variations in the nd isotopic composition of foraminifera from atlantic ocean sediments 143nd 144nd ratios have been measured in recent core top foraminifera from 25 sites throughout the atlantic ocean the average nd 0 value from this study agrees well with previous estimates of the average nd isotopic composition of the atlantic based on analyses of ferromanganese deposits and seawater samples however the larger data base and the nature of the samples have allowed us to identify distinct provenances of nd isotopes in the atlantic

variations of self potential and unsaturated water flow with time in sandy loam and clay loam soils abstract accurate assessment of soil water fluxes is essential in soil physics due to its direct implications in environmental agronomical or hydrological applications field estimations of soil water fluxes by classical hydraulic methods are often difficult to obtain moreover water fluxes are highly variable in space and time the obtainment of a reasonable estimate for this variable would require numerous measurement sites however such a requirement is rarely met thony et al cr acad sci paris earth planetary sci 325 1997 317 presented the experimental evidence of a linear relationship between the self potential sp and the unsaturated soil water flux therefore this relationship would allow the indirect assessment of the water flux using electrical measurements such an approach would appear much more flexible and easier to perform than the current hydraulic measurements the aim of this study is to experimentally investigate the existence and robustness of the flux sp relationship for different soil types and pedoclimatic conditions the soil water fluxes and the sp were monitored in a long term experiment involving two types of soils contrasting in hydraulic and electric properties the soils were placed in lysimeters which were instrumented with tensiometers and tdr probes for monitoring hydraulic heads and moisture content respectively unpolarizable sp electrodes temperature sensors and suction cups for collecting pore water were also installed in the lysimeters the sp and the fluxes were measured or calculated in the 30 40 cm depth section results show that the variations of the sp with time were clearly linked to both rainfall events and evaporation however in the long term the linear relationship between the unsaturated water flux and the sp evolves from strongly correlated to almost not correlated the slope sensitivity of the flux sp relationship varies with the soil type decreasing with more electrically conductive soil taking into account a varying soil electrode contact greatly improves the flux sp relationship at the scale of the rainfall event particularly when considering infiltration and drainage phases separately nevertheless at the scale of a year with alternated rainfalls and evaporation phases the robustness of the relationship decreases i e the coefficients of the relationship vary between events this variability could be related to time variations in electrical conductivity not so much to that of the soil water but rather to that of the water from the salted soil mud added to the sp electrodes at the time of installation this study points out methodological problems associated with the measurement of sp in shallow unsaturated soils over the long term and the need for designing specific electrodes for this purpose however in deep soils beneath the root zone environmental conditions generally vary slowly and lightly in comparison to surface horizons in this case and with our present set of sp measurement devices the flux sp relationship could be more stable than in the surface soil horizons and useful for examining aquifer recharge capillary rises or contaminant transfer

the fluvial geochemistry of the rivers of eastern siberia i tributaries of the lena river draining the sedimentary platform of the siberian craton abstract the response of continental weathering rates to changing climate and atmospheric pco 2 is of considerable importance both to the interpretation of the geological sedimentary record and to predictions of the effects of future anthropogenic influences while comprehensive work on the controlling mechanisms of contemporary chemical and mechanical weathering has been carried out in the tropics and to a lesser extent in the strongly perturbed northern temperate latitudes very little is known about the peri glacial environments in the subarctic and arctic thus the effects of climate essentially temperature and runoff on the rates of atmospheric co 2 consumption by weathering are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large rivers of eastern siberia the lena yana indigirka kolyma anadyr and numerous lesser streams which drain a pristine high latitude region that has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts common to western eurasia and north america the scale of the terrain sampled in terms of area is comparable to that of the continental united states or the amazon orinoco and includes a similarly diverse range of geologic and climatic environments in this paper the chemical fluxes from the western region the very large ancient and geologically stable sedimentary basin precambrian to quaternary of the siberian platform will be presented and compared to published results from analogous terrains in the tropical basins of china while the range in the chemical signatures of the various tributaries included here 60 sampled is large this mainly reflects lithology rather than the weathering environment the areal chemical fluxes are comparable to those of the chinese rivers being dominated by the dissolution of carbonates and evaporites the net consumption of atmospheric co 2 by aluminosilicate weathering is minor as it is in the tropical basins it is much smaller than in active orogenic belts in similar latitudes e g the fraser and yukon but comparable to those of the mackenzie tributaries that drain the eastern slope of the rockies lithology exerts the dominant influence in determining the weathering yield from sedimentary terrains and for a largely carbonate evaporite terrain climate does not have a direct effect

modification of streaming potential by precipitation of calcite in a sand water system laboratory measurements in the ph range from 4 to 12 spontaneous potentials associated with volcanic activity are often interpreted by means of the electrokinetic potential which is usually positive in the flow direction i e zeta potential of the rock is negative the water rock interactions in hydrothermal zones alter the primary minerals leading to the formation of secondary minerals this work addresses the study of calcite precipitation in a sand composed of 98 quartz and 2 calcite using streaming potential measurements the precipitation of calcite as a secondary mineral phase inferred by high calcite saturation indices and by a fall in permeability has a significant effect on the electrokinetic behaviour leading to a significant reduction in the zeta potential in absolute value and even a change in sign the measured decrease in zeta potential from 16 mv to 27 4 mv takes place as the ph rises from 4 to 7 while it remains constant at 25 1 mv as the ph increases from 8 to 10 5 for ph higher than 10 5 calcite precipitates and is expected to coat the quartz surface the measured zeta potential vary from 17 to 8 mv for ph ranging from 10 6 to 11 7 depending on the amount of precipitated calcite indicated by the decrease in permeability the observed change in sign of the electrical surface potential rules out the usual qualitative interpretation of sp anomalies in order to determine fluid circulations even at ph lower than 9 if calcite is widely present as a secondary mineral phase since the electrical surface potential of calcite depends also on co2 partial pressure and ca2 therefore sp anomalies as measured in hydrothermal field without mineralogical analyses of hydrothermal deposits and without geochemical fluid survey should be interpreted with caution

testing 87sr 86sr as a paleosalinity indicator on mixed marine brackish water and terrestrial vertebrate skeletal apatite in late paleocene early eocene near coastal sediments mississippi abstract mixed marine brackish water and terrestrial vertebrate skeletal apatite is found in the late paleocene early eocene tuscahoma and bashi formations of mississippi the co occurrence in these near coastal marine deposits of skeletal apatite with different provenances offers a unique opportunity for unraveling the effects of diagenesis on apatite 87sr 86sr composition with bearings on the use of this isotope pair as paleosalinity indicator the results show that the sr isotopes of all originally poorly ordered phases of skeletal apatite have extensively re equilibrated with pore water with significantly lower 87sr 86sr ratios than late paleocene early eocene seawater for example marine shark and ray teeth from the bashi formation all have clearly nonmarine 87sr 86sr ratios 0 7073 0 7075 compared with a coeval seawater ratio in the range 0 7077 0 7078 however separated shark tooth enamel with a high original crystallinity appears to have retained all or most of its in vivo sr isotopic signature until the present here we also show that 87sr 86sr results on recent vertebrate skeletal material from different environments are in good agreement with expected values for respective habitat earlier analyses of calcite material from the bashi formation indicated the existence of a shift in seawater 87sr 86sr to a lower value at the paleocene eocene boundary the strong influence of pore water with low nonmarine 87sr 86sr on the apatite in the bashi formation suggests that the proposed isotopic shift may be an artifact related to diagenetic processes

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

new evidence for subtropical warming during the late paleocene thermal maximum stable isotopes from deep sea drilling project site 527 walvis ridge the late paleocene thermal maximum lptm was a dramatic short term global warming event that occurred 55 ma warming of high latitude surface waters and global deep waters during the lptm has been well documented however current data suggest that subtropical and tropical sea surface temperatures ssts did not change during the event conventional paradigms of global climate change such as co2 induced greenhouse warming predict greater warming in the high latitudes than in the tropics or subtropics but nonetheless cannot account for the stable tropical subtropical ssts we measured the stable isotope values of well preserved late paleocene to early eocene planktonic foraminifera from south atlantic deep sea drilling project dsdp site 527 to evaluate the subtropical response to the climatic and environmental changes of the lptm planktonic foraminiferal 18o values at site 527 decrease by 0 94 from pre lptm to excursion values providing the first evidence for subtropical warming during the lptm we estimate that subtropical south atlantic ssts warmed by at least 1 4 c on the basis of possible changes in evaporation and precipitation the new evidence for subtropical sst warming supports a greenhouse mechanism for global warming involving elevated atmospheric co2 levels

neodymium isotope evolution of nw tethyan upper ocean waters throughout the cretaceous neodymium isotope compositions of twenty four fish teeth nineteen from the nw tethys and five from different locations within the tethys are interpreted to reflect the evolution of tethyan upper ocean water composition during the cretaceous and used to track changes in erosional inputs to the nw tethys and in oceanic circulation throughout the cretaceous the rather high end up to 7 6 of the nw tethyan upper ocean waters recorded from the late berriasian to the early aptian and the absence of negative excursions during this interval support the presence of a permanent westward flowing tethys circumglobal current tcc this implies that temperature variations during this time period inferred from the oxygen isotope analysis of fish tooth enamel were not driven by changes in surface oceanic currents but rather by global climatic changes the results presented here represent a significant advance over previously published cretaceous seawater nd isotope records our newly acquired data now allow the identification of two stages of low end values in the nw tethys during the early albian middle albian interval down to 10 and the santonian early campanian down to 11 4 which alternate with two stages of higher end values up to 9 during the late albian turonian interval and the maastrichtian used in conjunction with the oxygen isotope record the fluctuations of end values can be related to major climatic oceanographic and tectonic events that appeared in the western tethyan domain d 2005 elsevier b v all rights reserved

oxygen isotope variations in phosphate of biogenic apatites ii phosphorite rocks abstract phosphorites from sedimentary sequences ranging in age from archaean to recent were analysed for 18 o in both the po 4 18 o p and co 3 18 o c in the apatite lattice the oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts the use of the longinelli and nuti 8 temperature equation yields temperatures for recent phosphorites that are in good agreement with those measured in the field the 18 o p values of ancient phosphorites decrease with increasing age these changes with time are not likely to be due to post depositional exchange changes in 18 o values of seawater and variations of temperature with time can account for the 18 o p time trend but the latter explanation is preferred in ancient phosphorites 18 o c in structurally bound carbonate in apatite is not a reliable geochemical indicator

solubility equilibria in basalt aquifers the columbia plateau eastern washington u s a a speciation solubility geochemical model wateq2 was used to analyse geographically diverse groundwater samples from the aquifers of the columbia plateau basalts in eastern washington the groundwater samples compute to be at equilibrium with calcite which provides both a solubility control for dissolved ca and a ph buffer amorphic ferric hydroxide fe oh 3 a is at saturation or modestly oversaturated in the few water samples with measured redox potentials most of the groundwater samples compute to be at equilibrium with amorphic silica glass and wairakite a zeolite and are saturated to oversaturated with respect to allophane an amorphic aluminosilicate the water samples are saturated to undersaturated with halloysite a clay and are variably oversaturated with regard to other secondary clay minerals equilibrium between the groundwater and amorphic silica presumably results from the dissolution of the glassy matrix of the basalt the oversaturation with respect to the clay minerals other than halloysite indicates that their rate of formation lags the dissolution rate of the basaltic glass the modeling results indicate that metastable amorphic solids limit the concentration of dissolved si and suggest the same possibility for al and fe the results also suggest that the processes of dissolution of basaltic glass and formation of metastable secondary minerals are continuing even though the basalts are of miocene age and presumably have undergone a long history of contact with groundwaters the computed solubility relations are found to agree with the known assemblages of alteration minerals in the basalt fractures and vesicles if account is taken of both the difficulty of identifying amorphic phases and the slow rate of formation of clay minerals at low temperatures because the chemical reactivity of the bedrock will influence the transport of solutes in groundwater the observed solubility equilibria are important factors with regard to chemical retention processes associated with the possible migration of nuclear waste stored in the earth s crust specifically the occurrence of secondary minerals will enhance the sorption of dissolved radionuclides speciation solubility geochemical models provide an important means of determining these solubility equilibria relationships

neodymium isotopic reconstruction of late paleocene early eocene thermohaline circulation abstract high resolution fish tooth nd isotopic records for eight deep sea drilling project and ocean drilling program sites were used to reconstruct the nature of late paleocene early eocene deep water circulation the goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4 5 c warming of deep and bottom waters at the paleocene eocene boundary the paleocene eocene thermal maximum petm event the combined set of records indicates a deep water mass common to the north and south atlantic southern and indian oceans characterized by mean nd values of 8 7 and different water masses found in the central pacific ocean nd 4 3 and caribbean sea nd 1 2 the geographic pattern of nd isotopic values before and during the petm suggests a southern ocean deep water formation site for deep and bottom waters in the atlantic and indian ocean basins the nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the petm this finding is consistent with the pattern of warming established by recently published stable isotope records suggesting that deep and bottom water warming during the petm was gradual and the consequence of surface water warming in regions of downwelling

high resolution dating of deep sea clays using sr isotopes in fossil fish teeth abstract strontium isotopic compostitions of ichthyoliths microscopic fish remains in deep sea clays recovered from the north pacific ocean odp holes 885a 886b and 886c are used to provide stratigraphic age control within these otherwise undatable sediments age control within the deep sea clays is crucial for determining changes in sedimentation rates and for calculating fluxes of chemical and mineral components to the sediments the sr isotopic ages are in excellent agreement with independent age datums from above diatom ooze below basalt basement and within cretaceous tertiary boundary the clay deposit the 87 sr 86 sr ratios of fish teeth from the top of the pelagic clay unit 0 708989 indicate an late miocene age 5 8 ma as do radiolarian and diatom biostratigraphic ages in the overlying diatom ooze the 87 sr 86 sr ratio 0 707887 is consistent with a cretaceous tertiary boundary age as identified by anomalously high iridium shocked quartz and sperules in hole 886c the 87 sr 86 sr ratios of pretreated fish teeth from the base of the clay unit are similar to late cretaceous seawater 0 707779 0 707519 consistent with radiometric ages from the underlying basalt of 81 ma calculation of sedimentation rates based on sr isotopic ages from hole 886c indicate an average sedimentation rate of 17 7 m myr in unit ii diatom ooze 0 55 m myr in unit iiia pelagic clay and 0 68 m myr in unit iiib distal hydrothermal precipitates the sr isotopic ages indicate a period of greatly reduced sedimentation or possible hiatus between about 35 and 65 ma eocene paleocene with a linear sedimentation rate of only 0 04 m myr the calculated sedimentation rates are generally inversely proportional to cobalt accumulation rates and ichthyolith abundances however discrepancies between sr isotope ages and cobalt accumulation ages of 10 15 myr are evident particularly in the middle of the clay unit iiia oligocene paleocene

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

formation of hydrothermal carbonate in lake tanganyika east central africa abstract hydrothermal activity is observed in the shallow water environment of lake tanganyika chimneys and crusts consisting of mixtures of aragonite and magnesian calcite are associated with recent and subrecent hydrothermal fluids emerging from the lake floor the 13c values of the carbonates mean 13 c 2 1 indicate carbonate precipitation from hydrothermal co2 13 c 8 6 at temperatures between 16 and 33 c monomineralic samples only the 18o values of the carbonates range from 1 6 to 2 this is in accord with similar low carbonate formation temperatures from 17 to 37 c if present day hydrothermal solutions 18o 1 4 to 2 7 would be the source for the carbonates however absolute temperature measurements of the fluids are distinctly higher 50 104 c thus the carbonates precipitated at lower temperatures probably from mixtures of hydrothermal fluids with lake water

genesis of chlorine and sulphur in fumarolic emissions at vulcano island italy assessment of ph and redox conditions in the hydrothermal system chlorine and sulphur bearing compounds in fumarole discharges of the la fossa crater at vulcano island italy can be modelled by a mixing process between magmatic gases and vapour from a boiling hydrothermal system this allows estimating the compounds in both endmembers magma degassing cannot explain the time variation of sulphur and hcl concentrations in the deep endmember which are more probably linked to reactions of solid phases at depth before mixing with the hydrothermal vapours based on the p t conditions and speciation of the boiling hydrothermal system below la fossa the hcl and stot contents in the hydrothermal vapours were used to compute the redox conditions and ph of the aqueous solution the results suggest that the haematite magnetite buffer controls the hydrothermal fo2 values while the ph has increased since the end of the 1970s the main processes affecting ph values may be linked to na ca exchanges between evolved seawater feeding the boiling hydrothermal system and local rocks while na is removed from water calcium enters the solution undergoes hydrolysis and produces hcl lowering the ph of the water the increasing water rock ratio within the hydrothermal system lowers the ca availability so the aqueous solution becomes less acidic seawater flowing towards the boiling hydrothermal brine dissolves a large quantity of pyrite along its path in the boiling hydrothermal system dissolved sulphur precipitates as pyrite and anhydrite and becomes partitioned in vapour phase as h2s and so2 these results are in agreement with the paragenesis of hydrothermal alteration minerals recovered in drilled wells at vulcano and are also in agreement with the isotopic composition of sulphur emitted by the crater fumaroles

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

streaming potential measurements 2 relationship between electrical and hydraulic flow patterns from rock samples during deformation streaming potential and resistivity measurements have been performed on fontainebleau sandstone and villejust quartzite samples in a triaxial device during compaction uniaxial compression and rupture measurements on individual samples do not show any clear intrinsic dependence of the streaming potential coefficient with permeability an apparent dependence of the streaming potential coefficient with permeability is however observed during deformation the effect of surface conductivity is taken into account and is small compared with the observed changes in the streaming potential coefficient the observed dependence is therefore interpreted in terms of a difference in the evolution of the electrical and hydraulic connectivity patterns during deformation this effect causes the streaming potential coefficient and consequently the inferred potential to be reduced by a geometrical factor r g representing the electrical efficiency of the hydraulic network estimates of the r g factor varying between 0 2 and 0 8 for electrolyte resistivity larger than 100 m are obtained by comparing the values of the potential inferred from intact rock samples with the values obtained from crushed rock samples where the geometrical effects are assumed to be negligible the reduction of the streaming potential coefficient observed during compaction or uniaxial compression suggests that the tortuosity of the hydraulic network increases faster than the tortuosity of the electrical network before rupture an increase in the streaming potential coefficient associated with the onset of dilatancy was observed for three samples of fontainebleau sandstone and one sample of villejust quartzite the changes in streaming potential coefficient prior to failure range from 30 to 50 during one experiment an increase in the concentration of sulfate ions was also observed before failure these experiments suggest that observable streaming potential and geochemical variations could occur before earthquakes

variations in the strontium isotope composition of seawater during the paleocene and early eocene from odp leg 208 walvis ridge we refined the strontium isotope seawater curve for the paleocene and early eocene by analysis of samples recovered from the walvis ridge during ocean drilling project odp leg 208 the highest sr 87 sr 86 values occurred in the earliest paleocene at similar to 65 ma and generally decreased throughout the paleocene reaching minimum values between 53 and 51 ma in the early eocene before beginning to increase again at similar to 50 ma a plausible explanation for the sr 87 sr 86 decrease between 65 and 51 ma is increased rates of hydrothermal activity and or the eruption and weathering of large igneous provinces e g deccan traps and north atlantic strontium isotope variations closely parallel sea level and benthic delta o 18 changes during the late paleocene and early eocene supporting previous studies linking tectonic reorganization and increased volcanism to high sea level high co2 and warm global temperatures

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

effect of spatial correlation of cone tip resistance on the bearing capacity of piles abstractthe cone tip resistance qc from cone penetration tests cpts is widely used to determine the bearing capacity of piles although it is widely known that soil properties are spatially correlated the spatial correlation of qc is not considered in the current methods for predicting the bearing capacity of piles in this paper a probabilistic approach is presented for predicting the bearing capacity of driven piles in clay by considering the spatial correlation between qcsvn the spatial average of qc of the bottom soil layer within the pile length and qcbv the spatial average of qc over an interval near the pile base parametric studies are conducted to evaluate the effect of the spatial correlation between qcsvn and qcbv on the bearing capacity of piles the results indicate that it is important to consider the spatial correlation between qcsvn and qcbv in the probabilistic prediction of the bearing capacities of piles ignoring the spatial correlation between qcsvn and qcbv will underestima

rare earth element evolution of phanerozoic seawater recorded in biogenic apatites rare earth element ree contents of marine biogenic apatites have been shown to record seawater compositions a data base of available and newly acquired rare earth element ree contents of marine biogenic apatites has been created to assess the past seawater ree compositions to ensure that this data base contains only the pristine ree signals altered samples characterized by very low la sm n ratios where n stands for ree ratios normalized to the nasc composition gromet et al 1984 geochim cosmochim acta 48 1984 2469 acquired during apatite recrystallization are not included in the database these data reveal a change in the tethyan seawater composition between 110 and 80 ma after the end of the cretaceous the ree chemistry of seawater remains constant until present day this seawater composition change is likely due to concurrent changes in ree scavenging processes a strong correlation between decreasing sm yb n ratios and increasing ce anomalies for samples deposited during the 80 110 ma period is observed as ce anomalies are attributed to ocean water redox conditions changes in ree scavenging could reflect an evolution from stratified and poorly oxygenated waters towards well mixed and oxygenated waters this could have resulted from changing current patterns stemming from the contemporaneous opening of the atlantic ocean a major change in middle and late cretaceous oceanic circulation linked to plate tectonics would have favored the colonization of pelagic environments

neodymium isotopes in planktonic foraminifera a record of the response of continental weathering and ocean circulation rates to climate change the neodymium nd isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka here we present the first nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative reductive techniques the data along with mn ca ratios suggest that cleaned foraminifera provide a reliable record of nd in seawater and hold out the prospect of using nd in foraminifera to examine changes in seawater that accompany glacial interglacial climatic cycles the principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic fe mn coatings these contain large amounts of nd and other trace elements but can be cleaned off using highly reducing reagents mn ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range 10 100 mol mol that has yielded success in studies of transition elements in forams mass balance modelling suggests that for residual mn ca ratios 100 mol mol nd added to the foram in the coating will never shift the measured nd isotope composition significantly away from the seawater value acquired by the foram test in the water column additionally nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids finally core top planktonic foraminifera for two sites have nd isotope compositions that are identical to local surface seawater the data we present here for labrador sea forams over the past 2 5 m y are interpreted in terms of changes in the seawater isotopic composition the data show a pronounced shift from end values of 12 to 19 in the period 2 5 1 5 ma this change is interpreted to result from the initiation of northern hemisphere glaciation and the increased derivation of labrador sea nd via ice rafting from archaean terranes in central canada in combination with stable isotope and foraminiferal relative species abundance data the new nd data are consistent with the surface hydrography of the labrador sea being dominated by a fluctuating balance between cold polar waters containing unradiogenic nd and warm subtropical waters containing more radiogenic nd the major change in labrador sea nd that is observed in the past 2 5 ma can on its own account for the change in the nd isotope composition of north atlantic deep water over the same time period

identifying late miocene episodes of connection and isolation in the mediterranean paratethyan realm using sr isotopes abstract after decades of research the timing and nature of late miocene connections between the mediterranean paratethys and the global ocean are still speculative the hydrologic flux implications of exchange or isolation are central to all hypotheses for generating the major lithological changes that represent the messinian salinity crisis moreover differences in the hydrologic fluxes envisaged are the primary distinction between models despite this these fluxes remain largely unconstrained this paper describes the basis for using sr isotope data innovatively combined with salinity data through hydrologic budget modelling to determine the timing and nature of mediterranean hydrologic connectivity we examine the hypotheses for three late miocene events to illustrate how this approach allows us to test implied hydrologic scenarios and exclude incompatible models 1 pre evaporite restriction of the mediterranean 2 the initiation of salt precipitation 3 connection between the sea of marmara and both paratethys and the mediterranean during the messinian this process suggests that the atlantic mediterranean exchange was significantly reduced up to three million years before evaporite precipitation it also indicates that end member hypotheses for initiating salt precipitation in the mediterranean desiccation and connected basin models are inconsistent with sr isotope data a contrasting model where evaporite formation was triggered by atlantic transgression into a strongly evaporation dominated mediterranean is shown to be more compatible with available datasets the application to sea of marmara samples indicates that salinity changes in the basin were not caused by changes to the amount of inflow from either paratethys or the mediterranean other possible as yet untested applications important for constraining different aspects of the messinian salinity crisis are highlighted

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

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

evidence for triassic salt domes in the tunisian atlas from gravity and geological data abstract detailed gravity data were analyzed to constrain two controversial geological models of evaporitic structures within the triassic diapiric zone triassic massifs of jebel debadib and ben gasseur of the northern tunisian atlas based on surface observations two geological models have been used to explain the origin of the triassic evaporitic bodies 1 salt dome diapiric structure or 2 a salt glacier the gravity analysis included the construction of a complete bouguer gravity anomaly map horizontal gravity gradient hgg map and two and a half dimensional 2 5d forward models the complete bouguer gravity anomaly map shows a prominent negative anomaly over the triassic evaporite outcrops the hgg map showed the location of the lateral density changes along northeast structural trends caused by triassic cretaceous lithological differences the modeling of the complete bouguer gravity anomaly data favored the diapiric structure as the origin of the evaporitic bodies the final gravity model constructed over jebel debadib indicates that the triassic evaporitic bodies are thick and deeply rooted involving a dome diapiric structure and that the triassic material has pulled upward the younger sediment cover by halokinesis taking in account kinematic models and the regional tectonic events affecting the northern margin of africa the above diapirs formed during the reactive to active to passive stages of continental margin evolution with development of sinks otherwise this study shows that modeling of detailed gravity data adds useful constraints on the evolution of salt structures that may have an important impact on petroleum exploration models

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

rare earth elements and stable isotope geochemistry δ13c and δ18o of phosphorite deposits in the gafsa basin tunisia rare earth elements ree and stable isotope compositions 13c and 18o of shark teeth and phosphatic coprolites were analyzed from the lower maastrichtian layers of the el haria formation and two sequences of the paleocene eocene p e chouabine formation in the gafsa basin south western of tunisia in order to trace the sedimentological climatic and oceanographic conditions the ree chemistry and their distribution in the two archives are the same for each of the studied layers indicating that the coprolites and shark teeth experienced the same early diagenetic environments however major differences occur between the maastrichtian and the p e reflecting changes in the depositional conditions the early maastrichtian burial environment tended to be more anoxic with ree derived from reduced feo while in the p e the ree patterns mimic the modern oxic suboxic seawater the ree source from remineralisation of organic coating could have more significance the oxygen isotope compositions of the structural phosphates 18opo4 indicate a stable and warm climate during both studied time intervals a small offset 0 4 in the 18o value between the coprolites and shark teeth show minor thermal gradient between bottom and surface water the pronounced negative shift of 3 4 in 13c values recorded in the upper part of the chouabine formation was ascribed to the paleocene eocene boundary at the same time the lack of negative change in the 18o is explained by the semi closed situation of the gafsa basin which situation also played an important role in the evolution of the organic matters in the sediment resulting in the exceptional low 13c values

migration of sharks into freshwater systems during the miocene and implications for alpine paleoelevation trace element and isotopic compositions of fossilized shark teeth sampled from miocene marine sediments of the north alpine molasse basin the vienna basin and the pannonian basin generally show evidence of formation in a marine environment under conditions geochemically equivalent to the open ocean in contrast two of eight shark teeth from the swiss upper marine molasse locality of la moliere have extremely low 18o values 10 3 and 11 3 and low 87sr 86sr ratios 0 707840 and 0 707812 compared to other teeth from this locality 21 1 22 4 and 0 708421 0 708630 the rare earth element ree abundances and patterns from la moliere not only differ between dentine and enameloid of the same tooth but also between different teeth supporting variable conditions of diagenesis at this site however the ree patterns of enameloid from the exotic teeth analyzed for o and sr isotopic compositions are similar to those of teeth that have o and sr isotopic compositions typical of a marine setting at this site collectively this suggests that the two exotic teeth were formed while the sharks frequented a freshwater environment with very low 18o content and sr isotopic composition controlled by mesozoic calcareous rocks this is consistent with a paleogeography of high elevation 2300 m miocene alps adjacent to a marginal sea

a box model of the late miocene mediterranean sea implications from combined 87sr 86sr and salinity data 1 under certain conditions the strontium isotope ratio in the water of a semi enclosed basin is known to be sensitive to the relative size of ocean water inflow and river input combining sr isotope ratios measured in mediterranean late miocene successions with data on past salinity one can derive quantitative information on the mediterranean hydrological budget at times before and during the messinian salinity crisis msc previous studies obtained this hydrological budget by inverting the salinity and strontium data with steady state solutions to the conservation equations of salt strontium and water here we develop a box model with a time dependent set of equations to investigate the coeval evolution of salinity and sr ratios under different water budgets gateway restrictions and riverine sr characteristics model results are compared with the salinity and strontium ratio data from the mediterranean with a present day water budget strontium ratios in the mediterranean never reach the observed messinian values regardless of gateway restriction and water budget however a model with tripled river input as inferred for the late miocene is able to reproduce the sr ratios observed the onset of the msc can be explained with a simple restriction of the gateway s between the mediterranean and atlantic lower evaporite gypsum formed in a basin with less outflow to the atlantic than modeled in previous studies because of the large late miocene river input evaporite thicknesses predicted by our model and consistent with the messinian sr ratios are on the low end of the thickness range inferred from seismics

seasonal stable isotope evidence for a strong asian monsoon throughout the past 10 7 m y o of wet season rainfall was signi cantly morenegative 29 5 smow prior to 7 5 ma than after 26 5 smow if this change is attributable to a lessening of the amounteffect in rainfall this agrees with oral and soil geochemical datathat indicate increasing aridity beginning at 7 5 ma keywords tibetan plateau monsoon stable isotopes paleohydrology seasonality introductionthe tibetan plateau is the engine that drives the modern asianmonsoon by generating a high altitude region of low pressure in thesummer as the plateau heats and a region of high pressure in the winteras the plateau cools hastenrath 1991 during the summer warm airrises from the plateau pulling moist air off the ocean across the indiansubcontinent and into the highlands this results in heavy summer rain fall on the subcontinent the opposite occurs in the winter resultingin cold dry air spilling off the plateau and effectively excluding rainfrom the subcontinent thus the presence of a strong wet season dry season alternation implies the presence of a plateau broad and highenough to drive the monsoon the timing of the uplift of the plateau remains a matter of con siderable debate because there are few direct indicators of paleotopog raphy in the geologic record consequently past workers in tibet re lying on indirect indicators of uplift have proposed dates ranging from40 to 3 4 ma on the basis of initiation of potassic volcanism chunget al 1998 turner et al 1993 or extension on the plateau harrisonet al 1995 coleman and hodges 1995 changes in marine sedimen tation rates burbank et al 1993 sediment types rea et al 1998 or biota nigrini and caulet 1992 kroon et al 1991 and changesin stable carbon isotope and palynological patterns on the indian sub continent quade et al 1989 chen 1981 although different areasof the plateau may have risen at different times many workers haveinferred rapid simultaneous uplift of large areas of the plateau at 7 8ma by a process such as lithospheric delamination molnar et al 1993 this inference was based on the following approximately coevalphenomena a major change in plant communities of the indian sub continent quade et al 1989 and shifts in marine upwelling patternsthat are linked to an intense monsoon kroon et al 1991 althoughthere is strong evidence for signi cant climate change at 7 8 ma it isunclear whether this is the onset of the monsoon the oral transitionseems to have been a global rather than local phenomenon cerling etal 1997 and monsoonally driven upwelling may have already beenpresent by 10 12 ma nigrini and caulet 1992 kroon et al 1991 because there is an intimate association between the intense sea sonality of the modern monsoon and a high tibetan plateau and be cause evaporation can be unambiguously recognized in the d

hydrothermal system beneath aso volcano as inferred from self potential mapping and resistivity structure abstract we conducted self potential sp surveys sequentially from part to part over the central cones of aso volcano since august 1998 by december 2001 the compiled sp map revealed large sp anomalies on the central cones the main feature of the sp map is a w shaped profile along the ns transect over the central cones it is probable that this characteristic sp profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect a positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect to evaluate this sp anomaly we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three dimensional resistivity structure a layered structure obtained from a time domain electromagnetic tdem field experiment was used for the resistivity model the estimated current source is 300 a being located in a conductive layer around the sea level meanwhile sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of nakadake this value was used to estimate the equivalent current in either case of electro kinetic ek mizutani h ishido t 1976 a new interpretation of magnetic field variation associated with the matsushiro earthquakes j geomag geoelectr 28 179 188 or rapid fluid disruption rfd process johnston m j s byerlee j d lockner d 2001 rapid fluid disruption a source for self potential anomalies on volcanoes j geophys res 106 b3 4327 4335 this comparison suggests that the former process is preferable to explain the observed sp anomaly from these results we infer a large scale hydrothermal system beneath the central cones of aso volcano in which the fluid flow initiates from the surrounding area converging to the central vent to transport the heat and materials up to the crater lake of nakadake through a vapor filled conduit

distribution and volcano structural control of zeolites and other amygdale minerals in the island of martinique f w i abstract zeolites and other amygdale minerals have a widespread occurrence in martinique the central and east part of the island is composed of pre pliocene submarine formations hyaloclastitic tuffs pillow lavas swarms of dikes and domes here zeolites occur in about 10 well defined areas where specific associations constitute discrete zones of progressive metamorphism four zones are established which are believed to reflect temperatures ranging from 100 to 200 c within the outer zone i several of the following minerals occur together heulandite or clinoptilolite mordenite chabazite mesolite analcime and thomsonite characterize a narrow zone ii stilbite is widespread in zone iii and laumontite characterizes inner zone iv the lamentin thermal area is mainly com posed of recent monogenetic volcanoes age the distribution of zeolites and other amygdale minerals is not related to regional metamorphism brought about by burial but rather to areas of well defined heat flow where suitable fluids were available roots of deeply eroded volcanoes shallow magmatic intrusions and zones of intensive faulting could have provided the necessary heat required such structures are referred to in this communications as heat flow domes

constraints on miocene oceanography and climate in the western and central paratethys o sr and nd isotope compositions of marine fish and mammal remains abstract the paratethys evolved as a marginal sea during the alpine himalayan orogeny in the oligo miocene sediments from the northern alpine molasse basin the vienna and the pannonian basins located in the western and central part of the paratethys thus provide unique information on regional changes in climate and oceanography during a period of active alpine uplift oxygen isotope compositions of well preserved phosphatic fossils recovered from the sediments support deposition under sub tropical to warm temperate climate with water temperatures of 14 to 28 c for the miocene 18o values of fossil shark teeth are similar to those reported for other miocene marine sections and using the best available estimates of their biostratigraphic age show a variation until the end of the badenian similar to that reported for composite global record the 87sr 86sr isotope ratios of the fossils follow the global miocene seawater trend albeit with a much larger scatter the deviations of 87sr 86sr in the samples from the well constrained seawater curve are interpreted as due to local input of terrestrially derived sr contribution of local sources is also reflected in the end values consistent with input from ancient crystalline rocks e g bohemian massif and or mesozoic sediments with end 7 excluding samples showing local influence on the water column an average end value of 7 9 0 5 may be inferred for the miocene paratethys this value is indistinguishable from the end value of the contemporaneous indian ocean supporting a dominant role of this ocean in the western and central paratethys

revised phosphate water fractionation equation reassessing paleotemperatures derived from biogenic apatite oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite more prone to diagenetic alteration however recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques this questions the applicability of the phosphate water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data in this work we present a new phosphate water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at controlled temperature and with monitored water oxygen isotope composition the new equation reveals a similar slope but an offset of about 2 to the earlier published equations this work has major implications for paleoclimatic reconstructions using oxygen isotopes of biogenic apatite since calculated temperatures have been underestimated by about 4 to 8 c depending on applied techniques and standardization of the analyses

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

gradual changes in upwelled seawater conditions redox ph from the late cretaceous through early paleogene at the northwest coast of africa negative ce anomaly trend recorded in fossil bio apatite abstract marine vertebrate fossils from late cretaceous early paleogene shallow marine phosphorites of morocco were investigated for their trace element compositions and neodymium isotopic ratios in order to constrain marine and depositional conditions the various analyzed fossils are separated into two groups with different geochemical compositions 1 shark tooth enameloid with generally lower cu ba rare earth elements rees and u and higher na zn and sr concentrations than 2 dentine bone and coprolites these differences are related to the originally different structures of these fossils all the fossils revealed very similar shale normalized ree patterns with negative ce anomaly and heavy ree enrichment mimicking the ree pattern of modern oxic seawater the results therefore suggest ree uptake by the fossils from an early diagenetic pore fluid that was dominated by seawater importantly the ce anomaly does not vary among the different types of fossil remains and the values are very similar in a given layer moreover a step wise shift towards lower ce ce values from older to younger beds is apparent nd isotope analyses across the phosphorite succession yielded minor variation with an average end t value of 6 2 0 4 n 12 indicating no major changes in the ree source during the studied interval the relatively radiogenic values reflect tethyan connection and or important contribution of a mafic nd source from weathering in the region the age related trend in the ce anomaly is interpreted to be due to changes in redox and or ph conditions of the upwelling seawater on the shallow shelf areas the driving force of these changes was probably an extended global oceanic circulation especially enhanced connection and water exchange between the north and south atlantic

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

oxygen strontium and neodymium isotope composition of fossil shark teeth as a proxy for the palaeoceanography and palaeoclimatology of the miocene northern alpine paratethys the upper marine molasse sediments of southern germany were deposited during the early to middle miocene a period of significant change for the global miocene palaeoceanography palaeoclimate and the regional palaeogeography because of the ongoing alpine himalayan orogeny to address the influence of the alpine uplift on climate and oceanography of the northern alpine molasse basin a combined o sr and nd isotope study was undertaken on fossil teeth from sharks synodontaspis sp galeocerdo cf aduncus chaenogaleus sp and button like teeth from the bony fish of the upper marine molasse chrysophrys molassica average 18o values for hydroxyapatite of teeth from two sites are 20 3 1 0 6 and 21 2 1 0 5 while their average 87sr 86sr and 143nd 144nd ratios are 0 70850 0 00001 2 and 0 70882 0 00003 2 and 0 51220 and 0 51223 both at 0 00001 2 respectively by comparison to the sr evolution curve for the global ocean the sr isotope compositions suggest ages of about 22 and 17 ma for the teeth these ages are in good agreement with the depositional ages which suggests open marine conditions open marine conditions are also compatible with 1 lower average 18o values and 87sr 86sr ratios for the one site compared to higher 18o values and higher 87sr 86sr ratios for the other site 2 estimates for seawater temperatures which are similar to other estimates from deposits of similar latitude and age 3 a comparison of seawater temperatures with average ambient air temperature estimates deduced from continental palaeoclimate indicators nd isotope compositions are compatible with an influence of the north atlantic on the paratethys assuming constant salinity and seawater oxygen isotope composition a 4 c cooling can be inferred from average 18o values of the teeth between 22 and 17 ma this is similar to trends observed for foraminiferal records from the mediterranean tethys but different from foraminiferal and molluscan records of the north atlantic and the north sea during this period and allows for the possibility that the alpine orogeny had an influence on the regional circum alpine climate

strontium isotopes in biogenic phosphates from a neogene marine formation implications for palaeoseawater studies abstract neogene marine deposits of nw france faluns are rich in a variable array of well preserved phosphatic vertebrate fragments many of these are of the same age as the host sediments and consist of the remains of fish mammals and reptiles whilst others are clearly mesozoic turonian in age we have determined the sr isotopic composition of 24 phosphatic samples in order to study the efficacy of using the method to date the neogene materials and to investigate the effects of diagenesis and seawater alteration on the terrestrial material the sr isotope results obtained on the ichthyoliths and the other neogene marine vertebrates suggest an age of 11 ma for the base of the host sediments tortonian which corresponds precisely with the palaeontological data in contrast the initial isotopic composition of the contemporaneous terrestrial mammals and reptiles which should record higher continental sr ratios are close to the value of their marine counterparts the same trend is observed for a sample of shark s tooth of mesozoic age where the sr isotopic composition approaches a neogene value the results demonstrate that alteration by seawater or interstitial waters is able to introduce significant quantities of sr into the phosphate leaching experiments carried out on the materials does not remove this secondary strontium and we were unable to establish the original values of the terrestrial material our conclusion is that the use of sr isotopes to characterise phosphatic materials must be viewed with caution particularly if the materials are reworked

strontium isotopic signatures in the enameloid and dentine of upper cretaceous shark teeth from western alabama paleoecologic and geochronologic implications abstract the 87sr 86sr isotopic composition of the enameloid tips of teeth of scapanorhynchus texanus a common and widespread upper cretaceous shark differs from that found in the dentine inner portions of the same teeth using a marine 87sr 86sr isotopic evolution curve we converted the 87sr 86sr isotopic composition of different sections of the teeth to numerical ages portions of fossil teeth dominated by enameloid but that include some dentine yield numerical ages 74 2 0 8 ma 2 standard error s e that fall within the upper cretaceous and are consistent with the known geologic age range of these fossils as the proportion of dentine present in samples of the teeth increases the 87sr 86sr derived numerical ages trend from biostratigraphically reasonable upper cretaceous ages to those that are far younger and biostratigraphically impossible about 32 ma i e oligocene this deviation in isotopic composition and numerical age is likely the result of post burial diagenetic alteration of dentine which is generally more susceptible to such alteration than enameloid to avoid the contaminating effects of dentine we sampled only the enameloid portion of twelve s texanus teeth by scratching their surfaces the enameloid scratch samples yield numerical ages 78 8 0 4 ma 2 s e older than those obtained for any of the sectioned samples this suggests that sampling only the surface enameloid of shark teeth is useful in reducing spurious isotopic results arising from post burial alteration of teeth the numerical age for the enameloid scratch samples is consistent with the known early campanian early maastrichtian occurrence of s texanus in north america and with the radiometric age of the deposit from which these samples were recovered

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

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

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

nd isotope evidence for the evolution of the paleocurrents in the atlantic and tethys oceans during the past 180 ma the nd isotopic composition of atlantic and tethys seawater as deduced from marine phosphorites varied considerably during the past 180 ma the early tethys and central atlantic seawater from 180 to 160 ma ago early middle jurassic had a nd isotopic signature identical to that of the pacific end 6 suggesting that pacific seawater entered the newly forming tethys basin however with time continental runoff draining into the young basin became more important and led to a decrease in the nd isotopic composition and finally a decoupling from the pacific ocean during the late early cretaceous 120 90 ma ago atlantic and tethys seawater reached continental crust like nd isotopic composition values end 10 which could reflect high weathering rates induced by the warm and humid climate at that time in the time span between 80 and 50 ma late cretaceous early tertiary the nd isotopic composition of both tethys and atlantic seawater strongly increased towards pacific seawater values in the case of the atlantic ocean this change has been correlated with the opening of the south atlantic which enabled the more radiogenic pacific seawater to travel westwards around the southern edge of africa into the south and finally the north atlantic in the case of tethys seawater we have to assume that during this period large masses of pacific seawater entered the tethys again directly through the indian tethys seaway the renewed importance of this seaway might be related to the late cretaceous early tertiary first order global sea level highstand the most abrupt change towards lower more crust like values occurred in the early miocene 25 17 ma ago in the south and north atlantic as well as in the tethys during this period the143nd 144nd isotope ratios dropped from 0 5124 end 4 2 down to 0 5122 end 8 this change indicates a diminishing influx of pacif seawater into the atlantic and tethys oceans and can be correlated with the breakdown of the circum equatorial circulation patterns of the world oceans due to plate tectonics from 20 to 17 ma ago miocene the nd isotopic composition of the atlantic ocean increased again and reached values as high as 0 5123 end 6 6 whereas tethys seawater remained at low values this decoupling can be correlated with the incipient complete isolation of the tethys the nd isotopic composition was henceforth controlled by the continental runoff from surrounding land masses the major increase in the nd isotopic composition observed in the atlantic can be related to the opening of the drake passage and establishment of the circum antarctic current system this allowed pacific seawater to enter directly the south atlantic around antarctica a renewed drop in the nd isotopic composition of atlantic seawater during the late miocene can be related to the onset of north atlantic bottom water formation and its subsequent upwelling

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures