nitrogen isotopic composition of ammoniated phyllosilicates case studies from precambrian metamorphosed sedimentary rocks ammonium concentrations in phyllosilicates from archean and proterozoic schists and carbonates were evaluated by fourier transform infrared microspectrometry aftir the y 15 nair values of structural nitrogen in these phases were subsequently measured by laser mass spectrometry a rapid estimate of the concentration of nh4 in biotite by aftir allows the preselection of the samples to be analyzed for their isotopic composition micas from 1 90 2 09 ga metasediments from finland and from 1 025 1 500 ga biotite schists from the moine succession in scotland have high concentrations of structural ammonium between 176 and 1549 ppm suggestive of a biological origin for the nitrogen the heavy nitrogen isotopic signatures y 15 n 4 9x to 19 7x of structural nh4 in these micas are considered consistent with biological denitrification in operation at the time of sedimentation evidence for denitrification in the mesoproterozoic is in agreement with geological and geochemical data for abundant free oxygen in the atmosphere facilitating the stability of marine no3 sequences of early archean ca 3 8 ga garnet mica schists from the isua supracrustal belt isb in southern west greenland contain biotite rich in nh4 between 233 and 512 ppm and nitrogen isotopic signatures y 15 n 1 9x to 5 9x which possibly point to an early evolution of ammonium assimilation and or nitrogen fixation this result appears to be consistent with molecular phylogenetic studies in the bacterial and archaeal domains which suggest that nitrogen fixation and ammonium assimilation were metabolic features of the last common ancestor lca of all organisms d 2004 elsevier b v all rights reserved

mantle flow in regions of complex tectonics insights from indonesia 1 indonesia is arguably one of the tectonically most complex regions on earth today due to its location at the junction of several major tectonic plates and its long history of collision and accretion it is thus an ideal location to study the interaction between subducting plates and mantle convection seismic anisotropy can serve as a diagnostic tool for identifying various subsurface deformational processes such as mantle flow for example here we present novel shear wave splitting results across the indonesian region using three different shear phases local s sks and downgoing s to improve spatial resolution of anisotropic fabrics allows us to distinguish several deformational features for example the block rotation history of borneo is reflected in coast parallel fast directions which we attribute to fossil anisotropy furthermore we are able to unravel the mantle flow pattern in the sulawesi and banda region we detect toroidal flow around the celebes sea slab oblique corner flow in the banda wedge and sub slab mantle flow around the arcuate banda slab we present evidence for deep sub 520 km anisotropy at the java subduction zone in the sumatran backarc we measure trench perpendicular fast orientations which we assume to be due to mantle flow beneath the overriding eurasian plate these observations will allow to test ideas of for example slab mantle coupling in subduction regions

extreme 13ccarb enrichment in ca 2 0 ga magnesite stromatolite dolomite red beds association in a global context a case for the world wide signal enhanced by a local environment abstract the palaeoproterozoic positive excursion of 13 c carb is now considered as three positive shifts of 13 c carb separated by returns to 0 which all occurred between 2 40 and 2 06 ma this isotopic event is unique in terms of both duration 300 ma and 13 c enrichment up to 18 the mechanism responsible for one of the most significant carbon isotopic shifts in earth history remains highly debatable to date 13 c of 10 to 15 cannot be balanced by organic carbon burial forg as there is no geological evidence for an enhanced corg accumulation prior to or synchronous with the excursion instead termination of these excursions is followed by formation of a vast reservoir of 13 c depleted organic material 45 at shunga and by one of the earliest known oil generation episodes at 2 0 ga none of the three positive excursions of 13 c carb is followed by a negative isotopic shift significantly below 0 as has always been observed in younger isotopic events reflecting an overturn of a major marine carbon reservoirs this may indicate that forg was constant implying that the mechanism involved in the production of corg was different onset of intensive methane cycling resulting in c change is another possibility the majority of sampled 13 c carb rich localities represents shallow water stromatolitic dolostones red beds and evaporites formed in restricted intracratonic basins and may not reflect global 13 c carb values closely spaced drill core samples n 73 of stromatolitic dolostones from the 1980 27 ma tulomozerskaya formation in the onega palaeobasin russian karelia have been analysed for 13 c carb and 18 o carb in order to demonstrate that different processes were involved in the formation of 13 c carb rich carbonates the 800 m thick magnesite stromatolite dolomite red beds succession formed in a complex combination of environments on the karelian craton peritidal shallow marine low energy protected bights barred basins evaporative ephemeral ponds coastal sabkhas and playa lakes the carbonate rocks exhibit extreme 13 c enrichment with 13 c values ranging from 5 7 to 17 2 vs v pdb mean 9 9 2 3 and 18 o from 18 6 to 26 0 vs v smow mean 22 0 1 6 the tulomozerskaya isotopic excursion is characteristic of the global 2 4 2 06 ga positive shifts of carbonate 13 c 12 c although it reveals the greatest enrichment in 13 c known from this interval an external basin s is considered to have provided an enhanced corg burial and global seawater enrichment in 13 c the global background value for the isotopic shift at tulomozero time ca 2 0 ga is roughly estimated at around 5 an explosion of stromatolite forming microbial communities in shallow water basins evaporative and partly restricted environments high bioproductivity enhanced uptake of 12 c and pene contemporaneous recycling of organic material in cyanobacterial mats with the production and consequent loss of co2 and ch4 are believed to be additional local factors which may have enhanced 13 c from 5 up to 17 such factors should be taken into account when interpreting carbon isotopic data and attempting to discriminate between the local enrichment in 13 c and globally enhanced 13 c values we propose that many previously reported 13 c values from other localities where environmental interpretations are not available or have not been taken into account may not represent the global 13 c values

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

portales valley a meteoritic sample of the brecciated and metal veined floor of an impact crater on an h chondrite asteroid a shower of meteorite fragments fell at 0730 h local time on 1998 june 13 near the town of portales new mexico thus far 51 pieces of the portales valley h6 meteorite have been recovered this meteorite has an unusually large number of metallic veins some of these veins are also unusually thick having widths on the order of centimeters these wide veins have fine widmanstatten structure which is the first time it has been seen in an ordinary chondrite this structure indicates the metallic veins and the host chondrite cooled slowly these veins appear to have been produced by shock metamorphic processes which we infer produced a 20 km diameter impact crater on an h chondrite planetesimal

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

the age of the gunflint formation ontario canada single zircon u pb age determinations from reworked volcanic ash the gunflint formation a paleoproterozoic chemical clastic sedimentary assemblage outcropping to the immediate northwest of lake superior became famous in 1954 as containing the oldest fossil assemblage known at that time older microfossils have since been discovered but the gunflint procaryotes remain one of the most diverse precambrian fossil communities the finding of possible multicellular organisms in correlative lithic units in michigan has recently added to the need for an exact age of the formation zircons were extracted from rainout and storm reworked volcanoclastic beds in the upper portion of the gunflint formation a euhedral zircon population has yielded a 1878 3 1 3 million years bp u pb age believed to be nearly synchronous with the depositional age this not only provides a precise age for the community of organisms but also strongly supports a back arc extensional setting for the animikie basin rather than a foreland trough resume la formation de gunflint un assemblage sedimentaire chimique et clastique datant du paleoproterozoique affleurant immediatement au nord ouest du lac superieur est devenue celebre en 1954 car elle contenait les plus an ciens assemblages fossiliferes connus a cette epoque de plus anciens microfossiles ont ete decouverts depuis mais les procaryotes de gunflint demeurent l une des communautes fossiles precambriennes les plus diversifiees la decouverte

svecofennian detrital zircon ages implications for the precambrian evolution of the baltic shield metasediments intruded by 1 90 1 87 ga old plutonic rocks form the oldest major proterozoic crustal component in the svecofennian domain of the baltic fennoscandian shield their ndtdm model ages and conventional multigrain zircon u pb ages between 2 4 and 2 1 ga have previously been interpreted either as mixing ages between 1 9 ga old juvenile materials and a minor archaean component or as actual rock and protolith ages to resolve the ensuing controversy 120 individual detrital zircons from svecofennian metasediments in sweden and finland were analysed using the shrimp ion microprobe the oldest materials in this array are a 3 44 ga old zircon from the tampere schist belt in finland and a 3 32 ga old crystal from southeastern sweden about 30 of the analysed crystals are 2 97 2 60 ga old while 65 have ages between 2 12 and 1 88 ga thus there is no evidence of 2 6 2 1 ga old protoliths but the age range of the proterozoic zircons indicates that a major area of 2 1 1 9 ga old crust was in erosional position 1 9 ga ago this implies that the formation of palaeoproterozoic crust in the baltic shield or its one time close neighbourhood must have commenced 100 200 ma earlier than hitherto assumed in conjunction with previously obtained isotopic data the youngest detritus ages of the present study constrain the age of svecofennian sedimentation it can also be concluded that the archaean zircons found in quartzites from southern sweden may have been derived from source areas to the southwest of the central svecofennian marine depositional basin the so called bothnian basin separating southern sweden from the archaean craton in the northeastern part of the shield

chemostratigraphy of carbonates from the minas supergroup quadrilatero ferryifero iron quadrangle brazil a stratigraphic record of early proterozoic atmospheric biogeochemical and climactic change the ca 2 42 ga old gandarela formation overlies the finely laminated caue banded iron formation bif of the itabira group minas supergroup brazil and consists of red carbonate facies bif grading upsection into buff dolomites and limestones which are locally stromatolitic carbonates of the gandarela formation have 1 3 c values ranging narrowly from 1 6 to 0 4 permil versus pdb n 93 the cercadinho formation at the base of the overlying piracicaba group is a thick arenaceous succession with rare thin carbonates that have 1 3 c values ranging from 3 3 to 5 4 permil n 12 stromatolitic dolomites of the overlying fecho do funil formation have pb pb carbonate age 2 11 0 11 ga babinski and others 1995 that provide the minimum age for this unit and 1 3 c values ranging from 5 6 to 7 4 permil n 69 at present we find no evidence in brazil for the any of the three early paleoproterozoic glacial events recognized in 2 45 to 2 22 ga sedimentary successions in north america given the radiometric constraints however it is possible that geological and geochemical traces of these ice ages are missing along the unconformity between the gandarela and cercadinho formations if correct carbonates of the gandarela formation may provide a record of the carbon isotope composition of the seawater prior to any of the paleoproterozoic ice ages combined with other available 1 3 c data results from the gandarela formation suggest that seawater preceding the ice ages was not significantly enriched in 1 3 c on the other hand the carbon isotopic signature of the cercadinho carbonates and chemical composition of the cercadinho arenites are consistent with deposition after the end of the glacial epoch and likely during the early stage of ca 2 22 to 2 1 ga carbon isotope excursion the 1 3 c values of marine carbonates of the fecho do funil formation are consistent with carbon isotope record of contemporaneous carbonate successions worldwide providing additional evidence for a global biogeochemical anomaly at ca 2 22 to 2 1 ga these compositional and isotopic changes allow integration of the minas supergroup into the global record of the paleoproterozoic evolution as well as correlation with other successions of similar age

two billion year old isotopically heavy carbon evidence from the labrador trough canada forty eight samples of bulk carbonates were studied from the dunphy portage alder uve denault and abner formations and the undivided pistolet subgroup in the labrador trough quebec canada the carbonate units occur as a number of thick beds up to 300 m within 100 600 m thick formations they are interbedded with siliciclastic sediments and are composed of crystalline sparry micritic allochemical and stromatolitic dolostones the carbonate rocks are recrystallized and metamorphosed up to amphibolite grade they are chemically dolostones and include chemical or biochemical laminated and massive dolostones dolorudites dolarenites and dololitites which were deposited in shallow water dunphy denault and abner formations to relatively deep water uve formation marine environments reef facies are present in the denault and abner formations the dunphy portage alder and uve formations deposited between 2 17 and 2 14 ga yield isotopically heavy values of 13c pdb ranging from 5 3 to

a u pb age for mineralized nipissing diabase gowganda ontario concordant baddeleyite and rutile analyses from mineralized nipissing diabase at gowganda s castle mine yield a u pb age of baddeleyite is a primary phase of the diabase therefore the age dates the magmatic emplacement the genesis of rutile is less certain rutile could have formed during an episode of alteration veining and ag mineralization in which case the u pb age would also date the secondary event and demonstrate that ag mineralization was related to the nipissing magmatism however a primary magmatic origin of the rutile cannot be completely excluded for now thus the u pb age may not constrain the time of ag mineralization further research is needed to clarify this point

chemostratigraphy of the paleoproterozoic duitschland formation south africa implications for coupled climate change and carbon cycling the paleoproterozoic duitschland formation lies stratigraphically beneath the timeball hill formation which contains the only unequivocal glacial unit of this era in the transvaal basin south africa lithologic evidence in paleoproterozoic successions of north america however indicates the existence of three discrete and potentially global ice ages within this 300 my interval carbonates of the duitschland formation are significantly enriched in 13c up to 10 1 permil in the upper part of the succession above a notable sequence boundary in contrast the lower part of this unit contains carbonates with consistently negative 13c values trace and major element compositions of these carbonates as well as carbon isotopic compositions of coexisting organic matter support a primary origin for the markedly positive carbon isotope anomaly the stratigraphic constraints indicate that 13c enriched carbonates were deposited prior to paleoproterozoic glaciation in southern africa similar to carbonates stratigraphically beneath neoproterozoic glacial diamictites worldwide also mirroring the neoproterozoic record are strongly negative 13c values in cap carbonates atop glacial diamictites in paleoproterozoic strata of wyoming and ontario the litho and chemostratigraphic constraints indicate that the interval of negative carbon isotope values in well preserved carbonates of the lower duitschland formation may reflect a second paleoproterozoic ice age in the transvaal succession this interpretation is further supported by recently discovered bullet shaped clasts with striations in diamictite from the basal part of the succession thus the emerging temporal pattern of carbon isotope variations and glaciation in the paleoproterozoic has a close analogue to neoproterozoic events suggesting a coupling of climatic and biogeochemical changes at both ends of the eon

sm nd and pb isotopic study of mafic rocks associated with early proterozoic continental rifting the peropohja schist belt in northern finland the perapohja schist belt in northern finland rests unconformably on archaean granitoids and marks the early stages of proterozoic crustal evolution in the fennoscandian baltic shield 2440 ma old layered mafic intrusions predate the supracrustal and ca 2200 ma old sills of the gabbro wehrlite association intrude the lowest quartzites and volcanics runkaus of the sequence the sm nd mineral isochron of the penikat layered intrusion gives an age of 2410 64 ma the initial nd values of the penikat intrusion nd 2440 1 6 and the runkausvaara sill nd 2200 0 suggest that these mafic magmas were contaminated by older crustal material the sm nd and pb isotopic results on the 2 44 2 2 ga old runkaus volcanics indicate mobility of pb fractionation of sm nd during late greenschist facies metamorphism and crustal contamination the pb pb data provide an age of 1972 80 ma with a high initial 207pb 204pb ratio 1 8 49 while scattered sm nd data result in an imprecise age of 2330 180 ma with an initial nd value of about zero secondary titanite gives an u pb age of ca 2250 ma the jouttiaapa basalts in contrast ascended from the mantle without interaction with older crust these lree depleted tholeiites mark a break in continental sedimentation and yield a sm nd age of 2090 70 ma their initial nd 4 2 0 5 implies that the subcontinental early proterozoic mantle had been depleted in lree for a long period of time the first lava flows are strongly depleted in lree suggesting that their source was significantly more depleted than the source of mid ocean ridge basalts today

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

multiple sulfur isotopes of sulfides from sediments in the aftermath of paleoproterozoic glaciations geochemical evidence reported from paleoproterozoic sediments has long been used to evaluate the transition from the anoxic archean atmosphere to an oxygenated atmosphere sulfur isotopes 32s 33s 34s and 36s in sedimentary sulfides and sulfates are an especially sensitive means to monitor this transition such that the timing of the paleoproterozoic great oxidation event can be investigated using mass independently fractionated mif sulfur isotope systematics expressed as 33s here we report data from 83 individual analyses of pyrite pyrrhotite and chalcopyrite on a new suite of 30 different samples from finland south africa wyoming and ontario that span 600 my and follow one or several snowball earth events in the paleoproterozoic the samples were measured using a high resolution secondary ion mass spectrometry technique in multicollection mode that investigates multiple sulfur isotopes in microdomains 30 m within individual sulfide grains while preserving petrographic context we focused on sediments deposited in the aftermath of the paleoproterozoic glaciations between 1 9 and 2 2 ga to trace fluctuations in atmospheric o2 concentrations that were likely affected by an interplay of o2 sinks in the atmosphere and the upper ocean and continental crust and by the emergence and diversification of aerobic organisms our results demonstrate that mif sulfur isotopes are absent in sediments deposited after the period of protracted global cooling in the paleoproterozoic and independently confirm observations that mif ceased during this time we interpret our results by integrating 33s and 34s data in sulfides 13c data in carbonates and the estimated timing of glaciation events in the paleoproterozoic data strongly hint at the presence of microbial sulfate reduction and fluctuations in the concentration of dissolved seawater sulfate and or in 34ssulfate in the aftermath of glaciations and likely were affected by changing erosion rates and nutrient delivery to the oceans these changes modulated the population of primary producers especially oxygenic photosynthesizers and led to fluctuations in the abundance of atmospheric o2 co2 and ch4 our results support the interpretation that the world wide 13ccarb excursion observed between 2 25 and 2 05 ga karhu and holland 1996 was a period of significant accumulation of o2 in the atmosphere

positive δ13c excursion in carbonate and organic fractions from the paleoproterozoic aravalli supergroup northwestern india abstract carbon and oxygen isotopic investigations have been carried out on the archean and paleoproterozoic carbonate rocks of the udaipur region in the aravalli mountain belt northwestern india the study has led to the interesting finding of 13 c enrichment in the carbonate rocks of the jhamarkotra formation 13 c carb up to 11 1 v pdb belonging to the 2200 1900 ma paleoproterozoic aravalli supergroup further it is observed that the organic carbon from phosphorite bearing stromatolitic dolomites of the same formation are also enriched in 13 c 13 c org up to 11 1 however it must be emphasized that the 13 c enriched carbonates and the organic fractions are from different stratigraphic levels although in the same formation the former being at a lower stratigraphic level a critical analysis of the field geological petrological as well as the isotopic data indicates that the observed 13 c excursion in the carbonate carbon is not due to local causes such as methanogenesis or evaporitic conditions the shallow water environment of deposition of these carbonates as well as the immediately overlying formations rules out the stratified ocean model for the observed excursion the model involving high sedimentation rates and organic carbon burial has been preferred to explain the 13 c excursion in the carbonates of the jhamarkotra formation the 13 c enrichment in organic fraction occurred in localized regions of the aravalli sedimentary basin where high productivity was supported by phosphorous supply indicating that the diffusion limited pathways of organic carbon fixation were operative in the paleoproterozoic itself the 13 c enriched carbonate rocks of the jhamarkotra formation serve as the indian example for the paleoproterozoic global 13 c excursion

sedimentation rates basin analysis and regional correlations of three neoarchaean and palaeoproterozoic sub basins of the kaapvaal craton as inferred from precise u pb zircon ages from volcaniclastic sediments abstract calculation of sedimentation rates of neoarchaean and palaeoproterozoic siliciclastic and chemical sediments covering the kaapvaal craton imply sedimentation rates comparable to their modern facies equivalents zircons from tuff beds in carbonate facies of the campbellrand subgroup in the ghaap plateau region of the griqualand west basin transvaal supergroup south africa were dated using the perth consortium sensitive high resolution ion microprobe ii shrimp ii dates of 2588 6 ma and 2549 7 ma for the middle and the upper part of the nauga formation indicate that the decompacted sedimentation rate for the peritidal flat to subtidal below wave base stratifera and clastic carbonate facies southwest of the ghaap plateau at prieska was of up to 10 m ma when not corrected for times of erosion and non deposition dates of 2516 4 ma for the upper gamohaan formation and 2555 19 for the upper monteville formation indicate that some 2000 m of carbonate and subordinate shale sedimentation occurred during 16 ma to 62 ma on the ghaap plateau for these predominantly peritidal stromatolitic carbonates decompacted sedimentation rates were of 40 m ma to over 150 m ma bubnoff units the mixed siliciclastic and carbonate shelf facies of the schmidtsdrif subgroup and monteville formation accumulated with decompacted sedimentation rates of around 20 b for the kuruman banded iron formation a decompacted sedimentation rate of up to 60 b can be calculated thus for the entire examined deep shelf to tidal facies range archaean and phanerozoic chemical and clastic sedimentation rates are comparable four major transgressive phases over the kaapvaal craton followed by shallowing upward sedimentation can be recognized in the prieska and ghaap plateau sub basins in griqualand west and partly also in the transvaal basin and are attributed to second order cycles of crustal evolution first order cycles of duration longer than 50 ma can also be identified the calculated sedimentation rates reflect the rate of subsidence of a rift related basin and can be ascribed to tectonic and thermal subsidence comparison of the calculated sedimentation rates to published data from other archaean and proterozoic basins allows discussion of general precambrian basin development siliciclastic and carbonate sedimentation rates of archaean and palaeoproterozoic basins equivalent to those of younger systems suggest that similar mechanical chemical and biological processes were active in the precambrian as found for the phanerozoic particularly for stromatolitic carbonates matching modern and neoarchaean sedimentation rates are interpreted as a strong hint of a similar evolutionary stage of stromatolite building microbiota the new data also allow for improved regional correlations across the griqualand west basin and with the malmani subgroup carbonates in the transvaal basin the nauga formation carbonates in the southwest of the griqualand west basin are significantly older than the gamohaan formation in the ghaap plateau region of this basin but are in part correlatives of the oaktree formation in the transvaal and of parts of the monteville formation on the ghaap plateau

erratum to sulfur isotopic compositions of individual sulfides in martian meteorites alh84001 and nakhla implications for crust regolith exchange on mars earth planet sci lett 184 2000 23 35

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