rare earth geochemistry of old phosphorites and probability of syngenetic precipitation and accumulation of phosphate1in memory of richard p sheldon1 abstract old vendian early cambrian phosphorites of the world demonstrate seawater like patterns in their rare earth element ree distributions but are depleted in heavy ree they also show a broad range of variation in total and elemental abundances primary bedded structureless phosphorites contain only 15 ppm total ree ree while granular pelletal varieties contain up to 650 ppm ree were incorporated into phosphate grains diagenetically during prolonged periods of transport and redeposition a higher surface mass ratio in pelletal phosphorites contributed to their enrichment in the ree s in primary bedded structureless phosphorites immediate burial of phosphate syngenetically precipitated and accumulated in situ at the sediment water interface prevented the later incorporation of the ree large deposits of vendian early cambrian phosphorites have originated by both processes primary bedded varieties occur in deeper water facies and granular phosphorites accumulated closer to the shore in terms of their ree geochemistry old granular phosphorites are almost indistinguishable from their phanerozoic counterparts indicating that both were deposited by the same mechanisms primary bedded structureless phosphorites were only deposited on a large scale at the beginning of the phanerozoic

paleoenvironmental conditions of organic rich upper permian dalong formation shale in the sichuan basin southwestern china abstract organic geochemical and trace element analysis of a suite of 33 samples collected from the shangsi section of the upper permian dalong formation located near guangyuan in the northwestern sichuan basin have been used to better understand the marine depositional environment of its shale lithofacies a 15 m thick black shale interval near the middle of the formation is enriched in total organic carbon toc 1 1 14 4 mean 6 4 the n alkane terpane and sterane biomarker distributions of the shale suggest that its organic matter is of predominantly marine algal origin pr ph pr n c17 ph n c18 and gammacerane c30 hopane ratios demonstrate that reducing conditions prevailed during its deposition this interpretation is supported by the redox sensitive abundance of mo and the trace element redox ratios ni co v cr u th and v v ni all of which indicate deposition in a euxinic anoxic setting the mo toc relationship in the dalong shales plots mid way between those of sediments in the present day saanich inlet and cariaco basin suggesting a moderately restricted depocentre however the 13corg values of these shales reveal that their organic matter is isotopically much lighter than that found in modern euxinic sediments implying extremely anoxic bottom waters and a slow down of oceanic circulation during the late permian

late precambrian pennatulids sea pens from the eastern yangtze gorge china paracharnia gen nov abstract pennatulids preserved as membranous carbonised compressions from the shibantan member dengying formation sinian system in the eastern yangtze gorge hubei province represent the first genuine discovery of the late precambrian ediacara type metazoan remains in china the specimens were initially referred to charnia ford 1958 and described as c dengyingensis by ding and chen in 1981 a re examination of the type material and comparing it with other late precambrian frond like forms particularly those from the ediacara assemblage of south australia and from the charnwood assemblage of england indicate that this chinese species represents a distinct genus paracharnia gen nov its characteristic polyp leaves individually free standing on distinct leaf stalks along the lateral sides of the median stem resemble those of many living sea pens represented by pennatula and contribute a significant feature to the precambrian charniidae glaessner 1979 its close association with abundant macroscopic algal remains of vendotaenia sp and its proximity to the overlying basal cambrian small shelly fossil assemblages in the same succession emphasise its palaeontological and biostratigraphic significance

predatorial borings in late precambrian mineralized exoskeletons the late precambrian tube forming cloudina the earliest known animal to produce a mineralized exoskeleton shows evidence of having been attacked by shell boring organisms of more than 500 tubes from shaanxi province china 2 7 have rounded holes 40 to 400 micrometers in diameter the relation between the size of the holes and the width of the bored tubes suggests that the attacking organism was a predator selecting its prey for size if true this would be the oldest case of predation in the fossil record and would support the hypothesis that selection pressures from predation was a significant factor in the evolution of animal skeletons around the precambrian cambrian boundary

application of the ce anomaly as a paleoredox indicator the ground rules much attention has been paid in recent years to the potential application of the ce anomaly measured in various marine phases as a paleoceanographic indicator of widespread marine anoxia in this paper we present and discuss results from recent studies of present day rare earth element ree distributions and hence ce anomaly distributions in the marine environment which are particularly pertinent to paleoceanography subsequently we review and discuss the validity of the recent literature in which ce anomalies have been employed as paleoredox indicators

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

identification of primary ce anomaly signatures in fossil biogenic apatite implication for the cambrian oceanic anoxia and phosphogenesis based on ree analyses of 105 world wide distributed cambrian fossil apatite samples and eight late neoproterozoic phosphate concretions a close relationship is established between the concentrations of mree and ce anomalies shale la smn ratios of 0 35 is suggested as a critical value for the discrimination of the natural ce anomaly acquired during pre burial early diagenesis by biogenic apatite from an artificial ce anomaly induced due to the calculation ce anomalies in apatites with flat ree distribution and la smn ratio 0 35 may be used as indicative of oceanic anoxia

rare earth major and trace element composition of monterey and dsdp chert and associated host sediment assessing the influence of chemical fractionation during diagenesis abstract chert and associated host sediments from monterey formation and deep sea drilling project dsdp sequences were analyzed in order to assess chemical behavior during diagenesis of biogenic sediments the primary compositional contrast between chert and host sediment is a greater absolute sio2 concentration in chert often with final sio2 98 wt this contrast in sio2 and si al potentially reflects precursor sediment heterogeneity diagenetic chemical fractionation or both sio2 concentrations and si al ratios in chert are far greater than in modern siliceous oozes however and often exceed values in acid cleaned diatom tests compositional contrasts between chert and host sediment are also orders of magnitude greater than between multiple samples of the host sediment calculations based on the initial composition of adjacent host observed porosity reductions from host to chert and a postulated influx of pure sio2 construct a chert composition which is essentially identical to observed sio2 values in chert thus precursor heterogeneity does not seem to be the dominant factor influencing the current chert composition for the key elements of interest in order to assess the extent of chemical fractionation during diagenesis we approximate the precursor composition by analyzing host sediments adjacent to the chert the sio2 concentration contrast seems caused by biogenic sio2 dissolution and transport from the local adjacent host sediment and subsequent sio2 reprecipitation in the chert along with sio2 other elements are often added with respect to al to monterey and dsdp chert during silicification although absolute concentrations decrease the two monterey quartz chert nodules investigated in contrast to the opal ct and quartz chert lenses formed primarily by extreme removal of carbonate and phosphate thereby increasing relative sio2 concentrations dsdp chert formed by both carbonate phosphate dissolution and sio2 addition from the host manganese is fractionated during chert formation resulting in mno al 2 o 3 ratios that no longer record the depositional signal of the precursor sediment ree data indicate only subtle diagenetic fractionation across the rare earth series ce ce values do not change significantly during diagenesis of either monterey or dsdp chert eu eu decreases slightly during formation of dsdp chert la n yb n is affected only minimally as well during formation of one monterey opal ct chert lens ree al ratios show subtle distribution changes at gd and to a lesser extent near nd and ho ree compositional contrasts between diagenetic states of siliceous sediment and chert are of a vastly smaller scale than has been noted between different depositional environments of marine sediment indicating that the paleoenvironmental ree signature is not obscured by diagenetic overprinting

rare earth elements and stable isotope geochemistry of early cambrian chert phosphorite assemblages from the lower tal formation of the krol belt lesser himalaya india abstract the neoproterozoic cambrian transitional sequence in the mussoorie and garhwal hills of the lesser himalaya is represented by dolomites of the upper krol formation and chert phosphorite assemblages of the lowermost tal formation these rocks provide valuable information regarding the assumed existence of a stratified ocean during the terminal neoproterozoic and beginning of earliest cambrian nemakit daldynian the isotopic compositions of carbonate and organic carbon in the transition profile can be best interpreted as reflecting an oceanic anoxic event oae prior to the phase of early cambrian phosphate formation the chert phosphorite beds record negative ce and positive eu anomalies while ce is an important paleooceanic redox indicator eu is rather immobile under normal diagenetic conditions the observed eu anomaly is linked to the high ba content in these phosphorites and is indicative of an anoxic or sulfate reducing diagenetic environment the suggested stratification of the ocean during the late neoproterozoic and nemakit daldynian times would have been linked to the reduction of oxygen supply to the zone below the redoxcline causing 12 c and p rich organic matter previously produced in the photic zone to be trapped in large quantities within the deeper anoxic zone this would in turn increase the 13 c content of the water in the photic zone moreover in the deeper anoxic waters reduction of ce4 to ce3 would result in an enrichment of dissolved ce as ce3 upwelling of this anoxic bottom stratum would bring the 12 c and ce enriched waters back to the oxic marine realm however on entering the highly oxic productive zone the excess ce is expected to be removed from the water by oxidation to insoluble ce4 followed by precipitation or preferential scavenging due to these oxidation reactions the waters of the shallow oxic zone would tend to become rapidly depleted in ce in other words ocean mixing and upwelling during the early cambrian were ultimately responsible for the transport of 12 c p and ce to the oxic shelves sharp drops in both 13 c carb and 13 c org support the existence of oceanic anoxia followed by oceanic mixing at this juncture of earth history the large spread of the 34 s values of early diagenetic pyrites within the phosphorite bearing sequence in contrast to the limited spread of 13 c carb values suggests that phosphatisation took place under exclusively suboxic diagenetic non sulfate reducing condition and pyritisation began only when phosphate layers entered the zone of sulfate reduction

diagenetic constraints on the use of cerium anomalies as palaeoseawater redox proxies an isotopic and ree study of cambrian phosphorites seawater rare earth element ree distributions show heavy ree enrichment and cerium depletion but these characteristics are only rarely found in ancient marine authigenic minerals such as carbonate fluorapatite and calcite this enigma may be due to changing ree distributions in seawater through time or to post depositional redistribution of ree differentiating between these two factors is however far from straightforward as their relative importance is likely to vary and evidence is often ambiguous in this article we present ree as well as strontium and sulphur isotope data for basal cambrian phosphorites of south china which confirm the emerging rule of thumb that granular phosphorites seldom reveal extreme departures from the seawater norm and tend to undergo therefore less diagenetic alteration of ree spectra than skeletal apatites and other phosphate types this study reveals stratigraphic trends in ce anomalies ce ce that could be taken to imply the preservation of a palaeoenvironmental signal however further investigation of our data shows that such trends in phosphorites can also be caused by post depositional alteration which tends to 1 increase ree contents 2 reverse ce depletion 3 alter eu anomalies and 4 concentrate preferentially the middle ree mree further alteration which may be due to weathering has led to hree depletion and positive la and y anomalies tetrad effect this is the first study where ceanom and phosphate bound sulphate s isotope values could be compared for one particular stratigraphic section which provides us with an additional tool for the interpretation of diagenetic redox conditions least altered phosphorites from meishucun that yield a strongly negative ceanom constrain early cambrian seawater 34s to about 33 we conclude that phosphorite ceanom primarily records variations in the local conditions of diagenesis while outlining some special cases in which diagenetic redox conditions may broadly reflect local bottom water redox conditions

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

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

geochemical fluxes related to alteration of a subaerially exposed seamount nintoku seamount odp leg 197 site 1205 hole 1205a was drilled on nintoku seamount which lies in the midportion of the emperor seamount chain this seamount was emergent 56 myr ago but was submerged by 54 ma so the lavas have endured weathering in both subaerial and submarine environments we have studied the petrology mineralogy and geochemistry of intercalated altered basalts breccias and soil samples recovered at hole 1205a to quantify the chemical exchanges between the seamount and seawater and or meteoric fluids the secondary mineralogy is relatively uniform throughout the section and comprises smectite fe oxyhydroxides iddingsite and ca carbonates soils are composed of variably altered basaltic clasts in a matrix of kaolinite smectite and vermiculite with minor goethite hematite and magnetite throughout the basement section altered basalts breccias and soils are depleted in si mg ca na sr rb and ba and enriched in fe fe3 fet up to 1 18o up to 20 and 87sr 86sr ratios are strongly elevated relative to primary igneous values differences in the 87sr 86sr ratios define an upper alteration zone with 87sr 86sr close to 56 ma seawater 0 7077 from a lower alteration zone where 87sr 86sr are less elevated 0 704 the lower alteration zone likely reflects interaction with a subaerial oxidizing fluid at low temperature this zone probably retained most of the original subaerial weathering signature the upper alteration zone was altered through circulation of large quantities of cold oxidizing seawater that partially overprinted the subaerial weathering chemical characteristics altered samples were compared to estimated protolith compositions to calculate chemical gains and losses global chemical fluxes are calculated for the entire basement section using different lithological proportions models and different rates of oceanic island emplacement although the global construction rate of ocean islands is small compared to igneous accretion at mid ocean ridges the magnitude of the chemical changes indicates that ocean islands and seamounts may be a significant contributor to the chemical budget of the oceans

rare earth elements in seep carbonates as tracers of variable redox conditions at ancient hydrocarbon seeps marine hydrocarbon seeps are dynamic systems which are typically reflected in complex lithologies of limestones forming at these sites in order to test if seep limestones with their multiple generations of carbonate phases reflect variable redox conditions the rare earth element ree patterns of limestones from five ancient hydrocarbon seep localities hollard mound middle devonian iberg mississippian beauvoisin oxfordian canyon and satsop river oligocene and marmorito miocene have been investigated the total ree contents vary widely 0 3 43 7 p p m early microcrystalline phases tend to show higher contents than spatially associated later phases microspar sparite and blocky cement the shale normalized ree patterns of the carbonates show both negative and positive ce anomalies even for individual deposits suggesting that the redox conditions varied significantly it is apparent that in addition to anoxic conditions oxic conditions were common in some ancient seep environments intermittent oxygenation is presumed to have resulted from abrupt changes in fluid flow

multiple controls on the paleoenvironment of the early cambrian marine black shales in the sichuan basin sw china geochemical and organic carbon isotopic evidence abstract in order to understand the paleoenvironment of the early cambrian black shale deposition in the western part of the yangtze block geochemical and organic carbon isotopic studies have been performed on two wells that have drilled through the qiongzhusi formation in the central and southeastern parts of sichuan basin it shows that the lowest part of the qiongzhusi formation has high toc abundance while the middle and upper parts display relative low toc content redox sensitive element mo and trace elemental redox indices e g ni co v cr u th and v v ni suggest that the high toc layers were deposited under anoxic conditions whereas the low toc layers under relatively dysoxic oxic conditions the relationship of the enrichment factors of mo and u further shows a transition from suboxic low toc layers to euxinic high toc layers on the basis of the mo toc relationship the qiongzhusi formation black shales were deposited in a basin under moderately restricted conditions organic carbon isotopes display temporal variations in the qiongzhusi formation with a positive excursion of 13 c org values in the lower part and a continuous positive shift in the middle and upper parts all these geochemical and isotopic criteria indicate a paleoenvironmental change from bottom anoxic to middle and upper dysoxic oxic conditions for the qiongzhusi formation black shales the correlation of organic carbon isotopic data for the lower cambrian black shales in different regions of the yangtze block shows consistent positive excursion of 13 c org values in the lower part for each section this excursion can be ascribed to the widespread early cambrian transgression in the yangtze block under which black shales were deposited

paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite abstract rare earth element concentrations in biogenic apatite of conodonts fish debris and inarticulate brachiopods were determined in over 200 samples from cambrian to modern sediments tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory interexperiment or interspecies related variations clearly show that no resolvable fractionation of ree occurs incorporation of ree in biogenic apatite of recent fish debris occurs near the sediment water interface soon after deposition and reflects characteristics of seawater the original ree signature apparently survives subsequent burial and diagenesis cerium variations in fish debris from modern environments are controlled by redox potential ce is fractionated by co precipitation with metallic oxides under oxidizing conditions this fractionation produces a negative ce anomaly ce anom in seawater that is reflected in the sedimented fish debris conversely no fractionation of ce occurs under reducing conditions resulting in ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions extrapolation of observations of the redox control of ce anom in modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower paleozoic and lower triassic oceans whereas in the upper paleozoic the world ocean was generally oxidizing

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

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

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

high resolution p t t paths from δ18o zoning in titanite a snapshot of late orogenic collapse in the grenville of new york we characterize oxygen isotope zoning within single titanite crystals from the carthage colton mylonite zone ccmz adirondack mountains new york state united states by ion microprobe smooth gradients of 18 o up to 0 6 over 90 m resulted from diffusive exchange of oxygen during cooling from peak metamorphic temperatures of 650 700 c modeling of the observed profile indicates punctuated cooling rates of 30 60 c m y along the ccmz set within long periods of much slower cooling these results indicate a previously unrecognized period of rapid cooling along the ccmz that is interpreted to result from the post ottawan collapse of the grenville mountain belt and exhumation of the central adirondack highlands at ca 1050 ma

application of the apatite oxygen paleobarometer aop across the neoproterozoic cambrian transition abstract fluorescence signatures of samarium3 substituted into apatite for calcium2 have been shown experimentally to correlate with oxygen availability such substituted apatite being a principal diagenetic mineral emplaced in shallow water environments during the neoproterozoic cambrian global phosphogenic event coeval with the cambrian explosion of life the occurrence of sm3 substituted apatite encrusting infilling and permineralizing components of shallow water microbial communities suggested that quantification of these fluorescence signatures might provide a widely applicable mineral based paleobarometer by which to measure oxygen concentrations in the environment in which such apatite precipitated to test this hypothesis fluorescence spectroscopic analyses have been carried out on the sm3 substituted apatite of photic zone microscopic fossils and fossil associated ooids of near shore facies of the ediacaran doushantuo south china and early cambrian chulaktau south kazakhstan formations and of the open ocean apatite biomineralized phytoplanktonic scale fossils characodictyon of the mid neoproterozoic tonian fifteenmile group yukon canada results obtained quantified by the newly devised apatite oxygen paleobarometer metric indicate a low

paleo sedimentary environment in relation to enrichment of organic matter of early cambrian black rocks of niutitang formation from xiangxi area china abstract early cambrian organic rich black rocks are extensively distributed in the southern china in this study we have discussed the relation of paleo sedimentary environments with enrichment of organic matter based on toc data we divided the niutitang formation into three parts upper middle and lower the amount of total organic carbon in the lower 1 55 wt and the upper part 1 35 wt of niutitang formation is significantly smaller than the middle part 8 0 wt which suggest initial transgression and regression stages of the sea level respectively the middle part from both sections longbizui and sancha contains higher toc content which is a clue of intense transgression stage of sea level with high bio productivity kerogen type index kti using different macerals specify the organic matter in these black rock series is mainly type i with a minor amount of type ii1 moreover these black rocks were deposited in weak to moderately restricted hydrographic conditions the heterogenic mineral composition was also observed in these black rocks including quartz clay gypsum pyrite barite dolomite and plagioclase quartz content in the middle part is relatively higher than the upper and the lower part displays a strong positive relation with toc which suggests the main source of quartz during deposition of the middle part was biogenic quartz during early cambrian period due to extension between the yangtze and the cathaysian plate the hydrothermal fluids rich in uranium vanadium molybdenum zinc barium etc from the deeper part of the earth crust and entered the ocean basin through extensional remnant fissures and cracks and due to upwelling phenomena entered to the shelf area these nutrient rich deep crustal fluids at the surface of the sea enhanced the evolution and breeding of planktons and other marine life meanwhile it upsurges the bio productivity additionally it creates bottom water hypoxia which is favourable for the preservation of organic matter in the sedimentary rocks the main factors responsible for the enrichment of organic matter in these early cambrian black rock series of niutitang formation were a hydrographic restriction hydrothermal activities and paleo redox conditions respectively

eumetazoan fossils in terminal proterozoic phosphorites phosphatic sedimentary rocks preserve a record of early animal life different from and complementary to that provided by ediacaran fossils in terminal proterozoic sandstones and shales phosphorites of the doushantuo formation south china contain eggs egg cases and stereoblastulae that document animals of unspecified phylogenetic position small fossils containing putative spicules may specifically record the presence of sponges microfossils recently interpreted as the preserved gastrulae of cnidarian and bilaterian metazoans can alternatively be interpreted as conventional algal cysts and or egg cases modified by diagenetic processes known to have had a pervasive influence on doushantuo phosphorites regardless of this interpretation evidence for doushantuo eumetazoans is provided by millimeter scale tubes that display tabulation and apical budding characteristic of some cnidaria especially the extinct tabulates like some ediacaran remains these small benthic colonial fossils may represent stem group eumetazoans or stem group cnidarians that lived in the late proterozoic ocean

δ18o and ree contents of phosphatic brachiopods a comparison between modern and lower paleozoic populations 18o values of both carbonate 18 7 25 1 and phosphate 15 1 16 7 components of the francolite from the fossil brachiopod shells are interpreted as the result of a partial resetting of pristine isotopic compositions the similarity of hat shape ree patterns of some lower ordovician linguloids with those of extant littoral specimens suggests the preservation of a 500 myr old record of ree marine chemistry in agreement with the known paleogeography the phosphatic brachiopods have been deposited in a coastal environment under shallow and oxygenated marine waters however the contents and distribution of ree in some strongly altered brachiopod shells reveal an alteration of the original negative ce anomalies and both nd and sm enrichments that transformed the initial hat shape patterns of linguloids into strongly convex or bell shape patterns

seep carbonates and preserved methane oxidizing archaea and sulfate reducing bacteria fossils suggest recent gas venting on the seafloor in the northeastern south china sea seep carbonates formed by the synergistic metabolism of methane oxidizing archaea moa and sulfate reducing bacteria srb have been found in many places worldwide but have not been found to date in the south china sea mud volcanoes and shale diapirs have been reported in the south china sea however and microscope and geochernical analysis of carbonates dredged where bottom simulating reflectors bsr suggest the presence of gas hydrate on the northeastern continental slope of the south china sea suggest that the carbonates are hydrocarbon seep related carbonates the carbonates we dredged are chimney like and preserve moa srb fossils their very light carbon isotopic compositions 51 25 to 51 76 parts per thousand suggest that their carbon was derived from microbial methane oxidization these seep carbonates and their preserved moa srb fossils imply gas venting has occurred recently on the seafloor in the northeastern continental slopes in the south china sea c 2005 elsevier ltd all rights reserved

the ree and end of 40 70 ma old fish debris from the west african platform ree concentrations and nd isotopic compositions have been determined in late cretaceous early cenozoic fish debris from west african and israeli platform sediments and show a strong regional control independent of time except for those from the northern morocco it is suggested that although diagenetic fluids do not contribute ree s directly to the phosphatic debris they may significantly change the ce anomaly and the end t value of the epicontinental seas which in turn control the ree in marine phosphates it is shown that over the investigated period the north moroccan shelf seawater was progressively flushed by deep north atlantic water

rare earth element contents of jurassic fish and reptile teeth and their potential relation to seawater composition anglo paris basin france and england the rare earth element ree chemistry of jurassic shelf seawater from western europe anglo paris basin was investigated by analyzing the fish and reptile teeth deposited in shallow to deeper water 200 m environments ree patterns in apatites are controlled by the host sediments vertebrate teeth sampled from the siliciclastic sediments calcareous sandstones and shales show flat shale normalized ree patterns that reflect the dominant influence of the continental source from which the ree were derived carbonate deposits protected from the clastic sources contain fish and reptile teeth whose ree patterns reflect more accurately the ree composition of the overlying water column the ree patterns are similar through the bajocian to the oxfordian and are characterized by a depletion in heavy rare earth element dy ybn 1 8 5 0 compared to modern seawater compositions dy ybn 0 8 0 9 the fractionations among hree in the jurassic seawater are more efficient than in modern oceans and increases with depth instead of decreasing these hree removal processes operated as early as the paleozoic and disappeared during the late cretaceous the fractionation of hree relative to lree is correlated with the increasing depth of the basin as indicated by two independent criteria that are the sedimentary structures and the oxygen isotope composition of coexisting brachiopods the dy ybn ratio of the marine biogenic phosphates can be used as a proxy of paleo water depths at the scale of a water mass ce anomalies ce in biogenic apatite bearing limestones are variable and systematically negative relative to modern surface seawater and bathonian values mean ce 0 63 0 10 weak ce anomalies during the callovian mean ce 0 21 0 09 suggest the onset of more reducing conditions this redox change coincided with an increase of seawater temperatures as suggested by the oxygen isotope compositions measured on the same teeth we speculated that the callovian low ce could result from a decrease in the po2 due to the warming of seawater

the ree composition and petrography of apatite in 2ga zaonega formation russia the environmental setting for phosphogenesis the first significant p rich deposits appear in the global rock record during the paleoproterozoic around 2 ga however the specific triggers that led to apatite precipitation are still under debate the ca 2 ga zaonega formation karelia russia contains p rich intervals in its upper part with abundantly occurring apatite these apatites have been studied for their rare earth element ree composition using laser ablation inductively coupled plasma mass spectrometry la icp ms with an emphasis on the environmental condition during phosphogenesis petrographic observations by scanning electron microscopy sem integrated with la icp ms results allow recognition of variously recrystallized apatite and distinction of best preserved diagenetic apatite which presumably records syn depositional ree characteristics diagenetic apatite exhibits moderately negative ce anomalies that indicate an at least partially oxygenated water column a variable but typically positive eu anomaly is consistent with geologic evidence suggesting intensive magmatic activity and hydrothermal influence during apatite precipitation we conclude that phosphatic sediments in the paleoproterozoic zaonega formation record phosphogenesis in a vent seep influenced setting that experienced fluctuating redox conditions at the sediment water interface

paleo climatic and paleo environmental evolution of the neoproterozoic basal sedimentary cover on the rio de la plata craton argentina insights from the δ13c chemostratigraphy abstract the sierras bayas group of the tandilia system constitutes the neoproterozoic sedimentary cover of the rio de la plata craton in argentina that accumulated amid the breakup of the rodinia supercontinent and subsequent assembly of gondwanaland evidence for glaciation in the villa monica formation vmf at the base of the succession comes in the form of iron rich laminated sediments containing dropstones composed predominantly of basement crystalline rocks and quartzites that are sequentially overlain by a phosphatic mudstone and a 40 m thick stromatolitic dolomite subtidal facies preserve columnar forms similar to post glacial tubestone stromatolites seen in the neoproterozoic records these morphologies suggest rapid growth associated with elevated seawater alkalinity and high rates of carbonate accumulation records the vmf dolomites in our four studied sections near olavarria sierras bayas area reveal a pronounced negative to positive 13 c up section that is similarly to these cap carbonates and others worldwide our sedimentological and geochemical study of the vmf sections reveal consistent carbon and oxygen isotope trends that may be useful for detailed intra basinal correlations samples of the vmf fabric retentive dolomite preserve an unusually narrow range of non radiogenic strontium isotopic compositions 0 7068 to 0 7070 that are consistent with cryogenian limestone facies in the potential namibian and brazilian equivalents exceptional preservation of 87 sr 86 sr compositions suggest the possibility of primary dolomite precipitation in post glacial seawater and furthermore that ree patterns and distributions may yield similar insights to redox conditions in the depositional basin in particular the vmf dolomites reveal depleted lree abundances a negative ce anomaly positive la and gd anomalies and low y ho values as a whole these observations suggest oxidizing post glacial seawater conditions associated with significant freshwater inputs into the basin global warming and increases in primary productivity and organic carbon burial linked to the buildup of oxygen the positive 13 c trend and the increase in stromatolite biodiversity in the vmf

palaeoenvironment and carbon isotope stratigraphy of upper proterozoic carbonates of the yangtze platform the 13c values for phanerozoic marine carbonates display secular trends mainly in the range 1 to 2 1 these have been interpreted as primary features reflecting changes in the carbon isotope composition of dissolved bicarbonate in seawater brought about largely by variations in the proportions of carbon being sequestered in the oxidized and reduced carbon reservoirs1 2 carbon isotope trends are not as well established for the precambrian but there are indications that upper proterozoic sequences contain carbonates with unusually high 13c values3 9 here we present the results of the first carbon isotopic study of the upper proterozoic carbonate strata from the type locality of the sinian system in the yangtze gorges sections near yichang south china and discuss their implications for accumulation of organic matter we also compare the results for these chinese strata with 13c trends in other upper proterozoic cambrian sequences and assess the extent to which such isotopic data can be used to make stratigraphic correlations between widely spaced sequences

lower cambrian apatitic stromatolites and phospharenites related to the glacio eustatic cratonic rebound sahara algeria abstract at the end of the early cambrian glacial event occurring on the west african craton the tillite surface was marked especially in the northeastern part of the taoudenni basin by noticeable topographic relief after deglaciation the eustatic rise in sea level led to deposition over all the west african craton of a thin but widespread carbonate unit containing lower cambrian shelly fossils at the ice cap periphery isostatic rebound of the craton resulted in uplift of the topographic highs and weathering of the carbonate during fluctuations of relative sea level before the return to marine transgressive conditions a succession of events took place first in the submerged areas stromatolitic phosphorite in flat domal to columnar buildups accreted followed by growth of dolomitic ministromatolites laterally phospharenitic beds oncolites and phosphatic grains accumulated under water in the depressions the stromatolites and oncolites are made of carbonate fluorapatite characteristic of coastal environments glauconite is closely related to apatite and suggests conditions of a sea level rise in respect to phosphatization precipitation of dolomite calcite and evaporite postdates phosphatization and glauconitization indicating a regression and a chemical concentration due to a warm and perhaps arid climate apatitic stromatolites and oncolites resulted from in situ precipitation within bacterial mats this phosphogenesis corresponds to the major early paleozoic phosphogenetic event

the development of middle rare earth element enrichments in freshwaters weathering of phosphate minerals abstract many phosphatic minerals of biogenic authigenic and diagenetic origin are distinguished by rare earth element ree compositions which have a well developed middle rare earth element mree enrichment defined by a gradual increase in the shale normalized ratios of ree toward the middle of the ree series la to lu also the ree composition of dissolved matter in the waters of the amazon fly and sepik rivers as well as other river lake and ground waters have well developed mree enrichments the development of mree enrichments was studied through a series of leaching experiments using river bank sediments from the amazon fly sepik and mississippi rivers a well characterized phosphate mineral rich shale with a pronounced mree enrichment in its bulk composition was also leached in order to better assess the relationship between the weathering of phosphate minerals and the formation of mree enriched solutions the two leaching solutions per sediment consisted of filtered lake water at ph 5 and the same water adjusted to ph 2 leaching experiments with the four river sediments result in extensive fractionation whereby the ree compositions of the solutions develop mree enrichments from starting sediments that show no mree enrichments the ph 2 leachates have much higher concentrations of the ree and more fully developed mree enrichments than do the ph 5 leachates the mree enrichments at ph 2 usually form within an hour of starting the experiments the phosphatic shale results show that there is preferential release of large amounts of mree at ph 5 as well as at ph 2 demonstrating the weather ability of the phosphatic minerals at phs of natural freshwaters the sepik river ph 5 experiment also shows significant mree enrichment under near neutral conditions the development and retention of the mree enrichments in the leaching solutions is accompanied by an increase in dissolved phosphate concentrations although the magnitudes of the mree enrichment do not directly correlate with the percent of phosphate released the experimental data suggest that the preferential dissolution of phosphatic minerals during weathering can result in extensive ree fractionation between bulk river sediment and water leading to freshwaters with mree enrichments

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

rare earth geochemistry of phosphorites abstract the abundance of rare earth elements ree s in francolite increases with increasing age as a result of post depositional enrichment abundances are higher in pelletal samples than in non pelletal ones because the higher surface mass ratio of pelletal francolite promotes enrichment during diagenesis onshore francolite has higher ree abundances than that found offshore distribution patterns in francolite may be similar to those reported for open ocean water or shale depending upon the dominant source of the ree s different patterns result from weathering and deep burial diagenetic modification of the original patterns and abundances negative ce anomalies occur in francolites containing structural sulphur that is isotopically indistinguishable from seawater of the same age zero or positive anomalies occur in francolites which contain sulphur that is isotopically lighter than seawater

distribution of rare earth and some trace elements in tertiary phosphorites from the senegal basin and their weathering products abstract the distribution of rare earth and some trace elements is studied in the eocene phosphate deposits of farim saliquinhe lam lam and n diendouri ouali diala from the mauritania senegal guinea basin the depth of weathering varies between the three deposits the strong weathering of lam lam is marked by the leaching of apatites ca phosphate and the appearance of epigenetic crandallites al ca phosphate in the void spaces that have resulted from leaching of apatites and then of crandallites ferruginous and kaolinitic fillings are epigenised in millisites al ca phosphate all the studied phosphates have high ree ba and sr abundances and present shale normalized patterns with a negative ce anomaly of variable intensity clay minerals of sediments smectites and of weathered rocks kaolinites are characterized by low ree and high v zn cu cr sc and zr abundances they have no ce anomaly the comparison of the ree patterns and of the trace element abundances lead to three important conclusions at first the genesis of al ca phosphates is marked by specific leaching of heavy ree relative to the light ones then millisites have a ree abundance and a ce anomaly less pronounced than those of apatites and crandallites they show also v zn cu cr sc and zr abundances like clay minerals these facts can be related to their epigenetic formation from clay minerals last but not least the negative ce anomaly of epigenetic crandallites follows the same trend as in apatites therefore this anomaly cannot constitute a proof of the primary character for apatites if such variations should be related to the paleogeographic setting of studied deposits they must be considered with prudence

spatial and temporal variations in carbon and sulfur isotopic compositions of sinian sedimentary rocks in the yangtze platform south china abstract eight stratigraphic sections from the yangtze platform south china were selected for a study of spatial and temporal variations in carbon and sulfur isotope compositions of sinian sedimentary rocks carbon isotope compositions of carbonate from lower sinian strata deposited between pulses of glacial diamictite range from 3 9 to 9 9 the more negative values recorded from mn carbonates suggest that in part the carbon was derived from the oxidation of organic matter during early diagenesis in the upper sinian strata 13c varies with the facies they are positive for the platform carbonates whereas they are negative from about 3 to 12 for the carbonates formed in or near basin environments it is evident that post depositional alteration accounts for the strongly negative 13c values however some information on primary isotopic compositions can be obtained by evaluating sample quality the primary 13c values of carbonates from the doushantuo formation are ca 3 to 4 and from the dengying formation as low as 6 34s values for pyrite from the lower sinian rocks are highly positive and range from values near the coeval seawater sulfate up to ca 60 in contrast 34s values for pyrite from the upper sinina rocks are negative down to 27 to 30 the feature of sulfur isotopic composition for the lower sinian rocks is consistent with the late proterozoic sulfur isotopic record it might be explained by the supercontinent model many basins on the yangtze block in a supercontinent tectonic background had limited or no access to the open ocean and the basin waters contained sulfate with considerably higher 34s values than the coeval seawater for a geologically long period an alternative explanation is based on the sulfate minimum zone smz modal because of the slow sinking of organic matter bacterial sulfate reduction would be important in the lower sinian shallow water environment particularly in the smz the residual sulfate might have been significantly enriched in 34s so that pyrite produced in closed diagenetic system would yield very positive 34s values

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