neoproterozoic snowball earth simulations with a coupled climate ice sheet model ice sheets may have reached the equator in the late proterozoic era 600 800 myr ago according to geological and palaeomagnetic studies possibly resulting in a snowball earth but this period was a critical time in the evolution of multicellular animals posing the question of how early life survived under such environmental stress here we present computer simulations of this unusual climate stage with a coupled climate ice sheet model to simulate a snowball earth we use only a reduction in the solar constant compared to present day conditions and we keep atmospheric co2 concentrations near present levels we find rapid transitions into and out of full glaciation that are consistent with the geological evidence when we combine these results with a general circulation model some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

rare earth element characteristics of paleoproterozoic cap carbonates pertaining to the sausar group central india implications for ocean paleoredox conditions abstract the paleoproterozoic era is marked by significant changes in the level of oxygen in the atmosphere and chemistry of the ocean and the presence of world wide glaciation geochemistry of chemogenic sediments provide clues to these changes the sausar group 2478 2250 ma of central india is one of the few places in the world where paleoproterozoic glacial unit overlained by a cap carbonate horizon has been identified major trace and rare earth element ree contents of paleoproterozoic cap carbonates of the sausar group have been analysed for their implications for ocean redox conditions during interglacial periods of the huronian glaciation the la la gd gd lusn lasn and y ho ratios of the cap carbonate reflect their pristine marine nature conspicuous ce anomaly ce ce up to 1 75 accompanied by the enrichment of fe mn zn and u provides insight into the redox state of the ocean at the time of deposition of the cap carbonate succession based on these observations we infer anoxic depositional conditions in the basin during the interglacial period of the paleoproterozoic glaciation before the great oxidation event goe and the level of oxygen in the atmosphere fluctuating between 10 5 and 10 2 of the present atmospheric level pal

rare earth patterns with positive cerium anomaly in alkaline waters from lake van turkey abstract the distribution of rare earth elements has been studied for aerobic alkaline ph 9 6 carbonate rich waters from lake van turkey shale normalized ree ree sn patterns display an almost linear increase from the light to the heavy rees and strong positive ce sn anomalies there exist neither positive nor negative gd sn anomalies the ree sn patterns are consistent with domination of ree speciation in solution by poly carbonato complexes generating enrichment of the heavy rees that is even more pronounced than that seen in seawater this is the first report of positive ce sn anomalies observed in ree sn patterns of aerobic natural waters these anomalies apparently result from stabilization of penta carbonato ce iv complexes in solution leading to enhanced abundances of ce in comparison with its trivalent ree neighbours thus in remarkable contrast to seawater positive ce sn anomalies may be general features of alkaline carbonate rich and aerobic lake waters

oxidative mobilization of cerium and uranium and enhanced release of immobile high field strength elements from igneous rocks in the presence of the biogenic siderophore desferrioxamine b abstract polyvalent trace elements such as the high field strength elements hfse are commonly considered rather immobile during low temperature water rock interaction hence they have become diagnostic tools that are widely applied in geochemical studies we present results of batch leaching experiments focused on the mobilization of certain hfse y zr hf th u and rare earth elements from mafic intermediate and felsic igneous rocks in the presence and absence respectively of the siderophore desferrioxamine b dfob our data show that dfob strongly enhances the mobility of these trace elements during low temperature water rock interaction the presence of dfob produces two distinct features in the rare earths and yttrium rey patterns of leaching solutions regardless of the mineralogical and chemical composition or the texture of the rock type studied bulk rock normalized rey patterns of leaching solutions with dfob show i a very distinct positive ce anomaly and ii depletion of la and other light rey relative to the middle rey with a concave downward pattern between la and sm these features are not observed in experiments with hydrochloric acid acetic acid or deionized water in dfob bearing leaching solutions ce and u are decoupled from and selectively enriched relative to light rey and th respectively due to oxidation to ce iv and u vi oxidation of ce3 and u4 is promoted by the significantly higher stability of the ce iv and u vi dfob complexes as compared to the ce iii and u iv dfob complexes this is similar to the relationship between the ce iv and ce iii pentacarbonate complexes that cause positive ce anomalies in alkaline lakes however while formation of ce iv carbonate complexes is confined to alkaline environments ce iv dfob complexes may produce positive ce anomalies even in mildly acidic and near neutral natural waters siderophore promoted dissolution processes also significantly enhance mobility of other immobile hfse and may not only cause or modify ce anomalies and th u fractionation but also mobilization of and fractionation between zr hf th and redox insensitive rey during weathering pedogenesis diagenesis and incongruent dissolution of particles in seawater and freshwater siderophores may significantly affect the use of hfse as geochemical tools concave downward light rey patterns may be used as a biosignature for water rock interaction in the presence of siderophores enhanced and preferential mobilization of u relative to th in the presence of siderophores may produce th u signals comparable to those indicative of weathering under oxidized conditions which might constrain the use of u concentrations and th u ratios as a paleoredox proxy the enhanced mobilization of zr and especially hf from igneous rocks in the presence of dfob might have implications for the use of the latter as a tracer for the impact of continental weathering on seawater chemistry because siderophore complexes affect the particle reactivity of hf and zr they may prevent effective removal of terrigenous hf and zr during aggregation coagulation of riverine particles in estuaries siderophore promoted solubilization and stabilization might hence be an additional way to transport continental hf and zr to the oceans furthermore siderophore enhanced mobilization may also have implications for the remediation techniques employed to immobilize hfse such as u th and rey at nuclear waste and reprocessing sites and at rey ore processing plants where soils are commonly contaminated with these sometimes radioactive heavy metals

broadband hydroseismograms observed by closed borehole wells in the kamioka mine central japan response of pore pressure to seismic waves from 0 05 to 2 hz 1 we obtained broadband hydroseismograms by monitoring the pore pressure changes of a rock mass in the kamioka mine using borehole wells the wellhead was sealed to maintain an undrained condition under which there is no flow of water through the interface between the well and the rock mass this reduces the wellbore storage effect which can cause a high frequency cutoff response for systems of conventional open wells and rock mass using these closed borehole wells 16 hydroseismograms were recorded for earthquakes in a range of magnitudes of 4 5 7 9 and epicentral distances of 1 0 71 6 direct p waves sv waves converted to p and rayleigh phases are clearly observed on the hydroseismograms the similarity between hydroseismograms and seismograms reveals a clear relationship between radial ground velocity and pore pressure the relationship is expressed as a zero order system which is characterized by no distortion or time lag between the input and output and the pore pressure has no coupling with shear deformation these results are consistent with an undrained constitutive relation of linear poroelastic theory and confirm that the relation is valid for the seismic frequency range we determined in situ values of pore pressure sensitivity to volumetric change of the rock mass which were then used to estimate in situ skempton coefficients with values of 0 70 0 85

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

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

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

assessing the utility of fe al and fe speciation to record water column redox conditions in carbonate rich sediments abstract geochemical proxies based on fe abundance fe al and fe speciation have been widely applied to marine sediments in order to unravel paleo depositional redox conditions though geological time to date however these fe proxies have only been calibrated in relation to modern and ancient fine grained siliciclastic marine sediments this clearly limits their use particularly in relation to carbonate rich sediments and rocks to address this we here explore the applicability of fe based redox proxies in carbonates through three approaches first we have compiled fe al data for modern marine sediments to investigate variability in fe enrichments as a function of carbonate content and depositional setting second we have expanded this approach with a compilation of new and existing fe speciation data for modern and ancient marine sediments deposited under oxic and euxinic anoxic sulfidic water column conditions finally we show new data from paired limestone and dolomite sample sets to demonstrate the potential significance of deep burial dolomitization on the fe speciation redox proxy modern marine sediments deposited under oxic conditions show no relationship between fe al and carbonate content these sediments have an average fe al ratio of 0 55 0 11 with some higher values potentially being attributable to steady state early diagenetic remobilization of fe towards the sediment water interface in contrast significant fe al enrichments occur as a consequence of water column fe mineral formation and deposition either under anoxic conditions or due to input of anoxic hydrothermal fluids into oxic seawater iron speciation data also show no direct correlation with carbonate content and instead three groups can be distinguished based on total fe fe t and organic c contents sediments deposited under oxic water column conditions with fe t 0 5 wt generally plot below the lower fe hr fe t siliciclastic reference threshold 0 38 for distinguishing anoxic environments regardless of carbonate content also consistent with siliciclastic calibrations carbonate rich sediments deposited under anoxic water column conditions tend to have fe hr fe t ratios 0 38 in contrast oxic carbonate rich sediments with low fe t hr fe t ratios suggesting that the use of fe speciation for such samples is not appropriate for evaluating water column redox conditions taken together our data suggest that an fe t content of 0 5 wt rather than carbonate content represents the most suitable basis for identifying whether carbonate rich sediments are appropriate for fe based redox proxy analyses analysis of burial dolostones suggests that the fe speciation proxy may also be compromised by deep burial dolomitization where there has been a source of mobile fe to enrich rocks during recrystallization however pre screening can identify such samples this new assessment expands the utility of fe based redox proxies to also incorporate appropriate carbonate rich rocks provided that care is taken to assess the possible impact of deep burial dolomitization

the behavior of rare earth elements in seawater precise determination of variations in the north pacific water column abstract we present new highly precise and accurate data for ten rare earth elements rees in two water column profiles and in bottom waters from three additional localities in the north pacific our results presented here and in an earlier publication indicate that the water column in the western north pacific is stratified with respect to the isotopic composition of nd as well as nd la sm nd and er la both the nd isotopic and the ree data show that ree transport is strongly influenced by horizontal advection even in the sluggish circulation of the pacific in general rees increase in concentration with depth at mid latitude they reach a maximum concentration at about 3000 m and then decrease to the bottom at high latitude heavy rees reach a maximum concentration near 3000 m whereas light rees continue to increase in concentration with depth the deep water maximum and bottom water depletion is interpreted as an advective feature resulting from the flow of a lower concentration of rees in antarctic bottom water under a higher concentration of rees in the north pacific concentrations of rees do not show a linear relationship with those of si indicating that the ree cycle is not directly coupled to that of the si cycle ree element ratios i e nd la correlate with hydrographie properties which suggests that major features of the ree patterns may be conserved during lateral transport comparison of our ree data to those in previously published reports on pacific seawater shows that the identification of ree distributions affected by advection is only made possible by the high precision analysis we developed for this study the ce concentration we observe is relatively constant over 200 4500 m depth at both sites where we have complete profiles this unique constancy of ce is in contrast to the contiguous rees la and nd which show substantial concentration variations with depth

trace metal evidence for changes in the redox environment associated with the transition from terrigenous clay to diatomaceous sediment saanich inlet bc abstract we measured the concentrations of redox sensitive trace metals mn v mo u cd and re in sediments from odp leg 169s hole 1033b in saanich inlet british columbia to determine changes in redox conditions associated with the onset of laminated sediments at 12 5 kyr the most striking result is a large peak in authigenic re along with detrital levels of mo at the glacial terrigenous clay diatomaceous sediment transition in contrast the underlying glacial terrigenous clay which extends throughout the bottom section of the core is chemically similar to detrital concentrations either cowichan river particulates or average shale values these data suggest a period of oxic bottom waters but reducing pore waters this could be due to the dramatic transformation of saanich inlet during the late deglaciation from an open bay to an inlet which restricted circulation and slowed bottom water oxygen renewal a peak and gradual increase in authigenic mn in younger sediments subsequent to the re peak suggests that increasingly oxic conditions followed the authigenic enrichment in re these conditions could be connected to the younger dryas cooling period which was coincident with an increase in well oxygenated upwelled waters on the west coast of north america that form the bottom waters of saanich inlet metal concentrations in a gray clay bed 11 kyr are similar to their concentrations in the glacial terrigenous clay implying that they have a common source authigenic enrichments of re with little authigenic mo and cd suggest that before the deposition of this bed bottom waters were oxic and pore water oxygen was consumed in the top centimeter or less laminations above the clay layer suggest anoxic conditions which are also indicated by higher authigenic mo and cd and slightly lower re mo ratios in these sediments the basin remained mostly anoxic after the gray clay was emplaced as seen by continuous authigenic enrichment of the redox sensitive trace metals these results are consistent with increased stratification of the water column brought about by an influx of fresh water to the basin by a large flood

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

enrichment of redox sensitive trace metals u v mo as associated with the late hauterivian faraoni oceanic anoxic event the faraoni level is a short lived oxygen deficient event that took place during the latest hauterivian in order to improve our understanding of the palaeoenvironmental conditions that occurred during this event we have analysed the contents of several redox sensitive trace elements u v mo as co cd cu zn ni pb cr from bulk limestone samples of late hauterivian early barremian age from three reference sections u v mo and as show consistent and significant enrichments during the faraoni event whereas the other redox sensitive trace elements analysed here are not systematically enriched in order to explain this discrepant behaviour we propose that the faraoni level was deposited during a period of anoxic conditions near the sediment water interface the distinctive peaks in u v mo and as contents are traceable throughout the three studied sections and represent a good correlation tool which helps to identify the faraoni level and its equivalents in the western tethyan realm and outside of the tethys for example a peak in u contents in upper hauterivian sediments of the northwestern pacific realm odp leg 185 site 1149 may well be an expression of the faraoni event in this particular basin

identification of earthquake signals from groundwater level records using the hht method summary coseismic signals of groundwater levels are generally obtained by subtracting the responses of atmospheric pressure earth tides and precipitation from the observed data however if the observations are conducted without nearby barometers pluviometers or earth tide data for correction coseismic signals are often difficult to extract in this case the hilbert huang transform hht is used to obtain the instantaneous frequencies and amplitudes for every point of the decomposed intrinsic mode functions imfs from groundwater level data for differentiating the related frequency dependent responses without a further auxiliary input the extracted coseismic signals show intense amplitude pulses that are clearly seen in the third imf in addition two types of coseismic signals can be readily distinguished in the results from the hht transform one is an instantaneous short time signal induced by the passing of seismic waves another coseismic signal is a sustained signal induced by the nearfield earthquake occurring near the hualien station taiwan and shows a positive correlation between the earthquake distance and magnitude our results generally show that using the hht transform improves our understanding of automatic detection of the coseismic signals from the groundwater level

effective use of cerium anomalies as a redox proxy in carbonate dominated marine settings abstract rare earth elements and yttrium rey have a distinct distribution pattern in seawater and this pattern may be faithfully preserved in carbonate sediments and rocks anomalous concentrations of redox sensitive cerium ce compared with neighbouring rey originate in oxic water column conditions and as such ce anomalies can provide a potentially useful redox proxy in carbonate dominated marine settings the methods used to extract rey from carbonates vary widely and may suffer from widespread leaching of rey from accessory non carbonate minerals and organic matter limiting the application of ce anomalies for palaeo redox reconstruction we have systematically compared different methods on 195 carbonate samples with varying purity carbonate from both modern and ancient environments we used sequential leaching experiments in nitric acid to identify the most seawater like portion of the carbonate sample where contributions from non carbonate minerals and organic matter are minimised we also compared the results of sample dissolution in different types and strengths of acid our results confirm that rey concentrations can be inadvertently contaminated by partial leaching of clays and fe oxyhydr oxides during a single step digestion and we suggest a pre leach of 20 of the sample followed by a partial leach of 40 of the sample to selectively dissolve carbonate we suggest that rey studies are optimised in carbonates with 85 caco 3 and show that dolomites behave differently during the leaching process and must be treated separately we present rey patterns for modern carbonate rich sediments from a range of environments and show that seawater rey are faithfully preserved in some non skeletal carbonate but modified leaching procedures are necessary for impure unlithified or organic rich carbonate sediments we combine rey with fe speciation data to identify how fe oxides and clays contribute to the rey signal and explore how the two proxies can be used together to provide a complex and high resolution redox reconstruction in carbonate dominated marine environments

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

undrained poroelastic response of sandstones to deviatoric stress change deformation of porous crustal rock through diagenesis tectonic loading or other processes can change pore volume and affect fluid pressure the largest stress induced pore pressure changes occur when fluid is trapped in pores in an undrained condition we have measured the undrained poroelastic response of two sandstones to changes in mean and deviatoric stress pore pressure was found to respond to mean stress m in the usual manner p b m b ranging from 0 4 to 0 7 nearly independent of the ambient deviatoric stress state however variations in deviatoric stress d 1 3 2 at constant mean stress were also found to induce a reversible elastic pore pressure response to stress levels up to and exceeding 80 percent failure stress i e p d m const the coefficient became more negative with increasing deviatoric stress level in sandstone and ottawa sand samples that is represents a dilatant response where increased deviatoric stress causes a decrease in pore pressure the poroelastic response to deviatoric stress is explained in terms of anisotropic matrix stiffening due to closure of crack like pore space or flattening of grain contacts at high ambient stress levels and can be important in calculations of earthquake stress transfer

chemostratigraphy of the neoproterozoic mirassol d oeste cap dolostones mato grosso brazil an alternative model for marinoan cap dolostone formation abstract we have conducted a detailed study of the neoproterozoic mirassol d oeste cap dolostones that overlay the glacial diamictites of the puga formation 635 ma amazon craton brazil in order to understand the formation of these post glacial dolostones petrographic features indicate that the dolostones are primary to early diagenetic in origin and precipitated in a moderately shallow water platform corresponding to a carbonate ramp during transgressive conditions major and trace element contents as well as c and o isotopic signatures are consistent with an anoxic sediment influenced by sulphate reducing bacteria such an environment is known to provide favourable conditions for the precipitation of dolomite as observed nowadays in modern hypersaline lagoons isotopic compositions of tube like structures suggest local upward fluid seepage from the underlying cap dolostone our data concur with geochemical data from other neoproterozoic cap dolostones to support a microbially mediated model in specific environmental conditions for the formation of these unusual deposits worldwide

palaeoenvironmental changes at the frasnian famennian boundary in key european sections chemostratigraphic constraints abstract the study aims to put constraints on global environmental changes which took place during the frasnian famennian f f transition by using a geochemical multiproxy approach for this several key european f f boundary sections deposited in different palaeogeographic settings were selected including in addition to the stratotype and parastratotype sections of coumiac montagne noire france and steinbruch schmidt branau germany respectively also some other sections thoroughly characterized by other authors the drilling budesheimer bach prumer mulde germany kowala section holy cross mountains poland la serre france changes in the detrital flux along the sections were evaluated on the basis of both variations in mineral composition and in some diagnostic element ratios like ti al the biogenic flux was assessed as a function of the corg content the input of nutrients or the palaeoproductivity was determined by the p2o5 and ba in excess the degree of anoxia during deposition was constrained by determining the concentration of redox sensitive metals e g fe mn in the bulk sediment of specific element ratios e g v cr as well as the size of pyrite grains together with the degree of pyritization dop in the budesheimer bach core the hydrothermal and volcanic influence in the sedimentary record was detected using e g the al al fe mn and zr al2o3 ratios the kellwasser horizons are characterized by a general decrease in the detrital input together with the increase of al normalized concentration of some of the transition metals these changes are interpreted as reflecting a relative sea level rise and a higher hydrothermal influence in contrast to these the establishment of dysoxic anoxic conditions in the depositional environment as well as the increase of organic matter burial are not always restricted to the kellwasser horizons kwh moreover the hydrothermal influence can lead to misinterpretation with respect to redox conditions and productivity due to the additional input of some specific elements our results indicate the coincidence of sea level rise with hydrothermalism and volcanism during the deposition of the kwh in the area of south laurussia and north gondwana the resulting enrichment in metals and nutrients is coupled in several f f boundary sections with a higher microbial activity as already observed by some authors these effects coupled with a general lowering of the degree of oxygenation of the water bodies could have played a significant role in the demise of the biota

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

large scale slope instability at the southern margin of the ediacaran yangtze platform hunan province central china thirteen stratigraphical sections from the doushantuo formation hunan province central china indicate large scale mass wasting of the yangtze platform margin between the late neoproterozoic glaciation and the earliest cambrian numerous sedimentary discontinuities due to regional slides olistostromes and slumps have modified the stratigraphy between the shallow water carbonate platform margin and the siliciclastic slope slide blocks are predominantly gently deformed and are largely composed of shallow water dolomitized limestones slide sheets may reach a regional extent of up to 5000 km 2 and are embedded in anoxic shales at an unknown water depth

seawater rare earth element patterns preserved in apatite of pennsylvanian conodonts past workers have used rare earth element patterns recorded in biogenic apatite as proxies for original seawater chemistry to explore the potency of this approach we analyzed pennsylvanian conodonts from limestones gray shales and black shales of the fort scott and pawnee formations desmoinesian and swope and dennis formations missourian in kansas missouri and iowa u s a analysis of individual platform conodonts from seven taxa using laser ablation inductively coupled plasma mass spectrometry la icp ms revealed a consistent enrichment in the middle rare earth elements mree analogous mree enrichment has been observed in authigenic apatite and bulk samples of phosphate rich black shales from the same formations importantly however phosphate depleted shales intimately associated with the p rich intervals are relatively depleted in mree these antithetic patterns argue convincingly for secondary migration from the bulk sediment into the phosphate and the extent of mree enrichment in the conodonts is correlated positively with the total ree content mree enrichment in conodonts does not vary systematically as a function of lithology stratigraphic level conodont genus geographic location or with independent estimates of paleoredox conditions in the bottom waters collectively these results argue for postmortem diagenetic ree uptake resulting in a pronounced and progressive mree enrichment any cerium anomalies if initially present were masked by diagenetic uptake of ree paleoenvironmental interpretations of conodont ree particularly for samples exhibiting mree enrichment should therefore be viewed with caution

rare earth elements in the water column of lake vanda mcmurdo dry valleys antarctica abstract we present data on the composition of water from lake vanda antarctica vanda and other lakes in the mcmurdo dry valleys of antarctica are characterized by closed basins permanent ice covers and deep saline waters the meromictic lakes provide model systems for the study of trace metal cycling owing to their pristine nature and the relative simplicity of their biogeochemical systems lake vanda in the wright valley is supplied by a single input the onyx river and has no output water input to the lake is balanced by sublimation of the nearly permanent ice cap that is broken only near the shoreline during the austral summer the water column is characterized by an inverse thermal stratification of anoxic warm hypersaline water underlying cold oxic freshwater water collected under trace element clean conditions was analyzed for its dissolved and total rare earth element ree concentrations by inductively coupled plasma mass spectrometry depth profiles are characterized by low dissolved ree concentrations la ce

reconstructing paleoceanographic conditions during the middle ediacaran evidence from giant ooids in south china abstract the ediacaran was a period of intense environmental change in earth history transient pulses of oxygenation and shifts in ocean chemistry have been interpreted from a range of geochemical proxies including rare earth elements and yttrium rey but it is still a challenge to reconstruct paleoceanographic conditions due to the scarcity of reliable recorder in this study we explore the possibility that a newly discovered deposit of giant ooids in the nanshanping outcrop in south china contains a relatively intact record of the ree composition of ediacaran seawater providing an important window into the redox state of the surface ocean at this time these ooids are relatively large in size 1 6 mm and exhibit densely banded laminae a regional chemostratigraphic correlation shows that the giant ooid bearing succession in south china is in the upper part of the second ediacaran positive carbon isotopic shift ep2 and thus its occurrence was not associated with the shuram excursion additionally the occurrences of giant ooid bearing oolites in different blocks were not synchronous during the middle ediacaran in situ laser ablation analysis of giant ooid cortices reveals that the shale normalized rey patterns are similar to those of modern seawater including depleted light rees superchondritic y ho ratios and positive la anomalies yet no ce anomalies 1 0 0 15 in numerous ooid cortices seems to indicate a suboxidized condition of surface ocean in south china at that time the petrographic and geochemical evidence support the weak diagenetic alteration of the pure giant ooids during burial they formed in open ocean settings with energetic hydrodynamic environments and were affected by early dolomitization that might preserve mostly original petrographic fabrics and rey signatures from further diagenetic overprinting the characteristics of ce anomalies and rey compositions acquired from the giant ooids indicate that the surface ocean was suboxidized in south china during the late stage of ep2 implying the very low atmospheric o2 level at that time our results suggest that giant ooids may be a reliable analytical target that provide a snapshot into palaeoceanographic conditions during this crucial period of dynamic changes in early earth history

seafloor precipitates and c isotope stratigraphy from the neoproterozoic scout mountain member of the pocatello formation southeast idaho implications for neoproterozoic earth system behavior abstract macroscopic seafloor precipitated crystal fans are rare in post paleoproterozoic strata but they are more common in the unusual carbonates that cap certain neoproterozoic glacial strata the uppermost carbonate and marble unit of the scout mountain member of the neoproterozoic pocatello formation younger than 667 5 ma contains seafloor fans records negative 13 c values and lies within a transgressive sequence all features consistent with such post glacial carbonate units it does not however rest directly upon a known glaciogenic deposit or sequence boundary instead it occurs within a cyclic upward fining succession that overlies an erosional contact on the pink dolostone post glacial carbonate atop the late sturtian scout mountain member diamictites it is possible that the carbonate unit in question is a cap carbonate and thus requires recognition of an additional glaciation recorded in the pocatello formation alternatively it may imply that means independent of glaciation such as overturn of an anoxic ocean foster the deposition of cap like carbonates independent of post glacial processes thus neoproterozoic carbonate units with unusual lithofacies and negative carbon isotope values need not indicate the aftermath of low latitude glaciation additionally the radiometrically calibrated 13 c record of the pocatello formation demonstrates that the interval from 700 to 580 ma has more variation than previous compilations would suggest

ocean acidification in the aftermath of the marinoan glaciation boron isotope patterns preserved in cap carbonates deposited in the aftermath of the younger cryogenian marinoan ca 635 ma glaciation confirm a temporary ocean acidification event on the continental margin of the southern congo craton namibia to test the significance of this acidification event and reconstruct earth s global seawater ph states at the cryogenian ediacaran transition we present a new boron isotope data set recorded in cap carbonates deposited on the yangtze platform in south china and on the karatau microcontinent in kazakhstan our compiled 11b data reveal similar ocean ph patterns for all investigated cratons and confirm the presence of a global and synchronous ocean acidification event during the marinoan deglacial period compatible with elevated postglacial p co2 concentrations differences in the details of the ocean acidification event point to regional distinctions in the buffering capacity of ediacaran seawater

manganese rich deposits in the mesoproterozoic gaoyuzhuang formation ca 1 58 ga north china platform genesis and paleoenvironmental implications abstract the redox state of the surface ocean atmosphere system has long been considered to have been remarkably stable during the mid proterozoic ca 1800 800 ma however there is a growing body of evidence that supports dynamic redox fluctuations during this time sedimentary mn enrichment in the ca 1 58 ga gaoyuzhuang formation north china may represent an important archive of mid proterozoic paleoenvironmental conditions we present a sedimentological and geochemical study of the mn rich carbonate succession in the gaoyuzhuang formation in order to further elucidate the genesis and paleoredox implications of this mn rich deposit we suggest that the mn rich interval was deposited in deep subtidal environments close to storm wave base manganese occurs either as millimeter sized mn oxide pyrolusite nodules or as mn rich dolomite which features moderately positive i ca mg values 0 5 1 7 mol mol and ce anomalies 1 1 1 2 in contrast the underlying and overlying carbonates that lack mn oxides were deposited in a shallow subtidal environment above fair weather wave base they have relatively low i ca mg values

frequency characteristics of the response of water pressure in a closed well to volumetric strain in the high frequency domain 1 oscillations of water pressures and crustal strains due to the seismic waves of the 2010 chile earthquake were observed in japan the oscillations of water pressures observed over the frequency range of 0 002 to 0 1 hz were negative proportional to the oscillations of volumetric strains the responses of water pressures in closed wells are frequency dependent the expression for the response of water pressure in a closed well to crustal strain is developed based on the poroelastic theory the expression developed in the present paper describes the frequency characteristics of the responses the response is useful for the estimation of rock properties in addition the responses of water pressure due to tidal volumetric strain are estimated and compared with the responses due to the seismic waves

rapid sea level rise in the aftermath of a neoproterozoic snowball earth earth s most severe climate changes occurred during global scale snowball earth glaciations which profoundly altered the planet s atmosphere oceans and biosphere extreme rates of glacioeustatic sea level rise are predicted by the snowball earth hypothesis but supporting geologic evidence has been lacking we use paleohydraulic analysis of wave ripples and tidal laminae in the elatina formation australia deposited after the marinoan glaciation 635 million years ago to show that water depths of 9 to 16 meters remained nearly constant for 100 years throughout 27 meters of sediment accumulation this accumulation rate was too great to have been accommodated by subsidence and instead indicates an extraordinarily rapid rate of sea level rise 0 2 to 0 27 meters per year our results substantiate a fundamental prediction of snowball earth models of rapid deglaciation during the early transition to a supergreenhouse climate

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

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

marinoan glaciation in east central brazil abstract remnants of a neoproterozoic glaciation in east central brazil are represented by thin diamictite layers jequitai formation and correlative units locally overlying striated pavements on the sao francisco craton the diamictites are covered by the sete lagoas formation of the basal bambui group which is generally accepted to be a typical cap carbonate sequence although most authors have preferred a mid cryogenian post sturtian age for it based mainly on pb pb whole rock data the sete lagoas formation bears lithostratigraphic and isotopic characteristics that are identical to early ediacaran cap carbonates worldwide including a basal thin 0 10 m pale and flinty cap dolostone preserving a drop in 13c values from around 3 2 to 4 5 with associated 18o around 5 and crystal fan facies interpreted as aragonite pseudomorphs ediacaran zircons have been recovered from the middle of the sete lagoas formation constraining the deposition of its upper half to be younger than 610 ma rodrigues 2008 although there is an unconformity below the point where the zircons were collected it is short lived as suggested by the identical typically ediacaran 87sr 86sr values above and below 0 7074 0 7076 carbonate clasts from the jequitai formation and correlative diamictite bearing units in the fold belts that surround the sao francisco craton canabravinha and serra do catuni formations display similar ranges in 13c 6 7 to 2 6 suggesting the erosion of a pre glacial carbonate platform with negative 13c values i e the islay and or trezona anomalies the cratonic carrancas formation on the other hand yielded pale dolostone clasts with 13c in a small range between 4 2 and 3 4 and 18o values around 6 5 these clasts could be derived from the cap dolostone unit itself in which case the carrancas formation would represent resedimented basal sete lagoas formation and imply that sections of the sete lagoas formation sitting atop the carrancas formation are incomplete the base truncated sections have confused previous attempts to correlate the sete lagoas formation with other cap carbonate successions in light of the available lithostratigraphic isotopic and u pb zircon data we propose that the sete lagoas formation represents a basal ediacaran cap carbonate sequence 635 610 ma deposited after the marinoan glaciation in east central brazil

chilean earthquakes aquifer responses at the russian platform we studied hydrogeological responses to the passage of seismic waves from the chilean earthquakes with ms 7 6 at epicentral distances of about 126 the variation in the levels of confined and unconfined aquifers was analyzed under platform conditions at the mikhnevo geophysical observatory near moscow russia synchronous recording of seismic and hydrogeological data enabled us to evaluate the amplitude frequency response of aquifers the study shows that medium response to dynamic impact depends on various physical parameters of the aquifers

a water well sensitive to seismic waves the water level in an observation well edy has been monitored with high frequency sampling 1 sec large changes in the water level are observed in this well which correspond to dynamic strain changes due to the passage of long period seismic waves for example fluctuations of more than 200 cm were observed after a m 8 1 earthquake 1200 km from the observation site the response characteristic of the water level to strain change was investigated by comparison with nearby volumetric strain changes the response curve has a peak of sensitivity and a phase transition at periods of 18 19 seconds at the resonant period the sensitivity is as large as 15 mm per 10 9 strain

aftermath of a snowball earth 1 using a simple 3 box model of the ocean atmosphere system we simulate the cycling of carbon and strontium in the aftermath of a global glaciation model simulations include the delivery of alkalinity to seawater from intense carbonate and silicate weathering under high pco2 conditions as well as ocean mixing air sea gas exchange and biological productivity the 13c of the first carbonate precipitated after the glaciation depends on the pco2 temperature the saturation state of the surface ocean and kinetic effects associated with mineral precipitation with no biological productivity the model produces 13c values between 1 and 3 consistent with observations this is in direct contradiction with arguments by kennedy et al 2001a who suggest that the 13c value of dissolved carbon in a snowball ocean and directly afterward must be 5 kennedy et al assume the carbon isotope cycle is in steady state which does not apply to a global glaciation and also neglect any effect of high pco2 on the carbonate chemistry of seawater a major difference between our findings and the qualitative predictions of hoffman et al 1998 is our interpretation of the cap dolostone as representing an interval dominated by carbonate weathering of exposed continental shelves as a result the 2 drop in the 13c observed in the cap dolostone is unlikely to be the product of rayleigh distillation of atmospheric co2 via silicate weathering instead we interpret the 2 drop in the 13c values as indicative of an increase in sea surface temperature which lowers the fractionation between co2 and carbonate kinetic isotope effects associated with rapid precipitation from a highly supersaturated surface ocean may also be important rayleigh distillation of atmospheric co2 via silicate weathering is a viable explanation for the continued drop in the 13c values in the limestone sequence above the cap dolostone with biological productivity and carbonate weathering driving a slow increase in 13c values once pco2 levels decline our study also simulates the cycling of strontium in seawater in contrast to the finding of jacobsen and kaufman 1999 and kennedy et al 2001a model simulations show a drop in 87sr 86sr of less than 0 001 during 5 million years of global glaciation and an increase of less than 0 001 over the entire episode of silicate weathering our calculations emphasize the importance of considering the changes in seawater chemistry due to high pco2 in evaluating the snowball earth hypothesis

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

transfer functions of the well aquifer systems response to atmospheric loading and earth tide from low to high frequency band 1 the transfer functions of the well aquifer systems response to atmospheric loading and earth tide can be used to calculate the well aquifer properties due to the low signal to noise ratio the study on barometric response at frequencies higher than 8 cycles per day cpd for short is almost blank using the recorded water level and barometric pressure as well as the corresponding theoretical tidal volumetric strain at 17 well stations in china we obtained continuous barometric and tidal responses of the well aquifer systems by cross spectra estimation it shows that the barometric responses are stable at low frequencies 0 1 0 5 cpd while fluctuate at tidal frequencies 0 5 8 cpd in the high frequency band 8 30 cpd by stacking the transfer functions to suppress the noise we obtained stable barometric responses for the first time according to the low and high frequency barometric responses we can better judge whether the aquifers are confined in the timescale that we focused and whether the wellbore storage effect can be ignored and expect to determine the fluid flow properties of the aquifers more reliably for the three aquifers whose water table drainage and wellbore storage effects are ignored we used the barometric and tidal responses to estimate their formation properties which are consistent with previous results the tidal strain sensitivities are related to the aquifer lithology which are mainly controlled by the compressibility of the porous matrixes with different porosities and different aspect ratio fractures

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

rare earth elements and sr and nd isotopic compositions of dissolved and suspended loads from small river systems in the vosges mountains france the river rhine and groundwater abstract the aim of this study is to characterize the evolution of the rare earth elements ree in non mature streams from small catchment areas in the vosges mountains downstream to more mature plain rivers including the river rhine the dissolved load ree distribution patterns of the low ph vosges streams are very different from those of high ph plain rivers indicating that different physico chemical parameters control ree transport in these different water systems the plain rivers and groundwater show similar ree distribution patterns with a strong negative ce anomaly and heavy rare earth element hree enrichment in addition the river rhine has a positive gd anomaly which is of anthropogenic origin similar to the world s major rivers the light rare earth element lree enrichment in the plain rivers is mainly ph controlled their sm nd and 143 nd 144 nd isotope ratios are close to average continental crust values this is not the case for the less evolved non mature and low ph vosges streams their high sm nd and 143 nd 144 nd ratios but low 87 sr 86 sr ratios suggest that chemical alteration of accessory middle rare earth element mree enriched minerals such as apatites from rocks in the catchment area control the ree abundances of these waters a comparison of the dissolved load ree distribution patterns with those of the principal lithologies in the corresponding drainage basins illustrates that especially the eu anomalies of the vosges streamlets are strongly lithology dependent leaching experiments indicate that the suspended load is isotopically very inhomogeneous the ree distribution patterns of the suspended load leachates have no similarities with those of the corresponding dissolved load indicating that the leachable reservoir not only contains adsorbed ree but also ree from leachable mineral phases their 143 nd 144 nd sm nd and 87 sr 86 sr ratios support this suggestion being always higher and lower respectively than those of their corresponding dissolved loads they rather point to the presence of relic primary apatite in the leachable portion of the suspended load the flat paas normalized ree distribution patterns the high 87 sr 86 sr and low 143 nd 144 nd isotopic ratios of the corresponding residues suggest secondary silicate phases such as clay minerals in the residual phase of the suspended load leachates and corresponding residual phases define alignments in the sm nd isochron diagram whose slopes define ages ranging between 200 and 390 ma indicating that the mineral phases in the suspended load retain some memory of their primary precursor minerals in the hercynian granitic source rocks

manganese flux from continental margin sediments in a transect through the oxygen minimum the flux of manganese from continental margin sediments to the ocean was measured with a free vehicle benthic flux chamber in a transect across the continental shelf and upper slope of the california margin the highest fluxes were observed on the shallow continental shelf manganese flux decreased linearly with bottom water oxygen concentration and the lowest fluxes occurred in the oxygen minimum zone at a depth of 600 to 1000 meters although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow coastal waters the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the pacific ocean

sedimentary environment of ediacaran sequences of south china trace element and sr nd isotope constraints abstractpost marinoan sedimentary rocks from the yangtze block in south china were investigated to seek constraints on their provenance genetic relationship with paleoclimate depositional environment and changes sedimentary rocks from the doushantuo formation in the jiulongwan section of the yangtze block were collected for whole rock trace elements and sr nd isotopic analyses flat to slightly middle rare earth element ree enriched ree plus yttrium patterns negative to positive ce anomalies ce ce of 0 86 1 40 positive la anomalies la la of 1 02 1 42 and suprachondritic y ho ratios 36 8 49 5 obtained for the doushantuo cap carbonates indicate their deposition in a fluctuating inner shelf setting where freshwater and seawater mixed together and the influence of hydrothermal fluid from the seafloor is absent all doushantuo carbonates and shales have variable sr isotopic compositions with initial sr isotopic ratios 0 704030 0 712720 that support significant river water contribution durin

stratified oceans and oxygenation of the late precambrian environment a post glacial geochemical record from the neoproterozoic of w mongolia the late neoproterozoic 750 545 ma was a time of revolutionary environmental change recurrent glaciation and tectonic upheaval which culminated in the evolution of metazoans and animal biomineralization geochemical data are presented for a post glacial 700 ma limestone succession from w mongolia 87 sr 86 sr is used to constrain the timing of early diagenetic exchange stratigraphic trends to high d 13 c carb and d 13 c org mirror sea level fluctuations which we argue is consistent with the hypothesis that late precambrian ocean chemistry was controlled by vertical stratification repeated establishment of stratification 700 545 ma would have led to greater oxygen availability in the surface environment a causal link between this oxygenation and the further evolution of animals is proposed

uptake and fractionation of rare earth elements on hydrothermal plume particles at 9 45 n east pacific rise abstract particulate samples 0 45 m from a neutrally buoyant hydrothermal plume at 9 45 n on the northern east pacific rise were collected using large volume in situ filtration and analyzed for fe al mn ni and fourteen rare earth elements ree the sm fe ratio a proxy for overall ree fe and nd er light heavy ree fractionation increased moderately with decreasing particulate fe chemically the sense of these relationships matched that documented previously in the tag plume on the mid atlantic ridge german et al 1990 although particulate fe was about 10 fold lower at 9 45 n spatial trends relative to the vent source however were opposite of expectation because slow fe ii oxidation and fe iii colloid aggregation over this interval led to increased particulate fe 10 26 nm with distance from source field and sherrell submitted after subtraction of non plume background particle composition plume particles at 9 45 n and tag had indistinguishable ranges of light ree enriched fractionation relative to ambient seawater and had very similar sm fe therefore kd for fe oxyhydroxides demonstrating that plume particles in both oceans reflect to a first degree the local seawater ree composition within plume ree variations at 9 45 n were investigated using a simple mixing model which accounts for the bulk fe al mn variations in the plume using two endmembers fresh hydrothermal oxyhydroxide precipitates and ridge crest background particles composed largely of locally resuspended sediment sm fe and nd er plot linearly with mixing ratio r 0 96 implying that the observed ree trends result from mixing of these two endmembers extrapolation to the composition of pure hydrothermal precipitates suggests that nd er is fractionated relative to seawater by a factor of 1 8 during adsorption onto fresh fe oxyhydroxide particles the ridge crest background particles are 5 fold higher in sm fe and nd er is 2 49 relative to seawater partly a result of enriched terrigenous component in the resuspended matter a reinterpretation of ree at tag reveals that positive curvature in ree vs fe plots argued previously to reflect continuous ree uptake i e increasing kd german et al 1990 may result from local depletion of the dissolved ree pool by partitioning onto fe particles at fe 100 nm similar drawdown effects could contribute to the variable degrees of curvature observed for all seawater source particle reactive species in plumes that are sampled at high particulate fe concentration in sum ree behavior in hydrothermal plumes is more consistent with equilibrium adsorption and mixing of distinct particle types than with kinetic uptake control precise measurements of rees in modern ridge crest metalliferous sediments could be compared to the endmember composition calculated from the plume data to evaluate long term changes in ree of the hydrothermal component

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

fast or slow melting of the marinoan snowball earth the cap dolostone record article i nfo the end of the neoproterozoic era is punctuated by two global glacial events marked by the presence of glacial deposits overlaid by cap carbonates duration of glacial intervals is now consistently constrained to 3 12 million years but the duration of the post glacial transition is more controversial due to the uncertainty in cap dolostone sedimentation rates indeed the presence of several stratabound magnetic reversals in brazilian cap dolostones recently questioned the short sedimentation duration a few thousand years at most that was initially suggested for these rocks here we present new detailed magnetostratigraphic data of the mirassol d oeste cap dolostones mato grosso brazil and bomb spike calibrated ams 14 c data of microbial mats from the lagoa vermelha rio de janeiro brazil we also compile sedimentary isotopic and microbiological data from post marinoan outcrops and or recent depositional analogues in order to discuss the deposition rate of marinoan cap dolostones and to infer an estimation of the deglaciation duration in the snowball earth aftermath taken together the various data point to a sedimentation duration in the range of a few 10 5 years

distribution of rees and yttrium among major geochemical phases of marine fe mn oxides comparative study between hydrogenous and hydrothermal deposits abstract mineralogy and geochemistry of the ferromanganese oxides collected from two seamounts in the andaman sea have been investigated with special reference to the solid phase partitioning behavior of rare earth elements rees bulk elemental compositions indicate that the oxides from a volcanic cratered seamount csm are hydrothermal while those from another seamount sm2 are hydrogenous in origin the distributions of rees and yttrium in four geochemical phases viz easily exchangeable mn oxide fe oxyhydroxide and residual of csm oxides were distinctly different from that of sm2 oxides in csm oxides the rees and yttrium are mainly associated with fe oxyhydroxide phase while in sm2 oxides both mn oxide and fe oxyhydroxide phases contain the major fraction of these elements the exchangeable and residual phases of both hydrothermal and hydrogenous oxides have extremely low ree content the shale normalized negative ce anomalies and relative enrichment of heavy ree characteristic of hydrothermal oxides are retained in fe oxyhydroxide phase in hydrogenous oxides the positive ce anomalies occurred in both fe and mn oxide phases while negative y anomalies were found only in fe oxyhydroxide phase the phase distribution of rees and yttrium in hydrothermal oxides is described in terms of co precipitation and adsorption of their halide complexes and available free ions in hydrothermal solutions instead adsorption of major carbonate species from seawater primarily regulates the partitioning of rees among the co existing phases of hydrogenous oxides

cerium anomaly variations in ediacaran earliest cambrian carbonates from the yangtze gorges area south china implications for oxygenation of coeval shallow seawater abstract the late neoproterozoic ocean witnessed the naissance of animals which is believed to have been stimulated by an increase in oxygen levels in the ocean however apart from the emergence of animal fossils little supporting evidence has been found for the rise of oxygen in shallow seawater here we present ce anomaly data a redox proxy with a higher reduction potential than many other redox proxies for carbonates from well preserved marine successions the doushantuo formation dengying formation and lower yanjiahe formation of the ediacaran period and the upper yanjiahe formation of early cambrian on the neoproterozoic yangtze platform in the yangtze gorges area in order to constrain the redox evolution of the shallow marine environment calculated ce anomalies were screened using the following criteria al 36 in acetic acid leached carbonate to target samples that preserve primary seawater ree features and ce anomalies the samples satisfying this screening show seawater like ree distribution patterns in leached carbonates and may have recorded ce anomalies of the seawater from which the carbonates precipitated these data show that the doushantuo formation has ce ce values between 0 92 and 0 71 the dengying formation between 0 90 and 0 40 and the yanjiahe formation between 0 52 and 0 72 the ce ce values of the doushantuo formation suggest that shallow waters during the doushantuo stage 635 551 ma were anoxic to suboxic from the bottom to the top of the dengying formation ce ce values decrease systematically which cannot be explained by a change in depositional depth of the carbonate but suggests that the shallow waters became more oxygenated during the dengying stages from 551 ma to ediacaran cambrian boundary these results may provide direct evidence for an increase in oxygen levels in the shallow marine environment during the ediacaran period

late neoproterozoic cap carbonates mackenzie mountains northwestern canada precipitation and global glacial meltdown the 3 27 m thick cap carbonate overlying marinoan ice brook formation glacigene sediments and keele formation carbonate and terrigenous clastic rocks consists of two distinctive stratigraphic units a lower splintery buff weathering microcrystalline dolostone of extensive lateral uniformity comprises mm laminated peloidal sediment with local low angle hummocky like cross stratification micro ridges and synsedimentary tepees all elongated per pendicular to depositional strike this dolostone is unconformably overlain by an upper limestone that exhibits pro nounced facies variation from inboard peloidal lime grainstone and mudstone to shelf edge cementstone to outboard lime wackestone and mudstone calcite cementstones range from isolated crystal fans in laminated limestone to huge decimetre scale crystal arrays to hemispherical and elongate crystal stromatolites wholly composed of acicular crystals that form decametre scale reeflike structures crystal stromatolites are precipitates and replaced microbiolites that con structed biostromes and bioherms like those on many flat topped reef rimmed platforms the calcite crystals have all the physical and chemical attributes of neomorphosed aragonite this aragonite extensively replaced sediment and microbiolite just below the sea floor and grew upward into the overlying water column such interpreted massive synsedimentary replacement is rare in geological history and attests to the highly saturated state of the immediate postglacial ocean all sediment is interpreted to have been caco3 originally low and constant 18 o values reflect diagenetic modification of these carbonates although chemical attributes such as sr and c isotopes in some lithologies are near pristine lower dolostones virtually identical to most other coeval marinoan caps worldwide were part of a global precipitation event of remarkable similarity upper limestones are a more local phenomenon deposited during sea level rise in an aragonitic sea returning to equilibrium after global glaciation low 87 sr 86 sr ratios and varying 13 c values with carbonate sedimentary facies indicate that both units must have formed relatively rapidly prior to significant flu vioglacial runoff or that the influence of this runoff on the chemistry of seawater along continental shelves was mini mal the cap carbonate is thus interpreted to have formed in two steps 1 during initial marine ice melting accompanied by oceanic overturn and upwelling preceding continental margin rebound and 2 during initial stages of sea level rise accompanying continental deglaciation while confirming brief but extensive carbonate precipitation from an ocean highly perturbed by global glaciation the rocks also suggest that this event did not permanently affect either late neoproterozoic ocean chemistry or the contained marine biosphere 1262

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

diagenetic uptake of rare earth elements by bioapatite with an example from lower triassic conodonts of south china abstract the distribution patterns of rare earth elements rees are frequently used as proxies for ancient seawater chemistry or paleomarine environmental conditions however recent work has shown that diagenesis can lead to remobilization and inter elemental fractionation of rees and that these effects often occur in conjunction with redox reactions in sediment porewaters here we review existing literature on the diagenetic fluxes of rees in marine sediments and porewaters in order to systematize existing knowledge on this subject rees undergo significant redistribution among sediment phases during both early and late diagenesis as a consequence of adsorption and desorption processes remobilization of rees commonly leads to inter elemental fractionation variously leading to enrichment or depletion of the light middle or heavy ree fractions further ree remobilization can be facilitated by redox changes e g through reductive dissolution of host phases in suboxic and anoxic porewaters characteristic ree distribution patterns develop through these processes 1 a flat distribution signifying predominantly terrigenous siliciclastic influence 2 a middle ree bulge probably due to adsorption of light and heavy rees to mn and fe oxyhydroxides respectively and 3 heavy ree enrichment indicative of hydrogenous seawater influence note all patterns in this paper are normalized to the ree composition of average upper continental crust or ucc in the second part of this study we undertake an analysis of the ree distributions in conodonts and whole rock samples from west pingdingshan a permian triassic boundary section in south china using ree th and y ho ratios we show that almost all of the conodont samples have a strong diagenetic overprint and that the hydrogenous ree fraction is small and not isolatable furthermore the conodonts contain two diagenetic ree components one characterized by low ree 100 300 ppm high ree th ratios 1000 strong middle ree enrichment and eu eu ratios of 1 5 2 0 and the second by high ree 300 2000 ppm low ree th ratios 20 30 little or no middle ree enrichment and eu eu ratios of 1 0 the first component exhibits a pronounced middle ree bulge that represents an early diagenetic signature associated with suboxic conditions possibly related to adsorption of rees onto fe mn oxyhydroxides in the shallow subsurface environment the second component shows a flat ree distribution that is similar to both our whole rock samples and average ucc indicating derivation from rees released from detrital siliciclastics e g clay minerals probably at a range of burial depths from shallow to deep failure of the conodont samples to yield an isolatable hydrogenous component demonstrates that bioapatite does not always preserve a primary marine ree signature given that bioapatite rees have been widely used for this purpose often on the assumption of minimal or no diagenetic influence our findings are likely to necessitate a re evaluation of the results of many earlier studies in general we counsel caution in inferring a hydrogenous origin for rees in bioapatite owing to frequent diagenetic alteration of ree distributions

zn isotope evidence for immediate resumption of primary productivity after snowball earth the ediacaran period began with the deglaciation of the ca 635 ma marinoan snowball earth and the deposition of cap dolostones on continental shelves worldwide during post glacial sea level rise these carbonates sharply overlie glacial sediments deposited at low paleolatitudes and preserve negative carbon isotope excursions the snowball earth hypothesis invokes an almost complete cessation of primary productivity in the surface ocean because assimilatory uptake of zn appears to fractionate its isotopes zn isotope ratios measured in carbonate precipitated in the surface ocean should track fluctuations in primary productivity here we report the first zn isotopic data together with carbon and oxygen isotopic profiles from a neoproterozoic cap dolostone the nuccaleena formation in the flinders ranges south australia we interpret the zn isotopic data in terms of a two stage evolution of the deglacial ocean slightly 66 zn enriched values at the base of the cap dolostone indicate immediate resumption of the biological pump upon melting of the surface ocean but this signal was diluted by intense surface runoff that drove 66 zn 66 zn 64 zn versus the jmc lyon reference values down to the composition of continentally derived zn a subsequent rise in 66 zn records a vigorous increase in primary production and export from a nutrient laden surface ocean

oxygenation history of the neoproterozoic to early phanerozoic and the rise of land plants there has been extensive debate about the history of earth s oxygenation and the role that land plant evolution played in shaping earth s ocean atmosphere system here we use the rare earth element patterns in marine carbonates to monitor the structure of the marine redox landscape through the rise and diversification of animals and early land plants in particular we use the relative abundance of cerium ceanom the only redox sensitive rare earth element in well preserved marine cements and other marine precipitates to track seawater oxygen levels our results indicate that there was only a moderate increase in oceanic oxygenation during the ediacaran average cryogenian ceanom 1 1 average ediacaran ceanom 0 62 followed by a decrease in oxygen levels during the early cambrian average cryogenian ceanom 0 90 with significant ocean anoxia persisting through the early and mid paleozoic average early cambrian early devonian ceanom 0 84 it was not until the late devonian that oxygenation levels are comparable to the modern average of all post middle devonian ceanom 0 55 therefore this work confirms growing evidence that the oxygenation of the earth was neither unidirectional nor a simple two stage process further we provide evidence that it was not until the late devonian when large land plants and forests first evolved that oxygen levels reached those comparable to the modern world this is recorded with the first modern like negative ceanom values 0 6 occurring at around 380 ma frasnian this suggests that land plants rather than animals are the engineers responsible for the modern fully oxygenated earth system

siderophore promoted transfer of rare earth elements and iron from volcanic ash into glacial meltwater river and ocean water abstract the rare earth elements ree are a group of trace elements that have short marine residence times and that in river lake and marine surface waters are typically associated with organic and inorganic particles explosive volcanic eruptions such as the 2010 eruptions of eyjafjallajokull volcano in iceland produce volcanic ash particles which can be an important source of iron and other nutrients for aquatic organisms to become bioavailable however this iron needs to be solubilized by complexing agents such as siderophores a well studied example of such a chelator is the biogenic siderophore desferrioxamin b dfob based on results from incubation experiments with glacial meltwater rich river waters from southern iceland which are rich in suspended volcanic ash and that had been incubated with and without dfob respectively we here show that siderophores not only enhance the release of iron but also promote the mobilization of ree from these particles in the presence of dfob partial dissolution of volcanic ash and presumably other lithic particles produces a flux of dissolved ree into ambient waters that is characterized by depletion of the light ree over the middle ree and by selective enrichment of cerium due to the formation of dissolved ce iv dfob complexes in siderophore rich environments this siderophore bound ree flux has the potential to modify the concentrations and distribution of the dissolved ree and of the isotopic composition of dissolved nd in glacial meltwaters river waters and seawater and might be a component of the boundary effects between shelf sediments and seawater which are assumed to account for the missing nd flux to seawater thermodynamic data further suggest that siderophore promoted element mobilization could also be important for other polyvalent trace elements such as hf

petrological and geochemical characteristics of the botryoidal dolomite of dengying formation in the yangtze craton south china constraints on terminal ediacaran dolomite seas abstract recent studies suggest that the massive precambrian dolomite successions were likely the products of specific seawater conditions known as dolomite seas however whether these so called dolomite seas existed in the terminal ediacaran ocean has not yet been constrained the widespread botryoidal dolomite with well preserved sedimentary fabrics from the upper ediacaran dengying formation ca 551 to 545 ma south china can be potentially an ideal target to constrain this issue results showed that within the botryoidal dolomite fibrous dolomite cements are the dominant constituent part and either grew upward from microbialite layers or occurred in sheet cracks within the microbialites implying a syn sedimentary diagenesis two different types of fibrous cements are newly redefined fascicular and radial slow dolomite well preserved chemical and cathodoluminescent zonations and length slow optical characters are direct evidence for syn sedimentary primary dolomite precipitation different with the previous alternative interpretations of mimetic dolomitization of aragonite or high mg calcite precursors in contrast microbialite matrix consists of finely crystalline dolomicrite and preserved microbial fabrics reveling an early mimetic dolomitization of aragonitic precursors the dolomite precipitation and mimetic dolomitization likely occurred in coeval seawater or seawater type fluids as indicated by comparable 13c and 87sr 86sr data with global changes in particular the presence of primary dolomite cement precipitates within botryoidal dolomite can reflect that the specific dolomite seas associated with anoxic or even euxinic shallow water conditions inferred by redox sensitive trace elements and rees and increased microbial activity also prevailed in the terminal ediacaran ocean however the occurrence of dolomite seas was not one occasional event but common even if not persistent in the early to terminal neoproterozoic oceans this study helps to improve the understanding of dolomite problem and ubiquitous distribution of precambrian dolomite worldwide

co seismic response of water level in the jingle well china associated with the gorkha nepal mw 7 8 earthquake abstract changes in co seismic water levels associated with the gorkha nepal earthquake 25 april 2015 mw 7 8 were recorded in the jingle well in shanxi province china longitude e112 03 latitude n38 35 about 2769 km from epicenter based on the observed water levels we clearly identified signals relating to p s and surface waves however the water temperature recorded at a depth of 350 m shows no co seismic changes a spectrum analysis of co seismic variations of water level shows that the oscillation frequency and amplitude of water level in the borehole are determined by the natural frequency of the borehole which is not associated with the propagation of seismic waves the borehole aquifer system shows a large amplification associated with ground vibrations generated by earthquakes considering the local hydro geological map and the temperature gradient of the jingle well a large volume groundwater reservoir model can be used to explain these processes due to seismic wave propagation the volume of a well confined aquifer expands and contracts forming fractures that change the water flow in the well confined aquifer water levels oscillate simultaneously with high amplitude ground shaking during earthquakes however the water in the center of the underground reservoir remains relatively stationary without any changes in the water temperature in addition a possible precursor wave is recorded in the water level at the jingle well prior to the gorkha earthquake

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

trace and rare earth elemental investigation of a sturtian cap carbonate pocatello idaho evidence for ocean redox conditions before and during carbonate deposition abstract this study examines the trace element and ree y geochemistry of a thin pink dolomite in the scout mountain member of the pocatello formation idaho the pink dolomite meets the criteria of a cap carbonate and provides an opportunity to examine ocean redox state and hydrothermal inputs on the margin of laurentia at the terminal stages of the sturtian glaciations here high resolution chemostratigraphy of the dolomite shows that the local marine conditions were rapidly changing during cap emplacement normalized trace metal concentrations of zn cd cu cr mn and ni suggest that transiently reducing conditions prevailed immediately following the initial deposition of the pink dolomite enrichments in eu suggest a hydrothermal vent source for marine waters present during deposition the pink dolomite lacks evidence for persistent sulfide mineralization and its associated enrichments in mo suggesting that anoxia was restricted to areas below the sediment water interface no notable enrichments are recorded in the glacial diamictite though the signal might be masked by high rates of sedimentation our data suggest that the deposition of the pink dolomite progressed through 1 the overturn of local ocean containing a strongly stratified hydrothermally influence water column 2 the delivery of micronutrients to the shallow ocean 3 a biotic bloom in response to micronutrient availability and 4 related organic matter scavenging of metals finally we argue that this period of anoxia was brief and conditions quickly returned to an environment of oxic deposition

cerium a chemical tracer for paleo oceanic redox conditions abstract the ce anomalies found in marine carbonates provide a sensitive indicator for the study of paleo oceanic redox conditions the dependency of cce the observed ce concentration and cepo04 the activity of the cepo4 complex to the po2 ph and pco2 of seawater can be used for deciphering some aspects of the paleo ocean chemistry and is log c ce log cepo 0 4 13 2 0 25 log p o 2 3 0 ph 1 95 0 25 log p o 2 1 50 log p co 2 1 50 log ca the ph which is related to pco2 and po2 are major factors for controlling the ce concentration in seawater therefore ce anomalies ceas ce observed ce interpolated between la and pr or nd serve as indicators for ph or pco2 or po2 changes nearly uniform ce abundances found in pacific 5000 m water columns piepgras and jacobsen 1988 and the ceas in ichthyoliths can be explained using this model a general cea shift in sediments from d s d p holes 525a 530a b 516 516f suggest that the entire south atlantic water redox condition changed from reducing to oxidizing at 56 my in the north atlantic the galicia margin samples show a redox change between 132 148 my indicating active surface currents between the atlantic ocean and the shallow sea off the iberian peninsula the carbonate samples from d s d p hole 316 in the central pacific yielded an average cea of 0 15 0 01 which is 2 3 the ceas observed in deep pacific seawater by piepgras and jacobsen 1988 the relative enrichment of ce in these samples is ascribed to coprecipitation of ce oh 4 onto fe mn o coatings the striking similarities in the trace element profiles of ree sc hf th and ceas and the low u abundances 0 08 ppm in many marine carbonates indicate insignificant ce redox and trace elemental concentration changes for the pacific ocean over the past 95 my no significant ce redox change occurred in the pacific ocean within k t boundary one 240 my china limestone deposited under oxic sedimentary conditions yielded a cea of 0 53 calculations indicate a pco2 of 1 9 present value prevailed over the 240 my tethyan ocean u th ratios and low u concentrations are diagnostic indicators for obtaining reliable ceas in marine carbonates and perhaps for biogenic apatites and conodonts as well

rare earth element cycling in the pore waters of the bering sea slope iodp exp 323 abstract we studied the diagenetic behavior of rare earth elements rees in a highly productive passive margin setting of the bering sea slope site u1345 was drilled during the integrated ocean drilling program expedition 323 at a water depth of 1008 m currently in the center of an oxygen minimum zone pore water concentrations of fourteen rees were determined down to 140 meters below the seafloor mbsf the ree concentrations were higher in the pore water than the deep seawater indicating that there was significant liberation from the sediments during diagenesis there was a major peak at 10 mbsf that was more pronounced for the heavy ree hree this peak occurred below the sulfate methane transition zone 6 3 mbsf and coincided with high concentrations of dissolved iron and manganese at 2 mbsf there was a minor peak in ree and mn contents below 40 mbsf the ree concentration profiles remained constant the ce anomaly was insignificant and relatively constant paas normalized ce ce 1 1 0 2 throughout the depth profile showing that the ce depleted in seawater was restored in the pore water hree enrichment was observed over the entire 140 m except for the upper 1 m where a middle ree mree bulge was apparent ree release in shallow depths 2 4 mbsf is attributed to the release of light rees lrees and mrees during the organoclastic reduction of mn oxides in anoxic sediments the high hree concentrations observed at 10 mbsf can be attributed to the reduction of fe and mn minerals tied to anaerobic oxidation of methane or less significantly to ferromagnesian silicate mineral weathering the upward diffusion flux across the sediment water interface was between 3 for tm and 290 for ce pmol m 2 y 1

rare earth major and trace elements in chert from the franciscan complex and monterey group california assessing ree sources to fine grained marine sediments abstract rare earth element ree major and trace element analyses of 77 samples from the mesozoic franciscan complex and miocene monterey group of california usa indicate that magnitudes of the ce anomaly ce ce and total ree abundances sree in these rocks are controlled dominantly by a the amount of included metalliferous material b the amount of direct terrigenous input and c the overall burial rate the relative importance of these individual processes varies across an ocean basin in such a way that ree relative fractionations and sree correspond with its depositional environment our conclusions are supported by an extensive review of published ree data from various river coastal open ocean and ridge influenced waters as well as terrigenous pelagic and metalliferous sediment the chert sequences record deposition in spreading ridge open ocean basin and continental margin environments the relative importance of metalliferous and terrigenous influences and the role of scavenging from seawater may be estimated from a sample s inferred depositional distance km from the spreading ridge the major element chemistry and the stratigraphie context the ce ce values are low 0 29 in the vicinity of spreading ridges and trend to successively higher 1 values with decreasing metalliferous and increasing terrigenous influences other ree indicators ree lu n la n eu eu also respond to metalliferous and terrigenous influences near the spreading ridge chert ree appears determined by burial rate while shale ree responds to metalliferous abundance in open ocean and continental margin environments ree is controlled by sediment exposure time and therefore is related inversely to burial rate ree data are consistent with the major elements fe2o3 mno and al2o3 in reflecting the respective metalliferous and terrigenous sources p2o5 and cao do not vary with ce ce in any environment but cao shows a weak negative correlation with ree trace element trends e g v cr cu ge si rb sr y th u in general can similarly be accounted for in the context of depositional position relative to metalliferous and terrigenous inputs rees in chert appear less affected by post depositional processes than either major or trace elements indicating that rees are better tools for paleoceanographic or tectonic reconstructions that are based on chert chemistry this work complements recent efforts to elucidate the factors determining large scale ree distributions in marine sediments and has direct bearing on previous attempts to use the ce anomaly in older rocks and sediments as a recorder of secular variations and anoxic events in the overlying water column

do archean chemical sediments record ancient seawater rare earth element patterns rare earth elements ree concentrations of archean and proterozoic chemical sediments are commonly used as proxies to study secular trends in the geochemistry of precambrian seawater in addition similarities in the ree signatures of archean chemical sediments and modern seawater have led researchers to argue that some archean rocks originated as biochemical precipitates i e microbial carbonates in shallow marine e g peritidal environments however terrestrial waters including river water and groundwater also commonly exhibit ree fractionation patterns that resemble modern seawater here we present the seawater like ree data for ground

evidence for intense ree scavenging at cold seeps from the niger delta margin for many trace elements continental margins are the location of intense exchange processes between sediment and seawater which control their distribution in the water column but have yet to be fully understood in this study we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium we determined dissolved and total dissolvable td concentrations for ree and well established tracers of fluid seepage ch4 tdfe tdmn and nd isotopic compositions in seawater samples collected above cold seeps and a reference site i e away from any fluid venting area from the niger delta margin we also analyzed cold seep authigenic phases and various core top sediment fractions pore water detrital component easily leachable phases uncleaned foraminifera recovered near the hydrocast stations methane tdfe and tdmn concentrations clearly indicate active fluid venting at the studied seeps with plumes rising up to about 100 m above the seafloor depth profiles show pronounced ree enrichments in the non filtered samples td concentrations within plumes whereas filtered samples dissolved concentrations exhibit slight ree depletion in plumes relative to the overlying water column and display typical seawater ree patterns these results suggest that the net flux of ree emitted into seawater at cold seeps is controlled by the presence of particulate phases most probably fe mn oxyhydroxides associated to resuspended sediments at the reference site however our data reveal significant enrichment for dissolved ree in bottom waters that clearly relates to diffusive benthic fluxes from surface sediments neodymium isotopic ratios measured in the water column range from end 15 7 to 10 4 evidence that the end values for antarctic intermediate waters aaiw differed from those reported for the same water mass at open ocean settings shows that sediment water interactions take place in the gulf of guinea at each site however the bottom water end signature generally differs from that for cold seep minerals easily leachable sediment phases and detrital fractions from local sediments ruling out the possibility that seepage of methane rich fluids and sediment dissolution act as a substantial source of dissolved nd to seawater in the gulf of guinea taken together our data hence suggest that co precipitation of fe mn oxyhydroxide phases in sub surface sediments leads to quantitative scavenging of dissolved ree at cold seeps preventing their emission into bottom waters most probably it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine nd cycle at the niger delta margin

trace and rare earth element geochemistry of phosphate nodules from the lower cambrian black shale sequence in the mufu mountain of nanjing jiangsu province china abstract phosphate nodules are abundant in the lowermost section of the lower cambrian black shale sequence along a ne trend belt in the yangtze platform south china in this study we examined the neoproterozoic cambrian mufu mountain section near nanjing of jiangsu province and conducted a detailed trace and rare earth element ree study on the phosphate nodules we employed a step leaching acid dissolution protocol of 1 m hac and 1 m hcl respectively to separate carbonate from phosphate mineral contributions in the nodules both the hac leached and hcl leached fractions of the phosphate nodules show similar symmetrical variations in trace and ree concentrations and ratios the total rees and a number of redox sensitive trace metals such as v cr mo ni abundances show a systematic increase from the core to rim whereas the u and mn abundances decrease from the core to rim in most of the nodules similar trends are also observed for the rb sr u th co ni and v ni ratios but these trends in the hac leached fractions are less pronounced than the hcl leached fractions all of the hcl leached fractions for the nodule cores show seawater like shale normalized ree patterns but the rims of the nodules display slightly mree enriched and hree depleted patterns we suggest that the phosphate nodules may have formed in a basinal setting beneath a stratified water column during early cambrian and the compositional variations of rees and redox sensitive trace elements from the core to rim may record a changing redox condition and fluid mixing during different stages of nodule growth the cores of the nodules preserve more pronounced negative ce anomalies and progressively hree enriched patterns which may retain primary early cambrian seawater chemistry whereas the nodule rims record chemistry consistent with changed redox conditions and or influences from pore fluids such as generated from degradation of organic matter

systematic variations in c o and sr isotopes and elemental concentrations in neoproterozoic carbonates in namibia implications for a glacial to interglacial transition abstract we analyzed c o and sr isotopic compositions of neoproterozoic cap carbonates overlying a glacial deposit in namibia to trace environmental changes following the glaciation the three isotopic records showed coherent and phased changes that corresponded to the stratigraphic variation a lower rhythmite unit had three intervals which were distinguished by isotopic variations and mineral type in the basal interval 13 c increased exponentially from a negative value 4 3 pee dee belemnite pdb 13 c values were relatively constant in the middle interval and increased again to positive values in the top interval indicating a phased removal of 13 c depleted carbon from the surface ocean the gradual increase to larger values 6 in the upper stromatolite unit was interpreted to reflect a change in seawater composition resulting from biological activity after environmental recovery from the glacial episode 18 o values and sr isotopic ratios decreased in the basal interval and approached stable values in the middle interval they increased in the upper interval and fluctuated in the stromatolite unit on the basis of geochemical screening criteria for detecting diagenetic alteration of sr isotopes the middle interval of the rhythmite unit with a minimum 87 sr 86 sr ratio of 0 70685 was interpreted to have retained the primary value or to have the least altered sr isotopic composition the basal interval which had ratios 0 718 at its base as high as those of old sialic rocks was interpreted as having altered sr isotopic ratios the high sr isotopic ratios at the base of this interval gradually decreased to near the minimum value at the top of the interval and other isotopic compositions and trace element concentrations showed systematic variations such systematic variations except for the variation in na concentration can be explained by a progressive diagenetic fluid rock interaction alternatively they might reflect a compositional transition from a local transport limited water following the glaciation to global well mixed seawater

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 ree content of some hydrothermal fluids ree concentrations were determined in solutions from submarine hydrothermal vents on the east pacific rise and for the first time from continental geothermal fields in tibet and bulgaria they indicate that in hydrothermal systems ree are immobile at temperatures below 350 c and for water rock ratios of 105 nd values of submarine solutions and anhydrites 4 7 to 6 2 suggests recharge on the sedimentcovered flanks of the ridge carbonate anions as measured by alkalinity appear to increase the solubility of heavy ree somewhat but not to the extent that substantial amounts of ree could be driven out from rocks by hydrothermal activity

constraints in using cerium anomaly of bulk sediments as an indicator of paleo bottom water redox environment a case study from the central indian ocean basin abstract the total rare earth elements ree abundance along with major and a range of trace element chemistry of twenty eight sub sections in a 5 m long sediment core aas 05 gc 02 from the central indian ocean basin shows a distinct ree fractionation sediments from the top 1 m of the core have comparatively low ree abundance close to average shale with a sample shale ree ratio very close to 1 strongly suggesting a dominantly terrigenous source the down core ree abundance shows a nearly two fold increase ree 167 341 ppm with depth and the ree strongly co varies with mn ti p and smectite inter element correlations and the shale normalized ree patterns suggest that light middle and heavy ree are selectively carried by terrigenous mn oxide and authigenic phosphate phases respectively suggesting a distinct ree fractionation these fractionation effects become more pronounced with increasing depth in the core the cerium ce anomaly in marine sediments is used as one of the promising tools to trace paleo bottom water redox conditions and this varies in the sediments from 0 10 to 0 08 the ce anomaly in general is positive in the top 4 m but the top 1 m have higher ce anomaly mn ti and ce ti suggest sediment deposition relatively under more oxic bottom water condition the negative ce anomaly between 4 and 5 m depth which could be interpreted to indicate a suboxic anoxic environment the redox environment inferred by the ce anomaly is compared to a number of other redox sensitive parameters to test its reliability these include mn content total organic carbon u th authigenic uranium cu zn and v cr ratio that all suggestive of deposition of sediments under oxygenated bottom water condition thus the negative ce anomaly observed between 4 and 5 m core depth does not represent a suboxic anoxic environment but is more likely due to the retention of a negative ce anomaly caused by authigenic phosphate and authigenic fe rich smectite which is formed by the reaction between iron oxyhydroxide and biogenic opal suggests an early diagenetic process and is in equilibrium with seawater ree early diagenetic process is responsible for the part of negative ce anomaly observed here therefore we suggest that the ce anomaly of bulk sediments as an indicator of paleo ocean bottom water redox conditions needs to be used with a caution

testing models for post glacial cap dolostone deposition nuccaleena formation south australia sedimentologically and geochemically distinctive carbonate sequences consistently drape the glacial deposits associated with the younger cryogenian ice age the presence of ice rafted debris in the basal dolostone implies that at least the lower portion of the cap sequence records deglaciation an isochronous model proposes that cap dolostones were deposited synchronously around the world regardless of water depth whilst a diachronous model proposes that deposition tracked glacioeustatic flooding during deglaciation the nuccaleena formation of the adelaide rift complex arc south australia exhibits many of the unique sedimentary features observed in other younger cryogenian cap dolostones around the world some bedforms are the product of wind driven oscillatory flow thus constraining post glacial dolostone deposition to 400 m these sedimentary features are absent in the deepest basinal facies in the northern arc suggesting that this region was below storm wave base even at the glacial sea level lowstand in the north flinders ranges there is a distinct relationship between lateral facies variability in the pre syn and post glacial sediments and the axes of 50 km scale structural folds the northern fold limbs are characterised by basinal facies whilst the southern limbs are associated with upper slope facies we interpret the abrupt facies transitions to reflect lower slope to upper slope shelf breaks across a series of linked south facing half grabens the majority of cap dolostone carbon isotope records show monotonic declines in 13c of 2 with starting points between 0 5 and 3 5 an isochronous model implies a 3 0 lateral gradient from platform to lower slope that varies dramatically on a short spatial scale and non systematically with palaeobathymetry if pre and syn glacial facies are used to infer palaeobathymetry and cap dolostones are deposited diachronously as sea level rises during deglaciation then 13c values becomes progressively lighter with time implying that cap dolostone deposition tracked the glacioeustatic sea level rise over a series of half grabens that deepened to the north the carbon isotope dataset cannot rule out uniquely isochronous or diachronous models given the high frequency spatial variability of 13c values temperature cannot be the dominant control on the isotopic variability of the cap dolostone

stable isotope composition and rare earth element content of vertebrate remains from the late cretaceous of northern spain lano did the environmental record survive abstract oxygen and carbon isotope measurements have been performed on phosphatic remains from faunal associations dinosaurs crocodiles turtles and fish of the late cretaceous continental and marine sediments from northern spain basque country the environmental meaning of the oxygen isotope record in fossil reptiles is discussed on the basis of known paleoecology modern fauna analogs and apatite chemistry rare earth elements ree co32 and po43 contents fossil remains in sandstones and argillites from two localities urria and cuezva have low down to 16 and scattered 18o po4 co3 and 13c values with ree patterns characterized by strong middle ree enrichments these geochemical compositions of the biogenic apatites have most likely been acquired during a multi stage late diagenesis involving complete recrystallization of the apatite in the presence of aqueous fluids ree contents of fossils preserved in the clayey sands from the site of lano suggest that samples have only been affected by early diagenesis despite the diversity of analyzed taxa and the close association of marine sharks and rays and freshwater species crocodiles and turtles evolving in a littoral environment the narrow range of phosphate 18o values is interpreted as reflecting the temperature and isotopic composition of groundwaters that prevailed in the burial environment the potential information relative to the physiology and thermal regime of the vertebrates has been erased during the process of early diagenesis if all oxygen in the phosphate has exchanged with groundwaters the oxygen isotope composition of vertebrate remains suggests that a warm climate t 20 25 c prevailed in northern spain during the late cretaceous

positive cerium anomaly in the doushantuo cap carbonates from the yangtze platform south china implications for intermediate water column manganous conditions in the aftermath of the marinoan glaciation abstract oxygenation exerted an important control on the emergence and diversification of metazoans in the aftermath of the marinoan glaciation however the relationship between the oceanic dissolved o2 do levels and early metazoan evolution remains equivocal to provide a temporal and spatial reconstruction of the redox conditions for this critical interval this study investigates the early ediacaran cap carbonate deposits within intra shelf facies at three localities in the three gorges area the yangtze platform south china trace and rare earth elements are sequentially extracted from the carbonate fraction for pristine temporal seawater signals the member ii dolostones of the duoshantuo formation which overlies the cap carbonates show a negative ce anomaly no ce anomaly is observed in the lower units of the cap carbonates in contrast positive ce anomalies ce ce 1 3 in the uppermost part of the cap carbonates are observed in all studied sections these positive ce anomalies are accompanied by high mn fe ratios ranging from 5 04 to 14 96 and slightly positive mree anomalies suggesting that a fe mn oxyhydro oxide coparticipation occurred during the cap carbonate deposition the positive ce anomalies may result from the reductive dissolution of the ce enriched mn oxyhydro oxides across a mn iv mn ii redoxcline in a distinct manganous water wedge that was sandwiched between well oxygenated and anoxic ferruginous deep water layers this wedge may have exhibited low oxygen conditions with approximately 10 m do dissolved oxygen in comparison to the 90 m do expected in an oxic setting and 0 m do in an anoxic setting therefore the presence of a positive ce anomaly in the uppermost part of the cap carbonates indicates a new intermediate manganous condition and further elucidates the water column redox structure that existed following the end of the marinoan glaciation early ediacaran metazoans were possibly restricted to fully oxygenated conditions and were absent in the manganous or ferruginous rich environments

iodine records from the ediacaran doushantuo cap carbonates of the yangtze block south china abstract late neoproterozoic cap carbonates formed following the cryogenian glaciations may record information about the significant climate change and ocean chemistry evolution immediately after the snowball earth events large negative carbon isotope anomalies and enigmatic sedimentary structures have been identified from the post marinoan cap carbonates across the globe but their formation mechanism remains debatable due to difficulties of distinguishing overlapped chemical signatures and diagenetic alterations in this study we present i ca mg profiles of four sections from a shallow to deep water transect of the basal doushantuo cap carbonates one of the most extensively studied ediacaran units in south china most samples have i ca mg values lower than 1 mol mol with a few exceptions in the shelf sections up to 2 5 mol mol all calcite samples with extremely low 13c have iodine signal below detection limit suggesting carbonate precipitation from anoxic seawater or diagenetic fluids among the four sections the slope section has the lowest i ca mg values suggesting that it may have experienced more extensive fluid buffered diagenesis and more severe loss of io3 in combination with available major trace rare earth element and isotope data the temporal i ca mg variations support freshwater mixing and deep water upwelling in proximal sites and transient oxidation during deposition of the doushantuo cap carbonates