quantification of the effects of eustasy subsidence and sediment supply on miocene sequences mid atlantic margin of the united states we use backstripping to quantify the roles of variations in global sea level eustasy subsidence and sediment supply on the development of the miocene stratigraphic record of the mid atlantic continental margin of the united states new jersey delaware and maryland eustasy is a primary infl uence on sequence patterns determining the global template of sequences i e times when sequences can be preserved and explaining similarities in miocene sequence architecture on margins throughout the world sequences can be correlated throughout the mid atlantic region with sr isotopic chronology 0 6 m y to 1 2 m y eight miocene sequences correlate regionally and can be correlated to global 18 o increases indicating glacioeustatic control this margin is dominated by passive subsidence with little evidence for active tectonic overprints except possibly in maryland during the early miocene however early miocene sequences in new jersey and delaware display a patchwork distribution that is attributable to minor tens of meters intervals of excess subsidence backstripping quantifi es that excess subsidence began in delaware at ca 21 ma and continued until 12 ma with maximum rates from ca 21 16 ma we attribute this enhanced subsidence to local fl exural response to the progradation of thick sequences offshore and adjacent to this area removing this excess subsidence in delaware yields a record that is remarkably similar to new jersey eustatic estimates we conclude that sea level rise and fall is a fi rstorder control on accommodation providing similar timing on all margins to the sequence record tectonic changes due to movement of the crust can overprint the record resulting in large gaps in the stratigraphic record smaller differences in sequences can be attributed to local fl exural loading effects particularly in regions experiencing largescale progradation

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

oxygen isotope exchange in a two layer model of oceanic crust abstract a numerical model is presented for the transport and exchange of oxygen isotopes in an idealized two layer oceanic crust basalt carbonate that is saturated with a non advecting pore fluid open to the overlying ocean the model allows for time varying sedimentation rate porosity chemical diffusivity and temperature dependent 18o fractionation factors reaction is modeled as solution precipitation of calcite in the carbonate sediment and as modified solution precipitation basalt dissolves smectite precipitates in the basalt layer generic models using input parameters that are typical of those measured in dsdp odp cores and constant sedimentation rates illustrate the behavior of the system sufficiently well to allow first order effects to be discerned that have important implications for paleotemperature and ocean floor weathering studies the solution precipitation reactions allow oxygen to be exchanged between the low 18o basalt layer and the high 18o carbonate sediment through the medium of the pore fluids this results in 18o increasing upwards in the basalt and decreasing downwards in the sediment pore fluid 18o values decrease with depth from zero to values of 1 to 3 at the basalt sediment interface and to values of 7 to 15 within the basalt because reaction rates are slow relative to diffusion in the pore fluid high frequency 18o variations in the solid are preserved indefinitely but the amplitude of the variations decreases as e rt where r is the reaction rate fraction reacted per unit time the results suggest that the diagenetic shifts of the 18o values of benthic and high latitude planktonic foraminifera samples younger than oligocene age are typically negligible for samples older than 50 ma diagenetic effects are typically significant and generally cause estimates of bottom and high latitude surface ocean temperatures in the cretaceous and early tertiary to be too high on the other hand the model suggests that diagenesis will shift the 18o values of low latitude planktonic foraminifera to higher values and that paleotemperature estimates of low latitude surface waters particularly in the eocene and oligocene may be too low using a synthetic 18o record for dsdp site 167 we demonstrate how numerical models can be used to correct specific measured records for diagenesis this approach could provide a means of extracting paleotemperature information from heavily altered late cretaceous and older samples and for quantifying the subtle effects of diagenesis on the 18o record at all sites

quantifying the effect of diagenetic recrystallization on the mg isotopic composition of marine carbonates abstract the mg and sr isotopic compositions 26mg and 87sr 86sr of pore fluids and bulk carbonates from ocean drilling project site 1171 south tasman rise 2148 2 m water depth are reported in order to evaluate the potential of diagenesis to alter carbonate based geochemical proxies in an open marine system given the trace amounts of mg in marine carbonates relative to coexisting pore fluids diagenesis can alter carbonate 26mg a promising proxy for seawater 26mg that may help elucidate long term changes in the global mg cycle constraints on the effect of diagenetic recrystallization on carbonate 26mg are therefore critical for accurate proxy interpretations this study provides context for assessing the fidelity of geochemical proxy reconstructions using the primary components i e foraminiferal tests and nannofossils of bulk carbonate sediments we find that pore fluid 26mg values on the dsm3 scale at site 1171 increase systematically with depth from 0 72 to 0 39 in the upper 260 m while the 26mg of bulk carbonates decrease systematically with depth from 2 23 to 5 00 in the upper 260 m this variability is ascribed primarily to carbonate recrystallization with a small proportion of the variability due to down hole changes in nannofossil and foraminiferal species composition the inferred effect of diagenesis on bulk carbonate 26mg correlates with down core changes in mg ca sr ca na ca and 87sr 86sr a depositional reactive transport model is employed to validate the hypothesis that calcite recrystallization in this system can generate sizeable shifts in carbonate 26mg model fits to the data suggest a fractionation factor and a partition coefficient that are consistent with previous work assuming calcite recrystallization rates of 7 ma constrained by sr geochemistry in addition either partial dissolution or a distinctly different previous diagenetic regime must be invoked in order to explain aspects of the elemental chemistry and 87sr 86sr of relatively deep sediments from holes a and c this study indicates that the dynamics of a given sedimentary system can significantly alter bulk carbonate geochemistry and presents a framework for considering the potential impact of such alteration on picked archives such as foraminiferal tests and nannofossils ultimately this study contributes to the development of 26mg as a proxy for seawater 26mg by quantifying the susceptibility of carbonate 26mg to diagenetic alteration particularly in sediments in open marine systems this study suggests that because of the sensitivity of carbonate 26mg to diagenetic recrystallization it can in certain systems be used to quantify the impact of diagenesis on carbonate based geochemical proxies

the phanerozoic δ88 86sr record of seawater new constraints on past changes in oceanic carbonate fluxes the isotopic composition of phanerozoic marine sediments provides important information about changes in seawater chemistry in particular the radiogenic strontium isotope 87sr 86sr system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric co2 concentrations however the 87sr 86sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium sr output flux which is primarily controlled by the burial of calcium carbonate caco3 at the ocean floor the sr budget of the phanerozoic ocean including the associated changes in the amount of caco3 burial is therefore only poorly constrained here we present the first stable isotope record of sr for phanerozoic skeletal carbonates and by inference for phanerozoic seawater 88 86srsw which we find to be sensitive to imbalances in the sr input and output fluxes this 88 86srsw record varies from 0 25 to 0 60 vs srm987 with a mean of 0 37 the fractionation factor between modern seawater and skeletal calcite 88 86srcc sw based on the analysis of 13 modern brachiopods mean 88 86sr of 0 176 0 016 2 standard deviations s d is 0 21 and was found to be independent of species water temperature and habitat location overall the phanerozoic 88 86srsw record is positively correlated with the ca isotope record 44 40casw but not with the radiogenic sr isotope record 87sr 86sr sw a new numerical modeling approach which considers both 88 86srsw and 87sr 86sr sw yields improved estimates for phanerozoic fluxes and concentrations for seawater sr the oceanic net carbonate flux of sr f sr carb varied between an output of 4 7x1010mol myr and an input of 2 3x1010mol myr with a mean of 1 6x1010mol myr on time scales in excess of 100myrs the f sr carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the aragonite and calcite sea episodes on time scales less than 20myrs the f sr carb seems to be controlled by variable combinations of carbonate burial rate shelf carbonate weathering and recrystallization ocean acidification and ocean anoxia in particular the permian triassic transition is marked by a prominent positive 88 86srsw peak that reflects a significantly enhanced burial flux of sr and carbonate likely driven by bacterial sulfate reduction bsr and the related alkalinity production in deeper anoxic waters we also argue that the residence time of sr in the phanerozoic ocean ranged from 1myrs to 20myrs

calcium isotopes in deep time potential and limitations abstract calcium is an essential element in the biogeochemical cycles that regulate the long term climate state of earth the removal of co2 from the ocean atmosphere system is controlled by the burial of carbonate sediments caco3 ultimately linking the global calcium and carbon cycles this fundamental link has driven the development of the stable calcium isotope proxy with application to both ancient skeletal and non skeletal bulk carbonate sediments calcium isotope ratios 44 40ca have been used to track long term changes in seawater chemistry e g aragonite vs calcite seas and to elucidate short term climatic perturbations associated with mass extinction events however developments in the calcium isotope proxy have shown that 44 40ca values in carbonate minerals also are sensitive to changes in precipitation rates mineralogy and diagenesis thereby complicating the application of the proxy to the reconstruction of global cycles first inorganic carbonate precipitation experiments have demonstrated that carbonate 44 40ca values are sensitive to precipitation rates with higher rates generally leading to larger fractionation second 44 40ca values are sensitive to carbonate mineralogy with inorganic aragonite and calcite being on average 1 5 and 0 9 depleted relative to contemporaneous seawater respectively the effects of both changes in carbonate mineralogy and precipitation rates affect primary and secondary minerals but are particularly pronounced during carbonate diagenesis where relatively slow rates of recrystallization and neomorphism can lead to significant changes in bulk sediment 44 40ca values third changes in faunal composition expressed in skeletal fossil archives can lead to large changes in carbonate 44 40ca values that are decoupled from changes in global cycles nevertheless when these factors are appropriately considered the application of calcium isotopes in ancient carbonate sediments becomes a powerful tool for understanding biogeochemical processes that operate over many scales from diagenetic changes within the sediment pore space to regional changes across ancient carbonate platforms and to global changes in seawater chemistry through time importantly the processes that contribute to variability in carbonate 44 40ca values are likely to impact other carbonate bound proxies highlighting the potential for calcium isotopes as a tool to better understand the variability of other isotope systems

ca isotopes in carbonate sediment and pore fluid from odp site 807a the ca2 aq calcite equilibrium fractionation factor and calcite recrystallization rates in pleistocene sediments abstract the calcium isotopic compositions 44ca of 30 high purity nannofossil ooze and chalk and 7 pore fluid samples from odp site 807a ontong java plateau are used in conjunction with numerical models to determine the equilibrium calcium isotope fractionation factor s f between calcite and dissolved ca2 and the rates of post depositional recrystallization in deep sea carbonate ooze the value of s f at equilibrium in the marine sedimentary section is 1 0000 0 0001 which is significantly different from the value 0 9987 0 0002 found in laboratory experiments of calcite precipitation and in the formation of biogenic calcite in the surface ocean we hypothesize that this fractionation factor is relevant to calcite precipitation in any system at equilibrium and that this equilibrium fractionation factor has implications for the mechanisms responsible for ca isotope fractionation during calcite precipitation we describe a steady state model that offers a unified framework for explaining ca isotope fractionation across the observed precipitation rate range of 14 orders of magnitude the model attributes ca isotope fractionation to the relative balance between the attachment and detachment fluxes at the calcite crystal surface this model represents our hypothesis for the mechanism responsible for isotope fractionation during calcite precipitation the ca isotope data provide evidence that the bulk rate of calcite recrystallization in freshly deposited carbonate ooze is 30 40 myr and decreases with age to about 2 myr in 2 3 million year old sediment the recrystallization rates determined from ca isotopes for pleistocene sediments are higher than those previously inferred from pore fluid sr concentration and are consistent with rates derived for late pleistocene siliciclastic sediments using uranium isotopes combining our results for the equilibrium fractionation factor and recrystallization rates we evaluate the effect of diagenesis on the ca isotopic composition of marine carbonates at site 807a since calcite precipitation rates in the sedimentary column are many orders of magnitude slower than laboratory experiments and the pore fluids are only slightly oversaturated with respect to calcite the isotopic composition of diagenetic calcite is likely to reflect equilibrium precipitation accordingly diagenesis produces a maximum shift in 44ca of 0 15 for site 807a sediments but will have a larger impact where sedimentation rates are low seawater circulates through the sediment pile or there are prolonged depositional hiatuses

low temperature stable mineral recrystallization of foraminiferal tests and implications for the fidelity of geochemical proxies abstract fossilized foraminiferal tests are widely used as proxies to constrain paleoenvironments including past sea surface and bottom water temperatures and the chemical composition of ancient seawater however relatively little is known about the extent to which calcareous foraminiferal tests exchange with seawater prior to burial in this study we used a 45ca radiotracer approach to quantify the extent and rate of foraminiferal calcite fluid exchange over a three month period modern foraminiferal tests exhibited faster exchange with a 45ca spiked solution 2 6 10 4 to 2 0 10 5 mol m2 d than fossil foraminiferal tests 7 6 10 5 to 5 3 10 6 mol m2 d from odp site 807 the impact of dissolved si on the exchange rate of modern foraminifera was minimal 2 6 10 4 to 9 2 10 6 mol m2 d unlike foraminiferal calcite inorganic calcite exchanged at remarkably slow rates 6 6 10 6 to 5 9 10 7 mol m2 d suggesting that biogenic calcite is more reactive than inorganic calcite increased ca2 mg2 and sr2 concentrations in fluids from parallel tracer free reactors indicated preferential dissolution of tests though there was no overt change in test morphology during experiments as imaged by scanning electron microscopy and micro ct scanning time dependent box model simulations of 45ca as well as aqueous elemental chemistry support the hypothesis that calcite fluid exchange occurred via dissolution reprecipitation of foraminiferal tests that was induced by intra test chemical heterogeneity the short term exchange reactions investigated in this study are comparable to the reactions that can occur in the seawater column and at the sediment seawater interface this work suggests that dissolution reprecipitation in such settings has the potential to overprint the chemistry of foraminiferal tests without overt physical alteration which can lead to a potential bias in paleoenvironmental reconstructions model based estimates suggest a maximum of 2 3 c alteration of mg ca based temperatures over experimental time scales model efforts also suggest that the diagenetic trajectories in mg ca 18 o space for instance are impacted by the partition coefficient of mg in calcite mg as well as by the mechanism of alteration this is demonstrated for i the ratio of exchange to dissolution and ii the relative rate of high mg calcite to low mg calcite reaction we have illustrated that the mechanism of alteration in addition to water rock ratios determine diagenetic trajectories finally surface reaction has implications for our ability to constrain fractionation factors in experimental and natural systems the experimental observations suggest that exchange between tests and solution is nominal over 100 days experiments aimed at deducing fractionation factors rely on the equilibration of bulk solid and fluid since these are the readily analyzed reservoirs we quantify the fraction of carbonate 5 that must react so that surface reaction does not impact the interpretation of ca isotopic fractionation factors and discuss the implications for more fluid dominated elements such as mg and o

seawater sr isotopes at the cretaceous tertiary boundary abstract seawater 87 sr 86 sr values increase abruptly by 28 10 6 across the cretaceous tertiary boundary ktb this small but rapid shift is superimposed on the larger scale structure of the seawater sr isotope curve the time scale of radiogenic sr addition appears to be too rapid to reconcile with sources associated with volcanism and we show that the amount of sr required to produce even this small increase is too large to be derived from 1 a kt bolide of the size constrained by the ir anomaly 2 continental crust ejecta from the impact of such a bolide 3 soot from global wildfires initiated by an impact or 4 any combination of these sources the probable source of the radiogenic sr is enhanced continental weathering but the high rate of increase appears to rule out processes such as sea level regression glaciation or tectonism a plausible mechanism for rapid addition of radiogenic sr to the oceans is enhanced weathering associated with globally distributed acid rain ph 1 which is a proposed by product of a bolide impact 51 epsl vol 83

diagenesis and sr isotopic evolution of seawater using data from dsdp 590b and 575 new sr isotopic and concentration analyses of bulk carbonate and porewaters from a carbonate rich miocene section sampled at dsdp site 575 are reported and used along with our earlier data from a section of similar age at dsdp site 590b in a numerical model to determine for each site the rate of sr exchange during diagenesis and the degree to which this amount of exchange has shifted the87sr86sr of the bulk carbonate from the ratio each increment of sediment had when first deposited despite the fact that the two sites have very different water depth 4536 m at 575 vs 1299 m at 590b different sedimentation rate 10 m my at 575 vs 40 m my at 590b and significantly different porewater sr2 gradients we find that the rate of sr exchange as a function of sediment age is almost indistinguishable between the two sites the rate of sr exchange determined at the two sites is such that the resulting shift in bulk carbonate87sr86sr due to diagenesis is small compared to the total range of87sr86sr values measured but large compared to the analytical uncertainty of the individual isotopic ratio measurements by taking this shift into account we reconstruct the original87sr86sr of each increment of carbonate sampled which when plotted as a function of age becomes our best estimate of the sr isotopic evolution of seawater because sr is very well mixed in the ocean at any given time there is a single worldwide value of seawater87sr86sr therefore if we are quantitatively accounting for the effect sr exchange we should find the same seawater evolution curve regardless of what dsdp site is used when we compare the observed bulk carbonate87sr86sr vs age at the two sites they are seen to differ by amounts that are sometimes large compared to the analytical uncertainties of the measurements however when these data are corrected for the post depositional sr isotopic shifts predicted by our diagenetic model we find almost perfect agreement this agreement suggests that we have made a realistic determination of the rate of sr exchange and its consequences in terms of shifting the87sr86sr of the bulk carbonate and more importantly that sr isotopes can be used to correlate marine sediments with an accuracy comparable to the very small analytical uncertainties of modern isotopic measurements

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

evaluating the ca isotope proxy the use of ca isotopes as a proxy for mass flux imbalances in the ca cycle is evaluated critically a compiled ca isotope record for the last 45 ma derived from bulk nannofossil ooze and with a temporal resolution of 0 5 ma and an interpretation of the record are presented in the context of the global ca cycle this analysis which assumes that nannofossil ooze records isotopic variations in seawater indicates a dynamic ca cycle in the cenozoic such dynamic behavior has serious implications for the c cycle and suggests feedbacks between the ca and c cycles to stabilize or buffer the oceanic carbon reservoir alternative applications of the ca isotope proxy are investigated using numerical models to determine the extent to which ca isotopes are sensitive to other aspects of the ca cycle the results of the simulations are applied to specific cases in the cenozoic the simulations illustrate how variations in the global fractionation factor between calcium carbonate and seawater can produce trends similar to those observed when comparing previously published ca isotopic compositions of marine barite to the nannofossil ooze record the large drop in the 44 ca value of bulk nannofossil ooze near the eocene oligocene boundary can be reconciled in two ways either as a substantial increase in weathering relative to sedimentation or as an indicator of changing depositional mode within the ocean though the preferred interpretation is not clear at present it is evident that ca isotopes stand to be a unique proxy for ca cycling once the isotope systematics are elucidated

sr isotopic variation in shallow water carbonate sequences stratigraphic chronostratigraphic and eustatic implications of the record at enewetak atoll sr isotope data from two boreholes within the lagoon at enewetak atoll have been used to evaluate the use of such data to correlate date and monitor sea level change in shallow water carbonate sequences correlative stratigraphic intervals of relatively invariant 87sr separated by abrupt transitions to lower 87sr with increasing depth are recognized in both boreholes conversion of 87sr values to age via calibration with the seawater 87sr trend with age indicates that correlative and synchronous deposition of atoll sediments occurred at 0 4 1 2 and 2 1 ma in contrast a 5 m y hiatus is recognized in one borehole but not the other sr isotope stratigraphy sis is a powerful stratigraphic and chronostratigraphic tool in shallow water carbonate sequences only when significant secular variation of 87sr occurs and retention of depositional 87sr values is demonstrated the latter is best demonstrated when 87sr data are integrated with 18o 13c sr content data and petrographic observations several diagenetically altered intervals have greater 87sr values low 13c values and low sr ca ratios relative to adjacent intervals a combination that is consistent with open system meteoric diagenesis calcite cements from these intervals have early pleistocene 1 2 ma 87sr values despite their occurrence well within the late pliocene 2 1 ma sequence thus local sedimentological and diagenetic processes have produced intralagoon variability in the sis of the two boreholes complicating subsurface stratigraphic correlations the occurrence of anomalously young calcite cement relative to adjacent limestone is a direct response of the interaction of sea level change and meteoric phreatic diagenesis whereby overlying metastable carbonates with greater 87sr values are dissolved during periods of atoll emergence and sea level lowstand liberating sr and soil gas co2 to the pore fluid which is then incorporated into downflow meteoric phreatic diagenetic calcite the stratigraphic relation between the sites of carbonate dissolution and diagenetic calcite precipitation suggest an early pleistocene 1 2 ma sea level fall of between 34 and 64 m moreover the stratigraphic position and inferred age of paleophreatic lens calcite when backtracked for subsidence suggest that early pleistocene 1 2 ma sea level was 72 81 m range of 60 100 m below present sea level the enewetak record of early pleistocene sea level lowstand elevation agrees reasonably well with proxy sea level records inferred from sequence stratigraphy and deep sea foraminiferal 18o data however the enewetak record of the amplitude of early pleistocene sea level change is more consistent with the deep sea foraminiferal 18o proxy than the sequence stratigraphy proxy

atmospheric structure and momentum balance during a gap wind event in shelikof strait alaska abstract gap winds occur in topographically restricted channels when a component of the pressure gradient is parallel to the channel axis aircraft flight level data are used to examine atmospheric structure and momentum balance during an early spring gap wind event in shelikof strait alaska alongshore sea level pressure ridging was observed vertical cross sections show that across strait gradients of boundary layer temperature and depth accounted for the pressure distribution geostrophic adjustment of the mass field to the along strait wind component contributed to development of the observed pressure pattern boundary layer structure and force balance during this event was similar to that often observed along isolated barriers however the rossby radius was lager than the strait width and atmospheric structure in the strait exit region indicates transition of the flow to open coastline conditions two across strait momentum budgets show that the coriolis force and across strait pressure gradient w

strontium isotope stratigraphy for the late cretaceous a new curve based on the english chalk marine 87sr 86sr decreases from 0 70775 in the cenomanian to 0 70730 in the middle turonian before increasing in a near linear manner to 0 70775 in the early maastrichtian this variation has been defined using samples from the english chalk that are closely integrated with the macrofossil and microfossil biostratigraphy of northwestern europe with this new isotope curve a stratigraphic resolution is attainable in correlation that is typically 0 8 ma for the santonian and campanian stages isotopic and biostratigraphic correlations between dorset and norfolk in the uk agree within the limit of analytical error in 87sr 86sr authors

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

perspectives on geochemical proxies the impact of model and parameter selection on the quantification of carbonate recrystallization rates abstract diagenetic reactions in marine sediments such as the recrystallization of carbonates can impact the accuracy of paleo environmental and paleo climatic reconstructions by geochemical proxies the extent to which the recrystallization of carbonates affects the chemistry of sedimentary archives depends on the reaction rate extent of isotopic disequilibrium and duration of reaction the reaction rate which is obviously critical can be constrained by the elemental and isotopic compositions of pore fluids such constraints are affected by assumptions regarding the temperature in the sedimentary column relative to the temperature of formation the burial rate pore fluid advection the composition of the sediments carbonate rich versus siliciclastic and the porosity of the sediment column in this study we use a steady state analytical solution to the diagenetic equations to constrain depth dependent reaction rates and extents of recrystallization based on the ca isotopic compositions of pore fluids in sedimentary columns at multiple ocean drilling sites sites 807 984 1170 and 1171 which encompass a diverse range of sedimentary compositions and conditions we find that carbonates in siliciclastic sediments are generally less altered by diagenesis than their carbonate rich counterparts the discrepancy in recrystallization rates between siliciclastic and carbonate rich sedimentary sections is however significantly smaller than previously estimated suggesting that siliciclastic archives are not immune to diagenetic effects while we find that diagenesis can decouple contemporaneous proxies of sea surface temperature mg ca and 18o our calculations also reveal that 18o based temperature estimates are more robust in siliciclastic sections relative to carbonate rich sections sensitivity tests of the calculated extent of recrystallization suggest that uncertainties in porosity and burial rate are generally the greatest sources of error to proxy reconstruction from diagenetically altered sediments the conclusions drawn using the analytical solution are benchmarked against a depth dependent forward numerical model using the crunchflow software steefel et al 2015 ultimately this comparison demonstrates that the assumptions necessary in deriving the analytical solutions have a relatively minor impact on the resulting conclusions

rapid change in strontium isotopic composition of sea water before the cretaceous tertiary boundary a critical aspect of the debate over the origin of the chemical biological and climatological perturbations that characterize the cretaceous tertiary boundary k t boundary is the timescale and detailed pattern of the extinctions and geochemical changes whether the development of the anomalies was catastrophic over tens to hundreds of years or more gradual 103 to 106 years whether the anomalies occur exactly at the boundary or precede it and whether the chemical and biological signatures represent one event or can be resolved into several discrete events are issues fundamental to identifying the cause of the marked changes to determine the timing and rate of change of strontium isotope evolution of sea water during the five million years preceding the k t boundary we analysed foraminifera from an exceptionally thick palaeontologically well characterized marine k t section exposed at bidart southwest france we found a rapid increase in 87sr 86sr of ocean water 1 5 to 2 3 myr before the boundary the increase may be explained by a 10 increase in continental strontium flux to the oceans over a period of about 1 myr

vadose zone infiltration rate at hanford washington inferred from sr isotope measurements i sr isotope ratios were measured in the pore water acid extracts and sediments of a 70 m vadose zone core to obtain estimates of the long term infiltration flux for a site in the hanford doe complex in eastern washington state the 8 7 sr 8 6 sr values for the pore waters decrease systematically with depth from a high value of 0 721 near the surface toward the bulk sediment average value of 0 711 estimates of the bulk weathering rate combined with sr isotopic data were used to constrain the long term century to millenial scale natural diffuse infiltration flux for the site given both steady state and nonsteady state conditions the models suggest that the infiltration flux for the site is 7 3 mm yr the method shows potential for providing long term in situ estimates of infiltration rates for deep heterogeneous vadose zones

variations in the strontium isotopic ratio of seawater during the miocene stratigraphic and geochemical implications a composite strontium isotopic seawater curve was constructed for the miocene between 24 and 6 ma by combining 87sr 86sr measurements of planktonic foraminifera from deep sea drilling project sites 289 and 588 site 289 with its virtually continuous sedimentary record and high sedimentation rates 26 m m y was used for constructing the oligocene to mid miocene part of the record which included the calibration of 63 biostratigraphic datums to the sr seawater curve using the timescale of cande and kent 1992 across the oligocene miocene boundary a brief plateau occurred in the sr seawater curve 87sr 86sr values averaged 0 70824 which is coincident with a carbon isotopic maximum cm o m from 24 3 to 22 6 ma during the early miocene the strontium isotopic curve was marked by a steep rise in 87sr 86sr that included a break in slope near 19 ma the rate of growth was about 60 ppm m y between 22 5 and 19 0 ma and increased to over 80 ppm m y between 19 0 and 16 ma beginning at 16 ma between carbon isotopic maxima cm3 and cm4 of woodruff and savin 1991 the rate of 87sr 86sr growth slowed and 87sr 86sr values were near constant from 15 to 13 ma after 13 ma growth in 87sr 86sr resumed and continued until 9 ma when the rate of 87sr 86sr growth decreased to zero once again the entire miocene seawater curve can be described by a high order function and the first derivative d87sr 86sr dt of this function reveals two periods of increased slope the greatest rate of 87sr 86sr change occurred during the early miocene between 20 and 16 ma and a smaller but distinct period of increased slope also occurred during the late miocene between 12 and 9 ma these periods of steepened slope coincide with major phases of uplift and denudation of the himalayan tibetan plateau region supporting previous interpretations that the primary control on seawater 87sr 86sr during the miocene was related to the collision of india and asia the rapid increase in 87sr 86sr values during the early miocene from 20 to 16 ma imply high rates of chemical weathering and dissolved riverine fluxes to the oceans in the absence of another source of co2 these high rates of chemical weathering should have quickly resulted in a drawdown of atmospheric co2 and climatic cooling through a reversed greenhouse effect the paleoclimatic record however indicates a warming trend during the early miocene culminating in a climatic optimum between 17 and 14 5 ma we suggest that the high rates of chemical erosion and warm temperatures during the climatic optimum were caused by an increase in the contribution of volcanic co2 from the eruption of the columbia river flood basalts crfb between 17 and 15 ma the decrease in the rate of crfb eruptions at 15 ma and the removal of atmospheric carbon dioxide by increased organic carbon burial in monterey deposits eventually led to cooling and increased glaciation between 14 5 and 13 ma the crfb hypothesis helps to explain the significant time lag between the onset of increased rates of organic carbon burial in the monterey at 17 5 ma as marked by increased 13c values and the climatic cooling and glaciation during the middle miocene as marked by the increase in 18o values which did not begin until 14 5 ma

the front range blizzard of 1990 part i synoptic and mesoscale structure abstract over 1 m of snow fell in the foothills of southeast wyoming and northeast colorado during the storm of 6 7 march 1990 the heavy snowfall combined with strong winds to product blizzard conditions resulting in major highways being closed for several days the heaviest snow fell in the vicinity of a narrow northerly barrier jet that developed in place along the front range of the colorado rockies strong warm air advection from the southeast was observed during the development of the barrier jet there was no cold air advection from the north rapid intensification of the barrier jet took place only after precipitation started and was concurrent with the development of heavy precipitation a mesoscale front marked the transition from southeasterly to northerly flow this front remained very close to the rain snow line and progressed toward the east at 1 2 m s 1 for about 15 h melting precipitation appears to be the dominant process contributing to the development of the barrier jet and mesoscale f

sr ca variations in cretaceous carbonates relation to productivity and sea level changes abstract we present high resolution sr ca measurements on coccolith dominated pelagic carbonates of berriasian valanginian albian santonian and campanian maastrichtian age from dsdp sites and tethyan land sections carbonate sr ca varies by up to 80 over both long and short timescales and may reflect either temporal variations in seawater sr ca or variable sr partitioning in biogenic carbonates numerical models of seawater sr and ca budgets indicate that while sea level changes can cause comparably large variations in the seawater sr ca ratio the timing and pattern of predicted sr ca variations agrees poorly with the carbonate record reef crises unrelated to sea level changes may also elevate seawater sr ca and in some cases the record of reef crises corresponds to increasing carbonate sr ca changes in sr partitioning likely due to changes in calcareous nannoplankton productivity also appear to control carbonate sr ca in these records cretaceous carbonate sr ca broadly covaries with indicators of productivity derived from microfossil ecology recent studies in sediment core tops and cultures have shown that sr partitioning in coccolith carbonate is strongly influenced by changes in coccolithophorid growth and calcification rate where the effects of changing seawater sr ca can be constrained by independent geological data carbonate sr ca measurements could provide a valuable perspective on changes in the productivity of calcareous nannoplankton and variations in the carbonate and carbon cycle in the cretaceous

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

a windstorm in the lee of a gap in a coastal mountain barrier abstract this paper describes a localized windstorm that struck some areas of northwest washington state on 28 december 1990 with winds exceeding 45 m s 1 resulting in extensive property damage treefalls and power outages arctic air originating within the interior of british columbia descended into a mesoscale gap in the coast cascade mountains and then accelerated ageostrophically to the west this gap acceleration is explained quantitatively by a three way balance among the pressure gradient force friction and inertia the flow maintained its integrity as a narrow current of high speed air as it exited the gap and subsequently accelerated over water troughing in the lee of the cascade mountains enhanced the horizontal pressure gradient over northwest washington this pressure gradient approximately balanced frictional drag resulting in only minimal acceleration farther south the flow decelerated as the current spread out horizontally

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

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

numerical models for diagenesis and the neogene sr isotopic evolution of seawater from dsdp site 590b abstract a numerical model for the diagenetic exchange of sr between carbonates and their pore fluids during sedimentation and compaction has been developed the model has been applied to data from dsdp site 590b in order to assess the accuracy with which the sr isotope record in the carbonate sediment reflects that of seawater the most important process affecting the sr in the solid carbonate is exchange with the pore fluid due to solution reprecipitation but the concentration or isotopic composition of sr in the solid itself gives little or no information as to the magnitude of this exchange the key to determining the rate of exchange is the pore fluid where the variations of sr2 and87sr 86sr with depth are very sensitive indicators the logical structure of applying the model to data from dsdp 590b is to find by successive iteration an ocean history i e the initial87sr 86sr and sr concentration of each increment of carbonate deposited and a rate of sr exchange between pore water and solid carbonate such that the model matches the present sr concentration and87sr 86sr of both pore water and solid carbonate once all the data are matched the model provides an estimate of the rate of sr exchange due to solution reprecipitation and the evolution of87sr 86sr in seawater over the past 20 million years for dsdp 590b we find that solution reprecipitation decreases rapidly with depth from a near surface value of about 10 per million years to about 1 per million years below 200 m this rate of exchange of sr results in the carbonates of dsdp 590b preserving an accurate record of the sr isotopic evolution of the ocean over the past 5 million years but for ages greater than 5 million years the87sr 86sr ratio of the carbonate is systematically displaced from that of the seawater in which it was deposited the maximum difference is of order 5 10 5

rock fracture grouting with microbially induced carbonate precipitation microbially induced carbonate precipitation has been proposed for soil stabilization soil strengthening and permeability reduction as an alternative to traditional cement and chemical grouts in this paper we evaluate the grouting of fine aperture rock fractures with calcium carbonate precipitated through urea hydrolysis by the bacteria sporosarcina pasteurii calcium carbonate was precipitated within a small scale and a near field scale 3 1 m2 artificial fracture consisting of a rough rock lower surfaces and clear polycarbonate upper surfaces the spatial distribution of the calcium carbonate precipitation was imaged using time lapse photography and the influence on flow pathways revealed from tracer transport imaging in the large scale experiment hydraulic aperture was reduced from 276 m to 22 m corresponding to a transmissivity reduction of 1 71x10 5 m2 s to 8 75x10 9 m2 s over a period of 12 days under constantly flowing conditions with a modified injection strategy a similar three orders of magnitude reduction in transmissivity was achieved over a period of three days calcium carbonate precipitated over the entire artificial fracture with strong adhesion to both upper and lower surfaces and precipitation was controlled to prevent clogging of the injection well by manipulating the injection fluid velocity these experiments demonstrate that microbially induced carbonate precipitation can successfully be used to grout a fracture under constantly flowing conditions and may be a viable alternative to cement based grouts when a high level of hydraulic sealing is required and chemical grouts when a more durable grout is required

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

an observational study of fronts and frontal mergers over the continental united states abstract the stormscale operational and research meteorology fronts experiment systems tests storm fest field program was carried out over the central united states to investigate the structure and dynamics of fronts and their attendant precipitation systems adjacent to complex topography and to evaluate new observing networks and analysis techniques for mesoscale research and weather forecasting this study presents the analysis of data taken between 8 and 10 march 1992 which was the most active period of storm fest this three day observing period was characterized by the passage of an extratropical cyclone and related fronts the synoptic scale conditions related to the cyclone and frontal evolutions are described multiple frontal zones i e pacific and arctic cold fronts quasi stationary polar front dryline maritime warm front and associated regions of precipitation are documented and their origins and interactions are explored these features both well defined and subtle were observed wi

palaeohydrology of the lower cretaceous pre salt lacustrine system from rift to post rift phase santos basin brazil abstract large oil accumulation discoveries in the last decade in the pre salt rock succession off the brazilian coast aroused renewed interest in carbonate reservoirs prompting several studies aiming at unravelling the conditions of formation of these rocks despite that there are still many gaps in the knowledge concerning environmental conditions of the deposition of the pre salt carbonates of santos basin located at the southeastern brazilian margin in this study we present and discuss a new suite of geochemical and biostratigraphic data of the lacustrine rift to post rift succession broadly correlated with itapema and barra velha formations of the santos basin whose deposition occurred in the aptian the integration of the petrographic biostratigraphic and geochemical data serves the ultimate purpose of the study which is to apply the new radiogenic strontium data as a proxy for the reconstruction of the evolution of the lake hydrology associated with the deposition of the carbonates of the itapema and barra velha formations these data are integrated into numerical models whose results bring new ideas on the general hydrologic conditions of the lake system and on its evolution through time the mass balance calculations indicate that two end members alone can account as potential sources of sr to the palaeolake a mafic and a felsic component respectively the latter likely contributed with significantly higher fluxes roughly one to two and up to four orders of magnitude higher than the former end member for most of the depositional history in order to generate the 87sr 86sr trends observed in the carbonate rocks finally the results obtained from the integration of the observations with the numerical models point to decreasing fluxes of water with time as contributed from both sources suggesting that the formation of the deposits became very likely constrained to progressively more evaporitic and alkaline lake waters these results also open up a new window into the environmental conditions of the interior gondwana continent immediately prior to the definitive opening of the south atlantic ocean

hafnium isotope stratigraphy of ferromanganese crusts a cenozoic record of hafnium isotopic compositions of central pacific deep water has been obtained from two ferromanganese crusts the crusts are separated by more than 3000 kilometers but display similar secular variations significant fluctuations in hafnium isotopic composition occurred in the eocene and oligocene possibly related to direct advection from the indian and atlantic oceans hafnium isotopic compositions have remained approximately uniform for the past 20 million years probably reflecting increased isolation of the central pacific the mechanisms responsible for the increase in87sr 86sr in seawater through the cenozoic apparently had no effect on central pacific deep water hafnium

detailed record of the neogene sr isotopic evolution of seawater from dsdp site 590b a detailed study of strontium isotope variations in neogene marine carbonate sediments from deep sea drilling project site 590b using techniques that allow the 87sr 86sr ratio to be determined to better than 0 00001 gives a high resolution record of the sr isotopic evolution of seawater the data show that the rate of change of the marine 87sr 86sr ratio has varied significantly even on time scales as short as 1 m y periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic sr from the continents coupled with a decreased submarine carbonate dissolution rate greater carbonate compensation depth periods of relatively slowly changing 87sr 86sr follow major marine transgressions on the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth it is inferred that the effects of sea level variations are modified by climatic factors that affect the intensity of continental weathering and runoff the effects of sea floor generation rate variations are not discernible for the neogene the maximum attainable stratigraphic resolution using sr isotopes is between 0 1 and 2 m y for this time period

effects of coastal orography on landfalling cold fronts part i dry inviscid dynamics abstract in this study the interaction of cold fronts with idealized coastal terrain typical of the western united states and canada is considered two issues are examined first what are the factors that determine the strength of the coastal winds and second what are the orographic effects on the frontal evolution to address these issues the authors utilize a two dimensional boussinesq terrain following coordinate numerical model in which a uniform prescribed flow is forced to move over a plateau the resultant across mountain velocities are characterized by a zone of strongly decelerated flow upstream of the windward slope and a train of inertia gravity waves downstream a barrier jet oriented parallel to the mountain is produced by the coriolis force the variations of the magnitude of the upstream deceleration and the barrier jet over a wide range of froude numbers and rossby numbers are described steady linear theory applied to flow over a plateau shows that the upstream deceleration is dete

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

effects of ocean acidification on the marine calcium isotope record at the paleocene eocene thermal maximum highlights 44ca was measured in bulk carbonate and barite at two sites over the petm diagenetic effects on 44ca are observed associated with ocean acidification multiple sites and proxy archives necessary to reconstruct the past accurately abstract carbonates are used extensively to reconstruct paleoclimate and paleoceanographic conditions over geologic time scales however these archives are susceptible to diagenetic alteration via dissolution recrystallization and secondary precipitation particularly during ocean acidification events when intense dissolution can occur despite the possible effects of diagenesis on proxy fidelity the impacts of diagenesis on the calcium isotopic composition 44ca of carbonates are unclear to shed light on this issue bulk carbonate 44ca was measured at high resolution in two pacific deep sea sediment cores odp sites 1212 and 1221 with considerably different dissolution histories over the paleocene eocene thermal maximum petm 55 ma 55 ma the 44ca of marine barite was also measured at the deeper site 1221 which experienced severe carbonate dissolution during the petm large variations 0 8 0 8 in bulk carbonate 44ca occur in the deeper of the two sites at depths corresponding to the peak carbon isotope excursion which correlate with a large drop in carbonate weight percent such an effect is not observed in either the 1221 barite record or the bulk carbonate record at the shallower site 1212 which is also less affected by dissolution we contend that ocean chemical changes associated with abrupt and massive carbon release into the ocean atmosphere system and subsequent ocean acidification at the petm affected the bulk carbonate 44ca record via diagenesis in the sedimentary column such effects are considerable and need to be taken into account when interpreting ca isotope data and potentially other geochemical proxies over extreme climatic events that drive sediment dissolution

on the utility of quantitative modeling to the interpretation of ca isotopes abstract though the utility of calcium isotopes is broad examples of applications are still relatively sparse some of this paucity as with many metal isotope systems may derive from a perception that the analytical tool is difficult to access alternatively potential users may be deterred by a sense that calcium isotopes are ambiguous difficult to interpret and or complicated by too many interrelated processes here we provide an overview of the quantitative modeling approaches available to facilitate interpretation of calcium isotopes in earth systems in particular their ability to push interpretations beyond the qualitative while no method is perfect the variety of approaches described here offer an accessible toolset that is incredibly valuable we suggest that the calcium isotope community should be expanding the use of such techniques noting their limitations and striving to improve upon current methods over time

climatology of barrier jets along the alaskan coast part i spatial and temporal distributions abstract this paper investigates the temporal and spatial climatology of coastal barrier jets in the gulf of alaska the jets are divided into two categories based upon the origin of the air involved classic barrier jets fed primarily by onshore flow and hybrid jets fed primarily by gap flow from the continental interior the analyses are compiled from five years 1998 2003 of synthetic aperture radar images from the radarsat 1 satellite totaling 3000 images thermodynamic and kinematic data from the ncep reanalysis is used in the interpretation of the results the majority of coastal barrier jets occur during the cool season with the coastline near mount fairweather and the valdez cordova mountains experiencing the greatest number of barrier jets hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of cross sound yakutat bay and icy bay some interannual variability in the total number of jets is observed coastal barrier jet formation is associate

effects of diagenesis on the isotopic record of late paleogene tropical sea surface temperatures abstract oxygen isotope records of planktonic foraminifera indicate that late eocene and oligocene tropical sea surface temperatures were as much as 8 c lower than present at a time when high latitude sea surface temperatures were higher than present using a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate the effects of diagenesis on bulk carbonate 18 o records for the cenozoic are quantified for four tropical sites most of the observed variations in measured 18 o values at all sites can be accounted for by diagenetic effects there are no systematic trends that support substantial variations in tropical sea surface temperatures beyond diagenetic effects with the possible exception of the early eocene for which the data are consistent with slightly higher sea surface temperatures reconstructions based on oxygen isotope records of planktonic foraminifera which indicate cooler tropical sea surface temperatures for the eocene and oligocene may be artifacts of diagenetic recrystallization as such records are particularly sensitive to diagenetic effects

a multiwinter analysis of channeled flow through a prominent gap along the northern california coast during caljet and pacjet abstract experimental observations from coastal and island wind profilers aircraft and other sensors deployed during the california land falling jets experiment of 1997 98 and the pacific land falling jets experiment of 2000 01 2003 04 were combined with observations from operational networks to document the regular occurrence and characteristic structure of shallow 400 500 m deep cold airstreams flowing westward through california s petaluma gap from the central valley to the coast during the winter months the petaluma gap which is the only major air shed outlet from the central valley is 35 50 km wide and has walls extending at most a modest 600 900 m above the valley floor based on this geometry together with winter meteorological conditions typical of the region e g cold air pooled in the central valley and approaching extratropical cyclones this gap is predisposed to generating westward directed ageostrophic flows driven by along gap pressure differences two case studies and a fiv

conditions of rhodochrosite nodule formation in neogene pleistocene deep sea sediments evidence from o c and sr isotopes calcic rhodochrosite occurs as nodules around burrows in late neogene early pleistocene pelagic sediments of the galapagos ridge in the guatemala basin eastern equatorial pacific dsdp leg 68 site 503 growth was accomplished in the suboxic zone delta

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

high resolution stable isotope records from the upper cretaceous rocks of italy and spain glacial episodes in a greenhouse planet high resolution 13c and 18o records from upper albian to lower santonian pelagic carbonates of the contessa quarry section in italy exhibit large positive oxygen isotopic excursions of 1 in the lower cenomanian and upper turonian coniacian strata within the uncertainties of biostratigraphic correlation these positive excursions appear to correspond to times of large sea level regressions in global sequence stratigraphic sea level curves several lines of evidence suggest that the major 18o excursions in contessa reflect episodes of global cooling and not differential diagenesis numerical models of oxygen isotope exchange during diagenesis show that a high contrast in the degree of alteration would be required to produce these signals as artifacts of diagenesis and lithological data provide no evidence for such large contrasts in the degree of alteration furthermore although precise correlation with a section in the south of spain is hampered by stratigraphic complexities the general sequence of major positive 18o excursions is reproduced it is unlikely that differential diagenesis would produce similar artifacts in multiple sites one explanation for the link between episodes of global cooling and sea level falls is that global cooling events led to polar ice sheet accumulation lowering sea level although ice free conditions have been inferred from evidence for a much warmer climate in late cretaceous time our results suggest that the relationship between continental high latitude ice sheets and overall climatic warmth warrants further examination

models for the coupled sr sulfate budget in deep sea carbonates a numerical model for the sr and sulfate budgets during deposition of deep sea carbonate sediments was developed and used to fit porewater sr2 and so42 data from dsdp sites 593 590 574 573 572 516 and 289 the sr and sulfate budgets are coupled whenever the porewaters become saturated with respect to celestite srso4 models for the porewater sr and sulfate at sites 593 590 516 and 289 suggest that porewater sr concentrations are controlled by the precipitation of celestite and predict maximum celestite concentrations of the order of 0 02 wt for sediments at sites 593 590 and 289 and trace amounts of celestite at site 516 the actual amount of celestite predicted by the model is not well constrained because it depends on the as yet poorly known value of the equilibrium distribution coefficient for sr between calcite and porewaters the fact that celestite has been found in sediments from sites 590 and 593 is used to derive an upper bound for the sr distribution coefficient that suggests that all laboratory determined values for the sr distribution coefficient between calcite and porewater are too large the occurrence of celestite at sites 593 590 516 and 289 does not significantly change earlier estimates of the rates of solution reprecipitation of calcite and its consequences in terms of shifting the sr content or sr isotopic composition of the bulk sediment from what the sediment incorporated when originally deposited the sulfate data at sites 593 and 590 are best fit by invoking a flow of porewater within the sediments of the order of 75 m ma the sr and sulfate concentrations in porewaters from sites 572 573 and 574 never reach celestite saturation and thus the two budgets are decoupled both the sr and the sulfate data require that all three sites have abundant unaltered seawater flowing in the underlying basement and can only be modeled if seawater concentrations of sr and sulfate are imposed as boundary conditions at both the sediment water interface and the bottom of the section model sulfate profiles for sites 572 573 and 574 confirm prior estimates of the rate of porewater flow at these sites that were made using sr data

calcium isotopic evidence for rapid recrystallization of bulk marine carbonates and implications for geochemical proxies abstract strontium and calcium isotopic data for bulk carbonate solids and pore fluids from odp sites 1170 and 1171 are presented the data suggest that bulk carbonate sediments actively exchange with coexisting pore fluids over tens of millions of year time scales recrystallization rates constrained by sr isotopes and sr elemental data are 3 per ma at 1170a and 7 per ma at 1171a the pore fluid chemistries at both sites are affected by advection which occurs in the downwards direction at 1170 25 m ma and upwards at 1171a 250 m ma both the direction and the rate of advection are reflected by the width of the diffusive boundary layer for sr at both 1170a 300 m and 1171a 50 m compared to odp site 807a 150 m where no chemically detectable advection is occurring recrystallization is supported not only by interpretations of pore fluid data but also by the alteration of the bulk solid this is especially true at 1171a where advection drives significant alteration of sr ca mg ca and 87sr 86sr numerical simulations of pore fluid geochemical and isotopic evolution over tens of millions of years conducted with a depositional time dependent reactive transport model suggest that recrystallization rates in the upper tens of meters of the sedimentary section at both sites are more rapid than suggested by the sr geochemical data when the sr constrained rates are applied to the pore fluid ca isotope data the model does not predict pore fluid 44ca within analytical uncertainty the simulations indicate rates that are initially 20 to 40 per ma in young

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

variations in the marine ca cycle over the past 20 million years a 20 million year marine ca isotope record is constructed based on measurements of 36 nannofossil ooze samples from dsdp site 590 the ca isotopic composition d 44 ca relative to our bbulk earthq average of carbonate ooze samples varies between 0 2 and 0 9 and the inferred d 44 ca of seawater calcium varies between 1 1 and 0 4 modern seawater value is 0 95 on our scale fluctuations in the seawater ca isotope ratio occur in 2 to 4 million year intervals and indicate that the supply and removal of ca from the oceans are seldom in balance the ca isotope record is used to reconstruct past weathering fluxes and marine calcium concentrations the inferred marine concentration of ca fluctuates by about f20 on 2 4 million year time scales and by about f50 over the 20 million year record these variations are presumably superimposed on the previously inferred 100 million year variations the seawater ca concentration was about 0 5 times present at 20 ma and generally increased until 6 ma 1 7 times present local maxima in seawater calcium concentrations occur at 6 4 and 4 ma preceding periods of enhanced marine productivity and high mass accumulation rates at site 590 while the calculated calcium concentrations are sensitive to the assumed d 44 ca value for the weathering flux the 2 4 million year features of the derived

strontium isotope stratigraphy of kita daito jima atoll north philippine sea implications for neogene sea level change and tectonic history abstract a detailed chronology of a 432 m core from kita daito jima an atoll on the philippine sea plate has been obtained by strontium isotope stratigraphy the atoll carbonate extends to late oligocene age the top 100 m plio pleistocene section of the core has been dolomitized and dolomite also extends to middle miocene sediments sr isotopes identify two dolomitization events at 2 and 5 ma atoll growth appears to have been continuous between 18 8 and 24 3 ma and the fit of the growth history to a standard model provides a successful confirmation of darwin s subsidence theory the atoll growth appears to have commenced about 42 ma ago 6 ma after volcanism producing a 2 km column of atoll carbonate in agreement with bathymetry the subsidence model defines an apparent loss of 360 m of the sedimentary record since the early middle miocene boundary the amount in excess of the 100 m associated with sea level fall is attributed to plio pleistocene uplift at rates of 20 30 m ma associated with the forebulge of the philippine sea plate prior to its subduction uplift rates have also been estimated using a the heights of dated last interglacial coral reefs on kita daito jima and nearby minami daito jima 17 m ma and 29 m ma b sr isotope ages of calcites from surface samples on minami daito jima 21 m ma and c contrasts in elevation with okino daito jima 100 km away 22 m ma the locations of hiatuses and ages of dolomitization indicate sea level falls of 80 m at 17 16 ma 30 m at 16 15 ma 125 m at 11 ma and 90 m at 5 ma and at 2 ma the data have been combined with those from enewetak atoll to produce a curve of sea level change for the neogene

partial diagenetic overprint of late jurassic belemnites from new zealand implications for the preservation potential of δ7li values in calcite fossils the preservation potential and trends of alteration of many isotopic systems e g li mg ca that are measured in fossil carbonates are little explored yet extensive paleoenvironmental interpretations have been made on the basis of these records here we present a geochemical dataset for a late jurassic 153 ma belemnite belemnopsis sp from new zealand that has been partially overprinted by alteration we report the physical pathways and settings of alteration the resulting elemental and isotopic trends including 7li values and li ca ratios and assess whether remnants of the primary shell composition have been preserved or can be extrapolated from the measured values the 18o and 13c values as well as sr ca and mn ca ratios were analysed along two profiles in addition 6 samples were analysed for 87sr 86sr sr ca and mn ca ratios five samples from the same specimen and 2 from the surrounding sediment were analysed for 7li values li ca sr ca and mn ca ratios and are compared to results for 6 other late jurassic belemnite rostra belemnopsis sp andhibolithes sp from the same region the 87sr 86sr ratios are lower less radiogenic in the most altered part of the rostrum whereas 7li values become more positive with progressive alteration the direction and magnitude of the trends in the geochemical record indicate that one main phase of alteration that occurred in the late cretaceous caused most of the diagenetic signature in the calcite despite relatively deep burial down to 4 km and thus elevated temperatures this diagenetic signature has subsequently been preserved even for the highly mobile element lithium suggesting that primary lithium isotope values can be maintained over geological timescales at least in thick macrofossil shells our best 7li estimate for pristine late jurassic 155 148 ma belemnites is 27 1 which points to a late jurassic seawater 7li of 29 32 compatible with the modern value of 31

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

assessing seawater basalt exchange of strontium isotopes in hydrothermal processes on the flanks of mid ocean ridges we have measured the87sr 86sr of discharging geothermal waters from three ridge flank hydrothermal systems 1 the galapagos mounds hydrothermal field on 0 7 myr old crust 2 a region with crustal age of 4 6 myr on the west flank of the east pacific rise at 19 s and 3 an area having a crustal age of 3 myr in the mariana trough a back arc spreading center half spreading rates at our study sites range from 1 to 8 cm yr and our sites include both normal spreading centers and a back arc basin our sites thus span the range of ridge flank tectonic environments at each of our study sites the hydrothermal nature of our study samples is confirmed by supporting heat flow and chemical evidence our results show that the87sr 86sr of these ridge flank hydrothermal solutions is virtually identical to that of modern seawater indicating that sr isotope exchange on the ridge flanks occurs too slowly to be quantitatively important in the oceanic mass balance of the sr isotopes

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

constraining magnesium cycling in marine sediments using magnesium isotopes abstract magnesium concentrations in deep sea sediment pore fluids typically decrease down core due to net precipitation of dolomite or clay minerals in the sediments or underlying crust to better characterize and differentiate these processes we have measured magnesium isotopes in pore fluids and sediment samples from ocean drilling program sites 1082 1086 1012 984 1219 and 925 that span a range of oceanographic settings at all sites magnesium concentrations decrease with depth at sites where diagenetic reactions are dominated by the respiration of organic carbon pore fluid 26mg values increase with depth by as much as 2 because carbonates preferentially incorporate 24mg low 26mg the increase in pore fluid 26mg values at these sites is consistent with the removal of magnesium in mg carbonate dolomite in contrast at sites where the respiration of organic carbon is not important and or weatherable minerals are abundant pore fluid 26mg values decrease with depth by up to 2 the decline in pore fluid 26mg at these sites is consistent with a magnesium sink that is isotopically enriched relative to the pore fluid the identity of this enriched magnesium sink is likely clay minerals using a simple 1d diffusion advection reaction model of pore fluid magnesium we estimate rates of net magnesium uptake removal and associated net magnesium isotope fractionation factors for sources and sinks at all sites independent estimates of magnesium isotope fractionation during dolomite precipitation from measured 26mg values of dolomite samples from sites 1082 and 1012 are very similar to modeled net fractionation factors at these sites suggesting that local exchange of magnesium between sediment and pore fluid at these sites can be neglected our results indicate that the magnesium incorporated in dolomite is 2 0 2 7 depleted in 26mg relative to the precipitating fluid assuming local exchange of magnesium is minor at the rest of the studied sites our results suggest that magnesium incorporated into clay minerals is enriched in 26mg by 0 to 1 25 relative to the precipitating fluid this work demonstrates the utility of magnesium isotopes as a tracer for magnesium sources sinks in low temperature aqueous systems

strontium isotopic composition of pliocene and pleistocene molluscs from emerged marine deposits north american arctic high precision strontium sr isotopic measurements were obtained for 53 pliocene and pleistocene molluscan shells from emerged marine deposits around the coasts of arctic north america to test whether such data can be used for chronostratigraphic purposes 87sr 86sr ratios from sr isotopic measurements on many marine fossils from arctic ocean borderland sites are broadly consistent with their expected values based on independent age control and on a comparison with the sr isotopic evolution of seawater recorded in deep sea cores all 87sr 86sr ratios measured for shells from middle and late pleistocene deposits are consistent with expected values but only 9 of 22 ratios in shells from older deposits are consistent with independent age estimates aberrant 87sr 86sr ratios are consistently higher than expected at nome alaska and baffin island canada all 87sr 86sr ratios are higher than expected because these shells were formed along the pacific ocean and atlantic ocean margins respectively their h

strontium isotope ratios of the eastern paratethys during the mio pliocene transition implications for interbasinal connectivity paratethys represents the large basin that extended from central europe to inner asia comprising the north alpine foreland pannonian and dacian basins the black sea and caspian sea connectivity between these subbasins and the connectivity of paratethys with the open ocean varied drastically because of pervasive tectono climatic processes affecting the region here we investigate the biogenically produced carbonates of the dacian basin for strontium analyses to monitor changes in connectivity water geochemistry and palaeoenvironment during the mio pliocene transition diagenetic evaluation showed that not all contamination could be removed but that the strontium content of our samples was not affected by post depositional processes 87sr 86sr ratios of ostracods and molluscs are in good agreement and show relatively constant values of 0 70865 0 70885 these are much lower than coeval mio pliocene ocean water 0 7089 0 7090 which indicates that no long standing connection existed to the mediterranean the newly obtained strontium ratios for paratethys are best explained by a mixture of danube dnieper and don river waters implying connectivity between dacian basin and black sea during the latest miocene earliest pliocene we observed no evidence for connectivity to the caspian sea during this period the 87sr 86sr ratios of the dacian basin are similar to the ones measured in the mediterranean upper evaporites lago mare facies the major fresh water deluge at the end of the messinian salinity crisis could thus have been caused by drowning of eastern paratethys waters into the mediterranean

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

the seawater sr ca ratio in the past 50 myr from bulk carbonate sediments corrected for diagenesis abstract the strontium calcium sr ca ratio in paleoseawater is important for evaluating the global fluxes of continental weathering products and carbonate deposition in the oceans existing reconstructions of the paleoseawater sr ca ratio using different methods give conflicting results we use a modeling approach to estimate paleo sr ca for the past 50 million years that uses pore fluid chemistry and bulk sediment measurements of carbonate ooze and chalk from the ontong java plateau as input the effects of diagenesis in modifying the sr ca ratio recorded in bulk carbonate sediments are estimated using a reactive transport model and those effects are accounted for in determining the initial sr ca ratio of the biogenic carbonate sediments the sr ca of the paleo oceans is calculated based on an effective partition coefficient k sr bio 0 198 inferred from sr ca in modern sediments the model simulates deposition of sediments on the seafloor reactions between pore fluid and solid dissolution and precipitation of calcite and diffusion within the pore fluid measured pore fluid sr ca and sulfate concentrations provide input for the sr model this approach applied to four ocean drilling program odp sites 803 805 806 807 that have long cenozoic records of carbonate deposition indicates that the sr ca ratio of seawater has increased slowly over the past 50 million years from a value of about 8 mmol mol to the modern value of 9 4 with fluctuations of about 1 over 10 myr periods this result is consistent with previous estimates based on foraminifera and coral aragonite but differs from recent estimates obtained with other approaches the near constant seawater sr ca over the past 50 million years is consistent with likely weathering sources to the oceans the fluctuations suggest that there were modest shifts in the aragonite calcite ratio of marine carbonate

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

towards an understanding of the ca isotopic signal related to ocean acidification and alkalinity overshoots in the rock record abstract in this contribution we explore the idea that the ca isotope proxy has utility as an indicator of carbonate authigenesis i e post depositional precipitation of caco3 within the sedimentary package given the strong contrast in isotopic fractionation factor between the formational and diagenetic environments ca isotopes have the potential to fingerprint carbonate authigenesis when it occurs close to the seawater sediment interface we demonstrate that ca isotopes are particularly applicable to exploring ocean acidification events and potentially ocean anoxic events and focus our attention on ocean acidification related to the paleocene eocene thermal maximum petm we present three scenarios that vary in the magnitude and duration of the carbon fluxes that are simulated using an earth system model of intermediate complexity cgenie and we use the cgenie output to constrain the upper boundary conditions of 1 d reactive transport models of authigenesis and recrystallization in the sedimentary section along with simple mixing calculations the models inform our exploration of the hypothesis that authigenic carbonate induced by a saturation state overshoot during the petm explains recently published ca isotope records and perhaps bulk carbonate records over ocean anoxic event oae 2 our simulations suggest that fractionation factor variability does not explain the petm 44ca records and we propose a 44ca caco3 space framework to assist with the elucidation of authigenic additions over time scales that are short relative to the residence time of ca in the ocean 1 ma ultimately we find that the authigenic zone generated in the sedimentary column may be influenced by alkalinity overshoots or redox state the caco3 produced in this zone can overprint temporal signals with depth dependent signals that reflect lithology and sedimentation rate and need not be spatially uniform even when driven by a global event ultimately we demonstrate the utility of ca isotopes for exploring short time scale climatic events and a quantitative framework to guide interpretations

calcium isotope evidence for suppression of carbonate dissolution in carbonate bearing organic rich sediments pore fluid calcium isotope calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep sea sediments containing abundant clay and organic material this type of study of deep sea sediment diagenesis provides unique information about the ultra slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo environmental information in carbonate fossils for this study calcium isotope ratios 44 40ca of pore fluid calcium from ocean drilling program odp sites 984 north atlantic and 1082 off the coast of west africa were measured to augment available pore fluid measurements of calcium and strontium concentration both study sites have high sedimentation rates and support quantitative sulfate reduction methanogenesis and anaerobic methane oxidation the pattern of change of 44 40ca of pore fluid calcium versus depth at sites 984 and 1082 differs markedly from that of previously studied deep sea sites like 590b and 807 which are composed of nearly pure carbonate sediment in the 984 and 1082 pore fluids 44 40ca remains elevated near seawater values deep in the sediments rather than shifting rapidly toward the 44 40ca of carbonate solids this observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate rich sites the data are fit using a numerical model as well as more approximate analytical models to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material our models give mutually consistent results and indicate that calcite dissolution rates at sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate rich sites and the rate correlates with the abundance of clay our calculated rates are conservative for these sites the actual rates could be significantly slower because other processes that impact the calcium isotope composition of sedimentary pore fluid have not been included the results provide direct geochemical evidence for the anecdotal observation that the best preserved carbonate fossils are often found in clay or organic rich sedimentary horizons the results also suggest that the presence of clay minerals has a strong passivating effect on the surfaces of biogenic carbonate minerals slowing dissolution dramatically even in relation to the already slow rates typical of carbonate rich sediments

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

reconstructing the oxygen isotope composition of late cambrian and cretaceous hydrothermal vent fluid oxygen isotope analyses 18o of 16 quartz epidote pairs from late cambrian betts cove and mings bight newfoundland ordovician thetford mines quebec canada and cretaceous troodos cyprus ophiolites are used to calculate the 18o of the hydrothermal fluids from which they crystallized we combine these with 3 quartz fluid inclusion measurements and 3 quartz magnetite measurements from the cambrian ophiolites to explore how the range in the 18o of submarine hydrothermal vent fluid has varied between the late cambrian cretaceous and today the range of calculated 18o values of vent fluid 4 to 7 4 is larger than that of modern seafloor hydrothermal vent fluid 0 to 4 we employ two numerical models to ascertain whether this range is most consistent with changes in paleo seawater 18o or with changes in the reactive flow path in ancient hydrothermal systems a static calculation of the vent fluid oxygen isotope composition as a function of the water rock ratio suggests that in an ocean with a lower 18o than today the range of vent fluid 18o should be larger our data however show little evidence that the 18o of the ocean was much lower than the global ice free value of 1 2 a dual porosity model for reactive flow through fractured and porous media is used to model the relative evolution of the 87sr 86sr and 18o of vent fluid in contact with rock our 87sr 86sr and 18o for cretaceous epidotes suggest the strontium concentration of the cretaceous oceans may have been much higher than at present the 87sr 86sr and 18o data from cambrian epidotes are strikingly different from the younger samples and are difficult to model unless fluid rock interaction in the cambrian hydrothermal systems was substantially different it is also possible that some of the quartz epidote veins have been reset by obduction related metamorphism our data suggest that the high calcium to sulfate ratio in early and cretaceous seawater may have affected the degree of strontium isotope exchange causing hydrothermal fluids to have 87sr 86sr closer to that of seawater than in modern systems

fluid flow in deep sea carbonates estimates based on porewater sr abstract fluid flow of up to 200 m myr is documented in thick about 500 m deep sea carbonate sections by numerical modeling of the porewater sr 2 and 87 sr 86 sr profiles at dsdp sites 572 573 and 574 these sites were selected as likely candidates for significant fluid flow in the sedimentary part of the section because it had already been shown that they are underlain by rapidly flowing fresh seawater in the basaltic basement the nature of the exercise is to fit the porewater sr properties at these sites by finding a common rate of sr exchange as a function of sediment age and a local rate of vertical fluid flow the flow rates determined in this way are 20 m myr upwards at site 574 20 m myr downwards at site 573 and 200 m myr downwards at site 572 because of uncertainties of about a factor of 2 in the assumption of a common rate of sr exchange at all sites and trade offs between the sr exchange and fluid flow in determining the shape of sr 2 and 87 sr 86 sr profiles at a given site the precision of the method is of the order of 10 m myr thus at least at site 572 the sr properties of the interstitial waters provide a convincing measure of vertical fluid flow through a thick carbonate section

patterns of reef sedimentation and diagenesis in the miocene of cyprus abstract an early tertiary regressive sedimentary succession developed along an active plate margin in cyprus a varied clastic and carbonate succession of the miocene pakhna formation and then messinian evaporites culminate the regression within the pakhna formation two phases of reef growth were developed the aquitanian burdigalian terra member and the tortonian koronia member the terra member is exposed only in west and southeast cyprus mainly between pelagic carbonates the koronia member is exposed around the margins of the troodos massif in north south and west cyprus and on the akamas peninsula in northwest cyprus there was little tectonic influence on the growth pattern of the terra member reefs the koronia member reefs however are developed on up faulted blocks most of the koronia member fore reef facies and associated clastic input was shed into downfaulted basinal depocentres there are differences between the first and second miocene reef phases in cyprus in primary reef construction and in the level of background carbonate pelagic sedimentation the terra member reefs are dominantly framestones comprising faviids and domal poritids with several types of secondary reef dwelling corals there is no indication of a connection with the indo pacific coral faunal province benthonic foraminifera and fragments of crustose coralline algae are abundant in the off reef by contrast the koronia member is a bindstone comprising virtually monospecific laminar poritid corals but with coralline algae also playing a role in encrustation the koronia member off reef facies comprises decimetre thick beds of bioclastic reef detritus in north cyprus however beds of similar detritus centimetres in thickness are overlain by progressively thicker up to several metres debris flow sheets the terra member reefs have limited acicular fringe cement probably aragonitic this is overlain by an abundant marine bladed formerly high mg calcite cement later cements present in the reef facies include micritised calcite spars perhaps indicating microboring in cements during their precipitation neomorphism was extensive converting most cements to low mg calcite stable isotopic data for all the cyprus calcites exhibit depletion in the heavier isotopes 18 o and 13 c indicative of meteoric alteration the koronia member limestones show abundant indication of early lithification with fringing acicular aragonite and micrite cements stable isotopic data of the botryoidal aragonite cements indicate a marine origin the dolomite is thought to result from marine freshwater mixing and to be of pliocene age on the basis of stratigraphical solution replacement fabric and stable isotopic data sr isotopic data do not contradict a pliocene age dolomite characteristically replaces the pliocene fissure fill contents in southeast cyprus and off reef horizons in the terra member of west cyprus and koronia member of north cyprus the growth and burial history of miocene reefs contribute to the understanding of the tectonic history and palaeogeographical evolution of cyprus

modeling the effects of diagenesis on carbonate clumped isotope values in deep and shallow water settings the measurement of multiply isotopically substituted clumped isotope carbonate groups provides a way to reconstruct past mineral formation temperatures however dissolution reprecipitation i e recrystallization reactions which commonly occur during sedimentary burial can alter a sample s clumped isotope composition such that it partially or wholly reflects deeper burial temperatures here we derive a quantitative model of diagenesis to explore how diagenesis alters carbonate clumped isotope values we apply the model to a new dataset from deep sea sediments taken from ocean drilling project site 807 in the equatorial pacific this dataset is used to ground truth the model we demonstrate that the use of the model with accompanying carbonate clumped isotope and carbonate 18 o values provides new constraints on both the diagenetic history of deep sea settings as well as past equatorial sea surface temperatures specifically the combination of the diagenetic model and data support previous work that indicates equatorial sea surface temperatures were warmer in the paleogene as compared to today we then explore whether the model is applicable to shallow water settings commonly preserved in the rock record using a previously published dataset from the bahamas we demonstrate that the model captures the main trends of the data as a function of burial depth and thus appears applicable to a range of depositional settings

revisiting diagenesis on the ontong java plateau evidence for authigenic crust precipitation in globorotalia tumida the calcite tests of foraminifera lie in marine sediments for thousands to millions of years before being analysed to generate trace element and isotope palaeoproxy records these sediments constitute a distinct physio chemical environment from the conditions in which the tests formed storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration which has the potential to confound their palaeoceanographic interpretation a previous study of g tumida from the ontong java plateau western equatorial pacific found that preferential dissolution of higher mg chamber calcite and the preservation of a low mg crust on the tests significantly reduced whole test mg ca and sr ca brown and elderfield 1996 here we revisit these specimens with a combination of synchrotron x ray computed tomography sxct and electron probe micro analyses epma to re evaluate the nature of their diagenetic alteration the dissolution of higher mg calcite with depth was directly observed in the sxct data confirming the inference of the previous study the sxct data further reveal a thickening of the chemically and structurally distinct calcite crust with depth we propose that these crusts have a diagenetic origin driven by the simultaneous dissolution of high mg chamber calcite and precipitation of low mg crust from the resulting modified pore water solution while the breadth of the study is limited by the nature of the techniques the observation of both dissolution and re precipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes with significant impacts on the resulting palaeoproxy signals

fluid seepage velocities through marine sediments constrained by a global compilation of interstitial water so42 mg2 and ca2 profiles the depth dependence of the so42 mg2 and ca2 contents of interstitial waters extracted from sediments in 140 deep sea drilling project ocean drilling program integrated ocean drilling program drill holes on oceanic crust has been fit using a model of transport advection and diffusion and reaction these drill holes come from a range of crustal ages sediment types sediment thicknesses and sediment accumulation rates the best fitting specific discharge through the sediment at these locations is estimated to be generally 500 m myr 1 0 05 cm yr 1 where sediments are thicker than 100 m although an order of magnitude faster seepage is estimated for some locations with sediment tens of meters thick assuming that the drill holes are globally representative then seepage of fluids through marine sediments at specific discharges of a few hundred m myr 1 is estimated to be only a few percent of the total ridge flank hydrothermal fluid flux this is consistent with the previous suggestion that hydrothermal fluid exchange between the ocean and the crustal aquifer primarily occurs through basement outcrops chemical fluxes of so42 mg2 and ca2 across the sediment water interface globally excluding continental margins are estimated to be less than 10 of the riverine input to the ocean

the isotopic composition of strontium and sulfur in seawater of late permian zechstein age abstract the paleozoic minima of 87 sr 86 sr ratios and 34 s values in seawater are observed in anhydrite layers of the stassfurt a 2 and aller a 4 cycles of evaporation of late permian age in germany these minima were probably caused by extremely low rates of continental runoff and bacterial sulfate reduction thereafter conditions changed suddenly with a steeply increasing supply of radiogenic sr and of nutrients into seawater the latter induced a large growth in the production of organic material in bacterial activity in sediments and in the flow of isotopically heavy sulfur back into the oceans this large change in the cycles of s and sr as well as of c and o within the relatively short zechstein period 2 5 ma reflects a considerable modification of the plate tectonic and environmental conditions shortly before the beginning of the mesozoic era the ochoan deposition in the usa is probably of the same age as the stassfurt leine evaporation in w europe

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

quantitative strontium isotope models for weathering pedogenesis and biogeochemical cycling abstract isotopes of strontium sr are a useful tracer for weathering atmospheric fluxes cation biocycling and pedogenesis we present basic models for application of strontium isotopes to the soil vegetation atmosphere system the mathematical formulations fall into the general categories of 1 steady state models in which isotopic ratios remain constant over the time scale of interest and 2 time dependent models in which isotope ratios change through time in the steady state models fluxes of sr and other elements to the system are constant steady state models can be used to infer short term weathering rates from river and stream isotope compositions to determine fluxes to a single or multiple layer soil exchange solution system and to quantify nutrient fluxes to vegetation time dependent models involve a change in isotopic ratio from some initial value to a new value over the time period of interest in some cases the change may represent a shift from one steady state situation to a new one after a shift in one or more of the fluxes feeding the system examples of applications of time dependent models include identifying the dominant cation sources to an evolving soil exchange solution system and calculating weathering rates by measuring the isotopic compositions of primary soil minerals we use time dependent models to explain differences in the isotopic ratios of labile and carbonate sr from arid sites in hawaii with a basalt parent material isotopic signature and new mexico with an atmospheric isotopic signature these models suggest that the difference is due to a combination of low atmospheric strontium fluxes and high weathering rates in the hawaiian profile compared to the new mexico calcrete profile

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

the geochemistry and origin of the hydrothermal water erupted at lusi indonesia abstract the spectacular lusi mud eruption started in northeast java the 29th of may 2006 despite extensive research the origin of the erupted water remains elusive and poorly constrained here we present a comprehensive study of the geochemistry of lusi waters compared with those collected from surrounding areas all collected between 2006 and 2013 including data from mud volcanoes and volcano hosted hydrothermal springs within this broad context the geochemical characteristics of the fluids expelled in the lusi region suggest that we can classify the waters in three groups 1 meteoric waters expelled in cold springs and artesian wells 2 hydrothermal waters typically mixed with meteoric waters and 3 formation water from marine sediments altered by diagenetic processes such as clay mineral dehydration samples collected from the lusi crater are cl and na dominated up to 527 mm and 471 7 mm respectively similar to seawater indicating that altered sedimentary formation waters are predominant in this system in addition they are enriched in sr up to 808 4 m and other elements commonly associated with hydrothermal systems such as li up to 877 6 m compared to 26 m in seawater some of these elements are up to ten times enriched compared to seawater values high temperature fluid mineral interactions in the subsurface appear to have facilitated the transfer of li and other mobile elements into the fluids high temperature fluid mineral interaction reactions are also supported by si concentrations significantly higher compared to other sampled mud volcanoes in the island crater samples also show the highest 18o values 5 after correction for evaporation compared to 1 at the mv localities 87sr 86sr ratios vary between of 0 7077 and 0 7083 and seem to reflect a general mixture of fluids from clay mineral dehydration carbonate recrystallization alteration of volcanic rocks and hydrothermal imprint eight years of geochemical monitoring indicate that the composition of the deep sourced lusi fluids remain fairly constant through time thus our findings show that the lusi crater waters represent a regional geochemical anomaly and we suggest that a combination of high temperatures in the source region and fluid rock interactions with silicates and possibly carbonate rich lithologies can explain the data this is consistent with a model where the emitted gases migrate from a deep seated 4 km source region likely associated with the presence of hot igneous intrusions and or high t reactions related to the presence of neighbouring active volcanoes

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

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

oligocene miocene strontium isotopes stratigraphic revisions and correlations to an inferred glacioeustatic record this study tests and improves on previously published early and middle miocene 87sr 86sr marine correlations presents sr isotopic age correlations for this interval using the new timescale of cande and kent 1992 and evaluates sr isotopic changes against an inferred glacioeustatic proxy we generated a latest oligocene to early late miocene 87sr 86sr isotope record from ocean drilling program odp hole 747a this site provides an excellent magnetostratigraphic record during most of this interval for independent age estimates very good foraminiferal preservation and excellent core recovery comparisons of new 87sr 86sr data from hole 747a with previously published data from deep sea drilling project dsdp sites 608 miller et al 1991a and 588 hodell et al 1991 yield the following results 1 confirmation and refinement of the early miocene sr isotope changes 2 improved definition of the timing of the changes in slope of 87sr 86sr near 15 4 ma and 22 8 ma 3 improved sr isotopic age resolution for the middle miocene with resolution as good as 0 7 m y and 4 identification of an inflection in the sr isotope record at 28 0 ma based on the combined records from dsdp site 522 miller et al 1988 and odp hole 747a we have been unable to determine the cause of middle miocene offset between site 588 and hole 747a data although we believe it may be attributed to problems in the age assignments for hole 588a for the interval 14 11 ma and site 747 for the interval 11 8 ma because hole 747a results provide a better chronology than site 588 for most of the miocene and a better middle miocene sr isotope record than site 608 we propose that hole 747a serves as the best reference section for miocene 87sr 86sr variations from ca 23 to 11 ma using 87sr 86sr data from sites 522 608 and 747a we relate late eocene to early miocene inflections in the 87sr 86sr isotope record to oxygen isotope increases and decreases inferred to represent glacioeustatic events the decreases deglaciations observed in the 18o record apparently lead the 87sr 86sr inflections by 1 to 1 5 m y

the effects of diagenesis and dolomitization on ca and mg isotopes in marine platform carbonates implications for the geochemical cycles of ca and mg abstract the ca mg o and c isotopic and trace elemental compositions of marine limestones and dolostones from odp site 1196a which range in depth 58 to 627 mbsf and in depositional age 5 and 23 ma are presented the objectives of the study are to explore the potential for non traditional isotope systems to fingerprint diagenesis to quantify the extent to which geochemical proxies are altered during diagenesis and to investigate the importance of diagenesis within the global ca and mg geochemical cycles the data suggest that ca which has a relatively high solid to fluid mass ratio can be isotopically altered during diagenesis in addition the alteration of ca correlates with the alteration of mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks bulk carbonate 44 ca values vary between 0 60 and 1 31 srm 915a scale the average limestone 44 ca is 0 97 0 24 1sd identical within error to the average dolostone 1 03 0 15 1sd magnesium isotopic compositions 26 mg dsm 3 scale range between 2 59 and 3 91 and limestones 3 60 0 25 and dolostones 2 68 0 07 are isotopically distinct carbon isotopic compositions 13 c pdb scale vary between 0 86 and 2 47 with average limestone 1 96 0 31 marginally offset relative to average dolostone 1 68 0 57 the oxygen isotopic compositions 18 o pdb scale of limestones 1 22 0 94 are substantially lower than the dolostones measured 2 72 1 07 the isotopic data from 1196a suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories numerical modeling supports the contention that such trends can be interpreted as diagenetic and suggests that the appropriate distribution coefficient k mg associated with limestone diagenesis is 1 to 5 10 3 distinctly lower than those values 0 015 reported in laboratory studies with respect to mg isotopes the modeling also suggest that diagenetic fractionation factors of 0 9955 4 5 and 0 9980 2 are appropriate for limestone diagenesis and dolomitization respectively

authigenic carbonate formation rates in marine sediments and implications for the marine δ13c record abstract carbon isotope 13 c variations measured in carbonates have been attributed to large scale phenomena throughout earth history such as changes in atmospheric oxygen or global glaciations these interpretations follow from a model wherein the 13 c of marine dissolved inorganic carbon dic is controlled by the relative sedimentary burial rates of biogenic carbonate bc and organic carbon oc a new model proposes authigenic carbonate ac as a third major sedimentary c pool implying that 13 c anomalies are not necessarily indicative of extreme changes in the global carbon cycle and or atmospheric oxygen two conditions are required for ac formation to significantly alter bulk carbonate 13 c the ac isotopic composition must be at least 3 different from that of bc and the ac bc ratio must be 0 1 we use pore fluid ca and sr concentrations to estimate rates of ac formation in late cenozoic marine sediments then calculate relative fractions of ac oc and bc today ac is not expected to constitute a significant fraction of total sedimentary carbon ac oc bc globally however there are modern sites where local conditions promote elevated ac bc and anaerobic metabolisms can alter the 13 c of pore fluids we investigate these sites to determine what conditions might enable ac to alter 13 c of marine dic we find there is very little net addition of ac relative to bc but large quantities of ac form today across many settings via recrystallization in settings where remineralization of organic matter causes recrystallized carbonate to form with modified 13 c ac bc is generally too low for this recrystallization to significantly shift the 13 c of the bulk carbonate however exceptions are found in sites with very low bc and extensive methane oxidation suggesting that this environment type would need to be globally extensive in the past in order for ac formation to change the 13 c of marine dic

rock buffered recrystallization of marion plateau dolomites at low temperature evidenced by clumped isotope thermometry and x ray diffraction analysis abstract much debate exists on the extent to which early dolomites recrystallize and preserve the signature of their primary diagenetic setting here we combine clumped isotopes thermometry with x ray diffraction and thin section petrography to study dolomite recrystallization under shallow burial