compositional variability in oils and formation waters from the ayoluengo and hontomin fields burgos spain implications for assessing biodegradation and reservoir compartmentalization abstract the main scope of this work is the geochemical characterization of 12 crude oils and formation waters of the ayoluengo oilfield basque cantabrian basin nw spain to delineate its reservoir compartmentalization the ayoluengo oil characteristics were also compared with data obtained from crude oil and formation water of the hontomin 2 well located 25 km to the se of ayoluengo the 13 ayoluengo and hontomin oil samples are very similar in composition bulk properties and isotopic signature indicating that these oils are genetically related however the hontomin oil is more mature and it is slightly biodegraded which suggests some differences in the reservoir environments the molecular parameters of both oils confirm a marine origin related to a liassic source rock coincident with the occurrence of lateral facies changes along the sedano sub basin on the other hand the connate waters are analogous and both classified as chloride calcium type given the complex nature of the sedimentology and structures of the reservoir gas chromatographic fingerprints of the analyzed crude oils have been used to detect minor variations in composition that are indicative of reservoir compartmentalization

drimane type compounds in source rocks and fluids from fluvial deltaic depositional settings in the north west shelf of australia abstract fluvial deltaic petroleum systems with gas prone source rocks are difficult to assess because the released fluids generally lack biomarkers and this limits the implementation of traditional organic geochemistry screening however there are a number of compound classes yet to be investigated in order to establish novel parameters for correlation studies in fluvial deltaic geological settings in this study we have focused on drimane skeleton molecules c15 decalins particularly the compounds 1 2 2 5 5 pentamethyl trans decalin and 1 1 2 5 5 pentamethyl trans decalin termed herein as rearranged drimanes rd1 and rd2 respectively and drimane d in source rock extracts and fluids from fluvial deltaic petroleum systems in the carnarvon basin north west shelf of australia nws we have calculated the ratio rd1 rd2 d as proposed by ji et al ji l he c zhang m wu y li x 2016 bicyclic alkanes in source rocks of the triassic yanchang formation in the ordos basin and their inconsistency in oil source correlation marine and petroleum geology 72 359 373 and compared their results with samples from the nws our compilation of rearranged drimane ratios for a variety of lithologies suggests clay catalysed rearrangement of c15 decalins in siliciclastic source rocks from fluvial deltaic depositional environments therefore the mineral content seems to be a key factor controlling the isomerisation of decalins samples with higher clay content such as claystone from the brigadier formation have higher rd1 rd2 d ratios 6 and higher c29 diasterane c29 sterane 1 1 compared to silty claystone from the legendre formation 2 and 0 8 respectively the effects exerted by thermal maturity of the source rock and redox conditions of the depositional environment require further investigation although samples from the yanchang fomation and la luna formation where deposition occurred under more reducing conditions exhibit lower rearranged drimane ratios

the effect of clay minerals on diasterane sterane ratios to examine the effect of clay minerals on diasterane sterane ratios the mineral compositions of three sample sets of sedimentary rocks displaying a wide range of diasterane sterane ratios were analysed quantitatively diasterane sterane ratios do not to correlate with clay content but depend on the amount of clay relative to the amount of organic matter clay toc ratios this correlation may explain the high diasterane sterane ratios in crude oils and extracts derived from certain carbonate source rocks based on the concentrations of regular and rearranged steroids in the sample sets it is proposed that diasterenes are partly reduced to diasteranes and partly degraded during diagenesis in a ratio largely determined by the availability of clay minerals it is suggested that the hydrogen atoms required for reduction of the diasterenes originate from the water in the interlayers of clay minerals

geographic and seasonal distributions of brunt vaisala frequency and rossby radii in the north pacific and north atlantic abstract long term mean temperature and salinity profiles computed from an edited set of historical hydrographic data have been used to calculate mean profiles of density and brunt vaisala seasonal variations in internal rossby radii are everywhere surprisingly small

the microbial input in carbonate anhydrite facies of a sabkha palaeoenvironment from guatemala a molecular approach abstract nine representative rock samplesincluding four anhydrites an oil stained dolomite and a laminated mudstone source rock from a sabkha type palaeoenvironment la felicidad 1 well guatemala have been compared in order to tentatively characterize each facies by a geochemical signature each sample has been studied by using basic parameters toc rock eval pyrolysis yields and analyses of alkanes and aromatics by computerized gc ms the following families of compounds have been reviewed n alkanes branched and cyclic alkanes n alkylbenzenes benzohopanes monoaromatic steroids d ring aromatic 8 14 secohopanoids alkylnaphthalenes alkylphenanthrenes alkyldibenzothiophenes and triaromatic steroids despite close geochemical relationships of all the sample a more in depth investigation taking into account molecular patterns and semi quantitative data reveals significant differences among the samples anhydrites may be differentiated from carbonates which illustrates the efficiency of organic geochemistry in environmental palaeoreconstruction even in organiccarbon lean sediments toc 0 04 0 08 in anhydrites in these anoxic marginally mature sediments the strong predominance of triterpanes over steranes tt to st 20 associated with other molecular features leads to the conclusion that the main contribution to the organic matter of all facies is by bacteria several prominent components including novel families iso c23 and iso c27 alkanes tetracyclic terpanes d ring aromatic 8 14 secohopanoids 1 phenylpentadecane undecylnaphathalene and their mono and dimethylated counterparts have been interpreted as derived from halophilic bacteria these conclusions may be extended to all crude oils from the same area which may be considered as true bacterially derived petroleums the la felicidad 1 well data are discussed with reference to other palaeosabkha type sequences from the sw aquitaine basin france in which the bacterial input is less important however in these sabkha sequences 1 phenylpentadecane undecylnaphthalene and related structures have also been identified

black shale deposition and early diagenetic dolomite cementation during oceanic anoxic event 1 the mid cretaceous maracaibo platform northwestern south america thin laterally continuous organic rich dolomitic marlstones were deposited in the extended late aptian early albian epicontinental sea of northwestern south america these intervals are the proximal equivalents of thick hemipelagic black shale ammonitic floatstone couplets deposited in the distally stepped differentially subsiding part of the maracaibo platform the marlstones reflect the dynamic conditions resulting from orbital forcing mechanisms and can be genetically related to 1 minor sea level changes 2 proximal turnovers in marine productivity and 3 sudden climate shifts affecting mid cretaceous shoaling upward shallow marine carbonate cyclicity therefore the marlstones may well be linked to the multiple environmental perturbations collectively referred to as oceanic anoxic event 1 the interstitial euhedral dolomite has a medium crystallinity and exhibits unusual textural relations with framboidal pyrite and gypsum the authigenic mineral assemblage also includes quartz ca f apatite and barite which together with the chemical signals of dolomite point to an unsteady climate regime bulk rock biomarker parameters rare earth element geochemistry and iron speciation data point to widespread photic zone anoxia and transient shallow marine euxinia by the time of deposition with climatic instability driving the delivery of oxidized detritus from the hinterlands these conditions led to a schizohaline redox stratified environment favorable to dolomite precipitation in such a depositional setting the bio utilization of fe mn and sulfur for organic matter respiration sustained elevated pore water alkalinity and ph and allowed for the pre compactional growth of interstitial dolomite

triterpane and sterane biomarkers in the ya13 1 condensates from qiongdongnan basin south china sea triterpanes and steranes in condensates from the ya13 1 gas field qiongdongnan basin were monitored the ya13 1 condensates have unusual biomarker distributions dominated by terpanes and steranes derived from higher plants anomalously abundant 1 got oleanane and remarkably abundant bicadinanes are present in the ya13 1 condensates whereas the 17alpha hopane contents are extremely low taraxastane and significantly abundant 17alpha diahopanes occur in the condensates in addition a number of unknown c 29 and c 30 pentacyclic triterpanes including previously unreported compounds were detected in the condensates some of which are significantly abundant the unknown compounds may be terrestrial biomarkers c 29 homologues are relatively predominant among the regular and rearranged steranes the diasterane concentrations are markedly higher than those of regular steranes the maturity of the ya13 1 condensates is relatively high at the peak to late oil generation stage corresponding to 0 85 1 10 ro based on sterane and terpane and including bicadinane maturity parameters i e t t 1 r and 2t r bicadinane ratios the above maturity assessment result is different from that based on diamondoid maturity parameters ro 1 60 1 70 org geochem 25 1996 179 which can be explained by a contribution of hydrocarbons from two sources at different depths the ya13 1 condensates were probably generated from the yacheng and lingshui coal bearing source rocks buried both in the qiongdongnan basin 3400 5000 m and in the yinggehai basin 5000 m the possible contribution of lower maturity hydrocarbons from the yacheng and lingshui formations 3400 4100 m in the qiongdongnan basin to the ya13 1 gases and condensates should not be neglected c 2003 elsevier science b v all rights reserved

a predictive typology for characterising hydromorphology abstract whilst traditionally poorly quantified the link between physical habitat and ecological response in rivers is widely recognised and is currently rising up legislative and policy agendas in europe this is reflected in the water framework directive which dictates that hydromorphological condition of water bodies should be capable of supporting good ecological status methods are developed that integrate river system hydrology geomorphology and ecology and the complex interplay between these three variables whilst hydrological and biological methods for characterisation are relatively well established geomorphological methods are not effective characterisation of geomorphology physical habitat with full spatial coverage at a range of scales can be used to explore spatial interactions between habitat and biological data and potentially further our understanding of ecological response managers need to know what aspects of physical habitat and at which critical locations intervention will lead to greatest improvements in ecological condition this requires information on hydromorphological character and condition existing applied approaches for capturing geomorphological data are highly dependent on intensive fieldwork which is unlikely to be resourced at sufficiently extensive scales to meet management needs this paper outlines a typology approach for characterising the physical template of rivers it draws on a range of hydromorphological data to develop a framework for a channel typology with data collation from secondary sources followed by targeted fieldwork to i assess to what extent individual channel types are characteristic of field conditions and ii to collect information on reach scale variability within each type results suggest that characterisation of channel types based on stream power floodplain width and stream order does result in a distinct set of channel types field survey subsequently found that these types had a characteristic suite of patch scale habitat features flow types the approach was applied to a catchment where geomorphological processes exert a dominant control over physical habitat

on the choice of orbits for an altimetric satellite to study ocean circulation and tides the choice of an orbit for satellite altimetric studies of the ocean s circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite s measurements of sea level and the temporal and spatial distribution of the measurements three orbital parameters determine the temporal and spatial sampling characteristics of the satellite the orbital altitude the inclination of the orbit and the repetition period the eccentricity of the chosen orbit should be less than 0 001 to minimize altimeter errors caused by uncertainty in determining the time of each altimeter measurement and to maintain the rate of height variation over the oceans within the limits of the altimeter tracker the choice of the satellite s orbital altitude is constrained by the influences of atmospheric drag and errors in models of the gravity field which decrease with height and the required complexity of the altimeter e g the power and or antenna size required and the effect on satellite systems of radiation from earth s radiation belts which increase with height the choice of inclination is constrained by a desire to measure sea level over all the ocean by the requirement that the acute angle between intersections of the subsatellite track be as large as possible and by the time phasing of the repeat of the satellite s ground track as a function of inclination which determines the aliased frequencies of the measurements of the oceanic tides the choice of repetition period is constrained by tradeoffs between temporal and spatial coverage and by the aliasing of tidal constituents combining the above constraints leads to a set of orbits in a narrow range of altitude and inclination called here the topex poseidon window this window extends from 1100 to 1500 km altitude and 62 to 66 inclination for a 10 day repeat period and consists of three subwindows following lines of equal orbit plane precession there are four choices of orbits within these subwindows that overfly the planned calibration sites at bermuda and dakar these are at 64 80 and 1335 km 62 01 and 1252 km 65 84 and 1255 km and 62 69 and 1173 km these choices have a minimum separation between the aliased frequencies of the eight largest diurnal and semidiurnal tides of one cycle per 4 71 years one cycle per 4 86 years one cycle per 4 87 years and one cycle per 4 27 years respectively thus there will be less than one cycle separation over the nominal 3 years mission of these four choices the first at 64 8 and 1335 km is preferable because it is less sensitive to error in estimating the upcoming solar cycle which will be a maximum during the mission and because it is more nearly centered in terms of inclination than the other choices for other calibration sites other choices would have to be made additional work beyond the scope of this paper will also be necessary to determine if the topex poseidon mission requires a frozen orbit i e an orbit for which there are no long term variations in the eccentricity and argument of perigee of the orbit if a frozen orbit is required then the first and third choices listed above have frozen orbits with an eccentricity that is acceptable for topex poseidon

comparative microbial diversity and redox environments of black shale and stromatolite facies in the mesoproterozoic xiamaling formation abstract the composition of microbial communities and their relationship to ocean redox structure in the precambrian are topics of continuing interest in geobiology our knowledge of organismic diversity and environmental conditions during this time are mostly based on fragmentary paleontological and geochemical records and might be skewed accordingly in north china the xiamaling formation 1 37 ga is characterized by black shales of relatively low thermal maturity t max is 445 c and has been identified as a potential petroleum source rock to date however the biological sources of the organic matter and the environmental conditions prevalent during the deposition of these sediments remain unclear in this study we analyzed the hydrocarbon biomarker compositions of the xiamaling formation shales and a superjacent stromatolitic carbonate in order to shed light on the microbial diversity in the sedimentary environments they represent the hydrocarbons extracted from both sediments are dominated by low molecular weight n alkanes with a maximum at c 15 18 suggesting that bacteria and or algae were primary biotic precursors our inability to detect steranes in bitumen i and only traces of rearranged steranes in bitumen ii of black shales indicates that modern eukaryotic algae were either ecologically insignificant or not preserved due to a taphonomic bias the high relative concentration of hopanes and diahopanes ranging from c 27 to c 35 as well as monomethylalkanes suggests that cyanobacteria may have been the dominant primary producers and could have contributed to the biologically available nitrogen pool through n 2 fixation this observation is supported by the low nitrogen isotopic composition of the kerogens even though all facies zones appear to have been anoxic but not sulfidic on the basis of biomarker ratios and trace metals subtle but distinct molecular differences are observed between the stromatolite and the black shales which can be attributed to both lithologically controlled diagenetic rearrangements and differential biotic input the discrepancy between the presence of a large ucm and high abundances of alkyl lipids on one hand yet the absence of a stable carbon isotopic offset between lipids and kerogen on the other suggests that strong heterotrophic reworking might not be the sole source of the biodegraded fingerprint that is so typical for proterozoic bitumens and demands alternative explanations

seasonal variability of the north atlantic ocean a model intercomparison abstract the seasonal variability of the north atlantic ocean is investigated through a comparison of two different numerical models one is a primitive equation model pem forced with monthly wind stress and surface buoyancy flux the other is a quasi geostrophic model qgm forced with the monthly wind stress curl only both models include realistic bottom topography and are solved for spherical geometry we find a great diversity in the baroclinic rossby wave response over the models latitudinal span the diversity partly stems from the latitudinal variation of the internal rossby radius and therefore cannot be captured with plane models the qgm is used to investigate the coupling of barotropic and baroclinic modes over topography especially its role on the propagation properties of the baroclinic waves a comparison of the model solutions reveals that in midlatitudes the spatial variability of the density distribution and the finite amplitude aspects of the bottom topography are the most import

mudstones and embedded concretions show differences in lithology related but not source related biomarker distributions abstract the mudstones of the western australian gogo formation harbour numerous carbonate concretions which often contain preserved fossils of lagerstatte like quality these are especially notable in places where the mudstone has eroded giving way to nodule fields which afford valuable paleobiological records it is however a challenge to determine their paleoenvironmental context here we analysed concretions from a core drilled in the canning basin gogo formation at two different depths concretions were compared to the surrounding mudstone found at the same depth electron microscopy and x ray spectroscopy showed that the concretions were carbonate rich and contained detrital fragments biomarker data showed that mudstone and concretions had very similar distributions and presented marine biosignatures including indicators of anoxic depositional conditions a stratified water column and photic zone euxinia the concretions contained higher amounts of c 27 steranes indicating that more labile organic matter such as animal remains could have triggered concretion formation statistical analyses of the results showed that concretions and shales differed p p 31 homohopanes and hopane sterane ratios p

heterogeneity of free and occluded bitumen in a natural maturity sequence from oligocene lake enspel abstract sedimentation in oligocene lake enspel was rapidly terminated by a basaltic lava flow this introduced a preservational barrier while imparting a natural flash pyrolysis during which the organic matter in underlying stratigraphic units was subjected to rapid thermal maturation resulting in hydrocarbon generation samples from these strata exhibit a steep maturity gradient 0 25 1 07 optical vitrinite reflectance or ro over uniform organofacies this offers the opportunity to investigate bitumen generation during rapid thermal maturation mechanistically in particular the nature of bitumen 2 occluded bitumen which is only recoverable after the digestion of the mineral matrix and was frequently dismissed as an artifact of incomplete extraction elaborate sequential extraction of the contact metamorphic sequence of oil shales at enspel revealed systematic changes in bitumen composition these trend progressively towards those of occluded bitumen which exhibits a systematically elevated thermal maturity a higher degree of catalytic biomarker rearrangement and the conspicuous absence of molecular signatures from vascular plants that are present in the free bitumen one plausible explanation involves a contribution of allochthonous clay adsorbed organic matter to bitumen 2 this could represent a mixture of older reworked bitumen and an early diagenetic snapshot of clay adsorbed organic matter alternatively a close association of early generated bitumen with clay minerals may have led to enhanced isomerization and catalytically influenced uniformization of alkane signatures deviations from the expected relationships between various thermal maturity parameters suggest variable dependence on the time pressure temperature pathway i e metamorphic facies the maturation of organic matter likely behaves differently under a contact metamorphic regime or during rapid subsidence and exhumation as compared to slow maturation during regional subsidence our data also suggest that geologically brief shallow intrusive or extrusive magmatism might not be as destructive to the sedimentary hydrocarbon inventory as hitherto thought this study draws attention to the small scale compositional heterogeneity of bitumen that can be studied using sequential extraction methods more importantly it suggests that occluded bitumen could potentially harbor information on organic matter that pre dates in situ primary productivity and may be derived from allochthonous biomass and detrital input

source rock evaluation and nature of hydrocarbons in the khalda concession shushan basin egypt s western desert abstract organic geochemical studies were undertaken on 241 jurassic cretaceous ditch cuttings samples and 9 gases and 10 crude oils from some productive mesozoic pay zone intervals in the khalda concession shushan basin northern western desert egypt we aim to investigate source rock characteristics origin of gases nature of oils and their inferred source rocks and to establish genetic relationships the middle jurassic khatatba formation and older rocks contain organic rich mature coaly and carbonaceous shales which are the main source for hydrocarbons in egypt s western desert including the shushan basin which generally contains kerogen type iii with some contribution of type iii ii kerogen molecular and isotopic composition indicates that the khalda gases are of thermogenic origin a mature 0 6 2 0 ro source rock with terrigenous organic matter kerogen type iii was identified as a precursor of wet thermogenic gases in the shushan basin geochemical results indicate that the oil samples were derived from a source rock deposited mainly under oxic conditions and containing terrigenous organic matter biomarker data indicate that paraffinic oils and condensates from the shushan basin were derived from mature source rocks within the oil window the light hydrocarbon data suggests that the analyzed oils can be classified into two groups as a result of evaporative fractionation and maturation this signal of a secondary reservoir transformation which is not revealed by biomarker analysis emphasizes the importance of integrating biomarker and light hydrocarbon data to understand variations in the chemical composition and origin of oils

a giant oil seep at a salt induced escarpment of the sao paulo plateau espirito santo basin off brazil host rock characteristics and geochemistry abstract an international research cruise named iata piuna took place on the sao paulo plateau on may 2013 in the campos and espirito santo basins off brazil the cruise was carried ou on board the research vessel r v yokosuka that hosts the human operated vehicle hov shinkai 6500 it aimed at finding chemosynthetic communities composed of organisms capable of generating their own vital energy by metabolizing organic and inorganic compounds related to seeps identification of these organisms could provide information for understanding the origin of life since they may resemble primitive organisms that existed in the initial stages of life on earth during leg 2 may 10 24 2013 however dives on the northern part of the sao paulo plateau at the espirito santo basin led to the discovery of a giant oil seep the seep ca 3 nautical miles ca 5 6 km in length is located along an outcrop of eocene rocks on a salt induced escarpment of the plateau and at a water depth of ca 2700 m the 200 m relief of the seafloor suggests that the seep takes place along an active fault system driven by salt diapirism the oil was analyzed and identified as a severely biodegraded marine oil generated by carbonate rocks within a minibasin located to the east of the escarpment this represents valuable exploratory information because it proves that an active petroleum system is present in the context of minibasins associated with salt diapirism in the area

tracing of variabilities within a geological barrier by molecular organic geochemistry case of the callovo oxfordian sedimentary series in the east of the paris basin france abstract the callovo oxfordian claystones located at 500 m depth at bure meuse france are currently being investigated by andra the french national radioactive waste management agency for testing the feasibility of long term and deep geological nuclear waste disposal in order to evaluate its potential as a geological barrier it is very important to study assess and describe its physico chemical variability the molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter the chemistry of the depositional environment the preservation and diagenesis conditions it also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series the abundance of unsaturated biomarkers the distribution of steroids and hopanoids and cpi values 2 prove the thermal immaturity of the organic matter the co occurrence of plankton bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions the data also reveal that the organic matter was deposited under oxic and open sea conditions except for a brief event of photic zone anoxia at the beginning of the middle callovian in the claystones the geosynthesis of diasterenes is favored to the detriment of the formation of steranes especially in smectite rich levels and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays on the scale investigated the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view yet detailed investigation of specific molecular families indicates changes related to major claystone limestone transitions the homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub horizontal paleotopography on which they were deposited this study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers

correlating biodegradation to magnetization in oil bearing sedimentary rocks abstract a relationship between hydrocarbons and their magnetic signatures has previously been alluded to but this is the first study to combine extensive geochemical and magnetic data of hydrocarbon associated samples we report a detailed study that identifies a connection between magnetic mineralogy and oil biodegradation within oil bearing sedimentary units from colombia canada indonesia and the uk geochemical data reveal that all the oil samples are derived from mature type ii kerogens deposited in oxygen poor environments biodegradation is evident to some extent in all samples and leads to a decrease in oil quality through the bacterially mediated conversion of aliphatic hydrocarbons to polar constituents the percentage of oil components and the biodegradation state of the samples were compared to the magnetic susceptibility and magnetic mineralogy a distinct decrease in magnetic susceptibility is correlated to decreasing oil quality and the amount of extractable organic matter present further magnetic characterization revealed that the high quality oils are dominated by pseudo single domain grains of magnetite and the lower quality oils by larger pseudo single domain to multidomain grains of magnetite and hematite hence with decreasing oil quality there is a progressive dominance of multidomain magnetite as well as the appearance of hematite it is concluded that biodegradation is a dual process firstly aliphatic hydrocarbons are removed thereby reducing oil quality and secondly magnetic signatures are both created and destroyed this complex relationship may explain why controversy has plagued previous attempts to resolve the connection between magnetics and hydrocarbon deposits these findings reinforce the importance of bacteria within petroleum systems as well as providing a platform for the use of magnetization as a possible exploration tool to identify subsurface reservoirs and a novel proxy of hydrocarbon migration

control of facies maturation and primary migration on biomarkers in the barnett shale sequence in the marathon 1 mesquite well texas abstract a great deal is known about the genetic relationships between biomarkers and their biogenic precursors in organic rich rocks the same is true of the way in which biomarker compound ratios change during maturation on the other hand very little is known about whether a crude oil can fully retain its inherent compositional ancestry during expulsion from a source rock thanks to shales being characterized in great detail for their unconventional resource potential new information is gradually coming to light here we report on observations in biomarker geochemistry of a thermally mature core of the barnett shale in which organofacies and maturity are essentially the same but where intraformational sources and reservoirs have already been reported our results indicate that most biomarkers are not fractionated as the primary migration of petroleum within source rocks takes place the 20s 20s 20r ratio of c27 steranes is uniform in the whole source rock sequence while the 20s 20s 20r ratio of c29 steranes shows indistinctly high values in the reservoir unit the 20s 20s 20r ratio of diasteranes and the 22s 22s 22r ratio of c31 17 hopanes do not appear to have been fractionated which may be a result of the thermal isomerization reactions predominating over and masking out the possible fractionation effects diasteranes steranes ratios do not exhibit features that suggest an association with fractionation but rather are broadly correlated with lithology however compared to the diasteranes steranes ratios the ts ts tm ratio is much more sensitive to changes in mineral compositions variations in the ts ts tm ratio show a positive correlation r2 0 73 with mixed layer illite smectite content fractionation in the ts ts tm ratio if it has so occurred may be subsequently overprinted by in situ clay catalyzed reactions

aliased tidal errors in topex poseidon sea surface height data alias periods and wavelengths for the m2 s2 n2 k1 o1 and p1 tidal constituents are calculated for topex poseidon alias wavelengths calculated in previous studies are shown to be in error and a correct method is presented with the exception of the k1 constituent all of these tidal aliases for topex poseidon have periods shorter than 90 days and are unlikely to be confounded with long period sea surface height signals associated with real ocean processes in particular the correspondence between the periods and wavelengths of the m2 alias and annual baroclinic rossby waves that plagued geosat sea surface height data is avoided the potential for aliasing residual tidal errors in smoothed estimates of sea surface height is calculated for the six tidal constituents the potential for aliasing the lunar tidal constituents m2 n2 and o1 fluctuates with latitude and is different for estimates made at the crossovers of ascending and descending ground tracks than for estimates at points midway between crossovers the potential for aliasing the solar tidal constituents s2 k1 and p1 varies smoothly with latitude s2 is strongly aliased for latitudes within 50 degrees of the equator while k1 and p1 are only weakly aliased in that range a weighted least squares method for estimating and removing residual tidal errors from topex poseidon sea surface height data is presented a clear understanding of the nature of aliased tidal error in topex poseidon data aids the unambiguous identification of real propagating sea surface height signals unequivocal evidence of annual period westward propagating waves in the north atlantic is presented

pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments however one of the most distinctive characteristics the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum remains unresolved higher pregnane and homopregnane as well as c23 c26 20 n alkylpregnanes relative to the regular steranes were observed in samples collected from different petroleum basins in china these included precambrian marine carbonate derived petroleum nw sichuan basin lower paleozoic marine marl derived crude oils tarim basin and eocene hypersaline lacustrine carbonate source rocks and associated petroleum bohai bay basin however all of the samples have many common biomarker characteristics such as pristane phytane ratios 1 low amounts of diasteranes and high c29 c30 hopane 0 6 1 c35 c34 hopane mostly p 1 and dibenzothiophene phenanthrene dbt phen mostly 0 5 1 ratios revealing a contribution from anoxic carbonate marl source rocks deposited in restricted clastic starved settings we suggest that 5a l4b l7b pregnane and homopregnane as well as their higher c23 c26 homologues are geological products derived from steroids bound to the kerogen by a sulfurized side chain carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between c 20 and c 22 similar distributions occur in the short chain analogues of 4 methylsterane triaromatic steroid and methyltriaromatic steroid hydrocarbons providing circumstantial evidence for this proposal the ratio of pregnane and homopregnane to the total regular steranes and the ratio of c27 diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies in general high diasteranes and low pregnanes with homologues indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks low diasteranes with high pregnanes implies restricted sulfur rich conditions typical of anoxic carbonate source rocks furthermore the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings

detecting aliased tidal errors in altimeter height measurements a simple statistic is derived for quantifying the potential for the aliasing of tidal errors in a given linear estimate of sea surface height constructed from altimeter data the existence of m2 tidal constituent errors in geosat data processed in the traditional way i e with orbit errors removed using least squares fits to 1 cycle per revolution sinusoids which are of sufficient magnitude to alias into apparently westward propagating ocean features is demonstrated by artificially inducing aliasing the aliasing statistic presented here responds clearly to the induced aliasing and to actual aliasing caused by real data dropouts in the geosat data the potential for aliasing m2 tidal errors is shown to vary with latitude depending on the time interval between ascending and descending ground tracks near the location of interest the methods developed here are applied to geosat data from the northeast atlantic to demonstrate the presence of m2 tidal error aliasing in those data

currents fronts and eddy fluxes in the canary basin hydrographic data from two cruises in the canary basin meteor 57 july 1981 poseidon 86 april 1982 are analysed with respect to current distribution and lateral heat flux in the azores madeira region the first part of the data base consists of long transects of xbt and g e k measurements between cape finisterre north west spain and the northern canary basin where several year long current meter records exist further information is obtained by thermosalinograph surface data and by expendable current profilers xcp geostrophic currents are derived from xbt profiles using the tight temperature salinity relationship in the depth range of the warmwassersphare the results compare well with the g e k and xcp current observations the second part consists of ctd data from an eddy resolving box shaped ctd survey 500 500 km2 centered at the mooring location 33 n 22 w the observations are supplemented by satellite buoy trajectories horizontal parameter distribution is shown in terms of objectively contoured maps bands of spatially enhanced energetic structures seen in the long transects are further resolved by the box survey as a deep jet like current system cross the canary basin in a west east direction associated with this azores current is a frontal zone with near surface temperature and salinity steps of order 2 k and 0 3 practical salinity units the dynamic topography field can be decomposed into a linear background field a rossby wave and a mesoscale eddy field we find that major contributions to the meridional eddy heat flux are confined to the vicinity of the azores current frontal zone it is shown that the principal balance in the temperature equation is between heating by the mean horizontal advection terms and cooling by the eddy flux divergence

the global structure of the annual and semiannual sea surface height variability from geosat altimeter data the global structure of the annual and semiannual sea surface height variability is constructed from the first 2 years of the geosat exact repeat mission erm altimeter data the gem t2 orbits available for the first 2 years of the erm have an accuracy of 40 cm rms residual orbit error is modeled as one cycle per orbital revolution and is removed from collinear differences of arcs made of data from one full orbital revolution of the satellite the error in the schwiderski m2 tidal model must be estimated due to the fact that the tidal variability aliases to 1 15 cycles per year cpy and this frequency is not separable from 1 cpy with the 2 years of data an estimate of the m2 tidal error is made based on the particular temporal and spatial aliasing of the tide with this error removed a least squares fit of sine and cosine waves with annual and semiannual frequencies is made to the time series at every point along the ground track of the satellite this produces sine and cosine coefficients at the ground track points which are interpolated to a regularly spaced grid over the globe from the sine and cosine maps amplitude and phase may be obtained interpolation of the sine and cosine coefficients using different spatial scales is done to better observe the large scale phase changes and to remove small scale noise results show the phase relationships between major current systems large scale variations near the equator in the intertropical convergence zone itcz a 180 phase difference between the northern and southern hemispheres for the annual variability large scale westward propagating waves and other large scale gyre features

paleozoic oil source rock correlations in the tarim basin nw china we studied a suite of 40 oils and extracts of purported source rocks from the tarim basin in nw china the main group of oils comes from tazhong and tabei wells which sample the largest known petroleum accumulations in the basin these oils can be statistically correlated with extracts of ordovician rocks based upon high relative concentrations of 24 isopropylcholestanes and low relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes in contrast extracts from cambrian rocks have low relative concentrations of 24 isopropylcholestanes with high relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes although some tarim basin cambrian rocks yield high total organic carbon contents we see little evidence in the analyzed oil samples to suggest that they came from cambrian source rocks

vascular plant biomarker distributions and stable carbon isotopic signatures from the middle and upper jurassic callovian kimmeridgian strata of staffin bay isle of skye northwest scotland the molecular and stable carbon isotopic composition of higher plant biomarkers was investigated in middle to upper jurassic strata of the isle of skye northwest scotland aromatic hydrocarbons diagnostic of vascular plants were detected in each of nineteen sedimentary rock samples from the early callovian to early kimmeridgian interval a succession rich in fossil fauna including ammonites that define its constituent chronozones the higher plant parameter hpp and higher plant fingerprint hpf calculated from the relative abundance of retene cadalene and 6 isopropyl 1 isohexyl 2 methylnaphthalene ip ihmn exhibit several large fluctuations throughout the skye succession studied these molecular profiles contrast with both 1 the more uniform profiles previously observed in jurassic successions putatively of the same age from other palaeogeographical settings including the carnarvon basin western australia and 2 the steady rise in global sea level during this interval this suggests that the hpf profiles of jurassic marine successions may not be reliable indicators of global climate change our results indicate that other factors such as local tectonism resulting in changes to the relief and landscape of the hinterland likely influenced the palaeoflora and the mode of transport of its detritus into adjacent marine depocentres however the skye succession showed similar 13c profiles of total organic carbon toc comprising mainly fossil wood the vascular plant biomarker retene and a predominant phytoplanktonic biomarker phytane the apparent isotopic relationship between terrigenous and marine derived biomarkers supports a strong coupling of the atmosphere and ocean the maximum isotopic excursion occurs in the cardioceras cordatum ammonite biozone of the early to middle oxfordian which may be indicative of changes in atmospheric and oceanic levels of co2

origin of organic matter from tectonic zones in the western tatra mountains crystalline basement poland an example of bitumen source rock correlation abstract solid bitumens of unknown origin found in brittle tectonic shear zones cutting the crystalline basement of the western tatra mts show uniform geochemical characteristics that suggest a uniform source for the original hydrocarbons on the basis of gc ms data a similarity between these solid bitumens and organic matter dispersed in the mesozoic source rocks of podhale trough and sedimentary cover of the northern tatra mts is observed the organic matter in the mesozoic source rocks shows a higher maturation level than that in the solid bitumens the molecular composition of the organic matter in both the solid bitumens and the basement rocks is significantly different from that in the paleogene sedimentary rocks infilling the podhale trough these immature to early mature paleogene sedimentary rocks contain organic compounds typical of terrestrial plants both conifers simonellite and retene and angiosperms lupane oleanane and taraxastene which are absent in the solid bitumens and in the mesozoic source rocks water co2 fluid inclusions in quartz sealing the shear zones have marine like salinity a dominance of cacl2 and mg2 depletion suggesting genetic affinity to dolomitised carbonate rocks such as potential middle triassic source rocks the low maturity of the solid bitumen in the shear zones relative to its mesozoic source can be explained by continued maturation of the mesozoic source rocks after expulsion and migration into the shear zones the results of hydrocarbon generation modeling indicate that oil expulsion from the mesozoic source rocks its migration through the shear zones and the subsequent maturation of the mesozoic source rocks all occurred within a short oligocene time interval

precise maturity assessment over a broad dynamic range using polycyclic and heterocyclic aromatic compounds abstract the construction and reliable application of maturation indices is extremely important in deep earth exploration yet predicting levels of maturation on a molecular level especially at overmature stages is still a major challenge here we report robust broad ranging and precise maturity parameters that were developed using a continuous core of thermally overmature lacustrine deposits shahezi fm from the deep songke 2 well sk 2 songliao basin china augmented by shallow cores of lower maturity marine deposits posidonia shale from the hils syncline germany the novel indices presented here are based on the general process of thermally induced cyclization aromatization and aliphatic chain cracking of hundreds to thousands of compounds during maturation the newly developed parameters with an extremely broad dynamic range extending from catagenesis and into metagenesis vitrinite reflectances ro range from 0 9 to 2 2 are based on polycyclic and heterocyclic aromatic compounds measured using fourier transform ion cyclotron resonance mass spectrometry ft icr ms the high coefficient of correlations between the new maturity parameters with ro and tmax demonstrate their utility for assessing precisely the thermal maturity of overmature shales

late archean molecular fossils from the transvaal supergroup record the antiquity of microbial diversity and aerobiosis abstract cores recovered during the agouron griqualand drilling project contain over 2500 m of well preserved late archean transvaal supergroup sediments dating from ca 2 67 to 2 46 ga bitumen extracts of these strata were obtained using clean drilling sampling and analysis protocols that avoided overprinting syngenetic molecular fossil signatures with contaminant hydrocarbons comparisons of biomarker contents in stratigraphically correlated intervals from diverse lithofacies in two boreholes separated by 24 km as well as across a 2 gyr unconformity provide compelling support for their syngenetic nature the suite of molecular fossils identified in the late archean bitumens includes hopanes attributable to bacteria potentially including cyanobacteria and methanotrophs and steranes of eukaryotic origin this molecular fossil record supports an origin in the archean eon of the three domains of cellular life as well as of oxygenic photosynthesis and the anabolic use of o2

diagenetic and detrital origin of moretane anomalies through the permian triassic boundary abstract many biogeochemical anomalies coincide with the late permian extinction lpe 252 28 ma several mechanisms have been proposed to explain the moretane hopane anomaly that has been identified in samples from meishan gssp section in southeastern china here we report homohopane 2 and 3 methylhomohopane and lithological data for a drill core from the meishan section in southeastern china three intervals of elevated c 30 moretane hopane ratios are recorded in the lungtan yinkeng and helongshan formations moretane hopane ratios of c 31 34 homohopanes and the 2 and 3 methylhomohopanes display the same stratigraphic patterns as the c 30 moretane hopane record in light of the multiple and parallel moretane anomalies for the homohopane and 2 and 3 methylhomohopane series enhanced input from higher plant organic matter such as coal and peat does not adequately explain the observed isomer patterns correlation of high moretane hopane ratios with low c 35 homohopane index hhi and high hopane sterane values suggest increased input of hopanoids from oxic soils additionally moretane hopane ratios show excellent correlations with total clay percentages and specific clay types particularly chlorite illite and mixed layer illite smectite we conclude that a combination of episodic hopanoid input from soil bacteria and diagenetic effects related to redox and detrital clays generated the unique moretane hopane patterns at meishan similar relationships of ts ts tm with redox source indicators and lithology indicate that ts ts tm is affected by the same factors controlling the moretane hopane ratios berthierine a clay that requires reducing conditions for formation was detected in samples from the lungtan formation we are unable to determine from our results whether the berthierine is authigenic or detrital but future determination of the origin of berthierine at meishan may offer additional environmental insight no link between diasteranes and lithology was observed in this study suggesting that diasteranes are relatively unaffected by the detrital clay component of the meishan sediments in total the results point toward the complex role of source input lithology and depositional redox conditions in the transformation of organic matter during maturation future work is required to elucidate the lithological effects on diagenetic processes including biomarker genesis isomerization and thermal degradation

origin of low molecular weight alkylthiophenes in pyrolysates of sulphur rich kerogens as revealed by micro scale sealed vessel pyrolysis abstract micro scale sealed vessel mssv pyrolysis experiments have been conducted at temperatures of 150 200 250 300 330 and 350 c for various times on a thermally immature type ii s kerogen from the maastrichtian jurf ed darawish oil shale jordan in order to study the origin of low molecular weight lmw alkylthiophenes these experiments indicated that the lmw alkylthiophenes usually encountered in the flash pyrolysates of sulphur rich kerogens are also produced at much lower pyrolysis temperatures i e as low as 150 c as the major apart from hydrogen sulfide sulphur containing pyrolysis products mssv pyrolysis of a long chain alkylthiophene and an alkylbenzene indicated that at 300 c for 72 h no cleavage leading to generation of lmw alkylated thiophenes and benzene occurs in combination with the substantial production of lmw alkylthiophenes with a linear carbon skeleton at these conditions this indicated that these thiophenes are predominantly formed by thermal degradation of multiple poly sulfide bound linear c 5 c 7 skeletons which probably mainly originate from sulphurisation of carbohydrates during early diagenesis lmw alkylthiophenes with linear carbon skeletons seem to be unstable at mssv pyrolysis temperatures of 330 c either due to thermal degradation or to methyl transfer reactions lmw alkylthiophenes with a branched carbon skeleton most likely derive from both multiple poly sulfide bound branched c 5 c 7 skeletons and alkylthiophene units present in the kerogen

source rock lithology prediction based on oil diacholestane abundance in the siliceous clastic akita sedimentary basin japan in an effort to predict the source rock lithology from oil biomarkers in the akita basin the relationship of diacholestane abundance to clay mineral content thermal maturation and the oxic anoxic depositional conditions of representative mudstone samples has been investigated the relative diacholestane abundance of samples with similar maturity levels increases with increasing clay mineral content the oxic anoxic depositional conditions of the samples estimated by c35 homohopane index are less influential for diacholestane formation in the case of the yabase oil field samples a crossplot of the diacholestane abundance versus ethylcholestanes 20s 20s 20r and clay mineral content was applied to evaluate the source rock lithology of the yabase oils the source of this oil is consequently predicted to be the clay poor siliceous rocks of the miocene onnagawa formation although this study did not achieve quantitative clay content prediction the results demonstrate that this approach is useful for the characterization of source rock lithology especially for moderately mature oils

depositional environment and hydrocarbon source potential of the permian gondwana coals from the barapukuria basin northwest bangladesh article barapukuria coal basin is situated in dinajpur district of the northwestern part of bangladesh a total of eight coal samples have been collected from two different locations of the basin and analyzed using organic geo chemical and organic petrological methods the extracted organic matter of the studied samples is a mixture of type iii and type ii kerogen as evaluated by the source rock analyzer sra and pygc pyrograms the measured total organic carbon toc ranges from 61 to 74 wt and the recovered extractable organic matter eom varies from 27 561 to 41 389 ppm these results suggest that the coals are ranked as good quality source rock the hydrocarbon yield has been calculated which is also high and it ranges from 12 192 to 20 799 ppm the organic matter is thermally mature for hydrocarbon generation considering their tmax and measured mean vitrinite reflec tance values of 431 to 435 c and 0 72 to 0 81 ro respectively the hopane 22s 22s 22r moretane hopane ratio and sterane parameters are also in support of these thermal maturity assessment

biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of opalinus clay and posidonia shale in northern switzerland abstract samples from two argillaceous formations opalinus clay and posidonia shale of near identical maturity from northern switzerland were subjected to a geochemical characterisation of organic matter and to confined system pyrolysis experiments throughout the study area the characteristics of organic matter are similar indicating a spatially homogeneous sedimentary facies posidonia shale contains marine organic matter deposited in a reducing environment while a predominantly terrigenous source and a more oxidising environment of deposition was identified for opalinus clay in the western and central parts of the study area organic maturity is close to the onset of oil generation in the easternmost part a higher maturity has been reached due to a deeper burial below thick tertiary molasse deposits isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 c over 24 h bitumen yields increase along similar pathways for both opalinus clay and posidonia shale but the maximum values are displaced by 10 20 c data pertaining to maturity were determined from gc ms analyses of saturated hydrocarbons and specific attention was given to c 29 sterane and c 32 hopane isomerisation ratios the evolution of these parameters with rising temperature is slightly different in the two formations which is attributed to the contrasting organic facies the pyrolysis data together with literature data from natural basins were used to calculate kinetic parameters for c 29 sterane and c 32 hopane assuming a single step isomerisation scheme according to the arrhenius law the resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data activation energies are similar in both formations while the frequency factors are up to one order of magnitude higher for posidonia shale when compared to opalinus clay for the benken site maximum temperature during cretaceous burial was calculated on the basis of the kinetic data using the tti approach the resulting temperatures of 75 80 c are 5 10 c below those derived in the literature from apatite fission track analysis vitrinite reflectance and basin modelling

geochemical investigation oil oil and oil source rock correlation in the dezful embayment marun oilfield zagros iran the authors wish to thank m l bordenave for many fruitful discussions critical and helpful comments and reviewing an earlier draft of manuscript we also wish to thank hormoz ghalavand national iranian oil company for providing the oil samples and support provided by shahid beheshti university tehran chamran university ahwaz the work depended on support provided by technical staff at the university of aberdeen u k and kharazmi university the work was much improved by reviews and comments provided by anonymous reviewers

organic geochemical study and genetic correlation of natural gas oil and menilite source rocks in the area between san and stryi rivers polish and ukrainian carpathians abstract we studied the source rocks and petroleum accumulations in the carpathian mountains of the polish ukrainian border area between the san and stryi rivers a total of 108 oligocene menilite formation rock samples 12 oil and 15 gas samples accumulated in the oligocene reservoirs and one oil and gas sample from an upper cretaceous reservoir were analysed the aim of this study was to evaluate the petroleum potential of the menilite formation in this area and to evaluate potential genetic correlations between source rock and petroleum the menilite formation represents a prolific source rock with toc content ranging from 2 to 7 wt locally exceeding 20 wt algal type ii and mixed type ii iii kerogens dominate but sometimes type iii kerogen and rarely type i kerogen occur thermal maturity of the oligocene menilite formation increases from outer to inner tectonic units from the immature in the boryslav pokuttya and skole units to the overmature in the southern parts of silesian and dukla units as a consequence petroleum potential decreases in the same order geochemical analyses reveal that oil and gas generation and migration processes within the carpathian flysch succession are complicated all analysed oils were generated from the menilite formation during early and peak stages of the oil window associated gas is of low temperature thermogenic origin sometimes containing an admixture of microbial gas high temperature thermogenic gas occurs only in the polish part of the silesian unit

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

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

a red algal bloom in the aftermath of the marinoan snowball earth organic matter from the cap dolostones overlying the marinoan age glacigenic diamictites of the araras group amazon craton has been studied to reconstruct the post glacial ecosystem molecular fossils indicate that the post marinoan ecosystem was marked by an apparent decline in marine algal diversity the proliferation of red algae may be explained by environmental changes such as a massive nutrient input accompanying continental weathering after the ice thaw and a dimer light penetrating sea water due to the drowning of the platform in addition the presence of green sulphur bacteria indicates that sea water was stratified with an anoxic possibly euxinic i e sulphidic layer at the water sediment interface sulphur cycling probably occurred at the redox boundary as suggested by the recognition of active sulphate reduction this observation supports a microbially induced model for the formation of the cap dolostones

the werra cyclotheme upper permian fore sudetic monocline poland insights into fluctuations of the sedimentary environment from organic geochemical studies abstract a study of the extracts of samples recording a transgressive regressive succession of the werra cyclothem zechstein upper permian from the southern margin of the european permian basin the fore sudetic monocline poland provides an insight into major sources of organic matter and diagenetic processes the studied cross section comprises all lithologies representative for the european basin including transgressive sandstones weissliegend and organic rich shales kupferschiefer followed by carbonates as well as regressive anhydrites with intercalations of rock salt due to the variable influence of overlapping diagenetic processes that affected the organic matter i e maturation and late diagenetic oxidation related to base metal mineralisation a reliable comparison of the biomarker results is only possible for the major upper part of the section ca 38 m including carbonates and evaporites but not for the oxidised first 2 3 m from the base of the kupferschiefer the transition from carbonate to evaporate sedimentation is associated with a shift to predominant even c numbered n alkanes increased abundance of carotanes and high homohopane index reflecting enhanced reducing conditions the presence of the c25 regular isoprenoid squalane biphytane and the rapid decrease in the pristane phytane ratio in the evaporites are mainly controlled by the important contribution from both halophilic and methanogenic archaea the occurrence of gammacerane in the anhydrites suggests development of water column stratification at some stages of the sea regression this is associated with appearance of specific aryl isoprenoids with a lycopane carbon skeleton most likely related to botrycoccus braunii race l algae lycopane derivative occurrence suggests that such an algal race could have occurred since permian currently known recent eocene the presence of the abundant freshwater brackish algal biomarkers in evaporititic deposits can be envisaged in the costal part of the zechstein basin with temporary salt wedge estuary water stratification the algae bloomed in the top fertile fresh brackish water layer fed by rivers and the algal biomass was deposited on the sea floor covered with evaporitic brine the stratification periodically broke down during precipitation of the rock salt presumably due to a decrease in riverine water input as revealed by characteristic disappearance of gammacerane and hopane distributions similar to those observed for the carbonate rocks the methylphenanthrenes phenanthrene ratio was used together with methyldibenzothiophenes dibenzothiophene ratio to assess maturity these maturity estimations indicate that the peak of oil window has been reached which is confirmed by other biomarker maturity parameters based on sterane and hopane distributions the maturity stage of oil generation and expulsion was further confirmed by the presence of solid bitumen as cements in the sandstone underlying kupferschiefer and bitumen veins and lenses in the carbonates

organic geochemistry of the lower toarcian posidonia shale in nw europe abstract a suite of core and outcrop samples of the lower toarcian posidonia shale and time equivalent deposits was collected from multiple locations including southern germany swabian alb and franconian alb northern germany the east coast of great britain the netherlands and luxembourg in order to study major differences and similarities with respect to depositional environment and redox potential based on molecular geochemical data all samples are immature or in the early oil window with the highest thermal maturity occurring in the profile from great britain about 0 7 vitrinite reflectance molecular geochemical maturity parameters were used to quantify maturation in detail during shale deposition in the west cleveland basin great britain h 2 s was immediately consumed in the water column by terrigenous input supplying abundant reactive iron to form pyrite these samples are characterized by low dibenzothiophene phenanthrene ratios 95 of 2 and h 2 s in contrast sulfidic euxinic bottom waters possibly with enhanced salinity and stratified water column prevailed due to a more restricted iron supply in luxembourg northern germany and the franconian alb of southern germany a more oxygenated dysoxic bottom water column associated with anoxic sediments i e anoxic dysoxic boundary close to the sediment water interface prevailed in the swabian alb of southern germany despite observed changes within each vertical profile at each site large scale regional trends in depositional conditions can be clearly identified for the early toarcian

biomarker evidence for botryococcus and a methane cycle in the eocene huadian oil shale ne china the saturated and unsaturated hydrocarbons of two samples hd 19 and hd 21 from the same section of the middle eocene lacustrine huadian oil shale in ne china were identified and shown to be mainly from algal and bacterial sources comparison of the two samples provided an opportunity to explore the contribution from telalginite to the hydrocarbon profiles cells identified from microscopy as botryococcus in the telalginite of hd 21 were confirmed as belonging to the l race of b braunii from the presence of monoaromatic lycopane derivatives and small amounts of several lycopadienes lycopane was abundant and was probably derived from biohydrogenation of lycopadienes and related lipids on the basis of d 13 c values hopane distributions showed a dominance of those with the biological 17b 21b stereochemistry as expected for an immature shale with low amounts of 17b 21a hopanes moretanes and 17a 21bhopanes two hopenes were also abundant and assigned as c29 and c30 neohop 13 18 enes which occurred together with the c29 and c30 hop 17 21 enes these had depleted carbon isotope values 43 7 to 50 8 indicative of production by methane oxidizing bacteria methanotrophs the high proportion of hopanoids with carbon numbers c32 indicates extensive post depositional diagenetic alteration of bacteriohopanepolyols as well as a direct input of c30 hopanoids the data clearly indicate that there was active utilization of methane in this lacustrine depositional setting but isoprenoid hydrocarbon biomarkers for methanogens such as pentamethylicosane pmi and squalane were in surprisingly low abundance it is possible that these bacterial contributions were present as polar lipids the origins of an unusual c38 isoprenoid alkane assigned as bipristane are uncertain but may be from methanogens steranes and sterenes were relatively minor components but abundant diasterenes and 4 methyldiasterenes were present reflecting significant conversion of the original lipid composition by way of clay catalysed diagenesis the biomarker data suggest that the bottom waters in the original depositional environment had low o2 content but the sediments were probably neither sulfidic nor strongly reducing the high content of organic matter in the shale likely reflects both high but fluctuating productivity due to eutrophic conditions in the overlying water and good preservation in the sediments

origin of oils in the velebit oil gas field se pannonian basin serbia source rocks characterization based on biological marker distributions abstract twenty five crude oil samples from velebit oil gas field se pannonian basin serbia were investigated in order to define the depositional environment lithology thermal maturity and depth of burial of the corresponding source rocks saturated biomarkers n alkanes isoprenoids steranes and triterpanes were determined using gas chromatography gc and gas chromatography mass spectrometry mass spectrometry gc ms ms source and maturity parameters were calculated from the distribution and abundance of biomarker compounds and principal component analysis pca was used to interpret their relationships the velebit crude oils were generated from siliciclastic source rocks containing a mixture of terrestrial and marine organic matter that was deposited under a predominantly reducing environment probably in the distal marine portion of a delta maturation parameters indicated significant thermal maturity corresponding to peak oil generation age diagnostic biomarker ratios suggest that the source of velebit oils may be upper cretaceous older than most oils in the pannonian basin which are generated from tertiary sources these source rocks are thought to be at a present day depth of approximately 3000 m within or in close proximity to the oil field

a comparison of thermal maturity parameters between freely extracted hydrocarbons bitumen i and a second extract bitumen ii from within the kerogen matrix of permian and triassic sedimentary rocks abstract in this study we compared various maturity dependent aromatic steroid and triterpenoid hydrocarbon ratios in bitumens that are freely extractable from sedimentary rocks bitumen i with those in second extracts that comprised hydrocarbons closely associated with the kerogen mineral matrix bitumen ii bitumen ii was released through kerogen isolation and demineralisation using hcl and hf h3bo3 the samples studied although of similar age come from different localities they represent a range of facies and two kerogen types ii and iii and all were deposited under marine conditions the results show that the more stable isomers of methylnaphthalene mn and methylphenanthrene mp are relatively more abundant in bitumen ii the difference between the methylnaphthalene ratio mnr of bitumens i and ii when plotted against the ratio of clay to total organic carbon clay toc gives an excellent correlation r2 0 88 the highest clay toc ratio corresponds with the biggest difference in mnr for the respective bitumens consistent with the more stable isomers being preferentially retained within the clay kerogen matrix since the mp isomers are higher in bitumen ii than in bitumen i it was anticipated that their methylphenanthrene index mpi 1 values a commonly used measure of thermal maturity would also be different for most samples the measured mpi 1 in bitumen i is generally higher than that in bitumen ii except for three samples thus showing a bias towards a lower thermal maturity for the second extract the opposite is true of the mp ratio and mnr this may be attributed to the fact that phenanthrene p which is part of the denominator in mpi 1 is more stable than its methylated counterparts steroid and triterpenoid maturity parameters also showed differences between the two extracts with c27 diasterane sterane and ts ts tm being higher in bitumen i only the former parameter is positively correlated with the clay toc ratio suggesting that clay content probably influences the diagenetic transformation of steroid precursors to diasteranes the observed differences between the maturity parameters of bitumen i and bitumen ii may be especially important in sedimentary rocks that contain high percentages of clay minerals

oceanic tides from geosat altimetry direct tidal analysis of the altimetry from the geosat exact repeat mission s first year is used to derive estimates of the diurnal and semidiurnal oceanic tides the geoid is removed by collinear differences at 34 1 day separation and the orbit error is reduced by subtracting a slowly modulated 1 cycle revolution term a sequence of independent analyses at grid areas of 1 latitude 1 5 longitude using orthotide functions ensures complete definition of the diurnal and semidiurnal species global admittance maps for m2 and s2 within the latitudes 58 n and 59 s compare well with ground truth at 66 open ocean sites maps of differences between geosat and the naval surface weapons center model show important areas of the order of 10 15 cm the integral for the global power input from the moon gives 2 51 tw m2 0 44 tw s2 lower than many previous estimates but in agreement with figures deduced from a recent analysis of satellite orbits

cadalenes and norcadalenes in organic rich shales of the permian irati formation parana basin brazil tracers for terrestrial input or also indicators of temperature controlled organic inorganic interactions abstract cadalene isocadalene and a series of norcadalenes were identified in black shales of the permian irati formation in the northeastern and central eastern parana basin brazil the origin of their isomers with an isopropyl substituent is potentially related to higher plants and likely reflects the spreading of pteridophytes and gymnosperms after the glaciation of southern gondwana a general increase in the relative abundance of isocadalene 1 6 dimethyl 3 isopropylnaphthalene the isomer co occurs in with increasing thermal maturity at the base of the amaral machado quarry northeastern basin and refers to the acid catalyzed rearrangement of cadalene 1 6 dimethyl 4 isopropylnaphthalene the isomer due to the presence of montmorillonite via an organic inorganic interaction this localized and incipient maturation can be related to diabase sills of the serra geral formation similar maturation due to heating also affected the distribution of the norcadalenes by thermally stabilizing their isomers with an isopropyl substituent in addition to the formation of related compounds with an ethyl substituent based on this a norcadalene ratio is proposed which is the sum of the 1 6 dimethyl 4 ethylnaphthalene and 1 6 dimethyl 3 ethylnaphthalene over the sum of the 1 isopropyl 4 methylnaphthalene and 1 isopropyl 7 methylnaphthalene the results of this ratio and the established cadalene ratio resemble each other whereas samples from the sao mateus do sul quarry central eastern basin were not affected by thermal maturation and are characterized by a uniform distribution of the cadalenes and norcadalenes

observations in the canary basin and the azores frontal region using geosat data this paper discusses observations of the sea level in the azores frontal region and the canary basin as seen by the geosat altimeter frorn 5 to 45 w and 25 to 45 n two years of geosat exact repeat data were processed by colocating the data on a 0 06 grid then removing the mean by the along track difference method and removing the orbit error by a crossover analysis technique the data set was then interpolated by the successive correction method onto 15 day 0 5 maps to produce 47 residual height fields which were analyzed using complex empirical orthogonal functions eof and spectral analysis the results show that there is a region of high variability in the northwest corner reflecting the gulf stream extension and a region of medium variability at approximately 35 n reflecting the azores current the variability changes only slightly throughout the year with the winter season being the highest the data set also shows first mode baroclinic rossby waves between 30 and 35 n there is evidence that these rossby waves have different wavenumbers to the east and west of the mid atlantic ridge it is postulated that these waves have different generation mechanisms the mid atlantic ridge topography in the west and some other generation mechanism in the canary basin rossby waves are not apparent at 40 n

isomerisation rearrangement and aromatisation of steroids in distinguishing early stages of diagenesis abstract the distributions of proposed reactants and products of stages of early diagenesis of steroid hydrocarbons have been studied by gc and gc ms in a variety of downhole sequences of dsdp cores of various ages which include the san miguel gap walvis ridge gulf of california and falkland plateau the compounds comprise aliphatic and aromatic hydrocarbons such as diasterenes monoaromatic anthrasteroids and spirosterenes from the study of the progress of proposed reactions and of presumed product reactant relationships a pattern emerges that extractable lipid distributions can provide a means of distinguishing levels of early diagenesis which cannot be recognised readily from other methods a number of diagentic trends are evident such as progressive isomerisation at c 20 in diasterenes which occurs at different relative rates and temperature ranges in sediment sequences with different heat fluxes such studies allow investigation of the changes in biological marker compounds in the part of the continuum between changes during sediment deposition and the advent of catagenesis

exceptional preservation of hopanoid and steroid biomarkers in ediacaran sedimentary rocks of the east european craton abstract thermally unstable hopanes with a biological 17 21 h configuration hopanes hopenes hopanoic acids and hopanols were identified as important constituents of ediacaran to cambrian sedimentary rocks of the east european craton relatively high abundances of hopanes in relation to hopanes were identified in the petersburg area and eastern belarus while in volyn samples these compounds were found in traces in addition polar hopanoids including hopanols and hopanoic acids were found in most of the petersburg and some belarus and volyn sedimentary rocks the estimated equivalent of vitrinite reflectance for samples of lower maturity measured based on c31 s r ratio is in the range 0 28 0 49 rr while for those of higher thermal maturity this parameter corresponds to 0 41 0 57 rr the values of the c31 22s s r ratio are in agreement with above data and are in the range of 0 1 0 3 for the belarus and petersburg samples of 0 3 0 4 for volyn and of 0 4 0 5 for lithuania where hopanes and hopanols were not detected or are present as traces moreover there is good correlation r2 0 8 between c31 s r and c31ene h ene ratio values defined as ratio of c31 hopenes to hopanes which proves that less stable hopanes and hopenes are enriched in the same immature sedimentary rocks the remarkable occurrence of a significant portion of sedimentary hopanes retaining the biological stereochemical configuration confirms that exceptionally immature precambrian rocks can be found in some instances when these strata have undergone only a mild burial temperature history

effects of an oceanic anoxic event on the stable carbon isotopic composition of early toarcian carbon the early toarcian transgression is marked by the occurrence of organic carbon rich shales in large parts of western europe and in other parts of the world as well based on the positive carbon isotope excursion of pelagic limestones in the middle to upper part of the falciferum zone in several of the tethyan sections the widespread occurrence of the early toarcian shales was explained by an oceanic anoxic event oae jenkyns 1988 jenkyns and clayton 1997 the rapid burial of large amounts of organic carbon which is rich in 12 c would have led to a relative enrichment in 13 c of the global carbon reservoir and hence to an increase in delta 13 c of the limestones in southwest germany and a number of other locations both organic and inorganic carbon display a negative isotope excursion in the upper part of the tenuicostatum zone and the lower part of the falciferum zone synchronous to black shale deposition and predating the positive isotopic excursion kuspert 1982 1983 it is presently unclear what the exact cause for this widespread negative isotopic excursion is jenkyns and clayton 1997 the objective of our study was to examine if the negative carbon isotope excursion of organic matter om in the southwest german toarcian shales can be attributed to compositional changes of the om or if the excursion is related to variations in delta 13 c sub co2 aq in the photic zone to this end we analyzed the molecular and stable carbon isotope composition of om in ten samples spanning the early toarcian toc 2 5 10 5 percent hi 350 700 biomarker distributions and kerogen pyrolysates differ only slightly among the samples and delta 13 c values of primary production markers follow closely those of associated carbonate and kerogen delta 13 c sub carb toc this strongly suggests that differences in delta 13 c toc are related to differences in delta 13 c of co 2 aq in the photic zone supporting kuspert9s model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters evidence for euxinic conditions extending into the photic zone was found by the presence of derivatives of carotenoids such as isorenieratane from anoxygenic phototrophic sulfur bacteria their concentrations are extremely low in black shales from the tenuicostatum zone but are significant in the falciferum and bifrons zone with a maximum in the exaratum subzone suggesting that photic zone euxinia pze was a common feature of the early toarcian sea in southwest germany our data therefore support the kuspert model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters to the upper part of the photic zone resulting in a negative isotope spike the enrichment in 13 c in the middle of the falciferum zone which followed the negative spike may be attributed to the burial of isotopically light organic matter through worldwide black shale deposition