山东长岛黄土沉积物的磁性与碳酸盐特征及其环境意义初探

通过对长岛沉积物采样和磁性测试,分析和讨论了长岛黄土沉积物的磁性特征:该剖面磁性矿物的含量并不是很高,且以亚铁磁性矿物为主,磁性矿物的粒度主要以细粒为主,亚铁磁性矿物的变化在沉积物磁性变化中占主导地位.通过对沉积物磁性特征和碳酸盐特征的对比发现:该剖面沉积物磁化率和碳酸盐具有很好的对应关系,并且明显表现出4个阶段的主要变化,对应了暖湿和冷干的气候旋回.根据沉积物的磁化率与古气候环境的内在联系,结合碳酸盐含量变化情况,对该地区风成沉积物的物源变迁及环境演变也进行了初步探讨和分析.     

科尔沁沙地风沙沉积物磁学特征及其古环境意义初探

选取位于科尔沁沙地东北缘的六户屯剖面风沙沉积物为研究对象,进行系统的磁学特征和粒度分析。结果表明：六户屯剖面磁性矿物含量较少,磁学性质主要受亚铁磁性磁铁矿控制,并含有少量赤铁矿和针铁矿,磁性矿物粒度较细,以稳定单畴和超顺磁颗粒为主。沉积物中磁性矿物的粒度分布受风力大小与成壤强度的影响,单畴颗粒相对含量随风力的增强而增加,随土壤发育程度的增强而减少,χARM/χlf和χARM/SIRM可以指示冬夏季风的相对强弱。六户屯剖面磁性矿物粒度主要受冬季风强度及其动力分选作用的控制,磁性矿物粒度与沉积物总体粒度呈反相关;但在某些层位,夏季风影响下的成土过程对其改造作用不容忽视。成壤过程中形成的超顺磁颗粒是磁化率增强的主要因素,单畴颗粒对土壤发育适宜期磁化率的增加贡献相对较弱。     

新疆博斯腾湖全新世沉积磁性矿物组成与沉积环境探讨北大核心CSCD

中国西北干旱区湖泊沉积物存在磁性矿物种类复杂和磁化率普遍偏低等问题,使得利用环境磁学手段重建古环境、古气候的方法受到了限制。选择新疆博斯腾湖BST12B钻孔顶部岩芯(深度0~2.5 m)不同沉积相的代表性样品,进行载磁性矿物富集,并将原样品和富集获得的样品分别做XRD(X荧光衍射)岩石矿物检测。结果显示,所有湖相样品中均有黄铁矿和磁铁矿检出,而没有磁黄铁矿和针铁矿检出,说明博斯腾湖全新世湖相沉积物的主要磁性矿物是磁铁矿,并含有少量黄铁矿;富集获得的样品中粘土矿物(如绿泥石等)含量明显增加,石英、长石和方解石含量降低,富集后的残留样品的磁化率大幅度降低,说明粘土矿物对干旱区湖泊沉积物的磁学贡献不容忽视。结合沉积物粒度、色度、硫元素含量以及沉积物磁性矿物的组合特征推断,黄铁矿可以作为湖泊高水位的指示矿物种类,因而具有重建湖泊古水位变化的潜力,并应用到博斯腾湖的全新世湖泊环境重建,发现博斯腾湖BST12B钻孔位置早全新世为接近氧化环境的浅湖相环境,而中晚全新世为深湖相沉积环境并存在一个浅水的湖滨相沉积环境。研究结果说明,利用载磁性矿物富集的方法对干旱区湖泊沉积物中所含磁性矿物进行富集后检测是开展干旱区湖泊环境磁学研究的可行手段,对研究湖泊环境变化具有重要意义。     

新疆博斯腾湖全新世沉积磁性矿物组成与沉积环境探讨

中国西北干旱区湖泊沉积物存在磁性矿物种类复杂和磁化率普遍偏低等问题,使得利用环境磁学手段重建古环境、古气候的方法受到了限制。选择新疆博斯腾湖BST12B钻孔顶部岩芯(深度0~2.5 m)不同沉积相的代表性样品,进行载磁性矿物富集,并将原样品和富集获得的样品分别做XRD(X荧光衍射)岩石矿物检测。结果显示,所有湖相样品中均有黄铁矿和磁铁矿检出,而没有磁黄铁矿和针铁矿检出,说明博斯腾湖全新世湖相沉积物的主要磁性矿物是磁铁矿,并含有少量黄铁矿;富集获得的样品中粘土矿物(如绿泥石等)含量明显增加,石英、长石和方解石含量降低,富集后的残留样品的磁化率大幅度降低,说明粘土矿物对干旱区湖泊沉积物的磁学贡献不容忽视。结合沉积物粒度、色度、硫元素含量以及沉积物磁性矿物的组合特征推断,黄铁矿可以作为湖泊高水位的指示矿物种类,因而具有重建湖泊古水位变化的潜力,并应用到博斯腾湖的全新世湖泊环境重建,发现博斯腾湖BST12B钻孔位置早全新世为接近氧化环境的浅湖相环境,而中晚全新世为深湖相沉积环境并存在一个浅水的湖滨相沉积环境。研究结果说明,利用载磁性矿物富集的方法对干旱区湖泊沉积物中所含磁性矿物进行富集后检测是开展干旱区湖泊环境磁学研究的可行手段,对研究湖泊环境变化具有重要意义。     

渭河宝鸡市区段河床沉积物磁性特征分析

利用环境磁学的方法可以有效地示踪河流沉积物的物源,对渭河宝鸡市区段干流及其支流河床沉积物全面系统的磁学特征分析表明：渭河干流和支流沉积物的磁性矿物含量总体相对较高,磁性矿物类型主要以亚铁磁性矿物磁铁矿和磁赤铁矿为主,同时存在不完全反铁磁性矿物赤铁矿,磁晶粒以PSD（假单畴）和MD（多畴）颗粒为主。渭河干流沉积物的磁性特征在空间上表现出了一定的差异,根据χ_ARM/χ（非磁滞剩磁磁化率/磁化率）值的变化规律将渭河宝鸡市区段沉积物的来源分成了两段,第一段从宝鸡峡到神龙大桥,沉积物χ_ARM/χ 值逐渐减小,磁性颗粒逐渐变粗;第二段从神龙大桥到千河入渭口,沉积物χ_ARM/χ 值逐渐增大,沉积物的颗粒呈现出由粗变细的特征,指示了渭河宝鸡市区段河流沉积物存在一定的物源差异,渭河宝鸡市区段干流沉积物的物质来源主要以上游携带为主导,从神龙大桥向下游,支流对河床沉积物具有一定的贡献,北岸比南岸流域贡献的物质相对较多。     

新疆塔城地区黄土沉积的磁学特征及其对古环境变化的指示

西风区黄土沉积序列的磁化率变化特征比较复杂,磁化率与成壤强度之间的相关性在不同的区域环境中具有一定的差异。选取塔城地区黄土剖面作为研究对象进行较为系统的磁学特征分析。结果显示,塔城剖面的磁性矿物主要为磁铁矿、磁赤铁矿等亚铁磁性矿物,同时含有一定量的反铁磁性矿物和顺磁性矿物,磁畴状态主要是多畴（MD）和假单畴（PSD）。成壤作用影响单畴（SD）颗粒磁性矿物的相对含量,而对超顺磁（SP）颗粒的贡献有限。影响地层磁学性质的因素比较复杂,粒度与磁学参数的变化与区域的气候波动具有一定的对应关系。古土壤中磁性矿物浓度的降低以及钙积现象可能反映了成壤时期温暖干燥的气候条件,磁性矿物浓度的变化在一定程度上或许是对区域相对湿度状况的反映。     

阿拉善地区湖泊岩芯磁性特征记录的全新世环境变化

对居延海G36钻孔进行了系统磁性特征分析,并结合总有机碳含量和粒度等环境代用指标,在精确测年的基础上,探讨了居延海地区全新世时期以来的环境变化。结果显示,居延海岩芯磁性矿物主要存在于粗颗粒的沉积物中,载磁矿物为颗粒较粗的多畴磁铁矿;磁化率变化机制比较复杂,与干湿环境变化没有简单正（反）关系。根据G36沉积物环境代用指标的变化,大致可以将其分为4个干湿交替时期:6 700~4 600 a BP干旱时期,4 600~3 100 a BP湿润时期,3 100~2 500 a BP干旱时期以及1 800 a BP以来湖泊干涸。在这4个时期中,磁学参数记录了两次显著湿润事件和两次显著干旱事件。     

新疆塔城黄土古土壤磁化率特征及其影响因素

 对新疆塔城奴拉厚13 m的黄土-古土壤剖面磁化率、粒度、TOC、CaCO3进行了实验分析。结果表明,奴拉剖面粒度组成以粉砂(63~4 μm)为主,由于该区黄土磁化率受控于原生磁铁矿、磁赤铁矿和赤铁矿等较粗颗粒磁性矿物,而黏粒物质吸附的铁磁性矿物及成土过程中生成的超顺磁颗粒和磁性矿物较少,磁化率与细颗粒物质成负相关,与粗颗粒物质成正相关关系; 受生物成磁、化学作用以及TOC自身磁性的影响,磁化率与TOC表现出很强的正相关性; 对磁化率与CaCO3含量的相关性分析发现,两者关系密切,CaCO3含量对该区磁化率的独特变化有重要影响。     

粤北小流域河漫滩沉积物的粒度与磁性特征及其古洪水识别意义

随着全球气候变化加剧，台风和强降雨等导致的洪涝灾害频发。如何在沉积记录中有效识别洪水事件，对于查明洪水频发规律具有重要意义。文章对粤北小流域的河漫滩沉积断面（秀丰断面）的沉积物进行了系统的粒度分析和磁性测量，深入分析洪水期沉积层和平水期沉积层不同的粒度和磁学特征，试图为沉积记录的古洪水识别提供新途径。结果表明：1）沉积物粒度组成主要为粉砂，从洪水期沉积层往平水期沉积层有变细的趋势。其中，洪水期沉积层识别出3层含砂量和平均粒径（Mz）表现为较高峰值的洪水事件记录。2）不同沉积层中磁性矿物的组成和来源基本一致，以磁铁矿为主，含有部分赤铁矿。矿物来源除流域内母质自然风化产物外，还包含大宝山尾矿库的输入。3）沉积物主要为悬浮沉积，前汛期持续的长期高水位有利于沉积物分选和沉积，导致处于洪水期沉积层的磁性矿物偏细；随着水动力的增强，洪水期沉积层中识别出的3个洪水事件记录中细粒磁铁矿和赤铁矿含量从河漫滩中部向顶部方向依次增加，同时磁性颗粒粒径变粗。因此，结合磁性参数与对磁性矿物组分的分析能更准确地识别洪水事件。研究区域细颗粒磁铁矿和赤铁矿对饱和等温剩磁的贡献高值叠加粗颗粒磁铁矿贡献降低的磁学特征可作...     

渭河宝鸡市区段河床沉积物磁性特征分析北大核心CSCD

利用环境磁学的方法可以有效地示踪河流沉积物的物源,对渭河宝鸡市区段干流及其支流河床沉积物全面系统的磁学特征分析表明:渭河干流和支流沉积物的磁性矿物含量总体相对较高,磁性矿物类型主要以亚铁磁性矿物磁铁矿和磁赤铁矿为主,同时存在不完全反铁磁性矿物赤铁矿,磁晶粒以PSD(假单畴)和MD(多畴)颗粒为主。渭河干流沉积物的磁性特征在空间上表现出了一定的差异,根据χ_(ARM)/χ(非磁滞剩磁磁化率/磁化率)值的变化规律将渭河宝鸡市区段沉积物的来源分成了两段,第一段从宝鸡峡到神龙大桥,沉积物χ_(ARM)/χ值逐渐减小,磁性颗粒逐渐变粗;第二段从神龙大桥到千河入渭口,沉积物χ_(ARM)/χ值逐渐增大,沉积物的颗粒呈现出由粗变细的特征,指示了渭河宝鸡市区段河流沉积物存在一定的物源差异,渭河宝鸡市区段干流沉积物的物质来源主要以上游携带为主导,从神龙大桥向下游,支流对河床沉积物具有一定的贡献,北岸比南岸流域贡献的物质相对较多。     

红黏土磁化率增强机制

对于黄土-古土壤序列,磁化率增强机制已经被大家认可,并且磁化率被广泛作为古夏季风强弱变化的代用指标。红黏土伏于第四纪黄土之下,同为风成沉积物,对红黏土磁化率增强机制的研究程度不高,且对强发育红黏土获得比较低的磁化率值的原因不清楚。本文通过对佳县红黏土进行系统岩石磁学分析得出：(1) 红黏土磁性矿物种类以磁铁矿为主,同时含有一定量磁赤铁矿、赤铁矿;磁性矿物平均粒径为PSD颗粒;强发育层含有较多的软磁性矿物,弱发育层含有较多的硬磁性矿物。(2) χ、χfd和χARM两两之间表现出很好线性正相关关系,说明红黏土中含有大量SP和SD颗粒亚铁磁性矿物,这些细小磁颗粒是在成壤过程中产生,成壤作用导致古土壤层磁化率升高。(3) 红黏土χfd、χfd%值较高,说明经历较强的成壤过程,成壤环境与黄土高原黄土-古土壤序列类似,与阿拉斯加、西伯利亚黄土-古土壤明显不同。     

Basis for Paleoenvironmental Interpretation of Magnetic Properties of Sediment from Upper Klamath Lake (Oregon): Effects of Weathering and Mineralogical Sorting

Studies of magnetic properties enable reconstruction of environmental conditions that affected magnetic minerals incorporated in sediments from Upper Klamath Lake. Analyses of stream sediment samples from throughout the catchment of Upper Klamath Lake show that alteration of Fe-oxide minerals during subaerial chemical weathering of basic volcanic rocks has significantly changed magnetic properties of surficial deposits. Titanomagnetite, which is abundant both as phenocrysts and as microcrystals in fresh volcanic rocks, is progressively destroyed during weathering. Because fine-grained magnetite is readily altered due to large surface-to-volume ratios, weathering causes an increase in average magnetic grain size as well as reduction in the quantity of titanomagnetite both absolutely and relative to hematite. Hydrodynamic mineralogical sorting also produces differences in magnetic properties among rock and mineral grains of differing sizes. Importantly, removal of coarse silicate and Fe-oxide grains by sorting concentrated extremely fine-grained magnetite in the resulting sediment. The effects of weathering and sorting of minerals cannot be completely separated. These processes combine to produce the magnetic properties of a non-glacial lithic component of Upper Klamath Lake sediments, which is characterized by relatively low magnetite content and coarse magnetic grain size. Hydrodynamic sorting alone causes significant differences between the magnetic properties of glacial flour in lake sediments and of fresh volcanic rocks in the catchment. In comparison to source volcanic rocks, glacial flour in the lake sediment is highly enriched in extremely fine-grained magnetite.     

Environmental magnetic studies of sediment cores from Gonghai Lake: implications for monsoon evolution in North China during the late glacial and Holocene

Environmental magnetic studies were conducted on a 9.42-m-long sediment core from Gonghai Lake, North China. Radiocarbon dating indicates that the record spans the last 15,000 cal year BP. The principal magnetic mineral in the sediments is pseudo-single domain magnetite of detrital origin with minimal post-depositional alteration. Although the variations in the concentration of detrital magnetic minerals and their grain size throughout the core reflect inputs from both soil erosion and eolian dust, it is shown that their climatic and environmental significance changes with time. In the lowermost part of the core, ~15,000–11,500 cal year BP, the magnetic minerals were supplied mainly by bedrock erosion, soil erosion and dust input when climate ameliorated after the cold and dusty last glacial maximum. The increasing magnetic susceptibility (χ) in this interval may indicate a combination of changes in the lake environment together with catchment-surface stabilization and a decreasing proportion of dust input. In the central part of the core, ~11,500–1,000 cal year BP, the detrital magnetic minerals mainly originated from dust inputs from outside the catchment when the lake catchment was covered by forest, and catchment-derived sediment supply (and thus the lake sediment accumulation rate) were minimal. The generally low concentration of magnetic minerals in this part of the core reflects the highest degree of soil stability and the strongest summer monsoon during the Holocene. In the uppermost part of the core, the last ~1,000 years, detrital magnetic minerals mainly originated from erosion of catchment soils when the vegetation cover was sparse and the sediment accumulation rates were high. Within this part of the core the high magnetic susceptibility reflects strong pedogenesis in the lake catchment, and thus a strong summer monsoon. This scenario is similar to that recorded in loess profiles. Overall, the results document three main stages of summer monsoon history with abrupt shifts from one stage to another: an increasing and variable summer monsoon during the last deglacial, a generally strong summer monsoon in the early and middle Holocene and a weak summer monsoon in the late Holocene. The results also suggest that different interpretational models may need to be applied to lake sediment magnetic mineral assemblages corresponding to different stages of environmental evolution.     

磁化率与粒度,矿物的关系及其古环境意义

根据实测数据，对磁化率与粒度、矿物之间的关系进行了探讨。结果表明，沉积物粒度与磁化率的关系，与物源及沉积动力密切相关。因此，在一定条件下，可利用两者关系来反映物源或沉积动力。碎屑沉积物的磁化率主要取决于磁铁矿的含量，并由此建立了磁化率（Ｓ，１０＾－７ｍ＾３ｋｇ＾－１）与磁铁矿的百分含量（Ｐｍ）之间的回归方程Ｓ＝４９．１８Ｐｍ＋４９．５。由于磁铁矿为重矿物，在沉积物中常常与钛铁矿、磷钇矿、独居石、锆     

安徽巢湖全新世湖泊沉积物磁化率与粒度组合的变化特征及其环境意义

通过对获取的巢湖湖泊沉积岩芯的磁化率与粒度组合特征的分析,结合孢粉及相邻其它区域的环境考古资料,得出该岩芯柱样所反映的环境变化信息。结果表明:(1)巢湖湖泊沉积物磁化率曲线在117 cm以下总体上比较平稳而略有下降,117 cm以上人类活动所导致的侵蚀作用加剧使得磁化率值异常升高;(2)本岩芯柱样117 cm以下样品的磁化率强度与粘土的百分比含量呈正相关,而与粉砂组分的百分比含量成负相关;(3)根据磁化率与粒度组合变化特征,结合孢粉分析及全新世以来区域气候变化背景,9 870 Cal a B.P.以来的巢湖流域古气候环境演变可以划分6个不同的时期:9 870~7 000 Cal a B.P.,气候呈温和略干的特点;7 000~4 750 Cal a B.P.,气候温暖湿润;4 750~2 170 Cal a B.P.,流域气候温和干燥,巢湖湖盆局部地区可能出露水面以上;2 170~1 040 Cal a B.P.,气候总体上温和湿润,但是冷暖波动明显;1 040~2 00 Cal a B.P.流域处在温凉稍湿的时期,人类活动逐渐加强;200 Cal a B.P.至今,流域总体上处于相对温暖湿润阶段。     

A rock magnetic record from Lama Lake, Taymyr Peninsula, northern Central Siberia

An 11 m long sediment core ftorn Lama Lake, Northern Siberia, has been subjected to intense sedimentological, geochemical and rock magnetic analyses. According to a palynologic investigation the recovered sediments cover the whole Holocene and the late Pleistocene reaching back to about 17 ka. IRM acquisition experiments, hysteresis loop and back field as well as thermomagnetic measurements revealed magnetite in the pseudo-single domain range as the only remanence carrier. Sharp rock magnetic boundaries occur at 20 and 745 cm sub-bottom depth that are clearly linked to shifts in the median grain size of the magnetite. These boundaries are close to the present boundaries that bracket an anoxic zone between the subrecent and a late Pleistocene oxic section of the sediments. Within the anoxic section, magnetites are characterized by significantly larger median grain sizes but within a very narrow grain size range. The shift from fine grained magnetite within the oxic sediments to coarse grained magnetite is interpreted as the result of dissolution of the finest magnetite grains within the anoxic sediments. A significant shift of the Ti/Fe-ratio of the bulk sediment at a sub-bottom depth of 735 cm does not correspond to thermomagnetic properties, i.e. Curie-temperatures do not follow the variable Ti-content of the sediment.