early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

34s and 18o abundances differentiate upper cambrian and lower devonian gypsum bearing units district of mackenzie n w t an update previous sulfur isotope data for the lower devonian bear rock formation and the upper cambrian saline river formation in the district of mackenzie n w t have been supplemented by additional sulfu

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

variability in sulfur isotope records of phanerozoic seawater sulfate the s of seawater sulfate reflects processes operating at the nexus of sulfur carbon and oxygen cycles however knowledge of past seawater sulfate s values must be derived from proxy materials that are impacted differently by depositional and post depositional processes we produced new timeseries estimates for the s value of seawater sulfate by combining 6710 published data from three sedimentary archives marine barite evaporites and carbonate associated sulfate with updated age constraints on the deposits robust features in multiple records capture temporal trends in the s value of seawater and its interplay with other phanerozoic geochemical and stratigraphic trends however high frequency discordances indicate that each record is differentially prone to depositional biases and diagenetic overprints the amount of noise quantified from the variograms of each record increases with age for all s proxies indicating that post depositional processes obscure detailed knowledge of seawater sulfate s s value deeper in time

a sulfur isotope event at the end of the permian abstract a hypothesis of light sulfur injection to the ocean atmosphere system at the end of the permian was presented by kaiho et al kaiho k kajiwara y nakano t miura y kawahata h tazaki k ueshima m chen z q shi g r 2001 end permian catastrophe by a bolide impact evidence of a gigantic release of sulfur from the mantle geology 29 815 818 based on a negative shift of 34 s 32 s ratio of carbonate associated sulfate in south china this hypothesis was discussed in some papers with additional data in other areas however the cause and distribution of the negative shift has not been clarified here we show that a significant decrease in the 34 s 32 s ratio of carbonate associated sulfate occurred simultaneously in south china and hungary at the end of the permian coincident with the end permian mass extinction the cause of the abrupt negative shift of 34 s 32 s in these two distant sites is the injection of light sulfur to the surface ocean from the deep ocean rich in h 2 s or deposits rich in sulfide or the mantle this sulfur isotope event was likely caused by either an abrupt warming a bolide impact to the ocean mantle plume induced volcanism or a harmonizing of these possible direct causes are 1 massive release of h 2 s gas from the euxinic surface and intermediate waters due to abrupt warming by volcanic co 2 or impact shock wave in the ocean 2 a huge volcanism penetrated sediments or ore rich in sulfide 3 an extraterrestrial impact to sulfide rich sediments or ore deposit and 4 release of mantle origin sulfur by an impact of 70 km asteroid to the ocean these are four possible causes for a mass extinction there is also a possibility of a local oceanic event only in the tethys

evaluating the relationship between the carbon and sulfur cycles in the later cambrian ocean an example from the port au port group western newfoundland canada abstract we present a high resolution 34 s sulfate and pyrite and 13 c carbonate record from the middle upper cambrian port au port group a mixed carbonate siliciclastic succession exposed in western newfoundland canada the results illustrate systematic 34 s sulfate shifts of 15 over relatively short stratigraphic intervals 10 m likely 34 s sulfate pyrite ca 23 and a generally positive coupling between changes in 13 c carbonate and 34 s sulfate together these results indicate that middle to late cambrian sulfate concentrations were low and that the sulfate reservoir was more sensitive to change than it was in either terminal neoproterozoic or cenozoic oceans however a simple carbon c and sulfur s isotope box model of the late cambrian ocean illustrates that low sulfate concentrations alone fail to account for the 15 34 s sulfate shifts recognized in port au port strata such large shifts can be generated only if fluctuating oceanic redox is invoked marine anoxia forces reduced c s burial and elevated 34 s driving larger 34 s changes per mole of organic carbon buried the conclusion that later cambrian oceans featured both low sulfate levels and widespread subsurface anoxia supports hypotheses that link fluctuating marine redox conditions in the delayed recovery of skeletal animals and metazoan reefs from late early cambrian extinction

comment on record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years by amaelle landais et al

stratigraphy and environmental conditions of the terminal neoproterozoic cambrian period in oman evidence from sulphur isotopes terminal neoproterozoic and cambrian evaporite rocks worldwide record a marked sulphur isotope excursion to very heavy 34 s isotopes that reflect a period of significant burial of reduced sulphur new 34 s data from anhydrite and pyrite of the ara group in oman extend this record to arabia depositional history of the ara group spans c 8 ma across the terminal neoproterozoic cambrian boundary therefore these rocks provide a detailed record of sulphur isotopic evolution in this important time interval ara group sulphur isotope values include a mean 34 s anhydrite of 39 4 2 6 1 range 32 4 46 4 n 61 and a mean 34 s pyrite of 1 4 7 3 1 range 10 8 to 11 4 n 12 the isotope signatures were not altered significantly during diagenesis and are representative of the isotopic composition of parent waters in the basin marine bromine concentrations in halite and marine fossils in associated carbonate rocks indicate that these waters had a marine origin bacterial sulphate reduction was the dominant process leading to the segregation between isotopically heavy sulphur incorporated in evaporite rocks and isotopically light sulphur buried in pyrite and organic matter strong sulphate reduction operated in a hypersaline and partly anoxic basin these environmental conditions were also conducive to the preservation of organic material and make the ara group a prolific hydrocarbon province significant variation of the observed values is attributed to the inherent variability of bacterial sulphate reduction including partially closed system behaviour disproportionation processes limited diagenesis and possibly secular variation of sulphur isotopes within the basin ara group 34 s anhydrite values overlap with data from other terminal neoproterozoic to cambrian basins but the mean 34 s anhydrite is highest in oman this observation cannot be attributed solely to the specific anoxic conditions and strong bacterial sulphate reduction in oman because such conditions were widespread in most evaporite basins of the terminal neoproterozoic cambrian periods instead slight age differences between these basins can introduce a bias in the sulphur isotope curve excellent preservation of ara group deposits and in particular the precise age constraints make the ara group representative for the seawater sulphur isotopic composition at the terminal neoproterozoic cambrian boundary as a result of the inherent variability of bacterial sulphate reduction 34 s values at the lower end of the spectrum should be most representative for the global signal based on results of this study the global signal is estimated to be approximately 35 40

sulfur isotopes track the global extent and dynamics of euxinia during cretaceous oceanic anoxic event 2 the mesozoic era is characterized by numerous oceanic anoxic events oaes that are diagnostically expressed by widespread marine organic carbon burial and coeval carbon isotope excursions here we present coupled high resolution carbon and sulfur isotope data from four european oae 2 sections spanning the cenomanian turonian boundary that show roughly parallel positive excursions significantly however the interval of peak magnitude for carbon isotopes precedes that of sulfur isotopes with an estimated offset of a few hundred thousand years based on geochemical box modeling of organic carbon and pyrite burial the sulfur isotope excursion can be generated by transiently increasing the marine burial rate of pyrite precipitated under euxinic i e anoxic and sulfidic water column conditions to replicate the observed isotopic offset the model requires that enhanced levels of organic carbon and pyrite burial continued a few hundred thousand years after peak organic carbon burial but that their isotope records responded differently due to dramatically different residence times for dissolved inorganic carbon and sulfate in seawater the significant inference is that euxinia persisted post oae but with its global extent dwindling over this time period the model further suggests that only 5 of the global seafloor area was overlain by euxinic bottom waters during oae 2 although this figure is 30 greater than the small euxinic fraction present today 0 15 the result challenges previous suggestions that one of the best documented oaes was defined by globally pervasive euxinic deep waters our results place important controls instead on local conditions and point to the difficulty in sustaining whole ocean euxinia

carbon and sulfur isotopic fluctuations associated with the end guadalupian mass extinction in south china abstract concentrations of total organic matter toc carbon isotopic compositions of carbonate and organic matter 13 c carb 13 c org and sulfur isotopic compositions of carbonate associated sulfate 34 s sulfate across the guadalupian lopingian g l boundary were analyzed from identical samples of tieqiao section laibin guangxi province south china the 13 c carb values show a positive excursion from 0 45 to the peak of 3 80 in the laibin limestone member of the maokou formation followed by a drastic drop to 2 60 in the lowest heshan formation then returned to about 1 58 similar to the trends of the 13 c carb values 13 c carb org values also show a positive excursion followed by a sharp negative shift the onset of a major negative carbon isotope excursion postdates the end guadalupian extinction that indicates subsequent severe disturbance of the ocean atmosphere carbon cycle the first biostratigraphic 34 s sulfate values during the g l transition exhibit a remarkable fluctuation a dramatic negative shift followed by a rapid positive shift ranging from 36 88 to 37 41 these sulfate isotopic records suggest that the ocean during the g l transition was strongly stratified forming an unstable chemocline separating oxic shallow water from anoxic euxinic deep water chemocline excursions together with subsequent rapid transgression and oceanic anoxia were likely responsible for the massive diversity decline of the g l biotic crisis

lower triassic sulphur isotope curve of marine sulphates from the dolomites n italy abstract 6 evaporite samples from the latest permian to the late lower triassic have been sampled at marine carbonate sections in the southern alps the sulphur isotope ratio of the sulphate has been determined to learn about the changes of the marine 34s ratio during the investigated period as it is known from the literature that a profound change from depleted to heavily enriched 34s values occurred within the lower triassic the carbonates from the same sections have been analysed for their carbon isotope pattern as the carbon isotope curve of the lower triassic has a very distinct pattern it enables the stratigraphic location of the evaporite layers in the section thus it can be shown that the change in 34s already occurred at the dienerian smithian boundary or within the dienerian stratification and re mixing of ocean water are the most plausible interpretations for the observed isotope patterns

sulfur cycle in buried evaporites sulfur isotopes are potent indicators of the way in which sulfur behaves chemically during diagenesis we have studied sulfur isotope ratios 34s 32s from a number of minerals and compounds across the permian triassic boundary in the khuff formation abu dhabi the 34s in dissolved marine sulfate increased by 10 from the late permian to the early triassic despite precipitation of gypsum from permian and triassic seawater and its subsequent dehydration to anhydrite at depths greater than about 1000 m the primary marine stratigraphic sulfur isotope variation has been preserved in anhydrite in the khuff formation a combination of biostratigraphic and absolute age data show that this 10 shift occurred over 2 m y gypsum dehydration to anhydrite has not involved significant isotopic fractionation or diagenetic redistribution of material in the subsurface the sulfur isotope variation across the permian triassic boundary is also present in elemental sulfur and h2s at depths greater than 4300 m formed by reaction of anhydrite with hydrocarbons via thermochemical sulfate reduction this demonstrates that sulfate reduction has not led to isotope fractionation it also demonstrates that significant mass transfer has not occurred at least in the vicinity of the permian triassic boundary even though elemental sulfur and h2s are both fluid phases at depths greater than 4300 m thus despite two major diagenetic processes that converted the sulfur in gypsum into elemental sulfur and h2s by 4300 m burial and the potentially mobile nature of some of the reaction products the primary differences in sulfur isotopes have been preserved in the rocks and fluids all reactions occurred in situ there was no significant sulfur isotope fractionation and only negligible sulfur was added subtracted or moved internally within the system

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

δ34scas and δ18ocas records during the frasnian famennian late devonian transition and their bearing on mass extinction models abstract many proposed extinction mechanisms for the late devonian frasnian famennian boundary ffb mass extinction event include the spread of anoxia in bottom waters during the two kellwasser anoxic events which have in turn been linked to changes in continental weathering volcanic hydrothermal fluxes sea level and climate change although there is strong evidence for bottom water anoxia in epicontinental seas at tropical equatorial palaeolatitudes the global extent of these changes is poorly understood largely due to the lack of an oceanic and high latitude record in this study marine 34 s sulphate and 18 o sulphate records derived from the analysis of carbonate associated sulphate cas were constructed from ffb sections in belgium and poland in order to examine the effect of the postulated changes in ocean redox conditions on the global sulphur cycle the results reveal no overall changes in seawater 34 s sulphate and 18 o sulphate over the ffb interval suggesting that any changes in sulphur cycling namely relating to rates of pyrite burial and weathering were not significant on a global scale this supports the idea that the kellwasser events were not oceanic phenomena and that they were restricted to epicontinental seas at low latitudes the exception to the stability of the ffb 34 s sulphate record is a brief negative excursion during the mass extinction interval in the linguiformis zone albeit based on one datapoint at this level in two different sections this may be attributable to short sharp marine regression and an increased flux of light sulphur from weathered pyrite

a sulfur and strontium isotopic investigation of lower permian anhydrite palo duro basin texas u s a abstract lower permian wolfcamp and wichita carbonates and anhydrites palo duro basin texas panhandle record a change from a normal marine to marine evaporite depositional environment isotopic compositions of s and sr in anhydrite were determined to investigate the age of wolfcamp and wichita strata and the paragenesis of eight anhydrite forms bedded nodular mosaic wichita and replacive nodular wolfcamp anhydrites have s and sr isotopic compositions that record precipitation from early permian wolfcampian to leonardian seawater silicified nodular coarsely crystalline nodular fossil filling and vein filling anhydrites have enriched s isotopic compositions relative to permian seawater whereas euhedral and anhedral replacive anhydrites have depleted s the sr isotopic composition of most anhydrite forms indicates an early permian marine origin however sr in anhydrite veins is slightly radiogenic compared to permian seawater the sr isotopic compoition of bedded nodular mosaic anhydrite indicates as leonardian seawater source of material the 34 s values are slightly enriched relative to values predicted from the s age curve suggesting an excursion of the s isotopic evolution trend of early permian seawater replacive nodular anhydrite 87 sr 86 sr ratios are slightly higher than those of bedded nodular mosaic anhydrite reflecting incorporation of sr from older marine pore waters or replaced sediments or from dissolution of detrital siliciclastic minerals anhydrite paragenesis is interpreted from stratigraphic mineralogic petrographic and isotopic data bedded nodular mosaic and replacive nodular anhydrite precipitated as marine evaporite strata prograded across underlying normal marine carbonate sediments siliified and coarsely crystalline nodules and anhydrite fossil filling precipitated at essentially the same time as bedded and replacive nodular anhydrite but in environments where sulfate reduction was more extensive euhedral anhedral replacive anhydrite formed in shallower environments where s redox cycling occurred prior to caso 4 precipitation anhydrite vein fills formed last and incorporated radiogenic sr released during alteration of detrital siliciclastic grains

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

a neogene seawater sulfur isotope age curve from calcareous pelagic microfossils abstract until now our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites owing to the sporadic occurrence of evaporites through time the secular sulfur isotope age curve contains many gaps with little or no data in order to fill in some of these gaps particularly the neogene we have analyzed the sulfur isotopic composition of carbonate associated sulfate in carbonate tests of planktonic foraminifera other investigators have shown that sulfate may occur in biogenic calcites either lattice bound as micro fluid inclusions in adsorbed phases or as protein polysaccharides whatever the origin the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived as shown by results on recent calcareous foraminifera and macrofossils using this approach for study of miocene to recent pelagic marine sediments supplemented by new data for miocene marine evaporites from the gulf of suez we have found that the 34 s of seawater has decreased about 2 5 over the past 25 m y and that most of the decrease has occurred over the past 5 m y parallelling a decrease in the 13 c of dissolved oceanic bicarbonate from the same interval sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m y alternatively an increase in weathering rates over the past 5 m y would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species in either case the net result would be a decrease in atmospheric p o 2

the valais units in savoy france a key area for understanding the palaeogeography and the tectonic evolution of the western alps the valais units in savoy zone des breches de tarentaise have been re mapped in great detail and are subject of combined stratigraphic structural and petrological investigations summarized in this contribution the sediments and rare relics of basement together with cretaceous age mafic and ultramafic rocks of the valais palaeogeographical domain represent the heavily deformed relics of the former distal european margin external valais units and an ocean continent transition internal valais unit or versoyen unit that formed during rifting this rifting led to the opening of the valais ocean a northern branch of the alpine tethys post rift sediments referred to as valais trilogy stratigraphically overlie both external and internal valais successions above an angular unconformity formed in barremian to aptian times providing robust evidence for the timing of the opening of the valais ocean the valais units in savoy are part of a second and more external mid eocene high pressure belt in the alps that sutured the brianconnais microcontinent to europe top n d1 deformation led to the formation of a nappe stack that emplaced the largely eclogite facies internal valais unit versoyen onto blueschist facies external valais units the latter originally consisted of from internal to external the petit st bernard unit the roc de l enfer unit the moutiers unit and the quermoz unit ongoing top n d2 thrusting and folding substantially modified this nappe stack post 35 ma d3 folding led to relatively minor modifications of the nappe stack within the valais units but was associated with substantial top wnw thrusting of the valais units over the dauphinois units along the roselend thrust during w directed indentation of the adria block contributing to the formation of the arc of the western alps

bentonite geochronology marine geochemistry and the great ordovician biodiversification event gobe abstract attribution of ordovician climate forcing to explosive volcanism and the potential global importance of volcanism in ordovician biodiversification suggest the necessity of evaluating the relationships between k bentonite deposition and increasingly high resolution records of marine biogeochemical change globally ordovician strata preserve an extensive record of explosive volcanism including the widely recognized lower to middle ordovician famatina k bentonite suite in argentina and the upper ordovician millbrig deicke kinnekulle suite of north america and europe here we present high resolution id tims u pb zircon ages of k bentonites from measured sections of the san juan formation talacasto and cerro la chilca section of the argentine precordillera k bentonites from the argentine precordillera provide stratigraphically consistent i e younging upward ages that range from 473 45 0 70 ma to 469 53 0 62 ma and constrain the age of a low magnitude 2 globally recorded negative carbon isotope excursion evaluation of the timing of k bentonite deposition in the argentina precordillera relative to marine biostratigraphic and biogeochemical records provides insight into relationships between explosive volcanism and regional to global environmental change from a regional standpoint these ages provide critical direct evidence for a dapingian to earliest darriwilian age of the upper san juan formation at sampled localities these ages are consistent with carbon isotope data suggesting that the san juan formation in the region of its type section is coeval with only the base of the often correlated table head group of western newfoundland this data thus highlights the difficulties in using regional biostratigraphic data particularly within erosionally truncated or otherwise diachronous units to define the timeframe of carbon isotope chemostratigraphy new geochronological data also indicate that a discrete negative carbon isotope excursion within the san juan and table head formations is correlative to a globally recognized pre mdice negative excursion and indicates that this aspect of the marine carbon isotope record can be used as a discrete chronologic marker san juan formation bentonites however cannot be discretely correlated with observed environmentally significant changes in the middle ordovician marine geochemical records of carbon sulfur strontium or sea surface temperature these results suggest that the extent of volcanism represented by the famatina bentonite suite was insufficient to affect global surface environments and that the relationship between explosive volcanism and environmental change may not be straightforward as previously suggested

revised estimate of δ34s for marine sulfates from the upper ordovician data from the williston basin north dakota u s a analyses for 34s of 13 bedded marine anhydrite samples from the c anhydrite member of the red river formation upper ordovician in the north dakota portion of the williston basin represent an addition of 34s data to a portion of the s isotope age curve with few data previously published estimates of 34s for upper ordovician marine sulfates apparently are limited to 4 samples from the saskatchewan portion of the same basin an adjusted mean value of 25 5 was calculated for all known upper ordovician 34s determinations this value is approximately 2 to 3 lighter than the previous estimate which suggests that 34s of the world ocean during the upper ordovician may have been lighter than previously thought however because all 34s data are from one sedimentary basin additional s isotopic data from several globally distributed evaporite basins are needed to evaluate this hypothesis and further constrain 34s for the upper ordovician similar re examination of other portions of the s isotope age curve with limited amounts of data may increase our understanding of the secular variation in 34s

sulfur and oxygen isotopes in italian marine sulfates of permian and triassic ages evaporitic sulfates of permian and triassic ages from italian occurrences were analyzed for sulfur and oxygen isotopes in order to supplement the corresponding isotope age curves and to use isotopic data to trace the origin of the sulfate in hydrologic systems the sulfur isotopic composition age relationships obtained in this study generally agree with those found throughout the world in two cases i e in samples from the carniola di bovegno formation bergamo and brescia alps and from the lower part of the gracilis formation recoaro vicenza sulfur isotopes suggest different ages for the rocks than the formerly ascribed ones oxygen isotopic compositions show the same range from 10 5 to 18 5 without any consistent relationship with sulfur these ranges of values are almost identical to those published previously for sulfates of permian and triassic ages from other locations

the evolution of the lorraine evaporite basin implications for the chemical and isotope composition of the triassic ocean abstract during the upper triassic times about 75 m of halite with minor anhydrite was deposited in the lorraine basin samples of halite and sulfates were systematically collected from a borehole intersecting the sequence the chemical evolution of the original brine was investigated by x ray microanalysis of primary inclusions trapped in halite the original brines were of the na mg k ca cl type being consistent with the mineral association of halite and minor anhydrite their solute content can be reproduced by evaporation of present day ocean composition in an open basin however some modifications are required the inflow of a small excess of cacl 2 into the basin 1 2 to 1 9 of the total recharge is required to explain the low so 4 values analyzed in fluid inclusions the same inflow helps to explain more satisfactorily the low na and high cl contents the back reaction of the brine with previous ca sulfate that forms polyhalite could explain the low and variable k values analyzed the excess of ca with respect to present day seawater and the formation of so 4 poor evaporite sequences is the rule rather than the exception in the geological record we have not been able to assess the ultimate origin of the ca excess in the basin nevertheless the great variation of the so 4 content within short vertical distances centimeter scale suggests that these variations are due to processes taking place within the evaporite basin rather than to changes in the composition of the ocean at a global scale the isotopic composition of sulfur and oxygen was determined using samples of sulfates from the same borehole the 34 s values of 21 samples analyzed show a narrow variation 34 s 15 5 0 4 the 18 o values of eight samples analyzed show a wider range of variation 18 o 13 0 1 1 none of the processes which modify the values such as sulfate reduction or additional sulfate sources continental recycling of sulfates from the margins were clearly identified the values of 34 s sw 15 7 to 14 5 and 18 o sw 13 7 to 12 2 for the sulfate dissolved in the triassic ocean explain the values of the sulfates interbedded in the halite of the lorraine basin and most analyses reported in the literature

stratigraphy and depositional mosaics of lower clear fork and wichita groups permian northern midland basin texas the stratigraphy depositional environments and reservoir potential of the wichita group and overlying lower clear fork permian in the northern midland basin are described on the basis of seismic interpretations log correlations and lithologic analyses the wichita in this area is divided into a lower member of slope to basinal limestones and shales and an upper member of shelf dolomites varicolored shales and evaporites only a starved lower wichita section is present in areas to the south fusulinid evidence and physical correlations suggest that the wolfcampian leonardian boundary occurs within the wichita and ascends stratigraphically toward the north these data in conjunction with the upward shoaling aspect of the wichita establish a progradational relatio between shelf facies of the upper member and slope to basinal facies of the lower member the lower clear fork beneath the tubb member records continued southward progradation of similar shelf facies these lithologies are represented in the basin by limestones and shales beneath and possibly including lowermost dean sandstones depositional systems of the wichita and pre tubb clear fork sections are carbonate dominated rimmed shelves adjoining deeper basins periods of rapid progradation and offlapping shelf edge accretion were cyclic being coincident with periods of low sea level the tubb section records a change to a mixed siliciclastic and carbonate rimmed shelf system deposition of shelf tubb and basinal dean facies was related to a mosaic of cyclic reciprocal siliciclastic carbonate sedimentation rapid shelf outbuilding occurred at low sea level stands during the siliciclastic phases of sedimentation the formation of the shallow north platform was more a consequence of constructional sedimentary processes during the late wolfcampian and early leonardian than of structural influences over much of the northern midland basin study area potential stratigraphic hydrocarbon reservoirs are in wichita and lower clear fork strata such reservoirs occur as separate offlapping shelf marginal dolomitized oolite grainstone shoals rather than organic buildups as was described in earlier studies

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

correlation and comparison of seawater δ34ssulfate records at the permian triassic transition abstract correlation of carbonate associated sulfate cas 34 s analysed permian triassic p tr sections via conodont biostratigraphy and sequence stratigraphy shows distinct phases in the oceanic 34 s sulfate evolution during the period 1 million years m y either side of the p tr boundary a 34 s sulfate rise in the changhsingian prior to the end permian mass extinction is followed by a period of about 350 000 years of erratic and substantial 34 s sulfate movements range 1 to 28 the mass extinction occurring in the middle of this period the sharp swings in this phase indicate severe changes in the oceanic sulfur geochemistry and perhaps stages of ocean inhomogeneity low 34 s sulfate values coincide with the mass extinction horizon suggesting the extinction is related to an input of relatively 32 s enriched sulfur into the oceanic sulfate reservoir the source of this sulfur most likely being h 2 s from euxinic waters after the erratic 34 s sulfate phase there is a stabilisation of 34 s sulfate values 17 until the later griesbachian however there is a possibility of discrepant panthalassan and tethyan data sets during the early to mid griesbachian but this requires further work for confirmation 34 s sulfate values are erratic in the late griesbachian to early dienerian suggesting further perturbation of the sulfur cycle the poorly age constrained smithian record shows a wide range of 34 s sulfate values probably indicating swings during that time also the 34 s sulfate movements from the changhsingian to smithian indicate the permian triassic transition is a time of intense changes in the sulfur fluxes to and from the oceans and perhaps stages of ocean inhomogeneity

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

controls on δ 34 s and δ 18 o of dissolved sulfate in aquifers of the murray basin australia and their use as indicators of flow processes the usefulness of stable isotopes of dissolved so4 34s and 18o to study recharge processes and to identify areas of significant inter aquifer mixing was evaluated in a large semi arid groundwater basin in south eastern australia the murray basin the distinct isotopic signatures in the oxidizing unconfined murray group aquifer and the deeper reducing renmark group confined aquifer may be more sensitive than conventional chemical tracers in establishing aquifer connections 34s values in the unconfined murray group aquifer in the south and central part of the study area decrease along the hydraulic gradient from 20 8 to 0 3 the concomitant increasing so4 cl ratios as well as relatively low 18oso4 values suggest that vertical input of biogenically derived so4 via diffuse recharge is the predominant source of dissolved so4 to the aquifer further along the hydraulic gradient towards the discharge area near the river murray 34s values in the unconfined murray group aquifer increase and so4 cl ratios decrease due to upward leakage of waters from the confined renmark group aquifer which has a distinctly low so4 cl and high 34s 14 9 56 4 relatively positive 34s and 18oso4 values and low so4 cl in the renmark group aquifer is typical of so4 removal by bacterial reduction the s isotope fractionation between so4 and hs of 24 estimated for the confined aquifer is similar to the experimentally determined chemical fractionation factor for the reduction process but much lower than the equilibrium fractionation 70 even though the confined groundwater residence time is 300 ka years mapping the spatial distribution of 34s and so4 cl of the unconfined murray group aquifer provides an indicative tool for identifying the approximate extent of mixing however the poorly defined end member isotopic signatures precludes quantitative estimates of mixing fractions

the role of bacterial sulfate reduction during dolomite precipitation implications from upper jurassic platform carbonates the early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine anoxic organic rich sediments dominated by bacterial sulfate reduction bsr in such environments bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non stoichiometric highly disordered and metastable proto dolomite although the boundary conditions for the formation of modern proto dolomites are considered to be generally understood the role of bsr during limestone dolomitization in ancient marine environments remains questionable herein we present a study about the physicochemical conditions and processes which led to the formation of partly dolomitized limestone and dolostone in the presence of bsr on a stable carbonate platform during the upper jurassic at oker northern german basin the dolomite textures the spatial trace elemental patterns of the dolomite and of the surrounding limestone and the results of 18o and 13c isotope analyses reveal that the oker dolomite has been formed by the early diagenetic replacement of magnesian calcite precursors at temperatures between 26 c and 37 c we interpret the mineralizing fluids responsible for dolomitization as pristine marine to slightly evaporitic and reducing seawater being modified during shallow seepage reflux and or evaporitic tidal pumping the elevated 34scas values 17 9 to 19 7 v cdt of the oker dolomite compared to ambient upper jurassic seawater indicate that bsr facilitated dolomite formation for the first time we show that a linear anti correlation exists between decreasing carbonate associated sulfate cas contents in dolomite and increasing ordering ratio of the dolomite lattice structure with the degree of cation order in dolomite to be given by degree of cation order dol 0 018 cas dol 68 3 r2 0 98 this correlation implies that the cas content of sedimentary dolomite can be used as a measure for dolomite maturity the relationships between the ambient paleo environmental controls the resultant dolomitization pathways and subsequently the structure and the composition of the precipitating dolomite are presented and discussed in relation to the stability of modern and ancient proto dolomites throughout burial diagenesis

refining the extraction methodology of carbonate associated sulfate evidence from synthetic and natural carbonate samples sulfur and oxygen isotope analyses of trace and whole mineral sulfate are valuable in investigating diagenetic processes and the microbial communities that produced them seawater anoxia and paleoclimate oxygen isotopes are particularly useful in that they may also record alterations to the original isotope ratio be it from post depositional processes or oxidation of sulfide minerals during the chemical extraction procedure here we rigorously test several common methodological procedures of extracting carbonate associated sulfate cas for sulfur and oxygen isotope analyses in order to generate a method that will extract only the cas while preserving associated organic reduced sulfur and sulfides for analysis the results of these experiments on synthetically generated carbonates demonstrate that our proposed protocol sufficiently removes all non cas sulfate and does not result in oxidation of included sulfides analytical reproducibility standard deviation of synthetic carbonates is 0 1 1 for 34s and 0 3 1 for 18o extractions of low pyrite high organic matter geologic samples from the monterey formation across a range of facies types demonstrate a reproducibility 1 of 0 4 0 7 for 34s and 0 8 1 3 for 18o resulting from sample heterogeneity 34s and 18o from monterey formation samples do not demonstrate oxidation of organic matter suggesting our proposed protocol will preserve organic sulfur a high pyrite concentration jet rock concretion demonstrates that additional sulfate can be produced during the non cas leaching processes from oxidation of pyrite we show that pyrite from the jet rock concretion ceases to oxidize when the sample is leached under an anoxic environment

dynamic sulfur and carbon cycling through the end ordovician extinction revealed by paired sulfate pyrite δ34s geochemical records of the end ordovician hirnantian stage show parallel positive excursions in the stable isotope compositions of sedimentary pyrite sulfur 34spyr organic carbon 13corg and carbonate carbon 13ccarb these isotope excursions coincide with the end ordovician glaciation and mass extinction a relative increase in pyrite burial fpyr attributed to marine anoxia has been invoked to explain the sulfur isotope excursion and link oceanic redox conditions to the extinction of marine fauna an increase in fpyr would necessarily generate a parallel excursion of equal magnitude in the isotopic composition of coeval marine sulfate 34sso4 34sso4 here we present new high resolution paired sulfur isotope data from carbonate associated sulfate 34scas and pyrite from the hirnantian stage of western anticosti island quebec canada these data document a positive 20 enrichment in 34spyr comparable in magnitude to previous reports but no parallel excursion in 34scas this pattern provides new constraints on the origin of the 34spyr excursion and the nature of carbon sulfur coupling through hirnantian time specifically these observations preclude enhanced pyrite burial as the cause of the hirnantian 34spyr excursion and suggest the possible role of anoxia in the mass extinction may need to be reevaluated rather the global 34spyr excursion is best explained by a transient reduction in the isotopic fractionations expressed during microbial sulfur cycling epyr the epyr record shows a strong inverse correlation with 13c suggesting a mechanistic link between carbon cycling and processes controlling epyr during the hirnantian changes in sea level or marine redox state associated with glaciation could further impact the expression of the biological fractionation e g through syndepositional sediment reworking and or chemocline migration and resultant restricted exchange of porewater sulfate the magnitude of isotopic fractionation during microbial sulfate reduction is partially controlled by metabolic rates which are sensitive to the abundance type and lability of metabolically relevant substrates environmental change associated with the end ordovician glaciation may have elevated the flux of organic material to marine sediments or caused an increase in physical reworking of sediments leading to increased microbial sulfate reduction rates and reduced epyr as such the hirnantian 34spyr excursion may be viewed as a dynamic biological response to global climate change highlighting the connections between the carbon and sulfur biogeochemical cycles

δ34s and δ33s records of paleozoic seawater sulfate based on the analysis of carbonate associated sulfate abstract this study updates the 34s and 33s temporal records of paleozoic and early mesozoic seawater sulfate using analysis of carbonate associated sulfate of biogenic and whole rock carbonate the time resolution of carbonate samples studied here is on the order of millions of years which is longer than the timescale for homogenization of seawater sulfate sulfur one tenth of a million years but is comparable to the timescale for isotope evolution of sulfate in the oceans this 34s record confirms the long term decreasing trend that is discernible over the 250 million year timescale of sampling and the 33s record of seawater sulfate for the paleozoic is consistent with an average value of 0 002 0 004 2 540 251 ma that is distinct from the positive 33s observed today and inferred for the rest of the cenozoic both 34s and 33s records of seawater sulfate suggest the presence of shorter timescale variations that occur on timescales of tens of millions of years arguably driven by changes in intensity of sulfide oxidation in cycling of sulfur and or by rapid changes in sulfur influx to the oceans and its associated sulfur isotopes the permian triassic boundary marks a transition in co trajectories of 34s and 33s from in phase to anti phase the biogeochemical forcing that causes this is unclear this newly calibrated record remains consistent with an earlier assertion wu et al 2010 that the sulfur isotope fractionation 34ssw py between oceanic sulfate 34ssw and coeval sedimentary pyrite 34spy was smaller during the paleozoic than in the cenozoic and reached lowest values during the carboniferous the 34sin and 33sin estimates of influx sulfur to the oceans afforded by the isotope mass balance model for each geologic period throughout the paleozoic reveal a change from higher positive values of 34sin more negative values of 33sin approximately 0 030 to lower positive values of 34sin slightly negative values of 33sin approximately 0 003 this change is interpreted to reflect the evolution of the earth surface sulfur pool and the rapid recycling of newly formed evaporite sulfate minerals as arguably supported by our estimates of integrated erosion rates over geologic time for pyrite and evaporite 6 1 6 4 10 9 a 1 and 7 7 7 8 10 9 a 1 respectively

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

the sulphur isotopic composition of trace sulphates in carboniferous brachiopods implications for coeval seawater correlation with other geochemical cycles and isotope stratigraphy the carboniferous 34s record based on the analysis of structurally substituted sulphate sss in brachiopod shells is characterized by a significant decline from values around 21 1 in the tournaisian to 12 1 in the gzelian superimposed on this broad evolution is a higher order structure with a relative minimum in the late visean followed by a maximum in the bashkirian on the 107 year time scale 34s is positively correlated with 13ccarb in contrast to the long term negative linkage between sulphur and carbon observed for the entire phanerozoic this indicates that mechanisms other than the redox balance control the carbon and sulphur cycles on this time scale the 87sr 86sr and 34s records display parallel trends during the tournaisian to moscovian this positive correlation suggests that tectonics may be of importance for the evolution of 34s on time scales of 107 years a possible scenario to explain the co evolution of the isotope systems and their linkage to tectonism and palaeoclimate invokes an increased nutrient supply to the oceans during periods of enhanced uplift and continental weathering this nutrient flux may have resulted in increased burial of organic matter and enhanced bacterial sulphate reduction

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

marine to nonmarine facies transition in permian evaporites of the palo duro basin texas geochemical response the late paleozoic palo duro basin evolved from a marine to nonmarine environment as it was infilled the evaporitic part of the sequence leonardian through ochoan is composed of regressive carbonate anhydrite halite cycles that displaced open marine environments toward the south during basin filling systematic vertical changes in evaporite geochemistry through the evaporite section include increasing 87sr 86sr ratios and decreasing altered from marine 34s in anhydrite decreasing recycled bromide content of the halite and increasing meteoric influence on the stable isotopic composition of fluid inclusions in halite geochemical changes correspond to changes in evaporite sedimentology and document the evolution from marine dominated to partly nonmarine evaporites geochemical tracers when used with sedimentological and facies analysis provide reliable indicators of the sources of water and solutes in an anhydrite halite facies tract perennial intermittently stratified and ephemeral brine pool conditions affect the amount of synsedimentary recycling variable rates of reflux and marine recharge control residence times of brines in the depositional environment these are two key processes in relating evaporite geochemistry to depositional environment

particulate ba barite and acantharians in the southern ocean during the european iron fertilization experiment eifex 1 particulate biogenic ba sr and ca and barite crystal contents from suspended matter were compared with acantharian water column distributions and individual ba sr acantharian skeletal ratios during the european iron fertilization experiment eifex in the southern ocean in the upper 150 m results indicate that the particulate biogenic baxs signal is almost free of barite baso4 particles and follows the same evolution as biomass parameters implying that ba is incorporated into or adsorbed onto biologically derived biogenic particles of which acantharians could account nearly the whole surface baxs signal in contrast in the mesopelagic zone 150 1000 m particulate biogenic baxs is mainly composed of micro crystalline barite calculations indicate that the combined acantharian associated ba contents in the upper 150 m and between 150 500 m if entirely transformed into barite an unlikely condition and dispersed in the 150 1000 m layer could explain up to 20 of the mesopelagic baxs contents our results thus indicate that acantharians are probably not the major source of particulate ba barite in the water column they support the hypothesis that mesopelagic baxs is mostly built up as the result of biogeochemical processes within aggregates and its usefulness as a proxy of mesopelagic c remineralization

sulfur isotope records around livello bonarelli northern apennines italy black shale at the cenomanian turonian boundary sulfur isotope ratios for carbonate hosted sulfate show a rapid increase 6 to 9 m y across the livello bonarelli black shale marche umbrian apennines of italy which was deposited at the cenomanian turonian boundary in the middle cretaceous 93 5 ma the increase suggests that rates of pyrite burial increased substantially over the event resulting in a decrease of 9 27 in the oceanic reservoir of so 4 2 the enhanced pyrite burial may have significantly increased the flux of oxygen to the atmosphere 9 27 10 18 mol m y furthermore removal of the large amount of iron associated with this process might have had a profound effect on iron cycle

sulfur isotopic evidence for chemocline upward excursions during the end permian mass extinction the latest permian was a time of major change in ocean chemistry accompanying the greatest mass extinction of the phanerozoic to examine the nature of these changes samples from two well studied marine sections that span the permian triassic boundary have been analyzed the meishan and shangsi sections located in southern china isotopic analysis of the carbonate associated sulfate in these samples provides a detailed record of several isotopic shifts in 34scas approaching and across the ptb ranging from 30 to 15 vcdt with repeated asynchronous fluctuations at the two locations we interpret the patterns of isotopic shifts in conjunction with other data to indicate a shallow unstable chemocline overlying euxinic deep water which periodically upwelled into the photic zone these chemocline upward excursion events introduced sulfide to the photic zone stimulating a bloom of phototrophic sulfur oxidizing bacteria we hypothesize that elemental sulfur globules produced by these organisms and 34s depleted pyrite produced in the euxinic water column were deposited in the sediment later oxidation led to incorporation as cas this created the large changes to the 34scas observed in the latest permian at these locations

contrasting long term global and short term local redox proxies during the great ordovician biodiversification event a case study from fossil mountain utah usa abstract the great ordovician biodiversification event gobe was a time of pronounced radiation within the paleozoic and modern evolutionary faunas despite increases in metazoan diversity during both the cambrian and the ordovician recent geochemical evidence suggests that the early paleozoic may have experienced recurring deep ocean euxinia the dynamic connections between deep ocean redox and fossil rich shelf environments remain unclear but one way to elucidate these relationships is to study rocks formed during the gobe using both long term global and short term local redox proxies here we report geochemical results from the middle ordovician juab formation and kanosh formation at fossil mountain utah the kanosh formation has been interpreted by different workers either as an anoxic restricted basin or as a well oxygenated normal marine basin based on sedimentological and paleontological characteristics here we employ the sulfur isotopic composition of carbonate associated sulfate cas as a proxy for long term whole ocean redox changes during the middle ordovician we use the abundances of organic carbon and total sulfur as proxies for short term localized changes in redox during the deposition of the fossil mountain sediments organic carbon abundances are low overall average 0 7 wt maximum 1 2 wt using the most conservative estimate although some units may have had considerably higher organic content before burial total sulfur is uniformly low with an average value of 0 02 wt and a maximum value of 0 07 wt the total sulfur and organic carbon abundance results suggest that anoxia was not prevalent in the depositional environment of the juab and kanosh formations similarly the sulfur isotopic results correlate well with those reported from time equivalent strata in newfoundland suggesting that the fossil mountain sediments were not deposited in a restricted basin even though the total sulfur and organic carbon data suggest that the local environment was not anoxic our sulfur isotopic results support the hypothesis that the global ocean was likely euxinic during the middle ordovician

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

black shale deposition on the northwest african shelf during the cenomanian turonian oceanic anoxic event climate coupling and global organic carbon burial high resolution geochemical records from a depth transect through the cenomanian turonian c t tarfaya basin northwest african shelf reveal high amplitude fluctuations in accumulation rates of organic carbon oc redox sensitive and sulphide forming trace metals and biomarkers indicative of photic zone euxinia these fluctuations are in general coeval and thus imply a strong relationship of oc burial and water column redox conditions the pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher frequency forcing determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event oae2 and its duration we propose that eccentricity is the main forcing factor at tarfaya and controlled fluctuations in wind driven upwelling of nutrient rich oxygen depleted intermediate waters from the adjacent atlantic and the periodic development of photic zone and bottom water euxinia on the mid cretaceous northwest african shelf accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six fold increase in oc burial from similar to2 g m 2 yr prior to the oae2 to similar to12 g m 2 yr during the oae2 photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing mass balance calculations imply that similar to2 of the overall global excess oc burial associated with the oae2 was deposited in the tarfaya basin an area that represented only similar to0 05 of the total global c t ocean floor in fact the lateral extent of similar black shales along the african continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the oae2

middle late ordovician darriwilian sandbian decoupling of global sulfur and carbon cycles isotopic evidence from eastern and southern laurentia abstract middle late ordovician sequences from the appalachian basin and arbuckle mountain regions of north america were analyzed for carbonate associated sulfate 34 s cas and pyrite 34 s pyr paired with carbonate 13 c carb and organic matter 13 c org chemostratigraphy two major negative drops in 34 s cas 12 excursions are recognized the older decline in 34 s cas occurs within the histiodella holodentata phragmodus polonicus conodont zones and the younger drop is within the cahabagnathus sweeti amorphognathus tvaerensis baltoniodus gerdae subzone zones these overall these negative shifts in 34 s cas have an antithetical relationship with positive shifts in 34 s pyr 10 and 13 c carb 2 recorded in the same successions the older negative 34 s cas shift is coincident with the widely documented mid darriwilian 13 c excursion mdice and the younger negative 34 s cas shift is coincident with another positive 13 c carb shift in the early sandbian geochemical modeling of these sulfur isotope shifts suggests that a decrease in the global rate of pyrite burial or isotope fractionation between seawater sulfate and sedimentary pyrite could account for these negative 34 s cas trends additionally a substantial increase in the weathering flux of pyrite to the global oceans could also explain these secular sulfur isotope trends while increased crustal weathering is broadly consistent with a sea level lowstand and the seawater 87 sr 86 sr isotope record of change in continental weathering in the late darriwilian stage of the ordovician geologic and geochemical proxy evidence do not support distinct pulses of continental weathering required to generate two separate negative shifts in 34 s cas these antithetical isotope trends may be best explained by changes in the marine redox state that significantly reduced microbially mediated pyrite burial and organic matter remineralization rates pulses of oceanic ventilation would have expanded habitable environments for marine organisms and thus is broadly consistent with major increases in biodiversification during this period of the ordovician

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

neoarchean carbonate associated sulfate records positive δ s anomalies mass independent fractionation of sulfur isotopes reported as 33s recorded in archean sedimentary rocks helps to constrain the composition of earth s early atmosphere and the timing of the rise of oxygen 2 4 billion years ago although current hypotheses predict uniformly negative 33 s for archean seawater sulfate this remains untested through the vast majority of archean time we applied x ray absorption spectroscopy to investigate the low sulfate content of particularly well preserved neoarchean carbonates and mass spectrometry to measure their 33 s signatures we report unexpected large widespread positive 33 s values from stratigraphic sections capturing over 70 million years and diverse depositional environments combined with the pyrite record these results show that sulfate does not carry the expected negative 33 s from sulfur mass independent fractionation in the neoarchean atmosphere

behavior of carbonate associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy abstract although carbonate associated sulfate cas is used widely as a proxy for the sulfur isotope composition of ancient seawater little is known about the effects of diagenesis on retention of primary 34 s signals our case study of the key largo limestone pleistocene florida is the first systematic assessment of the impact of meteoric diagenesis on cas properties geochemical and petrographic data show that meteoric diagenesis has affected the exposed coralline facies to varying degrees yielding differences now expressed as sharp reaction fronts between primary and secondary carbonate minerals within individual coral heads specifically analyses across high resolution transects in the key largo limestone show that concentrations of strontium and sodium decrease across the recrystallization front from original aragonite to meteoric low magnesium calcite by factors of roughly 5 and 10 respectively predictably 18 o values decrease across these same fronts the 13 c relationships are more complex with the most depleted values observed in the latest formed calcite such trends likely reflect carbon isotope buffering capacity that decreased as reaction progressed as well as protracted development of soil profiles and the associated terrestrial biomass and thus depleted 13 c during sea level lowstand conversely 34 s values of cas vary within a narrow buffered range from 20 6 to 22 6 compared to 20 8 22 0 of coeval pleistocene seawater across the same mineralogical transition despite sulfate concentrations that drop in the diagenetic calcite by an average factor of 12 collectively these data point to robust preservation of primary 34 s for carbonates that have experienced intense meteoric diagenesis which is encouraging news for those using the isotopic composition of cas as a paleoceanographic proxy at the same time the vulnerability of cas concentrations to diagenetic resetting is clear

a global perturbation to the sulfur cycle during the toarcian oceanic anoxic event abstract the mesozoic era was punctuated by intervals of widespread anoxia within the ocean termed oceanic anoxic events or oaes the chemostratigraphy of these intervals also contains evidence of transient perturbations to many biogeochemically important elemental cycles here we present high resolution sulfur isotope data from three stratigraphic sections spanning the toarcian oceanic anoxic event t oae of the early jurassic all sections show a similar increase in the sulfur isotope ratio of sulfate parallel to an overall positive excursion in carbon isotopes during the oae interval based on forward box modeling the sulfate s isotope excursion can be generated by transiently increasing the burial rate of pyrite in marine sediments likely deposited under euxinic i e anoxic and sulfidic conditions in the water column in addition modeling shows that prolonged recovery of the 34 s of seawater sulfate at least 8 ma after the initial rise associated with the oae was due to the relatively long residence time of sulfate in the jurassic ocean estimates from our modeling put the toarcian marine sulfate concentrations at 4 to 8 mm the similarity of the sulfur isotope records from the north european epicontinental or epeiric sea and tethyan continental margin suggests that local modification of the marine sulfur isotope signal was minimal a point explored with isotope mixing models importantly our results indicate that the sulfur isotope excursion reflects a globally significant perturbation in the sulfur cycle and that pyrite burial in the north european epeiric seaway alone cannot account for the excursion this study along with recent work from other phanerozoic intervals of widespread marine oxygen deficiency confirms that the sulfur cycle can be perturbed significantly by enhanced pyrite burial during periods of prolonged oceanic anoxia euxinia

environmental and diagenetic variations in carbonate associated sulfate an investigation of cas in the lower triassic of the western usa an integrated stable isotope elemental and petrographic analysis of early triassic spathian carbonates and evaporites along a proximal to deep environmental transect reveals significant variations in 34s composition of carbonate associated sulfate cas the variations in the 34s of cas are strongly correlated with the ca mg composition of carbonates suggesting that the variations are driven by the degree of dolomitization the 34s of dolostones and evaporites are similar to one another and exhibit lower 34s values than limestones from all localities three hypotheses may explain the differences in 34s between proximal dolostones evaporites and inner middle shelf limestones 1 limestones experienced anaerobic sulfate reduction and subsequent incorporation of 34s enriched sulfate into cas during diagenesis while dolostones did not this is unlikely because of the lack of correlation between 34scas and toc as well as other indicators of diagenesis 2 dolomitization controlled the 34scas in proximal paleoenvironments where the source of the 34s depleted fluids was either continentally derived or the result of rayleigh distillation during evaporite formation and 3 a 34s depth gradient existed during the early triassic such that limestones formed in distal waters are more enriched in 34s versus evaporites and dolostones formed in proximal settings we do not favor this hypothesis because the strong correlation between ca mg and 34scas implies that dolomitization controls the 34scas in these samples results from subtidal well preserved non dolomitized limestones suggest that the 34s of spathian seawater sulfate may have been heavier than previously suggested from analyses of evaporite deposits alone

stable isotopes in the sulfate evaporites from southeastern iowa u s a indications of postdepositional change sulfate evaporites of mid paleozoic age are exposed or can be found within several hundreds of meters below the surface across much of southeastern iowa in addition mesozoic jurassic evaporites have been mined from thick beds in north central iowa this study reports stable isotope analyses performed on twenty four samples representing each of the major evaporite units in the state values of 34s in all samples are consistent with those of sulfates of the same age on the global sulfur time line defined by previous investigators some samples however have 18o values that are as much as 6 lighter than sulfates of the same age on the global oxygen time line these anomalies were observed in both devonian and mississippian samples but only in a small region near ottumwa the cause of the anomalous values is not clear although circumstances suggest a chemical interaction with migrating fluids in this part of iowa devonian and mississippian strata host major aquifer systems whose waters may have disturbed the isotopic compositions of the evaporites or may have served in the past as conduits for other migrating fluids results of this survey suggest therefore that 34s values of iowa evaporites carry an undisturbed record of the isotopic composition of paleozoic seawater but that 18o has been affected by postdepositional changes and is no longer a reliable measure