stable isotope geochemistry of crude oils and of possible source rocks from new zealand 2 sulfur abstract the sulfur isotopic composition of new zealand low s crude oils and components asphaltenes absorptive filtration fractions and source rock components extracted hydrocarbons kerogen pyrite sulfates were determined oils from the taranaki basin have 34s values from 3 to 14 o the lower values possibly represent plant assimilation of fresh water sulphate higher values particularly those from the west coast basin around 20 suggest closed ocean basin conditions or fast sedimentation rate whereas negative 34s values from east coast basin suggest open ocean or low sedimentation rate conditions it is suggested than an oil source rock relation should show as a similarity in 34s values for total oil and source rock extract kerogen and pyrite shale samples analysed plot outside the corresponding oil range and cannot be considered as possible source rocks however coal samples from the maui 4 well and nelson outcrops show strong isotopic correlations with the taranaki oils

contemporaneous early diagenetic formation of organic and inorganic sulfur in estuarine sediments from st andrew bay florida usa estuarine sediment samples were collected from nine stations in st andrew bay near panama city florida usa contrasting grain size and varying concentration of organic carbon allowed a comparative study of the relationships among organic degradation processes sulfur cycling and diagenetic removal of dissolved sulfide produced by bacterial sulfate reduction abundance and sulfur isotopic composition were determined for dissolved sulfide dissolved sulfate pyrite humic acid sulfur fulvic acid sulfur and elemental sulfur presence of free dissolved sulfide and enrichment in 34s of porewater sulfate in samples from organic rich muddy sediments of st andrew bay indicate high rates of sulfate reduction and anoxic conditions below 5 mm depth such conditions are not reflected in samples from organic poor sandy near shore sediments collected from highly productive areas occupied by seagrass beds in this estuarine system pyrite and fulvic acid sulfur are the largest sinks for sulfide produced by bacterial sulfate reduction strong correlation between abundances of pyrite and fulvic acid sulfur suggests coincident formation in the uppermost 10 cm of sediment large differences in isotopic composition between these two species and consistent enrichment in 34s of the fulvic acid fraction however indicate two different reaction pathways abundance and sulfur isotopic composition of humic acid and fulvic acid sulfur suggest that organic sulfur is derived from mixing between 1 34s depleted sulfur with an unknown oxidation state that was recycled from bacterial hydrogen sulfide and 2 34s enriched sulfur interpreted as primary biosynthetic sulfur originally assimilated from dissolved sulfate samples taken from sandy sediment localities where aquatic vascular plants are rooted in the anoxic zone show a strong depletion in 34s in the fulvic acid sulfur fraction suggesting recycled hydrogen sulfide as the dominant source of organic sulfur

pore water distributions of dissolved copper and copper complexing ligands in estuarine and coastal marine sediments the distributions and seasonal variability of total dissolved cu tdcu and cu complexing ligands in sediment pore waters have been investigated at two contrasting sites in the chesapeake bay two ligand classes which differ on the basis of the conditional stability constants k9 of their cu complexes were detected at all depths at both sites at the sulfidic muddy mid bay sta m concentrations and values of log k9 ranged from 390 12 500 nm and 7 2 8 9 respectively for the stronger ligand class l1s and 75 6 420 nm and 6 2 7 9 for the weaker ligand class l2s at the bioturbated sandy sta s in the lower bay respective concentrations and values of log k9 ranged from 135 807 nm and 7 6 10 2 for l1s and 40 1 410 nm and 6 6 9 2 for l2s for comparison one pore water profile from a slope station off of the chesapeake bay also showed the presence of two ligand classes with respective concentrations and values of log k9 of 140 270 nm and 8 11 for l1s and 30 180 nm and 7 10 forl2s these ligands are in large excess relative to ambient tdcu concentrations 0 1 24 3 nm thereby maintaining very low inorganic cu concentrations typically 0 1 to 100 pm and a high degree of organic complexation 87 2 99 9 of cu in bay and slope sediment pore waters thus virtually all tdcu fluxing from these sediments is complexed during sediment water exchange a relatively small fraction of the tdcu is exchanged as inorganic species which are widely regarded as the most bioavailable form of cu higher ligand concentra tions at sta m suggest that sulfide or organic ligands containing reduced s contribute to the pool of complexing ligands however the exact nature and sources of the ligands in bay pore waters are not known the progressive increase in conditional stability constants of the cul 2s complexes from the mid bay to the slope sediments may reflect differences in biological or chemical processes at each site as well as differences in the type of cu complexing organic matter total ligand concentrations l1s 1 l2s are 15 to 100 times higher in the upper intervals of the pore waters relative to ligand concentrations in the bottom waters of the chesapeake bay 30 60 nm consistent with previous observations of fluxes of these ligands from the sediments to overlying waters these results suggest that sediments are potentially significant sources of cu complexing ligands to the overlying waters of the chesapeake bay and perhaps other shallow water estuarine and coastal environments copper complexing ligands released from sediment pore waters may play an important role in influencing cu speciation in overlying waters copyright 2000 elsevier science ltd

early diagenetic alteration of organic matter by sulfate reduction in quaternary sediments from the northeastern arabian sea abstract hemipelagic sediments from the northeastern arabian sea off pakistan were analyzed by geochemical and microscopical methods to study the importance of bacterial degradation processes on the quantity and composition of sedimentary organic matter om on the basis of elemental analysis of total organic carbon toc and total sulfur ts the decay of om by sulfate reducing bacteria were calculated concentrations of total iron reactive iron total nitrogen tn total phosphorus tp and hydrogen indices hi were used to assess organic matter reactivity and redox conditions stable sulfur isotopic compositions provided further information about pathway timing and mechanisms of sulfate reduction microscopical observations indicate that throughout the study area om is amorphous 75 95 in almost all samples with only a small contribution of terrigenous om bacterially mediated sulfate reduction leads to continuously decreasing toc ts ratios from 0 4 m to a burial depth of 2 3 m at this depth the anaerobic oxidation of particulate organic matter ceases sulfate reduction in this narrow interval accounts for the decay of up to 70 of the om which has primarily entered the anoxic domain during the bacterially mediated diagenesis preferential consumption of nitrogen and phosphorus containing organic compounds can be observed and quantified the regeneration of up to 60 of tn and more than 50 of tp can lead to a feedback of nutrients to the seawater this recycling process may contribute to the high productivity in the northeastern arabian sea

geochemistry of inorganic and organic sulphur in organic rich sediments from the peru margin abstract we have determined 1 the abundance and isotopic composition of pyrite monosulphide elemental sulphur organically bound sulphur and dissolved sulphide 2 the partition of ferric and ferrous iron 3 the organic carbon contents of sediments recovered at two sites drilled on the peru margin during leg 112 of the ocean drilling program sediments at both sites are characterised by high levels of organically bound sulphur obs obs comprises up to 50 of total sedimentary sulphur and up to 1 of bulk sediment the weight ratio of s to c in organic matter varies from 0 03 to 0 15 mean 0 10 such ratios are like those measured in lithologically similar but more deeply buried petroleum source rocks of the monterey and sisquoc formations in california the sulphur content of organic matter is not limited by the availability of porewater sulphide isotopic data suggest that sulphur is incorporated into organic matter within a metre of the sediment surface at least partly by reaction with polysulphides most inorganic sulphur occurs as pyrite pyrite formation occurred within surface sediments and was limited by the availability of reactive iron but despite highly reducing sulphidic conditions only 35 65 of the total iron was converted to sulphide 10 30 of the total iron still occurs as fe iii in surface sediments the isotopic composition of pyrite is similar to that of both iron monosulphide and dissolved sulphide either pyrite like monosulphide formed by direct reaction between dissolved sulphide and detrital iron and or the sulphur species responsible for converting fes to fes2 is isotopically similar to dissolved sulphide likely stoichiometries for the reaction between ferric iron and excess sulphide imply a maximum resulting fes2 fes ratio of 1 1 where pyrite dominates the pool of iron sulphides at least some pyrite must have formed by reaction between monosulphide and elemental sulphur and or polysulphide elemental sulphur s0 is most abundant in surface sediments and probably formed by oxidation of sulphide diffusing across the sediment water interface in surface sediments s0 is isotopically heavier than dissolved sulphide fes and fes2 and is unlikely to have been involved in the conversion of fes to fes2 polysulphides are thus implicated as the link between fes and fes2

a jurassic counterpart for modern kopara of the pacific atolls abstract two types of laminated sediments are compared in this paper the kimmeridgian bituminous laminites of orbagnoux french southern jura mountains and the present day kopara of the french polynesia atolls or kiritimati christmas island from the pacific ocean the kopara is made of laminated sediments several tens of centimetres thick that cover the floors of most shallow 3 rich laminae the top few centimetres host a succession of bacterial populations from aerobic to strictly anoxic most carbonate grains are precipitated in situ due to bacterial activity s l the kimmeridgian bituminous laminae of orbagnoux are partly made of flat stromatolites that show many similarities with the kopara this analogy allows us to refine the interpretation of the southern jura platform where laminated organic matter rich carbonates were deposited in many places

organic matter preservation and sulfur uptake in sediments from the continental margin off pakistan abstract the bulk and molecular geochemical characteristics of a suite of kerogens isolated from organic matter rich sediments from the pakistan margin has been characterised by elemental analysis rock eval pyrolysis and pyrolysis gas chromatography py gc special attention was given to the geochemistry of alkylthiophenes which are thought to reflect the incorporation of sulfur into organic matter om in the context of early diagenetic sulfate reduction organically bound sulfur comprises up to 60 of total sedimentary sulfur the weight ratios for organic sulfur s org over organic carbon c org varies from 0 01 in some of the recently deposited sediments to 0 11 in older samples the results show that sulfur incorporation into organic matter occurs primarily within the upper few meters of the sediments the amount of sulfur which can be incorporated into the organic matter clearly depends on the quality of om the hydrogen index values hi which characterise the total amount of generated hydrocarbon equivalents of the pyrolysate in mg hc equiv g c org are related to the extent of reworking of organic matter either in the water column or at the sediment water interface or to remineralization processes by sulfate reduction itself which is strongly controlled by the availability of reactive iron high quality organic matter characterised by elevated hi values is capable of sequestering higher amounts of sulfur as expressed by the thiophene content which represent the organically bound sulfur of the pyrolysate in mg g c org as indicated by the ratio of thiophenes versus hi which characterises the proportion of thiophenes in the total pyrolysate sulfurisation of organic matter seems to be terminated at a ratio of 0 01

carbon and sulfur relationships in marine senonian organic rich iron poor sediments from israel a case study abstract in fe poor and organic rich marine sediments reduced s is mainly organic due to the lack of reactive fe these sediments e g carbonates cherts phosphates have high c s organic carbon total reduced sulfur ratios which are as a rule 3 and may reach 5 or 6 at times even 10 in organic rich rocks these high ratios are characteristic for these fe barren sediments and are very different from those found in marine sediments where pyritic s is the main reduced sulfur species they may be explained by the escape of h 2 s to the atmosphere the interpretation of c 1bs plots in these sediments is also quite different one reason for the s intercept in these plots is the presence of pyritic s and thus contrary to the conventional plots this intercept seems to have no environmental significance on the other hand the s c slope appears to be a paleoenvironmental indicator low slopes 0 2 indicate restricted to normal aerobic environments c 1bs plots have been used to interpret environments of deposition in such sediments from two cycles of organic rich fe poor senonian sediments in several basins in central and southern israel both cycles appear to have been deposited in restricted environments the campanian mishash formation environments of deposition appear to be in general more oxic than those of the maastrichtian ghareb formation as an independent comparison for the c s results the degree of pyritization dop was calculated for some samples the dop results confirmed the c s results it should be stressed that in such low fe environments even dop results should be used with caution

sedimentary sulfur geochemistry of the paleogene green river formation western usa implications for interpreting depositional and diagenetic processes in saline alkaline lakes abstract the sulfur geochemistry of the lacustrine paleogene green river formation colorado utah and wyoming usa is unlike that of most marine and other lacustrine rocks distinctive chemical isotopic and mineralogical characteristics of the formation are pyrrhotite and marcasite high contents of iron mineral sulfides strikingly enriched in 34 s cyclical trends in sulfur abundance and 34 s values and long term evolutionary trends in 34 s values analyses that identified and quantified these characteristics include carbonate free abundance of organic carbon 0 13 47 wt total iron 0 31 13 wt reactive iron 70 of total iron total sulfur 0 02 16 wt acid volatile monosulfide s av disulfide s di 70 of total sulfur sulfate s so 4 and organosulfur s org isotopic composition of separated sulfur phases 34 s di av up to 49 and mineralogy morphology and paragenesis of sulfide minerals mineralogy morphology 34 s di av and 34 s org have a distinctive relation reflecting variable and unique depositional and early diagenetic conditions in the green river lakes when the lakes were brackish dissimilatory sulfate reducing bacteria in the sediment produced h 2 s which initially reacted with labile iron to form pyrite framboids and more gradually with organic matter to form organosulfur compounds during a long lived stage of saline lake water the amount of sulfate supplied by inflow decreased and alkalinity and ph of lake waters increased substantially extensive bacterial sulfate reduction in the water column kept lake waters undersaturated with sulfate minerals a very high h 2 s so 4 ratio developed in stagnant bottom water aided by the high ph that kinetically inhibited iron sulfidization progressive removal of h 2 s by coeval formation of iron sulfides and organosulfur compounds caused the isotopic composition of the entire dissolved sulfur reservoir to evolve to 34 s values much greater than that of inflow sulfate which is estimated to have been 20 a six million year interval within lake uinta cores records this evolution as well as smaller systematic changes in 34 s interpreted to reflect 100 000 year lake level cycles when porewater was exceptionally reducing unstable fes phases eventually recrystallized to pyrrhotite during diagenesis a much later reaction related to weathering altered pyrrhotite to marcasite

a lightweight gravity corer for undisturbed sampling of soft sediments a lightweight portable gravity corer is described that collects up to 3 m long 10 cm diameter undistrubed cores from sediments of exceptionally high porosity the corer employs a triple o ring seal to hold sediments in an unsupported catcher free plastic barrel simply by suction author

sulphur incorporation in jurassic marine mudrocks and their bitumens at low thermal maturity cleveland basin england abstract the distribution of sulphur between pyrite kerogen elemental sulphur and the aromatic fraction of mudrock bitumens has been quantitated in two cored sections of immature marine kimmeridgian strata which have experienced different levels of thermal stress strata in the two boreholes ebberston and reighton were deposited in different basinal settings basinal marine and platform respectively and occasional euxinic laminated horizons are present at ebberston otherwise dysoxic deposition was the norm at both localities pyrite the dominant sulphur carrier in all the mudrocks has a sulphur isotopic composition consistent with mineralisation in a system mainly open to sulphate diffusion kerogens are mostly low sulphur atomic s c and account for between 5 and 10 of rock sulphur although occasionally up to 30 kerogen sulphur is closely correlated with toc and highest in laminated mudrocks consistent with most effective sulphurization of kerogen under anoxic conditions although kerogen compositions in both cores vary with organic richness no systematic differences in organic input between the borehole localities are recognised geochemically some thermal effects on sulphur geochemistry are therefore interpreted from a comparison of stratigraphically equivalent sections from the two cores bitumen yields and abundances of aromatic sulphur in the more thermally stressed ebberston section although variable are generally much higher than in the reighton section and are partly related to kerogen sulphur content this is tentatively attributed to thermal release of additional extractable bitumen from macromolecules elemental sulphur s0 in bitumen is unrelated in abundance to other sulphur species and isotopically heavier than coexisting pyrite overprinting of minor preserved diagenetic s0 by secondary oxidation of pyrite appears likely the distributions of individual sulphur aromatic compound classes have features related both to maturity and stratigraphy

the influence of humic substances on the geochemistry of iodine in nearshore and hemipelagic marine sediments iodine is characteristically enriched at the surface of hemipelagic and nearshore sediments deposited under oxygenated conditions in such sediments bulk i corg ratios usually decrease with depth to values which are characteristic of anoxic sediments reflecting a preferential release of i during early diagenesis there is some debate as to whether sedimentary i is associated with the iron oxyhydroxide phase or with the organic fraction and whether the decrease in i corg with depth is due to the dissolution of the iron oxyhydroxides or the decomposition of labile organic matter it is shown that in a surficial hemipelagic sediment sample and in a nearshore sediment core i is mainly associated with the organic fraction and moreover that humic substances are involved in the surficial iodine enrichment laboratory experiments on the uptake and release of i by and from sedimentary humic substances also suggest a mechanism whereby humic materials reduce iodate at the sediment water interface to an electrophilic i species which further reacts with the organic matter to produce iodinated organic molecules during burial this excess i could be displaced from the organic matrix by nucleophiles such as sulphide ions or thiosulphate thus providing a possible explanation for the decrease in i corg ratio with depth observed in many nearshore and hemipelagic sediments

evolutionary changes over the last 1000 years of reduced sulfur phases and organic carbon in varved sediments of the santa barbara basin california abstract sediments from the santa barbara basin sbb of the last 1000 years were analyzed for elemental sulfur se mineral sulfide sulfur sm lipid based organically bound sulfur sx residual organically bound sulfur so total organic carbon toc and total nitrogen tn the approximate annual resolution of the time series data permitted us to evaluate the influence of oceanic variables on the benthic environment and the accumulating varved sediment in the sbb a bacterial mat community at or near the sediment surface is influencing sediment porosity and the production and distribution of se early diagenesis dampens the amplitude of environmental signals in the geochemical time series the concentrations of sm and so increase with burial depth at the expense of decreasing concentrations of sx and se at depths greater than 5 5 cm corresponding to an age of 7 years sm becomes the largest pool of reduced sulfur it requires approximately 500 years of primarily bacterially mediated diagenesis equivalent to a burial depth of 1 4 m for sbb sediments to gradually approach and finally enter the region assumed to represent typical normal marine sediments on a plot of weight percent toc vs sm

radionuclide transport in fast channels in crystalline rock recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock the present paper sets out to investigate radionuclide transport in such channels including diffusion into the rock matrix it is shown that the uptake from a cylindrical hole in a matrix is much more effective per unit contact area than a flat surface semi infinite solid comparison of diffusion from cylindrical and slit formed channels shows that the differences in interfacial flux are minor a slit formed channel may therefore be approximated by a cylindrical one diffusional transport in the matrix is then treated as one dimensional instead of two dimensional which gives a considerable numerical simplification a simple estimate of the penetration depth into the cylindrical region i e the location of the diffusional front is proposed by using the integrated finite difference method a number of radionuclide transport calculations are performed for the case of flow and dispersion in a cylindrical channel coupled to diffusion and sorption in the matrix

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

sulphur and iron geochemistry of holocene coastal peats nw germany a tool for palaeoenvironmental reconstruction abstract a drill core from the marshlands of nw germany covering the entire holocene was analysed at high resolution by geochemical xrf cirm ms and microfacies methods diatoms thin sections sem in order to provide information about the palaeoenvironmental development in addition microbial experiments were carried out with sulphate reducing bacteria srb and cellulose fermenting fungi in seawater using peat as substrate the core contains an intercalated reed peat layer 2 73 3 02 m and a basal peat 5 78 6 42 m the basal peat consists in the lowest part of fen woodland and raised bog peat while the upper part is formed by a reed peat bed the peat layers are characterised by a distinct enrichment of pyrite with negative bulk sediment 34 s values av 11 5 range 2 6 to 26 7 reflecting microbial sulphate reduction in some peat intervals under almost open system conditions with respect to the input of seawater sulphate pyrite occurs exclusively with framboidal texture in close vicinity to the organic matter which indicates localised pyrite formation at the decay site in microenvironments with high concentrations of dissolved fe microbial experiments reveal that peat does not represent an appropriate substrate for srb and that srb have to rely on the preceding decomposition of peat by other microorganisms in microenvironments the total sulphur content of the peat layers averages to 7 8 wt with a maximum value of 28 2 wt unusually found within the basal peat at the transition of fen woodland and raised bog peat the pyrite enrichments can be explained by two different scenarios which are related to the intensity of the sea level rise the first scenario applies to a moderate sea level rise and is decisive for the reed peats where pyrite formation coincides with peat growth a brackish zone is assumed for the peat forming environment which is influenced by iron rich freshwater and sulphate rich seawater as the freshwater forms the major fe source the amounts of pyrite increase to a certain degree with decreasing salinity in this environment the palaeosalinity is estimated by the investigation of littoral and pelagic diatoms the second scenario applies to the extensive pyrite formation within the basal peat at the transition of fen and bog peat this pyrite was likely formed after peat growth favoured by a steep sea level rise thin sections of this peat interval reveal clastic layers 1 3 mm with completely pyritised interfaces as these clastic layers contain marine pelagic diatoms e g paralia sulcata we propose that they are caused by tidal channel activities during a phase of a steep sea level rise the marine incursion led to a partial buoyancy of the basal peat at weak transition zones i e the transition from fen to bog peat as a result of the bouyancy marine suspended particulate matter can be introduced laterally in between the peat sections when the peat settles down a clastic layer remains whose interface with the peat may have favoured the inflow of waters of higher salinity therefore an enhanced formation of pyrite was possible due to the combination of sulphate rich ground water and iron rich peatland waters

determination of organic degradation rates in 100 my old sediments application to cretaceous black shale intervals from demerara rise odp leg 207 abstract thick organic rich albian to santonian black shale sequences were recovered from ocean drilling program sites 1261 and 1257 on the demerara rise offshore surinam at depths of 564 and 174 m below seafloor bsf respectively total organic carbon toc concentration varies between 3 9 and 17 3 wt rock eval pyrolysis parameters and elemental analysis indicate that the kerogen samples are of type ii thermally immature and with well preserved organic matter the hydrogen index hi values fluctuate between 608 and 765 mg hydrocarbon hc g toc and correlate well with c n and the sorg c atomic ratios indicating varying early diagenesis conditions between samples higher c n and sorg c values for kerogen from site 1261 suggest more reducing depositional conditions than at site 1257 long term organic diagenesis is marked by a linear decrease in the oxygen index oi at site 1261 from 34 to 22 mg co2 g toc ester and carboxyl functional groups are the main target of the degradation as inferred from the decrease in c o and o c c fourier transform infrared spectroscopy ftir bands as well as in the ch oh and the o ch3 chx n bands in 13c nuclear magnetic resonance nmr spectra degradation rate at site 1261 determined combining quantitative nmr spectra and bulk elemental characterization is between 1 7 and 12 1 mol m3 yr per 1 toc at the lower end of reported rates in a similar context kerogen samples from site 1257 do not show any decrease in oxygen content with depth indicating significantly lower degradation rate we propose that the long term exposure to moderate temperature 30 c at site 1261 activated the organic matter thereby sustaining microbial diagenesis

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

the early diagenetic formation of organic sulfur in the sediments of mangrove lake bermuda due to a low mineral content the sapropelic sediments depositing in mangrove lake bermuda provide an excellent opportunity to explore for possible additions of sulfur to organic matter during the early stages of diagenesis we evaluated early diagenetic organic sulfur transformations by monitoring the concentrations and stable isotopic compositions of a number of inorganic and organic sulfur pools thereby accounting for all of the sulfur in the sediments we have identified and quantified the following sulfur pools porewater sulfate porewater sulfide elemental sulfur pyrite sulfur hydrolyzable organic sulfur hyos chromium reducible organic sulfur cros and nonchromium reducible organic sulfur non cros of the organic sulfur pools the non cros pool is by far the largest followed by cros and finally hyos by 60 cm depth these pools contribute respectively to 85 7 9 and 3 6 of the total solid phase sulfur the hyos pool is probably of biological origin and shows no interaction with the sulfur compounds produced during diagenesis by contrast cros is produced most likely from the diagenetic addition of polysulfides to functionalized lipids in the upper h2s poor elemental sulfur rich region of the sediment a portion of this sulfur pool is unstable and decomposes on contact with the h2s rich porewaters the portion of cros that remains in the sulfidic waters appears to readily exchange sulfur isotopes with h2s while some of the non cros pool is of biological origin some is also formed by the diagenetic addition of sulfur to organic compounds in the upper h2s poor region of the sediment by contrast with cros non cros is not diagenetically active in the h2s rich porewaters overall somewhere between 27 and 53 of the organic sulfur buried in mangrove lake sediments is of diagenetic origin with the remaining organic sulfur derived from biosynthesis we extrapolate our mangrove lake results and calculate that in typical coastal marine sediments between 11 and 29 mol g 1 of organic sulfur will form during early diagenesis of which 2 5 mol g 1 will be chromium reducible

isotopic composition and speciation of sulfur in the miocene monterey formation reevaluation of sulfur reactions during early diagenesis in marine environments the timing and pathways of early diagenetic sulfur transfer from dissolved species in pore waters to solid inorganic and organic compounds in sediments have been studied in the miocene monterey formation santa maria basin onshore california correlation between concentrations of total organic carbon toc and total sulfur ts in addition to concentrations of titanium aluminum total iron and reactive iron have been used to infer organic matter reactivity redox conditions and relative rates of clastic and biogenic input for each lithofacies isotopic compositions of six sulfur species acid volatile disulfide kerogen bitumen sulfate and elemental have provided information regarding relative timing of sulfur incorporation sulfate diffusivity in the upper centimeters of the sediments and the sources of sulfur for individual species isotopically the disulfide species expresses the greatest fractionation relative to estimated values of miocene seawater sulfate 22 cdt on average disulfide is depleted in 34s by 10 4 relative to kerogen and by 9 9 relative to acid volatile sulfide the 34s of bitumen shows no systematic change relative to 34skeregon suggesting the presence of migrated bitumen isotopic similarity of sulfate and elemental sulfur to sulfides and bitumen indicates that sulfate and elemental sulfur are chemical and or biological oxidation products derived from sulfides and bitumen consistent ordering of isotopic values for sulfur species disulfide acid volatile sulfide kerogen indicates that pyrite precipitated nearest to the sediment water interface under mildly reducing conditions and with little or no decrease in sulfate concentration relative to seawater enrichment of 34s in acid volatile sulfide and kerogen sulfur resulted from formation of these species at greater depths or in restricted micro environments under more reducing conditions and with low concentrations of porewater sulfate the formation of acid volatile sulfide after pyrite but during early diagenesis is significant because it implies more strongly reducing conditions than are generally recognized in deep water marine sediments

paired organic matter and pyrite δ34s records reveal mechanisms of carbon sulfur and iron cycle disruption during ocean anoxic event 2 abstract the sulfur s isotope composition of pyrite in the sedimentary record has played an important part in our understanding of the evolution of biogeochemical cycles throughout earth history however the kinetics of pyritization are complex and depend strongly on the reactivity and mineralogy of available iron as a second major sink for sulfide in anoxic sediments organic matter om provides essential context for reconstructing the distribution and isotopic composition of environmental sulfide to first order roughly parallel pyrite and om 34 s profiles reflect changes in sulfide while independent patterns require alternative explanations including changes in iron availability or om characteristics we apply this framework to ocean anoxic event 2 oae 2 94 mya a period of enhanced burial of reduced c and s in om and pyrite that has been associated with an expansion of reducing marine conditions we present paired s isotope records for pyrite and om along with profiles of om s c ratio and s redox speciation from four well characterized lithologic sections with a range of depositional environments pont d issole cismon tarfaya basin and demerara rise to reconstruct both local redox structure and global mechanisms impacting the c s and fe cycles around oae 2 om sulfurization appears to be a major control on om preservation at all four sites similar to modern anoxic environments there is a positive correlation between om s c ratios and toc concentrations for sites with more reducing conditions implying a link between om sulfurization and burial at consistently anoxic sites like tarfaya basin and demerara rise strongly sulfurized om with a consistent s redox speciation and s isotope composition most likely formed rapidly in sinking particles before during and after oae 2 particle hosted om sulfurization may therefore have been a central mechanism facilitating the massive burial of om in anoxic environments during this and other periods of enhanced global carbon burial at the same time a nearly 25 negative shift in the 34 s values of pyrite but not om occurs at multiple globally distributed sites prior to the onset of oae 2 indicating slower pyritization reactions that likely reflect changes in iron delivery due to expanding regional or global anoxia the combination of pyrite and organic s isotopes thus provides novel constraints on the interwoven cycles of carbon iron and sulfur across a major carbon cycle perturbation

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

speciation and stable isotopic compositions of humic sulfur in mud sediment of the east china sea constraints on origins and pathways of organic sulfur formation abstract humic sulfur is commonly the most important pool of organic sulfur os in marine sediments and also important for the budget of total sedimentary sulfur in this study contents and stable sulfur isotopic compositions of hydrolyzable organic sulfur hyos humic acid sulfur ha s and fulvic acid sulfur fa s in one core collected from the east china sea ecs inner shelf were determined to investigate the sources and pathways of os formation and to compare diagenetic geochemistry of ha s and fa s hyos in the core is essentially biological in origin and diagenetically refractory with a fairly low fraction of labile sulfur bearing biomolecules ha s in the core is largely terrigenous residual bio os while fa s is a mixture of marine bio and diagenetic os diag os with the diag os fractions between 44 and 71 both ha s and fa s contents in the core are at the lower ends of the corresponding values reported in the literature the ha in the sediments is diagenetically inert subject to neither significant diagenetic sulfurization nor bio os mineralization loss while the fa is reactive prone to both sulfurization and decomposition loss of diagenetically bound os low contents of humic s i e ha s fa s in the core may suggest that os burial has only minor contribution to the burial of total sulfur in the sediments due to generally low om sulfurization

deglaciation chronology and revegetation in northwestern ontario along a 420 km transect in northwestern ontario canada sediments from four lakes were analyzed with respect to lithology pollen and macrofossils radiocarbon dates show that the region was deglaciated between ca 11 500 and 8000 years bp and periods of both rapid ice retreat and readvance influenced the history of glacial lake agassiz in the south the ice sheet was succeeded by a lengthy interval of park tundra with stands of spruce ash and elm the ash and elm seem to have disappeared during a suggested cool period 11 100 10 200 years bp farther north the park tundra phase lasted not more than 50 100 years after ca 10 200 years bp before boreal trees dominated the climatic change around 10 200 years bp permitted the very rapid migration of spruce larch birch and jack or red pine into northwestern ontario from northern minnesota the migration routes for pinus strobus white pine alnus rugosa and a crispa were divided however one from the south south of lake superior and one from t