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

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

geochemical evidence for widespread euxinia in the later cambrian ocean it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking gill et al present sulphur isotope data from cambrian rocks at six different locations around the world and find a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time a prolonged period of anoxia during the cambrian may explain the previously enigmatic peculiarities seen in the fossil record it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking now sulphur isotope data from cambrian rocks at six different locations around the world is presented with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time with the help of a box model these isotope shifts support the idea of large scale anoxic and sulphidic conditions in the later cambrian ocean widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long term inhibitor of evolutionary radiation on early earth in recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later cambrian oceans1 2 possibly influencing evolutionary events during this time1 2 3 physical evidence of widespread anoxia in cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored here we present sulphur isotope records from six globally distributed stratigraphic sections of later cambrian marine rocks about 499 million years old we find a positive sulphur isotope excursion in phase with the steptoean positive carbon isotope excursion spice a large and rapid excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation4 5 numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large scale anoxic and sulphidic euxinic conditions independently molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia these results identify the spice interval as the best characterized ocean anoxic event in the pre mesozoic ocean and an extreme example of oxygen deficiency in the later cambrian ocean thus a redox structure similar to those in proterozoic oceans6 7 8 may have persisted or returned in the oceans of the early phanerozoic eon indeed the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in cambrian oceans

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

a negative carbon isotope excursion defines the boundary from cambrian series 2 to cambrian series 3 on the yangtze platform south china a globally recorded negative carbon isotope excursion characterizes the transition from cambrian series 2 to cambrian series 3 this transition is also well exposed in sedimentary successions on the yangtze platform and the wuliu zengjiayan section guizhou province south china has been proposed as a potential global stratotype section and point gssp for this boundary here we report delta 13 c carb values for the jianshan and the wuliu zengjiayan sections both sections display a progressive decrease in delta 13 c from values around 3 parts per thousand upwards in stratigraphy to a pronounced delta 13 c minimum with values as low as 6 9 parts per thousand at the proposed boundary level and a return to delta 13 c values between 0 and 1 parts per thousand in the upper part of the sections the delta 13 c minimum is thought to be caused by a transgressive event flooding the shelf area with 13 c depleted basinal anoxic bottom water our delta 13 c data are in good agreement with carbon isotope profiles recorded elsewhere these define the so called roece event redlichiid oleneliid extinction carbon isotope excursion cf zhu et al 2006 2007 and may reflect the perturbation of the global carbon cycle during the cambrian series 2 to cambrian series 3 transition c 2009 elsevier b v all rights reserved

spatial distribution of average vorticity in the high latitude ionosphere and its variation with interplanetary magnetic field direction and season 1 we present a technique to measure the magnetic field aligned vorticity of mesoscale plasma flows in the f region ionosphere using line of sight velocity measurements made by the super dual auroral radar network superdarn vorticity is often used as a proxy for magnetic field aligned current fac intensity in the ionosphere but also provides information about turbulent processes in the ionosphere and magnetosphere using 6 years 2000 2005 inclusive of vorticity measurements made by six superdarn radars in the northern hemisphere we have compiled for the first time maps of average vorticity across the northern polar ionosphere these maps have been subdivided according to different seasonal and interplanetary magnetic field imf conditions the variations in the morphology of the vorticity maps with imf direction match very closely those seen in maps of average fac intensity determined using different methods and instrumentation suggesting that vorticity is a good proxy for fac in an averaged sense the variations in the morphology of the vorticity maps with season show differences from those seen in the fac maps illustrating that ionospheric conductance plays a major role in determining the differences between measurements of vorticity and fac

seasonal and diurnal variations in ampere observations of the birkeland currents compared to modeled results we reduce measurements made by the active magnetosphere and planetary electrodynamics response experiment ampere to give the total birkeland field aligned current flowing in both hemispheres in monthly and hourly bins we analyze these totals using 6 years of data 2010 2015 to examine solar zenith angle driven variations in the total birkeland current flowing in both hemispheres simultaneously for the first time a diurnal variation is identified in the total birkeland current flowing consistent with variations in the solar zenith angle a seasonal variation is also identified with more current flowing in the northern southern hemisphere during bartels rotations in northern southern summer for months close to equinox more current is found to flow in the northern hemisphere contrary to our expectations we also conduct the first test of the milan 2013 model for estimating birkeland current magnitudes with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the birkeland currents with season and time of day the modified model using the value of d averaged by bartels rotation scaled by 1 7 is found to agree with the observed ampere currents with a correlation of 0 87 in the northern hemisphere and 0 86 in the southern hemisphere the improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model the correlation of the residuals is found to be consistent with more current flowing in the northern hemisphere this new observation of systematically larger current flowing in the northern hemisphere is discussed in the context of previous results which suggest that the northern hemisphere may react more strongly to dayside reconnection than the southern hemisphere

reconstructing earth s surface oxidation across the archean proterozoic transition the archean proterozoic transition is characterized by the widespread deposition of organic rich shale sedimentary iron formation glacial diamictite and marine carbonates recording profound carbon isotope anomalies but notably lacks bedded evaporites all deposits refl ect environmental changes in oceanic and atmospheric redox states in part associated with earth s earliest ice ages time series data for multiple sulfur isotopes from carbonateassociated sulfate as well as sulfi des in sediments of the transvaal supergroup south africa capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric massindependent sulfur isotope fractionation in phase with sulfur is the earliest recorded positive carbon isotope anomaly convincingly linking these environmental perturbations to the great oxidation event ca 2 3 ga

ediacaran growth of the marine sulfate reservoir abstract the sulfur isotope record as preserved in sedimentary sulfate and sulfide minerals reflects the progressive oxidation of earth s surface environment the latest proterozoic to early paleozoic marine sulfur isotope record is distinguished by unusually high 34 s values in marine sulfates and sulfides geological considerations and sulfur isotopic data indicate that the 34 s enrichment of the marine sulfate reservoir was the result of a rapid increase in the net fractionation between sedimentary sulfate and pyrite 34 s without a compensatory decline in the fractional burial rate of pyrite f pyr a simple one box model in which 34 s is linked non linearly to marine so 4 is used to explore the response in sedimentary sulfur isotope records 34 s sulf and 34 s pyr to an increasing marine sulfate reservoir the model results when compared with a compilation of existing 34 s sulf and 34 s pyr data suggest that the marine sulfate reservoir grew rapidly to roughly phanerozoic levels in the middle ediacaran period before the gaskiers glaciation and prior to the onset of the shuram wonoka negative 13 c anomaly it is further hypothesized that p o 2 levels rose prior to the onset of this extreme perturbation to the global carbon cycle permitting the oxidation of a previously euxinic deep ocean and appearance of the first ediacaran fauna by ca 575 ma despite the enormous demand on oxidants implied by this large magnitude and long duration carbon isotope anomaly

a stable isotope study of pyrite formation in the late pleistocene and holocene sediments of the black sea the abundance and isotopic composition of total and pyrite sulphur have been determined in a core in the central black sea pyrite varies in concentration from roughly 2 wt in the sapropel unit 2 to 0 8 wt in the modern horizon unit 1 and ca 0 1 wt in the lowermost horizons of unit 3 lake beds an intermediate mud flow horizon and the upper part of the lake beds have similar values to those in the modern sediments the degree of pyritization dop is lowest 0 05 in the lower lake beds and highest 0 55 in unit 1 the sapropel has values of ca 0 48 34spyrite varies from a minimum of 37 in the sapropel to 33 in unit 1 up to 15 in the upper lake beds and 0 in the lower lake beds the unit 1 and sapropel values are similar to the 34s values reported by fry et al 1991 of dissolved sulphide immediately below the water column oxic anoxic interface 36 to 38 but significantly heavier than those in the deep waters of the basin ca 41 these results are interpreted as a reflection of the presence of four different types of pyrite in the sediments of the black sea 1 pyrite in units 1 and 2 that is formed within the upper part of the water column immediately below the oxic anoxic interface where 34s of dissolved sulphide is 36 2 pyrite in the mud flow layer lying between unit 1 and the sapropel unit 2 with a significantly heavier isotopic composition that was formed around the margins of the basin under conditions that were probably more closed with respect to dissolved sulphate than those in which the pyrite in units 1 and 2 were formed 3 pyrite in the upper part of the lake beds unit 3 that was formed under closed system conditions by reaction between excess reducible fe remaining in these freshwater sediments and downward diffusing sulphate and or sulphide from the overlying organic rich sapropel and 4 pyrite in the lower part of the unit 3 representing a phase formed from the ambient sulphate in the freshwaters of the late pleistocene lake the isotopic information supports earlier suggestions that pyrite in the modern sediments of the black sea forms mainly in the water column with only minor amounts forming in the sediment because of the severe fe limitation of the bottom sediments that accumulate 2 000 m below the main fe and hs reaction zone at the oxic anoxic interface at shallow depths in the water column

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

reconstructing marine redox conditions for the transition between cambrian series 2 and cambrian series 3 kaili area yangtze platform evidence from biogenic sulfur and degree of pyritization the transition between series 2 and series 3 of the cambrian period was a time of environmental perturbations and biological innovations a generally positive sulfur isotopic composition of sedimentary pyrite with delta s 34 pyrite values between 1 7 and 373 is consistent with a biological origin via reduction of strongly s 34 enriched seawater sulfate no substantial changes in the redox conditions of the water column are discernible from the dop record and the sulfide sulfur isotopic composition is independent of dop in particular an excursion towards less is enriched values immediately preceding the proposed level of the cambrian series 2 to cambrian series 3 transition this level is also characterized by a negative carbonate carbon isotope excursion believed to reflect the transgressive flooding of the shelf with basinal anoxic waters low dop values would suggest that these might have been ferruginous rather than sulfidic c 2013 elsevier b v all rights reserved

sulfur cycling in the aftermath of a 635 ma snowball glaciation evidence for a syn glacial sulfidic deep ocean we have analyzed 34 s sulfate and pyrite 18 ocarbonate and 13 ccarbonate and major and trace elemental concentrations including extractable fe and mn phases in four sections of the maieberg formation the cap carbonate sequence to the marinoan glaciation in northern namibia 34 ssulfate profiles and other geochemical characteristics in the basal transgressive cap dolostone keilberg member are nearly identical in all sections and indicate deposition from a water mass with very low sulfate concentrations in the overlying interval that consists of rhythmites deposited during the transgressive high stand large geochemical disparities occur between sections that we interpret to have been deposited in open ocean versus restricted settings in the former a large negative shift in 34 ssulfate of 20 above the cap dolostone accompanies a change in mineralogy from dolomite to limestone a sharp decrease in 18 o and 13 c and a positive spike in fe and mn concentrations in the latter dolomite persists above the cap dolostone 34 ssulfate increases abruptly 18 o and 13 c are invariant and a spike in mn and fe concentrations is present but subtle these contrasting geochemical signatures in coeval sections can be explained by strong lateral chemical gradients that developed as cold euxinic deep water and a cap of warm oxic brackish water flooded the continental shelf during the post glacial transgression the geochemical di e rences between open ocean and restricted sections diminishes upsection presumably recording the gradual mixing and homogenization of the waters along the otavi platform

paired δ34s data from carbonate associated sulfate and chromium reducible sulfur across the traditional lower middle cambrian boundary of w gondwana abstract in this study we present the first high resolution data from coupled 34 s analyses of carbonate associated sulfate cas and chromium reducible sulfur crs from three lower middle cambrian sections in western gondwana cas and crs were extracted and analyzed from marine dolostone limestone and nodular limestone from spanish and french successions in parallel carbonate samples were also analyzed for 13 c carb 18 o carb and major trace element concentrations ca fe mg mn sr 34 s cas values vary between 17 6 and 33 2 with a maximum cas concentration of ca 900 ppm 34 s crs data show a similar broad range between 5 1 and 29 7 with maximal crs contents up to ca 3700 ppm notably there is little stratigraphic variation in the 34 s cas data in each of the sections confounding inter basinal chemostratigraphic correlations nonetheless the absolute differences in 34 s cas between sections as well as variations in cas and crs concentrations are attributed to paleoenvironmental differences between proximal and distal parts of the carbonate ramp as well as effects of subaerial exposure and riverine input thus the generated 34 s cas data deliver not only valuable paleoecological and paleoenvironmental information they also illustrate a heterogeneity in the seawater sulfate sulfur isotopic composition of the western gondwanan ocean consequently the lack of correlation between our gondwanan 34 s cas data and time equivalent sections of laurentia and siberia is probably not only caused by the absence of an internationally accepted biostratigraphic correlation but rather supports the view that sulfate was non conservative anion in seawater during the cambrian period

seasonal dependence of large scale birkeland currents the seasonal dependence of large scale birkeland currents has been determined from the analysis of vector magnetic field data acquired by the triad satellite in the northern hemisphere statistical characteristics of single sheet i e net currents and double sheet birkeland currents were determined from 555 triad passes during the summer and 408 passes during the winter more complicated multiple sheet current systems were not included in this study the average kp value for the summer events is 1 9 and for the winter events is 2 0 the principal results include the following 1 the single sheet birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season the single sheet currents are also observed more often in the summer than in the winter as much as 2 to 3 times as often depending upon the mlt sector 2 the intensities of the single and double sheet birkeland currents on the dayside from approximately 1000 mlt to 1800 mlt are larger during the summer in comparison to winter by a factor of about 2 3 the intensities of the double sheet birkeland currents in the nightside the dominant system in this local time do not show a significant difference from summer to winter 4 the single and double sheet currents in the dayside between 0600 and 1800 mlt appear at higher latitudes by about 1 to 3 during the summer in comparison to the winter these characteristics suggest that the birkeland current intensities are controlled by the ionospheric conductivity in the polar region the greater occurrence of single sheet birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it since the intensities of birkeland currents are larger during periods of greater ionospheric conductivity an important source but perhaps not the only source of these currents must be a voltage generator in the magnetosphere possibly related to the convective electric field

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

mechanism for burgess shale type preservation exceptionally preserved fossil biotas of the burgess shale and a handful of other similar cambrian deposits provide rare but critical insights into the early diversification of animals the extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft bodied fossil assemblages has remained enigmatic since walcott s initial discovery in 1909 here we demonstrate the mechanism of burgess shale type preservation using sedimentologic and geochemical data from the chengjiang burgess shale and five other principal burgess shale type deposits sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation low sulfate concentrations in the global ocean and low oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability subsequently rapid entombment of fossils in fine grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments a permeability barrier provided by bed capping cements that were emplaced at the seafloor is a feature that is shared among burgess shale type deposits and resulted from the unusually high alkalinity of cambrian oceans thus burgess shale type preservation of soft bodied fossil assemblages worldwide was promoted by unique aspects of early paleozoic seawater chemistry that strongly impacted sediment diagenesis providing a fundamentally unique record of the immediate aftermath of the cambrian explosion

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

mass occurrence of oncoids at the cambrian series 2 series 3 transition implications for microbial resurgence following an early cambrian extinction abstract the traditional lower middle cambrian transition cambrian series 2 series 3 transition is marked by the first major biotic extinction of the phanerozoic eon this biotic crisis has been arguably linked to changes in ocean chemistry and or marine environments but their casual relationships remain controversial to better understand the microbial responses to paleoceanographic changes across this critical transition we have studied the environmental conditions for mass occurrence of oncoids in the western north china platform oncoids at the lower middle cambrian transition form 1 to 3 m thick massive beds show spherical subspherical morphology and contain 8 14 light dark cortical laminar couplets the light laminae are thicker and contain densely intertwined filamentous cyanobacteria that have calcified sheaths and a prostrate growth pattern the dark laminae are thinner and rich in organic matter relics pyrite framboids and heterotrophic bacteria in most oncoids cortical laminae show the same growth orientation for more than five light dark laminar couplets suggesting much less frequent grain overturning than generally thought both light and dark laminae contain well preserved organomineralization fabrics textures including extracellular polymeric substances epss nanoglobules polyhedrons and micropeloids suggesting oncoid formation in shallow marine environments with high alkalinity and active sulfate reduction the presence of pyrite framboids and heterotrophic bacterial relics implies anoxic dysoxic bottom water conditions stratigraphic correlation indicates that time equivalent oncolites and other microbialites are widespread not only in north china but also in other early cambrian successions globally the mass occurrence of oncoids coincides with the kalkarindji large igneous province of australia a prominent negative 13 c excursion roece or redlichiid olenellid extinction carbon isotope excursion a significant increase in 87 sr 86 sr and a large positive shift in 34 s the coincidence of these events suggests that the early cambrian biotic crisis may have been caused by an ocean anoxic event resulting from enhanced volcanic release of co 2 global warming and increased continental weathering preservation of massive oncolites is likely related to decreased metazoan grazing following an early cambrian biotic crisis during which archaeocyathids and many early cambrian trilobite taxa went to extinction the oncoid mass occurrence provides evidence for the resurgence of microbial life in anoxic dysoxic marine shelf environments concomitant with the early cambrian extinction event

carbonate carbon isotope evolution of seawater across the ediacaran cambrian transition evidence from the keping area tarim basin nw china sedimentary rocks from the ediacaran cambrian boundary record important biological climatic and geotectonic changes during this time to date only few geochemical investigations on the upper ediacaran upper cambrian rocks in the tarim basin have been carried out here we report high resolution 13 c carb records from the penglaiba the wushi phosphorite and the dongergou sections from ediacaran cambrian series 3 in the keping area of the tarim basin the sections display several obvious 13 c carb shifts 13 c carb values increased from 3 to 6 7 across the qigebulage formation moreover a negative 13 c carb shift across the ediacaran cambrian boundary is apparent 13 c carb values decreased to a minimum of 9 8 in the wushi phosphorite section 7 7 in dongergou section and 5 4 in penglaiba section followed by a positive carbonate carbon isotopic excursion across the yuertusi formation into the middle of the overlying xiaoerbulak formation furthermore more or less invariable positive 13 c carb values characterize the middle and upper xiaoerbulak formation the most negative 13 c carb value 14 3 occurred near the base of the shayilik formation which is the absolute minimum value among the studied sections of the cambrian series 2 to cambrian series 3 transition in the world the 13 c data from keping tarim basin are in good agreement with carbon isotope profiles recorded in south china and these events may reflect the perturbation of the carbon cycle in the tarim basin during the ediacaran cambrian and the cambrian series 2 cambrian series 3 transitions

deep water dissolved iron cycling and reservoir size across the ediacaran cambrian transition abstract the majority of the deep ocean was likely under ferruginous conditions during the first four billion years of earth s history as the atmosphere was gradually oxygenated the sources sinks redox cycling and reservoir size of dissolved iron in the deep ocean are likely to have changed dramatically whether deep water was thoroughly oxygenated by the time of the ediacaran cambrian transition and the relationship of this oxygenation to the cambrian explosion remains debated to explore the degree of oceanic oxygenation and its effect on cambrian explosion we measured the iron isotopic composition 56fe of bulk rock i e cherts and mudstones shales through the piyuancun and hetang formations using samples collected from the chunye 1 core on the lower yangtze block in western zhejiang the limited variation in 56fe values 0 55 during the end ediacaran and cambrian stages 1 3 to

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

a major sulphur isotope event at c 510 ma a possible anoxia extinction volcanism connection during the early middle cambrian transition a new approach to constraining seawater 34s and sulphate concentration using francolite bound sulphate reveals an abrupt increase in 34s to 50 around the early middle cambrian boundary such high 34s values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500 700 gl 1 we argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the kalkarindji large igneous province of northern australia and that it triggered the collapse of early metazoan reef ecosystems during the latest early cambrian mass extinctions of the last 260 myr have all coincided with enhanced volcanic activity while several are also associated with positive shifts in seawater 34s extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution

a global carbon isotope excursion spice during the late cambrian relation to trilobite extinctions organic matter burial and sea level abstract the steptoean positive carbon isotope excursion spice marks a global oceanographic event that confirms intercontinental correlations between different biogeographic realms based on agnostids and other blue water trilobites the spice excursion is documented from sections in laurentia kazakhstan china and australia where it begins with the mass extinction at the base of the pterocephaliid biomere steptoean stage in laurentia and at coeval extinction horizons in gondwana and perigondwana terranes the peak of spice 5 coincided with a time of maximum regression in laurentia spice is similar in this regard to excursions that coincide with glacio eustatic falls such as in the late ordovician a plausible scenario involves the transformation of ocean circulation between two states which led to enhanced coastal upwelling and benthic extinctions the lack of evidence for glaciation indicates that the coeval sea level fall sauk ii sauk iii event resulted from tectonic or hydrologic changes that remain poorly understood at this time

combined u pb hafnium and oxygen isotope analysis of zircons from meta igneous rocks in the southern north china craton reveal multiple events in the late mesoarchean early neoarchean abstract we report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from lushan in the far south of the trans north china orogen of the north china craton that reveal the oldest rocks yet dated from the orogen a detailed investigation of the internal structures of zircons combined with targeted sims u pb and oxygen isotope analyses and icp ms hf zircon analyses has resulted in the discovery of previously unknown geological events in the north china craton magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829 18 ma to 2832 11 ma in the tonalites and from 2838 35 ma to 2845 23 ma in amphibolite hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination oxygen isotope ratios in zircons range from 5 1 to 7 3 vsmow with high 18 o results recorded only from metamorphic domains the earliest stage of metamorphic zircon growth present in all four samples analyzed in this study occurred between 2772 17 22 in the tonalites and 2776 20 and 2792 12 ma in the amphibolites a younger metamorphic event at 2638 61 in the tonalite and between 2671 13 and 2651 13 ma in the amphibolites is recognized in zircons from three of the four samples investigated this is the first time that metamorphic events at either of these times have been recorded in the north china craton importantly there is no evidence for the 1 8 ga high grade metamorphic event that is manifest in the northern and central parts of the trans north china orogen