hydrogeochemical classification of deep formation waters abstract deep formation waters from western europe russia and north america are classified by the major water components ca2 cl mg2 na and barium sulphate ratios the data are used to identify important hydrogeochemical processes e g halite dissolution and albitisation that lead to the different composition of formation waters two significant water types are identified na cl water and na ca cl water furthermore differences in formation water according to stratigraphical units are shown for deep reservoirs in the north german basin and the north sea based on the collected hydrogeochemical data development trends are stated for the formation waters and albitisation is favoured as the main process causing ca enrichment

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

fast ground water mixing and basal recharge in an unconfined alluvial aquifer konza lter site northeastern kansas abstract ground water chemistry and water levels at three levels in a well nest were monitored biweekly for two and a half years in a shallow unconfined floodplain aquifer in order to study the dynamics of such shallow aquifers the aquifer in northeastern kansas consists of high porosity low hydraulic conductivity fine grained sediments dominated by silt and bounded by fractured limestone and shale bedrock results show that the aquifer underwent chemical stratification followed by homogenization three times during the study period the length of time between maximum stratification and complete homogenization was 3 5 months the chemical parameters most useful for demonstrating the mixing trends were dissolved nitrate and sulfate higher nitrate concentrations were typical of unsaturated zone water and were sourced from fertilizer applied to the cultivated fields on the floodplain variations in sulfate concentrations are attributed to dissolution of rare gypsum in limestone bedrock and variable evapoconcentration in the unsaturated zone the mixing of three chemically different waters entrained unsaturated zone water water entering the base of the floodplain aquifer and water in residence before each mixing event was simulated the resident water component for each mixing event was a fixed composition based on measured water chemistry in the intermediate part of the aquifer the entrained water composition was calculated using a measured composition of the shallow part of the aquifer and measurements of soil water content in the unsaturated zone the incoming basal water composition and the fractions of each mixing component were fitted to match the measured chemistry at the three levels in the aquifer a conceptual model for this site explains 1 rapid water level rises 2 water chemistry changes at all levels in the aquifer coincident with the water level rises 3 low measured hydraulic conductivity of the valley fill and apparent lack of preferential flow pathways 4 minuscule amounts of unsaturated zone recharge and 5 dissolved oxygen peaks in the saturated zone lagging water level peaks we postulate that rainfall enters fractures in bedrock adjacent to the floodplain this recharge water moves rapidly through the fractured bedrock into the base of the floodplain aquifer the recharge event through the bedrock causes a rapid rise in water level in the floodplain aquifer and the chemistry of the deepest water in the floodplain aquifer changes at that time the rising water also entrains slow moving nitrate rich unsaturated zone water altering the chemistry of water in the shallow part of the aquifer vertical chemical stratification in the aquifer is thus created by the change in water chemistry in the upper and lower parts of the saturated zone as the water level begins to decline the aquifer undergoes mixing that eventually results in homogeneous water chemistry the rise in water level from the recharge event also displaces gas from the unsaturated zone that is then replaced as the water level declines following the recharge event this new oxygen rich vadose zone air equilibrates rapidly with saturated zone water resulting in a dissolved oxygen pulse in the ground water that peaks one half to 2 months after the water level peak this oxygen pulse subsequently declines over a period of 2 6 months

groundwater and microbial processes of alabama coastal plain aquifers 1 we integrate groundwater geochemistry microbiology and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of alabama our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface sequential peaks of ca2 mg2 k and na along flow paths indicate that separation of ions may be driven by cation exchange microbial mediated reactions are important for the formation of several discrete hydrochemical zones containing fe2 mn2 sr2 and so42 rich groundwaters elevated fe2 mn2 and sr2 concentrations may be derived from bacterial iron and manganese reduction high sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction denitrification the presence of denitrifying and sulfur oxidizing bacteria in water further supports these reactions major ion compositions and d and 18o values are used to determine the source of salinity and the nature of mixing of different groundwaters three water types were identified these include carbonate groundwater brines associated with evaporites and groundwater of meteoric origin groundwater age differences and flow velocities were calculated using the 36cl cl ratios calculated groundwater flow velocities within the eutaw and tuscaloosa aquifers are about 0 20 m yr and 0 15 m yr respectively we modeled basin scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the gulf coast the modeling result shows that the buried jurassic louann salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density driven advection and hydrodynamic dispersion the modeling results are consistent with cl br ratios and o h isotope signatures which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation the predicted groundwater flow pattern reveals the mixing of meteoric water carbonate groundwater from the ordovician knox group and saline brines associated with the louann salt the hydrologic model is consistent with the hydrochemical facies distribution in the alabama coastal plain

deeper groundwater chemistry and geochemical modeling of the arsenic affected western bengal basin west bengal india abstract a regional scale hydrogeochemical study of a 21 000 km2 area in the western bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers spatial trends of solutes and geochemical modeling indicate that carbonate dissolution silicate weathering and cation exchange control the major ion chemistry of groundwater and river water the main aquifer water has also evolved by mixing with seawater from the bay of bengal and connate water the isolated aquifers contain diagenetically altered water of probable marine origin the postoxic main aquifer water exhibits overlapping redox zones metal reducing sulfidic and methanogenic indicative of partial redox equilibrium with the possibility of oxidation in micro scale environments the redox processes are depth dependent and hydrostratigraphically variable elevated dissolved as in the groundwater is possibly related to fe iii reduction but is strongly influenced by coupled fe s c redox cycles arsenic does not show good correlations with most solutes suggesting involvement of multiple processes in as mobilization the main river in the area the bhagirathi hoogly is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry arsenic in water of smaller streams jalangi and ichamati is probably introduced by groundwater discharge during the dry season

regional variations in formation water chemistry major and minor elements frio formation fluids texas 1 spatial variation of major element content na ca and cl in formation waters in the oligocene frio formation texas show that mixing occurs vertically and that the chemistry of ca rich fluids varies from northern coastal to southern texas relative amounts of major and minor elements sr mg and k in ca rich fluids from south texas differ from those in other areas of texas and also are different from updip mesozoic fluids such differences seem to preclude the known mesozoic fluids as a source of ca in the south texas frio formation fluids barring complicated nonuniform water rock alteration changing the mesozoic fluid composition approximately coast parallel and strike parallel cross sections show that ca rich fluids in the frio are usually found at depth some anomalies occur where fluids are present near piercement structures and in a relatively large part of south texas in the latter region ca rich fluids exist above the top of geopressure suggesting that they may have been emplaced before geopressure became widespread 2 3 m y ago because there are no shallow ca rich fluids in the vicinity of major river systems in south texas meteoric fluids may have flushed ca rich fluids out of the areas near the rivers during past pluvial periods this process does not preclude the dilution of formation water by clay dehydration reactions another process that has been proposed to explain deep dilute formatio waters in gulf basin reservoirs

physical and chemical controls on the composition of waters in sedimentary basins abstract the composition of subsurface waters is determined not only by diagenetic reactions but also by physical processes of fluid convection and hydrodynamic dispersion the south west louisiana gulf coast provides an instructive field example of the net effects of diagenetic reaction and solute transport on pore water compositions in a regional siliciclastic sequence most formation waters here have compositions totally unlike the compositions of the connate meteoric and marine fluids that were buried with their host sediments at the time of deposition dissolved chloride has been generated by the subsurface dissolution of salt domes and has been pervasively transported by fluid flow throughout most of the upper 3 km of the sedimentary section the simultaneous systematic variation in dissolved na k mg ca and alkalinity with chloride in these waters supports the hypothesis that metastable thermodynamic buffering by silicate carbonate mineral assemblages is a first order control on fluid compositions the chemical potential of chloride or alternatively total anionic charge appears to be a master variable which ranks in importance with such other variables as pressure and temperature in driving diagenesis in this region this variable is controlled largely by physical processes of advection and dispersion in the upper 3 km of the section and by dehydration reactions in deeper mudstone dominated sediments where the composition of the fluid is largely rock buffered the ultimate origin of the fluid and its pathway of chemical evolution may be obscured at least in terms of major solute composition non buffered components such as cl and br or isotopic compositions are more likely to retain information on original end member fluid compositions and reaction pathways

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

patterns of groundwater salinity changes in a deep continental oceanic transect off the southeastern atlantic coast of the u s a abstract manheim f t and paull c k 1981 patterns of groundwater salinity changes in a deep continental oceanic transect off the southeastern atlantic coast of the u s a in w back and r letolle guest editors symposium on geochemistry of ground water 26th international geological congress j hydrol 54 95ndash 105 investigations of formation fluid salinities in a transect from western georgia to the edge of the blake plateau off the coast of georgia show surprisingly similar hydro chemical features offshore and onshore a fresh brackish wedge of groundwater 25g kg total dissolved solids lies beneath the shelf to a depth of 900 m on land brackish waters extend to a maximum depth of 1 2 km below sea level in lowndes county georgia in deeper horizons hypersaline brines 100g kg occur in lower cretaceous strata these strata have a pronounced evaporitic anhydritic character in the offshore segment strong salinity gradients in interstitial waters signify buried evaporite deposits at drill sites beneath the blake plateau

formation and emplacement ages of the masirah ophiolite sultanate of oman hornblende separates from gabbros and biotite separates from crosscutting potassic granites of the masirah ophiolite have been analyzed by conventional k ar techniques the gabbros have late jurassic early cretaceous ages 126 158 ma and the granites have broadly similar ages 124 146 ma because the gabbros are likely to give ophiolite formation ages and the granites ophiolite emplacement ages it can be concluded that the masirah ophiolite was emplaced very soon after formation the late jurassic early cretaceous ages contrast with the middle cretaceous ages 90 95 ma of the semail ophiolite confirming earlier suggestions that the masirah ophiolite cannot simply be a right laterally displaced fragment of the semail ophiolite but is instead an uplifted block of indian ocean crust the formation and emplacement of the masirah ophiolite are discussed in the context of the late mesozoic evolution of the western indian ocean

thermal subsidence and generation of hydrocarbons in michigan basin temperature histories for selected stratigraphic horizons in the michigan basin are computed from three dimensional continually filled subsidence models mechanical evolution of the michigan basin is modeled as flexure of the lithosphere caused by thermal contraction results are compatible with the subsidence record of the sediments and free air gravity anomalies paleotemperature is determined from excess temperature due to the thermal anomaly plus burial temperature predicted from subsidence curves for an equilibrium temperature gradient of 22 c km 1 2 f 100 ft surface temperature of 20 c 68 f and an equilibrium surface heat flow of 1 1 hfu excess temperature paleotemperature and surface heat flow do not exceed 15 c 27 f 110 76 c 230 f and 2 5 hfu respectively these estimates are consistent with upper limits set by paleomagnetic studies the low value for excess temperature is caused by concentration of the thermal anomaly below 15 km 9 mi in agreement with gravity results the great depth of the thermal anomaly can explain the lack of evidence for an initial heating event prior to subsidence once the thermal history of the sediments is specified the oil potential of the basin can be determined from laboratory derived kinetic equations for degradation of kerogen to petroleum for the michigan basin predicted temperature conditions are sufficient for source rock 25 conversion of type i and type ii kerogen only in ordovician and older rocks in the southern peninsula of michigan by this model petroleum found in rocks younger than ordovician would have had to migrate upward from the older rocks geochemical studies of dundee devonian and trenton ordovician crude oils in michigan are compatible with this interpretation niagaran silurian crude oils appear to come from a different source than the dundee and trenton oils if their source is silurian rocks on the flanks of the basin either the scheme used to calculate maturity is not applicable to these oils or the temperature of the source rocks was significantly higher in the past than today more likely the model underestimates the depth of burial of silurian source rocks near the center of the basin especially in local regions of downfaulting

a numerical model for the formation of saline waters due to diffusion of dissolved nacl in subsiding sedimentary basins with evaporites abstract numerical modeling by a finite difference method incorporating the effects of vertical variations in pressure temperature salinity and porosity shows that mass transport by diffusion may be a major brine forming process in sedimentary basins containing halite beds vertical fluxes of dissolved nacl are greatest when the subsidence rate is slow at subsidence rates of 20 m m y 1 more than 250 m of salt can be dissolved over 150 m y at rapid subsidence rates such as 500 m m y 1 pore waters are advected downward so rapidly that although a diffusion front develops above the evaporite this front moves downward as the evaporite subsides and diffusive fluxes at shallow depths are thus low however under such conditions the pore water column becomes gravitationally unstable as a result of thermally induced density inversions and the potential for convective overturn is enhanced with accompanying advective salt flux upward although dissolution and diffusion of nacl are important processes in the burial history of evaporites they are not adequate by themselves to produce the regional salinity versus depth profiles that are actually observed in some sedimentary basins diffusion induced gradients progressively increase with depth whereas gradients actually observed in sedimentary basins tend to decrease with depth the difference is presumably due to the activity of other mass transport mechanisms such as advection convection and dispersion

chlorine isotope distribution in formation waters texas and louisiana theoretically the chlorine isotope ratio 37cl 35cl can aid in identifying chloride sources and in distinguishing chloride transport mechanisms among formation waters if ratio differences exist among samples we measured the chlorine ratios of 18 formation water samples from oil fields along the texas louisiana gulf coast representing depths between 2 016 and 4 267 m chloride concentrations of samples ranged from 4 to 94 874 g l the chlorine ratios ranged from 1 24 to 0 58 pmil with respect to standard mean ocean chloride or smoc precision 0 12 pmil and enrichment of 37cl correlates with increasing concentration we also compared the isotope ratios of samples from within the weeks island salt dome with adjacent formation waters in louisiana all ratio measurements on the salt are between 0 1 and 0 3 pmil and for the formation waters are between 0 0 and 0 22 pmil the probability that the salt measurements differ from the waters is 99 we conclude that significant chlorine isotope ratio differences exist among formation waters and between the waters and potential sources in the gulf coast region and that the chlorine ratio will be a valuable tool in interpreting chloride geochemistry in this region

peraluminous potassium rich granitoids in the semail ophiolite potassic granites are found as dikes and small stocks in the uppermost part of the mantle sequence of the semail ophiolite predominantly in the northern and less frequently in the central and southern part new chemical analyses show that the biotite granites lie on the same evolutionary trend as the quartz diorites and tonalites occurring as late intrusives in the gabboro and mantle sequence based on mineral chemistry the p t conditions of andalusite cordierite bearing pegmatoidal granites were calculated giving pressures of 1 8 2 2 kbar and a solidus within the stability field of andalusite hydrothermal experiments on five natural granite and tonalite compositions gave minimum melting between 650 and 675 c at 2 kbar at 700 c excess h2o there is already 70 80 melt from the granitic starting compositions potassic granites in the ophiolite can be the result of extreme fractional crystallization in the late intrusive series granitic melts can also be produced by a two stage process in which fluids escaping from the underlying metamorphic sole trigger partial melting of the more felsic members in the ophiolite series two mica granites and pegmatites in the underlying metamorphic sole possibly melting products of amphibolites and biotite gneisses are contemporaneous these escaping fluids could also explain the pb and sr isotopic compositions of the leucocratic dikes indicating variable crustal contamination

perched brine plumes above salt domes and dewatering of geopressured sediments previous studies have shown that there is a brine plume with more than 160 g l 1 total dissolved solids tds in the subsurface perched above welsh salt dome in south louisiana the occurrence of this plume has been postulated to be due to the expulsion of geopressured fluids up a fault on the flank of welsh dome the process that resulted in formation of the anomalous brine plume near welsh dome is of importance because hydrocarbon production is approximately coincident with the brine plume in map plan although in cross sections the brine plume actually occurs a few hundred meters above hydrocarbon production zones using a variable density groundwater flow model sutra we tested the hypothesis that a pulse of fluid flow up the fault could result in brine formation near the top of the dome when the permeability of the geopressured zone was very low in our simulations brine formation in the hydropressured zone occurred entirely by brine density flow and flow was downward along the fault flanking the dome above a certain threshold permeability for the geopressured zone between 10 7 darcy and 10 5 darcy in the vertical direction geopressured fluids were forced up the fault and brine formation occurred above the dome rather than on the flank brines can theoretically form above salt domes in very short geologic times 10 1 ma by expulsion of waters from the geopressured zone below but the fluid effluxes required are gigantic and appear to be unsustainable over large time intervals such as 10 ma

the origin of oceanic plagiogranites from the karmoy ophiolite western norway both field relationships and geochemical characteristics indicate two suites of plagiogranitic and related rocks coexisting in the higher parts of the karmoy ophiolite of western norway the plutonic zone of this ophiolite can be subdivided into three complexes the east karmoy igneous complex the visnes high level complex and the veavagen igneous complex and plagiogranitic rocks are well developed in the first two of these within the east karmoy igneous complex plagiogranites are associated with high temperature pre basic dyke shear zones rare earth element modelling indicates that these plagiogranites were derived by anatexis of amphibolite hydrated diabase assuming a starting material consisting of 40 hornblende and 60 plagioclase and that batch melting occurred within the stability field of hornblende in comparison plagiogranite occurs in a number of bodies in the upper part of the visnes high level complex and forms a sandwich horizon together with biotite diorites and epidosites between a roof assemblage of dykes microgabbros and magnetite gabbros and a floor assemblage of layered and non layered gabbros the r e e modelling of the petrogenesis of this series of plagiogranites indicates that they were derived by filter pressing of a differentiated interstitial liquid to the vari textured gabbros although the distribution of highly hygromagmatophile elements such as k rb ba etc cannot be explained satisfactorily by this model alone depletion in these elements appears to be an autometasomatic effect

advection and diffusion in a variable salinity confining layer a numerical model that simulates groundwater flow and solute transport for cases in which fluid properties are variable was applied in one dimension vertical to the shallow low permeability clayey confining layer in donana national park in southwestern spain the salinity in the 80 m thick confining layer decreases from a brine near the land surface to fresh water near its base results of model simulations indicate that the system could be in or close to a steady state condition the model calibration was very sensitive to small variations in individual model parameters and was nonunique in the sense that equally good calibrations could be achieved by compensatory joint perturbations in the permeability diffusion coefficient and overall governing hydraulic gradient at present there is probably an upward flow of the order of 1 mm yr 1 to 1 cm yr 1 and a balance in the solute flux between upward advection and downward diffusion the time scale of calculated responses to changes in boundary conditions in this low permeability system ranges from thousands to hundreds of thousands of years when considering extremes within the range of uncertainty of values of the evaluated parameters

history of diagenetic fluids in a distant foreland area middle and upper pennsylvanian cherokee basin kansas usa fluid inclusion evidence abstract analysis of fluid inclusion data in diagenetic cements from pennsylvanian limestones and sandstones of the cherokee basin in southeastern kansas reveals the succession of diagenetic fluids in a distant foreland of the arkoma ouachita system this succession includes early low salinity 0 0 2 4 wt nacl eq fluids of meteoric affinity fluid i followed by low temperature na ca cl brines fluid ii with salinities between 8 4 and 24 1 wt nacl eq fluids i and ii were present in the system during precipitation of early stage calcite cements at temperatures less than about 50 c another na ca cl brine fluid iii with salinity up to 25 wt nacl eq was present in the system later at temperatures of maximum burial at least 80 85 c and higher fluid iii is followed by a na cl brine fluid iv with salinities about 19 21 wt nacl eq characterized by temperatures distinctly higher than maximum burial up to 150 c fluid iii and fluid iv were entrapped during precipitation of late stage baroque dolomite and fe dolomite in pennsylvanian limestones and late stage fe dolomite and ankerite in pennsylvanian sandstones the record of progression from fluid iii to fluid iv may have been partially obscured by thermal re equilibriation of some inclusions during migration of fluid iv fluids with na ca cl chemistry fluid ii and iii were either indigenous subsurface fluids of the cherokee and arkoma basins or might have originated as reflux fluids in a permian evaporitic basin of central kansas later na cl brine fluid iv originated in deeper parts of the arkoma ouachita system and might have acquired their salinity by dissolution of hypothetical salts buried beneath the ouachitas temperatures recorded by fluid inclusions in late diagenetic carbonates are 20 60 c higher than those calculated for the maximum burial of the studied section this thermal anomaly suggests an advective heat transfer from the arkoma ouachita system onto the shelf of the cherokee basin related to the invasion of late diagenetic fluids

modeling subsurface flow in sedimentary basins groundwater flows that arise in sedimentary basins from the effects of topographic relief buoyant convection sediment compaction erosional unloading and combinations of these driving forces can be described using quantitative modeling techniques models can be constructed to consider the effects of heat and solute transport petroleum migration and the chemical interaction of water and rocks the accuracy of model predictions however is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions estimating past conditions such as topographic relief and knowledge of how physical and chemical processes interact over gelogic time scales progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology rock mechanics and geochemistry

the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a abstract land l s and prezbindowski d r 1981 the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 51ndash 74 systematic chemical variation exists in formation water collected from a dip section through lower cretaceous rocks of south central texas chemical variation can be explained by an interactive water rock diagenetic model the cyclic lower cretaceous shelf carbonates of the edwards group dip into the gulf of mexico coast geosyncline and can be considered to a first approximation as part of a complex aquifer contained by paleozoic basement beneath and by relatively impermeable upper cretaceous clay and chalk above the hydrodynamic character of this carbonate system is strongly controlled by major fault systems major fault systems serve as pathways for vertical movement of basinal brines into the lower cretaceous section formation water movement in this sytem has strong upfault and updip components the parent na ca cl brine originates deep in the gulf of mexico basin at temperatures between 200 and 250 c by the reaction halite detrital plagioclase quartz water albite brine other dissolved components originate by reaction of the fluid with the sedimentary phases k feldspar calcite dolomite anhydrite celestite barite and fluorite significant quantities of pb zn and fe have been mobilized as well as the brine moves updip out of the overpressured deep gulf of mexico basin and encounters limestones of the stuart city reef trend the buried platform margin small amounts of galena precipitate in late fractures continuing to rise upfault and updip the brine becomes progressively diluted on encountering significant quantities of dolomite in the backreef facies the ca rich brine causes dedolomitization although thermochemical consideration suggests that small amounts of several authigenic phases should precipitate most have yet to be found minor amounts of several kinds of calcite spar are present however as the brine evolves by dilution and by cooling no systematic changes in any cation cl ratio occur except for regular updip gain in mg as a result of progressive dedolomitization the formation water highly diluted by meteoric water eventually discharges along faults as hot mineral water

evolution of veins and sub economic ore at strassegg paleozoic of graz eastern alps austria evidence for local fluid transport during metamorphism the north eastern part of the graz paleozoic thrust sheet at strassegg austria is characterised by metamorphic assemblages that reflect increasing temperature conditions from 3008c in hangingwall to around 5508c in footwall units the main quartz andror carbonate vein generation cuts the schistosity at moderate to low angles is folded with the schistosity and is commonly boudinaged there is a correlation between vein and the host rock mineralogy additionally the d 18 o and 13 d c signatures of vein minerals quartz andror carbonates vary systematically with the isotopic signature of the host rock and its minerals within individual units d 18 o of vein quartz has a narrow range of values in contrast with a larger variation in both with d 18 o and d 13 c of carbonates at strassegg the greenschist unit hosts an as au mineralisation arsenopyrite

variation in chemical composition of oil field brines with depth in northern louisiana and southern arkansas implications for mechanisms and rates of mass transport and diagenetic reaction abstract abstract dickey 1966 1968 has pointed out that there is a nearly linear increase in total dissolved solids tds content with depth in oil field waters in areas of northern louisiana and southern arkansas similar relations exist in portions of east central louisiana and central mississippi a re examination of brine analyses in the region shows that these linear increases in tds are primarily the result of linear increases in na and cl concentrations with depth other dissolved components such as mg ca sr ba hco3 so4 and trace constituents can show more complex variations in concentration with depth it is proposed here that the linear gradients for na and cl reflect the on going steady state mass transport of these constituents upward from thousands of feet of depth to the near surface na and cl concentrations at depths exceeding 8 000 to 10 000 ft 2438 to 3048 m are maintained at constant high levels by the subsurface dissolution of halite low dissolved salt concentrations are maintained at the near surface by recharge of meteoric waters the types of mass transport processes which could produce such nearly linear profiles are limited to molecular diffusion thermal diffusion soret effect and eddy diffusion preliminary estimates of fluxes and mass transport velocities which could result from these processes suggest sodium and chloride ions could be migrating upward at velocities approaching a centimeter per year non linear but systematic variations in the concentrations of other components with depth may reflect the presence of local stratigraphic sources and sinks of material zones of depletion of dissolved calcium for example may represent areas of active precipitation of calcite if the mass transport coefficients for these non conservative components can be estimated then limits can be put on the absolute rates of on going diagenetic processes of considerable interest is the possibility that dissolved or entrained hydrocarbons are also involved in active vertical migration the systematic study of brine chemistry promises to provide important clues to the understanding of processes and rates of fluid migration and hydrocarbon migration in the region