geochemistry of major and trace elements and pb sr isotopes of a weathering profile developed on the lower cambrian black shales in central hunan china abstract this paper reports a geochemical study on the major and trace elements and pb sr isotopes of a weathering profile developed in the lower cambrian black shales in central hunan china six weathering horizons were identified and sampled vertically throughout the profile the chemical composition of the profile consists of variable concentrations of the major elements fe2o3 feo mno mgo cao na2o and p2o5 and of less variable concentrations of sio2 tio2 al2o3 and k2o the chemical change caused by weathering is estimated by mass balance calculations and the results show that the element mobility is characterised by substantial loss of sio2 feo cao k2o na2o loi cr v ba cs rb sr u and th and moderate loss of al2o3 mgo fe2o3 ni cu pb tl sn sc ge and ree y the high field strength elements tio2 sn sc u ga ge zr hf nb and ta were immobile during weathering the chemical changes and the pb sr isotopic data suggest that four types of chemical reactions occurred the oxidation of sulphide minerals e g pyrite and organic carbon os the dissolution of less resistant clinochlore ia calcite and p bearing minerals dl the dissolution of detrital albite and microcline da and the transformation of clay tc minerals e g muscovite and illite smectite these chemical reactions then led to two stages of geochemical processes an early stage of chemical differentiation and a later stage of chemical homogenisation the chemical differentiation dominated by the os dl and da reactions led to the leaching of mobile elements e g mgo na2o k2o p2o5 sr and ree and the redistribution of some less mobile elements e g sio2 and al2o3 in contrast the chemical homogenisation which was caused by tc reactions led to the leaching of both mobile and less mobile elements from the system and ultimately transformed the weathered black shales into soil soils derived from black shales in south china might result from the above two geochemical processes

mobility and fractionation of rare earth elements in argillaceous sediments implications for dating diagenesis and low grade metamorphism abstract we report sm nd and rb sr data for the fine fractions of lower paleozoic argillaceous rocks from wales uk and new york usa spanning the range of low grade metamorphic conditions from the diagenetic zone zeolite facies to the epizone greenschist facies in all cases leaching of the fine fractions results in a high 147 sm 144 nd 0 09 0 29 acid soluble component and a complementary low 147 sm 144 nd 0 05 0 14 residual component the observed fractionation is an ancient feature related to diagenesis burial and metamorphism the magnitude of sm nd fractionation between leachates and residues as well as the resulting sm nd ages vary as a function of grain size and metamorphic grade uncleaved welsh mudrocks of the diagenetic zone yield sm nd leachate residue ages of 453 484 ma in agreement with their llanviian to caradocian biostratigraphic ages whereas higher grade rocks of the anchizone and epizone yield sm nd ages as young as 413 ma these ages are transitional between the time of deposition and the time of regional deformation related to the acadian orogeny at 390 ma distinct convex upward rare earth element ree patterns of the leachates suggest that the precipitation of early diagenetic apatite controls the trace element budget of the rock forcing a depletion of middle rees on the subsequently formed diagenetic phyllosilicates the amount of organic matter present and the extent of later prograde reactions are probable modifiers of this fractionation process ordovician and devonian clastic rocks associated with the trenton and onondaga limestones of new york yield single sample and multi sample sm nd isochron ages that agree well with their biostratigraphic ages of 454 ma and 390 ma respectively the ree fractionation observed in shale leachates of the ordovician utica formation is related to ca mg of the bulk rock and hence to the composition of the diagenetic carbonate cement in all cases the sm nd system remained closed subsequent to the peak of diagenesis or metamorphism including the north american rocks that show no evidence of being isotopically reset during widespread remagnetization of the subjacent limestone units in the late paleozoic

facies and beddding sequences in shelf storm deposited carbonates fayetteville shale and pitkin limestone mississippian arkansas abstract the fayetteville shale miss is a black marine shale that was deposited on a southward deepening ramp in northern arkansas it is conformably overlain by skeletal oolitic grainstones of the pitkin limestone and together they form a shoaling upward succession of 1 deep muddy shelf 2 storm dominated muddy shelf and 3 ooid skeletal shoal and shoreface facies rhythmically bedded limestones of the upper fayetteville shale and some lower pitkin ooid grainstones are interpreted to be shelf storm deposits because of their stratigraphic position and bedding sequences upper fayetteville limestone beds are transitionally positioned between cephalopod bearing black shales deep muddy shell underneath and cross bedded ooid grainstones shoal and shoreface above fayetteville and pitkin beds are similar to other reported shelf storm deposits in that they contain hummocky cross stratification hcs and unidirectional climbing ripple cross stratification thought to have been laid down by combined flows six principal types of bedding sequences were noted in order of increasing water depth and or distance from the inferred shore 1 cross bedded and planar laminated beds with some keystone vugs beach 2 graded units of coarse skeletal ooid grainstone shoreface 3 planar laminated and hummocky cross stratified limestones lower shoreface 4 hummocky cross stratified limestones and thin shales storm dominated muddy shelf 5 fine grainstones with parallel laminae in lower half followed above by climbing ripple cross stratification storm dominated muddy shelf and 6 structureless lime mudstones and black shale deep muddy shelf reconstruction of the ancient shelf suggests that it sloped southward at 0 08 to 0 14 and the water depth at 30 km estimated width of storm dominated shell was 40 to 70 m the paleolatitudinal position of northern arkansas 5 15 s indicates that strong tropical storms or hurricanes rather than intense winter storms were responsible for eroding carbonate sediment from lower shoreface environments and depositing it as much as 30 km offshore in the muddy shelf

origin of siderite concretions in microenvironments of methanogenesis developed in a sulfate reduction zone an exception or a rule abstract the mississippian shales from wardie scotland were deposited in a large normally brackish water basin they host siderite concretions with 13c values ranging from 3 5 to 12 1 which show that sulfate reduction and methanogenesis contributed to the production of bicarbonate fossils are found within each of the concretions suggesting that the decay of these organic remains provided a catalyst for concretionary growth the pore water was freshened which is indicated by the very negative 18o values from 12 8 to 4 7 many features indicate that the concretions are very early diagenetic precompactional precipitates the concretions are mostly homogeneous only a few exhibit complex concentric zoning the microstructure of the homogeneous concretions indicates a pervasive growth however their isotopic composition reveals a clear trend towards lighter 13c and 18o values from the center to the edge it is proposed that the concretions grew due to methanogenesis in microenvironments around large organic remains which acted as nuclei we suggest that this process may be one of the reasons for the very common occurrence of cements as mineral concretions not as disseminated precipitates along beds these microenvironments developed entirely within the sulfate reduction zone which resulted in the establishment of isotopic gradients in bicarbonate dissolved in the pore water across these microenvironments these gradients were caused by fast consumption of sulfate by the intensive oxidation of organic remains this resulted in the isotopic trends preserved in the homogeneous concretions the formation of the zoned concretions proceeded generally concentrically but detailed observations suggest that pervasive growth also contributed to their formation afterwards all the concretions were deeply buried probably within the oil window where late diagenetic phases crystallized mainly kaolinite quartz and sulfides

temporal changes in ostracod assemblages during the past 10 000years associated with the evolution of the red river delta system northeastern vietnam abstract eighty five species belonging to 46 genera of ostracoda were recovered from 169 samples in three sediment cores vn nb and ga from the red river delta plain northeastern vietnam from a q mode cluster analysis we recognized three biofacies biofacies a b and c biofacies b is subdivided into biofacies bi and bii the environment of biofacies a is interpreted as open marine those of biofacies bi and bii as marine to brackish water and brackish water respectively and that of biofacies c as oligohaline to mesohaline brackish water the holocene sediments consist of estuarine sediments deposited under relatively high sea levels following transgression deposited during 11 8 5 cal kyr bp overlain by deltaic sediments deposited under relatively low sea levels following regression and the ostracod assemblages reflect these changes the estuarine sediments of the early holocene transgression are characterized by ostracod biofacies bi an erosional surface marks an abrupt change to the shelf environment accompanied by sediment starvation the interval around this surface identified as the maximum flooding surface is characterized by ostracod biofacies a during the subsequent delta progradation the sedimentary environment changed from a prodelta to delta front and then to a delta plain and the corresponding ostracod assemblages changed from biofacies a to bi bii and then c in ascending order taken together our results show that the temporal changes in ostracod assemblages since 10 cal kyr bp are closely related to the evolution of the red river delta system and can serve as good indicators of paleoenvironmental changes

mineralogy and geochemistry of silicate sulfide and oxide iron formations in norway evidence for fluctuating redox states of early paleozoic marine basins laterally extensive silicate and sulfide iron formation associated with jasper hematitic chert beds and volcanogenic massive sulfide vms deposits in norway provide evidence of early mineral assemblages and redox conditions within coeval early paleozoic seawater calculated detrital free compositions record mixed hydrothermal e g fe cu and seawater biogenic e g si ni s ree p components rare earth element ree patterns are characterized by small to large negative ce anomalies and insignificant to locally large positive eu anomalies reflecting seawater ree carried to the seafloor by fe p rich particles later modified by diagenetic processes protoliths of silicate iron formation precipitated in anoxic and intermittently euxinic deep waters by the diagenetic modification of amorphous si fe oxyhydroxides and or si fe ooh gels based on possible modern analogues in the red sea diagenetic minerals include nontronite greenalite stilpnomelane magnetite manganosiderite apatite and iron sulfides in sulfide iron formation a local predominance of pyrrhotite over pyrite records highly reducing conditions caused by organic material the geochemical data provide evidence for mn fe p shuttle and redox processes in a stratified basin with oxic or suboxic shallow waters and silica concentrations much higher than those of modern seawater hydrothermal plume derived fe present within the anoxic layer and near the chemocline formed mixed valence oxyhydroxides and silicates and intermittently sulfides by reaction with aqueous si and h2s respectively the latter derived from bacterial reduction of seawater sulfate at the chemocline major sustained fluxes of hydrothermally derived reductants fe2 mn2 h2s h2 produced from large seafloor systems such as lokken may have changed the redox state of seawater in local and possibly regional basins from weakly or moderately oxic to intermittently anoxic or euxinic conditions

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

mercury spikes at the devonian carboniferous boundary in the eastern part of the rhenohercynian zone central europe and in the south china block abstract mercury hg chemostratigraphy is an efficient tool for tracing distal volcanism as suggested in many recent studies in our research we focused on hg and other trace element contents in two devonian carboniferous boundary sections from two different and spatially distant areas the lesni lom section czech republic was located in the south eastern part of the laurussia plate and the duli guangxi china section in the south china plate in both studied sections the highest hg hg fexs or hg al values occurred at the devonian carboniferous boundary in lesni lom organic matter remineralization was connected with origin of pyrite which sequestered a part of the hg content the decoupling of hg and toc within the duli section strata and the significant correlation with al and fe may suggest that hg is hosted primarily by clay particles derived from the landmass into the marine realm mercury was also incorporated into pyrites but the poor correlation between hg and ts total sulfur indicates a possible loss of s during oxygenation events in the lesni lom section and partly in the duli section fe and mn redox cycling may have played an important role in sediment hg content both sections were influenced by widespread hydrothermal and volcanic activity indicated by positive eu anomalies msi fe ti zr al2o3 and ti al2o3 values it remains to be clarified whether besides the interplay of local magmatic activity and redox oscillations there may have been some additional influence of the multi phase viluy large igneous province although its younger phase 364 4 1 7 ma slightly precedes the hg anomalies obtained

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

stratigraphic model for glacial eustatic pennsylvanian cyclothems in highstand nearshore detrital regimes lower distal positions on gently sloping shelves ramps affected by pennsylvanian glacial eustatic sea level fluctuation display classic marine transgressive regressive cyclothems which are separated by exposure surfaces or by shallow marine to thin terrestrial beds deposited at lowstand in contrast higher shelf proximal positions display marginal marine units and coastal plain coal beds deposited at marine highstand and separated by thicker terrestrial units both marine and terrestrial strata deposited in high shelf positions underwent significant fluvial incision and valley formation during long stands of lower sea level resulting in discontinuous erosional remnants and subsequent localized terrestrial deposition on irregular leached and eroded surfaces examples from the appalachian illinois and sydney basins display features such as erosional disconformities with rotated slumps buried hilltops preserving erosional remnants of marine units colluvially reduced landscape relief and buried

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

geochemistry of the upper triassic black mudstones in the qiangtang basin tibet implications for paleoenvironment provenance and tectonic setting abstract the qiangtang basin is the largest mesozoic marine basin in the tibetan plateau the upper triassic black mudstones are among the most significant hydrocarbon source rocks in this basin here we present geochemical data for the upper triassic black mudstones to determine their paleoenvironment conditions provenance and tectonic setting to achieve these 30 black mudstones formed in various sedimentary environments were collected from the zangxiahe zana and bagong formations the results show that the total ree concentrations of mudstones from these formations range from 169 to 214 ppm 204 to 220 ppm and 141 to 194 ppm respectively all samples have chondrite normalized ree patterns with enrichment of lree depletion of hree and negative eu and ce anomalies specifically mudstones from the bagong formation exhibit higher negative eu anomalies and lower ree contents than those from the zangxiahe and zana formations mudstones from the zangxiahe and zana formations with low sr ba and sr cu ratios indicate the humid climate whereas the high sr ba and sr cu ratios of rocks from the bagong formation suggest the arid climate the low u th cu mo zn v cr and ni co ratios of rocks from the zangxiahe zana and bagong formations are indicators of oxidized conditions the bivariate diagrams tio2 vs al2o3 tio2 vs zr la th vs hf and co th vs la sc reveal that mudstones from the zangxiahe and zana formations were potentially derived from intermediate igneous rocks whereas mudstones from the bagong formation were probably sourced from felsic igneous rocks their source rocks are mostly deposited in the collisional setting ree of mudstones from the zangxiahe zana and bagong formations were possibly originated from terrigenous detritus with minor non terrigenous contributions into the zana samples the ree contents of these mudstones are controlled mainly by terrigenous detrital minerals rather than by the paleoclimate paleoredox conditions or organic matter however calcite minerals could dilute ree therefore the ree contents of the bagong formation mudstones are significant lower than those of the zangxiahe and zana formations mudstones

evidence for basin restriction during syn collisional basin formation in the silurian arisaig group nova scotia the arisaig basin in nova scotia canada provides a regional sedimentary record of an early silurian basin subsidence on the microcontinent of avalon the lower members of the arisaig group beechill cove and lower ross brook formations are likely to be deposited in a basin formed during syn to post collisional rifting subsidence driven by the collision of avalon and baltica the evolution of this constricted basin can be tracked by examining the geochemistry of the sedimentary rocks deposited within the basin here we report on the chemostratigraphy of the arisaig group a series of siliciclastics with a focus on understanding the redox chemistry during sedimentation the trace and major element geochemistry of this group provides insight into the oceanographic and geological processes that were influencing its depositional environment in particular concentrations of u v mo ni cd and pb indicate regional shifts in ocean redox state which serve as a proxy for changes in ocean circulation and regional tectonic activity we find evidence for anoxic conditions near the base of ross brook formation and attribute this anomaly in redox status to a significant change in physical mixing in the region trace element concentrations indicate that this anoxic event was associated with poor circulation rather than elevated productivity and organic matter burial based on these data we confirm that these sediments are deposited in a tectonically formed basin during a period of limited ocean circulation

oceanic environmental changes on a shallow carbonate platform yangou jiangxi province south china during the permian triassic transition evidence from rare earth elements in conodont bioapatite abstract paleoceanic environmental stresses e g expanded anoxia elevated siliciclastic fluxes are thought to have been important factors in the latest permian mass extinction lpme here we investigate changes in redox conditions and siliciclastic fluxes during the permian triassic transition in south china through in situ analysis of the rare earth element ree composition of albid crowns of single conodont elements measured using laser ablation inductively coupled plasma mass spectrometry la icp ms for comparison we also analyzed rees in the sediment matrix enclosing the conodonts i e whole rock samples the study locale yangou was located on a shallow carbonate platform on the eastern margin of the yangtze platform to minimize the influence of detrital siliciclastics and thus enhance the chances of recovering a hydrogenous seawater sourced ree signal the analyzed conodonts exhibit ree patterns consistent with mixed hydrogenous seawater and lithogenous siliciclastic sources with specimens from below the lpme horizon showing dominantly hydrogenous influences y ho 50 and those from above the lpme horizon showing dominantly lithogenous influences y ho

rare earth element redistribution and its effects on the neodymium isotope system in the austin glen member of the normanskill formation new york usa abstract three groups of ree patterns are observed for the sandstones and shales of the middle ordovician austin glen member of the normanskill formation one sandstone sample is enriched in middle and light rare earth elements the majority of samples are light rare earth element lree enriched with negative eu anomalies and flat heavy rare earth elements hrees whereas a third group appears to have lost lrees and middle rare earth element mrees homogeneous neodymium isotopic compositions for all samples at about the time of deposition nd 470 ma 8 2 1 1 2sd indicate that the source of the austin glen member was well mixed and that the neodymium had a long term enriched history the differences in the shape and abundances of the ree patterns combined with the neodymium isotope characteristics of the samples lead us to the conclusion that samarium and neodymium were fractionated and that the neodymium isotopic system might have been disturbed at about the time of deposition 470 ma most samples appear to have been affected by this process the two most altered shales lost about half of their neodymium and their sm nd ratios are higher than the sm nd ratios of average shales these two shales give clearly erroneous mantle extraction ages but the average tdm of the provenance can still be deduced 1700 1800 ma from the least disturbed sandstones with normal upper crustal sm nd ratios accordingly this study demonstrates that the rees may be transported and neodymium isotopes may be reequilibrated under certain sedimentary conditions e g diagenesis however in spite of evidence for ree redistribution provenance information tdm original ree patterns may still be inferred

environmental control on concretion forming processes examples from paleozoic terrigenous sediments of the north gondwana margin armorican massif middle ordovician and middle devonian and sw sardinia late ordovician abstract concretions of various compositions are common in the paleozoic terrigenous successions of the north gondwana margin this study focuses on phosphatic p and siliceous si concretions present in some successions of the armorican massif nw france and sw sardinia w italy it shows that they consist of mudstones fine to very fine grained sandstones or shellbeds with a more or less abundant p cement and form a continuum between a phosphatic end member and a siliceous biogenic end member the p 2 o 5 contents are ranging from 0 26 to 21 5 and are related to apatite the sio 2 contents vary from 25 to 82 and are linked both to a terrigenous phase and to a biogenic silica phase concretions showing the lower p contents p 2 o 5 2 al 2 o 3 5 comparison with the surrounding sediments shows that all the concretions are enriched in chlorite and in middle rare earth elements la s gd s 0 12 0 72 and some of them in y up to 974 ppm rare earth elements more than 300 ppm and sr 260 880 ppm the concretions with highest biogenic silica concentrations are contained in the outer shelf sediments whereas the other concretions are present from the proximal part of the inner shelf to the outer shelf a genetic model in two stages is proposed during early diagenesis the dissolution of shells and degradation of organic matter progressively enrich the pore water in dissolved si ca and p when the suboxic zone is reached p precipitation begins leading to the formation of protoconcretions in shallow environments the relative permeability of sediments and the winnowing or reworking of the upper few centimetres by bottom currents allow for suboxic conditions to be maintained leading to p rich concretion formation in deeper environments the anoxic zone is reached more rapidly thereby preventing extensive phosphogenesis nevertheless in the protoconcretions the early p cement preserves pore spaces from compaction in the presence of biogenic siliceous particles the fluids are enriched in dissolved silica and diffuse towards the protoconcretions silica precipitation can thus occur later in the intergranular spaces

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 ree and yttrium in stream waters stream sediments and fe mn oxyhydroxides fractionation speciation and controls over ree y patterns in the surface environment we have collected 500 stream waters and associated bed load sediments over an 400 km 2 region of eastern canada and analyzed these samples for fe mn and the rare earth elements ree y in addition to analyzing the stream sediments by total digestion multi acid dissolution with metaborate fusion we also leached the sediments with 0 25 m hydroxylamine hydrochloride in 0 05 m hcl to determine the ree y associated with amorphous fe and mn oxyhydroxide phases we are thus able to partition the ree into dissolved 0 45 lm labile hydroxylamine and detrital sediment fractions to investigate ree fractionation and in particular with respect to the development of ce and eu anomalies in oxygenated surface environments surface waters are typically lree depleted la sm nasc ranges from 0 16 to 5 84 average 0 604 n 410 where the ree are normalized to the north america shale composite have strongly negative ce anomalies ce ce nasc ranges from 0 02 to 1 25 average 0 277 n 354 and commonly have positive eu anomalies eu eu nasc ranges from 0 295 to 1 77 average 0 764 n 84 in contrast the total sediment have flatter ree y patterns relative to nasc la sm nasc ranges from 0 352 to 1 12 average 0 778 n 451 and are slightly middle ree enriched gd yb nasc ranges from 0 55 to 3 75 average 1 42 most total sediments have negative ce and eu anomalies ce ce nasc ranges from 0 097 to 2 12 average 0 799 and eu eu nasc ranges from 0 39 to 1 43 average 0 802 the partial extraction sediments are commonly less lree depleted than the total sediments la sm nasc ranges from 0 24 to 3 31 average 0 901 n 4537 more mree enriched gd yb nasc ranges from 0 765 to 6 28 average 1 97 and ce and eu anomalies negative and positive are more pronounced the partial extraction recovered on average 20 of the fe in the total sediment 80 of the mn and 21 29 of the rees ce 19 and y 32 comparison between rees in water partial extraction and total sediment analyses indicates that rees y in the stream sediments have two primary sources the host lithologies i e mechanical dispersion and hydromorphically transported the labile fraction furthermore eu appears to be more mobile than the other ree whereas ce is preferentially removed from solution and accumulates in the stream sediments in a less labile form than the other rees y despite poor statistical correlations between the rees y and mn in either the total sediment or partial extractions based on apparent distribution coefficients and the ph of the stream waters we suggest that either sediment organic matter and or possibly d mno2 feooh are likely the predominant sinks for ce and to a lesser extent the other ree in the stream sediments

petrology and origin of phosphate nodules from the midcontinent pennsylvanian epicontinental sea abstract midcontinent pennsylvanian phosphate nodules concretions that occur in widespread black and gray shales have not been largely affected by reworking processes that commonly enrich other phosphate deposits with respect to p a sequence of events consisting of 1 upwelling 2 development of a prolific pelagic biota 3 decay of dead pelagic organisms and fecal material that released p to the interstitial waters of the black muds and 4 cementation by apatite pyrite quartz and calcite is proposed to have formed the phosphate nodules prior to compaction of the enclosing shales phosphate nodules are best developed at the top and sometimes bottom of black shale units indicating that nodular growth was enhanced near the boundary between anoxic and disoxic conditions the conditions under which these phosphates formed are generally similar to those cited for holocene pericontinental phosphorites this study provides an example of an epicontinental phosphate deposit that fits cook and mcelhinny s 1979 spatial and temporal model for distribution of pericontinental phosphorites

experimental studies of ree fractionation during water mineral interactions ree release rates during apatite dissolution from ph 2 8 to 9 2 rare earth elements ree release rates were measured during the open system dissolution of natural apatite at 25 c 2 8 ph 9 2 and at ionic strengths ranging from 0 001 to 0 02 mol kg all inlet solutions were ca ree and p free in agreement with previous studies apatite dissolution rates determined from outlet solution ca concentrations decrease monotonically with increasing ph outlet solution molar ree ca ratios differ from that of the dissolving apatite during the experiments this behaviour is interpreted to stem from dissolution or precipitation of minor quantities of rhabdophane ree po4 nh2o this interpretation is supported by solute speciation calculations which indicate that ree are retained in the solid phase when the outlet fluids are supersaturated with respect to nd rhabdophane ksp 10 24 5 0 5 but preferentially released when the outlet fluids are undersaturated with respect to nd rhabdophane the relative concentrations of the ree in the outlet solutions suggest that the secondary rhabdophane is slightly enriched in light ree ce to eu the results of this study suggest that rhabdophane dissolution and precipitation during apatite fluid interaction plays a major role in controlling surface and ground water ree signatures

the rare earth element chemistry of estuarine surface sediments in the chesapeake bay abstract concentrations of rare earth elements ree were measured in the fine fraction of shallow surface sediments from the lower chesapeake bay as studies suggest that coagulation of colloids dominates the removal of ree from the dissolved load in low salinity regions of estuaries ree in sediments showed spatial heterogeneity both laterally and longitudinally we observed the influence of salinity on the spatial and temporal variability in total ree content and on eu anomalies lower total ree was found in sediments deposited along the eastern shore the chemistry of the mid bay islands was distinct with higher overall ree content and slightly more positive ce anomaly values positive ce ce in the mid bay are attributed to coriolis acceleration restricting freshwater flow towards the west away from the islands leading to oxidative removal of ce from the pore waters to the sediments the presence of positive eu eu in sediments deposited along the eastern shore is linked to salinity we suggest that unique local conditions along the eastern shore possibly including submarine groundwater discharge of nutrient rich reducing waters combined with organic matter decay and the predominance of oceanic water flow toward this region leads to the development of a strong localized salinity gradient this study demonstrates the utility of ree sediment chemistry in identifying and resolving local and estuarine wide geochemical processes

assessing the application of trace metals as paleoproxies and a chemostratigraphic tool in carbonate systems a case study from the mississippian limestone of the midcontinent united states abstract trace metals have been successfully used to reconstruct geochemical seawater conditions of both modern and ancient environments the majority of these efforts have been limited to marine shales with little work on carbonate systems applying similar methods of trace metal analysis on carbonate dominated rocks may provide valuable insight into the paleoseawater chemistry such as redox state and productivity of ancient carbonate systems this study evaluates the application of trace metals as paleoproxies in carbonate rocks middle ramp wackestones to grainstones from the mississippian limestone in the midcontinent were analyzed using inductively coupled plasma mass spectrometry icp ms for both the carbonate fraction and the bulk fraction trace metal content our data show that productivity proxies such as cd and p are captured within the carbonate fraction and may reflect seawater chemistry of the system high cd and moderate bionutrient p ni zn enrichments indicate primary productivity in the system though it is difficult to quantify to what extent vanadium cr u and mo appear to be primarily associated with the bulk fraction content and correlate well with al content indicating a detrital origin furthermore v u and mo show no significant enrichments and mo fe ratios correlate with those of shales from a modern oxic shelf this suggests that anoxic or euxinic conditions in the water column were not present trace metal content of carbonate rocks have the potential to be used in paleoenvironmental reconstruction of carbonate systems though challenges exist such as the lack of comparable carbonate trace metal data bias of trace metal incorporation pathways into carbonates and diagenetic alteration

rare earth element geochemistry of laminated diatom mats from tropical west pacific evidence for more reducing bottomwaters and higher primary productivity during the last glacial maximum rare earth elements ree along with selected major and trace elements were measured in laminated ethmodiscus rex diatom mats and associated sediments diatomaceous clay and pelagic clay in two sediment cores collected from the parece vela basin of the eastern philippine sea ree distributions are characterized by strong enrichment of middle ree mree and heavy ree hree over light ree lree and slight enrichment of mree over hree this distribution pattern suggests that ree compositions of the laminated e rex diatom mats were not the product of e rex blooms an inference also supported by the fact that ti normalized ree concentrations are not clearly different from those in the diatomaceous clay and pelagic clay comparison of ree patterns with the vertical distribution of authigenic phases in the sediment indicates that lree were dominantly associated with detrital materials whereas mree and hree were selectively enriched by mn oxyhydroxides and authigenic phosphates in the pelagic clay a weak negative ce anomaly cannot be linked to oxic depositional conditions but instead is attributed to the retention of a negative ce anomaly associated with authigenic phosphates in the laminated e rex diatom mats a weak positive ce anomaly is consistent with depositional sulfidic anoxic conditions and is interpreted to represent enhanced scavenging of reduced aqueous ce3 by barite in a strongly reducing environment moreover variably negative to positive ce anomalies in the diatomaceous clay may reflect the concurrent operation of the two processes controlling ce accumulation in the laminated e rex diatom mats and pelagic clay the study cores show a ubiquitous positive eu anomaly owing to the presence of volcanic materials the smaller eu anomaly in the laminated e rex diatom mats and diatomaceous clay relative to that in the pelagic clay may be attributed to the release of reduced eu2 from mineral phases to the sediment pore water under strongly reducing conditions previous studies have shown that the advection of lower circumpolar water lcpw strengthened during the last glacial maximum lgm which should have resulted in better ventilation of the deep eastern philippine sea evidence presented here for more reducing bottomwater conditions during the laminated e rex diatom mats formation implicates elevated primary productivity and enhanced organic sinking fluxes as primary controls on redox changes in the eastern philippine sea during the lgm enhanced primary productivity and more reducing bottomwaters during the laminated e rex diatom mats deposition resulted in a larger respired carbon pool in the deep eastern philippine sea which may have been part of a larger scale modulation of atmospheric co2 variation during pleistocene glacial interglacial cycles by deep ocean carbon storage c 2011 elsevier b v all rights reserved

redox productivity and paleotectonic studies in the southern tethyan margin of northern tunisia abstract in northern tunisia the cenomanian turonian sediments are characterized by organic rich material these deposits are commonly attributed to the bahloul formation and record the worldwide oae2 event in general the bahloul formation is related to paleogeographic and tectonic events these results suggest that multiple causes including primary productivity sea level changes climatically driven organic carbon burial and structural framework this formation is composed of three differentiated units the first unit u1 is composed of laminated limestones with small intercalations of marls caco 3 varies between 48 and 83 the second unit u2 is characterized by very thin beds of marls argillaceous and laminated limestones caco 3 ranging from 57 to 85 lastly the third unit u3 is represented by a set of thick black shales with some levels of marls isotopic 13 c carb study shows a large positive excursion in the bahloul formation it is characterized by three peaks that exceed 3 first and the second peaks are identified at the lower unit u1 with isotopic values recording 3 2 and 3 3 respectively third peak is recorded in the middle of the unit u2 and it attains 3 2 this section records important toc values reaching up to 3 84 in unit u1 with average values exceeding 3 the rock eval data shows a marine organic matter with kerogen type ii 429 max 435 c which can generate oils a significant enrichment of major and trace elements are also recorded which took place during the deposition of the bahloul formation in general high levels of p cu and ni indicate a high surface primary productivity which led to the accumulation of large quantities of organic matter on the sea floor

provenance and depositional setting of paleozoic chert and argillite sierra nevada california abstract the shoo fly complex the remnants of an early to middle paleozoic subduction system contains the culbertson lake allochthon included in the culbertson lake allochthon are the post cambrian and pre upper devonian quartz hill toms creek and mcmurray lake cherts geochemical data derived from these three units plot on the fe2o3 tio2 versus al2o3 al2o3 fe2o3 and lan cen versus al2o3 al2o3 fe2o3 discrimination diagrams within either the continental margin island arc field or that part of the pelagic field overlapping the continental margin island arc field these relationships a e consistent with the presence of argillaceous turbidites interstratified with radiolarite and suggest a relatively distal continental island arc setting where muddy turbidity currents episodically interrupted pelagic deposition specimens from the quartz hill and toms creek cherts with al2o3 tio2 values 20 make up group i samples whereas specimens with al2o3 tio2 values 10 are classified as group ii samples the al2o3 tio2 ratios of group ii specimens suggest derivation from mafic rock mean th sc and th u values as well as lree enriched patterns are consistent with this interpretation and indicate a source area dominated by alkalic seamount or ocean island material the al2o3 tio2 ratios of group i samples indicate a source area with an average andesitic to rhyodacitic composition chondrite normalized ree distribution patterns as well as mean th sc and th u value support such an interpretation samples from the mcmurray lake chert have al2o3 tio2 values ranging between 19 and 28 and ree patterns characterized by lree enrichment negative eu anomalies and slightly fractionated hree patterns these features along with mean th sc and th u values indicate a source area dominated by old upper continental crust the location of the source area s supplying material to cherts and argillites of the culbertson lake allochthon is unknown however existing tectonic models commonly portray the source of old upper continental crustal material in the shoo fly complex as being located somewhere along the western north american continental margin whereas the source of island arc debris is portrayed as being located in a fringing arc system our data suggest that a relatively high standing seamount or ocean island probably resided on the subducting oceanic plate thus our work supports the idea that al fe ti th sc and the rees in chert and argillite deposited in proximal continental island arc settings can be used to assess the characteristics of sources supplying particulate matter to ancient t ench systems

thin widespread pennsylvanian black shales of midcontinent north america a record of a cyclic succession of widespread pycnoclines in a fluctuating epeiric sea

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

a petrographic approach for evaluating trace element mobility in a black shale abstract at the time of deposition black shales record geochemical information related to the provenance and conditions of deposition for that rock these initial geochemical conditions are susceptible to alteration and overprinting by the aggressive processes of black shale diagenesis in this study we evaluate a sequence of ordovician black shales from the southern welsh basin for the presence of such a diagenetic overprint through use of cathodoluminescence backscattered electron imaging reflected light microscopy fission tracks and microprobe elemental mapping we can discern textural relationships with in the welsh black shales the relationships observed constrain a paragenetic sequence and overall diagenetic history including the early diagenetic formation of pyrite apatite rare earth element ree rich and carbonate and later formation of diagenetic monazite ree u rich and late stage carbonate the chemical reactions necessary to produce this mineral sequence require postdepositional redistribution of ree including changing cerium anomalies ce ce and uranium as a result ree u and their associated isotopic systems sm nd and u pb can reflect a diagenetic overprint rather than the source area and depositional conditions the paragenetic sequence described in this study records several postdepositional changes in the whole rock mineralogy among these changes are the formation of ree rich apatite and ree and u rich monazite the formation of these phases requires that ree and u are being redistributed on at least a mineral scale and that the initial depositional and provenance information recorded by the whole rock has been disturbed therefore the approach used in this study to carefully characterize the paragenetic sequence from the llandeilo caradoc black shales should be considered necessary in order to fully evaluate the usefulness of trace element proxies susceptible to diagenetic redistribution

tracing the composition and origin of fluids at an ancient hydrocarbon seep hollard mound middle devonian morocco a nd ree and stable isotope study abstract for the first time nd isotope signatures combined with rare earth element ree concentrations were used in investigations of ancient seep carbonates the study was performed on the fossil hydrocarbon seep deposit of the middle devonian hollard mound eastern anti atlas morocco where nd isotopes ree concentrations and carbon and oxygen isotope ratios were measured to investigate the origin former migration pathways and composition of fluids relatively high end values compared to local eifelian seawater as well as consistently appearing positive eu anomalies in mree enriched shale normalized ree patterns of the seep carbonates provided evidence for interaction between the seeping fluids and the lower devonian basaltic volcaniclastics underlying the studied seep deposit strongly reducing conditions and increased temperature of methane formation could have constituted an additional factor in the eu enrichment of the investigated carbonate phases the presence of exclusively negative ce anomalies in these carbonates is in line with observations of other workers that seep limestones may not necessarily display positive ce anomalies indicative of precipitation under anoxic conditions the negative ce anomalies are attributed here to mixing between anoxic pore waters and oxic ce depleted seawater necessary to enable carbonate precipitation at seeps the methane rich fluids ascended most likely from below the volcaniclastic unit and inherited the enriched end signatures and positive eu anomalies due to fluid rock interactions during their seepage to the seafloor the carbon isotope data are most consistent with thermogenic origin of methane although contribution of abiotic and biogenic methane sources cannot be excluded our results indicate that neodymium isotope and rare earth element analyses constitute one of the most valuable tools for reconstructing former fluid migration patterns the study shows also that nd isotopes and eu anomalies can serve as sensitive tracers of fluid rock interactions at submarine springs

orogenesis vs diagenesis can we use organic rich shales to interpret the tectonic evolution of a depositional basin abstract black shales from the southern appalachian basin and the southwest welsh basin have anomalous u pb and nd model ages suggesting syn and post depositional resetting of the sm nd and u pb isotopic systems this alteration to the primary detrital signature of these two shale sequences is indicative of black shale diagenetic depositional processes that obscure paleo environmental and provenance information recorded prior to and during deposition the trace element and isotopic signatures of these two shale sequences reveal a syn post depositional history that is de coupled from the coeval orogenic history of the region making it difficult to reconstruct the tectonic and oceanographic conditions present at the time of deposition both the ordovivian welsh basin and the devonian appalachian basin sequences host ree and u bearing diagenetic phosphate minerals that play a critical role in the whole rock ree and u budgets in the welsh basin shales early diagenetic apatite and a later monazite phase dominate the ree budget and cause the redistribution of ree early in the basin s history ca 460 ma this redistribution is recorded by the sm nd system 450 90 ma and the nd model ages that are anomalously old by as much as 20 t dm 2 0 ga this early history is complicated by a permo triassic fluid event affecting the whole rock u budget and resetting the u pb isotopic system at 193 45 ma the appalachian basin sequence appears to have a much less complicated history yet still records a significant disturbance in both the sm nd isotopic system 392 76 ma and the pb isotopic system 340 50 ma at about the time of deposition ca 365 ma these two sequences suggest a pattern of diagenetic disturbance common to black shales these processes are unique to black shales and must be considered when interpreting provenance and paleo environmental information from the black shale sequences although these rocks are susceptible to alteration the alteration may provide extensive information on the post depositional history of the basin while still retaining some primary depositional information if black shale processes are considered during the interpretation of isotopic and trace element signatures from organic rich shales it may be possible to recover an extensive basin history

preservation of successive diagenetic stages in middle triassic bonebeds evidence from in situ trace element and strontium isotope analysis of vertebrate fossils abstract bonebeds comprise reworked and time averaged constituents of different phosphatic vertebrate remains and hence provide an ideal substrate for the study of long and short term diagenetic processes to test whether trace elements u sr ree and 87 sr 86 sr ratios can be used for distinguishing between successive diagenetic signals we performed geochemical analyses on vertebrate remains bones teeth scales and coprolites from two triassic bonebeds located near palzem germany trace element analysis was done on 170 vertebrate remains by la icp ms while 87 sr 86 sr ratios were determined for 39 bioclasts using la mc icp ms although a low inter and intra bioclast ree variability indicates long term open system behaviour the observed ree patterns suggest the preservation of different diagenetic stages a distinct difference in the geochemical composition exists between dark luminescent sem cl domains and greyish ones dark domains represent dense diagenetically more resistant material of low porosities such as enamel and ganoine these domains display distinctly lower ree contents and a higher inter clast variability than those of various grey tones together with lower hence more seawater like 87 sr 86 sr ratios this argues for a preservation of an earlier diagenetic signal notably most dark domains are characterised by negative eu anomalies while all grey ones display positive eu anomalies with the exception of eu both domains display almost identical ree patterns with different concentrations indicating that late diagenetic ree uptake is not necessarily accompanied by fractionation processes in vertebrate bioclasts negative eu anomalies are most likely inherited from eu depleted surface waters possibly as a result of eu depleted aeolian input conversely positive eu anomalies were presumably affected by eu enriched late diagenetic fluids with a possible high temperature origin causing a fractionation of europium our study therefore demonstrates the potential of high resolution geochemical analysis in bonebed strata to disentangle different stages of diagenesis and to detect least altered areas in vertebrate fossils for recovering pristine palaeoenvironmental signals

changes in depositional environment for the past 35 years in the thane creek central west coast of india inferences from rees metals and magnetic properties the role of diagenetic processes in influencing the behaviour of metals fe mn cu ni zn rare earth elements rees and environmental magnetic parameters in two sediment cores from a polluted creek environment the thane creek mumbai was investigated the sediment age was determined using 210pb analysis silty clays were dominant sediments in both the cores mineralogy showed the presence of quartz calcite and plagioclase feldspar in bulk sediments while smectite was the abundant clay mineral in the finer fraction the mean ree in both the cores was lower than in post archaean average australian shale paas the paas normalized ree patterns showed mree and hree enrichment with strong positive eu and y anomalies the source rocks in the hinterland played an important role on the ree composition magnetic mineralogy showed dominance of magnetite both the cores showed low magnetic concentration of al ti fe and mn coinciding with high magnetic grain size at the middle portions the early diagenetic changes at the middle portion of the cores were masked by significant abundance of clay content at the creek head and with oc and fine magnetite at the lower creek region metals cu ni zn enrichment factor 1 5 and magnetic concentration in sediments were enriched in both the cores suggesting of an anthropogenic source

glacial eustatic base level climatic model for late middle to late pennsylvanian coal bed formation in the appalachian basin abstract late middle late pennsylvanian middle allegheny and lower conemaugh marine units in the appalachian basin represent the distal edges of glacial eustatic marine incursions of the midcontinent sea onto the detrital apron of the appalachian highlands because these marine units typically overlie coal beds the main environment of formation of this type of coal bed appears to have been that of a coastal swamp migrating ahead of transgression as base level rose the water table continually rose and the swamp was further nourished and surrounding vegetation kept thick enough to inhibit detrital influx by rainfall from the expanding nearby source of moisture even in parts of the appalachian cyclic succession with no marine units upper allegheny monongahela dunkard the coal beds rep esent the wettest part of the climate cycle of cecil 1990 sandwiched between detrital units representing seasonal wet dry climates when sediment was most readily mobilized and antipodal to nonmarine limestones representing the driest climates throughout this time the appalachian basin was in the center of the tropical zone of a nearly accreted megacontinent quite distant 4000 km from permanent oceanic sources of moisture climate modeling without considering inland seas or orographic effects on winds shows that the tropical zone of such a large land mass would have suffered from a severe deficit in rainfall and soil moisture although further modeling shows that the appalachian orogenic highlands would have drawn in moisture to ncrease rainfall in their vicinity they also may have impeded the normal westward flow of moisture laden easterly winds the western source for enough moisture to form coal beds was most likely the north american midcontinent sea during major highstand this sea would have covered about 2 million km2 and provided both high base level and abundant nearby moisture for enough continual rainfall to keep the coastal peat swamps widespread fresh and relatively detritus free in the appalachian basin in contrast during major lowstand it would have covered only about 200 000 km2 with its shoreline about 1500 km away and it apparently provided less consistent moisture to the appalachian basin then because most nonmarine limestones and paleosols formed there during the e times contain evidence of drier climates therefore upper allegheny monongahela and dunkard coal beds most probably formed when the midcontinent sea was approaching highstand and stood just west of the presently preserved outcrop thus they likely represent the coastal lowland equivalent of a marine unit at highstand farther west this constrained time of peat formation and preservation in a variety of coastal environments prior to and during marine highstand is responsible for the discrete and widespread nature of the coal bed interval in a typical depositional cycle or cyclothem a pattern that stands in contrast to the complicated relations of overlying and underlying detrital units which reflect the segregation of sand and mud into a complex mosaic of local deltaic and ter estrial subenvironments that developed when sea level rainfall and the water table were lower

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

redistribution of rare earth elements during diagenesis of turbidite hemipelagite mudrock sequences of llandovery age from central wales

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

anoxia and fluctuating climate recorded from the devonian carboniferous black shales tethys himalaya india a multi proxy approach due to inaccessibility and tough conditions high altitude low oxygen region very less information is available about the indian tethys himalayan sequences particularly geochemical data are scarce an attempt is made in the present study to evaluate the sediment geochemistry and paleo redox conditions of devonian carboniferous black shales from the spiti region tethys himalaya using multi proxy approach besides black shales this paper also provides the first in depth study of the geochemistry of phosphatic nodules hosted by the black shales that will allow primary and secondary processes to be understood geochemical investigations particularly redox sensitive trace element ratios for e g v v ni 0 5 ni co 4 3 7 2 v cr 2 and positive ce anomalies suggest deposition of these black shales under sub oxic to anoxic marine conditions thus recording an ocean anoxic event in the region these ocean anoxic events of devonian carboniferous spiti black shales which possess distinctive geochemical signatures can very well be correlated with global events such as hangenberg events and the lower alum shale event the span of the chemical index of alteration cia values 54 78 variation of 4si parameter 82 3 and c values 0 1 0 6 recorded in the black shales strongly indicate varying degrees of weathering conditions in the source area which in turn reflect fluctuating climatic conditions prevailing during the deposition of these sediments in devonian carboniferous period in the spiti region the distinct geochemical characteristics such as y sr and rare earth element ree enrichments particularly middle ree enrichments with a hat shaped pattern with high p2o5 contents up to 14 wt distinguish the nodules from the host rocks black shales sem scanning electron microscope results supplemented by xrd x ray diffraction studies of the nodules show the dominance of calcium silica and phosphatic phases the diversity of clay minerals significant variations in mineralogical composition and lack of any continuous vertical trend in the nodules suggest a relatively low impact on the primary environmental signal by burial diagenesis

fine scale la icp ms study of redox oscillations and reey cycling during the latest devonian hangenberg crisis moravian karst czech republic abstract trace elementsand reey distribution of thinly laminated limestone laminite and underlying pre event calciturbidite siphonodella praesulcata conodont zone deposited in association with the hangenberg black shale event were analyzed using laser ablation inductively coupled plasma mass spectrometry these deposits were also analyzed by carbonate petrography and scanning electron microscopy our study documents the origin of authigenic microbial limestones during the latest devonian hangenberg extinction event when unusual oceanic conditions appear to have enhanced precipitation of calcite within microbial carbonates detrital contamination of the calciturbidite and laminated limestone is very low as demonstrated by low contents of al zr ti and th these deposits display only limited degree of early diagenetic overprint of limestones and some of them fall within or very close to the seawater field elevated u and mo enrichments and covariation patterns reflect the episodic establishment of oxic to euxinic bottom condition during deposition of the laminite the oxic conditions that existed during accumulation of the underlying calciturbidite were likely the result of turbidity current introduction of oxygen into the bottom environment ree contents of both the laminite and calciturbidite are nearly ten times higher than those of most modern carbonates and similar to devonian microbialites from the canning basin calciturbidite display a prominent mreen bulge shale normalized ree patterns of the overlying laminite are similar to those of modern seawater and devonian microbialites from the canning basin lree depletion and progressive enrichments in heavier ree reflecting the dominance of authigenic carbonate phases minor contamination is bound to apatites siliciclastic minerals pyrites and organic matter the element content of authigenic phases benefited from fe and mn oxyhydroxide redox cycling negative ce and positive eu anomalies low y ho ratios and very low al al fe mn ratios suggest an influence of diluted high temperature hydrothermal fluids perhaps related to latest devonian rift magmatism in the eastern part of the rhenohercynian zone the proliferation of anachronistic facies following the devonian carboniferous d c extinction event recognized in moravia and traced worldwide seems to share some features in common with anachronistic carbonate sequences documented in the aftermath of the end permian mass extinction

glacial eustatic sea level curve for early late pennsylvanian sequence in north central texas and biostratigraphic correlation with curve for midcontinent north america at least 30 transgressive regressive cycles of deposition are recognized from the upper desmoinesian east mountain shale to the mid virgilian wayland shale in north central texas maximum regressive deposits are typically paleosol mudstones and fluvial sand stones maximum transgressive deposits are typically widespread ammonoid bearing conodont rich dark phosphatic shales in more major cycles and persistent fossiliferous shales or limestones overlying terrestrial deposits in more minor cycles delta complexes dominate the regressive sequences of many cycles using biostratigraphic criteria of first last sole or acme occurrence of ammonoid conodont and fusulinid taxa we correlate 17 cycles in the texas sequence directly with 17 glacial eustatic cycles of similar magnitude in the northern midcontinent this correlation suggests that glacial eustacy was the basic control over the cyclic sequence in texas that tectonic masking of the eustatic signal by nearby orogenic movement in texas was negligible and that delta shifting though conspicuous was only a secondary control over the cyclicity there minor cycles recognized between the correlated cycles also match well enough between texas and the midcontinent to further discount potential tectonic or deltaic masking of glacial eustatic cyclicity this strengthens the likelihood of correlating glacial eustatic events across larger parts of north america and perhaps with other parts of the world

diagenetic uptake of rare earth elements by conodont apatite abstract the rare earth element ree composition of bioapatite has long been used as a proxy for ancient seawater chemistry and paleomarine environmental reconstruction based on the assumption of preservation of a hydrogenous seawater derived ree signal recent work however has begun to question the provenance of rees in conodonts emphasizing the importance of rees released by the lithogenous fraction of the sediment and subsequently adsorbed onto conodont apatite in the burial environment here we investigate patterns of ree and trace element abundance in conodonts and their host sediments from the early to late ordovician huanghuachang and chenjiahe sections of hubei province south china several lines of evidence indicate that rees in the conodont samples were acquired mainly from clay minerals in the host sediment during burial diagenesis 1 rees in conodonts show a strong positive correlation to th and other lithogenic elements 2 conodonts and whole rock samples show general patterns of ree and trace element enrichment that are highly similar to each other and bear no resemblance to seawater elemental concentrations 3 similar patterns are observed in triassic conodonts and whole rock samples and 4 y ho ratios in conodonts are mostly 90 of rees from lithogenous sources conodonts show pronounced middle rare earth element mree enrichment a pattern that is unambiguously of diagenetic origin owing to its association with lower y ho ratios with increasing mree enrichment of conodont samples u concentrations and la n yb n ratios shift from high to low and mn concentrations from low to high these patterns suggest that conodont diagenesis was initiated at shallow burial depths under suboxic conditions i e in the zone of mn iv and fe iii reduction but continued at greater burial depths with most acquisition of secondary rees at later diagenetic stages our findings indicate that 1 conodont apatite frequently does not preserve a recognizable hydrogenous ree signal and 2 the results of many earlier studies in which rees in bioapatite were used as a paleoseawater proxy may need re evaluation

rare earth element variation in phosphate nodules from midcontinent pennsylvanian cyclothems abstract the rare earth element ree geochemistry of phosphate nodules from eastern kansas and northeastern oklahoma is dominated by patterns that are generally flat or are enriched in middle ree mree flat patterns are typical of phosphate nodules preserved in thick shales and in nodules from shales deposited nearest to detrital sources the flat patterns are probably derived from terrigenous constituents in the host shale mree enrichment is evident in phosphate found in relatively thin shales and in distal shales we suggest that the mree enriched pattern reflects the contribution of mree enriched fecal phosphate the initial mree enrichment mechanism may have been analogous to that in which some modern algae preferentially extract mree from water of marine composition the mree enric ed signature may be preserved only in phosphate nodules that formed where terrigenous input was so low that it did not mask the characteristic fecal pattern rare ce depletion patterns reflect a primary seawater ree source that has not been obscured by fecal or detrital components

more reducing bottom water redox conditions during the last glacial maximum in the southern challenger deep mariana trench western pacific driven by enhanced productivity abstract the modern southern mariana trench is characterized by oligotrophic surface waters resulting in low primary productivity and well oxygenated bottom waters this study investigates changes in the redox conditions of bottom waters in the southern mariana trench during the last glacial maximum lgm and their potential causes we measured major trace and rare earth elements ree in three gravity cores gc03 gc04 and gc05 and one box core bc11 retrieved from the southern challenger deep at water depths from 5289 to 7118 m the upper sediment layers of both gc05 and bc11 are dominated by valve fragments of the giant diatom ethmodiscus rex forming laminated diatom mats ldms 14c ams dates of bulk organic matter show that the ldms accumulated between 18 4 and 21 8 kyr b p corresponding to the lgm modest enrichments of u and mo along with weak or absent ce anomalies in the ldm point to suboxic conditions during the lgm in contrast non ldm samples exhibit little to no enrichment of redox sensitive elements as well as negative ce anomalies indicating deposition under oxic bottom water conditions the ce anomalies are considered valid proxies for bottom water redox conditions because ree signatures were acquired in the early diagenetic environment as indicated by strong p ree correlations and middle ree enrichment associated with early diagenetic cycling of fe mn oxyhydroxides in the sediment column followed by capture of the ree signal by biogenic and or authigenic apatite we postulate that the more reducing bottom water conditions during the lgm were linked to increased primary productivity induced by enhanced asian dust input as shown in earlier studies the increased primary productivity associated with ethmodiscus rex blooms in the eastern philippine sea played a significant role in capturing atmospheric co2 during the lgm consequently the magnitude of atmospheric co2 sequestration by giant diatom blooms during the lgm may have been greater than previously envisaged

elemental distributions and neodymium isotopic compositions of silurian metasediments western maine usa redistribution of the rare earth elements abstract pelitic schists from the lower garnet to lower staurolite zones from the rangeley perry mountain and smalls falls formations of western maine were analyzed for major elements trace elements and neodymium isotopes these formations were derived from highlands created during the taconian orogeny deposited into a trough and metamorphosed during subsequent orogenic events most major and trace element abundances relative to al 2 o 3 were statistically identical between zones of the same formation as well as between formations although the average major element composition of these formations are the same there are systematic variations in some elements notably plots of sio 2 vs al 2 o 3 and k 2 o vs al 2 o 3 suggest that most of the variation could be produced by mixing of a fairly constant ratio of clay minerals and feldspar with varied amounts of quartz due to sorting in the sedimentary system different amounts of these minerals should not influence the shape of the ree patterns of the metapelites but higher amounts of quartz and feldspar may dilute the rees and most elemental abundances of the clay minerals and lead to lower elemental abundances the major difference between the samples within the perry mountain formation are different lree and mree abundances relative to al 2 o 3 which are not correlated to differences in major element or other trace element abundances relative to al 2 o 3 the samples in the perry mountain with higher lree and mree abundances have for example 42 3 8 3 ppm and those with low abundances have 5 6 3 6 ppm the samples with the high ree abundances of the perry mountain formation are similar in abundances and ree patterns to those of the rangeley and smalls falls formations typical of mudstones derived from granitoids another difference between the low and high ree abundance samples are the calculated t dm model ages the high ree abundance samples of the perry mountain formation show t dm similar to the samples of the rangeley formation with ages of about 1 7 1 8 ga the perry mountain samples with low ree abundances however give unrealistically old t dm s between 2 5 and 5 3 ga these unrealistically old t dm s are due to the relatively high sm nd ratios compared to crustal values which are characteristic of samples of the perry mountain formation with lower ree abundances we therefore suggest that these samples may be indicators for open system behavior of the neodymium isotopic system the timing of this disturbance of the neodymium isotope system is difficult to determine and cannot be tied to weathering or a definite postdepositional event the complexities of the data suggest more than one resetting event the most likely event that could have produced much of the movement of the lrees and mrees could have been due to small scale migration between anoxic hemipelagites and turbidite mudstones during diagenesis but some migration may have continued during metamorphism in order to reconcile the neodymium isotopic data

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

catastrophic flood disturbance and a community s response to plant resilience in the heart of the texas hill country abstract the blanco river which flows through the limestone balcones canyonlands of central texas usa experienced catastrophic flooding in may 2015 that resulted in significant biogeomorphic disturbance to its riparian corridor high resolution aerial and satellite imagery from pre and post flooding for a 55 km reach of river were used to map and categorize patterns of disturbance by degree of severity ranging from complete floodplain stripping to no disturbance the most severe disturbance occurred within the floodway near the channel and decreased with lateral distance into the 100 and 500 year floodplains disturbance patterns previously identified in the literature including meander scour parallel chute scour convex bank erosion and macroturbulent scour were all present following this event as well as substantial disturbance proximal to tributary confluences in the aftermath of this event treefolks a local nonprofit organization engaged with the community to actively replant and restore the riparian corridor of the blanco river on public and private lands these reforestation efforts supplement the natural passive recovery of the riparian corridor enabling the system to recover more quickly and be resilient to future flood events

effect of diagenesis on trace element partitioning in shales abstract in order to investigate the partitioning of trace elements in mineral phases of black shales and diagenetic remobilization of trace elements within these phases we isolated major black shale components sulfide carbonate silicate and organic and analyzed the isolated fractions as well as corresponding whole rock for their trace element composition by drc icp ms this study focused on black shales of different grades of thermal maturity from the ordovician utica shale magnafacies of quebec usm immature tmax 20 50 c ro 140 c ro 1 analysis of the isolated rock fractions revealed that the carbonate fraction preserves a sea water like rare earth elements ree abundance pattern with enrichment of the heavy rare earth elements hree dy lu relative to light rare earth lree la sm the sulfide and organic fractions show a slight enrichment in the lree mass balance calculations showed that the organic fraction contains up to about 20 of total trace element content of the whole rock with the sulfide and carbonate fractions each containing less than 10 the partitioning and fractionation of trace elements between different phases may have important implications for paleoenvironmental reconstructions and provenance studies our data suggest that the whole rock signature may be less representative of source area or depositional environment but rather reflects the diagenetic history this is especially the case in organic rich sediments such as black shales where the organic fraction hosts up to 20 of the trace element content of the whole rock

raman spectral elemental crystallinity and oxygen isotope variations in conodont apatite during diagenesis abstract conodont apatite has long been used in paleoenvironmental studies often with minimal evaluation of the influence of diagenesis on measured elemental and isotopic signals in this study we evaluate diagenetic influences on conodonts using an integrated set of analytical techniques a total of 92 points in 19 coniform conodonts from ordovician marine units of south china were analyzed by micro laser raman spectroscopy m lrs laser ablation inductively coupled plasma mass spectrometry la icp ms high resolution x ray microdiffraction hxrd and secondary ion mass spectrometry sims each conodont element was analyzed along its full length including the albid crown hyaline crown and basal body in either a whole specimen i e reflecting the composition of its outer layer or a split specimen i e reflecting the composition of its interior in the conodonts of this study the outer surfaces consist of hydroxyfluorapatite and the interiors of strontian hydroxyfluorapatite ionic substitutions resulted in characteristic raman spectral shifts in the position ss1 and width ss2 of the 1 po43 stretching band although multiple elements were enriched sr2 mg2 and depleted fe3 mn2 ca2 during diagenesis geochemical modeling constraints and known raman spectral patterns suggest that sr uptake was the dominant influence on diagenetic redshifts of ss1 all study specimens show lower ss2 values than modern bioapatite and synthetic apatite suggesting that band width decreases with time in ancient bioapatite possibly through an annealing process that produces larger more uniform crystal domains most specimens consist mainly of amorphous or poorly crystalline apatite which is inferred to represent the original microstructure of conodonts in a subset of specimens some tissues especially albid crown exhibit an increased degree of crystallinity developed through aggrading neomorphism however no systematic relationship was observed between crystallinity and raman spectral or elemental parameters oxygen isotopes show substantial variation within the conodont study specimens albid crown is on average 0 28 0 32 more depleted in 18o equivalent to 1 2 1 4 c higher temperatures than hyaline crown and basal body and the interiors of conodont elements are 1 08 0 37 more depleted in 18o equivalent to 3 0 6 4 c higher temperatures relative to their outer layers although albid crown is widely regarded as better preserved than other conodont tissue types its 18o depleted composition and greater development of secondary crystallinity suggest that in fact it may be the most strongly altered tissue type we conclude that raman spectral la elemental and hxrd microstructural data can provide useful information about the extent of diagenetic alteration of conodont elements and that such information should be taken into consideration in using conodont elemental and oxygen isotope data in paleoenvironmental studies

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

geochemistry of trace elements and their relations with organic matter in kuh e sefid phosphorite mineralization zagros mountain iran abstract the kuh e sefid phosphorite is located in zagros fold thrust belt in the ramhormoz area northeast of khuzestan province phosphorite mineralization occurred as phosphorite lenses of eocene age hosted by the pabdeh formation the aim of this study is to investigate the role of organic matter in trace metal portioning during phosphorite mineralization in the kuh e sefid deposit field observations and petrographic studies indicate that the host rock of mineralization is mainly consists of shale marl and limestone with textures varying from wackestone to packestone phosphoritic components such as authigenic apatite pellets intraclasts fish skeletal fragments and micro fossils are present moreover non phosphorite minerals including calcite glauconite pyrite iron oxide and to a lesser extend montmorillonite with microcrystalline quartz occurred in phosphorite lenses nasc normalized patterns of rees showed the enrichment of heavy rare earth elements hree and negative ce anomaly with co existence of slightly negative and positive eu anomalies represent a transitional change from oxic to anoxic sedimentation conditions during mineralization importantly ni co versus v cr ratios and v v ni diagrams confirmed dysoxic to anoxic conditions for the hydrocarbon bearing phosphorite and hosted shales while non hydrocarbon bearing phosphorites exhibit oxic conditions the ftir studies revealed qualitative information about the component bonds and nature of the organic matter and mineral organic bonds like oh carboxylic oh carboxylic acid c o c c alkaline group ch2 c c aromatic ch aliphatic and aromatic stretching associated with phosphate mineralization it seems that there is a link between a relatively high concentration of trace metals i e rees u co zn ni v sr and mo and phosphorites enriched in organic matter especially those of aromatic hydrocarbon groups

geochemistry of rare earth elements in early diagenetic miocene phosphatic concretions of patagonia argentina phosphogenetic implications abstract phosphatic concretions in the early miocene shallow marine clastic deposits of the gaiman formation gaiman fm show typical major element ratios rare earth element ree patterns and total ree contents these characteristics are similar within different stratigraphic levels and geographic locations of the unit in central north patagonia argentina and suggest a common process for the origin of the concretions major element oxides in concretions are grouped into a clastic group si al ti k and fe that mostly corresponds to the silicates in the terrigenous fraction and an authigenic group p ca and total rees that corresponds to authigenic francolite and calcite mn is the only element that exhibits a separate behavior most likely because of its high mobility in seawater major element ratios in host shales are similar to those of the clastic fraction within the concretions and coquinas concretions are slightly depleted in lrees and slightly enriched in hrees in comparison to shales and display a weak negative ce anomaly their la yb and la sm ratios indicate rees incorporation from pore water without strong postdepositional recrystallization or strong adsorption y anomalies and la nd ratios in concretions are equivalent to seawater or slightly lower suggesting that gaiman concretions did not undergo intense diagenesis but they were probably formed from phosphatic solutions impoverished in y and la as a result of rees release to solution from organic complexes in the early diagenesis flat linear ree patterns also support an early diagenetic origin for the concretions via quantitative precipitation of phosphate from oxic suboxic pore waters water circulation through burrows at the miocene seawater sediment interface improved ion diffusion and pore water renewal in the sediments allowing the development of a widened early diagenetic oxic suboxic zone and the precipitation of phosphate with a homogeneous ree pattern

the controls on the major and trace element variation of shales siltstones and sandstones of pennsylvanian permian age from uplifted continental blocks in colorado to platform sediment in kansas usa shales siltstones and sandstones of pennsylvanian permian age from near the source in colorado to those in the platform in eastern colorado and kansas have been analyzed for major elements and a number of trace elements including the rees the near source sandstones are significantly more enriched student t test at better than the 99 confidence level in sio2 and na2o concentrations and more depleted in al2o3 fe2o3 total tio2 th hf sc cr cs rees y and ni concentrations and laco and lani ratios than the near source shales and siltstones most likely due to more plagioclase and quartz and less clay minerals in the sandstones than in the shales and siltstones there are no significant differences in k2o and sr concentrations and eueu lalu lase thsc thco and crth ratios between the near source sandstones and the near source shales and siltstones samples of the molas hermosa and cutler formations near the source that were formed in different environments in the same area contain no significant difference in eueu lalu lasc thsc thco and crth ratios so a generally silicic source and not the environment of deposition was most important in producing these elemental ratios for example crth ratios of near source shales siltstones and sandstones range from 2 5 to 17 5 and eueu range from 0 48 to 0 78 which are in the range of sources of sediments derived from mainly silicic and not basic sources near source shales and siltstones contain significantly higher student t test and more varied concentrations of most elements al2o3 fe2o3 mno tio2 ba th hf ta co sc rees nb y but significantly lower concentrations of na2o and eueu than platform shales and siltstones in kansas e g la 65 7 40 and eueu 0 55 0 07 in near source shales and siltstones and la 23 7 8 7 and eueu 0 64 0 08 in platform shales and siltstones the sio2 and cao concentrations are not significantly different in platform shales and siltstones compared to the near source shales and siltstones so dilution of other minerals by quartz and calcite is not the main reason for the lower concentration of most elements in the platform relative to the near source shales and siltstones rather the lesser concentrations of most elements in clay minerals of the platform shales and siltstones can account for the lower concentration of most elements compared to corresponding near source shales and siltstones the lower concentrations of many elements in clay minerals in the platform shales and siltstones may be a result of having been derived from recycling of clay minerals from older rocks the greater homogeneity of elemental concentrations of the platform shales and siltstones compared to those in the source is also consistent with homogeneous mixing of such recycled material also there is no significant difference in thsc laco thco lani and crth ratios of the near source sedimentary rocks in colorado to the platform shales and siltstones in kansas and the latter are also consistent with derivation from mostly silicic source rocks

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

geochemical investigation of the lower cambrian mineralised black shales of south china and the late devonian nick deposit canada abstract lower cambrian tommotian black shales of the niutitang formation south china host a thin accumulation 5 20 cm of ni mo platinum group elements pge au ni as zn cu v and rare earth elements ree of all known deposits the late devonian ni mo pge sulphide horizon in black shales of the nick deposit selwyn basin in canadian yukon presents the strongest similarity with the niutitang formation polymetallic layer in the present study samples of the mineralised layer and host shales in south china from two mine sites zunyi and sancha were investigated in order to further characterise the prevailing redox conditions and mechanisms involved in the metal concentration process at both sites additional comparison with the nick deposit mineralised layer was also undertaken bulk geochemical analysis including pge analysis were conducted on all samples along with m scale investigation of metal distributions and associations by x ray fluorescence xrf mapping and synchrotron xrf mapping the comparison of the two sites from south china highlights strong similarities in metal enrichment factors pge and ree distribution patterns are also highly similar and suggest a source from seawater strong variations in elemental distributions at m scale were observed at both sites most likely related to intense variations in redox conditions in the sediment the comparison with the nick deposit highlights a stronger enrichment in ni and zn in the nick deposit and a greater variety of minerals in the niutitang shales the pge and ree distributions of both the nick deposit and the niutitang shales however present highly similar patterns and support an origin from seawater the present study provides further insight into mineralisation style and processes in these mineralised black shales highlighting the importance of redox conditions and re emphasizing the role of organic matter in the formation of these mineralised layers

mineralogic controls on ree mobility during black shale diagenesis abstract the llandeilo caradoc black shales of southwest wales u k record a paragenetic sequence that requires redistribution of rare earth elements ree on a mineralogic scale during diagenesis the main evidence for this redistribution is formation and replacement of ree rich apatite and monazite and variations in whole rock ree patterns the processes that produce these mineralogic changes create a diagenetic overprint on the llandeilo caradoc black shales that obscures geochemical information related to both provenance and paleoenvironmental conditions of deposition periods of open system conditions existed during the diagenetic alteration of the llandeilo caradoc black shales which allow an evaluation of the extent and timing of the ree redistribution inferred from petrography the observed variations in la sm ratios in the whole rock ree patterns are strong evidence that ree were redistributed on a scale greater than an individual hand sample this change in the whole rock ree pattern altered the cerium anomaly by as much as 20 and produced a range in the sm nd ratio from 0 14 to 0 20 this change in the whole rock sm nd ratio indicates a disturbance in the sm nd isotopic system at about 460 ma that can be directly linked to the formation and dissolution of diagenetic apatite and monazite during diagenesis one effect of this disturbance is to alter the range in nd model age for the llandeilo caradoc black shales from 1 6 to 1 8 ga to about 1 4 to 2 25 ga thus complicating any interpretation of provenance the ability to link petrographic observations from a black shale to measurable whole rock geochemical changes provides us with one tool to evaluate the presence of a diagenetic overprint on trace elements commonly used in paleoenvironmental reconstruction

taphonomy of lacustrine fish fossils of the parnaiba basin northeastern brazil spatial and causative relations of konservat lagerstatten in west gondwana during jurassic cretaceous abstract fossil bonanzas called konservat lagerstatten provide geological windows to the ecology of ancient life communities these deposits often occur as cluster of fossil localities with similar geographic locations geological ages and facies as the fossils were generally preserved during special periods and large scale events in earth history within environments with exceptional taphonomic conditions this work applied petrological and geochemical analyses to evaluate the taphonomic pathway of a konservat lagerstatten in the muzinho shale upper jurassic lower cretaceous of the parnaiba basin northeastern brazil these lacustrine deposits include interbedded limestones and fossiliferous black shales deposited in anoxic non euxinic and saline environment black shales contain articulated skeletons of fish fossils characterised by three dimensional preservation of the skeletal tissue the polytypical assemblage includes diverse ontogenetic stages and is concentrated in a specific stratigraphic level mass mortality was triggered by anoxia probably established by stratified water column high c flux and thermocline demise the specimens are encased in kerogen bearing siliciclastic laminae and cementstone microfacies both microbially induced the fossils were cemented by eodiagenetic poikilotopic calcite that filled the skeletal articulation including bone trabeculae and voids originally filled by bone marrow the short distance similar fossil assemblages ages and coincident palaeoenvironments suggest that muzinho shale parnaiba basin and crato formation araripe basin compose a cluster of exceptional preservation in west gondwana lava flows and outgassing related to the central atlantic magmatic province camp resulted in the subaereal exposure of volcanic plains acid rains and subsequent co2 greenhouse crisis camp magmatism was especially voluminous in northern brazilian basins enhancing nutrient rich waters and lacustrine eutrophication due to intensified chemical weathering in this area probably other konservat lagerstatten remain unreported in west gondwana despite similar causative events the individual taphonomic pathways of muzinho shale and crato formation are very different suggesting that in these cases local phenomena affected authigenesis and diagenesis

scale and timing of rare earth element redistribution in the taconian foreland of new england clastic sedimentary rocks deposited on eastern north america in response to the taconian orogeny commonly have sm nd isotope relationships indicating substantial isotope disturbance near or subsequent to the time of sedimentation that may be associated with severe depletion in light rare earth elements lree affected units normanskill formation austin glen and pawlet members frankfort formation and perry mountain formation are widely separated both geographically western new york to western maine and stratigraphically middle ordovician to silurian a model is proposed for the most likely explanation of the observed ree and sm nd isotope relationships involving a two stage process in the first stage ree are redistributed on a mineralogical scale dissolution precipitation on a sample scale often with the involvement of ree enriched trace phases such as apatite and monazite this stage typically takes place during diagenesis but may also take place later during metamorphism and or recent weathering and results in isotope re equilibration on a sample scale the second stage occurs when one or more of these phases is redissolved and ree are transported on large advective scales where lree enriched phases are involved this gives rise to lree depletion in whole rocks the timing of this second stage cannot be constrained from sm nd isotope data and may take place at any time subsequent to the isotope re equilibration such complex histories of ree redistribution may result in serious errors in estimating nd model ages but not in estimating the nd isotope composition at the age of sedimentation thus sm nd ratios even of unmetamorphosed sedimentary rocks have to be carefully evaluated before the calculation of depleted mantle model ages for the provenance

contrasting depositional models for pennsylvanian black shale discerned from molybdenum abundances some black shales contain 1 000 ppm mo comparable to conventional ores these include mo rich pennsylvanian black shales that were deposited rapidly near shore as epeiric seas inundated peat swamps while coeval beds less enriched in mo accumulated slowly offshore concentration of mo probably resulted from retention of the metal by organic matter in acidic pore fluids characteristic of nearshore deposits thus in pennsylvanian shales where organic productivity is significant mo variations may be used to distinguish nearshore from offshore conditions enrichments in mo occur in black shales of other ages therefore a high mo content may be useful as a general criterion for nearshore environments and other conditions with strong ph gradients

trace element geochemistry and sedimentary provinces a study from the tasman geosyncline australia abstract the abundances of la th u and hf have been determined in flysch sequences of the tasman geosyncline australia the arc derived graywackes differ from those of rifted continental margins and marginal basins in containing low abundances of la th u and hf la 9 2 1 7 ppm th 1 4 0 6 ppm u 0 52 0 2 ppm hf 2 1 0 6 ppm reflecting similar low abundances in the andesitic source rocks graywackes of rifted continental margins and marginal basins in contrast are mature and characterised by high abundances of la th u and hf la 39 9 9 ppm th 16 0 6 ppm u 3 40 0 5 ppm hf 7 9 ppm mirroring increased abundances in the granitic and sedimentary source rocks sedimentary rocks deposited in inter arc basins show wide dispersion but have characteristics intermediate between these two types the th u ratio for magmatic arc sediments is 2 7 for most other sedimentary rocks it remains uniform at 4 5 0 3 for sediments having andesitic and dacitic rocks as provenance the la th ratios are 6 7 and 4 5 respectively this ratio remains constant at 2 6 for most quartzose sedimentary rocks

meganodular limestone of the pagoda formation a time specific carbonate facies in the upper ordovician of south china abstract the decimeter scale 3 d network structure of the upper ordovician pagoda formation in south china has been an enigmatic sedimentary feature and a case of non uniformitarian carbonate depositional system without modern analog the network bands are developed pervasively throughout the entire pagoda formation superficially resembling desiccation or syneresis cracks especially in bedding plane view with decimeter scale sub polygonal to irregularly sinuous patterns detailed petrographic analysis however shows that the crack like network bands have the same carbonate matrix skeletal grains and overall fabrics as the rock they surround in this study we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time specific lithofacies it originated from prolonged growth of nodular carbonate controlled by the convergence of several geological and paleoclimatic factors including a a protracted sea level highstand lasting for about 5 myr b an interval of tectonic quiescence favoring the dominance of carbonate production with minimal siliciclastic input and c location of the south china paleoplate in the hurricane free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases normally 15 120 m depths favoring long term uninterrupted growth of caco3 meganodules on a mid shelf substrate this study corroborates recent paleogeographic reconstructions that position the south china paleoplate on the equator during the late ordovician

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

the controls on the major and trace element evolution of shales siltstones and sandstones of ordovician to tertiary age in the wet mountains region colorado u s a a vertical section of shales siltstones and sandstones from ordovician to eocene age in a limited geographic area east of the wet mountains and sangre de cristo mountains in colorado have been analyzed for major elements and a variety of trace element concentrations including the ree in addition the petrography of the sandstones has been determined the quartz rich arenites contain considerably lower concentrations of most elements relative to coexisting shales or siltstones at the same outcrop the arkosic sandstones contain similar to lower concentrations of most elements compared to coexisting shales or siltstones in the same area accordingly the average concentrations of al2o3 fe2o3 mgo tio2 loi rb th co sc cr cs nb y and ree are significantly lower in all sandstones relative to all shales and siltstones the exceptions are sio2 na2o and ba concentrations and the eu eu lasc and thsc ratios as they are higher in the sandstones than the shales and siltstones there is no significant difference in the mno cao k2o and sr concentrations or the sollaco thco lani crth and lalucn ratios of the average sandstones relative to the shales and siltstones many of these differences may be related to the higher quartz and feldspar and lower clay mineral amounts in the sandstones than in the shales and siltstones for example average lasc thsc eueu and lalucn ratios of th arkosic sandstones tend to be higher than the coexisting shales and siltstones due to enrichment of the arkoses in feldspar relative to the other minerals e g eueu 0 82 0 19 in average arkoses in the trinidad vermejo raton poison canyon and cuchara formations eueu 0 63 0 19 in average shales and siltstones in the same formations in addition the elemental concentrations and ratios are more variable for most elements in the sandstones than the shales and siltstones this suggests that the shales are rapidly homogenized near the source the elemental fractionation in the arkosic sandstones due to enrichment of feldspar relative to other minerals suggests that they are poorer indicators of provenance that the associated shales whereas the more homogeneous elemental distributions in the shales and siltstones suggest that they may be better indicators of provenance than the sandstones nevertheless the elemental ratios that are most similar in the sandstones and in the shales and siltstones are consistent with their derivation from similar average intermediate to silicic source rocks

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

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

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

micron scale distribution of metals in cambrian metalliferous shales south china insights into local biologically driven redox disequilibrium abstract early cambrian black shales of the niutitang formation are found across the yangtze platform in a 1600 km belt extending across south china a thin organic matter rich layer in the lowermost part of this formation contains exceptional concentrations in mo ni se re os as hg sb ag au pt pd and ag due to their extreme metal enrichment these black shales provide a rare opportunity to study the interface between semi metals metals and biogenic material we report the first detailed m scale investigation of metal distributions and associations in samples from two sites zunyi and sancha located hundreds of km apart using a combination of analytical techniques including x ray fluorescence xrf mapping scanning electron microscopy sem synchrotron based xrf mapping electron probe micro analyser epma particle induced x ray emission pixe probe and x ray absorption near edge structures xanes imaging strong m scale variations in metal and semi metal distributions were highlighted by synchrotron based xrf mapping of samples from both sites at both locations u is present within phosphorite nodules arsenic mo and se are particularly abundant in the organic rich matrix showing strong associations with organic matter nickel however shows different distributions between the two sites it is mainly present in association with the organic matter at the sancha site while it is found in abundance in millerite at the zunyi site suggesting slightly different local conditions at zunyi favouring ni s associations over ni organic matter at both sites biogenic structures were re mineralised with laminations dominated by different metals indicating a likely control of organic matter over metal distributions in addition the xanes imaging highlighted different redox states of as over m scale areas while as 1 appears to be mainly present in pyrite as 3 was mainly detected in association within the carbon and mos2 mixed layer phase mosc overall the present results emphasize the complexity of metal associations in this mineralised layer the significant role of organic matter in the accumulation and precipitation of metals and semi metals in these metalliferous shales and highlight how biogenic activity can induce m scale variations in redox conditions in sediments

resolving eolian volcanogenic and authigenic components in pelagic sediment from the pacific ocean abstract we measured major and trace element concentrations in the operationally defined chemically extracted residual aluminosilicate component of sediment from ocean drilling program sites 1215 and 1256 in the central and eastern equatorial pacific ocean and found that this residual component contains volcanogenic and authigenic aluminosilicates in addition to inferred eolian material while the residual component younger than 20 ma from the central pacific odp site 1215 is similar compositionally to upper continental crust and suggests an increase in the delivery of asian dust material since 20 ma the residual in sediment older than 20 ma indicates significant amounts of volcanogenic and authigenic materials volcanogenic debris comprises as much as 40 of the residual between 23 40 ma which coincides with the mid tertiary ignimbrite flare up that occurred in much of western north america the residual component extracted from the 50 ma biogenic sediment reflects authigenic signatures seawater like negative cerium anomalies and elevated fe si ratios the previously interpreted increase in an andesitic detrital source in north pacific locations may instead be authigenic material presenting significant challenges for many paleoclimate proxies additionally in the eastern pacific odp site 1256 the residual component contains 70 of volcanogenic material most likely originating from central america and also includes refractory barite the ability to separately identify eolian volcanogenic and authigenic materials in the aluminosilicate component of pelagic sediment allows resolution respectively of the climatic geologic and chemical processes contributing to the paleoceanographic archive in this critical oceanic region

redox fluctuations during the ediacaran cambrian transition nanhua basin south china insights from cr isotope and ree y data abstract reconstructing fluctuations in marine and atmospheric redox conditions during the late precambrian early cambrian is essential to better our understanding of the link between oxygen and biological evolution this study presents ree y and cr isotopic data together with toc data and redox sensitive trace metal concentrations of marine black shales and cherts from the cambrian jiumenchong formation and ediacaran liuchapo formation from south china in order to improve our understanding of the redox conditions in the nanhua basin during this critical time period the liuchapo formation records negative ce anomalies and highly fractionated 53cr values of up to 1 06 0 09 suggesting deposition under oxic conditions and implying high oxidative weathering rates during the end of the ediacaran the overlying jiumenchong formation is characterised by a stratigraphic upward decrease in 53cr values to typical igneous values as well as a decrease in negative ce anomalies and an increase in positive eu anomalies suggesting an increase in detrital content due to more aeolian weathering and deposition under anoxic conditions at the beginning of the cambrian the latter is also confirmed by the trends in v cr and th u ratios which further indicate an eventual return to dys oxic seawater conditions during the early cambrian

provenance of paleozoic mudstones in a contact metamorphic aureole determined by rare earth element th and sc analyses sierra nevada california rare earth element ree th and sc analyses of mudstones from the contact metamorphic aureole of the middle jurassic emigrant gap composite pluton support the idea that the lower paleozoic lang black oak spring and zion hill sequences are composed of detritus derived from a continental landmass on ree distribution diagrams our samples exhibited 1 no systematic change as a result of varying metamorphic grade 2 light ree enrichment trends and 3 eu anomalies that vary from 0 46 to 0 93 and average 0 66 on a la th sc ternary diagram our data cluster within the fields of passive margin sediment and post archean australian shale paas these new data in conjunction with the quartz rich character of sandstones the absence of volcanic material and precambrian detrital zircon ages suggest that clastic material in the lang black oak spring and zion hill sequences was derived from a continental landmass that may have been north america or alternatively some continental fragment oceanward of early paleozoic north america

controls on rare earth element distributions in ancient organic rich sedimentary sequences role of post depositional diagenesis of phosphorus phases abstract the processes that dictate the formation and preservation of rare earth element ree signatures in ancient marine black shales are incompletely understood thus potentially limiting the utility of the rees as geochemical tracers here we report on whole rock ree analyses of six black shale formations from different ages and depositional settings which fall within three general groupings group 1 is characterized by low whole rock ree content ree n la n n la n n la n 2 yb n la n 250 g g and moderately middle ree enriched patterns gd n la n 1 5 2 5 yb n la n 1 representative samples from these groups were selected from the marcellus and hushpuckney shales and subjected to a multi step leaching procedure to isolate four extractable p phases reducible authigenic carbonate associated detrital apatite organic in group 1 samples with low carbonate content 3 rees were hosted mainly in the organic 50 of ree and siliciclastic fractions 37 whereas in samples with greater carbonate content 25 caco 3 rees were hosted mainly in carbonate associated phases 53 in group 2 rees were hosted mainly in the carbonate associated 64 and organic fractions 30 and in group 3 rees were hosted mainly in the carbonate associated 60 detrital apatite 23 and siliciclastic fractions 16 authigenic phases include minerals such as carbonate fluorapatite and authigenic calcite that if present tend to dominate the whole rock ree inventory in the absence of carbonate whole rock ree content depends on the relative ree contributions of the organic and siliciclastic fractions

oligocene to holocene glauconite phosphorite grains from the head of the cape canyon on the western margin of south africa abstract glauconite and carbonate fluorapatite cfa are significant components of the condensed upper oligocene to holocene sediment succession recovered from the western margin of southern africa the detailed texture and geochemistry of these glauconite phosphorite grains are reported here within the stratigraphic framework established on the outer continental shelf in the head of the cape canyon area three texturally and stratigraphically distinct glauconite grain types are recognised oligo miocene infilled foraminiferal tests mio pliocene green and quaternary dark green to black grains most of these glauconitic grains include a minor to significant amount of cfa the upper oligocene to lower miocene sediment succession is dominated by fine sand sized benthic and planktic foraminifera glauconite grains constitute 20 50 of the sediment and represent tests infilled by variable proportions of glauconite and cfa cement with the test wall replaced by cfa only glauconite cfa formation during the late oligocene to early miocene was associated with warm water upwelling coupled with third order marine transgressions rare earth element ree chemistry indicates that sub oxic conditions prevailed during diagenesis mio pliocene green and quaternary dark green to black medium sand sized glauconite grains constitute between 20 and 95 of these predominantly siliciclastic sediments the green to black glauconite grains are texturally different but have similar major and ree chemistry since the mid miocene formation of glauconite cfa grains is associated with cold water upwelling and detrital fe rich terrigenous mud deposition in oxic to suboxic bottom waters analogous to the holocene coast parallel organic rich mudbelt on the shelf the texture of these grains indicates repeated cycles of glauconite and cfa authigenesis during marine transgressions and winnowing and reworking during marine regressions

resetting of neodymium isotopes and redistribution of rees during sedimentary processes the early proterozoic chelmsford formation sudbury basin ontario canada abstract the rees abundances and neodymium isotope compositions of sandstones and siltstones from the early proterozoic chelmsford formation reveal that the rees in some samples were redistributed during the early proterozoic by surficial processes and that prior to redistribution the nd isotope system was partially reset the chelmsford formation is a coarse grained turbidite sequence the youngest of three clastic units that fill the sudbury basin in ontario it is constrained to have been derived from nearby late archean superior province rocks by petrography major and trace element chemistry and pb isotopic compositions of whole rocks and feldspar although ree patterns and nd model ages for samples from around the base of the formation reflect their derivation from undisturbed superior province rocks tdm 2800 ma five samples from higher in the stratigraphic section show evidence that up to 60 of their la has been removed and sm nd has increased by up to 60 these samples also have anomalously high nd model ages tdm 3400 to 4400 ma the presence of pronounced positive ce anomalies in the samples with anomalous tdm indicates the influence of surficial processes on the ree composition the data scatter about a vertical array on a plot of f sm nd vs ndt 1800 nd calculated at 1800 ma approximately the depositional age with values of f sm nd between 0 45 and 0 14 mixing of nd from other sources is difficult to reconcile with the petrography major and trace element geochemistry and nd and pb isotopes removal of an lree enriched phase from the sedimentary system provides a viable mechanism to produce the ree and nd isotopic characteristics of the chelmsford formation samples neodymium isotopes require that this phase was partially isotopically equilibrated with the matrix sediment near the time of sedimentation this study shows the dangers of indiscriminate use of nd model ages in provenance studies and demonstrates that the simultaneous examination of sm nd and nd isotopes on f sm nd vs nd or isochron plots is required for the recognition of sedimentary redistribution of the ree