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

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

biomarker maturity parameters for high maturities calibration of the working range up to the oil condensate threshold abstract in a study of oils and source rocks from the kimmeridge clay united kingdom and the hanifa qatar formations several biomarker maturity parameters with working ranges up to vr e vitrinite reflectance equivalent 1 0 oil condensate threshold have been identified and calibrated this represents a significant improvement compared to commonly used biomarker maturity tools sterane and hopane isomerisation with their maturity maximum of approximately vr e 0 7 early part of oil window these new parameters are 1 the absolute concentrations of steranes and hopanes decreasing gradually with increasing maturity 2 the ratio of tricyclic terpanes tricyclic terpanes hopanes increasing with maturity 3 the ratio of diasteranes 14 h 17 h steranes depending both on maturity and on source rock lithology and 4 the ratio of t s t m 22 29 30 trisnorneohopane 22 29 30 trisnorhopane increasing rapidly at very high maturities during artificial maturation experiments the biomarker maturities described in the natural samples were also known to be time temperature dependent up to rather severe laboratory heating conditions this corresponds with the working range up to high maturity levels as observed in the natural samples

particle transport in the bari canyon southern adriatic sea to define the sediment transport pathways along the southern adriatic shelf and slope two oceanographic cruises were carried out in the southern adriatic in july 2004 and in march april 2005 to study the role of the bari canyon system on sediment dispersal three moorings including sediment traps and current meters have been deployed near the bottom at depths of 600 m for one year march 2004 march 2005 two moorings were deployed within the canyon station b in the northern branch and station c in the southern branch and one on the adjacent open slope north of the canyon system station a total mass fluxes tmfs measured by sediment traps were always higher in the canyon than on the adjacent slope the highest values were measured at station c average 8 07 g m 2 d 1 roughly double those of station b 3 07 g m 2 d 1 and the lowest outside the canyon at station a 1 69 g m 2 d 1 the highest tmf were recorded in spring 2004 a period characterized by the lowest water temperatures and the highest current speeds up to 72 cm 1 which were associated with the highest across slope current component along the canyon axes the simultaneous variations of fluxes occurring at the three stations imply that similar processes are active along the entire southern adriatic margin and that they are amplified inside the canyon in spring a vein of southward flowing north adriatic dense water naddw was observed along the adriatic shelf this was related to an enhanced across slope current component which was responsible for the higher particle fluxes both on the open slope and at the canyon stations these data suggest that the bari canyon is an efficient conduit for sediment from the adriatic continental shelf to the deep basin downcore profiles of 210 pb in sediments collected below the traps have been used to estimate sediment mass accumulation rates mars on a century scale on the open slope the annual trap flux recorded in 2004 2005 was lower than mar on the contrary in the bari canyon the annual trap flux was higher than mar indicating that the lateral advection of particles becomes predominant and that a fraction of the particles intercepted by sediment traps was only in transit through the canyon 2007 elsevier b v all rights reserved

conflicting sterane and aromatic maturity parameters in neogene light oils eastern chepaizi high junggar basin nw china abstract the saturated and aromatic hydrocarbon maturity characteristics of crude oils from the eastern chepaizi high in the junggar basin of northwest china were analyzed in detail the results show that sterane maturity parameters for light oils from the neogene shawan formation differ from other maturity parameters sterane c 29 20s 20s 20r and c 29 ratios indicate low maturity while aromatic hydrocarbons indicate high maturity we infer that light oils from the shawan formation have higher maturity than cretaceous and jurassic crude oils and were generated at equivalent vitrinite reflectance of 0 9 1 2 it can be concluded that the shawan light oils originated mainly from deeply buried highly mature jurassic source rocks southeast of sikeshu sag southwest of shawan sag and west of huomatu anticline belt during upward migration crude oils generated from jurassic source rock dissolved less mature cretaceous bitumen resulting in a mixture with apparently conflicting parameters phase fractionation during migration also could have contributed to the anomalously low sterane maturity parameters

climate of the past 2500 years in the gulf of taranto central mediterranean sea a high resolution climate reconstruction based on δ18o and δ13c of globigerinoides ruber white we present a high resolution isotope stratigraphy based on globigerinoides ruber white over the past 2500 years in the gulf of taranto central mediterranean g ruber white reflects summer conditions in the gulf of taranto but is influenced by two major surface water masses the western adriatic current wac and the ionian surface water isw and their variations on a decadal to multicentennial scale our analysis of the 13c and 18o of g ruber white allows the distinction of several climatic periods the roman warm period rwp 450 0 bc with relatively wet and warm conditions and a higher influence of the wac the roman classical period rcp ad 1 200 characterized by salinity increase resulting from circulation changes the dark ages cold period dcp ad 500 750 where wetter conditions in the gulf of taranto region are coherent with an increase dominance of the wac the medieval warm period mwp with wet and warm conditions in the first and a gradual drying in the second half and finally the transition from the mwp to the little ice age lia which is characterized by continuing dry conditions

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

constraints on the structure and tectonic development of the early mesozoic south georgia rift southeastern united states seismic reflection data processing and interpretation seismic reflection data collected by the consortium for continental reflection profiling cocorp over the buried triassic jurassic south georgia rift reprocessed in order to improve the upper 5 s of reflection time provide a window into the regional deep structure of the rift and delineate variations in basin structure and depositional styles located at the southernmost extent of the north american east coast early mesozoic rift system the structure of the south georgia rift basin has previously been known only from scattered drilling and potential field interpretation leaving the internal and boundary as well as the deep structure unknown the reflection data reveal that the south georgia basin consists of a broad complex terrane of isolated synrift grabens with intervening structural highs in contrast with earlier concepts of a single narrow trough or an amorphous sag basin two main subbasin depocenters are observed in west and west central georgia the largest of which is more than 100 km in width and the deepest at least 7 km at its inferred base analysis of the reflection data indicates that the distinct structural and seismic stratigraphic character of the reflection packages is analogous to other better studied extensional provinces e g north american basin and range the reprocessing of the reflection data provides a view of contrasting styles of faulting and subsidence within the rift the structural style of the subbasins varies drastically along strike changing from 1 a narrow asymmetric graben bordered by a planar and more deeply penetrating normal fault to 2 a broad and roughly symmetric graben bordered by a shallower dipping possibly listric fault along which extension may have been accommodated at depth by a low angle detachment or by a more complex system of high angle faults only limited crustal extension is suggested by the narrower graben and planar fault 1 whereas much greater extension would be expected from the wider graben bordered by a listric low angle fault 2 such a dual style of basin formation is predicted by segmented plate models of variable extension along continental margins and intracratonic rifts and may imply a significant change in crustal rheology along the developing rift integration of the interpretation of the regional structure of the south georgia basin with that of the deeper crustal structure as inferred from the 16 s reflection time cocorp data indicates that the synrift basins developed mainly over the upper plate of the alleghanian late paleozoic suture between north america and west africa the major subbasin border faults dip northward in an antithetic relation to the predominantly northward vergence of the suture zone the border faults thus do not appear to have reactivated antecedant structure although the development of the south georgia rift appears to have approximately coincided with early mesozoic thinning of the crust in the southeastern united states no horizontally layered or laminated lower crust is observed as has been associated with other more fully rifted terranes e g north american basin and range continental shelf around british isles however the moho discontinuity appears to have formed as a dynamic feature superimposed on late paleozoic compressional structure probably associated with early mesozoic rifting these findings thus support the interpretation that the south georgia rift developed as a major early mesozoic depocenter and possible incipient spreading center associated with the initial formation of the central atlantic ocean

evidence for biodegradation and evaporative fractionation in west sak kuparuk and prudhoe bay field areas north slope alaska abstract oils from the west sak kuparuk and prudhoe bay fields on the north slope of alaska display geochemical evidence for a complex petroleum filling history that includes multiple sources and alteration by evaporative fractionation and biodegradation source specific biomarkers in west sak oils indicate generation from the same source rocks in approximately the same proportions as prudhoe bay field oil consistent with the hypothesis that oil spilled from the deeper prudhoe accumulation and remigrated about 10 miles laterally and 5000 feet vertically into the west sak field west sak oils are moderately biodegraded but exhibit anomalously high concentrations of gasoline range saturate and aromatic compounds interpreted as a secondary gas condensate charge that arrived after biodegradation of the spilled prudhoe oil the shallowest west sak oils have less secondary gas condensate charge lower api gravities and reduced concentrations of methylcyclopentane benzene cyclohexane 3 methylhexane heptane methylcyclohexane and toluene relative to the deepest west sak zone a oils the carbon isotopic compositions of these c6 and c7 compounds in the shallowest west sak reservoirs are heavier than those of the deepest west sak oil reservoirs by up to 3 and the isotopic compositions of saturate compounds are altered more than those of aromatic compounds the heavier isotopic compositions of c6 and c7 compounds in the shallow west sak reservoirs are interpreted to result from a kinetic isotope shift caused by light biodegradation of the secondary gas condensate charge west sak field solution gas is also interpreted as biodegraded based upon its dryness 98 methane relatively high isobutane n butane ratio the presence of isotopically heavy carbon dioxide and isotopically light methane and propane that is isotopically heavier than either ethane or butane the isotopic compositions of methane and carbon dioxide in west sak gas suggest that biogenic methane was generated during co2 reduction under anaerobic conditions the isotopic compositions of c6 and c7 compounds in the deepest least biodegraded west sak oils are nearly identical to those of the underlying oils from the kuparuk field but differ from the prudhoe bay field oils the kuparuk field is therefore postulated as the source of the secondary gas condensate charge observed in oils from the west sak field ratios of toluene heptane and heptane methylcyclohexane in kuparuk oils provide independent evidence for loss of gas and condensate from the kuparuk reservoir by the process of evaporative fractionation and the oils subjected to the most evaporative fractionation are isotopically heavier in the c6 c7 range the isotopic compositions of west sak zone a c6 and c7 hydrocarbons suggest that a slight 0 8 isotopic fractionation resulted from evaporative fractionation of the gas condensate charge from the kuparuk field oil accumulation north northeast striking faults that connect the kuparuk and west sak reservoirs provide a potential migration pathway for the secondary gas condensate charge through 3000 feet of intervening shale this model of west sak oil biodegradation subsequent secondary gas condensate charge and further biodegradation has implications for development of north slope west sak oil reserves because heavily biodegraded west sak oils that lack a secondary gas condensate charge may be too viscous to develop by conventional waterflooding methods

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

contrasting accreted terranes in the southern appalachian orogen basement beneath the atlantic and gulf coastal plains and west african orogens abstract a variety of lithostratigraphic units may be outlined within the pre mesozoic crystalline basement of the atlantic and gulf coastal plains these include 1 a group of metamorphic rocks of variable grade together with deformed and retrogressed granite in southwestern alabama and southeastern mississippi wiggins uplift hornblende and biotite within higher grade units record 40ar 39ar post metamorphic cooling ages of 310 300 ma 2 a suite of contrasting igneous rocks granite basalt and agglomerate and serpentinite which occurs along the brunswick altamaha magnetic anomaly in southwestern alabama and 3 an extensive apparently coherent tectonic element the suwannee terrane comprised of undeformed granite in which biotite records 40ar 39ar post magmatic cooling ages of 530 525 ma low grade felsic metavolcanic rocks a suite of high grade metamorphic lithologies st lucie metamorphic complex in which hornblende yields 40ar 39ar post metamorphic cooling ages of 515 510 ma and a succession of lower ordovician middle devonian sedimentary rocks characterized by gondwanan fauna the west african orogens mauritanides bassarides and rokelides record a locally complex polyphase tectonothermal evolution the earliest event corresponded to westward rifting of a continental fragment from the west african craton at 700 ma this led to development of a rift facies lithotectonic succession which included sedimentary units and intracontinental igneous sequences rifting was limited and a western ensialic arc began to develop by 680 ma the associated convergence culminated in an episode of folding and metamorphism at 650 ma pan african i orogenesis following widespread deposition of late paleozoic glacial and flyschoid sediments a second tectonothermal event occurred between 550 and 500 ma pan african ii orogenesis the west african orogens were marked by general tectonic quiescence throughout most of the early and middle paleozoic late paleozoic 300 ma collision of gondwana and laurentia resulted in eastward translation of previously tectonized mauritanide units over their foreland and emplacement at highest structural levels of previously imbricated nappes which include sequences with uncertain palinspastic origins the late paleozoic hercynian transport was largely intracontinental and only westernmost portions of the exposed mauritanides record an associated penetrative tectonothermal overprint characteristics of pre mesozoic basement units which comprise the suwannee terrane in the florida subsurface suggest they represent extensions of the bassaride rokelide orogen there is no apparent record of paleozoic tectonothermal activity in the suwannee terrane this contrasts markedly with penetrative late paleozoic reworking of basement units in the wiggins uplift this suggests that a major dextral transcurrent fault was active during the late paleozoic and that proximal basement units were directly involved in collisional aspects of pangea assembly the various basement units of the coastal plain are not correlative with any of the non laurentian terranes exposed in the southern appalachian orogen e g carolina terrane of the eastern piedmont which accreted in the ordovician devonian to exterior positions along the eastern margin of the north american craton these exotic appalachian terranes were transported into their present structural positions during late paleozoic collision of gondwana and laurentia they are separated from gondwanan elements of the suwannee terrane by a suture approximately marked by the brunswick altamaha magnetic anomaly

dense low salinity outflow from the adriatic sea under mild 2001 and strong 1999 winter conditions 1 quasi synoptic temperature salinity and oxygen measurements in the adriatic and northern ionian seas mediterranean sea during two different winter conditions are presented in addition to the confirmation of previous knowledge about deepwater formation in the eastern mediterranean measurements give more insight into processes in the adriatic sea in winter and especially into the fate of the dense low salinity water masses transported by the west adriatic current wac and its spreading into the ionian sea a mild winter season without dense water production in the shallow areas of the adriatic sea was encountered during a cruise in february 2001 dense water outflow restricted to the deeper parts of the strait of otranto was nevertheless present during that mild winter and also in previous records of a cruise in autumn 1999 thus even in times of no deepwater production in the southern adriatic sea observations reveal a continuous flow of adriatic deep water adw through the strait of otranto and downslope in the northern ionian sea strong winter conditions are represented by a cruise carried out in february 1999 at that time cold and fresh water with density higher than that of south adw was observed on the italian shelf the dense coastal current is continued around cape santa maria di leuca at the heel of the italian boot in the gulf of taranto where the width of the shelf rapidly decreases dense coastal water is released to depth and transformed by intrusion and mixing with ambient water plumes and patches with horizontal extensions smaller than distances of a station grid are resolved by towed measurements in the 200 m upper layer with a multisensor chain products of coastal water transformation may be found at any depth on the western slopes of the ionian sea the new observations of dense water carried by the wac and plunging down to the level of neutral buoyancy in the gulf of taranto seem to confirm the hypothesis that the wac could be the origin of cold lenses found below the thermocline in the central ionian sea sellschopp and onken 2000

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

lithospheric sources of north florida usa tholeiites and implications for the origin of the suwannee terrane abstract sr nd and pb isotopic data for mesozoic tholeiites from six drillholes in northern florida suwannee terrane indicate derivation of the magmas from a source that was slightly incompatible element enriched with respect to bulk earth probably continental lithospheric mantle variably contaminated by more enriched crust initial isotopic compositions of the florida tholeiites show a considerable range 87 sr 86 sr 0 7059 to 0 7097 end 4 6 to 0 1 206 pb 204 pb 18 30 to 18 65 207 pb 204 pb 15 57 to 15 66 and 208 pb 204 pb 38 22 to 38 35 these compositions are distinctly different from those of mesozoic alkali basalts from the subsurface of southwestern florida heatherington a l mueller p a 1991 geochemical evidence for triassic rifting in southwestern florida tectonophysics 188 291 302 it is suggested that the north florida tholeiites were derived from within the continental lithosphere in contrast with mesozoic volcanic rocks from southwestern florida which have been previously suggested to be related to a mantle plume sm nd isotope systematics suggest derivation of the tholeiites from a 1 ga source a similar age to that proposed by pegram pegram w j 1990 development of continental lithospheric mantle as reflected in the chemistry of the mesozoic appalachian tholeiites usa earth and planetary science letters 97 316 331 for the source of tholeiitic basalts within the carolina terrane this supports proterozoic tectonic models which suggest that both the suwannee and carolina terranes had affinities with south american portions of gondwana containing 1 ga crust specifically the sunsas rondonian province nance murphy 1996 mueller p a kozuch m heatherington a l wooden j l offield t w koeppen r p klein t l nutman a p 1996 evidence for mesoproterozoic basement in the carolina terrane and speculations on its origin in nance r d thompson m d eds avalonian and related peri gondwanan terranes of the circum north atlantic gsa special paper 304 pp 207 218

petroleum geochemistry of middle magdalena valley colombia abstract twenty five crude oil samples from tertiary reservoirs in the middle magdalena valley colombia were studied by geochemical methods in order to understand their genetic relationships the oils were probably derived from both calcareous and siliciclastic facies of the upper cretaceous la luna formation some oils in the eastern margin contain relatively higher concentrations of land plant derived biomarkers than the remaining oil samples the molecular compositions of the oils observed in this study appear to be consistent with the inferred depositional sequence of anoxic marine pelagic carbonate facies in the north and western sectors of the middle magdalena valley while the eastern sector received a higher proportion of clastic input biomarker maturity parameters indicate that most of the oils were generated from the early phase of the oil window except for the colorado 38 oil that was generated during the peak of the oil window geochemical data support local generation and migration of the middle magdalena oils as opposed to longer distance migration from the region of the eastern cordillera the range of oil gravities measured in the middle magdalena valley is attributed to organic facies variations different levels of biodegradation and late charge of condensate rather than to thermal maturity and migration related effects

late holocene climate variability in the adriatic sea central mediterranean planktic and benthic foraminifera assemblages from a set of sediment cores collected on the adriatic shelf and the southern adriatic deep basin provide compelling evidence of submillennial scale environmental changes during the last 6000 years repeated peaks in globigerinoides sacculifer represent warm dry intervals including the mediaeval warm period the roman age the late bronze age and the copper age the last occurrence lo of g sacculifer 550 years bp approximates the base of the little ice age lia significant turnovers in the structure of the water column reflect changes in the rate of formation and depth of flow of the north adriatic dense water naddw and the levantine intermediate water liw about 7500 years bp the benthic oxygen isotope records mark the timing when the naddw formation intensified on the slope and shifted to its modern route about 5500 years bp when sea level reached its modern high stand oxygen isotope records of intermediate planktic dwellers indicate a northward intrusion of the liw on the slope the oscillating isotope trends during the last five millennia document a discontinuous invasion of liw into the central adriatic possibly reflecting short term climate changes with weakened liw production during colder and wetter intervals

temperature and productivity influences on u37k and their possible relation to solar forcing of the mediterranean winter to assess the extent and nature of human induced climate change we need to understand natural climate variability this heavily relies on proxy based climate reconstructions calling for excellent understanding of the conditions represented by the proxies here we report on an alkenone based u37k sea surface temperature sst proxy record originating from south italian marine sediments and covering 1305 a d to 1979 a d with a 3 87 year resolution the shallow water cores extracted from the gallipoli terrace in the gulf of taranto were dated by the torino group with high accuracy over the last two millennia using radiometric and tephroanalysis methods on the basis of comparison with historical and satellite derived climate and productivity data we propose that u37k reflects mainly sst of the cooler part of the year and is modified by variation in magnitude and timing of peak alkenone production on the seasonal temperature cycle comparison of the u37k record with the record of atmospheric 14c a proxy for solar energy variability shows a high correlation r 0 73 for the period between 1420 a d and before human interference with the 14c record by combustion of fossil carbon and the release of radioactive isotopes by nuclear tests this suggests a centennial scale solar forcing we propose that wind induced mixing resulting from mediterranean climate dynamics plays a crucial role in translating solar activity to alkenone productivity and sst during the cooler part of the year

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

geochemistry of oils and condensates k field offshore taiwan a case study in migration fractionation abstract the k field offshore taiwan produces mainly gas along with small amounts of condensates and paraffinic oils detailed geochemical analyses of 21 fluids have shown that they belong to a single family generated from mixed organic matter derived from microbial gymnosperm and angiosperm sources deposited in a fluvio deltaic environment maturity assessment using several molecular indicators shows that the liquid hydrocarbons have maturities equivalent to vitrinite reflectances of around 0 7 0 9 the source and maturity evidence indicate the fluids were generated in situ from late oligocene miocene coals and shales associated with the reservoirs large variations are observed in the bulk properties of the condensates and paraffinic oils e g api gravities from 32 to 58 certain molecular source indicators e g pr ph ratios from 5 1 to 9 2 and carbon isotopes e g 13c values of saturated hydrocarbon fraction from 28 9 to 26 9 pdb these variations are ascribed to the process of evaporative fractionation in which a gas condensate cap separates from its associated oil and migrates to a shallower reservoir in the k field thermogenic gas resulting from volcanic activity during the middle upper miocene provided the necessary gas charge to the emplaced oils this study provides the first documentation of the effect of evaporative fractionation on a wide range of saturated and aromatic biomarker and carbon isotope indicators commonly measured in crude oils and condensates recognition of the process of migration fractionation and understanding its effect on petroleum composition are critical because molecular and isotopic geochemical parameters are widely used in oil to oil and oil to source correlations as well as indicators of alteration source type and thermal maturity

oil source rock correlation using carbon isotope data and biological marker compounds cook inlet alaska peninsula alaska rock and oil samples from the cook inlet alaska peninsula area were analyzed to determine the source of the commercial hydrocarbons produced in the cook inlet basin from lower tertiary nonmarine sandstone reservoirs rock eval hydrogen index analysis and organic carbon content were used to identify the most favorable rock samples for solvent extraction and carbon isotope gas chromatographic gc and gas chromatrographic mass spectrometric gcms analyses on the basis of organic matter richness five nonmarine tertiary coal and shale samples and 12 marine mesozoic upper triassic and middle jurassic shale samples were selected a total of 28 oil and condensate samples from producing wells oil stem tests field separators and seeps were used for oil oil and oil source rock correlation on the basis of biomarker and carbon isotope data four of the shallower oils and condensates are from nonmarine source rocks and 24 of the deeper oils are sourced from marine shales geochemical and regional geologic considerations indicate the following conclusions the upper tertiary nonmarine oils and condensates associated with commercial microbial gas accumulations are geochemically similar to the immature organic matter in the tertiary nonmarine rocks in the upper cook inlet marine oils in lower tertiary nonmarine reservoirs originated from middle jurassic rocks that matured during themore pliocene to holocene in the lower cook inlet alaska peninsula area oils migrated from both upper triassic and middle jurassic source rocks during the late cretaceous to early tertiary although three petroleum systems are identified this study on the petroleum potential in a convergent margin setting indicates that only one of these three systems was responsible for the 1 2 billion bbl of recoverable oil in the lower tertiary nonmarine reservoirs less

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

petroleum isotopic and biomarker composition related to source rock organic matter and depositional environment abstract a multivariate approach has been developed that separates oils derived from organic matter in nonmarine shales marine shales and marine carbonates some or all of the following analyses were completed on 43 oils from known source rocks 1 c30 sterane and monoaromatic steroid biomarker ratios and 2 stable carbon and hydrogen isotope compositions of whole oil saturates and aromatics three group discriminant analysis of the 28 oils whereall biomarker and isotopic data are available results in no misclassifications at a significance level of 99 using only carbon and hydroogen isotopic data for whole oils saturates and aromatics results in correct classifications of 82 for oils derived from marine shale organic matter and 100 for oils from the other two sources triangular plots probabilities can be used to distinguish oils derived from the three source rock organic matter end members several publications describe classifications of marine vs nonmarine oils using stable carbon isotope ratios of the whole oil or the saturate and aromatic fractions our results confirm that these methods do not completely differentiate oils by source

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

tectonic implications of paleozoic and mesozoic igneous rocks in subsurface of peninsular florida abstract abstract the extensive mesozoic and cenozoic sedimentary sequences of peninsular florida rest unconformably upon a basement of dominantly volcanic rocks major and trace element analyses of samples from six deep oil test wells in north central and south central peninsular florida suggest the existence of two distinct volcanic provinces the northern province contains calc alkalic andesitic to rhyolitic rocks similar to those found along modern convergent ocean continent plate boundaries the southern province is apparently a bimodal suite of basaltic and rhyolitic rocks these rocks exhibit certain geochemical features which suggest they were generated in a continental rifting environment associated with a mantle plume available age data indicate the northern volcanic province is at least early paleozoic in age while the volcanism in the south occurred during the early mesozoic

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

geochemical correlation of oil from the ayoluengo field to liassic black shale units in the southwestern basque cantabrian basin northern spain abstract a study of the liassic sequence in the basque cantabrian basin has shown the presence of organic rich toc hi and s 2 up to 8 7 760 and 56 5 mg g respectively pliensbachian early toarcian black shales that constitute the only feasible source rock for ayoluengo oil the stratigraphical and sedimentological data show that these black shales developed into a major transgressive sequence of hemipelagic lotharingian toarcian facies which suggests the presence of anoxic or near anoxic bottom water conditions in troughs during their deposition the 13 c composition and a detailed study of the linear branched isoprenoid steroid and hopanoid aliphatic hydrocarbons in these shales marls and the ayoluengo oil confirms this hypothesis specifically the 13 c values of the total solvent extract of the thicker shale no 2 and the oil are 29 93 and 29 88 respectively also a close similarity in the relative compositions of steranes and hopanes is observed between these samples the distributions of these compounds exhibit several distinct features the steranes in this shale and crude oil are characterized by a depletion of c 28 vs c 27 and c 29 homologues 24 vs 32 and 44 respectively which is consistent with the carbon number sterane distributions generally observed among upper paleozoic to liassic rock sourced oils furthermore hopanes and steranes are characterized by their high relative content of rearranged molecules diasteranes 13 h 17 h and 13 h 17 h series are the dominant compounds among the steranes and significant amounts of 18 h 17 methyl 28 norhopanes c 27 c 29 and c 30 homologues and 17 h 15 methyl 27 norhopanes c 30 homologue are found in the hopanoid hydrocarbons conversely the proportion of these rearranged molecules in other sediment samples from the same formation decrease with increasing carbonate content rearrangement is generally related to catalytic effects due to clay minerals which is in agreement with the lithology of the source rock attributed to the ayoluengo oil

reservoir geochemistry of south pass 61 field gulf of mexico compositional heterogeneities reflecting filling history and biodegradation abstract cluster analysis of gc data for gasoline and mid range hydrocarbon ratios from fifty one south pass 61 field oils reveals geochemically similar oil clusters corresponding to geographically coherent groups insight into the groupings is obtained from examination of indicators of geochemical processes e g anaerobic biodegradation aerobic biodegradation and extensive remigration of light ends six duplicate samples collected in 1986 and 1992 as well as replicate runs on a single sample showed excellent analytical reproducibility subtle but consistent differences in both gasoline and oil range hydrocarbon maturity indicators are observed between the east west and far west flanks of the field suggesting filling of different segments of the reservoir from different kitchens at slightly different stages of thermal maturity or with slightly different chemical character the west flank of the salt dome was charged with slightly more thermally mature petroleum than the east flank the stratigraphically oldest and deepest sand on the far west flank has received the most mature petroleum different fluid contacts and gors are observed in different sands and different fault blocks the stacked pay geometry of the field and widespread faulting have led to considerable remigration of gas and condensate as observed in other fields in the gulf of mexico thompson 1987 biodegradation varies in severity with depth and reservoir zone but is frequently overprinted by remigration of light end hydrocarbons anaerobic biodegradation by sulfate reducing bacteria is probably the cause of light to moderate alteration in intermediate depth pliocene sands which are hydraulically connected to the salt dome with dissolution of anhydrite from the salt dome providing the sulfate widespread late pyrite formation in reservoir sandstones is inferred to represent the ultimate sink for reduced sulfur from sulfate reduction during oil biodegradation co produced water compositions suggest no oxygenated freshwater infusion

effect of water washing on c15 hydrocarbon fraction of crude oils from northwest palawan philippines recognition and subsequent correlation of biodegraded and or water washed oils with their unaltered counterparts has been a long recognized problem in petroleum geochemistry because water washing and biodegradation can occur concurrently it is difficult to delineate the individual effects of these two oil altering processes especially on the c15 hydrocarbon fraction both processes can cause an oil to become enriched in sulfur and to have a lower api gravity owing to loss of the more volatile components thus the altered oil may appear to be a high sulfur crude of low maturity altered and unaltered oil fractions extracted from cores of a water washed carbonate reservoir offshore northwest palawan were studied to observe the effect of alteration on correla ion parameters water washing resulted in the following changes 1 depletion of 13c in the c15 branched cyclic alkane fraction whereas virtually no change occurred in isotope composition of the aromatic fraction 2 selective loss of dibenzothiophenes followed by loss of aromatic hydrocarbons and 3 virtually no change in steranes or tricyclic and pentacyclic terpanes with the exception of enhancement of 17 agr h norhopane and decrease of 18 agr h trisnorhopane in situations of severe water washing mild biodegradation also occurred as indicated by the loss of n alkanes and possible selective loss of n alkanes having less than 25 carbon atoms relative to branched alkanes cycloalkanes and aromatic components because cycloalkanes and aromatic hydrocarbons are not generally preferentially utilized by bacteria as long as n alkanes are present the changes observed in these two fractions most likely result from water washing because of the potential for extreme compositional changes in the n alkane and aromatic fractions the most useful correlation parameters between the altered and unaltered oils are sterane and terpane distributions stable carbon isotope ratios are also useful however more studies of oils in which water washing is known to have occurred need to be made to explain the general response or various responses of the isotopic composition of oils to water washing

organic geochemistry and petrography of tertiary coals and carbonaceous shales from argentina a series of eight tertiary coal and carbonaceous shale samples with vitrinite reflectance values between 0 50 and 0 58 were extracted fractionated and the saturated and aromatic hydrocarbons analysed for characteristic components by gc and gc ms additionally a microscopical study was undertaken in order to obtain a more precise picture of the samples under investigation the saturated hydrocarbon fractions displayed the typical n alkane distribution for coals of this rank with cpi values between 2 0 and 3 1 among the branched cyclic compounds pristane and homohopane were recognised as relevant components pointing to an oxic depositional environment detection of benzohopanes c32 c35 in the aromatic hydrocarbon fractions suggests that bacteriohopanetetrol was a significant constituent of the coal biomass taking into consideration the pr ph ratios ash contents and microscopical characteristics of the samples aspects of the possible degradation of hopanetetrol to homohopane are discussed resin derived diterpenoids with the phyllocladane and kaurane skeleton were tentatively identified and although minor compounds they are interpreted to be a sign of the contribution of podocarpaceae and araucareaceae to the coal swamp aromatic compounds were dominated by alkylnaphthalene derivatives presumably formed by c ring cleavage and aromatisation of higher plant derived pentacyclic triterpenois which were main components in the high boiling range of the fractions investigated angiosperms especially fagaceae are postulated as source for these polycyclic compounds and hence for some of the polyalkylated aromatic bicyclics detected

po river plume on the adriatic continental shelf dispersion and sedimentation of dissolved and suspended matter during different river discharge rates abstract suspended matter and dissolved nutrients were studied in the prodelta of the po river northern adriatic sea immediately after one of the greatest floods of the last century which occurred in october 2000 and in four successive seasonal conditions hydrology total suspended matter tsm particulate organic carbon poc and particulate nitrogen pn content organic carbon stable isotopes 13 c poc particle grain size spectra phytoplankton and dissolved inorganic nutrients i e nitrate nitrite ammonium phosphate and silicate were measured in different discharge conditions to describe processes occurring in the po river delta the main effect of high river discharge was a large volume of low salinity water at the surface that extended over the entire study area the concentration of most sampled variables decreased along a dilution gradient from the po river distributaries mouths to the offshore for tsm at the surface riverine input and dilution were the main factors affecting its distribution at the bottom however increased tsm in the nearshore was due to rapid sinking of suspended matter at the river mouth while resuspension and advection dominated the transport of near bottom sediments offshore at 15 20 m depth in the offshore where resuspension was active an increase in ammonium and decrease in oxygen supported the presence of regeneration processes occurring at the bottom during the october 2000 flood event high nutrient concentrations promoted new production triggering an algal bloom in the southern region of the study area the origin of particulate organic carbon in the river delta was then estimated from a mixing model based on 13 c poc values and carbon nitrogen c n molar ratios and as the contribution of three distinct sources of organic carbon were determined i e marine riverine and terrestrial the riverine end member accounted for 50 of the surface poc and generally decreased towards the offshore the terrestrial carbon contribution was generally the least abundant 20 28 at the surface and at depth respectively and exhibited peak values 30 40 during the october 2000 flood last the marine contribution was the most abundant at the bottom 40 and generally increased offshore during the october 2000 flood the fluvial contribution of particulate organic carbon that is the terrestrial and riverine fractions represented approximately 80 of the total particulate organic carbon in the po river delta

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