records of carbon and sulfur cycling during the silurian ireviken event in gotland sweden abstract early silurian 431 ma carbonate rocks record a ca 4 5 positive excursion in the stable isotopic composition of carbonate carbon 13ccarb associated with this isotopic shift is a macroevolutionary turnover pulse known as the ireviken event the onset of this carbon isotope excursion is commonly associated with a shallowing upward facies transition that may have been accompanied by climatic change as indicated by a parallel positive shift 0 6 in the stable isotopic composition of carbonate oxygen 18ocarb however the relationships among carbon cycle perturbations faunal turnover and environmental changes remain enigmatic here we present a suite of new isotopic data across the ireviken event from multiple sections in gotland sweden these samples preserve no systematic change in 18ocarb but show positive excursions of equal magnitude in both carbonate 13ccarb and organic 13corg carbon in addition the data reveal a synchronous perturbation in sulfur isotope ratios manifest as a ca 7 positive excursion in carbonate associated sulfate 34scas and a ca 30 positive excursion in pyrite 34spyr the increase in 34spyr values is accompanied by a substantial concomitant increase in stratigraphic variability of 34spyr the relatively constant offset between the 13ccarb and 13corg excursions throughout the ireviken event could be attributed to increased organic carbon burial or possibly a change in the isotopic composition of co2 sources from weathering however a positive correlation between carbonate abundance and 13ccarb suggests that local to regional changes in dissolved inorganic carbon dic during the shallowing upward sequence may have been at least partly responsible for the observed excursion the positive excursion recorded in 34scas suggests a perturbation of sufficient magnitude and duration to have impacted the marine sulfate reservoir an inverse correlation between cas abundance and 34scas supports the notion of decreased sulfate concentrations at least locally consistent with a concomitant increase in pyrite burial a decrease in the offset between 34scas and 34spyr values during the ireviken event suggests a substantial reduction in the isotopic fractionations epyr expressed during microbial sulfur cycling and pyrite precipitation through this interval decreased epyr and the concomitant increase in stratigraphic variation in 34spyr are typical of isotope systematics observed in modern shallow water environments associated with increased closed system behavior and or oxidative sedimentary reworking during early sediment diagenesis while the isotopic trends associated with the ireviken event have been observed in multiple locations around the globe many sections display different magnitudes of isotopic change and moreover are typically associated with local facies changes due to the stratigraphic coherence of the carbon and sulfur isotopic and abundance records across the ireviken event and their relationship to changes in local depositional environment we surmise that these patterns more closely reflect biogeochemical processes related to deposition and lithification of sediment than global changes in carbon and sulfur burial fluxes

sustained low marine sulfate concentrations from the neoproterozoic to the cambrian insights from carbonates of northwestern mexico and eastern california abstract stratigraphic carbonate carbon isotope trends are similar for correlative ediacaran and cambrian carbonates of sonora mexico and death valley california in contrast the sulfur isotope compositions of both carbonate associated sulfate cas and pyrite in the two regions exhibit unique trends with high degrees of stratigraphic variability we have established that the sulfur records are coeval using 13c chemostratigraphy and biostratigraphic markers where present over short stratigraphic intervals 34scas variability is consistent with regionally low marine sulfate concentrations during this period values of 34s 34scas 34spyr range from 5 8 to 27 1 and average 11 consistent with limited net fractionation during bacterial sulfate reduction which is additional evidence for low sulfate concentrations modeling based on these regional sulfur isotope trends suggests sustained low sulfate conditions throughout the neoproterozoic and well into the cambrian with concentrations of 2 mm or lower when all of the available sulfate proxy data from our work and previously published studies are considered most neoproterozoic and cambrian successions exhibit trends consistent with low seawater sulfate the persistent and complete disagreement in 34ssulfate among multiple basins was briefly interrupted 580 million years ago coincident with the onset of the wonoka shuram carbon isotope anomaly and again near the termination of series 3 of the cambrian characteristics generally unrecognized in older rock units during these two intervals similar stratigraphic trends in 34scas are recorded globally whereas absolute values remain distinct among individual basins however these periods of broad isotopic trend agreement coincide with large magnitude sulfur isotope excursions which also point to low seawater sulfate concentrations therefore although brief intervals of isotopic homogeneity exist the neoproterozoic and cambrian ocean must have been dominated by low sulfate throughout ultimately the recognition of persistently low sulfate well into the paleozoic raises questions about the relationships between sulfate concentration in seawater and its primary controls including ocean oxygenation and its influence on metazoan evolution

geochemical implications of sulfate in sedimentary carbonates abstract sulfate content reaches maximum partitioning in inorganically deposited mn calcite from aqueous solution when the carbonate contains 4 wt mno similar partitioning was also found for sr which rises to a maximum when calcite sediments contain 0 5 wt mno the behavior of the sulfate is explicable in terms of substitution of co 2 3 by so 2 4 this argument for the distribution of so 2 4 in inorganically formed carbonates is also consistent for sulfate in marine carbonates ir spectra of recent biogenic carbonates revealed no organic but only inorganic sulfate indicating that the sulfate occupies lattice sites in the carbonates total sulfate content of recent calcitic marine carbonates and pleistocene limestones increases with increasing mg content up to a maximum near 2 3 wt mg and decreases at larger mg contents this decrease in the sulfate content of these marine carbonates from that incorporated originally into the carbonate lattices is attributed to gradual exsolution during diagenesis in subaerial fresh water or on the sea floor in low so 2 4 waters the sulfate in coralline algae apparently increases the mg content above that predicted from observed shifts in the x ray diffraction peaks based upon so 2 4 free calcites

isotopic evidence for a sizeable seawater sulfate reservoir at 2 1 ga abstract the 2 1 ga tulomozero formation deposited on the fennoscandian shield consists of shallow marine carbonate and siliciclastic rocks dissolution breccias and widespread syndepositional marine evaporites now mostly present as pseudomorphs after ca sulfates this study investigates sulfates hosted in three different proxies to constrain the sulfur isotopic composition of seawater sulfate acknowledging the presence of different types of sulfates carbonate associated sulfate cas breccia associated sulfate bas and sulfate relicts rs in a variety of lithologies of the tulomozero formation a widely used and accepted proxy for the ambient seawater sulfate sulfur isotopic composition is carbonate associated sulfate which was extracted from carbonate samples across the entire tulomozero formation in addition sulfate was extracted from a siliciclastic dissolution breccia which is suggested to have formed after dissolution of sulfate evaporites the sulfate sulfur isotopic composition from both lithologies was measured ex situ 34 s cas 10 9 2 7 34 s bas 9 0 1 1 ubiquitous pseudomorphs after ca sulfates occur in the tulomozero formation and contain m size anhydrite and barite relicts their sulfur isotopic composition was measured in situ by secondary ion mass spectroscopy sims 34 s anhydrite 9 6 1 0 34 s barite 11 0 3 1 sulfur isotope data from carbonate rocks breccias and the sulfate relicts match the existing 34 s record of seawater sulfate during that time and show no distinct stratigraphic variations indicating that the seawater sulfate sulfur isotopic composition remained unaffected from environmental changes during the time of deposition of the tulomozero formation physical evidence for widespread precipitation of sulfate rather than abundant chloride suggests a modern style evaporite sequence with carbonates followed by sulfate and then chlorides however this requires a minimum sulfate concentration of 2 5 mm in the ambient seawater consequently the evidence for persistent evaporitic sulfate deposition in the tulomozero formation implies a substantial seawater sulfate reservoir at 2 1 ga according to the estimated minimum depositional time from the thickness of the carbonate rocks of the formation the residence time of seawater sulfate is expected to have been at least 5 ma the available data support the existence of a sizeable seawater sulfate reservoir in the mid paleoproterozoic ocean in fact more than 10 of the modern sulfate reservoir

the association of hydrogen with sulfur on mars across latitudes longitudes and compositional extremes nasa jet propulsion lab nasa mars data analysis program nnx07an96g nnx10aq23g mdap grants nnx12ag89g nnx13ai98g lsu s college of science and geology and geophysics

environments favoring dolomite formation at cold seeps a case study from the gulf of mexico abstract dolomite rarely occurs in modern marine environments while it is ubiquitous in the geological record this apparent contradiction made the formation mechanism of dolomite a long standing problem haunting sedimentologists however dolomite is a constituent of many modern seep carbonates providing an opportunity to investigate the conditions favoring dolomite formation at low temperatures in the shallow subseafloor this study reports the petrology mineralogy carbon and oxygen stable isotopic compositions as well as sulfur isotopic compositions of both carbonate associated sulfate cas and chromium reducible sulfur crs of a set of dolomite bearing carbonates from two seep sites gc140 and gb382 on the northern slope of the gulf of mexico the 13c values of carbonates vary from 50 0 to 3 2 v pdb confirming that carbonate minerals mostly resulted from methane oxidation the corresponding 18o values range from 2 6 to 5 9 v pdb reflecting formation close to equilibrium with seawater composition all carbonate samples with dolomite show similar petrologies and lack skeletal remains of seep dwelling metazoans the homogenous texture of microcrystalline dolomite agrees with its formation in the shallow subseafloor dolomite bearing samples reveal 18ocas 34scas slopes of 0 425 and 0 435 for the two study sites respectively such high slopes are significantly different from the smaller slopes of seep carbonates consisting of calcite from gulf of mexico seeps suggesting low overall sulfate reduction rates during dolomite formation this explanation is also supported by relatively high 34scrs values ranging from 29 4 to 19 0 v cdt and the positive correlation of these values with dolomite contents interestingly an approximately stoichiometric dolomite sample yielded the most positive 34scrs value indicating a formation environment typified by low replenishment of seawater sulfate at a supposedly relatively deep sulfate methane transition zone smtz overall these results confirm that dolomite formation is facilitated where the smtz is situated at relatively great depth where sulfate reduction rates are slowed down due to the buildup of high contents of dissolved sulfide and low seawater sulfate replenishment

sulfur isotope change across the early mississippian k o kinderhookian osagean δ13c excursion abstract paired carbonate associate sulfate cas sulfur isotopes 34 scas pyrite sulfur isotopes 34 spy and cas oxygen isotopes 18 ocas across the early mississippian k o 13 c excursion are documented from two sections of a west dipping carbonate ramp in the southern great basin western u s a a 4 6 positive 34 scas anomaly accompanied by negative shifts in 34 spy and 18 ocas is found within the k o 13 c excursion in the section with a broader 13 c excursion 34 s 34 s 34 scas 34 spy increases from 15 to 45 and 13 ccarb drops from 7 to 4 at the same stratigraphic interval if this 34 scas anomaly represents a global phenomenon the large magnitude 4 6 and short duration shorter than that of 13 c suggest an unusual pyrite burial event that expanded from sediments to the ocean water column in this scenario the areal and volumetric expansion of sulfate reduction and pyrite burial was likely triggered by abundantly available organic matter near the peak of the k o 13 c excursion during which organic carbon production and burial may have reached a maximum thus substantially expanding the oxygen minimum zone omz numerical simulations suggest that pyrite burial rates 2 5 5 times higher than that of the modern ocean followed by sulfide oxidation are required to produce the observed 34 scas anomaly in a sulfate rich so4 28 mm early mississippian ocean alternatively the sulfur and cas oxygen isotope anomalies may record local sulfur cycling in a foreland basin where changes in weathering input and bottom water redox conditions in response to sea level fall and cooling resulted in isotope changes in both scenarios either local or global the integrated carbon sulfur and cas oxygen isotope data suggest a much more dynamic sulfur cycle across the k o 13 c excursion than has been previously suggested

a 2 3 million year lacustrine record of orbital forcing from the devonian of northern scotland detailed sedimentological examination of onshore sections through cyclic lacustrine deposits of the middle devonian succession of northern scotland has been augmented with offshore data to allow the construction of a continuous 2 3 myr record of orbital forcing these data provide an important record of climatic variance through the devonian which by comparison with other records from this time can significantly improve our understanding of the devonian global climatic system precessional and eccentricity cycles are shown to be dominant by the direct measurement and extrapolation of depositional rates in well exposed sections as well as the analysis of ratios between primary and modulating cycles spectral analysis has confirmed the presence of regular cycles throughout the offshore data which provide a far longer record of orbitally forced cyclicity than previously available the presence of a half precession cycle is also suggested similar up section variations in cycle thicknesses are recorded from both the onshore and offshore succession these variations and those in cycle symmetry are related to a trend from an underfilled to a balanced fill basin state of further importance in controlling cycle thickness is the period of each cycle during which lacustrine conditions and therefore lake level controlled accommodation existed

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

testing carbonate associated sulfate cas extraction methods for sulfur isotope stratigraphy a case study of a lower middle ordovician carbonate succession shingle pass nevada usa abstract sulfur isotopes measured from sedimentary rocks are used to reconstruct the global sulfur cycle and chemostratigraphic correlation relative and absolute changes in the sulfur isotopic composition of the ocean 34sseawater are essential for estimating changes in redox conditions in ancient environments particularly for geochemical models that utilize isotope mass balance thus accurate estimates of 34sseawater must be measured using a laboratory protocol optimized for the extraction of primary sulfate preserved as carbonate associated sulfate cas by removing any contaminant secondary sulfate e g from diagenetic pyrite oxidation here we use two cas extraction protocols on lower middle ordovician carbonate rocks to test the degree to which similar absolute values and stratigraphic trends in 34scas are produced by different cas extraction methods one method processes carbonate powders once with a single rinse of a 10 nacl solution to remove sulfate minerals or weakly bonded sulfate ions followed by a rinse in 5 6 bleach to remove organically bound sulfur before dissolution in hydrochloric acid hcl the second method treats carbonate powders with three rinses of nacl without a bleach rinse to more aggressively remove secondary sulfate before dissolution in hcl isotopic results show that samples treated in three nacl rinses produce 34scas values that are on average 7 more positive than samples treated with a single nacl rinse but a similar stratigraphic trend is preserved in samples processed with either method we interpret the difference in 34scas between methods to reflect the incomplete removal of secondary sulfate derived from the oxidation of 32s enriched pyrite when employing only a single nacl rinse surprisingly rocks with low cas concentrations 10 mg kg using both methods show no significant difference in 34scas values as well as no significant difference in pyrite concentrations and pyrite 34s 34spy between methods samples with low cas concentrations are likely altered and secondary sulfate sourced from pyrite oxidation has likely become incorporated into recrystallized carbonate minerals or incorporated into pore filling calcite cement all of which is captured as cas results suggest that both cas extraction protocols can produce broadly similar 34scas trends but a single nacl rinse may not completely remove contaminant sulfate sorbed onto carbonate grains and thus will not yield meaningful data for reconstructing 34sseawater this has clear implications for modeling studies aimed at reconstructing paleo redox conditions using 34s data assumed to record global 34sseawater trends if these 34s data are generated using a non optimized cas protocol

redox dependent distribution of early macro organisms evidence from the terminal ediacaran khatyspyt formation in arctic siberia abstract the ediacaran period witnessed the first appearance of macroscopic animal life in earth s history however the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain in part due to the dearth of integrated paleobiological and chemostratigraphic datasets in this study a comprehensive geochemical analysis was conducted on the fossiliferous khatyspyt formation in arctic siberia in order to gain insights into the ediacaran paleoenvironments this study was designed to specifically address the relationship between paleoredox conditions and ediacaran fossil occurrences in the khatyspyt formation our data reveal a dramatic shift in pyrite sulfur isotope compositions 34 s pyrite from ca 20 to ca 55 and this shift is intriguingly associated with the first occurrence of ediacara type macrofossils at the studied section suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms based on multiple lines of sedimentological and geochemical evidence we propose that the development of oceanic euxinia which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal ediacaran period may have locally prohibited the colonization of ediacara type organisms and resulted in low 34 s pyrite values in the lower khatyspyt formation in the middle and upper khatyspyt formation progressive secular transition from euxinic to non euxinic and more habitable conditions may have allowed for the colonization of ediacara type and other macro organisms

variability in ice motion at a land terminating greenlandic outlet glacier the role of channelized and distributed drainage systems we use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land terminating greenlandic outlet glacier we find a close agreement between horizontal ice velocity vertical ice velocity and modelled subglacial water pressure over the course of a melt season on this basis we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction a process itself driven by fluctuations in basal water pressure originating in subglacial channels this process is not captured by traditional sliding laws linking water pressure and basal velocity which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

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

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

middle upper ordovician darriwilian sandbian paired carbon and sulfur isotope stratigraphy from the appalachian basin usa implications for dynamic redox conditions spanning the peak of the great ordovician biodiversification event abstract the evans ferry section from the appalachian basin of eastern north america has been analyzed for chemostratigraphic trends to elucidate possible causal mechanisms facilitating the great ordovician biodiversification event gobe paired stable isotope 13c and 34s analyses were used in this carbonate dominated locality from the appalachian basin to reconstruct the marine redox states during this key period of rapid biodiversification this succession is one of the most expanded sandbian stage upper ordovician deposits known from north america and it allows new high resolution reconstructions of long term global carbon and sulfur cycle fluctuations the integrated geochemical and sequence stratigraphic investigation presented here from the laurentian epeiric seaway allows for possible identification of the contraction and expansion of reducing water masses during the middle late ordovician that may have been linked to global marine paleoredox dynamics utilizing new conodont based 87sr 86sr isotope stratigraphy along with previous conodont biostratigraphy we can confidently correlate our stable isotope profiles to other carbonate successions globally carbonate facies indicate that this area experienced partial restriction from open marine conditions during certain intervals in the sandbian these semi restricted environments record carbon 13ccarb isotope trends that are secular in nature as they can be correlated to other successions across laurentia and baltica we identify several intervals when 13ccarb and 34scas carbonate associated sulfate trends are decoupled these inverse stratigraphic trends are at times followed by parallel positive shifts in 13ccarb and 34scas causal mechanisms for the observed decoupled 13c and 34s trends may include a wide variety of factors such as more closed system local biogeochemical processes associated in part with diagenesis or they could instead reflect variations in the global fluxes of organic matter and pyrite burial linked to changing marine paleoredox conditions the positive covariation in trends presented here likely represents transient increases in organic carbon and pyrite burial in response to expansion of reducing marine environments

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

stratification and mixing of a post glacial neoproterozoic ocean evidence from carbon and sulfur isotopes in a cap dolostone from northwest china abstract to improve our knowledge about the geochemical and environmental aftermath of neoproterozoic global glaciations we analyzed stable isotopes 13 c 18 o 34 s and elemental concentrations ca mg s sr fe and mn of the 10 m thick zhamoketi cap dolostone atop the tereeken diamictite in the quruqtagh area eastern chinese tianshan available chemostratigraphic data suggest that the tereeken diamictite is probably equivalent to the marinoan glaciation our new data indicate that organic and carbonate carbon isotopes of the zhamoketi cap dolostone show little stratigraphic variations averaging 28 2 and 4 6 respectively in contrast sulfur isotopes show significant stratigraphic variations carbonate associated sulfate cas abundance decreases rapidly in the basal cap dolostone and 34 s cas composition varies between 9 and 15 in the lower 2 5 m in the overlying interval cas abundance remains low while 34 s cas rises 5 and varies more widely between 10 and 21 the range of 34 s py of the cap dolostone overlaps with that of 34 s cas but direct comparison shows that 34 s py is typically greater than 34 s cas measured from the same samples hypotheses to explain the observations must account for both the remarkable sulfur isotope enrichment of pyrites and the inverse fractionation we propose that cas and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin or a basin with a sulfate minimum zone in this model cas was derived from shallow oxic surface waters with moderate sulfate concentration and depleted in 34 s due to the post glacial influx of sulfur from continental weathering in contrast pyrite was derived from anoxic bottom waters or a sulfate minimum zone with low sulfate concentration and 34 s enrichment due to long term syn glacial sulfate reduction the rapid shift in cas abundance and sulfur isotope composition within the cap dolostone is interpreted to reflect the mixing of the two reservoirs after initial deglaciation comparison with other post marinoan cap carbonates shows significant spatial heterogeneity in 34 s cas which together with strong temporal variation in 34 s cas points to generally low sulfate concentrations in post marinoan oceans

carbon sulfur and oxygen isotope evidence for a strong depth gradient and oceanic oxidation after the ediacaran hankalchough glaciation in order to understand spatial variations of stable isotope geochemistry in the quruqtagh basin northwestern china in the aftermath of an ediacaran glaciation we analyzed carbonate carbon isotopes 13ccarb carbonate oxygen isotopes 18ocarb carbonate associated sulfate sulfur 34scas and oxygen isotopes 18ocas and pyrite sulfur isotopes 34spy of a cap dolostone atop the ediacaran hankalchough glacial diamictite at four sections the four studied sections ykg mk h and zbs represent an onshore offshore transect in the quruqtagh basin our data show a strong paleobathymetry dependent isotopic gradient from the onshore to offshore sections 13ccarb values decrease from 2 to 16 vpdb whereas 18ocarb values increase from 4 to 1 vpdb both 34scas and 34spy show stratigraphic variations in the two onshore sections mk and ykg but are more stable in the two offshore sections h and zbs 18ocas values of onshore samples are consistent with terrestrial oxidative weathering of pyrite we propose that following the hankalchough glaciation seawater in the quruqtagh basin was characterized by a strong isotopic gradient the isotopic data may be interpreted using a three component mixing model that involves three reservoirs deep basin water surface water and terrestrial weathering input in this model the negative 13ccarb values in the offshore sections are related to the upwelling of deep basin water where anaerobic oxidation of dissolved organic carbon resulted in 13c depleted dic whereas sulfur isotope variations are strongly controlled by surface water sulfate and terrestrial weathering input derived from oxidative weathering of pyrite the new data provide evidence for the oceanic oxidation following the hankalchough glaciation

a global transition to ferruginous conditions in the early neoproterozoic oceans eukaryotic life expanded during the proterozoic eon1 2 5 to 0 542 billion years ago against a background of fluctuating ocean chemistry2 3 4 after about 1 8 billion years ago the global ocean is thought to have been characterized by oxygenated surface waters with anoxic and sulphidic waters in middle depths along productive continental margins and anoxic and iron containing ferruginous deeper waters5 6 7 the spatial extent of sulphidic waters probably varied through time5 6 but this surface to deep redox structure is suggested to have persisted until the first neoproterozoic glaciation about 717 million years ago8 9 10 11 here we report an analysis of ocean redox conditions throughout the proterozoic using new and existing iron speciation and sulphur isotope data from multiple cores and outcrops we find a global transition from sulphidic to ferruginous mid depth waters in the earliest neoproterozoic coincident with the amalgamation of the supercontinent rodinia at low latitudes we suggest that ferruginous conditions were initiated by an increase in the oceanic influx of highly reactive iron relative to sulphate driven by a change in weathering regime and the uptake of sulphate by extensive continental evaporites on rodinia we propose that this transition essentially detoxified ocean margin settings allowing for expanded opportunities for eukaryote diversification following a prolonged evolutionary stasis before one billion years ago

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

marine redox conditions in the middle proterozoic ocean and isotopic constraints on authigenic carbonate formation insights from the chuanlinggou formation yanshan basin north china abstract to improve our understanding of ocean chemistry and biogeochemical cycling following the termination of large scale paleoproterozoic iron formation if deposition 1 85 billion years ago ga we conducted a fe s c mo geochemical study of the 1 65 ga chuanlinggou formation yanshan basin north china despite the cessation of if deposition our results suggest the presence of anoxic but non euxinic ferruginous conditions persisted below the surface mixed layer for the deepest portion of the continental rifting basin and that this pattern is apparently independent of the local organic carbon content however our paired s isotope data of carbonate associated sulfate and pyrite suggest presence of sulfate in pore fluids which is not consistent with insufficient sulfate for bacterial sulfate reduction in the water column despite evidence for deposition under anoxic conditions sedimentary molybdenum mo concentrations are mostly not enriched relative to average continental crust this relationship is consistent with the notion that sulfide dominated conditions in the water column and or the sediments are required for mo enrichment and validates past assertions that mo enrichment patterns in ancient shales track both the local presence and global distribution of euxinia specifically in addition we identified extensive diagenetic carbonate precipitation in the upper chuanlinggou formation with only moderately negative 13 c values 3 4 1 4 we propose with support from a numerical model that these diagenetic carbon isotope values were most likely derived from precipitation of carbonates dominantly in the methanic zone within the sediments diagenetic carbonate precipitation in the methanic zone is likely to have been more extensive in the proterozoic than the phanerozoic due to porewater oxidant limitation

astronomical forcing of meandering river behaviour milankovitch cycles in devonian of east greenland abstract a more than 1100 m thick succession dominated by single and multistorey sandstone bodies from the upper devonian kap graah group in east greenland is interpreted as a meandering river and associated overbank deposits the sandstone bodies display well developed lateral accretion bedding and are interpreted to be deposited as point bars in a well exposed section 215 m thick individual sandstone bodies have been analized quantitatively in order to compare the individual palaeochannel characteristics the results indicate cyclic variations in discharge channel slope and channel size the cycles are of the order of c 20 m thick with superimposed c 100 m mega cycles both are interpreted as reflecting cyclic variations in precipitation rate the cycles are interpreted as being governed by astronomical forcing of the climate reflecting milankovitch type precession cycles in the order of 20 000 years with modulation by c 110 000 years eccentricity mega cycles this study confirms that the precession and eccentricity cycles exhibit the main forcing on low latitude monsoonal climate

caliche as a geological repository for atmospheric sulfate 1 recent studies demonstrate that important information on sulfur source oxidation pathway transport pattern and reaction kinetics of atmospheric oxidation of sulfur gases can be uncovered by measuring multiple isotope compositions of the oxidation product secondary atmospheric sulfate sas sas from earth s distant past however is rarely preserved in the rock records because of its high solubility and small quantity we report here from the measurement of 47 modern and fossil caliche samples that caliches contain variable amounts of carbonate associated sulfate cas and the 17o values of the cas range from 0 12 to 2 32 with most values higher than the background value of 0 05 for seawater sulfate indicating the presence of an sas component derived from the oxidation of sulfur gases by atmospheric ozone or related oxidants this study demonstrates that caliche a pedogenic carbonate common in the geologic record could serve as a repository for ancient sas

spatial and temporal evolution of ediacaran carbon and sulfur cycles in the lower yangtze block south china abstract major radiations of microscopic and macroscopic eukaryotes occurred respectively in the early and middle ediacaran period various hypotheses have been proposed to attribute these evolutionary events to changes in ocean redox conditions to date published models of the ediacaran ocean in south china have largely been focused on the upper and middle yangtze blocks as opposed to the slope and basin sections of the lower yangtze block where the oldest complex macrofossils of the ediacaran i e the 600 ma lantian biota are preserved to achieve a holistic understanding of the record of ocean chemistry in the entire yangtze block we carried out carbon 13ccarb and 13corg and sulfur 34scas and 34spyr isotopic investigations of four new sections i e wujialing meishuxia wangfu and zhushuwu in the lower yangtze block in addition to one previously reported drill core at lantian the doushantuo and lantian formations at these sections represent shelf margin upper slope lower slope and deep basin environments in conjunction with previous work on sections of the upper and middle yangtze blocks our study reconstructs the redox structure of the entire ediacaran ocean in south china the new results show profound 13ccarb negative excursions in the slope and deep basinal sections which can be correlated to the en3 and shuram excursions at a global scale notably the 13ccarb and 34spyr profiles from shelf to basinal sections show distinct spatial and temporal patterns which can be explained by model of a redox stratified ocean during the early and middle ediacaran period the finding of isotopically light 34s depleted pyrite from this time suggests that the oceanic chemocline extended to intermediate depth integrating this study with existing ecological and taphonomic data it is likely that marine redox stratification in the early ediacaran limited the spatial distribution of early metazoans in the lower yangtze block

hydrothermal metal supplies enhance the benthic methane filter in oceans an example from the okinawa trough abstract anaerobic oxidation of methane aom is an important process that regulates methane budget in the global carbon cycle sulfate is traditionally regarded as the most important electron acceptor for aom however recent studies reveal that reactive metal reduction driven aom metal aom may also present on natural environments partitioning the methane c sink from anaerobic oxidation between sulfate reduction driven aom sulfate aom and metal aom is thus becoming a scientific challenge to be addressed this study aimed to show that metal aom has a potential to complement sulfate aom especially when methane seeps met sediments enriched in iron and manganese oxides supplied by hydrothermal plumes samples of authigenic carbonate were collected from the cold seeps on the western slope of the okinawa trough ot a semi enclosed back arc basin with cold seeps and hydrothermal activities coexist spatially petrologic and mineralogical observations provided faithful evidence of a close genetic relationship between goethite and authigenic carbonates likely indicating the presence of metal aom although some contributions of organoclastic fe reduction cannot be ruled out the most possible place of metal aom was between the lower part of the sulfate methane transition zone smtz and the immediate upper part of the methanogenic zone the characteristics of 13ccarb 53 7 to 3 3 vienna peedee belemnite vpdb also point to our carbonate samples as the products of aom these authigenic carbonates was further identified as three possible types of carbonate of different sources sulfate aom metal aom and hydrothermal carbonates depending on the correlations among concentrations of carbonate associated sulfate cas 13ccarb and 18ocarb based on these findings we tentatively suggested that the reduction of reactive metals carried by hydrothermal plumes might drive the methane oxidation in the adjacent cold seep areas resulting in the precipitation of unique carbonates and enhancement the efficiency of the benthic methane filter this study reported the coupling or interaction between the two extreme submarine environments by metal aom for the first time which might help in understanding and improving the global carbon and metal cycles now and in the past

lower maastrichtian cyclostratigraphy of the bidart section basque country sw france a remarkable record of precessional forcing abstract cyclostratigraphic analysis of the maastrichtian limestone marl alternations of bidart sw france allows the hypothesis of orbital control on lithological cycles to be evaluated magnetic susceptibility ms oxygen and carbon isotope measurements sampled at a high resolution are analyzed using various cyclostratigraphic tools a statistically significant orbital signal is detected with a remarkable record of the precession corresponding to the limestone marl couplets this well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the ms and 13 c records based on the 100 kyr eccentricity cycle the total duration of the section is estimated at 1 44 0 22 myr correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled bidart 13 c record to the astronomically calibrated 13 c signal of odp hole 762c shows that the studied section extends from 71 5 to 70 ma covering the upper part of chron c32n 1n and 2 3 of chron c31r oxygen isotope data suggest a 2 c cooling of sea surface temperatures during the studied interval when placed on the long term 18 o trend of the bidart section this interval is here recognized as the onset of the early maastrichtian cooling event with its excellent record of the precessional forcing the bidart section along with other sections of the basque country is a useful tool for the refinement of the maastrichtian timescale

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

stretching the envelope of past surface environments neoproterozoic glacial lakes from svalbard the oxygen isotope composition of terrestrial sulfate is affected measurably by many earth surface processes during the neoproterozoic severe snowball glaciations would have had an extreme impact on the biosphere and the atmosphere here we report that sulfate extracted from carbonate lenses within a neoproterozoic glacial diamictite suite from svalbard with an age of similar to 635 million years ago falls well outside the currently known natural range of triple oxygen isotope compositions and indicates that the atmosphere had either an exceptionally high atmospheric carbon dioxide concentration or an utterly unfamiliar oxygen cycle during deposition of the diamictites

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

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