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1.
The eastern Alaska Beaufort Sea coast is characterized by numerous shallow (2–5 m) estuarine lagoons, fed by streams and small rivers that drain northward from the Brooks Range through the arctic coastal plain, and bounded seaward by barrier islands and shoals. Millions of birds from six continents nest and forage during the summer period in this region using the river deltas, lagoons, and shoreline along with several species of anadromous and marine fish. We examined biogeochemical processes linking the benthic community to the overall food web structure of these poorly studied but pristine estuaries, which are largely covered by 1.8 m of ice for 10 months annually. In summer, these lagoons are relatively warm with brackish salinities (5–10°C, S = 10–25) compared to more open coastal waters (0–5°C, S > 27). The stable isotopic composition of organic materials in sediments (i.e., benthic particulate organic matter) and water column suspended particulate organic matter from both streams and lagoons are largely indistinguishable and reflect strong terrestrial contributions, based upon δ13C and δ15N values (−25.6‰ to −27.4‰ and 1.4‰ to 3.3‰, respectively). By comparison, shifts toward more heavy isotope-enriched organic materials reflecting marine influence are observed on the adjacent coastal shelf (−24.8‰ to −25.4‰ and 3.4‰ to 5.3‰, respectively). The isotopic composition of lagoon fauna is consistent with a food web dominated by omnivorous detritovores strongly dependent on microbial processing of terrestrial sources of carbon. Biomagnification of 15N in benthic organisms indicate that the benthic food web in lagoons support up to four trophic levels, with carnivorous gastropod predators and benthic fishes (δ15N values up to 14.4‰) at the apex.  相似文献   

2.
Measurements of15N/14N in dissolved molecular nitrogen (N2), nitrate (NO 3 − ) and nitrous oxide (N2O) and18O/16O in N2O [expressed as δ15N and δ18O, relative to atmospheric N2 and oxygen (O2), respectively] have been made in water column at several locations in the Arabian Sea, a region with one of the thickest and most intense O2 minima observed in the open ocean. Microbially-mediated reduction of NO 3 − to N2 (denitrification) in the oxygen minimum zone (OMZ) appears to greatly affect the natural isotopic abundances. The δ15N of NO 3 − increases from 6‰ in deep waters (2500 m) to 15‰ within the core of the denitrifying layer (250–350 m); the δ15N of N2 concurrently decreases from 0.6‰ to 0.20‰ Values of the isotopic fractionation factor (ε) during denitrification estimated using simple advection-reaction and diffusion-reaction models are 22‰ and 25‰, respectively. A strong decrease in δ15N of NO 3 − is observed from ∼ 200m (> 11‰) to 80m (∼ 6‰); this is attributed to the input of isotopically light nitrogen through nitrogen fixation. Isotopic analysis of N2O reveals extremely large enrichments of both15N and18O within the OMZ, presumably due to the preferential reduction of lighter N2O to N2. However, isotopically light N2O is observed to accumulate in high concentrations above the OMZ indicating that the N2O emitted to the atmosphere from this region cannot be very heavy. The isotope data from the intense upwelling zone off the southwest coast of India, where some of the highest concentrations of N2O ever found at the sea surface are observed, show moderate depletion of15N, but slight enrichment of18O relative to air. These results suggest that the ocean-atmosphere exchange cannot counter inputs of heavier isotopes (particularly18O) associated with the stratospheric back flux, as proposed by previous workers. This calls for additional sources and/or sinks of N2O in the atmosphere. Also, the N2O isotope data cannot be explained by production through either nitrification or denitrification, suggesting a possible coupling between the two processes as an important mechanism of N2O production.  相似文献   

3.
The sedimentary succession of Gallocanta lake, a closed saline lake located in the Iberian Range (NE Spain), documents two successive lacustrine stages: (1) brackish lake stage and (2) shallow saline lake stage. The saline stage corresponds to the present-day situation in which the lake water properties are mainly controlled by a strongly negative annual water balance. The carbonates of the brackish lake stage have relatively constant δ18O values, however, they are rather high (δ18ODo = 2.4‰ and δ18OCc = 4.5‰ mean values) suggesting a hydrologically closed lake with a long residence time of the waters. δ18O values of carbonates from the saline stage vary greatly, and are lighter than in the previous stage (δ18ODo = 0.5‰, δ18OCc = −0.7‰, δ18OMgs = −2.3‰ mean values). These carbonates also precipitated in a hydrologically closed lake, but in equilibrium with a lake water of more variable isotopic composition. The δ13C values for carbonates of both stages reflect a mixing of different pools of carbon, but during saline stage δ13C values have been more controlled by the equilibrium of the lake waters with atmospheric CO2. During the current stage, calcite and dolomite precipitate in Gallocanta lake mainly during spring and summer, although dolomite precipitation is more favoured towards the summer. Magnesite precipitates at the beginning of autumn, when the first rainfall re-dissolves the saline surface crust, producing saline waters with a high Mg2+ content. The isotopic composition of lake waters sampled in 2005 are far higher than those calculated from the carbonates. It is considered that this could be due to two factors: either because there have not been many extremely dry years (like the year 2005) during the development of the lake, or because the physical and chemical characteristics of the lake waters in such conditions are not appropriate for the development of these minerals.  相似文献   

4.
The Oylat spa is located 80 km southeast of Bursa and 30 km south of Ineg?l in the Marmara region. With temperature of 40°C and discharge of 45 l/s, the Oylat main spring is the most important hot water spring of the area. Southeast of the spa the Forest Management spring has a temperature of 39.4°C and discharge of 2 l/s. The G?z spring 2 km north of the spa, which is used for therapy of eye disease, and cold waters of the Saadet village springs with an acidic character are the further important water sources of the area. EC values of Main spring and Forest Management hot spring (750–780 μS/cm) are lower than those of Saadet and G?z spring waters (2,070–1,280 μS/cm) and ionic abundances are Ca > Na + K > Mg and SO4 > HCO3 > Cl. The Oylat and Sızı springs have low Na and K contents but high Ca and HCO3 concentrations. According to AIH classification, these are Ca–SO4–HCO3 waters. Based on the results of δ18O, 2H and 3H isotope analyses, the thermal waters have a meteoric origin. The meteoric water infiltrates along fractures and faults, gets heated, and then returns to surface through hydrothermal conduits. Oylat waters do not have high reservoir temperatures. They are deep, circulating recharge waters from higher enhanced elevations. δ13CDIC values of the Main spring and Forest Management hot spring are −6.31 and −4.45‰, respectively, indicating that δ13C is derived from dissolution of limestones. The neutral pH thermal waters are about +18.7‰ in δ34S while the sulfate in the cold waters is about +17‰ (practically identical to the value for the neutral pH thermal waters). However, the G?z and Saadet springs (acid sulfate waters) have much lower δ34S values (~+4‰).  相似文献   

5.
Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO3 type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO4 chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ18O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ18O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and regional flow regimes gets older towards the basins` margin with coeval enrichment in F− and depletion in NO3 −. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic fluoride. The basins salinization is still at an early stage.  相似文献   

6.
To characterize the isotopic composition of organisms at the base of the food web and the controls on their variability, the concentration and δ13C isotopic composition of dissolved inorganic carbon (DIC) and plankton δ13C, δ15N, and δ34S were measured. The measurements were made during periods of high and low river flow in Apalachicola Bay, Florida, United States, over 3 yr. DIC concentration and δ13C values were related to salinity, indicating that conservative mixing of riverine and marine waters was responsible for the overall distributions. The usefulness of DIC δ13C data for characterizing the trophic processes within the estuary was dependent upon the residence time of water within the season. Plankton δ13C values varied from −22‰ to −30‰ and were directly related to estuarine DIC δ13C, offset by a factor of roughly −20‰. This offset factor varied with salinity. Values of δ34S in estuarine plankton (station means ranged from 11.4‰ to 13.1‰) were depleted relative to marine plankton (17.7±0.4‰) possibly due to the admixture of34S-depleted sedimentary sulfide with estuarine samples. Values of δ34S in plankton were not related to δ13C values of plankton and were only weakly correlated to the salinity of the water from which the plankton were collected, indicating that marine sulfate was the primary source of planktonic sulfur. Values of δ15N in plankton varied from 5.5‰ to 10.7‰ and appeared related to dominance of the sample by phytoplankton or zooplankton. Estuarine plankton was15N enriched relative to offshore plankton and estuarine sediment.  相似文献   

7.
In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment. In addition, mangrove leaves and particulate organic matter were collected and measured for δ13C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ13C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ13C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ13C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ13C values in mangrove sediments. However, the shifts of δ13C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with values of C/N > 12 and δ13C < −25‰, and C/N < 12 and δ13C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ13C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ13C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ13C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ13C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem.  相似文献   

8.
The Eastern Iberian Central System has abundant ore showings hosted by a wide variety of hydrothermal rocks; they include Sn-W, Fe and Zn-(W) calcic and magnesian skarns, shear zone- and episyenite-hosted Cu-Zn-Sn-W orebodies, Cu-W-Sn greisens and W-(Sn), base metal and fluorite-barite veins. Systematic dating and fluid inclusion studies show that they can be grouped into several hydrothermal episodes related with the waning Variscan orogeny. The first event was at about 295 Ma followed by younger pulses associated with Early Alpine rifting and extension and dated near 277, 150 and 100 to 20 Ma, respectively (events II–IV). The δ18O-δD and δ34S studies of hydrothermal rocks have elucidated the hydrological evolution of these systems. The event I fluids are of mixed origin. They are metamorphic fluids (H2O-CO2-CH4-NaCl; δ18O=4.7 to 9.3‰; δD ab.−34‰) related to W-(Sn) veins and modified meteoric waters in the deep magnesian Sn-W skarns (H2O-NaCl, 4.5–6.4 wt% NaCl eq.; δ18O=7.3–7.8‰; δD=−77 to −74‰) and epizonal shallow calcic Zn-(W) and Fe skarns (H2O-NaCl, <8 wt% NaCl eq.; δ18O=−0.4 to 3.4‰; δD=−75 to −58‰). They were probably formed by local hydrothermal cells that were spatially and temporally related to the youngest Variscan granites, the metals precipitating by fluid unmixing and fluid-rock reactions. The minor influence of magmatic fluids confirms that the intrusion of these granites was essentially water-undersaturated, as most of the hydrothermal fluids were external to the igneous rocks. The fluids involved in the younger hydrothermal systems (events II–III) are very similar. The waters involved in the formation of episyenites, chlorite-rich greisens, retrograde skarns and phyllic and chlorite-rich alterations in the shear zones show no major chemical or isotopic differences. Interaction of the hydrothermal fluids with the host rocks was the main mechanism of ore formation. The composition (H2O-NaCl fluids with original salinities below 6.2 wt% NaCl eq.) and the δ18O (−4.6 to 6.3‰) and δD (−51 to −40‰) values are consistent with a meteoric origin, with a δ18O-shift caused by the interaction with the, mostly igneous, host rocks. These fluids circulated within regional-scale convective cells and were then channelled along major crustal discontinuities. In these shear zones the more easily altered minerals such as feldspars, actinolite and chlorite had their δ18O signatures overprinted by low temperature younger events while the quartz inherited the original signature. In the shallower portions of the hydrothermal systems, basement-cover fluorite-barite-base metal veins formed by mixing of these deep fluids with downwards percolating brines. These brines are also interpreted as of meteoric origin (δ18O< ≈ −4‰; δD=−65 to −36‰) that leached the solutes (salinity >14 wt% NaCl eq.) from evaporites hosted in the post-Variscan sequence. The δD values are very similar to most of those recorded by Kelly and Rye in Panasqueira and confirm that the Upper Paleozoic meteoric waters in central Iberia had very negative δD values (≤−52‰) whereas those of Early Mesozoic age ranged between −65 and −36‰. Received: 9 June 1999 / Accepted: 19 January 2000  相似文献   

9.
The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia. Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160℃. Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are -3.0‰– -8.75‰ and -55.8‰– -71.3‰, respectively, reflecting the characteristics of mixed fluid of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and -77‰, respectively, showing the characteristics of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are -8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source. Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic sandstones, thus providing necessary energy for the formation of uranium ores.  相似文献   

10.
We measured fluxes of NH4+ and NO3− and δ15N of NH4+, sediment, and porewater NH4+ from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH4+ flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not differ along the estuary. The δ15N of regenerated NH4+ ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰. Based on differences between the δ15N of regenerated NH4+ and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after remineralization of NH4+. Differences between the δ15N of regenerated NH4+ and the δ15N of porewater NH4+ provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH4+ underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification, NH4+ flux released 1.4 mol N m−2 year−1 to the water column and could provide 42% of phytoplankton nitrogen requirements.  相似文献   

11.
The aim of this study was to determine geochemical properties of groundwater and thermal water in the Misli Basin and to assess thermal water intrusion into shallow groundwater due to over-extraction. According to isotope and hydrochemical analyses results, sampled waters can be divided into three groups: cold, thermal, and mixed waters. Only a few waters reach water–rock chemical equilibrium. Thermal waters in the area are characterized by Na+–Cl−–HCO3−, while the cold waters by CaHCO3 facies. On the basis of isotope results, thermal waters in the Misli basin are meteoric origin. In particular, δ18O and δ2H values of shallow groundwater vary from −10.2 to −12.2‰ and −71.2 to −82‰, while those of thermal waters range from −7.8 to −10.1‰ and from −67 to −74‰, respectively. The tritium values of shallow groundwater having short circulation as young waters coming from wells that range from 30 to 70 m in depth vary from 10 to 14 TU. The average tritium activity of groundwater in depths more than 100 m is 1.59 ± 1.16, which indicates long circulation. The rapid infiltration of the precipitation, the recycling of the evaporated irrigation water, the influence of thermal fluids and the heterogeneity of the aquifer make it difficult to determine groundwater quality changes in the Misli Basin. Obtained results show that further lowering of the groundwater table by over-consumption will cause further intrusion of thermal water which resulted in high mineral content into the fresh groundwater aquifer. Because of this phenomenon, the concentrations of some chemical components which impairs water quality in terms of irrigation purposes in shallow groundwaters, such as Na+, B, and Cl−, are highy probably expected to increase in time.  相似文献   

12.
Natural gases of shallow reservoirs with the carbon isotopic compositions of methane ranging from -50‰ to -60‰ (PDB) were considered as mixed gases of biogenic and thermogenic origins previously and some of them were considered as low-mature (or low temperature thermogenic) gases lately. In this paper natural gases with the carbon isotopic compositions of methane in the above range were identified using the molecular and stable carbon isotopic compositions of methane, ethane and propane. The mixed gases of biogenic and mature thermogenic origins display the characteristics of δ 13 C1 ranging from -50‰to -60‰,δ13C2 ＞ -35‰,Δvalues (δ13C3 -δ13C2) ＜ 5‰ and C1/∑C2 ratios ＜ 40. Immature to low-mature gases display the characteristics of δ 13 C1 ranging from - 50‰ to - 60‰, δ13 C2 ＜- 40‰,Δ values (δ13C3 -δ13C2) ＞7‰, and C1/∑C 2 ratios ＞60.  相似文献   

13.
The Kara Sea is an area uniquely suitable for studying processes in the river-sea system. This is a shallow sea into which two great Siberian rivers, Yenisei and Ob, flow. From 1995 to 2003, the sea was studied by six international expeditions aboard the R/V Akademik Boris Petrov. This publication summarizes the results obtained, within the framework of this project, at the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Various hydrogeochemical parameters, concentrations and isotopic composition of organic and carbonate carbon of the sediments, plankton, particulate organic matter, hydrocarbons, and dissolved CO2 were examined throughout the whole sea area at more than 200 sites. The δ13C varies from −22 and −24‰ where Atlantic waters enter the Kara Sea and in the North-eastern part of the water area to −27‰ in the Yenisei and Ob estuaries. The value of δ13C of the plankton is only weakly correlated with the δ13C of the organic matter from the sediments and is lower by as much as 3–4‰. The paper presents the results obtained from a number of meridional river-sea profiles. It was determined from the relations between the isotopic compositions of plankton and particulate matter that the riverwaters carry material consisting of 70% detrital-humus matter and 30% planktonogenic material in the river part, and the material contained in the off-shore waters consists of 30% terrigenous components, with the contribution of bioproducers amounting to 70%. The carbon isotopic composition of the plankton ranges from −29 to −35‰ in the riverine part, from −28 to −27‰ in the estuaries, and from −27.0 to −25% in the marine part. The relative lightness of the carbon isotopic composition of plankton in Arctic waters is explained by the temperature effect, elevated CO2 concentrations, and long-distance CO2 supply to the sea with riverwaters. The data obtained on the isotopic composition of CO2 in the surface waters of the Kara Sea were used to map the distribution of δ13CCO 2. The complex of hydrocarbon gases extracted from the waters included methane, C2–C5, and unsaturated C2=–C4= hydrocarbons, for which variations in the concentrations in the waters were studied along river-estuary-sea profiles. The geochemistry of hydrocarbon gases in surface fresh waters is characterized by comparable concentrations of methane (0.3–5 μl/l) and heavier hydrocarbons, including unsaturated ones. Microbiological methane with δ13C from −105 to −90‰ first occurs in the sediments at depths of 40–200 cm. The sediments practically everywhere display traces of methane oxidation in the form of a shift of the δ13C of methane toward higher values and the occurrence of autogenic carbonate material, including ikaite, enriched in the light isotope. Ikaite (δ13C from −25 to −60‰) was found and examined in several profiles. The redox conditions in the sediments varied from normal in the southern part of the sea to highly oxidized along the Novaya Zemlya Trough. Vertical sections through the sediments of the latter exemplify the complete suppression of the biochemical activity of microorganisms. Our data provide insight into the biogeochemistry of the Kara Sea and make it possible to specify the background values needed for ecological control during the future exploration operations and extraction of hydrocarbons in the Kara Sea. Original Russian Text ? E.M. Galimov, L.A. Kodina, O.V. Stepanets, G.S. Korobeinik, 2006, published in Geokhimiya, 2006, No. 11, pp. 1139–1191.  相似文献   

14.
Quartz–carbonate–chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate subsolvus unmixing of a homogenous H2O–CO2–CH4–(N2)–Na–(K)–Cl fluid into a H2O–Na–(K)–Cl solution and a vapour-rich CO2–(H2O, CH4, N2) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400°C. Pressure estimates indicate a burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75°C/26 MPa, but pressure decrease to sublithostatic conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between 200 and 250°C and salinities of <5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite, and dolomite by decrepitation yielded δDH2O values from −89 to −113 ‰, δ13CCH4 from −26.9 to −28.9‰ (VPDB) and δ13CCO2 from −12.8 to −23.3‰ (VPDB). The low δD and δ13C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the Stavelot–Venn massif. The metamorphic fluid was focused along major thrust faults of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics.  相似文献   

15.
Stable and radiogenic isotope composition of stratiform Cu–Co–Zn mineralization and associated sedimentary rocks within the Boléo district of the Miocene Santa Rosalía basin, Baja California Sur, constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition. Stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column. Near-shore limestone at the base of the Boléo Formation is characterized by modified marine carbon (δ 13CPDB=−6.0 to +4.4‰) and oxygen (δ 18OSMOW=+19.5 to +26.2‰) isotope composition due to the influx of 13C- and 18O-depleted fluvial water. Sulfate sulfur isotope composition (δ 34SCDT=+17.21 to +22.3‰ and δ 18OSMOW=+10.7 to +13.1‰) for basal evaporite and claystone facies are similar to Miocene seawater. Strontium isotopes are less radiogenic than expected for Miocene seawater due to interaction with volcanic rocks. Low S/C ratios, high Mn contents and sedimentological evidence indicate the basin water column was oxidizing. The oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore-space filling by Cu–Co–Zn sulfides to produce disseminated sulfides. Quartz–Mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118°C. Sulfur isotopes indicate the following sources of sulfide: (1) bacterial sulfate reduction within the sedimentary pile produced negative δ 34S values (<−20‰) in framboidal pyrite; and (2) bacterial sulfate reduction at high temperature (80–118°C) within the sedimentary pile during the infiltration of the metal-bearing brines produced Cu–Co–Zn sulfides with negative, but close to 0‰, δ 34S values. Isotope modeling of fluid-rock reaction and fluid mixing indicates: (1) sedimentary and marine carbonates (δ 13C=−11.6 to −3.2‰ and δ 18O=+19.0 to +21.8‰) precipitated from basin seawater/pore water that variably mixed with isotopically depleted meteoric waters; and (2) hydrothermal calcite (δ 13C=−7.9 to +4.3‰ and δ 18O=+22.1 to +25.8‰) formed by dissolution and replacement of authigenic marine calcite by downward-infiltrating metalliferous brine and brine-sediment exchange, that prior to reaction with calcite, had mixed with isotopically depleted pore water. The downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of Cu sulfides along the upper contact of pyrite-bearing laminae. The co-existence and textural relationships among framboidal pyrite, base metal sulfides, carbonate and Mn–Fe oxides (including magnetite) within mineralized units are consistent with carbonate replacement and high-temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions.  相似文献   

16.
The Qinghai-Xizang Plateau is an area where a large number of salt lakes are distributed. We have collected several hundred samples of natural waters over the Plateau since 1976 and carried out researches on their hydrogen and oxygen isotopes. The results indicate that theδD and δ18O values of the salt lake waters over the Plateau range from −64.1 to +12.4‰ and from −11.19 to +8.62‰, respectively. From the different types of surfaces, ground and lake waters of various salinities it is inferred that the compositions of H and O isotopes in the initial water of Qinghai Lake areδD=−55.0‰ and {ie336-1}; and those in the original water from the lakes in northern Xizang, areδD=−116.0‰ and {ie336-2}. Brines in the salt lakes are derived from rain water through prolonged circulation. Oilfield water also makes some contribution to the salt lakes in the Qaidam Basin. Similar slopes of evaporation lines of water isotopes are noticed for the Qinghai Lake area and northern Xizang. This is attributed to the evolution of the isotopes in these water bodies in an environment of middle latitude and high elevation.  相似文献   

17.
Whereas most of the reported δ34S values of dissolved sulphate are positive in the Llobregat basin, Calders stream, which is a tributary of the Llobregat River, is characterised by negative values. Stream waters, sampled monthly between 1997 and 1998, and quarterly in 1999, show an overall increase in δ34S from −10‰ to 0‰, coupled with an increase in Na and Cl concentration. On the other hand, the oxygen isotopic composition of dissolved sulphate, δ18O, displayed an opposite trend with a slight decrease, from +9‰ to +6‰. Detailed sampling up stream in November 2000 indicated that, contrary to most of the surficial waters of the Llobregat basin with a δ34SSO4 mainly controlled by evaporites, in Calders stream, sulphate is derived from pyrite oxidation. The dual-isotope approach, coupled with chemical data, allowed us to identify the contribution of 34S-rich sulphate effluents from anthropogenic sources, while mixing models, calculated between natural and anthropogenic sources, enabled us to estimate their contribution. Sudden increases of δ34S and δ18O of dissolved sulphate in stream waters are believed to be caused by a sulphate reduction process related to oil spillage. The long-term enrichment in δ34S, coupled with a decrease in δ18OSO4, from Jan-97 to Aug-99, is interpreted as a progressive increase in the contribution of pig manure.  相似文献   

18.
In 2005 and 2006, hydrogeochemical study was carried out in the bipartite Wiśniówka Mała pit lake of the Holy Cross Mountains (south-central Poland). This is the largest acidic water body in Poland. This report presents the element concentrations in the water and sediment, stable sulfur and oxygen isotope ratios in the soluble sulfates, and stable oxygen isotope ratio in the water. The scope of the investigation also encompassed mineralogical examinations (scanning electron microscope, X-ray diffraction) of the sediment. The results of this study show that there is a spatial and temporal variability in concentrations of most elements and sulfur isotope ratios in the examined pit lake. The water of the western pond displayed a lower pH with a mean of 3.73 and higher conductivity (390 μS cm−1) as well as higher concentrations of sulfates (156 mg L−1) and most of the cations and anions. The concentrations of Fe2+ and Fe3+ averaged 0.8 and 0.4 mg·L−1. In contrast, the eastern pond water revealed a higher pH (mean of 4.36), lower conductivity (293 μS cm−1) and lower sulfate (90 mg L−1) and trace metal levels. Similar variations were recorded in the stable sulfur isotope ratios. The δ34SV-CDT(SO4 2−) values in the water of the western pit pond were in the range of −6.7 to −4.6‰ (mean of −5.6‰), whereas that in the eastern pit pond ranged from −2.2 to −0.9‰ (−1.6‰). The alkalinity of the entire lake water was below 0.1 mg·L−1 CaCO3. No distinct difference in the δ18OV-SMOW(SO4 2−) was noted between the western and eastern pit ponds. Compared to the Purple Pond in the Sudetes (Poland) and similar sites throughout the world, the examined pit lake is highlighted by distinctly low concentrations of sulfates, iron and other trace metals. Based on this and other studies performed in the Holy Cross Mountains, a conclusion can be drawn that the SO4 2− in the Wiśniówka Mała pit lake water is a mixture of SO4 2− derived from the following sources: (1) pyrite oxidation (especially in the western pond water), (2) leaching of soluble sulfates from soils and waste material, as well as (3) subordinate deposition of airborne sulfate precipitation.  相似文献   

19.
 Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ18O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ18O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ18O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ18O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ18O partial melts of xenoliths that had been hydrothermally altered and depleted in 18O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous hornblendes from the plutonic rocks have δ18O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The 18O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures, indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange. The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based partly on the observation that coexisting plagioclase has been extensively depleted in 18O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus isotopic equilibration with meteoric–hydrothermal fluids. Received: 22 March 1994 / Accepted: 26 January 1995  相似文献   

20.
The 18O and 2H (HDO) compositions are summarized for sampled springs (n = 81) within the Elwha watershed (≈692 km2) on the northern Olympic Peninsula. Samples, collected during 2001–2009, of springs (n = 158), precipitation (n = 520), streams (n = 176), and firn (n = 3) assisted the determinations for meteoric composition of recharge waters. The local mean water line (LMWL) is defined as δ2H = 8.2δ18O − 9.3 for the watershed. Recharge history is surmised from groundwater ages ranging from 5 ± 3 years (apparent 85Kr) to 9,490 ± 420 14C cal years BP. About 56% of the springs were recharged over the last 1,000 years while 13% of springs were recharged over 5,000 years ago. Spring HDO values fluctuate between −11.8 to −15.6‰ δ18O and −90.9 to −119.4‰ δ2H. Deuterium excess values predominate around 4–6‰. The HDO proxy records from springs suggest a pronounced paleoclimate shift in air masses near 5,000 year BP on the Peninsula.  相似文献   

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