geochemical and isotopic composition of organic matter in the kupferschiefer of the polish zechstein basin relation to maturity and base metal mineralization vs the present depth of the kupferschiefer soluble organic matter som yields and relative proportions of saturated and aromatic hydrocarbons of the som provide evidence for an oxidative alteration of organic matter in highly mineralized kupferschiefer samples near the rote faule zones this is confirmed by differences in the composition of the saturated and aromatic hydrocarbon fractions of the soluble organic matter saturated hydrocarbons from rote faule samples are dominated by short chain n alkanes and higher abundances of pristane and phytane relative to heptadecane n c17 and octadecane n c18 respectively compared with samples more distant to the rote faule zone compositional changes of the aromatic hydrocarbon fractions with decreasing distance to that zone are characterized by the occurrence of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene to methylphenanthrenes that are attributed to demethylation reactions and resulted in a decrease of the methylphenanthrene index mpi 1 kupferschiefer samples from the barren zone of the polish basin do not show these alteration patterns the observed variations in organic matter composition with burial depth are consistent with changes due to increasing thermal maturation maturity assessment is achieved from mpi 1 and the methyldibenzothiophene ratio mdr from the relationship between the maturity of organic matter in terms of vitrinite reflectance values and depth of the kupferschiefer strata a continuous increase in reflectance of vitrinite is obtained within the polish basin the alteration pattern of organic matter related to base metal mineralization of the kupferschiefer corresponds to changes in the isotopic composition of organic carbon and calcite kerogen within or close to rote faule zone is enriched in 13c caused by the preferential release of isotopically light organic compounds through progressive degradation of organic matter the opposite tendency towards lower 13c and 18o values of calcite provides evidence for isotopic exchange between carbonate and the oxidizing ore bearing solutions and for organic matter remineralization in contrast organic matter and calcite from the kupferschiefer do not show regular trends in 13c with increasing thermal maturation

hydrocarbon potential and depositional environments of oligo miocene rocks in the eastern carpathians vrancea nappe romania abstract the oligocene to early miocene fine grained succession in the eastern carpathians includes from base to top the lower menilite lmm bituminous marl bmm lower dysodilic shale ldsm and upper dysodilic shale udsm members these stratigraphic units constituting the main hydrocarbon source rocks in the eastern carpathians have been studied in an outcrop section to determine its depositional environment and hydrocarbon potential the lmm contains high amounts of toc but because of low thickness its source potential is limited the organic matter of the overlying bmm is mainly derived from autochthonous marine organisms including bacterial biomass toc contents are moderate because of dilution by carbonate minerals calcareous nannoplankton dates the bmm into nannoplankton zones np21 22 salinity and redox conditions varied from reduced to slightly enhanced and from strictly anoxic to dysoxic the ldsm contains carbonate free black shale and sandstone beds deposited in a depositional lobe under anoxic conditions despite of high hi values land plants form a significant part of the organic matter channel fill sediments form the top of the ldsm the lower part of the early miocene udsm accumulated in a lobe whereas its upper part represents a basin plain setting mttc ratios reflect a trend from slightly enhanced to slightly decreased normal marine salinity the presence of aryl isoprenoids suggests a temporary photic zone anoxia controlled by salinity variations both marine and terrestrial biomass contributed to the organic matter a major change towards oxic conditions occurred at the boundary between the udsm and the overlying gura soimului formation the studied succession can generate 6 t of hydrocarbons per square meter all members are oil prone but yield oil with different biomarker characteristics this allows the identification of oil generated from different lithostratigraphic units

laterally varying structure and kinematics of the molasse fold and thrust belt of the central eastern alps implications for exploration the molasse deposits of the central eastern alps are partly incorporated into a fold and thrust belt that recently has come into exploration focus the structural style and timing of deformation varies significantly alongstrike regional three dimensional seismic and well data interpretation indicate three different structural segments from east to west 1 the sierning imbricates have a decollement close to the base of the molasse sequence and consist of varying numbers of thrust sheets alongstrike early miocene shortening of the molasse is at least 6 2 km 3 9 mi overthrusting of the internal penninic and helvetic wedge since the oligocene accommodated at least 25 km 15 5 mi of additional shortening 2 the regau segment is dominated by one to two small thrust sheets above a shallow detachment this segment is dominated by overthrusting of the alpine wedge 3 the perwang imbricates consist of an oligocene wedge with complex deformed thrust sheets above a detachment horizon in upper cretaceous marls minimum shortening in the imbricates is 18 5 km 11 5 mi with overthrusting 33 3 km 20 7 mi all shortening estimates have an uncertainty of approximately 20 to 35 the laterally varying thrust belt architecture results from predeformational conditions e g sediment thickness mechanical stratigraphy and basement dip in the sierning imbricates hydrocarbon trap definition and charge issues are exploration risks in the regau segment exploration is focused on the subthrust play the perwang imbricates have hydrocarbon shows but no economic discoveries charge and seal issues are the main risks the petroleum systems in the context of the structural evolution are not yet fully understood

influence of maturity on carbazole and benzocarbazole distributions in crude oils and source rocks from the sonda de campeche gulf of mexico abstract carbazole geochemistry has been studied for a petroleum system in which vertical migration is prominent and where reservoirs are locally sourced an essentially uniform organofacies of organicrich tithonian source rocks from the sonda de campeche gulf of mexico covering a well defined maturity sequence 0 36 1 29 rr and associated crude oils 0 49 0 92 rc from palaeocene reservoirs formed the sampling base comparison of the distribution of alkylcarbazoles and benzocarbazoles in rock bitumens and oils revealed that fractionation due to primary expulsion had no effect on the distribution of shielded exposed carbazoles within crude oils perhaps more importantly the benzocarbazole ratio in both rock extracts and crude oils increased with maturity indicating that this parameter cannot be directly used as a migration indicator in petroleum systems where vertical migration through faults and fissures represents the main avenues of oil migration

late quaternary water level variations and vegetation history at crooked pond southeastern massachusetts abstract sediment cores collected along a transect in crooked pond southeastern massachusetts provide evidence of water level changes between 15 000 cal yr b p and present the extent of fine grained detrital organic accumulation in the basin inferred from sediment and pollen stratigraphies varied over time and indicates low water levels between 11 200 and 8000 cal yr b p and from ca 5300 to 3200 cal yr b p this history is consistent with the paleohydrology records from nearby makepeace cedar swamp and other sites from new england and eastern canada and with temporal patterns of regional changes in effective soil moisture inferred from pollen data the similarities among these records indicate that 1 regional conditions were drier than today when white pine pinus strobus grew abundantly in southern new england 11 200 to 9500 cal yr b p 2 higher moisture levels existed between 8000 and 5500 cal yr b p possibly caused by increased meridonal circulation as the influence of the laurentide ice sheet waned and 3 drier conditions possibly contributed to the regional decline in hemlock tsuga abundances at 5300 cal yr b p although sea level rise may have been an influence moist climatic conditions during the late holocene were the primary reason for a dramatic rise in water table elevations

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

a 780 year annually resolved record of indian ocean monsoon precipitation from a speleothem from south oman 1 meteorological records of monsoon rainfall in the indian ocean are generally less than 100 years long the relative brevity of these records makes it difficult to investigate monsoon variation on decadal and centennial timescales to determine what factors influence the intensity of rainfall on these timescales or to place possible changes in the twentieth century into a broader historical context development of a geologic proxy for rainfall that records annual variation in the monsoon over much longer time periods than are covered by instrumental records would be a significant step forward we have developed an annually resolved record of monsoon rainfall variation for the past 780 years based on annual layer thickness and stable isotope analyses of a laminated stalagmite from southern arabia our results show that monsoon variation over the past century is not outside of the range of the past 800 years decreasing monsoon rainfall over the past century is related to increasing sea surface temperature in the indian ocean spectral analyses of the record are dominated by cycles that are similar to those observed in records of solar activity on centurial timescales decadal to interannual cycles in the record appear to originate in the tropical pacific ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 3354 meteorology and atmospheric dynamics precipitation 1854 1620 global change climate dynamics 3309 1699 global change general or miscellaneous keywords monsoon paleoclimate rainfall indian ocean speleothem oxygen isotopes

geochemical characterisation of middle devonian oils in nw alberta canada possible source and maturity effect on pyrrolic nitrogen compounds abstract molecular geochemical compositions of a suite of middle devonian sourced and reservoired oils from the rainbow zama shekilie sub basins in n w alberta canada reveal the presence of at least two oil families in the study area the distribution of each oil family is geographically restricted to a single sub basin consistent with the oils being sourced locally within a series of closed generation migration trapping systems the diversity in the biomarker distributions of the oils indicates the wide range of depositional environments and source materials existing in each sub basin rather than mixing of end member oils across different sub basins clear maturity differences are observed between the oils from the rainbow and zama subbasins pre cretaceous thermal anomalies along the reactivated regional precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the middle devonian source rocks in the study area we infer that depositional environment and thermal maturity have had a strong impact on the geochemical characteristics of the saturated and aromatic hydrocarbons in the rainbow shekilie zama oils but may not influence the pyrrolic nitrogen compounds to a significant extent however recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the pyrrolic nitrogen compounds are used to characterize petroleum migration

terminal pleistocene holocene palaeoenvironmental changes revealed by mineral magnetism measurements of lake sediments for dali nor area southeastern inner mongolia plateau china abstract mineral magnetic properties sirm arm hirm and s ratios are presented for two ams 14c dated pit sequences of lake sediments recovered from haoluku and liuzhouwan 43 n 117 e the two sites fall in the semi humid to semi arid climate transition zone dali nor area of the southeast inner mongolia plateau china complemented by data for loss on ignition loi total organic carbon toc carbon nitrogen c n grain size and pollen these mineral magnetic measurements provide additional insights into environmental changes occurring at this area over the last 13 500 years conditions were extremely dry and windy as shown by the low sirm arm and hirm and high s ratios before 13 500 yr bp the environment began to ameliorate gradually since then and a further humidification occurred at 10 300 yr bp in haoluku the northern site and at 9400 yr bp in liuzhouwan the southern one as implied by the increased but only moderately high sirm arm and hirm and decreased s ratios as indicated by the remarkably increased sirm arm hirm and s ratios a deterioration commenced at 5600 yr bp in haoluku and at 4700 yr bp in liuzhouwan in haoluku conditions have been generally dry and windy since 5600 yr bp despite a minor amelioration at 4500 3000 yr bp a short but marked amelioration occurred at 1200 700 yr bp in liuzhouwan s ratios seem to be a reliable indicator of environmental aridity for this area

the influence of source depositional conditions on the hydrocarbon and nitrogen compounds in petroleum from central montana usa abstract the hydrocarbon and pyrrolic nitrogen compound compositions of 21 crude oils from reservoirs in the heath tyler amsden and swift morrison formations of central montana have been investigated by combined gas chromatography mass spectrometry the biomarker and aromatic hydrocarbon data enabled recognition of three composition types within the heath tyler amsden oils the swift morrison oils displayed different hydrocarbon characteristics and are classified as a separate oil group a number of geochemical parameters e g dibenzothiophene phenanthrene c 20 triaromatic steroid hydrocarbon c 20 c 28 triaromatic steroid hydrocarbons indicate strong variations in petroleum composition from north to south across the region oils from the central montana uplift with high relative c 27 diasteranes c 29 steranes and ts ts tm suggests increasing clay contribution to the source while abundant gammacerane indicates the development of hypersaline conditions with restricted circulation oils from the bull mountain basin represented by the amsden oils show relatively low c 27 diasteranes c 29 steranes and ts ts tm ratios indicating increasing carbonate contribution to the source while the decrease of a gammacerane contribution suggests decreasing salinity levels which may explain the dominance of tricyclic terpane and hence their precursors to the source organic matter while the changes recorded by the biomarker and aromatic hydrocarbon compositions show strong regional variations the nitrogen compounds do not respond so strongly however weak trends coinciding with source carbonate content were apparent in the following ratios 1 8 dimethylcarbazole 1 8 dimethylcarbazole 1 ethylcarbazole and carbazole sum of c 2 carbazoles the second parameter may be responding to variations in salinity since it co varies with the behaviour exhibited by the tricyclic terpanes the source information that can be extracted from biomarkers and aromatic hydrocarbons suggests that primary migration and compositional fractionation during expulsion has exerted little influence on this fraction of petroleum meanwhile primary migration and compositional fractionation during expulsion appear to effect the carbazole and benzocarbazole distributions thereby limiting their application as indicators for source rock facies composition

periodicity of climate conditions and solar variability derived from dendrochronological and other palaeoclimatic data in high latitudes abstract the periodicity of climatic processes in the barents sea region and along the arctic ocean coast during several hundred years has been studied by analyzing the tree ring chronologies for the regions close to the northern timberline in the barents sea region cyclicities of climatic processes with periods of around 90 30 35 22 23 18 and 11 12 years have been established by spectral analysis of the data for the kola peninsula wavelet analysis of annual series of conifer tree rings generalized for 10 regions along the northern timberline from the kola peninsula to chukotka for the period 1458 1975 has revealed the same periodicities for the vast areas of northern russia climatic cyclicity with a period of about 35 years is known as the bruckner cycle climatic cycles with periods of around 90 22 23 and 11 12 years correlate well with the corresponding solar activity cycles a possible solar forcing of periodic climatic processes and its nonlinear influence on the atmosphere ocean continental system are discussed

moisture changes and fluctuations of the westerlies in mediterranean central chile during the last 2000 years the laguna aculeo record 33 50 s abstract the multi proxy study of lacustrine sediments from laguna aculeo 33 50 s provides detailed information about moisture changes in the lowlands of mediterranean central chile during the last 2000 years the lake lies just at the northern border of the strong westerlies influence with dry summers and humid winters geochemical sedimentological and diatom analyses provide evidence for an arid period between cal 200 bc and ad 200 and a subsequent increase in moisture after cal ad 200 abundant clastic layers in the core represent flood events periods with a higher frequency of flood events indicate an increased intensity of the westerlies more winter frontal system activity and possibly enso related variability probably comparable to modern conditions in mediterranean central chile periods of high clastic input occur around cal ad 200 400 500 700 especially around cal ad 1300 1700 and around ad 1850 1998 during the last 50 years at least eight flood events were detected correlating mainly with el nino years a very short drier period also occurred in the late 1960s in recent decades human impact has resulted in a eutrophication of the lake

geochemical evidence for the use of magnetic susceptibility as a paleorainfall proxy in the tropics abstract several workers have estimated paleomonsoonal rainfall using proxies that are related to wind strength upwelling productivity chemical weathering and pedogenesis in an earlier work on sediments of thimmannanayakanakere tk a lake in southern india shankar r prabhu c n warrier a k vijaya kumar g t sekar b 2006 a multidecadal rock magnetic record of monsoonal variations during the past 3700 years from a tropical indian tank journal of the geological society of india 68 447 459 we suggested that magnetic susceptibility lf may be used as a proxy to estimate the paleomonsoonal rainfall in tropical regions this was based on the positive correlation between magnetic susceptibility of tk sediments and instrumental rainfall data and backed up by historical records and paleoclimate proxy data from widely separated regions of india in this paper we provide geochemical data results of cbd extraction and elemental analysis and their statistical analysis pca to support our earlier proposition that lf may be used as a proxy for paleomonsoonal rainfall in the tropical regime the cbd treatment of sediment samples reduced the average lf from 132 to 64 10 8 m3 kg 1 average fd from 12 91 to 2 01 10 8 m3 kg 1 and average fd from 8 9 to 3 showing that the samples do contain pedogenic magnetite further samples of high low rainfall periods showed a higher lower reduction in the magnetic parameters suggesting a higher lower content of pedogenic magnetite metal al ratios fe al ti al na al mn al pb al zn al cu al k al ca al mg al and sr al are positively correlated most of them at the 1 level with lf suggesting that the tk sediments are derived mainly from the catchment in particular ti al k al and k na ratios that are good indicators of chemical weathering intensity cwi start increasing from 2 cal ka b p onwards corresponding to increasing lf increasing rainfall from this time as chemical weathering is principally driven by rainfall temperature being constant in tropical regions data on cwi indicators provide support to the hypothesis that lf estimates paleomonsoonal rainfall principal component analysis of geochemical and magnetic data shows that three important factors explain the variance in the data set terrigenous pedogenic rainfall and carbonate low rainfall or drought thus our data strengthen shankar et al s shankar r prabhu c n warrier a k vijaya kumar g t sekar b 2006 a multidecadal rock magnetic record of monsoonal variations during the past 3700 years from a tropical indian tank journal of the geological society of india 68 447 459 hypothesis that magnetic susceptibility may be used as a proxy for monsoonal rainfall in the tropical milieu we have proposed a model to explain pedogenesis chemical weathering intensity and carbonate precipitation which are all related to rainfall in the tk catchment

generation mixing and alteration of thermogenic and microbial gas in oil deposits the case of the alpine foreland basin austria abstract molecular and stable isotope compositions were determined for forty eight gas samples taken from wells producing oil form cretaceous and eocene reservoirs gas was expelled from source rock at various maturity levels 0 6 1 2 rr gas maturities based on stable carbon isotopes are in general agreement with those found in oils nevertheless results revealed that most fields trap methane derived from a source which is not thermogenic shallow northeastern reservoirs trap methane interpreted as secondary microbial in origin the same process is proposed here as source of methane in western deposits moreover those gases are enriched in 2 h isotope suggesting different methanogenesis pathways fields along the southern margin of the alpine foreland basin where reservoir temperature exceeds 80 c host methane generated during primary organic matter degradation thus eocene and lower oligocene layers should be considered as potential source rocks this study gives new insight to filling history of traps and revealed a more complicated geological background and hydrocarbons generation than have been assumed until now

speleothem evidence for changes in indian summer monsoon precipitation over the last 2300 years speleothems from a well ventilated dolomitic cave in the pokhara valley central nepal preserve a mineralogic record of indian summer monsoon variability over the past 2300 yr annually deposited aragonite layers formed between 2300 and 1500 yr b p indicating reduced monsoon precipitation and increased cave aridity whereas alternating calcite aragonite laminae deposited after 1500 yr b p record elevated summer monsoon precipitation and increased cave humidity dense optically clear calcite layers deposited from 450 5 to 360 20 yr b p 1550 to 1640 a d indicate a less evaporative cave environment and suggest moister and or cooler conditions possibly related to climatic change associated with the onset of the little ice age

temporal resolution of an oil charging history a case study of residual oil benzocarbazoles from the gidgealpa field reservoired oil is usually a mixture of multiple discrete petroleum charges unravelling the contribution and character of each charge is amongst the most daring challenges in petroleum geochemistry this paper describes an approach that involves the evaluation of both free and residual oils to reconstruct the history of petroleum accumulation within the multireservoir gidgealpa field located in the cooper and eromanga basins of central australia porewall coating residual oils form by reservoir wetting processes and grow continuously by adsorption of polar compounds retaining molecular information on the first oil that was present in the pore system such sequentially recovered residual oils proved useful in reconstructing the record of oil charges to the gidgealpa ridge using araucariacaean markers for source discrimination and the benzocarbazole a a c ratio bcr for identification of the source region five discrete charging events were distinguished in contrast to most previous studies benzocarbazole distributions were found to be independent of lithofacies organic facies and maturity however alkylated carbazoles did exhibit a pronounced facies dependency the application of alkylcarbazoles as source markers in the study area provides the first evidence of the expulsion of petroleum from cambrian marine source rocks in the underlying warburton basin 2007 elsevier ltd all rights reserved

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

holocene weak monsoon intervals indicated by low lake levels at hulun lake in the monsoonal margin region of northeastern inner mongolia china a 170 cm long sediment core spanning the last 10 000 years was recovered from hulun lake in the northeastern margin of the east asian summer monsoon the sediment core was analyzed at 1 cm intervals for grain size distribution and sedimentary component partition these data provide a proxy record of the monsoon variability on millennial to centennial scales during the holocene we used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions three coarse components representing nearshore suspension saltation and traction together with the sand fraction percentage and the median grain size of bulk samples indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation higher percentages of the nearshore components accompanied by more sand fraction proportions and coarser median grain sizes reflect lower lake stands resulting

sedimentation in lake malawi east africa during the past 10 000 years a continuous paleoclimatic record from the southern tropics a suite of piston cores recovered from lake malawi 9 14 s 34 35 e east africa in 1986 has been analyzed for major and minor elements organic c and n calcium carbonate and diatoms an internally consistent stratigraphy was constructed from calcium carbonate abundance and variations in the two most abundant diatom genera stephanodiscus and melosira with age control obtained primarily from 14c dating of the carbonate differences with time in fe abundance in a transect of cores from different water depths have been interpreted to reflect changes in chemocline depth the depth to the chemocline was on the order of 100 m shallower than present prior to 3500 yr b p indicating less seasonality carbonate production and preservation appears to be related to climatically induced changes in both salinity and chemical distributions in the water column the carbonate which precipitates from surface waters is most abundant during the interval from about 10 000 to 6000 yr b p this micrite most likely represents periods of low lake level when salinity increased and carbonate precipitation was enhanced sedimentary evidence suggests that lake levels were 100 150 m lower than present during this period this record is different from climatic trends in northern intertropical africa but appears to also be related to changes in insolation and monsoon circulation this is the northernmost basin in africa reported to exhibit a southern hemisphere response to the early holocene northern hemisphere summer insolation maximum the climatic hingeline north of lake malawi 9 s implied by our results is significantly south of that indicated by general circulation model simulations however the cores show evidence for periods of abrupt climate change during the interval of generally arid climate

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

the origin of hydrocarbon source rocks in the austrian molasse basin eocene oligocene transition organic rich rocks schoneck formation from five wells representing a section across the northern paleo slope of the austrian molasse basin were studied using a multi method approach including petrography x ray diffraction organic and inorganic geochemistry and c and n isotopes of the organic material organic matter accumulation commenced during the latest eocene and was dependent on variations of currents salinity organic productivity and nutrient supply initial marl deposition and phosphorite formation under dysoxic conditions was followed by organic rich mud deposition associated with benthic and photic zone anoxia this paleoceanographic situation resembles the first isolation of the western central paratethys deposition of organic rich rocks terminated during lower oligocene time when changing current patterns and decreasing salinity caused a breakdown of water column stratification even though the schoneck formation is an excellent source rock major differences exist in the petroleum potential of the schoneck formation deposited in upper and lower basin slope settings the schoneck formation from the upper slope is characterised by toc contents up to 12 and hi values between 500 and 600 mghc gtoc in the lower slope settings toc values are generally below 2

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

el nino and related monsoon drought signals in 523 year long ring width records of teak tectona grandis l f trees from south india abstract we present a 523 year a d 1481 2003 tree ring width index chronology of teak tectona grandis l f from kerala southern india prepared from three forest sites dendroclimatological investigations indicate a significant positive relationship between the tree ring index series and indian summer monsoon rainfall ismr and related global parameters like the southern oscillation index soi a higher frequency of occurrence of low tree growth is observed in years of deficient indian monsoon rainfall droughts associated with el nino since the late 18th century prior to that time many low tree growth years are detected during known el nino events probably related to deficient indian monsoon rainfall the general relationship between ismr and el nino is known to be negative and the spatial correlations between our kerala tree ring chronology and sea surface temperatures ssts over the nino regions follow similar patterns as those for ismr this relationship indicates strong enso related monsoon signals in the tree ring records these tree ring chronologies with a high degree of sensitivity to monsoon climate are useful tools to understand the vagaries of monsoon rainfall prior to the period of recorded data

oil origin and secondary migration pathway in the bonan sag bohai bay basin china abstract the oil origin and secondary migration pathways were investigated in the bonan sag using basin modeling and petroleum geochemical data including biomarker assemblages of saturated hydrocarbons and pyrrolic nitrogen compounds the modeling of secondary oil migration pathway was performed based on the reconstruction of burial thermal maturity and oil generation histories modeling results are calibrated by the distribution of oil wells and oil fields as well as traced secondary oil migration pathways inferred from pyrrolic nitrogen compounds carbazole parameters were selected to trace the secondary oil migration pathway based on the investigation of oil origin three groups of oils sourced from source rocks of the third and fourth members of shahejie formation es3 and es4 have been identified in this study group oils from es3 source rocks mainly occurred in the center of sag group oils from es4 source rocks occurred in the margin regions group oils were interpreted to be the mixed sources from es3 and es4 source rocks three oil migration pathways can be traced by pyrrolic nitrogen compounds based on varied carbazole parameters the major stages of oil generation of es3 and es4 source rocks occurred at about 30 20 ma and 5 0 ma which coincided with oil charge periods secondary oil migration pathways have been predicted successfully by the oil migration modeling in the bonan sag based on the calibration with oil wells oil fields and the traced oil migration pathways by pyrrolic nitrogen compounds favorable zones located on the primary secondary oil migration pathways at the periods of oil charge may be the prospective regions for oil exploration in the bonan sag

effect of maturity and petroleum expulsion on pyrrolic nitrogen compound yields and distributions in duvernay formation petroleum source rocks in central alberta canada abstract a quantitative study of pyrrolic nitrogen compounds was conducted on a series of marine carbonate petroleum source rock extracts taken from the upper devonian duvernay formation in the central alberta portion of the western canada sedimentary basin with increasing thermal maturity concentrations of various pyrrolic nitrogen compounds in the rock extracts increase drastically together with significant compositional variations related to alkyl substitution position the study provides circumstantial evidence for adsorptive interactions operating between organic nitrogen compounds and solid organic mineral phases in subsurface sedimentary rocks during petroleum generation and expulsion the absolute concentrations and relative distributions of pyrrolic nitrogen compounds in the extracts of different maturity ranges provide background information for the calibration of such data in migrated petroleums as an independent measurement of secondary oil migration range of duvernaysourced oils in the basin

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

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

tropical east african climate change and its relation to global climate a record from lake tanganyika tropical east africa over the past 90 kyr abstract forcing mechanisms of tropical climate in continental areas remain poorly understood due in large part to a lack of continuous long term high fidelity records sediment core t97 52v from lake tanganyika provides new insight into the timing and mechanisms behind east african climate change over the past 90 kyr this record is particularly important because other than a recently recovered scientific drill core from lake malawi there are no other continuous well dated records from east africa prior to 60 ka the high resolution age model presented here provides a large degree of age certainty for the past 45 kyr and our suite of proxies allows a thorough examination of lake tanganyika s dynamics from core stratigraphy and chemical analyses we present evidence of a lake level drop greater than 400 m sometime prior to 90 ka much greater than that inferred for the lgm suggesting a period of intense aridity sometime around 100 ka additionally core t97 52 v preserves evidence of worm burrows detected by x radiographic imagery as indicated by burrow shaped deposits of iron oxide indicating a shallow lake at the time of deposition of that material intermittently high lake levels between 78 ka and 72 ka developed at the same time as a weakened asian monsoon and a pluvial phase in northeast brazil suggesting a global reorganization of climate possibly forced by a reduction in orbital eccentricity over the past 60 ka this core preserves the same events recorded in a core collected 100 km away in the southern basin of lake tanganyika including an unexplained increase in biogenic silica at 37 ka suggesting that this vast lake is responding coherently across both major bathymetric basins to regional and global climate forcing

internal structure and emplacement mechanism of composite plutons evidence from mt kinabalu borneo the internal structure and emplacement mechanisms of composite plutons are investigated using new field data from the composite late miocene granitic intrusion of mt kinabalu in northern borneo the pluton was emplaced in the upper to middle crust in the late miocene at the contact between the ultramafic basement and sedimentary cover rocks structural data indicate that emplacement occurred during regional nnw sse oriented extension challenging tectonic models that involve contemporaneous regional compression the six major units forming the pluton were accommodated by upward flexure of the cover rocks with most magma pulses emplaced successively beneath their predecessors however the irregular 3d internal structure of the pluton also reflects preferential emplacement of successive units along the granite country rock contact of previous units in preference to the basement cover rock contact exploited by the initial units this study highlights the complex emplacement mechanisms and internal structure of composite intrusions and assesses how they differ from models of tabular emplacement

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

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

the diagenetic history of oligocene miocene sandstones of the austrian north alpine foreland basin abstract diagenesis is an essential tool to reconstruct the development of reservoir rocks diagenetic processes precipitation and dissolution have an influence on pore space the present paper aims to study the diagenetic history of deep marine sandstones of the austrian alpine foreland basin to reach that goal sediment petrology and diagenetic features of more than 110 sandstone samples from water and gas bearing sections from gas fields within the oligocene miocene puchkirchen group and hall formation has been investigated special emphasis was put on samples in the vicinity of the gas water contact gwc the sediment petrography of sandstones of puchkirchen group and hall formation is similar hence their diagenesis proceeded the same way in fact primary mineralogy was controlled by paleo geography with increasing transport distance and diverse detrital input sediment petrographically investigated sandstones from the water bearing horizon seemed quite comparable to the gas bearing sediments in general they can be classified as feldspatic litharenites to litharenites and display porosities of up to 30 and permeabilities of up to 1300 md the carbon and oxygen isotopic composition of bulk carbonate cements from these sandstones range from 3 8 to 2 2 and from 7 5 to 0 2 vpdb however near the gas water contact gwc a horizon with low porosities during early diagenesis the first carbonate generations formed first a fibrous calcite and afterwards a micritic calcite precipitated further siliciclastic minerals such as quartz and feldspar k feldspar and minor plagioclase exhibit corroded grains occasionally clay minerals illite smectite chlorite formed as rims around detrital grains late diagenesis is indicated by the formation of a low permeable zone at the gwc

holocene variations of monsoon rainfall in rajasthan two reconstructed histories of the monsoon rainfall in rajasthan show that the monsoon was weak or absent in latest glacial time with the advent of holocene climatic patterns fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history the two reconstructions separated by only 150 km have some features in common and some striking differences both show maximum monsoon amounts in the early holocene with a roughly two thirds decrease to the present both show salinization in sub boreal time both show long intervals of near complete desiccation in the last four millennia the shorter term variations however are not closely parallel these shorter term variations may be explained in terms of the behavior of the present day interannual variability

sedimentological and carbonate data evidence for lake level variations during the past 3700years from a southern indian lake abstract over the years several proxies have been developed to reconstruct rainfall variability however most rely on indirect approaches to provide qualitative paleorainfall estimate in an attempt to obtain a more direct measure of paleorainfall shankar et al 2006 explored the rock magnetic properties of lake sediments from thimmannanayakanakere tk in tropical southern india they proposed the use of magnetic susceptibility as a proxy for rainfall in the tropics warrier and shankar 2009 provided geochemical evidence in support of this proposition here sedimentological and carbonate data is provided as further evidence to bolster shankar et al s 2006 proposition high low values of lf indicate high low rainfall in the region of tk during the past 3700 years particle size variations suggest that the sand was high low during arid humid periods when the tk lake level was low high hence a negative correlation is documented between sand and lf along with other rock magnetic parameters hirm an indicator of magnetically hard minerals like haematite and goethite is suggestive of a relatively arid climate the high low hirm values in tk sediments indicate arid humid conditions for this reason sand is positively correlated with hirm by contrast fine silt and clay contents are low during low rainfall periods and vice versa thus both fine silt and clay contents are positively correlated with lf and other rock magnetic parameters but negatively correlated with hirm magnetic minerals reside principally in the fine silt fraction of tk sediments as evidenced from the positive correlation between fine silt content and magnetic susceptibility carbonate content too is indicative of paleorainfall conditions being high low during arid humid climatic conditions based on the lf sand and carbonate data we have inferred lake level variations in tk during the past 3700 years

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

charging of carboniferous volcanic reservoirs in the eastern chepaizi uplift junggar basin northwestern china constrained by oil geochemistry and fluid inclusion substantial amounts of petroleum were recently discovered in the carboniferous andesite tuff breccia and basalt reservoirs of the chepaizi uplift in the western junggar basin however the charging history of the carboniferous petroleum reservoir is poorly understood oil oil correlation studies indicate that all of the oils were mainly derived from the middle permian wuerhe formation source rocks possibly mixed with a small contribution from carboniferous baogutu formation source rocks in the neighboring changji sag based on the petrographic and microthermometry of fluid inclusions two hydrocarbon charging episodes are defined these episodes were characterized by a low peak range homogenization temperature th distribution 80 c 90 c and high salinity 13 22 13 42 wt nacl and a high peak range th distribution 120 c 130 c and low salinity 4 89 11 72 wt nacl respectively through one dimensional basin modeling and pressure volume temperature composition simulation the burial thermal histories for wells p61 p66 p668 and p663 were reconstructed and their trapping temperatures of the hydrocarbon inclusions were calculated to be higher than their corresponding highest paleotemperature i e 56 8 c 53 7 c 60 9 c and 58 1 c respectively implying fast hydrocarbon charging processes promoted by deep hydrothermal fluids associated with the hydrocarbon generation history sealing process of the hongche fault and regional tectonic evolution these two hydrocarbon charging events were deduced as the adjustments of oils previously accumulated along the hongche fault zone because of the tectonic extension in the paleogene and regional tilting in the neogene respectively the general direction of oil charging was traced from south to north and from east to west as indicated by the molecular parameters of nitrogen bearing compounds and c20 c21 triaromatic steroids c20 c21 c26 c28 triaromatic steroids ta i ta i ii which roughly coincided with the active fracturing

time variations of erosional force and grain size in pleistocene lake sediments abstract theoretical investigations on models of the developmental processes of erosional features show that the time variations in erosional force have more sensitive influence on the time fluctuation of eroded material such as sediments in lakes than that of the quantity representing erosional features such as volume of mountains time sequences of grain size distributions from the pleistocene sediments in lake biwa central japan indicate dominant periodicities of about 40 000 and 20 000 yr very close to those predicted from the milankovitch theory the time variations of the grain size parameters which may be indicators of erosional forces are very similar to that of the caloric summer insolation in the northern hemisphere

a high resolution record of late quaternary upwelling along the oman margin arabian sea based on planktonic foraminifera planktonic foraminiferal abundances fluxes test sizes and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western arabian sea to determine the short term changes in the southwest monsoon we have carried out a high resolution time series analysis of three upwelling indices total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species globigerina bulloides from ocean drilling program odp site 723a oman margin western arabian sea spanning the last 19 kyr in addition we have determined the relationships between upwelling intensity and the relative abundance fluxes and shell concentrations of various planktonic foraminiferal species upwelling indices suggest that from 19 to 16 ka 22 to 18 2 cal kyr b p the sw monsoon was relatively strong compared to the period 15 8 to 12 5 ka 17 8 to 13 8 cal kyr b p the intensification of the sw monsoon took place at 12 ka 13 1 cal kyr b p and reached a peak between 10 and 5 ka 10 6 and 4 8 cal kyr b p the high resolution data further demonstrate that the sw monsoon has started weakening from 5 ka 4 8 cal kyr b p and the weakest phase was in place at 3 5 ka 3 cal kyr b p which coincides with evidence of an arid climate in western tibet fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the sw monsoon winds after the last glacial period globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling the other species whose fluxes are influenced by this upwelling change are in order from strongest to weakest response globigerinita glutinata globigerinoides ruber neogloboquadrina dutertrei globigerinella aequilateralis globigerina falconensis and globigerinoides sacculifer the relative abundances of g bulloides and g ruber increased during intense upwelling whereas the relative abundances of g glutinata n dutertrei g falconensis and g sacculifer did not increase during this period which might be due to differences in the productivity of various species in relation to upwelling change therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the arabian sea than relative abundance data

from shale oil to biogenic shale gas retracing organic inorganic interactions in the alum shale furongian lower ordovician in southern sweden methane rich gas occurs in the total organic carbon rich alum shale furongian to lower ordovician in southern sweden the lower part of the thermally immature alum shale was impregnated by bitumen locally generated by heating from magmatic intrusions from the carboniferous to the permian organic geochemical data indicate that the migrated bitumen is slightly degraded in the upper alum shale where methane is the main hydrocarbon in thermovaporization experiments centimeter size calcite crystals occur that contain fluid inclusions filled with oil gas or water the alum shale is thus considered a mixed shale oil biogenic shale gas play the presented working hypothesis to explain the biogenic methane occurrence considers that water soluble bitumen components of the alum shale were converted to methane a hydrogeochemical modeling approach allows the quantitative retracing of inorganic reactions triggered by oil degradation the modeling results reproduce the present day gas and mineralogical composition the conceptual model applied to explain the methane occurrence in the alum shale in southern sweden resembles the formation of biogenic methane in the antrim shale michigan basin united states in both models melting water after the pleistocene glaciation and modern meteoric water may have diluted the contents of total dissolved solids tds in basinal brines such pore waters with low tds contents create a subsurface aqueous environment favorable for microbes that have the potential to form biogenic methane today biogenic methane production rates with shale as the substrate using different hydrocarbon degrading microbial enrichment cultures in incubation experiments range from 10 to 620 nmol per gram and per day

influence of migration distance maturity and facies on the stable isotopic composition of alkanes and on carbazole distributions in oils and source rocks of the alpine foreland basin of austria abstract the austrian part of the alpine foreland basin has been studied previously by organic geochemical methods to establish oil oil and oil source rock correlations the lateral distance of oil fields to the position of mature source rocks lower oligocene schoneck and eggerding formations beneath the alpine nappes in the south suggests long distance migration up to 50 km minor compositional trends in w e direction were obtained reflecting differences in depositional environment facies and maturity of potential source rocks therefore the oil and source rock samples are thought to provide valuable insights into carbazole distributions in relation to migration distance maturity and facies compound specific carbon isotope analyses on n alkanes and isoprenoids reflect the w e trend already seen within the total hydrocarbon fractions the observed trend toward lighter 13 c values of alkanes from oil fields in a w e direction are consistent with lower 13 c values of organic matter in unit c and similar differences obtained from sediments of the schoneck formation at wells oberhofen 1 w and molln 1 e the 13 c patterns of n alkanes and isoprenoids are in agreement with data obtained from the potential marine source rocks schoneck formation of the oils the hydrogen isotopic composition of short chain n alkanes c 15 19 of most oil samples are lower than the data obtained from the extracts of the marine permian kupferschiefer of the polish zechstein basin at similar maturation stages only the oils from the western oil fields yield d values of n alkanes comparable to those obtained from marine source rocks the data imply brackish water conditions during deposition of unit c of the schoneck formation differences in the position of d of isoprenoids in relation to the respective maturation trend line are most probably related to calibration errors alkylated carbazoles and benzocarbazoles are only present in sufficient amounts for quantification in oils sampled from the eastern fields rock extracts of the schoneck formation from drill cores molln 1 5200 m depth 0 92 rr and from the marginally mature ca 0 6 rr samples from well oberhofen 1 4300 m depth obtained sufficient amounts of carbazoles the significantly different concentrations of benzocarbazoles in the extracts around 10 g g at oberhofen 1 50 g g at molln 1 are related to maturity differences whereas the predominance of 1 methylcarbazole in the oberhofen samples is inferred to reflect differences in source rock facies in the oils from the eastern deposits neither the concentration ratios of methylcarbazoles nor the benzocarbazole ratio show indications for the influence of facies differences maturity of oil expulsion is estimated on the basis of mpi 1 rc 0 76 0 88 confirmed by sterane isomerization parameters the results argue for a minor influence of maturity differences on the benzocarbazole ratios of the oil samples the obtained ratios and the reservoir source fractionation parameters calculated from the data of molln 1 source rocks and the respective oils show a systematic decrease with the estimated migration distance the results argue for the applicability of benzocarbazoles for the assessment of relative differences in migration distances in oil plays characterized by minor differences in source rock facies and maturity during oil expulsion

hydrocarbon migration in the multiple sourced petroleum system in the northwestern junggar basin northwestern china constraint from geochemical and phase fractionation analysis oil mixing and absence of source rock samples make it difficult to identify the hydrocarbon migration routes in a petroleum system we provide a case study in the northwestern junggar basin to show that combined geochemical and phase fractionation analyses are robust tools to unravel the complex hydrocarbon migration processes the study rebuilds a migration history that multiple sourced hydrocarbons migrated mixed accumulated and fractionated along the evolution of regional tectonics in detail the shawan and mahu sags expelled the early stage hydrocarbons during the late triassic and late jurassic respectively because of their variable subsidence these hydrocarbons charged the entire area based on the evidence from bitumen and oil inclusions during the early cretaceous both sags subsided rapidly and expelled their late stage hydrocarbons these hydrocarbons first mixed along unconformities in the sags which generated mixed source oils and induced gas washing subsequently they further mixed with or displaced the encountered early stage oils during migration along the basal unconformity of the upper permian into the area causing a horizontal distribution of oil maturity zones in addition gases flowing through the early stage oils induced gas washing again creating heavy oils condensate oils and mixed gases after the late stage oils finally accumulated in fractured volcanics migration fractionation caused the remigration of light end compositions this study also shows the strong control of structures on hydrocarbon migration the unconformity network provided opportunities for long distance migration and widespread mixing of multiple sourced hydrocarbons whereas the paleoridge line of the zhongguai high defined the boundary of regional migration

east african climate change and orbital forcing during the last 175 kyr bp abstract variations in the temporal and spatial distribution of solar radiation caused by orbital changes provide a partial explanation for the observed long term fluctuations in african lake levels the understanding of such relationships is essential for designing climate prediction models for the tropics our assessment of the nature and timing of east african climate change is based on lake level fluctuations of lake naivasha in the central kenya rift 0 55 s 36 20 e inferred from sediment characteristics diatoms authigenic mineral assemblages and 17 single crystal 40ar 39ar age determinations assuming that these fluctuations reflect climate changes the lake naivasha record demonstrates that periods of increased humidity in east africa mainly followed maximum equatorial solar radiation in march or september interestingly the most dramatic change in the naivasha basin occurred as early as 146 kyr bp and the highest lake level was recorded at about 139 133 kyr bp this is consistent with other well dated low latitude climate records but does not correspond to peaks in northern hemisphere summer insolation as the trigger for the ice age cycles the naivasha record therefore provides evidence for low latitude forcing of the ice age climate cycles

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

stable carbon isotope variation of n alkanes in central graben oils while isotope analysis of bulk fractions is a well tried and useful tool in oil correlation use of compound specific isotope ratio mass spectrometry cs irms of individual hydrocarbons is still in its infancy this technique has been developed over the past few years as a useful research tool but its potential in petroleum exploration has yet to be demonstrated in this paper both bulk fraction and individual hydrocarbon isotopic data were acquired their use was evaluated and compared with traditional geochemical measurements such as gas chromatography and gc ms data on 72 oils from the norwegian sector of the central graben were acquired data include 13c isotope composition of whole oil and topped oil as well as saturated and aromatic hydrocarbon nso and asphaltene fractions and 13c isotopic composition of individual n alkanes in the range nc4 to nc35 the same samples were also analysed by capillary gc and gc ms gc gc ms and bulk fraction isotope data suggest that many of the analysed greater ekofisk oils e g valhall edlfisk i e within the lindesnes ridge inversion zone have more than one source facies outside of this area particularly towards the northwest oils are probably mainly from a single source facies the isotopic compositions of individual hydrocarbon compounds also reveal the same divisions in addition several further features were observed the normal alkanes of many of the greater ekofisk oils are more depleted in 12c between nc20 nc25 than at higher or lower molecular weight possibly representative of the original microbial precursors other oils have relatively uniform n alkane isotope profiles with n alkanes which are enriched in 12c relative to the n alkanes of oils with the other type of profile the two different isotope profiles are interpreted as being separate source facies the least mature greater ekofisk oils also become more enriched in 12c with decreasing molecular weight mature oils from this area tend to have very similar n alkane isotope values throughout the measured n alkane range the higher maturity oils and condensates have n alkanes nc8 the tentative interpretation of this is that the highly mature oils condensates are sourced only from highly mature source rocks i e of a condensate window maturity and are not products of thermal alteration in the reservoir

abrupt younger dryas cooling in the northern tropics recorded in lake sediments from the venezuelan andes a radiocarbon dated sediment record from laguna de los anteojos a cirque lake in the merida andes of venezuela indicates that warmer and wetter atmospheric conditions occurred in the northern tropics at the onset of the bolling 14 600 cal yr bp and abruptly colder and drier conditions around the time of the younger dryas yd geochemical and clastic sediment analyses from los anteojos show that glaciers advanced at 12 850 cal yr bp reached their yd maximum extent at 12 650 cal yr bp and then retreated until complete deglaciation of the watershed at 11 750 cal yr bp the onset of warmer conditions that ended the coldest phase of the yd occurred several hundred years earlier at los anteojos than in the high latitudes of the northern hemisphere during the peak yd glacial advance glacier equilibrium line altitudes in the region were 360 to 480 m lower and temperature was 2 2 to 2 9 c colder than modern independent palynological evidence from the los anteojos sediment core indicates that the northern andes were more arid and at least 2 3 c colder during the yd the direction and timing of glacial fluctuations in venezuela are consistent with observations of marine sediment records from the cariaco basin that suggest abrupt cooling occurred at 12 850 cal yr bp followed by a shift to higher temperature after 12 300 cal yr bp the timing and pattern of climatic changes in northern south america are also consistent with paleoclimate records from the southern tropical andes that suggest a southward shift in the position of the intertropical convergence zone occurred at the start of the cooling event followed by a return to wetter conditions in northern south america during the late stages of the yd the early warming of the tropical atmosphere and invigoration of the hydrologic cycle likely contributed to the shift to increased temperature in the higher latitudes of the northern hemisphere at the end of the late glacial stage

mineral magnetic analysis of a weathering surface within glacigenic sediments at glanllynnau north wales a number of weathering horizons have been identified within glacigenic sediment sequences in north wales and have been instrumental in determining various proposed late quaternary event chronologies this paper applies the techniques of mineral magnetic analysis to such a sediment sequence at glanllynnau the presence or otherwise of evidence for weathering processes on the upper surface of the criccieth till which is overlain by further glacial materials is examined despite a marked colour variation between the weathered and non weathered components of the criccieth till their mineral magnetic properties suggest little or no variation in iron oxide assemblages the consequences of this for the environmental interpretation of the sediment sequence are discussed

oil oil and oil source rock correlations in the alpine foreland basin of austria insights from biomarker and stable carbon isotope studies abstract the alpine foreland basin is a minor oil and moderate gas province in central europe in the austrian part of the alpine foreland basin oil and minor thermal gas are thought to be predominantly sourced from lower oligocene horizons schoneck and eggerding formations the source rocks are immature where the oil fields are located and enter the oil window at ca 4 km depth beneath the alpine nappes indicating long distance lateral migration most important reservoirs are upper cretaceous and eocene basal sandstones stable carbon isotope and biomarker ratios of oils from different reservoirs indicate compositional trends in w e direction which reflect differences in source depositional environment facies and maturity of potential source rocks thermal maturity parameters from oils of different fields are only in the western part consistent with northward displacement of immature oils by subsequently generated oils in the eastern part of the basin different migration pathways must be assumed the trend in s s r isomerisation of c29 steranes versus the 20r 20r c29 steranes ratio from oil samples can be explained by differences in thermal maturation without involving long distance migration the results argue for hydrocarbon migration through highly permeable carrier beds or open faults rather than relatively short migration distances from the source the lateral distance of oil fields to the position of mature source rocks beneath the alpine nappes in the south suggests minimum migration distances between less than 20 km and more than 50 km biomarker compositions of the oils suggest oligocene shaly to marly successions i e schoeneck dynow and eggerding formations as potential source rocks taking into account their immature character best matches are obtained between the oils and units a b marly shale and c black shale of the normal schoneck formation as well as with the so called oberhofen facies results from open system pyrolysis gas chromatography of potential source rocks indicate slightly higher sulphur content of the resulting pyrolysate from unit b the enhanced dibenzothiophene phenanthrene ratios of oils from the western part of the basin would be consistent with a higher contribution of unit b to hydrocarbon expulsion in this area differences in the relative contribution of sedimentary units to oil generation are inherited from thickness variations of respective units in the overthrusted sediments the observed trend towards lighter 13c values of hydrocarbon fractions from oil fields in a w e direction are consistent with lower 13c values of organic matter in unit c

biomarker geochemistry of a foreland basin the oligocene menilite formation in the flysch carpathians of southeast poland black shales of the menilite formation the source rock for oils in the carpathian overthrust belt display a large variability in their bulk and molecular geochemical parameters biomarker and stable carbon isotope analyses indicate a variable contribution from different algae particularly dinoflagellates and diatoms and cyanobacteria this is reflected by specific predominantly sulfurised biomarkers e g c35 homohopanoids c25 highly branched isoprenoids and marine n alkanes and by particular distributions of steranes and 4 methylsteranes comprising 24 nor and 24 methyl 27 norcholestanes and related novel steranes with a methylation at c 23 the presence of hopanoids of methanotrophic origin 13c up to 57 implies a temporarily enhanced full methane cycle in a marine environment which affected the isotopic composition of organisms dwelling in the upper photic zone the presence of isorenieratene derivatives indicate periods of euxinic conditions within the photic zone in all investigated sub basins

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

past monsoon rainfall variations in peninsular india recorded in a 331 year old speleothem an actively growing stalagmite collected from a cave located in the hills of the western ghats in the uttar kannada district of karnataka india has been studied for stable isotope ratios of oxygen and carbon width of growth layers and grey level changes distinct carbonate layers alternate coarse and compact are seen in cross section each couplet of compact and coarse layer is found to represent a single year a total of 331 such couplets has been counted indicating that the stalagmite started growing in ad 1666 and continued until it was sampled stable isotope ratios of oxygen i 18o and carbon i 13c show variations ranging from 13 6 to 7 9 and from 2 7 to 1 6 respectively we have reconstructed past rainfall changes of the cave site using the amount effect in i 18o of rain speleothem i 18o and instrumental rainfall data from the associated climate subdivision show a significant correlation r 0 62 decadal average several sharp spikes of enrichment and depletion in 18o are indicative of the past deficiency and excess in rainfall most of the severe drought years recorded independently by meteorological observations are found registered in the stalagmite layers during the 331 year period rainfall was highest at ad 1666 and lowest around ad 1900 the stalagmite generated past rainfall record can serve as a reasonable proxy for testing monsoon models

carbazole distributions in carbonate and clastic source rocks abstract carbazole the benzocarbazoles and their alkyl derivatives have been studied from rock extracts to assess the contribution of facies and maturity in controlling their distribution carbonates from the keg river formation elk point group middle devonian western canada consisting of two different facies reflecting deposition under trangressive and regressive events were used to assess facies influences to study maturation a uniform organo facies of organic rich posidonia shale lower toarcian jurassic northern germany from 0 48 to 1 45 r r was used the organic rich lower keg member deposited under photic zone anoxia contained predominantly c 4 c 5 carbazoles by contrast the upper keg river member deposited under regressive higher salinity environment contains predominantly carbazole itself 1 methylcarbazole and a high abundance of benzo c carbazole relative to benzo a carbazole the distribution of the c 1 to c 3 carbazoles was seen to vary with facies an examination of the carbazole derivatives within the posidonia shale reveals that maturation strongly influences the distribution of carbazole methylcarbazoles 1 8 dimethylcarbazole 1 ethylcarbazole benzo a carbazole and benzo c carbazole quantitative determination of these compounds indicates a maximum yield at 0 88 r r for all derivatives with the exception of carbazole which displays as a maximum at 0 53 r r a systematic variation of compound ratios with maturity to 0 88 r r suggests that selective isomerisation destruction generation of carbazole derivatives may occur in contrast to earlier publications which stress the importance of carbazoles as migration markers in migrated oils the results presented here indicate that facies and maturation do play a significant role in controlling the distribution of carbazole derivatives in source rocks and other sediments

sedimentation on the inner shelf of the east china sea magnetic properties diagenesis and paleoclimate implications abstract high resolution magnetic analysis was performed on the 19 22 m core md06 3040 27 43 3663 n 121 46 8822 e 46 m water depth from the east china sea ecs inner continental shelf which was recovered during the images xiv md155 marco polo 2 cruise of the r v marion dufresne ipev magnetic grains are mainly transported to the inner shelf from erosion on mainland china delivered by the yangtze river nine 14 c ams dates indicate that the core spans about the last 10 4 ka with an average sedimentation rate of nearly 2 mm yr the primary magnetic mineral assemblage of the uppermost sediments contains magnetite with some contributions from hematite and greigite two main stepwise changes are observed in the magnetic mineral content due to post depositional reductive diagenesis the first occurs from the top of the core to 3 5 m and is characterized by reduction of both the magnetite and hematite contents the second occurs at 8 45 9 m and is characterized by a loss of fine grained ferrimagnetic material variations in the magnetic mineral content of this core are related to geochemical and redox environment changes in the ecs through the oxic suboxic sulfidic methanic zones from top to bottom despite significant reduction of a large amount of the ferrimagnetic mineral content due to diagenesis intervals characterized by lower magnetic mineral concentrations and higher coercivities are still identified at 0 45 0 6 1 5 1 7 2 9 3 1 4 4 4 7 5 3 5 7 5 9 6 1 and 8 2 8 4 ka these intervals are in phase within dating errors these intervals are in phase with weak summer monsoon events which indicate that a relationship between magnetic results and paleoclimatic events is partially preserved

organic geochemical evidence of postglacial paleoenvironmental evolution of the comeya peatland asturias n spain abstract comeya peatland is located in picos de europa national park n spain at 851 m above sea level representing the continuous postglacial infill of a hollow growth rate 0 4 mm yr during the last 15 000 cal yr bp three intervals can be distinguished in the profile the bottom one with ash content close to 90 which is previous to the peatland installation in the area and is followed by an interval with oscillating ash content 30 60 probably related to alluvial fan sedimentation the uppermost one corresponds to the peat deposit with ash content generally close to 10 the present day vegetation consists of sphagnum species with herbaceous plants and heathers the study comprises the analysis of some biomarkers with potential as palaeoenvironmental proxies quantified by gas chromatography mass spectrometry supported by bulk 13 c and 15 n isotopic the biomarker assemblage is dominated by the n alkanes and methyl ketones with medium to high molecular weight and odd number of carbons the biomarker ratios indicate an enrichment in sphagnum characteristic compounds at 120 250 cm 3150 6350 cal yr bp reflecting more humid conditions this episode coincides with higher c n atomic ratio higher values of 13 c and lower of 15 n the wetter conditions of this interval are also shown by the depleted d values of the n alkane particularly those related with mosses as n c 23 and n c 25 and the enriched 13 c values of both n alkanes and methyl ketones segregation of 13 c values has been observed for homologues series in comeya peat with medium molecular weight n alkanes typical of mosses living in waterlogged environments being enriched in 13 c values compared with higher molecular weight n alkanes typical of woody and herbaceous plants of drier habitats this study has shown a slight enrichment of 13 c values of methyl ketones compared to n alkanes the differences being not conclusive to support a common or different origin for both compound classes

a 1500 year el nino southern oscillation and rainfall history for the isthmus of panama from speleothem calcite received 25 february 2004 revised 28 may 2004 accepted 6 august 2004 published 30 october 2004 1 the effect of the el nino southern oscillation enso on tropical rainfall variations of the past 2 millennia is largely unknown high resolution monsoon records are sparse despite the role of enso in generating global hydrologic anomalies in modern climate to investigate the relationship between enso and the central american monsoon we generated a high resolution 2 9 years sample oxygen isotope monsoon rainfall record from a u th dated stalagmite 180 b c to 1310 a d from the isthmus of panama we present evidence for a weakened monsoon during the high medieval 1100 1200 a d and the classic maya collapse 750 950 a d rainfall decreased and was more variable after 550 a d and the period 900 1310 a d was drier than the preceding millennium a weaker monsoon corresponds with increased el nino variability and our data display statistical variance in the enso band we conclude that enso variation has forced isthmian rainfall and may have contributed to hemispheric climatic anomalies at this time index terms 1040 geochemistry isotopic composition chemistry 1620 global change climate dynamics 3309 1854 hydrology precipitation 3354 3344 meteorology and atmospheric dynamics paleoclimatology 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 keywords paleoclimate el nino southern oscillation speleothem medieval climatic anomaly intertropical convergence zone panama

correlation between hydrogen isotope ratios of lipid biomarkers and sediment maturity abstract we investigated the influence of thermal maturity on the hydrogen isotope ratios of sedimentary hydrocarbons to prove that the isotope ratio of hydrocarbons mirrors paleoclimate signatures d values from n alkanes and acyclic isoprenoids of two sediment sections kupferschiefer ks 258 ma and posidonienschiefer ps 184 ma with different maturation history were investigated both covered thermal maturity from 0 48 to 1 3 rc vitrinite reflectance and reflectance calculated from mpi1 sediment burial up to 4500 m caused thermal maturation of organic matter in the ks horizon from the early zechstein basin of poland whereas contact metamorphic thermal maturation originated in the early toarcian ps posidonienschiefer of the north german vlotho massif the d values of the extracted n alkanes positively correlate with thermal maturity in the ks y 56 mpi1 x 160 vsmow and in the ps y 104 mpi1 x 200 vsmow the d values of isoprenoids i e pristane phytane were even more enriched with increasing maturity y 179 mpi1 x 341 vsmow in the ks y 300 mpi1 x 415 vsmow in ps these results explain why isotope ratios of n alkanes and isoprenoids in mature sediments are generally enriched in d and do not have the expected isotopic difference between n alkanes and isoprenoids of 190 moreover the correlation between sediment maturity parameters and d values suggests that after correction the d values of n alkanes can be used to reconstruct climate and environment in the geological past