sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

an anaerobic 3400 ma shallow water microbial consortium presumptive evidence of earth s paleoarchean anoxic atmosphere abstract a microbial consortium preserved in shallow water carbonaceous chert of the paleoarchean 3400 ma strelley pool formation pilbara craton northwestern western australia is composed of copiously abundant globular cobweb like swirls of randomly oriented filaments intermingled with laterally extensive flat laminated masses of subparallel filaments the shallow water possibly mudflat like habitat of the biocoenose is established by its geological setting and intimately intermixed association with millimetric quartz radiating laths and rosettes interpreted to be pseudomorphs after evaporitic gypsum anhydrite the indigenousness and syngenicity of the permineralized fossils to the encompassing chert their uncompacted minimally altered life like spatial distribution and their biogenicity and bacterial affinity are shown by optical microscopic raman spectroscopic and confocal laser scanning microscopic analyses in situ that document the mineralogy of their embedding matrix and their cylindrical filamentous morphology cellularity and kerogenous composition by comparison with mid precambrian and modern sulfur cycling ecosystems and consistent with sulfur isotopic data and their intimate co existence with copious microgranular pyrite and pseudomorphs evidently after sulfate the swirled aggregates are interpreted to be anaerobic sulfuretums in contrast the intermixed flat laminated components like microbes of fossil and modern stromatolitic mat communities are interpreted to be co occurring light requiring phototrophs whether such phototrophs were anoxygenic photosynthesizers like extant photosynthetic bacteria e g chloroflexaleans or facultatively anaerobic cyanobacteria cf oscillatoria limnetica their anoxygenic metabolism seems plausibly established given its great age shallow water habitat and anaerobic microaerophilic physiology this evidently first reported occurrence from the fossil record of anoxygenic phototrophs and of a microbial sulfuretum phototroph consortium is consistent with the supposition that earth s paleoarchean environment was essentially anoxic and suggests that o2 producing photosynthesis may have been a later evolutionary innovation

multiple sulfur isotopes from paleoproterozoic huronian interglacial sediments and the rise of atmospheric oxygen mass dependently fractionated mdf sulfur isotopes in sedimentary sulfides and sulfates can provide information on the past activity of microbial metabolisms and serve as a proxy for the concentration of seawater sulfate in conjunction with these proxies mass independently fractionated mif sulfur isotopes can be used to track the rise of atmospheric oxygen the anoxic oxic transition of the surface environment in the paleoproterozoic has been constrained by mif sulfur in 2 47 ga sulfides from western australian banded iron formations and the absence of mif in diagenetic sulfides from 2 32 ga black shales in the transvaal supergroup south africa we report new multicollector ion microprobe data for individual sulfides from water lain sedimentary units in the 2 45 2 22 ga huronian supergroup ontario canada the authigenecity of sulfides in these units is interpreted on the basis of host lithology mode of distribution sulfide chemistry and mdf sulfur isotopes sulfides interpreted to have an authigenicsedimentary origin from the mckim fm have a range of 0 7 in 33 s values and those in the pecors fm preserve small magnitude mif 33 s values up to 0 88 which we propose represents the last remnants of an anoxic atmosphere high 34 s values up to 31 2 and near zero 33 s values in authigenic sulfides from the stratigraphically higher espanola and gordon lake fms suggest local variations of seawater sulfate concentrations and or 34 ssulfate consistent with increased atmospheric o2 levels mif sulfur is absent from the marine record after the second huronian glaciation which is analogous to the record of the transvaal supergroup where mif is absent from the upper part of the interglacial sequence our results suggest that the possible simultaneous demise of mif sulfur isotopes at these two localities may serve as a useful global geochemical marker to correlate paleoproterozoic supergroups we propose a new biogeochemical model where enhanced weathering rates during paleoproterozoic post glacial thawing served as a critical stimulus for interglacial blooms of oxygenic photosynthesis the demise of methane and ultimately to the irreversible rise in atmospheric oxygen

accumulation of transition metals and metalloids in sulfidized stromatolites of the 3 48 billion year old dresser formation pilbara craton abstract stromatolites of the 3 48 billion year old dresser formation pilbara craton western australia provide some of the oldest convincing evidence of life on earth here we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals cr mn co ni cu zn mo se ag sn au hg and pb and metalloids as sb and te in unweathered samples of strongly sulfidized stromatolites from drill cores high resolution elemental mapping and in situ compositional analysis of sulfides pyrite and sphalerite show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive nano porous pyrite enriched in autochthonous organic matter which forms the major petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites repeated cyclic alternations of various transition metals and metalloids most importantly ni and zn plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation because transition metals and metalloids generally have strong affinities for organic matter and can play active roles in biochemical processes we interpret these element accumulations in the dresser formation stromatolites to be the result of binding to organic matter of living microbial communities and or dead biomass and perhaps also microbial utilization collectively our results show that the precise characterization of transition metal metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity even in some of earth s oldest stromatolites

sedimentological control on saturation distribution in arctic gas hydrate bearing sands abstract a mechanistic model is proposed to predict explain hydrate saturation distribution in converted free gas hydrate reservoirs in sub permafrost formations in the arctic this 1 d model assumes that a gas column accumulates and subsequently is converted to hydrate the processes considered are the volume change during hydrate formation and consequent fluid phase transport within the column the descent of the base of gas hydrate stability zone through the column and sedimentological variations with depth crucially the latter enable disconnection of the gas column during hydrate formation which leads to substantial variation in hydrate saturation distribution one form of variation observed in arctic hydrate reservoirs is that zones of very low hydrate saturations are interspersed abruptly between zones of large hydrate saturations the model was applied to data from mount elbert well a gas hydrate stratigraphic test well drilled in the milne point area of the alaska north slope the model is consistent with observations from the well log and interpretations of seismic anomalies in the area the model also predicts that a considerable amount of fluid of order one pore volume of gaseous and or aqueous phases must migrate within or into the gas column during hydrate formation this paper offers the first explanatory model of its kind that addresses converted free gas reservoirs from a new angle the effect of volume change during hydrate formation combined with capillary entry pressure variation versus depth

sulfur isotope and trace element data from ore sulfides in the noranda district abitibi canada implications for volcanogenic massive sulfide deposit genesis we examine models for volcanogenic massive sulfide vms mineralization in the 2 7 ga noranda camp abitibi subprovince superior province canada using a combination of multiple sulfur isotope and trace element data from ore sulfide minerals the noranda camp is a well preserved vms deposit rich area that is thought to represent a collapsed volcanic caldera due to its economic value the camp has been studied extensively providing a robust geological framework within which to assess the new data presented in this study we explore previously proposed controls on mineralization within the noranda camp and in particular the exceptional au rich horne and quemont deposits we present multiple sulfur isotope and trace element compositional data for sulfide separates representing 25 different vms deposits and showings within the noranda camp multiple sulfur isotope data for this study have 34sv cdt values of between 1 9 and 2 5 and 33sv cdt values of between 0 59 and 0 03 we interpret the negative 33s values to be due to a contribution of sulfur that originated as seawater sulfate to form the ore sulfides of the noranda camp vms deposits the contribution of seawater sulfate increased with the collapse and subsequent evolution of the noranda caldera an inference supported by select trace and major element analyses in particular higher concentrations of se occur in samples with 33s values closer to 0 as well as lower fe zn ratios in sphalerite suggesting lower pressures and temperatures of formation we also report a relationship between average au grade and 33s values within au rich vms deposits of the noranda camp whereby higher gold grades are associated with near zero 33s values from this we infer a dominance of igneous sulfur in the gold rich deposits either leached from the volcanic pile and or directly degassed from an associated intrusion

variations in atmospheric sulphur chemistry on early earth linked to volcanic activity the nature of the atmospheric sulphur cycle on the early earth has been difficult to reconstruct an analysis of sulphur isotopes from 3 2 billion year old volcanic rocks suggests that episodic volcanism released pulses of sulphur dioxide that was then broken down by ultraviolet photodissociation

volcanic degassing hydrothermal circulation and the flourishing of early life on earth a review of the evidence from c 3490 3240 ma rocks of the pilbara supergroup pilbara craton western australia abstract new data gathered during mapping of c 3490 3240 ma rocks of the pilbara supergroup in the pilbara craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism for most cherts fossil hydrothermal fluid pathways are preserved as silica barite fe bearing veins that cut through the footwall and up to the level of individual bedded chert units but not above indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events silica barite fe bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units and occurred under alternating high sulphidation and low sulphidation conditions these veins provided pathways to the surface for elements leached from the footwall e g si ba fe and volcanogenic emissions from underlying felsic magma chambers e g co 2 h 2 s hs so 2 stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of warrawoona group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and or degassing of these magmas heat from these intrusions drove episodes of hydrothermal circulation listric normal faulting during caldera collapse produced basins with restricted circulation of seawater eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components thereby providing habitats suitable for early life forms fossil stromatolites from two distinct stratigraphic units in the north pole dome grew in shallow water conditions but in two very different geological settings with different morphologies stratiform and domical stromatolites in the stratigraphically lower c 3490 ma dresser formation of the warrawoona group are intimately associated with barite and chert precipitates from hydrothermal vents suggesting that component microbes may have been chemoautotrophic hyperthermophiles evidence of shallow water to periodically exposed conditions active growth faulting and soft sediment deformation indicates that the volcanogenic emissions were erupted into a shallow water tectonically active caldera and concentrated therein to produce an extreme habitat for early life widespread conical and pseudocolumnar stromatolites in the c 3400 ma strelley pool chert at the base of the unconformably overlying kelly group occur in shallow marine platform carbonates silicification was the result of later hydrothermal circulation driven by heat from the overlying newly erupted euro basalt the markedly different morphology and geological setting of these only slightly younger stromatolites compared with the dresser formation suggests a diversity of microbial life on early earth the biogenicity of putative microfossils from this and younger hydrothermal silica veins in the warrawoona group remains controversial and requires further detailed study

multiple sulfur isotope constraints on sulfate driven anaerobic oxidation of methane evidence from authigenic pyrite in seepage areas of the south china sea abstract multiple sulfur isotope signatures and secondary ion mass spectroscopy sims sulfur isotope compositions of pyrite from two seafloor sites dh cl11 and hd109 in seepage areas of the south china sea were measured in order to study isotope effects of sulfate driven anaerobic oxidation of methane so 4 aom the multiple sulfur isotopes of pyrite reveal variable ranges for both sites 34 s between 44 1 and 2 9 for dh cl11 and between 43 8 and 1 6 for hd109 33 s between 0 02 and 0 17 for dh cl11 and between 0 03 and 0 14 for hd109 sims analysis reveals an extreme variability of 34 s values between 50 3 and 2 7 in dh cl11 between 50 1 and 52 4 in hd109 for three types of pyrite 1 framboids 2 zoned aggregates with radial overgrowth surrounding a framboidal core and 3 euhedral pyrite crystals the synchronous changes of geochemical proxies sulfate and methane concentrations 34 s sulfate and 18 o sulfate 34 s pyrite and pyrite content at the sulfate methane transition zone smtz at site dh cl11 are interpreted to be induced by so 4 aom under steady state conditions in contrast pyrite content and 34 s value fluctuations throughout core hd109 suggest that the sediment at this site was affected by multiple pyritization events during diagenesis multiple sulfur isotope signatures of early diagenetic pyrite i e with low and high 34 s values the latter above 315 cmbsf in dh cl11 above 70 cmbsf in hd109 in the upper sediment column suggest that organoclastic sulfate reduction osr and sulfur disproportionation generated the observed isotopic signatures in contrast to the early diagenetic 34 s depleted framboids the higher sims 34 s values of overgrowth and euhedral crystals suggest a late diagenetic 34 s enriched pool of dissolved sulfide derived from so 4 aom at the current and paleo smtzs interestingly pyrite resulting from so 4 aom in the smtz at site dh cl11 reveals a distinct pattern with higher 33 s values different from pyrite resulting from osr and sulfur disproportionation therefore paired 34 s and 33 s values may allow to differentiate osr and so 4 aom although a full understanding of the isotope effects associated with so 4 aom is hampered by uncertainties on the actual electron transfer mechanism in the syntrophic so 4 aom consortium

paleoarchean sulfur cycle and biogeochemical surface conditions on the early earth barberton south africa abstract this study presents the first multiple sulfur isotope dataset on sulfides from the ca 3 5 3 2 ga onverwacht group in the paleoarchean barberton greenstone belt bgb of south africa in situ 34 scdt and 33 s values of pyrite n 568 are reported from a wide range of hydrothermal volcanic and sedimentary environments and are used to explore mid archean biogeochemical sulfur cycling samples are from fresh drill core collected by the barberton scientific drilling project that intercepted cherts metabasalts and sheared ultramafics of the 3 3 3 35 ga kromberg formation the sedimentary units of the 3 432 ga noisy formation and the unconformably underlying metabasaltic pillow lavas of the 3 472 ga hooggenoeg formation pyrite in quartz carbonate veins in the lower diamictite of the noisy sequence records the largest range and most negative 34 scdt values so far reported from an archean terrain 34 s cdt 55 04 to 27 46 the noisy sediments also contain detrital and diagenetic pyrites with a significant variation in 33 s of between 0 62 to 1 4 and 34 scdt of between 7 00 and 12 6 interpreted to reflect tectonic exposure of these early sediments to atmospheric shallow marine conditions early marine pyrites from the kromberg cherts also display strong positive 33 s values up to 2 50 with narrow range in 34 scdt values 6 00 to 1 50 whereas hydrothermal veins in the basal ultramafic shear zones preserve magmatic values 0 this study reveals a potential proto tectonic control on atmospheric geodynamic and hydrothermal environments available for early sulfate reducing and or methanogenic microbes in the paleoarchean no evidence for microbial sulfate reduction or disproportionation was identified in the kromberg cherts despite previous morphological claims for microbial life highly variable and negative 34 scdt values were found in the noisy turbidites and hooggenoeg pillow lava breccia supporting the presence of microbial sulfate reduction in early tectono sedimentary basins and in the paleoarchean sub seafloor respectively in light of current controversies surrounding sulfur isotope studies in similar aged rocks of the pilbara craton west australia we argue that microbial elemental sulfur disproportionation was not a preferred metabolic pathway on the paleoarchean earth

two coexisting sulfur metabolisms in a ca 3400 ma sandstone a sandstone from the ca 3400 ma strelley pool formation of western australia contains pristine micron sized pyrite intimately associated with organic material coating framework quartz grains a synsedimentary to early diagenetic origin for this pyrite is indicated by its occurrence in black bedded sandstone at the base of the formation and in reworked black clasts higher up in the formation high resolution multiple sulfur isotope analysis 32s 33s 34s using secondary ion mass spectrometry nanosims and large radius ion microprobe reveals 34svcdt vienna canyon diablo troilite values between 12 and 6 and 33s values between 1 65 and 1 43 from pyrite grains within a single thin section a large spread of 34s values over only 5 10 m together with the spatial association of pyrite with carbon and nitrogen indicates biological processing of sulfur the presence of both 33s and 33s signals overprinted by significant mass dependent 34s fractionation in this pyrite population indicates for the first time that both microbial sulfate reduction of aqueous sulfate 33s and microbial disproportionation of elemental sulfur 33s were co occurring in an open marine sedimentary hosted ecosystem in the paleoarchean

in situ quadruple sulfur isotopic compositions of pyrites in the ca 3 2 2 72 ga metasedimentary rocks from the pilbara craton western australia abstract the sulfur mass independent fractionation s mif of mesoarchean is distinct from the other archean periods by the dampened magnitudes of 33s and a steeper slope of 36s 33s compared with the archean reference array ara according to previous studies however samples available of this interval are limited owing to poor or no preservation additionally the majority of the data were obtained by analysis of bulk rocks thus are essentially the sulfur isotopic compositions of mixed sulfur components due to multiple stages of post diagenesis overprints and modifications this study systematically measured the multiple sulfur isotopic compositions of pyrites nodular disseminated in ca 3 2 2 72 ga metasedimentary rocks from the pilbara craton western australia where one of the best preserved archean records occur using the upgraded shrimp si after detailed pyrite generation and genesis investigation by bse imaging and naocl etching the results show that 33s values of the diagenetic pyrites in these metasedimentary rocks range from 2 4 to 0 8 such a range is inconsistent with the other archean intervals and any experiment producing s mif so far where the magnitude of the maximum positive 33s value is considerably larger than the corresponding minimum negative 33s value the dampened positive 33s is explained in several ways from the perspective of production and preservation including original photochemical products with larger magnitudes of negative 33s than positive 33s in a different atmospheric composition non zero 33s of initial so2 different mechanism producing s mif chain formation and destruction of positive 33s by subduction the downward 36s 33s deviations from ara in the diagenetic pyrites of 2 72 ga tumbiana formation can be attributed to modifications induced by microbial activities this is based on the negative 0 9 33s 36s values similar to biological products and the large range of negative 34s values the downward 36s 33s offsets in the hydrothermally altered diagenetic pyrites of 2 78 ga mt roe basalt are most likely mixing of primary sulfur on ara with later sulfur disobeying ara the upward 36s 33s deviations in the diagenetic pyrites of 2 93 ga mosquito creek formation likely reflect different atmospheric composition

sulphur isotope evidence for an oxic archaean atmosphere the presence of mass independently fractionated sulphur isotopes mif s in many sedimentary rocks older than approximately 2 4 billion years gyr and the absence of mif s in younger rocks has been considered the best evidence for a dramatic change from an anoxic to oxic atmosphere around 2 4 gyr ago this is because the only mechanism known to produce mif s has been ultraviolet photolysis of volcanic sulphur dioxide gas in an oxygen poor atmosphere here we report the absence of mif s throughout approximately 100 m sections of 2 76 gyr old lake sediments and 2 92 gyr old marine shales in the pilbara craton western australia we propose three possible interpretations of the mif s geologic record 1 the level of atmospheric oxygen fluctuated greatly during the archaean era 2 the atmosphere has remained oxic since approximately 3 8 gyr ago and mif s in sedimentary rocks represents times and regions of violent volcanic eruptions that ejected large volumes of sulphur dioxide into the stratosphere or 3 mif s in rocks was mostly created by non photochemical reactions during sediment diagenesis and thus is not linked to atmospheric chemistry

coupled fe and s isotope variations in pyrite nodules from archean shale ron and sulfur isotope compositions recorded in ancient rocks and minerals such as pyrite fes2 have been widely used as a proxy for early microbial metabolisms and redox evolution of the oceans however most previous studies focused on only one of these isotopic systems herein we illustrate the importance of in situ and coupled study of fe and s isotopes on two pyrite nodules in a c 2 7 ga shale from the bubi greenstone belt zimbabwe fe and s isotope compositions were measured both by bulk sample mass spectrometry techniques and by ion microprobe in situ methods secondary ion mass spectrometry sims spatially resolved analysis across the nodules shows a large range of variations at micrometer scale for both fe and s isotope compositions with 56 fe and 34 s values from 2 1 to 0 7 and from 0 5 to 8 2 respectively and 33 s values from 1 6 to 2 9 the fe and s isotope variations in these nodules cannot be explained by tandem operation of dissimilatory iron reduction dir and bacterial sulfate reduction bsr as was previously proposed but rather they reflect the contributions of different fe and s sources during a complex diagenetic history pyrite formed from two different mineral precursors 1 mackinawite precipitated in the water column and 2 greigite formed in the sediment during early diagenesis the in situ analytical approach reveals a complex history of the pyrite nodule growth and allows us to better constrain environmental conditions during the archean

structural analysis of syn depositional hydrothermal veins of the 3 48 ga dresser formation pilbara craton australia abstract the lower chert unit of the 3 48 ga dresser formation pilbara craton western australia hosts earth s oldest convincing evidence of life in the form of stromatolites in a depositional setting that has been interpreted as either a shallow marine lagoon an active volcanic caldera or a basin deposited during regional extension understanding the environment where early life thrived is important not only for early life studies on earth but in the search for life on mars and for understanding the setting for the origin of life structural analysis of the extensive network of syn depositional hydrothermal chert barite veins that immediately underlies the dresser was undertaken in order to test if deposition occurred within an evolving caldera system or during regional extension over 190 hydrothermal veins were mapped for their geometry and relative age relationships bedding orientations were recorded within nine fault bounded structural sub blocks and used for back rotating the measured veins to their original orientation the results show that 1 there are four main vein systems including three that were emplaced during deposition of the dresser formation lower chert unit and a fourth that was emplaced within syn to post depositional listric growth faults 2 the majority of veins were sub vertical prior to regional tilting 3 the first three vein systems show mutually cross cutting relationships 4 vein densities and the number of vein systems vary between sub blocks 5 conjugate vein networks ne sw and nw se dominate two middle and northern sub blocks these results show that the first three vein systems were emplaced through fracturing under a stress regime with a vertical 1 vertical conjugate fractures are consistent with sandbox models of overburden fracturing during emplacement and discharge of a magma chamber in a volcanic caldera areas of single vein orientations reflect marginal areas of the caldera system dominated by radial or by ring faults the veins in late listric growth faults represent the final period of caldera collapse which controlled the depositional thicknesses of overlying strata possibly during subsequent regional extension these results document an unique setting for earliest life on earth within shallow water and terrestrial deposits of an active low eruptive caldera setting

pyrite in a sulfate poor paleoarchean basin was derived predominantly from elemental sulfur evidence from 3 2 ga sediments in the barberton greenstone belt kaapvaal craton abstract multiple sulfur isotope variability in archean sedimentary rocks provides constraints on the composition of the earth s earliest atmosphere the magnitude and sign of mass independent anomalies reflect not only atmospheric processes but also transformations due to the archean marine sulfur cycle prior to preservation into sedimentary pyrite the processes affecting the archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear here we combine iron fe and multiple sulfur s isotope data in individual pyrite grains with petrographic information and a one dimensional reactive transport model to investigate the sources of fe and s in pyrite formed in a paleoarchean sedimentary basin pyrites were selected from mudstones sandstones and chert obtained from a drill core in the ca 3 2 ga mapepe and mendon formations of the fig tree and onverwacht groups respectively in the barberton greenstone belt kaapvaal craton south africa pyrite textures and 56 fe distinguish early diagenetic pyrite formed with pore water ferrous iron disseminated grains with average 56 fe pyrite 0 from late diagenetic pyrite formed through sulfidation of iron oxide minerals layered and aggregate forms with average 56 fe pyrite 1 mass dependent s isotope variability in pyrite was small 34 s pyrite ranged from 1 1 to 3 3 with a correspondingly minor spread in 33 s pyrite ranging from 0 3 to 2 1 and 36 s pyrite ranging from 3 08 to 0 27 that indicates a lack of post depositional re working with other distinct sulfur sources our combined fe and s isotope data are most readily explained with pyrite sulfide derived from microbial reworking of solid elemental s iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed the lack of a negative 33 s signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis consistent with low sulfate concentrations in the paleoarchean ocean

sulfur and oxygen isotope fractionation during sulfate reduction coupled to anaerobic oxidation of methane is dependent on methane concentration highlights naturally enriched aom biomass was studied in high pressure continuous incubation we report the first s and o isotope fractionation values by sulfate reduction coupled to aom from culture studies there is a tight link between methane concentration and s and o isotope fractionation s and o isotope fractionation values indicate reversibility of energy limited microbial processes the wide range of environmental s and o isotope signatures can be explained abstract isotope signatures of sulfur compounds are key tools for studying sulfur cycling in the modern environment and throughout earth s history however for meaningful interpretations the isotope effects of the processes involved must be known sulfate reduction coupled to the anaerobic oxidation of methane aom sr plays a pivotal role in sedimentary sulfur cycling and is the main process responsible for the consumption of methane in marine sediments thereby efficiently limiting the escape of this potent greenhouse gas from the seabed to the overlying water column and atmosphere in contrast to classical dissimilatory sulfate reduction dsr where sulfur and oxygen isotope effects have been measured in culture studies and a wide range of isotope effects has been observed the sulfur and oxygen isotope effects by aom sr are unknown this gap in knowledge severely hampers the interpretation of sulfur cycling in methane bearing sediments especially because unlike dsr which is carried out by a single organism aom sr is presumably catalyzed by consortia of archaea and bacteria that both contribute to the reduction of sulfate to sulfide we studied sulfur and oxygen isotope effects by aom sr at various aqueous methane concentrations from 1 4 0 6 mm1 4 0 6 mm up to 58 8 10 5 mm58 8 10 5 mm in continuous incubation at steady state changes in the concentration of methane induced strong changes in sulfur isotope enrichment view the mathml sourcees34 and oxygen isotope exchange between water and sulfate relative to sulfate reduction o o as well as sulfate reduction rates srr smallest view the mathml sourcees34 21 9 1 9 21 9 1 9 and o o 0 5 0 20 5 0 2 as well as highest srr were observed for the highest methane concentration whereas highest view the mathml sourcees34 67 3 26 1 67 3 26 1 and o o 2 5 1 52 5 1 5 and lowest srr were reached at low methane concentration our results show that view the mathml sourcees34 o o and srr during aom sr are very sensitive to methane concentration and thus also correlate with energy yield in sulfate methane transition zones aom sr is likely to induce very large sulfur isotope fractionation between sulfate and sulfide i e 60 60 and will drive the oxygen isotope composition of sulfate towards the sulfate water oxygen isotope equilibrium value sulfur isotope fractionation by aom sr at gas seeps where methane fluxes are high will be much smaller i e 20 to 40

evolution of the oceanic sulfur cycle at the end of the paleoproterozoic here we present new measurements of 32 s 33 s 34 s and 36 s in sedimentary sulfides and couple these measurements with modeling treatments to study the sulfur cycle of a late paleoproterozoic marine basin we target the transition in ocean chemistry from the deposition of paleoproterozoic iron formations gunflint formation biwabik formation trommald formation and mahnomen iron formations to the inferred sulfidic ocean conditions recorded by overlying shale rove formation the data suggest that certain features of the global sulfur cycle such as a control by sulfate reducing prokaryotes and low mm concentrations of oceanic sulfate were maintained across this transition this suggests that the transition was associated with changes in the structure of the basin scale sulfur cycle during deposition of these sediments sulfide data from the iron formations are interpreted to reflect sedimentary sulfides formed from microbial reduction of pore water sulfate that was supplied through steady state exchange with an overlying oceanic sulfate reservoir the sulfide data for the euxinic rove formation shales reflect the operation of a sulfur cycle that included the loss of sulfide by a rayleigh like process we suggest that the prevalence of large and variable heavy isotope enrichments observed in rove formation sulfide minerals reflect a sustained and significant net loss of sulfide from the euxinic water column either as a result of a shallow chemocline and degassing to the atmosphere or as a result of a water column pyrite sink the inclusion of 36 s measurements in addition to 32 s 33 s and 34 s illustrates the mass dependent character of these sedimentary environments ruling out contributions from the weathering of archean sulfides and pointing to at least modest levels of sustained atmospheric oxygen 10 5 present atmospheric levels of o2

multiple sulphur and iron isotope composition of detrital pyrite in archaean sedimentary rocks a new tool for provenance analysis abstract multiple s 34 s and 33 s and fe 56 fe isotope analyses of rounded pyrite grains from 3 1 to 2 6 ga conglomerates of southern africa indicate their detrital origin which supports anoxic surface conditions in the archaean rounded pyrites from meso to neoarchaean gold and uranium bearing strata of south africa are derived from both crustal and sedimentary sources the latter being characterised by non mass dependent fractionation of s isotopes 33 s as negative as 1 35 and large range of fe isotope values 56 fe between 1 1 and 1 2 most sediment sourced pyrite grains are likely derived from sulphide nodules in marine organic matter rich shales sedimentary exhalites and volcanogenic massive sulphide deposits some sedimentary pyrite grains may have been derived from in situ sulphidised fe oxides prior to their incorporation into the conglomerates as indicated by unusually high positive 56 fe values sedimentary sulphides without significant non mass dependent fractionation of s isotopes were also present in the source of some conglomerates the abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high p o 2 as the cause for the absence of significant non mass dependent fractionation processes in the 3 2 2 7 ga atmosphere rounded pyrites from the c 2 6 ga conglomerates of the belingwe greenstone belt in zimbabwe have strongly fractionated 34 s 33 s and 56 fe values the source of which can be traced back to black shale hosted massive sulphides in the underlying strata the study demonstrates the utility of combined multiple s and fe isotope analyses for provenance reconstruction of archaean sedimentary successions

geochemistry of pyrite from diamictites of the boolgeeda iron formation western australia with implications for the goe and paleoproterozoic ice ages abstract sediments of the ca 2400 ma turee creek group of western australia are coincident with the oxygenation of earth s surface associated with the great oxidation event goe diamictite within the boolgeeda iron formation from the boundary ridge section at the duck creek syncline was previously correlated to the glaciogenic sediments of the meteorite bore member of the turee creek group at the hardey syncline martin 1999 the meteorite bore member is considered correlative and time equivalent with the paleoproterozoic glacial diamictites of the 2 45 2 22 ga huronian supergroup in north america if the diamictite units at boundary ridge correspond to worldwide paleoproterozoic glaciations they should also record the disappearance of mass independently fractionated mif sulfur triple s isotope compositions for pyrites from the boundary ridge sections were measured in situ by a multi collector ion microprobe and yielded both mass dependently fractionated mdf and mif sulfur isotope values 33 s values from 0 44 to 6 27 trace element heterogeneities are indicated by measurements at multiple spatial scales within rounded pyrites in the boundary ridge section consistent with multiple generations of pyrite that incorporated sulfur processed in an anoxic atmosphere a compilation of s isotope data from pyrite in the boundary ridge diamictites analyzed in this study and previous work williford et al 2011 defines multiple 34 s vs 33 s arrays consistent with an origin of detrital pyrite from the underlying hamersley and fortescue groups sulfides in a shale unit from the boundary ridge section plot along the terrestrial fractionation line but still retain positive mif s this and detrital pyrite suggest low atmospheric oxygen immediately before the initiation of paleoproterozoic ice ages this data is inconsistent with a correlation to glacially influenced successions within the north american huronian supergroup in which the mif s signal permanently disappears the diamictites at the duck creek syncline are older than the meteorite bore member because their stratigraphic position is within the boolgeeda iron formation that underlies the turee creek group which is separated from the meteorite bore member by nearly 1000 m of the kungarra shale at the hardey syncline

micro scale quadruple sulfur isotope analysis of pyrite from the 3480 ma dresser formation new insights into sulfur cycling on the early earth abstract we report in situ quadruple sulfur isotope analysis 32s 33s 34s and 36s of a pyritized microbial mat from the 3480 ma dresser formation pilbara craton western australia these data yield positive 34s and 33s indicative of sulfur sourced from a pool with similar character as the putative atmospheric elemental sulfur channel of pavlov and kasting 2002 contrary to previous data from the dresser formation however this pyrite is heavily depleted in 36s with a 36s 33s slope of c 3 6 much steeper than slopes typically seen in other early archean rock successions 36s 33s 1 which suggests either a different atmospheric signature for deposited s or a different pool altogether significant micro scale isotopic heterogeneity is observed within the microbial mat 34s 1 6 to 6 7 33s 0 4 to 2 6 36s 3 1 to 8 1 implying a role for microbial s metabolism while metabolic s cycling has been shown to shift 36s to lower values microbial metabolization of s does not appear sufficient to account for the full range of 36s we conclude that the isotopic composition of the pyrite was controlled by the relative proportions of mass independently fractionated mif s0 and sulfate derived sulfur incorporated into polysulfide pyrite precursors during reactions in the microbial mat the dominance of the mif s0 isotopic signature 34s 33s 36s indicates that contributions from the sulfate derived sulfur pool were relatively small consistent with low concentrations of sulfate in archean seawater and that contributions from a non sulfate pool were significant micro scale isotopic heterogeneity in the pyrite points to mixing between the two sulfur pools in selected micro environments within the microbial mat the particularly negative 36s observed here reveals a 3480 ma sulfur reservoir with novel 36s 33s chemistry whose significance now requires further investigation

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved

δ13c and δ15n in the ornithogenic sediments from the antarctic maritime as palaeoecological proxies during the past 2000 yr abstract in this paper we have examined carbon and nitrogen isotopic compositions in two ornithogenic sediment profiles from the ardley island and barton peninsula of antarctica for palaeoecological changes during the past 2000 yr the 13 c values of the two sediment profiles range from 22 26 to 19 15 pdb in core g and from 24 01 to 19 87 in profile a showing that the predominant carbon source in the sediments plausibly comes from terrestrial and aquatic plants in antarctic such as mosses lichens and algae in lakes as these 13 c values are also close to those in the fresh lake sediments that are not influenced by penguin guano one may not use the 13 c values as evidence for the influence of guano on the sediments the 15 n values of the two profiles range from 4 75 to 18 34 air and from 5 17 to 10 38 for core g and core a respectively the 15 n variations have positive correlations with the trends of the bio element contents in the sediments as the levels of these bio elements in ornithogenic sediments had been used to reconstruct the changes of historical penguin population and tundra vegetation abundance and diversity we then suggest that the 15 n records can be utilized to study palaeoecological processes of penguin our results show that penguin population and activity has generally decreased over the past 2000 yr from 1300 to 900 yr bp and from 1790 to 1860 ad penguin population and activity experienced two strong decreases it will be interesting to understand the cause of these decreases

sulfur isotopic trends and iron speciation from the c 2 0 ga pilgujarvi sedimentary formation nw russia abstract sulfide sulfur isotope values and iron speciation data are reported here for sediments from the 2 0 ga old pilgujarvi sedimentary formation pechenga greenstone belt nw russia sulfides are abundant throughout the c 1400 m thick turbiditic sandstone siltstone shale succession and present as pyrite and pyrrhotite a stratigraphic trend is discernible with respect to sulfide mineralogy and sulfur isotopic compositions changing up section from highly to less variable and positive 34 s values the occurrence of pyrrhotite particularly high in the upper part of the section is thought to be the result of decomposition of pyrite during low grade metamorphism this is evidenced by the crystallographic habit and sulfur isotopic composition of the different sulfide minerals the 34 s of both sulfur species is quite variable in the lower part of the formation 9 5 to 18 7 while the upper part displays a smaller fluctuation in 34 s 4 4 13 3 the pyrrhotite is generally depleted in 34 s by approximately 3 6 average isotopic difference between pyrrhotite and pyrite compared to the pyrite this shift in the sulfur isotopic composition results from thermal decomposition of pyrite the overall spread in 34 s is indicative for the microbial reduction of sulfate but 34 s values suggest a sulfate limited environment in the upper part of the formation we note however that the sulfate limitation is restricted to the pore water realm caused by high sedimentation rates that inhibited a sufficiently high sulfate flux from the overlying water column into the sediment based on iron speciation data a previous characterization of the depositional environment as non euxinic can be specified more precisely we note that the siliciclastic succession of the pilgujarvi sedimentary formation was deposited under anoxic and ferruginous water column conditions derived from high ratios of fe hr fe t and low ratios of fe py fe hr

a field guide to finding fossils on mars the martian surface is cold dry exposed to biologically harmful radiation and apparently barren today nevertheless there is clear geological evidence for warmer wetter intervals in the past that could have supported life at or near the surface this evidence has motivated national aeronautics and space administration and european space agency to prioritize the search for any remains or traces of organisms from early mars in forthcoming missions informed by 1 stratigraphic mineralogical and geochemical data collected by previous and current missions 2 earth s fossil record and 3 experimental studies of organic decay and preservation we here consider whether how and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early mars we conclude that noachian hesperian fe bearing clay rich fluvio lacustrine siliciclastic deposits especially where enriched in silica currently represent the most promising and best understood astropaleontological targets siliceous sinters would also be an excellent target but their presence on mars awaits confirmation more work is needed to improve our understanding of fossil preservation in the context of other environments specific to mars particularly within evaporative salts and pore fracture filling subsurface minerals

palaeolimnological evidence for marked holocene environmental changes on signy island antarctica lake sediment cores from heywood and sombre lakes on signy island south orkney islands antarctica have yielded a conformable radiocarbon chronology for the holocene and a high resolution record of environmental change the lakes share a common climate and geology but have distinct catchments this provides an opportunity for using lake sediments to differentiate between local within lake catchment events and those at a regional scale analyses of various biological and physical remains from the lakes suggest that both catchments have undergone considerable changes during the last 5700 years macrofossils moss and crustacean remains are more abundant in the late holocene being associated with a period of high sediment accumulation which is related to diatom evidence for more nutrient rich conditions at the sites this is inter preted as a response to a holocene climate optimum at c 3800 1300 14 c yr bp the record is consistent with other lake ice and ocean core studies although the climate optimum appears to have persisted for a longer period at signy island

sulfidization of 3 48 billion year old stromatolites of the dresser formation pilbara craton constraints from in situ sulfur isotope analysis of pyrite abstract this study reports in situ sulfur isotope analyses 32s 33s 34s and 36s of pyrite in strongly sulfidized stromatolites from the 3 48 billion year old dresser formation pilbara craton australia these data shed light on sulfur reservoirs and sulfide precipitation processes and provide clues for the contribution of sulfur cycling microbes to sulfidization sulfur isotope signatures derived from mass dependent fractionation mdf monitored by 34s and mass independent fractionation mif here 33s and 36s of pyrite in stromatolites and of microscopic pyrite within associated barite allow for the identification of distinctive sulfur sources i magmatic hydrothermal sulfide h2s with 34s and 33s 0 ii magmatic hydrothermal sulfate so42 with a mdf signature mdf so42 34s 10 and 33s 0 iii photochemically derived sulfate with a mif signature mif so4 34s 6 and 33s 3 0 iv photochemically derived elemental sulfur s0 with 34s 0 and 33s 0 the sulfur isotope data suggest that sulfidization was largely driven by reduction of intermixed mdf so42 and mif so42 bulk signature of 34s 5 and 33s 1 4 and dilution of produced h2s 34s 12 and 33s 1 4 by native h2s in magmatic hydrothermal fluids the 34s shifts up to 17 generated by sulfate reduction are consistent with both thermochemical reactions and influence of sulfate cycling microbes the latter which may have facilitated rapid pyrite precipitation and preservation of microbial remains that are entombed within the petrogenetically earliest pyrite generation of stromatolites collectively our data are consistent with ancient stromatolite growth in proximity to shallow marine hydrothermal vents where hydrothermal fluids contributed to sulfidization that may have been further influenced by sulfur cycling microbes

quadruple sulfur isotope analysis of ca 3 5 ga dresser formation new evidence for microbial sulfate reduction in the early archean abstract multiple sulfur isotope system is a powerful new tracer for atmospheric volcanic and biological influences on sulfur cycles in the anoxic early earth here we report high precision quadruple sulfur isotope analyses 32s 33s 34s 36s of barite pyrite in barite and sulfides in related hydrothermal and igneous rocks occurring in the ca 3 5 ga dresser formation western australia our results indicate that observed isotopic variations are mainly controlled by mixing of mass dependently md and non mass dependently fractionated non md sulfur reservoirs based on the quadruple sulfur isotope systematics 34s 33s 36s for these minerals four end member sulfur reservoirs have been recognized 1 non md sulfate 34s 5 2 33s 3 1 2 md sulfate 34s 10 3 3 non md sulfur 34s 6 33s 4 and 4 igneous md sulfur 34s 33s 0 the first and third components show a clear non md signatures thus probably represent sulfate and sulfur aerosol inputs the md sulfate component 2 is enriched in 34s 10 3 and may have originated from microbial and or abiotic disproportionation of volcanic s or so2 our results reconfirm that the dresser barites contain small amounts of pyrite depleted in 34s by 15 22 relative to the host barite these barite pyrite pairs exhibit a mass dependent relationship of 33s 34s with slope less than 0 512 which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation 0 515 the barite pyrite pairs also show up to 1 difference in 36s values and steep 36s 33s slopes which deviate from the main archean array 36s 33s 0 9 and are comparable to isotope effects exhibited by sulfate reducing microbes 36s 33s 5 to 11 these new lines of evidence support the existence of sulfate reducers at ca 3 5 ga whereas microbial sulfur disproportionation may have been more limited than recently suggested

primary sulfur isotope signatures preserved in high grade archean barite deposits of the sargur group dharwar craton india abstract we report in situ and bulk s isotope analyses of the 3 2 ga old barite deposit of the sargur group dharwar craton india compared with the two other coeval barite deposits in western australia pilbara craton warrawoona and sulfur springs group and south africa kaapvaal craton onverwacht and fig tree group the rocks of the sargur group have experienced pervasive ductile deformation and equilibrated under high grade metamorphic conditions which could have caused partial s isotope re equilibration however in situ techniques revealed high spatial heterogeneities in 34 s of up to 18 in barite bearing pyrites as well as similar 33 s anomalies compared to the associated sulfate indicating bacterial sulfate reduction isotope effects and a minor impact of the pervasive ductile deformation and metamorphism on the primary diagenetic signatures our data in associated silicate rocks define consistent trends in 33 s 34 s and 36 s 33 s reflecting metamorphic reworking of primary photolytic signatures with sulfide deriving from thermal reduction of the barite sulfate at 400 c our results match the previous data obtained on other early archean barite deposits this strongly suggests that similar sulfur sources were at play over the three continents during the production and preservation of atmospheric sulfate and elemental sulfur aerosols this also confirms that the different early archean barite deposits known on earth formed during periods of intense subaerial volcanism and record volcanic photolytic signatures different from those common in the archean

paleoarchean sulfur cycling multiple sulfur isotope constraints from the barberton greenstone belt south africa mass dependent and mass independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the barberton greenstone belt 3550 3215 ma south africa provide constraints for sulfur cycling on the early earth four different sample suites were studied komatiites and tholeiites barite massive and disseminated sulfide ores and non mineralized black shales variable but generally slightly positive 34s values between 0 7 and 5 2 negative 33s values between 0 50 and 0 09 and a negative correlation between 34s and 33s as well as between 33s and 36s for komatiites and tholeiites from the komati formation and from the weltevreden formation are outside the expected range of unfractionated juvenile sulfur instead results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater barite from the mapepe formation displays positive 34s values between 3 1 and 8 1 and negative 33s values between 0 77 and 0 34 the mass independent sulfur isotope fractionation indicates an atmospheric sulfur source notably photolytic sulfate whereas the positive 34s values suggest bacterial sulfate reduction of the marine sulfate reservoir non mineralized black shale samples from the presumed stratigraphic equivalent of the mapepe formation show positive 34s values between 0 0 and 1 3 and positive 33s values between 0 59 and 2 45 these results are interpreted to result from the reduction of photolytic elemental sulfur carrying a positive 33s signature positive 34s values ranging from 0 7 to 3 5 and slightly negative 33s values between 0 17 and 0 12 characterize massive and disseminated sulfides from the bien venue prospect results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source but a contribution from recycled seawater sulfate which would be indicative of submarine hydrothermal activity cannot be ruled out massive and disseminated sulfides from the m hlati prospect are distinctly different from massive and disseminated sulfide from the bien venue prospect they show negative 34s values between 1 2 and 0 1 and positive 33s values between 2 66 and 3 17 thus displaying a sizeable mass independent sulfur isotopic fractionation again these samples clearly exhibit the incorporation of an atmospheric mif s signal the source of sulfur for these samples has positive 33s values suggesting a connection with photolytic elemental sulfur in conclusion the sulfur isotope signatures in paleoarchean rocks from the barberton greenstone belt are diverse and indicate the incorporation of different sources of sulfur for komatiites and tholeiites barite and massive and possibly also disseminated sulfides from bien venue multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin while massive and disseminated sulfides from m hlati and non mineralized black shales are related to a second photolytic elemental sulfur end member

mass independent isotope effects in archean 2 5 to 3 8 ga sedimentary sulfides determined by ion microprobe analysis we report sulfur isotope anomalies with 33 s the deviation from a mass dependent fractionation line for the three isotope system 34 s 32 s vs 33 s 32 s ranging up to 2 within individual archean sedimentary sulfides from a variety of localities our measurements which are made in situ by multicollector secondary ion mass spectrometry unequivocally corroborate prior bulk measurements of mass independent fractionations mif in sulfur and provide additional evidence for an anoxic atmosphere on the earth before 2 ga this technique also offers new opportunities for exploring ancient sulfur metabolisms preserved in the rock record the presence of mif sulfur in sulfides from a 3 8 ga fe rich quartzite from akilia island west greenland is consistent with a marine sedimentary origin for this rock copyright 2003 elsevier science ltd

evaluating the role of microbial sulfate reduction in the early archean using quadruple isotope systematics abstract microscopic pyrites with low 34 s 32 s ratios in 3 47 gyr old sedimentary barites from north pole australia have been interpreted as evidence for microbial sulfate reduction and or sulfur disproportionation in the early archean we show that these microscopic sulfides have similar to slightly less negative 33 s and slightly more negative 36 s values compared to the enclosing sulfate crystals this finding is consistent with a primary mass independent signature overprinted by biological sulfate reduction as calibrated by previous experimental laboratory culture studies however it is inconsistent with an overprint by abiological sulfate reduction or sulfur disproportionation as predicted by isotope exchange theory and laboratory culture studies thus our multiple sulfur isotope measurements support the contention that sulfate reducing microbes had evolved by 3 47 billion years ago

reworking of atmospheric sulfur in a paleoarchean hydrothermal system at londozi barberton greenstone belt swaziland anomalous fractionation of the minor isotopes of sulfur 33s 36s in archean pyrite is thought to reflect photochemical reactions in an anoxic atmosphere with most samples falling along a reference array with 36s 33s 1 small deviations from this array record microbial sulfate reduction or changes in atmospheric source reactions here we argue that reworking of atmospheric sulfur with distinct minor sulfur isotope ratios 36s 33s 1 produced additional variability in sulfide 33s and 36s values in a 3 52 ga hydrothermal barite deposit at londozi barberton greenstone belt swaziland in situ measurement of the four stable sulfur isotopes in pyrite revealed 36s 33s relationships and a 36s 33s trend 3 2 0 4 which is significantly different from the co variation between 36s and 33s in the co existing barite that reflects ambient paleoarchean seawater sulfate this argues against biological or thermochemical sulfate reduction at the time of barite deposition and requires incorporation of sulfide generated in a chemically distinct atmosphere before 3 52 ga we propose a model that combines reworking of this sulfur by hydrothermal leaching deep mixing with juvenile sulfur and surface mixing with biogenic sulfide to explain the observed variation in 34s 33s and 36s these interactions between abiotic and biological processes in the londozi hydrothermal system complicate the interpretation of biosignatures based on deviations in 33s and 36s from the archean reference array

sulfur isotope mass independent fractionation in impact deposits of the 3 2 billion year old mapepe formation barberton greenstone belt south africa abstract theoretical and experimental studies have shown that atmospheric so 2 isotopologue self shielding effects in the 190 220 nm region of the solar spectrum are the likely cause for mass independent fractionation of sulfur isotopes s mif the main products of this photochemical reaction so 3 and s 0 typically define a compositional array of ca 33 s 34 s 0 06 0 14 this is at odds with the generally observed trend in archean sulfides which broadly defines an array of ca 33 s 34 s 0 9 various explanations have been proposed including a diminution of 34 s caused by chemical and biogenic mass dependent fractionation of sulfur isotopes s mdf mixing with photolytic products produced during felsic volcanic events or partial blocking of the low wavelength part of the spectrum due to the presence of reduced atmospheric gases or an organic haze early in earth history large meteorite impacts would have ejected dust and gas clouds into the atmosphere that shielded solar radiation and affected global climate it is thus likely that at certain time intervals of high meteorite flux the atmosphere was significantly perturbed having an effect on atmospheric photochemistry and possibly leaving anomalous sulfur isotopic signatures in the rock record here we describe the sulfur isotopic signatures in sulfides of spherule beds s2 s3 and s4 of the barberton greenstone belt south africa in particular in spherule bed s3 and to a lesser extent s4 a trend of ca 33 s 34 s 0 23 is observed that closely follows the expected trend for so 2 photolysis in the 190 220 nm spectral range this suggests that an impact dust cloud deposited as spherule beds which sampled the higher region of the atmosphere specifically incorporated products of so 2 photolysis in the 190 220 nm range and blocked photochemical reactions at higher wavelengths 250 330 nm band by implication the generally observed archean trend appears to be the result of mixing of different mif s sources arising from a variety of photochemical reactions that took place in the lower part of the atmosphere

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

mass dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles abstract sulfur isotope studies of post archean terrestrial materials have focused on the ratio 34s 32s because additional isotopes 33s and 36s were thought to carry little information beyond the well known mass dependent relationship among multiple isotope ratios we report high precision analyses of 33s and 36s values defined as deviations of 33s and 36s from ideal mass dependent relationships for international reference materials and sedimentary sulfides of phanerozoic age by using a fluorination technique with a dual inlet isotope ratio mass spectrometer measured variations in 33s and 36s are explained as resulting from processes involve branching reactions two or more reservoirs formed or mixing irreversible processes in closed systems rayleigh distillation amplify the isotope effect we outline how this new isotope proxy can be used to gain new insights into fundamental aspects of the sulfur biogeochemical cycle including additional constraints on seawater sulfate budget and processes in sedimentary sulfide formation the isotope systematics discussed here cannot explain the much larger variation of 33s and 36s observed in archean rock records furthermore phanerozoic samples we have studied show a characteristic 33s and 36s relationship that differs from those measured in archean rocks and laboratory photolysis experiments thus high precision analysis of 33s and 36s can be used to distinguish small non zero 33s and 36s produced by mass dependent processes from those produced by mass independent processes in archean rocks and extraterrestrial materials

gold accumulation in the archaean witwatersrand basin south africa evidence from concentrically laminated pyrite abstract concentrically laminated pyrite is a relatively common although volumetrically minor component of auriferous conglomerates in the archaean ca 3 0 2 7 ga witwatersrand basin of south africa this type of pyrite contains high amounts several tens of ppm of au but the origin of the pyrite is debated and the timing of au deposition in these grains is not known in order to constrain the formation of pyrite we have studied concentrically laminated pyrite and other coexisting types of pyrite inclusion rich massive pyrite by analysing the contents and distribution of au and other trace elements by laser ablation icp ms the s and fe isotope composition by sims and the mineral inclusions by scanning electron microscope and laser raman spectroscopy trace element maps indicate that concentrically laminated pyrite is enriched in sb mn au ag tl cu mo mn and contains two types of gold finely dispersed au invisible gold with au ag 0 1 and likely of primary origin and au inclusions with au ag 10 of secondary origin the study of mineral inclusions revealed the presence of muscovite chlorite fine grained carbonaceous matter monazite ti oxides and quartz iron and multiple s isotopes suggest that concentrically laminated pyrite and inclusion rich pyrite were formed from two separate pools of s and fe with different isotope characteristics sulfur was derived from atmospheric s that had undergone mass independent isotope fractionation to form so 4 2 with negative 33 s that constituted concentrically laminated pyrite and elemental s with positive 33 s that formed inclusion rich pyrite iron pools were derived from partial oxidation of fe 2 so that concentrically laminated pyrite formed from a low 56 fe residual fe 2 average 0 2 and inclusion rich pyrite formed from a high 56 fe fe 3 pool average 2 7 biological activity may have been involved in the reduction of so 4 2 causing a wide spread of 34 s values 25 s reducing microorganisms as well as in the partial oxidation of fe 2 anaerobic photosynthetic fe reducers or photosynthetic o 2 producers and in the formation of pyrite from fe 3 dissimilatory fe reducers we propose that concurrent biogenically mediated pyrite formation and au trapping suggest that microbial activity was responsible for the accumulation of au and other trace elements e g sb mn ag tl cu mo mn which are commonly enriched in organic matter rich sediments