin system of the western pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology the system s relative geologic simplicity and the well exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics its general history provides analogs to ancient convergent margin terranes exposed on land and helps to explain the chemical mass balance in convergent plate margins the mariana convergent margin s long history of sequential formation of volcanic arcs and extensional back arc basins has created a series of volcanic arcs at the eastern edge of the philippine sea plate the trenchward edge of the overriding plate has a relatively sparse sediment cover rocks outcropping on the trench s inner slope are typical of the early formed suprasubduction zone s lithosphere and have been subjected to various processes related to its tectonic history pervasive forearc faulting has exposed crust and upper mantle lithosphere many large serpentinized peridotite seamounts are within 100 km of the trench axis from these we can learn the history of regional metamorphism and observe and sample active venting of slab fluids ocean drilling recovered suprasubduction zone lava sequences erupted since the eocene that suggest that the forearc region remains volcanologically dynamic seismic studies and seafloor mapping show evidence of deformation throughout forearc evolution large portions of uplifted southern forearc are exposed at the larger islands active volcanoes at the base of the eastern boundary fault of the mariana trough vary in size and composition along strike and record regional differences in source composition their locations along strike of the arc are controlled in part by cross arc structures that also facilitate formation of submarine volcano chains extending from the base of the fault westward into the back arc basin the western boundary is the west mariana ridge the western portion of the volcanic arc active prior to formation of the mariana trough the trough evolved in a two stage extension process of rifting and subsequent seafloor spreading the back arc basin varies along strike from rifted arc lithosphere with scattered volcanoes but no real spreading center in the north to a complex mid ocean type spreading center south of 20 n the change from initial rifting to true seafloor spreading is also evident across the mariana trough from rifted topography near the west mariana ridge to spreading ridges in the central to eastern basin south of 20 n this morphologic change indicates an early stage of extension with basin and range type topography predominant and volcanism restricted to fissure eruptions along fault block boundaries the spreading ridges and abyssal hill morphology evolved later as new lithosphere was generated at elongate volcanic ridges located in the center of rift valleys the center of extension intersects the active volcanic front differently at either end of the mariana trough in the north extension is by rifting of arc lithosphere where it intersects the arc in the south a major strike slip fault extends from the trench axis across the forearc through the volcanic arc and into the back arc basin arc magmas apparently leak along this fault zone into the forearc and the back arc spreading center the complexity of interrelated tectonism and magmatism in this convergent margin is daunting but studies of arc systems such as this provide the best hope of interpreting many of the exposed terranes accreted to continents comparison of subaerial terranes with recent studies of intraoceanic convergent margins will add to our understanding of plate interactions and of the evolution of the volcanic arcs and extensional back arc basins generated within such environments

tertiary deltaic and lacustrine organic facies comparison of biomarker and kerogen distributions abstract biological marker and kerogen compositional data in tertiary deltaic and lacustrine settings were compared and contrasted the two settings are represented by a coals and organic carbon rich shales in a ick deltaic sequence from the far east constituting three distinct organic facies and b humic coals and spropelic oil shales in a restricted intermontane freshwater lacustrine sequence from western montana u s a constituting two distinct organic facies wedistinguish the organic facies in each depositional setting by systematic differences in gross compound class distributions kerogen and infrared spectral characteristics molecular character of pyrolyzates sterane carbon number distribution and sterane hopane ratios the kerogens of the three deltaic organic facies are characterized by varying quantities of vitrinite resinite sporinite cutinite and fluorescent amorphinite triterpane distributions reveal numerous terrigenous compounds including oleanane oleanenes and unidentified c 30 presumably resin derived components the two organic facies of the freshwater lacustrine setting are distinguishedased upon either a vitrinite or an alganite fluorescent amorphinite predominance in the kerogen numerous characteristics facies related markers are also present including dehydroabietane land plant resins and 4 methylsteranes perhaps from freshwater dinoflagellate input the available molecular and petrographic data are evaluated and characteristics are proposed for distinguishing five organic facies of these two depositional settings the successful simultaneous use of molecular geochemistry and organic petrography in this study provides a format for refining the organic facies concept

changes in hydrocarbon maturity indices with coal rank and type buller coalfield new zealand abstract the buller coalfield south island new zealand is an inverted late paleogene basin that contains middle eocene bituminous coals which exhibit considerable variation in both coal rank across basin and coal type in seam twenty two fractionated bitumen extracts of brunner coal measures coal samples from 12 drillholes were analyzed by gc and gc ms to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window 0 56 1 26 ro max the carbon preference index pristane phytane and isoprenoid n alkane ratios evolve throughout the high volatile bituminous b rank stage while other biomarker ratios 18 h 22 29 30 trisnorneohopane 17 h 22 29 30 trisnorhopane ts tm 18 h 21 h 30 norneohopane c 29 ts 17 h 21 h 30 norhopane and c 30 diahopane hopane do not show appreciable change in value until medium volatile bituminous rank various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window in particular the methylphenanthrene index and vitrinite reflectance are positively correlated over the entire bituminous rank range however subtle changes in depositional conditions variable coal type complicate these rank estimates within a given coal seam variation in cpi isoprenoid n alkane and hopane sterane ratios appear to be related to the hydrogen content of the coal while the homohopane index and the oleanane hopane ratio covary with sulfur content as with depressed vitrinite reflectance values mpi is similarly lowered in the perhydrous samples the mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted however changes in bacterial activity and community with marine incursion appear to play an important role due to these anomalies none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank

biological marker distribution and significance in oils and rocks of the monterey formation california abstract the biological marker distributions of several oils core extracts and solid bitumens of the monterey formation of california have been studied sterane terpane and monoaromatic steroid hydrocarbons were analyzed in samples from the san joaquin los angeles ventura and santa maria basins the sterane patterns of both oils and extracts are characterized by 1 a low relative concentrations of diasteranes 2 b low 20s 20r 5 14 17 ethylcholestane ratios 3 c relatively high concentrations of cholestane vs methyl and ethylcholestane isomers san joaquin basin samples contain significant amounts of the 5 isomer which is generally absent in samples from other basins the carbon number distribution of 5 14 17 20r steranes is similar for all oils regardless of api gravity depth or basin location and is suggestive of open marine depositional conditions for the source material involved 17 h l8 h 21 h 28 30 bisnorhopane is present in almost all samples certain san joaquin basin oils and extracts contain 1 a a series of 25 nor hopanes including 25 28 30 trisnorhopane 2 b a distinctive monoaromatic steroid hydrocarbon distribution 3 c an aliphatic hydrocarbon fraction devoid of n paraffins biological marker characteristics suggest that the monterey oils examined originated early in the maturational sequence from elastics poor source material api gravities of the monterey formation oils examined vary monotonically with 1 a bisnorhopane hopane ratios 2 b aromatized regular sterane ratios and 3 c the concentration of monoaromatized steranes relative to terpanes and regular steranes these oil gravity correlations exist regardless of sample depth or basin location

constraints upon the use of 24 ethylcholestane diastereomer ratios as indicators of the maturity of petroleum abstract we have measured the ratio 20 s 20 s 20 r the relative abundances of the 24 ethylcholestane diastereomers in nine pairs of closely adjacent samples of coals and shales which represent a range of geological ages and different sedimentary basins within some sample pairs the values were similar in others they were very different the differences between the values for coal and shale members of pairs are attributed to effects of sediment matrix type upon the processes which cause the changes in the ratio the kinetic parameters e and s for the changes in the 20 s 20 s 20 r ratio have been estimated using previously published measurements for the hod 1 well shale and jupiter 1 well coal and these values were found to be very different the process in the coal sequence has a much lower activation energy and is therefore less responsive to differences in heating rate regimes than is the case for the shale sequence values of the 20 s 20 s 20 r ratio in two other sequences are shown to be consistent with this explanation and the implications of these observations for the practice of using sterane isomer ratios for assessment of maturity of sediments and crude oils are discussed