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1.
Amy J.V. Riches Yang Liu James M.D. Day Igor S. Puchtel Douglas Rumble III Harry Y. McSween Jr. Richard J. Walker Lawrence A. Taylor 《Polar Science》2011,4(4):497-514
We report the petrography, mineral and whole-rock chemistry (major-, trace-, and highly-siderophile element abundances, and osmium and oxygen isotope compositions) of a newly recognized lherzolitic shergottite, Yamato (Y) 984028. Oxygen isotopes (Δ17O = 0.218‰) confirm a martian origin for this meteorite. Three texturally distinctive internal zones and a partially devitrified fusion crust occur in the polished section of Y 984028 studied here. The zones include: 1) a poikilitic region with pyroxene enclosing olivine and chromite (Zone A); 2) a non-poikilitic zone with cumulate olivine, interstitial pyroxene, maskelynite and Ti-rich chromite (Zone B) and; 3) a monomict breccia (Zone C). The pyroxene oikocryst in Zone A is chemically zoned from Wo3–7En76–71 in the core region to Wo33–36En52–49 at the rim, and encloses more Mg-rich olivine (Fo74–70) in the core, as compared with olivines (Fo69–68) located at the oikocryst rim. Constraints from Fe–Mg partitioning between crystals and melt indicate that constituent minerals are not in equilibrium with the corresponding bulk-rock composition, implying that Y 984028 represents a cumulate. The whole-rock major- and trace-element compositions, and initial 187Os/188Os value (0.1281 ± 0.0002) of Y 984028 are similar to other lherzolitic shergottites and this sample is probably launch-paired with Y 793602, Y 000027, Y 000047, and Y 000097. The Os isotopic composition and highly-siderophile element (HSE) abundances of Y 984028 and other lherzolitic shergottites are consistent with derivation from a martian mantle source that evolved with chondritic Re/Os. 相似文献
2.
The distribution pattern of the trace elements Rb, Sr, Nd and Sm for Yamato 984028 (Y984028) is consistent with its classification as a lherzolitic shergottite. The Sm–Nd mineral isochron of this lherzolitic shergottite defines its age to be 170 ± 10 Ma for an initial ?Nd = +11.6 ± 0.2. The corresponding Rb–Sr mineral isochron yields an identical age of 170 ± 9 Ma and an initial 87Sr/86Sr = 0.710389 ± 0.000029. The concordant Sm–Nd and Rb–Sr isochron ages suggest that Y984028 crystallized 170 ± 7 Ma ago contemporaneously with five other lherzolitic shergottites and ten enriched basaltic and olivine-phyric shergottites. The age, Sr- and Nd- isotopic signatures further suggest that Y984028 and Y-793605, and also probably Y000097 could come from a single magmatic body. Using a two-stage evolution model, the time-averaged 87Rb/86Sr-ratio for the mantle source of the parent magma of Y984028 is ～0.182, within the range of 0.178–0.182 that has been reported for other lherzolitic shergottites. The corresponding time-averaged 147Sm/144Nd-ratio for the source mantle of its parent magma is super-chondritic at ～0.217, implying its source was a depleted mafic part of the Martian mantle similar to that of diabasic shergottite Northwest Africa (NWA) 1460. Rb, Sr, Sm and Nd distributions in Y984028 are likely produced by pyroxene and olivine accumulation, probably from a NWA 1460-like parental melt, in an intrusive magma body. 相似文献
3.
Shin Ozawa Masaaki Miyahara Eiji Ohtani Makoto Kimura Yoshinori Ito 《Polar Science》2011,4(4):550-557
Yamato 984028 (Y984028) is a newly identified lherzolitic shergottite, recovered from the Yamato Mountains, Antarctica, in 1999. As part of a consortium study, we conducted petrographic observations of Y984028 and its melt vein in order to investigate its shock metamorphism. The rock displays the typical non-poikilitic texture of lherzolitic shergottite, characterized by a framework of olivine, minor pyroxene (pigeonite and augite), and interstitial maskelynite. Shock metamorphic features include irregular fractures in olivine and pyroxene, shock-induced twin-lamellae in pyroxene, and the complete conversion of plagioclase to maskelynite, features consistent with those found in other lherzolitic shergottites. The melt vein is composed of coarse mineral fragments (mainly olivine) entrained in a matrix of fine-grained euhedral olivine (with several modes of compositional zoning) and interstitial glassy material. Some coarse olivine fragments consist of an assemblage of fine-grained euhedral to subhedral olivine crystals, suggesting shock-induced fragmentation, recrystallization, and/or a process of sintering. The implication is that the fine-grained olivine crystals in the matrix of the melt vein represent complicated crystallization environments and histories. 相似文献
4.
Experimental calibration of lake-sediment spectral reflectance to chlorophyll a concentrations: methodology and paleolimnological validation 总被引：1，自引：0，他引：1
Alexander P. Wolfe Rolf D. Vinebrooke Neal Michelutti Benoit Rivard Biplob Das 《Journal of Paleolimnology》2006,36(1):91-100
Chlorophyll a preserved in lake sediments reflects, in part, past primary production. This study assesses the spectral properties of sedimentary
chlorophyll a using visible-near infrared reflectance (VNIR) spectroscopy, with the objective of establishing a new, non-destructive paleolimnological
proxy. Reflectance spectra were determined from a dilution series (n = 10) involving incremental additions of pulverized modern algae to a lake sediment matrix of low organic content. This enabled
an assessment of the development of sediment reflectance spectra in relation to different sediment chlorophyll a concentrations, and subsequent regression of spectral features against measured concentrations of chlorophyll a and derivatives obtained by high performance liquid chromatography (HPLC). The experiment demonstrates that ubiquitous troughs
in sediment reflectance near 675 nm are attributable to chlorophyll a and derivative compounds. A significant correlation (r
2 = 0.98, P < 0.01) was obtained between the area of the reflectance trough in the 650–700 nm interval and summed concentrations of chlorophyll
a, all derivative isomers, and degradational pheopigments. A simple linear inference model derived from this experiment was
applied to a down-core sequence of VNIR spectra from a productive prairie lake (Alberta, Canada), where it produced inferred
sediment chlorophyll a concentrations in concordance with HPLC measurements. Although a larger training set is desirable to further refine the inference
model, the analyses reported here demonstrate that reflectance spectroscopy provides a rapid, semi-quantitative method for
assessing the chlorophyll a content of lake sediments. 相似文献
5.
This study tests the hypothesis that Fourier-transform infrared spectroscopy (FTIRS) of lake sediments can be used to infer
past changes in tree-line position and total organic carbon (TOC) content of lake water. A training set of 100 lakes from
northern Sweden spanning a broad altitudinal and TOC gradient from 0.7 to 14.9 mg/l was used to assess whether vegetation
zones and TOC can be modelled from FTIR spectra of surface sediments (0–1 cm) using principal component analysis (PCA) and
partial least squares (PLS) regression. Preliminary results show that FTIRS of lake sediments can be used to reconstruct past
changes in tree line and the TOC content of lake water, which is hardly surprising since FTIRS registers the properties of
organic and minerogenic material derived from the water mass and the drainage area. The FTIRS model for TOC gives a root mean
squared error (RMSECV) of calibration of 1.4 mg/l (10% of the gradient) assessed by internal cross-validation (CV) yielding
an Rcv2 of 0.64. This should be compared with a near-infrared spectroscopy (NIRS) and diatom transfer function for TOC from the same
set of lakes, which have a Rcv2 of 0.61 and 0.31, and RMSECV of 1.6 and 2.3 mg/l, respectively. The FTIRS-TOC model was applied to a Holocene sediment core
from a tree-line lake and the results show similar trends as inferences from NIRS and pollen from the same core. Overall,
the results indicate that changes in FTIR spectra from lake sediments reflect differences in catchment vegetation and TOC,
and that FTIRS-models based on surface-sediment samples can be applied to sediment cores for retrospective analysis. 相似文献
6.
分形方法在庐山第四纪沉积环境研究中的应用* 总被引：6，自引：0，他引：6
沉积物中Fe3+/Fe2+的值与形成时的古温度有益指数关系。假定Fe3+/Fe2+的值沿剖面的变化具有自相关性,那么它所反映的古温度变化是一条分形曲线。本文以庐山大校场剖面为例,根据孢粉和Fe3+/Fe2+的测试数据,建立了一个推算古温度的非线性公式。据此推算的古温度表明,本区中更新世以来共有3次明显的冷暖波动,最高年均温在22℃左右,最低达3℃左右,出现在末次冰期。未发现有低于0℃者。由粒度分数维的概念,推导出的计算公式可作为混杂堆积物粒度分布特征的度量指标。根据计算,该剖面主要接近于泥石流和石冰川的粒度分数维,而与冰碛物的粒度分数维有较大差别。综上得出,本区沉积物成因主要是间冰期季风气候下的山地泥石流和沟谷流水的洪-冲积及冰期干冷的冰缘环境下的冻融堆积。 相似文献
7.
《Polar Science》2007,1(1):45-53
NWA1241 is an unusual monomict ureilite, consisting mainly of pigeonite, olivine, suessite, and carbonaceous materials. The modal ratio of pyroxene/(olivine + pyroxene) is higher than those of common monomict ureilites. Metallic phases in NWA1241 are mainly suessite, although metals in common ureilites are mainly kamacite. The high ratio of pyroxene to olivine and the abundant occurrence of suessite make the meteorite unusual. The suessite coexists with magnesian olivine and pyroxene in NWA1241, and this mineral assemblage indicates that the suessite was produced from FeO-bearing olivine and Ni-bearing kamacite at temperatures around 1500–1400K and oxygen fugacity of 10−18–10−20 bars.Most ureilites experienced two-stage reduction. Stage-I reduction was a smelting process in ureilite parent bodies (UPB's) to form the framework of monomict ureilites. Stage-II reduction took place after catastrophic destruction of the UPB's to eject many fragmental blocks into space, where suessite (NWA1241) or Si-bearing kamacite (common ureilites) were produced together with the formation of reversely zoned olivines. 相似文献
8.
The Wuyo-Gubrunde Horst in the northeastern Nigeria consists of migmatite gneiss, unaltered, altered, and sheared porphyritic granites, pegmatites, aplites, basalts, and sandstone. Uranium has been reported in rhyolite, sheared rocks, and sandstone within the area. The petrogenesis of the granitoids and associated rocks in the area was evaluated in the light of new geochemical data, which showed that the U content of altered porphyritic granite is highest and hydrothermal-related. The granitoids are metaluminous, sub-alkaline, and S-type granite, and have evolved by partial melting of crustal material emplaced at moderate depth of 20–30 km in a syn-to late-collisional within-plate tectonic setting. The negative Eu/Eu* anomaly and high (La/Yb)N ratio of the granitoids indicate magma fractionation. The low SiO2 (<53%) and high Fe2O3 (10%) of the altered porphyritic granite compared to other similar rock units suggest pervasive alteration. The associated basalts are tholeiitic, emplaced within continental plate tectonic setting, and enriched in Ni, V, Nb, Sr, and light rare earth elements, and they have SiO2, Fe2O3, V, Th, and Co contents that are similar to those of the altered porphyritic granites. The U occurrence in the Wuyo-Gubrunde Horst is believed to be sourced from the adjoining Bima sandstone in the Benue Trough, which locally contains carbonaceous zones with anomalously high concentrations of U. The Fe2+/Fe3+ redox fronts formed by alteration of the iron-rich basalts provided the requisite geochemical barrier for U-bearing hydrothermal fluid, causing enrichment of U leached and mobilized from the sandstone through fractures in the rocks. 相似文献
9.
荷叶塘陨石是1998年降落的一块普通球粒陨石。本文在对荷叶塘陨石的岩石学和矿物化学特征分析的基础上,划分了荷叶塘陨石的岩石类型和次级岩石类型。荷叶塘陨石橄榄石的Fa值在0.6-48.8之间,平均值为23.2,PMD为60.1%;低钙辉石的FS值在0.6-49.0之间,平均值为9.1,PMD为97.5%。结合橄榄石Fa值的PMD与次级岩石类型关系、橄榄石中的Cr含量、铁纹石中富Ni颗粒的数量密度等,综合判断荷叶塘陨石的化学-岩石类型为L3.3,由此表明该陨石是一块热变质程度非常低的L型非平衡普通球粒陨石。 相似文献
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12.
西宁陨石具有典型的球粒结构,球粒轮廓依稀可辨-模糊,基质重结晶程度中-高等,次生斜长石粒度5-40μm,部分颗粒大于50μm。橄榄石和低钙辉石的化学成分均一：球粒中橄榄石Fa24.7-25.2,平均Fa24.9,相对标准偏差PMD值0.64%;低钙辉石Fs21.3-21.9 En 77.6-78.2 Wo 0.46-0.57,平均Fs21.5,Fs的PMD值0.84%。说明该陨石已达热力学平衡状态,为平衡型普通球粒陨石。根据该陨石结构构造特征、金属含量、矿物化学组成特征和热变质特征（平衡温度为778℃）,西宁陨石被划分为L群普通球粒陨石,岩石类型为5型,但已开始向6型过渡。该陨石的冲击变质程度为S3,风化程度W0。陨石母体形成之后遭受了冲击变质作用和热变质作用,导致原始球粒破碎、脱玻化和基质重结晶。 相似文献
13.
Studies were conducted at a Livestock Farm in an arid region of Pakistan, to determine the uptake of mineral nutrients from the food of buffaloes. Samples of feed, water, forage, soil as well as blood, milk, urine, and faeces of the animals were collected and analysed for K+, Ca2+, and Fe2+ during summer and winter. The results showed that the concentrations of K+ and Ca2+ in plants were low, whereas that of Fe2+ was high. In animals, K+ was not found in the milk in significant amounts, rather it was excreted in the urine. The calcium taken in by the animals was used for the synthesis of milk, as a result of which low Ca2+ concentrations were detected in urine. Mineral nutrient concentrations (K+ and Ca2+) in forage plants and water were lower than the optimum requirement of the animals, as a result of which blood plasma contained lower amounts of minerals (K+ and Fe2+) than that of the normal animals or critical limits. From the findings of the present study, it can be concluded that the buffaloes raised at the livestock farm had a severe deficiency of mineral nutrients, particularly K+ in lactating and Fe2+ in both lactating and non-lactating animals. Feed supplements, that can overcome these deficiencies, should be used for the optimum growth, milk production and resistance to diseases. 相似文献
14.
基于氢氧同位素与水化学的 潮白河流域地下水水循环特征 总被引：23，自引：1，他引：23
为了研究变化环境下潮白河流域地下水水循环规律,通过现场调查,结合环境同位素及水化学应用,对潮白河流域浅层和深层地下水采样,测定其氢、氧环境同位素及水化学成分,通过分析其变化特征判明地下水的补给来源以及各含水层的相互联系。降水和地下水中的环境同位素δD和δ18O组成分析表明,降水是山前地下水的主要补给源,山区浅层地下水受蒸发影响非常强烈。水化学研究结果表明,山区地下水水质以 Ca2+和 HCO-3为主,属Ca2+-Mg2+-HCO-3型地下水。山前地下水类型为Ca2+-Mg2+-HCO-3、 Na+-K+-HCO-3、Mg2+-Ca2+-HCO-3和 Ca2+-Mg2+-Cl--SO2-4。平原区地下水为Mg2+, Na+和HCO-3。滨海冲积海积平原为Ca2+-Mg2+-HCO-3型和Ca2+-Mg2+-Cl--SO2-4型地下水。水化学分析证实了越流补给的存在。Ca2+ 和 HCO-3离子均呈山区高、山前和平原低、而滨海增高的趋势。沿潮白河流向地下水类型变化为:Ca2+-Mg2+-HCO-3 Na+＝K+-HCO-3 Ca2+-Mg2+-HCO-3。 相似文献
15.
Holocene soils/paleosols in the Okstindan Mountains,Nordland: stratigraphy and extractable Fe and Al 
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下载免费PDF全文 William C. Mahaney R.G.V. Hancock 《Geografiska Annaler: Series A, Physical Geography》2015,97(2):355-373
A chronosequence of surface and buried soils in moraines and outwash, ranging in age from Middle to Late Holocene, i.e., Little Ice Age, and forming under alpine and subalpine vegetation in the Okstindan Mountains of central‐north Norway (66o N) (Oksskolten) was studied to determine if topographic/stratigraphic setting, weathering characteristics, soil/paleosol properties, SEM/EDS analysis, and extractable Fe and Al could be used to elucidate information on paleoenvironment and age. The geochemical data previously published and geological mapping by the Norwegian Geological Survey indicate a uniform parent material in these profiles. Slight geochemical anomalies of higher U, Th and Br in organic‐rich horizons are related to vegetation and/or higher water content at various times, confirmed by extractable Fe evidence. The data interpretation also shows that extractable Fe, principally Feo, is useful in identifying previous perched water tables, possibly generated by permafrost. The activity ratio of Feo/Fed (oxalate to dithionite) and the ratio Fed/Fet (dithionite to total Fe) appear useful in distinguishing older from younger soils on the basis of the conversion of ferrihydrite to goethite+hematite. Pyrophosphate extracts, proved useful in determining movement of organically bound Al, and showed a pronounced difference between the alpine and subalpine environments. Oxalate‐extractable and dithionite‐extractable Al proved of little value in relative age determination, presumably because sodium dithionite does not extract all crystalline Al. 相似文献
16.
We describe the petrography and mineralogy of six CV3 carbonaceous chondrites. LAP02206, LAP02228, LAP04843, and GRA06101 are classified as oxidized Allende-like chondrites (CV3oxA). RBT04143 and QUE97186 are classified as members of the reduced subtype (CV3red). Chondrules in the CV3oxA chondrites show extensive Fe–Mg zoning. Fe-rich olivine in the rims of the CV3oxA chondrules are 16O-poor relative to Mg-rich olivine in the cores, suggesting that in addition to Fe and Mg, oxygen was exchanged between chondrules and matrix during weak thermal metamorphism. The CV3red chondrites appear to have formed through various processes. QUE97186 shows chondrule flattening with a preferred orientation, which is interpreted to have resulted from shock impact at a pressure of ～20 GPa. The post-shock residual heat (～1000 °C) is likely to be responsible for the restricted Fe/Mg ratios of matrix olivine. Based on the degree of Fe–Mg homogenization of matrix olivines, we estimate the spatial scale of the shock-heated region to be ～1 m. RBT04143 is a breccia containing many clasts of two types of lithologies: reduced-type material and very weakly altered material. 相似文献
17.
Veronika Gälman Johan Rydberg Andrei Shchukarev Staffan Sjöberg Antonio Martínez-Cortizas Richard Bindler Ingemar Renberg 《Journal of Paleolimnology》2009,42(1):141-153
Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H+, e?, Fe3+, SO4 2?, H2CO3 and included the formation of solid phases such as Fe(OH)3 (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO3. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)3/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves. 相似文献
18.
Ma Jiayi Xie Shuyun Liu Dan Carranza Emmanuel John M. He Zhiliang Zhang Mohai Wang Tianyi 《Natural Resources Research》2021,30(2):1291-1303
Dissolution of carbonates in acidic fluids, which has attracted much research attention in recent years, is of great significance for the formation of high-quality reservoirs. The dissolution stage under low temperature and low pressure in shallow burial is one of the most important processes of reservoir dissolution and transformation. However, the dissolution dynamics of carbonate rocks in shallow burial and their formation have been controversial for a long time, and there are still disputes in the dissolution processes about how associated minerals and accessory minerals (e.g., pyrite) in carbonate reservoirs influence the formation of secondary pores. Additional metal ions in acidic fluids can change fluid properties and dissolution processes, and consequently affect reservoir quality. However, there are few laboratory studies done on the effect of associated minerals on the dissolution dynamics of carbonates. To clarify the specific impact of Fe-bearing associated minerals and Fe3+ on the dissolution of carbonates in shallow burial reservoirs, six samples of typical carbonate rocks in the Zigui area of Hubei Province, China were studied. The dissolution kinetics of carbonates in dilute hydrochloric acid and sulfuric acid solutions containing metal ions (Fe3+/Ca2+/Mn2+) at ambient temperature and pressure (T?=?25 °C, P?=?1 atm) were studied, by laboratory dissolution experiments combined with numerical simulations using PHREEQC. The results show that the Fe3+ is of great significance on the dissolution of carbonate rocks, while the influences of Ca2+ and Mn2+ are relatively weak. The dissolutions degrees of micritic limestone (ZG-L25), dolomitic limestone (ZG-L7) and dolomite (ZG-D9) were better than the other carbonates under the influence of metal ions (Fe3+/Ca2+/Mn2+) in acid solutions. Therefore, the dolomite reservoir of the Cambrian Qinjiamiao Formation, the dolomitic limestone reservoir of the Tianheban Formation and the limestone reservoir of the Triassic Daye Formation in the Zigui area are potential high-quality reservoirs. The carbonate reservoirs associated with Fe-bearing minerals were easier to dissolve and formed secondary pores under shallow burial. This process is beneficial to the formation of high-quality reservoirs. Moreover, the addition of Fe3+ into hydrochloric acid solution may be conducive to improving the reservoirs acidizing effect. Furthermore, the results gave innovative results from multiple perspectives of geo-material science and computational geosciences, which may provide new avenues for in-depth study of carbonate dissolution in shallow burial based on water–rock reaction, chemical dissolution, computational simulation, and geological background.
相似文献19.
The chemistry of precipitation, snow pack and surface water has been analysed on 205 samples collected during the 2001 field season at 25 selected sites within the Latnjavagge drainage basin in arctic–oceanic northern Swedish Lapland. Additionally, daily discharge and yield of dissolved solids have been calculated for several subcatchments and the entire Latnjavagge catchment during the years 2000, 2001 and 2002. Chemical water analysis included the components Ca2+, Mg2+, Na+, K+, Fe2+, Mn2+, Cl−, NO3−, SO42− and PO43−, with SO42− and Ca2+ being the dominant ones in the surface water. Solute concentrations and chemical denudation were low, but showed significant differences within the basin. In areas of shade, longer snow cover, frozen ground and thin regolith, concentrations over the summer were perceptible but so low that solutes brought into the basin from precipitation could be detected in the surface water. In one locality, it was even found that lake water could reflect snowmelt to such an extent that the solute concentration was less than that of summer precipitation. The highest concentrations were found at a radiation-exposed, W-facing, vegetated, moderately steep slope with relatively thick regolith that was thawed at the time of snowmelt in early June. In such well-drained sites with continuous subsurface water flow, a maximum of contact between water and mineral particles could take place. The concentration values revealed differences in the rate of thawing of frozen ground between shaded areas and/or areas at higher altitude on the one hand and radiation-exposed areas on the other. A comparison with published results from Kärkevagge a few kilometres to the northwest as well as from other periglacial locations indicates that the chemical denudation values from Latnjavagge are more representative of periglacial oceanic environments than the values from the Kärkevagge catchment, which shows especially high chemical denudation rates. The investigation in Latnjavagge stresses the importance of spatial variability within even small catchments of homogeneous lithology as it demonstrates that solute concentrations from different subbasins can differ substantially dependent on exposure to radiation, duration of snow cover and frozen ground conditions, regolith thickness and possibly also to vegetation cover and slope angle as factors steering water turbulence and retention of drainage. 相似文献
20.
Chin Yik Lin Mohd. Harun Abdullah Baba Musta Sarva Mangala Praveena Ahmad Zaharin Aris 《Natural Resources Research》2011,20(1):45-56
A total of 20 soil samples were collected from 10 boreholes constructed in the low lying area, which included ancillary samples
taken from the high elevation area. Redox processes were investigated in the soil as well as groundwater in the shallow groundwater
aquifer of Manukan Island, Sabah, Malaysia. Groundwater samples (n = 10) from each boreholes were also collected in the low lying area to understand the concentrations and behaviors of Fe
and Mn in the dissolved state. This study strives to obtain a general understanding of the stability behaviors on Fe and Mn
at the upper unsaturated and the lower-saturated soil horizons in the low lying area of Manukan Island as these elements usually
play a major role in the redox chemistry of the shallow groundwater. Thermodynamic calculations using PHREEQC showed that
the groundwater samples in the study area are oversaturated with respect to goethite, hematite, Fe(OH)3 and undersaturated with respect to manganite and pyrochroite. Low concentrations of Fe and Mn in the groundwater might be
probably due to the lack of minerals of iron and manganese oxides, which exist in the sandy aquifer. In fact, high organic
matters that present in the unsaturated horizon are believed to be responsible for the high Mn content in the soil. It was
observed that the soil samples collected from high elevation area (BK) comprises considerable amount of Fe in both unsaturated (6675.87 mg/kg) and saturated horizons (31440.49 mg/kg) compared
to the low Fe content in the low lying area. Based on the stability diagram, the groundwater composition lies within the stability
field for Mn2+ and Fe2+ under suboxic condition and very close to the FeS/Fe2+ stability boundary. This study also shows that both pH and Eh values comprise a strong negative value thus suggesting that
the redox potential is inversely dependent on the changes of pH. 相似文献