osmotic generation of anomalous fluid pressures in geological environments osmotic pressures are generated by differences in chemical potential of a solution across a membrane but whether osmosis can have a significant effect on the pressure of fluids in geological environments has been controversial because the membrane properties of geological media are poorly understood anomalous pressures large departures from hydrostatic pressure that are not explicable in terms of topographic or fluid density effects are widely found in geological settings and are commonly considered to result from processes that alter the pore or fluid volume which in turn implies crustal changes happening at a rate too slow to observe directly yet if osmosis can explain some anomalies there is no need to invoke such dynamic geological processes in those cases here i report results of a nine year in situ measurement of fluid pressures and solute concentrations in shale that are consistent with the generation of large up to 20 mpa osmotic pressure anomalies which could persist for tens of millions of years osmotic pressures of this magnitude and duration can explain many of the pressure anomalies observed in geological settings they require however small shale porosity and large contrasts in the amount of dissolved solids in the pore waters criteria that may help to distinguish between osmotic and crustal dynamic origins of anomalous pressures

geodynamic control on carbonate diagenesis petrographic and isotopic investigation of the upper jurassic formations of the paris basin france abstract the oxfordian and kimmeridgian carbonates of the eastern edge of the paris basin display poor reservoir properties stable isotope investigation of these non recrystallized cements through both microdrilling sampling and in situ sims secondary ion mass spectrometry analysis shows that they originated from slightly buffered meteoric fluids 3 smow to 8 smow flowing through the malm carbonate aquifers of the eastern edge of the paris basin after a review of the post upper jurassic history of the paris basin it appears that meteoric water supplies leading to such cementations were associated with the evolution of the basin s geodynamic setting and notably with the lcu late cimmerian unconformity major event which corresponds to the uplift of the london brabant massif denudation of the oxfordian and kimmeridgian carbonates on the southern flank of the london brabant massif to the north of the study area then lead to lateral recharging of the associated aquifers with meteoric fluids this scenario is similar to the one proposed to explain cementations of the jurassic carbonates in the wessex weald basins which emphasizes the main role played by the cretaceous unconformities over carbonate diagenesis at the scale of the northwestern tethys margin

the origin and timing of multiphase cementation in carbonates impact of regional scale geodynamic events on the middle jurassic limestones diagenesis paris basin france the middle jurassic carbonates of the eastern part of the paris basin display surprisingly low values of porosity and permeability 15 and k 0 5 md the main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs a fate that did not befall their equivalents in deeper central parts of the paris basin using petrographic and geochemical analyses stable o and c isotopes sr isotopes major elements we identify six calcitic spar stages two dolomite stages and several episodes of fracturing and stylolitization ordered in paragenetic sequence cement quantification shows the predominance of two blocky calcite cement stages 75 of total cementation o and sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped jurassic seawater and meteoric water or from buffered meteoric waters in the geological history of the paris basin major meteoric water inputs were possible during the early cretaceous when the middle jurassic carbonates cropped out at its northern and eastern borders lateral meteoric recharge may have occurred as a result of two separate uplift events late cimmerian unconformity and late aptian unconformity and the related exposures of carbonates to the north of the study area this palaeohydrological circulation brought about a significant reduction of porosity from 40 to 10 through calcite cement precipitation the early cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the london brabant massif across all of northwestern europe a subsequent dolomite and calcite cementation stage accounts for about 5 of the total cement volumes this late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the late oligocene extension episode

noble gases in crude oils from the paris basin france implications for the origin of fluids and constraints on oil water gas interactions in order to investigate the potential of noble gases to trace the dynamics of oil reservoirs we have analysed the abundance and isotopic composition of all noble gases he ne ar kr and xe in crude oils from the paris basin france using a new extraction and purification procedure the main oil reservoirs are presently located in the jurassic dogger limestone and in the triassic keuper sandstone but hydrocarbons originated from a common source rock formation located in the interbedded liassic sequence despite this common origin the abundance and isotopic ratios of the noble gases differ between the dogger and the keuper the isotopic compositions of kr and xe are indistinguishable from that of air 3he 4he ratios higher than those predicted from radiogenic production in the sediments or in the crust are attributed to the occurrence of mantle derived 3he in the basin each sedimentary sequence is characterised by well defined and homogeneous 21ne 22ne and 40ar 36ar ratios which average 0 0306 0 0008 and 312 10 for the dogger and 0 0367 0 0012 and 664 30 for the keuper respectively the main source of radiogenic noble gases appears to be the continental crust underlying the basin with possible regional contributions of noble gas isotopes produced in the sediments the helium and argon isotopic ratios of the dogger oils are very similar to those observed in geothermal waters flowing in the dogger aquifer throughout the basin demonstrating that noble gases in oils derive from associated groundwaters oil reservoirs in the paris basin therefore accumulate noble gases from wide regions of the continental crust through cross formational flow of groundwaters and subsequent partitioning into oil this observation implies that noble gases cannot be directly used to date oils but can provide time constraints if 1 water oil interactions are quantified and 2 the residence time as well as the noble gas characteristics of associated groundwaters are known oil water gas partitioning processes are well recorded in the fractionation of noble gas elemental abundance two distinct processes have been identified 1 accumulation of atmosphere derived ang and radiogenic noble gases both initially dissolved in groundwaters resulting in a positive correlation between absolute amount of ang and the extent of heavy noble gas fractionation and 2 subsequent fractional degassing resulting in a negative correlation between ang abundance and heavy noble gas fractionation degassing is particularly evident for the keuper oils and might have occurred in the reservoirs following hydrodynamic gas stripping the ang abundance in the dogger reservoirs requires that about one order of magnitude more water than presently observed has interacted with the oil given current estimates of the residence time for groundwaters in the dogger aquifer the duration of oil water interaction is in qualitative agreement with a palaeocene oligocene age for the major episode of secondary oil migration in the paris basin high xenon contents in keuper reservoirs suggest that they have experienced hydrodynamic interactions between flowing waters and oils for long time and that the trias might have reached hydrostatic condition only recently

paleoenvironments of the mid ordovician upper caradocian trenton limestones of southern ontario canada storm sedimentation on a shoal basin shelf model abstract the mid ordovician caradocian limestones of southern ontario were deposited on a shelf undergoing collision with a magmatic arc within the general deepening upwards sequence shoals and islands complicate the facies patterns around these shoals and islands carbonate sediments can be divided into nine lithotypes reflecting shallow agitated to deep quiet marine environments many of these lithotypes show good evidence of storm deposition the lithotypes can be grouped into natural associations which define shoal intershoal slope and basinal facies though the basins were probably less than 100 m deep the closest recent analogues of these ordovician environments occur on the arabian shelf of the persian gulf and on the sahul shelf of northern australia which is undergoing collision with the banda arc in both these environments local shoal basin shelf topography controls the detailed carbonate shelf sedimentation which on a large scale is controlled by storm and tsunami effects on a seaward sloping ramp such shoal basin and ramp models now seem more suitable in explaining carbonate facies in epeiric seas than the flat slope models previously proposed glacio eustatic sea level changes may have controlled the larger aspects of carbonate sedimentation on the ordovician shelf as they did and continue to do now on the recent shelves such changes may explain the localization of the variety of ordovician hardgrounds which we previously described

stable isotope conservation and origin of saline waters from the middle jurassic aquifer of the paris basin france abstract seventy nine samples of formation water from geothermal boreholes oil field and ground water wells tapping the dogger middle jurassic limestone reservoir of the paris basin have been analyzed for their 2h 18o tds bromide and chloride contents geostatistical mapping of 2h and of 18o contents and their variations with chloride content indicate that both isotopes have a common origin and a similar behaviour within the aquifer the 2h and 18o values increase progressively from the outcrops toward a zone where temperature cl and tds values are high the 2h and 18o values are very uniform in this zone and do not show any relation with formation temperature in contrast to what is generally observed in other sedimentary basins a discussion of isotopes exchange with the carbonate matrix for oxygen and with h2s for deuterium shows that such processes are not controlling the heavy isotope contents of groundwaters this is attributed to the relatively short residence time of groundwaters in the aquifer both 2h and 18o contents of groundwater may thus be considered as conservative tracers in the dogger aquifer of the paris basin and their initial contents are modified only by fluid mixings complex mixing processes account for stable isotope composition tds cl and br values of the dogger fluids all mixtures include a brine component meteoric water percolated and dissolved halite in the triassic aquifer secondary brine this saline solution mixed with some residual primary brine then migrated via vertical faults into the dogger aquifer such migration is found to be in agreement with data from fluid inclusions in late carbonate cements from the liassic and dogger strata the requirement that these units were exposed implies that meteoric invasion could not have occurred before the tertiary successive mixings of the brine with several types of meteoric waters depleted in heavy isotopes account for the present isotope and chemical compositions of the dogger fluids

anion exclusion effects in compacted bentonites towards a better understanding of anion diffusion abstract diffusion of 36cl in compacted bentonite was studied using through diffusion out diffusion and profile analysis techniques both the bulk dry density of the bentonite and the composition of the external solution were varied increasing the bulk dry density of the bentonite resulted in a decrease of both the effective diffusion coefficient and the cl accessible porosity increasing the ionic strength of the external solutions resulted in an increase of both the effective diffusion coefficient and the cl accessible porosity this can be explained by anion exclusion effects donnan exclusion at high ionic strength values i 1 m nacl the cl accessible porosity approaches the interparticle porosity this interparticle porosity is the difference between the total and interlayer porosity of the bentonite the interlayer porosity was found to depend on the degree of compaction up to a bulk dry density of 1300 kg m 3 the interlayer is built up of 3 water layers between 1300 and 1800 kg m 3 the interlayer water is reduced from 3 to 2 layers of water above 1800 kg m 3 evidence for a further decrease to 1 layer of water was found these findings are in agreement with x ray data found in the literature showing a decrease of the basal spacing of montmorillonite the main clay mineral in bentonite with increasing degree of compaction the relationship between the effective diffusion coefficient of cl and the diffusion accessible porosity can be described by an empirical relationship analogous to archie s law to predict the effective diffusion coefficient of cl in compacted bentonite the diffusion coefficient of cl in water the bulk dry density and the ionic strength of the pore water have to be known

flow of formation water in the jurassic of the paris basin and its and discussion effects the jurassic of the paris basin is a major target for oil and geothermal exploitation interpretation of data from numerous wells reveals that the spatial distribution of fluid and reservoir parameters is heterogeneous with correlated anomalies for temperature and geochemistry the multidisciplinary approach used to describe these typical characteristics shows that hydrodynamics provides the key to explain observed deviations from the usual correlations with depth as a consequence of the coupling between hydrodynamics and fluid properties the analysis of induced effects is a calibration criterion which can be used to improve the numerical simulation of the regional flow path compared to the results of the constant density approach the new computer flow scheme both gravity and density driven is more consistent with the thermal and chemical anomalies observed the refined analysis including density effects confirms the existence of a confined area and a mixing zone around paris previously identified by geochemical investigations

chlorine transport processes through a 2000 m aquifer aquitard system abstract in the paris basin in france the callovo oxfordian cox is currently studied over a 250 km2 surface area by the french national radioactive waste management agency in order to assess the feasibility of long term underground nuclear waste repository the cox is a 140 m thick clay rich layer which is part of the 2000 m aquitard aquifer system constituting the sedimentary cover in such sedimentary context the transport processes of potential contaminants can be represented by both vertical diffusion and horizontal advection through the most permeable layers chloride is used as a natural conservative tracer and is monitored in term of concentrations and isotopic composition 37cl for both pore and groundwater during this study the samples were collected from three boreholes located in the center of the studied zone one of them est433 going down to 2000 m depth the main solute transport process is shown to be vertical diffusion from the massive keuper halite level to the rest of the sedimentary pile this global diffusive system can be occasionally disturbed by horizontal circulation of groundwater occurring in the oxfordian and dogger limestone formations therefore these circulations cut the global diffusive system in a succession of independent diffusive systems in this study the data set was implemented in a simplified 2d solute transport model and scenarii reproducing known history in term of paleo circulations inside the system were applied and allowed to obtained a good fit of the data model results showed that paleo circulations occurring between 145 ma and 110 ma still have an impact on current distribution of chloride in the system especially for 37cl the model highlights the need of the presence of a circulation spatially limited at the base of the liassic formation to fit the data the best fit obtained indicated current residence time of 500 ka in the dogger and oxfordian with respective onset of the circulations at 20 ma and 5 ma

origin and evolution of fluids from mud volcanoes in the barbados accretionary complex a large collection of fluids 54 interstitial fluids and four expelled fluids were sampled at the manon site at the outer edge of the barbados accretionary complex these warm fluids up to 20 c are expelled by sub marine 5000 mbsl mud volcanoes consisting of diapirs unchanneled flow and diatremes channeled chlorine stable isotope ratios of these fluids were measured by irms with a reproducibility of 0 05 1 versus smoc standard mean ocean chloride a large range of 37cl between 5 3 and 0 1 is observed data from each volcanic structure describe a mixing between seawater and a low 37cl fluid the whole set of data is interpreted as the result of a mixing between two deep components and seawater the two deep fluids are chemically distinct e g in ca mg k li sr and br contents and br cl ratio they display low and significantly different 87sr 86sr ratios 0 707790 and 0 707892 respectively and 37cl values 4 51 and 5 24 respectively physicochemical processes such as mineralogical transformation diffusion compaction or ion filtration are known to fractionate chlorine stable isotopes and can produce fluids with negative 37cl values ion filtration due to sediment compaction appears to be the more likely process to explain the negative 37cl values observed at the manon site a model for the generation of these signatures is proposed where a residual negative 37cl fluid reservoir is created at the bottom of the prism or the sediment pile further compaction fracturing and or dewatering of the slab may flush out these fluids and focus them towards the decollement zone mixing between the fluids and ultimately with seawater and water released during gas hydrate destabilizations may explain the data set within the individual cores and between the different structures

chloride and chlorine isotopes 36cl and δ37cl as tracers of solute migration in a thick clay rich aquitard system detailed vertical profiles of dissolved cl and its isotopes 36cl and 37cl provided new information on the origin and systematics of this conservative tracer in pore waters of a thick aquitard system the aquitard system consists of surficial quaternary clay rich till 80 m thick deposited 30 20 kyr b p overlying cretaceous marine clay 76 m thick deposited 71 ma the distribution of cl 37cl and br showed the presence of five distinct end members for cl the top of the unoxidized till a regional aquifer underlying the cretaceous clay two localized geological heterogeneities sand streaks in the till and glacial meltwater emplaced with the till and still present at depths of between 36 and 60 m numerical simulations of the transport of cl from the sand streaks indicated that this geochemical profile has been developing throughout most of the holocene the 36cl measurements showed that the age of the dissolved cl in the upper cretaceous clay is likely between 0 75 and 1 9 myr the 36cl measurements further suggested that the dissolved cl in the till was not directly derived from the underlying cretaceous clay finally it was not possible to quantify the effects of isotopic fractionation of 37cl relative to 35cl because of diffusion in this aquitard system

chlorine transfer out of a very low permeability clay sequence paris basin france 35cl and 37cl evidence abstract the marine callovo oxfordian clay formation is found at a depth around 410m in the eastern part of the paris basin france it is a very low permeability formation investigated by the french agency for nuclear waste management andra to study the feasibility of a radioactive waste disposal examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation this study uses chlorine isotopes to investigate long term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks detailed chlorine concentration and 37cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers the dogger at the bottom and the oxfordian kimmeridgian tithonian unit at the top they are discussed in terms of chlorine budget and hydrogeological processes clay pore waters and aquifer waters show strong chlorine concentration depletion a steep cl concentration gradient from the dogger at 500m in depth 2500 mg l to the oxfordian kimmeridgian tithonian aquifer near the surface 10 mg l is associated to a v shaped profile of the 37cl values modelling cl transport shows that a hydrodynamic dispersion process explains cl concentration and 37cl profiles in oxfordian limestone this process implies a mean upward flux of chloride in the 2 6 10 8 8 2 10 8 mole m2 yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride the modelling and knowledge of underground water transfer suggest a maximum effective cl hydrodynamic vertical dispersion coefficient vertical cl transport coefficient of 7 6 10 10 m2 s chlorine transfer through the callovo oxfordian clay since deposition 160my ago can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events such as early diffusion ion filtration etc

effect of confining pressure on the diffusion of hto 36cl and 125i in a layered argillaceous rock opalinus clay diffusion perpendicular to the fabric abstract the through and out diffusion of hto 36cl and 125i in opalinus clay an argillaceous rock from the northern part of switzerland was studied under different confining pressures between 4 and 15 mpa the direction of diffusion and the confining pressure were perpendicular to the bedding confining pressure had only a small effect on diffusion an increase in pressure from 4 to 15 mpa resulted in a decrease of the effective diffusion coefficient of 20 diffusion accessible porosities were not measurably affected the values of the effective diffusion coefficients de ranged between 5 6 0 4 10 12 and 6 7 0 4 10 12 m2 s 1 for hto 7 1 0 5 10 13 and 9 1 0 6 10 13 m2 s 1 for 36cl and 4 5 0 3 10 13 and 6 6 0 4 10 13 m2 s 1 for 125i the rock capacity factors measured were circa 0 14 for hto 0 040 for 36cl and 0 080 for 125i because of anion exclusion effects anions diffuse slower and exhibit smaller diffusion accessible porosities than the uncharged hto unlike 36cl 125i sorbs weakly on opalinus clay resulting in a larger rock capacity factor the sorption coefficient kd for 125i is of the order of 1 2 10 5 m3 kg 1 the effective diffusion coefficient for hto is in good agreement with values measured in other sedimentary rocks and can be related to the porosity using archie s law with exponent m 2 5

establishing constraints on groundwater ages with 36cl 14c 3h and noble gases a case study in the eastern paris basin france abstract groundwaters from the tithonian kimmeridgian oxfordian and upper dogger aquifers within the eastern part of the paris basin france were characterised using 3 h 14 c and 36 cl and noble gases tracers to evaluate their residence times and determine their recharge period this information is an important prerequisite to evaluating the confinement properties of the callovo oxfordian clay formation sandwiched between the oxfordian aquifer and the dogger aquifer currently being investigated by the french nuclear waste management agency andra for radioactive waste disposal data presented in this paper are used to test 4 hypotheses 1 the oxfordian limestone is isolated from the overlying tithonian kimmeridgian surface aquifer this first hypothesis is supported by the presence of measurable 3 h activities in groundwaters from the surface aquifer 6 11 tu and by its absence in groundwaters derived from deeper aquifers 2 the callovo oxfordian clay sequence in the vicinity of the url serves as an effective barrier to advective flow and transport between the underlying upper dogger aquifer and the overlying oxfordian limestone aquifer this second hypothesis is supported by relatively low concentrations of cl 3 5 78 mg l 1 na 15 145 mg l 1 br 0 08 0 4 mg l 1 and 4 he rad 0 2 2 3 ccstp g 1 and slightly higher 36 cl cl ratios 2 7 59 10 15 at at 1 in groundwaters from the oxfordian aquifer compared to those from the upper dogger aquifer 345 4027 mgcl l 1 402 2390 mgna l 1 1 8 22 2 mgbr l 1 1 6 37 2 ccstp he g 1 1 5 10 15 at 36 cl at 1 cl 3 groundwaters from the oxfordian aquifer in the vicinity of url are pre holocene with residence times exceeding 10 ka geochemical and isotopic lines of evidence for this hypothesis include a 13 c values measured on oxfordian aquifer waters that are close to 13 c of the aquifer matrix reflecting strong isotopic exchange over several thousand years b noble gas temperatures that indicate recharge temperatures between 3 and 8 6 c lower by 2 7 c than the modern average temperature in this area c radiogenic 4 he concentrations between 0 16 10 5 and 2 3 10 5 ccstp g 1 of water about 2 3 orders of magnitude greater than the 4 he concentration of air equilibrated water 4 groundwater residence time for the upper dogger aquifer in the vicinity of the url probably exceed several hundred thousand years such long residence times are indicated by the accumulation of radiogenic he up to 37 10 5 ccstp g 1 assuming a closed system primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of well defined 36 cl cl input ratio knowledge about the 4 he rad sources for oxfordian and dogger aquifers knowledge about transport processes occurring through the dogger aquifer and the extensive dilution of initial 14 c activities by dissolution exchange with aquifer matrix overall however although the data presented in this paper remain semi quantitative due to inevitable intrinsic limitations of the methods none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the url

geochemical evidence for efficient aquifer isolation over geological timeframes aquitards layers of rock having low permeability have been suggested as potential long term reservoirs for toxic materials such as nuclear or chemical waste but information about the isolation properties of aquitard layers is essential to evaluate whether they can indeed be used safely as reservoirs here we investigate the long term mobility of groundwaters between two aquifers surrounding an aquitard layer in the eastern recharge area of the paris basin france using helium isotopes as a geochemical tracer the deeper trias sandstone aquifer which lies above the crystalline basement accumulates radiogenic 4he and primordial 3he from large regions of the crust and mantle at rates comparable to the degassing of the whole crust1 and of mid ocean ridges2 we show that the overlying carbonate dogger aquifer which is separated from the trias aquifer by an aquitard layer consisting of a 600 m succession of shales and clays is stagnant and has been extremely well isolated from the trias over the past several million years this finding together with previous studies at the centre of the paris basin3 4 shows that diffusive mass transfer across aquitards is negligible and that cross formational flow in basins takes place preferentially in faulted areas

37cl 35cl variations in a diffusion controlled groundwater system abstract groundwaters in the low permeability quaternary glacial deposits of southwestern ontario commonly exhibit increasing cl concentrations with depth because these deposits were formed in a freshwater glacial environment and because cl is not derived from weathering of these deposits previous investigations hypothesized that upward diffusion of saline formation waters from the shallow bedrock caused this cl trend this hypothesis was tested by measuring 37 cl 35 cl ratios in the groundwaters from two typical sites and comparing the results with theoretically derived isotopic distributions produced by diffusion 37cl measurements expressed relative to standard mean ocean chloride smoc ranged from 0 8 to 2 2 and vertical profiles showed a gradual enrichment in 35cl relative to 37cl with increasing distance upward from the bedrock till interface 537cl distributions were simulated with a mathematical solute transport model incorporating the effects of kinetic isotopic partitioning a sensitivity analysis indicated that the model results were affected by the groundwater velocity the isotope enrichment factor and diffusion times agreement between the simulated and observed cl isotope profiles was obtained using a groundwater velocity of 0 an isotopic enrichment factor of 1 0012 and diffusion times ranging from 14 000 to 16 000 years based on these results we conclude that the isotopic enrichment in 35cl was caused by upward diffusion over a period of about 15 000 years this diffusion period is consistent with what is known about the quaternary history of the area

natural tracer profiles across argillaceous formations argillaceous formations generally act as aquitards because of their low hydraulic conductivities this property together with the large retention capacity of clays for cationic contaminants has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste in several countries programmes are under way to characterise the detailed transport properties of such formations at depth in this context the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large scale and long term transport behaviour of these formations here tracer profile data obtained by various methods of pore water extraction for nine sites in central europe are compiled data at each site comprise some or all of the conservative tracers anions cl br water isotopes delta 18 o delta 2 h and noble gases mainly he based on a careful evaluation of the palaeo hydrogeological evolution at each site model scenarios are derived for initial and boundary pore water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites using transport parameters derived from laboratory or in situ tests the comprehensive results from this project have been reported in mazurek et al 2009 here the results for three sites are presented in detail but the conclusions are based on model interpretations of the entire data set in essentially all cases the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles transport by advection has a negligible influence on the observed profiles at most sites as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data the advantages and disadvantages of different conservative tracers are also assessed the anion cl is well suited as a natural tracer in aquitards because its concentration varies considerably in environmental waters it can easily be measured although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue the stable water isotopes are also well suited but they are more difficult to measure and their values generally exhibit a smaller relative range of variation chlorine isotopes delta 37 cl and he are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence it is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion leading to relatively sharp changes of boundary conditions can be considered as a pre requisite to obtain well interpretable tracer signatures on the other hand gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation

helium isotope fluxes and groundwater ages in the dogger aquifer paris basin the dogger aquifer of the paris basin has been shown to be first order homogeneous in its helium concentration and its helium isotopic ratio although slight differences are noted in relation to specific chemical water types the helium isotopic composition of the dogger aquifer contains a small component of mantle helium that is associated with a magmatic input although the heat accompanying this magma is small constraints on the age of the overlying albien aquifer are used to calculate the flux of helium out of the dogger this constraint allows a calculation of the residence time of waters in the dogger aquifer of 4 myr 50 which is significantly longer than estimates derived from hydrologic models and hydrologic testing it is possible that the hydrologic ages and the helium ages can be reconciled by a vertically layered dogger aquifer with gradients in he salinity and fluid flow vertical profiles of fluid composition helium concentration and permeability are required in the paris basin to resolve this question

knowledge of the three french underground laboratory sites abstract from march 1994 to august 1996 andra conducted a large reconnaissance work on three sites for possible underground research laboratories these surveys highlighted for each site the presence of a geological formation the properties of which meet the requirements of the french fundamental safety rules on the east site the selected formation is a 130 m thick argillite layer on the gard site the layer is composed of close packed siltites which are 200 400 m thick on the vienne site a hercynian granodiorite batholith was found under a 160 m thick jurassic overdurden

stable chlorine isotopes in halite and brine from the gulf coast basin brine genesis and evolution stable chlorine isotope data used in conjunction with other geochemical parameters are useful in determining the origin of solute in formation waters with salinity different from that of seawater jurassic salt in the gulf coast basin has 37cl ranges of 0 5 to 0 3 bedded and 0 0 to 0 5 diapiric the values for bedded salt are consistent with a 37cl value of 0 0 for jurassic seawater chloride as in modern oceans the slightly higher values for diapiric salt are possibly caused by incongruent solution of halite formation waters have a 37cl range of 1 9 to 0 7 waters with 37cl 0 2 low salinity water from geopressured aquifers appears to have resulted from shale dewatering low 37cl values in such water are related to low mcl mna a parameter indicating dewatering but show no general relationship to cl br they are consistent with diffusion of chloride from allochthonous brine diffusion can generate domains of water with negative 37cl on a scale of hundreds of meters in 104 106 years and may also generate positive 37cl chloride in residual source brine

waves and currents on natural beaches a quasi 3 d numerical model a realistic model of detailed sediment transport in coastal areas must include an accurate and complete description of the wave climate and wave induced currents over the study area the present paper summarizes different aspects of detailed wave and current calculations as the initial step to a more complete model for coastal processes a pc based quasi 3 d model is developed and calibrated with laboratory experiments performed on a simulated infinitely long natural beach tests were carried out for several wave conditions for regular and random long crested wave fields and for two sand sizes

diffusion of anionic species in callovo oxfordian argillites and oxfordian limestones meuse haute marne france abstract diffusive parameters of tritiated water hto and several anionic tracers 36cl 125i 35 so 4 2 and 75 seo 3 2 were determined in the callovo oxfordian argillite formation meuse haute marne france and also in the oxfordian limestone formation located just above twenty two drillcore samples from depths of 150 480 m and from almost each lithofacies along the same borehole est205 were tested three distinct and complementary experimental set ups were used batch column filled with crushed argillite and through diffusion experiments associated with a thorough characterisation of the rock care being taken to maintain redox conditions tritiated water behaviour is similar to water which diffuses in the total porosity of the rock tritiated water and anionic tracers displayed analogous diffusive behaviour in calcareous samples with ea anion ea hto 1 and de anion de hto close to 0 85 i e the ratio of their diffusion coefficients in free water lower and scattered values were observed in the lower part of the oxfordian limestones which is characterized by the presence of mineralogical heterogeneities and dolomitic diagenesis in the callovo oxfordian argillite formation diffusive fluxes of 36cl 125i and 35 so 4 2 are similar but lower than that of hto the diffusive behaviour analogy between i and cl was verified as de halide de hto and ea halide ea hto ratios were always lower than 1 this reduction in diffusivity is a consequence of the anionic exclusion which limits the diffusion accessible porosity to a value lower than the total porosity for anions a weak sorption of i and so 4 2 on argillite samples was always observed whatever the technique used in the case of i this sorption appears to be partly reversible and kinetically controlled very low values of diffusive parameters were obtained for 75 seo 3 2 and are still not well explained last diffusive parameters of each radioactive tracer tested can be plotted according to archie s law which therefore allows an estimation of de non reactive species from the knowledge of both the sample total porosity and the corresponding exponent m 2 for argillite samples