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1.
The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer
System (Botucatu and Piramboia aquifers) in S?o Paulo State, Brazil. Trends of dissolved species concentrations and geochemical
modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater
chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na–HCO3 type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of
groundwater flow and at present is located near to the cities of Sert?ozinho and águas de Santa Barbara (wells PZ-34 and PZ-148,
respectively) in a shallow confined area, 50–70 km from the recharge zone. Part of the sodium probably enters the Guarani
Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution
of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of
mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani
Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ
2H and δ
18O values in groundwater downgradient. Values of δ
13C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ
13C(DIC) in deep geothermal wells are very high (>–6.0‰) and probably indicate isotopic exchange with carbonates with δ
13C about –3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination
to the Guarani Aquifer System.
Electronic Publication 相似文献
2.
3.
Peter J. Biancani Ruth H. Carmichael Joshua H. Daskin William BurkhardtIII Kevin R. Calci 《Estuaries and Coasts》2012,35(1):121-131
We measured seasonal effects of wastewater treatment plant (WTP) effluent on growth, survival, and accumulation of microbes
in oysters near a major WTP in Mobile Bay, AL. Despite higher nutrients near the WTP, seasonal conditions rather than distance
affected chlorophyll a concentration and oyster growth. In summer and fall, when oyster growth was higher, δ15N‰ in oysters near the WTP changed through time to reflect δ15N‰ in effluent (approx. −4‰). Microbial indicators (male-specific coliphage, fecal coliforms) were highest in oysters near
the WTP in all seasons and correlated with δ15N‰ in fall and summer. Increased riverine discharge and slower acquisition of δ15N‰ likely confounded correlations in winter/spring. Although we did not detect gross ecological effects of wastewater exposure
for oysters, data indicated wastewater-derived particles entered the local food web and accumulated in oysters. These data
highlight the importance of using multiple indicators of wastewater exposure and considering both seasonal and spatial effects
when defining wastewater influence on a system or species. 相似文献
4.
Galip Yuce 《Environmental Geology》2007,51(5):857-868
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
5.
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
6.
Twenty private wells and ten stream locations were sampled to assess the source and fate of dissolved nitrate in the Cedar
River watershed of Iowa, USA. The average levels of nitrate in groundwater decreased from 39.5 mg/L in May, to 38 mg/L in
July, to 30 mg/L in September. Although several surface water samples exceeded MCL in May, most values dropped to below 20 mg/L
by July and September. The decreasing N levels were attributed to the gradual uptake of nitrate by growing crops as well as
the cyanobacterial growth in the aquatic systems. The δ15N values of dissolved nitrate in groundwater ranged from +0.45 to +5.35‰, whereas those in surface water ranged from +1.48
to +5.16‰. The results suggested that commercial fertilizers and soil organic nitrogen were probably mixed up in their transport
pathways. A fertilizer-only source would provide much lower delta values, whereas soil nitrogen would provide higher than
observed delta values. Denitrification was considered unlikely because of the low δ15N values, high nitrate concentrations, and moderately high DO content in groundwater. Animal wastes were not found as a possible
source of nitrate in the water. This is supported by the low chloride concentrations and lower than 10‰ delta values in the
water samples. The study demonstrates that nitrogen isotope data in coordination with the dissolved nitrate levels and land
use can be effectively used in nitrogen source identification and its transformation studies. 相似文献
7.
Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system,southwest of North China Plain 总被引:4,自引:0,他引:4
Fadong Li Guoying Pan Changyuan Tang Qiuying Zhang Jingjie Yu 《Environmental Geology》2008,55(5):1109-1122
Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population,
quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess
these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical
evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis
and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed
of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater
was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex
(Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion
exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred
water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study
area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal
end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical
evolution, and groundwater flow paths in the complex alluvial fan aquifer system. 相似文献
8.
Wang Yong Hou Zengqian Mo Xuanxue Dong Fangliu Bi Xianmei Zeng Pusheng 《Frontiers of Earth Science》2007,1(3):322-332
More than 140 middle-small sized deposits or minerals are present in the Weishan-Yongping ore concentration area which is
located in the southern part of a typical Lanping strike-slip and pull-apart basin. It has plenty of mineral resources derived
from the collision between the Indian and Asian plates. The ore-forming fluid system in the Weishan-Yongping ore concentration
area can be divided into two subsystems, namely, the Zijinshan subsystem and Gonglang arc subsystem. The ore-forming fluids
of Cu, Co deposits in the Gonglang arc fluid subsystem have δD values between −83.8‰ and −69‰, δ18O values between 4.17‰ and 10.45‰, and δ13C values between −13.6‰ and 3.7‰, suggesting that the ore-forming fluids of Cu, Co deposits were derived mainly from magmatic
water and partly from formation water. The ore-forming fluids of Au, Pb, Zn, Fe deposits in the Zijinshan subsystem have δD
values between −117.4‰ and −76‰, δ18O values between 5.32‰ and 9.56‰, and Δ13C values between −10.07‰ and −1.5‰. The ore-forming fluids of Sb deposits have δD values between −95‰ and −78‰, δ18O values between 4.5‰ and 32.3‰, and Δ13C values between −26.4‰ and −1.9‰. Hence, the ore-forming fluids of the Zijinshan subsystem must have been derived mainly
from formation water and partly from magmatic water. Affected by the collision between the Indian and Asian plates, ore-forming
fluids in Weishan-Yongping basin migrated considerably from southwest to northeast. At first, the Gonglang arc subsystem with
high temperature and high salinity was formed. With the development of the ore-forming fluids, the Zijinshan subsystem with
lower temperature and lower salinity was subsequently formed.
Translated from Mineral Deposits, 2006, 25(1): 60–70 [译自: 矿床地质] 相似文献
9.
Ratan K. Majumder M. A. Halim B. B. Saha Reo Ikawa Toshio Nakamura Makoto Kagabu Jun Shimada 《Environmental Earth Sciences》2011,64(5):1343-1352
A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers,
Bangladesh using environmental isotope (2H, 18O, 13C, 3H, and 14C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ2H = 7.7 δ18O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ18O and δ2H). The δ18O and δ2H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling
evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the
shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU,
which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of 14C activity is associated with the heavier δ13C values, which indicates the presence of geochemical reactions affecting the 14C concentration along the groundwater flow system. Both vertical and lateral decrease of 14C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which
discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the
Bengal Delta aquifers, Bangladesh. 相似文献
10.
Axel Horst Jürgen Mahlknecht Miguel Angel López-Zavala Bernhard Mayer 《Environmental Earth Sciences》2011,64(7):1931-1941
Chemical compositions and stable isotope ratios of water and sulphate were used to characterise sources and processes responsible
for elevated concentrations of sulphate and other constituents in groundwater from aquifers at Colima State along Mexico’s
Pacific Coast. The δ18O and δ2H values of the groundwater were similar to those of precipitation indicating a meteoric origin, and recharge processes are
relatively uniform in large parts of the study area with only slight local evaporation effects. δ34Ssulphate and δ18Osulphate analyses indicated that high sulphate concentrations of up to 1,480 mg/l are mainly due to dissolution of evaporites and
volcanic exhalations. Chloride is largely related to sources other than seawater. The Marabasco sub basin is affected by anthropogenic
contamination through manganese and iron ore mining activities. The obtained knowledge regarding sources and areas of contamination
will be essential for the development and design of a water quality monitoring program in the study area. 相似文献
11.
Multiple origins of zircons in jadeitite 总被引:1,自引:1,他引:0
Bin Fu John W. Valley Noriko T. Kita Michael J. Spicuzza Chad Paton Tatsuki Tsujimori Michael Bröcker George E. Harlow 《Contributions to Mineralogy and Petrology》2010,159(6):769-780
Jadeitites form from hydrothermal fluids during high pressure metamorphism in subduction environments; however, the origin
of zircons in jadeitite is uncertain. We report ion microprobe analyses of δ18O and Ti in zircons, and bulk δ18O data for the jadeitite whole-rock from four terranes: Osayama serpentinite mélange, Japan; Syros mélange, Greece; the Motagua
Fault zone, Guatemala; and the Franciscan Complex, California. In the Osayama jadeitite, two texturally contrasting groups
of zircons are identified by cathodoluminescence and are distinct in δ18O: featureless or weakly zoned zircons with δ18O = 3.8 ± 0.6‰ (2 SD, VSMOW), and zircons with oscillatory or patchy zoning with higher δ18O = 5.0 ± 0.4‰. Zircons in phengite jadeitite from Guatemala and a jadeitite block from Syros have similar δ18O values to the latter from Osayama: Guatemala zircons are 4.8 ± 0.7‰, and the Syros zircons are 5.2 ± 0.5‰ in jadeitite and
5.2 ± 0.4‰ in associated omphacitite, glaucophanite and chlorite-actinolite rinds. The δ18O values for most zircons above fall within the range measured by ion microprobe in igneous zircons from oxide gabbros and
plagiogranites in modern ocean crust (5.3 ± 0.8‰) and measured in bulk by laser fluorination of zircons in equilibrium with
primitive magma compositions or the mantle (5.3 ± 0.6‰). Titanium concentrations in these zircons vary between 1 and 19 ppm,
within the range for igneous zircons worldwide. Values of δ18O (whole-rock) ≅ δ18O (jadeite) and vary from 6.3 to 10.1‰ in jadeitites in all four areas. 相似文献
12.
The isotopic composition of dissolved boron, in combination with the elemental concentrations of B, Cl and salinities in freshwater-seawater mixed samples taken from the estuary of the Changjiang River, the largest one in China, was investigated in detail in this study. Brackish water and seawater samples from the estuary of the Changjiang River were collected during low water season in November, 1998. Boron isotopic compositions were determined by the Cs2BO^+2-graphite technique with a analytical uncertainty of 0.2‰ for NIST SRM 951 and an average analytical uncertainty of 0.8‰ for the samples. The isotopic compositions of boron, expressed in δ^11B, and boron concentrations in the Changjiang River at Nanjing and seawater from the open marine East Sea, China, are characterized by δ^11B values of -5.4‰ and 40.0‰, as well as 0.0272 and 4.43 mg B/L, respectively. Well-defined correlations between δ^11B values, B concentrations and Cl concentrations are interpreted in terms of binary mixing between fiver input water and East Sea seawater by a process of straightforward dilution. The offsets of δ^11B values are not related to the contents of clastic sediment and to the addition of boron. These relationships favor a conservative behavior of boron at the estuarine of the Changjiang River. 相似文献
13.
Dreissena polymorpha is an exotic freshwater bivalve species which was introduced into the Great Lakes system in the fall of 1985 through the release
of ballast water from European freighters. Utilizing individual growth rings of the shells, the stable isotope distribution
(δ18O and δ13C) was determined for the life history of selected samples which were collected from the western basin of Lake Erie. These
bivalves deposit their shell in near equilibrium with the ambient water and thus reflect any annual variation of the system
in the isotopic records held within their shells. Observed values for δ18O range from -6.64 to –9.46‰ with an average value of –7.69‰ PDB, while carbon values ranged from –0.80 to –4.67‰ with an
average value of –1.76‰ PDB. Dreissena polymorpha shells incorporate metals into their shells during growth. Individual shell growth increments were analyzed for Pb, Fe, Mg,
Mn, Cd, Cu, and V concentrations. The shells show increased uptake of certain metals during periods of isotopic enrichment
which correspond with warmer water temperatures. Since metals are incorporated into the shells, the organism may be useful
as a biomonitor of metal pollution within aquatic environments.
Received: 31 October 1996 · Accepted: 21 May 1997 相似文献
14.
Oxygen and hydrogen isotopes for the characteristics of groundwater recharge: a case study from the Chih-Pen Creek basin,Taiwan 总被引:5,自引:2,他引:3
Assessing the seasonal variation of groundwater recharge is important for effective management of groundwater resources. Stable
isotopes of oxygen and hydrogen were used to estimate the sources of groundwater and seasonal contributions of precipitation
to groundwater recharge in Chih-Pen Creek basin of eastern Taiwan. Based on the isotopes of precipitation (n = 177), two different local meteoric water regression lines (LMWL) can be obtained for the different seasons: δD = 8.0618O + 10.08 for wet season precipitation (May through October) and δD = 8.65δ18O + 17.09 for dry season precipitation (November through April). The slope and intercept of regression line for wet season
precipitation are virtually identical to the global meteoric water line (GMWL) of Craig (1961). In contrast to during dry season precipitation due to evaporation effect the intercept of 17.09 is much higher than of
the GMWL of 10. The results show the stable isotopes compositions of precipitation decrease with increasing rainfall amount
and air temperature, due to the amount effect of precipitation is pronounced. The amount effect is clearly but do not show
the temperature effect from January to December 2007. Using a mass-balance equation, a comparison of deuterium excess or d values of precipitation and groundwater indicates the groundwater consist of 76% wet season precipitation and 24% dry season
precipitation, representing a distinct seasonal variation of groundwater recharge in study area. About 79% of the groundwater
is recharged from the river water of the mountain watershed and 21% is from the rain that falls on the basin. 相似文献
15.
Barbara Vokal-Nemec Janina Szaran Andrzej Trembaczowski Stanislaw Halas Tadej Dolenec Sonja Lojen 《Aquatic Geochemistry》2006,12(3):199-220
Measurements were made of sulphur and oxygen isotope ratios of sulphate in some Slovenian rivers, lakes and tap waters. δ34S ranged from −0.2 to + 13.3‰, δ18O ranged from +4.9 to + 13.6‰, and the sulphate content varied from 0.8 to 41.4 mg/L. Rivers flowing from the Julian Alps
contain a very low amount of sulphate that is leached from a thin horizon of soil by rain. As confirmed by their low δ18O values, these sulphates do not enter the rivers directly in rain, but arise from biochemical cycling in the soil. The low
δ34S of this sulphate indicates that it originates from the oxidation of sedimentary sulphides. The evolution of sulphates along
the river course was investigated for the Sava and Ljubljanica rivers. The variations observed in sulphate from the waters
studied result from variations in the contribution of sulphates of different origin. Downstream the Sava River sulphate is
depleted in the heavy isotopes of both sulphur and oxygen, with δ-values gradually tending toward the δ-values of groundwater
sulphates in the watershed. In contrast, the δ-values of sulphate in the Ljubljanica River are almost constant and similar
to those of sulphate in local groundwater. Introduction of water from Italian and Slovenian mines was recorded in the Soča
River, where the lowest δ34S value of sulphate sulphur (−0.2‰) was observed. In addition, the influence of sulphate from the oxidation of sedimentary
sulphides was recorded in the Sotla River. No evidence was found for introduction of sulphate from factories. 相似文献
16.
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
17.
Dynamic analysis of the infiltration rate of artificial recharge of groundwater: a case study of Wanglong Lake,Pingtung, Taiwan 总被引:1,自引:1,他引:0
Yung-Chang Tu Cheh-Shyh Ting Hsin-Tien Tsai Jung-Wei Chen Cheng-Haw Lee 《Environmental Earth Sciences》2011,63(1):77-85
Although Pingtung plain is an agriculturally developed region, its limited hydrologic conditions have restrained the maximization
of its surface water resources. Due to the lack of proper management and sustainable utilization, groundwater has been overdrawn,
causing serious land subsidence and seawater intrusion. The present paper presents a pilot study for artificially recharging
groundwater using high-infiltration basins. Results of the geometric factor show that the large basin is ca. 6.8 times the
size of the small one, with the infiltration volume almost approaching 1 m3/day/m2. In the groundwater variation, the MW-2 is located immediately below the infiltration basin; therefore, its water level rises
more rapidly than that of MW-3. As for the infiltration volume, results of the experiment used the same basin since 2002,
which shows that the volumes gradually decreased from 12,136 to 5,555 m3/day. This is particularly evident in 2005 when volume decrease was at a maximum ca. 2,000 m3/day. Finally, the infiltration rate decreased from 22.76 to 7.15 m/day. The difference in infiltration rate between 2003
and 2005 has a maximum variation from to 15.2 to 10.33 m/day. In 2003, the addition of sand caused the infiltration rate to
fall to a minimum ca. 5.3 m/day. By extending the recharge time, the infiltration rate fell gradually similar to those identified
from 2005 to 2007. 相似文献
18.
Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ^18O values range from -0.3‰- -0.1‰) and lighter oxygen isotope (their δ^18O values range from -22.1‰- -19.5‰). Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process. 相似文献
19.
Hydrogeochemical controls and usability of groundwater in the semi-arid Mayo Tsanaga River Basin: far north province,Cameroon 总被引:2,自引:0,他引:2
Wilson Y. Fantong Hiroshi Satake Samuel N. Ayonghe Festus T. Aka Kazuyoshi Asai 《Environmental Geology》2009,58(6):1281-1293
Deuterium, δ
18O, major ions and dissolved silica in groundwater from semi-arid Mayo-Tsanaga river basin in the Far North Province, Cameroon
were used to trace hydrogeochemical processes that control their concentrations and to explore for usability of the water.
Electrical conductivity ranges from 57–2,581 μs/cm with alternating low and high values along the hydraulic gradient. Waters
from piedmont alluvium show low concentrations in major cations, which peak in Mg within basalt, Na within plain alluvium,
and Ca within basalt and the sandy Limani-Yagoua ridge. The initial dominant groundwater composition is CaHCO3, which did not evolve within the basalt and piedmont alluvium, but evolved to NaHCO3 in the granite and plain alluvium. The main processes controlling the major ions composition include the following: (1) dissolution
of silicates and fluorite; (2) precipitation of fluorite and carbonate; (3) cation exchange of Ca in water for Na in clay;
(4) and anthropogenic activities. The δD and δ
18O ratios vary from −35 to 0.7 and −5.3 to 1.1‰, respectively. The lowest and highest isotope ratios are observed in groundwater
within the downstream sandy Limani-Yagoua ridge and the upstream graintes respectively. Variation in isotope ratios depends
on altitude effect of −0.48‰ per 100 m between 600 and 850 m asl, and on evaporation, which had insignificant effect on the
water salinity. Seventy percent of the groundwater shows poor drinking quality and 90% is suitable for irrigation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
20.
Aaron J. Cavosie John W. Valley Noriko T. Kita Michael J. Spicuzza Takayuki Ushikubo Simon A. Wilde 《Contributions to Mineralogy and Petrology》2011,162(5):961-974
The oxygen isotope ratios (δ18O) of most igneous zircons range from 5 to 8‰, with 99% of published values from 1345 rocks below 10‰. Metamorphic zircons
from quartzite, metapelite, metabasite, and eclogite record δ18O values from 5 to 17‰, with 99% below 15‰. However, zircons with anomalously high δ18O, up to 23‰, have been reported in detrital suites; source rocks for these unusual zircons have not been identified. We report
data for zircons from Sri Lanka and Myanmar that constrain a metamorphic petrogenesis for anomalously high δ18O in zircon. A suite of 28 large detrital zircon megacrysts from Mogok (Myanmar) analyzed by laser fluorination yields δ18O from 9.4 to 25.5‰. The U–Pb standard, CZ3, a large detrital zircon megacryst from Sri Lanka, yields δ18O = 15.4 ± 0.1‰ (2 SE) by ion microprobe. A euhedral unzoned zircon in a thin section of Sri Lanka granulite facies calcite
marble yields δ18O = 19.4‰ by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble. Small oxygen isotope fractionations
between zircon and most minerals require a high δ18O source for the high δ18O zircons. Predicted equilibrium values of Δ18O(calcite-zircon) = 2–3‰ from 800 to 600°C show that metamorphic zircon crystallizing in a high δ18O marble will have high δ18O. The high δ18O zircons (>15‰) from both Sri Lanka and Mogok overlap the values of primary marine carbonates, and marbles are known detrital
gemstone sources in both localities. The high δ18O zircons are thus metamorphic; the 15–25‰ zircon values are consistent with a marble origin in a rock-dominated system (i.e.,
low fluid(external)/rock); the lower δ18O zircon values (9–15‰) are consistent with an origin in an external fluid-dominated system, such as skarn derived from marble,
although many non-metasomatized marbles also fall in this range of δ18O. High δ18O (>15‰) and the absence of zoning can thus be used as a tracer to identify a marble source for high δ18O detrital zircons; this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone
may not allow discrimination of coeval source rocks. Metamorphic zircon megacrysts have not been reported previously and appear
to be associated with high-grade marble. Identification of high δ18O zircons can also aid geochronology studies that seek to date high-grade metamorphic events due to the ability to distinguish
metamorphic from detrital zircons in marble. 相似文献