共查询到19条相似文献,搜索用时 62 毫秒
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通过固城湖沉积物中高分辨率的岩石磁学取样及其实验研究,取得了环境磁学参数及各种磁参数的比值随深度的变化曲线,结合其他气候指标和同位素年龄结果,表明湖泊沉积中磁参数及其比值的变化能与末次晚冰期以来的古气候变化很好地相对应,尤其是在4.00m和12.03m的气候转折点上,沉积物中环境磁参数及其比值同样出现明显的变化,有力地说明沉积物中磁参数及其比值能很好地记录湖泊沉积物沉积时的古气候变化,并且可用来认识古环境突变的界线. 相似文献
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对青海湖南盆沉积中心钻取的一根长18.6 m的高取芯率沉积岩芯(1F)进行磁化率测试显示,该岩芯在8.15~8.96 m和15.50~17.28 m两沉积段具有非常高的磁化率.详细的岩石磁学测量和矿物分析表明这两段沉积物中有大量的胶黄铁矿存在,其磁畴特征主要以单畴(SD)为主,并显示少量超顺磁(SP)颗粒特征,这是导致磁化率大幅升高的主要原因.胶黄铁矿的生成与硫酸盐还原作用密切相关,1F沉积岩芯中胶黄铁矿的发现表明青海湖在晚更新世具有非常适宜胶黄铁矿生成的硫酸盐还原环境. 相似文献
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本文选择内蒙古呼伦湖表层沉积物为研究对象,通过测量沉积物样品的室温下χ-T曲线、等温剩磁获得曲线和反向场退磁曲线、一阶反转曲线(FORC图)以及低温(20~300 K)下剩磁随温度变化曲线、Verwey转变温度,结合电子显微镜分析,获得了样品中磁性矿物组成信息.揭示出呼伦湖表层沉积物中磁性矿物含量较低,以假畴磁铁矿为主,含有部分单畴和多畴颗粒.这些结果对于理解呼伦湖沉积物的磁性信号、古环境和古气候重建等具有研究价值. 相似文献
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湖泊沉积物的矿物磁性测量及其环境应用 总被引:24,自引:7,他引:24
本文结合太湖沉积物的磁性研究,简要地阐述了湖泊沉积物磁性测量的方法与磁信息的环境应用,通过分析太湖沉积样芯的磁参数曲线所内含的环境信息,揭示了磁测方法在古湖沼学研究中的应用前景。 相似文献
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对杭州城区四个不同功能区块土壤进行了系统的环境磁学测定,结果表明城市土壤的磁化率平均值为128×10-8m3·kg-1,频率磁化率平均值3.6%(样品数=182),城市土壤呈现明显的磁性增强. 城市土壤的磁化率与频率磁化率呈极显著指数负相关,表明城市土壤磁性增强明显区别于自然成土过程引起的以超顺磁性(SP)颗粒为主的表土磁性增强机理. 统计分析表明,城市土壤磁化率与软剩磁和饱和等温剩磁(SIRM)呈显著直线正相关,说明亚铁磁性矿物是城市土壤剩余磁性的主要载体. 综合等温剩磁获得曲线、热磁曲线、磁滞回线等岩石磁学测定和SEM/EDX分析,城市土壤的磁性矿物以磁铁矿和赤铁矿为主,磁性矿物以假单畴-多畴(PSD-MD)颗粒存在,粒度明显大于成土过程形成的磁性颗粒,这些磁性颗粒主要来自燃料燃烧、汽车尾气等环境污染物. 因此,城市土壤磁测可作为城市土壤污染监测、污染空间分布和污染物来源判断的新手段. 相似文献
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Characteristics and genesis of maghemite in Chinese loess and paleosols: Mechanism for magnetic susceptibility enhancement in paleosols 总被引:4,自引:0,他引:4
Tianhu Chen Huifang Xu Qiaoqin Xie Jun Chen Junfeng Ji Huayu Lu 《Earth and Planetary Science Letters》2005,240(3-4):790-802
Morphological characteristics and microstructures of magnetic minerals extracted from Chinese loess and paleosols were investigated using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Our results indicate that maghemite in loess–paleosol sequences was transformed from magnetite through oxidation of magnetite. Maghemite transformed from eolian magnetite during chemical weathering has low-angle grain boundaries among maghemite nano-crystals. Some nano-crystalline maghemites with nanoporous texture resulted from microbe-induced precipitation of magnetite or transformation of poorly crystalline ferric Fe (oxy)hydroxides in presence of Fe-reducing bacteria. Aggregates of euhedral maghemite nano-crystals were transformed from magnetite magnetosomes. Both microbe-induced nanoporous magnetite and microbe-produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols. It is proposed that the formation of nano-crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility, although the total amount (weight percent) of magnetic minerals in both paleosol and loess units is similar. Our results also show that nano-crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi-arid soil environments instead of hematite, although hematite is a thermodynamically stable phase. This result also indicates that a decrease in crystal size will increase stability of maghemite. It is also inferred that surface energy of maghemite is lower than that of hematite. 相似文献
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亚洲大陆边缘海和陆表海在区域的物质和能量交换以及区域气候与环境演化过程中扮演了关键角色.磁性地层学和环境磁学方法是建立年代框架和环境演变序列的有效手段,但是,由于该地区边缘海和陆表海沉积物中磁性矿物来源十分复杂,磁性地层学和环境磁学研究的重要基础是要精细地解译沉积物的岩石磁学性质.为此,本文利用渤海南部莱州湾Lz908孔与钻孔附近的现代沉积物样品进行了详细的岩石磁学对比研究.结果显示,渤海南部沉积物中的磁性矿物主要是较粗颗粒(较大的准单畴至多畴)磁铁矿,还有少量磁赤铁矿,部分沉积物还含有赤铁矿和针铁矿,其中磁铁矿是特征剩磁的主要载体;莱州湾现代河流-海洋沉积物和钻孔样品之间的磁性特征无显著差异,说明莱州湾沉积物堆积之后尚未经历明显的沉积后期改造. 相似文献
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以热磁分析为主,对中国北方泥河湾盆地更新世河湖相地层中灰绿色粉砂和灰黄色粉砂/细砂两种典型沉积物进行了详细的岩石磁学研究,有效确定了这两类沉积物中磁性矿物的种类、粒度特征以及加热过程中磁性矿物的变化过程和产物,并对其包含的古环境意义进行了初步探讨.灰绿色粉砂样品主要含有磁铁矿和赤铁矿两种磁性矿物,磁性相对较弱,颗粒相对较细;灰黄色粉砂/细砂主要含有磁铁矿和磁赤铁矿,磁性相对较强,颗粒相对较粗.在氩气环境中经700℃加热处理后,这两种沉积物中的绿泥石都分解,并生成超细粒(处于超顺磁和单畴颗粒区间)的磁铁矿,导致磁化率大幅升高.因此泥河湾盆地沉积物的热磁特征可以用来检测样品中绿泥石的相对含量,进而反映该地区化学风化作用强度的变化.此外,灰绿色粉砂样品中绿泥石含量比灰黄色粉砂/细砂样品的含量高,在氩气中加热后,磁化率升高幅度也较高,可能反映了化学风化相对较弱的沉积环境. 相似文献
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《Marine pollution bulletin》2013,77(1-2):383-388
Metals and biogenic elements were analyzed from surface sediments collected from Zhelin Bay in the South China Sea in December 2008. The high concentrations of TOC, TN and BSi indicate the high nutrient level and diatom productivity in Zhelin Bay. The concentrations of metals were generally far lower than the effects-range-low (ERL) values that define pollutant levels. Enrichment factors (EF) and geoaccumulation indices (Igeo) suggest there are pollution levels of Cd, Cu and Zn at some stations. As, Cu, and Pb are potentially biotoxic in some stations. Correlation and principal component analyses indicate that most of the metals primarily originate from natural sources, and from maricultural activities as well. Mariculture contributes considerable Cd and Cu contamination. As and Pb comes primarily from combustion of gasoline and diesel fuel by ships. 相似文献
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Detailed rock magnetic investigations and mineralogical analysis were conducted on lacustrine sediments recovered from Zoigê
Basin, eastern Tibetan Plateau. Greigite, with fine and homogenous grain size, is found as a main magnetic carrier, which
is suspected to be of biochemical origin. In contrast to some reports, greigite within the sediments is not oxidized even
after exposure to air for a few years, which could be due to the fact that greigite is sealed by silicate. 相似文献
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Environmental mechanism of magnetic susceptibility changes of lacustrine sediments from Lake Hulun, China 总被引:1,自引:0,他引:1
The changes of magnetic susceptibility(κ) are correlated with those of corresponding sedimentological, geochemical, mineralogical and biological results, which verifies
thatκ can be taken as one of the environmental proxies. However, usually the exact origin of magnetic signal is poorly understood,
and is difficult to relate with the environmental evolution. Magnetic properties of material derived from the catchment and
sedimentary environment may affect the accumulation, preservation, or authigenesis and diagenesis of magnetic minerals. In
the Lake Hulun region in Inner Mongolia, it is found that muddy sediments, deposited during high water level period (corresponding
to humid climate), have comparatively highκ values. In contrast, the sandy sediments, deposited during low water level period (corresponding to arid climate), have lowκ values. Detailed rock magnetic investigation confirms that detrital magnetite derived from volcanic rocks in the catchment
exists in both muddy and sandy sediments. During high water level period, secondary ferrimagnetic iron sulphide was produced
in muddy sediments under relatively reductive conditions. Ferrimagnetic iron sulphide, coexisting with detrital magnetite,
predominates the magnetic properties of muddy sediments, resulting in increasingκ. This paper reveals the significance of authigenic ferrimagnetic iron sulphide produced after sediment deposition. 相似文献
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DONG Jin WANG Yong ZHANG ShiHong CHI ZhenQing YAO PeiYi & ZHAO ZhiLi 《中国科学:地球科学(英文版)》2012,(9):1494-1503
Spatial variations in lake sediments are a product of their depositional heterogeneities.To better correlate synchronous strata in Huangqihai Lake,two sections were excavated from the lake-center and the lake-shore.The study involved detailed lithology,mineralogy,and rock magnetic analysis.The results show that the frequency-dependent susceptibility,which is related to the content of super-paramagnetic minerals,is relatively easy to contrast between the two sections.However,mass susceptibility and saturation isothermal remanence,which are related to the content of total magnetic minerals,are difficult to contrast.A possible reason for this difference is that small-particle super-paramagnetic minerals are formed mainly during pedogenic processes,which correlates well with climate change and avoids the effects of local factors when corrections are made at the whole-lake scale.Both sections can be divided into three stages,which appear to be well correlated with previous results obtained through other environmental proxies. 相似文献
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《Marine pollution bulletin》2014,78(1-2):224-229
The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the sediment from the Hormuz strait, Persian Gulf. The sum of 16 PAHs (ΣPAH) concentrations varied from 72.17 to 277.77 ng g−1 dry weight, with an average value of 131.20 ± 59.29 ng g−1 dry weight. An ecological risk assessment of PAHs, indicated that adverse biological effects caused by acenaphthene and acenaphthylene occasionally may take place in the sediment of Hormuz strait. PAH source identification showed that the PAHs in the sediments come from pyrogenic and mixed origin. Based on classification of pollution levels, sediments from Hormuz strait could be considered as low to moderately polluted with PAHs. 相似文献
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风成黄土是陆地上分布最广泛的沉积物之一,记载了各种古气候演化信息.目前巴基斯坦的黄土研究甚少,磁化率与气候对应的变化机制研究尚未开展.本文对位于巴基斯坦印度河平原Bahawalpur地区新发现的黄土-古土壤剖面进行系统的岩石磁学研究,结合粒度和漫反射光谱(DRS)数据,讨论巴基斯坦黄土的磁化率变化机制.实验结果显示:Bahawalpur (BH)剖面黄土层主要的载磁矿物为磁铁矿,同时含有少量磁赤铁矿和针铁矿,磁性颗粒以原生的MD和PSD颗粒为主.相对于黄土层,古土壤层则是以针铁矿为主,含有顺磁性矿物和少量磁铁矿.BH剖面磁化率与成土作用关系和中国黄土高原典型剖面相反,磁化率的变化可能存在一个阈值12.8×10-8m3·kg-1,在阈值之上,强磁性矿物(磁铁矿、磁赤铁矿)占主导;阈值之下,以弱磁性矿物(主要是针铁矿)为主,这种磁性矿物的转变可能导致磁化率降低.本文可为今后利用磁化率解读该地区地层蕴含的古气候信息提供新线索.
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