are time and temperature the only constraints to the simulation of organic matter maturation abstract confined pyrolysis hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples toarcian shale and kerogen woodford shale and kerogen manakam coal and under different experimental conditions in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter results show that i experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models ii increasing confining pressure 300 1300 bars in gold cell experiments performed on woodford samples has a limited influence on the reduction rate of the oil potential the tsom total soluble organic matter yield and the structure of the polars iii the presence of excess liquid water 0 100 weight in confined pyrolysis experiments does not significantly influence organic matter maturation however comparisons with classic hydrous pyrolysis 200 weight water could indicate major differences in timing and composition of the tsom bitumen expelled fraction as well as of the solid residue it appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined hydrous pyrolysis conditions low partial pressure of products delay woodford kerogen conversion in addition results concerning the mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect iv increasing water pressure in hydrous conditions 220 1300 bars drastically lowers and delays woodford kerogen maturation quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis this study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation

sequence stratigraphy of gulf coast lignite wilcox group paleogene south texas abstract initial sequence stratigraphic analysis indicates that widespread lignite deposits in the paleogene strata of the gulf coast of the united states are found only in highstand systems tracts however not all highstand systems tracts contain widespread lignite bluffs rising above the nueces river in zavala county texas contain parts of two depositional sequences the lower sequence contains lignite and includes sediment of both the midway and wilcox groups paleogene all of the lignite in the lower sequence is in the highstand systems tract the upper sequence lacks lignite and consists entirely of sandstone and shale of the carrizo formation wilcox group high rates of siliciclastic sedimentation probably precluded formation of peat during deposition of the highstand systems tra t of the upper sequence direction and rate of relative change in sea level and other extrabasinal factors seem to have exerted a more fundamental control on the abundance and distribution of lignite in the paleogene strata of the gulf coast region than did factors related to depositional setting of the peat precursor

the expulsinator versus conventional pyrolysis the differences of oil gas generation and expulsion simulation under near natural conditions abstract the expulsinator provides a new technique to simulate generation and expulsion of hydrocarbons under near natural conditions this is realized by application of lithostatic pressure onto an intact source rock disc with undisturbed mineral matrix and kerogen network and by hydrous pyrolysis conducted in open flow through mode conventional pyrolysis methodologies serve well in generation kinetics assessment but are only of limited use for investigation of primary migration and expulsion due to destructive sample preparation inappropriate pressure regimes and pyrolysis in closed mode and or in the absence of water however comparison of results generated with conventional pyrolysis with expulsinator experiments is important to assess the performance of the generation and expulsion simulation carried out with the expulsinator thus the generation and expulsion behaviour of this new methodology has been compared with established pyrolysis methodologies like hypy and closed small vessel pyrolysis csvp and has been assessed by rock eval pyrolysis expulsinator experiments released higher amounts of bitumen than csvp this has been attributed to increased cross linking reactions of bitumen in case of the classic pyrolysis favouring formation of pyrobitumen differences in yields and composition of n alkanes were controlled not by generation kinetics exclusively but also by expulsion effects in particular delayed expulsion caused by geochromatography expulsinator conversion rates of toc exceeded 81 whereas those of hydrous csvp remained at 65 higher expulsinator toc conversion was accompanied by lower gas generation compared to csvp this is attributed to the open setup of the expulsion experiment which by rapid removal of products generated prevents their secondary alteration particularly polymerization to pyrobitumen and oil to gas cracking at higher temperatures hypy of expulsinator pyrolysis residues verified a low generation potential remaining after the expulsion experiment the expulsinator device delivers oil and gas generation data which can be applied in numerical modelling exercises

trace element mobility in dolomitic argillites of the mesoproterozoic belt purcell supergroup western north america the belt purcell supergroup comprises dolomite rich stratigraphic units in a dominantly siliciclastic succession where sedimentation spans 1400 1470 ma dolomitic units are variable mixtures of co sedimented argillite and primary carbonate post depositionally converted to secondary dolomite based on rare earth element ree relationships three distinct ree patterns are identified in the dolomite rich units type 1 t1d d dolomitic sample with ree patterns parallel to post archean upper continental crust pa ucc albeit at lower absolute abundances due to dilution by carbonate content type 2 t2d with heavy ree hree enrichment but light ree lree depletion relative to t1d and type 3 t3d with enrichment in lree and hree relative to t1d but erratic middle ree mree patterns there is a progressive increase of ree from t1d through t2d to t3d whereas for lree hree t2d t1d t3d t1d t2d and t3d represent three different snapshots of a continuous process in terms of timing dolomitization of calcite primary sediment in all samples likely took place broadly during burial diagenesis as inferred for most proterozoic dolomites t1d is easily explained by provenance however t2d and t3d cannot be related to provenance weathering or sedimentary sorting processes to explain higher concentrations of hree referenced to pa ucc and consequently developed in the sediment from a t1d precursor the same three ree signatures have been described in previous studies in counterpart siliciclastic counterparts throughout the belt purcell supergroup at three different locations mobility of normally stable ree is accompanied by mobility of normally isochemical high field strength elements hfse in t2d and t3d to give ree ree hfse hfse ree hfse and y hree fractionations no specific ree hfse signatures are apparent in the carbonate rich units as compared to their non dolomitic siliciclastic counterparts this unusual mobility of ree and hfse reflected in t2d and t3d is attributed to alkaline oxidizing post depositional brines salinity was derived from seawater sediment reactions dissolution of evaporite minerals and the smectite illite transformation whereas alkaline oxidizing conditions were promoted by groundwater interaction with mafic units in the basin co2 introduced into the system during episodic rifting with mantle degassing and interaction of syn sedimentary mafic intrusions with carbonate units at early stages of bps deposition intermittent brine activity inducing t2d and t3d patterns spanned 1 ga as recorded by secondary monazite grains with age distributions that correspond to large scale tectono thermal events in laurentia post depositional processes and redistribution of carbonate can have an impact on transitional stratigraphic contacts between dolomitic and siliciclastic units which may have been incorrectly described as primary due to sedimentary environment changes

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

carbon and hydrogen stable isotope variations in kerogen during laboratory simulated thermal maturation carbon and hydrogen stable isotope measurements on sapropelic and humic kerogen isolated from laboratory heated sediments reveal several isotopic trends an initial depletion of 13c and d 2h or deuterium in kerogen isolated from the heated sapropelic sediment appears to be the result of isotopic heterogeneity interaction with soluble organic matter and or volatilization of a heat labile fraction of the protokerogen during the main isotopic trend the sapropelic kerogen becomes enriched in 13c and d by about 5 and 50 ppt parts per thousand respectively theoretical calculations based on a rayleigh fractionation process suggest that this trend is largely controlled by the generation of isotopically light methane directly from the ker gen this argument also applies to the main hydrogen isotopic trend for the humic kerogen which becomes enriched in d by about 90 ppt the main 13c trend for the humic kerogen however results in a maximum enrichment in 13c of only about 1 6 ppt and appears to be largely controlled by factors other than methane a final depletion trend in 13c and d occurs for the sapropelic kerogen at very high temperatures this may be due to a reduced isotopic fractionation at higher temperatures or to the indirect generation of methane from kerogen through a liquid intermediate which is subsequently coked to pyrobitumen

effect of maturation on the indigenous δd signatures of individual hydrocarbons in sediments and crude oils from the perth basin western australia abstract we measured the stable hydrogen isotopic composition d of selected aliphatic hydrocarbons in nine sediments of various maturity and two crude oils all from the northern perth basin on shore western australia the sediments and crude oils are from the lower triassic hovea member sapropelic interval of the kockatea shale the n alkanes pristane and phytane from two immature sediments have d values that represent the expected isotopic compositions of their precursors phytane is enriched in deuterium d relative to pristane in all sediment extracts and crude oils this is attributed to either different sources or to different isotopic effects during their derivation from phytol with increasing maturity pristane and phytane become enriched in d while the n alkanes generally remain at a constant isotopic composition a more rapid enrichment of d in isoprenoids relative to n alkanes with increasing maturity suggests that hydrogen isotopic exchange is occurring via a carbocation mechanism the phytane diastereomer ratio for each of the sediments correlates linearly with the progressive enrichment of d in phytane and therefore maturity suggesting that significant hydrogen exchange occurs at the chiral carbons of phytane the d values of pristane and phytane from the crude oils are similar or more positive relative to the d values of the n alkanes the average d values of pristane and phytane for the sediments correlate well with equivalent vitrinite reflectance values as does the conventional biomarker maturity parameter t s t m indicating that d values may be useful for establishing maturity over a wider range than conventional biomarker parameters the results provide further evidence that care must be taken not to over interpret d values of sedimentary hydrocarbons in samples of high thermal maturity

provenance analysis using raman spectroscopy of carbonaceous material a case study in the southern alps of new zealand detrital provenance analyses in orogenic settings in which sediments are collected at the outlet of a catchment have become an important tool to estimate how erosion varies in space and time here we present how raman spectroscopy on carbonaceous material rscm can be used for provenance analysis rscm provides an estimate of the peak temperature rscm t experienced during metamorphism we show that we can infer modern erosion patterns in a catchment by combining new measurements on detrital sands with previously acquired bedrock data we focus on the whataroa catchment in the southern alps of new zealand and exploit the metamorphic gradient that runs parallel to the main drainage direction to account for potential sampling biases we also quantify abrasion properties using flume experiments and measure the total organic carbon content in the bedrock that produced the collected sands finally we integrate these parameters into a mass conservative model our results first demonstrate that rscm t can be used for detrital studies second we find that spatial variations in tracer concentration and erosion have a first order control on the rscm t distributions even though our flume experiments reveal that weak lithologies produce substantially more fine particles than do more durable lithologies this result implies that sand specimens are good proxies for mapping spatial variations in erosion when the bedrock concentration of the target mineral is quantified the modeling suggests that highest present day erosion rates in whataroa catchment are not situated at the range front but around 10 km into the mountain belt

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

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

use of hydrogen and carbon stable isotopes characterizing oils from the potiguar basin onshore northeastern brazil hydrogen and carbon isotopic abundances were measured in representative samples of marine evaporitic lacustrine and mixed oils from the onshore potiguar basin the isotopic data together with chemical compositions and geological information were used to investigate relationships among ddoil and d13coil and source thermal maturity biodegradation mixing and the distance of secondary migration of these oils the marine evaporitic oils are depleted in deuterium 135 to 114 and the lacustrine oils are enriched 101 to 88 values of dd for mixed oils are intermediate 113 to 104 between those of marine evaporitic and lacustrine oils showing that ddoil is a reliable tool to identify oils that differ genetically values of ddoil were not directly related to thermal maturation biodegradation or distance of the secondary migration hydrogen isotopic compositions of the oils can be related mainly to the ddwater in the paleoenvironments in which the primary producers lived therefore ddoil values can provide rough estimates of ddwater in the depositional environments of the source rocks and consequently may provide evidence about paleoclimatic conditions at the site marine evaporitic oils are enriched in 13c 26 5 to 25 7 and lacustrine oils are depleted 33 6 to 30 2 in 13c relative contributions of marine evaporitic and lacustrine sources to mixed oils thus can be calculated independently from carbon or hydrogen isotopic mixing models when these calculations are done independently the mixed oils separate into two families and a previously unrecognized component possibly associated with environments that formed during the lacustrine to marine transition is revealed the investigation thus demonstrates the superior resolving power of two element mixing systematics

determination of critical parameters for evaluating coal measure shale gas in china abstract coal measure shale is one of the most abundant types of marine continental shales in china two sets of typical coal measure shales in china are developed in the shanxi formation ordos basin and in the longtan formation guizhou province in this study thermal simulation rock pyrolysis and x ray diffraction experiments were used to analyze four coal measure shale samples collected from typical areas of china based on the study of hydrocarbon generation process of the samples the lower limits of thermal maturity ro of favorable and target areas for coal measure shale were 1 8 and 2 5 respectively the threshold ro value of oil generation in coal measure shale was preliminarily inferred to be 0 6 the gaseous hydrocarbon production per unit of s1 s2 after the gas generation threshold was linearly and positively correlated with ro the lower limits of total organic carbon toc corresponding to the favorable and target areas were 2 45 wt and 2 84 wt respectively combined with x ray diffraction experiments the diagenetic stage and the hydrocarbon generation model of coal measure shale were established and could be divided into four evolutionary stages the results of this study have direct scientific and practical significance for the evaluation of gas content and selection of areas in china for the extraction of coal measure shale

unique chemical and isotopic characteristics and origins of natural gases in the paleozoic marine formations in the sichuan basin sw china isotope fractionation of deep and high mature carbonate reservoir gases abstract large quantities of natural gases have recently been discovered in the marine carbonate formations in the sichuan basin southern china the origins and isotopic compositions of the gases are poorly understood and highly controversial we examined the chemical and isotopic compositions of the carbonate reservoir gases in marine formations from the sinian to lower triassic as well as shale gas from the silurian and cambrian formation in the sichuan basin it is found that the carbon isotopes of the carbonate reservoir gases had been evolved through three stages corresponding to pre rollover rollover and post rollover in the plot of 13c2 versus wetness which is consistent with that found in shale gas by tilley and muehlenbachs 2013 the unique carbon isotopic compositions indicate that both kerogen and oil cracking gas have contributed to the accumulation of the carbonate reservoir gases in the sichuan basin a mixing of two thermogenic gases with different maturities can cause the 13c reversal between methane and ethane which is commonly observed in the carbonate reservoir gases in the carboniferous permian and triassic formations and the shale gas in the silurian and cambrian formations in the sichuan basin we established two mixing models for quantitatively determining the contribution of each type gas for the natural gases in different formations kinetic extrapolation based on thermal history of the anyue gas field demonstrates that ethane cracking indeed occurred in the deep reservoir formations which may explain the disappearance of the 13c reversal for methane and ethane in the carbonate reservoir gases in the post rollover zone it is proposed that organic inorganic interactions may be responsible for the presence of d isotope rollover for methane in carbonate reservoir gases with ultra high maturity the organic inorganic interactions include thermal reactions between water and residual organic matters or carbons and hydrogen isotope exchange between water and methane and their mechanism needs further investigations in future

the geochemistry of late archaean microbial carbonate implications for ocean chemistry and continental erosion history trace element concentrations and combined sr and nd isotope compositions were determined on stromatolitic carbonates microbialites from the 2 52 ga campbellrand carbonate platform south africa shale normalised rare earth element and yttrium patterns of the ancient samples are similar to those of modern seawater in having positive la and y anomalies and in being depleted in light rare earth elements in contrast to modern seawater and microbialite proxies the 2 52 ga samples lack a negative ce anomaly but possess a positive eu anomaly these latter trace element characteristics are interpreted to reflect anoxic deep ocean waters where unlike today hydrothermal fe input was not oxidised and scavenged and rare earth elements were not coprecipitated with fe oxyhydroxides the persistence of a positive eu anomaly in relatively shallow campbellrand platform waters indicates a dramatic reversal from hydrothermally dominated archaean to continental erosion dominated phanerozoic rare earth element flux ratio the dominant hydrothermal input is also expressed in the initial sr and nd isotope ratios there is collinear variation in sr nd systematics which range from primitive values 87sr 86sr of 0 702386 and end of 2 1 to more evolved crustal ratios mixing calculations show that the range in trace element ratios e g y ho and initial isotope ratios is not a result of contamination by trapped sediment but that the chemical and isotopic variation reflects carbonate deposition in an environment where different water masses mixed calculated nd flux ratios yield a hydrothermal input into the 2 52 ga oceans one order of magnitude larger than continental input such a change in flux ratio most likely required substantially reduced continental inputs which could in turn reflect a plate tectonic causation e g reduced topography or expansion of epicontinental seas

survival of graphitized petrogenic organic carbon through multiple erosional cycles abstract graphite forms the endpoint for organic carbon metamorphism it is extremely resilient to physical biological and chemical degradation carbonaceous materials cm contained within sediments collected across taiwan and from the gaoping submarine canyon were analyzed using raman spectroscopy to determine the crystallinity this allowed the erosional and orogenic movements of petrogenic organic carbon ocpetro during the taiwanese orogeny to be deduced after automatically fitting and classifying spectra the distribution of four groups of cm within the sediments provides evidence that many forms of ocpetro have survived at least one previous cycle of erosion transport and burial before forming rocks in the western foothills of the island there is extensive detrital graphite present in rocks that have not experienced high grade metamorphism and graphite flakes are also found in recently deposited marine sediments off taiwan the tectonic and geological history of the island shows that these graphite flakes must have survived at least three episodes of recycling therefore transformation to graphite during burial and orogeny is a mechanism for stabilizing organic carbon over geological time removing biospheric carbon from the active carbon cycle and protecting it from oxidation during future erosion events

a comparison of pyrolysis products with models for natural gas generation abstract hydrous pyrolysis using progressive heating from 150 to 365 c is used to study the generation and isotopic composition of hydrocarbon gases and carbon dioxide different source rocks from the draupne heather dunlin and brent formations in the north sea a miocene brown coal from germany a coal from the middle jurassic ness formation in the northern north sea and a rich marine type source from the late jurassic kimmeridge clay formation onshore uk are studied the experimental results are related to vitrinite reflectance as a maturity reference parameter and to existing models for natural gas generation hydrous pyrolysis simulates the observed isotopic composition of natural systems fairly closely the largest deviations are found for methane which is most sensitive to fractionation effects the obtained results mainly reflect variations in source rock type and initial isotopic composition different maturity dependent trends are found between coal derived and marine type ii derived gases trends in the experimental data fit well with basic assumptions of existing models for natural gas generation

the isotopic structures of geological organic compounds organic compounds are ubiquitous in the earth s surface sediments and many rocks and preserve records of geological geochemical and biological history they are also critical natural resources and major environmental pollutants the naturally occurring stable isotopes of volatile elements d 13 c 15 n 17 18 o 33 34 36 s provide one way of studying the origin evolution and migration of geological organic compounds the study of bulk stable isotope compositions i e averaged across all possible molecular isotopic forms is well established and widely practised but frequently results in non unique interpretations increasingly researchers are reading the organic isotopic record with greater depth and specificity by characterizing stable isotope structures the proportions of site specific and multiply substituted isotopologues that contribute to the total rare isotope inventory of each compound most of the technologies for measuring stable isotope structures of organic molecules have been only recently developed and to date have been applied only in an exploratory way nevertheless recent advances have demonstrated that molecular isotopic structures provide distinctive records of biosynthetic origins conditions and mechanisms of chemical transformation during burial and forensic fingerprints of exceptional specificity this paper provides a review of this young field which is organized to follow the evolution of molecular isotopic structure from biosynthesis through diagenesis catagenesis and metamorphism

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

interactions between tectonics and fluid circulations in an inverted hyper extended basin example of mesozoic carbonate rocks of the western north pyrenean zone chainons bearnais france abstract interactions between fracturing fluid circulations and fluid chemistry in hyper extended margins are still poorly described as most of them are located offshore buried underneath post rift sediments the southern aquitaine basin and the northern pyrenees constitute an appropriate case study to investigate these interactions since a model of hyper extended margin with mantle exhumation during the lower cretaceous subsequently inverted was recently proposed from a field study we here describe three main sets of fractures set 1 to set 3 they are correlated with main stages of the geodynamic evolution of the basin corresponding to the liassic rifting the aptian cenomanian hyper extension and the pyrenean compression petrographic observations raman and micro thermometry analysis on fluid inclusions icp ms and isotope analysis permitted to determine chemistries temperatures redox conditions gas compositions oxygen and carbon isotopic signatures and ree contents of parent fluids for cements precipitated during each episode in particular saddle dolomite and chlorite precipitated in set 2 fractures during the hyper extension corresponding to the thermal peak at temperatures higher than 300 c the isotopic signature the high co2 content the occurrence of h2s and the high salinity of parent fluids suggest ascending magmatic fluids percolating across triassic evaporites the late and post hyper extensional phase is characterized by hydraulic brecciation in dolomitic formations a decrease in temperature and salinity a decrease in magmatic contribution in parent fluids a closing of the diagenetic system during burial and a switch to reducing conditions during the precipitation of quartz pyrite and calcite the pyrenean compressive phase associated with the third fracturing stage induced a reopening of the diagenetic system and favored a return to oxidizing conditions and infiltrations of meteoric fluids

evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis a case study using a brazilian source rock with type i kerogen abstract hydrous pyrolysis hp experiments were used to investigate the petroleum composition and quality of petroleum generated from a brazilian lacustrine source rock containing type i kerogen with increasing thermal maturity the tested sample was of aptian age from the araripe basin ne brazil the temperatures 280 360 c and times 12 132 h employed in the experiments simulated petroleum generation and expulsion i e oil window prior to secondary gas generation from the cracking of oil results show that similar to other oil prone source rocks kerogen initially decomposes in part to a polar rich bitumen which decomposes in part to hydrocarbon rich oil these two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation during bitumen decomposition to oil some of the bitumen is converted to pyrobitumen which results in an increase in the apparent kerogen i e insoluble carbon content with increasing maturation the petroleum composition and its quality i e api gravity gas oil ratio c 15 fractions alkane distribution and sulfur content are affected by thermal maturation within the oil window api gravity c 15 fractions and gas oil ratios generated by hp are similar to those of natural petroleum considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous age api gravity of the hp expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes c 15 fractions i e saturates aromatics resins and asphaltenes show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition gas oil ratios gor initially decrease from 508 131 m 3 m 3 during bitumen generation and remain essentially constant 81 84 m 3 m 3 to the end of oil generation this constancy in gor is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments alkane distributions of the hp expelled oils are similar to those of natural crude oils considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous age isoprenoid and n alkane ratios i e pristane n c 17 and phytane n c 18 decrease with increasing thermal maturity as observed in natural crude oils pristane phytane ratios remain constant with increasing thermal maturity through the oil window with ratios being slightly higher in the expelled oils relative to those in the bitumen generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous with the exception of elevated ethane contents the general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of hp to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality

chemical and isotopic properties of kukersites from iowa and estonia abstract kukersite samples from estonia and iowa were analyzed for elemental composition functional group distribution and carbon and hydrogen stable isotope ratios the elemental and hydrogen isotope values together with other analytical data suggest a higher thermal maturity for the iowa kukersite the wide carbon isotopic range of 9 3 among kukersites with unusually negative 13c values reaching 33 2 indicates isotopically variable carbon sources for production of biomass and thus major paleoceanographic differences between the environments supporting biosynthesis

stable isotope geochemistry of coals humic kerogens and related natural gases isotope systematics are well defined for conventional sapropelic type i ii kerogens and their associated bacterial and thermogenic natural gas products these geochemical tools are used to estimate source type maturity and depositional environment and as a correlation technique in many cases the natural gas signatures in near surface samples and drill cuttings can be used to classify or predict a deeper lying source rock or reservoir corresponding interpretative schemes for coals type iii kerogens and their associated hydrocarbons are progressing quickly the shift in attention to humic sources is driven primarily by depletion of conventional oil and gas resources and the economic and societal requirements of coal and coal bed methane carbon hydrogen and nitrogen stable isotope variations can be large between different coals and humic kerogens these differences can often be recognized in their bulk 13corg dorg and 15norg values isotope signatures of coals can be diagnostic of several factors including deposit age type geographic location maturity and generation history however these characteristic isotopic variations are substantially better defined by the c h and n isotope ratios of the separate maceral groups such as vitrinite exinite and inertinite this new application of stable isotopes at the maceral and compound levels have great potential to improve the interpretative precision over conventional whole coal or bulk techniques hydrocarbon gases including coal gases derived from coals and humic kerogens can be distinguished from type i ii sources based on their molecular rations i e c1 c2 c3 and by comparing their stable isotope compositions especially 13cch4 and dch4 the 13cc2h6 can also be valuable but ethane is generally present in small amount 1 vol and requires

rare earth elements distribution in granulite facies marbles a witness of fluid rock interaction abstract the rare earth element ree distribution of marbles from tranomaro se madagascar shows that the marbles have interacted with syn metamorphic fluids during the panafrican granulite facies metamorphism the tranomaro area is characterized by an extensive development of pyroxenites skarns variably mineralized in uranothorianite and enriched in ree zr across a meter scale marble pyroxenite contact the ree content increases from the most remote marble sample to the contact with the pyroxenite la from 19 8 to 129 ppm ree patterns in enriched marbles display a strong negative eu anomaly similar to those of pyroxenites this peculiar type of ree distribution results from fluid infiltration on a regional scale some marbles have similar ree characteristics progressive development of eu anomaly together with ree enrichment showing that some of them have interacted with fluids infiltration was hardly recognizable using c and o isotopic signatures because large isotopic variations were introduced during the pre granulitic history then ree distribution in high grade marble may be helpful in monitoring syn metamorphic fluid flow in the present case it is a more reliable tracer of fluid infiltration than stable isotopic compositions

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

impact of basin burial and exhumation on jurassic carbonates diagenesis on both sides of a thick clay barrier paris basin ne france several diagenetic models have been proposed for middle and upper jurassic carbonates of the eastern paris basin the paragenetic sequences are compared in both aquifers to propose a diagenetic model for the middle and late jurassic deposits as a whole petrographic optical and cathodoluminescence microscopy structural fracture orientations and geochemical 18o 13c ree studies were conducted to characterize diagenetic cements with a focus on blocky calcite cements and their connection with fracturation events four generations of blocky calcite cal1 cal4 are identified cal1 and cal2 are widespread in the dominantly grain supported facies of the middle jurassic limestones about 90 of the cementation whereas they are limited in the oxfordian because grain supported facies are restricted to certain stratigraphic levels cal1 and cal2 blocky spars precipitated during burial in a reducing environment from mixed marine meteoric waters and or buffered meteoric waters the meteoric waters probably entered aquifers during the late cimmerian jurassic cretaceous boundary and late aptian early cretaceous unconformities the amount of cal2 cement is thought to be linked to the intensity of burial pressure dissolution which in turn was partly controlled by the clay content of the host rocks cal3 and cal4 are associated with telogenetic fracturing phases the succession of cal3 and cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water rock ratios these meteoric fluids circulated along pyrenean oligocene and alpine fractures and generated both dissolution and subsequent cementation in oxfordian vugs in mud supported facies and in poorly stylolitized grainstones however these cements filled only the residual porosity in middle jurassic limestones in addition to fluorine inputs fracturation also permitted inputs of sulphur possibly due to weathering of triassic or purbeckian evaporites or h2s input during paleogene times

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

redistribution of rare earth elements during diagenesis of turbidite hemipelagite mudrock sequences of llandovery age from central wales

behavior of the rare earth elements and other trace elements during interactions between acidic hydrothermal solutions and silicic volcanic rocks southwestern japan abstract rare earth elements and other trace elements in some roseki deposits mostly pyrophyllite and sericite silicastones alunites and related rocks were determined in order to examine behavior of the trace elements in the acidic hydrothermal alteration of silicic volcanic rocks the analyzed concentrations were normalized to the probable unaltered original rock values inferred from the averaged data of some silicic volcanic rocks the trace element characteristics for those materials are as follows 1 most of the elements such as na fe ba and light ree were leached from the silicastones while heavy ree th hf and zr were retained in them 2 alunite samples have light ree enriched and heavy ree depleted features 3 the typical roseki deposits are characterized by middle ree depletions and have v shaped ree patterns on the normalized concentrations vs atomic number diagram such characteristic patterns of the roseki deposits can be explained by superimposition of the light ree enriched and heavy ree enriched materials such as alunite and silica it is important that trace element behaviors are highly selective and some elements e g yb lu hf and zr were strongly retained in the rocks even under strongly acidic hydrothermal processes

distribution of ree in the eastern belt supergroup montana u s a implications for stratigraphic correlations and basin evolution abstract shales of the mid proterozoic newland formation belt basin contain a geochemical marker horizon that is characterized by the appearance of negative eu anomalies in shale ree patterns ree pattern changes appear to be related to changes in weathering intensity and tectonic activity in the hinterland stratigraphic and sedimentologic considerations suggest that this ree marker horizon defines an approximate time line within the sequence comparison of ree patterns of the newland formation and the coarse clastic lahood formation that was deposited to the south shows that the lower portions of the newland formation were deposited prior to lahood sedimentation such a correlation implies that early belt sediments may have covered a much larger area than delineated by the outline of the present day belt basin and that contrary to earlier views of basin evolution the half graben configuration of the eastern belt basin was established at some later point of basin history

experimental controls on d h and 13c 12c ratios of kerogen bitumen and oil during hydrous pyrolysis abstract large isotopic transfers between water derived hydrogen and organic hydrogen occurred during hydrous pyrolysis experiments of immature source rocks in spite of only small changes in organic 13 c 12 c experiments at 330 c over 72 h using chips or powder containing kerogen types i and iii identify the rock water ratio as a main factor affecting d for water and organic hydrogen our data suggest that larger rock permeability and smaller rock grain size increase the h isotopic transfer between water derived hydrogen and thermally maturing organic matter increasing hydrostatic pressure may have a similar effect but the evidence remains inconclusive

stable hydrogen isotopic composition of hydrocarbons in torbanites late carboniferous to late permian deposited under various climatic conditions we measured the stable hydrogen isotopic composition d of selected aliphatic compounds in torbanites from scotland and australia covering the late carboniferous to the late permian the torbanites contain organic matter predominantly from a single algal source botryococcus braunii and are of similar thermal maturity the d values of n alkanes in the extracts appear to reflect the depositional palaeoclimate of each torbanite in response to the typical d values of meteoric waters the d values of n alkanes in torbanites deposited at high latitude under glacial conditions are depleted in deuterium by up to 70 relative to n alkanes in a torbanite deposited at low latitude under a tropical climate regime torbanites deposited in mid latitude regions under cool temperature conditions contain n alkanes with d values between those of n alkanes in tropical and glacial sediments a saw toothed profile of d values obtained for the n alkanes in the australian torbanites is attributed to a dual source system perhaps a predominant b braunii input with a second minor contribution from land plants pristane and phytane from two australian torbanites are significantly depleted in deuterium relative to n alkanes in the same samples and a significant difference between the d values of pristane and phytane is suggested to be caused by different sources for the two isoprenoids or isotope effects associated with their derivation from a common phytol precursor the offset between the d of values of n alkanes and isoprenoids is similar to that found in modern biological samples indicating that their indigenous d signatures may have been preserved for at least 260 280 million years

comparison of generative capacities for bitumen and gas between carboniferous coals from donets basin ukraine and a cretaceous coal from sabinas piedras negras basin mexico during artificial maturation in confined pyrolysis system abstract the goal of this work is to study the ability of two immature carboniferous coals from donets basin ukraine to act as source for oil heating experiments in confined medium were performed to compare the thermal behavior of these coals 1l1 dim r r 0 55 h c at 0 79 and 2c10yd r r 0 65 h c at 0 80 relative to a mature cretaceous coal from sabinas basin olmos r r 0 92 h c at 0 77 macerals analysis carried out on starting materials showed that olmos is exhausted in liptinite contrary to 2c10yd 20 vol and 1l1dim 6 vol the vitrinite content is lower for 2c10yd 59 vol than for olmos 84 vol and 1l1dim 80 vol solid bitumen occurs often dispersed in the raw coals both petrographic and geochemical analyses on starting materials revealed that the selected carboniferous donets coals have better potentialities for bitumen generation than the cretaceous sabinas coal the presence of long chain n alkanes n c 8 in the pyrolysis gc chromatograms indicates that the two raw carboniferous coals from donets basin can yield non volatile hydrocarbons under further thermal maturation it is speculated that some vitrinite macerals present in hydrogen rich carboniferous coals from donets basin can act as source rocks for oil as a matter of fact results showed that the oil window occurs between 1 0 r r and 2 0 r r for both cretaceous sabinas and carboniferous donets coals during confined pyrolysis as expected from geochemical and petrographic analyses of starting samples the carboniferous donets coals yielded more bitumen and hydrocarbons than cretaceous sabinas coal during artificial maturation low proportions of solid bitumen r r and 1 5 r r during confined pyrolysis of coals two solid bitumen groups have been identified which correspond to distinct phases of neo formation the drop in the solid bitumen content at higher ranks indicates that it contributes to generation of gas during experimental simulation moreover their morphology and porosity change with the level of maturity the porosity of the vitrinite matrix increases as well as the pore size with increasing maturity a relationship has been observed between the porosity and the weight loss the higher pore content of carboniferous donets coals is correlated with a higher generation of gas compared to cretaceous sabinas coal

high primary productivity during the ediacaran period revealed by the covariation of paired c isotopic records from south china abstract remarkable carbonate carbon isotope 13ccarb excursions accompanied by invariant organic carbon isotope 13corg values have been observed in many late neoproterozoic successions this decoupled relationship between 13ccarb and 13corg in the precambrian differs from most phanerozoic records which have been substantially imprinted by aqueous photosynthesis and it has been tentatively interpreted as resulting from exotic organic matter inputs or diagenesis in this study we present high resolution 13corg records in combination with previously published 13ccarb data from a continuous drill core from the yangtze platform of south china the studied interval spans the cryogenian nantuo formation the ediacaran doushantuo and dengying formations and the base of the cambrian yanjiahe formation the 13ccarb profile of this drill core can be reliably correlated with contemporaneous sequences and it reveals multiple negative 13ccarb excursions associated with phosphorite deposits intriguingly the 13corg profile exhibits a co varying trend with the 13ccarb profile and the coupled relationship between 13ccarb and 13corg is rare in geological records of the precambrian the 13corg values of the drill core vary from 22 13 to 34 12 and the overall isotopic difference 13ccarb org between 13ccarb and 13corg ranges between 19 61 and 34 58 most of the 13corg and 13ccarb org data can be interpreted in terms of oxygenic photosynthesis probably mainly by eukaryotic algae however it is possible that exotic organic matter most likely doc from the deep ocean may also have contributed to the sedimentary organic matter composition of specific intervals studied herein moreover high primary productivity in shallow water may have been sustained for a long period in phosphate rich conditions and the organic matter generated by photosynthesis may have been quantitatively sufficient to overwhelm the doc buffering effect in the total 13corg signal throughout the ediacaran period the enhanced burial of organic matter in sediments would gradually result in the accumulation of oxygen both in the ocean and atmosphere which would likely have paved the way for macroscopic animal evolution

origin source mixing and thermal maturity of natural gases in the panyu lower uplift and the baiyun depression pearl river mouth basin northern south china sea multiple natural gas fields have been discovered in the baiyun depression and the adjoining panyu lower uplift in the pearl river mouth basin northern south china sea the natural gases are associated with condensate and are characterized by relatively heavy carbon isotopes with methane and ethane 13c values ranging from 44 2 to 33 6 and 30 0 to 25 4 respectively nearly all methane and ethane are derived from oil prone type ii kerogen in the wenchang formation source rock whereas the heavy hydrocarbon gases propane butanes and pentanes are derived from both the wenchang and enping type iii kerogen formations based on an integrated comparison of carbon isotopic compositions of the natural gases typical type i ii and type iii kerogen derived gases and the enping and wenchang kerogens the gases from the eastern parts of the baiyun depression and the panyu lower uplift mainly originate from secondary oil cracking and primary kerogen cracking respectively the gases from the northern slope of the baiyun depression are a mixture of oil cracking and kerogen cracking gases both oil cracking and kerogen cracking gases were mainly generated from the wenchang formation source rock in the maturity range of 1 5 2 5 vitrinite reflectance with a corresponding present day depth range of 5400 6500 m 17 700 21 300 ft the apparent contribution of the wenchang formation to the discovered gas accumulations demonstrates that it is the most important source rock in the area instead of the enping formation the search for more gas derived from oil cracking will be the next natural gas exploration direction in the baiyun depression

water solubility and d h fractionation in the system basaltic andesite h2o at 1250 c and between 0 5 and 3 kbars abstract water solubilities in melt of basaltic andesite composition have been measured in the range 500 to 3000 bars 1200 1250 c the saturation curve obey an empirical relationship very close to the square root of pressure law of hamilton et al hamilton d l burnham c w osborn e f 1964 the solubility of water and effects of oxygen fugacity and water content on crystallisation in mafic magmas j petrol 5 21 39 the best fit is obtained by a power law h 2 o wt ap n p in b where a 0 05 0 01 and n 0 63 the departure from n 0 5 is mainly due to the increasing importance of dissolved molecular water at high pressures hydrogen isotopic fractionation between water vapor and total water dissolved in the melt d v m has been measured at 0 5 2 and 3 kb d v m decreases with pressure from 32 to 20 2 this variation is related to the increase in molecular water proportions relative to hydroxyl group when water solubility increases the variation of the d h ratios in water dissolved in such melts thus appears as a possible indirect measurement of the original oh h 2 o ratio of total dissolved water not subject to variation during quenching as the later is this correlation shows that the d v m isotopic fractionation at very high water vapor pressure tend toward a limit of 16 3 for basic magmas

gas accumulations in oligocene miocene reservoirs in the alpine foreland basin austria evidence for gas mixing and gas degradation two petroleum systems are present in the eastern austrian sector of the alpine foreland basin whereas oil and thermogenic gas in mesozoic and eocene reservoir rocks have been generated beneath the alps in lower oligocene source rocks relative dry gas in oligocene miocene clastic rocks deposited in the deep marine basin axial channel system puchkirchen channel is interpreted as microbial in origin detailed investigations of the molecular and isotope composition of 87 gas samples from 86 wells representing all producing fields with oligocene and miocene reservoir rocks suggest that the presence of pure microbial gas is rare and limited mainly to the northern basin flank e g kk field all other fields contain varying amounts of thermogenic gas which has been generated from a source rock with oil window maturity a relation with the underlying thermogenic petroleum system is obvious upward migration occurred along discrete fault zones e g h field or through low permeability caprocks local erosion of lower oligocene sediments the principal seal for the thermogenic petroleum system as well as a high percentage of permeable rocks within the puchkirchen channel favored upward migration and mixing of thermogenic and microbial gas all gas samples in oligocene miocene reservoirs are biodegraded biodegradation and the formation of secondary microbial gas resulted in gas drying therefore the gas samples analyzed in this study are relative dry despite significant contributions of thermogenic hydrocarbons biodegradation probably continues at present time the degree of biodegradation however decreases with depth

redistribution of rare earth elements during diagenesis of carbonate rocks from the mid proterozoic newland formation montana u s a abstract ree data for carbonate rocks from the mid proterozoic newland formation belt supergroup show variable degrees of relative ree enrichment when normalized to a composite shale of the newland formation most conspicuous are relative enrichments in lree s and positive eu anomalies possible coprecipitation of ree s in carbonates from seawater is much too small to account for the ree enrichment thus only diagenetic ree enrichment has to be considered by far the strongest lree enrichment is observed in carbonates with interbedded shales during diagenesis ree apparently moved from the shale partings to the adjacent limestone beds massive limestone units have considerably smaller ree enrichments except in proximity to shales suggesting that ree addition from formation waters is less efficient for supplying ree s than is local redistribution between shale and limestone beds early precipitation of diagenetic silica in pore spaces reduces ree enrichment in limestone beds by reducing their permeability dolostones are cemented by pervasive early diagenetic silica and lack significant ree enrichment except for eu probably because silica cement prohibited access of ree bearing pore waters positive eu anomalies indicate reduction of eu to the divalent state during diagenesis and relatively large mobility of divalent eu

rare earth element and yttrium rey geochemistry in carbonate reservoirs during deep burial diagenesis implications for rey mobility during thermochemical sulfate reduction abstract the impact of burial diagenesis especially deep burial related processes such as thermochemical sulfate reduction tsr on the distribution of rare earth elements and yttrium rey in diagenetic minerals in carbonate reservoir has gained little attention even though they may be unique indicators of the diagenetic system being closed or open to external influx of material trace element and rey concentrations 87 sr 86 sr 18 o and 13 c have been determined for limestone host dolomite pore filling calcite calcite 2 and late stage fracture filling calcite calcite 3 barite barite 2 and anhydrite anhydrite 3 from lower triassic feixianguan formation reservoirs in northeast sichuan basin china calcite 2 calcite 3 barite 2 and anhydrite 3 precipitated during deep burial from 110 c to 220 c demonstrated by petrology and fluid inclusion thermometry sr isotope analysis revealed that diagenetic carbonate minerals and anhydrite have largely identical 87 sr 86 sr ratios to triassic seawater indicating negligible input of sr from terrigenous sources and probably a relatively closed diagenetic environment for precipitation of these minerals carbon isotope analysis showed that calcite 2 has relatively low 13 c values down to 18 9 v pdb suggesting that they are tsr calcites with the carbonate derived from oxidized isotopically light hydrocarbons unlike the seawater like rey patterns of the limestone and dolomites calcite 3 and anhydrite 3 are enriched in rare earth elements ree and show light rare earth element enrichment and heavy rare earth element depletion exhibiting a chevron like pattern of shale normalized rey trends in contrast tsr calcite calcite 2 has similar ree to the host dolomite but a relatively flat rey sn pattern suggesting strong variations in elemental and ree compositions of the burial fluids significantly tsr calcite shows a prominent positive eu anomaly and an unusually high chondritic y ho ratio both yttrium versus holmium fractionation and eu 2 oxidation to eu 3 must have occurred during thermochemical sulfate reduction hence a positive eu anomaly and an elevated y ho ratio may be used as effective proxies to differentiate calcite resulting from tsr from ordinary calcite cement this is especially useful when carbon isotope analysis cannot be used to give an unambiguous interpretation of the origin of the calcite

sources of natural gases in middle cambrian reservoirs in polish and lithuanian baltic basin as determined by stable isotopes and hydrous pyrolysis of lower palaeozoic source rocks abstract origin of natural gases associated with oil and condensate accumulations within the middle cambrian sandstone reservoir of the polish and lithuanian baltic basin was characterised by means of molecular composition stable carbon isotopes of methane ethane propane butanes pentanes and carbon dioxide stable hydrogen isotopes of methane and stable nitrogen isotopes of gaseous nitrogen generated gas from potential upper cambrian tremadocian and llandovery source rocks by hydrous pyrolysis at 330 c and 355 c for 72 h was used to characterise thermogenic gas to evaluate correlation parameters based on molecular composition and stable isotopes the pyrolysis conditions represent gas generation during oil generation which appears to be the conditions represented by the natural gas accumulations and their low gors gas oil ratios the dryness of the pyrolysis and natural hydrocarbon compositions compare well but do not provide a means of distinguishing the contributions of each source rock to the natural gas accumulations the average 13 c value of the natural methane is 6 9 depleted in 13 c compared to methane generated in the hydrous pyrolysis experiments this difference is less for ethane and essentially nonexistent for propane butanes and pentanes tentatively this diminishing difference with increasing carbon number is attributed to kinetic effects resulting from higher experimental temperatures although the 13 c values of methane and ethane from the hydrous pyrolysis experiments are not useful in direct correlations with natural gas accumulations 13 c of propane butanes and pentanes is useful and indicates that the upper cambrian and tremadocian source rocks are the main contributors and that the llandovery source rocks are not significant contributors to the polish and lithuanian baltic natural gases polish natural gases with relatively higher methane and ethane are attributed to the mixing of drier more mature gases from deeper parts of the basin to the west carbon dioxide of natural gases was generated during thermogenic processes and gaseous nitrogen was generated from nh 4 rich illites of the clayey facies and from thermal transformation of organic matter of the lower palaeozoic strata hydrous pyrolysis gases have higher concentrations of co 2 h 2 s and h 2 than the natural gases this difference is attributed to reduction or loss of these highly reactive and soluble gases during migration and entrapment of the natural gases although co 2 concentrations between pyrolysis and natural gases are different the 13 c values of the former fall within the range of the latter

the petroleum generation potential and effective oil window of humic coals related to coal composition and age abstract a worldwide data set of more than 500 humic coals from the major coal forming geological periods has been used to analyse the evolution in the remaining hydrogen index hi and total quality index qi generation potentials with increasing thermal maturity and the effective oil window oil expulsion window all samples describe hi and qi bands that are broad at low maturities and that gradually narrow with increasing maturity the oil generation potential is completely exhausted at a vitrinite reflectance of 2 0 2 2 ro or tmax of 500 510 c the initial large variation in the generation potential is related to the original depositional conditions particularly the degree of marine influence and the formation of hydrogen enriched vitrinite as suggested by increased sulphur and hydrogen contents during initial thermal maturation the hi increases to a maximum value himax similarly qi increases to a maximum value qimax this increase in hi and qi is related to the formation of an additional generation potential in the coal structure the decline in qi with further maturation is indicating onset of initial oil expulsion which precedes efficient expulsion liquid petroleum generation from humic coals is thus a complex three phase process i onset of petroleum generation ii petroleum build up in the coal and iii initial oil expulsion followed by efficient oil expulsion corresponding to the effective oil window efficient oil expulsion is indicated by a decline in the bitumen index bi when plotted against vitrinite reflectance or tmax this means that in humic coals the vitrinite reflectance or tmax values at which onset of petroleum generation occurs cannot be used to establish the start of the effective oil window the start of the effective oil window occurs within the vitrinite reflectance range 0 85 1 05 ro or tmax range 440 455 c and the oil window extends to 1 5 2 0 ro or 470 510 c for general use an effective oil window is proposed to occur from 0 85 to 1 7 ro or from 440 to 490 c specific ranges for himax and the effective oil window can be defined for cenozoic jurassic permian and carboniferous coals cenozoic coals reach the highest himax values 220 370 mg hc g toc and for the most oil prone cenozoic coals the effective oil window may possibly range from 0 65 to 2 0 ro or 430 to 510 c in contrast the most oil prone jurassic permian and carboniferous coals reach the expulsion threshold at a vitrinite reflectance of 0 85 0 9 ro or tmax of 440 445 c

origin and history of waters associated with coalbed methane 129i 36cl and stable isotope results from the fruitland formation co and nm abstract the fruitland formation of the san juan basin was deposited during the late cretaceous and is associated with significant reservoirs of coalbed methane cbm the purpose of this study is to determine the origin and history of waters associated with the formation using long lived cosmogenic and stable isotope systems ratios of 129 i i and stable isotope values d and 18 o were determined in waters from close to 100 wells 36 cl cl ratios for a subset of these samples a significant group of samples has 129 i i ratios between 100 10 15 and 200 10 15 indicating minimum iodine ages close to 60 ma if these ages are corrected for the addition of fissiogenic 129 i they are compatible with the depositional age of the fruitland formation late cretaceous several sets of waters are clearly present within the data a group dominated by infiltration of recent surface waters is restricted to the uplifted basin margins with a lateral extent of less than 5 km from outcrop and is characterized by 129 i i ratios in excess of 1500 10 15 and meteoric d 18 o and 36 cl cl signatures the rest of the basin is characterized by several subsets of formation waters which have undergone variable degrees of iodine enrichment through diagenesis as well as variable degrees of dilution the first subgroup is found in coals of relatively low vitrinite reflectance and moderate enrichment of iodine this subgroup predominantly consists of entrapped pore fluids although it may also contain waters which infiltrated the coals at the time of the laramide uplift between 25 and 30 ma a second subgroup consists of formation waters associated with coals of high vitrinite reflectance despite subsequent uplift the high iodine concentrations and low 129 i i ratios of this subgroup as well as a moderate depletion of deuterium relative to 18 o suggest that these waters were not significantly altered since the time when diagenetic reactions occurred in the deepest portion of the basin a third subgroup with higher d and 18 o values as well as higher 129 i i ratios extends roughly west to east at the new mexico colorado state line and corresponds to a region of extensive fracturing of the coalbeds in this case the higher 129 i i ratios are probably due to contributions of fissiogenic 129 i through fracture flow perhaps from deeper formation waters our results do not support models of subsequent basin wide groundwater migration in the fruitland formation the combined use of 129 i and 36 cl with stable isotope studies provides valuable information as to the hydrologic history of coalbed methane deposits as well as their potential for commercial exploitation

abnormal carbon and hydrogen isotopes of alkane gases from the qingshen gas field songliao basin china suggesting abiogenic alkanes abstract it is great debate that the alkane gases of abiogenic origin would constitute a major portion of the commercial accumulation of the qingshen gas field songliao basin china in this study abiogenic gases characterized by heavy 13c1 values reversal of the usual carbon isotopic trend of c1 c5 alkanes very narrow variation in 2hc1 values and low ch4 3he ratios associated with high r ra values 1 were identified the hydrocarbon gas in the qingshen gas field is a mixture of thermogenic alkanes derived from cretaceous mudstone type i kerogen or jurassic coal type iii kerogen and abiogenic alkanes mainly ch4 from mantle degassing a quantitative estimation of abiogenic alkanes contribution to the qingshen gas field is made based on a 13c1 vs 13c2 plot about 30 40 of alkane gases in the qingshen gas field along with its helium are estimated to be derived from the mantle via magmatic activity particularly the abiogenic formation of ch4 generated from the reduction of co2 by hydrothermal activity may contribute our study suggests that abiogenic alkane gases in certain geological settings could be more widespread than previously thought and may accumulate into economic reservoirs

ree and their relevance to the development of the kupferschiefer copper deposit in poland abstract over one hundred samples representing mainly clayey organic and carbonate rich shales kupferschiefer but also other members of different ore sections including hangingwall dolomites z1 werra and footwall weissliegend sandstone lower permian have been collected in different mines of the lubin glogow mining district mainly near the contact transitional zone between the copper mineralized zone and secondarily oxidized rote faule rf zone in general the polish kupferschiefer shales are enriched in mree in comparison to nasc in a typical copper rich ore section the ree amounts and patterns depend on lithologies being generally similar in shales and dolomite ree vary among sandstones shales and dolomites average 73 143 and 85 ppm respectively probably reflecting mainly their clay contents sandstones have strongly convex ree patterns with positive eu and negative gd anomalies and depletion in lree and enrichment in mree relative to hree the ree patterns of shale and dolomite are similar to one another and rather flat with strong negative eu anomalies and a small positive gd anomaly in the case of shales the ree patterns of shales from the mineralized cu zone are generally convex mree enriched and have negative eu anomalies however in a section with cu zn and pb shales the ree pattern of pb bearing shales shows a positive eu anomaly in contrast to other shales and overlying dolomite more oxidizing conditions of deposition can be assumed for pb shales no significant differences between ree distributions in transitional and oxidized zones have been observed their ree patterns are more convex and are much higher av 247 ppm than those in the mineralized zone and they do not show eu anomalies the strongly convex pattern may suggest either enrichment in mree or relative depletion in lree due to localized precipitation of light ree minerals both in shales and in the uppermost part of the sandstones two unique sections one cu rich and one cu lean partly oxidized comprising three shale beds interbedded with dolomites have been compared generally ree contents are similar in these two sections also similar are changes in contents of ree between beds in both sections which decrease significantly upwards from 157 171 ppm to 54 60 ppm the ree patterns of the lowermost beds directly overlying sandstones are ramp like with lree enrichments the upper beds have concave ree patterns comparison between sections shows generally stronger negative eu and positive gd anomalies in the highly mineralized section there is a highly significant positive relationship between cu and ree contents in cu rich shales and slightly less significant negative relationship for their concentration in oxidized and transitional shales there is a moderate significant positive correlation between p 2 o 5 and ree contents in cu rich shales the observed differences in ree contents cannot be provenance dependent but have been caused by diagenetic processes possibly related to mineralization and oxidation processes europium anomalies generally reflecting different eh conditions in the deposit can be eliminated by the prolonged oxidation strong enrichment of the rf zones in ree may result from their desorption from large volumes of oxidizing including mineralizing solutions which probably emerged from the underlying molasse lithologies into the rote faule areas higher contents of ree in the lowermost shales suggest upward movement of solutions from the underlying sandstones also far away from the rf areas

significance of δdkerogen δ13ckerogen and δ34spyrite from several permian triassic p tr sections for the first time we report d of kerogen dkerogen for three permian triassic p tr sequences hovea 3 perth basin western australia jameson land east greenland and lusitaniadalen spitsbergen we have compared dkerogen with 13c of kerogen 13ckerogen and 34s of total reduced inorganic sulfur tris essentially pyrite 34spyrite of all the sections and for one sample set with 13c of carbonate 13ccarbonate to establish i similarities between the sections and ii evaluate whether these signals are local and or global stable isotope shifts occur for all three sample sets either at the p tr transition western australia or coinciding with the marine ecosystem collapse spitsbergen and east greenland dkerogen reflects organic matter om kerogen type and is not sensitive to the low level of thermal maturation reliable palaeoenvironmental information in terms of the use of d can therefore only be obtained for the p tr transition from hydrogen compound specific isotope analyses csia of biomarkers nabbefeld et al 2010b the negative shifts in 13ccarbonate primary and 13ckerogen are attributed to the release of 13c depleted carbon into the atmosphere whereas the isotopic excursions in 34spyrite relate to palaeoredox changes however the global coincidence in timing of the shifts in dkerogen 34spyrite and 13ckerogen suggests a relation between the sulfur carbon and hydrogen cycles the negative shifts in 13ccarbonate primary are in general attributed to the release of 13c depleted source of carbon into the oceans and atmosphere whereas 13ckerogen can reflect the latter in certain cases but can also be superimposed by varying sources of om kerogen type isotopic excursions in 34spyrite relate to global changes in the palaeoredox conditions that affect sulfur cycling in the ancient seas

a combined petrographical geochemical provenance study of the newland formation mid proterozoic of montana a provenance study was conducted on the mid proterozoic newland formation in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation sandstones of the newland formation are typically arkosic sands and arkoses with very well rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments the predominant feldspar types are k spar and microcline feldspar grains are smaller than quartz grains and feldspars show little alteration due to weathering detrital modes of newland sandstones qfl diagrams indicate that they were derived from a stable cratonic source these petrographical features imply a source area dominated by granites and granitoid gneisses semi arid to arid climate tectonic quiescence and overall peneplain conditions shales of the newland formation are dominated by illite quartz silt and fine crystalline dolomite they have small la th rations relatively large hf contents and small contents of cr co and ni all indicative of derivation from crust of granitic composition small tio 2 al 2 o 3 ratios also suggest source rocks of granitic composition the average chemical index of alteration cia for newland shales is 71 8 which in light of the probable granitoid source indicates modest amounts of chemical weathering relatively large sio 2 contents and large k 2 o na 2 o ratios reflect derivation from stable cratonic areas and tectonic quiescence thus in general the petrography of sandstones and geochemistry of shales provides the same provenance clues for the newland formation one notable discrepancy between the two approaches is that the sandstones indicate an arid to semi arid climate with very minor chemical weathering whereas the cia of the shales indicates at least modest amounts of chemical weathering this indicates on one hand the need to better calibrate the cia with a large variety of muds from modern climatic settings and on the other hand the possibility that this discrepancy is due to transport segregation

the isotopic composition of particulate organic carbon in mountain rivers of taiwan small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon poc to the oceans this input has implications for the geochemical stratigraphic record we have investigated the stable isotopic composition of poc 13corg in rivers draining the mountains of taiwan in 15 rivers the suspended load has a mean 13corg that ranges from 28 1 0 8 to 22 0 0 2 on average 37 samples per river over the interval of our study to investigate this variability we have supplemented suspended load data with measurements of poc in bedrock and river bed materials and constraints on the composition of the terrestrial biomass fossil poc in bedrock has a range in 13corg from 25 4 1 5 to 19 7 2 3 between the major geological formations using coupled 13corg and n c we have found evidence in the suspended load for mixing of fossil poc with non fossil poc from the biosphere in two rivers outside the taiwan central range anthropogenic land use appears to influence 13corg resulting in more variable and lower values than elsewhere in all other catchments we have found that 5 variability in 13corg is not controlled by the variable composition of the biomass but instead by heterogeneous fossil poc in order to quantify the fraction of suspended load poc derived from non fossil sources fnf as well as the isotopic composition of fossil poc 13cfossil carried by rivers we adapt an end member mixing model river suspended sediments and bed sediments indicate that mixing of fossil poc results in a negative trend between n c and 13corg that is distinct from the addition of non fossil poc collapsing multiple fossil poc end members onto a single mixing trend as an independent test of the model fnf reproduces the fraction modern fmod in our samples determined from 14c measurements to within 0 09 at the 95 confidence level over the sampling period the mean fnf of suspended load poc was low 0 29 0 02 n 459 in agreement with observations from other mountain rivers where physical erosion rates are high and fossil poc enters river channels the mean 13cfossil in suspended poc varied between 25 2 0 5 and 20 2 0 6 from catchment to catchment this variability is primarily controlled by the distribution of the major geological formations it also covers entirely the range of 13corg found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous poc if land sourced poc is preserved in marine sediments then changes in the bulk 13corg observed offshore taiwan could instead be explained by changes in the onshore provenance of sediment the range in 13corg of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans care should be taken in accounting for fossil poc in marine deposits supplied by active mountain belts

organic and inorganic geochemistry of ljubija siderite deposits nw bosnia and herzegovina the ljubija siderite deposits hosted by a carboniferous sedimentary complex within the inner dinarides occur as stratabound replacement type ore bodies in limestone blocks and as siderite sulfides veins in shale three principal types of ore textures have been recognized including massive dark siderite and ankerite siderite with zebra texture and siderite veins the ore and host rocks have been investigated by a combination of inorganic major trace and rare earth element concen trations organic characterization of hydrocarbons includ ing biomarkers and stable isotope geochemical methods isotope ratios of carbonates sulfides sulfates kerogen and individual hydrocarbons new results indicate a marine origin of the host carbonates and a hydrothermal metasomatic origin of the fe mineralization the differ ences in ore textures e g massive siderite zebra siderite are attributed to physicochemical variations e g changes in acidity temperature and or salinity of the mineralizing fluids and to the succession and intensity of replacement of host limestone vein siderite was formed by precipitation from hydrothermal fluids in the late stage of mineralization the equilibrium fractionation of stable isotopes reveals higher formation temperatures for zebra siderites around 245 c then for siderite vein around 185 c sulfur isotope ratios suggest permian seawater or permian evaporites as the main sulfur source fluid inclusion composition confirms a contribution of the permian seawater to the mineralizing fluids and accord with a permian mineralization age organic geochemistry data reflect mixing of hydrocarbons at the ore site and support the hydrothermal metasomatic origin of the ljubija iron deposits

an organic geochemical perspective on terrestrialization the colonization of land required new strategies for safe gamete diaspore dispersal and to cope with desiccation harmful radiation fire and gravity accordingly the morphology behaviour and physiology of the organisms changed here we explore to what extent physiological adaptations reflected in the molecular content of the sediments add to our understanding of the terrestrialization many compounds considered characteristic of land organisms do not provide valuable information from the fossil record since 1 they were not preserved 2 they occur or correspond to substances that evolved prior to the terrestrialization e g cutan vs algaenan cellulose or 3 they have been changed diagenetically and or catagenetically the latter leads to geo macro molecules without a chemical fingerprint relating them to their original bio macro molecules despite sometimes excellent morphological preservation of the organic remains nevertheless some molecular markers and their stable isotopes provide independent information on the terrestrialization process the odd predominance of n alkane surface waxes is a feature already apparent in early land plants and could with caution be used as such furthermore fossil terpenoids and their derivatives are valuable for reconstructing the evolution of major plant groups the radiation of the phenylpropanoid pathway with for example sporopollenin and lignin seems to be closely related to the evolution of land plants as for other disciplines occupied with unravelling past life and environment organic geochemistry relies heavily on the paradigm that the present provides a key to the past for organic geochemistry the biosynthetic pathways of living organisms provide such a key the biosynthetic differences between organisms provide insight into the evolution of biosynthetic pathways and this can be applied to and calibrated against the fossil record evolution also implies adaptation and by linking species ecology to their biochemistry the adaptive value of the biosynthetic pathways and the biomolecules produced may be resolved this biosynthetic link to environment can also be applied to the past for instance the notion that oxygen is required in steroid and non hopanoid triterpenoid synthesis implies that analysis of steroids in ancient sediments may help to unravel the early evolution of the atmosphere summons et al 2006 analogous to the oxygenation of the earth s atmosphere terrestrialization also required major adaptations of the terrestrializing organisms to the living conditions on land the conquest of land required the development or strengthening of supportive structures such as skeletons stems and roots to withstand earth s gravity without the support of water and to resist wind it also demanded water saving strategies such as arthropod and plant cuticles vertebrate skin and cork to survive low humidity environments and sometimes fire as well as the development of water conducting tissues in plants roots tracheids finally the higher exposure to harmful radiation required sunscreens such as pigments aromatic and other substances as uv filters whereas the endoand exoskeletal adaptations are intrinsically based on the formation of large biopolymers water saving and uv protection may be also realized by means of smaller molecules our working hypothesis is that the major changes in biosynthetic pathways which accompanied the terrestrialization of organisms are reflected in the molecular composition of the organic matter present in palaeozoic sedimentary rocks for instance a minor change in the biosynthesis of sporopollenin may have led to lignin in return we can expect the changes in composition of the organic matter om in palaeozoic rocks to help determine following evolutionary trends the question being asked is to what extent is our working hypothesis valid and what does this provide us with to understand terrestrialization we restrict ourselves to primary producers and arthropods since they have a rich fossil record both organic geochemically and as microand macroscopic remains we exclude other terrestrial heterotrophic life forms worms snails vertebrates etc since they do not usually leave a chemically characteristic signature in the sediments from vecoli m clement g meyer berthaud b eds the terrestrialization process modelling complex interactions at the biosphere geosphere interface geological society london special publications 339 11 36 doi 10 1144 sp339 3 0305 8719 10 15 00 the geological society of london 2010 organic matter analysis lipids and

from the highest to the deepest the gaoping river gaoping submarine canyon dispersal system abstract there are many different source to sink dispersal systems around the world and the gaoping river gpr gaoping submarine canyon gpsc provides an example especially as a canyon captured system the gpr a small mountainous river having an average gradient of 1 150 and the gpsc which links the river catchment to the deep sea basin represent two major topographic features around sw taiwan together they constitute a terrestrial to marine dispersal system that has an overriding impact on the source to sink transport of sediment in this region the gpsc extents from the mouth of the gpr through the shelf and slope and into the northeastern manila trench a distance of about 260 km it is a major conduit for the transport of terrestrial sediment and carbon to the south china sea and the landward transport of particles of marine and biological origin in the gpsc the dominant mode of suspended sediment transport is tidal oscillations and the net direction is up canyon in contrast sediment transport associated with episodic gravity driven events is down canyon the steady sedimentation of the tidal regime results in hemipelagic mud across the canyon floor whereas the gravity driven hyperpycnal regime causes turbidite erosion and deposition along the canyon thalweg typhoon induced river floods often lead to hyperpycnal plumes at the river mouth which directly and indirectly ignite hyperpycnal turbidity currents in the canyon forming an effective agent for transporting large amounts of terrestrial organic material modern and fossil carbon to the south china sea basin therefore the gpr gpsc represents a source to sink system in which terrestrial sediment in a mountainous catchment is promptly removed and transported to the deep sea by episodic gravity flows this is also a pathway by which modern terrestrial organic carbon is quickly and effectively delivered to the deep sea

anomalous iron distribution in shales as a manifestation of non clastic iron supply to sedimentary basins relevance for pyritic shales base metal mineralization and oolitic ironstone deposits in previous investigations nearshore pyritic shale horizons in the mid proterozoic newland formation were interpreted to be due to non clastic colloidal iron supply by streams new data on the chemical composition of shales in the newland formation support this interpretation in these shales fe and al show a positively correlated trend that intercepts the fe axis above the origin these relationships suggest control of fe by clays via iron oxide coatings on clay minerals and the presence of an additional non clastic iron component shales from stratigraphic intervals during which pyritic shale horizons were deposited plot above the fe al trend typical for the remainder of the newland formation

influence of maceral composition on geochemical characteristics of immature shale kerogen insight from density fraction analysis abstract variations in the relative proportions of individual macerals in shales can significantly influence the geochemical characteristics of bulk organic matter density fractions of kerogen from the thermally immature new albany shale devonian and mississippian with contrasting maceral compositions exhibit strong geochemical differences the parental shale is characterized by a vitrinite reflectance ro of 0 45 a total organic carbon content of 13 wt and a sulfur content of 6 2 wt organic matter is dominated by amorphinite and alginite with vitrinite and inertinite accounting only for 1 by volume alginite dominated density fractions density ca 1 0 1 15 g cm3 contain significantly more aliphatic hydrogen a stronger carboxyl carbonyl contribution and reduced fourier transform infrared spectroscopy absorbance in the 1000 to 1100 cm 1 region assigned to ether bonds c o c as compared to the amorphinite dominated density fraction density ca 1 2 1 6 g cm3 aromaticity generally increases from alginite dominated to amorphinite dominated fractions density fractions dominated by amorphinite are more deuterium depleted dn values of nonexchangeable hydrogen up to 105 than alginite rich density fraction dn values reach 90 in contrast changes in relative proportions of alginite and amorphinite in the new albany shale do not significantly affect the amount of isotopically exchangeable hydrogen in total hydrogen i e hydrogen exchangeability alginite is relatively 13c enriched whereas density fractions having a high content of amorphinite are relatively 13c depleted our results suggest that even small bulk geochemical and isotopic differences can gain relevance after deconvolution from maceral related variability the masking influence of maceral abundance patterns must be considered when interpreting bulk geochemical data as paleoenvironmental proxies the findings of this study on shale and type ii kerogen are relevant for all types of kerogens in sediments and rocks

isotopically exchangeable organic hydrogen in coal relates to thermal maturity and maceral composition hydrogen isotopic exchangeability hex and dn values of non exchangeable organic hydrogen were investigated in coal kerogens ranging in rank from lignite to graphite the relative abundance of hex is highest in lignite with about 18 of total hydrogen being exchangeable and decreases to around 2 5 in coals with ro of 1 7 to ca 5 7 at still higher rank ro 6 hex increases slightly although the abundance of total hydrogen decreases dn is influenced by original biochemical d h ratios and by thermal maturation in contact with water therefore dn does not show an overall consistent trend with maturity

meganodular limestone of the pagoda formation a time specific carbonate facies in the upper ordovician of south china abstract the decimeter scale 3 d network structure of the upper ordovician pagoda formation in south china has been an enigmatic sedimentary feature and a case of non uniformitarian carbonate depositional system without modern analog the network bands are developed pervasively throughout the entire pagoda formation superficially resembling desiccation or syneresis cracks especially in bedding plane view with decimeter scale sub polygonal to irregularly sinuous patterns detailed petrographic analysis however shows that the crack like network bands have the same carbonate matrix skeletal grains and overall fabrics as the rock they surround in this study we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time specific lithofacies it originated from prolonged growth of nodular carbonate controlled by the convergence of several geological and paleoclimatic factors including a a protracted sea level highstand lasting for about 5 myr b an interval of tectonic quiescence favoring the dominance of carbonate production with minimal siliciclastic input and c location of the south china paleoplate in the hurricane free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases normally 15 120 m depths favoring long term uninterrupted growth of caco3 meganodules on a mid shelf substrate this study corroborates recent paleogeographic reconstructions that position the south china paleoplate on the equator during the late ordovician

chemical variations in clay minerals of the archaean barberton greenstone belt south africa abstract four rock profiles of shales carbonates and greywacke type sediments were sampled from the mafic compositional influenced sedimentary fig tree group and from overlying more felsic related sedimentary moodies group of the archaean barberton greenstone belt in south africa clay separates of forty sedimentary rocks were examined by xrd and sem to study the mineralogical chemical and morphological variations of the constitutive illite and chlorite the clay minerals showed a significant k enrichment in the illites and mg and fe depletions in the chlorites upwards the stratigraphic sequence three independent parameters influenced these variations 1 a change in the origin of the source rocks 2 the host rock lithologies and 3 a tectono thermal recrystallization process

stratigraphic control of rare earth pattern types in mid proterozoic sediments of the belt supergroup montana u s a implications for basin analysis abstract within sediments of the helena embayment an eastern extension of the mid proterozoic belt basin montana u s a three different types of ree patterns were identified the lower part of the investigated sequence chamberlain shale and lower newland formation is a uniform shale interval which accumulated during a period of tectonic quiescence the ree patterns of these shales normalized to nasc are either flat or lree enriched lacking eu deficiencies the superjacent unit newland transition zone contains variable amounts of feldspathic sandstone it indicates rejuvenation of the hinterland and regression the uppermost unit upper newland formation consists of alternating packages of carbonates and shales ree patterns in shales of the newland transition zone and upper newland formation have negative eu anomalies this drastic change of ree patterns was observed in all stratigraphic sections the source rocks of the beltian sequence were probably dominated by granitoid gneisses and migmatites and rocks of this composition show negative eu anomalies against nasc in many other places the observed negative eu anomalies in the shales were probably inherited from the source rocks however the patterns of the chamberlain shale and the lower newland formation are not as easy to explain because the source rocks seem not to have changed during deposition of the beltian sequence perhaps more intense chemical weathering during chamberlain shale lower newland time obscured the negative eu anomalies in the residual clays adsorption of lree s on clays during transport may have caused the lree enriched patterns a change in tectonic regime and weathering intensity coincides with the stratigraphic distribution of the different ree pattern types thus stratigraphically controlled ree pattern distribution in a sedimentary basin may help to establish quasi time lines and may allow monitoring of tectonic pulses and of weathering conditions in the hinterland

the occurrences of the rare earth elements and the platinum group elements in relation to base metal zoning in the vicinity of rote faule in the kupferschiefer of poland abstract the concentrations of the lanthanide rare earth elements ree and pt group elements pge were measured in the kupferschiefer from the polish zechstein basin at and in proximity to the rote faule near the lubin mining district the rote faule is a zone of post depositional oxidation characterized by the presence of extensive amounts of fe iii oxides replacing syn sedimentary framboidal pyrite outward from the rote faule the remainder of the kupferschiefer is composed of cu and pb zn mineralized shale surrounding the rote faule and a non mineralized pyritic black shale in the central basin the leading hypothesis explaining the high concentrations of pge and ree in the kupferschiefer states that pge ree and the associated base metals were mobilized by oxidizing cl brines which migrated outward from the rote faule into the reduced kupferschiefer according to available thermodynamic data pge were in all likelihood present as chloro complexes in these oxidizing brines as geologically realistic concentrations of pt pd and au could be transported as chloro complexes the eh of these brines decreased as they migrated further from the rote faule and into the kupferschiefer base metals and pge were precipitated in the order of their decreased solubility in these brines as a result the concentrations of least soluble pge pt are highest in the rote faule and in the transition zone adjacent to the rote faule e g pt 202 537 ppb while the concentrations of the more soluble metals in these brines ag cu pb and re are highest in the reduced mineralized kupferschiefer the sources of the pge and ree are enigmatic it is likely that the metals were derived either from the underlying rotliegendes sandstones and volcanics the variscan basement rocks or the kupferschiefer shale whose metals were mobilized by saline oxidizing fluids released during intra continental rifting in the triassic period

stable carbon and hydrogen isotopes of natural gases sourced from the xujiahe formation in the sichuan basin china abstract the compound specific hydrogen and carbon stable isotope ratios of alkanes in natural gases from the xujiahe and jurassic formations in the western sichuan basin were investigated to distinguish between coal derived and oil associated gases all gases were determined to be coal derived and sourced from the xujiahe formation thermal maturities of the source rocks are expected to vary from 0 8 1 8 vitrinite reflectance ro according to the empirical relationship between the measured 13cch4 values and ro which is within the scope of the maturities of source rocks 0 7 2 1 in particular c1 3 alkanes of primary coal derived gases which have not undergone any secondary alteration become more enriched in deuterium with increasing molecular mass and the dch4 values increase with increasing thermal maturity of source rocks in the sichuan basin d values of coal derived gases sourced from terrigenous source rocks of the xujiahe formation are more negative than those of oil associated gases sourced from marine organic matter of the sinian permian and triassic formations

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

stable hydrogen and carbon isotopic ratios of coal derived and oil derived gases a case study in the tarim basin nw china abstract natural gases from the kuqa depression lunnan and tazhong low uplifts in the tarim basin of china were analyzed for stable hydrogen and carbon isotopic characteristics to compare the isotopic differences particularly of hydrogen between coal derived and oil derived gases gases from the kuqa depression are coal derived and sourced from middle lower jurassic coal measures possibly with a minor contribution from triassic lacustrine mudstones gases from the lunnan and tazhong low uplifts are thought to be sourced from cambrian lower ordovician marine sapropelic organic matter natural gases from the lunnan low uplift and ordovician strata in the tazhong low uplift are oil cracked and gases from the carboniferous and silurian strata in the tazhong low uplift are oil associated most gases have expected hydrogen isotopic distributions among c 1 c 3 alkanes i e 2 h ch4 2 h c2h6 2 h c3h8 however nearly all samples that show carbon isotopic reversal between c 1 and c 2 alkanes 13 c ch4 13 c c2h6 in the lunnan low uplift also have corresponding hydrogen isotopic reversal 2 h ch4 2 h c2h6 between these alkanes in the tazhong low uplift except for the silurian gases nearly all the carboniferous and ordovician gases have regular carbon isotopic distribution pattern among c 1 c 2 alkanes 13 c ch4 13 c c2h6 but with hydrogen isotopic reversal between c 1 and c 2 alkanes 2 h ch4 2 h c2h6 this probably indicates that except the influences of mixing with gases at different maturity hydrogen isotopes of natural gases are also sensitive to other processes such as hydrogen exchange between water and organic matter during thermal maturation no analytical differences in 2 h ch4 have been found between coal derived gases sourced from continental humic organic matter in the kuqa depression and the oil derived gases sourced from the carboniferous and silurian marine sapropelic organic matter in the tazhong low uplift all coal derived gases in the kuqa depression have 2 h ch4 values less than 150 while the oil cracked gases in the lunnan low uplift and the ordovician oil cracked gases in the tazhong low uplift have slightly greater 2 h ch4 values 150 however the silurian and carboniferous oil associated gases in the tazhong low uplift also have quite low 2 h ch4 values around 160 the clearly different hydrogen isotopic values of gases from different strata in the tazhong low uplift and the close hydrogen isotopic values between gases from the kuqa depression and silurian and carboniferous strata in the tazhong low uplift all imply that hydrogen isotopes of alkane gases are influenced by factors more than thermal maturity and depositional environments great care needs to be paid when using the hydrogen isotopes for gas genetic study and a combination with local geological settings and other geochemical features is suggested this is because hydrogen isotopes of alkane gases in one basin may be not applicable in the other basins

clumped isotopologue constraints on the origin of methane at seafloor hot springs abstract hot spring fluids emanating from deep sea vents hosted in unsedimented ultramafic and mafic rock commonly contain high concentrations of methane multiple hypotheses have been proposed for the origin s of this methane ranging from synthesis via reduction of aqueous inorganic carbon co2 during active fluid circulation to leaching of methane rich fluid inclusions from plutonic rocks of the oceanic crust to further resolve the process es responsible for methane generation in these systems we determined the relative abundances of several methane isotopologues including 13ch3d a clumped isotopologue containing two rare isotope substitutions in hot spring source fluids sampled from four geochemically distinct hydrothermal vent fields rainbow von damm lost city and lucky strike apparent equilibrium temperatures retrieved from methane clumped isotopologue analyses average 310 42 53 c with no apparent relation to the wide range of fluid temperatures 96 370 c and chemical compositions ph h2 co2 ch4 represented combined with very similar bulk stable isotope ratios 13c 12c and d h of methane across the suite of hydrothermal fluids all available geochemical and isotopic data suggest a common mechanism of methane generation at depth that is disconnected from active fluid circulation attainment of equilibrium amongst methane isotopologues at temperatures of ca 270 360 c is compatible with the thermodynamically favorable reduction of co2 to ch4 at temperatures at or below ca 400 c under redox conditions characterizing intrusive rocks derived from sub ridge melts collectively the observations support a model where methane rich aqueous fluids known to be trapped in rocks of the oceanic lithosphere are liberated from host rocks during hydrothermal circulation and perhaps represent the major source of methane venting with thermal waters at unsedimented hydrothermal fields the results also provide further evidence that water rock reactions occurring at temperatures lower than 200 c do not contribute significantly to the quantities of methane venting at mid ocean ridge hot springs

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

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