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1.
The possible contamination of a groundwater system with industrial wastewater originating from a paper mill factory has been investigated in Piteå, N. Sweden. Six samples were collected from the wastewater in the waste dump and twelve samples from the adjacent groundwater were analyzed for chemistry and sulfur isotopes. The industrial wastewater is a saline water consisting mainly of Na–HCO3–SO4, having a high pH and showing δ34S values between 7‰ and 9‰ affected by bacterial sulfate reduction. The groundwaters are relatively dilute, dominated by Na+, Ca2+ and HCO3−, but with varying concentrations as exemplified by sulfate with concentrations varying between 3 and 69 mg L− 1 while the δ34S values range from − 0.5‰ to 14.3‰. The data suggest that the main S sources in the waters are the bedrock sulfides and/or atmospheric deposition, which, sometimes, are overlapped by bacterial sulfate reduction. Contamination from the waste dump does not occur.  相似文献   

2.
Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ18O of − 8.3‰, δD of − 48.2‰,δ11B of 1.5‰, and 87Sr/86Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO4 type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ18O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ11B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and 87Sr/86Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO4 type water with the highest TDS (249.1 g/l, brine) and has δ18O of − 2.8‰, δD of − 45.8‰,δ11B of 21.2‰, and 87Sr/86Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ11B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.  相似文献   

3.
Individual and monthly precipitation samples from the polluted atmosphere of Bologna (Emilia-Romagna province) were collected during March 1996 to May 1997 and analyzed for major ions in solution and S isotopes in dissolved SO4.Weighted mean enrichment factors relative to seawater are found to be 1.0 for Na, 15.2 for K, 105 for Ca, 3.3 for Mg, 17.3 for SO4 and 663 for HCO−3. Very good positive correlations are observed for the Ca2+–Mg2+–HCO−3–SO2−4–NO−3 system, indicating that dissolution of Ca (±Mg)-carbonate particles by H2SO4 and HNO3 from combustion of oil and gas is a major process controlling the chemical composition of rain and snow. Na+ and Cl− in monthly precipitation derive essentially from sea spray, but the contribution of Na+ from continental sources is appreciable in a number of individual rains. NH+4 appears to be on average more abundant in spring and summer precipitation, its main sources being microbial activity in soils and application of fertilizers. K+ is probably of continental origin from soil dust.The S isotopic composition of SO4 is systematically positive, with mean δ34S values of +3.2±1.6‰ (n=40) in individual precipitation and +2.8±1.4‰ (n=12) in monthly precipitation. These isotopic compositions are interpreted in terms of a dominant contribution of S from anthropogenic emissions and subordinate contributions from biogenic and marine sources. Pollutant SO4 is estimated to have a δ34S value in the range +2.5 to +4.5‰, whereas a distinctive δ34S of −4.5‰ or lower indicates SO4 from oxidation of biogenic gases.The isotopic and chemical compositions of SO4 do not depend on wind direction, thus testifying to a mostly local source for pollutant S in the Bologna atmosphere.  相似文献   

4.
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.  相似文献   

5.
The Minqin Basin is a type area for examining stress on groundwater resources in the Gobi Desert, and has been investigated here using a combination of isotopic, noble gas and chemical indicators. The basin is composed of clastic sediments of widely differing grain size and during the past half century over 10 000 boreholes have been drilled with a groundwater decline of around 1 m a−1. Modern diffuse recharge is unlikely to exceed 3 mm a−1, as determined using unsaturated zone profiles and Cl− mass balance. A small component of modern (<50 a) groundwater is identified in parts of the basin from 3H–3He data, probably from irrigation returns. A clear distinction is found between modern waters with median δ18O values of 6.5 ± 0.5‰ and most groundwaters in the basin with more depleted isotopic signatures. Radiocarbon values as pmc range from 0.6% to 85% modern, but it is difficult to assign absolute ages to these, although a value of 20% modern C probably represents the late Pleistocene to Holocene transition. The δ13C compositions remain near-constant throughout the basin (median value of −8.1‰ δ13C) and indicate that carbonate reactions are unimportant and also that little reaction takes place. There is a smooth decrease in 14C activity accompanied by a parallel increase in 4He accumulations from S–N across the basin, which define the occurrence of a regional flow system. Noble gas temperatures indicate recharge temperatures of about 5.6 °C for late Pleistocene samples, which is some 2–3 °C cooler than the modern mean annual air temperature and the recharge temperature obtained from several Holocene samples. Groundwaters in the Minqin Basin have salinities generally below 1 g/L and are aerobic, containing low Fe but elevated concentrations of U, Cr and Se (mean values of 27.5, 5.8 and 5.3 μg L−1, respectively). Nitrate is present at baseline concentrations of around 2 mg L−1 but there is little evidence of impact of high NO3 from irrigation returns. Strontium isotope and major ion ratios suggest that silicate reactions predominate in the aquifer. The results have important implications for groundwater management in the Minqin and other water-stressed basins in NW China – a region so far destined for rapid development. The large proportion of the water being used at present is in effect being mined and significant changes are urgently needed in water use strategy.  相似文献   

6.
In this study, hydrochemical and isotope investigations were conducted in the Yanqi Basin to determine the chemical composition, and to gain insight into the groundwater recharge process in the Yanqi Basin. It mainly used hydrochemistry, environmental isotopes, and a series of comprehensive data interpretation, e.g., statistics, ionic ratios, and Piper diagram to obtain a better understanding of the functioning of the system. The following hydrochemical processes were identified as the main factors controlling the water quality of the groundwater system: weathering of silicate minerals, dissolution, ion exchange, and to a lesser extent, evaporation, which seemed to be more pronounced down gradient of the flow system. As groundwater flows from the recharge to discharge areas, chemical patterns evolve in the order of Ca2+–HCO3 ?, Ca2+/Mg2+–HCO3 ? to Ca2+–Mg2+–Cl?–SO4 2?, Na+–K+–Cl?–SO4 2? and Na+–Cl? according to lithology. The environmental isotope (δ 18O, δ 2H, 3H) measurements further revealed that precipitation was the main recharge source for the groundwater system; some local values indicated high levels of evaporation. Tritium and CFC analysis were used to estimate the ages of the different groundwater; the tritium values of the groundwater samples varied from 2.82 to 29.7 TU. The age of the groundwater at depths of <120 m is about 30–50 years. CFC values obtained for six samples to determine groundwater age; the age of the groundwater is about 20–50 years.  相似文献   

7.
Hydrochemistry of groundwater in Chithar Basin, Tamil Nadu, India was used to assess the quality of groundwater for determining its suitability for drinking and agricultural purposes. Physical and chemical parameters of groundwater such as electrical conductivity, pH, total dissolved solids (TDS), Na+, K+, Ca2+, Mg2+, Cl–, HCO3–, CO32–, SO42–, NO–3, F–, B– and SiO2 were determined. Concentrations of the chemical constituents in groundwater vary spatially and temporarily. Interpretation of analytical data shows that mixed Ca–Mg–Cl, Ca–Cl and Na–Cl are the dominant hydrochemical facies in the study area. Alkali earths (Ca2+, Mg2+) and strong acids (Cl–, SO42–) are slightly dominating over alkalis (Na+, K+) and weak acids (HCO3–, CO32–). The abundance of the major ions is as follows: Na+ Ca2+ Mg2+ > K+ = Cl– > HCO3–> SO42– > NO3– > CO32– . Groundwater in the area is generally hard, fresh to brackish, high to very high saline and low alkaline in nature. High total hardness and TDS in a few places identify the unsuitability of groundwater for drinking and irrigation. Such areas require special care to provide adequate drainage and introduce alternative salt tolerance cropping. Fluoride and boron are within the permissible limits for human consumption and crops as per the international standards.  相似文献   

8.
Groundwater samples were collected at a site in N Norfolk, UK, comprising a borehole penetrating Upper Chalk and piezometers open within the overlyinf glacial deposits and intervening, weathered Putty Chalk. The samples were analyzed for δ18O (water), δ34S and δ18O(SO4) and δ13C(HCO3) as well as major ions. Variations in solute concentration and isotopic composition with depth were found to be caused by limited groundwater circulation at the site and incomplete flushing of old groundwater. The isotopic data prove the existence of a mineralized palaeowater at depth, which has undergone SO4 reduction and is being slowly modified by mixing with recent groundwater circulating at a shallow depth in a more transmissive Chalk horizon. One measured δ18O (H2O) value of −8.25‰vsmow represents the lightest value reported for the Norfolk Chalk aquifer and is evidence for a component of Late Pleistocene recharge trapped at depth.The wide range of observed isotope ratios at the site, e.g.δ34S and δ18O SO4 between 7.8 to 27.8‰cdt and 5.2 to 20.0‰ovsmow respectively, demonstrates the importance of vertical stratification of solutes and the implications this has for interpreting spatial hydrochemical surveys of groundwater.  相似文献   

9.
The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water–rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triassic aquifer is dominated by HCO3 –, Ca2+, Mg2+ and δ13CDIC indicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has δ18O and δD values that plot near surface waters on the local and global meteoric water lines, and detectable tritium, likely reflecting recent (<50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg2+, Na+, Ca2+, K+, and Si, and has high alkalinity and δ13CDIC values, with low SO4 2– and NO3 – concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in 18O and 2H, and have 3H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer.  相似文献   

10.
The aim of this work is to evaluate the changes in groundwater chemistry in an alluvial aquifer in the Moa area. Surface and ground water, metallurgical waste and various geological material samples were collected in order to evaluate groundwater composition. The results show that the alluvial aquifer is polluted with SO42-, Mg2+and heavy metals. According to its major components in the alluvial aquifer, two types of groundwater are identified: magnesi-bicarbonated and sulphate-magnesic. Maximum SO42– and Mg2+ contents are more than 1000 mg/L, and are four times higher than the acceptable levels for human consumption of water. The high values of Cr(VI), Ni(II), Mn(II) Fe(total), SO42– and Mg2+ in alluvial aquifers are due to polluted recharge from metallurgical waste from the tailing dam. This recharge is favoured by the preferential flow due to desiccation cracks in metallurgical waste. Geochemical modelling showed that potentially toxic heavy metals might exist largely in the forms of MSO42– and M2+ in pore water of SAL metallurgical waste. All samples were supersaturated in goethite and hematite. Results from batch testing indicate that the heavy metals have two origins: natural, due to the existing ultramaphic rocks and laterites, and anthropogenic, by metallurgical waste rich in sulphate and (oxy)hydroxide minerals. These results highlight the need to locate and evaluate a new water source to supply the population of the city of Moa.  相似文献   

11.
The overexploitation of groundwater in some parts of the country induces water quality degradation. The untreated industrial effluents discharged on the surface causes severe groundwater pollution in the industrial belt of the country. This poses a problem of supply of hazard free drinking water in the rural parts of the country. There are about 80 tanneries operating in and around Dindigul town in upper Kodaganar river basin, Tamilnadu, India. The untreated effluents from the tanneries have considerably affected the quality of groundwater in this area. To assess the extent of groundwater deterioration, a detailed analysis of groundwater quality data has been carried out. The concentration of cations such as Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+) and Potassium (K+), and anions such as Bicarbonate (HCO3–), Sulphate (SO42–), Chloride (Cl–) and Nitrate (NO3–) in the groundwater have been studied. Apart from these constituents, pH, electrical conductivity (EC), total dissolved solid and total hardness (TH as CaCO3) were also studied. The correlation of these constituents with the EC has been carried out. The highest correlation is observed between EC and chloride with a correlation coefficient of 0.99. Progressive reduction in correlation coefficients for Mg2+, (Na+ + K+), Ca2+ and SO42– are observed as 0.91, 0.87, 0.86 and 0.56, respectively. It is found that the quality of groundwater in the area under investigation is deteriorated mainly due to extensive use of salt in the leather industries.  相似文献   

12.
Chemical and isotopic compositions have been measured on 62 microbial gases from Tertiary hemipelagic sediments in the Middle America Trench off Guatemala and from decaying kelp and surf grass currently accumulating in Scripps Submarine Canyon off southern California. Gases from the Middle America Trench have been generated primarily by the reduction of carbon dioxide; methane δ13C varies from −84‰ to −39‰, methane δD varies from −208‰ to −145‰, and carbon dioxide δ13 C varies from −27‰ to +28‰. Gases from Scripps Submarine Canyon have been generated primarily by acetate dissimilation; methane δ13 C varies from −63‰ to −43‰, methane δD varies from −331‰ to −280‰, and carbon dioxide δ13C varies from −17‰ to +3‰.Methane δ13C values as heavy as −40‰ appear to be uncommon for gases produced by carbon dioxide reduction and, in the Middle America Trench, are associated with unusually positive carbon dioxide δ13C values. However, based on the 25‰ intramolecular fractionation between acetate car☐yl carbon and methyl carbon estimated from the Scripps Submarine Canyon data, methane produced by acetate dissimilation may commonly have heavy δ13C values. The δD of methane derived from acetate is more negative than natural methanes from other origins. Microbial methane δD values appear to be controlled primarily by interstitial water δD and by the relative proportions of methane derived from carbon dioxide and acetate.The chemical and isotopic compositions of microbial gas and thermogenic gas overlap, making it difficult to determine the origins of many commercial natural gases from methane δ13C and C2+ hydrocarbon concentrations alone. Measurements of methane δD and carbon dioxide δ13C can provide useful additional information, and together with ethane δ13C data, help identify gases with mixed microbial and thermogenic origins.  相似文献   

13.
Cryogenic cave carbonate (CCC) represents a specific type of speleothem. Its precipitation proceeds at the freezing point and is triggered by freezing-induced concentration of solutes. Compared to classical speleothems (stalagmites, flowstones), CCC occurs as accumulations of loose uncemented aggregates. The grain sizes range from less than 1 μm to over 1 cm in diameter. Karst groundwater chemistry and its freezing rate upon entering the cave are responsible for highly variable grain morphology. Rapid freezing of water results in the formation of CCC powders with grain size typically below 50 μm. Slow freezing of water in caves (usually in systems where the CO2 escape is partly restricted; e.g., ice covered water pools) results in the formation of large mineral grains, with sizes from less than 1 mm to about 20 mm. The range of carbon and oxygen stable isotope compositions of CCC is larger than for a typical carbonate speleothem. Rapid freezing of water accompanied by a quick kinetic CO2 degassing results in large ranges of δ13C of the CCC powders (between –10‰ and +18‰ PDB). Slow freezing of water, with a restricted CO2 escape results in gradual increase of δ13C values (from −9‰ to +6‰ PDB; data ranges in individual caves are usually much more restricted), accompanied by a δ18O decrease of the precipitated carbonate (overall range from −10‰ to −24‰ PDB). These unusual trends of the carbonate δ18O evolution reflect incorporation of the heavier 18O isotope into the formed ice. New isotope data on CCC from three Romanian ice caves allow better understanding of the carbon and oxygen isotope fingerprint in carbonates precipitated from freezing of bulk water. CCCs are proposed as a new genetic group of speleothems.  相似文献   

14.
Miocene igneous rocks (diorites, andesites, dacites, rhyolites and microgranites) of Chetaibi and Cap de Fer massif, NE Algeria, are high-K calc-alkaline to shoshonitic rocks. Fresh diorites have δ34S and δ18O values ranging between −2.5‰ and +5.9‰, +6.5‰ and +6.7‰ respectively, indicating a mantle origin. The relatively low δ34S values (−5.4‰ to −12.2‰) and high δ18O (+8.3‰ to +9.0‰) of altered diorites indicate the input of a crustal component to the initial magma. The microgranites’ I-type signature is indicated by the geochemical data and the δ34S and δ18O values of −1.2‰ and −3.6‰, and +7.8‰ to +10.4‰ respectively. The andesites show a large variation of δ34S, between −33.2‰ and +25.7‰. Massive andesites with δ34S between +6.8‰ and +7.6‰ preserve a 34S-enriched mantle signature. The δ34S of the lava flows between +25.7‰ and +25.8‰ are attributed to open system magma degassing, whereas the low δ34S of two andesitic dyke samples (−13.7‰ and −33.2‰) strongly suggest a crustal sulphur input. High δ18O (+9.2‰ to +15.7‰) of andesites indicate post-magmatic alteration (mainly silicification); the flyschs with δ18O between of +13.3‰ and +21.7‰ are most likely the contaminant. Quartz veins within the andesites gave a δ18O value of +23.0‰ while silica-filling vesicles yielded a value of +13.8‰. Initial Sr-isotope data are rather high for all the rocks (diorites: 0.707–0.708, andesites: 0.707–0.710, and microgranites and rhyolites: 0.717–0.719), and because geochemical and stable isotope data do not indicate a substantial amount of crustal assimilation, an extensive enrichment of the mantle source by subducted sediments is called for. A metasomatized-mantle source, characterized by high radiogenic Sr and relatively high δ18O, has also been indicated for the genesis of similar Tertiary igneous rocks in the Western Mediterranean basin, e.g. the Volcanic Province of southeasten Spain [Benito, R., Lopez-Ruiz, J., Cebria, J.M., Hertogen, J., Doblas M., Oyarzun, R., Demaiffe, D., 1999. Sr and O isotope constraints on source and crustal contamination in the high-K calc-alkaline and shoshonitic neogene volcanic rocks of SE Spain. Lithos 46, 773–802] and some plutons of northeastern Algeria [Ouabadi, A., 1994. Pétrologie, géochimie et origine des granitoïdes peralumineux à cordiérite (Cap Bougaroun, Béni-Touffout et Filfila), Algérie nord-orientale. Thèse de Doctorat, Université de Rennes I, France, 257p; Fourcade, S., Capdevila, R., Ouabadi, A., Martineau, F., 2001. The origin and geodynamic significance of the Alpine cordierite-bearing granitoids of northern Algeria. A combined petrological, mineralogical, geochemical and isotopic (O, H, Sr, Nd) study. Lithos 57, 187–216].  相似文献   

15.
Stable carbon- and oxygen-isotope compositions of calcite and dolomite cements have been used to understand porewater evolution in the Upper Tertiary Hazeva Formation within the Dead Sea Graben, southern Israel. Sandstone samples were obtained from four boreholes in three tectonic blocks of the graben over depths of 253–6448 m, a variation that largely reflects differential subsidence of individual fault-bounded blocks. Early carbonate cements dominate diagenesis. Calcite occurs at <1600 m, but was replaced by dolomite at greater depths. Dolomite at 1600–2700 m is Fe-poor (<0.8 mol% FeCO3), and at 4700–6200 m, Fe-rich (0.5–7.2 mol% FeCO3). Magnesite, anhydrite and halite are the final diagenetic phases. Calcite has positively correlated δ18O (+21‰ to +25‰) and δ13C (−6‰ to −2‰) values that generally decrease with depth. Dolomite has a wider variation in δ18O (+18‰ to +30‰) and δ13C (−8‰ to −1‰) values, which also generally are lower with increasing depth. However, the δ13C and δ18O values of dolomite from the uppermost 400 m of the Hazeva Formation in the Sedom Deep-1 borehole are anomalous in spanning the entire range of stable carbon and oxygen isotopic compositions over this relatively small interval.The decreasing dolomite δ13C values likely indicate an increased contribution of carbon from organic sources with increasing depth. Except for the uppermost 400 m, Hazeva Formation dolomite in the Sedom Deep-1 borehole has stable carbon-isotope compositions that imply initial dolomitization at much shallower levels, prior to the preferential subsidence of this tectonic block. The oxygen isotopic compositions of the calcite cement are best explained by equilibration at present burial temperatures (≤55 °C) with porewater of meteoric origin. Its δ18O values increased from −5‰ at the shallowest depths to 0‰ at 1600 m. The dolomite oxygen isotopic compositions also reflect equilibration at present burial temperatures with porewaters ranging from 0‰ at 1600 m to +7‰ at 3600 m (100 °C). In the deepest fault block (Sedom Deep-1 borehole), however, increasingly Fe-rich dolomite has (re)equilibrated with porewater whose δ18O values decreased from +9‰ at 4750 m (120 °C) to +1‰ to +2‰ by 6200 m (150 °C).Much of the dolomite likely formed at relatively shallow depths from saline brines derived from precursors to the Dead Sea. These infiltrated the Hazeva Formation, mixing with and largely displacing meteoric water, and dolomitizing calcite. Rock–water ratios tended to be high during these processes. However, the upper 400 m of the Hazeva Formation in the deepest fault block were likely deposited during its rapid tectonic subsidence, and largely escaped the initial style of dolomitization pervasive elsewhere in the study area. These sediments were also capped by evaporites. This relatively thin interval likely became a preferential conduit for brines that escaped underlying and overlying strata, including the Fe-rich, lower 18O fluids (evolved seawater?) present in the deepest part of the graben. These rocks present the most promising target for the passage and accumulation of hydrocarbons in the study area.  相似文献   

16.
The chemical content of the Souss unconfined groundwater displays spatial variations in conductivity (between 400 and 6,000 µS cm-1). The chemical tracers (Cl-, SO42-, Sr2+, Br-), which characterize the different components of the groundwater, allowed the determination of the origin of water salinity. Cl- and SO42-, reaching respectively 2,000 and 1,650 mg L-1, display localized salinity anomalies. Br-/Cl- ratio distinguishes marine-influenced impoverished zones versus the oceanic domain. Thus, salinity anomalies can be attributed: (1) downstream, to a currently existing salt-encroachment (with added waste water) and sedimentary palaeosalinity, (2) in the middle-Souss, to High Atlas evaporites and to irrigation water recycling. Sr2+/Ca2+ ratio (evaporites if >1‰), confirms the evaporitic origin of the anomalies along the right bank of oued Souss. Furthermore, it facilitates the distinction between the different aquifer contributions (Cretaceous, Jurassic and Triassic), and it highlights leakage from deep Turonian limestones in the groundwater recharge system. To the south, recharge is from the Anti Atlas (evaporite-free) waters. Oxygen-18 measurements confirm the groundwater recharge from the High and Anti Atlas as piezometric maps and chemical tracers suggested, plus from leakage from the Turonian and the marine aquifers.  相似文献   

17.
The CO2 gas reservoir sandstones in the Hailaer Basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of CO2. The origins of dawsonite and CO2 in these sandstones were studied by petrographic and isotopic analysis. According to the paragenetic sequence of the sandstones, dawsonite grew later than CO2 charging at 110–85 Ma. The dawsonite δ18O value is 7.4‰ (SMOW), and the calculated δ18O values of the water present during dawsonite growth are from −11.4‰ to −9.2‰ (SMOW). This, combined with the NaHCO3-dominated water linked to dawsonite growth, suggests meteoric water being responsible for dawsonite growth. The δ13C values of gas phase CO2 and the ratios of 3He/4He of the associated He suggest a mantle magmatic origin of CO2-rich natural gas in Hailaer basin. Dawsonite δ13C values are −5.3‰ to −1.5‰ (average −3.4‰), and the calculated δ13C values of CO2 gas in isotopic equilibrium with dawsonite are −11.4‰ to −7.3‰. These C isotopic values are ambiguous for the dawsonite C source. From the geological context, the timing of events, together with formation water conditions for dawsonite growth, dawsonite possibly grew in meteoric-derived water, atmospherically-derived CO2 maybe, or at least the dominant, C source for dawsonite. It seems that there are few relationships between dawsonite and the modern gas phase of CO2 in the Hailaer basin.  相似文献   

18.
In the Lower Palaeozoic rocks of the Brabant Massif (Belgium), a recently discovered polysulphide mineralisation is related to a low-angle reverse shear zone. This shear zone has been attributed to the main early Devonian deformation event. Data from boreholes and outcrops allow a detailed investigation of the alteration pattern and palaeofluid flow along this shear zone. Macroscopic observations of the mineralogy and quantitative changes in the phyllosilicate mineralogy indicate that this shear zone is characterised by an envelope of intense sericitisation and silicification. In addition, chloritisation is associated with this alteration. The alteration zone may reach a thickness of 250 m. Ore mineralisation occurred synkinematically and is spatially related to the shear zone. The mineralisation consists of pyrite, marcasite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, stibnite and smaller amounts of tetrahedrite and other sulphosalts. It is concentrated in quartz–sulphide veins or occurs diffusely in the host rock. The mineralising fluids have a low-salinity H2O–CO2–CH4–NaCl–(KCl) composition and a minimum temperature of 250–320 °C. The δ18O values of quartz vary between +12.3‰ and +14.5‰ SMOW, and δD compositions of the fluid inclusions in the quartz crystals range from −65‰ to −35‰ V-SMOW. The δD and the calculated δ18O values of the mineralising fluids fall in the range typical for metamorphic fluids and partly overlap with that for primary magmatic fluids. The δ34S values, between +4.7‰ and +10.6‰ CDT, fall outside the interval typical for I-type magmas. Important migration of likely metamorphic fluids, causing a widespread alteration and a polysulphide mineralisation along a low-angle shear zone, has, thus, been identified for the first time in the Caledonian Anglo-Brabant fold belt.  相似文献   

19.
The Maastrichtian–Danian limestones of the Yacoraite Formation (northwestern Argentina) show carbon and oxygen isotopic values consistent with shallow marine conditions. The members of the formation respond to different sedimentary environments and are characterised by distinctive stable isotopes and geochemistry. The basal Amblayo Member is composed of high-energy dolomitic limestones and limestones with positive isotopic values (+2‰ δ13C, +2‰ δ18O). The top of the member reveals an isotopic shift of δ13C (−5‰) and δ18O (−10‰), probably related to a descent in the sea level. The sandy Güemes Member has isotopically negative (−2‰ δ13C, −1‰ δ18O) limestones, principally controlled by water mixing, decreased organic productivity, and compositional changes in the carbonates. The isotopically lighter limestones are calcitic, with a greater terrigenous contribution and different geochemical composition (high Si–Mn–Fe–Na, low Ca–Mg–Sr). These isotopic and lithological changes relate to the Cretaceous–Palaeogene transition. The Alemanía Member, composed of dolomitic limestones and pelites, represents a return to marine conditions and shows a gradual increase in isotopic values, reaching values similar to those of the Amblayo Member. The Juramento Member, composed of stromatolite limestones, shows isotopic variations that can be correlated with the two well-defined, shallowing-upward sequences of the member.  相似文献   

20.
Based on analysis of groundwater hydrogeochemical and isotopic data, this study aims to identify the recharge sources and understand geochemical evolution of groundwater along the downstream section of the Shule River, northwest China, including two sub-basins. Groundwater samples from the Tashi sub-basin show markedly depleted stable isotopes compared to those in the Guazhou sub-basin. This difference suggests that groundwater in the Tashi sub-basin mainly originates from meltwater in the Qilian Mountains, while the groundwater in the Guazhou sub-basin may be recharged by seepage of the Shule River water. During the groundwater flow process in the Tashi sub-basin, minerals within the aquifer material (e.g., halite, calcite, dolomite, gypsum) dissolve in groundwater. Mineral dissolution leads to strongly linear relationships between Na+ and Cl? and between Mg2++ Ca2+ and SO4 2??+?HCO3 ?, with stoichiometry ratios of approximately 1:1 in both cases. The ion-exchange reaction plays a dominant role in hydrogeochemical evolution of groundwater in the Guazhou sub-basin and causes a good linear relationship between (Mg2++ Ca2+)–(SO4 2??+?HCO3 ?) and (Na++ K+)–Cl? with a slope of ?0.89 and also results in positive chloroalkaline indices CAI 1 and CAI 2. The scientific results have implications for groundwater management in the downstream section of Shule River. As an important irrigation district in Hexi Corridor, groundwater in the Guazhou sub-basin should be used sustainably and rationally because its recharge source is not as abundant as expected. It is recommended that the surface water should be used efficiently and routinely, while groundwater exploitation should be limited as much as possible.  相似文献   

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