Evidence for a simple pathway to maghemite in Earth and Mars soils

Soil magnetism is greatly influenced by maghemite (γ-Fe₂O₃), the presence of which is usually attributed to the following: (1) heating of goethite in the presence of organic matter; (2) oxidation of magnetite (Fe₃O₄); or (3) dehydroxylation of lepidocrocite (γ-FeOOH). Formation of the latter two minerals in turn requires the presence of Fe(II) in the system. No laboratory experiment or soil study to date has shown whether maghemite can form from ferrihydrite, a poorly crystalline Fe(III) oxide [∼Fe_4.5(O,OH,H₂O)_13.5], below 250°C. However, ferrihydrite is the usual precursor of goethite (α-FeOOH) and hematite (α-Fe₂O₃), the most frequently occurring crystalline Fe(III) oxides in soils. Here is presented in vitro evidence that ferryhidrite can partly transform into maghemite at 150°C. This transformation occurs upon aging of ferrihydrite precipitated in the presence of phosphate or other ligands capable of ligand exchange with Fe-OH surface groups. This maghemite coexists with hematite and is a transient phase in the transformation of ferrihydrite to hematite, which is apparently stabilized by the adsorbed ligands. Its particle size is small (10 to 30 nm), and its X-ray diffraction pattern exhibits superstructure reflections. The possible formation of maghemite in Mars and in different Earth soils can partly be explained in the light of this pathway with minimal ad hoc assumptions.     

俄罗斯勘察加半岛热泉的地球化学和微生物学

勘察加半岛位于欧洲板块、北美板块和太平洋板块交汇的过渡带上,是世界火山活动最活跃的地区之一.其众多的热液系统不断的向地表释放地热气体和流体.以N2和CO2为主的地热气体也经常含有高浓度的H2,CH4和H2S.大气水和熔岩水构成了勘察加热泉水的主要源,水体温度从20 ℃到＞90 ℃不等.水化学性质变化同样显著,pH范围从3.1到9.8.热泉水溶解盐以氯化钠为主,同时包括K+,H3BO3,H4SiO4,Ca2+和SO42-等其他多种溶解组分.此区域也有以直链烷烃为主的石油形成.从勘察加的热泉系统中已分离出至少24种嗜热微生物.尽管其中大多数是异养微生物,但根据其生存环境的特点,自养微生物在热泉系统中可能同样很多.这些微生物对碳、硫和铁在热液系统中的生物地球化学循环有着非常重要的作用.目前,非培养的方法和生物定量的手段已用来研究勘察加热泉中微生物生态及其所具有的生物地球化学功能.     

Consistent grain size distribution of pedogenic maghemite of surface soils and Miocene loessic soils on the Chinese Loess Plateau

There is agreement that ultrafine maghemite grains (<100 nm) are responsible for the magnetic enhancement of Chinese loess. Recent studies show that grain size distribution of ultrafine pedogenic maghemite grains within the aeolian sequences on the central Chinese Loess Plateau deposited in the last 8 Ma is consistent. However, whether the observed grain size distribution of ultrafine pedogenic maghemite grains can be observed in the western Chinese Loess Plateau and modern soils is not entirely clear. Here we find that young surface soil samples across the Chinese Loess Plateau and early Neogene loessic soils from the western Chinese Loess Plateau also show consistent grain size distribution with that of ultrafine pedogenic maghemite grains on the central Chinese Loess Plateau. The fact that young surface soil samples show apparent magnetic enhancement suggests that the ultrafine pedogenic maghemite grains derive from oxidation of ultrafine magnetite grains. Copyright © 2009 John Wiley & Sons, Ltd.     

Geochemistry of the Kola River, northwestern Russia

The Kola River in the northern part of the Kola Peninsula, northwestern Russia, flows into the Barents Sea via the Kola Bay. The river is a unique place for reproduction of salmon and an important source of drinking water for more than 500,000 people in Murmansk and the surrounding municipalities. To evaluate the environmental status of the Kola River water, sampling of the dissolved (<0.22 μm) and suspended (>0.22 μm) phases was performed at 12 sites along the Kola River and its tributaries during 2001 and 2002. Major (Ca, K, Mg, Na, S, Si, HCO₃ and Cl) and trace (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, Ti, and Zn) elements, total and particulate organic C (TOC and POC), N and P were analysed. Comparison with the boreal pristine Kalix River, Northern Sweden, shows that, except for Na, Cl, Al, Cu and Ni, which exceed the concentrations in the Kalix River by as much as 2–3 times, the levels of other major and trace elements are close to or even below the levels in the Kalix River. However, the results also demonstrate that pollutants from the three major sources: (1) the Cu–Ni smelter in Monchegorsk, (2) the open-pit Fe mine and ore concentration plant in Olenegorsk, and (3) the Varlamov, the Medveziy and the Zemlanoy creeks, draining the area of the large agricultural enterprises in the lower part of the watershed, have a major influence on the water quality of the Kola River.     

Geochemistry of sediments from Lake Grand,Northeast Russia

Major and trace element distribution in the bottom sediments from Hole 13 drilled in Lake Grand, Magadan district, was studied using the method of principal components. It was established that geochemical characteristics are correlated with environmental changes. The sediments of cold MIS2 and MIS4 are characterized by the enriched TiO₂, MgO, Al₂O₃, Fe₂O₃, and Cr and low Na₂O, K₂O contents, which is related to the grain-size composition of sediments. Sediments of warm stages show an opposite tendency. High concentration peaks of iron, phosphorus, and manganese correspond to the accumulation levels of vivianite and ferromanganese rocks. Silica is represented by biogenic and abiogenic varieties. Maximum SiO₂ contents were found in the Late Holocene sediments and mark the high biological productivity of the basin. Revealed variations of some elements are correlated with the Heinrich events.     

Geochemistry of radium in soils of the Eastern United States

The abundance and chemical/mineralogical form of ²²⁶Ra, ²³⁸U and ²³²Th were determined on samples of soil and associated vegetation at 12 sites in the eastern United States. Progressive, selective chemical extraction plus size fractionation determined the abundance and radiometric equilibrium condition of these nuclides in 6 operationally defined soil fractions: exchangeable cations, organic matter, “free” Fe-oxides, sand, silt, and clay.In soils, profile-averaged ²²⁶Ra/²³⁸U activity ratios (AR) are within 10% of unity for most sites, implying little fractionation of U and Ra when the entire soil profile is considered. However, ²²⁶Ra greatly exceeds ²³⁸U activity in most surface soil (AR up to 1.8, av 1.22), in vegetation (AR up to 65, av. 2.8), in the exchangeable+organic fraction (AR up to 30, av. 13), in some soil Fe oxides (AR up to 3.5, av. 0.83) and in the C horizons of deeply weathered soils (AR up to 1.5).A major factor in Ra behavior is uptake by vegetation, which concentrates Ra>U and moves Ra from deeper soil to surface soil. Vegetation is capable of creating the observed Ra excess in typical surface soil horizons (AR up to 1.8, av. 1.22) in about 1000 a. Of the total Ra in an average A horizon, 42% occurs as exchangeable ions and in organic matter, but only 6–8% of the parent U and Th occur in these soil forms. In contrast, U is slightly enriched relative to Ra in Fe-oxides of A horizons, implying rapid chemical partition of vegetation-cycled U and Ra.In deeper horizons, transfer by vegetation and/or direct chemical partitioning of Ra into organic and exchangeable forms provides a source for unsupported ²²⁶Ra in Ra-rich organic matter, and leaves all soil minerals Ra-poor (AR=0.73). Organic matter evidently has a strong affinity for Ra.The phenomena discussed above are relevant to evaluation of indoor Rn hazard, and behavior of Ra at sites affected by radioactive waste disposal, phosphate tailings, Ra-rich brine, and uraniferous fertilizer.     

Mercury in European agricultural and grazing land soils

Agricultural (Ap, A_p-horizon, 0–20 cm) and grazing land soil samples (Gr, 0–10 cm) were collected from a large part of Europe (33 countries, 5.6 million km²) at an average density of 1 sample site/2500 km². The resulting more than 2 × 2000 soil samples were air dried, sieved to <2 mm and analysed for their Hg concentrations following an aqua regia extraction. Median concentrations for Hg are 0.030 mg/kg (range: <0.003–1.56 mg/kg) for the Ap samples and 0.035 mg/kg (range: <0.003–3.12 mg/kg) for the Gr samples. Only 5 Ap and 10 Gr samples returned Hg concentrations above 1 mg/kg. In the geochemical maps the continental-scale distribution of the element is clearly dominated by geology. Climate exerts an important influence. Mercury accumulates in those areas of northern Europe where a wet and cold climate favours the build-up of soil organic material. Typical anthropogenic sources like coal-fired power plants, waste incinerators, chlor-alkali plants, metal smelters and urban agglomerations are hardly visible at continental scales but can have a major impact at the local-scale.     

Geochemistry and petrology of superpure quartzites from East Sayan Mountains,Russia

Acta Geochimica - Quartzites are widespread within Earth’s lithosphere, but their highly pure varieties occur quite infrequently. With the development of alternative energy sources, including...     

Geochemistry of lead contaminated wetland soils amended with phosphorus

To remediate Pb contaminated soils it is proposed that phosphorus can be amended to the soils to transform the Pb into poorly soluble Pb-phosphate mineral phases. However, remediation strategies must account for variable Pb speciation and site-specific factors. In this study soil mineralogy and Pb speciation in soils from P-amended field trials at sites within the Coeur d’Alene River Basin in Idaho, USA were investigated. The soils are contaminated from mining activities and are enriched with Fe and Mn. Selective extraction of the soils indicated that the Fe oxides are poorly crystalline. XRD of the soil clay size fractions identified quartz, muscovite, kaolinite, siderite, lepidocrocite, and chlorite minerals. Amendment with P fertilizer dissolved the siderite. No Pb–phosphate minerals were detected by XRD. Electron microprobe analysis showed direct correlations between Pb, Fe, and Mn in the unamended soils, and negative correlations between Pb and Si. Lead and Mn were strongly correlated. In the amended soils Fe and P were strongly correlated. Results indicate that the Pb is associated with poorly crystalline Fe and Mn oxides, and that added P is primarily associated with Fe oxide phases. Comparisons of pore water Pb concentrations with chloropyromorphite and plumbogummite solubility suggest that in the phosphate-amended soils the pore waters are undersaturated in these phases, whereas several of the control soil pore waters were oversaturated, indicating the added phosphate suppressed the Pb solubility. Results from this research provide insight into the geochemistry occurring in the P-remediated soils that will help in making management and remediation decisions.     

The peculiarities of water acidification in European Russia and Western Siberia

Studies have proven the anthropogenic acidification of waters developing over the spacious territories of European Russia and West Siberia. The acidification is exhibited by the waters of small lakes characterized by bedrock consisting of granite and quartz formations. The acidified lakes of high water transparency, pH values below 6, and the prevalence of strong acids in the anion composition account for 4.4% of 201 lakes of European Russia and 8.2% of 166 explored lakes in the taiga and tundra regions of western Siberia. The main factor causing the development of acidification over the European Russia is the emission of technogenic sulfur by metallurgical smelteries. As for western Siberia, this is the combustion of associated gas at oil-producing enterprises. These processes combined with natural factors determine the complicated mechanism of anthropogenic acidification of waters.     

Geochemical evidence of aeolian deposits in European soils

Hafnium (Hf) and zirconium (Zr) concentrations measured in over 4100 agricultural soil samples from Europe were assessed with the focus on their relationship to the distribution of aeolian deposits, such as loess and coversands. Comparison of extractable (aqua regia; ICP‐MS) and total (XRFS) concentrations shows that only 1.0 to 1.7% of the total Hf and Zr is chemically extractable because of the resistant nature of their host minerals. Resistate minerals, such as zircon, are commonly found in the predominantly silty fraction of loess deposits. In this study a statistical analysis of total Hf and Zr soil data from areas with and without loess was carried out to derive threshold values of 10 mg kg^?1 (Hf) and 318 mg kg^?1 (Zr). These values were subsequently applied across the project area in an attempt to indicate the presence of aeolian deposits. The spatial distribution of above‐threshold concentrations suggests a more extensive and coherent loess belt across central and eastern Europe, providing additional evidence of loess across Brittany, Aquitaine and near the Vosges mountains in France as well as in the basins of central and northern Spain. Above‐threshold concentrations were also detected in loess regardless of its thickness, emphasising the importance of the abundance of zircon in the upper part of the soil profile rather than the actual thickness of the deposit. Soil data however, failed to indicate various loess facies within most of the Pannonian Basin, suggesting that this approach only works where deposits contain a sufficient amount of zircon. This may also explain why the extensive coversands across northern Germany and Poland were largely undetected. This study demonstrates that continental‐scale soil geochemical data can help identify and map the distribution of zircon‐rich loess and coversand, and subsequently enhance and improve current knowledge of the extent of these deposits.     

Geochemistry of Thermal Waters of Continental Margin of Far East of Russia

Studied waters belong to warm(T=30-50℃),alkaline(pH=8.9-9.3),low mineralized(TDS235 mg/1)Na-HCO_3 or Na-SO_4-HCO_3 thermal waters with high content of SiO_2(up to 81 mg/l)and F(up to 3.9 mg/1),occur on modern volcano-tectonic rejuvenated areas of Eastern Sikhote-Alin orogenic belt.Low~3He concentration as well as N_2/O_2 and N_2/Ar ratios exclude influence of deep mantle fluid.New rare earth element data constrain our understandmg of water-rock interaction occurring in the water source region.Meteoric origin of waters is proved by stable isotope values varying from-71‰to-136.1‰and from-10.8‰to-18.8‰forδ~2U andδ~(18)O respectively.REE patterns reflect high pH,resultfing from water-rock interaction and oxidative conditions.Calculations of deep aquifer temperature using Na-K and quartz geothermometers show 116.8-131.1°C and 82.2-125.8℃respectively.Presence of deep faults both with abnormal thermal gradient(~45-50 K/km)define unique geochemical shape of thermal waters of Sikhote-Alin,area,where no present volcanic activity is registered.     

Geochemistry of Cadmium in Mesozoic Phosphorites of the East European Platform

Cadmium is the most toxic admixture in mineral fertilizers. The Cd concentration in Mesozoic phosphorites, which are widespread in the East European Platform, has not been investigated. The present study was stimulated by the scanty and contradictory nature of the published data on this issue. We determined Cd concentration in 21 phosphorite samples from major deposits and checked the reliability of obtained results by external replicate analyses. It has been established that the Cd concentration in phosphorites varies from 5 ppm in the Late Jurassic–Early Cretaceous basin to 2 ppm in the Late Cretaceous basin. Cadmium does not enter the structure of phosphate and sulfide minerals. The Cd concentration is independent of the phosphorus abundance. However, all studied samples show a positive correlation of Cd with organic matter mainly contained in phosphates, supporting the biophilic nature of Cd. Mesozoic phosphorites of the East European Platform accumulated in epicontinental basins. They are significantly depleted in Cd relative to Mesozoic–Cenozoic phosphorites in pericontinental basins of the southern margin of the Tethys Ocean. The Cd concentration is more stable in Mesozoic phosphorites than in Mesozoic–Cenozoic deposits.     

Geochemistry and extractable Fe and Al in cold‐temperature soils of northwestern Siberia

The concentrations of major, minor and trace elements in three Cryosols from northwestern Siberia were analysed to determine profiles of geochemical uniformity, element mobility and the release and build‐up of extractable Fe and Al. The scope of this study involves weathering processes over all or part of the Lateglacial to the Holocene Epoch (<10 ka) in a cold environment. Iron and Al extracts are investigated to elicit information regarding profile age and palaeoclimate. ‘Free’ iron (Fe_d) relative to total Fe increases in the Ah + Bw horizons compared with the lower horizons, where oxidation is weaker. Low total Fe reflects reworked felsic deltaic and shallow marine deposits from the Permian to the early Tertiary, thereafter emplaced by episodic flooding of glacial meltwater from the Arctic Urals and/or the Kara Sea Ice Sheet. Organically complexed Al (Al_p), uniformly low in all soils, nevertheless shows trends indicating some downward movement, a rather unique occurrence in Arctic tundra soils. As indicated by the slow increase of oxihydrites, it may not be realistic to estimate the age of a profile by its physical characteristics. However, it appears possible to determine broad age ranges from the isotopic composition of water in soils. Copyright © 2009 John Wiley & Sons, Ltd.