Stable chlorine and carbon isotope measurements of selected chlorinated organic solvents

Stable Cl and C isotope ratio results for 3 selected chlorinated solvents, perchloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA) provided by 4 different manufacturers are presented. The isotope ratio for all compounds range between −3.5 and +6.0‰ forδ³⁷Cl and from −37.2 to −23.3%. forδ¹³C. The greatest³⁷Cl difference between manufacturers is observed in the TCE samples which showδ³⁷CI values of −2.5%o for PPG, +2.43‰ for ICI and +4.4‰ for DOW. TCAs show a smaller range (−2.4 to +2.0‰), while the TCEs have slightly different³⁷Cl contents. The¹³C data show the most distinctδ¹³C values for PCEs (−23.3 for DOW, −24.1 for Vulcan, −33.8 for PPG and −37.2‰ for ICI) while both TCEs and TCAs show a smallerδ¹³C range, but still distinct differences. These preliminary data suggest that each manufacturer and solvent type may have distinctiveδ⁶³⁷Cl andδ¹³C values. These results show that by using a combination of³⁷Cl and¹³C, there is a potential to indicate a specific source of chlorinated solvents, as well as an ability to delineate contamination episodes caused by these compounds in groundwaters.     

Paleoclimatic interpretation of the past 30 ka from isotopic studies of the deep confined aquifer of the North China plain

The δ¹⁸O and δD values in the deep confined aquifer beneath the North China Plain which is located at 112°30′E–119°30′E and 34°46′N–40°25′N, reflect differences in paleoclimatic conditions between the Holocene and the late Pleistocene. Groundwater samples whose ¹⁴C ages are between 12 and 25 ka B.P have ranges of −9.4 to −11.7‰ for δ¹⁸O and −76‰ to −85‰ for δD values. These very negative δ¹⁸O and δD values reflect the cold and arid climate in the last glacial period. The temperature estimated in this period is 6–9 °C cooler than that of the present. The entire ranges of δ¹⁸O and δD values for samples with ¹⁴C dating from 7 ka B.P to present are −7.7‰ to −10.2‰ and −63‰ to −73‰, respectively. The greater δ¹⁸O and δD enrichments of these samples indicate a period of relatively humid and warm climate in the Holocene. However, the wide ranges of δ¹⁸O (−9.0‰ to −11.1‰) and δD (−66‰ to −80‰) values for samples with ¹⁴C age ranging from 12 to 7 ka B.P. imply an unstable climatic condition of rapidly increasing temperature, which marks the transition from the Pleistocene to the Holocene.     

Origin of formation waters of S-E parts of the Bohemian Massif and the Vienna basin

Deep formation waters were sampled from boreholes on the S-E slopes of the Bohemian Massif. They are NaClHCO₃ 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 δDandδ¹⁸0 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 δD in the range from −50 to −80‰ (southern flanks) and about −80‰ (northern flanks).     

Controls on the regional-scale salinization of the Ogallala aquifer,Southern High Plains,Texas, USA

An extensive saline plume (>250 km²) within the regionally important unconfined aquifer in the Neogene Ogallala Formation overlies the Panhandle oil and gas field in the Southern High Plains, Texas, USA. Relative to upgradient Ogallala water, the plume waters have δ¹⁸O (−6.7 to −8.8‰) and δD (−42 to −88‰) values that tend to be depleted and have higher Cl (>150 mg/l) and SO₄ (>75 mg/l) concentrations. Various end-member-mixing models suggest that the plume composition reflects the presence of paleowaters recharged during Middle to Late Wisconsinan time rather than salinization associated with petroleum production. Paleowaters probably mixed with salt-dissolution zone waters from the underlying Upper Permian formations before discharging upward into the Ogallala Formation. Cross-formational discharge is controlled primarily by the geometry of the underlying units, as influenced by the Amarillo uplift, pinch-out of the laterally adjoining confined aquifer in the Triassic Dockum Group, variations in the saturated thickness of the Ogallala aquifer and the presence of potential pathways related to salt dissolution.     

Evaluation of boron isotopes in halite as an indicator of the salinity of Qarhan paleolake water in the eastern Qaidam Basin,western China

In this study, nineteen brine samples from the Qarhan Salt Lake (QSL) in western China were collected and analyzed for boron (B) and chlorine (Cl) concentrations, total dissolved solids (TDS), pH values and stable B isotopic compositions. The B concentrations and δ¹¹B values of brines in the QSL range from 51.6 mg/L to 138.4 mg/L, and from +9.32‰ to +13.08‰, respectively. By comparison of B concentrations and TDS of brines in QSL with evaporation paths of brackish water, we found that B enrichment of brines primarily results from strong evaporation and concentration of Qarhan lake water. Combining with comparisons of B concentrations, TDS, pH values and δ¹¹B values of brines, previously elemental ratios (K/Cl, Mg/Cl, Ca/Cl, B/Cl) and δ¹¹B values of halite from a sediment core (ISL1A), we observe good correlations between B concentrations and TDS, TDS and pH values, pH and δ¹¹B values of brines, which demonstrate that higher B concentrations and more positive δ¹¹B values of halite indicate higher salinity of the Qarhan paleolake water as well as drier paleoclimatic conditions. Based on this interpretation of the δ¹¹B values of halite in core ISL1A, higher salinity of the Qarhan paleolake occurred during two intervals, around 46–34 ka and 26–9 ka, which are almost coincident with the upper and lower halite-dominated salt layers in core ISL1A, drier climate phases documented from the δ¹⁸O record of carbonate in core ISL1A and the paleomoisture record in monsoonal central Asia, and a higher solar insolation at 30°N. These results demonstrate that the δ¹¹B values of halite in the arid Qaidam Basin could be regarded as a new proxy for reconstructing the salinity record of paleolake water as well as paleoclimate conditions.     

Boron and lithium isotopes as groundwater tracers: a study at the Fresh Kills Landfill,Staten Island,New York,USA

A study was conducted at the Fresh Kills landfill, Staten Island, New York to investigate the use of B and Li isotopes as tracers of mixing and flow in the groundwater environment. Four end-member waters are present at the Fresh Kills: freshwater, seawater, a geochemically distinct transitional groundwater (that occurs in the zone of mixing between seawater and freshwater) and landfill leachate. The δ¹¹B and δ⁶Li values of end-member waters are distinct and have isotopic compositions that reflect the solute sources: freshwater δ¹¹B∼+30‰, δ⁶Li∼−22‰; transition zone groundwaters δ¹¹B∼+20‰, δ⁶Li∼−27‰; seawater δ¹¹B+40 to +75‰, δ⁶Li−37 to−44‰; leachate δ¹¹B∼+10‰ (δ⁶Li not determined). Those wells influenced by seawater exhibited a clear chemical mixing trend, with seawater contributions ranging from 3 to 85%. Well waters with a high percentage of seawater (>30%) had δ¹¹B values that were within 1‰ of the seawater value (+40‰), whereas a trend of increasing δ¹¹B values (+55 to +75‰) was observed for wells with a lower percentage of seawater (<30%). δ⁶Li values for well waters impacted by mixing with seawater ranged from−37 to−44‰, significantly more negative than pure seawater (−31‰). This deviation from the isotopic composition of seawater, for both δ¹¹B and δ⁶Li values, represents non-conservative behavior and is likely the result of isotopic fractionation during ion exchange reactions. The wide range of δ¹¹B and δ⁶Li values and the distinct isotopic compositions of end-member waters makes B and Li isotopes useful for recognizing solute sources, however isotopic fractionation may limit their use as simple tracers of groundwater flow and mixing.     

Combined use of 15N and 18O of nitrate and 11B to evaluate nitrate contamination in groundwater

Isotopic composition of NO₃ (δ¹⁵N_NO3 and δ¹⁸O_NO3) and B (δ¹¹B) were used to evaluate NO₃ contamination and identify geochemical processes occurring in a hydrologically complex Basin and Range valley in northern Nevada with multiple potential sources of NO₃. Combined use of these isotopes may be a useful tool in identifying NO₃ sources because NO₃ and B co-migrate in many environmental settings, their isotopes are fractionated by different environmental processes, and because wastewater and fertilizers may have distinct isotopic signatures for N and B. The principal cause of elevated NO₃ concentrations in residential parts of the study area is wastewater and not natural NO₃ or fertilizers. This is indicated by some samples with elevated NO₃ concentrations plotting along δ¹⁵N_NO3 and NO₃ mixing lines between natural NO₃ from the study area and theoretical septic-system effluent. This conclusion is supported by the presence of caffeine in one sample and the absence of samples with elevated NO₃ concentrations that fall along mixing lines between natural NO₃ and theoretical percolate below fertilized lawns. Nitrogen isotopes alone could not be used to determine NO₃ sources in several wells because denitrification blurred the original isotopic signatures. The range of δ¹¹B values in native ground water in the study area (−8.2‰ to +21.2‰) is large. The samples with the low δ¹¹B values have a geochemical signature characteristic of hydrothermal systems. Physical and chemical data suggest B is not being strongly fractionated by adsorption onto clays. δ¹¹B values from local STP effluent (−2.7‰) and wash water from a domestic washing machine (−5.7‰) were used to plot mixing lines between wastewater and native ground water. In general, wells with elevated NO₃ concentrations fell along mixing lines between wastewater and background water on plots of δ¹¹B against 1/B and Cl/B. Combined use of δ¹⁵N and δ¹¹B in the study area was generally successful in identifying contaminant sources and processes that are occurring, however, it is likely to be more successful in simpler settings with a well-characterized δ¹¹B value for background wells.     

The utilization of boron and strontium isotopes for the assessment of boron contamination of the Cecina River alluvial aquifer (central-western Tuscany,Italy)

The groundwater B concentration in the alluvial aquifer of the upper Cecina River basin in Tuscany, Italy, often exceeds the limit of 1 mg L⁻¹ set by the European Union for drinking water. On the basis of hydrogeological and geochemical observations, the main source of the B contamination of groundwater has been attributed to past releases into streams of exhausted, B-rich geothermal waters and/or mud derived from boric acid manufacturing in Larderello. The releases were discontinued 25–30 years ago.This study confirms that the B dissolved in groundwater is anthropogenic. In fact, the δ¹¹B values of groundwater B match the range −12.2‰ to −13.3‰ of the Turkish B mineral (colemanite) processed in boric acid manufacturing, in the course of which no significant isotopic effects have been observed. This isotopic tracing of the Cecina alluvial aquifer occurs just below the confluence of the Possera Creek, which carries the B releases from Larderello. Strontium isotope ratios support this conclusion.At about 18 km from the Possera Creek confluence, the groundwater δ¹¹B drops to much more negative values (−22‰ to −27‰), which are believed to be produced by adsorption–desorption interactions between dissolved B and the aquifer matrix. The δ¹¹B of B fixed in well bottom sediments shows a similar variation. At present, desorption is prevailing over adsorption because the releases of B-rich water have ceased. A theoretical model is suggested to explain the isotopic trends observed.Thus, B isotopes appear to be a powerful tool for identifying the origin of B contamination in natural waters, although isotopic effects associated with adsorption–desorption processes may complicate the picture, to some extent.     

Stable oxygen and carbon isotopes of carbonate concretions of the Miocene Yeonil Group in the Pohang Basin,Korea: Types of concretions and formation condition

Carbonate concretions in the Miocene sedimentary rocks of the Yeonil Group in the Pohang Basin (Korea) were investigated in terms of stable oxygen and carbon isotope composition to delineate the origin and associated diagenetic environment for their formation. Carbonate concretions are widely distributed in all the sedimentary rocks in the Pohang Basin, showing that the calcitic concretions are preserved within the mass-flow deposits and the dolomitic ones mostly in the hemipelagic siliceous rocks (diatomites). Concretions can be classified into four different types, on the basis of the stable isotopic signatures, each of which represents its own geochemical range.Type I concretions are calcitic and are composed of micrite to microspar. They occur in the conglomerates and sandstones which were deposited by mass flows (debris flow to turbidity current). It shows relatively lower δ¹⁸O (− 14.0 to − 9.3‰) and δ¹³C (− 19.6 to − 8.4‰) values. These concretions grew in a sulfate reducing zone under the influence of residual ambient seawater which had been significantly modified by volcanogenic sediments. Type II concretions are also calcitic, composed mostly of micrite with minor microspar and found in the sandstones. These concretions are characterized by relatively high δ¹⁸O (+ 1.8 to + 2.4‰) and variable δ¹³C (− 17.3 to − 0.4‰) values. These isotopic signatures reflect that Type II concretions formed from just beneath the sediment/water interface down to the sulfate reducing zone through the early stage of methanogenesis. Type III concretions are also calcitic, and composed largely of micrite with a minor contribution of microspar. They are observed in hemipelagic mudrocks which were deposited under the influence of mass flows. They are characterized by intermediate to high δ¹⁸O (− 4.6 to + 1.6‰) and high δ¹³C (− 1.3 to + 8.8‰) values. These concretions grew in a methanogenic zone by residual ambient seawater and/or seawater slightly modified by reaction with volcanogenic sediments. Type IV concretions are dolomite with calcite inclusion, and occur in hemipelagic siliceous rocks. These concretions are mostly composed of micrite and characterized by variable δ¹⁸O (− 9.1 to + 0.7‰) and high δ¹³C (+ 3.1 to + 17.9‰) values, suggesting formation in the methanogenic zone, although the residual ambient seawater is slightly modified by volcanogenic sediments.The same type of the concretions is widely distributed throughout the basin and always shows its own distinctive stable isotopic signature. This means that the formation of the given type depends upon the lithology and composition of host sediments that are closely related to the depositional process of the fan-delta systems regardless of their localities. Further, the different types of concretions are also found at the different, but closely spaced stratigraphic levels in the same locality, displaying the distinctive diagenetic conditions for each type. Such preservation of the unique diagenetic signatures in individual type of concretion suggests that the concretions formed in a completely closed diagenetic system. Therefore, caution should be made to simplify and generalize the diagenetic condition for the formation of any concretions in a large sedimentary basin.     

Geochemical Constraints on the Origin and Evolution of Spring Waters in the Changdu‐Lanping‐Simao Basin,Southwestern China

Chemical and isotopic data were measured for 51 leached brine springs in the Changdu-Lanping-Simao Basin (CD-LP-SM), China. The predominance of Cl and Na, saturation indices of carbonate minerals, and Na/Cl and Ca/SO4 ratios of ~1 suggest that halite, sulphate, and carbonate are the solute sources. Integration of geochemical, δ18O, and δD values suggests that springs are mainly derived from meteoric water, ice-snow melt, and water-rock interactions. B concentrations range from 0.18 to 11.9 mg/L, with δ11B values of ?4.37‰ to +32.39‰, indicating a terrestrial source. The δ11B-B relationships suggest B sources of crustal origin (marine carbonates with minor crust-derived volcanics); we did not identify a marine or deep mantle origin. The δ11B values of saline springs (+4.61‰ to +32.39‰) exceed those of hot (?4.37‰ to +4.53‰) and cold (?3.47‰ to +14.84‰) springs; this has contributed to strong water-rock interactions and strong saturation of dissolved carbonates. Conversely, the global geothermal δ11B-Cl/B relationship suggests mixing of marine and non-marine sources. The δ11B-Cl/B relationships of the CD-LP-SM are similar to those of the Tibet geothermal belt and the Nangqen Basin, indicating the same B origin. These differ from thermal waters controlled by magmatic fluids and seawater, suggesting that B in CD-LP-SM springs has a crustal origin.     

Characterisation of chlorinated hydrocarbons from chlorine and carbon isotopic compositions: scope of application to environmental problems

A set of chlorinated hydrocarbons (TCE, PCE, DCM, 1,1,1-TCA, chloroform) provided by four manufacturers has been isotopically characterised for both C and Cl, using a new sensitive method. A very large range of δ¹³C (from −51.66 to −24.07‰/PDB) associated with a very large range of δ³⁷Cl (from −2.7 to +3.4‰/SMOC) was obtained. This range of δ³⁷Cl is much larger than that of inorganic Cl (±1‰ SMOC) and most individual solvents show a very distinct δ³⁷Cl compared to inorganic Cl isotopic signatures. Moreover, δ³⁷Cl/δ¹³C pairs are distinct from one solvent/manufacturer to another. In a δ¹³C versus δ³⁷Cl diagram, δ³⁷Cl / δ¹³C pairs show different trends for the products of a single manufacturer compared to another. This suggests that Cl isotopic compositions are probably highly fractionated during organic synthesis. The δ³⁷Cl values can be interpreted in terms of the probable manufacturing processes. Unlike the data published previously, with one exception, all the new results for samples reported here have positive δ³⁷Cl values which might differentiate natural Cl from that derived from degradation. This method has significant potential as a tool for investigating environmental pollution problems; in particular, it offers the possibility for validating models of transport and fate of pollutants.     

Br/Cl ratios and O, H, C, and B isotopic constraints on the origin of saline waters from eastern Canada

Saline groundwaters were recovered from undisturbed (Restigouche deposit) and active (Brunswick #12 mine) Zn-Pb volcanogenic massive sulfide deposits in the Bathurst Mining Camp (BMC), northern New Brunswick, Canada. These groundwaters, along with fresh to brackish meteoric ground and surface waters from the BMC, have been analyzed to determine their major, trace element and stable isotopic (O, H, C, and B) compositions. Saline groundwaters (total dissolved solids = 22-45 g/L) are characterized by relatively high Na/Ca ratios compared to brines from the Canadian Shield and low Na/Cl_molar and δ¹¹B isotopic compositions (−2.5‰ to 11.1‰) compared to seawater. Although saline waters from the Canadian Shield commonly have oxygen and hydrogen isotopic compositions that plot to the left of the global meteoric water line, those from the BMC fall close to the water line. Fracture and vein carbonate minerals at the Restigouche deposit have restricted carbon isotopic compositions of around −5‰ to −6‰. The carbon isotopic compositions of the saline waters at the Restigouche deposit (+12‰ δ¹³C_DIC) are the result of fractionation of dissolved inorganic carbon by methanogenesis. We suggest that, unlike previous models for shield brines, the composition of saline waters in the BMC is best explained by prolonged water-rock reaction, with no requirement of precursor seawater. We suggest that elevated Br/Cl ratios of saline waters compared to seawater may be explained by differential uptake of Br and Cl during groundwater evolution through water-rock reaction.     

Integration of geochemical and isotopic tracers for elucidating water sources and salinization of shallow aquifers in the sub-Saharan Drâa Basin,Morocco

In the arid sub-Saharan of southern Morocco, groundwater salinization poses a direct threat for agricultural production in six oases’ basins that are irrigated by water imported from the High Atlas Mountains. Here the geospatial distribution of salinity is evaluated in shallow groundwater, springs and surface waters in the Drâa Basin, integrating major and trace element geochemistry and isotopic tracers (O, H, Sr and B). The data show that water discharge from the High Atlas Mountains to the Upper section of the Drâa Basin is characterized by both low and high salinity, a distinctive low δ¹⁸O and δ²H composition (as low as −9‰ and −66‰, respectively), typical for meteoric water from high elevation, a ⁸⁷Sr/⁸⁶Sr range of 0.7078–0.7094, and δ¹¹B of 12–17‰. The Ca–Mg–HCO₃, Na–Cl–SO₄, and Ca–SO₄ compositions as well as the Br/Cl, ⁸⁷Sr/⁸⁶Sr, and δ¹¹B values of the saline water suggest dissolution of Lower Jurassic carbonates and evaporite rocks in the High Atlas Mountain catchment. Storage and evaporation of the imported water in a man-made open reservoir causes an enrichment of the stable isotope ratios with a δ¹⁸O/δ²H slope of <8 but no change in the Sr and B isotope fingerprints. Downstream from the reservoir, large salinity variations were documented in the shallow groundwater from the six Drâa oases, with systematically higher salinity in the three southern oases, up to 12,000 mg/L. The increase of the salinity is systematically associated with a decrease of the Br/Cl ratio, indicating that the main mechanism of groundwater salinization in the shallow aquifers in the Drâa oases is via salt dissolution (gypsum, halite) in the unsaturated zone. Investigation of shallow groundwater that flows to the northern Drâa oases revealed lower salinity (TDS of 500–4225) water that is characterized by depleted ¹⁸O and ²H (as low as −9‰ and −66‰, respectively) and higher ⁸⁷Sr/⁸⁶Sr ratios (∼0.7107–0.7115) relative to irrigation water and groundwater flow from the Upper Drâa Basin. This newly-discovered low-saline groundwater with a different isotopic imprint flows from the northeastern Anti-Atlas Jabel Saghro Mountains to the northern oases of the Lower Drâa Basin. This adjacent subsurface flow results in a wide range of Sr isotope ratios in the shallow oases groundwater (0.7084–0.7131) and appears to mitigate salinization in the three northern Drâa oases. In contrast, in the southern oases, the higher salinity suggests that this mitigation is not as affective and increasing salinization through cycles of water irrigation and salt dissolution appears inevitable.     

Metallogenesis and ore-forming time of the Changtuxili Mn–Ag–Pb–Zn deposit in Inner Mongolia: Evidence from C–O–S isotopes and U–Pb geochronology

This paper reports new geochronological (U–Pb) and isotope (C, O, and S) data to investigate the timing of mineralization and mode of ore genesis for the recently discovered Changtuxili Mn–Ag–Pb–Zn deposit, located on the western slopes of the southern Great Hinggan Range in NE China. The mineralization is hosted by intermediate–acidic lavas and pyroclastic rocks of the Baiyingaolao Formation. Three stages of mineralization are identified: quartz–pyrite (Stage I), galena–sphalerite–tetrahedrite–rhodochrosite (Stage II), and quartz–pyrite (Stage III). δ¹³C and δ¹⁸O values for carbonate from the ore vary from −8.51‰ to −4.96‰ and 3.97‰ to 15.90‰, respectively, which are indicative of a low-temperature alteration environment. δ³⁴S_V-CDT values of sulfides range from −1.77‰ to 4.16‰ and show a trend of equilibrium fractionation (δ³⁴S_Py ​> ​δ³⁴S_Sp ​> ​δ³⁴S_Gn). These features indicate that pyrite, sphalerite, and galena precipitated during the period of mineralization. The alteration mineral assemblage and isotope data indicate that the weakly acidic to weakly alkaline ore-forming fluid was derived largely from meteoric water and the ore-forming elements C and S originated from magma. During the mineralization, a geochemical barrier was formed by changes in the pH of the ore-forming fluid, leading to the precipitation of rhodochrosite. On the basis of the mineralization characteristics, new isotope data, and comparison with adjacent deposits, we propose that the Changtuxili Mn–Ag–Pb–Zn deposit is an intermediate-to low-sulfidation epithermal deposit whose formation was controlled by fractures and variability in the pH of the ore-forming fluid. The surrounding volcanic rocks yield zircon U–Pb ages of 160−146 ​Ma (Late Jurassic), indicating that the mineralization is younger than 146 ​Ma.     

Combining boron isotopes and carbamazepine to trace sewage in salinized groundwater: A case study in Cap Bon,Tunisia

The Korba aquifer on the east coast of Cape Bon has been overexploited since the 1960s with a resultant reversal of the hydraulic gradient and a degradation of the quality due to seawater intrusion. In 2008 the authorities introduced integrated water resources planning based on a managed aquifer recharge with treated wastewater. Water quality monitoring was implemented in order to determine the different system components and trace the effectiveness of the artificial recharge. Groundwater samples taken from recharge control piezometers and surrounding farm wells were analyzed for their chemical contents, for their B isotopes, a proven tracer of groundwater salinization and domestic sewage, and their carbamazepine content, an anti-epileptic known to pass through wastewater treatment and so recognized as a pertinent tracer of wastewater contamination. The system equilibrium was permanently disturbed by the different temporal dynamics of continuous processes such as cation exchange, and by threshold processes linked to oxidation–reduction conditions. The B isotopic compositions significantly shifted back-and-forth due to mixing with end-members of various origin. Under the variable contribution of meteoric recharge, the Plio-Quaternary groundwater (δ¹¹B of 35–40.6‰, a mean B concentration of 30 μmol/L, no carbamazepine, n = 7) was subject to seawater intrusion that induced a high δ¹¹B level (δ¹¹B of 41.5–48.0‰, a mean B concentration of 36 μmol/L, and n = 8). Fresh groundwater (δ¹¹B of 19.89‰, B concentration of 2.8 μmol/L, no carbamazepine) was detected close to the recharge site and may represent the deep Miocene pole which feeds the upper Plio-Quaternary aquifer. The managed recharge water (δ¹¹B of 10.67–13.8‰, n = 3) was brackish and of poor quality with a carbamazepine content showing a large short term variability with an average daily level of 328 ± 61 ng/L. A few piezometers in the vicinity of the recharge site gradually acquired a B isotopic composition close to the wastewater signature and showed an increasing carbamazepine content (from 20 to 910 ng/L). The combination of B isotopic signatures with B and carbamazepine contents is a useful tool to assess sources and mixing of treated wastewaters in groundwaters. Effluent quality needs to be greatly improved before injection to prevent further degradation of groundwater quality.     

Groundwater recharge,circulation and geochemical evolution in the source region of the Blue Nile River,Ethiopia

Geochemical and environmental isotope data were used to gain the first regional picture of groundwater recharge, circulation and its hydrochemical evolution in the upper Blue Nile River basin of Ethiopia. Q-mode statistical cluster analysis (HCA) was used to classify water into objective groups and to conduct inverse geochemical modeling among the groups. Two major structurally deformed regions with distinct groundwater circulation and evolution history were identified. These are the Lake Tana Graben (LTG) and the Yerer Tullu Wellel Volcanic Lineament Zone (YTVL). Silicate hydrolysis accompanied by CO₂ influx from deeper sources plays a major role in groundwater chemical evolution of the high TDS Na–HCO₃ type thermal groundwaters of these two regions. In the basaltic plateau outside these two zones, groundwater recharge takes place rapidly through fractured basalts, groundwater flow paths are short and they are characterized by low TDS and are Ca–Mg–HCO₃ type waters. Despite the high altitude (mean altitude ∼2500 masl) and the relatively low mean annual air temperature (18 °C) of the region compared to Sahelian Africa, there is no commensurate depletion in δ¹⁸O compositions of groundwaters of the Ethiopian Plateau. Generally the highland areas north and east of the basin are characterized by relatively depleted δ¹⁸O groundwaters. Altitudinal depletion of δ¹⁸O is 0.1‰/100 m. The meteoric waters of the Blue Nile River basin have higher d-excess compared to the meteoric waters of the Ethiopian Rift and that of its White Nile sister basin which emerges from the equatorial lakes region. The geochemically evolved groundwaters of the YTVL and LTG are relatively isotopically depleted when compared to the present day meteoric waters reflecting recharge under colder climate and their high altitude.     

Characterization of the hydrogen isotopic composition of individual n-alkanes in terrestrial source rocks

In order to characterize the H isotopic compositions of individual lipid compounds from different terrestrial depositional environments, the δD values of C-bound H in individual n-alkanes from typical terrestrial source rocks of the Liaohe Basin and the Turpan Basin, China, were measured using gas chromatography–thermal conversion–isotope ratio mass spectrometry (GC–TC–IRMS). The analytical results indicate that the δD values of individual n-alkanes in the extracts of terrestrial source rocks have a large variation, ranging from −140‰ to −250‰, and are obviously lighter than the δD of marine-sourced n-alkanes. Moreover, a trend of depletion in ²H(D) was observed for individual n-alkanes from different terrestrial depositional environments, from saline lacustrine to freshwater paralic lacustrine, and to swamp. For example, the δD values of n-alkanes from a stratified saline lacustrine environment vary from −140‰ to −200‰, δD for n-alkanes from swamp facies range from −200‰ to −250‰, while those from freshwater paralic lacustrine–lacustrine environments fall between the δD values of the end members. The shift toward lighter δD from saltwater to freshwater environments indicates that the source water δD is the major controlling factor for the H isotopic composition of individual compounds. In addition, H exchange between formation water and sedimentary organic matter may possibly be important in regard to the δD of individual n-alkanes. Therefore, other lines of geochemical evidence must be considered when depositional paleoenvironments of source rocks are reconstructed based on the H isotopic composition of individual n-alkanes.     

The Cipoeiro gold deposit,Gurupi Belt,Brazil: Geology,chlorite geochemistry,and stable isotope study

The Cipoeiro gold deposit, located in the Gurupi Belt, northern Brazil, is hosted by tonalites of 2148 Ma. The deposit is controlled by splays related to the major strike-slip Tentugal shear zone, and at the deposit scale, the mineralization is confined to ductile–brittle shear zones. Mineralization style comprises thick quartz veins and narrow and discontinuous quartz-carbonate veinlets associated with disseminations in altered host rocks. The postmetamorphic hydrothermal paragenesis is composed of quartz, calcite, chlorite, white mica (phengite), pyrite, and minor albite. Electron microprobe analysis of chlorites reveals a relatively uniform chemical composition at depths of more than 100 m. The chlorites are characterized by (Fe + Mg) ratios between 0.37 and 0.47 and Al^IV ranging between 2.22 and 2.59 a.p.f.u. and are classified as Fe-chlinochlore. Temperatures calculated by applying the Al^IV contents of chlorites yield a relatively narrow interval of 305 ± 15°C. Stable isotope (O, H, C, S) compositions have been determined in silicate, carbonate, and sulfide minerals. The δ¹⁸O and δD values of the mineralizing fluid range from +2.4 to +5.7 and from −43‰ to −20‰, respectively, and are interpreted as having a metamorphic origin. The δ¹³C values of fluid CO₂ are in the range −10.7‰ to −3.9‰, whereas the fluid δ³⁴S is around 0‰. Carbon and sulfur compositions are not diagnostic of their sources, compatible as they are with mantle, magmatic, or average crustal reservoirs. The hydrothermal paragenesis, chlorite–pyrite coexistence, temperature of ore formation, and sulfur isotope evidence indicate relatively reduced fO₂ conditions for the mineralizing fluid. Geologic, chemical, and isotopic characteristics of the Cipoeiro deposit are compatible with the class of orogenic gold deposits.     

δ13C values of coal-derived PAHs from different processes and their application to source apportionment

The ¹³C/¹²C isotopic ratios for coal-derived polycyclic aromatic hydrocarbons (PAHs) from a number of processes encompassing low and high temperature carbonisation, gasification and combustion have been determined using gas chromatography–isotope ratio mass spectrometry (δ¹³C GC–IRMS). The results, in conjunction with those for PAHs released under controlled laboratory pyrolysis conditions, indicate that the primary control on the isotopic values of coal-derived PAHs is likely to be the extent of ring growth required to form PAHs during processing. Thus, for relatively mild conversion processes such as low temperature carbonisation where the major aromatics are alkyl substituted 2–3 ring PAHs, the isotopic signatures are similar to those of the parent coals (−24 to −25‰ for UK bituminous coals). However, the δ¹³C values for the PAHs become lighter in going to high temperature carbonisation (−25 to −27‰), gasification (−27 to −29‰ for old Town gas plants in the UK) and combustion (−29 to −31‰) as the extent of ring condensation increases and confirming that the PAHs are not released as primary volatiles. To demonstrate the potential of applying these differences to source apportion environmental PAHs where major inputs from coals can be expected, soil and vegetation samples taken close to a low temperature carbonisation plant (Bolsover, North Derbyshire) have been analysed. In addition to low temperature coal tar, significant inputs of PAHs from transport fuels, high temperature carbonisation and possibly combustion (coal/biomass) have been inferred from the isotopic ratios, taken in conjunction with the differences in alkyl substitution patterns.     

Stable isotopic signatures of the modern land snail Eremina desertorum from a low-latitude (hot) dry desert—A study from the Petrified Forest,New Cairo,Egypt

This study was conducted on recent desert samples—including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum—which were collected at several altitudes (316–360 m above sea level) from a site in the New Cairo Petrified Forest. The soils and shell_{E. desertorum} were analyzed for carbonate composition and isotopic composition (δ¹⁸O, δ¹³C). The plants and organic matter_{E. desertorum} were analyzed for organic carbon content and δ¹³C. The soil carbonate, consisting of calcite plus minor dolomite, has δ¹⁸O values from −3.19 to −1.78‰ and δ¹³C values −1.79 to −0.27‰; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon δ¹³C values: −26.51 to −25.36‰ for C3-type, and −13.74 to −12.43‰ for C4-type plants.The carbonate of the shell_{E. desertorum} is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (δ¹⁸O_mean = −0.28 ± 0.22‰; δ¹³C_mean = −4.46 ± 0.58‰). Most of the δ¹⁸O values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matter_{E. desertorum} varies only slightly in bulk organic carbon δ¹³C values (−21.78 ± 1.20‰) and these values suggest that the snail consumed more of C3-type than C4-type plants. The overall offset in δ¹³C values (−17.32‰) observed between shell_{E. desertorum} carbonate and organic matter_{E. desertorum} exceeds the value expected for vegetation input, and implies that 30% of carbon in the shell_{E. desertorum} carbonate comes from the consumption of limestone material.