early cretaceous polarity chrons cm0 to cm11 recorded in northern italian land sections near brescia abstract three lower cretaceous pelagic limestone sections located in the lombardian prealps northwest of brescia record polarity chrons cm0 to cm11 the polarity chrons are correlated to nannofossil and foraminiferal events the polaveno section records polarity chrons cm3 to cm11 with excellent fit to the larson and hilde 1 polarity model derived from hawaiian oceanic magnetic anomalies this is the first complete magnetostratigraphic record in this interval and indicates that this part of the hawaiian polarity model represents an approximately constant spreading rate record the pie del dosso section records cm0 and cm1 with correlations to the biostratigraphic record the san giovanni section records part of the cm3 to cm9 interval with the cm6 to cm8 interval cut out by faulting the correlations of polarity chrons to nannofossil datum planes are generally consistent with previously published correlations based on data from the southern alps and central italy umbria we present new biostratigraphic data from a previously studied section capriolo southern alps which result in revised identification of cm0 and cm1 at this locality

conditions of formation and diagenetic evolution of upper proterozoic phosphate nodules from southern sweden evidence from petrology mineral chemistry and isotopes abstract dark gray to black cryptocrystalline francolite occurs as nodules 2 8 cm in diameter which are embedded in organic matter rich mudstones of the visingso group upper proterozoic southern sweden the 13cpdb values 18 4 to 0 98 of structural co2 complemented by studies of the petrographic character and strontium isotopic composition of francolite indicate precipitation in the suboxic and sulfate reduction zones francolite is intergrown with berthierine that has formed in the suboxic fe reduction zone calcite enriched in mn and to a lesser extent fe occurs as fracture and void fillings and as replacement of francolite mn and mg rich calcian siderites have precipitated as pseudomorphs after bacteria in the zone of microbial methanogenesis the carbon 13 c pdb 0 75 to 7 04 and oxygen 18 o pdb 14 21 to 10 58 isotopes of calcite suggest derivation of carbonate ions from microbial methanogenesis and from thermal decarboxylation of organic matter at temperatures of 60 to 80 c some of the void and fracture filling calcites 13 c 20 8 to 18 63 18 o 5 46 to 5 21 have however precipitated at lower temperatures 25 30 c in the sulfate reduction zone

paleomagnetism of the front range colorado morrison formation and an alternative model of late jurassic north american apparent polar wander a paleomagnetic study of the upper jurassic morrison formation in the front range of central colorado yields high unblocking temperature dual polarity magnetizations with respect to known paleohorizontal the inclinations absolute mean 57 3 degree 95 confidence interval 52 3 degree to 63 1 degree n 8 sites pass tilt and reversal tests whereas the dispersion in declinations can be attributed to apparent or real tectonic rotations and sedimentary processes the site centered colatitudinal locus of possible front range morrison poles partially overlaps the upper pole but it excludes the lower pole from the morrison formation on the colorado plateau as well as the 151 ma glance conglomerate pole from the basin and range province of southeastern arizona the authors offer various explanations for these disparities and suggest an alternative model of late jurassic north american apparent polar wander through approximately 70 degree n which is supported by late jurassic european poles with positive stability tests transferred to north american coordinates

paleomagnetism of middle late jurassic sediments from poland and implications for the polarity of the geomagnetic field abstract paleomagnetic data for the middle late jurassic sediments from nine localities of krakow czestochowa upland belonging to stable europe and from three valleys of the lower subtatric nappe belonging to mobile europe are presented the majority of the rocks investigated comprising limestones stromatolites and radiolarites were found to be normally magnetized natural remanent magnetizations nrm of reversed polarity were found in limestones and stromatolites of middle callovian age from the stable region and in one exposure of oxfordian radiolarites from the mobile region along one of the middle callovian sections studied the nrm direction of the specimens changed from r to n the mean paleomagnetic pole positions obtained for the krakow czestochowa upland lat 72 3 n long 150 4 e 95 7 3 and for the lower subtatric nappe lat 71 7 n long 132 2 e 95 4 3 are consistent with the data for stable europe lat 74 7 n long 147 1 e 95 5 0 the paleomagnetic results presented do not reveal any major relative rotations either within the lower subtatric nappe or between this area and the krakow czestochowa upland the reversed directions of nrm observed indicate the existence of a period of reversed field direction in the middle callovian and perhaps also in the oxfordian

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

carbon to phosphorus ratios in sediments implications for nutrient cycling defining the transformations of phosphorus p in sediments is critical to assessing the geochemical behavior of sedimentary p and the behavior of reactive p preactive poxide associated pauthigenic porganic relative to organic carbon corganic this study includes the determination of p components and corganic concentrations on samples from sites in the california current region ocean drilling program odp leg 167 sites 1010 1011 1012 1014 1016 and 1021 in the benguela current region odp leg 175 sites 1082 1084 and 1085 and on blake nose in the western atlantic odp leg 17 1b sites 1050 and 1052 sample depths range up to 650 m and ages range up to 65 ma our data demonstrate the transformation of labile forms of p porganic and poxide associated to pauthigenic throughout the sediment column in all redox states and at all sedimentation rates investigated until a substantial portion of reactive p is in the authigenic form 80 c p organic ratios are always greater than or equal to the redfield ratio in all of the sediments we studied sediments with corganic concentrations 2 wt have corganic preactive ratios less than the redfield ratio and corganic preactive ratios increase linearly with corganic consistent with degradation of corganic with age in general corganic preactive ratios for sediments with corganic concentrations 2 wt from a variety of redox states and sedimentation rates center around the redfield ratio although some ratios are as high as 3 times the redfield ratio however corganic preactive ratios up to 400 do not approach the high ratios observed for c p organic ratios up to 4500 because of the efficient transfer of labile forms of p to pauthigenic corganic preactive ratios better describe the geochemical behavior of sedimentary p

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

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

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

rare earth element and srnd isotope geochemistry of phosphate nodules from the lower cambrian niutitang formation nw hunan province south china abstract phosphate nodules are widely distributed in the early cambrian black shale sequence in yangtze platform south china in this study we carried out x ray diffraction major element rare earth element and sr nd isotopic studies on phosphate nodules from two pc c sections in hunan province south china two different types of phosphate nodules can be recognized based on ree and nd isotopic characteristics type 1 with seawater like ree patterns higher end t values and type 2 with hat shaped ree patterns and more negative end t values we suggest that the difference in ree patterns and nd isotopic compositions between the two types reflects changes in pore water geochemistry from seawater dominated towards diagenetic fluid dominated conditions during early diagenesis positive eu anomalies are displayed in most samples and are likely to record not only the anoxic environments but also the involvement of submarine exhalative hydrothermal fluids which prevailed in south china during early cambrian

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

ree patterns in latest neoproterozoic early cambrian phosphate concretions and associated organic matter abstract analyses of ree were conducted on phosphatic concretions and various types of associated organic matter in eight key latest neoproterozoic earliest cambrian inner to outer shelf marine phosphatic successions that are distributed worldwide a pronounced ree fractionation during diagenetic degradation of the organic matter has been revealed selective mree incorporation and bulk ree contents in some kerogens organic megascopic fossils and humic acid are compatible with those recorded in associated phosphate the similarity of ree patterns in apatite and organic matter suggests that early diagenetic microbial decomposition of organic matter does not only provide phosphorus and suitable sub oxic geochemical conditions but it is also a likely source of ree enrichment in authigenic apatite formed at shallow depths below the marine water sediment interface

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

a la icp ms analysis of rare earth elements on phosphatic grains of the ediacaran doushantuo phosphorite at weng an south china implication for depositional conditions and diagenetic processes the ediacaran doushantuo formation at weng9an south china hosts well preserved phosphatized microfossils known as the weng9an biota a laser ablation icp ms analysis of rare earth element ree characteristics of the fossil bearing black phosphorite unit of the doushantuo formation at weng9an was conducted with the aim of unravelling the depositional conditions and diagenetic processes during formation of the phosphorites spherical phosphatized microfossils and phosphatic clasts were analysed and the ree data display middle ree mree enriched shale normalized ree patterns the spherical phosphatized microfossils show an increase in total ree contents ree from core to rim negative correlations between ree and the extent of mree enrichment over the other ree indicated by la n sm n yb n sm n are observed for analysed spots within individual phosphatic grains which may be due to complex diagenetic history of the phosphatic grains with fluctuations in ree sources and chemical parameters in a high energy shallow water environment being additional factors the la n yb n and la n sm n characteristics of the phosphatic grains suggest they were mostly influenced by early diagenetic alteration rather than late extensive recrystallization the negative ce anomalies in the samples suggest they formed under oxic bottom water conditions positive eu anomalies are present in all samples and are likely to reflect involvement of hydrothermal fluids rather than changes in redox conditions of porewater overall this study has major implications for phosphorites as important archives for the study of geochemical proxies the ediacaran period and also evolutionary changes

paleomagnetism and late diagenesis of jurassic carbonates from the jura mountains switzerland and france a crucial fold test for magnetizations measured in bajocian through kimmeridgian limestones from the jura mountain region shows that rare blue gray limestones found in this sequence preserve a prefolding magnetization in contrast tan limestones which predominate in this sequence contain secondary magnetizations acquired after folding in the late miocene the postfolding magnetizations in tan limestones appear to be carried in goethite and because reversed as well as normal polarity directions are present the magnetization in these limestones is probably a post miocene pre brunhes 700 000 yr chemical remanent magnetization crm field relations between tan and blue gray limestones which are present in some cases in the same rock unit for example the hauptrogenstein suggest that the tan limestones may have formed from alteration of blue limestones whereas goethite pseudomorphs after pyrite are found in tan limestones the occurrence of pyrite in the blue limestones supports this model indicating that goethite could have formed from oxidation of pyrite abundant meteoric water probably was available for such an oxidation process during uplift of these strata subsequent to deformation natural remanent magnetization in blue limestones appears to be carried in magnetite the positive fold test for the characteristic magnetization in these rocks is significant at the 99 confidence level k values for 24 site mean directions before and after tilt correction are 9 3 and 43 2 respectively the simplest interpretation for the origin of observed remanence in magnetite in the blue limestones is a primary magnetization of depositional or biogenic origin characteristic directions in these rocks yield a mean paleopole position of 77 7n 148 4e k 26 0 a95 5 9 this pole is in reasonable agreement with one other upper jurassic pole from western europe and with other middle to upper jurassic poles from the atlantic bordering continents after rotation of these continents to a reconstructed configuration for middle to late jurassic time

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

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

middle triassic magnetostratigraphy and biostratigraphy from the dolomites and greece abstract magnetostratigrapic and biostratigraphic data across the anisian ladinian middle triassic boundary were obtained from the frotschbach seceda section from the dolomites region of northern italy and the vlichos section from the greek island of hydra where the aghia triada published section was also resampled the frotschbach seceda section includes two radiometrically dated u pb tuff levels and covers two of the three chief candidates for the position of the base of the ladinian namely at the base of the secedensis zone or the subsequent curionii zone the aghia triada section yields biochronological evidence for the base of the secedensis zone whose significance is however critically discussed in the light of the magnetostratigraphic correlation with frotschbach seceda the vlichos section can be correlated with aghia triada and frotschbach seceda by means of magnetic polarity stratigraphy and sparse fossil occurrences the satisfactory correlation of the magnetozones allows us to construct a composite geomagnetic polarity sequence tied to tethyan ammonoid and conodont biostratigraphy for about a 2 4 myr interval across the anisian ladinian boundary

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

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

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

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

theoretical constraints on true polar wander 1 for the present geologic epoch true polar wander tpw is relatively small but simple theoretical considerations suggest that it could have been larger in other epochs in this work we use scaling arguments to assess the qualitative behavior of tpw and a simple maxwell model to analytically describe how changes in mass anomalies translate into tpw unlike previous work we derive simple analytical estimates of tpw based on the characteristic amplitudes and timescales for changes in the moment of inertia we find estimates for both the amplitude and speed of tpw as a function of earth properties the following four main factors influence how large the maximum tpw can be the geological timescale over which the desired tpw occurs tpw the viscosity structure of the mantle which yields a weighted average viscosity the characteristic amplitude of the nonhydrostatic changes in the moment of inertia c and the added moment of inertia due to the equatorial bulge c a for the nominal values 3 1022 pa s and c c a 0 003 the maximum tpw is 61 over 100 myr and 8 over 10 myr the maximum tpw speed is only sensitive to c and c a and is 2 4 myr 1 for the nominal values tpw is shown to act as a low pass filter rapid changes in moment of inertia produce smaller and delayed tpw a consequence of this is that inertial interchange tpw does not have a different character than tpw tpw can have an important contribution to plate motions over relatively long timescales but not over shorter timescales our simple approach allows us to assess whether multiple tpw events are possible but the major uncertainty continues to be the mantle viscosity structure

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

sr and nd isotopic analysis of phosphorite sedimentation through one miocene high frequency depositional cycle on the north carolina continental shelf abstract a well developed seismic litho and biostratigraphic data base with good models for the formation and deposition of phosphate rich sediments exist for the upper cenozoic sediments on the north carolina continental margin this provides a unique opportunity to evaluate the potential of utilizing strontium and neodymium isotopic analyses to help unravel a complex genetic history of phosphate formation and deposition thirty one samples from three vibracores in onslow bay supplied hand picked concentrate subsamples of five phosphate grain types and thirty one concentrate subsamples of phosphate peloids for stratigraphic analysis all subsamples were analyzed for their sr isotope composition while only thirteen were analyzed for nd isotopes the 31 peloid samples represent three different stratigraphic units and include 1 holocene surficial sands with highly variable concentrations and types of reworked phosphate 2 pleistocene moldic carbonates with minor concentrations of black peloidal phosphate and 3 miocene mid burdigalian frying pan sequence unit 1 fps 1 of the pungo river formation with very high concentrations of multiple types of phosphate grains that decrease upsection and change grain types with changing lithofacies the latter unit represents deposition during one high frequency sea level cycle stratigraphic analysis utilized one grain type phosphate peloids for comparative purposes with the depositional model of riggs and mallette 1990 the sr and nd data cluster into significant categories that are coincident with these three major stratigraphic units sr and nd isotope compositions of selected phosphate grains from three phosphate rich depositional sequences are utilized to 1 date the initial miocene transgression of unit fps 1 of the pungo river formation 2 decipher processes of formation and deposition of major phosphate grain types through one miocene sea level cycle including the processes of in situ formation versus reworking 3 develop a sr and nd chronostratigraphy for evaluating changing patterns of continental margin sedimentation through high frequency depositional cycles 4 determine effects of reworking and weathering on the isotope signals between miocene pleistocene and holocene sediments 5 evaluate the suitability of utilizing sr and nd isotopes for detailed chronostratigraphic analysis of phosphorite sedimentation and 6 refine our understanding of the upper cenozoic evolutionary history of north carolina s continental margin

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

iron phosphate in the ediacaran doushantuo formation of south china a previously undocumented marine phosphate sink abstract ediacaran phosphorites capture the dynamics of the ultimate biolimiting nutrient phosphorus during perhaps the most critical transition of earth s climatic and ecological history concomitant with the neoproterozoic oxygenation event was the deposition of the first extensive phosphorites across marine shelves typically interpreted as a basinward shift in the locus of phosphogenesis facilitated by deep ocean oxygenation petrographic and spectroscopic analyses of proximal phosphorites from the ediacaran doushantuo formation near the yangtze gorges area of south china reveal the presence of interlaminated pristine muddy and granular phosphorites that were cemented by early diagenetic iron phosphate an additional previously undocumented seafloor p sink transmitted and reflected light microscopy cathodoluminescence microscopy and back scattered electron scanning electron microscopy were used to reconstruct the paragenesis of phosphorites at the wanjiagou section near zhangcunping hubei province and demonstrate that pristine phosphorite precipitated authigenically as francolite via microbially mediated phosphogenesis as evidenced by preserved microbial laminations along with filamentous and coccoidal microfossils subsequent tidal reworking of pristine hardgrounds and phosphatic mudstones produced minimally coated intraclasts and peloidal phosphatic grains that were cemented by iron phosphate soon after deposition but before compaction raman spectroscopy bulk sample and micro x ray diffractometry indicate the iron phosphate cement is composed of phosphosiderite strengite fe 3po4 2h2o the presence of phosphosiderite can be attributed to either syndepositional oxidation of phosphorites or thermal stabilization of vivianite fe2 3 po4 2 8h2o in both cases the occurrence of phosphosiderite represents the first direct evidence for iron phosphate minerals as a p sink during the ediacaran and suggests phosphogenesis may have partially proceeded in ferruginous porewaters in contrast to the redox independent process of francolite precipitation integration of petrographic and geochemical techniques such as those employed in this study offers the ability to corroborate p speciation analyses and provides an independent determination of p phase partitioning ultimately this approach is paramount in testing hypotheses that suggest ferrous iron phosphate minerals played a regulatory role in global proterozoic oxygenation

intra oceanic subduction shaped the assembly of cordilleran north america the western quarter of north america consists of accreted terranes crustal blocks added over the past 200 million years but the reason for this is unclear the widely accepted explanation posits that the oceanic farallon plate acted as a conveyor belt sweeping terranes into the continental margin while subducting under it here we show that this hypothesis which fails to explain many terrane complexities is also inconsistent with new tomographic images of lower mantle slabs and with their locations relative to plate reconstructions we offer a reinterpretation of north american palaeogeography and test it quantitatively collision events are clearly recorded by slab geometry and can be time calibrated and reconciled with plate reconstructions and surface geology the seas west of cretaceous north america must have resembled today s western pacific strung with island arcs all proto pacific plates initially subducted into almost stationary intra oceanic trenches and accumulated below as massive vertical slab walls above the slabs long lived volcanic archipelagos and subduction complexes grew crustal accretion occurred when north america overrode the archipelagos causing major episodes of cordilleran mountain building a new explanation for the origin of the accreted terranes that form the mountainous cordillera of western north america is proposed and tested stationary intra oceanic subduction deposited massive slab walls in the mantle and grew volcanic archipelagos at the surface which were overridden by and accreted to north america during cretaceous times the generally accepted account of how the geology of western north america developed involves the oceanic farallon plate acting as a conveyor belt sweeping crustal terranes onto the continental margin as it moves beneath the north american plate this model fails to explain many aspects of this accreted terrane and here karin sigloch and mitchell mihalynuk present an alternative model based on new tomographic images of lower mantle slabs and modelling of deep mantle structure in the region they propose that during the cretaceous period there were a series of island arcs west of north america beneath which proto pacific plates subducted into almost stationary trenches long lived volcanic archipelagos and subduction complexes grew above the slabs and then accreted onto north america as it overrode the archipelagos causing episodes of cordilleran mountain building

geochemical characteristics of phosphorite and carbonate nodules from the miocene funakawa formation western margin of the yokote basin northeast japan abstract phosphorite nodules were discovered in diatomite and diatomaceous mudstones of the late miocene funakawa formation in dewa height on the western margin of the yokote basin northeast japan they occur as small nodules cemented burrows and small trace fossils in diatom rich sediment that was deposited just above the contact between underlying siliceous shales the underlying shales are essentially devoid of fossils and the overlying bioturbated diatomaceous mudstones are fossil rich the underlying shale is rich in manganese mn calcite nodules and the overlying mudstone is rich in magnesian mg calcite nodules some phosphorite nodules exhibit a zonal structure caused by two phases of mg calcite cementation with or without mn calcite within the pore space of the nodule the phosphorus p content of these nodules exceeded 25 wt in p2o5 the principle phosphate mineral composing the nodules is fluor f carbonate apatite crystals which are a few m in length and cocoon shaped their aggregate includes a small amount of silica aluminum and water si al and h2o respectively the rare earth element ree composition of the phosphorite nodules is characterized by a positive europium eu anomaly and no cerium ce anomaly the biomarker distribution of the phosphorite nodules is characterized by low cpi low carbon number n alkane and high hopenes type hopane and isoprenoid ketone phosphorite nodules originate from the phosphate contained in diatoms the mineralization occurs in the bacterial sulphate reduction zone and bacteria appear to have played an important role in the concentration of p and precipitation of apatite

miocene phosphorites from the murray ridge northwestern arabian sea abstract phosphorites from the murray ridge nw arabian sea comprise nodules bioclasts and bone fragments the nodules are made up of a homogeneous light colored phosphate nucleus consisting of rivulariacean filamentous cyanobacteria and a thin dark grey colored phosphate cortex showing abundant microbial filaments and microborings the bioclasts comprise of 14 14 5 ma old planktonic foraminifers accepted as the time of deposition spherical to ovoid shaped apatite microparticles resembling fossil bacteria are distinct components in the bioclasts bone fragments exhibit apatite fillings the nodules and bone fragments consist entirely of carbonate fluorapatite cfa with low al k and th concentrations suggesting absence of continental detritus shale normalized ree patterns of the samples support a seawater derived composition the highly uniform initial nd values of 4 8 to 5 1 are interpreted as the seawater value at the onset of phosphatization 14 ma ago in contrast 87sr 86sr ratios show a large range of 0 709055 to 0 709124 corresponding to unusually young stratigraphic ages of 1 to 3 ma the data are interpreted as evidence for post depositional sr exchange of the recrystallizing phosphorites with fluids isotopically not much different from modern seawater it is concluded that the phosphorites formed under oxic shallow water conditions where microbial populations assimilated phosphorus primarily from seawater and mediated precipitation of cfa during early diagenesis at the sediment water interface on different substrates

apatite nodules as an indicator of depositional environment and ore genesis for the mesoproterozoic broken hill type gamsberg zn pb deposit namaqua province south africa nodules consisting of fluorapatite are concentrated as a discrete band in the polymetallic sulfide ore of the gamsberg deposit in central bushmanland south africa their shape zonal features and geochemistry in particular rare earth element ree abundances are similar to authigenic francolite concretions that precipitate during diagenesis in organic rich muds as a result the apatite nodules are regarded as primary the nodules have a strong lithostratigraphic control occurring at the transition of siliciclastic hosted pyrite sphalerite graphite mineralization to calc silicate hosted pyrrhotite sphalerite mineralization mineralogical and chemical evidence indicates that this transition also corresponds to a paleo redox boundary that separates sediments deposited under oxygen deficient conditions from those that developed in a more oxygenated environment the apatite nodules can morphologically and chemically clearly be distinguished from coarse apatite grains that occur in oxide facies iron formations stratigraphically above the ore horizon however similar ree profiles and in particular positive eu anomalies in both types of apatite are indicative of a close genetic relationship between the two units and favor a common hydrothermal origin of the p the contrasting morphologies and chemical signatures of the two occurrences can rather be attributed to differences in behavior of the phosphates during precipitation within the contrasting host sediments chemical versus fine grained clastic taking modern phosphorites as an analogue these results are used to postulate a genetic model for the deposition of the sulfide ore and associated iron formations the model envisages differentiation of the depositional basin into oxygen deficient basin facies hosting the sulfide ore and oxygenated shelf facies which are composed of manganiferous iron formations the intimate association of sedimentary apatite with base metal sulfides indicates that basin conditions were conducive to the precipitation of both phases this relationship might act as a potential exploration guide in similar basins elsewhere

two major cenozoic episodes of phosphogenesis recorded in equatorial pacific seamount deposits seamount phosphorites have been recognized since the 1950s but this is the first study to provide an in depth exploration of the origin and history of these widespread deposits representative samples from equatorial pacific cretaceous seamounts were analyzed for chemical mineralogical and stable isotope compositions the phosphorites occur in a wide variety of forms but most commonly carbonate fluorapatite cfa replaced middle eocene and older carbonate sediment in a deep water environment 1000 m element ratios distinguish seamount phosphorites from continental margin plateau and insular phosphorites uranium and thorium contents are low and total rare earth element ree contents are generally high ree ratios and shale normalized patterns demonstrate that the rees and host cfa were derived from seawater strontium isotopic compositions compared with inferred cenozoic seawater curves define two major episodes of cenozoic phosphatization late eocene early oligocene 39 34 ma and late oligocene early miocene 27 21 ma three minor events are also indicated the major episodes occurred at times of climate transition the first from a nonglacial to glacial earth and the second from a predominantly glacial to warm earth the paleoceanographic conditions that existed at those times initiated and sustained development of phosphorite by accumulation of dissolved phosphorus in the deep sea during relatively stable climatic conditions when oceanic circulation was sluggish fluctuations in climate sealevel and upwelling that accompanied the climate transitions may have driven cycles of enrichment and depletion of the deep sea phosphorus reservoir as temperature gradients in the oceans increased antarctic glaciation expanded and oceanic circulation and upwelling intensified expansion and intensification of the oxygen minimum zone may have increased the capacity for midwater storage of phosphorus supplied by dynamic upwelling around seamounts however the bottom waters never became anoxic during the phosphogenic episodes fluctuations in the ccd and lysocline co2 fluxes and changes in bottom water circulation and temperatures may have bathed the seamount carbonates in more corrosive waters which coupled with increased supplies of dissolved phosphorus promoted replacement processes the late eocene early oligocene phosphogenic episode recorded in seamount deposits is not matched by large phosphorite deposits in the geologic record whereas the late oligocene early miocene episode and middle miocene event are matched by large deposits distributed globally the seamount phosphorites are exposed at the surface of the seamounts and have been for most of the neogene and oligocene the phosphorites do not show signs of etching that would indicate substantial undersaturation of seawater phosphate with respect to cfa mass balance calculations indicate that about 5 4 19 1012 g of p2o5 are locked up in equatorial pacific seamount phosphorites that amount is equivalent to about 2 7 years of the present annual input from rivers

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

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

the 125 150 ma high resolution apparent polar wander path for adria from magnetostratigraphic sections in umbria marche northern apennines italy timing and duration of the global jurassic cretaceous hairpin turn a new high resolution apparent polar wander path apwp segment has been obtained from the magnetostratigraphy of four kimmeridgian to lower aptian sections in the northern apennines italy the use of paleomagnetic data for determination of the adria apwp was hampered by the large local rotations linked to apennine tectonics characterized by folds and thrusts developed during the neogene to overcome this problem we have computed relative rotations between time overlapping sections and realigned them in a common declination reference frame namely the bosso section we synthesized a new high resolution 150 to 125 ma apwp for adria which has a similar shape to the time equivalent segment of the synthetic apwp of africa of besse and courtillot j besse v courtillot apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr j geophys res 107 b11 2002 doi 10 1029 200jb000050 a 26 clockwise rotation of our combined adria apwp places it in almost perfect overlap with african data of same age confirming that the adria promontory moved coherently with africa during this time span whereas the counterclockwise rotation of adria with respect to africa was introduced later most probably during apennines orogenesis finally we discuss in relation with worldwide plate evolution the peculiar shape of our apwp which displays a hairpin turn during berriasian time and dates the main late jurassic early cretaceous change in plate motion at around anomaly m16

origin of chert nodules in the ediacaran doushantuo formation black shales from yangtze block south china abstract chert nodules are widely developed in ediacaran deposits of south china yet the mechanism responsible for their formation remains disputed petrological and geochemical studies of chert nodules and host shale of the ediacaran doushantuo formation of the yangtze block south china were carried out to more fully assess silicification of these deposits doushantuo chert nodules display a concentrically layered internal structure dominated by quartz and lesser concentrations of calcite carbonate fluorapatite organic matter pyrite and sphalerite individual layers become thinner from nodule centers to edges our results suggest that 1 doushantuo host black shale accumulated under persistent anoxic bottom water conditions and 2 chert nodules formed as a consequence of the anaerobic oxidation of methane focused along sulfate methane transition zones at shallow burial depth nodules likely originated from porous proto nodules that consisted of 13c depleted authigenic calcite produced by the anaerobic oxidation of methane decaying of organic matter within nodules helped to create porosity that was filled by authigenic calcite and also released phosphate and zinc ions to pore water thus favoring precipitation of carbonate fluorapatite and sphalerite silica supplied principally from the diagenesis of clay minerals of the host shale cemented the nodules and replaced early formed calcite the progressive infilling of residual porosity by 18o depleted pore fluids associated with increasing burial depth is reflected in the strongly negative 18ocarb values documented from the nodules thus the formation of doushantuo chert nodules reflects a protracted diagenetic history initiated by bacterial sulfate reduction and anaerobic oxidation of methane close to and within the sulfate methane transition zone and continued in association with the diagenetic release of silica from host shale as well hydrocarbon generation with increasing burial depth

elemental mobility in phosphatic shales during concretion growth and implications for provenance analysis shale normalized rare earth element ree patterns record variable redox conditions in coprolitic phosphorite concretions and their host shales from the pennsylvanian age cyclothems in the u s midwestern states of oklahoma kansas nebraska iowa and ohio as well as the mississippian age fayetteville shale of arkansas shale normalized enrichments in middle ree mree developed as the phosphatic concretions lithified under reducing conditions in pore waters of organic rich muds depletions in mree sm ho in host shales correspond to the mree enrichments in some nearby concretions rare and weak negative cerium depletions in both reworked and unreworked phosphorite concretions suggest exposure to oxygenated waters positive europium anomalies in thick phosphorite coatings on coprolitic phosphorite concretion cores suggest extreme reduction during lithification of the phosphorite coating flat ree patterns in both host shales and phosphorite concretions probably reflect detrital influence phosphate diagenesis can affect the trace element chemistry of black shale enough to alter provenance signals overall enrichment in ree in phosphorite relative to host shale suggests movement of ree as does the mree enriched phosphorite near the mree depleted host shale diagenetically mobile ree can affect la th sc relationships used in provenance analysis the extent of the diagenetic modification of la th sc distribution is related to the amount of p2o5 present typical la th sc distribution in host shale results when p2o5 values are below 0 5 high la abundance substantially skews la th sc distribution when p2o5 is above 5 0 but when p2o5 is between 0 5 and 5 0 the extent of the effect is unclear oxides of aluminum and other major elements may be useful in recording detrital influence and proximity to the shoreline in phosphorite concretions most of the concretions nearest to shoreline sources of detrital input have both flat ree patterns and elevated values of al2o3 al2o3 fe2o3

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

initiation of cataclastic flow and development of cataclastic foliation in nonporous quartzites from a natural fault zone abstract microstructural study of foliated quartz cataclasites of a segment of the towaliga fault zone georgia usa indicates that rock strain by cataclastic deformation occurred through microscopic displacements along a distributed system of shear bands the localized cataclastic flow in the bands was in turn the result of frictional sliding along a network of mesoscopic shear fractures that accommodated initial strains and were in part created by high fluid pressures in the fault zone the shear fractures at both the microscopic and mesoscopic scale were formed in the riedel r1 p and y orientations simultaneous displacements along these riedel shears produced the cataclastic foliation rhomb shaped and tabular quartz grain fabrics and straight stepped grain boundaries crystallization by fluids accompanied fracturing and possibly aided the cataclastic flow by forming muscovite and quartz crystals along fractures most fluid inclusion trails and quartz veins cut across the cataclastic features indicating that fluids which assisted the deformation later healed the fractures a right lateral sense of displacement is suggested for the cataclastic flow consistent with the kinematics of the mylonitization along the fault zone

removal of oceanic ree by authigenic precipitation of phosphatic minerals abstract early diagenetic phosphatic minerals containing rare earth elements ree are widespread in australian shallow marine sandstones of all ages most common is the aluminophosphate florencite ree al 3 po 4 2 oh 6 but the isomorphous and chemically intergrading phases crandallite gorceixite and goyazite all with up to several percent ree substituted for their major cation ca ba and sr respectively may also be present together they comprise up to 0 144 wt average 0 0134 wt of their host rocks the authigenic phosphates xenotime and apatite are also widespread but less common they all apparently precipitated within the diagenetic zones of sulphate reduction and methanogenesis as a result of reverse weathering reactions after the release of ree and po 4 by reduction of fe mn oxyhydroxides and the decomposition of organic material coating detrital particles as the aluminophosphates and apatite are enriched in light ree whereas xenotime concentrates heavy ree they collectively deposit light ree at a much greater rate la 129 10 9 g cm 2 yr 1 than heavy yb 0 40 10 9 g cm 2 yr 1 the total burial flux of light ree by shallow marine phosphatic precipitation is about 50 times greater than previously determined for deep sea sediments whereas heavy ree are buried at comparable rates this new sink produces a major imbalance in the marine ree budget requiring the existence of a substantial but currently unknown source to restore balance its size has important implications for the use of ree abundances distributions and isotopes as monitors of marine geochemical processes

comparison between datangpo type manganese ores and modern marine ferromanganese oxyhydroxide precipitates based on rare earth elements abstract datangpo type sedimentary manganese deposits which are located in northeastern guizhou province and its adjacent areas are mn carbonate type deposits hosted in black carbonaceous shale that represent a series of medium to large deposits containing a huge tonnage of reserves paas normalized rare earth element distribution patterns of manganese ores record hat shaped rey ree y plots characterized by pronounced middle rare earth element enrichment evident positive ce anomalies weak to strong positive eu anomalies and negligible negative y anomalies these rey geochemical characteristics are different from those of country rocks and record the processes and features of sedimentation and diagenesis manganese was precipitated as mn oxyhydroxide particles in oxidized water columns with the sorption of a certain amount of rare earth elements subsequently transforming from mn oxyhydroxides to rhodochrosite and redistributing rey in reducing alkaline pore water during early diagenesis a number of similarities can be observed through a comparison of datangpo type manganese ores and modern marine ferromanganese oxyhydroxide precipitates based on their rare earth elements the precipitation of datangpo type manganese ores is similar to that of hydrogenetic crusts and nodules based on their positive ce anomalies and relatively higher total rey concentrations however several differences also exist compared to hydrogenetic crusts and nodules datangpo type manganese ores record smaller positive ce anomalies lower total rey concentrations unobvious fractionation between y and ho and weak to strong positive eu anomalies these were caused by quicker sedimentary rates in the oxic water columns of the shallower basin after which pore water became strongly reducing and alkaline due to the degradation of organic matter in the early diagenetic stage in addition compared to typical deposits in the world datangpo type manganese ores are similar to hydrogenetic deposits and different than hydrothermal deposits all of these characteristics of manganese ores indicate that datangpo type manganese ores the principal metallogenic factors of which include oxidation conditions during deposition and reducing conditions during early diagenetic stages represent hydrogenetic deposits

paleomagnetism and tectonics of the jura arcuate mountain belt in france and switzerland abstract goethite and hematite in ferriferous oolitic beds of callovian age from the jura mountains switzerland france carry either pre and or post tectonic magnetization the frequent pre tectonic origin of goethite magnetization indicates a temperature range during formation of the arcuate jura mountain belt below the goethite neel temperature of about 100 c the scatter of the pre tectonic paleomagnetic directions d 11 5 e i 55 5 95 4 7 which reside both in goethite and hematite provides strong evidence that the arcuate mountain belt was shaped without significant rotation the paleomagnetic results support tectonic thin skinned models for the formation of the jura mountain belt

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

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

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

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

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

trace and rare earth element geochemistry of black shale and kerogen in the early cambrian niutitang formation in guizhou province south china constraints for redox environments and origin of metal enrichments abstract early cambrian black shales of south china not only host important sponge arthropod and other soft bodied fossils that have helped to trace early metazoan diversification but also show extreme enrichments of a number of trace metals in particular ni mo and v in this study we use a new approach by analyzing rare earth elements in kerogen extracted from the black shales together with a number of redox sensitive trace element compositions and total organic carbon toc concentrations in an early cambrian black shale sequence in zunyi guizhou province south china to place better constraints on the oceanic redox conditions and the origin of the extreme metal enrichment our data show significant negative ce anomalies ce ce as low as 0 4 occurring in kerogen which indicate an oxygenated surface environment of primary productivity in consistent with the concept that the organic matter is mainly derived from organisms in the euphotic zone mass balance calculation suggests that the kerogen associated ree can dominate the measured black shale ree budget while similarity between our measured ree patterns and those of similarly aged phosphorites indicates that the ree content of ancient phosphorites may have also derived initially from organic matter the redox sensitive trace elements such as u v mo and their ratios of u al v al and mo al in black shales show different correlation patterns with toc contents the upper black shales show a good metal toc correlation but such a correlation is absent in the lower part the lower black shales exhibit much higher metal enrichments compared to black sea sulphidic euxinic sediment this is taken to indicate the presence of sulphidic bottom waters during the deposition of the lower black shales including the ni mo ore layer in contrast anoxic non sulphidic conditions occurred during the deposition of the upper black shales taking all these geochemical data together we suggest that the early cambrian south china seaway was strongly stratified and stagnant and that euxinic bottom water conditions may have led to enrichment of the redox sensitive metals such as u v and mo in the lower black shales and in one case the occurrence of a polymetallic ni mo sulphide ore bed bearing an extraordinarily extreme metal enrichment which according to the mo toc and ni toc ratios and much other geochemical evidence may have been additionally influenced by hydrothermal input of metals within the rift basin as suggested by a number of previous studies

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