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101.
Chemical and strontium isotope characterization of rainwater at an urban site in Loess Plateau, Northwest China 总被引:3,自引:0,他引:3
Major ion concentrations and strontium isotopic ratios (87Sr/86Sr) were measured in rainwater samples collected at the urban site of Lanzhou, a city located on the Loess Plateau in the arid and semi-arid areas of northwest China. The rainwater samples possessed alkaline pH, at a reference level of 5.6, with a range of 6.82 to 8.28 and a volume-weighted mean (VWM) pH value of 7.70. The alkaline character of rainwater in Lanzhou is due to the result of neutralization caused by the alkaline soil dusts which contain large amount of CaCO3. It was observed that Ca2+ was the most abundant cation with a VWM value of 886 µeq l− 1 (115–2184 µeq l− 1), accounting for 87.8% of the total cations. Without considering HCO3−, SO42− and NO3− were dominant among the anions, accounting for 64.2% and 23.0%, respectively, of the total measured anions. Using Na as an indicator of marine origin and Al for terrestrial inputs, the proportions of sea salt and non-sea-salt elements were estimated from elemental ratios. The precipitation in this region has typical continental characteristics. The Sr concentrations varied from 0.004 to 0.885 µmol l− 1, and strontium isotopic ratios (87Sr/86Sr) lay in the range of 0.71025–0.71302, with an average of 0.71143. The 87Sr/86Sr ratios of Lanzhou rainwater are higher than that of seawater, which reflects contributions from the radiogenic Sr sources of the aerosols. The most suitable candidate for the source would be the soil dust originating from local and distant loess and desert areas. The 87Sr/86Sr ratios were used to characterize different sources of base cations in rainwater, suggesting that the samples could be interpreted in terms of combinations of at least three components: soil dust derived from the Loess Plateau and desert areas in northwest China (with 87Sr/86Sr ~ 0.7130), seawater (with 87Sr/86Sr ~ 0.70917), and anthropogenic inputs (with 87Sr/86Sr ~ 0.7103). The high 87Sr/86Sr ratio and Ca and Sr content in the rainwater from Lanzhou can be attributed to the dissolution of calcium carbonate in soil dust. 相似文献
102.
103.
Vojtěch Janoušek Graeme Rogers D. R. Bowes 《International Journal of Earth Sciences》1995,84(3):520-534
The Sr-Nd isotopic data for selected granitoids of the Central Bohemian Pluton show a broad negative correlation with the total range of (87Sr/86Sr)330 = 0.7051–0.7129 and
Nd
330
= +0.2 to –8.9. The older intrusions have more depleted Sr-Nd compositions and calc-alkaline geochemistry (Sázava suite), whereas the younger intrusions shift towards K-rich calc-alkaline (Blatná suite) and shoshonitic rocks (íany and ertovo bemeno suites) with more evolved isotopic signatures. The distribution of the data is interpreted as reflecting a diversity of sources and processes, rather than a single progressive crustal contamination trend. The Sázava suite could have originated by partial melting of metabasites, or of a mantle source with an isotopic composition close to bulk earth, or by hybridization of crustally-derived tonalitic and mantle-derived magmas. Variation within the Blatná suite is modelled by mixing between a moderately enriched [(87Sr/86Sr)330 0.708,
Nd
330
–3] mantle component with either an isotopically evolved metasedimentary component, or with more evolved magmas of the suite. The íany suite was most probably produced by partial melting of peraluminous lithologies, possibly of the adjacent Moldanubian unit. The ertovo bemeno suite evolved from strongly enriched mantle-derived magmas [(87Sr/86Sr)3300.7128,
Nd
330
–7], either through closed-system fractional crystallization or interaction with magma corresponding to leucogranites of the Central Bohemian Pluton. 相似文献
104.
论江苏溧水爱景山锶矿床勘探网度的合理性 总被引:2,自引:0,他引:2
江苏溧水爱景山锶矿床是我国特大型天青石锶矿床。由于我国至今未制定锶矿床地质勘探规范,地质勘查单位只能参照相类似矿种的规范进行勘探。探讨该矿床的合理勘探网度具有重要意义。对原网度控制程度进行了研究,用加密线进行了勘探检验,并利用采矿资料进行了对比验证,,得出用50m×50m的原勘探网度探求C级储量是合理的结论。 相似文献
105.
Isotope ratios and elemental concentrations in otoliths are often used as natural tags to reconstruct migratory movements and connectivity patterns in marine and anadromous fishes. Although differences in otolith geochemistry have been documented among geographically separated populations, inter-annual variation within locations is less frequently examined. We compared otolith isotope (δ18O and 87Sr:86Sr) and elemental ratios (Sr:Ca and Ba:Ca) from several annual cohorts of juvenile American shad (Alosa sapidissima) in three rivers. These four geochemical signatures distinguished among river-specific populations of this species at both large and small geographic scales, with δ18O and 87Sr:86Sr generating the majority of multivariate variation. We found significant variation among years for all variables in two to three rivers. However, the magnitude of variability differed among ratios, with δ18O ratios showing substantial inter-annual shifts while 87Sr:86Sr ratios were relatively stable across years. Sr:Ca and Ba:Ca ratios also varied among years. These results imply that investigators using environmentally labile signatures must quantify geochemical signatures for each cohort of interest in order to confidently identify origins of migrants. 相似文献
106.
R. L. Bunde J. J. Rosentreter M. J. Liszewski C. H. Hemming J. Welhan 《Environmental Geology》1997,32(3):219-229
The effects of calcium and magnesium on the distribution of strontium between a surficial sediment and simulated wastewater
solutions were measured as part of an investigation to determine strontium transport properties of surficial sediment at the
Idaho National Engineering Laboratory (INEL), Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho
State University, in cooperation with the U.S. Department of Energy. Batch experimental techniques were used to determine
strontium linear sorption isotherms and distribution coefficients (K
d's) using simulated wastewater solutions prepared at pH 8.0±0.1 with variable concentrations of calcium and magnesium. Strontium
linear sorption isotherm K
d's ranged from 12±1 to 85±3 ml/g, increasing as the concentration of calcium and magnesium decreased. The concentration of
sorbed strontium and the percentage of strontium retained by the sediment were correlated to aqueous concentrations of strontium,
calcium, and magnesium. The effect of these cation concentrations on strontium sorption was quantified using multivariate
least-squares regression techniques. Analysis of data from these experiments indicates that increased concentrations of calcium
and magnesium in wastewater discharged to waste disposal ponds at the INEL increases the availability of strontium for transport
beneath the ponds by decreasing strontium sorption to the surficial sediment.
Received: 8 November 1996 · Accepted: 6 January 1997 相似文献
107.
High-pressure synthesis of a new SrSi2O5 phase was performed at 16 GPa and 900°C by using a Kawai-type multianvil apparatus. The powder X-ray diffraction pattern of the compound was analyzed by Rietveld refinement based on the structure of a high-pressure polymorph of BaGe2O5, BaGe2O5 III. The structure is orthorhombic with space group Cmca and cell parameters of a = 5.2389(1) Å, b = 9.2803(2) Å, c = 13.4406(1) Å, V=653.46(2) Å 3 (Z=8, calc=4.549 g/cm3). The structure consists of layers containing SiO6 octahedra and SiO4 tetrahedra. In a unit layer, oxygen and strontium atoms are arranged in an approximation to hexagonal close-packing. The strontium atom is accommodated in a 12-coordinated site. Each SiO6 octahedron shares four corners with SiO4 tetrahedra and the other two corners with another SiO6 octahedra. The SiO6 octahedra are linked to each other to form SiO6 chains along the a-axis. This is the first known example of a silicate with a BaGe2O5 III-type structure. 相似文献
108.
Carbon,sulfur, oxygen and strontium isotope records,organic geochemistry and biostratigraphy across the Permian/Triassic boundary in Abadeh,Iran 总被引:6,自引:0,他引:6
Christoph?KorteEmail author Heinz?W.?Kozur Michael?M.?Joachimski Harald?Strauss Ján?Veizer Lorenz?Schwark 《International Journal of Earth Sciences》2004,93(4):565-581
Pelagic deposits at Abadeh represent a complete biostratigraphic record across the Permian/Triassic boundary (PTB). The presumed water depth during deposition of these sediments was between 60 and 90 m. Similar to other Permian/Triassic boundary sections, the succession at Abadeh is characterised by a negative carbon isotope shift of approximately 4. The values start to decrease in the lower C. changxingensis - C. deflecta s.l. Zone, reach –0.12 (V-PDB) in the uppermost Permian just below the PTB, remain low to the early I. isarcica Zone (–0.32) and increase subsequently in the upper I. isarcica Zone. For the time interval of the PTB negative carbon isotope excursion, between the C. iranica and the I. isarcica Zones, no correlation exists between the 13Ccarb and the 18Ocarb. The above observations argue against the conclusion of Heydari et al. (2001) that the carbon isotope event at the P/T transition is an alteration artefact and not a global signal. The decrease in 13Ccarb is accompanied by a ~5 (and potentially up to 10) increase in 34SSSS. Together, these features are thought to reflect a complex global event, notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves. For the carbon isotope drop, other factors, such as the collapse of ocean primary productivity may also have played a role. The 87Sr/86Sr ratios of Dzhulfian seawater show only a minor increase from 0.70705 to 0.70710, reaching 0.70720 in the Dorashamian. The increase becomes steeper in the Early Triassic reaching 0.70754 in the N. dieneri Zone. The rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost Permian (C. meishanensis - H. praeparvus Zone) and the lack of a dense land vegetation in the Early Triassic, prior to the Spathian (Upper Olenekian). 相似文献
109.
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
110.
Edward G. Purdy 《International Journal of Earth Sciences》2008,97(3):651-664
Sepkoski’s compendium of 28,730 marine genera was analyzed with a view toward comparing taxonomic diversity, strontium isotope
stratigraphy and sea-level changes. The fossil record analyses discriminated between origination, extinction and pass through
genera and collectively delineated changes in number of genera with time at the largely stratigraphic stage level. With notable
exceptions of the Cretaceous and Tertiary, taxonomic diversity generally paralleled both strontium isotope stratigraphy and
sea-level changes. Sampling bias was suggested in the Tertiary where an increase in genera numbers toward the Recent opposed
the downward trends of both strontium isotope and sea level curves. The removal of all Recent genera from the Sepkoski database
confirmed the bias in producing complimentary downward trends in all curves. Regression analysis of taxonomic diversity with
respect to sea level extent and time duration explained 82% of the variability of the remaining data. Sea-level fluctuations
are not always accompanied by significant changes in taxonomic diversity but strontium isotope analyses offers the potential
of constraining the extent to which the magnitude of changes are associated with time duration. 相似文献