effect of maturity on 13c12c ratios of individual compounds in north sea oils abstract carbon isotope variations in individual compounds are reported for north sea oils of variable thermal maturity using the pristane phytane ratio of the oils as an indication of source facies variation and molecular maturity ratios to determine maturity it is possible to differentiate the two effects in these samples maturity accounts for between 50 and 90 of the observed isotopic variation all values becoming heavier with increasing maturity typically by between 2 and 3 however source differences are also apparent with a terrestrially influenced source possibly the heather formation contributing material to the kimmeridge clay sourced oils the heather contribution is isotopically heavier than the kimmeridge oil for most compounds but is isotopically lighter for the isoprenoid hydrocarbons and some other branched compounds it is also more important for lower molecular weight hydrocarbons than for higher homologues

alkyldibenzofurans in terrestrial rocks influence of organic facies and maturation abstract dibenzofuran dbf dibenzothiophene dbt and phenanthrene phe have been determined along with their methyl derivatives mdbfs mdbts mps in coals carbonaceous shales and mudstones of lower cretaceous to upper carboniferous ages from the elmworth gas field canada and from the sakoa madagascar and ruhr coal germany basins the samples contained mainly terrestrial organic matter with thermal maturities in the 0 7 1 9 mean vitrinite reflectance rr range the pronounced predominance of mdbfs over mdbts in the sakoa samples is typical of plant debris deposited in lacustrine swamp environments onset of intense mdbf generation occurs at fairly low rank 0 77 rr as indicated by elevated concentrations of 50 120 g mdbfs g total organic carbon toc influences of lithology organic matter type and maturity on distributions of the target compounds were extracted from the molecular concentration data by multivariate statistical methods such as principal components analysis pca and fuzzy c means cluster analysis with nonlinear mapping nlm a specific source effect on 1 mdbt concentrations suggests that lichens contributed to the senescent coal forming forest in the sakoa coal basin alkyldibenzofurans hence are potential lichen biomarkers mdbfs can be used as maturity indicators only beyond 1 0 rr where ruhr coals displayed a distinct increase in the 1 4 mdbf ratio

sediment dispersal in the argentine basin evidence from visible light spectra abstract visible light reflectance spectra were determined for each of 236 core top samples from the argentine basin and surrounding areas the spectra were analyzed by taking the first derivative of the raw spectral curves and factor analyzing the first derivative values using wavelengths as variables we used a four factor solution that explains about 90 of the cumulative variance factors were evaluated by comparing factor loadings to first derivative curves from known minerals and mineral combinations by the mapped distributions of the factor scores and by comparison to factors from other areas the four factors represent in order of decreasing variance goethite terrigenous vs pelagic sedimentation organic matter and chlorite the goethite and chlorite factors are useful for interpreting sediment influx and dispersal goethitecomes from the falkland plateau and the argentine continental margin once introduce to the deep ocean goethite appears to be transported primarily by isobath parallel currents chlorite on the other hand is transported into the argentine basin by antarctic bottom water aabw and from the falkland plateau however along the falkland plateau chlorite is transported normal to the slope probably by gravitational processes

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

clay minerals as indicators of sources of terrigenous sediments their transportation and deposition bering basin russian alaskan arctic abstract cluster analysis of clay mineral abundances in surficial sediments from 52 stations revealed the presence of four station cluster groups within the bering basin and contiguous eastern aleutian trench forearc these results can be explained using two end members of terrigenous clay mineral sources and their admixtures the first end member cluster group i consists of the highest average concentration of illite 48 and chlorite plus kaolinite 40 and lowest of expandable minerals 12 in contrast the second end member cluster group iv has the highest concentration of expandable minerals 43 and lowest concentrations of illite 30 and chlorite plus kaolinite 27 the group i assemblages come from two regions the eastern aleutian trench forearc and the northwestern margin of the bering basin off koryak mountains east siberia clays in the former region are derived primarily from the meta sedimentary and meta volcanic rocks of the chugach mountains with infiltrations from alaska peninsula and are transported from the southeastern kodiak shelf of the gulf of alaska to the trench forearc by the alaska current alaskan stream similar clays are derived from the koryak mountains group iv clays located within the komandorsky and bowers basins and unmak plateau originated from the mio pliocene andesites and basalts of the eastern kamchatka peninsula and aleutian islands respectively it is postulated that group ii clays in the southcentral aleutian basin and bowers ridge basin area and group iii clays in the northern aleutian basin are mixtures obtained primarily from terrigenous sources of group i and iv the distribution patterns and boundaries of the cluster groups reflect the dispersal pathways of clays from the primary sources and the extent of their mixing by regional and local surface currents and mesoscale gyres eddies presumably the minor infiltration of anadyr river clays into group iii is a result of clay transport by episodic turbidity currents most of the clays derived from the alaska mainland and russia proper do not reach the bering basin as these clays are trapped within the bering sea shelf

the bering sea and paleoceanography abstract this paper serves as an introduction to the bering sea preceding the 14 contributed papers contained in this volume several parts of the paper are allocated for current reviews of the bering sea included in the review topics are geomorphology surface water circulation and the importance of the formation of intermediate waters representative results of previous paleoceanographic studies are also presented in particular focusing on spatial and temporal distributions of biosiliceous microfossils as well as isotopic analyses of carbon and nitrogen concerning changes in productivity and nutrients motivations behind the scientific expeditions conducted which resulted in the many papers included here are briefly discussed in order to illustrate the recent trend in paleoceanography in the bering sea and the adjacent regions brief summaries or highlights of each of the contributed papers are given in order to provide an overview of the volume

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

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

the summer hydrography and surface circulation of the east siberian shelf sea during the ice free summer season in 1995 the authors deployed and subsequently tracked 39 surface drifters to test the hypothesis that the discharge from the kolyma river forces a buoyancy driven coastal current from the east siberian sea toward bering strait the observed mean flow is statistically significant at the 95 level of confidence but its direction contradicts their initial hypothesis instead of a coastally trapped eastward flow the authors find a laterally sheared westward flow with maximum velocities offshore that correlate only weakly with the local winds at a daily wind dominated timescale the drifter data reveal spatially coherent flows of up to 0 5 m s21 the lagrangian autocorrelation scale is about 3 days and the lagrangian eddy length scale reaches 40 km this spatial scale exceeds the nearshore internal deformation radius by a factor of 3 however it more closely corresponds to the internal deformation radius associated with the offshore ice edge bulk estimates of the horizontal mixing coefficient resemble typical values of isotropic open ocean dispersion at midlatitudes hydrographic observations and oxygen isotope ratios of seawater indicate a low proportion of riverine freshwater relative to sea ice melt in most areas of the east siberian sea except close to the kolyma delta the observations require a reevaluation of the conceptual view of the summer surface circulation of the east siberian sea eastward buoyancy driven coastal currents do not always form on this shelf despite large river discharge instead ice melt waters of a retreating ice edge act as a line source of buoyancy that in 1995 forced a westward surface flow in the east siberian sea

families of miocene monterey crude oil seep and tarball samples coastal california biomarker and stable carbon isotope ratios were used to infer the age lithology organic matter input and depositional environment of the source rocks for 388 samples of produced crude oil seep oil and tarballs to better assess their origins and distributions in coastal california these samples were used to construct a chemometric multivariate statistical decision tree to classify 288 additional samples the results identify three tribes of 13c rich oil samples inferred to originate from thermally mature equivalents of the clayey siliceous carbonaceous marl and lower calcareous siliceous members of the monterey formation at naples beach near santa barbara an attempt to correlate these families to rock extracts from these members in the nearby cost continental offshore stratigraphic test ocs cal 78 164 well failed at least in part because the rocks are thermally immature geochemical similarities among the oil tribes and their widespread distribution support the prograding margin model or the banktop slope basin model instead of the ridge and basin model for the deposition of the monterey formation tribe 1 contains four oil families having geochemical traits of clay rich marine shale source rock deposited under suboxic conditions with substantial higher plant input tribe 2 contains four oil families with traits intermediate between tribes 1 and 3 except for abundant 28 30 bisnorhopane indicating suboxic to anoxic marine marl source rock with hemipelagic input tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher plant input tribes 1 and 2 occur mainly south of point conception in paleogeographic settings where deep burial of the monterey source rock favored petroleum generation from all three members or their equivalents in this area oil from the clayey siliceous and carbonaceous marl members tribes 1 and 2 may overwhelm that from the lower calcareous siliceous member tribe 3 because the latter is thinner and less oil prone than the overlying members tribe 3 occurs mainly north of point conception where shallow burial caused preferential generation from the underlying lower calcareous siliceous member or another unit with similar characteristics in a test of the decision tree 10 tarball samples collected from beaches in monterey and san mateo counties in early 2007 were found to originate from natural seeps representing different organofacies of monterey formation source rock instead from one anthropogenic pollution event the seeps apparently became more active because of increased storm activity

a study of the holzener asphaltkalk northern germany observations regarding the distribution composition and origin of organic matter in an exhumed petroleum reservoir abstract the holzener asphalkalk deposit is located on the southwestern flank of the hils syncline northern germany it consists of a series of kimmeridgian portlandian bitumen impregnated limestones cumulative thickness of nearly 200 m overlain unconformably by neocomian claystones and underlain by older jurassic and triassic sediments the most bitumen rich limestone layers have been extensively mined with the result that there is three dimensional access to what is probably an exhumed series of stacked petroleum reservoirs geochemical petrological and petrophysical techniques were used to gain some insight into the distribution and the source of the organic matter in two of the 13 layers of the deposit most disseminated organic matter was found to be soluble in organic solvents and rich in non hydrocarbons its distribution appears to be controlled by ooid versus carbonate matrix abundances the occurrence of fractures and degree of impregnation small meso to micro pores have high bitumen saturations whereas large pores meso to macro have much lower saturations mature petroleum is thought to have once filled all pores but alteration has probably removed as much as 85 of it mainly from the large pores regional geochemical considerations pyrolysis and stable carbon isotope data indicate that the original petroleum was most probably derived from the underlying posidonia shale toarcian source rock asphaltene pyrolysis data indicate that an algal lacustrine co source might have also contributed to the deposit

orbital and millennium scale environmental changes in the southern bering sea during the last glacial holocene geochemical and paleontological evidence the d 18 o benthic foraminiferal curve and ams 14 c radiocarbon data provide a representative age model for a southern bering sea sediment core gc 11 downcore profiles of d 18 oo fn pachyderma s and u auberiana carbonate and organic carbon contents species changes in the planktonic foraminifera assemblages and some diatom species show orbital mis 1 2 and 3 and millennium scale variability influenced by the alaska current flowing into the studied region three warmer episodes in the southern bering sea environment were assumed to be synchronous with do interstadials 8 12 and 14 in gisp 2 chronology during mis 3 more severe climate and environmental conditions in the southern bering sea during mis 2 occurred synchronously with the lgm within a 17 19 ka time span two well pronounced environmental warming events productivity spikes and changes in the pore water geochemistry separated by younger dryas cooling were observed at the base of mis 1 coeval with mwp 1a and 1b regional glacial primary productivity based on the calculation of the organic carbon mar similar to that found in the far northwestern pacific exceeded the late holocene values under conditions close to the present day r 2005 elsevier ltd all rights reserved

petroleum source maturity alteration and mixing in the southwestern barents sea new insights from geochemical and isotope data the hammerfest basin hb is an important area for petroleum exploration in the southwestern norwegian barents sea this contribution is aimed to characterize oils and condensates hosted in triassic and jurassic reservoirs establish genetic relationships and to assess maturity mixing and petroleum alteration processes the research was based on geochemical as well as bulk and compound specific stable carbon and hydrogen isotope analyses of oil and condensate samples from all major fields and discoveries in the hb including extracts from jurassic and triassic source rocks interpretations of light hydrocarbon composition and isotope data clearly identify four main petroleum groups affected by microbial degradation water washing evaporative fractionation and high thermal maturity level based on polycyclic aromatic hydrocarbons pahs marine and higher plant derived biomarkers and carbon isotopic composition 13c of individual petroleum hydrocarbons four petroleum families i iv are recognized in the hb and a distinction can be made among oils and condensates from different stratigraphic levels and sectors of the basin most oils and condensates from the hb consist of mixtures with small maturity variations however oils from middle triassic reservoirs in the goliat field showed larger maturity variations according to biomarker pah and light hydrocarbon maturity ratios in the hb geochemical and isotopic data allowed unraveling mixtures of hydrocarbons derived mainly from jurassic triassic and paleozoic source rocks

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

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

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

the effect of source and maturity on the stable isotopic compositions of individual hydrocarbons in sediments and crude oils from the vulcan sub basin timor sea northern australia abstract recent work has demonstrated the effect of maturation on the stable hydrogen isotopic compositions d of individual sedimentary hydrocarbons n alkanes pristane and phytane in a series of marine source rocks from the perth basin western australia there was an enrichment in deuterium d in the hydrocarbons with increasing maturity attributed to isotopic exchange associated with thermal maturation an initial large 115 biologically derived difference between the d values of n alkanes and isoprenoids gradually decreased as pristane and phytane became enriched in d while the n alkanes generally remained at constant isotopic composition this work has now been extended to include a series of late jurassic sediments from the lower vulcan formation of the vulcan sub basin timor sea northern australia where the d values of n alkanes and isoprenoids show similar trends to those observed for the perth basin the enrichment in d in isoprenoids correlates strongly with traditional maturity parameters and is shown to be related to the epimerisation of pristane and phytane pristane and phytane extracted from a post mature paqualin 1 sediment are significantly enriched in d relative to the n alkanes indicating that d enrichment persists at very high maturity more so for regular isoprenoids than n alkanes this supports the notion that hydrogen h d exchange causes the observed shift in d values and not free radical hydrogen transfer a mechanism is proposed which can account for both h d exchange and epimerisation of pristane and phytane in the sedimentary environment pristane is enriched in d relative to phytane throughout the vulcan sub basin sequences attributed to a lower relative algal input to the isoprenoids and indicating that they exchange hydrogen at similar rates during maturation crude oils and condensates from the sub basin were also analysed to evaluate their source and thermal maturity and the results complement previous molecular and stable carbon isotopic analysis the d values of n alkanes and regular isoprenoids largely support the previous classification of vulcan sub basin crude oils and condensates into two groups group a having a marine source affinity and group b a terrigenous source affinity some oils and condensates are suggested to be a mixture of sources a and b or a and other as yet unknown sources tenacious 1 crude oil formerly a group a oil contains n alkanes with more positive d values than other group a oils and is suggested to have been mixed with another source of more mature hydrocarbons the group a crude oils and condensates show an upward inflection in the n alkane d profile from n c 11 to n c 15 which is suggested to represent an addition of d enriched lower molecular weight n alkanes from a more mature wet gas condensate to an initial oil charge the small differences between the d values of the n alkanes and regular isoprenoids in the crude oils and condensates indicate that significant h d exchange has taken place implying that the samples were generated from mature source rocks

recent advances in petroleum isotope geochemistry abstract organic matter is isotopically heterogeneous lipids tend to be depleted in the heavy carbon and hydrogen isotopes as compared to carbohydrates and lignite the c and h isotopic composition of kerogens is determined by many factors such as environmental conditions during formation and deposition and variability of sources of organic matter stable isotope concentrations in mature kerogens are not significantly altered during maturation and hence reflect the variability of the organic matter during deposition isotope variations in kerogens therefore reflect to some extent the paleogeographic situation and can be used for paleoreconstruction a basin facies with anoxia and a marginal facies with detrital input can be differentiated isotopically in the toarcian of central europe coals are isotopically heterogeneous due to different isotopic composition of macerals inertinite and vitrinite tends to be enriched in deuterium as compared to exinite also boghead coals tend to be depleted in dueterium which possibly reflects various lipid contents of respective precursor materials petroleums can be genetically classified through the patterns of covariance of their compound classes carbonate and shale sourced petroleums may be additionally differentiated through their deuterium content the general world wide applicability of such genetic differentiations needs still to be proved carbon and hydrogen isotope variations in methane are genetically controlled bacterial methane in freshwater environments is characteristically depleted in deuterium even complex origins of natural gases can be unraveled using compositional and isotopic variations new analytical developments led to the application of carbon isotope analyses of gaseous hydrocarbons desorbed from sediments for geochemical surface exploration a discussion reveals that processes such as isotope effects during degassing and bacterial oxidation as well as indigenous formation of hydrocarbons may completely obscure the results

on exchange of water between the gulf of alaska and the bering sea through unimak pass we present the first long term current and bottom pressure observations from unimak pass alaska and adjacent locations on the gulf of alaska and bering sea shelves vector mean current recorded between march and august 1980 was 12 cm s toward 284 t or onto the bering sea shelf however magnitude decreased from 20 cm s to 6 cm s between the first and second halves of the record at shorter periods 3 10 days current fluctuations in the pass were strongly coherent k2 0 7 with the pressure difference measured along the axis of the pass and this was coherent with geostrophic wind estimates the results indicated that wind induced sea level perturbation was the dominant forcing mechanism for fluctuations relations among current bottom pressure pressure difference and geostrophic wind time series also showed that dynamic variaton on the gulf of alaska shelf was primarily responsible for current fluctuations in the pass hydrographic data indicated that a baroclinic current existed along the gulf of alaska coast and this flow became the long term mean flow through the pass we suggest that this feature was the extension of the kenai current the historic supposition that water is transported from the gulf of alaska into the bering sea was verified however the waters are of coastal origin rather than from the alaskan stream

sources and dispersal patterns of clay minerals in surface sediments from the continental shelf areas off alaska the three mineral suites were recognized in the gulf of alaska the glaciomarine sediments of fjords and the eastern shelf consist typically of the primary phyllosilicates micas and chlorites derived locally from argillite graywacke and metavolcanics under conditions of mild chemical weathering more glycol expandable clay minerals gecm in the north gulf substantiate clay supply to that region primarily from the yakataga and poul creek formations and to a lesser extent from the copper river the northern gulf clay mineral suite is transported to central prince william sound and northeast kodiak shelf by the alaska coastal current in the western gulf clay minerals adjacent to the alaska peninsula are derived principally from the susitna river via cook inlet whereas those of the outer shelf presumably have their provenance in kodiak island and the katmai ash submarine deposit in the southeast bering sea a progressive northwestward decrease in gecm from 65 to 11 is caused by a gradually decreased sediment export from the alaska peninsula and the aleutians with a possible minor increase in illite from the kuskokwin river the yukon river is the predominant clay source for the north bering sea as signified by an abrupt increase in that area of gecm 20 to 35 and of kaolinite chlorite ratios clay mineralogy indicates that the central chukchi sea is the major repository of the yukon clays suggesting that clay mineral stratigraphic studies have implications for interpretation of the quaternary paleogeography of beringia in the beaufort sea nearshore influence of different fluvial inputs and their dispersals by currents are sharply defined the lack of a definite pattern to the distribution of clay minerals in the outer continental shelf may be due to haphazard transport of clays by ice rafting and or reworking and redistribution of sediments resulting from ice gouging of the sea substrate movement of sediment to the west in the alaskan portion of the inner shelf of beaufort sea is evident an apparent seaward increase in illite gecm ratio in the colville delta is tentatively ascribed to regeneration of degraded illite micas by k fixation in saline waters an isolated area of sediment rich in expandable clay minerals in the central beaufort shelf presumably is relict

sea ice transport of riverine particles from the laptev sea to fram strait based on clay mineral studies the aim of this study was to identify pathways and processes of modern sediment transport from the siberian hinterland to the laptev sea and further to the arctic ocean clay mineral analyses were performed on riverine suspended particulate material spm surface sediments of the laptev sea shelf and sea ice sediments sis material collected during seven expeditions was included in this study clay mineral assemblages are used to decipher the distribution of riverine sediments on the shallow laptev sea shelf the entrainment of fine particles into newly forming ice and the transport of sis from the laptev sea towards the ablation areas a cluster analysis of our data set shows that the clay mineral assemblages of laptev sea shelf sediments and sis are controlled mainly by the input of riverine spm supplied by the khatanga lena and yana rivers whereas the western shelf clay mineral province is characterized by enhanced smectite concentrations supplied by the khatanga river the eastern laptev sea is dominated by illite discharged through the lena and yana rivers the sis smectite concentration serves as an indicator for sediment source areas on the circum arctic shelves subsequently the transpolar drift can be distinguished into a siberian branch fed from the eastern kara sea and the western laptev sea and a polar branch originating from the eastern laptev sea

the effect of maturation on the isotopic composition of fossil fuels abstract few measurements of the d h ratios in liquid and solid fossil fuels have been made additional isotopic data are reported here in the form of d h and 13 c 12 c ratios for crude oils and brown coals which occur together in the bass strait region of australia studies of petrographic fractions of these coals and of the changes in the isotopic composition of coals and coal extracts with increasing maturity show that the original d h ratios characteristic of contributing plant materials are more readily erased and homogenized during early diagenesis than the corresponding 13 c 12 c ratios

application of biological markers in the recognition of palaeohypersaline environments the hydrocarbon fractions of a marl sample from a messinian basin in the northern appenines and four oils rozel point oil utah and three seep oils from sicily were studied

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

diffuse spectral reflectance of surficial sediments indicates sedimentary environments on the shelves of the bering sea and western arctic abstract visible diffuse spectral reflectance dsr has been described by previous workers as an efficient tool for extracting lithological compositions clay minerals iron oxyhydroxides carbonates and diatoms in sedimentary material the spatial patterns of these components are essential to understanding the processes driving their distribution and accumulation in the marine environment some of these processes include sea ice variability nutrient supply current flow patterns current strength sediment supply provenance and bathymetry the dsr derivatives and varimax rotated principal component analysis vpca of the spectral data collected from 234 core samples identified five leading components that account for variations in sediment lithology of the surface samples from the bering sea and western arctic these spectral components were then matched to spectral standards to identify the mineral assemblages responsible for them the components responsible for the vpca trends are chlorite muscovite goethite phycoerythrin phycocyanin smectite calcite dolomite and illite chlorophyll a the spatial pattern of the inorganic components is indicative of provenance and processes controlling their transportation and depositional patterns while the organic components are indicative of areas of primary productivity and driving mechanisms the chlorite muscovite assemblage which is sourced dominantly from the yukon river has maximum values on the bering sea shelf this is the source of the chlorite muscovite transport to the chukchi sea the chlorite muscovite assemblage also has a main transport route to the aleutian basin in the northern bering sea shelf the chukchi sea on the western arctic ocean shelf is a region of highly reducing condition this is based on the lowest values for the goethite phycoerythrin phycocyanin assemblage supported by the high carbonate concentrations at this location the carbonate distribution pattern on the bering sea shelf also appears to be tidally influenced this is because their spatial pattern divides the bering shelf into three domains which are similar to the three hydrographic domains on the bering shelf a function of tidal influence the smectite assemblage reaches maximum values along the coast of the chukotka peninsula in the chukchi sea denoting the chukotka peninsula as a major source area of smectite and supporting the notion for volcanically derived sediment to the chukchi sea another likely source of smectite to the chukchi sea is via the bering strait the illite in the illite chlorophyll a assemblage shows maximum values and distribution on the western arctic ocean shelf indicating the western arctic ocean shelf to be a main province of illite all the high values of the illite chlorophyll a component on the bering sea shelf are chlorophyll a from diatoms our results support the usefulness of the dsr method as an effective and efficient tool for provenance analysis and understanding the processes controlling sediment and biologic distribution in this case in the marine environment

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

predicting the generation of heavy oils in carbonate evaporitic environments using pyrolysis methods abstract a series of low maturity kerogen and asphaltene samples of a sulphur rich mediterranean carbonate source rock sequence as well as two associated oil samples were analysed by different pyrolysis methods the source rock was characterised by the occurrence of four different lithotypes three of which possessed source potential elemental analysis revealed that each source lithofacies contained a distinct kerogen type comprising type i s for shale intercalations type ii s in the laminated lithofacies and low sulphur type ii in the pure carbonate portions of the source rock pyrolysis gas chromatography using coupled fid and hecd detectors provided a more detailed insight into kerogen asphaltene composition than afforded by rock eval pyrolysis bulk kinetic analysis demonstrated that asphaltenes and type i s kerogens were the most labile species present in the source rocks type ii s kerogens often quoted as the major source of heavy oils were the most stable of the sulphur rich organic matter types the occurrence of various kerogen types with differing stabilities in the carbonate source rock analysed as determined by bulk pyrolysis fid implies that peak hydrocarbon generation in the source rock sequence is not confined to a single temperature but rather to a relatively large temperature range of roughly 20 c combination of bulk hydrocarbon generation kinetics and a multistep pyrolysis approach demonstrated that for carbonate evaporitic environments it is necessary to differentiate between early and late maturity products this is because the lower energies 46 49 kcal mol which may be attributed to s c bond cleavage reactions are empirically of greater importance especially in view of the fact that they may represent the main generation stage under natural conditions

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

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

carbon isotope composition of marine crude oils 1 a histogram of isotope 13 c values of 621 post ordovician marine oils shows a trimodal distribution within this distribution four groups of oils can be recognized on the basis of isotope 13 c values in conjunction with pristane phytane ratios and sulfur contents oils with isotope 13 c values of 32 0 to 28 0 o oo are mainly marine shale oils older than oligocene oils with isotope 13 c values of 28 0 to 23 5 o oo are mainly deltaic oils of varying geologic age or mesozoic carbonate oils and oils with isotope 13 c values heavier than 23 5 o oo are mainly marine shale oils of miocene age the isotope 13 c variation among oil groups is explained primarily by different factors that control the fractionation of carbon isotopes during primary production of rganic carbon miocene and younger marine shale oils are isotopically heavier than older marine shale oils because of decreased atmospheric co 2 concentration since 25 ma which has resulted in decreased isotope fractionation by marine plankton during photosynthesis deltaic oils are mostly derived from terrestrial organic matter and their isotope 13 c values reflect the time invariant average isotope 13 c value of land plant carbon at about 25 o oo mesozoic carbonate oils are isotopically heavy due mainly to salinity and temperature effects during primary production in restricted environments from which terrestrial organic matter is excluded processes that occur after oil generation generally have smaller effects on isotope 13 c values of oils as a result isotope 13 c val es of oils are useful for determining oil oil and oil source rock relationships and in conjunction with other geochemical properties can indicate the possible age and depositional environment of source rocks

ophiolitic and metamorphic assemblages of southeast anatolia and their significance in the geological evolution of the orogenic belt the southeast anatolian orogen may be divided into three roughly east west trending structural zones formed as a result of continental collision between the taurus platform and the arabian continent along the orogenic belt metamorphic and ophiolitic rocks occur widely the ophiolites represent remnants of the ocean or oceans which were totally consumed between these converging continental blocks during late cretaceous to miocene period metamorphic rocks formed from the oceanic as well as the continental rocks which were incorporated into a nappe stack during the consumption of the oceanic lithosphere and the progressive southward advance of the nappes toward the arabian continent the metamorphic units together with the ophiolite associations provide stratigraphic and petrologic evidence indicating time place and environment of formation of these units the metamorphic units also provide evidence of nappe transportation stages which are complementary to the data derived from the sedimentary successions in the evaluation of the orogenic evolution of southeast anatolian orogen

glacial interglacial sediment transport to the meiji drift northwest pacific ocean evidence for timing of beringian outwashing abstract a large sediment deposit known as the meiji drift located in the northwestern pacific ocean is thought to have formed from deep water exiting the bering sea although no notable deep water forms there presently we determine the terrigenous sources since 140 ka to the drift using bulk sediment 40ar 39ar and nd isotopic analyses on the silt sized 20 63 m terrigenous fraction from ocean drilling program odp site 884 to reconstruct paleo circulation patterns there are large changes in both isotopic tracers varying on glacial interglacial cycles during glacial intervals bulk sediment 40ar 39ar ages range between 40 and 80 ma while nd isotopic values range from end 1 to 2 during interglacial intervals sediments become much younger and more radiogenic with bulk sediment ages falling to 2 15 ma and nd isotopic values ranging between end 5 and 9 these data and quantitative comparison to potential source rocks indicate that the young kamchatkan and aleutian arcs lying nw and ne of the meiji drift contribute the majority of sediment during interglacials conversely older source rocks such as those drained by the yukon river and northeast russia are the dominant origin of sediments during glacials mixing model calculations suggest that as much as 35 45 of the sediment deposited in the meiji drift during glacials is from the bering sea it remains unclear whether thermohaline type circulation or focussing of bering sea flow lead to the glacial interglacial sediment source changes observed here

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

stepwise chemical degradation of immature s rich kerogens from vena del gesso italy stepwise chemical degradation involving cleavage of ester bonds koh meoh sulfide and remaining ester bonds li etnh2 ether bonds hi lialh4 and sub units linked to aromatic moieties ruo4 has been carried out on the kerogens of two immature sulfur rich marls iv 1 4 and 1 8 toc ca 1 5 from evaporitic cycle iv of the gesosso solfifera formation messinian vena del gesso italy up to 80 of the organic matter was converted to solvent soluble material with the greatest proportion released by li etnh2 the majority by far of the extracts comprises polar macromolecular material which is thought to correspond to high molecular weight sub units of the kerogen quantification of the small amounts 1 of the released gc amenable components indicates that diagenetic sulfurization was more important in the case of kerogen iv 1 4 but that the extent of oxygen sequestration was similar in both cases the distributions of biomarkers released by ether cleavage of the desulfurized residue and polar fraction showed differences which reveal heterogeneity in the building blocks making up different macromolecular fractions

aromatic compounds in crude oils and source rocks and their application to oil source rock correlations in the tarim basin nw china abstract ten series of aromatic hydrocarbons biphenyls naphthalenes phenanthrenes anthracenes retenes chrysenes benzoanthracenes dibenzofurans fluorenes and dibenzothiophenes isolated from cambrian and ordovician marine carbonate source rocks in tabei and tazhong areas of the tarim basin and triassic and jurassic lacustrine mudstones and swamp coals in the kuche depression have been characterized by gc ms the same series of aromatic compounds have been isolated and characterized from crude oils of the tabei and tazhong uplift results presented in this paper describe the distribution of these aromatic compounds in crude oils and source rocks from the three different kinds of sedimentary environments similarities in distributions of the fluorenes and the dibenzothiophenes in the aromatic fractions suggest the tabei uplift oils are derived predominantly from the lower ordovician marine source rocks of tabei lunnan area on the south of luntai and the oils from tazhong uplift are mainly derived from upper cambrian lower ordovician and middle upper ordovician marine source rocks of tazhong area

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

the siberian coastal current a wind and buoyancy forced arctic coastal current we describe circulation and mixing in the siberian coastal current scc using fall shipboard measurements collected between 1992 and 1995 in the western chukchi sea the scc forced by winds siberian river outflows and ice melt flows eastward from the east siberian sea it is bounded offshore by a broad 60 km front separating cold dilute siberian coastal water from warmer saltier bering sea water the alongshore flow is incoherent because the current contains energetic eddies and squirts probably generated by frontal baroclinic instabilities these enhance horizontal mixing and weaken the cross shore density gradient along the scc path eventually the scc converges with the northward flow from bering strait whereupon it deflects offshore and mixes with that inflow deflection occurs where the alongshore pressure gradient vanishes that location varies on synoptic and seasonal timescales because this gradient depends on the winds buoyancy fluxes and the sea level difference between the pacific and arctic oceans deflection usually occurs on the chukchi shelf but the scc occasionally flows southward through bering strait such events are short lived 1 10 days and occur mainly in fall and winter under northerly winds scc transport is likely small 0 1 sv but its dilute waters could substantially freshen the bering strait inflow and affect the disposition of pacific waters in the arctic ocean arctic river outflows should preferentially form surface advected fronts rather than bottom advected fronts because vertical mixing energy is low on arctic shelves surface advected fronts are more susceptible to upwelling winds and for the scc the pressure gradient between the pacific and arctic oceans than bottom advected fronts the scc never developed in fall 1995 because of anomalously steady upwelling winds the western chukchi shelf could have formed upper halocline source water in the winter of 1995 1996

identification and origin of bitumen in neolithic artefacts from demirkoy hoyuk 8100 bc comparison with oil seeps and crude oils from southeastern turkey abstract two ring like artefacts from the aceramic neolithic site of demirkoy hoyuk in southeastern turkey were analysed using geochemical techniques in order to determine whether they were prepared using a bitumen amalgam or not the artefacts dated 8100 bc are early evidence of the innovative use of a petroleum based material to prepare pieces of ornaments beads rings etc for the elite of a neolithic settlement in order to trace the source of the presumed bitumen two oil seeps bogazkoy and yesilli were sampled to complete the genetic references geochemical data on crude oils from the main oil fields from the area were compiled basic geochemical data show that bitumen is present in the artefacts sterane and terpane patterns as well as carbon isotopic data on c 15 saturated and c 15 aromatic hydrocarbons allowed us to conclude that the demirkoy hoyuk bitumen and the bogazkoy oil seep were generated from a silurian source rock the detailed geochemical characteristics show however that the demirkoy hoyuk bitumen does not correlate perfectly with the bogazkoy oil this discrepancy suggests several explanations the real bitumen source may be elsewhere in the vicinity and has not been discovered or was at the bogazkoy oil seep location but with slightly different properties in neolithic times or has disappeared another possibility is that the slight molecular differences are due to weathering effects which affected the pristine bitumen within the archaeological sample

structure and deformation history of the bitlis suture near lake hazar southeastern turkey detailed mapping of the bitlis suture zone near lake hazar shows that it is composed of three tectonostratigraphic units which crop out as distinct north dipping thrust slices from south to north these are the puturge metamorphic complex the maden melange and the elazig igneous complex the puturge metamorphic complex consists of pre tertiary continental margin sediments metamorphosed to the greenschist facies during the campanian maastrichtian and deformed by four generations of structures these are in sequence 1 isoclinal folds and a transposition foliation 2 open folds crenulation cleavage and north dipping thrust faults 3 kink bands and 4 small displacement faults the maden melange represents middle eocene back arc basin sediments and volcanics metamorphosed to the greenschist facies and deformed by three generations of structures 1 a north dipping cleavage 2 kink bands and 3 small displacement faults the elazig igneous complex comprises an imbricated maastrichtian early eocene island arc and young marginal basin terrain thrust faults between units are north dipping listric and form a thin skinned system these features suggest the following deformational and tectonic history the puturge metamorphic complex was generated by isoclinal folding and metamorphism of sediments composing the arabian continental margin during campanian maastrichtian ophiolite obduction to the south the elazig arc developed on the deformed margin because of subsequent southward subduction of oceanic lithosphere the arc migrated to the north opening a back arc basin by the early eocene the back arc basin was filling with volcaniclastics of the maden melange and the elazig arc collided with a continent to the north during middle to late eocene convergence caused thrust stacking of the elazig maden and puturge complexes second generation deformation in the puturge complex and first generation deformation in the maden melange continued convergence with the arabian plate in the late miocene caused kink banding in the puturge and maden complexes since the late miocene this convergence has been accommodated by shortening and thickening along numerous internal faults

a reproducible and linear method for separating asphaltenes from crude oil abstract petroleum asphaltenes exhibit strong structural similarities to their parent kerogen thus they can be used to help determine the source rock characteristics of active kitchen areas and to reconstruct the filling histories of reservoirs the analysis of asphaltenes from compartmentalised reservoirs with complex charging and alteration histories presents a particularly difficult challenge because the in situ compositional variations are sometimes subtle it is therefore of paramount importance that asphaltene separation methods be utilised which are highly reproducible and linear thereby minimising experimental uncertainty and providing high resolution interpretative capability the asphaltene separation method described here is built on many that have been proposed before different parameters for asphaltene separation were investigated which influence the asphaltene amount and properties with the main focus on reproducibility and linearity gravimetric and thermal analysis techniques were used to evaluate yield and quality the developed asphaltene separation method described in detail has four sequential steps 1 dissolution of the oil in dichloromethane 1 vol methanol 2 addition of an excess of n hexane 3 settling time and 4 filtration purging and weighing this sequence of steps is repeated three times results concerning the reproducibility depending on solvent type solvent amount and aging time as well as the linearity depending on sample amount are presented

climatic interpretation of the luochuan and lingtai loess sections china based on changing iron oxide mineralogy and magnetic susceptibility abstract hematite and goethite estimated from diffuse reflectance spectra and magnetic susceptibility ms have been determined from both the luochuan and lingtai loess sections of the loess plateau of central china changing concentrations of these iron oxides and ms were used to determine paleoclimatic change based on a model that relates pedogenic production of hematite and magnetite to precipitation we propose two precipitation phases on the loess plateau during the last 2 6 ma from the wucheng red clay boundary up to paleosol s5 mis 13 precipitation on the loess plateau was moderate probably not frequently exceeding 450 mm yr and highly seasonal from s5 to the present precipitation during interglacial times has gradually increased to the present levels of 600 650 mm yr for the localities examined throughout the pleistocene spanning both glacial and interglacial conditions hematite to goethite ratios display a consistent decrease this decrease suggests that precipitation on the loess plateau has been getting less seasonal and or has been occurring during times when temperature was lower in addition to these long term changes it also appears that iron oxide records from the loess plateau exhibit 400 500 ka cycles from the wucheng red clay boundary to s5 these 400 500 ka cycles may be analogous to similar length cycles recorded in 13 c marine records in the south china sea and may be linked through weathering and silica production as a result of the asian monsoon

distribution of diatoms coccolithophores and planktic foraminifers along a trophic gradient during sw monsoon in the arabian sea the distribution of diatoms coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean 0 100 m across the upwelling area off the oman coast to the central arabian sea during may june 1997 and july august 1995 the number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration nitrate phosphate silicate caused by upwelling vegetative cells of chaetoceros dominated the diatom assemblage in the coastal upwelling area towards the more nutrient depleted and stratified surface waters to the southeast the number of diatoms decreased coccolithophore and planktic foraminiferal numbers increased and floral and faunal composition changed in particular the transition between the eutrophic upwelling region off oman and the oligotrophic central arabian sea was marked by moderate nutrient concentration and high coccolithophore and foraminifer numbers florisphaera profunda previously often referred as a lower photic zone species was frequent in water depths as shallow as 20 m and at high nutrient concentration up to 14 mol no3 l 1 and 1 2 mol po4 l 1 to the oligotrophic southeast of the divergence cell densities of coccolithophores declined and umbellosphaera irregularis prevailed throughout the water column down to 100 m depth in general total coccolithophore numbers were limited by nutrient threshold concentration with low numbers 70 103 cells l 1 at low no3 and po4 the components of the complex microplankton succession diatoms coccoliths and planktic foraminifers and possibly others should ideally be used as a combined paleoceanographic proxy consequently models on plankton ecology should be resolved at least for the seasonality to account for the bias of paleoceanographic transfer calculations

application of quotient normalization technique to minimize errors in diffuse spectral reflectance data collected under various conditions abstract visible and near infrared vnir derivative spectroscopy of diffuse spectral reflectance dsr data can be a potent method to extract lithological information from sediment cores however synthesis of multiple dsr data sets collected with different instruments from sediment obtained at different times could subject the dsr measurements to errors arising from disparity in depositional environment sample processing methods and storage conditions here we apply a quotient normalization technique to set these data in a common reference frame as a first step in our vnir derivative spectroscopic analysis the effectiveness of the quotient normalization technique is illustrated with samples from the bering and west arctic sea shelves this is because of access to sediment samples collected by several coring expeditions at different times in the past over a range of locations dsr measurements were obtained from eleven groups of core samples processed under two conditions under one of the conditions they were quotient normalized while in the other they were not lithological proxies in these cores from both conditions were extracted using varimax rotated principal component analysis vpca these lithologies are chlorite muscovite goethite phycoerythrin phycocyanin smectite calcite dolomite and illite chlorophyll a these lithological proxies were then plotted spatially using gis kriging software the spatial distributions of the vpca extracted lithologies under the two conditions were compared with lithologies obtained by previous workers in the study site the lithologies after quotient normalization were found to be more consistent with previously published results for clay mineralogy determined by x ray diffraction xrd the quotient normalized data also showed a lower variance in the interpolated data sets relative to the second processing condition which is the norm used for comparison we conclude that the quotient normalization technique is an effective scaling tool for minimizing errors from combining dsr data sets collected during multiple coring expeditions

compound specific carbon isotope analysis of natural and artificially generated hydrocarbons in source rocks and petroleum fluids from offshore mid norway stable carbon isotope signatures of individual hydrocarbon components provide important information on the source rock facies of oils as well as their asphaltene fractions despite maturity variations and secondary processes such as phase fractionation and biodegradation our study is based upon petroleum fluids and source rock samples from offshore mid norway where the main source rock is the marine shales of the upper jurassic spekk formation an alternative source is provided by coals and coaly shales of the lower jurassic are formation in terms of maturity the source rock samples are distributed throughout the main phase of oil generation in this study compound specific carbon isotope analysis has been performed on thermal extracts and kerogen pyrolysates of the source rocks as well as on the oils and the pyrolysis products of their asphaltenes we demonstrate that trends of absolute isotope data and specific isotopic fingerprints after normalizing the data are useful for petroleum source rock correlations the carbon isotope ratios of the n alkanes separate the are from the spekk formation samples in both thermal extracts and kerogen pyrolysates becoming less negative with increasing terrestrial input the spekk samples also tend to become isotopically heavier with increasing maturity while the are samples do not show any systematic difference with increasing maturity the carbon isotope ratios of the n alkanes also discriminate between the oils as well as the asphaltenes from the fluids the individual components generated by pyrolysis of kerogens are isotopically heavier than those from the thermal extracts this is expected from models of kinetic isotope effects which predict that the isotopically lightest products are generally released at an earlier stage in the maturation process a similar isotopic difference is also observed between the pyrolysis products of asphaltenes and the original oils derived from the same source rock type however in a sample where the oil and its asphaltene fraction originate from two different source rocks the opposite relationship between the carbon isotope composition of the oil and its asphaltene fraction is observed bulk isotope data of kerogen concentrates pyrolysates and the residue after pyrolysis of the source rock samples as well as bulk isotope data of whole oils are also presented we show that besides separating are from spekk the bulk carbon isotope values of the spekk samples are considerably heavier than the n alkanes from the thermal extracts whereas those of the are samples are almost equal

clay mineral dispersal patterns in the north bering and chukchi seas abstract characterization of the clay mineralogic constituents of the m e s d equivalent spherical diameter size fraction of contemporary marine and fluvial sediments from the north bering sea chukchi sea region and adjacent land areas has resulted in delineation of suites dominated by broadly defined illitic and expandable group components with lesser amounts of chlorite and kaolinite distribution patterns elucidated indicate net northward transport of sediments relatively enriched in the expandable group with predominant terrigen ous source from the yukon river system this material is distributed across the study area in a medial zone along a general north south trend with peripherally decreasing relative amounts of this expandable group component and concomitant relative increases in the illitic components these patterns are consistent with known physical oceanographic and regional geologic relationships in terms of sediment sources transport processes and depositional mechanisms the foregoing suggest further that consideration of the stratigraphic relationships of these clay mineral component types as a function of time in relevant marine sediments north and south of the present bering strait should be informative with respect to regional quaternary paleogeography as related to global sea level fluctuations during glacial and interglacial episodes

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

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

shallow slides in compacted high plasticity clay slopes shallow slide failures in embankments constructed of high plasticity clays create costly maintenance problems on highway projects and can threaten the integrity of water retaining earth structures this paper investigates the mechanisms of stability degradation that lead to these slope failures the failure mechanism involves moisture infiltration into the slope surface that leads to decreases in suction and soil shear strength both the degree and time rate of strength loss are investigated based on stability and moisture diffusion analyses respectively stability analyses indicate that the failures are associated with destabilizing hydraulic gradients in the pore water and the suction level at the surface of the slope declines to a limiting suction of about u 2 pf when exposed to moisture moisture diffusion analyses indicate that the time rate of strength degradation is controlled by the depth and spacing of desiccation cracks that form in the soil mass and the moisture diffusion properties of the soil the stability and moisture diffusion models described above were evaluated in light of 34 documented shallow slides in texas high plasticity clays

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

the deglacial history of surface and intermediate water of the bering sea the lithology of deglacial sediments from the bering sea includes intervals of laminated or dysaerobic sediments these intervals are contemporaneous with the occurrence of laminated sediments from the california margin and gulf of california which suggests widespread low oxygen conditions at intermediate depths in the north pacific ocean the cause could be reduced intermediate water ventilation increased organic carbon flux or a combination of the two we infer abrupt decreases of planktonic foraminifer d 18 o at 14 400 and 11 650 yr bp which may be a combination of both freshening and warming on the shirshov ridge the abundance of sea ice diatoms of the genus nitzschia reach local maxima twice during the deglaciation the latter of which may be an expression of the younger dryas these findings expand the extent of the expression of deglacial millennial scale climate events to include the northernmost pacific r 2005 elsevier ltd all rights reserved

biomarkers and carbon isotopes of oils in the jurassic smackover trend of the gulf coast states u s a abstract the geochemistry of 25 oils from 23 fields in alabama and the mississippi and louisiana arkansas jurassic salt basins was evaluated results show that the oils were generated by a carbonate source rock which was deposited under highly anoxic conditions and which contains mainly marine derived organic matter the mississippi and louisiana arkansas oils are geochemically similar indicating similar depositional environments for the source although the alabama oils were also derived from a carbonate source rock they are dissimilar to the mississippi and louisiana arkansas oils terpane biomarkers suggest that in addition to marine derived organic matter the source for the alabama oils had an organic input from a more near shore paralic environment i e with a component of terrestrially derived kerogen within each area the oils are similar therefore the norphlet and upper smackover oils in alabama share a common source and the upper smackover cotton valley and some of the lower tuscaloosa oils where production is from faulted structures in mississippi also share a common source maturities of the oils in the three areas vary from low in the updip mississippi salt basin high in the louisiana arkansas salt basin to very high in portions of alabama based on the maturity of oils in mississippi oil generation and migration commenced during the cretaceous when the source was at modest levels of thermal maturity oils migrated relatively short distances into nearby reservoir rocks some oils reached high maturities in the reservoirs resulting in abundant late forming bitumen and pyrobitumen deposition in pore spaces