the role of the calcium carbonate calcium phosphate switch in the mineralization of soft bodied fossils authigenic minerals play an important role in the preservation of most soft bodied fossils the greatest detail is preserved in apatite calcium phosphate but its precipitation is usually inhibited by the high concentrations of hco 3 in aqueous settings nonetheless investigations of soft bodied biotas have revealed very early authigenic calcite crystal bundles in close association with phosphatized soft tissues this demonstrates that the geochemical controls on soft tissue mineralization are dynamic and act on a very local scale direct comparisons with experimental results permit the conditions of fossilization to be inferred

trace fossils and substrates of the terminal proterozoic cambrian transition implications for the record of early bilaterians and sediment mixing the trace fossil record is important in determining the timing of the appearance of bilaterian animals a conservative estimate puts this time at 555 million years ago the preservational potential of traces made close to the sediment water interface is crucial to detecting early benthic activity our studies on earliest cambrian sediments suggest that shallow tiers were preserved to a greater extent than typical for most of the phanerozoic which can be attributed both directly and indirectly to the low levels of sediment mixing the low levels of sediment mixing meant that thin event beds were preserved the shallow depth of sediment mixing also meant that muddy sediments were firm close to the sediment water interface increasing the likelihood of recording shallow tier trace fossils in muddy sediments overall trace fossils can provide a sound record of the onset of bilaterian benthic activity

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

secular change in the precambrian silica cycle insights from chert petrology chert deposits preserve a record of secular change in the oceanic silica cycle the evolutionary radiation of silica secreting organisms resulted in a transition from abiological silica deposition characteristic of the archean and proterozoic eons to the predominantly biologically controlled silica deposition of the phanerozoic comparative petrography of phanerozoic and precambrian cherts indicates that an earlier change in chert deposition occurred toward the end of the paleoproterozoic era ca 1 8 ga in neoproterozoic and mesoproterozoic strata early diagenetic chertification is largely restricted to peritidal environments these early diagenetic cherts typically occur as nodules or discontinuous beds within carbonate deposits that have similar depositional textures the cherts formed primarily by carbonate replacement with subsidiary direct silica precipitation some of the paleoproterozoic cherts associated with iron formations however are distinctly different from younger cherts and appear to have formed largely by direct silica precipitation at or just below the seabed these primary cherts lack ghosts or inclusions of carbonate precursors have fine scale grain fracturing possibly from syneresis exhibit low grain packing densities and are not associated with unsilicified carbonate deposits of similar depositional composition cherts in some paleoproterozoic iron formations e g the gunflint formation northwestern lake superior region are composed of silica types similar to those in phanerozoic sinters e g the devonian rhynie and windyfield cherts scotland such cherts may provide evidence that basinal and perhaps global oceanic silica concentrations were higher during the paleoproterozoic era than at later times

mineralogical constraints on the paleoenvironments of the ediacaran doushantuo formation assemblages of clay minerals are routinely used as proxies for paleoclimatic change and paleoenvironmental conditions in phanerozoic rocks however this tool is rarely applied in older sedimentary units in this paper the clay mineralogy of the doushantuo formation in south china is documented providing constraints on depositional conditions of the ediacaran yangtze platform that host the earliest animal fossils in the geological record in multiple sections from the yangtze gorges area trioctahedral smectite saponite and its diagenetic products mixed layer chlorite smectite corrensite and chlorite are the dominant clays through the lower 80 m of the formation and constitute up to 30 wt of the bulk rock saponite is interpreted as an in situ early diagenetic phase that formed in alkaline conditions ph 9 the absence of saponite in stratigraphically equivalent basin sections 200 400 km to the south indicates that alkaline conditions were localized in a nonmarine basin near the yangtze gorges region this interpretation is consistent with crustal abundances of redox sensitive trace elements in saponitic mudstones deposited under anoxic conditions as well as a 10 difference in the carbon isotope record between yangtze gorges and basin sections our findings suggest that nonmarine environments may have been hospitable for the fauna preserved in the yangtze gorges which includes the oldest examples of animal embryo fossils and acanthomorphic acritarchs

the phosphorus cycle in coastal marine sediments the concentration of dissolved phosphate in sediment box cores from the laurentian trough in the gulf of st lawrence increased sharply across the sediment water interface from 2 0 mol po4 1 in the bottom water to 6 3 mot po4 1 in the top cm remained almost constant at this value down to 5 15 cm depth and then increased rapidly with further depth in the region of constant concentration phosphate is buffered by sorption equilibria with the sediment the production rate of phosphate the sorption capacity of the sediment and the thickness of the diffusive boundary layer at the sediment water interface appear to control the shape of the pore water profile even though the buffering places an upper limit on the concentration gradient across the sediment water interface and hence on the flux the phosphate flux to the overlying water is controlled by the production rate of phosphate within the sediment a model is proposed to relate sediment chemistry to phosphorus fluxes

diagenetic evolution of the upper devonian phosphorites alborz mountain range northern iran abstract the upper devonian mixed siliciclastic carbonate stratigraphic succession of the geirud formation in the alborz mountain range north of iran hosts numerous phosphorites and phosphatic rocks these phosphorites which represent one of the most globally important deposits in the devonian have gained little attention regarding their genesis and diagenetic evolution this study focuses mainly on the post depositional changes that occurred during shallow to deep burial diagenetic evolution and subaerial weathering of the geirud phosphorites the phosphorites consist of phosphatic massive mudclasts detritus rich lithoclasts bioclasts and bones formed by several stages of phosphogenesis and erosion reworking winnowing and condensation associated with famennian sea level changes the phosphatic clasts consist of early diagenetic poorly crystalline carbonate fluorapatite cfa and pyrite cementing detrital quartz illite muscovite rutile and zircon phosphatic clasts are intensely compacted with sutured grain contacts along which dissolution and reprecipitation of chemically refined well crystalline cfa with a bright blue cathodoluminescence and illite occurred during deep burial diagenesis similarly quartz shows deformation planar features overgrowth cement was developed as a result of pressure dissolution in phosphatic sandstones followed by precipitation of ferroan dolomite ankerite and chlorite in secondary porosity subaerial weathering led to oxidation of pyrite and generation of acidic ph condition under which ca and p from phosphates fe and s from pyrite fe ca mg and mn from ferroan carbonates and al and si from aluminosilicates were released to form goethite psilomelane calcite gypsum and crandallite the paas normalized rare earth elements rees show bell shaped patterns with middle rees enrichment positive eu anomaly and a weak negative ce anomaly this implies recrystallization of cfa in phosphorites and phosphatic rocks during deep burial diagenesis deviating from the modern seawater like ree patterns in this regard deep burial diagenesis affecting the upper devonian geirud phosphorites is possibly a common process in the proterozoic paleozoic phosphorites in northern iran and elsewhere in the world

the age of the nantuo formation and nantuo glaciation in south china a u pb sensitive high resolution ion microprobe shrimp age of 654 5 3 8 ma from an ash bed immediately below the nantuo formation in south china provides the lowest age constraint for the nantuo glaciation which has been correlated with the global marinoan glaciation a u pb shrimp age of 636 3 4 9 ma from a fallout tuff within the basal layer of the nantuo formation along with the existing age of 635 2 0 6 ma from its overlying doushantuo cap carbonate suggests that the traditionally defined nantuo formation may have been deposited in a short time period at the end of the nantuo glaciation in combination with available ages globally the data support a relatively short duration and rapid termination of marinoan glaciations

rare earth element and sr nd isotope geochemistry of phosphatic rocks in neoproterozoic ediacaran doushantuo formation in zhangcunping section from western hubei province south china abstract phosphatic rocks are widely distributed in neoproterozoic ediacaran doushantuo formation in yangtze platform south china in this study we examined samples from the zhangcunping section in western hubei province with major element rare earth element ree and sr nd isotopic analyses on the phosphorites and the host dolostone rocks we employed an acid leaching method to separate the carbonate acetic acid leachable and phosphate hydrochloric acid leachable fractions in all the samples the geochemical differences between the different fractions can be recognized based on the p2o5 ree contents and sr nd isotopic characteristics the carbonate fractions in the rocks display low total ree concentrations with seawater like ree patterns super chondritic y ho ratios moderate negative ce anomalies and positive eu anomalies indicating these carbonates have retained the signatures of paleo seawater on the contrary the phosphate fractions display high total ree concentrations with hat shaped ree patterns generally lower y ho ratios weak negative ce anomalies and positive eu anomalies which may have recorded the features of diagenetic fluids negative ce anomalies and positive eu anomalies displayed in the carbonate fractions of the studied samples may also indicate the anoxic environments of ocean basins in south china during the deposition of the neoproterozoic ediacaran doushantuo formation a geochemical comparison between lower phosphorite layer and upper phosphorite layer indicates a greater degree of diagenesis occurred in the lower phosphorite layer than the upper phosphorite layer the negative end t values of the samples suggest continental crustal sources for the rees and the lower values in the phosphorite samples 6 9 to 6 0 than the dolostone samples 5 5 to 3 8 may suggest different processes for them and it is likely that the rees in the phosphorites have been modified by diagenetic fluids with ree contributions of pore fluids derived from the clastic silicates in the strata which generally have lower end t values whereas the dolostone took the rees from the ambient seawater mainly

geological setting of the early devonian rhynie cherts aberdeenshire scotland an early terrestrial hot spring system abstract the drilling of nine cored boreholes including a deep hole 233 m to a gabbroic basement in the vicinity of the rhynie chert locality has resulted in a major revision of the structure and stratigraphy of the area the main new structural element recognized is a low angle extensional fault system which defines the western edge of a half graben containing the early devonian succession the fault system was the main conduit for the fluids that fed the hot springs and a heat source to the southeast of rhynie is indicated rapid and unexpected lateral and vertical variations in lithology together with new lithological units have been identified the latter include a thick unit of intensely altered lapilli tuffs which are unique to the rhynie basin and to other devonian basins in ne scotland analysis of these lithologies in conjunction with the new structural model allows the succession at rhynie to be correlated with the succession in the rest of the basin and a model of basin evolution and hot spring development to be constructed siliceous sinters were deposited by multiple episodes of hot spring activity and are variably interbedded with shales sandstones and minor tuffs in a unit about 35 m thick sinter deposition was ultimately controlled by repeated subsidence along the basin margin geothermal activity was probably widespread in northern britain in the early devonian but the surface deposits are unlikely to be preserved the rhynie deposit has survived due to a fortuitous combination of circumstances

microfossils or pseudofossils cu co sulphide microfeatures in the neoproterozoic katangan supergroup democratic republic of congo abstract in this paper we investigate a group of microfeatures discovered in the mineralised neoproterozoic mines subgroup of the katangan copperbelt democratic republic of congo drc at the mashitu south cu co deposit the features are bacillus shaped composed of cu co sulphides and occur within syn diagenetic apatite veins in a low grade metasedimentary shale they exhibit a range of evidence for biogenicity including indicators of cellular complexity and were therefore investigated as candidate microfossils of chasmoendolithic prokaryotes however our study found that the features are likely to be pseudofossils formed from abiogenic rutile crystals which have been replaced by sulphides in such a way as to mimic biogenicity indicators this method of sulphide replacement adds to the list of possible false positives in the search for early life and emphasises the importance for micropalaeontological studies to consider such features with a sceptical holistic approach and rigorous scientific method

petrographic and sims pyrite sulfur isotope analyses of ediacaran chert nodules implications for microbial processes in pyrite rim formation silicification and exceptional fossil preservation abstract the lower ediacaran doushantuo formation in the yangtze gorges area contains exceptionally preserved microfossils including the earliest known animal resting eggs and embryos these fossils are preserved in cm sized chert nodules which typically have a microbial mat fragment in the center a silica cortex a pyrite rim and an outer rim of blocky calcite petrographic analysis indicates that the formation of the blocky calcite rim postdates that of the pyrite rim and silica cortex the pyrite rim grew centripetally during early diagenesis representing a reaction front that was determined by the dynamics between ambient fe2 and h2s the latter of which was derived from bacterial sulfate reduction bsr of mat fragment in nodule center the silica cortex was formed pervasively through replacement of carbonate sediments prior to compaction secondary ion mass spectroscopy sims sulfur isotopes of individual pyrite crystals 34spy sims in pyrite rims and matrices show highly positive values 15 2 39 8 the pyrite rims do not show an isotopic gradient between small crystals formed in outer rim during early diagenesis and large crystals formed in inner rim during subsequent overgrowth although rim pyrite in the same chert nodule has consistent 34spy sims values there are significant spatial and stratigraphic variations in 34spy sims values of both matrix and rim pyrite overall isotopic fractionation between pyrite and carbonate associated sulfate cas is small

early entombment within silica minimizes the molecular degradation of microorganisms during advanced diagenesis most ancient organic microfossils delicately preserved in 3d have been found in cherts although entombment within silica has been shown to promote morphological preservation the impact of early silicification on the molecular evolution of fossilized microorganisms during burial remains poorly constrained here we report results of advanced fossilization experiments performed under pressure 250 bars and temperature 250 c conditions typical of sub greenschist facies metamorphism for different durations up to 100 days on microorganisms experimentally entombed or not within a silica gel the experimental residues have been characterized using xrd and xanes spectroscopy the present study demonstrates that entombment within silica limits the degradation of microorganism molecular signatures likely through specific chemical interactions despite the progressive conversion of silica into quartz during the experiments extrapolation of the present results suggests that such protection may persist during geological timescales the present experimental study provides molecular evidence that in addition to morphologies cherts may support the chemical preservation of remains of ancient life the present results thus constitute a step forward towards the reconstruction of the original chemistry of pu tative fossilized microorganisms

geomagnetic paleointensity for the last 100 kyr from the sub antarctic south atlantic a tool for inter hemispheric correlation abstract we report relative paleointensity proxy records from four piston cores collected near the agulhas ridge and meteor rise south atlantic the mean sedimentation rate of the cores varies from 24 cm kyr to 11 cm kyr the two cores with mean sedimentation rates over 20 cm kyr record positive remanence inclinations at 40 41 ka coeval with the laschamp event age models are based on oxygen isotope data from three of the cores augmented by radiocarbon ages from nearby core rc11 83 and by correlation of paleointensity records for the one core with no oxygen isotope data the relative paleointensity proxy records are the first from the south atlantic and from the high to mid latitude southern hemisphere prominent paleointensity lows at 40 ka and 65 ka as well as many other features can be correlated to paleointensity records of comparable resolution from the northern hemisphere the records are attributable in large part to the global scale field and therefore have potential for inter hemispheric correlation at a resolution difficult to achieve with isotope data alone

acritarchs from the doushantuo formation at liujing section in songlin area of guizhou province south china implications for early middle ediacaran biostratigraphy abstract a taxonomically diverse and morphologically disparate microfossil assemblage is recovered from the upper doushantuo formation in the liujing section of songlin area guizhou province including acanthomorphic and sphaeromorphic acritarchs multicellular algae and filamentous cyanobacteria acritarch mengeosphaera membranifera sp nov is newly erected and genus cymatiosphaeroides and several species c forabilatus c kullingii bacatisphaera baokangensis are emended in the systematics the acanthomorphic species are dominated by cymatiosphaeroides forabilatus and mengeosphaera membranifera sp nov the liujing assemblage shares many species with other ediacaran coeval assemblages from south china australia siberia the east european platform india mongolia and svalbard and indicates a significant taxonomic similarity to the global age diagnostic assemblages new occurrence of those known taxa in the liujing succession documents the biodiversity of the ediacaran acritarchs in south china the liujing assemblage extends the palaeogeographic distribution of the ediacaran acritarchs and may be assigned to the tanarium conoideum cavaspina basiconica assemblage zone that was recognized in the yangtze gorges area of south china alternatively it could be partially correlated with the barren interval between t conoideum c basiconica assemblage zone and the overlying tanarium pycnacanthum ceratosphaeridium glaberosum assemblage zone

exceptional fossil record distribution of soft tissue preservation through the phanerozoic preservation of soft bodied fossil biotas konservat lagerstaten that preserve traces of volatile nonmineralized tissues readily degraded by bacteria are not evenly spaced through geologic time when compared to outcrop area exceptional faunas appear to be over represented in the cambrian and jurassic these concentrations in time correspond to particular environments indicating that controls on the distribution of exceptional faunas may have operated on a global scale the reduction in the number of exceptional faunas after the cambrian may reflect the evolution and diversification of deep bio turbators specific conditions favoring stagnation and episodic burial were required to ensure preservation in younger rocks

diatomaceous origin of siliceous shale in eocene lake beds of central british columbia the abundance of diatoms in neogene lacustrine sediments and their apparent scarcity in paleogene deposits have long perplexed geoscientists but siliceous shales from eocene lake beds of central british columbia provide new insights major element geochemistry x ray diffraction patterns and relict diatom frustules suggest that eocene beds at horsefly mcabee and princeton originated as lacustrine diatomite that underwent diagenetic alteration to produce siliceous shale the combination of high sio2 and low al2o3 values and the presence of opal ct x ray diffraction peaks provide a distinctive geochemical fingerprint for biogenic silica deposits that have been remineralized the discovery of diatomaceous geochemical signatures in siliceous shales may prove to be a useful tool for extending the geologic record of diatoms perhaps helping to reduce the apparent discrepancy between fossil evidence and evolutionary interpretations based extant species

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

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

jellyfish lake palau regeneration of c n si and p in anoxic marine lake sediments sediment cores from jellyfish lake were processed under an inert atmos phcre and the pore waters extracted and analyzed for the following parameters ph titration alkalinity ta cl h4si04 pod3 nh4 ca2 mg2 sod2 and h2s additionally in one set of pore water samples core lo the 613c of the x0 was also determined the ta h4si04 pod3 nh and h s increased with depth in the pore waters above anoxic bottom water values h s values increased to 3 8 pm in one case both h sio and pod3 concentrations increased to a maximum value and then decreased with depth suggesting removal into solid phases the h sio concentrations are equal to or greater than pore water values observed in sediments underlying upwelling areas pod3 concentrations are in general lower than pore water values from terrigenous nearshore areas but higher than nearshore carbonate pore water values from florida bay or bermuda the ca2 cl and mg2 cl ratios show slight decreases in the top 15 20 cm suggesting that authigenic carbonate may be forming this suggestion is supported by the fact that the pore waters are saturated with respect to caco due to the very high tas the 613c measurements of the pore water x0 are from a shorter core these measurements reach their most negative concentration at 72 cm and tilen become slightly heavier this change is accompanied by a decrease in ta suggesting the onset of methanogenesis at this location in this core

origin of the ediacaran weng an and kaiyang phosphorite deposits in the nanhua basin sw china abstract the weng an and kaiyang phosphorite deposits are located in central guizhou southwestern china and formed within the sinian ediacaran doushantuo formation a systematic investigation of the geology mineralogy and geochemistry of these phosphorites was conducted to constrain the redox environment origin and genetic mechanisms of ediacaran phosphorite in the lower ore layer layer a the phosphate minerals are mainly globular phosphate intraclasts which are characterized by special sedimentary and reworking textures including microgranular sedimentary isopachous cement shrinkage crack and spongy texture the phosphate minerals from the upper layer layer b have microbial phosphate components namely embryo and algae like microfossils these phosphatic microfossils have biological structures and both consist of interior structure and isopachous wall the p2o5 concentration of phosphorites in layer a reach 32 31 somewhat higher than that in layer b 28 7 whereas the p content in globular phosphate intraclasts 40 05 resemble that of the microbial phosphate component 41 19 rocks from layer a have left inclining post archean australian shale paas normalized rare earth element ree distributions with higher ce anomalies ceanom ranging from 0 12 to 0 01 average 0 07 in contrast rocks from layer b have hat shaped paas normalized ree distributions with lower ceanom ranging from 0 32 to 0 23 average 0 28 these geochemical characteristics suggest that hydrothermal fluids mixed with normal seawater might have contributed to metallogenesis and the redox environment transitioned from anoxic to oxic from layer a to b we conclude that the lower doushantuo globular intraclasts formed by the mechanical reworking of previous phosphatic sediments which were dominated by the strong mechanical power of seawater the upper doushantuo microbial phosphorite on the other hand formed by microbially mediated accretionary growth

elemental geochemistry of lower cambrian phosphate nodules in guizhou province south china an integrated study by la icp ms mapping and solution icp ms abstract the late ediacaran to early cambrian transition was a critical interval in earth history during which both the environment and life experienced dramatic change relationships between these events however are widely debated this time interval also witnessed the occurrence of massive phosphate deposits studies on the characteristics origins and depositional context of this geochemical archive may provide important insights into not only the ore forming process but also the coevolution of the earth surface system here phosphate nodules from two sections jinsha and songtao are investigated using in situ la icp ms mapping and solution icp ms methods elemental images and factor analyses of the la icp ms dataset show that ca p and sr are evenly distributed and co enriched within the nodule whereas iron related elements fe as and mo are roughly present as concentric layers the paas normalized ree patterns of the jinsha samples exhibit moderately negative ce anomalies and pronounced mree enrichments possibly related to uptake of ree released by iron oxyhydroxides during early diagenesis in contrast the songtao samples are characterized by more seawater like signals with significantly lower ce ce and higher eu eu values these positive eu anomalies are ascribed to active submarine hydrothermal vents along the yangtze platform margin based on a compilation of published ce ce data we suggest that the prominent negative ce anomalies during the ediacaran cambrian phosphogenesis give evidence of possible link between p dynamics and ocean oxygenation

affirming life aquatic for the ediacara biota in china and australia the ediacara biota has been long championed as a snapshot of the marine ecosystem on the eve of the cambrian explosion providing important insights into the early evolution of animals fossiliferous beds in the eponymous ediacara member of south australia have been recently reinterpreted as paleosols and ediacara fossils as lichens or microbial colonies that lived on terrestrial soils this reinterpretation here dubbed the terrestrial ediacara hypothesis would fundamentally change our views of biological evolution just prior to the cambrian explosion we take a comparative paleobiology approach to test this hypothesis the ediacara member shares a number of forms with assemblages in ediacaran marine black shales in south china shales that show no evidence of pedogenesis thus the shared ediacara fossils and by extension other co occurring fossils are unlikely to have been terrestrial organisms a terrestrial interpretation is also inconsistent with functional morphological evidence some of the shared forms are not morphologically adapted to address the most critical challenges for terrestrial life e g mechanical support and desiccation thus the terrestrial ediacara hypothesis can be falsified on comparative paleobiological and functional morphological grounds and we urge paleopedologists to critically reevaluate evidence for pedogenesis in the ediacara member and other ediacaran successions

microbial sequestration of phosphorus in anoxic upwelling sediments organic phosphorus is removed from the ocean by its conversion to phosphorite laboratory incubations suggest that bacteria catalyse phosphorite formation and that the rate of conversion is greatest under anoxic conditions phosphorus is an essential nutrient for life in the ocean phosphorus burial regulates marine primary production1 2 phosphorus is removed from the ocean by sedimentation of organic matter and the subsequent conversion of organic phosphorus to phosphate minerals such as apatite and ultimately phosphorite deposits3 4 bacteria are thought to mediate these processes5 but the mechanism of sequestration has remained unclear here we present results from laboratory incubations in which we labelled organic rich sediments from the benguela upwelling system namibia with a 33p radiotracer and tracked the fate of the phosphorus we show that under both anoxic and oxic conditions large sulphide oxidizing bacteria accumulate 33p in their cells and catalyse the nearly instantaneous conversion of phosphate to apatite apatite formation was greatest under anoxic conditions nutrient analyses of namibian upwelling waters and sediments suggest that the rate of phosphate to apatite conversion beneath anoxic bottom waters exceeds the rate of phosphorus release during organic matter mineralization in the upper sediment layers we suggest that bacterial apatite formation is a significant phosphorus sink under anoxic bottom water conditions expanding oxygen minimum zones are projected in simulations of future climate change6 potentially increasing sequestration of marine phosphate and restricting marine productivity

rare helical spheroidal fossils from the doushantuo lagerstatte ediacaran animal embryos come of age a small quantity of helically coiled spheroidal fossils has been recovered from acid digestion of phosphorite samples from the ediacaran doushantuo formation south china these fossils consist of an internal body enclosed in a sculptured envelope that is very similar to that of doushantuo animal eggs and blastula embryos such as megasphaera ornata a hallmark of these fossils is a three dimensional spiral structure which always consists of three clockwise coils and occurs on both the envelope and the internal body the spiral structure consists of a spiral tunnel or canal flanked by two raised levees and it is punctured by a series of holes some specimens show evidence of uncoiling invagination along the spiral structure or bipectinate furrowing on the band between canals a possible ontogenetic link between these helical spheroidal fossils and megasphaera ornata is suggested by similar size similar envelope sculptures and co occurrence we tentatively interpret these fossils as postblastula embryos related to megasphaera ornata thus they may represent the most advanced embryonic fossils so far known from the ediacaran although their adult morphologies and phylogenetic affinity remain unknown

apatite glaucony association in the ediacaran doushantuo formation south china and implications for marine redox conditions abstract major phosphogenic events took place in the late paleoproterozoic and the ediacaran both of which followed an episode of atmospheric oxygenation these apparent coincidences have led to suggestions that the precambrian phosphorus cycle was partly regulated by oceanic redox conditions although direct evidence is lacking in this paper we report the discovery of glaucony in drill cores from the phosphorite rich ediacaran doushantuo formation at weng an south china which provides new insights into redox conditions and geochemical cycles during the deposition and early diagenesis of the lower doushantuo formation the presence of flaser and lenticular bedding in the sandstones suggests deposition in a tidally influenced shallow water environment apatite is present as millimeter scale flasers in sandstones but more commonly as intraclastic grains glaucony typically occurs as interstitial aggregates cementing and replacing detrital minerals and phosphatic grains with an upsection decrease in abundance the doushantuo glauconies have consistently high k2o 7 6 9 6 wt in particular phosphorite hosted glaucony has generally higher total iron tfe2o3 than sandstone hosted glaucony consistent with al3 fe3 substitution in the octahedral site as supported by raman peaks slightly shifted towards lower wavenumbers for higher fe content a decrease in detrital input probably resulted in limited al availability during early diagenesis which in turn led to the waning of glaucony upsection the phosphate grains do not show any negative ce anomalies consistent with precipitation of authigenic apatite in suboxic environments with insignificant preferential remobilisation of ce during deposition and early diagenesis ree y features show variable diagenetic ree enrichment in phosphorites but identical concave down patterns the wide occurrence of glaucony cement further documents the presence of a generally suboxic early diagenetic environment on the seafloor which was in active exchange with bottom seawater slight fluctuations of redox states in the porewater and bottom water would have promoted the cycling of fe enrichment of phosphate and ree and extensive glaucony authigenesis therefore the glaucony bearing phosphorites in the doushantuo formation are a direct result of fe redox driven diagenesis apatite glaucony association likely forms in suboxic environments and is considered as a useful mineralogical proxy for paleoredox conditions on the precambrian ocean floors

cnidarian like embryos associated with the first shelly fossils in siberia phosphatized spheroids similar to 0 5 mm in diameter in the lower cambrian manykay formation at the bol shaya kuonamka river in northern sakha yakutia are interpreted as cnidarian embryos of late developmental stages one of the poles has a double cro

paleoceanographic constraints on precambrian phosphorite accumulation baraga group michigan usa abstract the palaeoproterozoic baraga group ca 1850 1 ma of northern michigan is a 1200 m thick sedimentary succession of marine clastic iron formation chert and phosphatic sedimentary rocks that accumulated at the peak of the world s first major phosphogenic episode lithofacies stacking patterns are interpreted to record the flooding of the nuna continental margin during two sea level cycles the base of the first sequence is marked by a transgressive lag on archean basement that is transitional into a highstand accumulation of sandstones deposited in peritidal environments the bottom of the second sequence is characterized by a chert and carbonate unit with numerous subaerial exposure surfaces deposited in intertidal to supratidal environments this chert grades upward into subtidal deposits composed of interbedded organic rich mudstone and sandstone the highstand and falling stage systems tracts are composed of progradational deltaic deposits sequences were framed using the newly discovered sudbury impact ejecta horizon as a datum its emplacement approximately coincides with unrelated environmental changes that increased the delivery of river borne sediment to the nuna margin iron bearing minerals ankerite siderite and pyrite show that ferrous iron was present in peritidal to deep marine environments ankerite dominates nearshore settings where pyrite is absent pyrite occurs in deeper progradational deltaic deposits where sulfide was produced by bacterial sulfate reduction phosphorite is restricted to shallow water sediments of the first sequence and the lowstand of the second sequence precipitation is interpreted to be the result of fe redox pumping just below the sediment water interface where photosynthetically produced nearshore oxygen oases impinged on the seafloor such shallow water phosphorite accumulation is in stark contrast to many phanerozoic depositional systems in which phosphogenesis occurs across the shelf this difference likely reflects the dissimilarity in the oxygenation state of the seafloor in the precambrian fe redox pumping and thus phosphogenesis was restricted to shallow water settings with a suboxic seafloor in the phanerozoic phosphorite forms in the full spectrum of shelf environments because the entire seafloor is generally well oxygenated the concentration of bioavailable p in neritic environments during the proterozoic may have played a major role in the development of benthic microbial ecosystems and evolving eukaryotes

a petrographic and geochemical study of carbonate and silica phases from the ediacaran doushantuo formation in the three gorges area of south china implications for diagenetic conditions abstract the carbonate of the ediacaran doushantuo formation contains various silica phases in the three gorges area of south china to better understand the diagenetic conditions under which these silica phases formed we carried out a petrographic and geochemical study of the silica phases and the coadjacent carbonate phases at the xiaofenghe section xfh in the three gorges area of south china five types of silica phases can be distinguished based on petrographic characteristics s1 and s2 are composed of microcrystalline quartz in chert nodules and disseminated in the host dolostone respectively s3 is composed of the megaquartz while s4 and s5 are microcrystalline quartz and fibrous silica respectively both replacing calcite cement six distinct types of carbonate can be recognized including the host matrix carbonate c1 sparry calcite nodules c2 calcite around chert nodules c3 dispersed calcite cement within chert nodules c4 fine micropeloidal calcite cements c5 and calcite veins c6 sedimentary structures suggest that formation of the s1 through s5 silica phases and c2 through c5 carbonate phases occurred during early burial diagenesis and therefore their formation recorded early diagenetic conditions assuming that ediacaran surface seawater temperature ranged from 28 to 39 c surface seawater 18o values can be calculated based on the oxygen isotopic composition of the host dolostone matrix c1 which range from 6 to 0 4 to 0 and 2 to 0 for the d2 d3 and d4 subunits of the doushantuo formation respectively based on the 18o values of chert nodules and beds mainly phase s1 diagenetic temperatures can be constrained to between 27 and 60 c under such low diagenetic temperatures the primary geochemical signatures of the host dolostone such as ree y patterns 13ccarb and 34spy values are likely to be preserved those silica phases without evidence of contamination of continental silicate detritus show characteristic ree y patterns with minor light ree depletions positive la eu and gd anomalies negative ce anomalies and slightly super chondritic y ho ratios implying that the source of silica may be derived from seawater negative ce anomalies in the silica phases in d2 through d4 subunits indicate that the bottom seawater or early diagenetic porewater was oxic at the time of silica precipitation

recurrent anoxia recorded in shallow marine facies at zhangcunping western hubei china throughout the ediacaran to earliest cambrian abstract in order to reconstruct the redox history of surface seawater for ediacaran shallow marine facies on the yangtze platform as well as to understand its implications for geological events oxidation and phosphatization and early evolution of life we have conducted a systematic high resolution investigation on microfacies analyses pyrite morphology as well as sulfur and carbon contents in a continuous carbonate ediacaran cambrian succession drilled 407 core in the zhangcunping area of western hubei south china the framboidal pyrites and snav toc nav non acid volatile sulfur based redox reconstruction show a dynamic history of recurrent shallow marine anoxia the early aftermath of the marinoan glaciation cap dolomite to phosphorites was characterized by either absence of pyrite or dominated by large framboids low toc contents and phosphorite deposition as well as well preserved microfossils indicating a minor oxygenated dysoxic to oxic photic shallow marine ecosystem meanwhile the uppermost doushantuo and dengying formations were potentially fully oxygenated due to the lack of pyrites as well as low snav and toc contents correlating with macrofossil assemblages miaohe biota and ediacara biota found in western hubei a major oxygenated marine ecosystem can be outlined for the late ediacaran in addition a complicated diagenetic microfabric overprints the fine microstructure of microfossils preserved in phosphorites leaving remarkable taphonomic puzzles for future study

carbon isotope variability across the ediacaran yangtze platform in south china implications for a large surface to deep ocean δ13c gradient new isotope data obtained from relatively conformable carbonate rich strata of the ediacaran yangtze platform in south china reveal substantial 13 c variability in platform sections four negative 13 c anomalies with a nadir down to 8 pdb are present in the interval between the cap carbonate level 635 ma and the precambrian cambrian boundary 542 ma while in slope and basinal sections 13 c values are negative through the entire doushantuo formation 635 551 ma if these 13 c values are close to their primary seawater signature they imply a strong 10 surface to deep ocean 13 c gradient that is consistent with long term deep ocean anoxia and the presence of a large dissolved organic carbon doc reservoir the two prominent negative 13 c excursions within the doushantuo formation above the cap carbonate level are associated with shoaling and local exposure of the platform the anomalies may thus record remineralization of a large oceanic doc pool via sulfate reduction that transferred 13 c depleted carbon from the oceanic doc reservoir to the surface ocean during regression inconsistencies in ediacaran 13 c profiles globally and variations in south china in particular highlight the need for further evaluation of local departures in 13 c from an inferred average seawater signature

phosphogenesis aragonite fan formation and seafloor environments following the marinoan glaciation abstract carbonates in the sete lagoas formation sao francisco craton brazil preserve a record of chemical biological and oceanographic changes that occurred during the ediacaran period the base of this formation constitutes a post glacial cap carbonate which contains seafloor precipitates carbonate and barite crystal fans as well as various authigenic and diagenetic minerals apatite pyrite and barite here we present petrographic and geochemical data on this unit and discuss the significance of its mineral association for marine environments following the marinoan snowball earth glaciation for the first time we report well developed apatitic cements in a neoproterozoic cap carbonate isopachous and intergranular void filling cements encrust and surround seafloor precipitated fan crystals that precipitated as aragonite we propose a model for the origin of this mineral association which relates phosphogenesis and aragonite fan formation to a single set of environmental conditions according to this model the boundary between oxic and anoxic conditions was located at or just below the sediment water interface burial of iron oxyhydr oxides below this boundary liberated phosphate to pore water and provided fuel for iron reduction iron reduction released fe2 which inhibited nucleation of carbonate and allowed for aragonite growth on the seafloor concurrently iron pumping shuttled phosphate from the water column to the sediment and perhaps in conjunction with organic phosphorus remineralization via anaerobic microbial pathways created conditions conducive to phosphate mineralization this model corroborates the hypotheses that aragonite crystal fan formation requires the presence of an inhibitor to carbonate nucleation in addition to high alkalinity and that fe2 serves as this inhibitor overall our work documents a close association between aragonite crystal fan formation and phosphogenesis at the beginning of the ediacaran illuminates the paleoenvironments of cap carbonates with seafloor precipitates and contributes to understanding of phosphogenesis following low latitude glaciations

germanium silica ratios in diagenetic chert nodules from the ediacaran doushantuo formation south china abstract germanium silica ge si ratios of dolostone and mudstone hosted chert nodules from the ediacaran 635 542 ma doushantuo formation in the yangtze gorges area south china are reported these chert nodules typically have a calcite rim a pyrite rim and a silica core the latter sometimes containing disseminated pyrite the silica core was precipitated by early diagenetic replacement of carbonate and silty muddy sediments two types of chert nodules are identified based on their mineralogy and geochemistry type 1 chert nodules are poor in disseminated pyrite in the silica core they also have low al and show a strong positive correlation between al contents and ge si with a near zero or negative intercept in contrast type 2 chert nodules contain abundant disseminated pyrite in the silica core and show a weakly positive correlation between ge si ratios and al contents with a large positive intercept on the ge si axis the ge si of doushantuo nodules are greater than those of cretaceous deep sea cherts suggesting that the ge si ratio of ediacaran seawater porewater was greater than the cretaceous due to the more effective discrimination against ge by inorganic opal precipitation relative to biogenic opal precipitation the positive correlation between ge si and al can be interpreted using a mixing model with a pure chert characterized by a low ge si ratio and an al rich endmember characterized by a high ge si ratio the latter is most likely represented by a clay component but the model based estimate of the ge si ratio inferred for the al rich clay endmember is much higher than that of phanerozoic clay minerals these high ge si ratios for the clay endmember may be related to the generally high ge si ratio of ediacaran seawater but could also be related to clay organic matter interactions organic matter absorbed to clays could provide an additional source of ge because certain organic molecules are known to have a high affinity for ge due to their strong metal ion chelating properties the high ge si ratio of the al rich endmember in type 1 chert nodules suggests that ge in porewaters from which these cherts precipitated may have been dominated by ge organic complexes the low ge si ratio inferred for the al rich endmember in type 2 chert nodules is therefore taken to indicate that ge was released from organic matter perhaps due to anaerobic degradation of organic matter accompanied by the formation of pyrite and was redistributed between clay organic endmembers and pure chert resulting in a non zero intercept in the ge si vs al 2 o 3 plots these observations suggest that a strong terrestrial influence in a restricted sedimentary basin or a high content of dissolved organic carbon in ediacaran seawater and porewater may have contributed to the dominance of ge organic complexes in the doushantuo basin in the yangtze gorges area

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

fossil preservation through phosphatization and silicification in the ediacaran doushantuo formation south china a comparative synthesis phosphatized and silicified microfossils preserved through replication of organic templates by authigenic calcium phosphate and silica respectively form through mechanistically similar mineralization processes but under notably different conditions in order to characterize the environments and taphonomic processes associated with these preservational pathways we compare phosphatized and silicified fossil assemblages in the ediacaran doushantuo formation south china in terms of stratigraphic and paleogeographic distribution preservation and biodiversity several differences are recognized 1 phosphatization and silicification both occurred in sub tidal doushantuo sediments but phosphatized fossils generally occur in shallower sub tidal facies than silicified fossils 2 although both phosphatized and silicified fossils are preserved three dimensionally the latter are typically more compressed and 3 whereas phosphatized assemblages are numerically dominated by multicellular acritarchs putative metazoan eggs and embryos silicified assemblages are dominated by prokaryotes these differences can be explained by environmental and taphonomic distinctions phosphatized fossils occur in intraclastic phosphorites and phosphatic carbonates and were likely fossilized near the suboxic anoxic boundary in sediments under oxic bottom waters with redox and biogeochemical gradients conducive to p remineralization phosphate burial via iron pumping and calcium phosphate precipitation reworking and winnowing of phosphatized fossils preferentially concentrated certain taxa prior to final burial in contrast silicified fossils typically occur in chert nodules which formed deeper in the sediment column in ferruginous pore waters and perhaps under ferruginous bottom waters where bacterial sulfate reduction and pyrite formation created low ph conditions conducive to calcite dissolution and silica precipitation once formed chert nodules mostly remained in situ but some were reworked with turbidites and olistostromes developed in slope facies despite these distinctions phosphatized and silicified fossil assemblages in the doushantuo formation generally overlap in time and space and representatives of all major groups and many common genera of doushantuo organisms are present in both phosphorites and cherts consequently although both preservational pathways have paleoenvironmental and taphonomic biases their relative biases on taxonomic presence absence data are minimal given sufficient sampling efforts and paleobiologic and biostratigraphic information based on presence absence but not abundance data from the doushantuo formation appears to be robust

possible ree constraints on the depositional and diagenetic environment of doushantuo formation phosphorites containing the earliest metazoan fauna abstract the neoproterozoic doushantuo formation south china preserves a unique assemblage of what are probably the earliest metazoan fossils sponges cnidarians and bilaterians in the world that could contribute to a better understanding of early faunal evolution on earth the formation spans an interval of dramatic biological chemical and climatic change in weng an mine in southwest china extensive paleontological investigations show embryonic larval and adult animal fossils occur in the upper ore bed of the doushantuo phosphorite but no animal forms have been found in the lower ore bed taphonomy and experiments on fossilization suggest that no fauna lived on or in the lower ore bed as it was deposited rare earth element ree data for the doushantuo phosphorites in weng an document the paleoenvironmental condition under which the phosphorites were deposited the shale normalized ree patterns of the upper phosphorite bed upb are characterized by old vendian early cambrian phosphorite patterns the ree patterns of the lower phosphorite bed lpb are significantly different with less negative ce anomalies and less lree and hree depletion the ree characteristics suggest that the doushantuo phosphorites record seawater condition at the time of sediment deposition and are not affected by subsequent diagenesis the ree compositions of the doushantuo phosphorites show that the marine depositional environment changed from anoxic in the lower ore bed to oxic in the upper ore bed the uniquely diverse and abundant doushantuo eukaryote fossil accumulations at weng an thus may be related to a change from anoxic to oxic bottom water conditions

remarkable preservation of microbial mats in neoproterozoic siliciclastic settings implications for ediacaran taphonomic models abstract it is beyond doubt that the appearance of infaunal bioturbation and metazoan biomineralization across the ediacaran cambrian transition irreversibly affected the nature of marine sediment architecture and biogeochemistry here we review those changes in relation to their likely effect upon the processes of fossil preservation especially within siliciclastic sediments processes of soft tissue preservation in siliciclastic settings from the ediacaran period including microbes and microbial mats as well as ediacaran macrofossils are here reviewed within this context highlighted examples include the exceptional preservation of microbes found in association with wrinkle structures and ediacaran macrofossils in england and newfoundland replicated by silicate minerals and in the white sea region of russia replicated by iron sulphide these occurrences show that soft tissue preservation in siliciclastic settings went well beyond that typical for ediacaran macrofossils alone and also extended to similar modes of preservation in associated microbes using these new observations it can be argued that several existing explanations for ediacaran fossil preservation can be united within a biogeochemical model that involves evolution of the sediment mixed layer across this transition

evidence of archean life stromatolites and microfossils abstract fossil evidence of the existence of life during the archean eon of earth history 2500 ma is summarized data are outlined for 48 archean deposits reported to contain biogenic stromatolites and for 14 such units that contain a total of 40 morphotypes of described microfossils among the oldest of these putatively microfossiliferous units is a brecciated chert of the 3465 ma apex basalt of western australia the paleoenvironment carbonaceous composition mode of preservation and morphology of the apex microbe like filaments backed by new evidence of their cellular structure provided by two and three dimensional raman imagery support their biogenic interpretation such data together with the presence of stromatolites microfossils and carbon isotopic evidence of biological activity in similarly aged deposits indicate that the antiquity of life on earth extends to at least 3500 ma

organic composition and diagenetic mineralization of microfossils in the ediacaran doushantuo chert nodule by raman and petrographic analyses abstract we studied microfossils and their embedding matrix minerals from chert nodules in the ediacaran doushantuo formation of the yangtze gorges area in south china using raman spectroscopy as well as transmitted and polarized light microscopy the microfossils are composed of organic carbonaceous material with weak structural organization ordering which indicates a low degree of thermal maturation and alteration raman spectral disparity of carbonaceous material among different portions vesicle inclusion of microfossils reveals some differences in organic composition and structure of their precursor biological matters the mineral phases of silica matrix that entombs the microfossils are recognized as opal ct cryptocrystalline quartz and their transitional phases overall raman spectral analyses and petrographic observations document a complete and continuous sequence of silica phase transformation from opal ct to quartz when reconstructing the diagenetic history of sediments and mineralization process of microfossils in a localized microenvironment the silica in pore waters precipitated preferentially at the periphery of microorganisms in the form of opal gradually decreasing in abundance as it transformed into more stable cryptocrystalline quartz the recrystallization took place in cryptocrystalline quartz to form grains authigenic fluorapatite readily precipitated in the vicinity of some microfossils and within their degraded organic fragments while apatite was crystallizing around organisms and their biostructures silica precipitated in the surrounding voids inhibiting the space of potential apatite crystallization the silicification and phosphatization of microfossils occurred in the microbial sulfate reduction msr zone of the sediment column and both were driven by the localized ph change resulting from msr and pyrite precipitation in the microenvironment thus facilitating the exceptional fossil preservation in the doushantuo chert nodules

terminal proterozoic cyanobacterial blooms and phosphogenesis documented by the doushantuo granular phosphorites i in situ micro analysis of textures and composition abstract in order to ascertain the origin of granular phosphorites and the roles of microorganisms in phosphogenesis we conducted comprehensive petrographic surveys and correlated in situ micro analyses of granular phosphorites from the doushantuo formation near yichang south china phosphatic granules display organically zoned internal structures often associated with abundant cyanobacteria like microfossils the internal ultrastructure of the granules as documented by raman microspectroscopy scanning electron microscopy sem and transmission electron microscopy tem is characterized by randomly oriented apatite nano crystals embedded with ubiquitous carbonaceous particles in the apatite groundmass these represent primary textures formed by the rapid growth of apatite provided with abundant nucleation sites within microbial biofabrics nanosims elemental mapping revealed close correspondence of carbon and nitrogen with microfossil structures at the cellular and sub cellular level we propose that the doushantuo granules themselves were formed by microbially mediated accretionary growth followed by rapid phosphatization occurring at the sediment water interface extracellular polymeric substances eps produced by cyanobacteria would have played crucial roles in these processes by promoting aggregated granule growth in addition to providing nucleation sites for apatite crystallization while previous studies have suggested a dominant role of sulfur metabolizing microorganisms in the precipitation of phosphate in phosphorites new observations indicate that the emplacement of most sulfur bearing minerals in the doushantuo phosphorites postdate phosphatization itself our new model of phosphorite formation thus places cyanobacterial eps as an earlier key component of the mineralization of the doushantuo granular phosphorites

age and implications of the phosphatic birmania formation rajasthan india abstract the birmania inlier in western rajasthan india contains important phosphate deposits the depositional age of which is poorly constrained here we provide the first direct age constraints for the phosphate bearing birmania formation using a combination of paleontological and detrital zircon u pb data the occurrence of the multicellular algal fossil wengania exquisita in phosphatic chert of the birmania formation suggest that it was deposited during the ediacaran detrital zircon age distributions contain prominent populations of 1 7 1 9 ga grains with subordinate younger grains that range from 650 to 980 ma the distribution broadly resembles those from neoproterozoic strata from both cratonic and himalayan india but like zircon age distributions from the marwar group lacks 1 0 1 2 ga grains which may suggest that both areas shared similar local sources the lack of zircon grains younger than 650 ma is consistent with an ediacaran depositional age because almost all cambrian or younger strata from india have yielded cambrian or latest neoproterozoic age grains these findings raise the possibility of a previously unrecognized late neoproterozoic episode of phosphogenesis on the india craton the presence of wengania exquisita further supports strong palaeogeographic affinity between the india and south china during the neoproterozoic and cambrian

the silica cycle in the precambrian abstract whereas the modem silica cycle is heavily dependent on the biology of silica secreting organisms such as the diatoms the precambrian silica cycle was dominated by inorganic reactions among dissolved silica clay and zeolite minerals and organic matter there is no evidence for deposition of a layered amorphous silica but abundant evidence for diagenetic silicification in the neoproterozoic the time period chosen for this analysis the influx of silica to the neoproterozoic ocean would have been governed as today by the balance among tectonism weathering and hydrothermal input the evidence of neoproterozoic rocks favors tectonic and weathering regimes not very dissimilar to those of the early phanerozoic and hydrothermal inputs significantly altered at certain periods one flux would have been very different the present diffusional influx of silica from interstitial waters into the oceans would have been altered to an efflux from the oceans to interstitial waters reactions of dissolved silica with inorganic phases would have controlled silica concentrations at a level of about 60 ppm this figure is based on experimental determinations of solubility and silica sorption on clay minerals and zeolites as silica in interstitial waters was lowered by opal ct precipitation a diffusional efflux from the ocean into the sediment was set up silicification would have started in early diagenesis as opal ct precipitated from interstitial waters diffusion of silica from overlying seawater declined as the sediment was buried a few hundred meters and the diffusion path lengthened during this still relatively shallow burial silicification continued but this time powered by hydrologie transport of dissolved silica from coastal plain sediments during transgressions and regressions thus the major removal of silica from the neoproterozoic ocean took place by diagenetic reactions

eight armed ediacara fossil preserved in contrasting taphonomic windows from china and australia we report the preservation of the eight armed ediacara fossil eoandromeda octobrachiata as carbonaceous compressions in the doushantuo black shale of south china and as casts and molds in the rawnsley quartzite in south australia the contrasting preservational styles in two taphonomic windows indicate that e octobrachiata may have had a relatively recalcitrant organic integument which rules out its close comparison with giant agglutinated foraminifers such as xenophyophores its octaradial symmetry and dextrally spiraling arms suggest that it may be a diploblastic grade animal sharing some features with cnidarians and ctenophores although its phylogenetic affinity remains open it is the first and only unambiguously identified ediacaran macrofossil that occurs in two drastically different taphonomic windows thus bridging the conventional biological and taxonomic gaps between the ediacara and miaohe biotas which collectively record the earliest known macroscopic and complex life

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

redox architecture of an ediacaran ocean margin integrated chemostratigraphic δ13c δ34s 87sr 86sr ce ce correlation of the doushantuo formation south china abstract early diagenetic silicification and phosphatization of the ediacaran doushantuo formation ca 635 to 551 ma in south china offer extraordinary taphonomic windows into the early evolution of multicellular eukaryotes including various algal groups and potentially animals in order to understand how the ecological and taphonomic distribution of these ediacaran eukaryotes was controlled by oceanic redox conditions it is critical to reconstruct the redox architecture of the sedimentary basin recently two alternative redox models have been proposed to account for the geochemical and sedimentary features of the doushantuo formation one argues that the unit was deposited on a continental margin where a metastable sulfidic wedge was dynamically maintained by a sulfate concentration gradient between shelf and basinal environments the other contends that the sulfidic water mass was largely restricted to the intra shelf basin behind a rimmed margin these two models make different predictions about the stratigraphic completeness and correlation of the doushantuo formation to test these predictions we generated high resolution time series trends of multiple isotopic and elemental tracers including 34s 87sr 86sr and ce ce to facilitate an integrated chemostratigraphic correlation between inner shelf xiaofenghe intra shelf jiulongwan and outer shelf yangjiaping and zhongling sections our correlations suggest that both the inner and outer shelf sections are stratigraphically incomplete relative to the intra shelf section the euxinic wedge model should be reconsidered insofar as it is based on a miscorrelation between sections viewed from our revised chemostratigraphic framework euxinic conditions on the platform appear to have been largely restricted to the intra shelf basin carbonates in the upper doushantuo formation at jiulongwan and their stratigraphic equivalents are characterized by a profound negative carbon isotope anomaly i e the shuram excursion coincident with a drop in pyrite sulfur isotope values and a significant rise in 87sr 86sr from 0 7080 to 0 7090 the integrated stratigraphic data from south china suggest that the onset of the shuram excursion is associated with enhanced oxidative continental weathering that delivered radiogenic strontium as well as sulfate to the ediacaran basin

source of silica and silicification of the lowermost cambrian yanjiahe formation in the three gorges area south china abstract the rise of siliceous organisms is generally considered to have driven the abrupt decrease of silica in the ocean during the ediacaran cambrian e c interval even if the exact timing and biological triggers of this event are still debated although ediacaran cambrian chert depositions are widely distributed multiple evidences converge to support their hydrothermal origin in this study we provide petrographic study supplemented by elemental concentration sem and raman spectral data on the siliceous rocks from the yanjiahe formation the three gorges area south china in order to ascertain the origin of included silica and discuss the involved processes of silica deposition contrary to most previous studies our analyses suggest that studied cherts mainly resulted from biogenic silica and subsidiary from abiotic precipitation influenced by surrounding hydrothermal activity and from detrital input the deposition model of silica includes direct deposition of siliceous bioclasts secondary replacement of carbonate by dissolved biosilica and microbial induced silicification from seawater the sink of silica recorded in the yanjiahe formation was characterized of a transition from typical precambrian to phanerozoic process in addition micropalaeontological and taphonomical analyses of the yanjiahe formation revealed two pulses of microfossil abundance and diversity in the fortunian and stage 2 respectively they can be correlated with a regression and an enrichment in dissolved phosphate that probably derived from enhanced detrital flux

carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the ediacaran doushantuo formation the ediacaran doushantuo formation dst is renowned for exceptionally preserved precambrian fossils including metazoans some of these fossils particularly microfossils such as multicellular algae and acanthomorphic acritarchs are preserved in dst chert nodules to better understand the geomicrobiological processes that contributed to the authigenic formation of dst chert nodules and facilitated exceptional fossil preservation we analyzed organic matter in these chert nodules and the surrounding matrix calcareous mudstone using multiple in situ techniques confocal laser raman spectroscopy micro fourier transform infrared spectroscopy ftir and secondary ion mass spectroscopy sims we found strong ultrastructural chemical and isotopic heterogeneities in the organic matter as indicated by the raman spectral parameter i 1350 1600 ranging from 0 49 to 0 88 the infrared spectral index r3 2 from 0 12 to 0 90 and an estimated 13corg sims range of 44 v pdb these micron scale heterogeneities imply that the organic matter preserved in the dst chert nodules is derived from different carbonaceous sources in a diverse microbial ecosystem including eukaryotic and or prokaryotic photoautotrophs as well as chemotrophs involved in the fermentation and probably anaerobic oxidation of organic remains thus the microbial ecosystems in ediacaran ocean waters and sediments were more complex than previously thought and these microbial processes controlled dynamic micro environments in dst sediments where chert nodules were formed and fossils were mineralized the results also show that variations in the relative abundances activities and interactions of co existing microorganisms in dst sediments may have modulated 13corg shifts causing local decoupling between 13corg and 13ccarb as measured in bulk samples

microbial dissolution of clay minerals as a source of iron and silica in marine sediments interactions between microbes and minerals have the potential to contribute significantly to the global cycles of various elements and serve as a link between the geosphere and life in particular the microbially mediated cycle of iron within marine sediments is closely tied to the carbon cycle the dissolved iron that serves as a nutrient is thought to be primarily drawn from well known pools of highly reactive bioavailable iron and iron complexes iron contained within the crystal lattice of clay minerals the most abundant materials found at the earth s surface is not thought to be part of this pool here we analyse the mineral composition of middle cambrian aged mudstones from the western united states we find intergrown mineral aggregates of quartz pyrite and calcite on the basis of mineral phase relationships and temperatures of crystallization derived from stable isotopes of oxygen we infer that mineral dissolution driven by microbes released iron and silica to the surrounding sediment pore waters and led to the subsequent precipitation of the observed minerals the microbial extraction of structurally coordinated fe3 from clay minerals after their deposition in marine sediments may liberate a fraction of iron previously considered unavailable and may be important in iron and silica cycling in marine sediments interactions between microbes and minerals are evident in modern global elemental cycles relationships between minerals in cambrian mudstones indicate that such interactions may have released otherwise unavailable mineral bound iron and silica into the ancient oceans

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

phosphogenesis around the proterozoic phanerozoic transition there was a very significant and widespread phosphogenic event around the proterozoic phanerozoic transition this is reflected in the occurrence of many major and minor latest proterozoic and cambrian phosphate deposits phosphorites in asia australia africa and south america as well as minor occurrences in many other parts of the world the major peak in phosphogenesis was in the tommotian with lesser events in the ediacaran and the lenian bracketed by other minor though significant events recent evidence on the timing of proterozoic phosphogenesis does not now support the suggestion of a phosphogenesis glaciation link these peaks in phosphogenesis are taken as evidence that there was a marked increase in the phosphate content of the shallow seas at about this time possibly as a result of the circulation of deep phosphorus rich ocean waters into the photic zone not only was this responsible for the formation of phosphorites but it also had a profound effect on the biota and may have been a driving mechanism for the cambrian faunal explosion and the initiation of biomineralization

microbial silicification in iodine pool waimangu geothermal area north island new zealand implications for recognition and identification of ancient silicified microbes silicified microbes provide evidence for some of the earliest life forms on earth they are extremely important to understanding the early development of life and the conditions that allowed its development such discussions commonly rely on comparisons with extant taxa and therefore depend upon the preservation style of the microbes and in particular the preservation of the taxonomically important features silicified microbes are deceptive they commonly appear to be well preserved even though their taxonomically critical features have been destroyed by silicification an understanding of the early taphonomic processes that influence microbial silicification can be obtained by studying extant microbes that are being silicified in modern hot spring pools iodine pool located in the waimangu geothermal area on the north island of new zealand is ideal for this purpose the spring water has a temperature of 69 100 c a ph of 8 3 9 0 and 440 457 ppm sio 2 glass slides left in the shallow marginal waters of this pool for 90 h became covered with thin layers of opaline silica discrete opal a spheres unsilicified microbes pseudofilaments partly silicified microbes and silicified microbes the rapidly silicified microbes appear well preserved with their general morphology diameter length and presence or absence of septa being readily apparent most of the silicified microbes however lack the key features that would allow accurate comparisons with extant taxa only two of the silicified microbes can be tentatively allied with the unsilicified forms despite being found side by side on the same glass slide these problems in identifying modern rapidly silicified microbes suggest that identifications of ancient silicified microbes can be problematic and must be treated with caution

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

integrated chemostratigraphy of the doushantuo formation at the northern xiaofenghe section yangtze gorges south china and its implication for ediacaran stratigraphic correlation and ocean redox models abstract the ediacaran doushantuo formation in the yangtze gorges of south china plays an important role in our understanding of biological evolution global correlation and ocean redox conditions because of the availability of high resolution paleontological and geochemical data and numerous radiometric dates however integrated study has been focused on the jiulongwan section that was largely deposited below wave base in a restricted shelf lagoon jiang et al 2011 zhu et al 2011 studies of shallower water successions are lacking and this presents a challenge to test ediacaran stratigraphic correlation and ocean redox models to fill this knowledge gap we conducted a high resolution integrated study of the doushantuo formation at the northern xiaofenghe nxf section approximately 35 km to the northeast and paleogeographically updip of the jiulongwan section with the exception of the basal 20 m nxf sediments were deposited above normal wave base integrated biostratigraphic and chemostratigraphic data indicate that the 140 m thick nxf section correlates with the lower doushantuo formation member i and much of member ii i e the lower ca 70 m of the formation at jiulongwan geochemical data from nxf and other doushantuo sections indicate that euxinic conditions may have been limited to a shelf lagoon represented by the jiulongwan section that was restricted between the proximal inner shelf and a distal shelf margin shoal complex at least during early doushantuo time following the deposition of the doushantuo cap dolostone further integrated studies are necessary to test whether euxinic conditions existed in open marine shelves in south china and elsewhere during the ediacaran period

phosphorus phosphorites and skeletal evolution at the precambrian cambrian boundary clustering of sedimentary phosphate deposits around the precambrian cambrian boundary is related to a global phosphogenic event this event probably resulted from a complex interplay of factors and had a profound effect on the biota with high concentrations of phosphorus in the photic zone producing an increase in the total shallow marine biomass faunal diversification the precipitation of skeletal structures and explosive evolution

comparative taphonomy and phylogenetic signal of phosphatized weng an and kuanchuanpu biotas abstract the ediacaran cambrian is a time with globally enhanced production of phosphorites this includes perhaps the two most famous deposits with variable cell and soft tissue phosphatization in microfossils the ediacaran doushantuo formation which contains the weng an biota and the lower cambrian kuanchuanpu formation and equivalents found in china a wide range of variables is responsible for phosphatization during this interval including depositional and geochemical conditions and microbial activity degree of microfossil phosphatization is widely dependant upon original cell and tissue types microfossils with non diagenetic morphologies that are iconic for modern crown group metazoans have had the highest level of acceptance for their interpreted phylogenetic affinity microfossils with these iconic morphologies are rare from the weng an biota but relatively common from the kuanchuanpu biota thus metazoan affinity for doushantuo microfossils has commonly relied on relatively simple and less well known morphologic features of embryonic organisms for which there is not a concensus on the nature of their phylogenetic signal differences in the phosphatized microfossil record between the weng an and kuanchuanpu biotas are due to the combination of a primary signal reflecting the initiation of the cambrian explosion and a secondary signal driven by a multitude of taphonomic processes operating at different levels of effectiveness during deposition of these two units

pb pb ages of neoproterozoic doushantuo phosphorites in south china constraints on early metazoan evolution and glaciation events the pb pb isochron ages of 576 14 ma for the upper part of the upper phosphorite bed upb this study and 599 4 ma for the lower part of the upb earth planet sci lett 201 2002 203 in the doushantuo formation in the weng an area south china suggest that the deposition of the upb lasted at least 5 ma and indicate that the observed microfossil assemblage animal remains multicellular algae and giant process bearing acritarchs in the doushantuo formation predates all well dated diverse ediacaran assemblages and represents the earlier paleontological record of eukaryotes radiation on earth the 576 14 ma age in the upper part of the upb approximates the age of a negative delta 13 c excursion near the boundary between the doushantuo and the overlying dengying formation if the doushantuo dengying boundary at the weng an area is equivalent to that in the yangtze gorges area this negative excursion might correlate to a post marinoan glaciation in south china suggesting that the ice age following doushantuo sediment deposition is younger than 590 ma the 599 4 ma age in the lower part of the upb earth planet sci lett 201 2002 203 represents the minimum age of the nantuo diamictites which are generally correlated with the marinoan glaciation c 2004 elsevier b v all rights reserved

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

quantitative evaluation of the biostratigraphic distribution of acanthomorphic acritarchs in the ediacaran doushantuo formation in the yangtze gorges area south china abstract doushantuo acanthomorphic acritarchs are large morphologically complex organic walled microfossils broadly constrained between the 635 ma nantuo glaciation and the 551 ma miaohe biota they are potential biostratigraphic tools for subdivision and correlation of the ediacaran system in south china however major variations in sedimentary facies and stratigraphic thickness present challenges in understanding the spatial and temporal distribution of these acritarchs further the distribution of acritarchs in the doushantuo formation is associated with the presence of early diagenetic chert and phosphate implying a certain degree of preservational bias and or environmental control the purpose of this paper is to document the stratigraphic distribution of doushantuo acritarchs and to quantitatively evaluate their biostratigraphic significance and possible taphonomic environmental biases based on high resolution paleontological data from six sections over 100 km in the yangtze gorges area south china a total of 1082 acritarch fossils were recorded from 84 chert horizons in the six sections of the study area these chert horizons are not uniformly distributed throughout the doushantuo formation thus the presence absence of early diagenetic chert does play a role in controlling the distribution of acritarchs the sampled chert horizons can be grouped into two stratigraphic intervals in the lower and upper doushantuo formation respectively based on regional stratigraphic correlation quantitative analysis shows that the two intervals are distinct taxonomically and largely independent of taphonomic or facies controls thus the two intervals can be regarded as assemblage biozones the lower biozone biozone 1 is numerically dominated by tianzhushania spinosa n 587 68 3 and meghystrichosphaeridium magnificum n 74 8 6 whereas the upper biozone biozone 2 is dominated by ericiasphaera rigida n 104 47 1 and tianzhushania spinosa n 34 14 1 the three most common genera meghystrichosphaeridium tianzhushania and ericiasphaera have been identified in all sections correspondence analysis ca detrended correspondence analysis dca discriminant analysis da and pairwise comparisons of samples spearman rank coefficient and jaccard chao index all consistently support biostratigraphic zonations thus the distribution of the doushantuo acanthomorphs is primarily controlled by biostratigraphic position of samples with facies and taphonomic differences playing a secondary role our case study suggests that acanthomorphic acritarchs can offer a viable tool for regional correlation of the ediacaran system

carbon isotope chemostratigraphy and sedimentary facies evolution of the ediacaran doushantuo formation in western hubei south china abstract the doushantuo formation of south china consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies is one of the key sedimentary units in the world for understanding ediacaran geobiological processes however stratigraphic correlation and sedimentary facies evolution of the doushantuo formation remain controversial sedimentary facies analysis of the well known sections of the yangtze gorges area and new sections in northern yichang western hubei indicate that the doushantuo succession in the yangtze gorges area was deposited in an offshore intra shelf basin within the yangtze platform in contrast the doushantuo formation in the northern yichang area which is characterized by one or a few phosphate rich horizons represents deposition on the subtidal or intertidal shelf and so is similar to the succession in the weng an area central guizhou province the carbon isotope profiles of the different sections exhibit significant variation which is interpreted to result from facies differences sequence and high resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the doushantuo formation on the yangtze platform the results confirm that a prominent negative 13ccarb excursion baince nadir down to 5 in the middle portion of the second sequence of the doushantuo formation is a widely traceable event baince together with three other 13ccarb excursions namely cance at the base wance near the first sequence boundary near the middle and dounce at the top of the doushantuo formation constitute a complete carbon isotope profile for the doushantuo formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the ediacaran period

the role of decay and mineralization in the preservation of soft bodied fossils abstract fossil deposits that preserve soft bodied organisms provide critical evidence of the history of life usually only more decay resistant materials e g cuticles survive as organic remains as a result of selective preservation and subsequent diagenesis to more resistant biopolymers permineralization the permeation of tissues by mineralizing fluids may preserve remarkable detail particularly of plants however evidence of more labile tissues e g muscle normally requires the replication of their morphology by rapid in situ growth of minerals i e authigenic mineralization this process relies on the steep geochemical gradients generated by decay microbes the minerals involved and the level of detail preserved which may be subcellular depend on a number of factors including the nature of microbial activity and amount of decay availability of ions and the type of organism that is fossilized understanding these controls is essential to determining the conditions that favor exce

a refined late cryogenian ediacaran earth history of south china phosphorous rich marbles of the dabie and sulu orogens abstract the late cryogenian ediacaran geological framework for south china is constructed principally from sedimentary successions preserved in the central and western regions of the yangtze block new stratigraphic and carbonate carbon isotope data allow us to extend that framework into the exhumed hp uhp subduction complexes of the eastern dabie and sulu orogens that separate the south and north china cratons those data show that marble and phosphorous rich p rich units in those complexes were originally part of an ediacaran shallow marine shelf carbonate platform the basal pebbly schist metadiamictite and lowermost p rich marble of the jinping formation haizhou group in the sulu orogen matches in both facies character and c isotope profile that of the marinoan equivalent glacial cap carbonate couplet of the nantuo and doushantuo formations the daxinwu formation susong group in the eastern dabie orogen contains a marble unit that has for several hundreds of metres a strikingly uniform c isotope profile of low 13c positive values and is overlain by a p rich graphitic schist these features match those of the late ediacaran to early cambrian dengying formation these correlations establish that the hp uhp metasedimentary rocks many of which were once considered to be palaeo to mesoproterozoic in age are a neoproterozoic age cover sequence of the continental margin of the yangtze block further their widespread development limits their utility as indicators of offset across the tan lu fault zone and instead favours tectonic models that interpret that feature as a continental scale tear fault formed during the mesozoic collision and suturing of the north and south china cratons

pyrite morphology and redox fluctuations recorded in the ediacaran doushantuo formation abstract recent geochemical studies of the doushantuo formation ca 635 551 ma in south china suggested that the ediacaran ocean was strongly stratified with an oxic surface layer above a euxinic wedge that was sandwiched within ferruginous deep waters this ocean redox model however was derived largely from the data obtained from stratigraphic sections in the yangtze gorges area that according to recent paleogeographic reconstruction were deposited in a restricted intrashelf lagoon in order to test the redox conditions in open ocean deep water environments we have conducted a detailed morphological analysis of authigenic pyrites from the upper to lower slope sections of the doushantuo formation in analogy to modern euxinic basins such as the black sea framboidal pyrites with smaller and less variable size distribution are taken as evidence for sulfide precipitation in euxinic water column while larger and more variable framboidal and euhedral pyrites are formed or diagenetically altered in sediments with an overlying oxic dysoxic water column except for a few brief intervals pyrites from the doushantuo formation in upper slope sections siduping and taoying sections are mainly of early diagenetic origin and do not record water column euxinia during deposition in contrast pyrites from the doushantuo formation in the lower slope section wuhe section are dominated by fine grained framboids indicative of pervasive water column euxinia below chemocline in both upper and lower slope sections temporal changes in genetic pyrite types occur at centimeter to decameter scales suggesting frequent chemocline fluctuations the overall decrease in abundance of framboidal pyrites toward the upper doushantuo formation in upper slope sections suggests increasing water column oxygenation and deepening of the chemocline macroalgae and metazoan fossils are found mainly from shale intervals without syngenetic pyrites in upper slope sections indicating the sensitivity of macroscopic eukaryotes to the ocean chemocline the redox fluctuations recorded by the doushantuo pyrites compels for comprehensive geochemical data in deep water successions to further test the existing paleoceanographic models of the ediacaran ocean

an integrated chemostratigraphic δ13c δ18o 87sr 86sr δ15n study of the doushantuo formation in western hubei province south china abstract high resolution isotopic analyses were conducted on core samples from the ediacaran doushantuo formation at the wangjiapeng section western hubei province in south china whereby two laterally traceable negative 13ccarb excursions en1 and en3 were recognized the magnitude and duration of these excursions permit intra basinal and inter basinal correlation which indicates that they probably represent a global change in seawater composition the occurrence of decoupled 13ccar 13corg with almost invariable 13corg values at wangjiapeng zhongling yangjiaping sections is consistent with remineralization of a dissolved organic carbon doc pool by means of sulfate reduction as recorded in en3 the synchronous presence of en3 a shift to higher 87sr 86sr and decrease of mn and fe contents and 15n values together points to a glacial influence whereby oxygenation and remineralization of reduced carbon produced 13c depleted dic glaciations cause a drop in sea level which itself leads to increased continental shelf area to be exposed to surface weathering and ultimately to enhanced delivery of radiogenic 87sr the increase of 87sr 86sr ratios sulfate and phosphate are consequences of surface runoff into oceanic environments and such perturbations induce biogeochemical changes

new lu hf and pb pb age constraints on the earliest animal fossils abstract the neoproterozoic doushantuo formation south china preserves a unique assemblage of early multicellular fossils and overlies rocks which are thought to have formed during an ice age of global extent the age of this formation is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon until now direct dating of sedimentary formations such as the doushantuo has been difficult and associated with large uncertainties here we show that dating of doushantuo phosphorites by a novel lu hf dating method and conventional pb pb geochronometry independently yield ages of 584 26 ma and 599 3 4 2 ma respectively these ages are in agreement with bio and chemostratigraphical observations and show that the doushantuo animal remains predate diverse ediacaran fossil assemblages making them the oldest unambiguous remains of metazoans currently known furthermore the pb pb age for the post glacial doushantuo rocks suggests that the neoproterozoic glaciation in china might predate glacial rocks in eastern north america commonly associated with the younger marinoan of two major neoproterozoic glaciations the combination of lu hf and pb pb dating shows considerable potential for dating other phosphorite successions and future application of these methods could therefore provide further constraints on proterozoic biological and environmental history

the biostratigraphic succession of acanthomorphic acritarchs of the ediacaran doushantuo formation in the yangtze gorges area south china and its biostratigraphic correlation with australia abstract abundant large acanthomorphic acritarchs from the ediacaran doushantuo formation in the yangtze gorges area south china are becoming useful tools for biostratigraphic subdivision and correlation of the ediacaran system despite limitations caused by facies control taphonomic bias and taxonomic problems based on thin section examination of chert samples collected from six sections of the doushantuo formation a clear stratigraphic distribution of acritarchs has allowed two assemblages of acanthomorphic acritarchs lower tianzhushania spinosa assemblage and upper tanarium anozos tanarium conoideum assemblage to be established these two assemblages which are found in the lower member ii and the upper member iii doushantuo formation respectively are constrained stratigraphically to the first and the second positive 13c excursions ep1 and ep2 respectively and are separated by a second negative 13c excursion en2 the lower t spinosa assemblage is dominated by the taxon t spinosa by comparison with the lower assemblage the upper t anozos t conoideum assemblage preserves more acanthomorphic acritarchs both in terms of number of individuals and in the diversity of the forms fifteen forms eotylotopalla delicata knollisphaeridium maximum echinosphaeridium maximum meghystrichosphaeridium magnificum schizofusa zangwenlongii sinosphaera rupina t anozos t conoideum tanarium irregulare variomargosphaeridium litoschum as well as the unnamed b c d e f and g forms are the predominant species in upper t anozos t conoideum assemblage among them the taxa t anozos and t conoideum occur in most great number and throughout the assemblage whereas the species t spinosa is presumed to have become extinct the upper t anozos t conoideum assemblage shares a number of species with the ediacaran complex acritarch palynoflora ecap in south and central australia including ceratosphaeridium glaberosum gyalosphaeridium pulchrum s zangwenlongii t conoideum t irregulare and v litoschum in addition the species t spinosa is not present in the ecap of australia hence the upper t anozos t conoideum assemblage of the doushantuo formation can be correlated with the ecap of south and central australia while the lower tianzhushania assemblage appears to be missing in south and central australia