rare earth elements in modern coral sands an environmental proxy the concentration rare earth elements and yttrium ree y were determined in coral sands from kavaratti island arabian sea india chondrite normalized ree y patterns show 1 high ree concentration particularly light ree lree enrichment 2 consistent negative ce anomaly 3 nearly chondritic y ho ratios all these features are consistent with the geochemistry of well oxygenated seawater with significant terrestrial contribution the seawater composition of nd yb ratio inferred from the coral record point to the dominance of lree more than the heavy ree hree the high terrestrial input rich in lree and property of adsorption scavenging processes of lree than that of hree may be the cause terrigenous contributions were detected on the basis of co occurring trace element concentrations sc hf and th and y ho ratio except for la the ree distribution coefficients kd ree s are between 100 and 300 kds are high comparing to the other elements in biogenic calcite which is attributed to detrital contamination during elemental incorporation this study may not reflect original seawater chemistry but it can be a good proxy to indicate proximity of corals to terrigenous input sources

hydraulic geometry river sediment and the definition of bedrock channels a growing literature deals with bedrock channels erosion processes within them and their role in landscape evolution formal definitions currently in use classify channels as bedrock when alluvial cover is discontinuous or thin this is equated with a physical property of the flow using up to date erosion laws and descriptions of channel dynamics we show that existing definitions are difficult to apply and may lead to conflicting classifications we propose the definition a bedrock channel cannot substantially widen lower or shift its bed without eroding bedrock applied to channels in taiwan this leads to a different classification than previous definitions by analysing at a station hydraulic geometry of these channels we show that the classification exposes different controls of sediment effects on dynamics of channels classified as alluvial and bedrock

trace fossils biology and taphonomy 1990 special topics in palaeontology 3 280 pp e17 95 pbk e40 00 hbk unwin hyman london isbn 004445 6867 pbk 3035 hbk

positive eu anomaly development during diagenesis of the k t boundary ejecta layer in the agost section se spain implications for trace element remobilization k t boundary geochemical anomalies have been used previously to support the impact event at the end of the cretaceous however impact models and assessment of the extraterrestrial contribution to the boundary sediments should also consider the diagenetic alteration of the impact signatures mineralogical and geochemical studies centring on redox proxies reveal differences in trace element concentrations at agost and caravaca se spain two of the most complete k t boundary sections these differences probably derive from variations in the diagenetic evolution of the ejecta layer several redox proxies such as extensive pyrite formation high authigenic uranium concentration and positive eu anomalies indicate very strong reducing conditions at agost positive eu anomalies are extremely unusual in sediments and in this case are interpreted to indicate a highly reducing environment in such conditions certain trace elements such as ir may have been remobilized thereby masking the original signature of the impact

the cretaceous tertiary boundary stratotype section at el kef tunisia how catastrophic was the mass extinction abstract the cretaceous tertiary k t boundary stratotype section at el kef tunisia represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known high resolution analysis of planktic foraminifera in two outcrops el kef i stratotype and el kef ii along with comparisons between planktic and benthic foraminifera calcareous nannofossils ostracods pollen and spores and dinoflagellates indicate that major changes across the k t boundary are registered only in benthic and planktic foraminifera and calcareous nannofossils biotic changes in benthic foraminifera are unique to el kef and similarly shallow continental shelf sections and appear to be the result of a sea level regression in the latest maastrichtian followed by a sea level rise across the k t boundary that was accompanied by expansion of the local oxygen minimum zone omz biotic changes in planktic foraminifera appear partly related to these conditions also but in general reflect more global oceanographic changes for instance species extinctions are gradual and selective as observed in k t sections worldwide rather than random and abrupt although there is a 69 decline in species richness between 25 cm below and 10 cm above the k t boundary only rare species disappeared their combined relative abundance constitute less than 20 of the total population about 52 of these extinct taxa 8 of the population are large ornate morphologically complex tropical subtropical forms that lived at or below the thermocline no planktic foraminifera from this depth range survived the k t boundary event all survivor taxa were surface dwellers living within the photic zone their relative abundance 80 dominates both cretaceous and early tertiary populations these data indicate that the k t biotic record in the shallow continental shelf section at el kef was significantly influenced by local conditions which combined with the latest maastrichtian sea level regression and subsequent sea level rise resulted in shallowing of the local omz relative to the sea surface shallowing of the local omz lead to the selective disappearance of benthic faunas and may have adversely affected the surviving photic zone dwellers the selective nature of species extinctions however appear to be related partly to long term global oceanographic changes which were accelerated at the k t boundary possibly by a bolide impact

trace fossils after the k t boundary event from the agost section se spain palaeogene trace fossils penetrate the uppermost cretaceous sediments in the agost section betic cordillera se spain chondrites targionii zoophycos isp planolites isp a planolites isp b thalassinoides isp a thalassinoides isp b thalassinoides isp c alcyonidiopsis longobardiae and diplocraterion parallelum have been identified a well developed endobenthic tiering pattern is interpreted the uppermost tier a represents major benthic activity in the shallowest sediments at or just below the seafloor recorded as bioturbated background only discrete rare planolites the next upper tier b displays the highest trace fossil diversity with planolites in the shallow levels and thalassinoides and alcyonidiopsis at slightly deeper ones the intermediate tier c contains randomly distributed thalassinoides and alcyonidiopsis cross cut by zoophycos and large and medium sized chondrites the deepest tier d contains zoophycos cross cut by medium and mainly small sized chondrites two interpretations are proposed 1 vertical partitioning of a singled multi tiered community under steady stable conditions in well oxygenated water bottom reflecting gradual changes deep into the sediment with decreasing oxygen pore water and benthic food and increasing substrate consistency and 2 sequential colonization and community replacement reflecting the work of two successive communities the first community mainly represented by planolites alcyonidiopsis and thalassinoides was produced in a shallow oxygenated soft substrate probably related to decreasing oxygen content and benthic food availability this community was replaced by deeply burrowing organisms that produced zoophycos and chondrites this sequential colonization can be determined by changes in environmental parameters related to the cretaceous palaeogene k t event or may have resulted from normal ecological and early diagenetic processes

environmental controls on biomineralization and fe mound formation in a low temperature hydrothermal system at the jan mayen vent fields abstract diffuse low temperature hydrothermal vents on the seafloor host neutrophilic microaerophilic fe oxidizing bacteria that utilize the fe ii supplied by hydrothermal fluids and produce intricate twisted and branching extracellular stalks the growth behavior of fe oxidizing bacteria in strongly opposing gradients of fe ii and o2 have been thoroughly investigated in laboratory settings to assess whether extracellular stalks and aligned biomineralized fabrics may serve as biosignatures of fe oxidizing bacteria and indications of palaeo redox conditions in the rock record however the processes controlling the growth of biogenic fe oxyhydroxide deposits in natural modern hydrothermal systems are still not well constrained in this study we aimed to establish how variations in the texture of stratified hydrothermal fe oxyhydroxide deposits are linked to the physicochemical conditions of the hydrothermal environment we conducted 16s rrna gene analyses microscopy and geochemical analyses of laminated siliceous fe mounds from the jan mayen vent fields at the arctic mid ocean ridge chemical analyses of low and high temperature hydrothermal fluids were performed to characterize the hydrothermal system in which the fe deposits form our results reveal synchronous inter laminar variations in texture and major and trace element geochemistry the fe deposits are composed of alternating porous laminae of mineralized twisted stalks and branching tubes mn rich horizons with abundant detrital sediment domal internal cavities and thin p and ree enriched lamina characterized by networks of 1 m wide fibers zetaproteobacteria constitute one third of the microbial community in the surface layer of actively forming mounds indicating that microbial fe oxidation is contributing to mound accretion we suggest that mn oxide precipitation and detrital sediment accumulation take place during periodically low hydrothermal fluid discharge conditions the elevated concentrations of p and ree in distinct laminae suggest fe cycling and accumulation of diagenetic species at depth in the deposits during hydrothermal quiescence and co precipitation of these species with fe oxyhydroxides at the mound surface with reinitiated hydrothermal discharge the origin of the low temperature hydrothermal source fluid and the fe deposits are evident by low lree hree ratios and negative eu anomalies which clearly differ from the lree and eu enrichment of nearby high temperature white smoker venting fluids our study demonstrates that hydrothermal fluctuations exert the primary control on the formation of laminae and the activity of fe oxidizing bacteria in marine hydrothermal fe deposits and indicates that ree patterns may be used to distinguish high temperature plume fallout and biomineralized low temperature fe deposits in the rock record

anthropogenic pb component in hydrothermal ochres from marsili seamount tyrrhenian sea abstract recent hydrothermal fe oxyhydroxide precipitates ochres were sampled during two submersible expeditions to the ne part of the marsili seamount summit se tyrrhenian sea the marsili ochres belong to type 1 primary sulfide poor fe oxyhydroxides according to the classification of hekinian et al hekinian r hoffert m larque p cheminee j l stoffers p bideau d 1993 hydrothermal fe and si oxyhydroxide deposits from south pacific intraplate volcanoes and east pacific rise axial and off axial regions econ geol 88 2099 2121 they are x ray amorphous highly metalliferous al al mn fe 0 4 low in si transition metals co ni cu zn pb and rare earth elements ree and enriched in b v and mo their chemical composition and ree distribution patterns indicate precipitation from low temperature hydrothermal fluid mixed with seawater measured pb isotope compositions in the ochres indicate that the pb is dominantly anthropogenic in origin by contrast the pb isotope ratios in the nearby higher temperature hydrothermal deposits from the panarea arc volcano show that the pb is derived mainly from local volcanic rocks the fact that the pb isotopic signature of the marsili ochres is controlled by recent anthropogenic input suggests that the fe oxyhydroxides precipitated from fluids depleted in transition metals the low 206pb 207pb ratios in the ochres reflect the contribution of pb from australian ores indicating precipitation of the ochres somewhere between present day and the beginning of australian pb import to europe the young age of the ochres and the presence of other hydrothermal deposits along the marsili crest suggest that the magmatic chamber beneath the seamount may still be alive this study represents the first observation of anthropogenic influence on submarine hydrothermal deposits

rare earth element geochemistry of ferromanganese crusts from the hawaiian archipelago central pacific abstract the rare earth element ree composition of ferromanganese deposits from the hawaiian archipelago was determined as part of a geochemical investigation into the origin and environment of deposition of crusts most samples exhibit shale normalized ree patterns which are typical of hydrogenous ferromanganese deposits patterns of two todorokite and manjiroite rich crusts are significantly different from those of the other samples the range of concentrations in typical hawaiian crusts sum of ree 0 15 0 25 wt is in the uppermost portion of that reported for deep sea fe mn nodules shallow water 2000 m as well as slightly greater ree fractionation large positive ce anomalies attributed to the oxidative scavenging at the mno 2 surface are observed on all samples except one the slight light ree lree depletion in shallow water crusts relative to deeper samples is discussed in terms of variations in the ree concentrations in the water column and the relative complexing behavior of the ree no significant trend in ce concentration with depth is observed partition coefficient calculations suggest that concentrations of trivalent ree in crusts are affected by their availability in seawater to a greater extent than by the composition of the scavenging ferromanganese oxide flocs

influence of the mediterranean outflow on the isotopic composition of neodymium in waters of the north atlantic the isotopic composition of neodymium in the water column of the eastern north atlantic near the strait of gibraltar has been determined for several depths the data show that the mediterranean outflow results in a significant shift in e nd 0 toward more radiogenic values of 143 nd 144 nd in the water column at a 1000 m depth this corresponds to a depth in the neighborhood of the salinity maximum associated with the mediterranean outflow the core of the mediterranean outflow gives e nd 0 9 8 as compared to e nd 0 12 in overlying and underlying waters demonstrating that the mediterranean waters are distinct from the atlantic from mixing considerations we estimate that pure mediterranean waters have e nd 0 6 possible sources of this relatively radiogenic nd could be from drainage of young continental terranes or the injection of remobilized nd from deep sea sediments that have a young radiogenic volcanic component new data from a depth profile in the western atlantic is presented comparison of nd data for the eastern north atlantic with that for the western north atlantic shows fundamental differences in the water column structures for e nd 0 while both regions show a pronounced maximum in e nd 0 the western basin maximum occurs at the near surface rather than at 1000 m in addition deep waters of the eastern basin are found to be more radiogenic than the western basin these differences indicate several sources of isotopically distinct nd in the north atlantic the deep waters of the north atlantic 1000 m have the lowest values of e nd 0 measured in the oceans we believe that the source of these low e nd 0 values which we associate with north atlantic deep water is either from freshwater drainage off the precambrian shields of north america and asia into the arctic ocean or from the injection of older continentally derived ree from deep sea sediments sm and nd concentrations are found to increase with depth and e nd 0 changes with depth indicating both vertical and lateral transport processes from different sources this suggests a surface source of nd and injection of ree into the water column from deep sea sediments or large scale bottom currents with high ree concentrations

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

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

geochemistry of rare earth elements in a neutral mine drainage environment anjir tangeh northern iran abstract this study investigates the geochemical characteristics of rare earth elements and yttrium ree y in the neutral mine drainage nmd and river water in the vicinity of the anjir tangeh coal washing plant mazandaran province northern iran the nmd water had a neutral ph along with high sulphate and bicarbonate concentrations the total concentrations of ree in the nmd water were lower than in the river water according to the north american shale composite nasc normalised concentrations the patterns of nmd showed heavy ree hree enrichment while the river water represented middle ree mree enhancement both negative europium eu and positive gadolinium gd anomalies were observed in the drainage and river water within the study area the sum of ree concentration increased gradually downstream of the discharging point of the plant reject water in contrast to decreasing of al fe mn and cu pb zn concentrations the river sediment with high fe concentrations was enriched with lanthanum la and cerium ce the overall ree pattern of the nmd approximates those of coal except for the depletion in light ree lree and the enrichment of eu dominant inorganic ree species in the river water included ln co3 2 and lnco3 while lnco3 ln co3 2 and ln so4 were the main complexes in the nmd the saturation index indicated that al and fe were both oversaturated in the drainage and river water which can control the fractionation of ree by the sorption process according to both hierarchical cluster analysis hca and principal component analysis pca ph al and p were the significant parameters in the ree distribution

use of high resolution ichnological and stable isotope data for assessing completeness of a k p boundary section agost spain high resolution ichnological analysis has been performed at the agost section betic cordillera southeast spain in order to assess the completeness of the k p boundary transition below the biostratigraphic resolution intrasubzone high resolution planktonic foraminifera biozonation revealed that the first appearance of the palaeogene index species does not coincide with the k p boundary but is located a few centimetres above and calibrated 65 7 6 7 ky later the k p boundary to establish the continuity of this first interval of the lowermost danian hedbergella holmdelensis subzone and the existence of any hiatus below biostratigraphic resolution trace fossil analysis was revealed to be a useful tool planolites thalassinoides and alcyonidiopsis structures belonging to the upper tiers colonizing at or immediately after the k p boundary event were studied focusing on the isotopic composition of the filling materials and the genesis of thalassinoides rapid firmground generation and thalassinoides tracemaker colonization is mainly attributed to cessation of precipitation and or deposition of calcium carbonate but an incipient lithification is not disregarded the d 13 c data obtained from trace fossils fit well with those corresponding to a the k p boundary layer from 1 00x to 1 30x b the stratigraphic interval between 2 5 and 5 0 cm above the k p boundary between 0 32x and 0 47x and c the interval between 7 0 and 11 0 cm above the k p boundary between 0 69x and 0 79x revealing continuity in the colonization from the k p boundary event to the dark clay deposition above this macrobenthic colonization occurred continuously during the dark layer deposition from the k p boundary layer including the first centimetres evidencing completeness and the absence of hiatuses below biostratigraphic resolution intrasubzone at the agost section d 2005 elsevier b v all rights reserved

fish debris as chemical scavengers of zirconium and lanthanum in oceanic environments zr and hf fractionation in marine phosphates abstract red clays foraminifer oozes and clayey carbonaceous oozes from the southeastern pacific ocean have been analyzed for p mn fe zr hf th and la in sediments located far from continental areas considerable amounts of la and zr 20 60 are carried in fish debris carbonate fluorapatite whereas hf and th are taken up preferentially by micronodules and fe mn oxyhydroxides red clays far from the continents exhibit the highest zr hf ratios 75 150 significantly higher than continental rocks and oceanic basalts 30 60 zr is concentrated relative to hf in fish debris the causes of this enrichment of zr in apatite and consequently its separation from its twin element hf are to be found in the greater complexing of hf which somewhat interferes with its incorporation in apatite relative to zr the ability of trace elements to enter carbonate fluorapatite decreases in the order la zr th hf

geochemistry of the rare earth elements in ferromanganese nodules from domes site a northern equatorial pacific abstract the distribution of rare earth elements ree in ferromanganese nodules from domes site a has been determined by instrumental neutron activation methods the concentrations of the ree vary markedly low concentrations characterize samples from a depression the valley in which quaternary sediments are thin or absent high concentrations are found in samples from the surrounding abyssal hills the highlands where the quaternary sediment section is relatively thick moreover the valley nodules are strongly depleted in the light trivalent ree lree and ce compared with nodules from the highlands some of the former showing negative ce anomalies the ree abundances in the nodules are strongly influenced by the ree abundances in coexisting bottom water some controls on the ree chemistry of bottom waters include a the more effective removal of the lree relative to the hree from seawater because of the greater degree of complexation of the latter elements with seawater ligands b the very efficient oxidative scavenging of ce on particle surfaces in seawater and c the strong depletion of both ce and the lree in or a larger benthic flux of the hree into the antarctic bottom water aabw which flows through the valley the distinctive ree chemistry of valley nodules is a function of their growth from geochemically evolved aabw in contrast the ree chemistry of highland nodules indicates growth from a local less evolved seawater source

trace element and stable c o and radiogenic sr isotope geochemistry of stromatolitic carbonate rocks of the mesoarchaean pongola supergroup implications for seawater composition abstract the mesoarchaean pongola supergroup hosts one of the oldest well preserved stromatolitic carbonate successions major and trace element geochemistry along with c o and sr isotopic analyses of three stratigraphic sections of stromatolitic carbonate rocks were undertaken in order to infer the depositional environment and to unravel the chemical characteristics of contemporaneous seawater the carbonate rocks consist mainly of dolomite and to a lesser extent ankerite their variable sr concentrations of 95 to 450 mg kg are interpreted as resulting from early to late dolomitization of metastable carbonates aragonite and or high mg calcite facies control and calcitization during meteoric diagenesis 18o values range from 19 6 to 12 0 vpdb and reflect recrystallization of carbonates caused by high water rock interactions during diagenesis and metamorphism a 13c value of 2 5 vpdb was measured in carbonate samples least affected by alteration and we suggest that it approximates the composition of dissolved inorganic carbon in coeval seawater the samples display variable 87sr 86sr isotopic ratios from as low as 0 708 to 0 777 these ratios are considerably higher than those expected in archaean open ocean water masses buffered by hydrothermal interaction with the mantle we interpret the highly radiogenic sr isotopic ratios in some carbonate samples to reflect isotopic exchange with radiogenic sr from siliciclastic volcaniclastic components in the samples and fluids from clay rich layers intercalated with the carbonates the least radiogenic sr isotopic ratio may approximate the mixed isotopic composition of seawater in the epicontinental basin and of riverine freshwater draining the kaapvaal craton the dolomitic carbonate samples show shale normalized rare earth element and yttrium distribution patterns that resemble those of modern ocean water with positive lasn gdsn and ysn anomalies superchondritic y ho ratios a small negative cesn anomaly and depleted light rare earth elements relative to the heavy rare earth elements these anomalies are not as pronounced as expected for an open marine setting which together with the sr isotopic results support a more restricted setting with riverine input and fluctuations in marine ingressions a convex upward shale normalized rare earth element and yttrium pattern is probably a result of several factors including organic matter complexation and element fractionation during estuarine mixing the small negative cesn anomaly may suggest small amounts of free oxygen in shallow waters due to local oxygenic microbial activity

application of laser ablation icp ms to determine high resolution elemental profiles across the cretaceous paleogene boundary at agost spain abstract a high resolution analysis of the distribution of major and trace elements across a cretaceous paleogene boundary kpgb was done using laser ablation inductivity coupled plasma mass spectrometry la icp ms and was compared with traditional distinct sampling and analysis at the agost site se spain a 22 cm long core containing the kpgb was recovered using a rolatec rl 48l drill within this interval the lowermost 5 cm correspond to the maastrichtian and the uppermost 17 cm to the danian the core section was resin embedded under o2 free conditions cut and polished for la icp ms continuous measurements with 10 m increments and a laser beam of 80 m elemental concentrations in discrete samples taken prior to embedding from the same core interval were determined by inductivity coupled plasma optical emission spectroscopy icp oes the la icp ms analyses in continuous mode considerably improve the resolution of geochemical profiles allowing the compositional variability at a micrometer scale within the ejecta layer to be detected in this study we obtained profiles with 255 data points for the ejecta layer interval compared to 3 data points obtained by traditional manual sampling and icp oes analyses yet our recovered core section showed a rather limited preservation of the ejecta layer this paper focuses on the presentation of la icp ms analysis as a particularly useful tool to investigate paleoenvironmental changes associated with bio events additionally the high resolution of major and trace elemental distribution made it possible to study remobilization across thin but distinct boundaries such as the kpgb

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

ichnological analysis of the bidart and sopelana cretaceous paleogene k pg boundary sections basque basin w pyrenees refining eco sedimentary environment abstract ichnological analysis of two cretaceous paleogene boundary sections at bidart se france and sopelana n spain has been conducted in order to refining eco sedimentary environment and to a make comparison with previous interpretations based on microfossils in both sections trace fossil assemblage is low diverse consisting of chondrites planolites thalassinoides trichichnus zoophycos and phycosiphon ascribed to the zoophycos ichnofacies however with distinct differences in the bidart section early danian dark filled trace fossil assemblage is more abundant in large thalassinoides zoophycos and larger chondrites and less abundant in trichichnus and small chondrites in comparison to the sopelana section sopelana is thus interpreted as a more offshore deeper section than bidart although both were located in the upper bathyal zone of the basin oxygenation below the sediment water interface was enough to favour a generalized total bioturbation of sediments the presence of chemichnia and trace fossils which tracemakers sequestered sediments from the sea floor in deep burrows zoophycos suggests at least periodical food deficiency the distribution and content of trace fossils across the k pg boundary do not change significantly revealing minor incidence of the k pg boundary event on the macrobenthic environment the k pg boundary transition including the boundary layer is nearly totally bioturbated hence a redistribution of microbiotic and abiotic components by tracemakers is possible

comparative mineralogical and geochemical clay sedimentation in the betic cordilleras and basque cantabrian basin areas at the cretaceous tertiary boundary abstract the mineralogy and geochemistry of the bulk rock and clay fraction of sediments deposited at the cretaceous tertiary transition and in the ktb layer have been investigated by various methods in two sections from the betic cordilleras agost caravaca and five sections from the basque cantabrian basin monte urko sopelana zumaya hendaye biarritz active terrigenous supply prevailed in both regions uring the latest maastrichtian and earliest paleocene very different clay associations occur in the regions smectite being dominant to the south and illite to the north the betic cordilleras series mainly reflects climate and weathering conditions as well as volcanic activity with the ktb layer displaying a specific source and diagenesis control expressed as increased amounts of smectite the sequences cropping out in the basque cantabrian basin mainly reflect tectonic activity and burial diagenesis the effects of which differ according to the palaeogeographical location the clay sedimentation patterns in the north and south iberian sections across the cretaceous tertiary passage are controlled overwhelmingly by regional or local geodynamic and diagenetic phenomena thus any global namely extraterrestrial influence cannot be identified

isotopic composition of neodymium in waters from the drake passage the isotopic composition of neodymium has been determined in seawaters from the drake passage the antarctic circumpolar current which controls interocean mixing flows through this passage the parameter e nd 0 which is a function of the ratio of neodymium 143 to neodymium 144 is found to be uniform with depth at two stations with a value which is intermediate between the values for the atlantic and the pacific and indicates that the antarctic circumpolar current consists of about 70 percent atlantic water cold bottom water from a site in the south central pacific has the neodymium isotopic signature of the waters in the drake passage by using a box model to describe the exchange of water between the southern ocean and the ocean basins to the north together with the isotopic results an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the pacific and the southern ocean concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth these results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo oceanographic studies

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

rare earth element uptake during olivine water hydrothermal interaction abstract ultramafic hosted hydrothermal vent systems link the hydrosphere with the peridotitic mantle via serpentinization here the fractionation and mobility of selected trace nd sm gd dy yb sr and ba and major cations si ca mg fe ni during seawater peridotite interaction was investigated through a series of experiments where natural olivine grains were reacted with an artificial seawater solution at a range of temperatures 15 90 c and grain size distributions no evidence for any significant olivine dissolution or precipitation of carbonate and fe oxy hydroxide phases was observed in these experiments experimental data show a strong decoupling of ree nd sm gd dy and yb from sr and ba under all experimental conditions with sr and ba remaining quantitatively in solution the ree were removed from the solution and were adsorbed onto olivine surface with kinetic rate constants i e uptake over time that increase with increasing temperature and increasing surface area i e decreasing particle size dysprosium and yb heavy ree hree were removed from solution with a faster rate than nd and sm light ree lree gadolinium is decoupled from this trend with a slower kinetic rate constant than sm the activation energies ea of ree adsorption on olivine were higher for nd and sm than dy and yb this suggests that the adsorbance of lree is generally more dependent on temperature than the hree the ea correlates well with the summed 1st 2nd and 3rd ionization energies of ree suggesting a link between kinetic rates of element adsorption and electron configuration of the 4f orbitals gadolinium has higher ea than the other analyzed ree consistent with the electron configuration of gd3 where all 4f orbitals are filled with one electron each these experimental data suggest that ree are adsorbed on the surface of olivine via inner sphere complexes under low temperature hydrothermal conditions when alteration processes are limited or extremely slow scavenging and fractionation of ree may occur within the recharge zone of peridotite hosted hydrothermal systems at relatively low temperatures

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

alkaline earth metal and rare earth element incorporation control by ionic radius and growth rate on a stalagmite from the chauvet cave southeastern france abstract a multi element study involving major alkaline earth cations mg ca sr ba and trace elements like na u mn y and rare earth elements ree in calcite of a stalagmite from the chauvet cave se of france was carried out using icp qms analysis this study focused on the chau stm6 stalagmite which displays a record of the last deglaciation until the end of the younger dryas with ages ranging from 33 kyr to 11 5 kyr bp in this study profiles of the alkaline earth elements sr and ba show concentrations increasing sharply at the beginning of the deglaciation while mg and u show a decreasing trend rey ree y concentrations decrease sharply during early deglaciation the clear record of the onset of the younger dryas by stable isotopes is not well marked by these elements the absence of a significant correlation between rey and mn suggests that ree were here not strongly bound to particulate colloidal phases but were mainly controlled by limestone groundwater interaction shale normalized ree patterns in stalagmite characterized by a negative ce anomaly and hree enrichment compared to lree is thought to mainly arise from the dissolution of bedrock since chau stm6 patterns are similar to those of the bedrock chau stm6 rey patterns are even more depleted in lree than those of the bedrock showing that part of the lree were removed from groundwater upstream from the stalagmite some particular rey pattern changes were observed for the different climatic conditions 1 glacial samples often display a more marked negative ce anomaly 0 3 and a high y ho ratio 0 6 2 bolling allerod and younger dryas samples display a variable and less pronounced anomaly 0 5 0 8 and a lower y ho ratio 0 35 0 55 climatic changes modified the rate of the stalagmite growth which likely caused a change in the properties of element incorporation in the calcite lattice consequently the concentration variations of mg ca sr ba u and rey would be directly controlled by ionic radii of each element

age determinations and growth rates of pacific ferromanganese deposits using strontium isotopes abstract 87 sr 86 sr ratios trace element and ree compositions and textural characteristics were determined for three hydrogenetic fe mn crusts one hydrothermal deposit and two mixed hydrothermalhydrogenetic crusts from the pacific the sr isotope data are compared to the sr seawater curve for the cenozoic to determine the ages and growth rates of the crusts the 87 sr 86 sr in the crusts does not increase monotonically with depth as expected if the sr were solely derived from seawater and perfectly preserved since deposition this indicates post depositional exchange of sr or heterogeneous sources for the sr originally contained in the crusts textures of hydrogenetic crusts generally correlate with sr isotopic variations the highest porosity intervals commonly exhibit the highest 87 sr 86 sr ratios indicating exchange with younger seawater intervals with the lowest porosity commonly have lower 87 sr 86 sr and may preserve the original sr isotopic ratios minimum ages of crust growth inception were calculated from dense low porosity intervals growth of the hydrogenetic crusts began at or after 23 ma although their substrates are cretaceous estimated average growth rates of the three hydrogenetic crusts vary between 0 9 and 2 7 mm ma consistent with published rates determined by other techniques within the marshall islands crust growth rates for individual layers varied greatly between 1 0 and 5 4 mm ma for one crust very low 87 sr 86 sr ratios occurred in detrital rich intervals hydrothermal fe mn oxide from the active lau basin back arc spreading axis valu fa ridge has an 87 sr 86 sr ratio with a predominantly seawater signature 87 sr 86 sr 0 709196 indicating a maximum age of 0 9 ma one crust from an off axis seamount west of gorda ridge may have begun precipitating hydrogenetically at 0 5 ma 0 709211 and had increasing hydrothermal or volcanic input in the top half of the crust indicated by a significantly lower 87 sr 86 sr ratio 0 709052

toarcian oceanic anoxic event induced unusual behaviour and palaeobiological changes in thalassinoides tracemakers abstract the early toarcian early jurassic global marine mass extinction is associated with one of the most important environmental perturbations of the mesozoic the toarcian oceanic anoxic event t oae usually interpreted as a global oceanic anoxic event in the lusitanian basin lb one of the reference areas for the study of the t oae despite an elevated extinction rate among marine invertebrates the anoxia hypothesis has been discarded based on geochemical and isotopic data in the fonte coberta section the t oae is characterised by the extinction of the previously well represented brachiopod taxa a decreased abundance of ammonoids and the establishment of a well developed endobenthic community mainly composed by thalassinoides tracemaker which indicates favourable environmental parameters at least for this community thus the palaeoenvironmental changes associated with the t oae event bear a minor incidence on the macrobenthic tracemaker community at the level of extinctions and changes in diversity or abundance yet they exert a major effect on the behaviour and palaeobiology of tracemakers the thalassinoides specimens show an exclusively horizontal development and unusual architectural features during the extinction interval tied to behavioural adaptations to nutrient availability and or substrate firmness smaller burrow diameters are registered at the base of the t oae and then an increase is observed during the t oae this could be associated with a palaeobiological response lilliput effect to palaeoecological changes at the beginning of the t oae followed by a progressive change to pre event environmental parameters this study therefore sheds light on how environmental alterations can determine specific behavioural and palaeobiology changes of the producer as reflected by variations in significant features of thalassinoides architecture

rare earth elements concentrations and speciation in rainwater from guiyang an acid rain impacted zone of southwest china abstract rare earth elements rees and major ions were determined in rainwater samples collected from guiyang in the acid rain impacted zone of southwest china the concentrations of total dissolved and acid soluble rees in rainwater are higher than those of most of the world s cities as well as the local surface water the dissolved ree concentrations are negatively correlated to ph in rainwater this is consistent with acidification of rainwater resulting in increasing ree concentrations speciation calculations using the phreeqc model predict that the free ree metal ion i e ln3 sulfate lnso4 oxalate lnox and lnox2 and fluoride lnf2 complexes were relatively important forms of dissolved ree although the contribution to rainwater acidity of oxalic acid is much lower than that of sulfuric acid the proportion of ree oxalate complexes is not lower than that of ree sulfate complexes in rain waters the rainwater is enriched in the middle rees mree compared to both the light rees lree and heavy rees hree ree phosphate complexes phosphatic minerals and a fe mn oxyhydroxide coating are more likely controls on the development of mree enrichment in the rainwater complexation of sulfate and ree played little role in the development of mree enrichment even though sulfate is the most important anion in acidic rainwater in the shale normalized ree pattern plot la showed a clear positive anomaly la might have two main anthropogenic sources in rainwater one of the important sources could be automobile emission another main source of excess la in rainwater could be the ree fertilizer that has been widely used in the agriculture of china for approximately 30 years

k t boundary extinction geologically instantaneous or gradual event evidence from deep sea benthic foraminifera a stepped pattern of benthic foraminiferal decimation survival and recovery identified across the cretaceous tertiary k t boundary at caravaca southeast spain suggests that an exceptionally large influx of nutrients reached the sea floor suddenly at the time of the k t extinction event rapid reestablishment of pre k t boundary environmental conditions followed our data demonstrate a close coupling between the collapse of the ecologic system in the upper water column at caravaca and a correspondent decimation of bottom dwellers on the sea floor the dramatic environmental collapse of deep water benthic foraminiferal communities at the end of the cretaceous at caravaca suggests that the k t boundary event was geologically instantaneous and catastrophic

chemical profiles in k t boundary section of meghalaya india cometary asteroidal or volcanic abstract the cretaceous tertiary boundary ktb exposed as a 1 5 cm thick limonitic layer in the um sohryngkew river basin in meghalaya is marked by enhanced concentrations of ir co ni os fe zn sb by factors of 4 to 1200 and ree by factors of 1 7 to 5 compared to the cretaceous shales ir concentration is generally 10 in 2 m thick broad band around the ktb abruptly reaching a peak concentration of 12 1 ng g 1 within the limonitic layer the os ir ratio at the ktb is 0 37 but in the adjacent shales it is 1 8 suggesting that the sources of these elements in the peak and the broad band may be different cretaceous planktonic foraminifera and dynocysts start disappearing before the ir rich limonitic layer was deposited but several diminutive cretaceous foraminifera survive after this layer the observations indicate that the extinctions are confined to a short span of time but are probably not as abrupt as anticipated by the asteroidal impact hypothesis the chemical data are discussed in terms of cometary asteroidal and volcanic hypotheses the profiles of ir and os ir can be understood in the frame work of a model of cometary impact in which cometary debris falls onto the earth preceding and succeeding the fall of the cometary nucleus

multistage hydrothermal alteration of gabbroic rocks from the failed mathematician ridge oxygen isotopic mineralogical and fluid inclusion data are presented for fresh and hydrothermally altered gabbroic rocks from the failed mathematician ridge the mathematician ridge though initially a fast spreading ridge presently has a deep central rift valley more typical of slow spreading rifts the inner rift walls expose rare plutonic rocks uncomplicated by proximity to deep large offset fracture zones undeformed mathematician ridge gabbros preserve most of the original texture and phase compositions and have been only slightly mineralogically or isotopically modified by post crystallization hydrothermal alteration metagabbros have been subjected to a pervasive ductile deformation and recrystallization to foliated rocks composed of aluminous amphibole low calcium plagioclase and ilmenite oxygen isotope and phase chemical data suggest this event began at temperatures of up to 700 c water rock ratios of less than one and produced modified seawater fluids with isotopic compositions of 3 5 6 0 the amphibolites are cross cut by multiple generation quartz epidote veins forming a network replacement of the amphibole grade mineralogies by greenschist grade mineralogies fluid oxygen isotopic compositions of 2 4 and a two phase separation in the fluid captured in conjugate vapor fluid inclusions are all associated with the formation of this network fluid inclusion data for the quartz indicate initial temperatures of over 500 c these samples may represent rocks from the 1 2 km deep plumbing system of black smoker type venting

fe oxide spherules infilling thalassinoides burrows at the cretaceous paleogene k p boundary evidence of a near contemporaneous macrobenthic colonization during the k p event a detailed ichnological analysis focused on thalassinoides structures recorded just below the cretaceous paleogene k p boundary layer of the agost section southeast spain aimed to evaluate macrobenthic colonization during the k p boundary event stereomicroscopy and field emission scanning electron microscopy analyses conducted on material filling in thalassinoides trace fossils reveal the presence of dark infill material that includes spherule like elements similar to those previously differentiated in the k p boundary layer energy dispersive x ray spectrometry indicates a ferruginous composition goethite spherules this represents the first record of spherules related to the k p boundary event within trace fossil infilling material the passive filling of this material into the thalassinoides bioturbation allows interpretation of the gravitational deposition just after thalassinoides trace maker colonization the absence of erosive sedimentary structures or other material deposited between the thalassinoides trace maker colonization and the spherule deposition is interpreted as evidence of rapid colonization during the k p boundary event nearly contemporary with the spherule layer deposition

carbon isotope evidence for the timing of the cretaceous palaeogene macrobenthic colonisation at the agost section southeast spain abstract the cretaceous palaeogene k t boundary section of agost southeast spain one of the most complete sections existing contains a well developed trace fossil assemblage composed of dark and light filled trace fossils registered in the uppermost cretaceous maastrichtian plummerita hantkeninoides biozone sediments the trace fossil assemblage reveals that significant macrobenthic colonisation occurred around the k t boundary interval however difficulties in recognising trace fossils affecting the k t boundary layer as well as in biostratigraphically characterising these trace fossils hindered a conclusive interpretation on the timing of this macrobenthic colonisation with the aim of this characterisation we determined the 13c of the carbonate fraction of dark and light filling materials from the trace fossils since the carbon isotope compositions of uppermost cretaceous and lowermost palaeogene materials are clearly different the data compiled provide evidence for a significant distinction between light filled trace fossils with 13c values higher than 1 6 peedee belemnite pdb and dark filled trace fossils with 13c values between 0 21 and 1 2 pdb most of these being lower than 0 7 pdb the comparison of these values with those from the uppermost maastrichtian to the lowermost danian sediments reveals that the macrobenthic colonisation occurred in different phases across the k t boundary interval

anomalies in rare earth distributions in seawater gd and tb we have measured profiles of the rare earth elements ree in atlantic and pacific ocean waters the data normalized versus shales exhibit a pronounced anomaly in gd relative to its neighbors eu and tb in the ree series such that the gd concentrations are high by 30 50 closer inspection reveals that the anomaly is made up of both elevated gd and depressed tb concentrations likely associated with solution chemistry shifts in the transition from an exactly half filled 4f electron shell anomalies in gd and tb solution complexation are also indicated by the turner whitfield dickson speciation model the overall trend of heavy ree iii enrichment in seawater and the gdtb anomaly described here tend to support scavenging as an important removal mechanism for the ree from seawater

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

non hydrothermal origin of apatite in sedex mineralization and host rocks of the howard s pass district yukon canada the howard s pass district hpd comprises 14 zn pb sedimentary exhalative sedex deposits and is located within the selwyn basin yukon canada although the hpd is renowned for its large accumulation of base metal sulfides in places the late ordovician to early silurian host rocks also contain abundant carbonate bearing fluorapatite cbfa this mineral is present stratigraphically be low within and above the sedex deposits and occurs as fine grained layers that are interbedded with cherty carbonaceous mudstone electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometric analysis reveal that mineral compositions and rare earth element yttrium ree y systematics respectively are remarkably similar throughout the stratigraphic succession north american shale composite nasc normalized la sm and la yb ratios indicate that the original ree compositions in cbfa have undergone only minor compositional modification subsequent to deposition uniformly negative ce anomalies indicate that the mineral formed in analogous manner to modern and ancient sedimentary phosphorites under suboxic bottom water conditions europium anomalies are mostly absent indicating that reduced slightly acidic high temperature hydrothermal fluids were not a major source of ree y to cbfa the chemical homogeneity of the mineral irrespective of its stratigraphic position indicates that a common process was responsible for its deposition within the sedimentary rocks of the hpd on the basis of the similarity of the ree patterns to modern and ancient phosphorites and the absence of positive eu anomalies we conclude that the cbfa is of hydrogenous origin and not hydrothermal as suggested by previous workers as such phosphorite formation in the hpd is casually related to sedex zn pb deposit formation

steep rock lake sedimentology and geochemistry of an archean carbonate platform abstract the 2800 ma mosher carbonate formation at steep rock lake in south central canada is one of earth s oldest limestone deposits it is both thick up to 500 m and relatively well preserved and was one of the first precambrian successions to be noted for evidence of early life it continues to provide information on the antiquity of such processes as photosynthesis the carbonate contains a variety of fabrics and facies from apparently fine grained bedded limestones with domal and columnar stromatolites atikokania radial fans and sheet cracks to closely packed metric scale hybrid domes of originally aragonite seafloor crust interlayered with fenestral fabric here we review previous work provide new observations concerning these sediments and their geochemistry and discuss the inception overall development and ultimate demise of the steep rock platform we divide the mosher carbonate into the lower hogarth member and upper elbow point member these units constitute a shallow water carbonate platform succession the hogarth member overlies eroded 3000 ma tonalite and is at least 120 m thick thin horizons of domal pseudocolumnar columnar and fenestral stratiform stromatolites and occasional layers of atikokania radial crystal fans occur within relatively fine grained thin bedded limestone with iron carbonate horizons in the upper part meter scale domes occur locally with sheet cracks and stromatactis the irregular laminae that build the small domal and columnar stromatolites are interpreted to be lithified mats and biofilms presumably cyanobacteria dominated fine grained well bedded facies of the lower hogarth member and its varied association of small stromatolites is interpreted to have accumulated in a relatively protected inner platform environment numerous very thin horizons of iron carbonate in the lower and upper parts of the hogarth member suggest temporally limited influence of iron rich offshore waters vertical trends in fe mn ba sr ce and 13 c probably reflect progressive restriction of circulation with at least one abrupt but short lived change back to more open seawater conditions the upper hogarth member with large banded domes and fenestral crusts and stromatolites is interpreted as back margin facies the overlying elbow point member is at least 70 m thick and appears to be entirely composed of innumerable juxtaposed elongate smooth and thickly layered domes lacking intervening sediment each dome is typically several meters across and composed of centimetric alternations of cuspate fenestral fabric possibly microbial and crystal fan fabric that is probably abiotic seafloor aragonite precipitate adjacent cuspate fenestral and crystal fan fabric show significant differences in concentration of 13 c sr ba fe and mn this giant dome facies is interpreted as a platform margin deposit in which alternating calcite aragonite mineralogies within each dome reflect a laterally fluctuating offshore redox boundary negative ce anomalies positive gd anomalies and reduced positive eu anomalies relative to laterally correlative deep water iron formation occur in the majority of crystal fan samples and in some cuspate fenestral fabric samples ca carbonate precipitation at the margin of an anoxic iron rich sea would have been promoted by oxygenic removal of iron from seawater otherwise fe carbonate would have been favored over ca carbonate precipitation the mosher carbonate formation is interpreted as an early marine oxygen oasis a shallow platform that favored cyanobacterial productivity was sufficiently isolated from open marine circulation for the seawater to become relatively oxygenated and where carbonate sediment aggradation was a positive feedback that sustained these shallow water conditions limestone accumulation terminated as transgressive suboxic and anoxic seawater deposited first manganese oxide rich and then manganese oxide poor iron formation sediments

how bioturbation obscured the cretaceous palaeogene boundary record the cretaceous palaeogene k pg boundary interval is often penetrated by burrows which may obscure stratigraphic and micropalaeontological records leading to misinterpretations of the sequence of events spanning the k pg boundary here we assess the role of burrowing organisms in the redistribution of benthic foraminifera across the boundary at bidart france and report a strong relationship between the behaviour represented by pre and post k pg trace fossils and their benthic foraminiferal content we further infer a brief interval of eutrophic conditions at the seafloor as reported from other locations which disappeared from the lowermost danian stratigraphic record and is represented only inside post k pg trace fossils hosted in cretaceous strata the combined study of trace fossils and microfossils is a powerful tool in eco stratigraphy and event stratigraphy and can yield important insights into the completeness of the k pg record especially at locations such as bidart where this interval has traditionally been assumed to be complete

how complete are cretaceous tertiary boundary sections a chronostratigraphic estimate based on graphic correlation cogent interpretations of data bearing on the cretaceous tertiary k t extinction controversy depend on the existence of accurate chronostratigraphic models for the various k t boundary sections we have employed the graphic correlation technique to summarize biostratigraphic and lithostratigraphic data from 15 intensively sampled k t boundary sections within a common chronostratigraphic model our results indicate that almost all of these sections along with 13 additional boundary sections not used to construct the model contain prolonged and in many cases multiple hiatuses of these 28 boundary sections only six were found to contain a continuous record of sediment accumulation across the k t boundary itself these six k t complete sections are el kef tunisia agost spain caravaca spain and three sections along the brazos river texas a comparative analysis of hiatus distributions among these 28 k t boundary sections also reveals the presence of systematic differences between continental shelf and deep sea depositional environments the lower danian interval immediately following the k t boundary and extending into biochronozones p0 and p1a is typically missing from the deep sea whereas boundary sections deposited in shallower middle neritic to upper slope environments are in most cases complete across the k t boundary these shallow neritic boundary sections however are in many instances disrupted by hiatuses at the p0 p1a boundary and again in the upper part of zone p1a these differential patterns of hiatus distribution between deep sea and continental shelf depositional settings appear to be linked to sea level fluctuations our data suggest that the apparently sudden mass extinction of planktonic foraminifera and anomalies in the occurrence of geochemical tracers that are characteristic of the k t boundary in deep sea sections may be artifacts of a temporally incomplete deep sea stratigraphic record

geochemistry of the krivoy rog banded iron formation ukraine and the impact of peak episodes of increased global magmatic activity on the trace element composition of precambrian seawater abstract pure superior type banded iron formation bif samples from the krivoy rog supergroup ukraine are excellent archives of ambient early precambrian seawater they show low concentrations of incompatible elements such as zr hf and th and shale normalized rare earths and yttrium rey sn patterns similar to those of modern seawater i e heavy rey sn enriched patterns with positive la sn gd sn and y sn anomalies lack of ce sn and presence of positive eu sn anomalies indicate rey contributions to anoxic ferruginous seawater from high temperature hydrothermal fluids the depositional age of the krivoy rog bif is ill defined but a late archean to paleoproterozoic age has been suggested based on u pb zircon ages for units stratigraphically above and below the bif we determined sm nd isotopic compositions of pure and impure samples from the krivoy rog bif which yield an errorchron with an apparent age of 2406 350 ma mswd 15 that falls within this broad age range all pure bif samples show chondrite normalized subscript cn rey patterns with strong positive eu cn anomalies that are typical for archean but rather rare and much less pronounced in proterozoic bifs associated schists also show archean rather than post archean style rey distributions the rey geochemistry of both chemical and epiclastic sediments therefore is more consistent with a late archean rather than a post archean depositional age of the krivoy rog supergroup initial nd values of impure bifs and of associated schist reveal variable contributions from ttgs less radiogenic in nd and a more radiogenic component possibly comprised of basement amphibolites or mafic volcanics of the stratigraphically underlying new krivoy rog group the purest krivoy rog bif representing local krivoy rog seawater displays an nd 2 60 ga value of 2 3 this value is less radiogenic than impure krivoy rog bifs or other near contemporaneous neoarchean pure chemical sediments to preserve this specific local isotopic fingerprint in anoxic archean seawater the krivoy rog bif must have been deposited in an isolated sea basin with limited exchange with ferruginous deep waters of the open ocean a compilation of rey data for high purity precambrian bifs reveals that eu cn eu cn ratios of precambrian seawater follow a general global evolution curve that shows specific peaks which reflect times of increased high temperature hydrothermal rey input into seawater following declining eu cn eu cn ratios from the eoarchean to the mesoarchean the ratios suddenly rise at 2 7 ga and reach a maximum at 2 6 ga indicating an increased flux of high temperature hydrothermal rey to neoarchean seawater which supports the hypothesis that times of widespread bif deposition coincided with periods of intense submarine hydrothermal activity probably triggered by major mantle plume events this association is supported by a strong increase of the nd t values of pure seawater archives at 2 7 2 6 ga which reflects an increased flux of mantle nd into seawater these results suggest that eu rey systematics and potentially nd systematics are robust tools to indentify episodes of enhanced mantle plume activity

the joffre banded iron formation hamersley group western australia assessing the palaeoenvironment through detailed petrology and chemostratigraphy abstract the joffre member of the brockman iron formation is by volume the largest single known banded iron formation bif in the world here we present detailed petrology and chemostratigraphy through the entire 355 m core section of this 2 45 billion year old unit oxide bif and silicate carbonate oxide bif dominate the lithology with minor amounts of interbedded stilpnomelane mudrock stilpnomelane rich tuffaceous mudrock and calcareous mudrock besides chert and magnetite the prominent mineralogy is riebeckite ankerite hematite stilpnomelane and crocidolite the bif is characterized by an average of 50 wt sio 2 and 44 5 wt fe 2 o 3 and an overall low abundance of al 2 o 3 2 sn of 0 24 the rey patterns also show a positive la sn anomaly no ce sn anomaly and a weakly developed positive y sn anomaly iron isotopes 56 fe with positive 56 fe values of 0 04 to 1 21 suggest that a large part of the hydrothermal iron was partly oxidized in the upper water column and subsequently precipitated as ferric oxyhydroxides no epiclastic grains have been found rather submarine hydrothermal fluids and fine grained volcanogenic detritus controlled bif chemistry the former source is reflected through a constant positive eu sn anomaly throughout the core average eu sn anomaly of 1 6 with a peak of 2 1 between 100 and 155 m depth while the latter source is best reflected through the stilpnomelane rich tuffaceous mudrock consisting of volcanic ash fall tuff with relict shards set in a stilpnomelane matrix the mudrock is overlain by well preserved wavy laminae and laminae sets of stilpnomelane microgranules that likely originated from re worked volcanic ash formed either on the seafloor or in the water column prior to deposition an enriched hree to lree pattern a high iron content 30 wt and a 56 fe value of 0 59 collectively imply that the mudrock facies interacted with the fe rich seawater prior to deposition the tio 2 zr ratio of the bif and the associated mudrocks suggest a felsic only source related to the same style of volcanics as the slightly younger woongarra rhyolites given the observation that the dominant control on the seawater chemistry was associated with felsic volcanics we speculate that the fine grained pelagic ash particles may have sourced bio available nutrients to the surface water this would have facilitated enhanced biological productivity including bacterial fe ii oxidation which is now recorded as the positively fractionated 56 fe iron oxide minerals in the joffre bif alongside submarine hydrothermal input to the basin the dominant control on the ocean chemistry seems to have been through volcanic and pyroclastic pathways thereby making the joffre bif poorly suited as a chemical proxy for the study of atmospheric oxygen and its weathering impact on local landmasses

archaean phosphates a case study of transformation processes in apatite from the barberton greenstone belt multiple tools have been used to determine the sensitivity of phosphates from the early archaean barberton greenstone belt to transformation the assessment of the degree of transformation is crucial for verifying data about the parameters of the paleo environment from the obtained results three generations of phosphates can be distinguished group a is observed in cherts and banded iron formation bif early generation fluor hydroxyapatite that precipitated from seawater it is characterized by flat rare earth element ree patterns with a positive eu anomaly and high y ho ratio in the range of 54 70 apatites in this group lack any visible indicators of secondary alterations at the micro and nanoscales fourier transform infrared spectra indicate that these apatites are relatively rich in water and due to cationic substitution their oh stretching regions exhibit complex ordering and numerous component bands the characteristics observed in the cherts and silicified felsic volcaniclastics of group b imply advanced metasomatic alteration they exhibit light and heavy ree depletion and an absence of water in the halogen site nanoscale investigations reveal cracks pores nanofluid inclusions and nanochannel like structures as well as inclusions group c is represented by igneous derived apatites that partially reflect their igneous origin the phosphates are predominantly fluorapatite with typical magmatic apatite ree distribution patterns imaging at the micro and nanoscales indicates that they partially preserve the signature of igneous origin it seems that some of the analyzed apatite partially preserved their primordial features therefore they might be used for the reconstruction of archaean abiotic systems

rare earth elements and yttrium in seawater icp ms determinations in the east caroline coral sea and south fiji basins of the western south pacific ocean abstract using inductively coupled plasma mass spectrometry icp ms vertical profiles of yttrium and all the rare earth elements rees in seawater were obtained at three locations in the western south pacific the east caroline coral sea and south fiji basins based on the data we have analyzed the inter ree iii relationships and found that ree iii s heavier than dy and particularly close neighbors show strong coherencies in their oceanic behavior considering that the heavy ree iii s are less particle reactive than the light and middle ree iii s and that they have very tight correlations with regressions passing almost through the origin the neighboring element ratios of the heavy ree iii s behave virtually conservatively and are suitable as tracers of water masses the dy ho er system is practically good because its dynamic range signal to noise ratio is large in the ocean the highest ho dy ratios 0 31 are found in intermediate and deep waters throughout the western south pacific which overlie the antarctic bottom water with a low ho dy ratio 0 27 these high ho dy waters are probably formed in the polar and subantarctic frontal zone and advect northward ree iii data provide better insights into the deep water recirculation in the south pacific than those discussed based upon the regular oceanographic properties alone

rare earth distributions with a positive ce anomaly in the western north atlantic ocean from the vertical distributions of the rare earth elements ree in the sargasso sea we now report the first profiles of pr tb ho tm and lu in seawater together with profiles for la ce sm eu and yb the first observations of positive ce anomalies in seawater are ascribed to reducing inshore sediments as a source for ce ref 1 all vertical profiles are consistent with adsorption of trivalent rare earths by settling particles possibly siliceous or calcareous followed by their release at or near the sea floor on dissolution of the carriers the very different ce profile demonstrates the additional effects of oxidation reduction reactions

the geochemistry and mineralogy of the cretaceous tertiary boundary at agost southeast spain abstract this paper gives the mineralogical and geochemical results of research made on the k t boundary in the agost stratigraphic sequence belonging to the intermediate units of the betic cordilleras spain in this sequence the abathomphalus mayaroensis globigerina cretacea and parvularugoglobigerina eugubina zones are present and the k t level 2 mm is very well defined the k t boundary is characterized by a decrease in carbonate content an increase in the proportion of smectites and the presence of spherules of fe oxides and k feldspar we have detected a considerable enrichment in platinum group elements ir 24 4 ppb as sb zn fe ti cr ni v co sr among other elements and an depletion in ca and rare earth elements the fe oxide spherules are enriched in most of these trace elements we suggest that these spherules were formed as a product of the alteration of pyrite originating in an oxygen depleted marine environment in which abundant sulphides and organic complexes would have formed and scavenged the metals 87 sr 86 sr ratio for the k t boundary is similar to the values reported for oceanic waters of the same age the pge values normalized to c1 chondrites are very different to those corresponding to meteoritic composition post depositional processes could have brought about a differential enrichment of these elements although meteorite impact cannot be discounted we suggest that volcanic phenomena and early diagenetic processes were related to the chemical anomalies of the k t boundary

chemical composition of thalassinoides boxwork across the marine k pg boundary of central new jersey u s a thalassinoides isp burrow networks filled with green to dark bluish gray glauconite pellets occur in the cretaceous to paleogene hornerstown formation and in the uppermost 1 2 m of the underlying upper cretaceous navesink and new egypt formations at many central new jersey cretaceous paleogene k pg boundary sections near the base of the hornerstown formation is a renowned bonebed the main fossiliferous layer mfl which contains isolated to articulated cretaceous marine reptiles turtles birds and crocodiles interpreted as a thanatocoenosis we investigated the bulk chemical composition of the burrow fill and surrounding matrix in the largely unconsolidated sections of the k pg interval at two sites inversand and walnridge meirs farm new jersey using a niton xl3t xrf analyzer to place them in proper stratigraphic context bulk matrix zr and ti concentrations decrease up section as a result of transgression deepening and increased distance from source areas in contrast an increase in k is attributed to greater amounts and maturity of the glauconite due to decreasing sedimentation rates zr and ti concentrations in burrow fills below the mfl are virtually the same as in overlying sediments above the mfl and much less than in the surrounding matrix this suggests that burrows in the cretaceous strata were passively filled with paleogene sediments k concentrations of burrow fills are generally intermediate between the high values encountered in the paleogene matrix and the lower values of the cretaceous matrix although this may have resulted from removal of glauconite during bioturbation and burrow filling it is more likely that immature glauconite was sequestered in the burrow fills below the depth of glauconitization before it could attain full maturity therefore burrows originating above the formational contact at or above the mfl penetrate as much as two meters into underlying cretaceous sediments and are passively filled with paleogene sediment burrows originating above the mfl may translocate diagnostic danian microfossils shocked quartz and ir effectively diffusing the k pg boundary this research demonstrates that care must be taken in sampling pervasively bioturbated strata to avoid incorporating stratigraphically younger burrow fill sediments

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

cretaceous tertiary boundary problem on shallow carbonate platform carbon and oxygen excursions biota and microfacies at the k t boundary sections dolenja vas and sopada in sw slovenia adria cp abstract the transition of maastrichtian to danian in sw slovenia was studied in two shallow marine carbonate successions apart from the extinction of some biota the k t boundary is reflected also in carbonate isotopic composition and in geochemistry the k t boundary is characterized by 20 cm to 1 m thick sedimentary breccia of intertidal origin extreme depletion in the 13 c content up to 8 was found in dolenja vas section just at this boundary it related to global climatic changes caused by impact of extraterrestrial body followed by the destruction and combustion of terrestrial plants slight enrichment in 13 c content up to 2 is evident at danian selandian boundary too

rare earth element geochemistry of groundwaters from a thick till and clay rich aquitard sequence saskatchewan canada rare earth elements ree were determined in groundwater samples collected from a thick till and clay rich aquitard sequence located in southern saskatchewan canada the groundwaters are na mg so4 type waters that range from highly concentrated brines e g i up to 2 moles kg near the ground surface to relatively dilute waters i 0 04 moles kg at depth the majority of these groundwaters have ph values between 7 and 8 although the deepest samples are more alkaline 9 ph 9 6 groundwater ree concentrations are relatively constant in the overlying till but increase by up to a factor of 50 in the underlying clay bedrock shallow groundwaters have heavy ree hree enriched shale normalized patterns whereas the ree patterns of the deep groundwaters are relatively flat solution complexation modelling indicates that variations in ree patterns reflect differences in solution complexation across the ree suite in the shallow groundwaters strongly adsorbed positively charged carbonate complexes lnco3 sulfate complexes lnso4 and free metal ion species ln3 dominate the speciation of light rees lree whereas hrees occur chiefly as more stable negatively charged dicarbonato complexes i e ln co3 2 for the deepest groundwaters however all of the rees are predicted to occur in solution as dicarbonato complexes the large hree enrichments of the shallow groundwaters reflect the greater affinity of the positively charged lree solution species to adsorb to clay minerals or coatings on clay minerals in the aquitard sequence compared to the more stable negatively charged hree dicarbonato complexes on the other hand the flat ree patterns of the deep groundwaters reflect the dominance of the negatively charged dicarbonato complex for all rees the solution complexation model along with the strong positive correlation between rees and co32 f 0 79 r 0 95 and to a lesser extent ph 0 57 r 0 72 indicates that carbonate ion concentrations and thus ph exert important controls on aqueous ree concentrations in these groundwaters

dissolved rare earth elements distribution in the solomon sea abstract trace elements and isotopes teis were measured as part of the geotraces pandora cruise july august 2012 r v l atalante among them rare earth elements rees as pertinent tracers of land ocean inputs and water mass transformations this work discusses results of 19 dissolved ree dree profiles measured using a trispike method in the coral sea and inside and at the exits of the solomon sea a semi enclosed sea with complex topography and straits overall drees except the insoluble ce show nutrient like profiles i e depleted at the surface and enriched at depth illustrative nd concentrations range from 5 pmol kg at the surface to 25 pmol kg at 5000 m depth however local dree enrichments are observed mostly in the straits indispensable solomon and vitiaz straits and along the island coasts a box model allows calculating and discussing the fate of the drees in the different water layers flowing through the solomon sea finally subtle variations revealed by la ce eu anomalies and the normalized light versus heavy ree ratio expressed as ndn ybn allows the identification of specific mechanisms affecting the distribution of the different drees the positive eu anomaly observed in the surface layers reflects the basaltic origin of external inputs consistent with the intensive weathering and or volcanic activity affecting the surrounding islands these data also confirm that the distributions of heavy drees like yb are better correlated to the dsi concentrations than that of the other rees this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

ichnological analysis of the cretaceous palaeogene boundary interval at the caravaca section se spain abstract ichnological analysis of the cretaceous palaeogene k pg boundary at caravaca betic cordillera southeast spain reveals significant data for the interpretation of the k pg boundary event the uppermost maastrichtian marls below the cretaceous palaeogene k pg boundary at caravaca contains the dark coloured trace fossils chondrites targionii planolites thalassinoides zoophycos and alcyonidiopsis the composition of trace fossil associations in the upper maastrichtian and lower danian marls is generally the same yet much more poorly preserved in the latter showing in general no ichnological evidence of a severe macroinfaunal crisis at the k pg boundary the dark coloured trace fossils penetrate from two bioturbated horizons in the dark boundary layer separated by two horizons with primary lamination the ichnofauna rapidly recovered after the k pg event following deposition of the lower parallel laminated bed 14 mm thick that occurs in the dark boundary layer above the k pg boundary zoophycos is the deepest trace fossil penetrating as far as 90 cm below the k pg boundary probably in stiff or partly firm substrate which was dewatered to some extent during the slow accumulation of the danian dark boundary layer the firmness probably prevented the chondrites trace maker from deeper burrowing the maastrichtian sediments may be contaminated with danian microfossils due to bioturbation

trace fossil evidence suggests widespread dwarfism in response to the end cretaceous mass extinction braggs alabama and brazos river texas as a proxy for the body size of the tracemaker burrow diameter provides information on fundamental characteristics such as organism biology and behavior furthermore changes in this endobenthic parameter provide insight into the timing and recovery of burrowing organisms in response to large scale processes operating in ancient trophic systems we herein report a decrease in burrow size in thalassinoides dominated ichnoassemblages across the cretaceous paleogene k pg boundary in well studied shallow marine sections along the brazos river and cottonmouth creek texas and at braggs alabama at the cottonmouth creek and brazos river localities thalassinoides isp occurring above the previously reported negative 13c shift and the first occurrence of unequivocal danian planktonic foraminifera are 17 smaller in short axis diameter and 22 smaller when diameters are corrected for sediment compaction mean k 27 15 7 12 mm mean pg 21 13 6 88 mm n 53 than those excavated and filled prior to deposition of a hummocky cross bedded ejecta bearing sandstone complex commonly interpreted as the chicxulub event deposit across the k pg boundary at braggs diameters dth of simple maze thalassinoides structures from similar recurring depositional facies abruptly decrease by 22 mean k 13 08 1 86 mm mean pg 10 21 1 87 mm n 26 the cretaceous and paleogene burrows were preserved in beds of similar lithology suggesting that the reduction in size is not attributed to sedimentological factors at both localities up section trends in dth are statistically significant 0 05 equal variance t test non parametric mann whitney u test a reduction in dth above the k pg boundary reflects dwarfing within the post extinction endobenthic community these ichnological trends are similar to those recently documented at more impact distal sites along the new jersey coastal plain dwarfing during the early recovery stages of the end cretaceous mass extinction as recorded by trace fossils was widespread and occurred within siliciclastic carbonate and glauconite producing depositional environments since this ichnological signal in shallow marine successions appears to be a general phenomenon across the crisis interval trace fossil analysis provides a potential in situ field method for constraining and correlating the stratigraphic position of the event particularly in the absence of other macroscopic microscopic and geochemical indicators

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

the lovisa stratiform zn pb deposit bergslagen sweden structure stratigraphy and ore genesis medium to high grade metamorphosed 1 9 ga stratiform syngenetic zn pb ag sulfide deposits comprise an economically important type of ore deposit in the bergslagen lithotectonic unit of the fenn

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

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

rare earth elements and yttrium in lithotypes of bulgarian coals abstract rare earth element and yttrium abundances in vitrain xylain liptain fusain and whole coal samples from bulgarian coal deposits have been studied vitrain xylain and liptain are depleted while fusain is enriched in ree and y as compared to the whole coal samples from which they were selected chondrite normalized patterns show relative enrichment of light lree against heavy hree rare earth elements negative eu anomaly and positive lu anomaly the shale normalized patterns of the lithotypes reveal an increase from lree to hree while those of the whole coal samples and mineral interlayers are less fractionated the petrographic composition of the coals is of secondary importance for the concentration of the ree and y the main factors are the source area and the input of dissolved ree and y into the coal depositional sites

palaeoenvironmental changes during the danian selandian boundary interval the ichnological record at the sopelana section basque basin w pyrenees abstract ichnological analysis was conducted in the danian selandian d s boundary interval from the sopelana section basque basin northern spain to improve characterization of the recently defined global stratotype section and point of the base of the selandian stage middle paleocene in the nearby zumaia section and to interpret the danian selandian boundary event with its associated palaeoenvironmental changes the trace fossil assemblage of the boundary interval is relatively scarce and shows low diversity consisting of chondrites planolites thalassinoides trichichnus and zoophycos which cross cut a diffuse burrow mottled background typical of a normal burrowing tiered community distribution of trace fossils shows local drops in abundance and diversity just above the d s boundary and about half a metre upwards into the succeeding selandian generally the selandian part of the section has slightly lower trace fossil diversity and abundance this is interpreted as due to a higher detrital food supply corresponding to a sea level fall in contrast to a decreased food supply during the selandian sea level rise smaller scale fluctuations of trace fossil diversity and abundance are also interpreted as due more to food content fluctuations in the sediment than to oxygenation of pore waters results reveal the minor influence of an extreme warming event hyperthermal conditions at the d s boundary which affected the whole benthic habitat contrarily a probable major effect of sea level fluctuations can be envisaged which determined variations in siliciclastic input and food content

rare earth element zonation in pacific ferromanganese nodules abstract the lower surfaces of ferromanganese nodules from the north equatorial pacific ocean which are enriched in mn cu and ni and the upper surfaces which are enriched in fe p and co have been analyzed for la ce nd sm eu gd dy er and yb the ree contents are lower and the ce anomaly is smaller in the lower surfaces than in the upper surfaces the magnitude of the ce anomaly increases with decreasing mn fe ratio indicative of a seawater origin the zonal distribution of the other ree supports the conclusion derived previously from inter nodule and nodule sediment relationships that diagenetic fixation of rare earths in sediments affects their enrichment by nodular iron oxyhydroxides

ultimate removal mechanisms of elements from the ocean abstract the surface complex formation model can adequately explain the observed partitioning of most of the elements between seawater and pelagic clays and between river water and river suspended particles the adsorption of elements on the hydrous oxide surface of iron oxide manganese oxide and clay minerals is the most important ultimate removal mechanism of most of the elements from the ocean

distribution de l uranium du thorium du zirconium du hafnium et des terres rares tr dans des grains de phosphates sedimentaires abstract u th zr hf and ree contents have been determined in phosphate grains from central tunisia southern france montagne noire and the southeastern pacific and in organic fractions humic acids kerogens and stable residues separated in paleocene eocene phosphates of the gafsa metlaoui basin central tunisia due to adsorption phosphatic pellets concentrate high zr ree and th contents and fish debris takes up considerable amounts of zr but not of hf a separation of zr from hf related to the adsorption of zr preferred to hf in apatite and a clear positive correlation between zr and ree contents are found we also note a more or less pronounced fractionation between light and heavy ree which is influenced mainly by organic complexes as shown from the clear enrichment of the heavy ree in each of all of the organic fractions

development and application of a sensitive and rapid analytical method to determine the rare earth elements in surface waters abstract a new cost effective method to determine the 14 rare earth elements ree s in waters to levels as low as 0 2 1 0 ng l 1 ppt has been established inductively coupled plasma mass spectrometry icp ms is used for measurement following automated preconcentration using the dionex metpac cc 1 resin of iminodiacetate functionality the free ree ion is chelated onto the resin while alkali and alkaline earth elements are washed through and separated enabling the method to be applied to seawater as well as fresh water the eluant 0 8 m hno 3 provides an ideal medium for analysis by icp ms and the suite of elements determined can be expanded to include first row transition elements cd pb and u based on replicate analyses of control samples and data for field and laboratory duplicate samples lakes and streams relative standard deviations are better than 10 except where concentrations are below 5 ng l 1 application of this method to 135 lake waters in the baie d espoir region of newfoundland indicates a contamination is not introduced from sampling bottles nalgene lpe or during the filtering and acidification process even at low ng l 1 levels b there is a high degree of correlation in element distribution patterns between lake waters and their corresponding centre lake sediments for yb and tb c the chondrite normalized plots for water and sediment are similar in shape and show consistent patterns within geological units but are distinct between such units and d the powerful potential of ree concentrations in surface water for geochemical mapping

geochemistry and mineralogy of sediments and authigenic carbonates from the malta plateau strait of sicily central mediterranean relationships with mud fluid release from a mud volcano system a mud volcano field was recently discovered within the malta plateau in the strait of sicily central mediterranean sea box core sediments and associated authigenic carbonates have been collected in water depths of 140 170 m from two distinctive sectors of the area and analyzed for major trace and rare earth elements stable isotopes and mineralogy relative homogeneity in the mineralogy and geochemistry of bulk sediments and 210pb activity distributions argue against an active mud ejection activity in the malta plateau western sector the sediments show high concentrations of fe as sb and mo exceeding the background values estimated for the strait of sicily active fluid seepage in this area is thought to be responsible for these enrichments and for the formation of authigenic carbonate crusts evidence of bacterial involvement in carbonate mainly aragonite formation is recorded in the authigenic crusts which contain flat and spiralled filaments resembling beggiatoa like sulphide oxidising bacteria and biofilm like remains which occur inside the interspaces carbonate crusts consistently show extremely negative 13c values down to 49 that suggest contribution of carbon originating from anaerobic methane oxidation heavy oxygen isotopic compositions of the authigenic carbonates 2 3 higher than those in box core sediments are interpreted as due to precipitation from fluids enriched in 18o due to seepage of deep isotopically heavy relict messinian brines

opportunistic behaviour after the toarcian oceanic anoxic event the trace fossil halimedides abstract we present an analysis of the first well documented record of the trace fossil halimedides in lower jurassic toarcian sediments from the west iberian palaeomargin lusitanian basin portugal the abundant and well preserved specimens allow a detailed ichnological characterization supporting interpretation of the associated palaeoenvironmental conditions in terms of substrate consistency firmgrounds food availability and ethology of tracemaker agrichnial sequestrichnia behaviour the appearance of this enigmatic trace is just after the toarcian oceanic anoxic event t oae in agreement with previous records associated with oceanic anoxic events as the oae 1 and oae 2 however in the case study oxygenation at the seafloor can be discarded as the major factor inducing colonization by halimedides tracemakers the rapid appearance of this trace after the t oae is related to the opportunistic behaviour of the tracemaker agrichnial sequestrichnia behaviour capturing and storing food particles together with efficient microbial gardening favoured rapid colonization of the comparatively oligotrophic seafloor in a transgressive context the record of halimedides could be appraised as a tool to evidence significant palaeoenvironmental changes such as those associated with bio events

terrestrial evidence for the lilliput effect across the cretaceous paleogene k pg boundary abstract recent research has demonstrated that the lilliput effect reduction of body size in biota associated with the aftermath of mass extinctions affected all trophic levels in the marine realm following the cretaceous paleogene k pg event however it is unclear if this size change was strictly a marine signal or a global phenomenon that also affected continental ecosystems herein we present the results of an ichnological proxy for body size of soil dwelling insects across the k pg boundary in big bend national park texas u s a quantitative efforts focused on naktodemasis bowni which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci these traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments as an approximation for the body size of the subterranean insects this dataset indicates that a smaller n bowni diameter dn is statistically correlated

lateral and vertical variations in contaminated sediments from the tinto river area huelva sw spain incidence on tracemaker activity and implications of the palaeontological approach abstract geochemical and ichnological analyses of the tinto river area sw spain reveal the presence of macro tracemakers colonizing highly contaminated soils we found high concentrations of heavy metals and related elements mainly accumulated in the upper parts biofilms and thin salty crusts some concentrations including those of cu zn and as exceed the intervention levels for natural areas and indicate potentially toxic conditions ichnological analysis reveals the presence of biogenic structures produced by the activity of the earthworm lumbricus terrestris and the coleoptera platystethus both alternatives for colonization can be correlated with those used by fossil tracemakers and they serve to better understand biotic recovery after bio events in the past

phosphate stromatolites from condensed cephalopod limestones upper jurassic southern spain upper jurassic phosphate stromatolites of the almola sierra southern spain encrust macrofossils and hardgrounds and form oncoids included within pelagic condensed fossiliferous limestones their accretion was determined by bacterially mediated precipitation of phosphate by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera phosphorous trace elements and rare earth elements were concentrated from degraded organic matter and seawater by stromatolite building communities which mediated the formation of phosphate rich and fe al si rich organic gels under oxic conditions favouring the precipitation of amorphous mineral precursors acp and fe al si oxyhydroxides the observed ce enrichment for some stromatolites is explained by oxidative scavenging of ce4 from seawater by fe mn oxyhydroxides the bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure and later changed to carbonate fluorapatite haematite and poorly crystalline fe rich clays under postoxic conditions phosphatization of trapped carbonate particles also occurred the phosphate stromatolites formed on a sediment starved pelagic swell during periods of no carbonate sedimentation and hardground development stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis sedimentation and erosion suggesting episodic changes in the sedimentary environment although some of the parameters that controlled phosphate precipitation associated with the stromatolites local high organic productivity sediment starvation moderate depth of deposition and physicochemical conditions were similar to those found in modern and ancient phosphogenic settings the palaeogeographical framework and the intensity of sedimentary processes were different to those of the world s major phosphorite deposits

rare earth element geochemistry and the tetrad effect abstract the tetrad effect is found in the rare earth elements la lu and results from increased stability at quarter half three quarter and complete filling of the 4f electron shell suggestions that this effect is observed in ree patterns of seawater and other geological samples marine phases the mineral kimuraite late stage granitic rocks the mineral uraninite and siliciclastic sediments are not compelling in the cases of seawater and the carbonate mineral kimuraite a discontinuity at gd may be attributed to the tetrad effect but the complexity of the overall controls on these ree distributions leaves such an interpretation uncertain at best unusual ree patterns in leucogranites and pegmatites are best explained by fractionation of trace minerals notably apatite apparent tetrad anomalies in uraninite rees disappear when normalised to upper crustal i e shale abundances analytical difficulties probably explain apparent tetrad effects in some seawater limestone and siliciclastic ree patterns

changes of ge si ree y and smnd isotopes in alternating fe and si rich mesobands reveal source heterogeneity of the 2 54 ga sijiaying banded iron formation in eastern hebei china abstract the north china craton ncc is one of the most important regions hosting abundant banded iron formations bifs the 2 54 ga sijiaying bif the best preserved and most extensive deposit in eastern hebei is intercalated and closely associated with meta volcanic rocks of the luanxian group in this context major and trace element and sm nd isotopic analyses of individual mesobands of a sijiaying bif specimen were conducted to characterize the source and depositional environment over a transient period low al 2 o 3 tio 2 and high field strength elements hfses concentrations show that the bif is relatively detritus free shale normalized rare earth and yttrium distributions ree y of individual bif mesobands exhibit positive la anomalies enrichment in hree relative to lree and mree and suprachondritic y ho ratios which are typical features of marine waters throughout the archean and proterozoic the presence of consistently positive eu anomalies indicates a significant high t hydrothermal input while the absence of true ce anomalies suggests deposition from an anoxic water column by comparison with other typical bifs e g the isua bif from greenland the kuruman bif from south africa the sijiaying bif is depleted in hree and appears to record variations in solute fluxes related to changing intensities of hydrothermal activity these features coupled with sm nd isotopic relations and ge si distributional patterns point to two decoupled sources controlling the depositional environment of the bif and thus reveal source heterogeneity for silica and iron of the sijiaying bif high fe fluxes were associated with seafloor vented hydrothermal fluids which received their sm nd isotopic signature from alteration of depleted oceanic crust whereas significant amounts of silica were associated with ambient seawater whose ree signature was controlled by solutes derived from weathering of nearby mesoarchean continental landmasses the old up to 3 0 ga nd t dm model ages of si rich mesobands of the bif support such a scenario