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1.
Environmental assessment of Dhaka City (Bangladesh) based on trace metal contents in road dusts 总被引:1,自引:0,他引:1
Geochemical analysis of street dusts was conducted to evaluate the environment of Dhaka City, Bangladesh. Dust samples were
collected from different areas (industrial, commercial, and residential) of Dhaka City, and their major, trace and rare earth
elements (REE) were determined. Samples from the commercial area had Pb concentrations double those of the industrial and
residential areas. Contents of Zn, Cu, Ni, and Cr in the industrial areas were greater than those in the commercial and residential
areas. The REE patterns of all dusts in Dhaka are similar and are comparable to the average upper continental crust. The condition
of the Dhaka environment was compared to that in Japan and other baseline sediments using Zn–Fe2O3 and Pb–Fe2O3 diagrams. Zn–Fe2O3 trends for the dusts show steep inclination compared to the baseline sediment and the Japanese urban sediment trends. Dhaka
lake data show enrichment of Zn over the dusts, suggestive of Zn pollution from poorly controlled industrial sources. In contrast,
on the Pb–Fe2O3 diagram, Dhaka dusts have greater Pb contents than lake sediments, probably due to the higher traffic density in the commercial
area compared to the residential area including the area around the lake. The results suggest that higher levels of Pb and
Zn in street dusts in Dhaka can most likely be attributed to the anthropogenic sources like vehicle emissions to the atmosphere
and a rapid development. 相似文献
2.
MATTHIAS MOROS WOLFRAM LEMKE ANTOON KUIJPERS RUDOLF ENDLER JØRN BO JENSEN OLE BENNIKE FRANZ GINGELE 《Boreas: An International Journal of Quaternary Research》2002,31(2):151-162
Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several distinct reflectors. The physical, sedimentological, mineralogical and geochemical properties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS 14C data and biostratigraphic information were gathered. Based on this multi‐proxy approach, seven lithostratigraphic units (AI, AII, B to F) were distinguished. These consist of fine‐grained clay, silt and mud, and are separated from each other by thin basin‐wide traceable sandy layers (Sab‐Sef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain‐size fraction >63μm. In addition, some of the quartz‐grain‐dominated sandy layers cause the strong reflection lines recorded in seismoacoustic profiles. The sandy layers are interpreted to reflect enhanced hydrodynamic energy induced by episodes of basin‐wide water‐level low‐stand conditions. These low stands resulted from water‐level drops that occurred frequently during the Baltic Sea's history and presumably affected the entire Baltic basin. The thick fine‐grained units AI, AII to F, in which coarser material is absent, represent water‐level high‐stands. We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and after the Billingen‐1 regression, respectively. We assign the most prominent sandy layer Sab to the final drainage of the Baltic Ice Lake (Billingen‐2), whereas the sandy layers between units B, C., D and E are related to the Yoldia Sea and Ancylus Lake regressions of the Baltic Sea's history. The uppermost fine‐grained unit F with its high organic carbon content contains marine sediments deposited after the Littorina Transgression. The macroscopically well‐visible sediment colour change from reddish/brown‐to‐grey, previously interpreted as a regional stratigraphic boundary, varies from core to core. It has been shown by our new data that this colour change has a diagenetic origin, and thus does not represent a stratigraphic boundary. Previous subdivisions therefore have to be revised. 相似文献
3.
Two cores of sediments, named NR and EB, were collected in the Simbock Lake (Mefou watershed, Yaoundé) to assess their provenance and the degree of heavy metal pollution based on mineralogical and geochemical data. The sediments are sandy, sand-clayey to clayey, and yellowish brown to greenish brown, and with high amounts of organic matter (average value of TOC is 1.95%). The sediments are mainly composed of quartz, kaolinite, accessory goethite, smectite, rutile, feldspars, illite, gibbsite, and interstratified illite-vermiculite. Fourier transform infrared (FT-IR) spectroscopy shows that kaolinite is less crystallized in the NR core than in the EB core. The Index of Compositional Variability (ICV), Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and the Rb/Sr and K2O/Rb ratios indicate a high weathering intensity in the source area. These sediments have low contents in Al2O3, Fe2O3, Na2O, K2O, MgO, and CaO as well as high values in SiO2, P2O5, TiO2, and MnO relative to the upper continental crust. The concentrations of Cr, V, Ba, and Zr are higher in the NR core than those in EB. The total rare earth element (REE) content varies between 78 and 405 ppm. The light REE are abundant (LREE/HREE ~?18–59; avg.?=?25.61). The chondrite-normalized REE patterns exhibit (i) negative Eu anomaly (Eu/Eu* ~?0.38–0.62; avg.?=?0.5), (ii) slight positive Ce anomaly (Ce/Ce* ~?1.11–1.34; avg.?=?1.11), and (iii) high REE fractionation ((La/Yb)N ~?12.3–51.75; avg.?=?25.61). The enrichment factor (EF) shows that the Mefou watershed through the Simbock Lake sediments is slightly polluted by the agricultural and urban activities. 相似文献
4.
Geochemistry and mineralogy of shallow alluvial aquifers in Daudkandi upazila in the Meghna flood plain, Bangladesh 总被引:1,自引:0,他引:1
M. Aziz Hasan Mattias von Br?mssen Prosun Bhattacharya Kazi Matin Ahmed Arif Mohiuddin Sikder Gunnar Jacks Ondra Sracek 《Environmental Geology》2009,57(3):499-511
The shallow alluvial aquifers of the delta plains and flood plains of Bangladesh, comprises about 70% of total land area are
mostly affected by elevated concentrations of arsenic (As) in groundwater exposing a population of more than 35 million to
As toxicity. Geochemical studies of shallow alluvial aquifer in the Meghna flood plain show that the uppermost yellowish grey
sediment is low in As (1.03 mg/kg) compared to the lower dark grey to black sediment (5.24 mg/kg) rich in mica and organic
matter. Sequential extraction data show that solid phase As bound to poorly crystalline and amorphous metal (Fe, Mn, Al)-oxyhydroxides
is dominant in the grey to dark grey sediment and reaches its maximum level (3.05 mg/kg) in the mica rich layers. Amount of
As bound to sulphides and organic matter also peaks in the dark grey to black sediment. Vertical distributions of major elements
determined by X-ray fluorescence (XRF) show that iron (Fe2O3), aluminum (Al2O3) and manganese (MnO) follow the general trend of distribution of As in the sediments. Concentrations of As, Mn, Fe, HCO3
−, SO4
2− and NO3
− in groundwater reflect the redox status of the aquifer and are consistent with solid phase geochemistry. Mineralogical analysis
by X-ray diffraction (XRD) and scanning electron microscopy (SEM) fitted with energy dispersive X-ray spectrometer (EDS) revealed
dominance of crystalline iron oxides and hydroxides like magnetite, hematite and goethite in the oxidised yellowish grey sediment.
Amorphous Fe-oxyhydroxides identified as grain coating in the mica and organic matter rich sediment suggests weathering of
biotite is playing a critical role as the source of Fe(III)-oxyhydroxides which in turn act as sink for As. Presence of authigenic
pyrite in the dark grey sediment indicates active reduction in the aquifer. 相似文献
5.
Geochemical elements characteristics and sources of the riverbed sediment in the yellow river’s desert channel 总被引:1,自引:0,他引:1
The Yellow River flows through an extensive area of aeolian desert and extends from Xiaheyan, Ningxia Province, to Hekouzhen, Inner Mongolia Province, for a total of 1,000 km. In the desert channel of the Yellow River, the major chemical components are SiO2, Fe2O3, Al2O3, Ti, CaO, MgO, Ba, P, Mn, Ce, Co in which SiO2, Al2O3, Fe2O3, and Ti have significant value as indicators of the sources of the coarse sediment. The spatial distribution of the elements’ weight percentages and the ratios of Si/Ti, Si/Al between sediment sources and riverbed sediment of the Gansu reach and the desert channel of the Yellow River, indicating that the coarse sediments deposited in the desert reach of the Yellow River are mostly controlled by the local sediment sources; and due to the higher mobility of the fine sediments, they are primarily contributed by the local sediment sources and the tributaries that originate from the loess area of the upper reach of Yellow River. The results of R-factor analysis illustrate that the first component score mainly shows negative values in the desert channel, suggesting that the coarse sediments in this reach contain a higher content of Si and a lower content of Mg + Ca + Al + Fe, which further proves that the Ningxia Hedong, Inner Mongolian Wulanbuhe, and Kubuqi deserts are the primary sources of the coarse sediment in the desert channel of the Yellow River. 相似文献
6.
《Applied Geochemistry》2001,16(9-10):1201-1213
In a core of sub-aquatic sediment from Erhai Lake, southwestern China, 4 Fe species were identified as paramagnetic Fe3+, superparamagnetic Fe3+, hematite Fe3+, and paramagnetic high-spin Fe2+ using Mössbauer spectroscopy. The 120 cm core has a distinct lithological boundary at a depth of about 70 cm. Each Fe species has a distinctive distribution with depth. These results represent the redox conditions within the sediment, and also probably reflect the primary sedimentary environments. With increasing burial depth, hematite (Fe2O3) decreased, especially below depths greater than 25 cm, and finally disappeared at around 95 cm. The summed paramagnetic Fe3+ (superparamagnetic Fe3++paramagnetic Fe3+) did not change as much, only exhibiting a slight decrease at depths greater than 75 cm, about 5 cm beneath the lithological boundary within the core. The intensity of paramagnetic high-spin Fe2+ increased with depth. These vertical variations were in harmony with organic geochemical parameters such as TOC concentration, H-index and O-index, indicating that reducing conditions are strongly intensified in the sediment below 70 cm. The geological, organic geochemical and 14C data combined with the present Mössbauer spectroscopic study give a strong indication that the redox environment of Erhai Lake probably shifted rather rapidly from a deep reducing to a shallow oxic state at about 2 ka ago. 相似文献
7.
Relatively strongly magnetic fine components (< 30μm, XS-4J and DS-4J) which are most environmentally sensitive were separated from layer S5-1 in the Xifeng and Duanjiapo loess sections and analyzed by MPV-3 for their morphometric characteristics and reflectance, SEM-ESD for their element contents and XRD for their mineral phases, respectively. The results showed that minerals in both samples are dominated by detrial Fe-Ti oxides of aeolian origin. In sample XS-4J the reflectance and iron contents of magnetic minerals are usually high. In addition to magnetite (Fe3O4), maghemite (γFe2O3) and hematite (Fe2O3), some Fe-high oxide (72.25 wt%–86.67 wt%), ilmenite (FeTiO3), and magnetite-ulvöspinel [Fe(FeCr)O4, Fe (FeNi)O4] were also detected. In sample DS-4J obvious negative linear correlations were found between Ti and Fe, and the contents of Mn, Si, Al and Ca are usually high and the minerals are dominated by magnetite (maghemite), goethite (FeOOH) and limonite (containing Si and OH). In addition, the signs of corrosion of magnetic minerals and newly crystallized magnetite (maghemite) were recognized. Differences in the composition and assemblage characteristics of magnetite minerals between XS and DS reflect significant differences in source rocks and preserving conditions. 相似文献
8.
Liam Courtney‐Davies Sarah E. Gilbert Cristiana L. Ciobanu Simon R. Tapster Marcus W. Richardson Nigel J. Cook Benjamin P. Wade Max R. Verdugo‐Ihl Kathy Ehrig Daniel J. Condon 《Geostandards and Geoanalytical Research》2021,45(1):143-159
In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe2O3) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe2O3 were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology. 相似文献
9.
Microelectrode Study of Oxygen Uptake and Organic Matter Decomposition in The Sediments of Xiamen Western Bay 总被引:2,自引:0,他引:2
Sediment cores were sampled from Xiamen Western Bay at five sites during the summer and winter of 2006 and Hg–Au microelectrodes
were used to make on board measurements of the concentration gradients of dissolved oxygen, Mn2+, and Fe2+ within the sediments. The O2 concentrations decreased sharply from about 200 μmol L−1 in the bottom seawater to zero within a depth of a few millimeters into the sediment. Dissolved Mn2+ was detected below the oxic zones with peak concentrations up to 600 μmol L−1, whereas dissolved Fe2+ had peak concentrations up to 1,000 μmol L−1 in deeper layers. The elemental contents of organic carbon and nitrogen within the sediments were analyzed and their C/N
ratios were in the range of 9.0 to 10.1, indicative of heavy terrestrial origin. Sediments from two sites near municipal wastewater
discharge outlets had higher organic contents than those from the other sites. These high organic contents corresponded to
shallow O2 penetration depths, high dissolved Mn2+ and Fe2+ concentrations, and negative redox potentials within the sediments. This indicated that the high organic matter content had
promoted microbial respiration within the sediments. Overall, the organic content did not show any appreciable decrease with
increasing sediment depths, so a quadratic polynomial function was used to fit the curve of O2 profiles within the sediments. Based on the O2 profiles, O2 fluxes across the seawater and sediment interface were estimated to be in the range 6.07 to 14.9 mmol m−2 day−1, and organic carbon consumption rates within the surface sediments were estimated to be in the range 3.3 to 20.8 mgC cm−3 a−1. The case demonstrated that biogeochemistry within the sediments of the bay was very sensitive to human activities such as
sewage discharge. 相似文献
10.
《Applied Geochemistry》1993,8(1):51-65
Interstitial water samples and sediments were collected from acidified Woods Lake (pH= 5.0) to evaluate Pb profile stability and distribution between the solid and aqueous phases. A simple equation was developed to describe the distribution coefficient for Pb(KdPb), based on the sample moisture content and analyte concentrations in bulk sediment and pore water. In Woods Lake sediment KdPb values ranged from 6.7 × 104to6.7 × 105ml/g. The affinity of Pb for the solid phase was further demonstrated by inverting a sediment core and leaving it for 10 months in situ. Upon retrieval, the Pb profile was found to have remained intact over the same depth, albeit inverted, as in the surrounding sediment. Geochemical modeling using MINTEQA2 demonstrates that Pb solids that may reasonably be expected to precipitate were all undersaturated by several orders of magnitude with respect to the interstitial water, indicating that Pb was sorbed to, rather than precipitated in, Woods Lake sediment. 相似文献
11.
The stability of pumpellyite + actinolite or riebeckite + epidote + hematite (with chlorite, albite, titanite, quartz and H2O in excess) mineral assemblages in LTMP metabasite rocks is strongly dependent on bulk composition. By using a thermodynamic approach (THERMOCALC), the importance of CaO and Fe2O3 bulk contents on the stability of these phases is illustrated using P–T and P–X phase diagrams. This approach allowed P–T conditions of ~4.0 kbar and ~260 °C to be calculated for the growth of pumpellyite + actinolite or riebeckite + epidote + hematite assemblages in rocks containing variable bulk CaO and Fe2O3 contents. These rocks form part of an accretionary wedge that developed along the east Australian margin during the Carboniferous–Triassic New England Orogen. P–T and P–X diagrams show that sodic amphibole, epidote and hematite will grow at these conditions in Fe2O3‐saturated (6.16 wt%) metabasic rocks, whereas actinolite and pumpellyite will be stable in CaO‐rich (10.30 wt%) rocks. With intermediate Fe2O3 (~3.50 wt%) and CaO (~8.30 wt%) contents, sodic amphibole, actinolite and epidote can coexist at these P–T conditions. For Fe2O3‐saturated rocks, compositional isopleths for sodic amphibole (Al3+ and Fe3+ on the M2 site), epidote (Fe3+/Fe3+ + Al3+) and chlorite (Fe2+/Fe2+ + Mg) were calculated to evaluate the efficiency of these cation exchanges as thermobarometers in LTMP metabasic rocks. Based on these calculations, it is shown that Al3+ in sodic amphibole and epidote is an excellent barometer in chlorite, albite, hematite, quartz and titanite buffered assemblages. The effectiveness of these barometers decreases with the breakdown of albite. In higher‐P stability fields where albite is absent, Fe2+‐Mg ratios in chlorite may be dependent on pressure. The Fe3+/Al and Fe2+/Mg ratios in epidote and chlorite are reliable thermometers in actinolite, epidote, chlorite, albite, quartz, hematite and titanite buffered assemblages. 相似文献
12.
Nguo Sylvestre KANOUO Khin ZAW Rose Fouateu YONGUE Frederick Lin SUTHERLAND Sebastien MEFFRE Emmanuel NJONFANG Changqian MA Milan Stafford TCHOUATCHA 《Resource Geology》2012,62(3):316-324
Zircons and other heavy minerals (corundum, rutile, ilmenite, magnetite, sillimanite) are identified in the Nsanaragati gem corundum placer deposit, in the western part of the Mamfe sedimentary basin, SW Cameroon. These alluvial minerals have different morphological characteristics and zircons, in particular, vary mostly in colour and shape. They are reddish, brownish, yellowish, pink or colourless. These minerals form rounded and sub‐rounded alluvial grains, prismatic, pyramidal or dipyramidal crystals. Reddish zircons retain their original crystallographic shape. Trace element and U–Pb isotopic geochemical analyses of these reddish zircons, using the LA‐ICP‐MS method give significant Hf (4576–6334 ppm), Th (46–1565 ppm) and U (66–687 ppm) contents, with Th/U ratio ranging from 0.6 to 3.0. The 206Pb/238U corrected mean age gave 12.39 ± 0.55 Ma, which characterizes an Upper Cenozoic (Serravallian) magmatic event. The zircons are probably sourced from a magmatic field in the South eastern boundary of the Cross River Formation. The Cameroon Volcanic Line of basaltic and alkaline lavas and intrusions which lie east of the Mamfe Basin mostly range in age from 37 Ma to <1 Ma. The zircons may also relate to the Mount Bambouto plateau lavas which lie northeast of the Mamfe sedimentary basin and have an eruptive age range of 21–14 Ma. The oldest Nsanaragati reddish zircon ages overlap within error with the end stages of the Bambouto eruptions. This eruptive or a related episode provides a potential source for megacrystic reddish zircons within the Nsanagarati placer deposit. 相似文献
13.
We have investigated the effects of different Fe2O3 bulk contents on the calculated phase equilibria of low‐T/intermediate‐P metasedimentary rocks. Thermodynamic modelling within the MnO–Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (MnNKFMASHTO) chemical system of chloritoid‐bearing hematite‐rich metasedimentary rocks from the Variscan basement of the Pisani Mountains (Northern Apennines, Italy) fails to reproduce the observed mineral compositions when the bulk Fe2O3 is determined through titration. The mismatch between observed and computed mineral compositions and assemblage is resolved by tuning the effective ferric iron content by P–XFe2O3 diagrams, obtaining equilibration conditions of 475 °C and 9–10 kbar related to a post‐compressional phase of the Alpine collision. The introduction of ferric iron affects the stability of the main rock‐forming silicates that often yield important thermobaric information. In Fe2O3‐rich compositions, garnet‐ and carpholite‐in curves shift towards higher temperatures with respect to the Fe2O3‐free systems. The presence of a ferric‐iron oxide (hematite) prevents the formation of biotite in the mineral assemblage even at temperatures approaching 550 °C. The use of P–T–XFe2O3 phase diagrams may also provide P–T information in common greenschist facies metasedimentary rocks. 相似文献
14.
The uncommon Mg-rich and Ti-poor Zhaoanzhuang serpentine-magnetite ores within Taihua Group of the North China Craton(NCC) remain unclear whether the protolith was sourced from ultramafic rocks or chemical sedimentary sequences. Here we present integrated petrographic and geochemical studies to characterize the protoliths and to gain insights on the ore-forming processes. Iron ores mainly contain low-Ti magnetite(TiO_2 ~0.1 wt%) and serpentine(Mg#=92.42–96.55), as well as residual olivine(Fo=89–90), orthopyroxene(En=89–90) and hornblende. Magnetite in the iron ores shows lower Al, Sc, Ti, Cr, Zn relative to that from ultramafic Fe-Ti-V iron ores, but similar to that from metamorphic chemical sedimentary iron deposit. In addition, interstitial minerals of dolomite, calcite, apatite and anhydrite are intergrown with magnetite and serpentine, revealing they were metamorphic, but not magmatic or late hydrothermal minerals. Wall rocks principally contain magnesian silicates of olivine(Fo=83–87), orthopyroxene(En=82–86), humite(Mg#=82–84) and hornblende [XMg=0.87–0.96]. Dolomite, apatite and anhydrite together with minor magnetite, thorianite(Th-rich oxide) and monazite(LREE-rich phosphate) are often seen as relicts or inclusions within magnesian silicates in the wall rocks, revealing that they were primary or earlier metamorphic minerals than magnesian silicates. And olivine exists as subhedral interstitial texture between hornblende, which shows later formation of olivine than hornblende and does not conform with sequence of magmatic crystallization. All these mineralogical features thus bias towards their metamorphic, rather than magmatic origin. The dominant chemical components of the iron ores are SiO_2(4.77–25.23 wt%), Fe_2O_3 T(32.9–80.39 wt%) and MgO(5.72–27.17 wt%) and uniformly, those of the wall rocks are also SiO_2(16.34–48.72 wt%), Mg O(16.71–33.97 wt%) and Fe_2O_3 T(6.98–30.92 wt%). The striking high Fe-Mg-Si contents reveal that protolith of the Zhaoanzhuang iron deposit was more likely to be chemical sedimentary rocks. The distinct high-Mg feature and presence of abundant anhydrite possibly indicate it primarily precipitated in a confined seawater basin under an evaporitic environment. Besides, higher contents of Al, Ti, P, Th, U, Pb, REE relative to other Precambrian iron-rich chemical precipitates(BIF) suggest some clastic terrestrial materials were probably input. As a result, we think the Zhaoanzhuang iron deposit had experienced the initial Fe-Mg-Si marine precipitation, followed by further Mg enrichment through marine evaporated process, subsequent high-grade metamorphism and late-stage hydrothermal fluid modification. 相似文献
15.
M. G. Kale Ashwin S. Pundalik R. A. Duraiswami N. R. Karmalkar 《Journal of the Geological Society of India》2016,87(2):194-204
Soft sediment deformation structures such as slump folds, clastic dyke, syn-sedimentary faults and convolute bedding are present in the coarse–fine grained yellowish buff coloured sandstone, and interbedded reddish brown fine grained sandstone and yellowish–white siltstone at the Khari River section belonging to Rudramata member of Jhuran Formation (Upper Jurassic), Kutch. These soft sediment deformation structures are confined to lower and middle parts of the section and are invariably underlain as well as overlain by undeformed beds that have restricted lateral and vertical extent and occur in close proximity of Kutch Mainland Fault, thereby suggesting that these structures were formed by seismic activity and therefore represents seismites. 相似文献
16.
Two Holocene sediment cores were retrieved respectively from the enclosed Lake Daihai in the monsoon/arid transition zone
of North China and the Taihu Lake coast in the monsoonal area of the Yangtze delta, Eastern China. Distribution of major geochemical
elements and their ratios were employed to reveal the characteristics of Holocene climate and associated environmental implications
in the two regions. It is suggested that the temporal distribution of major elements serve as a useful indicator to denote
the variations of monsoon effective precipitation for the enclosed lake area. High values of resistant elements such as Al2O3, SiO2, TiO2, (FeO + Fe2O3), MnO in the lake sediments correspond to the depressed chemical weathering and weakened mon-soon effective precipitation,
while the highs of mobile and easy soluble elements such as MgO, CaO, Na2O reflect the enhanced chemical weathering and increased monsoon effective precipitation in the lake basin. In comparison,
the behaviors of the major elements in sediments of the Taihu Lake coast were largely controlled by the changes both in sea
transgression in the different Holocene time periods and the monsoon precipitation. The relatively highs of Al2O3, TiO2, (FeO + Fe2O3), in marine-influenced sediments suggest relatively strong coastal hydrodynamics and chemical weathering, and vice versa.
Meanwhile, the lows of SiO2, Na2O and CaO in the non-marine-influenced sediments also denote relatively strong hydrodynamics and chemical weathering due to
enhanced monsoon precipitation, and vice versa. Sedimentary environment should be taken into account when achieving a full
understanding of their climate implications. 相似文献
17.
The present study to find seasonal (September 2010–June 2011) heavy metal (Cd, Pb, Cr, Co, Ni, Zn, Cu, Fe, As) contamination and the origins thereof in surface sediments of Gökçekaya Dam Lake, as constructed on Sakarya River, the third-longest river in Turkey and the largest river of the Northwestern Anatolia. Upon analyses for the purpose thereof, heavy metal contamination in annual average concentrations in the lake sediment varied, respectively, as Fe > Zn > Cr > Ni > Cu > Pb > Co > As > Cd. Statistical assessments performed in order to see whether the average values of the heavy metal contamination as measured at stations placed in the lake changed by seasonal periods. There found statistically significant differences especially in Cd, Zn, and Pb between seasonal periods. In accordance with the Sediment Quality Index, Gökçekaya Dam Lake sediment was classified as “highly polluted” in terms of the amount of anthropogenic contaminants of As, Cr, Cu, Ni, Pb, and Zn. Enrichment factor and geoaccumulation index values (I geo) were calculated in order to geochemically interpret the source of contamination due to heavy metal concentration in the lake sediment and the level of pollution. The As, Co, Cr, Cu, Ni Pb, and Zn values demonstrated that the sediment was rich for anthropogenic contaminants. The lake was found especially rich for arsenic (14.97–34.70 mg/kg) and lead (68.75–98.65 mg/kg) in accordance with annual average values. In general the lake was geochemically characterized as “moderately contaminated” in terms of As, Co, Cr, Cu, Ni, Pb, and Zn content. 相似文献
18.
《Applied Geochemistry》1993,8(2):177-187
The bulk geochemistry of unconsolidated sands from river terraces in two drainage basins of contrasting geology in the Limagne rift valley, France, was studied. Data processing and interpretation was done with multivariate statistics, notably factor analysis. In the Allier drainage basin, underlain by volcanic rocks and crystalline basement, the abundance of basaltic rock fragments causes significantly higher bulk concentrations of TiO2, Al2O3, Fe2O3, MgO, CaO, P2O5, V, Cr, Ni, Zn, Sr, Zr and Nb. In the Dore basin, underlain only by crystalline basement, sands have a significantly higher SiO2, K2O, Rb and Pb content, originating from quartz, K-feldspars and micas. Comparison between different terrace levels shows the impact of weathering and changes in supplied sediment composition over time. Approximately 65% of the total variance in the basaltic element content in the Allier terrace sands can be explained by the combined effect of parent material and weathering. The effect of grain size on sediment composition is only significant for Al2O3, Na2O and Rb content in the Allier sands, and for TiO2, Fe2O3 and Nb content in the Dore sands. Approximately 60% of the total variability in these elements is grain-size related. These results show that the technique of studying the bulk geochemical composition of stream sediments has direct applications for mineral exploration and Quaternary research. 相似文献
19.
20.
《Resource Geology》2018,68(3):287-302
Banded iron formations (BIFs) are the most significant source of iron in the world. In this study, we report petrographic and geochemical data of the BIF from the Meyomessi area in the Ntem Complex, southern Cameroon, and discuss their genesis and the iron enrichment process. Field investigations and petrography have revealed that the studied BIF samples are hard; compact; weakly weathered; and composed of magnetite, subordinate quartz, and geothite. The geochemical composition of the whole rock reveals that iron and silica represent more than 98 wt% of the average composition, whereas Al2O3, TiO2, and high‐field strength elements (HFSE) contents are very low, similar to detritus‐free marine chemical precipitates. The total iron (TFe) contents range from 48.71 to 65.32 wt % (average of 53.29 wt %) and, together with the low concentrations of deleterious elements (0.19 wt % P on average), are consistent with medium‐grade iron ores by global standards. This interpretation is confirmed by the SiO2/Fe2O3total versus (MgO + CaO + MnO)/Fe2O3total discrimination plot in which most of the Meyomessi BIF samples fall in the field of medium‐grade siliceous ore. Only one sample (MGT94) plots in the high‐grade magnetite–geothite ore domain. The high Fe/Ti (376.36), Fe/Al (99.90), and Si/Al (29.26) ratios of the sample are consistent with significant hydrothermal components. The rare earth elements (REE) contents of the studied BIF samples are very low (∑REE: 0.81–1.47 ppm), and the Post‐Archaean Australian Shale (PAAS)‐normalized patterns display weak positive Eu anomalies (Eu/Eu*: 1.15–1.33), suggesting a syngenetic low‐temperature hydrothermal solutions, similar to other BIF worldwide. However, the Meyomessi BIFs show high Fe contents when compared to the other BIFs. This indicates an epigenetic mineralization process affected the Meyomessi BIF. From the above results and based on the field and analytical data, we propose that the genetic model of iron ores at the Meyomessi area involves two stages of the enrichment process, hypogene enrichment of BIF protore by metamorphic and magmatic fluids followed by supergene alteration as indicated by the presence of goethite in the rocks. 相似文献