西菲律宾海西部沉积物磁学特征及其环境意义

磁学参数作为有效的气候环境变化替代指标,能为古环境演变和沉积物物源研究提供有价值的信息。对取自西菲律宾海西部的GX72柱状样沉积物进行系统的环境磁学研究,测量了磁化率(χ)、非磁滞剩磁(ARM)、等温剩磁(IRM)、磁化率变温曲线(κ-T曲线)、磁滞回线等磁学参数或曲线。结果表明,GX72柱状样沉积物中携磁矿物以低矫顽力磁铁矿为主,粒径以较粗粒准单畴(PSD)为主,这些磁性颗粒主要来源于河流输入的陆源碎屑物质,风成粉尘较少。剖面上多个磁学参数呈现出相同或相反的变化趋势,反映古气候对沉积物磁学性质的制约。χ高值样品通常对应于高饱和等温剩磁(SIRM)值、低ARM/SIRM值、低χARM/χ值以及低χfd值;这类沉积物样品中磁性矿物的含量相对更高,粒度相对较大,可能形成于冷期(相对)。相反,χ低值样品通常对应于低SIRM值、高ARM/SIRM值、高χARM/χ值以及低χfd值,这类样品中磁性矿物的含量相对较低,粒径相对较小,代表相对暖期沉积。     

长江口水下三角洲Y7柱样磁性特征及其影响因素

以长江口水下三角洲380cm长的Y7柱样为对象,在磁性测量、地球化学和粒度分析的基础上,探讨了近百年以来长江口水下三角洲沉积物磁性特征变化及其影响因素.研究结果表明,磁铁矿是主导Y7柱样磁性特征的主要矿物,相比常量元素和粒度的均一组成,磁性特征存在显著的垂向变化.220cm以下,频率磁化率(χfd)、非磁滞剩磁磁化率(χARM)、磁化率(χ)、饱和等温剩磁(SIRM)、χARM/χ以及χARM/SIRM随深度增加而下降,而退磁参数S-100mT和S-300mT则呈相反变化趋势;220cm以上,χfd,χ,χARM/χ,χARM/SIRM以及S-100mT和S-300mT随深度变化不大,而SIRM和χARM则随深度增加呈现下降趋势.Y7柱样中硬剩磁(HIRM)随深度变化不大.结合Mn/Fe比值的变化,研究认为Y7柱样300cm以下层位,随深度增加沉积物磁性减弱和超顺磁颗粒急剧减少,还原成岩作用是重要因素之一,不完整反铁磁性矿物因相对稳定而导致其在磁性矿物组合中的比例上升.此外,长江中上游主要支流泥沙贡献率的变化可能会对Y7柱样磁性特征有一定影响,但尚需进一步的工作支持.     

大冶大港河水系沉积物中重金属来源分析

大冶铜绿山铜铁矿是长汀中下游重要的金属矿山之一,近年来矿山周边环境问题引起了广泛的关注.测试分析了大港河20件水系沉积物样品中重金属含量、磁化率和粒度等指标,运用平均富集因子和主成分分析方法探讨了沉积物中重金属元素的含量变化特征及元素之间的共生组合规律,评价了重金属的富集程度,并分析了其可能来源,得到以下基本认识:(1...     

应用磁测法快速检测石英砂中铁含量的研究

为了快速检测石英砂中铁含量，通过对安徽省凤阳县灵山工业园区30个湿法石英砂样品磁学参数和代表性样品中磁性离子含量的测量以及石英砂中铁含量与磁学参数相关关系的研究，提出石英砂中铁含量的磁学检测方法。通过在高纯石英砂中掺入不同质量磁选物的合成实验建立石英砂的磁化率(χ)、饱和等温剩磁(SIRM)与铁元素含量之间的标准曲线方程，合成实验结果显示石英砂的磁化率与铁含量在143.3×10^-6～500.0×10^-6范围内呈线性关系，相关系数R²=0.994 5,饱和等温剩磁与铁含量在67.9×10^-6～500.0×10^-6范围内呈线性关系，相关系数R²=0.999 2。实例检测结果显示，应用χ和SIRM测量石英砂中铁含量与应用分光光度法测量相比，相对误差分别在-9.83%～3.03%之间和-4.91%～2.42%之间，说明采用磁测法测量石英砂中铁含量是可行的，测量精度良好，采用SIRM测量精度较χ高，对石英砂进行700℃高温处理后，测量精度会增加。该研究为石英砂中铁含...     

罗布泊自生胶黄铁矿对磁性参数χARM/SIRM指示意义的影响

沉积物中磁性矿物的颗粒大小具有重要环境指示意义,是环境磁学研究的重要内容。磁性参数非磁滞剩磁磁化率/饱和等温剩磁（χ_ARM/SIRM）常被用于指示磁性颗粒大小,当沉积物磁性特征为较粗的多畴（MD）颗粒主导时表现为低值,而为较细的单畴（SD）颗粒主导时表现为高值。本研究对罗布泊盐湖LB剖面的沉积物进行了系统环境磁学测试,结果发现剖面中含有5个χ_ARM/SIRM值低于上覆层和下伏层的层位,指示其磁性颗粒较粗。但磁滞参数和扫描电镜结果显示这5个层位磁性颗粒明显细于上覆层和下伏层沉积物,显示χ_ARM/SIRM在这5个层位的指示意义失真。矿物鉴定结果显示这5个层位的主导磁性矿物为早期成岩成因的SD胶黄铁矿,赋存形态主要为颗粒团聚体、单颗粒或颗粒团聚体附着于硅酸盐矿物表面以及分布于薄片状硅酸盐内,这种赋存形态导致其具有较强的磁相互作用,并限制了χ_ARM的增加,最终造成χ_ARM/SIRM下降,指示意义失真。本研究显示当沉积物中存在胶黄铁矿等自生矿物时,利用比值参数χ_ARM/SIRM判断磁性矿物颗粒特征需谨慎。     

火电厂粉煤灰的矿物磁性及其环境意义

火电厂排放的粉煤灰是重要的大气颗粒污染物之一,利用粉煤灰的磁性监测环境污染是新近发展的新手段。应用矿物磁测技术和X射线衍射对浙江省主要电厂排放的粉煤灰的矿物磁性特征和磁性矿物学,以及与重金属元素的关系进行了研究,结果表明粉煤灰具有较高的磁化率（X）、软剩磁（IRM20mT）和饱和等温剩磁（SIRM）值,粉煤灰频率磁化率（Xfd）的平均值为2．5％,磁性矿物以多畴（MD）颗粒存在,粉煤灰的剩磁矫顽力（BCR）在42～53mT之间。矿物测试结合X射线衍射分析表明粉煤灰中的氧化铁矿物以FeO4和Fe2O3-α为主,粉煤灰的磁化率与Fe、Mn、Pb、Zn、Cu、CA含量呈显著线性正相关,相关系数（r）分别是0．924,0．866,0．725,0．756,0．945和0．867,磁化率可作为粉煤灰中重金属元素含量的代用指标。     

东海外陆架浅孔沉积物的岩性和磁性特征及成因讨论?

利用东海外陆架的10根柱状样，进行磁性、粒度、氯离子含量和粘土矿物分析。结果表明：在东海外陆架扬子浅滩前缘，浅部沉积地层自上而下可分为两层。上层为砂泥混合物，含大量贝壳碎片，磁化率与饱和等温剩磁较强，主要是磁铁矿富集所致，反映了冰后期海侵对晚更新世沉积物的强烈改造。研究还发现，现代海底表层沉积物中存在铁硫化物，它是浅海还原环境中铁磁性矿物次生变化的产物。下层为坚硬致密的黄褐色泥质粉砂和粉砂质泥（硬土层），磁化率与饱和等温剩磁较弱，但局部存在剩磁异常高，从矫顽力等磁性特征证明它是硫复铁矿的富集所致。另外，在硫复铁矿富集层中绿泥石和氯离子含量明显富集，反映该硬土层是早期海侵沉积物在末次冰期干冷气候条件下的风化产物。     

三门峡会兴沟剖面黄土—古土壤序列的岩石磁学研究

岩石磁学是古地磁学和环境磁学研究的基础,是鉴定岩石和沉积物中磁性矿物种类、粒度和含量的有效途径。对黄土高原东南部三门峡盆地的水沟—会兴沟旧石器遗址会兴沟剖面黄土—古土壤序列(S_0~S_8)进行系统的岩石磁学研究表明:本剖面沉积物的主要载磁矿物为磁铁矿、磁赤铁矿和赤铁矿,显示准单畴(PSD)磁性颗粒特征。所有磁学参数曲线均表现出基本一致的变化特征,与深海氧同位素曲线能够很好的对应,反映了第四纪以来的冰期—间冰期旋回中,东亚季风影响下的风尘黄土堆积中磁性矿物种类、粒度和含量的周期性变化特征。黄土中高矫顽力磁性矿物的相对含量要高于古土壤中的,而随着成土作用的加强,在古土壤中细粒的低矫顽力磁性矿物显著增加的同时,其中高矫顽力磁性矿物的绝对含量也相应增加。质量磁化率(χ)与非磁滞剩磁磁化率(χ_(ARM))和饱和等温剩磁(SIRM)及磁粒度参数χ_(ARM)/SIRM和χ_(ARM)/χ均呈明显的正相关关系,表明由成土作用产生的单畴(SD)颗粒和较小PSD颗粒对磁化率增强有显著的贡献。     

冲绳海槽现代沉积物磁学性质分布特征与环境的关系

选取东海陆架至冲绳海槽槽底平原的110个表层沉积样品,通过磁化率、等温剩磁、非磁滞剩磁和饱和等温剩磁等多种磁学参数测量试验手段,分析探讨了沉积物磁性与物质来源及环境的内在联系,指出不同沉积环境中,各磁性参数表现出不同的磁性特征。冲绳海槽东槽底平原沉积物因含有较多的火山物质,磁学特征与其它沉积环境有明显差异,各磁性参数特征值明显较强。CaCO3含量与磁性参数没有明显的相关性,但在高含量区可能对沉积物磁性矿物的含量具有稀释作用,使沉积物表现出相对减弱的磁性特征。     

大同盆地高砷地下水系统沉积物环境磁学特征

为了研究高砷含水层沉积物中砷与磁性矿物的关系, 对大同盆地高砷地区含水层钻孔样品进行了环境磁学和地球化学分析, 结果表明亚铁磁性矿物是决定含水层沉积物磁性特征的主要磁性矿物.通过对比砷和磁性参数在垂向上的变化趋势发现, 高砷含量往往对应着低的饱和等温剩磁(SIRM) 值, 揭示出砷和顺磁性矿物之间也存在联系.沉积物砷含量与磁性参数的相关系数均小于0.5 (α=0.05), 表明砷和亚铁磁性矿物及不完整反铁磁性矿物之间不存在明显的联系.在所有磁性参数中磁化率(χ)和砷含量之间相关性最显著, 相关系数均在0.4 (α=0.05) 左右, 低的相关系数与亚铁磁性矿物和不完整反铁磁性矿物对顺铁磁性矿物的稀释有关.该地区高砷地下水的形成可能与水铁矿及纤铁矿等砷的赋存矿物在还原条件下的还原溶解有关.      

武昌地区街道尘埃磁学特征及其对环境污染的指示意义

对在武昌地区4个功能区域(青山、洪山、东湖风景区、东湖开发区)主要交通街道收集的尘埃样品进行详细的环境磁学测量,包括质量磁化率、频率磁化率、等温剩磁退磁系数以及典型样品的磁滞回线参数等。研究结果表明:尘埃样品中剩磁载体均以亚铁磁性矿物为主,样品中的磁性颗粒呈现低矫顽力的磁铁矿特征,软磁性的磁性矿物是样品剩余磁性的主要载体。尘埃样品χ、SIRM的区域分布特征受区域周围工业、车流量及道路状况等多种环境因素的影响,在4个功能区域中存在明显的磁性差异:青山工业区污染较重,东湖开发区、洪山、东湖风景区次之;硬剩磁(HIRM)的分布可能指示了道路交通来源的磁颗粒特征,东湖开发区和青山工业区由于行驶的货车和重型车辆较多,表现出硬剩磁量值较高。与其他城市(兰州、西安、南京、徐州等)相比,整个武昌地区街道尘埃样品的磁性含量仍较高,说明在城市环境方面还有待于进一步改善和保护。     

Characterization of diamictons on the basis of their mineral magnetic properties in Murchisonfjorden,Nordaustlandet, Svalbard

Different grain-size fractions of 12 lithologically defined and 2 non-defined Weichselian glacial stage diamicton units from Nordaustlandet, Svalbard were studied for their mineral magnetic properties. The applied measurements included magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM), saturation isothermal remanent magnetization (SIRM), ‘backfield’ isothermal remanent magnetization (IRM) and several of their parametric ratios. The results indicated a poor correlation between the magnetic fingerprint of dry-sieved and wet-sieved diamicton samples. The dry-sieved samples had higher χ, ARM and SIRM values, suggesting a higher concentration of ferrimagnetic grains. This was probably because washing of the samples resulted in the loss of the most fine-grained ferrimagnetic material. Both sieving methods seem to be capable of discriminating different diamictons, but they cannot be used contemporaneously. The results only partially support previous findings of the chronostratigraphic correlation of diamictons. They indicate that in suitable conditions and within a limited area it is possible to discriminate (and group) glacigenic sequences based on the magnetic signature of their fine-grained fractions in the sample. For example and based on the mineral magnetic fingerprint, a diamicton unit that was described from the marine core (MUR 09/sor1/125–150) obtained from Isvika region most probably represents diamicton material that were derived from provenance areas related to the Middle Weichselian glacial stage. It was also noted that certain mineral magnetic parameters, such as SIRM/χ and SIRM/ARM ratio, had greater potential in discriminating diamicton units than others.     

Relationship between magnetic properties and heavy metals of urban soils with different soil types and environmental settings: implications for magnetic mapping

Two types of soil (fluvisols and anthrosols) were collected from different environmental settings (suburb and industrial area) in Wuhan, central China, aiming to examine the applicability of magnetic mapping for heavy metal pollution of urban soil in a large region. Magnetic measurements and chemical analysis indicated elevated magnetization and heavy metal concentrations of topsoils in the industrial area. Magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM) of fluvisols are much higher than those of anthrosols, but contrary for frequency-dependent susceptibility, indicating that soil magnetism strongly depends on the soil type/condition. Predominant magnetic carrier in topsoils in industrial area is pseudo-single-domain/multi-domain magnetite. Environmental scanning electron microscope/energy dispersive X-ray examination of the magnetic extracts from these topsoils revealed abundant spherical particles with diameters of 10–50 μm that are rich in iron-oxides, and could be attributed to the nearby industrial activities (e.g., steel work and power generation). Significant correlations were observed between magnetic concentration-related parameters (e.g., χ, ARM and SIRM) and concentrations of Cu, Pb, Zn, Hg and Tomlinson pollution load index. These results proposed that magnetic proxy mapping of soil pollution is an effective, fast and inexpensive tool for delineation of heavy metal pollution. However, interpretation of magnetic properties for such a purpose must be done on a site-specific basis, taking into account the possibilities of pedogenic enhancement/depletion under the specific soil conditions.     

The role of hematite–ilmenite solid solution in the production of magnetic anomalies in ground- and satellite-based data

Remanent magnetization (RM) of rocks with hematite–ilmenite solid solution (HISS) minerals, at all crustal levels, may be an important contribution to magnetic anomalies measured by ground and satellite altitude surveys. The possibility that lower thermal gradient relatively deep in the crust can result in exsolution of HISS compositions with strong remanent magnetizations (RM) was studied for two bulk compositions within the HISS system. Samples from granulite-terrane around Wilson Lake, Labrador, Canada contains titanohematite with exsolved ferrian ilmenite lamellae. Other samples from the anorthosite-terrane of Allard Lake, Quebec, Canada contain ferrian ilmenite with exsolved titanohematite lamellae. In both cases, the final exsolved titanohematite has similar Ti content and carries dominant magnetic remanence with REM (=NRM/SIRM, where NRM is the natural remanent magnetization and SIRM is the saturation isothermal remanent magnetization) that is comparable to the Ti-free end member. The RM was acquired prior to exsolution and the ilmeno-hematite-rich rock possesses thermal remanent magnetization (TRM), whereas rocks with hemo-ilmenite possess chemical remanent magnetization (CRM). In both cases, we found fairly large homogeneous grains with low demagnetizing energy that acquired intense RM. The magnetism of the ilmeno-hematite solid solution phases is not significantly perturbed by the continuous reaction: ilmeno-hematitetitanohematite solid solution. Hence, the occurrence of HISS in rocks that cooled slowly in a low intensity magnetic field will have an intense magnetic signature characterized by a large REM.     

The influence of particle size variations on the magnetic properties of sediments from the north-eastern Irish Sea

This paper considers the magnetic properties of a range of recent and contemporary sediments from the north eastern part of the Irish Sea. Principal component ordinations of the results show a close link between magnetic property variations and particle size. The magnetic properties of a subset of samples, particles sized by a combination of sieving and pipette analysis, confirm that variations in ferrimagnetic (‘magnetite’) grain size parallel those in particle size, despite the fact that the magnetic grains in the fine grades have diameters 1–2 orders of magnitude smaller than those of the particle size fraction in which they occur. This is best explained by postulating that the fine magnetic grains occur in the clay fraction but are present in declining concentrations in the coarser grades up to 4ø as an artefact of the pipette method. Most samples have a biomodal distribution of magnetic minerals, with a coarse mode associated with heavy minerals in the sands or coarse silts, and a fine mode in the clays. Magnetic susceptibility (x) and saturation isothermal remanent magnetization (SIRM) largely pick out the coarse mode where present; anhysteretic remanent magnetization (ARM) largely picks out the fine mode. The results open up the possibility of normalizing samples from these environments for particle size and, more specifically, clay content, by means of ARM or ARM/x values. The most likely source for the uniform and almost exclusive stable single domain magnetite, which dominates the magnetic properties of the clays, is thought to be bacterial magnetosomes. The measurements as a whole do not appear to hold much promise for discriminating sediment source types.     

Magnetic properties of urban topsoils and correlation with heavy metals: a case study from the city of Xuzhou, China

Heavy metals in urban topsoils have been shown to be very useful tracers of environmental pollution. Thus, their detailed studies are of great importance. Apart from expensive and time-consuming chemical methods, several simple, rapid and cheap proxy methods have been developed recently, one of them being based on rock-magnetic parameters. This examines the use of rock-magnetic methods designed to assess the degree of heavy-metal pollution of urban topsoils from the city of Xuzhou (China). The aim was to identify the magnetic properties and to link the “magnetic pollution” to the concentrations of the heavy metals. Since a strong correlation has been found between saturation isothermal remanent magnetization (SIRM) and the heavy metals, namely, Fe, Se, Ti, Sc, Ba, Bi, Pb, Cu, Zn, Cr and Mo, an anthropogenic contamination origin is thought to be the cause. The present study shows that SIRM is a fast, inexpensive and non-destructive method for the detection and mapping of heavy-metal-contaminated urban topsoils.     

Environmental magnetic and geochemical characteristics of Chennai coastal sediments,Bay of Bengal,India

In this study, environmental magnetic, heavy metal and statistical analyses were conducted on 21 surface sediments collected from Chennai coast, India, to examine the feasibility of heavy metal pollution using magnetic susceptibility. The Chennai coastal sediment samples are dominated by ferrimagnetic minerals corresponding to magnetite-like minerals. The percentage of frequency dependent magnetic susceptibility reflects the presence of super-paramagnetic/single domain magnetic minerals in Chennai harbour, Cooum and Adayar rivers sediments. High pollution load index in sample E1, E2, CH7, C11, C12 and A16 is mainly due to anthropogenic activities such as, harbour activities, Cooum and Adayar rivers input and industrial effluent. Factor analysis shows that the magnetic concentration dependent parameters (χ, χ _ARM and SIRM) covary with the heavy metal concentrations, suggesting that the input of magnetic minerals and heavy metals in Chennai coastal sediments are derived from the same anthropogenic sources. Strong correlation obtained between pollution load index (PLI) and concentration dependent parameters (χ, χ _ARM and SIRM) for the polluted samples with magnetic susceptibility excess of 50×10^− 8 m³kg^− 1. Significant correlations between heavy metals and magnetic susceptibility point out the potential of magnetic screening/monitoring for simple and rapid proxy indicator of heavy metal pollution in marine sediments.     

Investigating the potential of using environmental magnetism techniques as pollution proxy in urban road deposited sediment

The use of mineral magnetic techniques as pollution proxy for road deposited sediment was explored using various statistical approaches. Standard techniques were adopted for measurement of mineral magnetic and geochemical parameters. The analyses of magnetic parameters revealed that the samples were dominated by ferrimagnetic minerals and multidomain grains. This implied that the magnetic fractions in the samples might be of anthropogenic origin. Results also indicate that the samples were dominated by low coercive, magnetically soft minerals. Thermomagnetic curves confirmed magnetite as the remanence bearing magnetic mineral having a Curie point temperature of ~580 °C. The strong association observed between magnetic susceptibility, susceptibility of anhysteric remanent magnetization and saturation isothermal remanent magnetization and aluminum, titanium, manganese, iron, chromium and lead demonstrated that these metals occurred as ferrimagnetic particles of technogenic origin resulting from vehicular sources. Assessment of pollution status of the road deposited sediment identified silicon and lead as the priority pollutants of concern. Generally, pollution load index was <1 (mean, 0.66 ± 0.14), indicating that the samples were not polluted in the overall, but the metals were in the buildup stage requiring constant monitoring. The sources of pollutants from principal component and cluster analyses identified the sources of pollution to be mainly from vehicular emissions such as brake linings, exhaust materials, tire wear, corroded metal parts, abrasion of lubricating oil and road construction materials. This study found that mineral magnetic techniques offer great potential as pollution proxy for soil pollution studies.     

Magnetic properties of the Chelyabinsk meteorite: Preliminary results

This paper presents the distribution of magnetic susceptibility, χ₀, in fragments of the Chelyabinsk ordinary chondrite (LL5, S4, W0, fall of February 15, 2013) from the collection of the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, and results obtained by standard magnetic techniques for the meteorite material, including thermomagnetic analysis, measurements of natural remanent magnetization (NRM) and saturation isothermal remanent magnetization (SIRM), as well as the spectra of their alternating field demagnetization at amplitudes up to 170 mT, measurements of hysteresis loops and back-field remanence demagnetization curves at temperatures from 10 K to 700°C etc. The mean logχ₀ values for the light-colored (main) lithology of the meteorite material and impact-melt breccia from our collection are 4.54 ± 0.10 (n = 66) and 4.65 ± 0.09 (n = 38) (×10^?9 m³/kg), respectively. According to international magnetic classification of meteorites, Chelyabinsk falls within the range of LL5 chondrites. The mean metal content was estimated from the saturation magnetization, M _s, of the light- and dark-colored lithologies as 3.7 and 4.1 wt %, respectively. Hence, the dark lithology is richer in metal. The metal grains are multidomain at room temperature and show low coercive force, B _c (<2 mT) and remanent coercive force, B _cr (15–23 mT). The thermomagnetic analyses of the samples showed that the magnetic properties of the Chelyabinsk meteorite are controlled mainly by taenite and kamacite at temperatures >75 K. In the temperature range below 75 K, magnetic properties are controlled by chromite; the magnetic hardness of the samples is maximal at 10 K and equals to 606 and 157 mT for the light- and dark-colored lithologies, respectively.