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

feldspar diagenesis in the frio formation brazoria county texas gulf coast tremendous quantities of detrital feldspar have been dissolved or albitized below about 14 000 ft 4 267 m in the frio formation oligocene chocolate bayou field brazoria county texas some sandstones no longer contain any unmodified detrital feldspar grains material transfer involved in these reactions is immense affecting at least 15 of the rock volume thus albitization has important implications for several other diagenetic processes that involve feldspars or their components these processes include formation of secondary porosity precipitation of quartz and carbonate cements and the evolution of na ca cl formation water

hydrogeochemistry of deep formation brines in the central sichuan basin china abstract subsurface brines are abundant in the sichuan basin china five brine bearing aquifers have been identified within rocks of triassic age in the central part of the basin these are of two types brine bearing clastic and brine bearing carbonate aquifers brines in this region have high total dissolved solids and chemical species that are different from those of evaporatively concentrated seawater deep formation brines in clastic aquifers in which evaporites do not exist are characterized by high concentrations of ca sr ba br and i low concentrations of mg and k and lack of so4 and are dominated by the na ca cl type brines in carbonate aquifers which have interbeds of evaporites are characterized by high total dissolved solids low concentrations of ca mg and so4 and lack of ba and are of the na cl type the brines in clastic aquifers originate from connate continental sedimentary waters mixed with marine waters membrane filtration through shales has played an important part in modifying the chemical compositions and increasing the salinity of the brines those in carbonate aquifers are bittern marine sedimentary waters with chemical compositions mainly controlled by precipitation of evaporites

regional trends in water chemistry smackover formation southwest arkansas geochemical and physical controls we present results on regional geochemical analyses of formation waters from jurassic carbonate strata of the upper smackover formation from the southwest arkansas shelf gulf coast basin these formation waters have been noted in earlier studies for their exceptional salinities and abnormally br rich composition our detailed and regionally extensive database shows that chemical heterogeneities occur on a relatively small scale and have spatial relations to faults which may act as pathways for fluid migration from deeper and hotter portions of the stratigraphic section one of the most pronounced heterogeneities in water chemistry is an h 2 s rich anomaly in the center of the shelf enrichments in h 2 s are accompanied by large increases in alkali elements li k and b and b which could be produced by higher temperature diagenesis of clay minerals and feldspars in deeper seated siliciclastic strata bromide enrichments in all smackover formation waters are apparent from relations between br and cl contents as well as br and divalent cation carpenter function values as suggested by earlier studies of these waters evaporatively concentrated seawater expelled from associated thick monomineralic evaporite sections may be an important source of br cl and na whereas ca mg and sr concentrations have been modified by carbonate mineral recrystallization and dolomitization mineral equilibria exert significant controls on concentrations of ca mg sr and so 4 in these brines br enrichment likely was produced by halite recrystallization in fluids already enriched in br from seawater evaporation elevated cl br ratios occur in regional association with lower salinity water near t e south arkansas fault system consistent with halite dissolution during meteoric water recharge thus despite relatively uniform reservoir lithology and simple structural setting processes on small spatial scales have resulted in significant heterogeneity in water chemistry within a small area of the gulf coast sedimentary basin although movement of fluids along these fault systems is not demonstrated in our study the regional trends in geochemistry are strongly suggestive of their important role in controlling chemical heterogeneities in smackover formation waters

strontium isotopes in brines and associated rocks from cretaceous strata in the mississippi salt dome basin southeastern mississippi u s a abstract sr concentrations and 87 sr 86 sr ratios have been determined for brines from formations spanning most of the cretaceous in two oilfields in the mississippi salt dome basin and from local salt domes chalk sands and shales the selma group is predominantly a fossiliferous chalk whereas the remainder of the stratigraphic sequence consists of sands and shales with only minor carbonate phases the sampled interval ranges from 2000 to just over 4000 m below land surface sr concentrations range from 443 to 1718 mg kg 1 for brines from baxterville field and from 528 to 1762 mg kg 1 for brines from soso field brine 87 sr 86 sr ratios range from 0 7071 to 0 7116 at baxterville field and from 0 7083 to 0 7119 at soso field with the exception of brines from the selma chalk all 87 sr 86 sr ratios are more radiogenic than cretaceous seawater on plots of 87 sr 86 sr vs sr concentration brines from individual formations within a producing field occupy distinct non overlapping areas with the exception of a single sample in some cases individual reservoirs within formations can be distinguished brines from formations that are present in both fields which are 85 km apart do not have the same 87 sr 86 sr ratio in each field brine sr concentration increases with depth 87 sr 86 sr ratios increase with depth to 3000 m and then appear to level off these trends are interpreted to be caused by dissolution or recrystallization of carbonate minerals which contain significant amounts of non radiogenic sr and decomposition of rb rich detrital micas and k feldspar which are sources of radiogenic 87 sr salt and cap rock from domes in southeastern mississippi have an average 87 sr 86 sr ratio of 0 70707 consistent with a middle jurassic age for the louann salt in baxterville field chalk from the upper cretaceous selma group has a cretaceous seawater 87 sr 86 sr ratio of 0 7076 87 sr 86 sr ratios range from 0 7091 to 0 7111 for sr leached from sands and shales from both baxterville and soso fields if these values reflect the 87 sr 86 sr values of the easily dissolved interstitial carbonate phases they indicate that the calcite cements precipitated from sedimentary fluids which were more radiogenic than the seawater of that time but which were not as evolved as the brines which are now present alternatively they may reflect leaching of radiogenic sources

stable chlorine isotopes in hydrothermal processes abstract values of 37cl can now be routinely measured with an analytical precision of 0 2 as reported herein on fluid inclusion leachates from the elmwood gordonsville mississippi valley type deposit and formation waters from its host formation basin brines from the gulf coast and palo duro basins and fluid inclusion leachates and biotites from the bingham silver bell and panguna porphyry copper deposits isotopic measurements are not affected by reaction yield in the range 85 100 or by generation of free i2 during sample preparation in the elmwood gordonsville deposit five successive paragenetic stages of ore and gangue sphalerite fluorite calcite 2 barite and calcite 3 each yielded multiple 37cl measurements ranges of 37cl vary in alternating fashion between stages with more negative values sphalerite calcites 2 and 3 and those with more positive values fluorite barite an interface between two brine systems with 37 cl and 0 0 appears to have moved back and forth across the zone of mineralization brines from the gulf coast and palo duro basins are apparently bimodal in 37cl with modes near 0 9 and 0 0 consistent with the variation in 37cl observed in fluid inclusion leachates from elmwood gordonsville biotite in the bingham deposit has 37cl values up to 1 7 and chlorine isotopes that are fractionated with respect to salt rich hydrothermal fluid hydrothermal fluids in all three porphyry copper deposits studied have a 37cl range of 0 1 to 0 4 with the one exception of a 0 5 value at bingham loss of low 37 cl chloride in vapor may balance chloride with a net 37 cl 0 in the porphyry deposits

strontium isotopic signatures of oil field waters applications for reservoir characterization the 87sr 86sr compositions of formation waters that were collected from 71 wells producing from a pennsylvanian carbonate reservoir in new mexico display a well defined distribution with radiogenic waters up to 0 710129 at the updip western part of the reservoir grading downdip to less radiogenic waters as low as 0 708903 to the east salinity 2800 50 000 mg l displays a parallel trend saline waters to the west pass downdip to brackish waters elemental and isotopic data indicate that the waters originated as meteoric precipitation and acquired their salinity and radiogenic 87sr through dissolution of upper permian evaporites these meteoric derived waters descended perhaps along deeply penetrating faults driven by gravity and density to depths of more than 7000 ft 2100 m the 87sr 86sr and salinity trends record influx of these waters along the western field margin and downdip flow across the field consistent with the strong water drive potentiometric gradient and tilted gas oil water contacts the formation water 87sr 86sr composition can be useful to evaluate subsurface flow and reservoir behavior especially in immature fields with scarce pressure and production data in mature reservoirs sr isotopes can be used to differentiate original formation water from injected water for waterflood surveillance strontium isotopes thus provide a valuable tool for both static and dynamic reservoir characterization in conjunction with conventional studies using seismic log core engineering and production data roger barnaby has conducted stratigraphic studies of carbonates and siliciclastics in outcrop and subsurface for 15 years he holds a ph d from virginia polytechnic institute and a b s degree from east carolina university barnaby has worked on sedimentary successions of the gulf coast permian basin alaska north slope middle east and caspian region he maintains interests in carbonate diagenesis and geochemistry gregg oetting received an m a degree in geology in 1995 from the university of texas at austin he is the author of six publications concerning geochemical and strontium isotopic variations in edwards aquifer groundwaters for the past seven years oetting has traded energy futures for leading merchant energy concerns he works for an independent consulting business in houston texas guoqiu gao received his b s and m s degrees in geology from central south university hunan china and his ph d in geology from the university of texas at austin he works for a major oil company in houston texas his current interests lie in the field of geoscience computing

dedolomitization of dolocrete deposits in kuwait arabian gulf dedolomitization of a dolocrete profile hosted in mio pleistocene siliciclastic deposits in the area of kuwait city arabian gulf was investigated dolocrete dolomite crystals vary considerably in size shape and internal structure however they are mostly zoned zonation is usually due to the alteration of cloudy and clear zones the cloudy zones which are mostly formed of disordered metastable dolomite are more susceptible to dedolomitization than the stable well ordered clear zones two modes of dedolomitization were recognized the first involves complete dissolution of the metastable dolomite followed by precipitation of intracrystalline cavity filling calcite the second is a pseudomorphic replacement of dolomite by calcite this replacement takes place by the simultaneous dissolution of dolomite and precipitation of calcite in such a manner that the original dolomite fabrics are inherited in the dedolomite exposed and near surface dolocrete profile less than 5 m deep are almost completely dedolomitized and altered to secondary calcrete whereas subsurface profiles are slightly dedolomitized dedolomitization of the sub surface dolocrete profiles may indicate the effect of flushing by fresh groundwater which flows from west to east whereas the alteration of the exposed dolocrete profile could be attributed to be an effect of meteoric water a new mode of calcrete genesis by dedolomitization and or complete calcitization of precursor dolocrete is suggested

the origin of aqueous sulfate in frio pore fluids and its implication for the origin of oil field brines abstract the o and s isotopic composition of aqueous s0 4 in saline formation waters from the frio formation of s texas can be used to deduce the origin of the s0 4 the average o and s isotopic composition of aqueous s0 4 in frio brines is 13 4 smow and 8 2 cdt respectively the o isotopic compositions fall within the range of mesozoic and cenozoic seawater values and are interpreted to be derived from dissolved jurassic evaporites the s values appear to have been modified by the addition of light s derived from the oxidation of pyrite we conclude therefore that some of the chemical components in frio brines are derived from water rock interactions that occurred in much deeper units and that these components have migrated into the frio

brines of the siberian platform russia geochemistry and processing prospects abstract complex researches have focused on chloride brines in the large artesian basins of the siberian platform the highly concentrated ground brines are unique natural solutions that are fraught with unsolved mystery associated with their origin and the formation of their chemical composition most scientists believe that the most important process controlling the formation of these brines was interaction between palaeoseawaters and host rocks the newest geochemical and stable isotope data 18 2h 37cl 81br 87sr 86sr showed that chloride sodium ground brines of the siberian platform originated as the result of halogenous rock leaching whereas chloride calcium brines derive from buried bittern connate waters the main evolutionary process was a long interaction in the water rock system this paper also provides information on the vast resource of multicomponent brines so called liquid ores which are widespread over a large area of the siberian platform it is an unconventional hydromineral raw material whose use and exploitation has an extremely high potential as it may constitute a serious alternative to solid mineral deposits the innovative methodology and pioneering methods for the processing and extraction of valuable components especially li from brine are suggested

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

rare earth element geochemistry of upper ordovician cherts from the southern uplands of scotland caradoc and ashgill radiolarian cherts and siliceous mudstones from the southern uplands preserve primary rare earth element ree signatures which are comparable to those of more recent deposits from continental margin settings this is incompatible with the widely held view of these rocks as open ocean deposits incorporated in an accretionary prism and reinforces the model of deposition on an extensional continental margin the ree signatures can be used as fingerprints to differentiate between some of the fault bounded formations within the area they indicate the provenance of the mud grade siliciclastic material in these distal hemipelagites and are comparable with published ree data on grey wackes in the same successions this detailed analysis of the ree patterns in lower palaeozoic cherts demonstrates the usefulness of this approach in ancient orogens

meteoric modification of early dolomite and late dolomitization by basinal fluids upper arbuckle group slick hills southwestern oklahoma 1 thick massive dolomite units from the upper arbuckle lower ordovician peritidal carbonate sequence slick hills southwestern oklahoma provide insight into two important problems 1 modification of early dolomite and 2 late dolomitization early dolomite volumetrically dominant is nonluminescent to dully luminescent 87 sr 86 sr ratios of most early dolomite samples are similar to both early ordovician seawater and associated limestones consistent with an early origin from coeval seawater all early dolomite samples are characterized by low delta 18 o values 5 1 to 10 0 o oo pdb indicating postdepositional modification meteoric water buffered by younger carbonates with lower 87 sr 86 sr ratios was probably responsible for modification because lower sr concentrations delta 18 o values and 87 sr 86 sr ratios characterize the more intensively modified early dolomite samples meteoric modification probably occurred during emergence of the carbonate platform in the ordovician late dolomite volumetrically minor is brightly luminescent and occurs mainly in transition zones between early dolomite and associated limestone late dolomite has high 87 sr 86 sr ratios delta 18 o values 5 9 to 2 5 o oo pdb and fe and mn concentrations relative to early dolomite and associated limestone 87 sr 18 o fe and mn enriched fluids derived from the anadarko basin during the late paleozoic are proposed to have formed the late dolomite the fluids migrated through preexisting early dolomite aquifers and dolomitized limestones near the early dolomite limestone contacts which existed at that time although early dolomite remained more porous than limestone during early burial burial alteration by solution compaction and cementation by late dolomite have reduced porosity considerably better reservoir quality is expected to be associated with late dolomite in the arbuckle group

inclusions of sedimentary brines in post variscan mineralizations in the federal republic of germany a study by neutron activation analysis abstract the post variscan vein mineralizations in the federal republic of germany are characterized by highly saline fluid inclusions t e t mice 26 to 20 c t h 1 ca 22 000 60 000 mg kg 1 cl 85 000 200 000 mg kg 1 and br 550 2 600 mg kg 1 composition and salinity of the inclusion solutions are similar to brines in deep sedimentary basins it is assumed that formation waters of the na ca cl type migrated out of permo triassic sediment troughs into culmination zones of the variscan orogen where they were heated and caused mineralizations through cooling and mixing with sulfate bicarbonate waters when reascending

dedolomitization and calcite cementation in the middle devonian winnipegosis formation in central saskatchewan canada limestone consisting of finely to medium crystalline calcite mosaics is present in the upper part of the winnipegosis formation on the east central margin of the elk point basin where the overlying prairie evaporite deposits have been removed this type of crystalline limestone is interpreted as dedolomite based on petrographic observations the 18o and 13c values of the winnipegosis dedolomite vary from 12 8 to 11 9 vpdb vienna pee dee belemnite and from 0 5 to 1 7 vpdb respectively both values are significantly lower than those for the corresponding dolomite the 87sr 86sr ratios of the dedolomite are significantly higher between 0 7082 and 0 7087 the spatial distribution and geochemical data of the winnipegosis dedolomite suggest that dedolomitization was related to an influx of fresh groundwater and dissolution of the prairie evaporite anhydrite during the latest mississippian to the early cretaceous when the basin was subjected to uplift and erosion the winnipegosis dedolomite displays a series of replacement fabrics showing progressive calcitization of dolomite including the occurrence of dedolomite restricted along fractures and adjacent areas dolomite patches floating in the dedolomite masses and massive dedolomite with sparsely scattered dolomite relicts however the characteristic fabrics resulting from dedolomitization documented in the literature have not been observed in the winnipegosis dedolomite coarsely to very coarsely crystalline subhedral to euhedral calcite cement is restricted in the dedolomite the petrographic features isotopic compositions and homogenization temperatures coupled with the burial history of the winnipegosis formation constrain the precipitation of the calcite cement from a mixing of basinal brines and fresh groundwater during late cretaceous to neogene time the more negative c isotopic signatures of the calcite cement 5 3 to 2 3 vpdb probably reflect a hydrocarbon derived carbon

critical sensitivity and trans scale fluctuations in catastrophic rupture rupture in the heterogeneous crust appears to be a catastrophe transition catastrophic rupture sensitively depends on the details of heterogeneity and stress transfer on multiple scales these are difficult to identify and deal with as a result the threshold of earthquake like rupture presents uncertainty this may be the root of the difficulty of earthquake prediction based on a coupled pattern mapping model we represent critical sensitivity and trans scale fluctuations associated with catastrophic rupture critical sensitivity means that a system may become significantly sensitive near catastrophe transition trans scale fluctuations mean that the level of stress fluctuations increases strongly and the spatial scale of stress and damage fluctuations evolves from the mesoscopic heterogeneity scale to the macroscopic scale as the catastrophe regime is approached the underlying mechanism behind critical sensitivity and trans scale fluctuations is the coupling effect between heterogeneity and dynamical nonlinearity such features may provide clues for prediction of catastrophic rupture like material failure and great earthquakes critical sensitivity may be the physical mechanism underlying a promising earthquake forecasting method the load unload response ratio lurr

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

fluid rock interactions in the salt dome environment an introduction and review abstract the salt dome environment in the gulf of mexico coast u s a provides one of the most diverse and long lived records of fluid rock interactions in an active sedimentary basin dominated by saline formation waters the geochemical record most of which is isotopic appears to span a temperature range between earth surface temperatures and lower greenschist facies most mineral forming processes in the salt dome cap rocks appear to involve mixtures of warm saline formation fluids from deep basin sources and cool dilute meteoric waters papers in this issue of chemical geology document some of the current research on fluid rock interactions in the salt dome environment these papers highlight the diversity of opinion about salt dome processes offering clues for further research the present paper reviews some of the key and more current literature on salt dome geochemistry fluid convection around salt domes and fluid rock interactions within salt and within the salt dome environment

porosity evolution of the cambrian bonneterre dolomite south eastern missouri usa the cambrian bonneterre dolomite of south eastern missouri usa hosts the large mississippi valley type mvt lead zinc copper ore deposits of the region the bonneterre dolomite consists of dolomitized algal bioherms oolitic grainstone and associated lithologies that were deposited on a carbonate platform surrounding the precambrian age st francois mountains porosity was determined by point counting thin sections from cores and mines in the bonneterre dolomite and by gas porosimetry volumes of epigenetic cements were estimated by point counting cement filling micro and mesoporosity using cathodoluminescence cement volumes were added to present porosity to estimate porosities during various stages of mineralization prior to the onset of mineralization micro and mesoporosity in the bonneterre dolomite averaged approximately 19 precipitation of early dolomite cement roughly concurrent with the main period of sulphide deposition reduced average porosity to approximately 7 and closed off much of the intercrystalline pore space later cementation by dolomite prior to late stage sulphides reduced porosity to approximately 5 and late cementation by quartz further reduced porosity to the present average value of 4 periods of carbonate dissolution during mvt mineralization enhanced large scale megaporosity associated with fractures and breccias but did not significantly increase smaller scale porosity dolomite cementation associated with mvt mineralization porosity and permeability were facies controlled today as a result of mineralization large scale fractures and breccias control porosity and permeability this study indicates that dolomite porosity may undergo significant change during basinal brine migrations associated with mvt mineralization

albitized microcline grains of post depositional and probable detrital origins in brottum formation sandstones upper proterozoic sparagmite region of southern norway untwinned albite ab 99 4 an 0 4 or 0 2 grains forming during diagenesis and very low grade metamorphism are common in sandstones of the brottum formation upper proterozoic in the sparagmite region of southern norway these untwinned albite grains are usually clouded by vacuoles and tiny inclusions which are mostly made of carbonaceous material although some albite grains also contain some combination of carbonates quartz phengite chlorite pyrite halite and anatase the presence of microcline grains replaced partly by albite indicates that the albite grains are pseudomorphs after microcline chessboard albite which occurs in the brottum formation is suggested to be detrital in origin