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

nd isotope systematics of coarse and fine grained sediments examples from the middle proterozoic belt purcell supergroup sm nd isotopic compositions are reported for 20 fine and 5 coarse grained samples of the belt purcell supergroup of western north america varepsilon nd and sm nd ratios for fine grained belt purcell sediments are remarkably uniform indicating crustal residence ages ranging only from 1 6 to 2 1 ga varepsilon nd and sm nd ratios for coarse grained sediments however are much more varied and contain evidence of sm nd fractionation during sedimentary recycling assuming that this ree fractionation occurred between the time source areas were eroded and when sediment was deposited a new method of calculating crustal residence age intervals is derived for the coarse grained samples which serves to place constraints on the average time since source materials were extracted from the mantle the nd data from both sample groups provide an average age estimate of 2 0 pm 0 3 ga for the middle proterozoic crust from which most of the belt purcell supergroup was derived the isotopic data toge

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

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

postdepositional sm nd fractionation in sandstones implications for neodymium isotope stratigraphy abstract sandstone reservoirs from the norwegian continental shelf commonly show varying degrees of postdepositional fractionation of sm nd ratio apparently due to preferential incorporation of sm in the crystal lattice of diagenetic apatite based on data from leaching experiments an apatite mineral separate and petrography it is proposed that fractionation occurred mainly during closed system burial diagenesis as phosphate deposited on the sea floor recrystallized to apatite and incorporated rare earth elements ree from the surrounding rock matrix as a result the sm nd model age parameter in general contains two components of information a the true crustal age of the sediment and b a secondary component of sm nd fractionation which can be either negligible or dominant it is difficult to separate these components and thus correct for component b even in data showing no obvious signs of postdepositional fractionation model ages may be variably disturbed by subordinate amounts of diagenetic alteration however the isotope ratio 143nd 144nd is expected to be relatively resistant to alteration by secondary sm nd fractionation and should therefore be used rather than model age as the principal correlation parameter in stratigraphic studies in this way nd isotope stratigraphy can still be used as a valuable and unique tool for studies of provenance and correlation even in strata showing strong sm nd fractionation effects strongly sm nd fractionated horizons recognized by bulk rock sm nd ratios 0 23 may also be useful for stratigraphic correlation but it is clear that their occurrence reflects special depositional conditions rather than shifts in sediment provenance

breakup and conditions for stability of the northern larsen ice shelf antarctica the breakup of ice shelves has been widely regarded as an indicator of climate change1 with observations around the antarctic peninsula having shown a pattern of gradual retreat associated with regional atmospheric warming and increased summer melt and fracturing processes2 3 4 5 6 7 8 9 the rapid collapse of the northernmost section of the larsen ice shelf larsen a over a few days in january 1995 indicated that after retreat beyond a critical limit ice shelves may disintegrate rapidly here we use a finite element numerical model that treats ice as a continuum without fracture10 to examine the breakup history2 between 1986 and 1997 of the two northern sections of larsen ice shelf larsen a and larsen b from which we establish stability criteria for ice shelves analysis of various ice shelf configurations reveals characteristic patterns in the strain rates near the ice front which we use to describe the stability of the ice shelf on larsen a only the initial and final ice front configurations show a stable pattern larsen b at present exhibits a stable pattern but if the ice front were to retreat by a further few kilometres it too is likely to enter an irreversible retreat phase

petrology and geochemistry of cretaceous sedimentary rocks of the monte soro unit sicily italy constraints on weathering diagenesis and provenance abstract the mineralogy and chemical compositions of shale and sandstone alternations of cretaceous age of the monte soro unit sicily have been determined the clay minerals in the shales are mostly illite and i rich mixed layer i s reflected by enrichment in al2o3 k2o and chemically similar elements the sandstones are subarkose to quartz arenite the shales and sandstones have upper crustal rare earth element patterns and except for k2o they are depleted in alkaline and alkaline earth elements as a result of intense weathering the sandstone and shale mineralogy suggests a diagenetic history in which the sediments were subjected to temperatures in excess of 100 c during which interaction between some minerals in the shales and sandstones took place thus diagenetic quartz cementation and feldspar alteration in the sandstones and smectite illitization in the shales occurred together with the shales being a sink for potassium and the sandstones a sink for silicon negative europium anomalies bet

improving constraints on apatite provenance nd measurement on fission track dated grains detrital thermochronology is commonly used to locate source and improve the understanding of a region s long term development provenance detrital age data typically comprise a number of distinct age modes representing contributions from a number of different sources for methods such as apatite fission track ft this can present a challenge in that direct assignment of age modes to particular lithological or tectono stratigraphic units is rarely possible particularly when ancient orogenic sediments are examined a new approach described here is based on measuring nd isotopic data on single apatites by laser ablation icpms where the 143nd 144nd ratios are diagnostic of grain source by combining nd isotopic measurement with apatite ft analysis it is possible to link detrital apatite ft ages to specific rock unit sources the methodology and wider benefits of this new approach are discussed using examples from the himalaya and andaman islands geological society of london 2009

ree and other trace elements in a granitic weathering profile from serre southern italy abstract ree v cr ni rb sr y zr and nb behaviour in a granitic weathering profile in southern italy is studied in the saprolites of the considered profile depletion of v cr ni rb sr zr and nb is observed this is quite remarkable for sr and cr whereas ree and y are enriched in the more altered portion of the profile and especially in its m fraction such enrichment is associated with the lree hree fractionation and the positive ce anomaly the former results from an increased solubility of hree in a non acid environment as well as from the removal of the hree rich phases from the residual component the latter is related to the redox chemistry of ce which as ceo 2 is less soluble than the other ree no analogy is observed between the behaviour of ce and fe mn and cr saprolites also exhibit a negative eu anomaly which is mostly inherited from the parental material finally the influence of accessory minerals in the ree distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes this is especially true in the parent material sediment relationships

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

the use of chemical element analyses in the study of biostratigraphically barren sequences an example from the triassic of the central north sea ukcs

surface melting on antarctic peninsula ice shelves detected by passive microwave sensors a 13 year time series of spaceborne passive microwave radiance measurements over the antarctic peninsula ice shelves reveals a systematic increase in the duration of the summer melt season combined with data from meteorological stations on the antarctic peninsula the annual motion and long term trends of the 0 c isotherm can be monitored

diagenetic modification of sm nd model ages in tertiary sandstones and shales texas gulf coast sm nd model ages of sandstones and shales from the oligocene frio formation of south texas and the paleocene eocene wilcox group of south central texas increase with increasing depth of burial depleted mantle model ages tdm of frio shales increase from ca 800 ma at 1 km of burial to ca 1000 ma at 4km in frio sandstones tdm increases from ca 750 ma at 1 km to over 1200 ma at 4 km of burial in wilcox shales tdm increases from ca 1300 ma to ca 1500 ma over a burial depth of 1 5 to 4 5 km tdm of wilcox sandstones increases from ca 1450 ma at 2 5 km of burial to as much as ca 2000 ma at 4 0 km the sampling scheme employed minimizes but does not eliminate the possibility that these trends in tdm are due to detrital variability close correlation of these trends with diagenetic changes in the rock and evidence of rare earth element mobility preserved in the diagenetic products suggests that diagenesis has modified tdm diagenetic modification of tdm in frio sandstone and wilcox shale is due primarily to loss of radiogenic nd whereas increased 147sm 144nd produces elevated tdm in deeper wilcox sandstones the tdm of frio shales does not change appreciably with depth owing to the opposite effects on tdm of decreased 147sm 144nd and decreased nd 0 loss of radiogenic nd is due primarily to reactions involving unstable volcanic detritus which is more abundant in the frio than in the wilcox decreased 147sm 144nd in authigenic illite and consequent increased 147sm 144nd in pore fluids results in elevated tdm in wilcox and frio sandstones containing late diagenetic cement and in decreased 147sm 144nd in deeper frio shale the similar tdm trends observed in both units which have different detrital characteristics suggest that modification of sm nd model ages in siliciclastic rocks may be commonplace during burial diagenesis

temperature variations since 1750 ce inferred from an alpine lake in the southeastern margin of the tibetan plateau abstract high altitude regions are thought to be very sensitive to global climate change especially under current global warming however due to the lack of paleoclimate archives such as ice core and tree rings above the modern tree line limited paleoclimate data have been extracted to extend instrumental data over the past few centuries which will help understand the interannual to decadal scale climate variability in high altitude regions here we present a high resolution 1 6 yr quantitative temperature record from a remote alpine lake at the southeastern margin of the tibetan plateau by applying a novel proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts contrary to the often documented warming trend over the past few centuries but consistent with temperature record from the northern tibetan plateau our data show a gradual decreasing trend of 0 3 c in mean annual air temperature from 1750 to 1970 ce this result suggests a gradual cooling trend in some high altitude regions over this interval which could provide a new explanation for the observed decreasing asian summer monsoon in addition our data indicate an abruptly increased interannual to decadal scale temperature variations of 0 8 2 2 c after 1970 ce in terms of both magnitude and frequency indicating that the climate system in high altitude regions would become more unstable under current global warming

climatically induced retreat and collapse of northern larsen ice shelf antarctic peninsula the areal changes of the northern larsen ite shelf lis antarctic peninsula between march 1986 and march 1997 have been analyzed based on synthetic aperture radar images of the european remote sensing satellites ers 1 and ers 2 and on landsat images this analysis is complemented by data on ice motion and surface mass balance which have been obtained during several field campaigns since the early 1980s after a period of retreat coinciding with atmospheric warming and with decreasing net accumulation at the surface due to melt losses the two northernmost sections of lis disintegrated almost completely within a few days in january 1995 recent observations of the ice shelf section north of jason peninsula which is presently the northernmost section of lis show increased summer melt and intensification of the rifting processes probably causing accelerated retreat of this section in the near future the retreat and the disintegration event of lis indicate high sensitivity of ice shelves to prolonged perturbations of the mass balance

apatite overgrowth cement as a possible diagenetic temperature history indicator abstract grains of detrital apatite develop syntaxial apatite cement overgrowths during burial petrographic analysis of the distribution of such overgrowths in 453 thin sections from dominantly marine sandstones of late triassic to paleogene age on the norwegian continental shelf shows that apatite overgrowths are present only in samples with formation temperatures above approximately 90 c suggesting that authigenic apatite starts to form at this temperature apatite grains and apatite overgrowths are easily identified with a cathodoluminescence microscope thanks to the intense yellow green and orange cathodoluminescence colors shown by grains and overgrowths respectively presence of apatite overgrowths may therefore be a useful indicator of paleotemperatures above ca 90 c at least in marine sandstones

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

facies effects on the behaviour of nd and sr isotope systems in turbidite mudrocks during diagenesis a detailed sm nd epsilon nd and rb sr profile through a 30 cm thick section of silurian llandovery interbedded turbiditic and hemipelagic mudrocks from the central wales basin shows well marked chemical and isotopic trends the variations reflect an interplay of depositional mode and diagenetic fractionation sm and nd values are substantially higher and sm nd ratios tend to be lower in the organic rich hemipelagite layers due to diagenetic concentration in the hemipelagites there is a corresponding depletion in the turbidite mudstones epsilon nd values range from 0 8 to 7 1 and this is attributed to diagenetic modification of sm nd ratios causing scatter in back calculated epsilon values rubidium strontium ratios in this succession fall within a narrow range due to homogenization during diagenesis by contrast data from a hemipelagite dominated condensed succession near the northern margin of the welsh basin show a lower range of epsilon nd values and a higher scatter of rb sr values consistent with less fluid throughput during burial compaction and hence less diagenetic redistribution in these rocks these patterns demonstrate the sensitivity of mudrock trace element and isotope compositions to both small scale sedimentary structure and large scale basin architecture

evidence of recent climatic warming on the eastern antarctic peninsula air temperatures at the stations marambio esperanza and matienzo have been analysed to investigate recent climate change on the eastern part of the antarctic peninsula the data are compared with the station orcadas on the south orkney islands the longest record available in antarctica and with faraday on the western coast of the peninsula though the interannual variability is comparatively high and the stations are located in different climatic regimes a pronounced warming trend shows up in all records at marambio a temperature increase of 1 5 c has been observed since the beginning of the record in 1971 this is of similar magnitude as the increase at the station faraday on the west coast with 2 5 c for the longer period since 1945 the steady retreat and collapse of the northern larsen ice shelf coincided with this warming trend of particular importance for the ice shelf mass balance in this region are the summer temperatures which show a statistically significant warming trend at the stations marambio and esperanza the representativity of the summer temperatures of marambio for northern larsen ice shelf is confirmed by intercomparison with the parallel measurements at matienzo which is located on the ice shelf

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

effects of sedimentary sorting on neodymium isotopes in deep sea turbidites the study of neodymium model ages of sedimentary rocks has added considerably to our understanding of crustal growth and evolution so far however the possible effects of various sedimentary processes on nd isotope distributions have not been fully evaluated here we present nd isotope data for a series of sand mud pairs in modern deep sea turbidites from different tectonic settings which show that sands and muds commonly have significantly different nd isotope compositions that in only some cases are associated with differences in sm nd ratio differences are as great as 7 ndunits corresponding to nd model ages that differ by up to 0 44 gyr and may be explained by separation or unmixing of components from different sources during sedimentary transport and sorting for one sample heavy mineral fraction ation may be indicated these results have implications for studies of nd model ages in sedimentary rocks and for the interpretation of provenance from sedimentary petrography and geochemistry

34 year satellite time series to monitor characteristics extent and dynamics of larsen b ice shelf antarctic peninsula a variety of data are used to investigate larsen b which is at present the northernmost section of the larsen ice shelf recently declassified usargon satellite photographs of 1963 kosmos photographs of 1975 landsat images of 1986 1988 and 1990 ers 1 2 sar images from 1992 to1997 radarsat of 1998 and field surveys are used to analyze the areal extent surface characteristics and dynamic behaviour of this ice shelf sectionover more than three decades visible and radar imagery together with field observations are used synergistically to describe the ice shelf morphology including meltwater features and rifts in contrast to the retreat of the ice shelf sections in the north larsen b advanced steadily from 1963 to early1995 when the area decreased significantly due to a major calving event analysis of different satellite images indicates that melting is proceedingfurther south in coincidence with the regional warming trend in addition fracturing processes and rapid development of new rifts are observed associated with recent acceleration of ice motion close to the front all observations indicate that major calving events should be expected for this iceshelf section in the near future

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

ion probe measurement of rare earth elements in biogenic phosphates abstract the rare earth element ree distributions in individual fish teeth and conodonts have been measured by ion probe concentrations and la yb ratios show little variations except in the enamel which suggests that ree uptake from the sedimented biogenic debris takes place at the water sediment interface as an essentially quantitative process without fractionation late diagenetic disturbances remained of marginal importance hence ree in phosphatic debris might reflect the input from the overlying water column

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

samarium neodymium isotope stratigraphy of the lunde and statfjord formations of snorre oil field northern north sea two sequences of fluviatile sediments from snorre oil field are investigated by the sm nd isotopic method the results illustrate distinctly different source areas for the upper triassic upper member of the lunde formation and for the lower jurassic statfjord formation the lunde formation has sm nd provenance ages mainly in the range 1500 to 1700 ma which is not diagnostic of a specific source area the statfjord formation has provenance ages in the range 1700 to 2150 ma this is old within the context of source areas in the hinterland of the northern north sea and provenance partly from the archaean lewisian shield to the northwest is suggested intensive sampling through the statfjord formation in one well illustrates that the provenance ages evolve systematically with time the pattern provides a detailed record of how source areas evolved during deposition of these strata the possibility is recognized of correlating changes or trends in provenance between wells the data also suggest that sm nd ratios and isotopic compositions of these rocks are not significantly fractionated between fine and coarse grained sediments by mechanical or diagenetic processes

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

melange versus forearc contributions to sedimentation and uplift during rapid denudation of a young banda forearc continent collisional belt abstract new sedimentary geochemistry and petrographic analyses provide the most extensive sedimentary documentation yet of the rapid denudation of the young timor orogen the data from three basins including two widely separated well dated sections of the synorogenic megasequence of timor leste and a re dated dsdp 262 constrain the source and timing of detrital sediment flux during forearc continent collision along the timor sector of the banda arc the exhumed synorogenic piggy back basins formed above a melange unit that developed at the expense of a weak stratigraphic horizon in the mesozoic stratigraphy and was exhumed to the sea floor in latest messinian time following an interval of deep marine chalky marl sedimentation an increasingly muddy sediment flux indicates that the island of timor became emergent and shed sediment by 4 5 ma comparison of exhumed sections with similar patterns in the dsdp262 chemistry suggests that the sediment source was probably located some 50 60 km distant from the basin which is consistent with the aileu region of timor leste that shows an appropriate exhumation history all sedimentation between 4 5 and 3 2 ma was probably derived from a low relief rapidly eroding and mudstone dominated landscape with geochemical affinities to the triassic mudstone derived synorogenic melange the melange unit overlies and surrounds the banda terrane and was presumably structurally emplaced by propagation of a decollement through the triassic rocks during the collision after 3 2 ma sedimentation was dominated by hard rock lithologies of the banda terrane consisting of forearc cover and basement the latter including elements of metamafic rocks and metapelites this phase of sedimentation was accompanied by rapid uplift which may have been partly driven by a transient imbalance between rock uplift and denudation as resistant lithologies emerged from below melange like mudstone previous work has suggested that the timing of collision in timor leste and west timor was substantially different our reevaluation of dsdp 262 facies migration history in the context of the re dating presented here favours a relatively synchronous onset of uplift in both halves of the island but with different partitioning of strain between the foreland and hinterland in each half of the island

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

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

neodymium isotopic profiling of carbonate platform strata correlation between siliciclastic provenance signature and sequence stratigraphy abstract the nd isotopic composition of core samples from the mid carboniferous to upper permian finnmark carbonate platform is interpreted as representing their siliciclastic content the nd content of the carbonate fraction being relatively insignificant trends of upward increase in 143nd 144nd in these strata correlate with the two largest scale second order depositional sequences defined by previous sedimentologic study these trends are interpreted as the result of mixing between two hypothetical siliciclastic provenance terranes the relatively old low 143nd 144nd material dominating the base of each cycle is suggested to be derived from local caledonian basement the relatively young high 143nd 144nd material comprising the upper part of each cycle is suggested to be an open marine siliciclastic composition representing mixing of more widespread sources dominance of the basement provenance signature at the base of each second order sequence could reflect tectonic movements that exposed local basement areas to erosion the subsequent gradual shift to younger open marine provenance signature could result from progressive peneplanation or burial of the basement uplifts higher frequency depositional sequences have little to no effect on nd composition suggesting that these fluctuations in facies distribution were largely unrelated to patterns of siliciclastic supply this model implies that the mid asselian second order lowstand was a time of major siliciclastic bypass suggesting the possible existence in the nordkapp basin of extensive sandstones of this age the observed pattern of cyclic asymmetric 143nd 144nd variation should be a universal characteristic of finnmark platform stratigraphy and may therefore be useful for stratigraphic correlation between widely separated well locations the broader interest of these results is the demonstration that 1 the nd isotopic composition of even relatively pure carbonate rocks can reflect mainly the provenance signature of the siliciclastic component and 2 nd isotopic profiling of carbonate strata can indicate patterns of tectonic influence on depositional cyclicity

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

origin of chlorite enrichment and neodymium isotopic anomalies in haltenbanken sandstones thisis really two papers rolled into one we have chosen to present them together because both topics derive from the same series of nd isotopic analyses of some chlorite coated jurassic age sandstone reservoirs from the norwegian continental shelf the first topic is a comparison of the nd isotopic composition of chlorite rich vs chlorite poor sandstones to determine whether systematic differences in sediment provenance have controlled the occurrence of grain coating fe chlorite cement the results show that both chlorite rich and chlorite poor sandstones have a wide range of 143nd 144nd consistent with mixing of at least two main provenance terranes of differing mean crustal age in both groups this does not support the model of chlorite enrichment due to localized influx of an unique fe rich provenance component such as mafic igneous material but is consistent with an alternative model of chlorite enrichment by fe clay authigenesis on the sea floor localized by fluvial discharge into a nearshore marine setting the implication is that studies of depositional setting rather than sand provenance should be the key to predicting occurrence and geometry of high porosity zones in deeply buried sandstones with chlorite related porosity preservation the second topic deriving from this set of nd isotopic data concerns the discovery of an association between anomalously high smnd model ages and elevated contents of bulk rock phosphorous this sub set of the samples is anomalous in that the smnd model ages are too high to be interpreted as detrital provenance ages and also because smnd model age correlates with sm nd ratio furthermore the anomalous smnd signature can be removed by acid leaching leaving a residue with apparently non anomalous smnd characteristics analysis of an apatite mineral separate from one sample confirms that the anomalous smnd signature resides within diagenetic apatite the anomalies are suggested to result from ree fractionation due to the crystal chemistry of apatite which favors preferential incorporation of the intermediate weight ree thus increasing sm nd and smnd model age the apatite probably formed by recrystallization of phosphate that was present at the time of sand deposition either as organic detritus or as the product of precipitation on the sea floor the isotopic composition of the apatite indicates that sm nd fractionation occurred within the past 100 million years and thus was not syndepositional formation of the nd isotopic anomalies is therefore interpreted to be a burial diagenetic process involving local ree enrichment of apatite and complementary ree depletion of the surrounding rock mass experimental apatite melt partition coe cients determined at magmatic temperatures predict much lower sm nd fractionation than is observed in the present samples but we speculate that the degree of fractionation may increase greatly toward the lower diagenetic temperatures relevant for the present samples the discovery of these anomalies does not invalidate the use of smnd model age profiling as a stratigraphic correlation tool and provenance indicator but indicates that precautions should be taken when dealing with marine sandstones specifically data sets should be examined for correlation between smnd model age and sm nd ratio which may indicate the presence of anomalous fractionation effects even in such cases the isotopic ratio 143nd 144nd can provide a reliable provenance signature 1998 elsevier science ltd all rights reserved

rare earth element fractionation and concentration variations along a groundwater flow path within a shallow basin fill aquifer southern nevada usa abstract rare earth element ree concentrations were measured in 5 well water samples and 3 springs located along a groundwater flow path in a shallow tuffaceous alluvial aquifer from southern nevada usa the ree concentrations in these groundwaters decrease in the direction of groundwater flow a previous investigation demonstrated that ree solid liquid phase partitioning coefficients i e kd s for groundwaters from tuffaceous alluvial aquifers in southern nevada are relatively high mean kd 102 6 our groundwater ree data in conjunction with these kd s support strong sorption of aqueous rees to aquifer surface sites as the primary removal mechanism of rees from these groundwaters in addition relatively high aqueous ree concentrations occur at distinct locations along the groundwater flow path the elevated ree concentrations are explained by addition of deeper groundwaters influx of geothermal waters from a hot spring system differences in solution complexation and or mixtures of regional and local recharge sources solution complexation modelling of rees in the groundwaters indicate that carbonate complexes account for more than 99 of each rees in solution moreover groundwater yb nd ratios a measure of ree fractionation are associated with alkalinity hco3 co32 r 0 71 the data and speciation model results indicate that ree fractionation i e the observed heavy ree hree enrichments compared to rock sources is controlled by formation of progressively stronger carbonate complexes in solution with increasing atomic number which inhibits hree sorption compared to light rees lree and a greater affinity for the lrees to sorb to surface sites in the local tuffaceous alluvial aquifers compared to the hrees

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

comparison of isotopic and petrographic provenance indicators in sediments from tertiary continental basins of new mexico abstract isotopic variations of nd in sedimentary rocks provide a new tool for provenance determination we have compared the isotopic technique with classic petrographic indicators of provenance in sediments from two tertiary basins of the rio grande rift north central new mexico the siliciclastic sediments in these basins were derived from varying proportions of precambrian basement and oligocene volcanic rocks which are isotopically and petrographically distinct in the analyzed sediments a good correspondence exists between petrographic and isotopic provenance indicators the data also suggest that the isotopic tracer is more sensitive to minor detrital input from a second source than is the framework petrology the similar sm nd ratios for all analyzed sediments and the identical isot pic values of interlayered mudstone and sandstone indicate that no significant fractionation of sm and nd occurs during the formation of the sediments thus the nd model ages of the sediments preserve the crust formation age of the source the sr isotopic and concentration data show trends generally similar to the nd data but they do not indicate the sedimentary provenance as clearly this ambiguity is a consequence of strong rb sr source heterogeneities and rb sr fractionation during the sedimentary cycle

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

sr and nd isotopic evidence for punctuated clay diagenesis texas gulf coast we report rb sr sm nd and mineralogical data for leached whole rock 1200 m independent of the duration of burial the exchangeable sr in the clay has remained an open system and has undergone isotopic exchange since that time minimum fluid rock ratios of 0 2 to 2 are modeled from sr isotopic data consistent with rock dominated open system diagenesis leachates and residues of the 0 1 zm fraction below the smectite illite transition appear to have achieved nd isotopic equilibrium during clay diagenesis and show no signs of subsequent exchange the clay residues have low 147sm 144nd 0 085 indicating that authigenic illite has a lower sm nd ratio than its bulk rock protolith conversely the coexisting exchangeable ree inventory has elevated sm nd as reflected by leachate 14vsm 144nd as high as 0 188 this sm nd fractionation in conjunction with the preserved isotopic equilibrium may be useful for dating diagenesis and associated fluid rock interaction in older rocks

sm nd and u pb zircon isotopic constraints on the provenance of sediments from the amadeus basin central australia evidence for ree fractionation abstract the amadeus basin of central australia is a late proterozoic to late palaeozoic ensialic depositional basin located between two proterozoic basement blocks of different nd crustal formation ages the older arunta block t dm nd 2 0 to 2 2 ga u pb zircon ages 1 5 1 9 ga to the north and the younger musgrave block t dm nd 1 7 to 1 9 ga u pb zircon ages 1 0 1 7 ga to the south initial nd isotopic compositions of the amadeus basin sediments generally fall into the region defined by the evolutionary trajectories of these two basement blocks indicating that the sediments are dominated by essentially two source components the older arunta block 147 sm 144 nd 0 114 and nd 0 20 4 and younger musgrave block 147 sm 144 nd 0 118 and nd 0 14 7 and or their equivalents stratigraphically higher sediments plot more closely to the evolutionary trajectory of the musgrave block this result together with the average provenance ages indicates the proportion of material from the musgrave block increases as the sediments become younger the sm nd isotopic data preclude a substantial involvement of archaean sources u pb zircon ion probe analyses of the late proterozoic heavitree quartzite and the late cambrian goyder formation are consistent with the sm nd isotopic constraints most of the zircons from the basal heavitree quartzite give concordant u pb zircon ages of 1500 to 1900 ma consistent with derivation from an arunta type source whilst zircons from the younger goyder sandstone give six discrete u pb zircon age groups of 511 20 615 15 960 109 1190 54 1633 24 and 1878 48 ma indicative of a dominantly musgrave type source with a minor contribution from the arunta block or reworked preexisting amadeus basin sediments the two youngest u pb zircon ages probably indicate some contribution from late proterozoic cambrian volcanics in central australia or a previously unrecognised younger local source in the basement blocks the 511 20 ma constrains the maximum depositional age of the sediment the amadeus basin sediments have a surprisingly wide range of 147sm 144nd ratios 0 077 0 136 irrespective of grain size and rock types in addition the calculated t dm nd values for samples from the same stratigraphic unit are well correlated with 147sm 144nd ratios with samples of different stratigraphic units forming sub parallel arrays these phenomena are interpreted in terms of ree fractionation and preferential sorting of preexisting ree rich phases during sedimentary recycling and deposition this process can lead to either an increase or a decrease in 147sm 144nd ratio of a sediment relative to its source and therefore an erroneous estimate of its t dm nd provenance age a theoretical model is developed which accounts for the observed correlation between t dm nd and 147sm 144nd ratios for suites of stratigraphically related sediments and allows a reliable estimate to be made of the provenance age of individual stratigraphic units assuming the average 147sm 144nd ratio of the source is known or can be estimated the provenance age for each stratigraphic unit of the amadeus basin has been calculated using this method the sm nd isotopic systematics in the amadeus basin sediments suggest that 1 1 ree fractionation during sedimentary recycling can in some cases be an important factor and needs to be considered 2 2 the provenance of the amadeus basin sediments was controlled by local source regions and cannot be used to infer large scale continental averages hence some caution must be evoked in using sm nd isotopic constraints from restricted sampling for more generalised models of crustal evolution

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

change of sm nd isotope composition during weathering of till weathering of till in northern sweden results in the formation of well developed spodosols the till is dominated by 1 9 1 8 ga granitic material the ree are among the elements most strongly depleted during weathering and the loss of ree from the e horizon decreases as the atomic number increases to study if weathering leads to a change of the nd isotope composition we have analysed the nd isotopic composition of the various horizons including living plants and humus of two profiles of weathered till typic haplocryods in northern sweden as much as between 65 6 and 75 3 of the sm and nd in the 0 2 mm fraction has been lost from the e horizon and between 32 5 and 54 7 from the b horizon nd has been lost to a slightly greater extent than sm the two c horizon samples have end 0 values of 22 1 and 23 2 corresponding e horizon values are 18 1 and 20 2 the b horizon values are intermediate between the values of the e and c horizons it is concluded that the weathering leads to a change in the sm nd ratio resulting in a change of the sm nd isotope composition the plant and humus samples deviate even more from the unweathered till for one station the results could be interpreted as if the sm and nd taken up by the plants had similar isotope characteristics as the amounts of these elements released by weathering in the e horizon for the other station it is probable that the nd isotope composition of the organic samples is dominated by nd released by till weathering which however is mixed with another nd source possibly an airborne component the explanation to the change of isotope compostion in the till is that a larger proportion of the nd released by weathering is released from minerals with a lower sm nd ratio than the bulk soil compared with the amount released from minerals with a higher sm nd ratio although the various ree carrying minerals had the same initial nd isotopic composition 1 8 1 9 ga of decay of 147sm to 143nd has resulted in a higher present 143nd 144nd ratio in the minerals with a higher sm nd ratio

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

sm nd isotope systematics in deep sea sediments clay size versus coarser fractions sm nd studies were carried out on last glacial and holocene sediments from the labrador sea three grain size fractions were analyzed for each sediment the clay size fraction 2 m the fine cohesive silts 2 10 m and the coarse silts 10 63 m in most cases sm nd s ignatures are different from one grain size to anot her in addition different sm nd signatures are derived fr om the clay size fractions compared to the cohesive silt fraction indicating that the cohesive fraction is heterogeneous and that distinct origins in terms of source areas are implied silt fractions record the influence of supplies from the north american precambrian shield whereas clay size fractions 2 m are more sensitive to s edimentary input from the eastern basins in relati on with deep currents coupling sm nd studies on silt and c lay fractions may be a powerful tool to unravel the evolution of deep circulations versus detrital supplies

rare earth elements in weathering profiles and sediments of minnesota implications for provenance studies abstract the relative abundance of rare earth elements in sediments has been suggested as a tool for determining their source rocks this correlation requires that weathering erosion and sedimentation do not alter the ree abundances or do so in a predictable manner we find that the rare earth elements are mobilized and fractionated by weathering and that sediments derived from the weathered materials can display modifications of the original pattern of rare earth elements of some due to grain size sorting of the weathered material however the ree distribution pattern of the provenance terrane can be recognized in the sediments

nd isotopic and geochemical constraints on provenance of sedimentary rocks in the eastern officer basin australia implications for the duration of the intracratonic petermann orogeny sm nd isotopic and geochemical data from neoproterozoic to cambrian sedimentary rocks in the intracratonic eastern officer basin in central australia highlight the evolving provenance roles of the basement complexes that underlie and bound the basin initial e nd values of around 12 for the basal units indicate that both were largely derived from the late archaean to mesoproterozoic gawler craton which bounds the basin to the south at c 720 ma an influx of juvenile glacially derived sediment indicates partial uplift of the mesoproterozoic musgrave block along the basin9s northern margin in a regime interpreted to be broadly extensional at around 600 ma synchronous with the development of a foreland architecture there was a large influx of musgrave block derived sediments this is interpreted to mark the onset of the intracratonic petermann orogeny which was a long lived event or series of events spanning more than 70 ma subsequent to c 600 ma the nd isotopic composition of sequences within the officer basin indicates an increasing contribution from the gawler craton despite up to 45 km of denudation of part of the musgrave block this suggests that the majority of sediment derived from the petermann orogen bypassed the eastern officer basin for much of the history of the petermann orogeny

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