distinguishing climatic and tectonic signals in the sedimentary successions of marginal basins using sr isotopes an example from the messinian salinity crisis eastern mediterranean the evolution of oceanic 87 sr 86 sr through the tertiary has been sufficiently well documented to provide a useful stratigraphic tool for carbonate rich marine sediments which were deposited in basins connected to the global oceans in isolated basins sea water 87 sr 86 sr will diverge from coeval oceanic values thus if independent age information exists the geochemical signature can constrain the timing of isolation in marginal basins formed in tectonically active settings the timing of isolation is critical to the assessment of the relative importance of climate or tectonic controls on that event previously isolation has been assumed to coincide with the last occurrence of open marine fauna however in an example from the eastern mediterranean 87 sr 86 sr data challenge that assumption and can be interpreted as indicating a protracted period of isolation c 3 ma during which time marine conditions prevailed prior to the messinian salinity crisis at the end of the miocene this allows tectonic and climatic signals to be distinguished since although convergence of africa with eurasia was responsible for isolation of this part of the mediterranean it is more likely that later climatic change triggered desiccation

unusual diagenetic alteration of volcanoclastic sediments in the tonga fore are evidence from chemical and strontium isotopic compositions of interstitial waters abstract the depth variations in the major chemical components dissolved in interstitial waters from the tonga margin odp site 841 are much more pronounced than those usually observed in deep sea sediments the extensive alteration of volcanic miocene sediments to secondary minerals such as analcime clays and thaumasite forms a cacl2 rich brine the brine results from a high exchange of ca to na k and mg and an increase in cl concentrations due to removal of h2o from the fluid during the authigenesis of hydrous minerals the formation of thaumasite could have partly controlled the concentration of dissolved so4 hco3 and ca in the miocene sediments the strontium isotopic signature of the interstitial water suggests that alteration of the volcanic miocene sediments occurred a long time after sedimentation a transient diffusion model indicates that molecular diffusion was not prevented by lithologic barriers and that the formation of secondary minerals in the miocene sediment occurred over a short period of time e g 1 000 years the extensive diagenetic processes in the tonga margin were mostly caused by the recent intrusion of andesite sills and dikes into the miocene sediments

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

87sr 86sr and 18o 16o ratios of clays from a hydrothermal area near the galapagos rift as records of origin crystallization temperature and fluid composition abstract strontium and o isotope compositions of green clay minerals from sediment cores of three boreholes drilled into sites 424a and 509b and close to a hydrothermal mound site 424b near the galapagos spreading center dsdp legs 54 and 70 were determined the green clays consist mostly of a transition from fe smectite nontronite to glauconite 87sr 86sr ratios were measured on clay size fractions after gentle acid leaching and on the recovered leachates from different samples the 87sr 86sr ratios of the clay residues from both the 424a and b sites are well below the modern seawater value which points consistently to precipitation from hydrothermal fluids that contained variable amounts of seawater even away from mound however most of the clay residues from mound site 509b have 87sr 86sr ratios significantly above the seawater value suggesting the occurrence of a detrital component together with the new authigenic particles the clay minerals of the hydrothermal mound are mixed with detrital components and that of the sample taken outside but near the mound as a reference for the surrounding oceanic environment yields a hydrothermal signature crystallization temperatures of the clays range from 32 to 63 c assuming a 18o value of 2 2 for the mineralizing fluids hydrothermal fluids generated in the underlying oceanic crust mixed in varied proportions with ambient seawater and migrated into beds of the mound in a sequence of recurrent processes that ultimately resulted in the formation of the observed clay minerals no significant temperature differences were detected for crystallization of the k rich glauconite and k depleted nontronite the 87sr 86sr ratios of the sr leached off the clay particles are near the value of modern seawater inferring a progressive replacement of the hydrothermal fluids by seawater in the pore space of the mound sediments

diagenesis in tephra rich sediments from the lesser antilles volcanic arc pore fluid constraints we present sediment pore fluid and sediment solid phase results obtained during iodp expedition 340 from seven sites located within the grenada basin of the southern lesser antilles volcanic arc region these sites are generally characterized as being low in organic carbon content and rich in calcium carbonate and volcanogenic material in addition to the typical reactions related to organic matter diagenesis pore fluid chemistry indicates that the diagenetic reactions fall within two broad categories 1 reactions related to chemical exchange with volcanogenic material and 2 reactions related to carbonate dissolution precipitation or recrystallization for locations dominated by reaction with volcanogenic material these sites exhibit increases in dissolved ca with coeval decreases in mg we interpret this behavior as being driven by sediment water exchange reactions from the alteration of volcanic material that is dispersed throughout the sediment package which likely result in formation of mg rich secondary authigenic clays in contrast to this behavior sediment sequences that exhibit decreases in ca mg mn and sr with depth suggest that carbonate precipitation is an active diagenetic process affecting solute distributions the distributions of pore fluid 87sr 86sr reflect these competitive diagenetic reactions between volcanic material and carbonate which are inferred by the major cation distributions from one site where we have solid phase 87sr 86sr site u1396 the carbonate fraction is found to be generally consistent with the contemporaneous seawater isotope values however the 87sr 86sr of the non carbonate fraction ranges from 0 7074 to 0 7052 and these values likely represent a mixture of local arc volcanic sources and trans atlantic eolian sources even at this site where there is clear evidence for diagenesis of volcanogenic material carbonate diagenesis appears to buffer pore fluid 87sr 86sr from the larger changes that might be expected given the high abundance of tephra in these sediments part of this carbonate buffering at this site as well as throughout the region derives from the fact that the sr concentration in the non carbonate fraction is generally low 200 ppm whereas the carbonate fraction has sr concentrations approaching 1000 ppm

evolution of carbon cycle over the past 100 million years it is generally accepted that progressive cooling of global climate since the late cretaceous results from decreasing partial pressure of atmospheric co2 pco2 however details on how and why the carbon cycle evolved and how it would affect pco2 have not been fully resolved while the long term decline of pco2 might be caused by the decrease of volcanic degassing through the negative feedback between pco2 and silicate weathering seafloor spreading the major control of co2 degassing seems to have remained relatively constant alternative explanation known as uplift driven climate change hypothesis proposes that tectonic uplift may have enhanced the sink of atmospheric co2 by silicate weathering and thus produced the decline of pco2 however increasing weathering sink of co2 could deplete atmosphere all of its co2 within several million years while holding volcanic outgassing constant in this work major fluxes of long term carbon cycle are calculated based on a reverse model constrained by marine c sr and os isotopic records and the spreading rate of sea floor weathering of island basalt and continental silicate rocks are separated in the new model the results indicate a long term decline of island basalt weathering in consistent with the global cooling trend over the past 100 million years dramatic changes of the co2 fluxes associated continental silicate weathering reverse weathering volcanic degassing and the growth of organic carbon reservoir have been observed disturbance of atmospheric co2 cycle by these fluxes seems to be maintained by the concomitant adjustments of island basalt weathering that were sensitive to the pco2 controlled environment factors such as temperature and runoff the negative feedbacks between pco2 and weathering of island basalt might have played a significant role in stabilizing the long term carbon cycle

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

variability of carbonate diagenesis in equatorial pacific sediments deduced from radiogenic and stable sr isotopes the recrystallisation dissolution precipitation of carbonate sediments has been successfully modelled to explain profiles of pore water sr concentration and radiogenic sr isotope composition at different locations of the global ocean however there have been few systematic studies trying to better understand the relative importance of factors influencing the variability of carbonate recrystallisation here we present results from a multi component study of recrystallisation in sediments from the integrated ocean drilling program iodp expedition 320 321 pacific equatorial age transect peat where sediments of similar initial composition have been subjected to different diagenetic histories the peat sites investigated exhibit variable pore water sr concentrations gradients with the largest gradients in the youngest sites radiogenic sr isotopes suggest recrystallisation was relative rapid consistent with modelling of other sediment columns as the 87sr 86sr ratios are indistinguishable within 2 uncertainties from contemporaneous seawater 87sr 86sr ratios bulk carbonate leachates and associated pore waters of site u1336 have lower 87sr 86sr ratios than contemporaneous seawater in sediments older than 20 2 ma most likely resulting from the upward diffusion of sr from older recrystallised carbonates it seems that recrystallisation at site u1336 may still be on going at depths below 102 5 rmcd revised metres composite depth suggesting a late phase of recrystallisation furthermore the lower sr ca ratios of bulk carbonates of site u1336 compared to the other peat sites suggest more extensive diagenetic alteration as less sr is incorporated into secondary calcite compared to the other peat sites u1336 has an inferred greater thermal gradient and a higher carbonate content the enhanced thermal gradient seems to have made these sediments more reactive and enhanced recrystallisation in this study we investigate stable sr isotopes from carbonate rich deep sea sediments for the first time pore water 88 86sr increases with depth from 0 428 to values reaching up to 0 700 at site u1336 documenting an isotope fractionation process during recrystallisation secondary calcite preferentially incorporates the lighter sr isotope 86sr leaving pore waters isotopically heavy the 88 86sr values of the carbonates themselves show more uniform values with no detectable change with depth carbonates have a much higher sr content and total sr inventory than the pore waters meaning pore waters are much more sensitive to fractionation processes than the carbonates the 88 86sr results indicate that pore water stable sr isotopes have the potential to indicate the recrystallisation of carbonate sediments

minimal influence of recrystallization on middle miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial pacific stable carbon and oxygen isotopes 13c and 18o of foraminiferal tests are amongst the most important tools in paleoceanography but the extent to which recrystallization can alter the isotopic composition of the tests is not well known here we compare three middle miocene 16 13 ma benthic foraminiferal stable isotope records from eastern equatorial pacific sites with different diagenetic histories to investigate the effect of recrystallization to test an extreme case we analyzed stable isotope compositions of benthic foraminifera from integrated ocean drilling program site u1336 for which the geochemistry of bulk carbonates and associated pore waters indicates continued diagenetic alteration in sediments 14 7 ma despite this diagenetic overprinting the amplitudes and absolute values of the analyzed u1336 stable isotopes agree well with high resolution records from better preserved sites u1337 and u1338 nearby our results suggest that although benthic foraminiferal tests of all three sites show some degree of textural changes due to recrystallization they have retained their original stable isotope signatures the good agreement of the benthic foraminiferal stable isotope records demonstrates that recrystallization occurred extremely rapidly 100 kyr after deposition this is confirmed by the preservation of orbital cyclicities in u1336 stable isotope data and 18o values being different to inorganic calcite that would precipitate from u1336 pore waters during late recrystallization the close similarity of the benthic foraminiferal stable isotope records between the sites allows the well resolved paleomagnetic results of site u1336 to be transferred to sites u1337 and u1338 improving the global geological timescale

strontium isotopic compositions and paleoceanographic implication of fossil manganese nodules in dsdp odp cores leg 1 126 abstract strontium isotopic compositions of acetic acid hoac leachate fractions of eight manganese oxide deposits from the modern seafloor and of twenty one buried manganese nodules from cretaceous to recent sediments in dsdp odp cores were measured 87sr 86sr ratios of hoac leachates in all modern seafloor manganese oxides of various origins are identical with present seawater the 87sr 86sr ratios of the hoac leachates of buried nodules from dsdp odp cores are significantly lower than those of nodules from the modern seafloor and are mostly identical with coeval seawater values estimated from the age of associated sediments it is suggested that the buried nodules in dsdp odp cores are not artifacts transported from the present seafloor during the drilling process but are in situ fossil deposits from the past deep sea floor during cretaceous to quaternary periods the formation of deep sea fossil nodules prior to the formation of antarctic bottom water aabw indicates that the circulation of oxygenated deep seawaters have activately deposited manganese oxides since the eocene epoch or earlier

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

chemistry of interstitial waters and sediments in the norwegian greenland sea deep sea drilling project leg 38 interstitial waters of several sites drilled during the deep sea drilling project in the norwegian greenland sea during leg 38 have revealed substantial changes in dissolved constituents and in the 18o16o composition of interstitial waters studies of the chemical composition of the bulk sediments and their 1 m fraction indicate the presence of large amounts of volcanic ash especially in sites close to iceland the presence of authigenic clay minerals illite smectite suggests that alteration of this volcanic ash is an important process a study of site 348 reveals that dissolved ca gradients are caused mainly by transport from the underlying basalts but that decreases in mg and 18o h2o are largely due to reactions involving alteration of volcanic ash in the sediments studies of 87sr86sr distributions of dissolved sr confirm this process in those sites with high contents of volcanic matter on the other hand in sites where the chemical composition of dissolved constituents has been little influenced by alteration reactions 87sr86sr ratios reveal complete diffusive exchange with present day seawater

compositions and sources of fluids in sediments of the peru subduction zone sediments of the middle to lower slope regions of the peru continental margin drilled during ocean drilling program odp leg 112 contain interstitial waters with chloride concentrations as low as 454 mm cl equivalent to 20 dilution of seawater with fresh water strontium isotope data suggest that two separate fluid regimes are present a northerly one in which fluids contain more radiogenic sr than seawater 87sr 86sr up to 0 70996 possibly originating from continental crust and a southerly regime where fluids contain sr less radiogenic than seawater 87sr 86sr down to 0 70722 and which are also enriched in ca2 and depleted in mg2 and 18o that appear to have interacted with oceanic basement o c and he isotopic data support these interpretations

palaeoclimatic and chronostratigraphic interpretations from strontium carbon and oxygen isotopic ratios in molluscan fossils of quaternary seoguipo and shinyangri formations cheju island korea abstract palaeotemperatures and chronostratigraphies of the quaternary seoguipo and shinyangri formations cheju island south korea were investigated in terms of the strontium oxygen and carbon isotopic compositions of carbonate mollusc shells the 87sr 86sr ratios of mollusc shells from the seoguipo formation range from 0 70911 to 0 70914 which yield carbonate ages of 0 5 1 2 ma early to middle pleistocene using the linear equation between ages and 87sr 86sr ratios of quaternary seawater the 87sr 86sr ratio 0 70917 of aragonitic shells from the shinyangri formation provide late pleistocene ages 0 04 ma based on ams 14c dates of mollusc fossil shells from the shinyangri formation the depositional age of the formation has been extended to 1570 yr bp palaeotemperatures calculated on the basis of the oxygen isotopic composition of the calcitic mollusc shells from the seoguipo formation give a range of values from 12 6 to 19 1 c which is lower than the present day shallow seawater temperature 14 9 25 5 c in the vicinity of the seoguipo coast aragonitic mollusc shells from the shinyangri formation provide oceanic temperatures ranging from 22 5 to 29 8 c which is higher than present day seawater temperatures 14 1 23 2 c the calculated palaeotemperatures of the seoguipo and shinyangri formations are inferred to reflect cold and warm currents flowing over cheju island during the pleistocene to holocene

evidence from fluid seeps atop serpentine seamounts in the mariana forearc clues for emplacement of the seamounts and their relationship to forearc tectonics abstract the mariana forearc is a non accretionary forearc with numerous seamounts dredge hauls from these seamounts are composed primarily of serpentinite indicating a non volcanic origin in addition dredged carbonate samples reveal 1 the presence of aragonite in water depths greater than the aragonite compensation depth 2 unusual porosity and cement types 3 light carbon and heavy oxygen isotopic compositions and 4 an unusual trace element geochemistry of aragonite and calcite these mineralogic petrologic and geochemical characteristics formed the basis of a prediction that methane bearing fluids are venting from these seamounts subsequent to this prediction submersible dives on a mariana forearc seamount found and sampled chimneys seeping cool water that contains dissolved methane the serpentine substrate beneath the chimneys appears to form from cold gravitational flows of serpentine material fluid inclusion contents of chimney samples also show an earlier history of methane as well as longer chain hydrocarbons aromatics and acetate ions drilling into the flank and the summit of this seamount by the ocean drilling program during leg 125 confirmed the presence of methane other light alkanes and organic acids in the present day interstitial pore fluid of the cores the presence of aromatic compounds and organic acids if derived from the maturation of organic compounds indicates a thermogenic origin for these volatiles strontium isotopic ratios of the aragonitic chimney samples and of the present day interstitial waters range from present day seawater values to significantly lower values the strontium isotopic ratios of the pore waters within the seamount trend toward a relatively less radiogenic composition with increasing depth below the seafloor this strontium isotopic signature is probably not the consequence of near surface processes but more likely a contribution from an igneous source deeper in the lithosphere the lack of a large accretionary prism in the mariana forearc removes the complication of fluid contribution from dewatering of the prism by compression during convergence as in the oregon washington or barbados margins the organic compounds in the fluid inclusions and interstitial pore fluids as well as the isotopic and the geochemical composition of the carbonates and the dissolved constituents suggest that fluids are derived from dewatering compression and dehydration of subducted sediments and the subducting plate furthermore the composition of the fluid is influenced by thermal maturation of organics in subducted sediments as well as by a contribution from a deep igneous source

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

a positive trend in seawater 87sr 86sr values over the early middle frasnian boundary late devonian recorded in well preserved conodont elements from the holy cross mountains poland abstract over the early middle frasnian boundary interval late devonian the oceans experienced major changes in global carbon cycling and nutrient dynamics with a prominent positive carbon isotope shift at the base of the palmatolepis punctata zone middle frasnian the aim of this study was to construct seawater 87 sr 86 sr ratio curves for the pa transitans pa hassi zonal interval using well preserved conodont apatite from two sections in the holy cross mountains south central poland the final curves suggest that seawater 87 sr 86 sr values were steady at 0 70794 0 70799 during the transitans zone but began to rise in the early punctata zone towards a value of 0 70814 in the late punctata zone an increase of 0 0002 the increase in seawater 87 sr 86 sr values over the early middle frasnian boundary appears to be the second of two prominent short term rises in 87 sr 86 sr values which led to an overall shift in values from a givetian plateau of between 0 70780 and 0 70785 to a late frasnian plateau of between 0 7080 and 0 7082 correlation with a regional positive 13 c anomaly and evidence for eutrophication in the marine environment suggests that the causes of these phenomena may be linked and that the positive 87 sr 86 sr shift was caused by an increase in the continental flux of sr to the oceans i e the weathering flux a possible explanation for an increase in the weathering flux is the denudation of a new acadian eovariscan orogen which would have been mostly weathered in the humid warm tropical equatorial region

rb sr systematics of vendian cambrian claystones from the east european platform implications for a multi stage illite evolution a combined mineralogical chemical morphological and rb sr isotopic study of blue clays from the lower cambrian lontova unit shows that these minerals contain three generations ofillite the oldest detrital 2m illite particles are typicauy round with sharp borders sometimes rolled up and have a minimum isotopic age of 722 13 ma this generation of illite is mainly concentrated in the 0 6 2 zm size fractions of the samples the second generation of illite is represented by well crystallized lath type particles of 0 1 zm size with an age of 533 8 ma considered to be the sedimentation age faulting and or regional emergence during the ordovician to early silurian time probably induced extensive circulations of subsurface waters which precipitated an additional 0 1 gm generation of low temperature lath type illite particles at 430 480 ma ago the precambrian cambrian boundary may be set at 530 10 ma based on the data presented here leaching of different clay subfractions by ammonium acetate shows that illite particles of different generations crystallizcd in environments with different svsr z6sr ratios the varied environmental sr isotopic ratios were at least in part due to local interactions between the interstitial waters and the sedimentary mass additionally the initial stsr s6sr ratios of the clay particles from argillaceous sedimentary rocks were mostly higher than that of marine st

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

the cenozoic seawater 87sr 86sr curve data review and implications for correlation of marine strata the strontium isotopic ratio 87sr 86sr in seawater changes slowly over geologic time this variation is caused by changes in the relative contribution of sr from various isotopically distinct sources within the crust the most important of these are high ratio sialic rocks from continents and low ratio mafic volcanic and mafic intrusive rocks from continental margins and ocean basins a plot of sr isotope ratio versus age for phanerozoic marine samples produces a curve exhibiting many episodes of increasing and decreasing values this variation can be used as a basis for temporal correlation of marine carbonate sulfate and phosphate sediments temporal correlations can be made between high latitude and low latitude sequences deepwater and shallow water sequences and normal marine and restricted marine hypersaline hyposaline sequences satisfactory biostratigraphic correlations between such sequences are often hampered by either the absence of age diagnostic fossils or by the provinciality of faunal and floral assemblages rapid change that took place in the 87sr 86sr of seawater during most of the cenozoic makes this era particularly well suited for precise temporal correlation the seawater curve for the cenozoic is subdivided into three segments quaternary to mid miocene mid miocene to late eocene and late eocene to early paleocene the mid miocene to late eocene curve segment exhibits a particularly steep slope making this a promising interval for high resolution stratigraphic correlation although current data generally support the present configuration of the seawater curve some revision of the curve is probably required in the vicinity of the oligocene eocene boundary establishment of the general configuration of the seawater curve for the cenozoic has promoted efforts to refine the curve on the basis of construction of detailed sr isotope profiles within individual stratigraphic sequences a sr isotope profile at deep sea drilling project dsdp site 590b suggests a complex neogene seawater curve characterized by minor slope changes in the pliocene and miocene these slope changes are not specifically identified in the seawater curve constructed from multilocation data on the basis of this more complex curve and in the absence of diagenetic complications the ultimate neogene stratigraphic resolution is estimated to range from 0 1 to 2 million years both the verification and the general stratigraphic applicability of this more complex neogene curve are largely dependent on the degree of preservation of the original seawater ratio in marine samples

numerical models of diagenesis sediment properties and pore fluid chemistry on a paleoceanographic transect blake nose ocean drilling program leg 171b a critical issue in many paleoceanographic studies is the potential of diagenetic processes to compromise the fidelity of geochemical proxies e g 18o in deep sea carbonate sediments and microfossils a recently established strategy for dealing with this issue is to drill depth transects in anomalously shallowly buried and therefore presumably well preserved target sediments here we report the results of an experiment designed to test the validity of this approach we apply a simple one dimensional numerical model to complex pore water chemical profiles for ca mg sr 87sr 86sr and 18o observed in a shallowly buried paleoceanographic transect of paleogene and cretaceous age drilled on blake nose during ocean drilling program leg 171b we show that it is possible to reproduce these complex pore water profiles simply by invoking 1 a deep seated zone of chemical reaction well below the recovered sections and 2 minimal chemical alteration within the overlying recovered sediments but significant restriction of advective flow by embedded low porosity layers these results suggest that the sediments recovered during ocean drilling program leg 171b can be considered to be virtually chemically inert at their present burial depth their carbonate recrystallization histories having been largely limited to events during early 10 ma timescale burial these findings support the strategy of selecting unusually shallowly buried sections for paleoceanographic transect drilling ironically however the very attraction of targeting such sections the lack of overlying sediments dictates that it is not possible to use pore water chemistry to constrain the early diagenetic histories of such sections because of the diffusion of the pore water signal through the sediment water interface diffusional loss may also account for the absence of pore water chemical anomalies associated with the ooze chalk transition at blake nose however our work suggests that traditional interpretations of this boundary as the inferred locus of maximum rates of carbonate recrystallization require reevaluation

lithium sources in pore fluids of peru slope sediments and implications for oceanic fluxes high li concentrations up to a maximum of 1155 m are observed in the pore fluids of the peru convergent margin slope sediments at ocean drilling program sites 683 and 685 9 s the li concentration depth gradients are twice as steep as at site 682 and 688 11 s within the sediments the most important li sources are from aluminosilicate minerals biogenic opal a contains little li and thus dilutes the li concentration of the bulk sediments the sediment compositions and the thermal regimes are similar at 9 and 11 s suggesting there is an additional non sedimentary source for the observed high li concentrations in the northern pore fluids at 9 s the 87sr 86sr ratios reach a maximum value of 0 709958 the observed radiogenic 87sr 86sr values in the pore fluids support the suggestion that the additional li may derive from exchange reactions with underlying continental crust the high concentrations of li at 11 s may derive from basalt alteration at moderate to high temperatures as suggested by the non radiogenic 87sr 86sr ratios in these pore fluids which reach a minimum value of 0 707218 based on 1 li concentrations in the pore fluids in slope sediments from peru and several other margins and 2 an approximate estimate of fluid flux from continental margins into the ocean continental margins provide an estimated 1 to 3 1010 moles li yr to the ocean this source of oceanic li which has not been considered previously is of the same order of magnitude as some estimates of hydrothermal and river li fluxes and may have important consequences for the oceanic li isotope budget the sink is unknown for this newly discovered and possibly large li source but it may be more pervasive low temperature alteration of oceanic basement than previously estimated or burial of mineral phases such as authigenic clay minerals or metal oxyhydroxides which may be li rich

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

lithologic controls on calcite recrystallization in cenozoic deep sea sediments abstract interpretations of calcite strontium calcium records in terms of ocean history and calcite diagenesis require distinguishing the effects on deep sea calcite sediments of changes in ocean chemistry of different mixes of calcite depositing organisms as sediment contributors through time and space and of the loss of sr during diagenetic calcite recrystallization in this paper sr ca and 18 o values of bulk calcium carbonate sediments are used to estimate the relative extent of calcite recrystallization in samples from four time points core tops 5 6 9 4 and 37 1 ma at eight ocean drilling program sites in the equatorial atlantic ceara rise and equatorial pacific ontong java plateau and two eastern equatorial pacific sites the possibility that site to site differences in calcite sr ca at a given time point originated from temporal variations in ocean chemistry was eliminated by careful age control of samples for each time point with sample ages differing by less than the oceanic residence times of sr and ca the sr ca and 18 o values of 5 6 and 9 4 ma samples from the less carbonate rich eastern equatorial pacific sites and ceara rise site 929 appear to be less diagenetically altered than the sr ca and 18 o values of contemporaneous samples from the more carbonate rich sites it is evident from these data that both sr ca and 18 o in bulk calcite have been diagenetically altered in some samples 5 6 ma and older these data indicate that noncarbonate sedimentary components like clay and biogenic silica have partially suppressed recrystallization at the lower carbonate sites sr ca data from the less altered carbonate poor sites indicate higher oceanic sr ca relative to today at 5 6 and 9 4 ma

resetting of mg isotopes between calcite and dolomite during burial metamorphism outlook of mg isotopes as geothermometer and seawater proxy abstract magnesium isotopes are an emerging tool to study the geological processes recorded in carbonates calcite due to its ubiquitous occurrence and the large mg isotope fractionation associated with the mineral has attracted great interests in applications of mg isotope geochemistry however the fidelity of mg isotopes in geological records of carbonate minerals e g calcite and dolomite against burial metamorphism remains poorly constrained here we report our investigation on the mg isotope systematics of a dolomitized middle triassic geshan carbonate section in eastern china magnesium isotope analysis was complemented by analyses of sr c o isotopic compositions major and trace element concentrations and petrographic and mineralogical features multiple lines of evidence consistently indicated that post depositional diagenesis of carbonate minerals occurred to the carbonate rocks magnesium isotope compositions of the carbonate rocks closely follow a mixing trend between a high 26mg dolomite end member and a low 26mg calcite end member irrespective of sample positions in the section and calcite dolomite ratio in the samples by fitting the measured mg isotope data using a two end member mixing model an inter mineral 26mgdolomite calcite fractionation of 0 72 was obtained based on the experimentally derived mg isotope fractionation factors for dolomite and calcite a temperature of 150 190 c was calculated to correspond to the 0 72 26mgdolomite calcite fractionation such temperature range matches with the burial thermal history of the local strata making a successful case of mg isotope geothermometry our results indicate that both calcite and dolomite had been re equilibrated during burial metamorphism and based on isotope mass balance of mg the system was buffered by dolomite in the section therefore burial metamorphism may reset mg isotope signature of calcite and mg isotope compositions in calcite should be dealt with caution in studies of carbonate rocks with thermal history by contrast mg isotopes of dolomite are less prone to post depositional resetting due to a number of properties including high mg abundance and high thermodynamic stability and mg isotopes in dolomite may be a more robust recorder for original carbonate precipitates

submarine thermal springs associated with young volcanoes the teahitia vents society islands pacific ocean abstract hydrothermal solutions were sampled close to two summits of teahitia a submarine volcano from the southern extension of the society volcanic chain the temperatures measured within two vents were 30 c the vent solutions have a ph value around 5 3 and are enriched in fe mn si ba li and rees relative to ambiant seawater but show only a small decrease in mg and so4 concentrations the lowest measured 87sr 86sr is 0 70867 while the end is identical to those of the surrounding alkali basalt 2 5 the vent solutions from teahitia have chemical characteristics similar to pele s vents loihi seamount another mid plate volcano the exact temperature of seawater basalt interaction is difficult to constrain however the absence of positive eu anomaly in the fluids the particles and in the hydrothermal deposits from teahitia seems to exclude the participation of a high temperature component comparable as those involved in mid ocean ridge axis vents

fluid circulation in the oceanic crust contrast between volcanic and plutonic regimes vein carbonates from a variety of ocean crust environments have been analyzed for sr contents and sr and oxygen isotopic compositions veins from upper crustal lithologies typically have low formation temperatures 30 times that of hot smoker vent fluids veins from the gabbro lithologies at site 735b show both high 150 c and very low 10 c formation temperatures the high temperature carbonate veins have a large basaltic component low 87sr 86sr with low ca sr and probably formed before unroofing of this deep crustal block the low temperature veins have only a minor basaltic component and formed after unroofing but within 0 10 m y of crust formation hot smoker vent fluids represent the low ca sr limit of fluids recorded by carbonate veins and thus cannot describe the totality of the seawater ocean crust ca sr exchange budget

stable isotopes in late middle eocene to oligocene foraminifera oxygen and carbon isotope ratios in eocene and oligocene planktonic and benthic foraminifera have been investigated from atlantic indian and pacific ocean locations the major changes in eocene oligocene benthic foraminiferal oxygen isotopes were enrichment of up to l in 18o associated with the middle late eocene boundary and the eocene oligocene boundary at locations which range from 1 to 4 km paleodepth although the synchronous eocene oligocene 18o enrichment began in the latest eocene most of the change occurred in the earliest oligocene the earliest oligocene enrichment in 18o is always larger in benthic foraminifera than in surface dwelling planktonic foraminifera a condition that indicates a combination of deep water cooling and increased ice volume planktonic foraminiferal 18o does not increase across the middle late eocene boundary at our one site with the most complete record deep sea drilling project site 363 walvis ridge this pattern suggests that benthic foraminiferal 18o increased 40 m y ago because of increased density of deep waters probably as a result of cooling although glaciation cannot be ruled out without more data stable isotope data are averaged for late eocene and earliest oligocene time intervals to evaluate paleoceanographic change average 18o of benthic foraminifera increased by 0 64 from the late eocene to the early oligocene 18o maximum whereas the average increase for planktonic foraminifera was 0 52 this similarity suggests that the eocene oligocene boundary 18o increase was caused primarily by increased continental glaciation coupled with deep sea cooling by as much as 2 c at some sites average 18o of surface dwelling planktonic foraminifera from 14 upper eocene and 17 lower oligocene locations when plotted versus paleo latitude reveals no change in the latitudinal 18o gradient the oligocene data are offset by 0 45 also believed to reflect increased continental glaciation at present there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from eocene to oligocene time using oxygen isotopes

impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern hikurangi margin abstract we present geochemical data collected from volcanic ash bearing sediments on the upper slope of the northern hikurangi margin during the rv sonne so247 expedition in 2016 gravity coring and seafloor drilling with the marum mebo200 allowed for collection of sediments down to 105 meters below seafloor mbsf release of dissolved sr2 with isotopic composition enriched in 86sr 87sr 86sr minimum 0 708461 at 83 5 mbsf is indicative of ash alteration this reaction releases other cations in the 30 70 mbsf depth interval as reflected by maxima in pore water ca2 and ba2 concentrations in addition we posit that fe iii in volcanogenic glass serves as an electron acceptor for methane oxidation a reaction that releases fe2 measured in the pore fluids to a maximum concentration of 184 m several lines of evidence support our proposed coupling of ash alteration with fe mediated anaerobic oxidation of methane fe aom beneath the sulfate methane transition smt which lies at 7 mbsf at this site in the 30 70 mbsf interval we observe a concurrent increase in fe2 and a depletion of ch4 with a well defined decrease in 13 c ch4 values indicative of microbial fractionation of carbon the negative excursions in 13 c values of both dic and ch4 are similar to that observed by sulfate driven aom at low so 4 2 concentrations and can only be explained by the microbially mediated carbon isotope equilibration between ch4 and dic mass balance considerations reveal that the iron cycled through the coupled ash alteration and aom reactions is consumed as authigenic fe bearing minerals this iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals as estimated from sequential extraction analyses using a numerical modeling approach we estimate the rate of fe aom to be on the order of 0 4 mol cm 2 yr 1 which accounts for 12 of total ch4 removal in the sediments although not without uncertainties the results presented reveal that fe aom in ash bearing sediments is significantly lower than the sulfate driven ch4 consumption which at this site is 3 0 mol cm 2 yr 1 we highlight that fe iii in ash can potentially serve as an electron acceptor for methane oxidation in sulfate depleted settings this is relevant to our understanding of c fe cycling in the methanic zone that typically underlies the smt and could be important in supporting the deep biosphere

strontium and its isotopic composition in interstitial waters of marine carbonate sediments abstract the concentrations and isotopic compositions of strontium in interstitial waters from several dsdp sites where sediments consist chiefly of carbonate oozes and chalks are used as indicators of carbonate diagenesis by reference to a recently produced curve showing detailed variations in the87sr 86sr ratio of seawater with time carbonate sediments of the walvis ridge show increases in interstitial sr2 concentrations in the upper carbonate ooze sections with the highest concentrations near the ooze chalk boundary where maximum rates of carbonate recrystallization occur below this in situ production of sr2 diminishes and there is a diffusive flux of sr to an underlying sink presumably volcanogenic sediments or basalts leading to sr isotopic disequilibrium between carbonates and interstitial waters in some other sites however there is no apparent sr sink at depth and isotopic equilibrium is retained overall diffusive smoothing of profiles exerts an important control on the87sr 86sr ratios although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of mg2 loss and reflect a combination of a flux of sr2 from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter

nodular celestite in the chihsia formation middle permian of south china the middle permian chihsia formation of south china accumulated on a shallow shelf and consists mainly of black to dark grey micritic limestone rich in chert nodules and organic matter a unique type of nodular crystal cluster is distributed widely in the carbonate succession most crystal clusters consist of calcite some however are composed of celestite and geochemical microscopic and crystal morphological data suggest that celestite was the precursor of the calcite the celestite developed displacively within the sediments during early diagenesis before compaction and before local dolomitization of the host rock similar strontium isotopic values were obtained from the celestite clusters replacement calcite vein calcite and host rock the values are within the range of middle permian sea water the strontium in the celestite was furnished chiefly by either diagenetic alteration of strontium rich marine aragonite to strontium poor calcite or aragonite dissolution induced by aerobic oxidation of organic matter or both the sulphur isotopic values of the celestite are about 6 11 heavier than the sulphur isotopic value of sulphate in coeval sea water based on geological context this difference is attributed to microbial reduction of porewater sulphate in the chihsia sediments

sr isotopes as tracers in volcanic derived clay of martinique island lesser antiles hydrothermal vs seawater alteration abstract clay minerals in tertiary volcano sedimentary formations of martinique result from the alteration of pyroclastic and volcanoclastic rocks by hydrous fluids they consist exclusively of smectites of the beidellitic group their chemistry results from leaching of rb sr and k from volcanic material even though they are intercalated with typical marine deposits these minerals show no chemical or isotopic equilibration with seawater however they often contain more radiogenic sr than arc volcanics of the same age this radiogenic sr is similar to that released during magmatic crustal contamination and was driven by fluids that formed the hydrothermal clays in the volcanic lava flows pseudoisochrons suggesting mixing lines with low to very high radiogenic sr are recognized in clay minerals and volcanics indicating participation of fluids of different origins

the climatology of the stratospheric thin air model an improved two and a half dimensional chemical dynamical radiative model shows remarkably realistic behaviour in a number of respects the stratospheric mesospheric westerly jet slopes equatorwards with height and is split at mid latitudes in the southern hemisphere the parametrized orographic gravity waves exert a mid latitude drag and are important in splitting the jet and are possibly important in pre conditioning the stratosphere for a sudden warming a large easterly drag is required in the winter high latitude mesosphere in order to obtain a tropical mesospheric westerly jet the summer easterly jet maximum lies above the tropospheric jet due to gravity wave absorption in the lower stratosphere very realistic annual and semi annual cycles are produced in the model with a mesospheric semi annual oscillation forced by tidal drag and gravity waves planetary wave temperatures are also modelled well and wave amplitudes are correlated with the westerly jets in the lower stratosphere zonalmean ertel s potential vorticity gradients strongly influence the wave activity horizontal convergence and heating rates with descent being strongest equatorwards of the vortex edge this forms the basis for an explanation of the inter hemispheric asymmetry in the ozone column nitrous oxide distributions indicate too much equatorial ascent but show a double peak connected with the tropical circulation and steep horizontal gradients near the winter vortex edge

strontium isotope stratigraphy of the comanchean series in north texas and southern oklahoma pioneering studies in north texas and adjacent oklahoma played an important role in the paleontologic and stratigraphic development of the cretaceous in north america we have used the results from 135 strontium isotope analyses from fossils and rocks collected from 43 sites to define the middle cretaceous path of seawater 8 7 sr 8 6 sr during comanchean time the section represents an estimated duration of 19 3 m y from late aptian through late cenomanian the 8 7 sr 8 6 sr of seawater rises from 0 707318 13 errors given x 10 6 in the basal glen rose formation to reach a peak value of 0 707522 10 in the walnut clay then gradually declines to 0 707468 6 in the middle grayson marl the upper grayson marl and lower buda limestone 8 7 sr 8 6 sr values decline to 0 707422 9 then rise to near 0 707473 by the middle buda limestone the 8 7 sr 8 6 sr mean of the basal woodbine formation in the overlying gulfian series is in agreement with the middle buda value thirty of the analyzed samples yielded ratios higher than the mean determined for corresponding stratigraphic units the 8 7 sr 8 6 sr ratios from whole rock limestones and spar fillings of shells are inconsistent and more radiogenic than the best shell material all but two samples yielding aberrant ratios could be identified by using appearance and trace element content isotopic results from oyster and pectin shells with low mn and fe concentrations are remarkably consistent the agreement of results among samples collected from a stratigraphic interval at a single site with results from geographically removed sites in the same interval is strong evidence that these samples retain the original open marine 8 7 sr 8 6 sr of comanchean seawater the seawater variation defined here shows fine structure not apparent in previous work this definition can be used to better understand the complex relationship and timing between seawater 8 7 sr 8 6 sr variation ocean anoxic events mid ocean ridge production and subsequent climate and ocean productivity changes

the archean proterozoic transition evidence from the geochemistry of metasedimentary rocks of guyana and montana abstract chemical and isotopic compositions of ancient sedimentary rocks have in some cases provided evidence of first order changes yin the composition and extent of continental crust from the archean to the proterozoic we reversed the typical sampling pattern comparing metapelites and carbonates from proterozoic greenstone belts with those from an archean continental margin sequence and found the reverse of the typical age composition relations metapelites and volcaniclastic metagreywackes from the early proterozoic greenstone belts of northern guyana resemble those of many archean greenstone belts in ree trace and major element compositions mean ratios la sm 5 0 la th 5 1 eu eu 0 80 th u 3 4 median k 2 o na 2 o 0 8 schists from an archean continental marginal sequence in montana have compositions like many post archean metapelites derived from continental sources mean ratios la sm 6 8 la th 2 7 eu eu 0 67 th u 5 2 median k 2 o na 2 o 1 7 other archean continental basin sediments also resemble their post archean counterparts implying that upper continental crusts of these eras may not have differed significantly in these respects however temporal change may have occurred in upper crustal contents of ni and cr many archean clastic metasedimentary rocks of both continental and greenstone belt provenance have contents of these compatible elements higher than in their post archean equivalents dolomitic limestone from a greenstone belt of northern guyana has a very low 87 sr 86 sr ratio of 0 7007 such low values may reflect the local influence of mantle derived volcanic rocks during carbonate deposition diagenesis or metamorphism and they may not be reliable indicators of the evolution of sr in seawater archean dolomitic marbles from the continental marginal sequence of montana have 87 sr 86 sr ratios of 0 7065 and higher significantly more radiogenic than many accepted values for carbonates of archean greenstone belts

quantifying the impact of riverine particulate dissolution in seawater on ocean chemistry the quantification of the sources and sinks of elements to the oceans forms the basis of our understanding of global geochemical cycles and the chemical evolution of the earth s surface there is however a large imbalance in the current best estimates of the global fluxes to the oceans for many elements in the case of strontium sr balancing the input from rivers would require a much greater mantle derived component than is possible from hydrothermal water flux estimates at mid ocean ridges current estimates of riverine fluxes are based entirely on measurements of dissolved metal concentrations and neglect the impact of riverine particulate dissolution in seawater here we present 87sr 86sr isotope data from an icelandic estuary which demonstrate rapid sr release from the riverine particulates we calculate that this sr release is 1 1 7 5 times greater than the corresponding dissolved riverine flux if such behaviour is typical of volcanic particulates worldwide this release could account for 6 45 of the perceived marine sr budget imbalance with continued element release over longer timescales further reducing the deficit similar release from particulate material will greatly affect the marine budgets of many other elements changing our understanding of coastal productivity and anthropogenic effects such as soil erosion and the damming of rivers

the oligocene marine microfossil record age assessments using strontium isotopes a strontium isotope record for the latest eocene to earliest miocene has been produced for two well preserved deep sea sequences from the atlantic deep sea drilling project sites 516f and 563 which have magnetostratigraphic age control and four sequences from the pacific sites 77b 292 and 593 and atlantic site 529 which lack magnetostratigraphy the composite 87sr 86sr age record of sites 516f and 563 forms a comprehensive composite standard for the oligocene against which other sequences can be correlated unlike previously published 87sr 86sr oligocene sea water curves which have suggested that the sea water isotopic composition changed monotonically during the latest paleogene we note a distinct change in slope between the early oligocene 36 to 27 ma and the late oligocene to earliest miocene 27 to 20 ma the slope of the early oligocene segment is less steep than that of the late oligocene to earliest miocene we have fit two linear regression curves to the oligocene to early miocene seawater 87sr data of sites 516f and 563 which we use to establish sr isotope age relationships for the oligocene the 87sr age equations were used to evaluate the synchroneity of specific planktonic and calcareous nannofossil datum levels used to correlate oligocene sections although some datum levels appear to be synchronous between the atlantic and pacific our results show that others are diachronous along longitudinal gradients this is most evident in several last appearance datums that occurred earlier in the western equatorial pacific than in the eastern equatorial pacific this diachroneity extends into the atlantic where last occurrences were later than in the eastern equatorial pacific

evidence for slowly changing 87sr86sr in runoff from freshwater limestones of southern france abstract 87 sr 86 sr ratios have been determined in modern rivers and freshwater limestones dating from 65 ma to the present over an area extending from the pyrenees to the massif central southern france about 40 ma ago the alpine mountain range of the pyrenees was strongly uplifted by the alpine orogenic activity and its pre hercynian basement dominated by schists gneisses and granites was rapidly exposed from beneath its blanket of mesozoic marine limestones meanwhile the 87 sr 86 sr ratio of the rivers has remained remarkably constant in both space with the exception of the very few northernmost samples and time in this area extreme variations through the orogenic period are small with 87 sr 86 sr lying between 0 7073 and 0 7084 at 55 65 ma and 0 7077 0 7096 for the last 30 ma river sr is controlled by a nearly binary mixing of silicate 3 4 and 1 4 end members with negligible influence of evaporites it is inferred that the silicate sediment contribution ratio of the world average rivers to seawater sr changes at a very slow rate even taking major basaltic events into account does not alter this conclusion as their contribution to the river sr is very subordinated to other components it is inferred that the seawater 87 sr 86 sr secular main trend over the phanerozoic is controlled by hydrothermal alteration of oceanic basalts and slow variation of the limestone silicate contribution ratio to the riverine sr oceanic events changes in organic productivity and carbonate compensation depth ccd may produce intense short term variations but recovery of steady state seawater 87 sr 86 sr is delayed by 40 80 ma through diagenetic sr remobilization in carbonate sediments

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

isotopic evidence 87sr 86sr δ7li for alteration of the oceanic crust at deep rooted mud volcanoes in the gulf of cadiz ne atlantic ocean the chemical and isotopic composition of pore fluids is presented for five deep rooted mud volcanoes aligned on a transect across the gulf of cadiz continental margin at water depths between 350 and 3860 m generally decreasing interstitial li concentrations and sr 87 sr 86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin although highest li concentrations at the near shore mud volcanoes coincide with high salinities derived from dissolution of halite and late stage evaporites clayey terrigenous sediments are identified as the ultimate li source to all pore fluids investigated light delta li 7 values partly close to those of hydrothermal vent fluids delta li 7 11 9 parts per thousand indicate that li has been mobilized during high temperature fluid sediment or fluid rock interactions in the deep sub surface intense leaching of terrigenous clay has led to radiogenic sr 87 sr 86 ratios similar to 0 7106 in pore fluids of the near shore mud volcanoes in contrast non radiogenic sr 87 sr 86 ratios similar to 0 7075 at the distal locations are attributed to admixing of a basement derived fluid component carrying an isotopic signature from interaction with the basaltic crust this inference is substantiated by temperature constraints from li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures 200 degrees c for the least radiogenic pore fluids of the most distal location advective pore fluids in the off shore reaches of the gulf of cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous fine grained sediments resulting in a chemical and isotopic signature similar to that of fluids in near shore ridge flank hydrothermal systems this suggests that deep rooted mud volcanoes in the gulf of cadiz represent a fluid pathway intermediate between mid ocean ridge hydrothermal vent and shallow marginal cold seep due to the thicker sediment coverage and slower fluid advection rates the overall geochemical signature is shifted towards the sediment diagenetic signal compared to ridge flank hydrothermal environments c 2009 elsevier ltd all rights reserved

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

seawater circulation through the flank of the florida platform evidence and implications dense biological communities at the base of the florida escarpment depend on energy provided by reduced compounds for bacterial chemosynthetic production sharp gradients in the concentrations of ch4 h2s nh4 so42 cl na mg2 sr2 i and seabed 226ra2 exist in the sediments underlying these communities the compositions of this fluid departs from that of normal seawater indicating the importance of microbial and diagenetic reactions within the escarpment before it is advected to the seafloor the 87sr 86sr ratios in the seep fluids range from 0 70920 seawater to 0 70773 which requires addition of light mesozoic strontium 18o values 0 3 to 0 1 smow and d values 2 6 smov of these waters are similar to normal seawater values and do not indicate that either meteoric processes or gas hydrates are involved in the genesis of the seeping fluid concentrations of cl ca2 and na suggest that the fluids which arrive at the seafloor are a mixture of mostly seawater with 4 7 formation brine from within the florida bahama platform mesozoic brines within the florida platform occupy levels above the scarp base a density driven flow system in implied which involves mesozoic platform brines that are greatly diluted by seawater entrained through the flanks of the platform the observed depletion of sulfate in the seeping fluids requires that sulfate reduction must occur in the platform within the zone where the recharging seawater and platform brines mix in order to produce the high concentrations of biogenic methane observed methanogenesis is inferred to be occuring within the platform in a zone where sulfate reduction has gone to completion the zone where the mixing of brine and seawater occurs should be cooled by the flushing seawater and heavily corroded by under saturation occurring as a result of the mixing the platform interior mixing is non conservative because of the addition of light mesozoic sr2 and the relative depletion in mg2 with espect to cl ca2 and na2 concentrations the inferred uptake of mg2 and concurrent depletion of so42 on the flanks of this margin

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

seasonal and provenance controls on nd sr isotopic compositions of amazon rivers suspended sediments and implications for nd and sr fluxes exported to the atlantic ocean abstract this study reports daily water discharge and suspended sediment load concentrations and sm nd and rb sr isotopic systematics and major and trace elements concentrations of twelve monthly sampled suspended load sediments of the solimoes and madeira rivers the two major andean tributaries of the amazon during the year 2004 as observed in other long term monitoring studies of amazon rivers the maximum of suspended sediment load occurs before or during the rising water period i e during the rainy season in 2004 the solimoes river exported 289 10 6 tonnes of suspended sediments and the madeira river 294 10 6 tonnes which correspond to erosion rates of 129 and 214 t km 2 yr for the solimoes and madeira rivers basins respectively both the solimoes and madeira suspended sediments are enriched in lree over hree and exhibit similar mree enrichment the difference being that the madeira sediments are more fractionated than the solimoes ones when plotted in al 2 o 3 cao na 2 o k 2 o diagram the suspended sediments of the solimoes and madeira rivers exhibit two different weathering trends which suggests that these sediments evolved along two different trends starting from felsic rocks with different chemical compositions the nd isotopic compositions end of the solimoes sediments 8 9 to 9 9 are slightly more radiogenic than the corresponding values of the madeira sediments 10 8 to 12 1 the 87 sr 86 sr isotopic compositions of the madeira sediments 0 728 to 0 740 are significantly more radiogenic than those of the solimoes 0 713 to 0 717 together with other major elements and ree evidences these isotopic compositions suggest that the solimoes sediments are more influenced by andean volcanic arc detritus than the madeira sediments that might be due to input of young basaltic products owing to strong volcanic activity in ecuador mineralogical compositions as well as nd isotopic compositions do not vary seasonally based on our data set and on previous published studies we have calculated that the nd suspended sediment flux dominates the nd total flux i e dissolved suspended sediment exported to the atlantic ocean by the amazon river representing 98 of the nd total flux and having a global end isotopic composition of 10 3 contrary to nd isotopic compositions sr isotopic compositions vary seasonally in both rivers the explanation for this variation remains unclear we suspect increasing physical weathering during the rainy season to be the main cause of this seasonal control in favouring landslides and river bank erosion that might induce input of more radiogenic sediments not easily mobilized during low water level we calculated that the sr isotopic composition of the dissolved load exported by the amazon river to the atlantic ocean is not seasonally dependent and remain fairly constant 0 715 0 716 by contrast the sr isotopic composition of the suspended load is strongly affected by the seasonal variation varying from 0 714 in the dry season to 0 730 in the rainy season consequently the total sr isotopic composition dissolved suspended sediment is also seasonally controlled varying from 0 716 to 0 722 we finally suggest that large seasonally controlled sr isotopic variations of great river is a phenomenon that has been underestimated in previous paleo climatic and paleo oceanic studies and should be taken into account in further studies

stable δ13c δ18o and strontium isotopes through the paleocene at gebel aweina eastern tethyan region abstract stable 13 c 18 o and strontium 87 sr 86 sr isotopic records have been established through the paleocene section at gebel aweina in the eastern desert egypt the section has been formed in a shelf upper bathyal environment and spans the interval from planktonic foraminiferal zones p1d to p6a or p6b integrated evaluation of isotopic results and scanning electron microscope observations suggest that strontium and whole rock 13 c records reflect primarily original isotopic trends whereas 18 o and foraminiferal 13 c values have been severely affected by diagenesis the whole rock 13 c record exhibits a continuous increase of 4 from the early paleocene to middle late paleocene the increase is followed by a stepwise 13 c decrease of the same magnitude through the late late paleocene and onwards the gross trends of this 13 c record have earlier been registered in many coeval deep sea sections but there are also some significant disparities at aweina for example the paleocene carbon isotopic changes have a higher amplitude in the deep sea the mid to late paleocene 13 c increase has been interpreted to reflect high biological productivity and or changes in the global carbon mass balance the 13 c decrease in the upper part of the aweina section can be identified as the paleocene eocene transitional long term 10 3 kyr negative 13 c shift which may reflect a major reorganisation in global oceanic circulation patterns the well known latest paleocene deep sea benthic foraminiferal extinction event has been found in the upper part of the aweina section and coincides with a distinct and rapid 13 c decrease of 1 5 the benthic extinction event and the associated 13 c anomaly thus represent important stratigraphic markers also in more shallow environments the gebel aweina 13 c record shows considerably lower values compared to the global 13 c record during early and early late paleocene and in the latest paleocene in the early late paleocene foraminiferal zones p3a to the base of p4 the aweina 13 c values increase rapidly by 1 5 and converge with the global record thereafter the two records covary up to the benthic extinction event after which they diverge the convergence between the records may reflect sea level rise and more open water mass exchange between the eastern tethys and the world ocean the similarity of pilot 13 c records from greece and tunisia with the aweina record support this interpretation diagenetic processes however cannot be ruled out and further studies are required to determine the significance of the 13 c depletions in the eastern tethyan sediments the 87 sr 86 sr ratios through the paleocene at gebel aweina are remarkably invariable close to a value of 0 7077 this is the same trend that has been reported in some earlier detailed studies conducted on well preserved calcitic material from the paleocene indicating original sr isotopic signatures at gebel aweina the homogeneity of sr isotopic ratios throughout the paleocene contrasts with the prominent changes observed in the carbon isotope record indicating a decoupling of the mechanisms regulating the mass fluxes of these elements the invariable sr isotopic ratios suggest stable conditions as regards to relative changes in mass fluxes of riverine and or hydrothermal sr during the paleocene

evolution of the cenozoic carbon cycle the roles of tectonics and co2 fertilization cenozoic carbon fluxes associated with rock weathering sediment burial and volcanic degassing are calculated from the mass balance equations coupling marine isotopic records of carbon both organic and inorganic strontium and osmium the result is confirmed by the good match between modeled carbonate sedimentation rates and carbonate sedimentation rates previously integrated from ocean basins worldwide the coevolution between weathering and burial of carbonate suggests that marine carbonate accumulation was regulated mainly by the recycling of carbonate rocks which mediated the bicarbonate ion concentration of the oceans a reduction in co2 effusion to the atmosphere caused by reduced volcanic degassing from 52 to 15 ma and tectonically enhanced organic rock exhumation since 15 ma is also observed these changes in co2 effusion are balanced by concomitant changes in co2 sequestration by silicate weathering and organic carbon burial importantly we demonstrate a clear decoupling of modeled silicate weathering rates from global climate over the last 15 ma this observation is inconsistent with temperature mediated mineral dissolution acting as the key mechanism facilitating the co2 silicate weathering feedback process however we instead observe a clear coupling positive correlation between modeled silicate weathering organic carbon burial and atmospheric co2 concentration we suggest that co2 fertilization effects on terrestrial biomass productivity and plant weathering could have represented a major negative feedback process helping to balance atmospheric co2 at least during the cenozoic ice house periods

tertiary paleoceanic chemical variability unintended consequences of simple geochemical models five lines of concrete quantitative evidence about oceanic chemical composition during the past 65 m y can provide insights into the controlling processes and their temporal variations but the system constraints are not yet fully understood the calcium carbonate compensation depth mean carbon isotopic ratio and strontium isotopic ratio have all changed significantly during this time while changes in lithium to calcium and strontium to calcium ratios have been much smaller when these tracers are considered separately simple scenarios of changes in geochemical and geological factors can be used to explain the historical records these factors include 1 increases in continental chemical weathering rates and net continental fluxes to the oceans 2 changes in the isotopic composition of material weathered from continents to the oceans 3 decreases in the proportion of calcium carbonate deposited on continental shelves 4 changes in the deposition or weathering rates of certain types of sediments and 5 changes in hydrothermal circulation because these geochemical cycles are linked to each other and to others such as nutrients and global atmospheric carbon dioxide an explanation invoked for one tracer must satisfy the direction magnitude and timing of the patterns for all the tracers several simple scenarios for geochemical variations have been evaluated for their consequences both intended and unintended and compared to the historical records despite the attractiveness and possible justifications of some simple hypotheses for example decreases in organic carbon burial rates increases in carbonate weathering rates on the continents or increases in all continental weathering rates no one simple scenario appears to be consistent with both the timing and magnitude of the changes observed during the past 65 m y for all tracers considered the contradictions uncovered can be useful in defining what knowledge is crucial to further understanding of oceanic chemical history better knowledge is needed of absolute deep ocean sediment accumulation rates and their temporal variability of the extent and time scale of variability in the net carbon isotope input to the ocean from continental weathering of steady state fluxes for oceanic mass balances and the extent to which these mass balances approach steady state behavior and of the links and interactions between the geochemical cycles of various elements

constraining the marine strontium budget with natural strontium isotope fractionations 87sr 86sr δ88 86sr of carbonates hydrothermal solutions and river waters we present strontium sr isotope ratios that unlike traditional 87sr 86sr data are not normalized to a fixed 88sr 86sr ratio of 8 375209 defined as 88 86sr 0 relative to nist srm 987 instead we correct for isotope fractionation during mass spectrometry with a 87sr 84sr double spike this technique yields two independent ratios for 87sr 86sr and 88sr 86sr that are reported as 87sr 86sr and 88 86sr respectively the difference between the traditional radiogenic 87sr 86sr normalized to 88sr 86sr 8 375209 and the new 87sr 86sr values reflect natural mass dependent isotope fractionation in order to constrain glacial interglacial changes in the marine sr budget we compare the isotope composition of modern seawater 87sr 86sr 88 86sr seawater and modern marine biogenic carbonates 87sr 86sr 88 86sr carbonates with the corresponding values of river waters 87sr 86sr 88 86sr river and hydrothermal solutions 87sr 86sr 88 86sr hydend in a triple isotope plot the measured 87sr 86sr 88 86sr river values of selected rivers that together account for not vert similar18 of the global sr discharge yield a sr flux weighted mean of 0 7114 8 0 315 8 the average 87sr 86sr 88 86sr hydend values for hydrothermal solutions from the atlantic ocean are 0 7045 5 0 27 3 in contrast the 87sr 86sr 88 86sr carbonates values representing the marine sr output are 0 70926 2 0 21 2 we estimate the modern sr isotope composition of the sources at 0 7106 8 0 310 8 the difference between the estimated 87sr 86sr 88 86sr input and 87sr 86sr 88 86sr output values reflects isotope disequilibrium with respect to sr inputs and outputs in contrast to the modern ocean isotope equilibrium between inputs and outputs during the last glacial maximum 10 30 ka before present can be explained by invoking three times higher sr inputs from a uniquely glacial source weathering of shelf carbonates exposed at low sea levels our data are also consistent with the weathering peak hypothesis that invokes enhanced sr inputs resulting from weathering of post glacial exposure of abundant fine grained material

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

the rate and consequences of sr diagenesis in deep sea carbonates we have used a diffusion advection reaction model for sr exchange during deep sea carbonate diagenesis to determine the rate and consequences of sr exchange between porewaters and bulk carbonate at six dsdp sites 590b 575 593 516 305 and 289 where the required sr concentration and isotopic composition data for the interstitial waters are available from the literature the model can reproduce both the sr2 and 87sr 86sr profiles in the porewaters at each of the sites by adjusting the rate of sr exchange due to solution reprecipitation as a function of sediment age we find that the rate of solution reprecipitation at all of the sites is highest for the youngest sediment 1 10 m y and decreases by about an order of magnitude over the first 10 m y of sediment age the effect of this exchange on the properties of the bulk carbonate is to reduce the sr content by 5 25 depending primarily on the sedimentation rate and shift the 87sr 86sr by as much as 0 00004 from the value the sediment had when first deposited isotopic shifts of this magnitude are large compared to present analytical uncertainties and therefore should be corrected for when using bulk carbonate 87sr 86sr for stratigraphic correlation the average sr loss in the carbonate sections studied is about 15 from which we conclude that the sr flux from carbonate sediments to the overlying ocean is of the order of 15 of the riverine sr flux we also show that the isotopic composition of the diagenetic sr flux is at all times quite close to the contemporaneous seawater value and therefore this flux plays a very minor role in the overall sr budget that determines the sr isotopic composition of seawater the range of sr losses from bulk carbonate due to diagenesis that we calculate is too small to account for the typical decrease in sr content seen in pelagic carbonates as a function of age about 70 over the first 100 m y we conclude that this decrease is not the result of diagenesis and must involve some changing property of the ocean itself

reevaluation of early oligocene eocene and paleocene seawater strontium isotope ratios using outcrop samples from the u s gulf coast the cenozoic strontium isotope 87sr 86sr variation in seawater is largely defined using deep sea drilling project dsdp samples examination of non dsdp results particularly for the paleogene suggest that the original seawater curve of burke et al 1982 may lie above the true seawater ratio during this time to investigate this possibility we analyzed the 87sr 86sr for 230 paleogene rock and shell samples from the 83 sites in alabama mississippi and louisiana many of the samples are from classic sections on which the gulf coast paleogene stratigraphy was originally defined multiple analyses of samples from these units show very little scatter and in most cases precise agreement is obtained among geographically separated collection sites we believe that analysis of multiple samples from a unit of established age collected at more than one site yields results that most accurately define the actual seawater sr isotope ratio at any given time results from these units define a seawater variation line that tracks well within the range of dsdp data but is generally below the original seawater line of burke et al 1982 it is often assumed that samples from continental settings will exchange with high ratio sr thereby raising 87sr 86sr values our gulf coast samples which are derived from a continental setting yield individual 87sr 86sr values that are both higher and lower than the estimated contemporaneous seawater ratio an analysis of our gulf coast data and dsdp results show that the direction of isotopic exchange cannot be confidently predicted for individual samples based solely on their derivation from either continental or oceanic settings

a study of celestine equilibrium in marine sediments using the entire odp iodp porewater data base abstract the stability of celestine srso 4 in marine sediments has been investigated through the calculation of its saturation index at the in situ temperature and pressure using the entire odp iodp porewater composition data base 14 416 samples recovered from sediments collected during 95 odp and iodp legs that has been thoroughly corrected for missing data and inconsistencies the porewater in situ pressure has been obtained from depth data and the in situ sample temperature has been calculated from the bottom seawater temperature and from the measured thermal gradient when the latter is unavailable a default value of 35 c km or an assumed gradient similar to that of a site located close to the study area has been used molarities have been converted to molalities through the calculation of the porewater densities which have represented by an empirical function of the total dissolved solids load up to 150 g l ocean bottom waters are largely undersaturated with respect to celestine yet sediment porewater saturation is not uncommon it is reached in 83 boreholes i e about 10 of all boreholes drilled during 22 odp iodp legs celestine equilibrium can be reached through two different non exclusive causes a strontium increase in porewater linked to the dissolution of sr rich aragonite or biogenic calcite and precipitation of sr poor calcite carbonate recrystallization or an increase in the strontium and sulfate porewater concentrations linked to a salinity increase due to the presence of brines sediments at most of the sites exhibiting celestine equilibrium share common characteristics such as a carbonate rich lithology typically higher than 80 wt and a low organic carbon content generally below 1 wt these results indicate that modification of porewaters during burial diagenesis can easily lead to celestine saturation especially in carbonate rich sediments we then briefly discuss former interpretations of the presence of celestine in ancient and recent marine sediments as well as the consequences of the incorporation of celestine formation in diagenetic models using the porewater sr content and sr isotopic composition

repeated occurrences of methanogenic zones diagenetic dolomite formation and linked silicate alteration in southern bering sea sediments bowers ridge iodp exp 323 site u1341 abstract diagenetic precipitates such as dolomite and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments a 600 m thick sedimentary section recently drilled at integrated ocean drilling program iodp site u1341 on bowers ridge southern bering sea provides insight into such a 4 3 ma old paleo diagenetic archive hard lithified calcite dolomite layers and laminae of disseminated carbonate were recovered in diatom rich sediments over a depth range of 400 m carbon isotope values of the diagenetic carbonates between 16 6 and 14 4 vpdb and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon dic during elevated rates of organic carbon mineralization primarily via sulfate reduction at shallow sediment depth below the paleo seafloor diagenetic carbonates at 280 440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane aom at sulfate methane transition zones smtz these microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2 58 2 51 ma a minimum in sulfate concentrations in modern porewaters and low sedimentary ba al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone the minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations less radiogenic strontium and isotopically light calcium in the porewater it is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater the isotopic composition of porewater calcium was also influenced by ammonium calcium exchange on clay minerals and carbonate recrystallization our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites 2000 m water depth over prolonged timescales it shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization

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

fluid evolution and authigenic mineral paragenesis related to salt diapirism the mercator mud volcano in the gulf of cadiz the formation of mud volcanoes in the gulf of cadiz is closely linked to diapirism in the deep subsurface the mercator mud volcano mmv is a rare example where diapiric emplacement in addition to being key for upward fluid migration is also an important zone for fluid and mineral diagenesis the most intriguing findings in the near surface muds of the mmv are extremely high salinities of up to 5 2 m of nacl from diapiric and evaporitic halite dissolution and the occurrence of authigenic gypsum and anhydrite crystals both of which have not been observed to date in the gulf of cadiz employing a thermodynamic model we elucidate how the interplay of temperature pulses strong salinity gradients and fluid flow dynamically drive mineral dissolution and re formation the strong increase in salinity in the pore fluids has important implications for thermodynamic equilibria by significantly lowering the activity of water thereby raising the gypsum anhydrite transition zone from 1 km to about 400 m sediment depth at the mmv this transition is further shifted to immediately below the seafloor during intervals of active mud and fluid expulsion when the mv surface temperature is heated up to at least 30 c as a consequence precipitation of authigenic gypsum near the sediment surface 1 2 mbsf has been linked to the dissolution of evaporites below the mmv more precisely the mechanisms generating supersaturation in the ascending gypsum saturated mmv fluids are 1 the slow and constant cooling of these fluids along the geothermal gradient during their ascent leading to formation of ubiquitous micro crystals and 2 the more rapid cooling after a heat pulse or transport from greater and warmer depth during an active mud volcano phase leading to the precipitation of cm scale gypsum crystals or even fist size concretions the mmv fluids approaching the salt diapir from farther below have experienced a genesis similar to those of other mud volcanoes in the gulf of cadiz located above deep rooted faults these processes include clay mineral dewatering thermogenic degradation of organic matter and deep high temperature leaching of terrigenous sediments or continental crust

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

increased fluid flow activity in shallow sediments at the 3 km long hugin fracture in the central north sea the north sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species such as methane from the earth s interior to its exterior here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered 3 km long hugin fracture in the central north sea although venting of gas bubbles was not observed concentrations of dissolved methane were significantly elevated up to six times background values in the water column at various locations above the fracture and microbial mats that form in the presence of methane were observed at the seafloor seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane sediment porewaters recovered in close proximity to the hugin fracture indicate the presence of fluids from two different shallow 500m sources i a reduced fluid characterized by elevated methane concentrations and or high levels of dissolved sulfide up to 6 mmol l 1 and ii a low chlorinity fluid cl 305 mmol l 1 that has low levels of dissolved methane and or sulfide the area of the seafloor affected by the presence of methane enriched fluids is similar to the footprint of seepage from other morphological features in the north sea

late thermal evolution of the oman mountains subophiolitic windows apatite fission track thermochronology in the southern oman mountains high pressure metamorphic rocks of continental origin crop out beneath the cretaceous samail ophiolitic nappe we collected 14 samples from 15 to 1200 m above sea level and at various structural levels that show apatite fission track ages between 40 7 and 55 5 ma the mean confined track lengths vary from 13 08 to 13 70 m fission track data optimization shows that the subophiolitic units cooled slowly below 60 c at ca 53 ma then remained at low temperature until ca 19 ma i e during the weak postorogenic subsidence of the obduction belt the subophiolitic basement was reheated to 70 80 c at ca 7 4 ma before final cooling the reheating event is correlated with the late miocene pliocene zagros compressional phase post oligocene heating up to 80 c is also documented by stable isotope study of the post nappe eocene oligocene onlap both the paleocene and the pliocene quaternary denudation rates are close to 0 3 mm yr and compatible with isostatically assisted erosion processes

sr isotopes in interstitial waters of marine sediments from deep sea drilling project cores sr isotopic compositions of interstitial sea waters have been documented in detail with cores from 37 deep sea drilling project sites the 87sr 86sr ratios are sensitive indicators of diagenetic reactions involving alteration of volcanic matter dispersed in sediments and recrystallization of carbonates effects of basalt alteration reactions except possibly for hydrothermal signals and of alteration of continental debris are minimal carbonate recrystallization has a significant effect on the geochemical mass balance of sr but diffusion of unradiogenic strontium from interstitial waters has only a small effect on the 87sr 86sr ratio of ocean water

paleoenvironmental conditions and strontium isotope stratigraphy in the paleogene gafsa basin tunisia deduced from geochemical analyses of phosphatic fossils fossil shark teeth and coprolites from three major phosphorite occurrences in the gafsa basin southwestern tunisia were investigated for their geochemical compositions to improve local stratigraphy and to better assess paleoenvironmental conditions 87sr 86sr isotope ratios of shark teeth from the early maastrichtian el haria formation and from the early eocene metlaoui s s formation yielded sr isotope ages of 68 1 and 47 9 1 3 ma respectively which accord with the expected stratigraphic positions of these sediments conversely shark teeth from the paleocene eocene chouabine formation have large variation in sr isotope ratios even within individual layers after statistical treatment and then elimination of certain outlier samples three age models are proposed and discussed the most reasonable solution includes three subsequent sr ages of 61 8 2 2 ma 57 2 1 8 and 54 6 1 6 for layer ix layers viii v and layers iv 0 respectively three scenarios are discussed for explanation of the presence of the outliers 1 diagenesis 2 re working and 3 locally controlled seawater sr isotope ratio the most plausible account for the higher 87sr 86sr ratios relative to the global ocean in some fossils is enhanced intrabasinal re working due to low sea level conversely the sample with lower 87sr 86sr than the global seawater may link to diagenesis or to seawater influenced by weathering of late cretaceous marine carbonates which latter is supported by model calculation as well the end values of these fossils are very similar to those reported for paleogene and late cretaceous tethyan seawater and are compatible with the above interpretations the relatively low oxygen isotope values in shark teeth from the topmost phosphate bed of the chouabine formation together with the sr isotope results point toward recovering better connections with the open sea these 18o data reflect elevated ambient temperature which may link to the early eocene climatic optimum

spatial 87sr 86sr variations in formation water and calcite from the ekofisk chalk oil field implications for reservoir connectivity and fluid composition abstract the 87 sr 86 sr ratios of formation waters from the chalk of the ekofisk oilfield were measured using a new technique extracting salt residues from the interstices of core samples in the danian ekofisk formation the chalk matrix itself has 87 sr 86 sr and 13 c values characteristic of danian seawater even though 18 o data indicate the presence of varying quantities of diagenetic carbonate cement in the ekofisk formation porewater 87 sr 86 sr values are very constant range 0 70786 0 70810 the formation water probably contains locally derived sr from carbonate plus a small contribution from noncarbonate minerals with higher 87 sr 86 sr in the underlying tor formation chalk samples containing a mixture of primary chalk and later cement have 87 sr 86 sr values that rise with depth to a maximum of 0 70865 much higher than contemporaneous seawater porewater 87 sr 86 sr values increase even more dramatically with depth to a maximum of 0 70988 both cement and waters have been influenced by sr with a high 87 sr 86 sr probably derived from underlying sedimentary rocks comparison with waters brought to the surface together with produced oil indicates that the depthwise increase in 87 sr 86 sr reflects an increase in salinity from 50 000to 140 000 mg l total solute content this suggests that zechstein evaporites may be the source of the radiogenic sr in the tor formation the difference in isotope composition between carbonates and waters in the ekofisk and tor formations indicates that their hydrochemical systems have evolved differently during diagenesis this is due to the barrier effect of the ekofisk tight zone a hardground at the base of the ekofisk formation which effectively splits the reservoir vertically into two this study thus provides a new way of determining the positions of permeability barriers in oil reservoirs also demonstrated for the first time is the existence of vertical variations in salinity of water in oil such variations could have important implications for the calibration of resistivity logs and calculation of the amount of oil in place

a review of methane and gas hydrates in the dynamic stratified system of the blake ridge region offshore southeastern north america abstract the blake ridge region lies on the passive margin of southeastern north america and contains a large amount of methane gas hydrate the methane and methane gas hydrate are predominantly biogenic apparently produced by co2 reduction reflection seismics indicate that bottom simulating reflectors bsrs enclose 55 000 km2 with high amplitude bsrs covering 26 000 km2 ocean drilling program odp leg 164 drilled three deep holes on a 10 km long transect sites 994 995 and 997 water depth 2770 2798 m based on sampling and geochemical thermal seismic and borehole geophysical measurements gas hydrates are most likely present between 190 and 450 m in sediment column gas hydrate is most often disseminated throughout the sediment column although concentrations occur within specific sedimentary horizons within supposed fault zones and at the base of gas hydrate stability bghs where methane recycling produces more pervasive concentrations of gas hydrate estimates of gas hydrate inventory are based on a variety of methods including geochemical proxies vertical seismic profiling electric logging and measurements of in situ methane over the entire sediment column at least 2 4 of pore space volume 1 2 sediment volume is occupied by methane gas hydrates but average and maximum estimates are 5 4 and 12 respectively extrapolation of vertical gas hydrate and methane inventory over the area containing high amplitude bsrs yields estimates of 67 406 gt gigatons 1015 g of methane gas hydrate or 9 52 gt of methane and 2 6 27 gt of methane occurring as gas bubbles below the bghs average values are 185 gt of gas hydrate and 24 gt of methane as gas hydrate any gas hydrate occurring outside the area underlain by bsrs as suggested by geochemical evidence or that associated with low amplitude bsrs may increase these estimates by an unknown factor various data give conflicting pictures of mass transport with blake ridge sediments the data can be reconciled by viewing the upper sedimentary section accumulation of gas hydrate in the blake ridge sediments depends on the amount of methane leaving the system versus the amount of methane entering the gas hydrate stability zone ghsz over geologic time although there are some point sources of methane loss from the sediments e g seafloor seeps odp site 996 of unknown magnitude most of the documented methane loss occurs through diffusion and consumption at the sulfate methane interface smi by anaerobic methane oxidation amo 2 108 mol year 1 methane entering the ghsz at a rate of 1 3 109 mol year 1 indicates a methane trapping efficiency of 85 129i measurements suggest that the blake ridge system has accumulated gas hydrate over as much as 55 million years

major cation gradients in dsdp interstitial waters the role of diffusive exchange between seawater and upper oceanic crust abstract interstitial water analyses from dsdp legs 1 53 were surveyed to identify sites at which the dominant process supporting gradients of major seawater cations is alteration of the underlying oceanic crust sites with thin sediment cover are generally without gradients sites with appreciable sediment accumulation are generally with gradients the transition is probably the result of cessation of convective circulation within the sediments a model is developed for the diffusive flux through an accumulating unreactive sedimentary layer supported by continued reaction within the crust the model is consistent with the observations provided that convection within the crust extends to depths 1 km and that convective flow within the sediments ends once 100 150 m of sediment accumulates the model suggests a steady state gradient inversely proportional to the sedimentation rate this dependence is apparent in the data however some variation in the reaction rate is also required fluxes of mg and na are systematically related to the flux of ca which because of its mobility serves as a tracer of hydrolysis of the basalt when the ca flux is low the mg flux serves as the principal sink for alkalinity produced during basalt hydrolysis when the ca flux is high the mg flux becomes diffusion limited and nabearing alteration phases must form the fluxes resulting from these alteration reactions exert little influence on either the chemistry of seawater or that of the upper crust

sr and 87sr 86sr in estuaries of western india impact of submarine groundwater discharge abstract dissolved sr and 87sr 86sr are measured in the narmada tapi and the mandovi estuaries linked to the eastern arabian sea the concentration of dissolved sr and 87sr 86sr in the river water endmembers show significant differences reflecting the lithologies they drain the distribution of sr in all these estuaries shows a near perfect two endmember mixing between river water and seawater suggesting that there is no discernible net addition removal of sr from the estuarine waters in contrast 87sr 86sr shows non conservative behaviour in all these estuaries its distribution exhibits significant departure from the theoretical mixing lines a likely mechanism for this difference in the behaviour between dissolved sr and its 87sr 86sr is the discharge of submarine groundwater sgd which can modify the 87sr 86sr of the estuarine waters by exchange with sediments without causing measurable changes in sr concentration the impact of such an exchange process on the 87sr 86sr of the estuaries and therefore on the sr isotope composition of dissolved sr entering the arabian sea differs among the three estuaries and also between seasons in the narmada the non conservative behaviour of 87sr 86sr provides a handle to estimate the quantum of sgd to these estuaries the sr concentration 87sr 86sr ratio and salinity of the submarine groundwater and estimate of its fluxes to the narmada estuary have been made using inverse model calculations the model derived sgd flow rates are 5 and 280 cm day during pre monsoon and monsoon respectively the more radiogenic sr isotope composition of sgd relative to the seawater suggests that sgd acts as an additional source of 87sr to the arabian sea

lithium isotope geochemistry of pore waters from ocean drilling program sites 918 and 919 irminger basin the distribution of li isotopes in pore waters to a depth of 1157 m below seafloor is presented for odp sites 918 and 919 in the irminger basin offshore greenland lithium isotope data are accompanied by strontium isotope ratios to decipher diagenetic reactions in the sediments which are characterized by the pervasive presence of volcanic material as well as by very high accumulation rates in the upper section the lowering of the 87sr 86sr ratio below contemporaneous seawater values indicates several zones of volcanic material alteration the li isotope profiles are complex suggesting a variety of exchange reactions with the solid phases these include cation exchange with nh4 and mobilization from sediments at depth in addition to the alteration of volcanic matter lithium isotopes are therefore a sensitive indicator of sediment water interaction 6li values of pore waters at these two sites vary between 42 and 25 at shallow depths 100 mbsf rapid decreases in the li concentration accompanied by a shift to heavier isotopic compositions indicate uptake of li into alteration products a positive anomaly of 6li observed at both sites is coincident with the nh4 maximum produced by organic matter decomposition and may be related to ion exchange of li from the sediments by nh4 in the lower sediment column at site 918 dissolved li increases with depth and is characterized by enrichment of 6li the li isotopic compositions of both the waters and the solid phase suggest that the enrichment of li in deep interstitial waters is a result of release from pelagic sediments the significance of sediment diagenesis and adsorption as sinks of oceanic li is evaluated the maximum diffusive flux into the sediment due to volcanic matter alteration can be no more than 5 of the combined inputs from rivers and submarine hydrothermal solutions adsorption on to sediments can only account for 5 10 of the total inputs from rivers and submarine hot springs