alteration of hyaloclastites in the hsdp 2 phase 1 drill core 2 mass balance of the conversion of sideromelane to palagonite and chabazite this is the publisher s version also available electronically from http onlinelibrary wiley com

ground penetrating radar assisted saturation and permeability estimation in bimodal systems near surface investigations often require characterization of vadose zone hydraulic parameters conventional sampling or borehole techniques for estimating these parameters are costly time consuming and invasive all of which limit collection of hydrogeological data at a spacing needed for detailed site characterization incorporation of two or three dimensional densely sampled geophysical data with conventional hydrological data increases the amount of data available for the characterization and thus has the potential to significantly improve the hydraulic parameter estimates over those obtained from borehole data alone the hydraulic estimation procedure can be greatly improved by incorporating dielectric information potentially available from ground penetrating radar gpr a noninvasive high resolution geophysical method the procedures for collecting and processing gpr data in the format needed for the proposed estimation technique are relatively new and still a topic of research our method requires as a starting point the ability to estimate dielectric constants from gpr data numerical experiments were performed to investigate the general utility of the gpr assisted estimation technique under a range of conditions three bimodal systems were investigated each system being composed of a sand facies together with another facies with a larger clay volume fraction each facies was defined using characteristic values of clay content porosity and permeability using dielectric information and petrophysical relations degree of saturation and intrinsic permeability values at each location within the three systems were identified for bimodal systems a dielectric constant measurement corresponds to two possible values of saturation and intrinsic permeability at each location single values of saturation and intrinsic permeability were estimated from these values using the principle of maximum likelihood results from case studies demonstrate that a combination of gpr data with conventional borehole data significantly improves the estimates of saturation and has the potential to improve the estimates of permeability over those obtained from well bore data alone the proposed method should be especially advantageous for vadose zone characterization in areas favorable for gpr data acquisition where detailed hydraulic parameter information is required but the drilling of numerous boreholes is prohibited

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

the stability of gypsum in marine sediments using the entire odp iodp porewater composition database abstract the stability of gypsum in marine sediments has been investigated through the calculation of its saturation index at the sediment in situ temperature and pressure using the entire odp iodp porewater composition database 14416 samples recovered from sediments collected during 95 odp and iodp legs saturation is reached in sediment porewaters of 26 boreholes drilled at 23 different sites during 12 odp iodp legs as ocean bottom seawater is largely undersaturated with respect to gypsum the porewater ca content or its so4 concentration or both must increase in order to reach equilibrium at several sites equilibrium is reached either through the presence of evaporitic gypsum layers found in the sedimentary sequence and or through a salinity increase due to the presence of evaporitic brines with high concentrations of ca and so4 saturation can also be reached in porewaters of seawater like salinity 35 provided sulfate reduction is limited in this case saturation is due to the alteration of volcanogenic material which releases large amounts of ca to the porewaters where the ca concentration can reach 55 times its seawater value as for example at odp leg 134 site 833 at a few sites saturation is reached in hydrothermal environments or as a consequence of the alteration of the basaltic basement in addition to the well known influence of brines on the formation of gypsum these results indicate that the alteration of sediments rich in volcanogenic material is a major process leading to gypsum saturation in marine sediment porewaters therefore the presence of gypsum in ancient and recent marine sediments should not be systematically interpreted as due to hypersaline waters especially if volcanogenic material is present

electromagnetic traveltime tomography application for reservoir characterization in the lost hills oil field california electromagnetic em traveltime tomography has been applied for reservoir characterization at the lost hills oil field california four data sets at frequencies of 24 90 370 and 1000 hz were obtained along a pair of monitoring boreholes located 80 5 m apart traveltime information was first extracted from these em data sets using a wavefield transform with a ray series approximation the conductivity contrast of each layer is no greater than two in the region of interest so the first arrivals can be estimated within 5 error by the approximate scheme a nonlinear traveltime tomography algorithm adopting a fresnel zone concept was then applied to obtain the conductivity model between the boreholes the resultant conductivity image represents the conductivity structure between the boreholes this image is consistent with the results of both a finite difference inversion and the induction log obtained prior to waterflooding comparing the two conductivity images with the induction logs we observe major

foraminiferal evidence for holocene environmental transitions in the yaojiang valley south hangzhou bay eastern china and its significance for neolithic occupations abstract the transition from a marine influenced environment to a coastal plain setting during the early to middle holocene was crucial for early human occupation along the eastern china coast here detailed foraminiferal analyses were completed for two sediment cores yj1505 and yj1508 retrieved from the yaojiang valley yjv along the southern hangzhou bay coast of eastern china brief environmental changes in the yjv during the early middle holocene were recovered on the basis of radiocarbon chronology the assemblages and detrended correspondence analysis dca results of the foraminifera of both cores indicated that the yjv was evidently under a marine influence from 9200 to 7900 cal yr bp prior to that it was a fluvial incised valley the increasing trends in shallow marine foraminifera and the planktonic benthic foraminifera p b ratio showed that a transgressive period possibly occurred in the valley ca 9200 7900 cal yr bp and their following decreases suggested that a rapid regression process occurred thereafter the disappearance of foraminifera and formation of a peaty layer in core yj1505 ca 7600 6500 cal yr bp implied a brief environmental transition to a limnetic wetland setting in the valley centre which would have been attractive to early human settlers the disappearance of foraminifera in core yj1508 at the valley s eastern entrance suggested that most areas of the valley were located far from marine influence after ca 6250 cal yr bp then the limnetic wetland setting transitioned into a coastal plain environment attracting more people to the valley such a transition in the yjv would have provided more opportunities for ancient people and possibly catalysed the development of the hemudu culture hc for approximately two millennia

electromagnetic ray trace tomography electromagnetic em tomography can be used to estimate the distribution of electrical rock properties between boreholes for typical oil field well spacings and reservoir electrical characteristics crosswell em measurements are sensitive primarily to the electrical conductivity not the permittivity ray tracing methods normally associated with undamped propagating waves can also be applied to the rapidly attenuated diffusive em waves encountered in the petroleum reservoir environment thermal noise considerations place an upper limit of approximately 20 skin depths on the separation between wells

hydrothermal water rock interaction and the redistribution of li b and cl in the taupo volcanic zone new zealand abstract lithium b and cl occur as trace elements in the dominant protoliths rhyolite andesite and greywacke underlying high temperature hydrothermal systems in the taupo volcanic zone tvz the fluid mobility of li decreases substantially at 200 c 20 c with the pervasive deposition of quartz chlorite regardless of protolith and altering fluid compositions boron and cl are more fluid mobile than li at all temperatures with mobility affected by the rock type composition of circulating aqueous solutions and to a limited extent by incorporation of the trace elements in hydrothermal minerals uptake of b by clays decreases its mobility at 320 c occur compared to volcanic rocks the mobility of b and cl in greywackes is very low and thus the b cl signature of greywacke in hydrothermal aqueous solutions of the tvz is overwhelmed by the effects of rhyolite and andesite dissolution temperature dependent transitions from mg fe clays and phyllosilicates to k bearing illitic clays tend to decrease the mg li ratios in aqueous solutions at 200 c

an integrated chemical and stable isotope model of the origin of midocean ridge hot spring systems chemical and isotopic changes accompanying seawater basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs incorporating provision for addition and subtraction of a wide range of reactant and product minerals as well as cation and oxygen and hydrogen isotopic exchange equilibria the models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100 to 350 c with an overall water rock ratio of about 0 5 being constrained by an assumed 18 o h 2o at 350 c of 2 0 per mil h craig personal communication 1984 this is a realistic model because 1 the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust 2 the water rock ratio is high 50 at low temperatures and low 0 5 at high temperatures and 3 it allows for back reaction of earlier formed minerals during the course of reaction progress the results closely match the major element chemistry von damm et al 1985 and isotopic compositions craig et al 1980 of the hydrothermal solutions presently emanating from vents at 21 n on the east pacific rise the calculated solution chemistry for example correctly predicts complete loss of mg and so 4 and substantial increases in si and fe however discrepancies exist in the predicted ph 5 5 versus 3 5 measured and state of saturation of the solution with respect to greenschist facies minerals the calculated d h 2o is 2 6 per mil in excellent agreement with analytical determinations the calculated chemical mineralogic and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges humphris and thompson 1978 stakes and o neil 1982 as well as with data from ophiolites gregory and taylor 1981 predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite epidote chlorite tremolite greenschist assemblage at 350 c the models demand that the major portion of the water rock interaction occur at temperatures of 300 350 c interaction at temperatures below approximately 250 c results in negative 18 o h 2o shifts contrary to the observed positive 18 o values of the fluids exiting at midocean ridge vents hydrogen isotope fractionation curves by suzuoki and epstein 1976 lambert and epstein 1980 and liu and epstein 1984 among others are compatible with the model and require d h 2o to increase at all temperatures as a result of seawater basalt interaction

the temporal evolution of fluid flow through the tahiti barrier reef traced by sr isotopes and pore water chemistry abstract the internal fluid circulation of the tahiti barrier reef has been studied with sr isotopes and pore water chemistry the study is based on 15 sample series recovered over 2 years from a 150 m deep core drilled through the entire barrier reef down to the volcanic basement temperature data suggest that the interstitial fluids originate from seawater that penetrated the volcanic basement to at least 200 m depth on the ocean sided slope below the barrier reef subsequently the fluids migrated upward driven by buoyancy through the entire reef chemical evolution of the interstitial fluids is mainly controlled by basalt seawater interaction and by admixture of seawater from the open ocean during upward migration these processes are monitored with 87sr 86sr isotope ratios h4sio4 concentrations and alkalinity to give a picture of the evolution of interstitial fluid flow over 2 years the results indicate that the internal circulation patterns change through time the modifications concern mainly the residence time of the fluids within the volcanics and the intensity and localization of lateral seawater admixture within the karstified pleistocene reef

yangtze delta eastern china 2 late quaternary subsidence and deformation abstract late quaternary deposits examined on high resolution seismic profiles provide evidence of recent subsidence of the outer yangtze delta in the east china sea deformed late pleistocene strata and mud diapirs tilted bedding and gas deformed structures in holocene sequences record remobilization of underconsolidated sediment within and adjacent to the yangtze depocenter deformation types and their specific position relative to the depocenter record displacement of sediment as a result of quaternary overburden and probable compaction and deep seated tectonic motion the configuration of depositional sequences demonstrates that subsidence in the outer yangtze delta has continued from the late pleistocene to the present

runoff control of soil degassing at an active volcano the case of piton de la fournaise reunion island abstract airborne atmospheric and in situ soil gas analyses demonstrate that distal gas leaks are non existent at piton de la fournaise pf despite frequent eruptions airborne traverses made at a constant altitude indicated that no detectable large scale co 2 degassing occurs from the volcano in situ soil gas traverses co 2 4 he 222 rn across the active rift zones the summit crater and the caldera rims show both a lack of positive anomalies and evidence of strong depleted concentrations for he and co 2 with respect to air depletions in soil he is explained by intense rain water infiltration a more unexpected result lies in the very low co 2 concentrations down to 92 ppm in bare soils in the summit region such a depletion was not previously reported and is attributed to considerable basalt weathering operating as the result of huge runoff a model has enabled both the runoff and the co 2 consumption occurring within the basaltic layers to be calculated data obtained are consistent with values expected from large scale erosion models and with the local calculated diffusive flux of co 2 in soils the huge runoff together with the basaltic lithology of the volcano are found to be the main factor controlling the soil gas signatures at pf

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

crosswell electromagnetic tomography in steel cased wells the applicability of crosswell electromagnetic em tomography is limited when the boreholes are steel cased steel casing is typically eight orders of magnitude more conductive than the formations around the borehole consequently the high frequency signals which are needed to resolve the formation conductivity distribution in the interwell region cannot be radiated or received by antennas inside the casing introduction of small insulating gaps in the casing eliminates these problems by creating ports where signals can exit and enter the casing making the casing an electric bipole antenna the gapped casing can be operated in a shorted port or open port mode in the shorted port mode the voltage is specified at a source port and the current is measured at all the remaining shorted ports in the open port mode the current is specified at a source port and the voltage is measured at all the remaining open ports for high frequency shorted port operation the effective length of the casing bipole ant

ferric ferrous ratios h 2 o contents and d h ratios of phlogopite and biotite from lavas of different tectonic regimes complete chemical analyses including ferric and ferrous iron h2o contents and dd values for 16 phlogopite and biotite and 2 hornblende separates are presented samples were obtained from volcanic rocks from four localities 1 phlogopite phenocrysts from minette lavas from the western mexico continental arc 2 biotite and hornblende phenocrysts from andesite lavas from mono basin california 3 phlogopite and biotite from clinopyroxenite nodules entrained in potas sic lavas from the east african rift uganda and 4 phlogopite phenocrysts from a wyomingite lava in the leucite hills wyoming the fe 2 o 3 contents in the mi cas range from 0 8 to 10 5 wt corresponding to 0 09 to 1 15 fe 31 per formula unit pfu water contents vary from 1 6 to 3 0 wt corresponding to 1 58 to 3 04 oh pfu significantly less than would be expected for a site fully occupied by hydroxyl cation and anion based normalization procedures provide accurate mineral for mulae with respect to most cations and anions but are unable to generate accurate estimates of fe 31 yfe t a nd overestimate oh at the expense of o on the hydroxyl site these inaccuracies are present despite acceptable adjust ed totals and stoichiometric calculated site occupancies the phlogopite and biotite phenocrysts in arc related lavas from western mexico and eastern california have the highest fe 31 yfe t ratios 56 87 reflecting high magmatic oxygen fugacities dnno 51 2t o 15 in contrast to those from uganda 25 40 and the leucite hills 23 there is no correlation between the oh content and the fe 31 yfe t ratio in the micas values of k mgyfe 21 d 2s errors were calculated for three phlogo pite olivine pairs 0 12 0 12 0 26 0 14 0 09 0 12 two biotite hornblende pairs 0 73 0 08 and 1 22 0 10 and a single phlogopite augite pair 1 15 0 12 values of k fyoh d for two biotite and hornblende pairs could not be determined without significant error because of the extremely low f contents 0 2 wt of the four phases the dd values obtained in this study encompass a large range 2137 to 243 the phlogo pite and biotite separates from uganda have dd values of 270 to 249 which overlap those believed to represent primary mantle there is a larger range in dd values 2137 to 243 for phlogopite phenocrysts from west ern mexico minette lavas although their range in d 18 o values 5 2 6 2 is consistent with normal mantle it is unlikely therefore that the variable dd values reflect heterogeneity in the mantle source region of the minette magmas nor can the extremely low dd values reflect degassing of h2 or h2o since almost 100 loss of dis solved water in the magma is required an unrealistic scenario given the stability of the hydrous phenocrysts the very low dd values of the mascota minette phlogo pites require that the hydrogen be introduced from an external source e g meteoric water whatever the pro cess responsible for the observed hydrogen isotope com position it had no effect on the d 18 o value fo2 ah2o or bulk composition of the host magmas

fundamental processes controlling the first stage of alteration of a basalt glass by seawater an experimental study between 200 and 320 c the first stage of alteration of a basalt glass by seawater has been studied experimentally between 200 and 320 c under vapor pressure following both the chemical evolution of the reacting solutions during the experiments and the chemical and mineralogical transformations of the altered glass surface via microprobe scanning transmission electron microscope and resonant nuclear reactions the alteration is controlled by diffusion of dissolved species through an altered layer and not by surface chemical reaction selective removal of cations with respect to sio2 leads to the formation of a thick porous protonated surface layer enriched in sio2 aqueous diffusion of dissolved species from the reacting glass and from solution through the pores of this layer results in the formation of an amorphous silicate gel which is the precursor of normal crystalline clays saponites appearing in a later stage computer simulations of the alteration generated with the eq3 6 computer software package account for the chemical composition of the rim and the sequence of secondary minerals found in the experiments

oxygen isotope water relations in altered deep sea basalts low temperature mineralogical controls detailed analyses of oxygen isotope water relations in 3 13 and 109 ma old mid ocean ridge basalts reveal that to a first approximation the low temperature alteration of deep sea basalts in the upper few hundred metres of the igneous crust can be modelled as the partial conversion of basalt to smectite formed in isotopic equilibrium with seawater second order variations in 18o versus h2o plots are used to show that this approximation breaks down in detail because secondary mineral assemblages and mass transfer vary widely in response to subtle variations in temperature and or fluid flow strongly oxidized open systems can evolve relatively low i8o hydrous oxide rich assemblages if leaching is efficient dsdp deep sea drilling project site 396 or relatively anhydrous high 18o k feldspar rich assemblages if plagioclase breaks down site 417 compared with the clay mineral dominated assemblages common in somewhat more restricted flow environments zonal distribution and common superposition

time domain inversion of gpr data containing attenuation resulting from conductive losses many seismic data processing and inversion techniques have been applied to ground penetrating radar gpr data without including the wave field attenuation caused by conductive ground neglecting this attenuation often reduces inversion resolution this paper introduces a gpr inversion technique that accounts for the effects of attenuation the inversion is formulated in the time domain with the synthetic gpr waveforms calculated by a finite element method fem the jacobian matrix can be computed efficiently with the same fem forward modeling procedure synthetic data tests show that the inversion can generate high resolution subsurface velocity profiles even with data containing strong random noise the inversion can resolve small objects not readily visible in the waveforms further the inversion yields a dielectric constant that can help to determine the types of material filling underground cavities

seawater sediment basalt interactions stable isotope h o and elemental fluxes within the ordovician volcano sedimentary sequence of erquy brittany france the ordovician volcano sedimentary succession of erquy northern brittany is made of immature sediments thermally metamorphosed at the contact of intruding basic sills pillow lavas constitute the upper part of the sequence the trace element geochemistry of sills and pillow lavas suggests that they were derived from a tholeiitic source located beneath a passive margin this volcanic sequence was metamorphosed under low to moderate greenschist facies conditions in this study the direction and amplitude of chemical and isotopic fluxes in the basalt sediment water system were established and the oxygen and hydrogen isotope compositions of the aqueous fluid that reacted with the volcanic rocks were characterized cationic thermometry on chlorites and isotopic thermometry on plagioclase chlorite pairs indicate closure metamorphic temperatures in the range 200 250 c for the basaltic sills stable isotope compositions of iron rich chlorites 18o 5 5 d from 60 to 50 and plagioclases 18o from 9 to 10 reveal that the source of the fluid was certainly seawater the 18o variations within the sills are strongly correlated with the rate of progress of the main metamorphic reaction clinopyroxene plagioclase ilmenite chlorite albite epidote quartz sphene that produced major element mobility at the scale of the volcanosedimentary sequence calculation of elemental fluxes by mass balance combined with oxygen isotopic compositions of basalts shows that the highest water rock ratios 1 were at sill sediment boundaries and within pillow lavas at the top of the pile the volcanosedimentary sequence of erquy was a net sink for na and a source for ca no mg uptake could be detected whereas the hydrothermal alteration of the sediments released fe si and k trapped by the volcanic rocks the 18o value of the fluid reacting with sills appears to have shifted no more than 4 after percolation at low temperature through immature sediments 18o 12 the erquy volcano sedimentary sequence represents a marine hydrothermal system dominated by low temperature exchange which allowed a general 18o enrichment of the volcanic rocks and a 18o depletion of sediments

a time series of vent fluid compositions from 21 n east pacific rise 1979 1981 1985 and the guaymas basin gulf of california 1982 1985 a time series study of four hot spring fields at 21 n on the east pacific rise demonstrates that the solution compositions of mid ocean ridge hydrothermal vents are stable on a decadal time scale the ocean bottom seismometer obs national geographic smoker ngs and south west sw vents show no significant changes in the major element composition of their end member fluids since 1979 two of the vents obs and sw have maintained exit temperatures near 350 c since 1979 the ngs vent has remained close to 270 c since 1981 after cooling from 350 c in 1979 only one vent hanging gardens shows important changes in solution chemistry from 1981 to 1985 in 1985 this vent appears to have cooled 10 c relative to the other vents the depth of the reaction zone as determined by quartz geobarometry has increased by about 1 km at this vent the large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances rather the constancy of small interfield variations in solution composition is more consistent with control by rock buffering a 4 year time series study of hydrothermal vents in the guaymas basin also shows no significant changes in the major element composition of the end member fluids interfield differences in solution chemistry have been maintained from 1982 to 1985 this phenomenon is best explained in terms of an equilibrium model

pore water geochemistry and mixing processes within the tahiti barrier reef abstract we report a multi parameter study of hydrological and geochemical tracers in a deep borehole 150m of the tahiti barrier reef the principal objective was to characterize the origin of the reef interstitial waters and their exchange and mixing patterns with the surrounding ocean waters the measurements show that the hydrological and geochemical properties within the borehole at any given level are distinct from the oceanic composition the vertical distribution of the various tracers displays a coherent picture and identifies two major sources for the reef interstitial waters first a deep pacific water recharge from at least 350 m depth and second pacific surface waters that penetrate from the top and the upper section of the reef flanks the deep pacific waters are thought to infiltrate at the periphery of the volcanic edifice they move upward through the basaltic basement and on rising are further mixed inside the carbonate pile with the pacific surface waters

evidence of an early alteration process driven by magmatic fluid in mururoa volcano evidence for a deuteric alteration process induced by a magmatic fluid has been found in the feeder zone of the mururoa volcano french polynesia within the dikes where basaltic glass does not show any evidence of pervasive alteration vesicles are filled with dioctahedral smectites and calcite while olivine phenocrysts are replaced by dioctahedral smectites ankerite and calcite the 13c signature of carbonates the carbon and h2o content of the whole rocks and their impoverishment in deuterium are compatible with the presence of magmatic co2 during the crystallization of intruding lavas and exclude contamination by seawater mass balance calculations on selected thin sections photographs of partly filled up vesicles and replaced olivine crystals constrain assuming a closed system interaction the chemical composition of the initial fluid and the respective amounts of the initial solid phases involved in the alteration process thermodynamic modelings using the eq3 6 software package correctly predict the mineralogic chemical and isotopic exchanges accompanying alteration thus validating the closed system assumption the model which allows prediction of the influence of co2 on the alteration products shows that above a 0 25 co2 mole fraction in the initial fluid the alteration is entirely controlled by the chemical composition of the initial solid phases the presence of co2 implies the precipitation of dioctahedral smectites and carbonates instead of the magnesian smectites commonly observed in co2 free systems the mururoa feeder zone shows alteration features typical of a closed system interaction between the basaltic rock and a magmatic fluid in which seawater did not take part

holocene regression and the tidal radial sand ridge system formation in the jiangsu coastal zone east china abstract a radial tidal sand ridge system rtsrs spans more than 20 000 km 2 in the southwest yellow sea is fan shaped and stretches from qianggang toward the sea the marine rtsrs is located in a convergent divergent tidal current field cdtcf numerous drilling holes reveal an area of 3000 km 2 containing tidal sand strata in the jiangsu coastal plain on land adjacent to the marine rtsrs which stretches eastward from chengdong and is also a fan shaped with a central angle of 130 the tidal sand unit lies on a transgressive coastal barrier lagoon unit with an erosional surface between them and the latter unit is in turn lying on late pleistocene stiff mud the tidal sand unit is overlain by the littoral tidal flat unit and together they constitute the holocene regressive succession paleo current study reveals that a paleo current pattern similar to the modern marine cdtcf was present in the holocene sub aerial tidal sand strata therefore the sub aerial tidal sand bodies are deduced to be an ancient rtsrs that was formed during the holocene regression and gradually exposed and changed into land as the changjiang and huanghe deltas prograded both sub aerial and marine rtsrs should be formed in the same tidal depositional environment but in different development stages thus the radial tidal sand ridges in southwestern yellow sea should have formed not during the holocene transgression as most previous studies have inferred but in the process of holocene regression mineralogical analyses demonstrate that the sediment source of the sub aerial rtsrs initially came from the changjiang and later predominantly from the huanghe sea floor erosion by tidal currents may also provide sandy material to form the rtsrs drilling cores and ground penetrating profiles show that the paleo valleys in the study area are much smaller than the present distributaries of the changjiang river thus the presumption of direct sand supply by a large river to form the rtsrs through its apical area is cannot be supported after the sea level reached the present high stand the jiangsu coastline has been prograding seaward as the changjiang delta expanded and this progradation was accelerated when the huanghe debouched in the study area the nearshore part of rtsrs has been gradually changing into land while the entire rtsrs extends seawards in the process of the development the rtsrs apex changed from chengdong to qianggang at present the coastline is still moving seaward while the outer part of the rtsrs suffers from some erosion owing to reduction of sediment supply from both the changjiang delta and the abandoned huanghe delta

behavior of li rb and cs during basalt glass and olivine dissolution and chlorite smectite and zeolite precipitation from seawater experimental investigations and modelization between 50 and 300 c abstract this study investigates experimentally the behavior of li rb and cs during the hydrothermal alteration of a basalt glass and of forsterite the behavior of trace alkalis during the dissolution of a basalt glass and forsterite has been followed between 150 and 300 c rb and cs are preferentially leached from the glass while li exhibits a stoichiometric release with respect to silica on the other hand incongruent loss of li relative to si during forsterite dissolution reflects a crystallographic site energy control of the release of trace elements from crystalline silicates the partitioning of li rb and cs between hydrothermal solutions and chlorites smectites and zeolites has been experimentally investigated between 50 and 260 c the alteration phases were synthesized by altering silicate glasses in solutions containing the trace alkalis the lower the temperature the higher the exchange capacity of the mineral or the lower the ionic hydration energy then the more the element is incorporated into the solid phases computer simulations generated with the eq3 6 software package and our experimental data on distribution coefficients account for the behavior of alkali trace elements during the alteration of basalt glasses by seawater at mid ocean ridges

stable isotope compositions of sedimentary organic carbon in tampa bay florida u s a implications for evaluating oil contamination 13cpdb values for sedimentary organic carbon in tampa bay florida and adjacent riverine systems range from 28 up the rivers to 20 in the middle of the bay to 10 in several contiguous small bays along the gulf of mexico coastline these values reflect the compositions of the plant precursors that is c3 land plants phytoplankton and sea grasses respectively which predominate in each of these areas organic carbon percentages range from 5 0 to less than 0 1 with a moderately good correlation relative to the 63gm sediment grain size fraction 0 76for67samples in addition to providing another interesting scenario of 13c signatures that are useful in understanding the contemporary deposition of organic carbon on the one hand and ancient depositional environments on the other these data are also shown to be useful in assessing the contribution of oil residues to the sediments should an oil spill occur in tampa bay at some time in the future

low temperature alteration of basalt by interstitial seawater mururoa french polynesia chemical and isotopic analysis of interstitial fluids and secondary phases in two drill cores from the volcanic pile of the mururoa atoll french polynesia permits documentation of the lowtemperature alteration by seawater of basalt and secondary minerals as a function of rock water ratio r w up to 110 g l as r w increases in this system up to 70 g l the interstitial waters exhibit an almost total removal of mg and k a net decrease of ph and eh a marked enrichment in ca sr and si and depletion of 18o and d with further increases in r w above 70 g l a reversal of mg ca exchange is observed mg accumulates in the fluid while ca is removed in addition the enrichment of 18o and d is also observed in the fluids at these high r w these chemical and isotopic reversals are shown to result from the transformation of early precipitated mg rich saponite into ca na saponite chemical and isotopic reactions take place at two separate solid solution interfaces 1 1 an interface at the surface of the fresh basalt that leads to the formation of a hydrated amorphous layer which progressively crystallizes into clay and 2 2 a second interface between the interstitial bulk fluid and the resultant clay layer consequently geochemical codes which fail to account for both aqueous diffusion in altered layers and the existence of multiple reaction interfaces cannot accurately describe alteration at high rock water ratios

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

diffusive transport of water in porous fresh to altered mid ocean ridge basalts abstract studying diffusive transport in porous rocks is of fundamental importance in understanding a variety of geochemical processes including element transfer primary mineral dissolution kinetics and precipitation of secondary phases here we report new findings on the relationship between diffusive transport and textural characteristics of the pore systems on the example of mid oceanic ridge basalts having different degree of alteration but very similar bulk pore volume diffusion processes in porous basalts were studied in situ using h 2 o d 2 o exchange experiments the effective diffusion coefficients of water molecules increase systematically from 5 05 10 11 to 1 19 10 10 m 2 s for fresh and moderately altered basalts and from 2 40 10 11 to 6 72 10 11 m 2 s for completely altered basalt as temperature increases from 5 to 50 c the activation energy of the diffusion process increases from 12 29 0 71 kj mol for fresh and moderately altered basalts to 14 3 1 33 kj mol for completely altered basalt the results indicate that neither the bulk porosity nor the degree of alteration can be used as proxies for the efficiency of element transport during morb water interaction the formation of secondary phases that replace primary minerals and fill the pore space in the rock leads to the formation of tiny pores and phases with large specific surface area these factors might have a dominant control on the transport properties of altered basaltic rocks

submarine venting of phase separated hydrothermal fluids at axial volcano juan de fuca ridge since the discovery of high temperature venting on the east pacific rise in 19791 it has been expected2 3 because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation4 5 that phase separated fluids would discharge from ridgecrest vents although this notion is supported by the reported large deviations in vent fluid chlorinity relative to that of sea water 40 200 6 7 by observations of venting at p t conditions clearly within the two phase region 220 bar and 420 c 8 and by fluid inclusion data9 10 unequivocal identification11 of phase separated venting fluids has remained elusive here we report observations of chloride and metal depleted gas enriched fluids from a shallow vent field on the juan de fuca ridge which confirm the expectation that phase separated effluents are delivered to the deep ocean from some sea floor venting systems

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

palaeoenvironmental history of lake baikal during the last 23000 years abstract a sediment core recovered from lake baikal was studied in an attempt to elucidate the palaeoenvironmental history of an intra continental lake under the control of last glacial to post glacial climatic fluctuations the lake conditions were characterised by subdued primary production and increased turbidity conditions during the last glacial maximum terrestrial vegetation and the development of soil layers were reduced in the drainage areas the deglaciation suggested by increased terrigenous sand influx and biological productivity took place at around 18 000 yr b p responding to the increased insolation in the northern hemisphere high latitude the onset of wet and warm conditions at ca 12 000 yr b p brought on a maximum of aquatic production and forestal expansion between 7 000 and 6 000 yr b p since 5 000 yr b p enhanced blooming of diatoms has occurred due to an increased nutrient supply and dissolved silica input into the lake

postglacial transgression maximum documented by the core sediments of xixi wetland east china abstract constraining the timing of the postglacial transgression is of great significance to the origin of coastal wetlands distributed extensively in eastern china the high resolution chronological sequence from xixi wetland enabled us to explore interactions among the postglacial transgression sedimentary response and human activities in the surrounding hangzhou bay diversities of 12 ostracods 24 foraminifera and remains of oyster shells gastropods testate amoebae diatoms and vascular plants are indicative of the sedimentary facies grain size variables together with microfaunal records revealed seven stages of sedimentary evolution since the middle late pleistocene initial riverbed first transgression event floodplain early lagoon shallow marine bay late lagoon and final freshwater marsh the xixi basin experienced two distinct transgression events and sea level changes inferred from assemblages of ostracods and foraminifera the first transgression event is a minor transgression related to the moderate intensity of asian monsoon and moderately high sea level during the early mis 3 the second large scale transgression event established the sedimentary pattern of the modern xixi basin the finding of the transgression maximum in the early holocene about 11 0 7 0 cal ka bp highlighted the problem of reliable time of high sea level which is tightly related to the strong asian monsoon intensity and global rising sea level subsequent changes in the sedimentary environment played a key role on the neolithic human activities around the hangzhou bay the origin of the xixi wetland reflected the combined effects of a sand barrier and rising human activities since the middle holocene

acquisition of water chemistry in a mobile fissured basement massif its role in the hydrogeological knowledge of the la clapiere landslide mercantour massif southern alps france abstract groundwater flowpaths of the la clapiere landslide are studied by chemical and isotopic water analysis and modeling of the landslide springs in our case it appears that sulfate can be taken as a chemical tracer of the different flowpaths on the gneissic slope of la clapiere geochemical modeling explains sulfate concentrations from 0 to 130 mg l by dissolution of sulfurous minerals present in the gneisses such a variability of the concentrations measured in the springs is due to different infiltration paths direct paths through the basement so 4 2 10 60 mg l or indirect path through superficial deposits like screes or fluvio glacial terrains which cover the basement so 4 2 60 130 mg l the high concentrations 600 800 mg l cannot be explained by thermodynamic geochemical simulations and they reveal triassic gypsum dissolution hidden under the studied slope so two main flowpaths are differentiated in the la clapiere landslide 1 flow through low permeable triassic deposits pinched under the foot of the landslide 2 flow through a more permeable fissured basement with different flow paths and consequently with different transit times due to the anisotropic nature of the top and the central part of the landslide

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

hydrothermal alteration at mururoa atoll french polynesia abstract petrological study of altered aerial basaltic flows submarine pillow lavas and oceanitic basalts of a rift zone sampled in two drill cores in the mururoa atoll viviane 1000 m depth fuchsia 550 m depth shows that during hydrothermal alteration processes the secondary clay minerals evolve the following three different trends controlled by permeability of the rocks and by rock fluid interaction mg saponite al saponite and al montmorillonite in the basaltic pillow lavas first celadonite saponite assemblage crystallizes in fresh glass rich rocks in altered and brecciated rocks the latter mineral assemblage is followed by fe saponite and mg saponite in breccias the glass is replaced by fe saponite the residual voids are sealed by zeolites mainly phillipsite apophyllite or gypsum indicating an upper temperature limit of 65 c in the aerial basaltic flows massive rocks are affected by celadonite and random mixed layer chlorite saponite crystallizations in the strongly altered rocks veined or brecciated the primary minerals and glass are partly replaced by al saponites and locally by chabazite the same al saponite fills up the veins and constitutes the major part of the cement as rock fluid interaction increases the si al and ca content in the solution increases inducing the late precipitation of aluminous smectite and chabazite in the oceanitic basalts sampled in the rift zone massive rocks are affected by crystallization of secondary clay minerals which is governed by local equilibrium femg clay minerals talc mg saponite celadonite partly replace the olivine phenocrysts and al saponite replaces the glass in veined and brecciated rocks the paragenesis is dioctahedral al smectite silica amorphous for a temperature range 2 content in the solution

li and li isotopic composition of hydrothermally altered sediments at middle valley juan de fuca li and li isotopes have been measured in the clay fraction of sediments recovered from the middle valley hydrothermal site on the juan de fuca ridge the li content of pure detrital clays is 51 ppm while hydrothermal clays and carbonates have lower li 22 11 ppm however there is no clear relationship between the mineralogy of the hydrothermal alteration products and their li content the 7li value of the detrital clays is 5 8 hydrothermal clays and carbonates have 7li in the range of 3 9 to 7 8 these values do not seem to be dependent on the temperature at which they formed modelling of the li and li isotope systematics indicates that the fluid from which the alteration products form is significantly enriched in li higher than 10 000 mol kg 1 relative to pore fluids recovered from within the sediments up to 589 mol kg 1 wheat c g m j mottl 1994 data report trace metal composition of pore water from sites 855 through 858 middle valley juan de fuca ridge in mottl m j davis e e fisher a t slack j f eds proc odp sci res 139 749 755 and that this li is derived from sediment thus the alteration products are not in equilibrium with their conjugate pore fluids rather the alteration minerals formed at lower water sediment ratios this suggests that fluid flow pathways at middle valley were more diffuse in the past than they are today

an organic carbon isotopic record of glacial postglacial change in atmospheric pco2 in the sediments of lake biwa japan a 12 m piston core of sediment from lake biwa japan provides a high resolution record of sedimentary organic matter accumulation over the pleistocene holocene transition organic carbon concentrations are generally 1 2 in sediments deposited since 15 kyr ago c n ratios indicate that the organic matter is predominantly from aquatic production a shift in organic carbon isotopic composition from 21 to 25 occurs over the glacial postglacial boundary changes in lake productivity organic matter preservation sources of organic matter and water temperature can be eliminated as probable causes of the observed organic carbon isotopic shift annual overturn of lake waters and rapid dissolution of biogenic carbonates maintain equilibrium between atmospheric co2 and dissolved co2 in this lake the isotopic composition of organic matter buried in the sediments of lake biwa consequently appears to record the shift in atmospheric pco2 from 200 ppm to 280 ppm which occurred at the pleistocene holocene transition

behaviour of rare earth elements during seawater basalt interactions in the mururoa massif abstract the rare earth elements ree were analysed in the interstitial fluids in the basalts and in the alteration products clays and zeolites of mururoa atoll volcanic rocks french polynesia in order to investigate ree behaviour during seawater basalt interactions at low temperature the ree distribution coefficients between fluids and secondary products were calculated using the eq3 6 geochemical code the reversible irreversible character of the ree entrapment in secondary products was tested the ree concentrations in the clays are close to that of basalt the concentrations in zeolites are 10 times lower comparison of measured and modeled concentrations in solutions favours the irreversible incorporation assumption the affinity of the ree for the secondary products is shown to be high the calculated distribution coefficients range from 3 105 for lu and eu to 107 for ce in clays and from 104 to 7 105 in zeolites the distribution coefficients exhibit a progressive decrease from la to lu this behaviour is related to the greater stability of hree complexes relative to lree complexes in solution under reducing conditions in the interstitial fluids eh down to 500 mv eu undergoes reduction to the mobile eu ii this enhanced mobility is reflected by eu distribution coefficient being lower than those of adjacent ree the distribution coefficient of ce is higher as ce is trivalent in the fluids fractionation from the other trivalent ree was unexpected the calculated distribution coefficients of ree are lower in zeolites than in clays and this can be related to the spatial distribution and paragenesis of the secondary phases the dissolution of the basalt promotes the precipitation of clays at the basalt fluid interface and of zeolites in the bulk solution the ree released by dissolution are incorporated into the clays and further uptake occurs in zeolites for the ree left in solution

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

on crosswell diffusive time domain electromagnetic tomography summary we investigate the reconstruction of a conductive target using crosswell time domain electromagnetic tomography in the diffusive limit the work is a natural extension of our ongoing research in the modification of time domain methods for the rugged marine mid ocean ridge environment an environment characterized by extreme topography and pronounced variations in crustal conductivity on all scales we have proved both in theory and in practice that traveltime the time taken for an electromagnetic signal to be identified at a receiver following a change of current in the transmitter is an excellent robust estimator of average conductivity on a path between transmitter and receiver a simple estimate of the traveltime for a parallel electric dipole dipole system is the time at which the derivative of the electric field with respect to logarithmic time at the receiver reaches its maximum we have derived the fundamental relationship between the traveltime and the conductivity of the medium for a uniform whole space we have applied the concept of the traveltime inversion to the related crosswell problem and demonstrated reconstructions of finite targets based on tomographic analyses results show that the crosswell time domain electromagnetic tomography can supply useful information such as the location and shape of a conductive target

metalliferous mining geophysics state of the art in the last decade of the 20th century and the beginning of the new millennium the downturn in mining activity experienced during the 1990s did not preclude significant new developments in various areas of mining geophysics the methodology for acquiring and compiling data has kept pace with the latest technological developments from global positioning system navigation to raster displays and parallel computing wavelet transforms principal component analysis and fractals have begun to find successful applications in both processing and interpretation of geophysical data methods of quantitatively interpreting inverting anomalies in terms of 2 d and 3 d models of causative bodies are becoming common for the first time it is possible to make airborne gravity gradient measurements suitable for use in mineral exploration lower transmitter frequencies for airborne time domain electromagnetic em systems have enabled surveys in areas where conductive cover previously screened basement conductors the use of approximation algorithms has allowed the transformation of either time domai

high impact palynology in petroleum geology applications from venezuela northern south america this article documents the application of high impact palynology hip in the maracaibo basin of venezuela and its influence on such exploration and production aspects as regional planning and strategies risk reduction optimal drilling decisions and investment petroleum system modeling new discoveries and secondary recovery by fluid injection among others high impact palynology has been defined as the coupling of high resolution sequence biostratigraphy multidisciplinary work and the alignment of palynology with the attainment of business goals the first part of this article explains the high resolution ecostratigraphic methods used and the concept of integrated work applied the second part of the article shows the results obtained in selected case studies which illustrate the advantages of hip among the most relevant studies are high resolution ecostratigraphic frames at a basin level timing between structural trap formation and oil migration differentiation of petroleum systems in adjacent reservoirs the concept of palynoblocks in structurally complex areas to estimate missing sections stratigraphical models for exploratory wells with better predictions of target horizons fine scale reservoir correlations and discovery of new reservoirs the use of hip in other areas is recommended with palynology as a common in house practice within multidisciplinary teams formed especially for each specific task

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

petrology of the volcanic bedrock of mururoa atoll tuamotu archipelago french polynesia abstract the south pacific atoll of mururoa is located in the southeastern part of the tuamotu archipelago it is about 28 km long and represents the emergent part of a 60 km long submarine plateau this atoll is composed of submarine volcanic rocks resting on oceanic crust then above subaerial volcanic rocks and finally a coral coating about 300 m thick the volcanic rocks are markedly alkaline and this alkaline magmatic trend evolved by fractional crystallization from nepheline normative 10 wt basalts to quartz normative 5 wt trachyte fractionation of phlogopite played a significant role in this evolution the basic lavas contain olivine spinel magnetite ilmenite clinopyroxene and plagioclase phenocrysts rare feldspathoids occur in the groundmass of the hawaiites two trends can be distinguished the first one characterized by the presence of mica plagioclase and ilmenite has evolved under high p h 2 o the second characterized by amphibole richterite and arfvedsonite aegirine alkali feldspar and magnetite has evolved under lower p h 2 o and silica activity but higher f o 2 thermodynamic conditions of crystallization at depth deduced from olivine liquid plagioclase liquid and magnetite ilmenite equilibria are high temperature 1100 to 1200 c medium water pressure 1 to 1 5 kbar and medium to low oxygen fugacity 10 10 bar the mururoa magmas may have issued from fissures along the australes fault it may not result from the activity of the hot spot situated east of pitcairn island considered as responsible for the volcanism of others islands of the tuamotu archipelago fangataufa gambier pitcairn

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

seawater 87sr 86sr ratios along continental margins patterns and processes in open and restricted shelf domains abstract to better constrain the sr isotope budget in marginal domains without any fluvial inputs we analyzed the chemical composition and 87sr 86sr ratio of waters and shells from four locations two coastal lagoons one hemipelagic platform and one open marine shelf our results highlight homogeneous 87sr 86sr ratios typical of oligotrophic oceanic waters oow i e 0 709172 0 000023 in the pacific tatakoto atoll and along a mediterranean shore to offshore transect 25 km off banyuls sur mer bsm this attests that oceanic inputs from oligotrophic areas remain the main sr source in open shelf areas compared with submarine groundwater discharges sgd or particulate dissolution influences in bsm only foreshore data are more radiogenic possibly due to rainwater mixing local groundwater springs or more efficient particle dissolution in the intertidal zone in restricted areas we report variable 87sr 86sr ratios between the salses leucate france and oualidia morocco lagoons the first one has homogeneous 87sr 86sr ratio typical of oow except close to sgd in oualidia 87sr 86sr ratios decrease by 1 2 10 3 from oow values close to the atlantic inlet to progressively less radiogenic ones upstream within the interior of the lagoon these differences depend on several factors including the leaky restricted or choked morphology of lagoons modulating the oceanic sr inputs but also sgd fluxes whose 87sr 86sr ratios and sr concentrations are highly variable according to the nature of rocks leached in karstic aquifer in oualidia the low 87sr 86sr ratios correspond to high sr concentrations up to 150 mol l 1 issued from the dissolution of mesozoic evaporites leading to sgd fluxes accounting for 60 of the local sr budget through data compilation we show that similar 87sr 86sr gradients and processes prevail at the whole mediterranean scale finally we postulate that high coastal water retention times can also account for anomalous coastal 87sr 86sr ratios and that the combination of water mass restriction sgd bioadsorption and early diagenetic processes could decrease seawater sr concentrations in some marginal areas

sedimentary environment changes of the ningshao plain since the later stage of the late pleistocene evidence from palynology and stable organic carbon isotopes abstract a 45 3 m long core was collected from near the hemudu civilization site luojiang county zhejiang province 29 59 064 n 121 21 754 e which is located in the ningshao plain on the southern margin of hangzhou bay the core named the hmd core was divided into seven lithological layers with clay and silt as the main lithological components the sporopollen assemblages of this core combined with toc tn and stable organic carbon isotope 13 c toc analysis revealed the sedimentary environmental changes since the later part of the late pleistocene in the ningshao plain the study area changed from terrestrial fluvial flood plain facies before marine isotope stage mis 3 to shore plain during transgression in mis3 and became a freshwater lake during regression at the time of the last glacial maximum lgm the area started to become a semi salt lake influenced by sea water during 15 900 5000 cal bp in which time period the lake was deeper and the climate became gradually warmer later the seawater withdrew the lake began desalinating and then became swampy and accumulated peat until 1000 cal bp after that the area became dry land the results also indicate that the sediments of the core are of endogenous organic origin and the 13 c toc value was controlled by change in the concentration of atmospheric co 2 and thus was a response to global changes

fluid flow monitoring using electromagnetic probing high frequency electromagnetic probing is used to monitor the rate and direction of flow of fluids injected into the ground this method shows the potential for providing more detailed information than procedures presently used the experimental technique and the test of concept experimental results are discussed this technique has applications in oil reservoir engineering and in hydrology studies concerning storage of chemical wastes

loihi seamount hawaii a mid plate volcano with a distinctive hydrothermal system the initial discovery of deep sea hydrothermal vents at the galapagos rift1 2 has resulted in a decade of exploration and experimentation subsequent discoveries in the pacific3 8 and atlantic9 ocean basins have established the importance of these features as sources of mantle derived gases and solutes10 2 and as loci for heat dissipation13 14 polymetallic sulphide mineral deposition15 16 and geochemical exchange17 19 the presence of dense communities of bacteria and specialized macrofauna20 22 has called into question the absolute role of sunlight as the principal energy source for marine organisms until recently these deep sea vents were known only at or near plate boundaries but recent dredging23 24 near bottom water sampling25 27 and sea floor camera survey28 programmes have indicated that hydrothermal vents are present at the summit of loihi seamount a mid plate hotspot submarine volcano at the southern end of the hawaiian island chain29 here we report results obtained from sampling two active vent fields the fluid chemistry especially high co2 and fe presence of alkalic lavas and iron depositing bacteria and absence of macrofauna suggest that mid plate vents may differ from the hydrothermal vents found at mid ocean ridges

electrical conductivity and streaming potential coefficient in a moderately alkaline lava series abstract coupled hydraulic and electrical problems are being investigated with renewed interest in geophysical applications in this study electrical conductivity and streaming potential coefficient spc have been measured in the laboratory for crushed oceanite hawaite and trachyte samples from an almost complete moderately alkaline lava series from the mururoa atoll french polynesia for ph varying from 7 to 9 5 and ionic strength varying from 0 1 to 100 mmol l despite the closely related mineralogy of the rocks contrasted results are obtained for the surface conductivity as defined by revil and glover 0 10 0 07 ms m 8 3 0 2 ms m and 1 05 0 16 ms m for oceanite hawaite and trachyte respectively and for the inferred potential 6 6 0 3 mv 26 3 0 5 mv and 14 6 0 3 mv respectively the higher values obtained with hawaite suggest that electrical properties are controlled by secondary and accessory minerals such as clay minerals and zeolites resulting from low temperature seawater alteration rather than by the magmatic differentiation furthermore a synthesis of results obtained with 20 rock samples indicates that signatures of the alteration process may emerge from the study of the potential as a function of surface conductivity the results with the lava series can be used to derive estimates of the scaling of basalt resistivity and associated spc as a function of permeability for permeability values smaller than 10 15 m 2 the value of the spc can be dramatically affected by the value of the surface conductivity at least in the brittle crust a better knowledge of the contributions of clay minerals and zeolites to surface conduction is therefore needed both for the interpretation of electrical conductivity profiles and for the estimation of electrical variations associated with groundwater flow as could be produced for example during volcanic or tectonic cycles

integrating long offset transient electromagnetics lotem with seismics in an exploration environment1 the applications of electromagnetics have increased in the past two decades because of an improved understanding of the methods improved service availability and the increased focus of exploration in the more complex reservoir characterization issues for electromagnetic methods surface applications for hydrocarbon exploration and production are still a special case while applications in borehole and airborne research and for engineering and environmental objectives are routine in the past electromagnetic techniques in particular deep transient electromagnetics made up a completely different discipline in geophysics although many of the principles are similar to the seismic one with an understanding of the specific problems related to data processing initially and then acquisition the inclusion of principles learned from seismics happened almost naturally initially the data processing was very similar to seismic full waveform processing the hardware was also changed to include multichannel acquisition systems and the field procedures became very similar to seismic surveying as a consequence the integration and synergism of the interpretation process is becoming almost automatic the long offset transient electromagnetic lotem technique will be summarized from the viewpoint of its similarity to seismics the complete concept of the method will also be reviewed an interpretation case history that integrates seismic and lotem from a hydrocarbon area in china clearly demonstrates the limitations and benefits of the method