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1.
X-ray Diffraction of Dust Particles in Spring Beijing   总被引：1，自引：1，他引：0  
X-ray diffractometry was utilized to study the mineralogical characteristics of the inhalable particles (PM10) sampled during two dust storms in Beijing city on March 18th and May 21st, 2008. We confirm, for the first time, that there stably exists ammonium chloride in the atmosphere when temperature is low. The total sulfates particles were affected by relative humidity. Both species and concentration of sulfates decreased first and then grew back by the end of each dust storm. Koninckite, a phosphate mineral never reported as particulate aerosol before, was identified. Meanwhile, our result shows that a chemical modification on dust minerals occurs during long range transportation. PM10 samples collected during the period of dust storms were dominated by crustal minerals such as quartz, illite/ smectite, illite, chlorite, feldspar and calcite, and were notably higher in concentration than that in normal periods of time. The amounts of total sulfates, calcite and feldspar altered in each dust storm. It is derived from 24-hour isentropic backward trajectories that two dust events in spring 2008 originated in different sources.  相似文献   

2.
The Holocene lacustrine diatomaceous earth of Fayium,South West of Cairo,has been studied to define its minerals,chemistry,petrography and physical properties.Minerals were processed by way of calcination at 550℃ ,followed by acid leaching to reduce levels of mineral impurities.The diatomite is of biogenic opal A.with calcite as the main ganue mineral,quartz and clay minerals(smectite followed by kaolinite in abundance and a trace amount of illite).Silica in the diatomaceous earth accounts for about 63% on average.Positive correlation between CaO and CO2 indicates that Ca is present mainly as calcite.Al2O3,Fe2O3,MgO and K2O are attributed mainly to clay minerals.However,the physical properties of the diatomaceous earth as filter-aids and filler for paints and plastics are poor because of general high levels of impurities.The technological performances of the diatomaceous earth have been significantly improved owing to upgrading of diatoms through mineral processing trical.  相似文献   

3.
Hazardous air pollutants, including compounds of sulfur and toxic trace elements, are emitted during coal combustion. Geochemical studies of these constituents in coals provide information about their species, regional distribution and origins. The data are useful in understanding the cause and scope of human health problems related to these hazardous elements and in designing preventive or remedial measures. Sulfur in coal is a problem because sulfur dioxide emitted during coal combustion is a main source of acid rain. The sulfur isotopic evidence shows that sulfur in low-sulfur coal is derived primarily from parent plant materials. Sulfur enrichment in medium- and high-sulfur coals is caused by the sulfate in seawater that flooded the peat swamp during coal formation. The sulfur content of a coal is controlled primarily by the depositional environment of coal seams. Only pyritic sulfur can be removed by physical coal cleaning processes （coal preparation）. Sulfur dioxide emission can be reduced using clean coal technologies, such as flue-gas desulfurization, fluidized-bed combustion, and integrated gasification and combined cycle.  相似文献   

4.
The effect of Rayleigh distillation by outgassing of SO2 and H2S on the isotopic composition of sulfur remaining in silicate melts is quantitatively modelled.A threshold mole fraction of sulfur in sulfide component of the melts is reckoned to be of critical importance in shifting the δ^34S of the melts mith respect to the original magmas.The partial equilibrium fractionation in a magmatic system is evaluated by assuming that a non-equilibrium flux of sulfur occurs between magmatic volatiles and the melts,while an equilibrium fractionation is approached between sulfate and sulfide within the melts.The results show that under high fo2 conditions,the sulfate/sulfide ratio in a melt entds to increase,and the δ^34S value of sulfur in a solidified rock might then be shifted in the positive direction.This may either be due to Rayleigh outgassing in case the mole fraction of sulfide is less than the threshold,or due to a unidirectional increase in δ^34S value of the sulfate with decreaing temperature,Conversely,at low fo2,the sulfate/sulfide ratio tends to decrease and the δ^34S value of total sulfur could be driven in the negative direction,either because of the Rayleigh outgassing in case the mole fraction of sulfide is greater than the threshold,or because of a unidirectional decrease inδ^34S value of the sulfide.To establish isotopic equilibrium between sulfate and sulfide,the HM,QFM or WM buffers in the magmatic system are suggested to provide the redox couple that could simultaneously reduce the sulfate and oxidize the sulfide.CaO present in the silicatte Melts is also called upon to participate in the chemical equilibrium between sulfate and sulfide,Consequently,the δ^34S value of an igneous rock could considerably deviate from that of its original magma due to the influence of oxygen fugacity and temperature at the time of magma solidification.  相似文献   

5.
Classic physical and chemical treatments applied to separating clay minerals from the host sediments are often difficult or aggressive for clay minerals. A technique using cation exchange resins (amberlite IRC-50H and amberlite IR-120) is used to separate clay minerals from the host sediments. The technique is based on the exchange of cations in the minerals that may be associated clay minerals in sediments, such as Ca and Mg from dolomite; Ca from calcite, gypsum and francolite with cations carried by resin radicals. The associated minerals such as gypsum, calcite, dolomite and francolite are removed in descending order. Separation of clay minerals using cation exchange resins is less aggressive than that by other classic treatments. The efficiency of amberlite IRC-50H in the removal of associated minerals is greater than that of amberlite IR-120.  相似文献   

6.
《地学前缘(英文版)》2020,11(3):783-792
Geogenic dust is commonly believed to be one of the most important environmental problems in the Middle East.The present study investigated the geochemical characteristics of atmospheric dust particles in Shiraz City(south of Iran).Atmospheric dust samples were collected through a dry collector method by using glass trays at 10 location sites in May 2018.Elemental composition was analysed through inductively coupled plasma optical emission spectrometry.Meteorological data showed that the dustiest days were usually in spring and summer,particularly in April.X-ray diffraction analysis of atmospheric dust samples indicated that the mineralogical composition of atmospheric dust was calcite+dolomite(24%)palygorskite(18%)quartz(14%)muscovite(13%)albite(11%)kaolinite(7%)gypsum(7%)zircon=anatase(3%).The high occurrence of palygorskite(16%-23%) could serve as a tracer of the source areas of dust storms from the desert of Iraq and Saudi Arabia to the South of Iran.Scanning electron microscopy indicated that the sizes of the collected dust varied from 50 μm to0.8 μm,but 10 μm was the predominant size.The atmospheric dust collected had prismatic trigonal-rhombohedral crystals and semi-rounded irregular shapes.Moreover,diatoms were detected in several samples,suggesting that emissions from dry-bed lakes,such as Hoor Al-Azim Wetland(located in the southwest of Iran),also contributed to the dust load.Backward trajectory simulations were performed at the date of sampling by using the NOAA HYSPLIT model.Results showed that the sources of atmospheric dust in the study area were the eastern area of Iraq,eastern desert of Saudi Arabia,Kuwait and Khuzestan Province.The Ca/Al ratio of the collected samples(1.14) was different from the upper continental crust(UCC) value(UCC=0.37),whereas Mg/A1(0.29),K/Al(0.22) and Ti/Al(0.07) ratios were close to the UCC value(0.04).This condition favours desert calcisols as the main mineral dust sources.Analysis of the crustal enrichment factor(EF_(crustal)) revealed geogenic sources for V,Mo,Pb,Sr,Cu and Zn(2),whereas anthropogenic sources affected As,Cd,Cr and Ni.  相似文献   

7.
Multiple sulfur isotope ratios （^34S/^33S/^32S） of Archean bedded sulfides deposits were measured in the Yanlingguan Formation of the Taishan Group in Xintai, Shandong Province, East of China; 633S = -0.7%o to 3.8‰,δ^34S = 0.1‰-8.8‰, △^33S = -2.3‰ to -0.7‰. The sulfur isotope compositions show obvious mass-independent fractionation （MIF） signatures. The presence of MIF of sulfur isotope in Archean sulfides indicates that the sulfur was from products of photochemical reactions of volcanic SO2 induced by solar UV radiation, implying that the ozone shield was not formed in atmosphere at that time, and the oxygen level was less than 10-5 PAL （the present atmosphere level）. The sulfate produced by photolysis of SO2 with negative △^33S precipitated near the volcanic activity center; and the product of element S with positive △^33S precipitated far away from the volcanic activity center. The lower △^33S values of sulfide （-2.30‰ to --0.25‰） show that Shihezhuang was near the volcanic center, and sulfur was mostly from sulfate produced by photolysis. The higher △^33S values （-0.5‰ to -‰） indicate that Yanlingguan was far away from the volcanic center and that some of sulfur were from sulfate, another from element S produced by photolysis. The data points of sulfur isotope from Yanlingguan are in a line parallel to MFL （mass dependent fractionation line） on the plot of δ^34S--δ^33S, showing that the volcanic sulfur species went through the atmospheric cycle into the ocean, and then mass dependent fractionation occurred during deposition of sulfide. The data points of sulfur isotope from Shihezhuang represent a mix of different sulfur source.  相似文献   

8.
Thirty-seven Kupferschiefer samples from southwestern Poland were analyzed by microscopy, Rock-Eval approach and instrumental neutron activation analysis to understand the geochemical and morphological characteristics of kerogen present in the samples. The analytical results indicate that there are two different types of kerogens. One type was only subjected to thermal alteration processes, and the other was further oxidized after deposition of the sediment.In the oxidized samples migrabitumen was transformed into pyrobitumen. Rock-Eval analyses show a significant decrease in HI values in the oxidized samples and an increase in OI values in relation to the samples that were not influenced by oxidation. Variations in S2 versus Corg contents indicate a change in kerogen from Type II to Type III with progressing oxidation. The presence of pyrobitumen and the depletion of hydrogen in the altered kerogen allow one to conclude that the kerogen was used as hydrogen donor for thermochemical sulfate reduction(TSR).  相似文献   

9.
Water samples from the Wujiang River, a typical karst river system, were analyzed for major ion concentrations and δ^34S values of dissolved sulfate in order to identify the sources of sulfate, quantify the sulfate export flux and understand the role of sulfur cycling in chemical weathering rate of carbonate. Spatial variations in sulfate concentration and sulfur isotopic composition of tributaries over the catchment area are obvious, allowing to decipher S sources between rocks and atmosphere. According to the variations in sulfate concentration and isotopic composition, it is inferred that sulfate ions in the upper-reach river waters may have three sources, rain water, sulfate resultant from oxidation of pyrite in coal, and sulfate from sulfide deposits. In the lower reaches, the S isotopic composition of the samples lies mainly on a mixing trend between evaporite sulfate and rainwater sulfate, the contribution of sulfate from oxidation of pyrite being lesser. A pronounced seasonal variation in both content and isotopic composition of sulfate characterizes the Wujiang River. The average sulfate concentration of the waters is 0.65 mmol/L in winter, 0.17 mmol/L higher than that in summer. River water δ^34S values range from -15.7‰ to 18.9‰ in winter, while the δ^34S values of river waters in summer vary to a lesser extent than in winter, from -11.5‰ to 8.3‰. The δ^34S values of the main stream range from -6.7‰ to -3.9‰ in summer, averaging 3‰ lower than in winter. This indicates that in summer, when the discharge increases, the contribution of a source enriched in light isotopes to the atmosphere or the oxidation of pyrite in coal is more important.  相似文献   

10.
In order to constrain sulfur isotope compositions of ore-forming fluids, ore-forming temperature, source of sulfur and mechanism of sulfur reduction in the Huize lead-zinc ore field, based on sulfur isotope compositions from previous studies, new data of sulfur isotopic composition of primary sulfide of upper ore-bodies in Qilinchang and newly-found sulfate outside the deposits were utilized in this study. It show that 5 values of primary sulfide vary from 8. Oft∗ to 17. 68 ft∗ , and sulfur isotopes in ore-forming fluid have reached equilibrium; S'lS values of sulfur out side the deposits vary from 17. 95ft∗ to 24. 30ft∗ with average value of 20. 14ft∗ , yielding sulfur isotopic composition of ore-for ming fluids as 14. 14ft∗ by the Pinekney method for mineral association. The value is close to 5'4S of marine sulfate. Ore-forming temperature is calculated as 1 34 - 388by isotope geological thermometer. The results of fluid inclusion thermometer indicate that barites were crystallized from hydrothermal fluid, which is suggested that sulfur in ore-forming fluid probably originates from marine sulfate of stratum in and outside the deposits or hydrothermal barites found in ore district. Reduction mechanism of sulfate is likely to be themio-chemical sulfate reduction.  相似文献   

11.
Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcites were noticed in distinct intervals in a 32 m long piston core, collected in the gas hydrate- bearing sediments in the northern portion of the Krishna-Godavari basin, eastern continental margin of India at a water depth of 1691 m. X-ray diffraction and energy dispersive spectrum studies confirm presence of pyrite, gypsum, calcite, and other mineral aggregates. The occurrence of gypsum in such deep sea environment is intriguing, because gypsum is a classical evaporite mineral and is under saturated with respect to sea water. Sedimentological, geochemical evidences point to diagenetic formation of the gypsum due to oxidation of sulphide minerals (i.e. pyrite). Euhedral, transparent gypsum crystals, with pyrite inclusions are cemented with authigenic carbonates, possibly indicating that they were formed authigenically in situ in the gas hydrate-influenced environment due to late burial diagenesis involving sulphate reduction and anaerobic oxidation of methane (AOM). Therefore, the authigenic gypsums found in sediments of the Krishna-Godavari and Mahanadi offshore regions could be seen as one of the parameters to imply the presence of high methane flux possibly from gas hydrate at depth.  相似文献   

12.
Groundwater from karst subterranean streams is among the world’s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes’ sources is very important to ensure the normal function of life support systems. In this paper, thirty?five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca?HCO3 type or Ca (Mg)?HCO3 type. However, some hydrochemical types of karst groundwater were the K+Na+Ca?SO4 type (G25 site) or Ca?HCO3+SO4 type (G26 and G14 site), indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the 87Sr/86Sr varied from 0.70751 to 0.71627. The δ34S?SO42? fell into a range of ?6.8‰?21.5‰, with a mean value of 5.6‰. The variations of both 87Sr/86Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of 87Sr/86Sr vs. Sr2+/[K++Na+] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the δ34S value of potential sulfate sources. The variations of both δ34S and 1/SO42? values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sul?de mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) have contributed to solutes in karst groundwater. The influence of oxidation of sul?de mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.  相似文献   

13.
34samples of loess-paleosol from the Luochuan and Xifeng sections in the Loess Plateau,northern China were eparated into sand,silt and clay fractions and analyzed for their mineral compositions.The results indicate that there is almost no difference between loess and paleosol in mineral composition.Major mineral species are quartz,mica,feldspar and chlorite,accounting for about 88-92% of the total;other minerals are kandite,smectite,vermiculite and a few heavy minerals.The calcite,magnetite and hematite were not taken into consideration because of their removal in the process of sample preparation.The main difference with respect to the mineral composition of samples collected from different sections and different statigraphic levels lies in the amount and grain size of minerals hosted.Comparisons between the Luochuan section and the Xifeng section,between paleosol and loess and between the upper part and the lower part of some paleosol layers show that the formers contain less feldspar but more mica and vermiculite and are finer in grain size,indicating the co-occurrence of both biochemical weathering process responsible for mineral change and physical weathering process leading to grain-size change during the soil-forming processes.This result favours such an explanation of the soil-forming mechanism that loess deposition and paleosol development occurred synchronously,though the rate of soil formation was greater than that of loess deposition,thus leading to soil development.  相似文献   

14.
Qiongdongnan Basin has a tectonic geological background of high temperature and high pressure in a deep reservoir setting,with mantle-derived CO2.A water-rock reaction device was used under high temperature and high pressure conditions,in conjunction with scanning electron microscope(SEM)observations,to carry out an experimental study of the diagenetic reaction between sandstone at depth and CO2-rich fluid,which is of great significance for revealing the dissolution of deep clastic rock reservoirs and the developmental mechanism of secondary pores,promoting deep oil and gas exploration.In this study,the experimental scheme of the water-rock reaction system was designed according to the parameters of the diagenetic background of the deep sandstone reservoir in the Qiongdongnan Basin.Three groups of single mineral samples were prepared in this experiment,including K-feldspar samples,albite samples and calcite samples.Using CO2 as a reaction solution,a series of diagenetic reaction simulation experiments were carried out in a semi-closed high temperature and high pressure simulation system.A field emission scanning electron microscope(SEM)was used to observe the microscopic appearance of the mineral samples after the water-rock reaction,the characteristics of dissolution under high temperature and high pressure,as well as the development of secondary pores.The experimental results showed that the CO2-rich fluid has an obvious dissolution effect on K-feldspar,albite and calcite under high temperature and high pressure.For the three minerals,the main temperature and pressure window for dissolution ranged from 150℃to 300℃and 45 MPa to 60 MPa.Scanning electron microscope observations revealed that the dissolution effect of K-feldspar is most obvious under conditions of 150℃and 45 MPa,in contrast to conditions of200℃and 50 MPa for albite and calcite.Through the comparative analysis of experimental conditions and procedures,a coupling effect occurred between the temperature and pressure change and the dissolution strength and calcite.Under high temperature and high pressure,pressure changed the solubility of CO2,furthermore,the dissolution effect and strength of the sandstone components were also affected.The experiment revealed that high temperature and high pressure conditions with CO2-rich fluid has a significant dissolution effect on aluminosilicate minerals and is conducive to the formation of secondary pores and effective reservoirs.Going forward with the above understanding has important implications for the promotion of deep oil and gas exploration.  相似文献   

15.
The Jinshachang lead–zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan–Yunnan–Guizhou(SYG) Pb–Zn–Ag multimetal mineralization area in China.Sulfides minerals including sphalerite,galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite,quartz,and barite,making this deposit distinct from most lead–zinc deposits in the SYG.This deposit is controlled by tectonic structures,and most mineralization is located along or near faults zones.Emeishan basalts near the ore district might have contributed to the formation of orebodies.The δ34S values of sphalerite,galena,pyrite and barite were estimated to be 3.6‰–13.4‰,3.7‰–9.0‰,6.4‰ to 29.2‰ and 32.1‰–34.7‰,respectively.In view of the similar δ34S values of barite and sulfates being from the Cambrian strata,the sulfur of barite was likely derived from the Cambrian strata.The homogenization temperatures(T ≈ 134–383°C) of fluid inclusions were not suitable for reducing bacteria,therefore,the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district.Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur,it was not the main mechanism.Considering other aspects,it can be suggested that sulfur of sulfides should have been derived from magmatic activities.The δ34S values of sphalerite were found to be higher than those of coexisting galena.The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions,suggesting that the sulfur isotopic composition in ore-forming fluids had reached a partial equilibrium.  相似文献   

16.
Desert terrains in northern China are covered by widespread regolith sediments which mask geochemical signals from ore bodies and are major obstacles to mineral exploration. There is a critical need to study the vertical distribution of elements in this regolith and to establish optimum sampling and analytical methods. The aim of this study is to understand the dispersion and variation of elements throughout the cover in a vertical profile. The results demonstrate that the main elements show a distribution pattern of enrichment in clay layers in the vertical profile, i.e., most elements tend to be enriched in the most upper part of the profile above the orebodies except for some elements like Cu, Ca and Ag. Meanwhile, both fine (-160 mesh) and coarse (+20 mesh) fraction samples from clay-rich horizons are favorable samples and selective leaching of the elements absorbed on clays or oxide coatings is effective for localizing buried deposits. The distribution of active Cu and Mo is quite different because chalcopyrite is weathered into Cu sulfate and CuCO3, and is precipitated in alkaline environments in a layer below close to the surface. Mo is soluble in the alkaline environment so it can penetrate the caliche layer and be enriched on the surface of soil enriched with weakly cemented clay.  相似文献   

17.
Northern taiga ecosystems on hard gypsum outcrops were studied at the area of Plnega State Reserve in the Arkhangelsk region of Russia. Landscapes on gypsum outcrops are very specific and characterized by a dissected karst topography and predominance of soils formed on hard gypsum. Phytocenoses confined to soils on hard gypsum are oligotrophic and significantly differ from generally known boreal forests. In the northern taiga, these are open woodlands characterized by the prevalence of suppressed pines and larches and the presence of rare arcto-alpine species （e.g. Gypsophylla uralensis subsp, pinegensis） in the lower tiers. It was found that ecosystems on gypsum outcrops are very vulnerable for fires with slow processes of vegetation recovery. Chemical methods of rocks, soils and plants samples investigation include pH （potentiometrically）, humus （T＇urin＇s method）, nitrogen （K＇eldal＇s method） and total content of other 20 macro- and microelements （X-ray fluorescence analysis）. The analysis of hard gypsum and the local geochemical background of the Pinega region （glacial loamy deposits） showed that gypsum rock is enriched only in S, Ca, and Sr： it consists of 99% CaSO4＊2H2O and is non-calcareous according to pH levels and negative result of qualitative reaction with HCl. The contents of Br, Pb and N are close to those of moraine. But most of nutrients have concentrations insufficient for normal plant growth, e.g. K and Mn are found in quantities of 1/400 and less than 1/1000 of their contents in silicate loamy soils of the study area. Distribution of all chemical elements in the profiles of soils formed on gypsum shows that there is no accumulation of any eluvium during soil formation because of total dissolution of disintegrated gypsum material. In this specific soil litter is the main horizon of most of nutrient concentration and, therefore, its role for plants nutrition became more important than in soils on glacial loams. The fires destroying soil litter, which is extremely precious for the whole ecosystem on geochemically pure gypsum, also causes an intensive denudation of organic horizons on slopes of karst landforms.  相似文献   

18.
Mineral dust, including dust storm, fugitive and floating dust are the most important components of ambient aerosol in northern China during spring. Meanwhile, it goes through heating period when fossil fuel combustion acts as a dominant source. In order to understand the chemical characteristics of fine particles in North China, two sampling sites was established in Baotou City in the west of Inner Mongolia Autonomous Region and Wuwei City near the edge of Gobi to collect fine particles （PM 2.5） samples in the spring of 2004 and 2005, and analyze mass concentrations, ionic species and some element components of PM 2.5. The results indicated that dust events elevated the mass concentrations of particulate matter significantly, not only for coarse particles, but also for fine particles. Crustal components, organic matter and sulfates are three major compositions in fine particles, their mass concentrations and relative abundances are closely related with the frequency of dust events and coal combustion. The characteristics of fine particles are obviously diverse under different atmospheric conditions. （1） When the dust storms take place, the wind speeds are often higher than 10 m/s. A plenty of mineral aerosol is input from long distance, and also local soil dust is blown up to suspend in the air as particles. Therefore, the concentrations of PM 2.5 are enhanced dramatically. Mass concentrations and relative percentages of crustal components in PM 2.5 increased significantly during dust events. The mineral dust may help gas to particle conversation by heterogeneous reactions. Increases in mass concentrations of SO4^2-, NO3^- and NH4^＋ and organic matter in PM 2.5 were observed evidently. But their fractions in PM 2.5 do not increase simultaneously due to dilution of storing wind. （2） When wind velocity is lower （〈3 m/s）, air pollutants are accumulated, both mass concentrations of SO4^2-, NO3^- and NH4^＋ and organic matter, and their fractions in PM 2.5 increase, indicating severe anthropogenic pollution. The chemical characteristics of PM 2.5 in Baotou and Wuwei are also influenced by their industrial structure, topography and meteorological conditions.  相似文献   

19.
Pyrite framboids were found in the Permian-Triassic boundary at Meishan Section, while their sulfur isotopes were determined. The majority of framboids is less than 5 μm in diameter, with some large-sized framboids. Also, euhedral gypsums were observed in the boundary clay. The authors suppose that most of the pyrite framboids formed just below the redox boundary and stopped growing after entering the lower water column. The result indicates that it was probably lower dysoxia condition in the temporal ocean. Moreover, the authors also presume that some pyrite was oxidated to sulfates accompanying the fluctuation of redox condition, which would probably be the origin of the negative sulfur isotopes of gypsum and CAS reported before. In addition, sulfur isotope of framboidal pyrite suggests that sulfur is originated from bacterial sulfate reduction in anoxic condition. Therefore, this study confirms that the ocean was widely anoxic during the Permian-Triassic transitional period. However, the redox condition in temporal ocean was probably not stable, with short-term fluctuations.  相似文献   

20.
The determined results of the sulfur contents and isotopic composition of coal samples from major coal mines in 15 provinces and regions of China show that the coal mined in the north of China is characterized by higher ^34S and lower sulfur content, but that in the south of China has lower ^34S and higher sulfur content.During the coal-burning process in both indrstrial and daily use of coal as fuel the released sulfur dioxide is always enriched in lighter sulfur isotope relative to the corresponding coal;the particles are always enriched in heavier sulfur isotope.The discussion on the environmental geochemical significance of the above-mentioned results also has been made.  相似文献   

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