origin of formation waters of s e parts of the bohemian massif and the vienna basin abstract deep formation waters were sampled from boreholes on the s e slopes of the bohemian massif they are na cl hco 3 waters with tds in the range 6 52 g l 1 some of them are associated with gas and oil deposits the waters are rich in br and i and their dand 18 0 isotope compositions vary from 12 to 77 and 4 6 to 10 respectively the processes of concentration and dilution have been discussed based on deuterium and conservative element contents of the waters three regional groups can be identified in the plots br vs i and cl vs i the vienna basin samples vb southern s and northern n flanks of the bohemian massif bm the vb samples have as an end member brackish water with about 7 g l 1 cl about 40 marine component enriched in br and i this water has been later diluted by meteoric water of recent isotopic composition only 3 vb samples can be considered as derived from the dissolution of evaporites the salt content of the s and n end members is very close to or higher than sea water with an isotopic composition similar to the brackish water subaerial evaporation of diluted sea water is suggested as the process increasing salt content the evaporative enrichment of primary brackish solution can be estimated from extrapolation of cl vs i and br vs i plots to zero i about 25 mg l 1 br and 6 g l 1 cl for the southern flanks of the bm evaporated solutions were later diluted by meteoric waters with d in the range from 50 to 80 southern flanks and about 80 northern flanks

late anhydrite cements mark basin inversion isotopic and formation water evidence rotliegend sandstone north sea the lower permian rotliegend sandstone in the leman field today contains formation waters which are extremely saline 165 530 238 531 mg l with cation chloride ratios indicating mixing of zechstein marine evaporite brines with meteoric water ancient rotliegend formation waters inferred from the analyses of cements were similarly a mixture of marine brine and meteoric water 18o 0 3 smow d 16 smow the strontium isotopic compositions of present day formation waters 87sr 86sr 0 7107 are also consistent with mixing between late permian marine brines 87sr 86sr 0 707 and radiogenic strontium from a detrital source 87sr 86sr 0 720 0 730 isotopic analyses of texturally late intergranular and fracture filling anhydrite suggest waters very similar to the present day formation waters 34s values of anhydrite cements 10 cdt indicate that sulphate in the rotliegend originated from the stratigraphically overlying zechstein evaporites the 87sr 86sr 150 ratios of anhydrites 0 7080 0 7113 however suggest variable mixing of strontium sourced from the overlying zechstein evaporites with more radiogenic strontium derived from diagenetic reactions in the underlying carboniferous shales the oxygen isotope compositions of anhydrite reflect precipitation temperatures between 120 and 140 c from waters with a 18o composition similar to the present day formation waters approximately 0 smow these are the maximum inferred burial temperatures for the rotliegend sandstone in the leman field and would have occurred at maximum burial depths of 3 5 4 km 11 500 13 100 ft during the late jurassic early cretaceous at the start of basin inversion these data indicate an unusual short lived catastrophic event of cross formational flow through fractures which were tectonically induced by basin inversion pore fluids may have escaped from the overlying and underlying formations into the lower pressure rotliegend sandstone regional aquifer to drain this part of the basin

epithermal base metal vein mineralization in the southern uplands of scotland nature and origin of the fluids the sedimentary sequences of the southern uplands of scotland host numerous lead zinc copper silver vein deposits the genesis of which has never been adequately explained fluid inclusion and stable isotope analysis of vein minerals from these deposits indicate that for the vein stages studied the mineralizing fluids were low temperature 150 c high salinity 19 to 30 equiv wt nacl cacl2 modified meteoric waters a consideration of the availability of such fluids throughout the geological history of the southern uplands suggests a lower carboniferous dinantian age for the mineralization

supratidal evaporitic dolomite at ojo de liebre lagoon mineralogical and isotopic arguments for primary crystallization abstract this pair deals with a new site of dolomite formation in supratidal evaporite flats at the southernmost edge of the ojo de liebre evaporitic complex baja california mexico the sedimentary context is mostly siliciclastic except for calcareous outcrops around the flats both chemical and isotopic data on the interstitial solutions demonstrate a mixing between mg2 rich marine derived brines and calcium bicarbonate bearing continental waters which are subjected to concentration by capillary evaporation the lack of any in situ solid caco3 in the sedimentary matrix argues for direct crystallization of dolomite from aqueous solutions this is documented by the oxygen isotope compositions of the dolomite which are consistent with deposition under equilibrium conditions of ambient temperature and 18o of water of the interstitial solutions furthermore the low 13c values of the dolomites and the absence of living plants or organisms in the basin indicate that a fraction of the total dissolved inorganic carbon reservoir is biogenic and is mostly provided by continental groundwaters therefore crystallization of dolomite occurs within the sands infiltrated by solutions whose state of saturation relative to dolomite is mainly governed by the chemistry of continental groundwaters mixing with the inflowing marine brines

δ2h of water from fluid inclusions in proterozoic halite evidence for a deuterium depleted hydrosphere abstract 2h were measured in water present in tiny primary fluid inclusions trapped in mesoproterozoic 1 4 ga and neoproterozoic 0 8 ga halite crystals while the hydrogen concentrations range from 300 to 1500 ppm for the whole sample collection 2h values range from 74 to 54 vsmow for the mesoproterozoic halite sampled from the sibley group ontario canada and from 89 to 38 for the neoproterozoic halite from the browne formation officer basin australia the amount of evaporation required to precipitate halite is accompanied by a deuterium enrichment of 30 to 90 it means that the original aqueous solutions had 2h values comprised between 140 and 90 considering the estimated tropical paleolatitudes for both depositional environments surface waters were most likely significantly deuterium depleted relative to modern ones if such interpretation is partly at variance with the geological record it could be reconciliated with some modelling outputs of the long term water cycle indeed several mechanisms produce a progressive deuterium enrichment of the oceans those identified so far are the addition of deuterium rich extraterrestrial water cometary dust the loss of h during water photodissociation by ultraviolet radiation in the upper atmosphere and the isotopic fractionation that takes place during the hydroxylation of nominally anhydrous mantle rock forming minerals we also propose that the major process able to shift through time the 2 of the hydrosphere is the reduction of h2o into h2 during the serpentinization of mantle rocks at mid ocean ridges

authigenic potassium feldspar a tracer for the timing of palaeofluid flow in carbonate rocks northern calcareous alps austria

the origin and evolution of canadian shield brines evaporation or freezing of seawater new lithium isotope and geochemical evidence from the slave craton abstract new chemical and isotopic data for deep seated calcium chloride brine from the miramar con gold mine yellowknife n w t strongly suggest that the brine salinity is of marine origin diagnostic marine properties include uniformly elevated br cl ratios typical of seawater concentrated beyond halite saturation and li br ratios 0 0254 0 0325 and 6 li compositions 32 1 to 36 3 similar to seawater 32 3 the mean 6 li for all mine water samples of 35 1 may reflect minor uptake of li by secondary minerals this interpretation is supported by analyses of altered metabasalt from fault zones which is enriched in li but depleted in 6 li 14 7 to 15 6 relative to the unaltered metabasalt 5 4 the mechanism responsible for concentrating the hypersaline brine end member is not unequivocal as evidence exists to support both evaporative and cryogenic processes on the one hand the devonian sedimentary record in the great slave lake region in conjunction with yellowknife brine isotopic compositions 2 h and 34 s so 4 that are similar to various devonian fluids support an evaporative origin on the other hand the na cl br cl relationship in the brine strongly suggests a cryogenic mechanism regardless of the concentrative mechanism the chemical data indicate that the yellowknife parent brine was concentrated 28 to 30 fold relative to seawater the extreme depletion of mg and enrichment of ca in the brines accompanied by sr ca ratios similar to that of seawater are accounted for by dolomitization of an aragonite rich marine sediment by the brine before infiltration into the crystalline basement rocks subsequent alteration of silicate minerals in the shield added additional ca and sr to the brine as indicated by their radiogenic 87 sr 86 sr ratios up to 0 7147 based on mineral balance calculations the major mineral products of the cryogenic and evaporitic concentration and evolution paths are significantly different the cryogenic evolution results in some 15 mirabilite 60 hydrohalite and 18 dolomite whereas the major minerals formed from the evaporitic evolutionary sequence are 36 halite 8 gypsum 17 dolomite and 30 albite the great similarity between the calcium chloride brine from yellowknife and other such canadian shield brines indicates that they may share a common marine origin

stable chlorine isotopes in the palo duro basin texas evidence for preservation of permian evaporite brines experimental evaporation of seawater yields brines with 37cl from 0 0 initial to 0 9 in the palo duro basin brines with 37cl values overlapping the 0 1 to 0 4 range of halite evaporite can be generated by a set of processes including dissolution of halite in meteoric water such brines occur above and below an evaporite aquitard brines with 37cl values of 0 4 to 1 0 in the evaporite aquitard and in a deep brine aquifer cannot be generated by dissolution of halite considered with br and cl content d and noble gas content the 37cl data indicate that such brines originated as evapoconcentrated seawater high br evaporite brine formed directly from seawater on the eastern side of the basin whereas low br evaporite brines on the western side formed after an influx of meteoric water at the time of evaporite formation there has not been detectable vertical flow of meteoric water across the evaporite aquitard strata beneath the evaporite contain compartments that have been isolated geochemically since the permian

a lost tethyan evaporitic basin evidence from a cretaceous hemipelagic meta selenite red chert association in the eastern mediterranean realm

fluid compartmentalization and dolomitization in the cambrian and ordovician successions of the huron domain michigan basin abstract strata bound dolomite occurs in deep seated ordovician and cambrian sediments within the huron domain of southern ontario canada core samples were analyzed for petrographic stable and sr isotopic composition and fluid inclusion microthermometry to characterize dolomitization and evaluate diagenetic fluid composition the samples represented a range of host rocks from dolomitized limestones dolostones sandy dolostones and sandstones within ordovician black river group and underlying cambrian formation the petrographic and geochemical attributes have provided a basis to gain insight on the source fluids that modified these rocks as well as the possible timing of formation evidence indicates that the formations were subjected to high temperatures average 115 c that cannot be explained by burial history alone this suggests the occurrence and migration of hydrothermal fluids within the low permeability dolomite horizons possibly during paleozoic orogenesis dolomite and calcite fracture infill isotopic and fluid inclusion data point to two possibly individual diagenetic fluid systems i an earlier cambrian system that is characterized by a pronounced negative shifts in oxygen and carbon isotopic composition 18o average 9 0 for dolomite and 13 9 for calcite respectively and 13c 3 06 for dolomite and 4 82 for calcite respectively a more radiogenic sr87 sr86 ratios range from 0 70977 to 0 71100 warm th values range from 84 to 156 c for dolomite average 113 6 c and 87 141 c for calcite average 101 5 c and saline signature salinity range from 23 2 to 27 2 wt nacl eq for dolomite average 24 3 for dolomite and 23 6 wt nacl eq for calcite and ii a later ordovician system that is characterized by less negative shifts in both oxygen and carbon isotopes 18o average 8 7 for dolomite and 7 5 for calcite and 13c average 0 37 for dolomite and 0 36 for calcite respectively hypersaline salinity range from 22 4 to 30 1 wt nacl eq average 27 0 for dolomite and 27 5 to 29 7 for calcite average 29 2 comparable homogenization temperature th ranges from 85 to 132 c for dolomite average 109 6 c and 66 153 c for calcite average 107 2 c and a less radiogenic sr87 sr86 ratios range from 0 70818 to 0 71 000 fluid system the observation of highly discrete strata bound dolomites combined with only trace quantities of saddle dolomite and its associated geochemical signature suggest that diagenesis as a result of hydrothermal fluids was neither pervasive in volume or extent within the north western huron domain

hydrochemical and isotopic δ18o δ2h 87sr 86sr δ37cl and δ81br evidence for the origin of saline formation water in a gas reservoir abstract the permo triassic kangan gasfield in southern iran is composed of an aquifer the kangan aquifer ka and an overlying gas reservoir it is located in the kangan and dalan formations and consists predominantly of limestone and dolomite the kangan gasfield is exploited from 36 wells at depths from 2300 to 2860 m the quality of the produced formation waters pfw varies from fresh to saline with salinities of up to 60 000 mg l the present study aims to identify the origin of the salinity of the pfws the concentration of major ions li sr and br as well as 18o d 87sr 86sr 37cl and 81br isotope compositions of the ka water and pfw samples a fresh and a brine spring and the persian gulf water were all measured the suite of isotopic 37cl and 81br and hydrochemical data li cl and br concentrations and cf index in this study indicates that the salinity origin of the pfws is evaporated seawater which could be either the ka water or the intergranular saturated brine in the kangan gas reservoir kgr both derived from permo triassic evaporated seawater 18o and 87sr 86sr data exclude the ka water as the source of the saline pfw leaving the intergranular brine of the kgr as the most likely source although further isotopic and geochemical tests are needed to verify this this work also proposes for the first time the use of a li cl versus br cl diagram to distinguish between evaporate formation water water modified by halite dissolution and fresh water it is recommended to apply these comprehensive methods to deep brine aquifers especially related to gasfields

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

stable isotopes of lake and fluid inclusion brines dabusun lake qaidam basin western china hydrology and paleoclimatology in arid environments the qaidam basin underlain by salt is the largest 120 000 km2 on the qinghai tibet plateau western china numerous shallow to ephemeral saline lakes and dry saline pans are present on the qarhan salt plain dabusun lake the largest about 200 km2 contains high salinity na mg cl brines whereas it precipitates halite it is fringed by a potash salt flat the dominant inflow to dabusun lake the golmud river contains dilute na hco 3 rich meteoric waters dabusun lake brines fall on an evaporation trend given by d 3 3 18o 43 both d and 18o values increase with salinity which in turn varies considerably with flooding and evaporation the isotope compositions of the fluid inclusion brines from modern halite formed along the lake s edge are intermediate to those of dabusun lake brines and those from the salt flat shallow sediments beneath qarhan consist of interbedded salts and mud a short core section 1 3 1 7 m depth from the northern edge of dabusun lake was found to contain three dissolution surfaces and three mud partings the 18o values for fluid inclusions in 22 primary halite samples from this section show a record of episodic flooding lower 18o values followed by evaporation gradual increase in 18o values primary fluid inclusions in halite crystallized initially at the surface provide a geochemical record of surface brines their major element compositions varied through time more concentrated fluids indicate more arid conditions in the basin whereas wetter conditions prevailed during intervals of non salt deposition when laminated muds accumulated the isotope compositions together with the activity of h2o of fluid inclusions in primary halite were used to determine isotope variations in regional precipitation and hence paleoclimatic changes on the qinghai tibet plateau during the past 50 000 years

pervasive dolomitization with subsequent hydrothermal alteration in the clarke lake gas field middle devonian slave point formation british columbia canada the clarke lake gas field in british columbia canada is hosted in pervasively dolomitized middle devonian carbonates of the slave point formation the clarke lake field consists mostly of pervasive matrix dolomite and some saddle dolomite the latter varying in volume from about zero in limestones to normally 20 40 locally up to 80 in dolostones over any given 10 m 33 ft core interval some of the saddle dolomite is replacive some is cement and both varieties are associated with dissolution porosity and recrystallized matrix dolomite the major objective of this study is to identify the causes and timing of matrix and saddle dolomite formation specifically whether these dolomites are hydrothermal a comprehensive petrographic and geochemical examination indicates that pervasive matrix dolomitization was accomplished by long distance migration of halite saturated brines during the late devonian to mississippian fluid inclusion homogenization temperatures suggest about 150 uncorrected to 190c corrected at the time of matrix dolomitization these temperatures differ markedly from most published work on the dolomitized devonian reefs in the alberta basin south of the peace river arch where pervasive matrix dolomitization was accomplished by advection of slightly modified seawater at temperatures of about 60 80c and where no hydrothermal influence was ever present the saddle dolomites at clarke lake are not cogenetic with matrix dolomite and are not the product of hydrothermal dolomitization sensu stricto instead they formed through the hydrothermal alteration of matrix dolomite by way of invasion of a gypsum saturated brine during periods of extremely high heat flow and regional plate margin tectonics in the late devonian to mississippian fluid inclusion homogenization temperatures suggest that hydrothermal alteration occurred between 230 uncorrected and 267c corrected which is significantly higher than the maximum temperature of about 190c attained by the slave point formation during burial the sources of the halite and gypsum saturated brines are middle devonian evaporite depositional environments roughly 200 km 124 mi south and or east of clarke lake near the peace river arch

constraints of fluid inclusions and c o isotopic compositions on the origin of the dolomites in the xisha islands south china sea abstract the dolomite problem is a key issue in research on carbonate diagenesis and it is still a controversial scientific problem the origin of the neogene dolostones in the xisha islands has remained disputed until now however the geochemical characteristics of dolomite hosted fluid inclusions can potentially provide a relatively direct record of the origin and evolution of their dolomitizing fluid in this article based on the samples selected from the well xike 1 also known as zk 1 and xk 1 reef core of the xisha islands the hydrogen isotopic compositions and gas and liquid compositions of the fluid inclusions hosted in calcite and dolomite were analyzed meanwhile the isotopic compositions of carbon and oxygen in the calcite and dolomite minerals were also tested the origin of the dolomitizing fluid was traced in detail which provided important evidence for establishing the dolomitization model of the primary dolomites in the study area the main gas compositions of the dolomite hosted fluid inclusions are co2 h2o n2 and o2 which are similar to those of the atmosphere indicating that the dolomites in this area experienced a partly oxygenated diagenetic environment from high to low the cation concentrations of the liquid component in the dolomite hosted fluid inclusions are mg2 ca2 na and k whereas their main anion compositions are so42 cl and f which are characterized by high so42 concentrations and low cl br ratios the 13c values pdb of the dolomites range from 1 9 to 3 0 and their 18o values pdb range from 2 1 to 4 7 the calculated z values which can be used to trace the salinity of diagenetic fluid based on the 13c and 18o values of the dolomites range from 133 0 to 135 8 which are higher than that of modern seawater approximately 120 these data indicate that the dolomitizing fluid of the primary dolomites in the xisha islands is the high salinity concentrated seawater derived from a surface environment in addition the model of seepage reflux dolomitization can better interpret the dolomitizing process of the primary dolomites in the xisha islands

extracting mg isotope signatures of ancient seawater from marine halite a reconnaissance abstract the mg ca ratio of seawater fluctuated remarkably over the phanerozoic the processes that controlled the temporal variation in seawater mg ca ratio may also have caused the secular changes in mg isotope ratios of seawater therefore the mg isotope composition of seawater may be useful to understand the long term variation in seawater chemistry different sedimentary carbonates have been proposed as archives of ancient seawater mg isotope signatures but each type of carbonate has its limitations halite is a common mineral in evaporite deposits and their fluid inclusions may be used to infer the mg isotope composition of contemporary seawater in this study we developed a method to measure the isotope composition of mg in halite with an accuracy of better than 0 1 in 26mg the accuracy of the method was verified systematically using synthetic nacl solutions as well as holocene lacustrine halite samples from the dead sea the 26mg values of marine halite samples show a large variation ranging from 0 1 to 1 6 relative to the dsm3 international mg isotope standard the 26mg values of some ancient salt samples are lower than a published model curve for 26mg of seawater and such inconsistency could be explained by 1 isotopic evolution of brines due to mineral precipitation 2 entrapment of evaporite minerals into halite during halite precipitation or post depositional deformation 3 recrystallization and dissolution of pre existing mg minerals and 4 limitations of the model curve of seawater 26mg values collectively we suggest that mg isotopes in halite are a new geochemical proxy to study the secular variations in seawater chemistry syndepositional and post depositional processes of evaporite deposits our data highlight the importance of understanding the sedimentary background and textural details of evaporites for appropriate interpretations of mg isotope data from halite

a strontium oxygen and hydrogen isotopic composition of brines michigan and appalachian basins ontario and michigan abstract 87 sr 86 sr ratios of brine from samples from the michigan and appalachian basins in ontario and michigan covering the stratigraphic interval from the cambrian to mississippian vary from 0 708 to 0 711 with the exception of the salt units of the salina formation silurian most values are greater than seawater for the time in question indicating water rock interaction the sources of the radiogenic sr has not been identified all samples plot below the gmwl in 18 o 2 h space with the cambrian and ordovician samples closest to the line mixing of brines meteoric and glacial pleistocene water is indicated in some cases the more concentrated brines from each stratigraphic unit show a very narrow spread in values all the ordovician brines show a narrow range over a 200 km area for sr o and h isotopes indicating extensive lateral migration of the fluids strontium in the brine has not equilibrated isotopically with its host rock in some cases the late stage minerals saddle dolomite calcite and anhydrite have the same 87 sr 86 sr ratios as the brine indicating that they precipitated from the brine in isotopic equilibrium

the record of temperature wind velocity and air humidity in the δd and δ18o of water inclusions in synthetic and messinian halites abstract deuterium and oxygen isotope fractionations between liquid and vapor water were experimentally determined during evaporation of a nacl solution 35 g l 1 as a function of water temperature and wind velocity in the case of a null wind velocity slopes of d 18o trajectories of residual waters hyperbolically decrease with increasing water temperatures in the range 23 47 c for wind velocities ranging from 0 8 to 2 2 m s 1 slopes of the d 18o trajectories linearly increase with increasing wind velocity at a given water temperature these experimental results can be modeled by using rayleigh distillation equations taking into account wind related kinetics effects deuterium and oxygen isotope compositions of water inclusions trapped by the precipitated halite crystals were determined by micro equilibration techniques these isotopic compositions accurately reflect those of the surrounding residual waters during halite growth isotopic compositions of water inclusions in twenty natural halites from the messinian realmonte mine in sicily suggest precipitation temperatures of 34 4 10 c that match the homogenization temperatures obtained by microthermometry median 34 5 c the similarity between the measured and experimental slopes of the d 18o evaporation trajectories suggests that the effect of wind was negligible during the genesis of these halite deposits hydrogen and oxygen isotope compositions of water inclusions from realmonte halite also define a linear trend whose extrapolation until intersection with the mediterranean meteoric water line allows the characterization of the water source with d and 18o values of 70 10 and 11 5 1 5 respectively these results reveal that the huge amounts of salts deposited in sicily result from the evaporation of seawater mixed with a dominant fraction 50 of meteoric waters most likely deriving from alpine fluvial discharge

fluid transfers at a basement cover interface part ii large scale introduction of chlorine into the basement by mesozoic basinal brines significant fracture and porosity sealing characterizes the sedimentary cover basement interface in the northwestern margin of the aquitaine basin france dolomite and calcite and sometimes fluorite barite and quartz constitute most of the fracture fillings they contain primary inclusions of brines having chlorinities in the range of 3 3 to 5 5 mol cl kg solution with total homogenization temperatures in between 65 and 130 c for quartz and slightly lower for dolomite barite fluorite and calcite crush leach analyses indicate that brines are characterized by na k ratios of 5 to 40 na li ratios of 20 to 530 and cl br ratios of 200 to 1000 which are rather typical of deep basinal brines the fluid 18o signature is estimated to be 6 6 1 8 smow for a crystallization temperature of 100 20 c between 80 and 120 c and the d value is 30 10 smow the fluid source for the fracture filling mineral is interpreted as a deep sedimentary brine expelled during a period of maximum subsidence in the aquitaine basin which migrated along the sediment cover basement interface which is characterized by high permeabilities below the toarcian shales the sealing is likely to be linked to the mixing of the brines with dilute ascending hot waters these dilute waters infiltrated from emerged zones convected and heated at depth reaching temperatures of 100 c up to 150 c on the basis of cation geothermometry extensional activity of probable cretaceous age related to the gascogne gulf rifting could be considered as the most likely cause of a significant fluid migration event at the basement cover interface all along the margins of the french massif central these processes are large scale as shown by the similarities of mineral sequences fluid types and general features of most of the f ba pb zn deposits located at the basement sedimentary cover interface the mass transfer of cl linked to this stage is significant and accounts for the early introduction of large amounts of chlorine in the granitoid microporosity this probably explains the significant chlorine concentrations of the present day fluids recovered in the granitoid aquifer

geochemistry of formation waters from the wolfcamp and cline shales insights into brine origin reservoir connectivity and fluid flow in the permian basin usa abstract despite being one of the most important oil producing provinces in the united states information on basinal hydrogeology and fluid flow in the permian basin of texas and new mexico is lacking the source and geochemistry of brines from the basin were investigated ordovician to guadalupian age reservoirs by combining previously published data from conventional reservoirs with geochemical results for 39 new produced water samples with a focus on those from shales salinity of the ca cl type brines in the basin generally increases with depth reaching a maximum in devonian median 154 g l reservoirs followed by decreases in salinity in the silurian median 77 g l and ordovician median 70 g l reservoirs isotopic data for b o h and sr and ion chemistry indicate three major types of water lower salinity fluids 100 g l isotopically heavy o and h water in leonardian permian to pennsylvanian reservoirs 2 3 2 km depth is evaporated late permian seawater water from the permian wolfcamp and pennsylvanian cline shales which are isotopically similar but lower in salinity and enriched in alkalis appear to have developed their composition due to post illitization diffusion into the shales samples from the cline shale are further enriched with nh 4 br i and isotopically light b sourced from the breakdown of marine kerogen in the unit lower salinity waters 3 km depth which plot near the modern local meteoric water line are distinct from the water in overlying reservoirs we propose that these deep meteoric waters are part of a newly identified hydrogeologic unit the deep basin meteoric aquifer system chemical isotopic and pressure data suggest that despite over pressuring in the wolfcamp shale there is little potential for vertical fluid migration to the surface environment via natural conduits

quartz veins record vertical flow at a graben edge fulmar oil field central north sea the fulmar oil field lies at the faulted western margin of the central graben in the central north sea chalcedony and quartz and later dolomite occur as diagenetic cements in veins within the upper jurassic fulmar formation quartz in one particular vein contains primary aqueous fluid inclusions with homogenization temperatures ranging from 85 degrees to 140 degrees c with a mean of 117 degrees c the measured d18o of the authigenic quartz ranges from 25 1 to 27 1o oo smow the d18o of the water from which most of the quartz precipitated is calculated to have been around 8o oo which is significantly more positive than the measured present day formation water d18o of 4o oo quartz and chalcedony cements in the vein are postdated texturally by dolomite that has a d18o of 23 5o oo smow high salinities are recorded in the fluid inclusions in the quartz the majority ranging from 15 to 19 wt nacl equivalent also the quartz contains inclusions of anhydrite high salinity aqueous inclusions combined with anhydrite inclusions in the quartz and the 18o enriched calculated water composition suggest that the quartz precipitated from an evaporite influenced fluid the same fluid contributed mg for dolomite precipitation more deeply buried sections including the permian zechstein evaporites underlying the fulmar field are the most obvious source of an 18o enriched saline fluid mineralization of the vein resulted from cross formational flow of warm fluids from depth through the zechstein and into the jurassic succession over vertical distances of 600 2000 m fluids most probably migrated up faults and fractures during episodes of salt movement or overpressure release

a stable isotope study of microbial dolomite formation in the coorong region south australia abstract the coorong region of south australia is a classic location for the study of modern dolomite formation a number of ephemeral lakes here contain dolomite whilst other lakes in close proximity contain aragonite with minor magnesite our previous field and experimental work has revealed that sulphate reducing bacteria play a key role in overcoming kinetic inhibitors to dolomite formation in this area we here use a combination of oxygen carbon and sulphur isotopes to help to further constrain the processes leading to dolomite precipitation in modern hypersaline environments we report isotopic data from four dolomite and three aragonite containing lakes 34 s data for dissolved lake and porewater sulphates reveal 34 s enrichment of residual sulphate in all seven lakes consistent with bulk closed system microbial fractionation by sulphate reducing bacteria calculations using temperature dependent oxygen isotope fractionation factors between dolomite and the solution from which it precipitated are consistent with a strong microbial component to carbonate precipitation in these lakes a comparison of 18 o data from dolomite and aragonite sediment and from their associated lakewaters indicates seasonal mineral precipitation occurs late in the evaporative cycle of the lakes within a yoghurt like saturated mud horizon coincident with the zone of sulphate reduction surprisingly 13 c data from the carbonates do not show the characteristic wide range of values often associated with organogenic carbonates but instead show that these bacterially mediated precipitates incorporate carbon primarily from the inorganic lakewater reservoir partially diluted by an organic component a coorong type microbial model of dolomite formation may be particularly applicable to for example precambrian sedimentary dolomites where benthic microbial communities which are today restricted to extreme environments dominated the shallow marine ecosystem prior to the emergence of metazoa

isotopic geochemistry of the saratoga springs implications for the origin of solutes and source of carbon dioxide we report the results of an isotopic study designed to determine the source of solutes and carbon dioxide in the famed saratoga springs new york mineral waters these waters have thousands of milligrams per liter total dissolved solid concentrations and are highly charged with carbon dioxide gas the spring waters are cold 12 c and there is no local deep seated thermal anomaly they emerge through thick shale caprock along the surface expression of normal faults the 13c 5 8 to 0 8 vienna peedee belemnite of the dissolved inorganic carbon and elevated 3he 4he ratios suggest that the source of the co2 is the mantle or an ancient deep crystallized igneous melt the stable isotopic content of the spring waters defines a mixing line between modern local meteoric waters 70 and a component with heavier d but similar 18o values this trend and that of 87sr 86sr of dissolved strontium versus 1 sr are consistent with the hypothesis that canadian shield type brines contribute salinity to the springs these brines plausibly migrate from the adirondack mountains to the topographically low mcgregor fault system in the hudson river lowlands where the saratoga springs discharge

geochemistry of formation waters from the lower silurian clinton formation albion sandstone eastern ohio waters of the petroleum bearing clinton formation albion sandstone of eastern ohio are highly concentrated brines with average total dissolved solids tds of 250 000 ppm sodium calcium and chloride account for 97 of the tds distribution of divalent metal chlorides mcl 2 allows inference of an up dip paleoflow direction although present day flow is probably down dip solute distribution may have been emplaced during early basin development it thus provides a snapshot of paleoflow formation structure alone can not explain mcl 2 trends they probably also are controlled by regional variation in salt thickness major constituent data do not indicate that membrane filtration affected the waters high bromide content mean 1860 ppm of the waters indicates that they originated from evaporating seawater they probably are related genetically to the salina evaporite group calculations show that several subsequent diagenetic reactions can account for the observed major ion composition recrystallization of aragonite and dolomitization of calcite probably occurred as the waters moved through the big lime and or the packer shell carbonates cation exchange and chlorite formation probably altered water composition during interaction with shales of the cabot head formation and within the clinton minor constituents of the waters appear to be controlled by reactions with clays

the remaking of the mengyejing potash deposit in yunnan china evidence from rb sr isotopic systematics abstract the mengyejing potash deposit mpd is the first significant ancient potash deposit ever found in china and it was considered to have formed during the middle to late cretaceous the 87 sr 86 sr ratios of potash bulk samples suggest that both bedded and veined potash orebodies of the mpd have been affected by igneous activity resulting from decompression melting of a metasomatically altered depleted mantle from 16 ma to present the rb sr isotopic systematics of the potash bulk samples define several apparent isochrons ranging from 0 609 0 026 to 14 23 0 63 ma with the maximum age being consistent with previous k ar ages of the k bearing minerals from the mpd such isotopic signatures imply that the mpd may have been affected by multiple stage fluid flow events since the mid miocene consisting of hydrothermal fluids continental fresh water and or hot spring water it is very likely that the mpd is still affected by fluid flow events in modern times the mineral assemblage of halite sylvite with minor amounts of carnallite was formed due to the recrystallization and diagenetic modification by hydrothermal fluids some characteristics of halite photomicrographs and inclusions and the lack of original halite chevron patterns are also supportive of the hypothesis that the deposit has undergone a diagenetic modification and dissolution recrystallization processes

saline groundwaters in the canadian shield a first overview abstract the chemical and isotopic compositions of saline groundwaters and brines in the canadian shield are described the occurrence of such waters is very widespread not related to any specific rock type or mineralization and generally can be expected at depths below 1 km the most saline brines have salinities exceeding 200 g l 1 dissolved solids and their chemistries tend to suggest that in the past saline waters penetrated the canadian shield the original chemistry of these solutions was subsequently modified through strong rock water interactions and it appears that their final chemical compositions are independent of the original chemistries stable isotope analyses indicate that these waters are not simple evaporated seawater sedimentary basin brines hydrothermal solutions or residual ore forming fluids although any of these could be a precursor of the brines secondary isotope exchange reactions and the hydration of primary silicates accompanied by the formation of clay minerals could have modified not only the primary isotopic composition but may have also profoundly influenced the chemistries of these brines to be effective these processes would have had to occur in closed systems

large scale hot water migration systems around salt diapirs in the danish central trough and their impact on diagenesis of chalk reservoirs abstract fracture filling calcite from the piercement fields of east rosa skjold rolf north arne nils and vagn directly underlain by salt diapirs and the dome field dan overlying a deep seated salt structure have been studied by fluorescence and cathodoluminiscence microscopy fluid inclusion microthermometry and carbon and oxygen isotopes the carbon and oxygen isotope compositions of the reservoir matrix chalk have also been measured the temperature estimates obtained from fluid inclusion data suggest that the fracture filling calcite of the piercement fields precipitated during hot water flushing of the reservoirs the flushing system only existed around the salt diapirs and was probably related to expulsion of overpressured fluid from the surrounding sediments the thermal anomaly and the faults associated with the diapirs probably were important factors in focusing the ascending water by combining fluid inclusion thermometry with o isotope data for the fracture filling calcites ranges of o isotopic values of the flushing water are deduced in skjold rolf north arne nils and vagn 18o 1 to 7 smow values typical of sedimentary porewater of sea water origin in east rosa 18o 4 and 4 smow which combined with data on fluid inclusion salinities suggest that the flushing waters were responsible for substantial salt dissolution lower 18o values with shallower depth of burial suggest that the porosity of chalk in the shallower fields was more severely reduced by calcite cementation during the flushing event than in the deeper fields in the case of north arne nils vagn and dan 13c values of the fracture filling calcites are similar to those of normal chalk 0 5 to 3 5 however calcites from rolf skjold and east rosa are depleted by 1 8 6 2 and 16 7 respectively only in east rosa is the matrix chalk itself depleted in 13c range 2 0 to 0 7 the low 13c values are interpreted as the result of biodegration sulphate originating from the underlying diapirs was flushed into the reservoir and used by bacteria to degrade present hydrocarbons this process produced 13c depleted bicarbonate which was incorporated into the fracture filling calcites

δ34s of lower carboniferous anhydrite cumbria and its implications for barite mineralization in the northern pennines recent hydrocarbon exploration in the solway basin has revealed the existence of lower carboniferous paralic sediments which contain numerous discrete anhydrite beds anhydrite s isotope ratios from the easton 1 well are compared with new isotopic data from barite mineralization that occurs along the faulted southern margin of the northumberland solway basin and published data from the northern pennine orefield similarities betw een the 34 s of anhydrite and barites from major mines at haydon bridge and the alston district of the northern pennine orefield supports a lower carboniferous marine sulphate source for mineralization at these sites identification of extensive evaporite deposits hi the solway basin resolves several longstanding problems associated with mineralization hi the northern pennines including the source of barite sulphate and the origin of hypersaline mineralizing fluids in an earlier investigation of the s isotope geochemistry of carboniferous hosted barite mineralization in and around the alston district of thenothern pennine orefield npo fig 1a solomon et al 1971 drew attention to the similarity between the 34 s of lower carboniferous marine sulphate and the sulphur isotopic composition of barite deposits a model for barite mineralization was proposed in which deep circulating bacl 2 brines mixed with shallow et al 1971 is consistent with aspects of barite mineralization more recent studies of the evolution of pore fluid geochemistry in sedimentary basins land 1987 hanor 1994a b argue against a marine connate origin for the sulphate component

origin of brine in the kangan gasfield isotopic and hydrogeochemical approaches the kangan permo triassic brine aquifer and the overlying gas reservoir in the southern iran are located in kangan and dalan formations consisting dominantly of limestone dolomite and to a lesser extent shale and anhydrite the gasfield 2 900 m in depth and is exploited by 36 wells some of which produce high salinity water the produced water gradually changed from fresh to saline causing severe corrosion in the pipelines and well head facilities the present research aims to identify the origin of this saline water brine as a vital step to manage saline water issues the major and minor ions as well as 2h 18o and 37cl isotopes were measured in the kangan aquifer water and or the saline produced waters the potential processes causing salinity can be halite dissolution membrane filtration and evaporation of water the potential sources of water may be meteoric present or paleo seawater the na cl and i cl ratios versus cl concentration preclude halite dissolution concentrations of cl na and total dissolved solid were compared with br concentration indicating that the evaporated ancient seawater trapped in the structure is the cause of salinization 18o isotope enrichment in the kangan aquifer water is due to both seawater evaporation and interaction with carbonate rocks the 37cl isotope content also supports the idea of evaporated ancient seawater as the origin of salinity membrane filtration is rejected as a possible source of salinity based on the hydrochemistry data the 18o value and incapability of this process to dramatically enhance salinity up to the observed value of 330 000 mg l the overlaying impermeable formations high pressure in the gas reservoir and the presence of a cap rock above the kangan gasfield all prevent the downward flow of meteoric and persian gulf waters into the kangan aquifer the evaporated ancient seawater is autochthonous because the kangan brine aquifer was formed by entrapment of brine seawater during the deposition of carbonates gypsum and minor clastic rocks in a lagoon and sabkha environment the reliability of determining the source of salinity in a deep complicated inaccessible high pressure aquifer can be improved by combining various methods of hydrochemistry isotope hydrodynamics hydrogeology and geological settings

evolution of saline waters and brines in the benue trough nigeria abstract hydrogeochemical assessment of 40 saline waters and brines from 20 locations within the lower southern and middle regions of the benue trough nigeria are presented and discussed in terms of genesis of the primary salinity and subsequent hydrochemical evolution the total dissolved ions range from 5263 to 88 800 mg l and 5148 to 47 145 mg l in the lower and middle region respectively the saline waters and brines are characteristically na cl type enriched in ca and sr on the one hand and depleted in mg and so 4 on the other relative to the seawater evaporation trend ionic ratios na cl br systematic and divalent cations suggest two likely sources of primary salinity a fossil seawater source and dissolution of halite however water rock interaction involving mg uptake by clay minerals and possibly dolomitization during diagenesis appear to be responsible for further modification of the primary chemistry a conceptualized hydrogeological flow model for the brines is presented

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

geochemistry of tectonically expelled fluids from the northern coast ranges rumsey hills california usa tectonic compression has created abnormally high pressure on deep basinal fluids causing their expulsion from areally exposed upper cretaceous rock along the eastern margin of the california coast ranges the fluids emerge as near neutral perennial sodium chloride springs at high elevations with flow rates as high as 10 l per min higher spring discharges are more common around the exposure of a west vergent fault propagation fold axis spring waters range from 1000 to 27 000 mg l tds the least saline water 18o 7 5 closely represents local meteoric water that mixes with saline fluid 18o 5 3 and forms a slope of 3 5 on a d vs 18o plot a na 125 to 8000 mg l vs cl 150 to 17 000 mg l plot shows a linear dilution trend that extends close to but below the values for modern seawater calcium 75 3000 mg l is considerably enriched relative to seawater and forms a nonlinear trend with chloride in detail the na deficit defined by the difference between the measured na content and the na concentration on a hypothetical seawater dilution line is approximately balanced by the ca excess similarly defined by the seawater dilution line this relationship strongly suggests that the fluid is diluted seawater that is being modified by active albitization of plagioclase at different depths simultaneous b and 18o enrichment of the fluids accompanied by deuterium depletion further suggest that the seawater modification is influenced by clay diagenesis bicarbonate and sio2 concentrations show an inverse correlation with cl with most waters being saturated or slightly oversaturated with calcite and quartz at the discharge temperatures some freshwater springs with near meteoric stable isotope values may represent mixing of young groundwater from perched aquifers but in many cases the freshwater springs emerge along the same structures and have the same perennial nature as the saline fluids and expulsion of an older fresh groundwater component that is under abnormal fluid pressures cannot be ruled out basinal fluids elsewhere commonly show dilution trends with local meteoric water and in the case of the rumsey hills some of the dilute saline waters may indicate deep penetration of meteoric water 1 km in the pleistocene before the latest tectonic uplift geothermometry of the spring waters maximum 90 c suggest an origin from as deep as 4 0 km this depth is consistent with the depth of the core of a fault propagation anticline below the surface of the rumsey hills developed by active internal deformation of an east tapering wedge beneath the southwestern sacramento valley active tectonic compression causes near lithostatic fluid pressures in the shallow subsurface below the rumsey hills and volume strain within the core of the anticline that results in upward expulsion of the saline fluids from the indicated depths

geochemistry and hydrodynamics of deep basin brines palo duro basin texas u s a abstract permeable strata of the deep basin brine aquifer system underlie bedded permian evaporites in the palo duro basin texas panhandle formation water samples collected from four u s department f of energy test wells and two independent oil and gas company wells in the basin were analyzed for chemical and isotopic compositions to characterize the geochemical environment and to determine the origin and compositional evolution of the water formation waters are na cl brines that contain 140 to 290 g l total dissolved solids tds chemical and isotopic compositions suggest grouping the brine samples into one of two types samples from western palo duro basin have high cl br ratios sr isotopic ratios that are significantly more radiogenic than permian seawater or precipitates from permian seawater and oxygen isotopic compositions that are depleted with respect to values predicted for equilibrium with calcite under in situ conditions samples from central and eastern palo duro basin have low cl br ratios sr isotopic ratios only slightly radiogenic relative to permian marine sr and oxygen isotopic compositions that suggest equilibration with calcite the concentrations of major and minor ions appear to be controlled by equilibrium with calcite dolomite anhydrite celestite low albite microcline and na smectite high na activities drive ion exchange reactions which coupled with maintenance of chemical equilibrium elevate the concentrations of divalent cations and lower the concentrations of dissolved so 4 and carbonate the origin and evolution of deep basin brines are interpreted from chemical and isotopic compositions integrated with results of previous geological and hydrogeological investigations brines from western palo duro basin acquired salinity by dissolving halite along a lateral flow path from the recharge zone radiogenic sr was derived from detrital silicate minerals and oxygen isotopic equilibrium with aquifer minerals has not been attained brines from central and eastern palo duro basin originated as either recharge that achieved chemical and isotopic equilibrium with the host rock during long residence times or as permian seawater concentrated by evaporation regional chemical and isotopic variations augment the results of hydrogeological modeling brines in the western part of the basin flow from the west and southwest where siliciclastic sedimentary rocks predominate brines in the central and eastern parts of the basin flow from the south and southwest where carbonate strata predominate

origin of cacl brines in devonian formations western canada sedimentary basin abstract the majority of waters in devonian formations of the western canada sedimentary basin are high salinity ca cl brines this relatively rare type of brine is of economic interest because of its association with both oil and hydrothermal ore deposits these brines are important sources of ca2 mg2 and ore metals in sedimentary basins it is possible to generate the ca cl brines by modification of residual evaporite brines the evaporation of devonian sea water produced large quantities of gypsum and halite such as the prairie formation residual brines were not retained in the evaporating system quantities of dense halite saturated brine sufficient to account for the high salinity formation waters in the basin were lost syndepositionally the cl and br content of waters within devonian formations in the basin can be explained by dilution of the residual evaporite brines brine composition was modified as a result of density driven reflux to depths of several kilometers this placed concentrated brines in contact with precambrian basement rocks at elevated temperatures 100 300 c the most important reactions between the brine and basement rocks appear to involve albitization of feldspars further modification of the brines occured as cements formed in devonian carbonates volumetrically the most important of these is dolomite in addition some devonian carbonates were dolomitized during ascent along faults mg2 was lost from hot brines as dolomite formed

reactivity of evaporites during burial an example from the jurassic of alabama the jurassic louann salt was the first significant sedimentary unit to accumulate in the gulf of mexico sedimentary basin br cl and sup 87 sr sup 86 sr ratios of halite from a single core into the top of the formation record the evaporation of normal seawater to bittern stage the bittern zone today consists of intergrown halite and sylvite the br and rb contents of the solid phases along with sup 87 sr sup 86 sr ratios and rb sr systematics are inconsistent with precipitation of the existing phases from seawater evaporated in jurassic time rather petrography and fluid inclusion and solid phase chemistry from the bittern zone is consistent with postdepositional water rock interaction which diagenetically modified a marine bittern assemblage to halite sylvite the chemistry of the br and rb rich saline formation waters characteristic of this area today likewise may reflect water evaporite interaction during burial

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

the lavrion pb zn ag rich vein and breccia detachment related deposits greece involvement of evaporated seawater and meteoric fluids during postorogenic exhumation

the source and evolution of paleofluids responsible for secondary minerals in low permeability ordovician limestones of the michigan basin abstract in this study we report on the source and evolution of fluids associated with secondary vein and replacement minerals in low permeability carbonate units in the michigan basin this petrogenetic information was collected using thermometric data from fluid inclusions combined with c o and sr isotope data and focuses on mm or cm wide vein and vug minerals from ordovician limestones of the trenton and black river groups and cambrian sandstones in sw ontario canada primary fluid inclusions in dolomite represent fluid stage i and have the highest trapping temperatures ttrap in the sedimentary succession between 88 and 128 c primary inclusions in calcite stage ii and celestine and anhydrite stage iii represent the final stages of secondary mineral formation and have ttrap values of 54 78 c all three stages of vein minerals formed from brines with salinities of 31 37 wt cacl2 nacl eq that were saturated in halite and methane gas at the time of mineral growth three subsequent stages of secondary fluid inclusions were observed in the samples stages iv vi however no secondary vein minerals formed during these stages and they are interpreted as re mobilization and or minor fluid ingress along grain boundaries and micro fractures notably stage iv secondary inclusions are gas undersaturated with salinities of 32 34 wt cacl2 nacl eq and minimum ttrap values of 57 106 c and are interpreted to have formed during a late devonian mississippian regional heating event secondary minerals from the cambrian units and the shadow lake formation have 13c values of 6 1 to 2 5 vpdb 18o values of 14 6 to 24 2 vsmow and 87sr 86sr of 0 70975 0 71043 relative shifts of approximately 2 to 3 in 13c 4 in 18o and 0 002 in 87sr 86sr are observed upward across the boundary between the cambrian shadow lake units and the overlying gull river formation samples from the gull river and coboconk formations and the trenton group kirkfield sherman fall and cobourg formations have 13c values of 1 0 to 1 9 18o values of 18 9 to 28 1 and 87sr 86sr values of 0 70790 0 70990 the combined microthermometric and isotopic data for secondary minerals in the cambrian shadow lake units suggest they formed from hydrothermal brine with a geochemical signature obtained by interaction with the underlying precambrian shield or shield derived minerals in the cambrian sandstones previous u pb dating of vein calcite and rb sr dating of secondary k feldspar from the region suggests that brine ingress occurred during the late ordovician silurian the o and sr isotope variability in vein samples from the gull river and coboconk formations is interpreted as localized mixing of 18o enriched connate fluids with hydrothermal brine in comparison isotopic data for the trenton group indicate secondary mineral formation from connate fluids sourced from 18o enriched evolved seawater and or modified hydrothermal brine that experienced fluid rock interaction during transit through the underlying stratigraphy

depositional environments of marine dominated bedded halite permian san andres formation texas the interpretation of the depositional environments in which bedded halite is formed is a frontier of evaporite sedimentology facies studies supplemented by geochemical data define an evaporite shelf depositional environment for the halite of the san andres formation of the palo duro basin texas panhandle that is significantly different from modern and previously described ancient halite precipitating environments such as playas salinas sabkhas and barred basins a coastal palaeoenvironmental setting for the san andres halite is defined by its facies position between normal marine shelf carbonates and aeolian deposits the san andres brine pool extended over more than 10 000 km2 but was very shallow perennial brine pool conditions thick sequences of halite alternated with ephemeral brine pool conditions halite haloturbated mudstone halite mudstone interbeds and microkarst the depositional sequence in the perennial brine pool includes 1 flooding and minor dissolution of previously deposited halite 2 precipitation of a thin lamina of gypsum and 3 evaporation and precipitation of halite bottom growth forms of halite including chevrons and vertically elongated crystals are well preserved cumulates of foundered floating crystals and rafts were probably abundant but have been almost completely recrystallized mudstone interbeds in halite and microkarst features cut into bedded halite record the episodic interruption of brine pool deposition and the establishment of subaerial conditions vertically elongated karst pits originate at the palaeosurfaces cross cut primary brine pool fabrics and are filled with geopetal sediment and coarse halite cement mudstone interbeds and mixtures of mudstone and halite have been haloturbated by the alternating growth and dissolution of halite reflecting conditions of fluctuating salinity the geochemistry of halite from both ephemeral and perennial brine pool environments reflects the frequent influx of marine brine indicating that communication with the marine environments to the south was good considering that restriction was sufficient to precipitate halite

the origin and evolution of base metal mineralising brines and hydrothermal fluids south cornwall uk abstract a fluid inclusion geochemical study has been carried out on quartz from post variscan quartz carbonate base metal sulphide anhydrite fluorite veins hosted by palaeozoic basement porthleven menheniot cornwall and permo triassic sediments western approaches data indicate that the base metal mineralising fluids have a similar bulk chemical composition to the saline fluids found in the permo triassic basinal sequence and support the hypothesis that these basins are the source of the mineralising fluids cl and br systematics suggest that the brines were formed either by the evaporation of seawater or a seawater meteoric water mixture past the point of halite precipitation the major cation composition na ca k mg of the brines is not consistent solely with evaporation processes but may be explained by dolomitisation processes albitisation processes or both which are recognised in the basinal sequences the presence of seawater in the base metal mineralised veins suggests that the first marine incursions late triassic into the region must act as a lower age limit for the mineralisation the halogen chemistry of a second hotter 200 c more dilute 0 5 wt fluid identified in fault hosted e w trending veins in the porthleven area suggests that the chlorinity of these fluids has a magmatic origin circulation of these fluids in post variscan extensional structures was driven by the local high heat producing cornubian batholith the local high heat producing granites provided fracture permeability and a heat source that heated the base metal mineralising fluids as they entered the horst block and the dilute fluids circulating around the granites petrographic evidence suggests that both palaeohydrologic systems were active contemporaneously however each flow system was isolated in differently orientated structures and there is little evidence for fluid mixing

geochemical and isotopic evidence for a genetic link between canadian shield brines dolomitization in the western canada sedimentary basin and devonian calcium chloridic seawater hypersaline brines of marine origin deep within fractured crystalline rocks of the canadian shield are characterized by calcium chloride compositions with relatively low concentrations of magnesi

a fluid inclusion and stable isotope study of 200 ma of fluid evolution in the galway granite connemara ireland fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the caledonian galway granite these fluids were examined by petrography microthermometry chlorite thermometry fluid chemistry and stable isotope studies the earliest fluid was a h2o co2 nacl fluid of moderate salinity 4 10 wt nacl eq that deposited late magmatic molybdenite mineralised quartz veins v1 and formed the earliest secondary inclusions in granite quartz this fluid is more abundant in the west of the batholith corresponding to a decrease in emplacement depth within veins and to the east this fluid was trapped homogeneously but in granite quartz in the west it unmixed at 305 390 c and 0 7 1 8 kbar homogeneous quartz 18o across the batholith 9 5 0 4 n 12 suggests v1 precipitation at high temperatures perhaps 600 c and pressures 1 3 kbar from magmatic fluids microthermometric data for v1 indicate lower temperatures suggesting inclusion volumes re equilibrated during cooling the second fluid was a h2o nacl kcl low moderate salinity 0 10 wt nacl eq moderate temperature 270 340 c high d 18 2 low 18o 0 5 2 0 fluid of meteoric origin this fluid penetrated the batholith via quartz veins v2 which infill faults active during post consolidation uplift of the batholith it forms the most common inclusion type in granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of biotite and hornblende sericitization and saussuritization of plagioclase and reddening of k feldspar the salinity was generated by fluid rock interactions within the granite within granite quartz this fluid was trapped at 0 5 2 3 kbar having become overpressured this fluid probably infiltrated the granite in a meteoric convection system during cooling after intrusion but a later age cannot be ruled out the final fluid to enter the granite and its host rocks was a h2o nacl cacl2 kcl fluid with variable salinity 8 28 wt nacl eq temperature 125 205 c d 17 to 45 18o 3 to 1 2 13cco2 19 to 0 and 34ssulphate 13 23 that deposited veins containing quartz fluorite calcite barite galena chalcopyrite sphalerite and pyrite v3 correlations of salinity temperature d and 18o are interpreted as the result of mixing of two fluid end members one a high d 17 to 8 moderate 18o 1 2 2 5 high 13cco2 4 low 34ssulphate 13 high temperature 205 230 c moderate salinity 8 12 wt nacl eq fluid the other a low d 61 to 45 low 18o 5 4 to 3 low 13c 10 high 34ssulphate 20 23 low temperature 80 125 c high salinity 21 28 wt nacl eq fluid geochronological evidence suggests v3 veins are late triassic the high d end member is interpreted as a contemporaneous surface fluid probably mixed meteoric water and evaporated seawater and or dissolved evaporites whereas the low d end member is interpreted as a basinal brine derived from the adjacent carboniferous sequence this study demonstrates that the galway granite was a locus for repeated fluid events for a variety of reasons from expulsion of magmatic fluids during the final stages of crystallisation through a meteoric convection system probably driven by waning magmatic heat to much later mineralisation concentrated in its vicinity due to thermal tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic heat has abated

petrologic and geochemical attributes of fracture related dolomitization in ordovician carbonates and their spatial distribution in southwestern ontario canada abstract middle ordovician trenton group carbonates are fractured and extensively dolomitized along the axis of the algonquin arch in southwestern ontario hydrocarbon reservoirs formed where these dolomitized fracture zones penetrate otherwise impermeable host limestones three different types of dolomite d1 d2 and d3 are distinguished petrographic characteristics and 18 o values indicate that d1 formed during early diagenesis from middle ordovician seawater and recrystallized during progressive burial whereas fracture related replacive matrix dolomite d2 formed by hydrothermal fluids 68 99 c late stage saddle dolomite d3 and calcite c3 cements occlude fractures based on petrographic fluid inclusion and stable isotope data d3 dolomite and c3 calcite formed from warm 68 144 c saline 22 24 wt nacl cacl 2 hydrothermal fluids the least radiogenic 87 sr 86 sr values 0 70830 0 70842 of d2 are consistent with estimated values of devonian and silurian seawater whereas the slightly enriched 87 sr 86 sr ratios of d2 and d3 0 70902 0 70918 suggest their precipitation from fluids similar in composition to oil field brines rare earth element ree results of d2 d3 and c3 indicate enrichment in rees content of these mineral phases relative to undolomitized host rock the similarity in the average rees pattern of d2 d3 and c3 and the overlying blue mountain shale and basement rocks suggest progressive water rock interaction magnesium required for dolomite precipitation was supplied by mg rich seawater derived silurian and or devonian saline waters from dissolution of silurian evaporites which descended along faults and fractures to reservoir depths at the center of the basin while being heated hot basinal brines migrated laterally through basal sandstones and ascended into the network of faults and fractures and precipitated fracture related dolomite the abundance of fracture related dolomite in the periphery of michigan basin in southwestern ontario suggests that dolomitizing fluids originated from the michigan basin rather than appalachian basin

cross formational rising groundwater at an artesian karstic basin the ayalon saline anomaly israel it is proposed that a geothermal artesian karstic system at the central part of the yarkon taninim aquifer creates the ayalon saline anomaly asa whose mechanism has been under debate for several decades a 4 year long detailed groundwater monitoring was carried out at 68 new shallow boreholes in the ayalon region accompanied by a comprehensive survey of karstic voids results indicate the rising of warm brackish groundwater through highly permeable swarms of karstic shafts serving as an outflow of the artesian geothermal system the asa area contains hot spots where groundwater contrasts with normal water hundreds of meters away the asa temperature reaches 30 8 c w5 8c warmer than its surroundings chloride concentration reaches 528 mg l 50 100 mg l in the surrounding h2s concentration reaches 5 6 mg l zero all around and ph value is 7 0 compared with 7 8 around subsequently the hydrothermal water flows laterally of at the watertable horizon through horizontal conduits mixing with normal fresh water which had circulated at shallow depth following rainy seasons maximal watertable rise is observed in the asa compared to its surroundings regional hydrogeology considerations suggest that the replenishment area for the asa water is at the samaria mountains east of the asa the water circulates to a great depth while flowing westward and a cross formational upward flow is then favored close the upper sub aquifer s confinement border

relics of evaporated sea water in deep basins of the eastern mediterranean abstract reexamination of data on hypersaline bottom brines from the deep anoxic tyro and bannock basins in the eastern mediterranean reveals that despite their similar chlorinity 6 0 mole kg h 2 o their chemical composition is significantly different the brine in the tyro basin has a na chloride composition na cl 1 with conspicuously low ratios of conservative elements to chloride br cl 2 4 10 4 li cl 1 4 10 5 b cl 1 6 10 4 indicating dissolution of halite in contrast brines from the bannock basin are characterized by an mg chloride signature na cl 0 78 with relatively high ratios of conservative elements to chloride br cl 1 7 10 3 li cl 5 2 10 5 b cl 8 4 10 4 the contents of na mg k li cl br and b in the deep bannock brines brine ii are identical to those in evaporated sea water of a degree of evaporation of 12 13 whereas ca is enriched and so 4 is depleted in contrast to previous studies it is suggested that brine ii from the bannock basin is a relic of ancient evaporated sea water that was slightly modified by sulphate reduction and gypsum dissolution the interstitial ancient evaporated sea water was liberated and accumulated on the sea floor probably during the formation of the deep basins in the bannock area

palaeohydrodynamics of fluids in the brent group oseberg field norwegian north sea from chemical and isotopic compositions of formation waters generally the history of past sub surface fluid movements is difficult to reconstruct however the composition of oil field waters characterizes the origins and mixing processes that allow such a reconstruction we have investigated present day formation waters from brent group sedimentary rocks of the oseberg field in order to assess both their geochemical variations and their origin s water samples sampled at the separator produced from immediately above the oil water contact and from the aquifer water saturated zone below the oil water contact were taken from 11 wells across the field in addition 3 trace water samples were extracted from oil produced from higher up in the oil column the water samples were analysed for their chemical components and isotopic compositions conservative tracers such as cl br deltad and delta o 18 were used to evaluate the origin of the waters all formation waters can be characterised as na cl brines the separator samples are of aquifer origin indicating that aquifer water drawn up by the pressure reduction near the well is produced from the lower few tens of metres of the oil zone by defining plausible endmembers the waters can be described as mixtures of seawater 60 90 meteoric water 10 30 evaporated seawater primary brines 3 5 and possibly waters which have dissolved evaporites secondary brines alternatively using multidimensional scaling the waters can be described as mixtures of only 3 endmembers without presupposing their compositions in fact they are seawater very dilute brine and a secondary brine confirming the power of this approach meteoric water was introduced into the reservoir during the end brent and early cretaceous periods of emergence and erosion and partially replaced the marine pore fluids lateral chemical variations across the oseberg field are extremely small the waters from closer to the erosion surfaces show slightly stronger meteoric water isotopic signatures the primary and secondary brines are believed to come from permian and triassic evaporitic rocks in the deeply buried viking graben to the west and to have been modified by water rock interactions along their migration path these primary basinal brines have not been detected in the oil zone waters suggesting that the brines entered the reservoir after the main phase of oil migration there are indications that these external fluids were introduced into the reservoir along faults present day aquifer waters are mixtures of waters from different origins and hardly vary at a field scale they are different in composition to the water trapped in the present oil zone one of the oil zone samples is a very dilute brine it is thought to represent a simple mixture of seawater and meteoric water due to oil emplacement this geochemical signature was preserved in the waters trapped within the oil zone another oil zone water shows a very similar chemical signature to the aquifer waters but the chlorine isotopic signature is similar to that of the dilute oil zone water this water is interpreted to represent a palaeo aquifer water that is it was within the aquifer zone in the past but was trapped by subsequent emplacement of more oil these vertical differences can be explained by two features i emergence of the brent group sedimentary rocks in the early cretaceous allowed ingress of meteoric water ii subsequent rapid burial of viking graben rocks caused migration of petroleum and aqueous fluids into the adjacent less deeply buried oseberg field c 2001 elsevier science ltd all rights reserved

brines in the carboniferous sydney coalfield atlantic canada abstract formation waters within upper carboniferous sandstones in the sub sea prince and phalen coal mines nova scotia originated as residual evaporative fluids probably during the precipitation of windsor group lower carboniferous salts which underlie the coal measures salinity varies from 7800 to 176 000 mg l and the waters are na ca cl brines enriched in ca sr and br and depleted in na k mg and so4 relative to the seawater evaporation curve br cl and na cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30 the brines lie close to the meteoric line on h o isotopic plots but with a compositional range of 18o from 4 18 to 6 99 and of d from 42 4 to 23 5 distant from modern meteoric or ocean water mine water composition contrasts with that of nearby salt spring brines which are inferred to have originated through dissolution of windsor group evaporites by modern meteoric waters however a contribution to the mine waters from halite dissolution and from br in organic matter cannot be ruled out present concentrations of several elements in the brines can be explained by water rock interaction the original windsor brines probably moved up into the overlying coal measure sandstones along faults prior to the late triassic the high salinity and irregular salinity distribution in the phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile in contrast prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters basinal brines from which these modern formation fluids were derived may have been important agents in base metal and ba mineralisation from the mid carboniferous onwards as saline fluid inclusions are common in zn pb sulphide deposits in the region

geochemistry of hco 3 na thermal water from the gudian slope insights into fluid origin formation mechanism and circulation in the yitong basin northeast china abstract the goal of this paper is to systematically analyze the geochemical and isotopic characteristics 18o d t 13chco3 and doc of a hco3 na thermal water to determine its origin formation mechanism and circulation pattern in the gudian slope yitong basin northeast china schoeller diagrams and isotope data indicate that this thermal water is not connected to groundwater or river water and that its recharge source is immature water with low 18o and d values that originates from the changbaishan area this result was also confirmed by its doc 13c value approximately 24 which indicates that the c originates from c3 plants the analysis of na k mg diagrams indicates that the thermal waters except for one sample sjxk are fully equilibrated this observation combined with the results of the analysis for 18o d t and cation geothermometry data for the thermal water indicates that no water underwent mixing with cold water before arriving at the surface instead high temperature immature water flowed up from a deep reservoir and mixed with old formation water approximately 35 4 in the eocene reservoir these data indicate the occurrence of an interesting phenomenon in which the thermal water samples of the gd area exhibit a regression line with a negative slope and similar 18o values potentially due to the fractionation of co2 gas and a buffer of high hco3 concentrations rather than their short circulation times the high so4 cl b cl f cl and hco3 cl ratios and 13chco3 values ranging from 0 84 to 1 24 of these samples imply that magmatic volatiles have been dissolved in the thermal water however we cannot ignore the contributions of 13c from the leaching of limestone with a13c value of approximately 3 4 which is further supported by the br cl and hco3 cl ratios thus we analyzed the geological background and data collected from well chang 27 and deduced that a limestone stratum exists below the study area magmatic volatiles flow up through the lithospheric faults along the northwestern and southeastern edges of the basin encounter changbaishan area recharge water in the limestone reservoir form hot water with high concentrations of hco3 and then recharged into the eocene sandstone reservoir long term mineral hydrolysis and transformation reactions in the reservoir cause the concentrations of na to increase and lead to the formation of hco3 na water

origin of quartz cement in the lower ordovician dongjeom formation korea abstract this study deals with the origin of quartz cement developed in deeply buried mature sandstones intercalated in a thick carbonate sequence the dongjeom formation early ordovician korea is composed of three coarsening upward sequences and is divided into two facies according to depositional conditions with respect to changes in relative sea level transgressive facies and regressive facies the transgressive facies are characterized by calcite cemented allochem bearing sandstones whereas the regressive facies is characterized by non calcareous quartzose to arkosic sandstones quartz overgrowths occupy significant amounts of pore space average 16 in the regressive facies sandstones fluid inclusions reveal that quartz overgrowths precipitated between 110 and 165 c petrographical study and homogenization temperatures indicate that quartz overgrowths precipitated mostly during and after chemical compaction during the late diagenetic stage considering the 18 o values of detrital quartz grains and the volumes of quartz overgrowth the 18 o values of quartz overgrowth are estimated to range from 14 4 to 19 0 smow on the basis of mass balance silica for quartz overgrowths was principally derived from chemical compaction pressure solution of detrital quartz quartz overgrowths in the dongjeom sandstones precipitated from formation waters 2 1 to 2 5 smow that evolved from contemporary meteoric waters by diffusion

timing and chemistry of fluid flow events in the lawn hill platform northern australia mudrocks and carbonates of the isa superbasin in the lawn hill platform in northern australia host major base metal sulfide mineralization including the giant strata bound century zn pb deposit mineral paragenesis stable isotope and k ar dating studies demonstrate that long lived structures such as the termite range fault acted as hot fluid conduits several times during the paleoproterozoic and mesoproterozoic in response to major tectonic events illite and chlorite crystallinity studies suggest the southern part of the platform has experienced higher temperatures up to 300 degrees c than similar stratigraphic horizons in the north the irregular downhole variation of illite crystallinity values provides further information oil the thermal regime in the basin and shows that clay formation was controlled not only by temperature increase with depth but also by high water rock ratios along relatively permeable zones k ar dating of illite in combination with other data may indicate three major thermal events in the central and northern lawn hill platform lit 1500 1440 to 1400 and 1250 to 1150 ma this study did not detect the earlier century base metal mineralizing event at 1575 ma 1500 ma ages are recorded only in the south and correspond to the age of the late isan orogeny and deposition of the lower roper superbasin they may reflect exhumation of a provenance region the 1440 to 1300 ma ages are related to fault reactivation and a thermal pulse at similar to 1440 to 1400 ma possibly accompanied by fluid flow with subsequent enhanced cooling possibly due to thermal relaxation or further crustal exhumation the youngest thermal and or fluid flow event at 1250 to 1150 ma is recorded mainly to the cast of the tern lite range fault and may be related to the assembly of the rodinian supercontinent fluids in equilibrium with illite that formed over a range of temperatures at different times in different parts of the platform have relatively uniform oxygen isotope compositions and more variable hydrogen isotope compositions delta o 18 3 5 9 7 parts per thousand v smow delta d 94 to 36 parts per thousand v smow the extent of the 180 enrichment and the variably depleted hydrogen isotope compositions suggest the illite interacted with deep basin hypersaline brines that were composed of evaporated seawater and or highly evolved meteoric water siderite is the most abundant iron rich gangue phase in the century zn pb deposit which is surrounded by all extensive ferroan carbonate alteration halo modeling suggests that the ore siderite formed at temperatures of 120 degrees to 150 degrees c whereas siderite and ankerite in the alteration halo formed at temperatures of 150 degrees to 180 degrees c the calculated isotopic compositions of the fluids are consistent with o 18 rich basinal brines and mixed inorganic and organic carbon sources 6180 3 10 parts per thousand v smow delta c 13 7 to 3 parts per thousand v pdb in the northeast lawn hill platform carbonate rich rocks preserve marine to early diagenetic carbon and oxygen isotope compositions whereas ferroan carbonate cements in siltstones and shales in the desert creek borehole are o 18 and c 13 depleted relative to the sedimentary carbonates the good agreement between temperature estimates from illite crystallinity and organic reflectance 160 degrees 270 degrees c and inverse correlation with carbonate delta o 18 values indicates that organic maturation and carbonate precipitation in the northeast lawn hill platform resulted from interaction with the 1250 to 1150 ma fluids the calculated isotopic compositions of the fluid are consistent with evolved basinal brine delta o 18 5 1 9 4 parts per thousand v smow delta c 13 13 2 to 3 7 parts per thousand v pdb that contained a variable organic carbon component from the oxidation and or hydrolysis of organic matter in the host sequence the occurrence of extensive o 18 and c 13 depleted ankerite and siderite alteration in desert creek is related to the high temperature of the 1250 to 1150 ma fluid flow event in the northeast lawn hill platform in contrast to the lower temperature fluids associated with the earlier century zn pb deposit in the central lawn hill platform

new constraints on carbonate diagenesis from integrated sr and s isotopic and rare earth element data jurassic smackover formation u s gulf coast a reply isotopic sr s o c and trace element including rare earth element ree compositions of calcite cements metal sulfides and sulfate minerals from oolitic carbonate grainstones of the smackover formation jurassic southwest arkansas shelf constrain the mechanism of sulfate reduction and establish temporal relations between sulfur and carbonate diagenesis strontium isotopic values of calcite cements range from near jurassic age sea water values 0 7068 up to values of 0 7096 this evidence coupled with variation in o and c isotopic compositions and in cement zoning under cathodoluminescence suggests that calcite cement precipitated over the course of burial diagenesis strontium isotopic compositions of pyrite marcasite and native s range up to maximum values observed for calcite cements but galena and sphalerite are less radiogenic the sr contents of sulfides and native s are 30ppm but the rb content is sufficiently low that in situ growth of87sr would not dramatically alter the initial sr isotope ratio diagenetic sulfate minerals also exhibit a range of sr isotopic compositions anhydrites range from 0 7071 to 0 7081 while celestites are more radiogenic 0 7096 the ree patterns of early and late calcite cements and framework grains differ using sm yb ratios as an indicator of heavy vs light ree enrichment early calcites have sm yb ratios 1 whereas late calcite cements have ratios of 1 8 3 2 importantly both cement signatures differ from framework grain ratios 1 3 1 7 indicating lack of rock buffering in fluids from which the cements precipitated furthermore the sympathetic increase in sm yb and sr isotopic ratios from early to late calcites is consistent with input of light ree from siliciclastic sources sulfur isotopic compositions of metal sulfide minerals range from 32 to 8 cdt native s and anhydrite values 18 are near jurassic age sulfate values while celestites are heavier 28 although thermochemical sulfate reduction has been proposed to explain h2s in deeply buried carbonate units associated with evaporite s lack of s isotopic homogenization between sulfate and sulfide minerals lack of s isotopic equilibration of oil with reservoir so4 and the limited distribution of h2s rich brines in southwest arkansas demand a more complex origin

chemical constraints and origins of four groups of gulf coast reservoir fluids discussion the authors take to task stoessell and moore s 1983 review of some previous ideas on the origin of gulf coast formation fluids taking specific exception to their interpretation of data from the edwards formation six points are emphasized edwards brines are significantly enriched in bromide relative to chloride over seawater evaporated to halite saturation edwards brines have significantly higher k c1 and ca mg c1 ratios than seawater evaporated to halite saturation edwards brines cannot achieve molar ca mg ratios of 16 by dolomization progressive stabilization of metastable dolomite by updip fluid cannot raise the magnesium content of edwards water in the absence of dolomite dissolution the volume of brine contained in the cretaceous section exceeds any reasonable volume of hypothetical connate mesozoic brine and isotopic differences between edwards brines and jurassic seawater evaporated to halite saturation are extreme and therefore preclude recognition of any primary jurassic component in the current brines

the brine underlying the oak ridge reservation tennessee usa characterization genesis and environmental implications abstract the deep hydrogeologic system underlying the oak ridge atomic reservation contains brine its origin was assessed using existing and newly acquired chemical and isotopic data the proposed model which best fits the data is modification of residual brine from which halite has been precipitated potential sources for this brine are in the appalachian mountains in the east where bedded halite is documented and where the hydraulic gradient needed to move the residual brine exists other models such as ultrafiltration and halite dissolution were also evaluated in places contaminants such as radionuclides heavy metals nitrates and organic compounds have reached the deep system the chemical and isotopic features of the brine were examined with respect to its potential discharge contaminated in places into shallow freshwater systems the observations suggest that whereas the origin of the salts in the brine may be very old influx of recent water takes place consequently the brine is not isolated in terms of recharge and discharge from the overlying active and fresh water bearing units

dedolomitization review and case study of uncommon mesogenetic formation conditions abstract dedolomitization converts a dolomite into a calcite and conventionally is interpreted to form in an eogenetic or telogenetic diagenetic environment where meteoric water dissolves evaporites to supply excess calcium hydrologic connectivity between a dolostone and the surface water may then lead to a dedolomitized interval often times being a diagnostic indicator for an erosional unconformity subaerial exposure and or karst in contrast to the classic models we present a case study for pervasive burial dedolomitization unrelated to meteoric fluids dedolomitization of the zechstein 2 carbonate ca2 gas reservoir in nw germany is strongly altering reservoir quality on a regional scale the ca2 shows a textbook correlation between reservoir quality and mineralogy petrographic analyses show that approximately 80 of all observed calcite reveal a dedolomite microtexture causing a reduction of average matrix porosity by 5 to 10 compared to the dolomite dedolomite follows initial layering and abundantly forms massive concretions which are surrounded by compaction related curvature of the depositional layering in the dolomite host rock such an early burial timing is supported by a slight burial related shift of 3 18o and 1 13c towards lighter values in the dedolomites compared to dolomite an exceptionally large amount of calcium rich fluids must have been mobilized to account for 50 of the ca2 rock volume to be dedolomitized however core fabrics related to meteoric diagenesis such as karst fabrics or typical fresh water stable isotope signatures have been observed neither in the ca2 nor in over and underlying anhydrite beds instead excess calcium likely comes from gypsum to anhydrite conversion and pressure solution within over and underlying anhydrites an influx of strontium rich waters from the anhydrite beds is indicated by up to 5 times higher strontium contents measured in dedolomite fabrics compared to their dolomite host rock homogenization temperatures between 51 and 56 c measured in some early fluid inclusions in dedolomite textures further exclude a pristine meteoric water input and suggest fluid entrapment in a burial depth range of 900 to 1400 m comparing these results with literature data furthermore indicates that mesogenetic dedolomite is either volumetrically underestimated in other carbonate evaporite settings or formed under unique diagenetic conditions across the southern permian basin during zechstein times

basinal brines at the origin of the imiter ag hg deposit anti atlas morocco evidence from la icp ms data on fluid inclusions halogen signatures and stable isotopes h c o the imiter ag hg deposit is located in the precambrian volcano sedimentary formations of the saghro inlier eastern part of the anti atlas mountains morocco the orebodies consist of northeast southwest to east west veins and lenses hosted by cryogenian black shales and gray wackes and neoproterozoic conglomerates and are controlled by an east west fault network the so called imiter fault mineralogical and paleo fluid geochemistry investigations microthermometry raman spectroscopy la icp ms on individual inclusions bulk crush leach analyses and stable isotope data o h show that the main ag ore stage is related to circulation of deep basinal sedimentary brines na k mg salinity 16 7 to 26 wt nacl equiv molar cl br 330 18 o 2 15 2 35 smow and d 53 8 to 65 5 smow at temperatures of about 180 to 220 c and hydrostatic pressures the main driving mechanism for silver ore deposition is the dilution of ore bearing brines by a low salinity meteoric fluid containing a low density volatile component n 2 ch 4 co 2 t h 180 to 220 c 18 o 1 4 smow and d of about 28 2 smow silver content of the brines ranges from 2 to 30 mmol kg solution up to 3 200 ppm ag avg ag concentration about 900 ppm whereas the maximum ag content found in dilute waters is about 0 4 mmol kg solution 40 ppm the ore forming model proposed for the imiter deposit is 1 ag extraction from the basement by the penetration of deep basinal brines and 2 deposition in a structural trap through fluid mixing with recharge fluids this model is comparable to that described worldwide for the origin of pb zn f ba and u deposits near unconformities between basement and sedimentary basins similarities among the major ag deposits from the anti atlas imiter zgounder bou azzer strongly suggest that they resulted from a unique event likely related to the opening of the atlantic ocean the silver ores are superimposed on the same lineament as a preexisting uneconomic pan african co ni as system linked to magmatic intrusions but ag ores have no genetic relationship with them

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

on the occurrence and wider implications of anomalously low δd fluids in quartz veins south cornwall england a chemical and hydrogen isotopic study has been carried out on quartz hosted fluid inclusions from three different quartz carbonate sulphide sulphate veins from southwest england two fluid types have been identified in these veins by fluid inclusion microthermometry 1 a low temperature 80 150 c saline 20 27 wt nacl cacl2 equiv nacl cacl2 brine and 2 a moderate temperature 200 c low salinity 0 5 wt nacl equiv fluid d values for the brines range from 39 to 103 and values for the dilute fluids are in the range 46 to 79 both fluid types have at least some values of d which are defined as anomalous i e cannot be directly related to either a low d source fluid or to modification of a source fluid by common physicochemical processes such as evaporation or boiling examination of these data in the given geological context suggest the anomalously low values are unlikely to be attributable to analytical artifacts or post entrapment changes of the fluid inclusions similarly fluid interaction with a suitable mineral or organic phase cannot adequately explain the data we conclude that an as yet unidentified process is responsible for producing low d fluids in southwest england and that this may be a common phenomenon in low temperature basinal environments

tracking physicochemical conditions of evaporite deposition by stable magnesium isotopes a case study of late permian langbeinites magnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition we report mg isotopic values delta mg 26 dsm3 measured from an evaporite deposit of langbeinite k2mg2 so4 3 found in the permian salado formation we used these data to model mg isotope fractionation between langbeinite and its parent brine in addition both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment the salado langbeinite delta mg 26 values are relatively low and fall within a relatively narrow range 4 12 0 03 parts per thousand to 3 81 0 07 parts per thousand equilibrium fractionation factors between langbeinite and aqueous mg2 solutions were calculated using quantum chemical density functional theory all computations were performed at the b3lyp 6 31 g d p level solvation effects were addressed using a solvent model water droplet approach and mineral structures were investigated using volume variable cluster models vvcm the equilibrium mg isotopic fractionation factors a between langbeinite and model brine solution we obtained are 1 0005 1 0004 and 1 0003 delta mg 26 langb water approximate to 10 3 ln alpha 0 473 parts per thousand 0 390 parts per thousand and 0 322 parts per thousand at 10 degrees c 25 degrees c and 40 degrees c respectively these relatively large equilibrium fractionation factors indicate significant mg isotope fractionation between langbeinite and its parent brine during precipitation as langbeinite preferentially incorporates the heavier mg 26 and mg 25 isotopes rayleigh distillation modeling of the salado langbeinite s relatively light mg isotopic composition requires delta mg 26 dsm3 values of 4 parts per thousand for the parent brine models favor a precipitation temperature as high as 40 degrees c under equilibrium conditions potential disequilibrium precipitation conditions suggested by mg isotopic data also imply rapid deposition in a hot arid sedimentary environment prevailing in the southwestern u s during the late permian

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

hydrogeochemical processes involved in salt dissolution zones texas panhandle u s a permian evaporite deposits have been extensively dissolved beneath the perimeter of the southern high plains in the texas panhandle hydrologic and geochemical data were collected from six test wells to determine hydrogeochemical processes involved and the source and flow paths of ground water moving in salt dissolution zones geochemical similarities and hydraulic head relationships indicate that ground water dissolving halite and anhydrite moves downward from aquifers in post permian formations and follows flow paths influenced by topography holocene salt dissolution rates probably are lower than tertiary and pleistocene rates owing to regional changes in physiography and climate that probably decreased the amount of recharge to salt dissolution zones present as well as palaeohydrologic ground water velocities and salt dissolution rates are probably less beneath the southern high plains than in adjacent peripheral salt dissolution zones because of lower hydraulic conductivities and lower hydraulic head gradients salinities in peripheral salt dissolution zones are low 67 000 to 95 000 mg l 1 despite high solubility of halite reflecting relatively open circulation of ground water in interior salt dissolution zones beneath the southern high plains ground water circulation is low and water composition tends to reach halite saturation

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

chemical constraints and origins of four groups of gulf coast reservoir fluids pitzer s method for computing activity coefficients has been applied to reported fluid compositions in four groups of gulf coast reservoirs the mississippi and arkansas smackover formation the texas edwards group the texas frio formation and the louisiana miocene sequence the activity quotients in fluids from carbonate reservoirs imply a reaction relation between calcite and disordered dolomite in which ordering increases at higher temperatures this relationship indicates that an increasing mg ca molality ratio with decreasing temperature does not necessarily imply dolomite dissolution by an updip moving fluid instead it may reflect an approach to equilibrium between calcite and metastable dolomite activity quotients in fluids from clastic reservoirs imply a rea tion relation between chlorite illite potassium feldspar and quartz at temperatures above 100 c 212 f present fluid compositions in the smackover and the edwards appear to be related to the updip movement of louann brines from the gulf coast basin accompanied by dolomitization in particular bromide plots for the edwards fluids indicate simple dilution of louann brines with interstitial fluids similar plots for fluids from the smackover show the complicating effects of illite formation sylvite dissolution and halite recrystallization albitization may have occurred during fluid movement through clastics prior to entering the smackover and edwards present fluid compositions in the frio and miocene are apparently not related to louann brines the compositional data reflect the effects of halite dissolution the subsequent albitization of plagioclase and potassium feldspar and the dissolution of carbonates during secondary porosity formation

carbon and oxygen isotopic composition of carbonates from saliferous deposits of the pripyat trough belarus abstract 18o and 13c in accessory calcite and dolomite from salt rock and in intrasalt carbonate beds of the upper frasnian and upper famennian evaporite formations of the pripyat trough vary over a wide range within all the intrasalt carbonate interbeds four distinct groups of rocks have been recognised on the basis of their isotopic composition the ranges of variation of 13c pdb and 18o smow within these groups are respectively a 0 7 to 0 8 and 35 4 to 36 4 b 4 5 to 0 9 and 30 0 to 32 2 c 7 0 to 2 8 and 19 8 to 25 5 d 17 5 to 9 7 and 20 9 to 26 4 the isotopic composition of accessory carbonates is more uniform the main body of values falls within the range 11 to 3 for 13c and 18 to 25 for 18o the carbonate matter with the observed combinations of 13c and 18o could have been formed during sedimentation and diagenesis in sabkhas on subaetially exposed islands on evaporite depression slopes washed by sea water and freshwater and in stagnant zones with hot brines the carbon isotopic composition of intrasalt carbonate rocks is on the average lighter than that of accessory carbonates from the salts this shows that the organic matter was most readily accumulated in evaporite basins during non salt sedimentation

a hydrogeochemical approach to evaluate the occurrence and source of salinization in the shallow aquifers of the southeastern imphal valley in the indo myanmar range of northeast india the imphal valley is an intramontane basin confined within an anticlinorium of several anticlines and synclines in the disang group of rocks of tertiary age this valley of more than 2 million people is occupied by fluvio lacustrine deposits of quaternary age and is located in the central part of the indo myanmar range of northeast india the hydrogeochemical parameters of temperature ph orp tds na cl br ba b sr li 18o hco3 k mg ca no3 po4 so4 in 173 samples using ion chromatograph icp aes icp oes icp ms and 37 dugwells were studied to understand the occurrence and origin of salinization process for the first time the order of abundance of ions is identified as hco3 na cl ca mg k no3 po4 sr br b ba li so4 five hydrochemical facies na cl ca mg hco3 na hco3 ca mg hco3 cl and ca mg cl represent the types of waters the saline dominated water types na cl and na hco3 represent piedmont and the rest of the facies represent alluvial plain and flood plain groundwaters durov s diagram reveales initial and intermediate stages of groundwater evolution isotope 18o gibbs diagram and ions scatter plots suggest evaporation and crystallization processes leading to halite encrustation in the disang shales negative eh low no3 and the absence of so4 indicates reduced condition coupled with rich dissolve organic matters leading to elevation of salts in soils around piedmont where the rock type is exclusively of the disang shales trilinear plot correlation matrix and water table flow analysis suggest salinization of groundwater originates in piedmont groundwater and disseminates towards alluvial plain and flood plain along the flow path

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

conodonts from the kechika formation and road river group lower to upper ordovician of the cassiar terrane northern british columbia this study examines the lower paleozoic stratigraphy of the cassiar terrane from three key sections comprising an east west transect across the terrane the cassiar terrane west of the northern rocky mountain trench consists of a neoproterozoic to triassic succession and is a fragment of the cordilleran miogeocline that has been displaced northward the amount of displacement from its original position remains controversial conodonts from the cassiar terrane have been previously reported from only a few reconnaissance studies more than 3000 m of strata have been measured and examined in detail and 85 conodont samples collected a total of 926 identifiable conodont elements are assigned to 31 species representing 21 genera the conodonts are mainly representative of the midcontinent faunal realm but some also represent the atlantic realm conodonts from the upper kechika formation and base of the road river group are early ordovician tremadocian in age and those from the upper road river group rang

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

the origin of mediterranean interstitial waters relics of ancient miocene brines a re evaluation re examination of interstitial waters from sixteen mediterranean dsdp sites reveals that the high salinity values of these waters up to 350 g l do not reflect dissolution of underlying evaporites but are rather related to miocene evaporated sea water trapped in the sediments and modified by diagenetic reactions and advection diffusion only in two shallow sites was the chemical composition of the interstitial waters controlled by evaporite dissolution the large variations in the chemistry of the interstitial waters among different sites suggests that the mediterranean was divided into separate sub basins with different chemical compositions the composition of interstitial waters records the history of the mediterranean since early miocene as follows 1 salinization of the western mediterranean during the early and middle miocene 2 intrusion of low salinity water in the eastern basin during the middle miocene 3 desiccation by evaporation of the mediterranean during the messinian late miocene other processes such as sulphate reduction and dolomitization took place along the sedimentary section the diffusion advection processes in the interstitial water in addition to smoothing the contrasts within vertical profiles of chemical concentrations caused an upward shift in the liquid phase profile in respect to the solid phase changed the vertical trend in the case of an end member which became exhausted and brought about vertical changes associated with the porosity structure

chemical and isotope composition of the oilfield brines from mishrif formation southern iraq diagenesis and geothermometry abstract this paper focuses on the geochemical composition and isotope geochemistry of brines in the cenomanian turonian carbonate mishrif reservoir of southern iraq main dissolved constituents trace elements 2h and 18o 87sr 86sr mineral saturation indices and thermodynamic calculations were investigated in formation waters from the mishrif formation to obtain a better understanding of brine evolution and diagenetic effects over geological time previous published 11b data were also reinterpreted as a geothermometer tool the results are compared with previous published data for local oilfields and coeval formations in the arabian gulf the mishrif brine has a marine origin and is diagenetically modified to ca excess and na deficit formation waters are quartz supersaturated and are in equilibrium with chalcedony and calcite dolomite in the temperatures range of 50 75 c which is also confirmed by calcite water oxygen isotope fractionation and 11b geothermometer the potential role of clays in conditioning brine chemistry during diagenetic processes was highlighted by activity diagrams in particular their adsorption exchange effect on sodium could explain the lower temperature obtained by the na li geothermometer 42 6 c the 2h and 18o values show that oxygen isotope composition of the brines was isotopically more affected by interaction with limestone during diagenesis than seawater evaporation the main effect is an 18o enrichment on the brine starting from the smow value locally dilution by present day meteoric water was also detected rumaila south which is shifted towards the local meteoric water line the strontium isotope ratios range from 0 707713 to 0 707749 and correspond to a marine strontium of late cenomanian early maastrichtian age except for the majnoon sample which shows a more radiogenic value 0 708043 radiogenic strontium and gypsum and anhydride saturation indices of the majnoon sample could indicate the contribution of calcium and sulphate from the strontium rich sulphate minerals of the cambrian salt domes occurring in the oilfields of southern iraq the higher manganese concentration 4 mg l and the slightly higher temperature inferred by geothermometers up to 74 c in comparison with present day could indicate that the majnoon brine is a hot fluid probably related to a deeper structure such as the zagros foredeep fault

massive hydrothermal dolomites in the southwestern cantabrian zone spain and their relation to the late variscan evolution abstract large scale massive burial dolomitization affected upper carboniferous carbonates of the southwestern variscan cantabrian zone spain replacive and void filling dolomites formed and were post dated by calcite cementation the process of dolomitization was due to the circulation of hypersaline and hydrothermal marine derived brines controlled by rock anisotropies the dolomites probably formed in early permian time during post thrusting orocline formation in an extensional setting lithospheric delamination induced increased heat flow and allowed thermal convection of the fluids the dolomites from the cantabrian zone are excellently exposed and represent an interesting outcrop analogue for hydrocarbon reservoirs elsewhere in comparable geotectonic settings of the european variscan orogen large masses of similar dolomites could have formed if mg rich brines were available

the geochemistry of brines and minerals from the asse salt mine germany the chemistry and stable isotopes 18o d of highly concentrated chloride brines and minerals from the asse salt mine in the north of the federal republic of germany were studied chemical data indicate the occurrence of three types of brines a mg cl type of carnallitite origin with li 100 mg kg and c almost pure mgcl2 type brines with li 100 mg kg the first group may be subdivided into brines with li 4 0 mg kg and brines with li between 18 and 30 mg kg lithium is shown to be an efficient complementary tool in tracing the origin of the brines the complex evolution of carnallitite type brines is discussed in detail isotopic data of brines that were sampled directly from seepages presumably unaltered indicate that these brines are not a mixture with relatively fresh ground water from the overburden sediments the stable isotope composition 18o and d of hydration water in carnallite kieserite and polyhalite sampled from the asse mine were also studied it is shown that water extracted from the so called primary carnallite is isotopically different from water extracted from secondary carnallite the isotopic fractionation factors for 18o and d between carnallite hydration water and mother solution were studied in the laboratory assuming that crystallization water of the so called primary carnallite samples is not altered the isotopic composition of the mother solution is evaluated

diagenesis of the devonian southesk cairn carbonate complex alberta canada marine cementation burial dolomitization thermochemical sulfate reduction anhydritization and squeegee fluid flow abstract one of the largest geological features in the deep part of the alberta basin in western canada is the middle to upper devonian southesk cairn carbonate complex sccc the sccc is located at depths of about 5000 m adjacent to the disturbed belt of the rocky mountains rising to depths of 3000 m in a northeastward direction over a distance of 150 km the sccc produces oil and gas with up to about 30 h2s from several stratigraphic levels the diagenesis of the sccc was investigated by means of petrography and geochemistry stable isotope compositions were determined for fibrous calcite cements matrix dolomite saddle dolomite and sparry calcite fibrous calcites have stable isotope values of 18o 7 5 to 4 5 pdb and 13c 2 0 1 0 pdb matrix dolomite samples have stable isotope values of 18o 8 1 to 4 9 pdb and 13c 0 to 1 0 pdb saddle dolomite samples range from 18o 9 8 to 7 1 pdb and 13c 1 0 to 0 pdb sparry calcite samples have 18o 13 7 to 7 2 pdb and 13c 24 0 to 0 pdb the sr isotope values of all analyzed samples span a broad range from 0 7080 to 0 7320 showing considerable scatter but also one distinctive pattern i e values higher than 0 7220 occur only at depths in excess of about 4000 m whereas lower values scatter throughout the entire depth range furthermore the sr isotope values of sparry calcites decrease northeastward similarly the fluid inclusion homogenization temperatures of these calcites display a general decrease updip whereas the salinities show no general spatial trends the uncorrected homogenization temperatures range from about 85 to 180 c and the nacl equivalent salinities range from about 17 to 24 weight the d values of brines obtained from seven wells range from 79 to 20 smow and their 18o values range from 1 5 to 8 7 smow the sulfur isotope values of the dissolved sulfate ranges from 34s 10 1 to 24 5 cdt the sr isotope values of the brine samples range from 0 7109 to 0 7255 elemental sulfur isotope values cluster tightly around 34s 18 0 to 18 4 cdt the values of secondary anhydrites range from 34s 18 4 to 26 7 cdt values for solid bitumen vary from 34s 19 5 to 20 2 cdt integration of all data reveals a complex diagenetic evolution from the middle devonian to the recent the paragenetic sequence consists of 24 distinct diagenetic phases which have been grouped into 5 diagenetic stages stage i density driven convection in near surface settings likely superimposed on and or aided by tidal pumping facilitating marine cementation stage ii cellular convection facilitating pervasive matrix dolomitization aided by compaction stage iii hydrocarbon migration stage iv thermochemical sulfate reduction forming sour gas and regional squeegee flow forming sparry calcite cements and localized flow through faults stage v fluid flow driven by erosional rebound in the overlying mesozoic strata and remnant squeegee flow this study yielded several important results 1 the prolific repertoire of diagenetic textures found in the southesk cairn carbonate complex serves as a means of comparison for petroliferous carbonate complexes elsewhere especially in sour gas provinces close to orogenic fronts 2 the diagenetic evolution contains long periods of relative tranquility that were punctuated by several episodes of intense diagenetic activity 3 both thermochemical sulfate reduction and squeegee type fluid flow are recorded in late diagenetic sparry calcite cements 4 the effect of the various burial diagenetic episodes on the hydrocarbon reservoir properties throughout the entire reef complex was highly variable specifically matrix dolomitization thermochemical sulfate reduction and the emplacement of secondary and tertiary anhydrites affected the hydrocarbon reservoir properties throughout the entire reef complex on the other hand squeegee fluid flow was insignificant in terms of affecting the reservoir properties

timing and conditions of permian rotliegende sandstone diagenesis southern north sea k ar and oxygen isotopic data illitic clay ranging from pure illite to highly illitic illite smectite i s is the most abundant diagenetic phase in the eolian and sabkha facies of the rotliegende formation of the southern north sea and northeastern netherlands most k ar ages of diagenetic illite and i s in the eolian sandstones are between 100 and 175 ma illite formation is related to two major phases of tectonic activity the jurassic kimmerian orogenic movements and late cretaceous early tertiary inversion movements the burial depth of a sample at the time of diagenetic illite formation can be derived from the k ar age and the appropriate burial history curve illite formed in different localities at different times and at different depths generally diagenetic illite is more abundant in samples more deeply buried at the time of illite formation the correlation between illite formation and tectonic disturbance and the correlation between illite abundance and burial depth may be useful for predicting reservoir properties specifically we would expect reservoir permeability of the rotliegende in the study area to be least impaired by illite growth in those samples less deeply buried from the late jurassic through the late cretaceous calculated dgr18o values of most illite forming fluids lie between 0 and 4 pmil smow indicative of meteoric or marine waters modified by interaction with rock however 18o depleted fluids as low as 5 pmil indicative of a major meteoric component are inferred to have been involved in the formation of illite in the groningen gas field at a time when nearby sections of the rotliegende were eroded and exposed at the surface

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

evolution and origin of deep reservoir water at the activo luna oil field gulf of mexico mexico petroleum wells of the activo de produccion luna oil field at the mexican gulf coast are partially invaded by formation water at a production depth between 5000 and 6000 m measured 14c activities between less than 0 9 and 13 7 modern carbon reflect a homogenous late pleistocene early holocene age 40 10 ka for the regional infiltration of meteoric and marine water into the reservoir before infiltration both components were partially affected by atmospheric evaporation which explains the hypersaline composition of some formation waters very positive d18o values up to 12 5 of the formation waters are caused by strong secondary water rock interaction processes and reflect close to equilibrium conditions between the carbonate host rock and the fluids the formation of biogenic and or thermocatalytic methane in some parts of the petroleum reservoir is indicated by d13c values up to 20 4 southwest northeast directed hydraulic migration of the deep aquifer between camps sen and escuintle pijije caparroso is indicated by interference tests and pressure drawdown characteristics whereas northwest southeast trending thrust faults restrict communication toward the luna and tizon camps in the most northeastern part of the oil field on a local scale vertical zonation trends of the fluids with decreasing salinity toward upper parts of the common aquifer are related to separation processes by gravity and or by the rising of condensed vapor the migration of the fluids is mainly related to southwest northeast trending fractures and microfractures whereas northwest southeast and northeast southwest trending reverse and normal faults respectively behave irregularly as barrier or as flow conduits recently the extraction of petroleum caused an increased mobilization of the hydrodynamic aquifer system begin page 458

origin and evolution of formation waters from oil fields on the norwegian shelf abstract stable isotopes of h and o and chemical analyses of formation waters from upper triassic jurassic clastic reservoirs and cretaceous carbonate reservoirs offshore norway are employed to interpret the origin and evolution of these waters in both types of reservoir the formation waters become progressively enriched in total dissolved solids and the heavy isotope of o with increasing depth whereas deuterium varies erratically between 20 and 40 smow bromine analyses and stable isotope data indicate that the formation waters are mixtures of a brine end member formed by evaporation of sea water beyond the point of halite saturation and meteoric water the chemical and isotopic composition of the formation waters and general geological considerations suggest that the brines originated as connate waters in permian evaporites and were later expelled into overlying strata there is a disequilibrium stable isotope distribution between the bulk chalk formations and the formation waters and only minor diagenetic modification of the formation waters appears to have taken place in these reservoirs the formation waters from the clastic reservoirs on the other hand are modified by diagenetic reactions