Major,minor element chemistry and oxygen and hydrogen isotopic compositions of Marun oil‐field brines,SW Iran: Source history and economic potential

Cation and anion concentrations and oxygen and hydrogen isotopic ratios of brines in the Asmari Formation (Oligocene–early Miocene) from the Marun oil field of southwest Iran were measured to identify the origin of these brines (e.g. salt dissolution vs. seawater evaporation) as well as the involvement of water–rock reaction processes in their evolution. Marun brines are characterized by having higher concentrations of calcium (11 000–20 000 mg/L), chlorine (120 000–160 000 mg/L) and bromide (600–1000 mg/L) compared to modern seawater. Samples are also enriched in ¹⁸O relative to seawater, fall to the right of the Global Meteoric Water Line and local rain water, and plot close to the halite brine trajectory on the δD versus δ¹⁸O diagram. Geochemical characteristics of Marun brines are inconsistent with a meteoric origin, but instead correspond to residual evaporated seawater modified by water–rock interaction, most significantly dolomitization. In addition, anhydrite precipitation or sulphate reduction appears to be important in chemical modification of the Marun brines, as indicated by lower sulphate contents relative to evaporated seawater. Extensive dolomitization, the presence of anhydrite nodules and high salinity fluid inclusions in the upper parts of the Asmari Formation fit a model whereby the Marun brines likely originated from the seepage reflux of concentrated seawater during the deposition of the overlying Gachsaran Formation evaporites in the Miocene. Copyright © 2010 John Wiley & Sons, Ltd.     

The behavior of lithium and its isotopes in oilfield brines: evidence from the Heletz-Kokhav field, Israel

Twenty-four brine samples from the Heletz-Kokhav oilfield, Israel, have been analyzed for chemical composition and Li isotope ratios. The chemical composition of the brines, together with geological evidence, suggests derivation from (Messinian) seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization. The present salinity of the samples (18-47 g Cl/L) was achieved by dilution of the original evaporitic brine by local fresh waters. Like brines from other sedimentary basins, the Li/Cl ratios in the Heletz-Kokhav samples show a prominent Li enrichment (five-fold to eight-fold) relative to modern seawater. The isotopic ratios of Li, expressed in the δ ⁶Li notation, vary from −26.3 to −17.9‰, all values being significantly higher than that of modern seawater (−32‰) irrespective of their corresponding Li concentration (1.0-2.3 mg/L). The isotopic composition of Li and the Li/Cl ratio in the oilfield brines were acquired in two stages: (a) The original evaporated seawater gained isotopically light Li during the diagenetic interaction between the interstitial Messinian brine and the basin sediments. A parent brine with an elevated Li/Cl ratio was formed. The brine was later diluted in the oilfields. (b) The δ ⁶Li values of the final brines were determined during epigenetic interaction with the Heletz-Kokhav aquifer rocks. At the same time, the Li/Cl ratio inherited from stage (a) remained largely unchanged. This work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins.     

Multi-isotopic composition (δLi–δB–δD–δO) of rainwaters in France: Origin and spatio-temporal characterization

In the present work, the first results are reported for both Li and B isotope ratios in rainwater samples collected over a long time period (i.e. monthly rainfall events over 1 a) at a national scale (from coastal and inland locations). In addition, the stable isotopes of the water molecule (δD and δ¹⁸O) are also reported here for the same locations so that the Li and B isotope data can be discussed in the same context. The range of Li and B isotopic variations in these rainwaters were measured to enable the determination of the origin of these elements in rainwaters and the characterization of both the seasonal and spatio-temporal effects for δ⁷Li and δ¹¹B signatures in rainwaters. Lithium and B concentrations are low in rainwater samples, ranging from 0.004 to 0.292 μmol/L and from 0.029 to 6.184 μmol/L, respectively. δ⁷Li and δ¹¹B values in rainwaters also show a great range of variation between +3.2‰ and +95.6‰ and between −3.3‰ and +40.6‰ over a period of 1 a, respectively, clearly different from the signature of seawater. Seasonal effects (i.e. rainfall amount and month) are not the main factors controlling element concentrations and isotopic variations. δ⁷Li and δ¹¹B values in rainwaters are clearly different from one site to another, indicating the variable contribution of sea salts in the rainwater depending on the sampling site (coastal vs. inland: also called the distance-from-the-coast-effect). This is well illustrated when wind direction data (origin of air masses) is included. It was found that seawater is not the main supplier of dissolved atmospheric Li and B, and non-sea-salt sources (i.e. crustal, anthropogenic, biogenic) should also be taken into account when Li and B isotopes are considered in hydrogeochemistry as an input to surface waters and groundwater bodies as recharge. In parallel, the isotopic variations of the water molecule, vector of the dissolved B and Li, are also investigated and reported as a contour map for δ¹⁸O values based on compiled data including more than 400 δ¹⁸O values from throughout France. This δ¹⁸O map could be used as a reference for future studies dealing with δ¹⁸O recharge signature in relation to the characterization of surface waters and/or groundwater bodies.     

Origin of brines in the Upper Silesian Coal Basin (Poland) inferred from stable isotope and chemical data

Brines in the Miocene formations of the Upper Silesian Coal Basin have isotopic composition close to SMOW, which identifies them as the connate marine water. However, controversies exist on the origin of brines in the Carboniferous formations. Isotopic and hydrochemical data exclude any relationship to marine water and enrichment by evaporation. The most common brine which occurs at great depths can be identified as the oldest infiltration in a very hot climate (δ¹⁸O ⋟ −2‰, δD ⋟ −20‰, Cl⁻ content 34 to 140 g/L). This brine is free of SO₄²⁻ and U, and rich in Ba²⁺ and²²⁶Ra. Its salinity is probably related to the leaching of evaporites and intensive weathering of rocks during the Rotliegendes.Other brines are difficult to identify because their isotopic contents are within the range of mixing between the oldest brine and the Quaternary waters (δ¹⁸O ⋟ 10‰, δD ⋟ 70‰). Isotopic and hydrochemical data allow identification of several occurrences of brine formed by meteoric water of a warm Tertiary climate, after the last marine transgression in the Tortonian. That brine is rich in SO₄²⁻ and contains moderate contents of²²⁶Ra and U. Its salinity is thought to result from leaching of Miocene evaporites. Two other identified types of brines can be related to some infiltration periods before the last marine transgression. The sources in salinity of these 2 types remain unknown. Mining activity results in a common occurrence of mixed brines. When the Quaternary component dominates, its identification is easy from the isotopic composition, whereas the end brine component can ususally be identified by chosen ion ratios and the presence or lack of sulphates.     

Nature of ore-forming fluids of the Dal’negorsk deposit: Isotopic and geochemical parameters of the altered host rocks

Oxygen isotopic composition was studied in the altered host rocks of the Dal’negorsk borosilicate deposit in order to establish a boron source and the origin of ore-forming fluids responsible for deposition of economic borosilicate ore. The relationships between oxygen isotopic composition and geochemistry of the altered igneous rocks occupying various structural and temporal positions in the ore zone were studied, including premineral high-potassium minor intrusions located in the zones of datolite mineralization; alkali basalt, gabbro, and breccia from the sedimentary framework of the deposit; and postmineral basaltic andesite, basalt, and dolerite dikes. It was suggested that interaction of aqueous fluid with host rocks brought about not only variation in oxygen isotopic composition but also shifts in geochemistry of these rocks, especially as concerns the chemical elements contained in ore-forming fluid. The disturbance of oxygen isotopic system is typical of all studied rocks: δ¹⁸O values sharply decrease indicating interaction with aqueous fluid at elevated temperatures. The lowest δ¹⁸O (from −2.9 to +0.1‰) is characteristic of the premineral high-potassium and ultrapotassium minor intrusions from skarn-datolite zone. Igneous rocks from the sedimentary framework of the deposit have δ¹⁸O of +2 to −0.9‰ The δ¹⁸O of postmineral basaltic andesite, basalt, and dolerite dikes varies from 0 to +7‰ with increasing distance from the ore zone. The oxygen isotopic composition of aqueous fluid evidences its exogenic origin. The geochemical and isotopic characteristics of ore-forming fluid show that it could have been deep-seated subsurface water similar to the contemporary water of the Alpine fold zone, which contain up to 700–1000 mg/l B and is distinguished by high K, Li, Rb, Cs contents and high K/Na ratio. Similar geochemistry is characteristic of the fluid inclusions in quartz from ore zones. It cannot be ruled out that continental evaporites were a source of boron as well. The relationships between δ¹⁸O, K-Ar age, and geochemical parameters of premineral and postmineral altered intrusive bodies allow us to suggest that the subsurface B-bearing water discharged through narrow channels controlled by premineral basaltic bodies. The discharge was probably initiated by emplacement of basalt and dolerite dikes.     

Low-temperature isotopic exchange in obsidian: Implications for diffusive mechanisms

While a great deal is known about the interaction between water and rhyolitic glasses and melts at temperatures above the glass transition, the nature of this interaction at lower temperatures is much more poorly understood. This paper presents the results of a series of isotopic exchange experiments aimed at further elucidating this process and determining the extent to which a point-by-point analysis of the D/H or ¹⁸O/¹⁸O isotopic composition across the hydrated rim on a geological or archaeological obsidian sample can be used as a paleoclimatic monitor. Experiments were performed by first hydrating the glass for 5 days in water of one isotopic composition, followed by 5 days in water of a second composition. Because waters of near end-member compositions were used (nearly pure ¹H₂¹⁶O, ¹H₂¹⁸O, and D₂¹⁶O), the relative migration of each species could be ascertained easily by depth-profiling using secondary ion mass spectrometry (SIMS). Results suggest that, during hydration, both the isotopic composition of the waters of hydration, as well as that of intrinsic water remaining from the initial formation of the glass vary dramatically, and a point-by-point analysis leading to paleoclimatic reconstruction is not feasible.     

Origin and evolution of oilfield brines from Tertiary strata in western Qaidam Basin: Constraints from <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr, δD, δ<Superscript>18</Superscript>O, δ<Superscript>34</Superscript>S and water chemistry

Chemistry of major and minor elements, ⁸⁷Sr/⁸⁶Sr, δD, δ¹⁸O and δ³⁴S of brines were measured from Tertiary strata and Quaternary salt lakes in the western Qaidam Basin. The water chemistry data show that all oilfield brines are CaCl₂ type. They were enriched in Ca²⁺, B³⁺, Li⁺, Sr²⁺, Br⁻, and were depleted in Mg²⁺, SO₄ ²⁻, which indicated that these brines had the characteristics of deeply circulated water. The relationship between δD and δ¹⁸O shows that all data of these brines decline towards the Global Meteoric Water Line (GWL) and Qaidam Meteoric Water Line (QWL), and that the intersection between oilfield brines and Meteoric Water Lines was close to the local spring and fresh water in the piedmont in the western Qaidam Basin. The results suggest that oilfield brines has initially originated from meteoric water, and then might be affected by water-rock metamorphose, because most oilfield brines distribute in the range of metamorphosing water. The ⁸⁷Sr/⁸⁶Sr values of most oilfield brines range from 0.71121 to 0.71194, and was less than that in salt lake water (>0.712), but close to that of halite in the study area. These imply that salt dissolution occurred in the process of migration. In addition, all oilfield brines have obviously much positive δ³⁴S values (ranging from 26.46‰ to 54.57‰) than that of salt lake brines, which was caused by bacterial sulfate reduction resulting in positive shift of δ³⁴S value and depleteed SO₄ ²⁻ in oilfield brines. Combined with water chemical data and δD, δ¹⁸O, ⁸⁷Sr/⁸⁶Sr, δ³⁴S values, we concluded that oilfield brines mainly originate from the deeply circulated meteoric waters, and then are affected by salt dissolution, water-rock metamorphose, sulfate reduction and dolomitization during the process of migration. These processes alter the chemical compositions of oilfield brines and accumulate rich elements (such as B, Li, Sr, Br, K and so on) for sustainable utilization of salt lake resources in the Qaidam Basin.     

Salt Waters of the Northern Apennine Foredeep Basin (Italy): Origin and Evolution

The salt waters from the Emilia-Romagna sector of the Northern Apennine Foredeep have been investigated using major and trace element and stable isotope (δ²H, δ¹⁸O, δ³⁷Cl, δ⁸¹Br and ⁸⁷Sr/⁸⁶Sr ratio). Ca, Mg, Na, K, Sr, Li, B, I, Br and SO₄ vs. Cl diagrams suggest the subaerial evaporation of seawater beyond gypsum and before halite precipitation as primary process to explain the brine’s salinity, whereas saline to brackish waters were formed by mixing of evaporated seawater and water of meteoric origin. A diagenetic end-member may be a third component for mud volcanoes and some brackish waters. Salinization by dissolution of (Triassic) evaporites has been detected only in samples from the Tuscan side of the Apennines and/or interacting with the Tuscan Nappe. In comparison with the seawater evaporation path, Ca–Sr enrichment and Na–K–Mg depletion of the foredeep waters reveal the presence of secondary processes such as dolomitization–chloritization, zeolitization–albitization and illitization. Sulfate concentration, formerly buffered by gypsum-anhydrite deposition, is heavily lowered by bacterial and locally by thermochemical reduction during burial diagenesis. From an isotopic point of view, data of the water molecule confirm mixing between seawater and meteoric end-members. Local ¹⁸O-shift up to +11‰ at Salsomaggiore is related to water–rock interaction at high temperature (≈150°C) as confirmed by chemical (Mg, Li, Ca distribution) and isotopic (SO₄–H₂O) geothermometers. ³⁷Cl/³⁵Cl and ⁸¹Br/⁷⁹Br ratios corroborate the marine origin of the brines and evidence the diffusion of halogens from the deepest and most saline aquifers toward the surface. The ⁸⁷Sr/⁸⁶Sr ratio suggests a Miocene origin of Sr and rule out the hypothesis of a Triassic provenance of the dissolved components for the analyzed waters issuing from the Emilia-Romagna sector of the foredeep. Waters issuing from the Tuscan side of the Apennines and from the Marche sector of the foredeep show higher ⁸⁷Sr/⁸⁶Sr ratios because of the interaction with siliciclastic rocks.     

Geochemistry of deep formation waters in the Canning Basin,Western Australia,and their relationship to Zn‐Pb mineralization

The Canning Basin contains several Mississippi Valley‐type Zn‐Pb sulphide prospects and deposits in Devonian carbonate reef complexes on the northern edge of the Fitzroy Trough, and in Ordovician and Silurian marine sequences on the northern margin of the Willara Sub‐basin. This study uses the ionic composition and 5D, δ¹⁸O, δ³⁴S, ⁸⁷Sr/⁸⁶Sr isotopic data on present‐day deep formation waters to determine their origin and possible relationship to the Zn‐Pb mineralizing palaeofluids.

The present‐day Canning Basin formation waters have salinity ranging from typically less than 5000 mg/L up to 250 000 mg/L locally. The brines are mixtures of highly saline water, formed by seawater which evaporated beyond halite saturation (bittern water), with meteoric water ranging in salinity from low (<5000 mg/L) to hypersaline water (up to about 50 000 mg/L) formed by re‐solution of halite and calcium sulphate minerals. The original marine chemical composition of the bittern‐dominated brines was changed to that of a Na‐Ca‐Cl water by addition of Ca and removal of Mg and SO₄, initially by bacterial sulphate reduction and later by dolomitization of carbonate. Other reactions with terrigenous components of the sediment have provided additional Ca and Sr, including a small proportion of ⁸⁷Sr‐rich material. The δ³⁴S values of the bittern‐containing waters are within the range over which marine sulphate has fluctuated from the Ordovician to the Holocene, although one of the hypersaline waters has a value of +6.8%, indicating SO₄ of non‐marine origin. The pH of the bittern‐containing waters is low (about 5) and they contain significant concentrations of dissolved Fe (up to 120 mg/L).

The Canning Basin bitterns appear similar in origin and chemical composition to highly saline marine brines in the Mississippi Salt Dome Basin, USA, which are known to be either metal or sulphide‐rich depending on the organic content of the host rock. In the Canning Basin, mixing of the bittern water with the various types of meteoric water has resulted in decreases in salinity, Na, Ca, Mg, K, Sr, Li and Fe, and increases in HCO₃, SO₄ and pH.

Mixing of the bitterns with other types of metalliferous fluids and/or with sulphate‐containing hypersaline meteoric waters formed from the same marine evaporite sequence should produce ore‐precipitating fluids which are relatively hot and saline, and the resulting ore deposit should be of high grade and contain abundant sulphate minerals. In the southern Canning Basin, this type of mixing and the corresponding style of ore deposit is evident in the evaporite‐associated areas of Zn‐Pb mineralization near the Admiral Bay Fault. If the bitterns mix with low salinity HCO₃‐waters in near‐surface environments, then the ore‐precipitating fluids should have relatively low salinities and carbonate minerals would precipitate during later stages of mixing. In the Lennard Shelf, the present‐day formation waters, the style of the Zn‐Pb deposits, and range of salinity and temperature of the ore‐forming palaeofluids are consistent with this type of mixing.     

Brines in the Carboniferous Sydney Coalfield,Atlantic Canada

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 δ¹⁸O from −4.18 to −6.99 and of δD 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.     

Evolution of isotopic composition and deuterium excess of brines in the Sichuan Basin, China

The isotopic composition and parameters for deuterium excess of brines, which were sampled in the Si-chuan Basin, show obvious regularities of distribution. The brine isotopic composition shows distinct two systems of marine and terrestrial deposits, with the Middle Triassic strata as the boundary. Brine hydrogen isotopic composition of marine deposits is lower while oxygen isotopic composition is higher than that of the SMOW, respectively, indicating that the brines were derived from seawater with different evaporating degrees at different times. From the Sinian strata, up to the Cambrian, Permian Maokou Formation and the Triassic Jialingjiang Formation, the δD values of brines tend to become relatively positive with the strata becoming younger. Brines of terrestrial deposits are considered to have been derived from precipitation and their isotopic composition is close to the globe meteoric water line (GMWL). Brines of transitional deposits between marine and terrestrial ones (the Upper Triassic Xujiahe Formation) have δD and δ18O values falling between the two end members of marine deposit brines and precipitation, indicating that the brines are a mixture of precipitation and vaporing seawater. Water samples from the brine-bearing strata of different ages show various deuterium excesses (d) with an evident decreasing trend as the age of strata gets older and older. Brine-bearing strata of the Triassic Leikoupo-Jialingjiang Formation, the Permian Maokou Formation, the Cambrian and Sinian strata are all carbonate rocks which have experienced intensive water/rock reaction and the deuterium excess essentially changes with time. All brine-bearing-strata surrounding the basin or faults, as well as those brine wells exploited for resources, have been obviously influenced by the precipitation supply. Therefore, the deuterium excesses of their brines have increased to different extents, depending on the amount of involvement of meteoric water. The variation and distribution of d values of the brines from different Triassic strata are related to the embedded depth of the strata. The deuterium excesses of brines become lower with increasing burial depth of the strata.     

Hydrogen,oxygen, helium and strontium isotopic constraints on the formation of oilfield waters in the western Qaidam Basin,China

Surveys and exploration for oil and gas have revealed many oil-field brines in the Tertiary strata of the western Qaidam Basin, China. The source and formation of these brines are unclear. Brine samples collected from petroleum wells in the oilfield area were analyzed for their general chemical composition and for hydrogen, oxygen, strontium and helium isotopes in order to trace their origin, formation, and resource distribution. Results show that the concentrations of resources such as K, B, Sr, Br and Li are unusually enriched in oil-field brines and have excellent potential for development and utilization in future. The geology, H, O, Sr and He isotopic composition, the chemical composition, and the geophysical measurements all show that the tertiary oil-field brines predominantly originated from the deep mixture of formation water and magmatic residual fluids in the western Qaidam Basin. The tectonic geology, intense and frequent magmatic-hydrothermal activity as well as high ³He/⁴He ratio indicate that the magmatic fluids possibly originate from the upper mantle-derived magmatic fluids. Thus, according to our interpretation of the formation and evolution of the oilfield brine, this source is adequate for the volume and composition to be explored and utilized latterly.     

Hydrology of a spring complex, studied by geochemical time-series data, Acquarossa, Switzerland

A case study of three springs in Switzerland is used to demonstrate the value of geochemical time-series data as a powerful tool to study the dynamics of groundwater systems. Values of repeatedly measured parameters revealed intermixings of two water types: (a) a 29°C water, circulating to a depth of 1100 m and containing approximately 700 mg/l Ca, 2000 mg/l SO₄, 700 mg/l HCO₃, 20 mg/l of Na and Cl, 6 mg/l Fe, at least 47 mg/l SiO₂, and with an isotopic composition of δD = − 73.0‰ and δ¹⁸ O = −10.9‰, and (b) a 12°C or colder water, shallow, and of a post-1953 age, containing 420 mg/l TDI or less, very low in Na and Cl (4 mg/l or less), isotopic values of δD = −71.0‰ and δ¹⁸ O = −10.5‰ and tritium as in recent (post-bomb) precipitation.     

Water-rock interaction and chemistry of groundwaters from the Canadian Shield

The chemical and isotopic compositions of groundwaters in the crystalline rocks of the Canadian Shield reflect different degrees of rock-water interactions. The chemistry of the shallow, geochemically immature groundwaters and especially of the major cations is controlled by local rock compositions, whereby dissolution reactions dominate. Conservative constituents, such as chloride and bromide, however, are not entirely a result of such reactions but appear to be readily added from leachable salts during the initial stages of the geochemical evolution of these waters. Their concentration changes little as major cations increase, until concentrations of Total Dissolved Solids (TDS) reach 3000 to 5000 mg 1^?1. The isotopic composition of these shallow waters reflects local, present day precipitations.In contrast to the shallow groundwaters, the isotopic and chemical compositions of the deep, saline waters and brines are determined by extensive, low-temperature rock-water interactions. This is documented in major ion chemistries, ¹⁸O contents and strontium isotopic compositions. These data indicate that the deep brines have been contained in hydrologically isolated “pockets”. The almost total loss of primary compositions make discussions on the origin of these brines very speculative. However, all brines from across the Canadian Shield have a very similar chemical composition, which probably reflects a common geochemical history. The concentrations of some major and most minor elements in these fluids appear to be governed by reactions with secondary mineral assemblages.     

Geochemical and isotopic evidence for palaeo-seawater intrusion into the south coast aquifer of Laizhou Bay, China

This research aims to improve the current knowledge of groundwater salinisation processes in coastal aquifers using combined hydrochemical and isotopic parameters and inverse hydrochemical modelling. Field investigations were conducted in Laizhou Bay, which is the area most seriously affected by seawater intrusion in north China. During three sampling campaigns along a vertical transect in the Changyi-Liutuan area, 95 ground- and surface-water samples were collected for major ion and isotope analysis (²H/¹⁸O, ³H, ¹⁴C, ³⁴S). The groundwater changes along the general flowpath towards the coast from fresh (<1 g/L), brackish (1-10 g/L), saline (10-100 g/L) to brine water (>100 g/L). Molar Cl/Br ratios are close to those of seawater in almost all groundwater samples, indicating that brines and deep seawater evolved from different events of palaeo-seawater intrusion. Depleted isotopic signatures of brines and deep saline water point to a former, initially depleted seawater reservoir due to runoff dilution. Tritium and ¹⁴C activities in deep saline water below confining units indicate isolation from modern precipitation and significant residence times. Brine water shows a wide range of ³H and ¹⁴C ages due to the complex conditions of mixing without isolation from modern groundwater. Sulphur-34 isotope ratios support seawater intrusion as a possible salt origin, although this parameter does not exclude gypsum dissolution. The combined use of Cl and ¹⁸O yields four different end-members of groundwater, and three different mixing scenarios were identified explaining the hydrochemical composition of groundwater samples with intermediate salinity in the different areas. To improve understanding of the various water types and their related processes in a spatial context, a conceptual model was developed integrating the results derived from the presented data in a vertical cross-section. Results of three inverse modelling simulations using PHREEQC-2 show that all hypothetical mixing scenarios derived from conservative components are thermodynamically feasible. In all scenarios, mixing, ion exchange, dissolution of dolomite and precipitation of gypsum and calcite account for the hydrochemical changes.     

Comparison of stable isotopes,ratios of Cl/Cl and I/I in brine and deep groundwater from the Pacific coastal region and the eastern margin of the Japan Sea

Fifty-three samples, including brines associated with oil and natural gas reservoirs and groundwater samples from deep boreholes, were collected from the Pacific and Japan Sea coastal regions in Japan. The ¹²⁹I/¹²⁷I and ³⁶Cl/Cl ratios, and stable isotopes (δD and δ¹⁸O) are compared to investigate differences related to the geotectonic settings of the two regions. The δD and δ¹⁸O data indicate that brine and groundwater from the Pacific coastal region reflect mixing of meteoric water with connate seawater in the pores of sedimentary rocks. On the other hand, brine and groundwater from the Japan Sea coastal region have been hydrothermally altered. In particular, brines associated with petroleum accumulations at Niigata and Akita showed the same isotopic characteristics as fluids found in the Kuroko deposits of the Green Tuff region in northeastern Japan. There is little difference in the ³⁶Cl/Cl ratios in brine and groundwater from the Pacific and Japan Sea coasts. Most brine and some deep groundwater, except those from the Pleistocene Kazusa Group, have already reached the average secular equilibrium ratio of 9.9 ± 2.7 × 10⁻¹⁵ for their mudstone and sandstone reservoirs. There was no correlation between the ³⁶Cl/Cl ratios and differences in geotectonic setting between the Pacific and the Japan Sea coast. The molar I/Br ratio suggests that the I in all of water samples was of biogenic origin. The average ¹²⁹I/¹²⁷I ratio was 290 ± 130 × 10⁻¹⁵ to 294 ± 105 × 10⁻¹⁵ in both regions, showing no relationship to the different geotectonic settings. The uncontaminated brine and groundwater samples are likely to have retained the original ¹²⁹I/¹²⁷I ratios of marine I released from the old organic matter stored in sedimentary rock.     

Saline waters and residual brines in the Shiraz-Sarvistan basin,Iran

Origin of saline waters in the Shiraz-Sarvistan area, Iran, is determined by a combined isotopic (¹⁸O and D) and chemical characterization. Four types are recognized: (a) fresh water of the anticlinal carbonatic aquifer; (b) fresh and brackish runoff in the synclinal basins; (c) salt springs originating through dissolution of rock salt by type (a) fresh water; and (d) residual brines formed in synclinal closed drainage basins, through evaporation of former water types and loss of the relatively less-soluble salts.     

Characterisation and isotopic evolution of saline waters of the Outokumpu Deep Drill Hole,Finland – Implications for water origin and deep terrestrial biosphere

The isotopic composition of water and dissolved Sr as well as other geochemical parameters at the 2516 m deep Outokumpu Deep Drill Hole, Finland were determined. The drill hole is hosted by Palaeoproterozoic turbiditic metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granitoids. Sodium–Ca–Cl and Ca–Na–Cl-rich waters (total dissolved solids up to ca. 70 g L⁻¹) containing significant amounts of gas, mainly CH₄ (up to 32 mmol L⁻¹), N₂ (up to 10 mmol L⁻¹), H₂ (up to 3.1 mmol L⁻¹) and He (up to 1.1 mmol L⁻¹) discharge from fracture zones into the drill hole. This water is distinct from the shallow fresh groundwater of the area, and has an isotopic composition typical of shield brines that have been modified during long-term water–rock interaction. Based on water stable isotopes and geochemistry, the drill hole water profile can be divided into five water types, each discharging from separate fracture systems and affected by the surrounding rocks. The δ²H varies from −90‰ to −56‰ (VSMOW) and δ¹⁸O from −13.5‰ to −10.4‰ (VSMOW), plotting clearly above the Global and Local Meteoric Water Lines on a δ²H vs. δ¹⁸O diagram. The ⁸⁷Sr/⁸⁶Sr ratios range between 0.72423 and 0.73668. Simple two-component mixing between ²H and ¹⁸O rich end-member brine and meteoric water cannot explain the water stable isotopic composition and trends observed. Instead, hydration of silicates by ancient groundwaters recharged under different climatic conditions, warmer than at present, is the most likely mechanism to have caused the variation of the δ²H and δ¹⁸O values. Water types correlate with changes in microbial communities implying that different ecosystems occur at different depths. The different water types and microbial populations have remained isolated from each other and from the surface for long periods of time, probably tens of millions of years.     

Geochemistry of mineral water and gases of the Razdolnoe Spa (Primorye,Far East of Russia)

New isotopic and chemical data on the sodium bicarbonate water and associated gases from the Razdolnoe Spa located in the coastal zone of Primorsky Kray of the Russian Far East, together with previous stable isotope data (δ¹⁸O, δD, δ¹³C), allow elucidation of the origin and evolution of the groundwater and gases from the spa. The water is characterized by low temperature (12 °C), TDS – 2.5–6.0 g/L, high contents of B (∼5 mg/L) and F (4.5 mg/L) and low contents of Cl and SO₄. Water isotopic composition indicates its essentially meteoric origin which may comply with an older groundwater that was recharged under different (colder) climatic conditions. Major components of bubbling gases are CH₄ (68 vol%), N₂ (28%) and CO₂ (4%). The obtained values δ¹³C and δD for CO₂ and CH₄ definitely indicate the marine microbial origin of methane. Thus the high methane content in the waters relates to the biochemical processes and presence of a dispersed organic matter in the host rocks. Based on the regional hydrogeology and the geological structure of the Razdolnoe Spa, Mesozoic fractured rocks containing Na–HCO₃ mineral water and gases are reservoir rocks, a chemical composition of water and gases originates in different environmental conditions.     

Oxygen and hydrogen isotope ratios in freshwater chert as indicators of ancient climate and hydrologic regime

The oxygen and hydrogen isotopic composition of Eocene and Miocene freshwater cherts in the western United States records regional climatic variation in the Cenozoic. Here, we present isotopic measurements of 47 freshwater cherts of Eocene and Miocene age from the Great Basin of the western United States at two different sites and interpret them in light of regional climatic and tectonic history. The large range of δ¹⁸O of terrestrial cherts measured in this study, from 11.2‰ to 31.2‰ (SMOW: Standard Mean Ocean), is shown to be primarily the result of variations in δ¹⁸O of surface water. The following trends and patterns are recognized within this range of δ¹⁸O values. First, in Cenozoic rocks of northern Nevada, chert δ¹⁸O records the same shift observed in authigenic calcite between the Eocene and Miocene that has been attributed to regional surface uplift. The consistent covariation of proxies suggests that chert reliably records and retains a signal of ancient meteoric water isotopic composition, even though our analyses show that chert formed from warmer waters (40°C) than coexisting calcite (20°C). Second, there is a strong positive correlation between δ¹⁸O and δD in Eocene age chert from Elko, Nevada and Salina, Utah that suggests large changes in lake water isotopic composition due to evaporation. Evaporative effects on lake water isotopic composition, rather than surface temperature, exert the primary control on the isotopic composition of chert, accounting for 10‰ of the 16‰ range in δ¹⁸O measured in Eocene cherts. From authigenic mineral data, we calculate a range in isotopic composition of Eocene precipitation in the north-central Great Basin of −10 to −14‰ for δ¹⁸O and −70 to −100‰ for δD, which is in agreement with previous estimates for Eocene basins of the western United States. Due to its resistance to alteration and record of variations in both δ¹⁸O and δD of water, chert has the potential to corroborate and constrain the cause of variations in isotope stratigraphies.