a field study of hydraulic geochemical and stable isotope relationships in a coastal wetlands system both chemical and stable isotope data provide important supplemental information to more traditional hydraulic data and unravel the processes that underpin the large variations in chemical and stable isotopic composition within a coastal wetland system the system studied was the lake warden wetlands located in esperance in south coast of western australia the spatial and temporal variations of chemical and isotopic composition of the individual water bodies within the system were measured for an annual cycle in broad terms the groundwater levels appear to follow the topography but the distinct higher chloride and isotopic concentrations observed within the wetlands were not reflected in the low lying coastal plain groundwater the hydraulic analysis of the region surrounding the wetlands suggest that the wetlands are flow through bodies however the chemical and isotope information indicates the lakes almost invariably act as discharge points for the surface water flows and the north south groundwater flow the northeast southwest groundwater flow is along an observed paleochannel within the wetlands system and in this case the chemical and isotopic evidence are complimentary with the hydraulic study the study highlighted the importance of correcting the isotopic values for the salt effect in highly saline water the isotopic activity ratios of 2h 2ha of some samples were up to 15 higher than the uncorrected values the high salinity of the terminal lake in the wetlands chain also required implementation of a theoretical evaporative model to explain the lower enrichment of the isotopic results as compared to expectations for a shallow and ephemeral lake the inter lake variation in the theoretical evaporative model parameters coupled with a significant variation in the hydrochemistry and isotope composition suggests that the lakes within the wetlands system cannot be treated as single water body as is implied by the bathymetry survey

light hydrocarbon redistribution in a shallow core from the ravnefjeld formation on the wegener halvo east greenland abstract twenty nine core samples extending from the surface to 60 m depth from the upper permian organic rich ravnefjeld formation source rock of east greenland have been analyzed for detailed light hydrocarbon composition in addition complementary organic carbon and rock eval analysis as well as some mineralogical and permeability analyses were carried out the objective was partly to determine if the changes in light hydrocarbon composition reflect generation patterns i e small scale changes in kerogen type and amount or are controlled primarily by redistribution processes a second objective was to discuss possible modes by which hydrocarbon redistribution took place the interval examined in the ravnefjeld formation is overmature 1 75 ro organic carbon contents toc and hydrogen index values range mostly between 1 0 5 5 and 10 20 mg hc g toc respectively the amount of hydrocarbons present in the examined section represent only a fraction of the total amount generated petroleum expulsion efficiency pee exceeding 0 99 was calculated systematic changes of light hydrocarbon composition with depth indicate that effective redistribution has occurred over wide intervals in particular there is good evidence to suggest that there was major loss with chemical fractionation of molecular species by depletion into several zones of fractures and also towards the outcrop surface and that fracture occurrence is the single most important factor in controlling the present day hydrocarbon depth trends in this paper a novel scheme is presented for effective and objective comparison of hydrocarbon depth trends the application of this method to elucidation of the migration mechanisms responsible for fractionation during hydrocarbon loss in the fractured zones is illustrated

saltwater intrusion modelling in jorf coastal aquifer south eastern tunisia geochemical geoelectrical and geostatistical application marine intrusion is the most serious problem facing the coastal jorf shallow aquifer located in south eastern tunisia on the mediterranean sea jorf aquifer is intensively exploited to supply the growing needs of agriculture and domestic sectors this work proposes a multidisciplinary investigation involving hydro geochemical geoelectrical survey and geostatistical techniques for modelling the saltwater intrusion for this purpose 36 water samples were conducted and analysed electric conductivity ph total dissolved solids and major ions were measured and analysed pie and durov diagrams q mode hierarchical cluster and geostatistical analysis were considered to identify the main groundwater mineralization processes results revealed that the na cl ca so4 is the dominant water type suggesting that dissolution of halite and gypsum was the main mineralization source of groundwater in the central and southern part of study area however saltwater intrusion was shown to control groundwater quality essentially in coastal areas variographic analyses were used to select the variographic model that best fits the spatial development of apparent resistivity kriged apparent resistivity profiles showed an abnormal decrease of resistivity values in the coastal zone implying highly saline water because of seawater intrusion apparent resistivity values also decrease considerably in the faulted areas suggesting a contribution of faults to seawater intrusion finally saltwater mixing ratio was computed for each sample and a refined seawater intrusion map was developed copyright 2012 john wiley sons ltd

geochemical processes in the saltwater freshwater transition zone comparing results of a sand tank experiment with field data geochemical processes occurring in a stable transition zone between saltwater and freshwater were simulated in a 2d multi layer flow chamber experiment mixing calcite dissolution and oxidative degradation of organic matter were identified as the main controlling factors the results of the chamber experiment were compared to field data and verified by thermodynamic modeling similarity in most ion distributions suggests the general applicability of the experimental method differences in the redox conditions between field and experiment were reflected by the oxidants involved in the mineralization of organic carbon while field data show evidence of sulfate reduction the presence of oxygen in the laboratory experiment resulted in the reoxidation of sulfides

origin of shallow saline groundwater on the island of laeso denmark abstract shallow saline groundwater has a patchy occurrence in superficial postglacial marine sediments beneath coastal meadows and salt marshes on the southern shores of the island of laeso denmark the postglacial sequence consists of 1 2 m of marine sands and gravels resting on a slightly undulating platform of practically impermeable interglacial marine clay which makes up a confining layer or aquiclude the saline groundwater primarily occurs beneath the vegetated fringe and associated minor unvegetated sand pans of coastal meadows and salt marshes the salinity varies from 2 to approximately 17 and analyses of major ions indicate a prevailing marine composition the saline groundwater is supersaturated with respect to carbonates in the entire salinity range and slightly supersaturated with respect to gypsum with salinities above 10 however aragonite is the only precipitate recorded so far stable isotope analyses 2 h and 18 o plot fairly well along the local groundwater seawater mixing line indicating mixing of seawater with fresh meteoric groundwater in the proportion 0 50 in contrast the stable isotopic compositions show no correlation to the wide range of salinities recorded it is proposed that the thin cover of superficial deposits resting on a clay platform results in a relatively closed hydrochemical system in which increasing concentration of dissolved solids in the interstitial water is caused by transpiration which is known to abstract water from groundwater without leading to isotopic fractionation periodical precipitation dissolution of salt in topsoils of sand pans and from salt secreting halophytes may also be contributory causes of increasing salinity in the groundwater the spatial distribution of the saline groundwater most likely depends on the microtopography of the slightly undulating clay platform the dense saline shallow groundwater emerging from the vegetated fringe and sand pans and flowing toward the depressions in the clay platform percolates downward displacing lower salinity seawater and groundwater

origin and characteristics of brackish groundwater in abu madi coastal area northern nile delta egypt abstract hydrogeochemical and geoelectrical resistivity investigations were carried out to assess the origin and characteristics of a brackish groundwater in abu madi coastal area twenty six surface water shallow and deep groundwater samples were collected and analyzed for various ionic concentrations as well as oxygen and hydrogen stable isotopic contents in addition a total of 20 vertical electrical sounding sites were conducted to investigate layers thicknesses resistivities and to detect the water bearing layers then 2 d electrical resistivity tomography ert along two profiles in the study area was conducted to get information about the surface water effect on recharge the stable isotopic composition and the chloride concentrations strongly suggest that the deep groundwater in abu madi area is dominated by inland freshwater with a minor seawater component this groundwater was recharged during the first and the third holocene humid climatic cycles where the sea surface was about 125 and 25 m below the current sea level respectively the brackish nature and higher piezometric surface of the groundwater as well as the occurrence of vertical low salinity seawater zone in front of the study area support the possibility of submarine groundwater discharge the geoelectrical resistivity surveying on the other hand revealed a number of geoelectrical groundwater bearing layers the main water bearing layer in the study area is represented by the sixth geoelectrical layer which has relatively high resistivity and a considerable thickness being consistent with the hydrogeochemical observations ert results point to the presence of shallow water bearing layers recharged from the surface water drains with low resistivity and surface rain water of moderate resistivity results from the hydrogeochemical analyses and the different hydrogeological data are consistent with the high resistivity values of this geoelectrical layer however the overall high specific conductance and high sodium hazards indicate that the groundwater in the study area should be carefully treated before irrigation and domestic uses through mixing it with surface irrigation water

geochemical and isotopic investigation of the aquifer system in the djerid nefzaoua basin southern tunisia in the djerid nefzaoua region southern tunisia about 80 of agricultural and domestic water supply is provided by the complex terminal ct aquifer however 20 of this demand is provided by other hydraulically connected aquifers namely the continental intercalaire ci and the plio quaternary pq overexploitation of the ct aquifer for agricultural practices has contributed to the loss of the artesian condition and the decline of groundwater level which largely increased the downward leakage from the shallow pq aquifer excess irrigation water concentrates at different rates in the irrigation channels and in the pq aquifer itself then it returns to the ct aquifer and mixes with water from the regional flow system which contributes to the salinization of the ct groundwater a geochemical and isotopic study had been undertaken over a 2 years period in order to investigate the origin of waters pumped from the ct aquifer with an emphasis on its hydraulic relationships with the underlying and the overlying ci and pq aquifers geochemistry indicates that groundwater samples collected from different wells show an evolution of the water types from na cl to ca so4 cl dissolution of halite gypsum and anhydrite bearing rocks is the main mechanism that leads to the salinization of the groundwater isotopic data indicate the old origin of all groundwater in the aquifer system mixing and evaporation effects characterizing the ct and the pq aquifers were identified using 2h and 18o relationship and confirmed by the conjunction of 2h with chloride concentration

the potential application of stable isotopes for distinguishing indigenous versus migrated hydrocarbons in a mature shale sandstone sequence abstract bitumens isolated from kokelsumer heide no 1 corehole ruhr area f r g are indicative of the problem of resolving contributions of indigenous versus migrated fluids within a depth interval of approximately 50 m thermally mature shales containing types ii and iii organic matter and a coal seam 1 2 r m are all encountered in addition to interbedded sands that are present in the upper portion of this interval presented here is an approach based on the unique isotopic compositions of indigenous bitumens kerogens and migrating fluids which appears to enable the evaluation of the proportion of extracts which migrated from a source rock stable carbon isotope values of kerogens and of saturate and aromatic fractions of residual bitumens isolated from kokelsumer heide no 1 and reckelsumer heide no 2 corehole samples are used to estimate the relative contributions of the various sources to the bitumens preliminary results indicate that from 10 shale sequences to 100 sandstone sequences of the extractable materials i e bitumens could be characterized as a migrating fluid also stable carbon and nitrogen isotope values for kerogens and coal samples from the kokelsumer heide corehole can be used to verify previous geochemical and microscopic evidence for the existence of distinct kerogen types i and ii in this corehole

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

study on the hydrochemical characteristics of groundwater along the taklimakan desert highway groundwater is the only water source of the shelterbelt along the taklimakan desert highway in northwestern china understanding the hydrochemical zoning characteristics material source and hydrochemical processes of this desert groundwater is important for rational groundwater exploitation meanwhile determining the location of the dividing boundary which divides the influence ranges of the tarim river and the kunlun mountain river system on the desert groundwater is meaningful for the local desert hydrogeological study for these objectives 105 groundwater samples were investigated to obtain analytical data of groundwater chemistry and ionic relations methods including ratio graphs and gibbs plots were applied in the chemical analysis for these data chemical analysis shows that desert groundwater is characterized by cl so4 na mg and cl so4 na types with total dissolved solid tds of 2 80 29 77 g l spatial variation patterns of major ions tds and so42 cl molar ratio reveal clear four hydrochemical zones along the groundwater flow direction on one hand on the other hand these variation patterns also indicate that the boundary dividing the influence ranges of the tarim river and the kunlun mountain river system is the approximate location of well 030 ratio graphs show that the average molar ratios na k cl 1 05 and ca2 mg2 so42 0 93 are approximately equal to 1 and there is an approximately linear correlation between na k and so42 these results reveal that the groundwater composition is mainly influenced by dissolution of evaporate halite gypsum and mirabilite moreover ionic relations demonstrate that the dominating hydrochemical processes in the groundwater evolution are evaporation and cations exchange

electromagnetic induction in new zealand analogue model and field results abstract the behaviour of electric and magnetic variations over north island new zealand is studied with the aid of a laboratory analogue model the source field frequencies used in the analogue modelling simulate naturally occurring geomagnetic variations of 5 120 min periods in phase and quadrature magnetic and electric fields for a selection of traverses for the modelled region of north island are presented since north island is of a relatively narrow cross section the field responses even for inland locations are expected to show strongly the effects of the surrounding ocean the irregular coastlines as well as the strait between north and south islands lead to coastal and inland field anomalies due to induced currents being deflected and channelled to produce localized current densities the comparison of model results with field station measurements obtained earlier individually by ingham and by midha for sites in the northeastern central and southern near cook strait regions of north island demonstrates the large role the ocean has in the observed field responses differences in the model and field results at some sites are expected and should reflect the effects of the local geology and the conductive substructure related to the complex tectonics of the region not simulated in the model

salinization processes in paleowaters in coastal sediments of suriname evidence from δ37cl analysis and diffusion modelling in the coastal plain of suriname a stagnant body of fresh 250 mg l cl and moderately brackish 250 1000 mg l cl groundwater of meteoric origin is found in permeable tertiary formations this groundwater body formed during the last wisconsin regression extends offshore into deposits on the continental shelf the authors found that this paleowater is slowly being salinized by downward solute transport from overlying holocene marine clays and upward transport from saline cretaceous sediments the downward transport has been studied at two sites by relating analyses of chloride contents and 37cl 35cl isotope ratios in pore water with computer simulations of diffusive transport optimization of process parameters yielded an effective diffusion coefficient of and a fractionation factor of 1 0027 which agrees well with earlier studies with the computer model the following periods of marine influence were found 6000 4 100 yr bp and 10 000 500 yr bp at the sites located 20 and 3 km from the coastline respectively according to the diffusion model the downward flux of salts has not penetrated deeper than 100 m salts below this depth are thought to originate from the cretaceous sediments however groundwater chloride concentration and chlorine isotope data are scarce below this depth while uncertainty regarding the various regressions and transgressions precludes solute transport modelling clay layers at the base of the tertiary appear to inhibit the upward transport by lateral dispersive mixing at the tertiary cretaceous boundary oil reservoirs are also related to these clay seals the presence of the seal and perhaps the oil below can therefore be predicted by the chloride profile in the upper 250 m

investigation of groundwater mineralization in the hammamet nabeul unconfined aquifer north eastern tunisia geochemical and isotopic approach detailed hydrogeochemical and isotopic data of groundwaters from the hammamet nabeul unconfined aquifer are used to provide a better understanding of the natural and anthropogenic processes that control the groundwater mineralization as well as the sources of different groundwater bodies it has been demonstrated that groundwaters which show na cl and ca so4 cl water facies are mainly influenced by the dissolution of evaporates the dedolomitization and the cation exchange process and supplementary by anthropogenic process in relation with return flow of irrigation waters the isotopic signatures permit to classify the studied groundwaters into two different groups non evaporated groundwaters that are characterized by depleted 18o and 2h contents highlighting the importance of modern recharge at higher altitude evaporated groundwaters with enriched contents reflecting the significance infiltration of return flow irrigation waters tritium data in the studied groundwaters lend support to the existence of pre 1950 and post 1960 recharge carbon 14 activities in shallow wells that provide evidence to the large contamination by organic 14c corroborate the recent origin of the groundwaters in the study area

hydrogeochemistry and geothermometry of the carbonate evaporite aquifers controlled by deep seated faults using major ions and environmental isotopes abstract carbonate aquifers probably constitute the most important thermal water resources in non volcanic areas and are characteristic of great energy potential and easier production as the most ideal targets for development in the future the thermal waters in the aquifers within southeast chongqing sec of china occur in an extensive region with an area of 198 000 km2 which are mainly hosted in the cambrian and ordovician carbonate evaporite rocks the thermal waters are mainly in pristine conditions and their genesis has not yet been fully understood the occurrence of thermal waters in sec is closely related to the presence of deep seated faults which constitute pathways for the hydrothermal circulation in this study an investigation of water major ions and environmental isotopes from 14 hot springs and three drilled wells was carried out to examine their hydrogeochemical evolution and to estimate reservoir temperature the thermal waters have outflow temperatures from 19 to 54 2 c they are divided into two hydrochemical groups with the yushan fault as a boundary group a located to the west of the fault are characterized by facies of chloride sodium waters with higher tds group b to the east of the fault are more complicated sulfate bicarbonate chloride alkaline earth waters with lower tds the hydrochemical processes such as dissolution of carbonate gypsum and or anhydrite and halite the common ion effect and dedolomitization are evident based on the major ions and 34sso4 and 18oso4 the 18o and d compositions of the thermal waters suggest a meteoric recharge in a relatively wetter and colder climatic condition the silica geothermometers show that the average reservoir temperatures are 63 18 c for group a and 82 15 c for group b the corresponding average reservoir depths are estimated to be 2 5 0 7 km for group a and 3 2 0 7 km for group b the corrected 14c ages of the thermal waters average at 14 8 ka bp corresponding to the late pleistocene a conceptual circulation model is proposed for the thermal waters driven by gravity of topographic gradients the percolating groundwater circulates at a specific depth reaching a higher temperature and interacting with the host carbonate with imbedded evaporitic minerals gypsum and or anhydrite and additional halite for group a to be saline deep seated thermal fluids the fluids rise along faults and emerge at the surface as thermal springs the slow renewability rate of the thermal aquifers highlights the importance of assessing the resource before groundwater exploitation and extraction

origin of water salinity in a lake and coastal aquifer system the studied area is in the algerian northeast a number of interacting factors at the site are able to modify salinity the main influences are 1 the lithology 2 fedzara lake 3 marine waters and 4 a prolonged drought 1 the lithology is very clearly delineated by the outcrop of metamorphic formations gneiss marbles micaschists and quartzites and sedimentary formations limestones clay sandstones and sands all these formations can influence the chemical composition of waters 2 fedzara lake evacuates its salted waters via the wadi meboudja which connects with the wadi seybouse and the phreatic surface these lake waters might induce changes in salinity 3 the marine waters represent the third source of salinity change over pumping of water from wells and drillings can cause an imbalance to the fresh salted water interface 4 the effects of a local prolonged drought of more than 10 years may increase water salinity over pumping to augment water supply generates a fall in water levels and the drier atmosphere increases evapotranspiration both may contribute to increased salinity results of water analysis were used to observe the evolution of these various factors

the coast effect response in geomagnetic field measurements abstract two dimensional 2d numerical models of electromagnetic em induction for anomalous conductors in continental and island coastal regions are studied to determine constraints on ocean conductor separation distances that would permit to within an acceptable approximation a simple vector subtraction of the coast effect response the anomalous conductors are in the form of an upwelling or a depression in the asthenospheric conductive substratum at depth the coast effect response range yr is arbitrarily taken to be the distance from the ocean at which the b z b y n coast effect response is reduced to a value of 0 2 the response ranges are determined and presented empirically as a function of period for a range of conductive substratum depths island widths and ocean depths the response ranges are tested in 2d numerical models that include an anomalous conductor in the form of either an upwelling or a depression in the conductive substratum under the ocean and host earth the induction arrows for the anomalous conductor are shown to be in good agreement with the difference arrows obtained by subtracting the responses of a model without the anomalous conductor from the responses of the model that includes the anomalous conductor as an application difference arrows obtained by subtracting three dimensional laboratory analogue model coast effect responses from field site responses are employed in the interpretation of induction arrow responses available for a number of sites in the bohai bay region of china and the kii peninsula region of japan

a laboratory electromagnetic model study of the juan de fuca plate region the behaviour of the magnetic field variations over the juan de fuca plate region is studied using a scaled laboratory analogue model the model includes a simulation of the complex juan de fuca plate subducting the vancouver island region the subducting plate is modelled with a profile of increasing inclination from east to west horizontal offshore dipping at 10 under vancouver island and bending further under georgia strait to subduct the continent at 30 for the b c region and 45 for the washington oregon region the strike of the bending plate follows the general strike of the continental coastline with an abrupt change in direction 42 in the puget sound area the model substructure simulates a subducting plate overplated by a sediment layer several kilometres thick and underlain by a 30 km thick highly conducting upper asthenosphere the model source frequencies used simulate periods 5 120 min in the geophysical scale in phase and quadrature hx hy and hz magnetic field measurements for the modelled region are presented for an approximately uniform overhead horizontal source field for e and h polarizations electric field of the source approximately parallel and perpendicular respectively to the west coast of vancouver island the fields for three regions of the model over vancouver island over the olympic peninsula and over a linear portion of the u s coastline are examined in detail the general conclusion is that the effect of the dipping subducting plates is to significantly attenuate at short periods the maxima in the anomalies at the coastlines underlain by the 10 dipping plate while leading to anomalous vertical and horizontal fields over ranges as large as 500 km inland over a wide period range anomalous fields are observed over the offshore and inland knee bends of the subducting plates at all periods for both e and h polarizations for locations on land the in phase induction arrows point seaward and perpendicular to the strikes of the dipping plates for all periods while the quadrature arrows at short periods point landward and rotate to point seaward for periods greater than 20 min

the valhall field a geological overview abstract the valhall field is located within the central graben in the southern part of the norwegian north sea the discovery well 2 8 6 was drilled in 1975 and the field went on production in 1982 production is currently 55 000 barrels of oil per day the valhall field structure trends nw se and has an areal closure in excess of 60 000 acres the hydrocarbon column measures 200 m the structure is located on an elongate anticlinal feature called the lindesnes ridge which developed during late cenomanian to oligocene tectonic movements the geophysical evaluation of the field is complicated by the existence of a gas charged tertiary section which obscures the deeper seismic reflections vertical seismic profiles vsps have been utilized in an attempt to resolve the reservoir configuration reservoirs occur both in the tor formation maastrichtian and in the underlying hod formation turonian coniacian the tor formation is represented by a largely allochthonous chalk facies which thins regionally to the southwest a crestal graben is developed in which the tor formation is locally thick autochthonous chalks are characteristic of the hod formation primary porosity of the chalk varies between 36 to 50 on the crest of structure preservation of such high porosity is primarily due to formation overpressure inhibiting mechanical compaction of the chalk the field contains paraffinic oil of 36 api gravity it originated from the upper jurassic kimmeridge clay formation which is at peak oil generating capacity under the field at present day

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

experiments on adsorption and molecular sieving and inferences on primary migration in upper jurassic claystone source rocks north sea fine pores primarily slit shaped micropores in upper jurassic claystone source rocks were studied by gas adsorption at 20 c approximately 80 of the mesopore and micropore volume is penetrable to water only because of constrictions approximately 3 a wide the pore surface is nonpolar and probably characterized by kerogen covering the clay mineral surfaces water is not structured in the mesopores and micropores but readily forms a liquid phase without distinct monolayer formation n alkanes probably enter the pores end on and become adsorbed parallel with the surface these results apply to all samples studied irrespective of the degree of clay mineral diagenesis three migration types proposed for these claystone source rocks are 1 type a migration which at experimental conditions permits entry and removal of n alkanes isobutane neohexane cyclohexane and benzene in approximately equal amounts 2 type b migration which permits entry and removal of n alkanes isobutane and neohexane in approximately equal amounts but where only 20 of the pore volume and surface area is also open to cyclohexane and benzene and 3 type c migration which is intermediate between type a and type b the occurrence of the migration type is related to the reservoir oil composition in the samples studied tectonics and clay mineral diagenesis appear to have no influence on the migration type migration types may be related to past overpressured conditions but do not appear to be related to current pressures

environmental hydrogeology of the southern sector of the samborombon bay wetland argentina the samborombon bay wetland is located on the west margin of the rio de la plata estuary in the province of buenos aires argentina this paper analyses the geological geomorphologic soil and vegetation characteristics of the southernmost sector of this wetland and their influence on surface water and groundwater the study area presents three hydrologic units coastal dunes sand sheets and coastal plain coastal dunes and sand sheets are recharge zones of high permeability with well drained non saline soils and a few surface water flows changes in the water table are related to rainfall groundwater in coastal dunes is ca mg hco3 to na hco3 and of low salinity 590 mg l groundwater in sand sheets is mainly na hco3 with a salinity of about 1 020 mg l the coastal plain exhibits medium to low permeability sediments with submerged saline soils poorly drained groundwater is na cl with a mean salinity of 16 502 mg l a surface hydrological network develops in the coastal plain surface water levels near the shoreline are affected by tidal fluctuations far from the shoreline water accumulates because of poor drainage both sectors have na cl water but the former is more saline human intervention and sea level rise may affect the wetland severely

some effects of compaction and geological time on the pore parameters of argillaceous rocks graphical statistics have been applied to the pore size distribution curves of argillaceous rocks to characterize the changes in pore parameters that result from compaction and geological time the most striking characteristic of recently deposited sediment is the high variability in mean pore size and in the sorting and skewness of the pore system the mean pore size ranges from 15 to 980 nm sorting ranges from very well sorted to poorly sorted and skewness varies from systems in which small pores predominate over large ones to systems in which large pores predominate this high variability in pore structure represents the many environmental and mineral related variables that affect the pore system of newly deposited sediment the mean pore size of shales decreases with increasing compaction and approaches a limiting value of about 3 5 nm at depth within a geological time span of 50 m y and or depth of burial of about 1200 m most sediments have reached an irreversible well sorted pore size distribution early diagenetic processes apparently affect the skewness of pore systems more than compaction such that within about 50 m y the pore system is negatively skewed with small pores predominating over large sediments buried to a depth of 500 m or less exhibit a porosity range of 40 85 below 500 m porosity decreases linearly with burial depth no correlation exists between the surface area of shale pore systems and depth of burial geological age and the pore parameters mean pore size sorting and skewness

stable isotope studies and the hydrological regime of sabkhas in southern kuwait arabian gulf the marine sabkhas in al khiran kuwait were formed by sedimentary offlap and relative fall in sea level since the last holocene transgressive maximum 4500 4700 years bp in the absence of significant marine flooding of the coastal sabkhas today due to the presence of chenier ridges their hydrological regime is almost entirely controlled by sub surface continental groundwater influx this topographic hydrologic framework is also reflected in the isotopic data and to some extent in the chemistry of the groundwaters where the major ions show a steady evaporative concentration from inland to coast and from coast to sabkha with a high chloride plateau in the central parts of the marine sabkha monitoring of the groundwater table gwt over a three year period indicates that a when the gwt depths are 1 2 m the sabkha is in a state of depositional equilibrium b gwt fluctuations due to drawdown or recharge exceed 0 5 m yr 1 and c calculations based on measured fall in gwt levels porosities of the sediments and the volume of anhydrite formed in the sabkha suggest that in the last 4700 years since progradation commenced only about 2 4 cm yr 1 net of groundwater is lost from the sabkha surfaces a surprisingly low rate for this arid region this is interpreted as due to recharge of the marine sabkha hosted by marine sediments by significant lateral flow of continental groundwater from the regional system a process that maintains long term stability of the sabkhas and without which deflationary processes would dominate the oxygen and deuterium isotopic compositions of the marine and continental sabkha waters form a group 18o 0 2 d 10 7 isotopically distinct from local meteoric water and pleistocene formation waters they represent evaporation of the old formation waters with a characteristic increase in the heavier isotopes only sabkha waters in areas of tidal flooding the narrow creek areas can be shown to be evaporated seawater the 18 o and d values of the residual brine increase to about 6 and 23 respectively when they reverse and are arrested at the halite precipitation point only a minor amount of mixing between these two evaporated waters could take place isotopic analyses of sulphur and oxygen in dissolved sulphate of sabkha waters and precipitated mineral sulphate confirm a minor contribution of seawater sulphate 34s 19 2 18o 11 in the tidal areas but show that the bulk of the marine sabkha water sulphate 34s 14 2 18o 14 1 and coexisting sulphate minerals is dominantly of continental origin at al khiran gulf of sirte libya and in abu dhabi united arab emirates 34s values of sabkha sulphate decrease to 14 on the landward side close to the values between 13 and 16 for continental sabkhas and continental getch gypsum this pervasive homogeneous sulphate source may be recycled particulate sulphate distributed by major dust storms these results have important implications in evaporite sedimentology

an application of thin sheet electromagnetic modelling to the tasman sea abstract the method of thin sheet approximation is invoked for the ocean layer to model and interpret magnetotelluric mt data observed on the floor of the tasman sea between australia and new zealand a technique to remove 3d distortion from the observed seafloor mt data is developed from the thin sheet model mt responses the de distorted data then appear isotropic and are reinverted using 1d procedures this approach thus assists interpretation through a combination of 3d forward modelling procedures and 1d inversion a seafloor sediment layer is shown to have a strong effect on observed seafloor mt data also an exercise is carried out to compare the results given by the vertical gradient sounding vgs method with seafloor mt data the electrical conductivity structure beneath the tasman sea is analysed in terms of an upper mantle lithosphere and asthenosphere and a highly conducting lower mantle the observed anisotropy in seafloor mt data is diagnostic of a lithospheric conductivity of less than 10 4 s m 1 conductivity rises by two orders of magnitude below 80 km to greater than 10 2 s m 1 and is probably related to an asthenospheric layer in the upper mantle seismic interpretations similarly place a low velocity zone below a depth of 70 km at a depth of approximately 400 km the conductivity is approximately 1 s m 1 consistent with global estimates for the lower mantle there is little evidence for major change with age in the structure across the tasman sea

assessment of submarine groundwater discharge in the intertidal zone of laizhou bay china using electrical resistivity tomography abstract coastal zones are the most sensitive and vulnerable ecological environments in the world submarine groundwater discharge sgd is an important pathway for material transport between land and sea in the low lying coastal plains of coastal zones in the present study electrical resistivity tomography was used to monitor submarine groundwater discharge in the intertidal zone the salinity change ratio was derived using archie s law and manheim s equation and was used as an index to describe the dynamic discharge process a model of the seawater circulation process in the multilayer coastal aquifer system was established the model contains a window area between the upper unconfined and lower confined aquifer and a highly permeable channel in the upper silt layer the results of the study provide a theoretical basis and technical support for the rapid assessment of sgd in low lying coastal plains and will assist in the management of coastal zone environments

the continental slope experiment along the tasman project profile southeast australia abstract three seafloor magnetometers made recordings for up to 95 days between july and october 1986 at site across the continental slope of southeast australia along the profile of the 1984 tasman project of seafloor magnetotelluric exploration tpsme land magnetometers at tpsme sites at the coast and canberra were reactivated to give simultaneous recordings the seafloor magnetometers were at depths of 140 m 2240 m and 3380 m and spanned the continental shelf between the coastline and the closest inshore tpsme ocean floor site depth 4850 m this experiment complements the tpsme by giving a much sharper definition of the geomagnetic coast effect in this critical region data are presented in the form of parkinson arrows for comparison with previously derived tpsme results along the profile they show a strong coast effect with the maximum mid way down the continental slope the situation is closely two dimensional and using this approximation some simple models have been computed one which gives a relatively good fit at a period of 1 h comprises simply a conductive ocean overlying a uniform conductor at depth further work will be needed to determine whether lateral conductivity structure at depth is required to fit the data more closely

electromagnetic induction in the british isles region analogue model and field station results the results of a laboratory electromagnetic analogue model study which employs a horizontal inducing field over a simple model of the british isles region delineate the location and frequency dependence of the major coast effect induction anomalies of the scotland region contours of amplitudes amplitude ratios and in phase and quadrature parts of the model field measurements are presented the model vertical magnetic fields for two orthogonal source field polarizations and field station values for two hypothetical events for corresponding polarizations are compared while major discrepancies occur between model and field hz amplitudes the hz gradients across scotland which can be attributed to the coast effect are comparable in value although sometimes reversed in sign superimposed on this coast effect the field data indicate the existence of current concentrations associated with the great glen and the southern uplands faults and possibly also of currents within the scottish mainland near the east and west coasts

hydrogeochemical and isotopic evidence of groundwater salinization in a coastal aquifer a case study in jeju volcanic island korea abstract in order to identify the origin of saline groundwater in the eastern part of jeju volcanic island korea a hydrogeochemical and isotopic study has been carried out for 18 observation wells located in east and southeast coastal regions the total dissolved solid contents of groundwaters are highly variable 77 21 782 mg l oxygen hydrogen sulfur and strontium isotopic data clearly show that the saline water results from mixing of groundwater with seawater strontium isotopic compositions and br cl and i cl ratios strongly suggest that the source of salinity is modern seawater intrusion hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation exchange reactions the highly permeable aquifers at the east coastal region are characterized by low hydraulic gradient and discharge rate and high hydraulic conductivity as compared with other regions these properties enhance the salinization of groundwater observed in the study area based on the cl br and 18 o data seawater was determined to have intruded inland some 2 5 km from the coastline considering the poor correlation of sampling depth and cl concentrations observed the position of seawater freshwater interface is not uniformly distributed in the study area due to heterogeneities of the basaltic aquifers

geochemical and isotopic evidence of shallow groundwater salinization in a reclaimed coastal zone the yellow river delta china this paper aims to improve the current knowledge of groundwater salinization processes of a young coastal aquifer in the yellow river delta yrd and to assess the impact of both the transfer of irrigation water from the yellow river and seawater intrusion using a combination of hydrochemical isotopic measurements the major ion cl ratios generally closely follow the mixing line between freshwater end member the yellow river and saline water end members salt groundwater or seawater indicating the importance of mixing under natural and anthropogenic influences the examination of stable isotope in groundwater ranging from 9 0 to 3 5 for 18o and from 73 to 29 for d respectively and chloride concentrations 2 to 629 meq l confirms that the saline end member is associated with saltwater rather than present seawater and most groundwater samples are plotted on mixing lines between the yellow river and saltwater the similar range in stable isotopes 18o and d and cl compositions between saltwater and confined aquifer supports the hypothesis that upward seepage of confined saline water intruded the shallow aquifer moreover the deviations in some cases from mixing line imply water rock interaction is also important in dominant control on groundwater chemistry such as cation exchange so4 2 reduction and nacl solution the brackish water was characterized by slight excess of na and deficit of ca2 compared to non reactive mixing line this indicates that the coastal aquifer is generally freshening with respect to extensive irrigation network as well as the transfer from the yellow river for ecological recharge into wetland

evolution of groundwater salinity in the unconfined aquifer of bou areg northeastern mediterranean coast morocco the bou areg plain in the mediterranean coast at the north eastern of morocco is characterized by a semi arid climate the aquifer consists of two sedimentary formations of plio quaternary age the upper formation of fine silts and the lower one of coarse silts with sand and gravels the aquifer is underlain by marly bedrock of miocene age that dips toward the coastal lagoon of bou areg the hydrodynamic characteristics vary between 10 4 and 10 3 m s and transmissivities range between 10 4 and 10 1 m2 s the general direction of flow is sw to ne toward the lagoon the aquifer is crossed by the river selouane which also ends in the lagoon the groundwater is characterized by a high salinity that can reach 7 5 g l the highest values are observed in the upstream and in the downstream sectors of the aquifer the temporal evolution of the physico chemical parameters depends on the climatic conditions and piezometric variations the analysis of the spatio temporal distribution of the physico chemical parameters suggests different sources of groundwater salinization the seawater intrusion the influence of marly gypsum bearing terrains and the influence of anthropogenic products as the agricultural fertilizers which cause great nitrate concentrations that vary between 80 and 140 mg l

hydrochemical and isotopic investigation of a sandstone aquifer groundwater in a semi arid region el ma el abiod algeria this work present results of the hydrochemical and isotopic studies on groundwater samples from the study area chemical and environmental isotope data are presented and discussed in terms of the origin of dissolved species and of groundwater all of the investigated groundwater are categorized into two chemical types low and relatively high mineralized waters type interpretation of chemical data based on both thermodynamic calculations and stability diagrams suggests that the chemical evolution of groundwater is primarily controlled by water rock interactions interpretation of 18o and 2h suggests that the recharge of the investigated groundwater may result from differents mechanisms

the study of the hydrogeological setting of the chamshir dam site with special emphasis on the cause of water salinity in the zohreh river downstream from the chamshir dam southwest of iran dissolution of evaporite formations emergence of salty water springs and intrusion of deep saline waters are important causes in changing the quality of surface water the study area is part of the reservoir and downstream of chamshir dam which is located in watershed of the zohreh river 20 km southeast of gachsaran city southwest iran to construct powerhouse and related structures for supplying water to agricultural lands located in downstream of dam water quality of zohreh river was studied by eight sampling stations in the study area early studies showed that water quality of the zohreh river decreases severely downstream of the chamshir dam spatial variations diagram of major ions piper and composition diagrams of water samples in selected stations mark the presence of two slight and major contaminating zones at sampling station r4 and r5 in these zones concentration of ca so4 and na cl ions increase suddenly results of hydrogeological hydrochemical lithological and tectonics studies showed that even though there are several low discharges springs in the contaminated zone they cannot be related to surface dissolution of evaporate layers by zohreh river there is an important fault zone including chamshir faults i and ii in the contamination zones through which intrusion of sulfate brackish and chloride brine waters occur along the fault zone and then enter zohreh river below its base level in the absence of any surface evidence the fault zone is the main cause of salinity evaluation of water balance salinity in contaminated zones shows that the discharge rate of saline waters to the river is not low and cannot be separated these findings show that there are serious restrictions upon the purposes of the project

role of diffusion in primary migration of hydrocarbons the following effective diffusion coefficients d cm2 sec were determined for the diffusion of light hydrocarbons through the water saturated pore space of shales methane 2 12 10 6 ethane 1 11 10 6 propane 5 55 10 7 iso butane 3 75 10 7 n butane 3 01 10 7 n pentane 1 57 10 7 n hexane 8 20 10 8 n heptane 4 31 10 8 and n decane 6 08 10 9 on the basis of these new data a deterministic dynamic model was set up to simulate the diffusive transport of light hydrocarbons c1 to c10 from source rocks for eight documented source rock units representing a wid range of geologic conditions maturities of 0 40 to 1 35 mean vitrinite reflectance oil to gas prone kerogens the cumulative amounts of hydrocarbons escaping with time were calculated thus it was shown that diffusion represents an effective process for primary migration of gas but not for oil the rate of mass transport for gas from source rocks with geologic time can be sufficiently high to account for the origin of commercial size gas fields for example a cumulative amount of 109 kg of methane 1 5 109 std m3 or 5 3 1010 scf has escaped by diffusion in 540 000 years from a certain volume 1 000 km2 by 200 m thick of a high mature gas prone mesozoic source rock in western canada the origin of hydrocarbon accumulations with high gas to oil ratios in low mature sediments in geologically young basins early gases and condensates can be explained by an early phase of primary migration predominantly based on diffusion during the initial stages of the accumulation history of those fields extending up to millions of years under certain conditions the reservoir gas changes with geologic time from a methane rich to a wet gas composition at low maturity levels below about 0 6 rm even oil prone source rocks yield methane rich light hydrocarbon mixtures by migration through diffusion compositional trends among reservoir gases of several multiple pay gas fields in louisiana represent evidence for diffusive transport of hydrocarbons the variation in gas composition between the individual pay zones is controlled by increasing distances of diffusive transport of the hydrocarbons from a uniform source rock at depth to their present accumulation sites in the shallow pay zones compounds of high diffusivity are enriched for example in the sligo gas field of louisiana the methane ethane and the iso butane n butane ratios increase from 10 2 to 36 0 and from 0 86 to 1 13 respectively from the deepest to the shallowest of the five productive reservoir sands which are spread over a a depth interval of 5 500 ft 1 676 m diffusion of light hydrocarbons in the subsurface can also have economically adverse effects for example existing gas accumulations can be destroyed by dissipation the rate of this destruction was calculated for the harlingen gas field holland by diffusive loss through 400 m of shale cap rock the initial amount of methane in place of 1 93 109 std m3 6 8 1010 scf is reduced by one half over a period of 4 5 million years this leads us to propose the concept that large gas accumulations can persist through extended periods of geologic time only as dynamic systems reaching some kind of steady state equilibrium between diffusive loss through the cap rock and continuous replenishment from the source rock

hydrochemical variability associated with rainfall regime a case study in the coastal wetland of the outer rio de la plata estuary argentina in coastal wetlands the interaction between groundwater surface water and marine or estuarine water determines the water chemistry variations in the water balance may be of influence as well the objective of this work was to assess how the rainfall regime affects the hydrological and geochemical processes that regulate the quality of surface and groundwater in the samborombon bay coastal wetland we analyzed the water balances and chemical data of surface and groundwater during a dry and a wet period results show that the rainfall regime regulates water quality in the three hydrological units defined for the region i e groundwater in the coastal plain groundwater in the shell ridges and surface water in the coastal plain in the water balance corresponding to a dry period real evapotranspiration is similar to precipitation in such conditions in the coastal plain the halite and gypsum salts precipitate subsequently the rain or the tidal flow dissolves them and they enter the water table by infiltration the lowering of the water table favors the oxidation of sedimentary pyrite and the contribution of sulfates the oversaturation of calcium carbonates in groundwater causes their precipitation both in the coastal plain and in the shell ridges the chemistry of surface water depends on the influence generated by the tidal inflow and groundwater discharge during the wet periods precipitation is higher than real evapotranspiration leading to the infiltration of water excess toward the water table and the increase in surface runoff this causes a decrease in the concentration of ions dissolved by dilution this rainfall regime hinders the formation of evaporite salts gypsum and halite and leads to the undersaturation of groundwater with respect to calcite allowing the dissolution of carbonates as regards the chemical composition of the surface water in the coastal plain the surface runoff in the drainage basin is more significant than the groundwater discharge and the tidal inflow it can be concluded that the alternation of dry and wet periods in the samborombon bay wetland causes the rainfall regime to be a determining factor in the different hydrological and geochemical processes affecting the quality of surface and groundwater

an analogue model study of electromagnetic induction in the tasmania region abstract laboratory analogue model magnetic measurements are carried out for a model of the region including tasmania bass strait with its highly conductive deep sedimentary basins and the south coast of mainland australia the model source frequencies used simulate naturally occurring geomagnetic variations of periods 5 120 min in phase and quadrature magnetic hx hy and hz field measurements for the modelled region are presented for an approximately uniform overhead horizontal source field for e polarization electric field of the source in the n s direction and for h polarization electric field of the source in the e w direction large anomalous in phase and quadrature model magnetic fields are observed over bass strait and the coastal regions at short periods for both e and h polarization but with increasing period the field anomalies decrease more rapidly for e polarization than for h polarization the difference in response with polarization for the bass strait region is attributed to current induced in the deep ocean for all periods being channelled through bass strait for h polarization but not for e polarization the persistent large coastal field anomalies elsewhere for h polarization can be accounted for by the coastal current concentrations due to currents induced in the deep ocean for all periods deflected to the south and to the north by the shelving sea floor and channelled through bass strait and around the southern coast of tasmania the phenomena of current deflection and channelling for h polarization for the geometry of the southern australia coastline and associated ocean bathymetry is particularly effective in producing field anomalies for a large period range the coastal horizontal hx and hy field anomalies present for e polarization at short periods and for h polarization at all periods do not extend far inland and thus for inland station sites somewhat removed from the coast should not present serious problems for magnetic soundings in field work the sharp vertical field hz gradient over tasmania at short periods which is predominantly in the e w direction for e polarization and the n s direction for h polarization is strongly frequency dependent becoming almost undetectable at 60 min the behaviour of the hz field gradients however are very similar from traverse to traverse over inland tasmania and thus the effects of the ocean should not present too serious a problem in the interpretation of field station studies the discrepancies between model and field station results should be useful in mapping geological boundaries in the region

analogue model study of electromagnetic induction in the newfoundland region abstract the behaviour of magnetic field variations over the newfoundland canada region is studied using a scaled laboratory analogue model the model source frequencies used simulate periods of 100 s 300 s 900 s and 1800 s in the geophysical scale contour views of in phase and quadrature phase parts of the three magnetic field components for two orthogonal source field polarizations for 100 s and 1800 s period variations are shown large anomalous in phase and quadrature model magnetic fields are observed over the strait of belle isle and cabot strait for all four periods studied with the anomalous fields reaching maxima when the skin depth is of the order of six times the depth of the strait the cape effect that is the large field enhancements due to deflection of induced current at capes is observed for all four periods enhanced fields are observed at the continental shelf edge for 1800 s variations but not for 100 s variations a general shift in the anomalous field from the in phase to the quadrature part for all three magnetic components is found for increasing period the magnitudes and directions of inter station induction arrows and single station induction arrows are studied the two types of induction arrows differ when an anomalous horizontal magnetic field is present this is especially evident near the coastline for a period of 100 s for all periods studied the in phase induction arrows point towards the nearest and largest current concentrations in traversing the coastline the single station quadrature arrows reverse direction for the 100 s period but not for the 1800 s period the model results indicate that there is no preference for using either single station or inter station induction arrows with respect to minimizing the effects due to coastal variations for inland locations further the model results show that for periods studied 100 s 1800 s the coastal effects would not produce serious perturbations to the field measured over crustal anomalies within the central regions of newfoundland

an assessment of the seawater effect by geochemical and isotopic data on the brackish karst groundwater from the karaburun peninsula izmir turkey the study area is located in the center of the karaburun peninsula turkey where several karstic springs discharge near the coast 0 2 m above the sea level the most important discharge points are the ildiri and gerence springs groundwater obtained from ildiri springs and several drill wells provide water to the region during the summer periods the electrical conductivity values are between 1900 and 3900 s cm springs are slightly salty and are not used directly as drinking water salinity was observed in the spring waters under natural flow conditions the salinity values of the drillings and springs were measured in dry and wet seasons spring waters have conductivity values between 3000 and 4000 s cm preliminary surveys reveal that seawater contribution to ildiri springs is 6 5 maximum gerence spring waters discharge to the surface from a region very close to the sea the dominant cation is na and the dominant anion is cl conductivity values were between 7000 and 13 000 s cm gerence spring waters discharge to the sea with seawater contributions ratios between 8 5 and 20 3 depending on the seasonal changes while some spring waters discharge 0 5 1 0 m above sea level the rest of them discharge directly into the sea salinization of gerence spring water is higher than the other springs

hydrochemical and isotopical evidence of ground water salinization processes on the coastal plain of samborombon bay argentina summary salinization in coastal areas of the province of buenos aires argentina is a controlling factor of water quality and limits its exploitation for human uses and local ecological values coastal plains such as the one in the southern part of samborombon bay have a tidal morphology consisting of fine sediment deposits tidal channels and aeolian sand sheets each of them playing a hydrological role in this paper we describe the hydrological processes in the samborombon bay coastal plain using hydrochemical and isotopical data to provide evidence of salinization processes specific ionic relationships for surface and ground water samples from each formation are differ from those of sea water isotopic data also reveal infrequent participation of sea water in the coastal area water samples showing an evaporation trend in both surface and ground water we conclude that salinization has its origin in the occurrence of gypsum and halite as well as other chlorides from the coastal plain deposits rainfall recharge continental water inputs evaporation and long residence times define the hydrochemical and isotopical features of ground water which shows no signs of present sea water contribution sand sheets constitute local aquifers with lower salinity content continental surface waters as well as rainfall drainage via tidal channels have a dominant effect on surface water hydrochemistry notwithstanding tidal oscillations exploitation of water resources is thus limited to regionally extended aeolian sand sheet formations and to surface waters specifically those related to contributions of freshwater discharge from inland areas

geochemical processes in kandi basin benin west africa a combined hydrochemistry and stable isotopes approach abstract detailed hydrochemical and stable isotopic data of surface and groundwater were used to understand the geochemical processes occurring in the kandi basin in benin hydrochemical investigations show that waters in this basin are of low mineralization with values of total dissolved solids tds generally less than 1200 mg l water types in the basin are hco3 mg hco3 na cl na hco3 ca cl ca and most fall in mixture water type i e hco3 mixe and cl no3 mixe the mineralization is governed essentially by the dissolution of dolomite calcite aragonite and magnesite but not cation exchange reactions the stable isotope approach underlined the interchange phenomenon between aquifers in the basin direct recharge of aquifers by surface waters in some areas and recharge of aquifers by modern precipitation which influence the groundwater geochemistry in the basin anthropic origin of nitrates is underlined by stable isotopes

suitability assessment of deep groundwater for drinking and irrigation use in the djeffara aquifers northern gabes south eastern tunisia the multilayered djeffara aquifer system south eastern tunisia has been intensively used as a primary source to meet the growing needs of the various sectors drinking agricultural and industrial purposes the analysis of groundwater chemical characteristics provides much important information useful in water resources management detailed knowledge of the geochemical evolution of groundwater and assessing the water quality status for special use are the main objective of any water monitoring study an attempt has been made for the first time in this region to characterize aquifer behavior and appreciate the quality and or the suitability of groundwater for drinking and irrigation purposes in order to attend this objective a total of 54 groundwater samples were collected and analyzed during january 2008 for the major cations sodium calcium magnesium and potassium anions chloride sulfate bicarbonate trace elements boron strontium and fluoride and physicochemical parameters temperature ph total dissolved salts and electrical conductivity the evolution of chemical composition of groundwater from recharge areas to discharge areas is characterized by increasing sodium chloride and sulfate contents as a result of leaching of evaporite rock in this study three distinct chemical trends in groundwater were identified the major reactions responsible for the chemical evolution of groundwater in the investigated area fall into three categories 1 calcite precipitation 2 gypsum and halite dissolution and 3 ion exchange based on the physicochemical analyses irrigation quality parameters such as sodium absorption ratio sar percentage of sodium residual sodium carbonate residual sodium bicarbonate and permeability index pi were calculated in addition groundwater quality maps were elabortaed using the geographic information system to delineate spatial variation in physico chemical characteristics of the groundwater samples the integration of various dataset indicates that the groundwater of the djeffara aquifers of the northern gabes is generally very hard brackish and high to very high saline and alkaline in nature the water suitability for drinking and irrigation purposes was evaluated by comparing the values of different water quality parameters with world health organization who guideline values for drinking water piper trilinear diagram was constructed to identify groundwater groups where the relative major anionic and cationic concentrations are expressed in percentage of the milliequivalent per liter meq l and it was demonstrated that the majority of the samples belongs to so4 cl ca na cl so4 na ca and na cl hydrochemical facies as a whole all the analyzed waters from this groundwater have revealed that this water is unsuitable for drinking purposes when comparing to the drinking water standards salinity high electric conductivity sodium adsorption ratio and sodium percentages indicate that most of the groundwater samples are inappropriate for irrigation the sar vary from medium s2 to very high s4 sodicity therefore the water of the djeffara aquifers of the northern gabes is dominantly of the c4 s2 class representing 61 23 of the total wells followed by c4 s3 and c4 s4 classes at 27 27 and 11 5 of the wells respectively based on the us salinity classification most of the groundwater is unsuitable for irrigation due to its high salt content unless certain measures for salinity control are undertaken

an analogue model study of em induction for an island near bay and cape coastlines abstract laboratory electric and magnetic model measurements were carried out to examine how the addition of a nearby elliptical island to an otherwise complex continental coastline involving bays and capes affects electromagnetic induction in coastal regions irregularities in a coastline in the form of bays and capes lead to significant spatial field variations in coastal regions due to variations in density of induced current flowing in the ocean caused by current deflection or channelling by the coastal irregularities the addition of a nearby island which for the appropriate field polarization can result in current channelling through the strait greatly influences these field spatial variations for e polarization the case of the model electric field of the inducing source parallel to the strait and for short period 4 2 min studied here variations the effect on the fields of the model elliptical island in the shallow coastal ocean at points on the nearby continental coastline was to increase by factors as large as two to three the h y amplitudes at the centres of the bay and the cape and the e x amplitude at each bay cape and straight coastline in the region of the strait as compared with the values for coastline models without an offshore island for h polarization the case of the electric field of the source perpendicular to the strait the effect of the island was to increase by a factor of two to three the h z coastline values at the edge of the bay and to decrease by a similar factor the value at the edge of the cape further the spatial variations in the fields for both polarizations over the island and over the strait were strongly influenced by current channelling through the strait thus any interpretation of field station measurements on such an island on the sea floor in the strait or on the continent in coastal areas near an island should take into account the effects due to current concentrations in the strait particularly at short periods

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

study of variation in groundwater quality in a coastal aquifer in north eastern tunisia using multivariate factor analysis abstract this work focuses on the grombalia aquifer which constitutes the main water resource in northeast tunisia cap bon peninsula the recharge of this aquifer is ensured mainly by direct infiltration of rainwater through permeable layers under semi arid climatic conditions and increasing water demand for irrigation about 80 of the grombalia aquifer system shows different vulnerabilities to anthropogenic activities the total dissolved solids values range from 0 75 to 5 6 g l isotopic characterization with stable isotopes 2 h and 18 o of grombalia aquifer system identified geochemistry processes that control water chemistry in addition the multivariate statistical technique principal component analysis was used to identify the origin the recharge mode and geochemical processes controlling groundwater quality the principal reactions responsible for the hydrochemical evolution in the grombalia groundwater fall into three categories 1 denitrification process 2 dissolution of salts and 3 irrigation return flow process tritium data in groundwater from the study area suggest the existence of pre1950 and post1960 recharge

interaction of aquifer wetland in a zone of intensive agriculture the case of campo de dalias almeria se spain the campo de dalias almeria south eastern spain was the backdrop for the development of intensive agricultural activity during the 1970s due to the poor natural soil development the agriculturalists opted for a system that involved quarrying silt and clay deposits that could be used as soil in the greenhouses in parallel poor water quality in the upper aquifer caused the gradual abandonment of boreholes and a generalised rise in piezometric levels these factors have favoured the formation of a series of artificial wetlands in the abandoned clay pits onayar cabriles and balsa del sapo toad pond being the most significant in balsa del sapo the water column rose 3 5 m between october 2007 and february 2011 there has been a continuous fall in the electrical conductivity of the surface water which has gone from 14 500 s cm 1 in 2004 to 4 100 s cm 1 in 2013 the most recent concentrations are close to those found in the groundwater the same situation is detected for cl so4 and na ion concentrations in the surface and groundwater these data show the groundwater surface water interaction in the balsa del sapo nevertheless the sharp rise in surface water level has created a flood hazard due to the shallow topography of the area both for people living in the vicinity and their property this is an endorheic zone where a number of ramblas gullies draining the southern face of the sierra de gador mountains converge the campo de dalias is a spectacular example of the changes that can occur in a semiarid agricultural area as a result of intensive groundwater abstraction these changes are directly related to the management of water resources the most recent consequence of which is the increased risk of flooding hence there is a need to consider the management of these water resources to achieve a more sustainable use which is compatible with the environmental protection of the wetland and which will give some guarantee of flood protection for people and property

induction arrows for a buried conducting plate abstract a scaled electromagnetic analogue model is used to study the behaviour of single station induction arrows over a conducting plate embedded in a homogeneous poorly conducting medium for a profile crossing the edge of the conducting plate the in phase arrow for all locations points towards the bulk of the good conductor while the quadrature arrow reverses direction directly over the edge consistently pointing towards the edge the results also show that both the in phase and quadrature arrow lengths are reduced with increasing conductor thickness and depth of burial the model results are applied to examples of a uniform depth ocean and a conducting sill embedded in a poorly conducting earth

influence of the geologic and geomorphologic characteristics and of crab burrows on the interrelation between surface water and groundwater in an estuarine coastal wetland the interrelation between surface water and groundwater in intertidal flats is often studied through mathematical models in many cases these models need to be supported by an integral analysis of the geologic geomorphologic hydrologic and biological characteristics of the environment that are to be obtained from field surveys the marshy environment of the river ajo in the samborombon bay wetland argentina is a typical example of an estuarine coastal zone geologic and geomorphologic surveys were carried out as well as measurements of surface water and groundwater level changes as a response of the aquifer to tidal forcing the banks of the river ajo are either scarped with storm flats or mildly sloped with intertidal flats and numerous crab burrows sediments are mainly silty clayey with low permeability and lie over silty sandy layers at the erosion scarps the tidal wave enters the aquifer as a sub horizontal flow through the pore space of the sediments the tidal range in the aquifer depends on the lithological characteristics of the sediments and on the side changes of their hydraulic conductivity the rise of the water table at high water and its subsequent fall are nearly sinusoidal with a period similar to that of the tide at the river at the intertidal flats instead the tidal wave enters the aquifer mainly as a sub vertical flow through the crab burrows as the crab burrows are not interconnected they are not distinct pathways for preferential flow therefore the groundwater flux into the river is very slow during low water and the recovery of the water table takes a long time the tidal influence upon the water table on both kinds of banks affects only a narrow strip of the aquifer not only are the characteristics of the marshy environment of the river ajo representative of most of the samborombon bay wetland they can also be extended to other similar coastal wetlands to help preserve these invaluable environments

understanding the origin of salinization of the plio quaternary eastern coastal aquifer of cap bon tunisia using geochemical and isotope investigations as in many other semi arid regions the plio quaternary aquifer of the eastern coast of cap bon peninsula ne tunisia shows a parallel increase in overexploitation and mineralization of groundwater resources and so the water quality is deteriorating different methods using geochemistry ions na cl ca2 mg2 br and stable isotopes 18o 2h are compared with the hydrodynamic information for identifying the main processes involved in the increase of salinization along the coast intrusion of seawater resulting from groundwater overexploitation is identified but is not the only cause of qualitative degradation the development of irrigation that induces soil leaching and transfer of fertilizers to groundwater over the whole aquifer extent is another major reason for the increase in salinization a total of 48 groundwater wells were sampled to obtain additional information on the hydrochemical characteristics of the groundwater defined in previous studies

ionic and isotopic ratios for identification of salinity sources and missing data in the gaza aquifer abstract groundwater is the only source of fresh water in the gaza strip however it is severely polluted and requires immediate effort to improve its quality and increase its usable quantity intensive exploitation of groundwater in the gaza strip over the past 40 years has disturbed the natural equilibrium between fresh and saline water and has resulted in increased salinity in most areas salinization in the coastal aquifer may be caused by a single process or a combination of different processes including seawater intrusion upconing of brines from the deeper parts of the aquifer flow of saline water from the adjacent eocene aquifer return flow from irrigation water and leakage of wastewater each of these sources is characterized by a distinguishable chemistry and well known isotopic ratios in this paper na cl so4 cl br cl ca hco3 so4 and mg ca ionic ratios were used to distinguish different salinization sources 11b and 87sr 86sr isotopic composition were also included in the model to study their importance in this monitoring task the task of monitoring and the associated decision making process are characterized by a high degree of uncertainty with respect to input data and accuracy of models for this reason probabilistic expert systems and more specifically bayesian belief networks bbns are used to identify salinization origins the bbn model incorporates the theoretical background of salinity sources area specific monitoring data that are characteristically incomplete in their coverage expert judgment and common sense reasoning to produce a geographic distribution for the most probable sources of salinization the model is also designed to show areas where additional data on chemical and isotopic parameters are needed

multivariate statistical analysis of water chemistry in evaluating groundwater geochemical evolution and aquifer connectivity near a large coal mine anhui china major ion chemistry of groundwater from main aquifers near the dingi coal mine anhui china was analyzed with a suite of statistical techniques in an effort to understand aquifer connectivity and groundwater geochemical evolution fifty seven groundwater samples were analyzed from four aquifers the cenozoic top middle bottom aquifers and a permian coal strata aquifer with increasing depth of the aquifers groundwater became more mineralized showing greater hardness and salinity the dissolutions of halite and sylvite carbonate sulfate and silicate minerals were the primary processes controlling groundwater chemical compositions in the cenozoic bottom and coal strata aquifers while k na and hco3 originating from silicate mineral weathering were more enriched in the coal strata aquifer principal component analysis pca identified two principal components with the first component representing hardness variation and accounting for 57 5 of total variance and the second component 23 5 of total variance controlled primarily by salinity and sulfate reduction process the cenozoic bottom aquifer had greater hardness than other aquifers whereas the coal strata aquifer was characterized by higher salinity and larger influences of sulfate reduction cluster analysis revealed that the coal strata aquifer was largely isolated from the cenozoic aquifers with possible infiltration at discrete locations indicating that the high yield thick cenozoic aquifers may serve as a potential additional source for groundwater inrush into coal mines

groundwater salinization in shallow aquifers adjacent to a low altitude inland salt lake a case study at yuncheng basin northern china measurements of chemical composition and environmental isotopes were conducted to investigate the main geochemical processes controlling the salinization of shallow groundwater adjacent to an inland salt lake in the yuncheng basin hydrogeochemical and isotopic studies were carried out by collecting thirty shallow groundwater two rainfalls and one salt lake water samples from the study area about 80 of the shallow groundwater samples had total dissolved solids more than 500 mg l implying significant water quality deterioration in the study area shallow groundwater showed a clear increased salinity along regional flow paths toward the center of the basin where a salt lake is located results of environmental isotopes ionic ratio and saturation indices calculation indicated that the major geochemical processes responsible for groundwater salinization included dissolution of evaporites halite gypsum and mirabilite cation exchange and evapotranspiration groundwater salinization as a result of salt lake intrusion from the salt lake was limited to the northern shore of the lake

microdepression focused recharge in a coastal wetland la plata argentina depression focused recharge dfr has been well documented for the clay till plains of western canada kettle lakes of southeastern wisconsin the sandhills region of nebraska and elsewhere in this study the importance of dfr in a fine grained estuarine coastal plain environment with extremely low topographic relief is shown the southwestern coastal plain of the rio de la plata near the city of la plata argentina extends 8 9 km inland from the river and ranges in elevation from 0 to 3 m above sea level the holocene postpampeano sediments predominantly composed of silty clay in the study area mantle the coastal plain and exert a major control on the hydrodynamics of groundwater of the region the average hydraulic conductivity of the unit ranges from 1 0 10 9 m s 1 when estimated on a small scale single well and oedometer tests to approximately 1 0 10 8 m s 1 when estimated on a larger scale tritium profiles and seepage meters a study of the groundwater flow system has established that recharge is occurring in the marshes of the central coastal plain which are 0 5 1 0 m lower than the surrounding land a broad 50 cm high groundwater mound a significant feature in the context of a regional hydraulic gradient of 0 0005 was documented below the marshland using nests of monitoring wells recharge rates are further controlled by subtle 10 40 cm elevation variations within the marsh four nests of six monitoring wells each were installed in the marsh and sampled for tritium recharge rates were then estimated through calibration simulations using a 1 d analytical solute transport model in the two nests in the lower wetter areas recharge rates were estimated at 4 6 cm year 1 whereas estimated recharge rates in the higher drier areas ranged from 0 3 cm year 1 these differences are consistent with 1 near neutral vertical hydraulic gradients in higher areas vs persistent downward gradients in lower areas 2 chloride concentrations almost an order of magnitude lower in groundwater underlying lower areas than in that of higher areas due to flushing of older more saline groundwater in the lower areas and 3 isotopic evidence for evapotranspiration only in the higher areas the present study suggests that ponding of surface water in local depressions can lead to significant recharge from coastal wetlands this finding has implications for the study of water balance soil salinity and nutrient budgets in these environments 1997 elsevier science b v all rights reserved

the tamar conductivity anomaly magneto variational measurements in eastern tasmania have shown the presence of a conductivity anomaly coinciding with the tamar lineament magneto telluric observations indicate a shallow body 2 5 km deep with a high conductivity 0 2 1 s m 1 analogue model measurements made at the university of victoria have been used to correct for the effect of the oceans surrounding tasmania rather than model the form of the conducting body the results have been interpreted in terms of current flowing in a nnw sse direction in a channel 40 km wide with a sharp eastern edge and a more gradual tapering to the west the most likely explanation of the high conductivity is fractured rock saturated with conducting pore fluids

diagenesis and primary migration in upper jurassic claystone source rocks in north sea carbonate bands are common in central graben kimmeridgian upper jurassic claystone that is mature for oil generation x ray diffraction thermal analysis mossbauer spectroscopy thin section studies scanning microscopy and electron microprobe investigations showed that the bands are composed of claystone fragments coarse grains of dolomite quartz and siderite and diagenetic layer silicates all cemented to a certain degree by ankerite the diagenetic layer silicates are kaolinite being neoformed into muscovite in claystones adjacent to the carbonate bands ankerite fills pores about 50 m in diameter however claystone further away from the bands contains little ankerite gas adsorption with n2 kr and h2o together with microscopy showed porosity in the claystone is composed of a large amount of micropores and mesopores possibly with inlet constrictions and a few macropores with diameters of about 50 m in the carbonate bands microporosity and mesoporosity are probably located in the claystone fragments whereas several pores with diameters of about 50 m are present in the carbonate matrix the presence of claystone fragments fluid release structures and large amounts of diagenetic carbonates indicates that carbonate bands formed through fracturing possibly as a result of overpressuring porosity parameters indicate that fluid transport occurred by diffusion in the claystone matrix to claystone macropores and further through macropores in the carbonate bands out of the source rock the diagenesis of carbonates and clay minerals in the carbonate bands and in the claystone points to two migration stages an early migration of fresh neutral fluids and a later migration in connection with hydrocarbon migration of saline alkaline fluids

an analogue model study of em induction in the north china korea coastal region abstract the behaviour of the magnetic field variations over the north china korea coastal region is studied with the aid of a scaled laboratory analogue model the model source frequencies simulate naturally occurring geomagnetic variations of 3 60 min periods in phase and quadrature magnetic bx by and bz field measurements for the modelled region are presented for e and b polarizations large anomalous in phase and quadrature model magnetic fields are observed over the korea japan strait for e polarization and over the bohai strait for b polarization due to current channelling through the straits large responses of the peninsulas in the shallow coastal areas occur at short periods but decrease abruptly with increasing period in general the effects of peninsulas straits bays and irregularities in the coastlines play an important role in the magnetic field responses both on shore and off shore for this complex north china korea coastal region model and field site induction arrows are compared for three sites west of bohai bay