fractionation of sulfur isotopes during bacterial sulfate reduction in deep ocean sediments at elevated temperatures abstract a numerical model of sulfate reduction and isotopic fractionation has been applied to pore fluid so 4 2 and 34 s data from four sites drilled during ocean drilling program odp leg 168 in the cascadia basin at 48 n where basement temperatures reach up to 62 c there is a source of sulfate both at the top and the bottom of the sediment column due to the presence of basement fluid flow which promotes bacterial sulfate reduction below the sulfate minimum zone at elevated temperatures pore fluid 34 s data show the highest values 135 yet found in the marine environment the bacterial sulfur isotopic fractionation factor is severely underestimated if the pore fluids of anoxic marine sediments are assumed to be closed systems and rayleigh fractionation plots yield erroneous values for by as much as 15 in diffusive and advective pore fluid regimes model results are consistent with 1 077 0 007 with no temperature effect over the range 1 8 to 62 c and no effect of sulfate reduction rate over the range 2 to 10 pmol cm 3 d 1 the reason for this large isotopic fractionation is unknown but one difference with previous studies is the very low sulfate reduction rates recorded about two orders of magnitude lower than literature values that are in the range of mol cm 3 d 1 to tens of nmol cm 3 d 1 in general the greatest 34 s depletions are associated with the lowest sulfate reduction rates and vice versa and it is possible that such extreme fractionation is a characteristic of open systems with low sulfate reduction rates

model based analysis of δ34s signatures to trace sedimentary pyrite oxidation during managed aquifer recharge in a heterogeneous aquifer the oxidation of pyrite is often one of the main drivers affecting groundwater quality during managed aquifer recharge in deep aquifers data and techniques that allow detailed identification and quantification of pyrite oxidation are therefore crucial for assessing and predicting the adverse water quality changes that may be associated with this process in this study we explore the benefits of combining stable sulphur isotope analysis with reactive transport modelling to improve the identification and characterisation of pyrite oxidation during an aquifer storage and recovery experiment in a chemically and physically heterogeneous aquifer we characterise the stable sulphur isotope signal 34s in both the ambient groundwater and the injectant as well as its spatial distribution within the sedimentary sulphur species the identified stable sulphur isotope signal for pyrite was found to vary between 32 and 34 while the signal of the injectant ranged between 9 06 and 14 45 during the injection phase of the experiment both isotope and hydrochemical data together suggest a substantial contribution of pyrite oxidation to the observed temporally variable 34s signals the variability of the 34s signal in pyrite and the injectant were both found to complicate the analysis of the stable isotope data however the incorporation of the data into a numerical modelling approach allowed to successfully employ the 34s signatures as a valuable additional constraint for identifying and quantifying the contribution of pyrite oxidation to the redox transformations that occur in response to the injection of oxygenated water

late permian changhsingian conodont biozonation and the basal boundary ganxi section western hubei province south china four neogondolellid conodont interval zones were recognized across the changhsingian stage at ganxi section western hubei province south china they are in ascending order the clarkina wangi zone the clarkina changxingensis changxingensis zone the clarkina changxingensis yini zone and the clarkina meishanensis meishanensis zone the present study suggests that the base of the changhsingian can be defined by the first appearance datum fad of clarkina wangi within an evolutionary lineage from clarkina longicuspidata to clarkina wangi the wuchiapingian changhsingian boundary can be placed at the base of bed 104 at ganxi section south china because of the first occurrence of clarkina wangi

a three dimensional model of the m2 s2 n2 k1 and o1 tides in the celtic and irish seas abstract a three dimensional model using various parameterizations of eddy viscosity covering the celtic and irish sea region is used to examine the spatial distributions of the m2 s2 n2 k1 and o1 tidal elevations and phases computed cotidal charts and comparisons with observations from shore based and offshore gauges show good agreement comparisons are also made with a standard two dimensional model in shallow water regions the three dimensional model shows significantly less damping than the two dimensional model with an associated improvement in accuracy a detailed examination of differences between computed and observed tidal currents at over thirty locations having three or more current meters in the vertical show that the model can accurately reproduce the tidal current and its vertical profile in the eastern irish sea the region furthest from the model s open boundary good agreement with observations is obtained although in the deeper channel to the south of this the model over predicts current magnitude

carbon isotope stratigraphy across the permian triassic boundary a review abstract the palaeozoic mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon isotope excursion at the permian triassic p t boundary well known from a plethora of marine and continental sediments potential causes for this negative 13 c trend and their links to the latest permian mass extinction have been intensively debated in the literature in order to draw conclusions regarding causation a general 13 c curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background the most important features of the p t carbon isotope trend are the following the 4 7 13 c decline lasting 500 000 years is gradual and began in the changhsingian at the stratigraphic level of the c bachmanni zone the decreasing trend is interrupted by a short term positive event that starts at about the latest permian low latitude marine main extinction event horizon eh indicating that the extinction itself cannot have caused the negative carbon isotope excursion after this short term positive excursion the 13 c decline continues to a first minimum at about the p t boundary a subsequent slight increase is followed by a second occasionally two peaked minimum in the lower and middle i isarcica zone the negative carbon isotope excursion was most likely a consequence of a combination of different causes that may include 1 direct and indirect effects of the siberian trap and contemporaneous volcanism and 2 anoxic deep waters occasionally reaching very shallow sea levels a sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon isotope trend is questionable at least for the time span a little below the eh and somewhat above the p t boundary

δ13c evidence that high primary productivity delayed recovery from end permian mass extinction euxinia was widespread during and after the end permian mass extinction and is commonly cited as an explanation for delayed biotic recovery during early triassic time this anoxic sulfidic episode has been ascribed to both low and high productivity states in the marine water column leaving the causes of euxinia and the mechanisms underlying delayed recovery poorly understood here we use isotopic analysis to examine the changing chemical structure of the water column through the recovery interval and thereby better constrain paleoproductivity the 13c of limestones from 5 stratigraphic sections in south china displays a negative gradient of approximately 4 from shallow to deep water facies within the lower triassic this intense gradient declines within spathian and lowermost middle triassic strata coincident with accelerated biotic recovery and carbon cycle stabilization model simulations show that high nutrient levels and a vigorous biological pump are required to sustain such a large gradient in 13c indicating that early triassic ocean anoxia and delayed recovery of benthic animal ecosystems resulted from too much productivity rather than too little

stable isotopes of carbon and sulphur as indicators of environmental change past and present stable isotopes of carbon 12 c and 13 c and sulphur 32 s and 34 s are fractionated during some of the transformations between reservoirs in the global carbon and sulphur cycles the main processes controlling the isotopic composition of earth surface reservoirs are for carbon photosynthesis respiration and equilibration between oceanic dissolved inorganic carbon and atmospheric co 2 and for sulphur bacterial sulphate reduction and sulphide reoxidation thus the different reservoirs of carbon and sulphur in the global cycles attain characteristic isotopic compositions that can be used as a fingerprint for different carbon and sulphur sources and to track changes in the balance of carbon and sulphur stored in different reservoirs these isotopic signals can be used both to examine contemporary anthropogenic impacts on the cycling of carbon and sulphur and where isotopic compositions are faithfully preserved in ancient sediments to examine historical changes in global geochemical cycles through geological time a number of case studies are discussed to illustrate how isotopic techniques represent one of the most powerful and important tools available in the study of both the causes and affects of ancient and modern global environmental change

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

concretion morphologies reflecting diagenetic and epigenetic pathways abstract due to complex physicochemical processes concretions develop variable but distinctive morphologies reflecting the state of the sediment in subsequent stages of diagenesis and epigenesis they deserve a study and systematization in their own right at the same time concretional morphologies illustrate the effect of hierarchic self organization which is a basic element also in biological evolution

variations in pyrite texture sulfur isotope composition and iron systematics in the black sea evidence for late pleistocene to holocene excursions of the o2 h2s redox transition time dependent variations in the physicochemical properties of pyrite were investigated in four sediment cores from the black sea in the laminated deep basin sediments of unit i and unit ii 86 of pyrite particles are present as fine grained framboidal aggregates in these sediments the dominance of pyrite framboids with a narrow size distribution and maximum size 18 m is evidence of syngenetic water column pyrite formation subjacent to the o2 h2s boundary sediments from the basin margin collected below the impingement of the o2 h2s boundary contain an increased proportion of fine grained euhedral grains of pyrite relative to framboidal aggregates suggesting increased additions of diagenetic pyrite below the sediment water interface the more efficient reduction and sulfidation of iron in the water column of the central region of the basin implies a more reactive source of iron there compared to the basin margins and is tied to increasing pyrite as framboids and greater degrees of pyritization dop in the basin center relative to the basin margins an evaluation of fe s c relations indicates that pyrite formation was limited by sulfate availability during deposition of the oldest lacustrine sediments of unit iii c limited for upper unit iii due to the input of sulfate rich mediterranean seawater and fe limited in the laminated organic carbon rich sediments of units i and ii these changes in pyrite limiting factors occurred within 4 m of compacted burial representing 15 ka sediment fabric and framboid size distributions at a shallow basin margin site suggest that during two extended periods of unit ii deposition the o2 h2s transition retreated to depths below 200 m however during these same intervals the 34s of pyrite remains uniform compared to overlying and underlying laminated sediments implying that this chemical signature may not be uniquely tied to the position of the o2 h2s boundary relative to the sediment water interface but rather is likely related to biogeochemical processes

variability of sulphur isotope ratios in pyrite and dissolved sulphate in granitoid fractures down to 1km depth evidence for widespread activity of sulphur reducing bacteria euhedral pyrite crystals in 46 open bedrock granitoid fractures at depths down to nearly 1 km were analysed for sulphur isotope ratios 34s by the in situ secondary ion mass spectrometry sims technique and by conventional bulk grain analysis and were compared with groundwater data twenty nine of the fractures sampled for pyrite had corresponding data for groundwater including chemistry and isotopic ratios of sulphate which provided a unique opportunity to compare the sulphur isotopic ratios of pyrite and dissolved sulphate both at site and fracture specific scales assessment of pyrite age and formation conditions were based on the geological evolution of the area laxemar se sweden and on data on co genetic calcite as follows 1 the isotopic ratios of the calcite crystals 18o 13c 87sr 86sr were compared with previously defined isotopic features of fracture mineral assemblages precipitated during various geological periods and 2 the 18o of the calcites were compared with the 18o of groundwater in fractures corresponding to those where the calcite pyrite assemblages were sampled taken together the data show that all the sampled fractures carried pyrite calcite that are low temperature and precipitated from the current groundwater or similar pre existing groundwater except at depths of 300 to 600 m where water with a glacial component dominates and the crystals are from pre modern fluids an age of 10 ma are anticipated for the pre modern fluids the 34spyr showed huge variations across individual crystals such as 32 to 73 and extreme minimum 50 and maximum 91 values for this kind of extreme s isotopic variation at earth surface conditions there is no other explanation than activity of sulphur reducing bacteria coupled with sulphate limited conditions indeed the most common subgrain feature was an increase in 34spyr values from interior to rim of the crystal which we interpret are related to successively higher 34s values of the dissolved source so42 caused by ongoing bacterial sulphate reduction in fractures with low flow or stagnant waters the measured groundwater had 34sso4 values of 9 to 37 with the highest values associated with low sulphate concentrations these values are overall and especially in the sulphate poor waters down to 400 m somewhat higher than the anticipated initial values and can thus like for the 34s enriched pyrites be explained by a rayleigh distillation process driven by microbial sulphate reduction an intriguing feature was that the 34sso4 values of the groundwater were in no case reaching up to the values required to produce biogenic pyrite with 34s values of 40 to 91 to explain this feature we suggest that groundwater in low flow fractures with near stagnant water carrying sulphate and pyrite with high 34s is masked by high flow parts of the fracture system carrying groundwater that often contains sulphate in abundance and considerably less fractionated with respect to 34s and 32s in order to gain detailed knowledge of chemical processes and patterns in groundwater in fractured rock fracture mineral investigations are a powerful tool as we have shown here for the sulphur system

new species of the conodont genus hindeodus and the conodont biostratigraphy of the permian triassic boundary interval abstract four new species of the conodont genus hindeodus hindeodus eurypyge sp nov hindeodus inflatus sp nov hindeodus sp nov a and hindeodus sp nov b are described from the permian triassic transition in south china our study confirms the first appearance of hindeodus parvus at the gssp level base of bed 27c at meishan however at shangsi the first occurrence of h parvus is about 4 5 m above the event boundary analysis of conodont biostratigraphy of the meishan d section and the shangsi section suggest significant differences between the two sections these include the absence of h changxingensis wang from the shangsi section and the approximately 4 5 m of the shangsi section that contains h priscus kozur h latidentatus kozur and h eurypyge n sp below the first occurrence of h parvus these differences may be accounted for most easily by suggesting that there is a minor depositional hiatus at the permian triassic boundary gssp level as based on the first appearance of the conodont hindeodus parvus in meishan section d taxonomic re evaluation of hindeodus pa elements indicates that species of the genus can be broadly separated into two groups based on the morphology of the posterior portion of the element and on growth patterns the stable pa element morphology of hindeodus first developed in the carboniferous was replaced by a complex of rapid evolutionary change in the latest permian and early triassic with as many as 11 valid species of the genus in the permian triassic boundary interval which are probably descendants of only two species h typicalis and h n sp b we suggest that the dramatic change in conodont biofacies observed at the p t boundary in south china from neogondolella dominated faunas to hindeodus dominated faunas was caused by the introduction of a high component of silt beginning in bed 27 at meishan and bed 28 at shangsi that tipped the environmental balance in favor of hindeodus and isarcicella over neogondolella clarkina species we contend that hindeodus species were adaptable to higher levels of turbidity than neogondolella clarkina species and hence at meishan and shangsi it was not a matter of a drastic increase in the abundance of hindeodus but an exclusion of neogondolella

the argille varicolori unit in lucania italy a record of tectonic offscraping and gravity sliding in the mesozoic tertiary lagonegro basin southern apennines

anaerobic methane oxidation and a deep h2s sink generate isotopically heavy sulfides in black sea sediments the main terminal processes of organic matter mineralization in anoxic black sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2 4 m and methanogenesis below the sulfate zone the modern marine deposits comprise a ca 1 m deep layer of coccolith ooze and underlying sapropel below which sea water ions penetrate deep down into the limnic pleistocene deposits from 9000 years bp sulfate reduction rates have a subsurface maximum at the so42 ch4 transition where h2s reaches maximum concentration because of an excess of reactive iron in the deep limnic deposits most of the methane derived h2s is drawn downward to a sulfidization front where it reacts with fe iii and with fe2 diffusing up from below the h2s fe2 transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur the pore water gradients respond dynamically to environmental changes in the black sea with relatively short time constants of ca 500 yr for so42 and 10 yr for h2s whereas the fes in the black band has taken ca 3000 yr to accumulate the dual diffusion interfaces of so42 ch4 and h2s fe2 cause the trapping of isotopically heavy iron sulfide with 34s 15 to 33 at the sulfidization front a diffusion model for sulfur isotopes shows that the so42 diffusing downward into the so42 ch4 transition has an isotopic composition of 19 close to the 23 of h2s diffusing upward these isotopic compositions are however very different from the porewater so42 43 and h2s 15 at the same depth the model explains how methane driven sulfate reduction combined with a deep h2s sink leads to isotopically heavy pyrite in a sediment open to diffusion these results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth s history

extreme sulphur isotope fractionation in the deep cretaceous biosphere abstract isotopically light sulphur in sedimentary pyrite was generally predominant during the cretaceous as a consequence of volcanic and hydrothermal activity and bacterial sulphate reduction bsr however we report super high sulphur isotopic compositions of sedimentary pyrite 34 s 89 3 from late mid cretaceous sediments from the central apennines italy these exceptionally high 34 s values are not consistent with current models for interpreting the geological record for sulphur isotopes because these cannot explain the extreme isotopic fractionation observed in our study precise details of the mechanism for producing pyrite so highly enriched in 34 s remain elusive but the large variation in 34 s values 70 within the analysed samples and the considerable micro scale variations in 34 s up to 50 even within a single nodule indicate a complex mechanism of sulphate reduction and pyrite precipitation this includes early removal of isotopically light h 2 s by pyrite precipitation in the water column diffusion and advection of h 2 s and so 4 2 and finally bsr similar but less severe conditions occur in the black sea and in deep ocean sediments these new findings provide new insights for the interpretation of the palaeoceanographic conditions that prevailed during the mesozoic

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

background δ 34 s values of kupferschiefer sulphides in poland pyrite marcasite nodules regional background 34s values of pyrite marcasite nodules throughout the zechstein basin in poland have been measured to help estimate the proportion of externally derived sulphur in the kupferschiefer cu ag ores the 34s values of the 17 fes2 nodules measured range widely from 25 2 to 51 9 similar to the previously published 28 to 43 range in disseminated pyrite in the kupferschiefer the wide variation cannot be attributed to pyrite versus marcasite mineralogy amount of contained chalcopyrite or sphalerite carbonate versus shale host rock early versus late formation percent of included calcite or to size shape or texture there is also no relation with proximity to the centres of copper mineralization in southwestern poland where sulphides are typically isotopically heavier the 34s values do however vary directly with percent of host rock fragments included in the nodules repeat samples that were washed with acid or hot water show the same wide variation indicating that contamination by sulphate sulphur in the host rock is not a factor neither is organic sulphur because of its small volume instead the sulphur composition may be fundamentally controlled by the formation mechanism of the nodule whereby 34s rich sulphide is preferentially concentrated possibly replacing anhydrite lenses alternatively a network of host rock inclusions might act as a more accessible conduit for later 34s rich fluids to infiltrate the nodule and add to earlier 34s poor pyrite in the ore deposits higher 34s values of ore nodules suggest less indigenous sulphur in limestone than shale lithologies an isotopic temperature of 61 c from a chalcopyrite galena pair agrees with other estimates of 105 c higher values in ore nodules veinlets than in adjacent disseminations and the calculated 34spy value from a pyrite bornite mixture support the idea that metal bearing 34s rich fluids penetrated the kupfer schiefer through a network of fractures

ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites diffusive exchange as a guide to cooling history ion microprobe analysis of magnetites from the adirondack mountains ny yields oxygen isotope ratios with spatial resolution of 2 8 m and precision in the range of 1 1 sigma these analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of 18o at this scale high precision micro analyses of this sort will permit wide ranging new applications in stable isotope geochemistry the analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite magnetites are near to fe3o4 in composition and optically and chemically homogeneous a combination of ion probe plus conventional brf5 analysis shows that individual grains are homogeneous with 18o 8 9 1 smow from the core to near the rim of 0 1 1 2 mm diameter grains depth profiling into crystal growth faces of magnetites shows that rims are 9 depleted in 18o these low 18o values increase in smooth gradients across the outer 10 m of magnetite rims in contact with calcite these are the sharpest intracrystalline gradients measured to date in geological materials this discovery is confirmed by bulk analysis of 150 350 m diameter magnetites which average 1 2 lower in 18o than coarse magnetites due to low 18o rims conventional analysis of coexisting calcite yields 18o 18 19 suggesting that bulk 18o cc mt 9 3 and yielding an apparent equilibration temperature of 525 c over 200 c below the temperature of regional metamorphism consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories the data for oxygen in calcite under hydrothermal conditions at high p h2o indicates that diffusion is faster in magnetite and modelling of the low 18o rims on magnetite would suggest that the adirondacks experienced slow cooling after grenville metamorphism followed by a brief period of rapid cooling possibly related to uplift conversely the data for calcite at low p h2o show slower oxygen diffusion than in magnetite modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals suggesting that the low 18o rims form by exchange with late low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets in either case the ion microprobe results indicate that two distinct events are recorded in the post metamorphic exchange history of these magnetites recognition of these events is only possible through microanalysis and has important implications for geothermometry

organic maturation and ore precipitation in southeast missouri the sulfate reduction plus mixing hypotheses for the formation of mississippi valley type deposits have suffered from an inability to show a plausible mass balance between sulfate possible reductants and sulfide ores and a mechanism for mixing the reduced gas h 2 s with the metal bearing fluid both these problems are resolved by focusing on the gases mostly methane generated from the organic matter in the host carbonate rocks during thermal maturation caused by heat from the hydrothermal solutions in southeast missouri it appears that the volume of the bonneterre formation required to produce all the methane needed to reduce enough sulfate to precipitate all the ores is approximately the same as the volume of the brown rock facies which hosts most of the ore therefore it appears that metal and sulfate bearing solutions entered the bonneterre at lamotte sandstone pinchouts then followed permeability trends which coincided mainly with the oolitic grainstones associated with the stromatolite reef most of which are brown evolution of methane and other reducing compounds from the brown rock resulted in sulfate reduction and precipitation of sulfides several other regional and local factors in the geology of the area are found to be compatible with this idea

sources of environmental sulfur in the groundwater system southern new zealand abstract sulfide minerals commonly occur in sediments and basement rocks in southern new zealand as authigenic precipitates from groundwater below the oxygenated surface zone there are two principal potential sources for sulfur in the groundwater system weathering of sulfide minerals in the metamorphic basement and rainwater derived marine aerosols we present data for these two key sulfur sources metamorphic sulfide and associated hydrothermal au bearing veins within the otago schist average 34s 1 8 2 4 and an inland saline lake s derived entirely from rainwater 34s 21 4 0 8 we use these two end member 34s values to estimate the contributions of these sources of sulfur in authigenic groundwater sulfide minerals and in waters derived from oxidation of these sulfide minerals across a range of environments we show that authigenic groundwater pyrite along joints in the otago schist is derived primarily from metamorphic basement sulfur in contrast authigenic groundwater pyrite cementing miocene recent aquifers shows a substantial marine aerosol component and represents a distinct hydrogeological system we suggest that marine aerosols represent a significant flux to the terrestrial sulfur cycle that has been present through the groundwater system in otago over the past 20 million years

constraints on the late ediacaran sulfur cycle from carbonate associated sulfate we report new sulfur isotope compositions 34s in carbonate associated sulfate cas and pyrite from the lower nama group namibia 550 to 35 is highly unusual in earth history and in the terminal ediacaran is best explained by a high pyrite burial flux pyrite in the nama group is close in isotopic composition to coeval sulfate but the sulfur isotope fractionation between sulfate and pyrite varies widely among different studied basins suggesting highly heterogeneous redox and depositional conditions

implications of sulfur isotope fractionation in fracture filling sulfides in crystalline bedrock olkiluoto finland abstract a detailed investigation of 34 s 32 s ratios in fracture bound pyrite and marcasite was conducted at olkiluoto western finland in order to gain information on paleohydrogeochemical conditions in a deep groundwater 0 400 m b s l environment the bedrock at olkiluoto is being considered for a final repository of spent nuclear fuel the 34 s 32 s ratios were measured in situ on individual sulfide grains using secondary ion mass spectrometry sims supplemented by analyses from bulk sulfide material the 34 s values of pyrite and marcasite show considerable variations from 50 to 82 vcdt using published records and new data from fracture filling minerals the pyrite fillings were classified into groups representing distinct episodes of fracture mineral formation the 34 s values of these groups record a transition from hydrothermal activity to a low temperature groundwater environment the 34 s values of hydrothermal pyrite vary between 18 and 34 however hydrothermal pyrite that definitively precipitated at 128 245 c evidenced by fluid inclusion data from co genetic calcite is characterized by a more limited variation in 34 s from 8 6 to 3 9 the high variability of 34 s within the hydrothermal pyrite precipitates indicates that biogenic fractionation effects cannot be completely excluded hydrothermal pyrite precipitation is likely related to hydrothermal systems produced by mesoproterozoic rapakivi granite and diabase intrusions subsequent pyrite generations show a wider spread of 34 s values pyrite types representing formation temperatures from ca 50 to 90 c have 34 s values ranging from 40 to 82 and the latest low temperature 34 s from 50 to 78 the wide range of 34 s values is attributed to bacterial so 4 2 reduction affected by rayleigh fractionation under restricted so 4 2 input it can be calculated that the highest 34 s values in pyrite represent consumption of ca 90 of the original so 4 2 in the deep groundwater in a fracture section furthermore in situ variations of the 34 s values in pyrite grains indicate that pulses of fresh so 4 2 with relatively non modified s isotopic composition have periodically entered the fractures the latest low temperature pyrite formation event most likely occurred during the holocene period when brackish so 4 2 rich waters of the litorina sea infiltrated the fracture network at 8000 4000 bp providing substrate for so 4 2 reducing bacteria due to the complex quaternary history of the site and low temperature conditions existing for millions of years latest fracture filling calcite and pyrite may represent a compilation of several low temperature precipitation events the records of 13 c in calcite and 34 s in coexisting pyrite indicate that paleogroundwaters have been influenced by the migration of a redox front between methanic and sulfidic environments these findings can be used to consider the possible geochemical changes that may affect the materials used to contain spent nuclear fuel

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

widespread contamination of carbonate associated sulfate by present day secondary atmospheric sulfate evidence from triple oxygen isotopes the isotope composition of seawater sulfate is an important tracer of sulfur carbon and oxygen cycles in earth s deep past carbonate associated sulfate cas extracted by acid digestion is widely used as a proxy for sulfate in paleo seawater from which the carbonate minerals precipitated early and late diagenesis weathering and laboratory processing can in some cases compromise original seawater sulfate signals here we report that extracted cas can also be severely contaminated by recent atmospheric sulfate especially when the sampled carbonates are from outcrops in arid to semi arid climates or in heavily polluted regions our evidence comes from triple oxygen isotope compositions of sequentially extracted water leachable sulfate and acid leachable sulfate from carbonates of diverse ages from northwestern and north central china and southwestern north america independent of the age of the rocks almost all the water leachable sulfates and half of the acid leachable sulfates bear positive 17o anomalies clearly distinguishable from those of typical seawater sulfate because secondary atmospheric sulfate sas is the only source of sulfate known to bear positive 17o anomalies we conclude that sulfate extracted from carbonate outcrops in these regions has a significant component of sas because sas generally has a much lower 34s value than paleo seawater sulfate it could shift the 34s of the extracted cas to lower values and in some cases even lower than that of the co occurring pyrite i e the super heavy pyrite enigma reported in geological records our findings call for a re evaluation of many published outcrop based cas data and conclusions

a microbialite carbonate crust at the permian triassic boundary in south china and its palaeoenvironmental significance a 1 m thick carbonate crust layered and commonly domal caps crinoidal limestones on reef complexes of the top permian changxing formation in the huaying mountains eastern sichuan china the crust s stratigraphic level lies at a sharp change in facies and is overlain by poorly fossiliferous laminated micrites and shales of the lower triassic feixianguan formation the crust therefore appears to coincide with the end permian extinction event although the dating of the strata is currently imprecise the crust is composed mostly of digitate carbonate locally thrombolitic with remnant lobate fabric and resembles microbialites but is mostly recrystallised and a microbial origin is unconfirmed it is enclosed in micrite with pyrite crystals ostracode and other shell debris the crust is absent from interreef areas previous interpretations of karstification and calcrete formation are not upheld and the facies were deposited under water overlying sediments are low energy with abundant ferroan calcite and pyrite reflecting anoxia associated with rising sea level various interpretations of the crust are possible 1 it was organic and microbia grew preferentially on topographic highs of reef tops 2 microbia were a disaster biota in the absence of grazers 3 microbia took advantage of favourable conditions for calcification associated with a rapidly rising environmental co2 content during the late permian 4 the crust was an inorganic precipitate associated with co2 rich water microbial crusts are rare after the cambrian but whether this crust is organic or not its presence in these strata reinforces the view that oceanic atmospheric conditions in the permian triassic boundary interval were unusual

the origin of a mississippi valley type deposit in the viburnum trend southeast missouri petrologic and isotopic studies of the base metal sulfide mineralization in the buick mine have established the following paragenesis an early stage of fine grained pyrite and marcasite replaced the dolostone host rock the iron disulfides and dolostone were replaced by sphalerite during the main stage of sphalerite precipitation delta 34 s sp 16 5 to 19 0ppm following the sphalerite two main stages of galena were precipitated a cuboctahedral stage delta 34 s gn 21 3 to 10 0ppm during which galena replaced dolostone and sphalerite and grew in vugs in the dolostone and in the sphalerite and a cubic stage delta 34 s gn 10 5 to 0 9ppm the two stages of galena precipitation were separated by a period during which the main stage of sphalerite and the cuboctahedral galena were partially dissolved and bladed marcasite delta 34 s mc 2 3 to 4 1ppm was precipitated and followed by a period of mild etching of the cubic galena minor amounts of pale sphalerite delta 34 s sp 14 0 to 16 5ppm were then precipitated white and colorless rhombs of dolomite were precipitated at the same time as some of the main stage of sphalerite the cubic galena and the pale sphalerite after the pale sphalerite was precipitated chalcopyrite quartz and siegenite were precipitated followed by calcite and finally kaolinite the paragenetic and textural data for both galena and sphalerite in the buick mine strongly suggest that these minerals were precipitated and dissolved repetitively during ore formation similar textural evidence for galena reported by other workers for different mines in the viburnum trend implies that repetitive precipitation and dissolution of galena was probably an important process during the formation of the entire viburnum trend fluid inclusions in late quartz crystals coprecipitated with chalcopyrite have filling and freezing temperatures within the ranges reported for sphalerite from other parts of the viburnum trend demonstrating that the ore forming solutions in the viburnum trend were probably at temperatures in the range 105 degrees to 141 degrees c assuming a maximum pressure correction of about 11 degrees c and were extremely saline containing about 4 0 to 5 0 molal chloride consideration of typical chemical analyses of fluid inclusions from other mississippi valley type deposits suggests that the maximum likely concentration of dissolved co 2 in the ore forming solutions was about 0 05 molal at these concentrations the ore forming solutions that travelled to the site of deposition could have had ph9s about two units less than neutral and still have been in equilibrium with dolomite or calcite the ranges of sulfur and lead isotopic compositions of galena from the buick mine are very similar to those established by earlier studies of the old lead belt and adjacent subdistricts however the correlation of isotopically lighter sulfur with more radiogenic lead is much stronger for the viburnum trend suggesting that galena was precipitated from many solutions each of which carried lead and sulfur together and had different lead and overall sulfur isotopic compositions the textural paragenetic and isotopic data for the buick mine cannot be easily explained either by a sulfate reduction model in which sulfate was reduced by organic matter or methane or mixing models in which base metals and reduced sulfur were transported separately to the site of deposition instead the data strongly support a reduced sulfur model for ore formation according to which the base metals were transported together with reduced sulfur as h 2 s in the same solutions to the sites of deposition the reduced sulfur model is also supported by a theoretical calculation of the solubilities of galena and sphalerite which demonstrate that low but economically significant concentrations of lead or zinc could have been transported as chloride complexes together with equivalent concentrations of reduced sulfur at temperatures of 100 degrees to 150 degrees c and ph9s of one to two units less than neutral and could have been precipitated by ph increases cooling or dilution at the sites of deposition

isotopic evidence for an anomalously low oceanic sulfate concentration following end permian mass extinction abstract the cataclysmic end permian mass extinction was immediately followed by a global expansion of microbial ecosystems as demonstrated by widespread microbialite sequences disaster facies in shallow water settings here we present high resolution carbonate carbon 13 c carb and carbonate associated sulfate sulfur isotope 34 s cas records from the microbialite in the cili permian triassic p tr section in south china a stepwise decline in 13 c carb begins in the underlying skeletal limestone predating the main oceanic mass extinction and the first appearance of microbialite and reaches its nadir in the upper part of the microbialite layer the corresponding 34 s cas in the range of 17 4 to 27 4 is relatively stable in the underlying skeletal limestone and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite two episodes of positive and negative shifts occurred within the microbialite layer and exhibit a remarkable co variance of sulfur and carbon isotope composition the large amplitude of the variation in 34 s cas as high as 7 per 100 kiloyears suggests a small oceanic sulfate reservoir size at this time furthermore the 13 c carb and 34 s cas records co vary without phase lag throughout the microbialite interval implying a marine driven c cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations on the basis of a non steady state box model we argue that the oceanic sulfate concentration may have fallen to less than 15 perhaps as low as 3 of that in the modern oceans low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic sulfidic conditions prior to the main mass extinction by promoting methanogenesis and a build up of atmospheric ch 4 and co 2 low oceanic sulfate may have intensified global warming exacerbating the inimical environmental conditions of the latest permian

carbon sulfur iron systematics of the uppermost deep water sediments of the black sea box cores recovered during leg 4 of the 1988 r v knorr black sea oceanographic expedition from deep water regions of the basin were dominated by coccolith rich microlaminated unit 1 sediment and muddy gray turbidite layers both organic carbon oc and pyrite sulfur values for unit 1 display narrow ranges with mean concentrations of 5 3 1 1 1 wt and 1 3 0 3 wt respectively unit 1 is not enriched in pyrite s relative to sediments deposited under oxygenated bottom waters normal marine sediments with comparable oc concentrations carbon sulfur relationships evaluated on a calcium carbonate free basis to avoid spurious correlations resulting from dilution effects demonstrate that oc and pyrite s are essentially decoupled these observations combined with the persistence of elevated pore water sulfide to depth and a strong correlation between pyrite s and the detrital fe component argue strongly for limitation of pyrite formation in unit 1 by the availability of reactive fe unit 1 fe limitation is further indicated by degree of pyritization dop studies a measure of the extent to which the original potentially reactive fe has been transformed to pyrite these studies show sulfidation of reactive fe ranging from 57 to 78 with dop values independent of oc concentration unit 1 dop profiles suggest that the majority of the pyrite is formed in the sulfidic water column and or very close to the sediment water interface pyrite s concentrations of unit 1 when compared with the particulate reduced sulfur fluxes measured in time series sediment traps are compatible with predominantly water column pyrite formation because of the limitations in the supply of reactive fe associated with the comparatively high supply of oc the microlaminated sediment is characterized by c s ratios greater than those typical of holocene oxically deposited sediments the turbidite muds of the deep basin display high reduced s values relative to holocene normal marine sediments in samples with low oc concentrations low c s ratios this reflects pyrite formation under anoxic sulfidic bottom water conditions in a probable upper slope source region as well as during transport and final deposition intermediate dop values for the turbidites in part a product of their rapid rate of deposition reveal that fe limitation is ultimately not a factor and that further pyrite should form during burial however the very rapid rate at which unit 1 pyrite forms suggests fundamental differences between the overall reactivities of the fe phases associated with the microlaminated and turbiditic sediments the signature of water column anoxia with regard to sedimentary pyrite formation is clearly indicated by the high dop values of unit 1 and the comparatively high levels of s associated with the low concentrations of oc of the turbidite muds this agrees with similar conclusions based on studies of ancient sedimentary rocks

permian circumpacific deep water faunas from the western tethys sicily italy new evidences for the position of the permian tethys abstract circumpacific deep water faunas characterized mainly by radiolarians paleopsychrospheric ostracods and conodonts were found in the early middle and late permian deposits pertaining to the sicanian paleogeographic domain of western sicily near the western end of the eurasiatic tethys similar permian deep water faunas are known from the phyllite unit of crete and from oman in the latter area partly above oceanic crust all these occurrences indicate the presence of a late paleozoic tethys ocean immediately north of gondwana

sulfur isotope constraints on marine transgression in the lacustrine upper cretaceous songliao basin northeastern china abstract organic rich cretaceous source rocks of the petroliferous songliao basin in northeast china are considered to be lacustrine in origin but paleontological and organic geochemical evidence suggest episodic marine incursions as a test of this hypothesis we applied time series measurements of elemental and isotopic abundances on core and cutting samples to evaluate fluctuations in the sulfur and carbon cycles across the santonian campanian transition preserved in the upper yaojia and lower nenjiang formations the data reveal a spike in pyrite sulfur abundance and a marked negative excursion in 34s at the base of the nenjiang formation when the basin expanded to its maximal extent the elemental and isotopic data suggest that flooding was associated with rapid marine transgression that enhanced sulfate concentrations which promoted microbial sulfate reduction in anoxic bottom waters that were episodically euxinic subsequent restriction of the basin and a decline in marine influence is supported by progressive upsection 34s enrichment up to 30 in nenjiang member i which are interpreted to reflect the distillation of sulfate through enhanced pyrite burial followed by a gradual return to lacustrine conditions that prevailed in overlying strata

fluid inclusion evidence for solution mixing sweetwater mississippi valley type district tennessee fluid inclusions in fluorite from the appalachian mississippi valley type fluorite barite deposits of the sweetwater district in east tennessee indicate that the mineralizing solutions were sodium potassium chloride brines with an average temperature of 107 degrees c and an average salinity of about 16 equiv wt percent nacl a strong negative correlation of homogenization and freezing temperatures which was observed for inclusions from the southeast part of the district was interpreted to indicate that two solutions were present during fluorite deposition in this area a warm 160 degrees c less saline 12 solution and a cool 80 degrees c more saline 30 solution a connate source is considered likely for both solutions and the warm less saline solution appears to have come from at or beyond the east edge of the district mixing of these solutions could have caused ore deposition in the southeast belt although cooling probably caused deposition elsewhere in the district published data suggest that two similarly distinct solutions were present in the nearby east tennessee zinc district

fluid inclusion evidence for fluid mixing mascot jefferson city zinc district tennessee inverse correlation between homogenization temperature and salinity temperature of formation changes at near constant salinity and low salinity low to moderate temperature inclusion fluids are found in sphalerite formed in limestone an evolved basinal brine component was recognized by its characteristic temperature 100 degrees to 120 degrees c freezing point depression 1 fundamental chemical requirements for formation of pb zn ba f deposits from metal bearing basinal brines modified journal abstract

two episodes of environmental change at the permian triassic boundary of the gssp section meishan abstract high resolution stratigraphic records through the permian triassic boundary ptb interval of the global stratotype section and point gssp at meishan zhejiang province china reveal that the ptb crisis was not a single abrupt catastrophe a bed by bed analysis of environmental and biotic changes makes clear that the crisis can be resolved into two discrete episodes each consisting of three stages a unstably oscillating conditions b peak crisis conditions and c ameliorating conditions the first crisis episode commenced in bed 23 peaked in beds 24e 26 and ameliorated in beds 27 and 28 while the second crisis episode commenced in bed 29 peaked in beds 34 38 and ameliorated in beds 39 and higher the macroscopic mass extinctions happened not at the beginning nor the end of each cycle but at times when the crisis or perturbation of environments began these extinction events do not show detectable feedbacks to concurrent environmental changes in each episode cyanobacteria proliferation postdated the macroscopic extinction while proliferation of green sulfur bacteria predated the environmental crisis causational analysis between environmental and microbial changes show that geomicrobial functional groups exercised pronounced effects on the marine c n s cycles and ocean redox conditions during the ptb crisis it is possible thus that the microbial crises played an important role in strengthening or evening triggering the environmental crisis

carbon isotopic evidence for chemocline upward excursions during the end permian event abstract a negative shift in marine inorganic carbon isotope composition 13 c carb during the end permian mass extinction has been used as evidence for several different extinction mechanisms changes to the 13 c of organic matter and the difference between it and 13 c carb 13 c 13 c carb 13 c org have been examined at few locations with conflicting interpretations we examine the changes to both organic and inorganic carbon isotopes across the permian triassic boundary at two marine sections from south china meishan and shangsi and compare these to data from other previously published sections through these analyses we demonstrate that a decrease in 13 c occurred during the extinction event throughout the paleo tethys ocean the extent and intensity of the decrease varies by location averaging a negative shift of 5 several possibilities as to the cause of this shift exist including siberian trap volcanism a change in the terrestrial marine organic carbon input to the system or a change in the dominant marine biota brought about through environmental changes such as widespread ocean anoxia euxinia the decrease in 13 c observed at many of these sections across the event horizon is here interpreted to represent a shift from algae cyanobacteria to less fractionating phototrophic sulfur bacteria in marine shelf environments resulting from upward excursions of the chemocline these chemocline upward excursions would release euxinic water to the photic zone allowing phototrophic sulfur bacteria to thrive the limited available biomarker data are consistent with this interpretation

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

on the origin and significance of pyrite spheres in devonian black shales of north america abstract devonian black shales deposited on the north american craton contain abundant tasmanites cysts that are typically preserved as flattened circular discs on bedding planes work by the present authors shows that cysts can be preserved as pyrite infill casts that are expressed as sand size whole and geopetal half spheres of pyrite at the bases of thin black shale layers these occur in situ at many stratigraphic levels in the distal prodelta facies of the catskill delta complex of new york as well as in laterally equivalent black shales in tennessee and kentucky reworked pyrite casts usually dominated by whole spheres form lenticular lag accumulations and hydraulic placers together with plant debris and phosphatic particles bone debris conodonts an earlier model for the formation of pyrite spheres in gas bubbles is rejected in favor of formation within uncompressed tasmanites cysts direct observation of cyst cuticle in association with pyrite spheres suggests that localized bacterial sulfate reduction in tasmanites interior voids led to formation of localized pyrite deposition in a manner similar to that described from certain ammonoid chamber settings cyst fill commenced with formation of framboidal pyrite followed by later diagenetic pyrite cementation between framboids these fills show geopetal features and appear to have formed within the redox zone below the sediment water interface although described here from the upper devonian comparable pyrite textures are also known from proterozoic cambrian ordovician and silurian sediments they probably occur throughout the sedimentary record and in mudstone successions they may prove to be an important source of sand size grains in areas far removed from the basin margins as such they may be important for detection of erosive events and strong bottom currents and provide valuable information about the depositional history of mudstone successions

how sulfate driven anaerobic oxidation of methane affects the sulfur isotopic composition of pyrite a sims study from the south china sea abstract sulfate driven anaerobic oxidation of methane so4 aom in marine sediments commonly leads to the precipitation of pyrite it is however frequently challenging to unequivocally unravel the entire history of pyritization because of the common coexistence of so4 aom derived pyrite with pyrite resulting from organiclastic sulfate reduction osr to better understand how so4 aom affects pyritization in methane bearing sediments and how this can be identified we applied secondary ion mass spectroscopy sims to analyze the sulfur isotope composition 34s of authigenic pyrite in addition to sulfur isotope measurements of bulk sulfide and hand picked pyrite aggregates from the two seafloor sites hs148 and hs217 in the shenhu seepage area south china sea authigenic mostly tubular pyrite aggregates from these sites consist of three types of pyrite framboids zoned aggregates with radial overgrowths surrounding a framboidal core and euhedral pyrite crystals framboids with low sims 34s values as low as 41 6 at hs148 and 38 8 at hs217 are dispersed throughout the cores but are especially abundant in the shallow part of the sedimentary column i e above 483 cmbsf in hs148 above 670 cmbsf in hs217 these patterns are interpreted to reflect the dominance of osr during early diagenetic processes in the shallow sediments with increasing depth both 34s values of bulk sulfide minerals and hand picked pyrite aggregates increase sharply at 483 cmbsf in core hs148 and at 700 cmbsf in core hs217 respectively radial pyrite overgrowths and euhedral crystals become abundant at depth typified by high 34s values for hand picked pyrite moreover sims analysis reveals an extreme variability of 34s values for the three pyrite types on a small scale in these zones besides some moderately 34s enriched framboids most of the overgrowths and euhedral crystals display extremely high sims 34s values as high as 114 8 at hs148 and 74 3 at hs217 representing the heaviest stable sulfur isotope composition of pyrite ever reported to the best of our knowledge such an abrupt and extreme increase in 34spyrite values with depth is best explained by an enrichment of 34s in the pool of dissolved sulfide caused by so4 aom in the sulfate methane transition zone smtz the increase in 34s values from framboidal cores to overgrowth layers and euhedral crystals indicates continuous and finally near to complete exhaustion of dissolved sulfate at the smtz following a rayleigh distillation process so4 aom allowed for subsequent growth of later stage pyrite over the initial framboids part of which formed earlier and at shallower depth by osr the combination of a detailed petrographic study of authigenic pyrite with sims analysis of stable sulfur isotopes in organic rich strata proves to be a powerful tool for reconstructing the dynamics of sulfur cycling in modern and potentially ancient sedimentary sequences

stepwise and large magnitude negative shift in δ13ccarb preceded the main marine mass extinction of the permian triassic crisis interval abstract large perturbations to the global carbon cycle occurred during the permian triassic boundary mass extinction the largest extinction event of the phanerozoic eon 542 ma to present controversy concerning the pattern and mechanism of variations in the marine carbonate carbon isotope record of the permian triassic crisis interval ptci and their relationship to the marine mass extinction has not been resolved to date herein high resolution carbonate carbon isotope profiles 13ccarb accompanied by lithofacies were generated for four sections with microbialite taiping zuodeng cili and chongyang in south china to better constrain patterns and controls on 13ccarb variation in the ptci and to test hypotheses about the temporal relationship between perturbations to the global carbon cycle and the marine mass extinction event all four study sections exhibit a stepwise negative shift in 13ccarb during the late permian early triassic with the shift preceding the end permian crisis being larger 3 than that following it 1 2 the pre crisis shifts in 13ccarb are widely correlatable and hence represent perturbations to the global carbon cycle the comparatively smaller shifts following the crisis demonstrate that the marine mass extinction event itself had at most limited influence on the global carbon cycle and that both late permian 13ccarb shifts and the mass extinction must be attributed to some other cause their origin cannot be uniquely determined from c isotopic data alone but appears to be most compatible with a mechanism based on episodic volcanism in combination with collapse of terrestrial ecosystems and soil erosion

two pulses of extinction during the permian triassic crisis over 90 of marine species were lost during the end permian extinction fossil data show that the crisis in china was marked by two distinct phases of marine extinction separated by a 180 000 year recovery period

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

superheavy pyrite δ34spyr δ34scas in the terminal proterozoic nama group southern namibia a consequence of low seawater sulfate at the dawn of animal life sulfur isotope analysis 34 s of well preserved carbonates spanning an 10 ma interval of the terminal proterozoic nama group reveals that disseminated pyrite is consistently enriched in 34 s relative to coeval seawater sulfate as preserved in carbonate associated sulfate cas this observation is not consistent with the current paradigm for interpreting the geologic record of sulfur isotopes which assumes that pyrite 34 s 34 s pyr will be equal to or less than co occurring cas 34 s 34 s cas due to the kinetic isotope effect of bacterial sulfate reduction bsr that favors the lighter isotope of sulfur 32 s during sulfur oxygen bond breakage although the precise mechanism of pyrite sulfur isotope enrichment is debatable our combined observations of extremely 34 s enriched pyrite low bulk rock concentrations of sulfur from cas and pyrite and high frequency fluctuations in 34 s cas and 34 s pyr throughout the nama group carbonates point to very low concentrations of sulfate in portions of the terminal proterozoic ocean the additional occurrence of 34 s enriched pyrite in contemporaneous terminal proterozoic sections from poland and canada reveal that low seawater sulfate may have been widespread in the oceans at this time however the absence of such extremely 34s enriched pyrite from well preserved coeval carbonate sections in oman suggests that such conditions were not globally uniform low geographically varied concentrations of marine sulfate in terminal proterozoic time are consistent with elevated geographically varied concentrations of reactive nonpyritized iron in marine shales recently reported for this interval suggesting that high dissolved fe ii and low o 2 persisted in a range of marine facies as late as 543 ma tens of millions of years after the origin of animals yet prior to their major diversification in early cambrian time

explosive eruption of coal and basalt and the end permian mass extinction the end permian extinction decimated up to 95 of carbonate shell bearing marine species and 80 of land animals isotopic excursions dissolution of shallow marine carbonates and the demise of carbonate shell bearing organisms suggest global warming and ocean acidification the temporal association of the extinction with the siberia flood basalts at approximately 250 ma is well known and recent evidence suggests these flood basalts may have mobilized carbon in thick deposits of organic rich sediments large isotopic excursions recorded in this period are potentially explained by rapid venting of coal derived methane which has primarily been attributed to metamorphism of coal by basaltic intrusion however recently discovered contemporaneous deposits of fly ash in northern canada suggest large scale combustion of coal as an additional mechanism for rapid release of carbon this massive coal combustion may have resulted from explosive interaction with basalt sills of the siberian traps here we present physical analysis of explosive eruption of coal and basalt demonstrating that it is a viable mechanism for global extinction we describe and constrain the physics of this process including necessary magnitudes of basaltic intrusion mixing and mobilization of coal and basalt ascent to the surface explosive combustion and the atmospheric rise necessary for global distribution

hypersulfidic deep biosphere indicates extreme sulfur isotope fractionation during single step microbial sulfate reduction coexisting dissolved sulfide and sulfate from hypersulfidic interstitial waters of a 380 m long sediment core show a large isotopic difference of up to 72 caused by in situ microbial sulfate reduction this is considerably larger than the assumed biological maximum of 46 derived from laboratory studies with pure cultures of sulfate reducing bacteria similar high fractionations inferred from sedimentary metal sulfides have been previously explained by a multistage process involving sulfide reoxidation and disproportionation of sulfur intermediates our data show that extreme isotopic differences between sulfate and the reduced sulfur species can also be generated during microbial single step fractionation this result indicates that the sulfate reducing communities and or their cellular metabolic activities in the deep biosphere may differ from those observed in near surface sediments or the water column

characteristics of claystones across the terrestrial permian triassic boundary evidence from the chahe section western guizhou south china abstract x ray diffraction xrd scanning electronic microscopy sem and x ray fluorescence spectroscopy xfs studies were undertaken for claystones and or mudstones from the chahe section a terrestrial permian triassic boundary tptb section our results indicate that the compositions of claystones in the permian triassic boundary ptb interval beds 66f 68 outlined by biostratigraphy are different from claystones and or mudstones found either below or above the interval of the same section the clay minerals in the claystones of the ptb interval are mainly composed of illite montmorillonite interlayers with a few montmorillonites and chlorites the other claystones and or mudstones underlying and overlying the ptb consist of chlorites and or kaolinites some authigenic clastic minerals such as hexagonal dipyramid quartz and zircons are only found in claystones in the ptb interval from the chahe section and some marine ptb sections in western guizhou and eastern yunnan southwestern china in addition some elements are present in abnormal concentrations in the claystones of the ptb interval as well most important is that we found no spherules in all the claystones studied indicating no evidence of an extraterrestrial impact during the permian triassic transition the particular characteristics of the tptb claystones at the chahe section indicate their volcanic origin and thus provide a reliable auxiliary event marker for high resolution demarcation of the tptb in south china they are also indicative in the marine ptb claystones in south china thus the ptb claystones can be used as auxiliary markers for high resolution correlation of the ptb from marine facies to land in south china when direct fossil evidence in the ptb sequence is lacking

thrusting and strike slip tectonics in the alto molise region italy implications for the neogene quaternary evolution of the central apennine orogenic system the alto molise area belongs to the apennine orogenic belt which has been developing since the late cretaceous as a result of the europe africa collision this area is characterized by the complex superposition of different palaeogeographic domains that developed during the mesozoic along the passive southern margin of tethys ocean these domains have been subdivided into four main structural units from shallowest to deepest they are the sannio pelagic basin the latium abruzzi carbonate platform the molise pelagic basin and the apulia carbonate platform units until the present study the tectonic relationship among these units was thought to have been mainly determined by early messinian to late pliocene thrusting this paper reports the results of a new geometric and kinematic analysis of the alto molise area this new interpretation of the alto molise structural style indicates that strike slip tectonics played a primary role during post pliocene times greatly modifying the previous alto molise thrust structures two main tectonic events are recorded consisting of the pliocene thrusting of the molise domain onto the apulia platform followed by the post pliocene disruption and rotation of the pre existing compressional structures by n s oriented high angle right lateral strike slip faults these faults are manifest in the apulia platform as narrow shear zones but propagate towards the surface into wider belts of strike slip and oblique slip deformation we have compared our results with published structural palaeomagnetic and anisotropy of magnetic susceptibility ams data from the central apennines this comparison suggests that the superposition of the younger strike slip tectonic deformation on the older fold and thrust structures in the alto molise area is consistent with block rotation of a segmented orogen applied to the whole apennine system

insights into ore genesis of the jinding zn pb deposit yunnan province china evidence from zn and in situ s isotopes abstract the jinding zn pb deposit located in the mesozoic cenozoic lanping basin of southwest china has ore reserves of 220 mt with an average grade of 6 1 zn and 1 3 pb the mineralization is hosted by sandstone in the early cretaceous jingxing formation and limestone breccia in the paleocene yunlong formation mineralization in both types of host rocks is characterized by a paragenetic sequence beginning with marcasite sphalerite stage 1 followed by pyrite marcasite sphalerite galena stage 2 and then galena sphalerite pyrite sulfate carbonate stage 3 pyrite from these stages have different 33 s compositions with pyrite from stage 1 averaging 9 6 stage 2 averaging 8 9 and stage 3 averaging 0 3 sphalerite hosted by the sandstone has similar 66 zn values ranging from 0 10 to 0 30 in all stages of the mineralization but sphalerite samples from the limestone breccia hosted ore show variable 66 zn values between 0 03 and 0 20 our data on sphalerite precipitated during the earlier stages of mineralization has a constant 66 zn value and cogenetic pyrite displays a very light sulfur isotope signature which we believe to reflect a sulfur source that formed during bacterial sulfate reduction bsr the stage 3 sphalerite and pyrite precipitated from a late influx of metal rich basinal brine which had a relatively constant variable 66 zn isotopic composition due to open system isotope fractionation and a near zero 33 s composition due to the influence of abiotic thermochemical sulfate reduction from observed sulfates in the host rock

the organic geochemistry of two mississippi valley type lead zinc deposits the organic matter associated with two mississippi valley type deposits gays river nova scotia and shullsburg southwestern wisconsin has been characterized by petrographic isotopic spectrophotometric gas chromatographic and mass spectral methods comparisons were made of distributions of organic species identified from unmineralized and mineralized samples the primary variations in the distributions of organic species isolated from the two deposits reflect variations in host rock paleoecology facies and geologic age secondary effects were microbial degradation thermal maturation and mineralization mineralization in both deposits caused an increase in the concentrations of low molecular weight hydrocarbons the genetic model tested in this study presumed that mineralizing brines evolved from sedimentary basins and migrated to the ore host rocks this model implies that an epigenetic generation of organic matter should occur in the deposits in the gays river deposit the probable aquifer for the mineralizing solutions contained an organic distribution markedly different from the indigenous organic matter in the host reef and can be interpreted as a second epigenetic organic fraction added to the deposit evidence was not observed for an epigenetic organic generation in the shullsburg deposit the thermal maturity of the organic matter in the wisconsin district supports a previous estimate of 0 25 m y to form a major orebody in the district