黄土高原-阿拉善高原典型断面表土磁学特征研究

在黄土高原-阿拉善高原区域沿接近降水量最大梯度线方向系统采集了表土(包括沙漠和土壤)样品,详细研究了其环境磁学、粒度和有机质含量等环境替代指标的变化特征.结果表明,整个断面表土中的强磁性矿物主要为磁铁矿和磁赤铁矿,并含有赤铁矿.阿拉善高原表土中磁性矿物颗粒多为多畴(MD),总体含量偏低,磁性矿物中硬磁组分含量较高;黄土高原区表土中磁性颗粒多为准单畴(PSD),总体含量偏高,磁性矿物中软磁组分含量较高.进一步分析发现,在干旱地区,频率磁化率与降水有良好的相关性,而常用的磁化率不能较好地反映降水量变化.本研究指示在干旱地区应用单一磁化率指标解释环境变化需要谨慎.     

腾格里沙漠边缘表土磁学性质及其意义

通过对腾格里沙漠边缘表土进行岩石磁学的测试和分析,发现样品中的磁性矿物主要是铁的氧化物.主要为磁铁矿,其次为磁赤铁矿和赤铁矿.磁颗粒以多畴和准单畴为主.样品之间低频磁化率值相差很大,靠近雅布赖山附近的样品明显高于其他样品.频率磁化率普遍很弱,最大3.7％,反映了该沙漠边缘区的干旱条件下所进行的以物理风化为主的地质过程....     

阿勒泰地区表土磁学特性及变化机制研究

现代表土的磁学性质反映了物源、成土过程与气候环境之间的重要信息,对认识磁学参数在气候环境研究中的应用有重要意义.干旱区表土的磁学特性表现出极大的复杂性和差异性,为了理解不同气候和环境条件下表土磁学参数的特性、变化机制及控制因素,选择位于新疆北部阿勒泰地区不同景观带的表土样品作为研究对象.通过详细系统的环境磁学分析,并结合X衍射和粒度等方法,结果表明磁性矿物来源相对稳定,磁学性质主要由来自源区的粗颗粒软磁性矿物所主导,xif(低频磁化率)和SIRM(饱和等温剩磁)与磁性颗粒表现出正相关的关系,磁性矿物浓度越大,磁畴颗粒越粗;反之,浓度越低,颗粒越细.磁性矿物的浓度和颗粒大小在不同景观带表现出一.定的差异,荒漠带表土中磁性矿物的浓度较高,磁畴主要为粗颗粒的PSD(准单畴)+MD(多畴),而其他景观带(森林、灌丛、草原和湿地)矿物浓度明显较低,磁畴也相对较细.相比较,其他景观带表土受后期改造作用比荒漠区强,主要是由于在海拔升高到1300m之后,区域气候环境因素(如气温、降水以及蒸发)发生明显变化,导致强磁性矿物的破坏,土壤矿物浓度和粒径发生变化,磁性降低.成壤作用形成的SP(超顺磁畴)颗粒相对较少.     

东秦岭地区黄土堆积的岩石磁学特征及磁化率增强机制探索

对东秦岭地区洛南盆地的上白川、刘湾和丹江上游的二龙山黄土剖面进行了岩石磁学研究。结果表明,大部分黄土和古土壤样品的磁性矿物以磁铁矿和磁赤铁矿为主,古土壤中亚铁磁性矿物的含量比黄土的多,极少数黄土样品以反铁磁性矿物为主。亚铁磁性矿物和反铁磁性矿物的含量随成土作用增强而增加,成土作用形成的细粒亚铁磁性矿物包括超顺磁性和单畴（似单畴）颗粒,但以单畴和（或）似单畴为主。古土壤磁化率增强与这些土壤成因的细粒亚铁磁性矿物含量有关,显示出受气候变化控制的特点。东秦岭地区黄土岩石磁学性质与黄土高原地区的相似,但也存在一定差异,而且三个剖面之间磁化率值整体差别较大。温湿的气候和复杂的山区地形可能是导致这种差异的原因。     

澳大利亚中部Alice Spring红色表土磁学特征分析

炎热干旱的澳大利亚中部是现代正在形成红色地表的区域.围绕中部Alice Spring地区采集了一系列红色地表样品.这些红色样品按照岩性大致可以分为三类:砂土、沙丘砂和岩石.通过对这些样品详细的磁学测量,发现这三类样品存在明显磁学特征差异,红色砂土和沙丘砂样品磁化率较岩石样品高出许多(砂土和沙丘砂磁化率均值为93.82× 10-8m3/kg),红色岩石样品磁化率值最低(均值为23.2×10-8m3/kg);三者主要磁性矿物也不尽相同;磁颗粒均以超顺磁(SP)颗粒为主,而单畴(SD)颗粒含量少.研究区百分比频率磁化率xfd％均值为8.28％,较黄土高原西部表土(兰州为3.5％)高出许多.该区现代年降水量约300mm,比兰州(约330mm)还低,成土导致百分比频率磁化率增高却比兰州明显高出几倍.这可能反映了黄土高原表土频率磁化率增高与降水量密切相关;而在澳洲中部可能与持续高温成土条件和作用的时间存在更密切的关系.澳洲中部不论岩石还是表土均以红色为主.磁学实验表明,砂土和沙丘砂样品均以磁铁矿为主,三类样品普遍含一定量磁赤铁矿和赤铁矿的贡献,与地表红色外貌相符.说明澳洲红色地表过程很可能是黑色磁铁矿颗粒表面被长期氧化条件下形成的红色磁赤铁矿/赤铁矿所包裹的现象,使得澳洲中部广大地区岩石露头和地表沉积物,普遍形成一层红色染色层.     

天山北麓典型黄土沉积序列的磁学特征及主控因子初探

新疆黄土岩石磁学特征与地层性质的对应关系具有鲜明的区域特征.本文选取沙湾黄土剖面进行较为系统的岩石磁学分析.研究结果表明,沙湾剖面的磁性矿物组成与黄土高原及新疆北部其他黄土剖面相似,以亚铁磁性矿物(如磁铁矿、磁赤铁矿)为主要的载磁矿物,同时含有一定量的不完全反铁磁性矿物(如赤铁矿、针铁矿)和顺磁性矿物.假单畴(PSD)和多畴(MD)为样品的主要磁畴特征,部分土壤样品中磁性矿物磁畴状态表现为单畴(SD).进一步分析发现,磁化率与地层对应关系较为复杂,剖面3m以上地层中的磁化率及其他相关磁学参数与成壤强度呈现正相关关系,全新世以来发育的古土壤中磁化率值较高,细颗粒磁性矿物含量也较高;而3m之下地层中磁学参数显著表现为风力强度驱动变化模式.古风场强度的变化可能对剖面整体磁学性质具有一定的影响,成壤作用受到风动力条件的制约,主要决定了较细颗粒磁性矿物的含量变化.xARM/SIRM参数与磁化率相比对地层成壤强度的指示作用更为明显.     

花岗岩上发育的亚热带红土岩石磁学特征

本文对发育于花岗岩上的两个亚热带红土剖面进行了系统的岩石磁学研究,测试了磁化率、频率磁化率、等温剩磁、非磁滞剩磁、磁滞回线等常温磁学参数,选取代表性样品进行了高低温岩石磁学分析,拟探讨亚热带红土磁性矿物的特征及湿热环境下土壤中磁性矿物的转化规律。实验结果表明:亚热带红土的强磁性矿物为磁铁矿、磁赤铁矿;弱磁性矿物为赤铁矿和针铁矿,滞水土层中含有纤铁矿。花岗岩具有较强的磁性,在其上发育的红土也因此具有较强的磁性。花岗岩中的亚铁磁性矿物的磁畴以多畴占主导地位,随着风化强度的增强,逐渐形成较细粒的超顺磁与单畴磁性矿物。亚热带红土中的磁赤铁矿与位于半干旱区黄土高原成土作用形成的磁赤铁矿存在着磁学性质上的差异,表现为具有更高的居里点(约600℃和640℃),可能说明亚热带红土中的磁赤铁矿粒径更粗。两个剖面在磁学性质上存在着明显的差异,泉州剖面磁性矿物以磁铁矿为主,磁化率最高可达1823×10~(-8)m~3/kg,平均值为1033.1×10~(-8)m~3/kg,具有较低的剩磁矫顽力;福州剖面磁性矿物以磁铁矿和部分热稳定磁赤铁矿为主,磁化率最高为385.73×10~(-8)m~3/kg,平均值为91.5×10~(-8)m~3/kg。基于磁学参数分析,认为母质与后期成土作用共同造成了两个剖面的磁学性质差异,但后者起主导作用。磁化率在两个剖面中,均随着深度减小而减小,与温带地区表层土磁化率增强有很大区别。湿热环境条件下,强磁性矿物溶解或转化为弱磁性矿物的程度主导剖面磁化率变化。     

油气藏全空间磁学、地球化学与矿物学结构及意义--检验"烟筒效应"的形成机理

位于松辽盆地南部某油气田边缘一个油气显示井的磁性测量结果表明,岩石具有明显的磁性变异结构特征.以磁化率(κ)为例,在低缓的背景磁性上主要呈现高强度与中等强度的2类异常:大于400×10-5为强磁性,100×10-5～150×10-5为中等强度磁性.结合录井资料与地球化学分析解释可知,强磁性异常主要位于取样间隔的底部干层区,少数样品位于浅部油气显示层;中等强度异常主要位于2 700 m附近的油气显示层.岩石磁性与地球化学成分对应分析表明,油气显示层岩石的C1和C2成分与磁化率 (κ)、饱和磁化强度 (Js) 和饱和等温剩余磁化强度(SIRM)之间呈明显的正相关,与内禀矫顽力(Hc)为逆相关,而干层岩石相关性不明显.矿物成分分析显示,岩石中主要含铁矿物为磁铁矿、磁赤铁矿、赤铁矿、黄铁矿和菱铁矿.其中磁赤铁矿主要分布在具有中等磁性强度的油气显示层,而高含量(最高含量达12.5%)的磁铁矿主要位于底部干层.磁赤铁矿与赤铁矿、黄铁矿及菱铁矿含量之间相关特征初步表明,自生磁赤铁矿可能主要来源于原地赤铁矿与黄铁矿.推测油气显示层岩石中磁性偏软的磁赤铁矿属于烃蚀变的产物,为烃微渗漏效应(或烟筒效应)的全空间形成机理提供了新证据.     

佳县红粘土磁学性质

黄土/古土壤序列和红粘土均已被证明是风积成因,然而红粘土研究的程度远低于黄土/古土壤序列,比如强发育红粘土获得比较低磁化率值的原因并没有得到清楚解释,红粘土磁化率代用指标问题和红粘土搬运路径等问题还存在较大的争议,红粘土记录古气候意义研究也相对薄弱,因此加强对红粘土的研究,有助于对古气候的理解.佳县位于黄土高原与毛乌素沙漠交接地区,季风区与非季风区过渡地带.对佳县厚60m的红粘土样品进行系统磁学参数测量分析发现,佳县红粘土以软磁性矿物(磁铁矿、磁赤铁矿)为主,同时含有一定量硬磁性矿物(赤铁矿、针铁矿,主要是赤铁矿);强发育古土壤层含有较多软磁性矿物,弱发育古土壤层含有较多硬磁性矿物;磁颗粒粒径基本在0.2μm以下,x＞64×10-8m3/kg时,磁颗粒粒径小于0.1μm.剖面底部磁学参数变化存在异常,原因可能是:赤铁矿含量增加,超顺磁(SP)亚铁磁性颗粒含量急剧减少,单畴(SD)颗粒相对含量增加.该异常原因解释符合前人提出的成壤路径:水铁矿→SP磁赤铁矿→SD磁赤铁矿→SD赤铁矿.     

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。     

A preliminary study on the magnetic signatures of modern soil in Central Asia

In this study, magnetic techniques were used to characterize the surface soil from different geomorphologies (i.e., sand desert, oasis, Gobi, and dry lake) in Central Asia. Results demonstrate that the main magnetic minerals in the surface soil are magnetite, maghaemite and haematite with some paramagnetic materials. Cross plots of M _rs/M _s versus B _cr/B _c and χ_fd% versus χ_arm/saturation isothermal remanent magnetization (SIRM) indicate that the main magnetic grain sizes in surface soil are pseudo single domain (PSD) and multidomain (MD). The samples from West China (i.e., Tarim basin and Junggar basin) are dominated by magnetic minerals with larger grain size, while those from North China (i.e., Alxa plateau, Erdos plateau, and Mongolia plateau) are dominated by fine magnetic minerals. The similarity in magnetic mineral constitutions between the Chinese loess and the surface soils from Central Asia implies that the loess originated from a vast area of arid, semi-arid regions of Central Asia. The low value of concentration-dependent magnetic parameters indicates that the low concentration of magnetic minerals in the surface soils from Central Asia and the magnetic enhancement from the pedogenic take place in both the loess and the paleosols, although the progress is stronger in the latter. Translated from Quaternary Sciences, 2006, 26(6): 937–946 [译自: 第四纪研究]     

Magnetic characteristics of topsoil from Xinjiang, Northwestern China, and their implications

In this study, a set of environmental magnetic parameters (_{χlf, χfd}%, _χARM , SIRM, HIRM, SOFT and SIRM/_{χlf, χARM} /SIRM and _χARM /_χlf) of 331 top-soil samples from Xinjiang Uygur Autonomous Region of China were systematically measured and the magnetic characteristics and its environmental significance were discussed. Our results indicate that the main magnetic minerals of these top-soils are single-domain magnetite. The content of magnetic minerals in top-soils from north Xinjiang is higher than that from south Xinjiang; however, the content of hard magnetic minerals is higher in the topsoils from south Xinjiang. The top-soils from Yili region contain similar magnetic minerals as that from south Xinjiang, but with much stronger magnetic SP content due to higher pedogenic processes. The differences in magnetic characteristics among top-soils from different regions of Xinjiang might reflect the differences of regional climatic factors, especially the precipitation.     

Magnetic mineralogical variability along Deccan trap basalt borehole (KBH07), Koyna deep continental drilling program,western Maharashtra,India

A 1248 m long core (KBH 07, 17°18′07″ N; 73°47′28.2″E, 960m above msl) drilled up to basement in the Deccan traps from Koyna region was sampled at ～10m interval for magnetic mineralogical studies.Analysis of routine rock magnetic parameters (mass specific magnetic susceptibility: χ_lf, frequency dependence of susceptibility: χ_fd, susceptibility of anhysteretic remanance: χ_ARM, saturation isothermal remanance: SIRM, remanance coercivty: B_(0)CR, Soft_IRM, Hard_IRM, S-Ratio, SIRM/χ_lf, χ_ARM/χ_lf) and density (σ, gm/cc) depicted significant higher order temporal variation. The χ_lf varies between 13 and 309 x 10-8m3/kg and is independent of density variation. The χ_ARM, B_(0)CR and S-Ratios indicate majority of SD-PSD ferrimagnets with episodes of MD ferrimagnetic concentration and few hard coercivity components. The giant plagioclase lath bearing (GPB) horizons show highest variability of ferrimagnetic concentration marked by anomalous peaks. Overall the variability of rock magnetic parameters independent of lava flow units suggest that the changeover in magnetic mineral concentration, composition and domain size occur at major episodes in magma composition (e.g., primary source, crustal contamination and fractional crystallization). The studied parameters are therefore examined to mark intervals of (i) magma compositional changes, (ii) zones of oxidative conditions and (iii) rapid/slow cooling intervals demanding detailed petrologic studies. We identified one I order trend, four II order cycles and eight III order cycles for the purpose of correlation. Notable peak in χ_lf at 650–700m, the changeover in rock magnetic parameters at ～930 m and ～280 m can facilitate marker intervals while several higher order variations can be adopted for high resolution correlation to other boreholes in the region. The complex variation in rock magnetic parameters independent of flow units reflect temporal magnitudes of compositional variability, cooling and emplacement history that needs detailed petro-mineralogical attempts; and the present data is useful for high order inter-core correlations under the deep drilling program.     

A magnetic investigation of a loess/paleosol sequences record in Ili area

The pedogenic ferrimagnetic minerals have been considered to be the cause of magnetic susceptibility enhancement in loess deposits distributing in the Chinese Loess Plateau and Central Europe, while “wind intensity” mechanism is proposed to be responsible for the magnetic susceptibility enhancement of loess in Alaska and Siberia. However, the magnetic enhancement mechanism is still open for loess in Ili valley, Xinjiang Uygur Autonomous Region, China. To understand this, we conducted a rock magnetic investigation on Axike section that is located in Ili valley. Results show that transitional stage from magnetic (χ_lf) trough to magnetic (χ_lf) peak corresponds to soil units. The PSD and MD-grained magnetite dominate the magnetic properties of AXK sequences, and the main factor affecting magnetic properties is the concentration of ferrimagnetic fraction. For the “pedogenesis enhancement” and “wind intensity” model, it seems hard to explain the magnetic susceptibility enhancement in this area. For the concentration of fine-grained magnetite in magnetic mineral shows positive relationship with the intensity of pedogenesis, the magnetic parameters of loess deposit in Ili valley can be used to recover paleoclimatic variations.     

Heavy metal pollution in urban topsoils: mineralogical analyses and magnetic characterization

Urban soil samples collected from the city of Xuzhou were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for Pb and Zn. The samples were also investigated for mineralogy using X-ray diffraction, thermal analyses and scanning electron microscopy (SEM). The identified minerals are mainly composed of quartz and calcite as major minerals. Soil samples contained elevated Zn (2,049 ± 5,439 mg/kg) and Pb (115 ± 58 mg/kg). According to the index of geoaccumulation, the soils of the study area are considered to be moderately to strongly contaminated with respect to Zn, moderately contaminated with respect to Pb. The magnetic measurements indicate that the dominant magnetic components are multidomain grains of ferrimagnetic minerals and that superparamagnetic and stable single-domain ferrimagnetic grains and non-ferrimagnetic minerals are present in small magnetic concentrations in this area. The measured metals correlated positively with the determined magnetic parameters (χ, χ _ARM, SIRM and SOFT). This result suggests that simple, rapid, and non-destructive magnetic measurements could provide useful information about Pb and Zn pollution in Xuzhou urban surface soils.     

黄土频率磁化率与古气候冷暖变换

本文详细研究和对比了几个区域的黄土剖面,证明中国黄土地层发育的一致性;根据第5阶段以来黄土磁化率和深海氧同位素曲线特征的比较,证明中国黄土地层的连续性和全球气候变化的一致性。黄土地层的古气候信息强度与分辨率成反比,是全球信号和区域信号的叠加。黄土高原各地厚度或沉积速率的差别主要是1.7 Ma以来形成的。黄土地层频率磁化率数值随黄土和古土壤层的出现,分别呈波谷和波峰对应,说明在温湿条件下有许多细小(<0.03 μm)的铁磁性矿物形成,它可能是导致古土壤磁化率增高的最主要原因。这些磁颗粒的含量反映古气候温湿程度的强弱和持续时间的长短。黄土频率磁化率对古气候的突变或渐变研究可能具有十分重要的意义。     

东海陆架平北地区残留沉积磁性特征及其油气指示意义

本文利用1994－1995年在东海陆架平北地区获取的370个柱状样,对该区残留沉积物作磁性测试和磁性矿物鉴定,以进行陆架残留沉积物磁性特征与深部油气渗漏关系的研究。磁性测试显示本区存在磁化率异常和饱和等温剩磁异常两种磁性异常现象。根据磁性参数特征和多种矿物物理学鉴定结果,确定导致本区磁化率异常的矿物为陆源碎屑磁铁矿,导致剩磁异常的矿物为自生或次生铁硫化物胶黄铁矿和磁黄铁矿。证据显示本区剩磁异常是油气渗漏的产物;而磁化率异常则主要指示古滨海砂的分布。作者提出在本区的油气化探中,剩磁参数是有效的化探磁性指标。     

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.     

Variation and paleoclimatic significance of organic carbon isotopes of Ili loess in arid Central Asia

As an indicator for terrestrial paleovegetation, the stable isotopic composition of total organic matter (δ¹³C_org) in loess sediments has been widely used for paleoclimatic reconstruction in western Europe, the Great Plains of North America and the Chinese Loess Plateau (CLP). However, little is known about the variation and paleoclimatic significance of the loess δ¹³C_org in arid Central Asia (ACA). We report δ¹³C_org data from an Axike (AXK) loess/paleosol profile from the eastern Ili Basin, eastern Central Asia. Along the profile, the δ¹³C_org values were more negative in the paleosol layers observed in the field and were confirmed by environmental magnetic proxies and a higher concentration of total organic carbon (TOC), consistent with results for western Europe and the northwestern CLP. Our results demonstrate that the loess δ¹³C_org in this region documents mainly the response of δ¹³C of locally predominant C₃ plants to paleoclimatic variation, especially paleoprecipitation. Our results also suggest that the loess δ¹³C_org values in the area have the potential for quantitative paleoprecipitation reconstruction on the basis of detailed δ¹³C_org results from modern plants and surface soils in the future.