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1.
JOHN WALDEN JOHN P. SMITH ROGER V. DACKOMBE 《Boreas: An International Journal of Quaternary Research》1996,25(2):115-130
Data from heavy mineral analysis, X-ray fluorescence spectrometry (XRF) and X-ray diffractrometry (XRD) are compared with those obtained from mineral magnetic analysis for a range of glacial diamicton samples taken from the Quaternary sequence in the Isle of Man. These data show that the mineral magnetic approach offers a useful means of characterizing glacial sediments for purposes of lithostratigraphic correlation and provenance indication and that the magnetic data are of a comparable quality to those obtained from standard applications of the more traditional techniques. The heavy mineral and XRD data indicate that little post-depositional chemical alteration of the detrital composition of the sediments has taken place. The mineral magnetic, heavy mineral and XRF analysis suggests both similar lithostratigraphic relationships between the various diamicton units and consistent indications of their likely provenance. These are consistent with published, field-based, stratigraphic relationships of the same sediments and ice-flow directions in the Irish Sea Basin during the Devensian. 相似文献
2.
Continuous sedimentary gradients are only crudely expressed by standard facies and microfacies methods which are more appropriate to situations where changes occur in relatively discrete steps. In carbonate sediments and rocks, continuous gradients are often represented by the arrangement of component grain types in a relay, that is, a systematic shifting of the relative importance of the components. Subdivision of such relays into (micro)facies can only be arbitrary. Correspondence analysis is shown to be useful for detecting, isolating and describing relays. Particular use is made of the arch effect in which samples and components from data sets with a strong unidimensional structure (a relay) plot in the form of an arch in the plane of the first two factor axes. A relay index, indicating the position of samples in the relay, can be extracted from the analysis and plotted on maps and stratigraphic logs to reveal details of the sedimentary gradient in areal and/or stratigraphic context. Examples are given from: (i) Recent shallow-marine carbonate sediments from northern Norway, illustrating a relatively simple depositional setting where surface sediments are viewed in plan; and (ii) Lower Carboniferous carbonates of southwest England, representing a more complex regional study of a particular stratigraphic interval viewed in cross-section. In both examples the relays can be related to identifiable environmental gradients. 相似文献
3.
Empirical discriminant analysis classified multivariate data from 2174 geochemical reconnaissance samples from South Greenland, so that they were related to known geological units or characterized as outliers. Training sets, comprising 514 samples from 14 geologic units were selected in order to reflect only the background conditions of each geological unit. A smoothing parameter of 0.5 maximized correct classification of the training sets and extracted a reasonable number of outliers (289, 13% of the samples) representing geographically grouped anomalies. Plots of the geochemical samples classified into the geological units corresponded well to the geological map.Q-mode cluster analysis classified the 289 outliers into 30 groups with different element associations. All types of mineral occurrence known in South Greenland could be recognized amongst the clusters. For example, there were seven clusters which were characterized by samples with high U values and different associated elements each one related to a different type of U mineralization. Another cluster containing samples with high Zr, Nb, and Y values reflects recently discovered pyrochlore mineralization. Other clusters were explained on the basis of geological units which were too small to be mapped or included amongst the training sets.Empirical discriminant analysis successfully reduced the multivariate data to one map, which made it easier to evaluate the varying element levels over the different geological units. Incorrectly classified samples require follow-up in order to appraise the accuracy of the geological mapping. Classification of the outliers by cluster analysis assists both in identifying samples influenced by mineral occurrences and in predicting the type of mineralization to be expected, thereby substantially aiding in the selection of areas for mineral exploration. 相似文献
4.
A range of mineral magnetic measurements have been carried out on archaeological sediments from Orkney and Cyprus. In a soil profile from Orkney, a magnetic enhancement factor of over 200 is observed in susceptibility data between the bedrock and a Norse sediment. The magnetic enhancement is associated with an increase in superparamagnetic grains probably caused by burning. Until now it has proved difficult to confirm the presence of superparamagnetic grains in natural samples using room temperature magnetic measurements. However, clear differences are to be found between the hysteresis loops of various magnetic domain states, including superparamagnetism. An algorithm has been developed to unmix hysteresis loops in terms of constituent domain states of ferrimagnetic iron oxides. Unmixing 128 hysteresis loops of archaeological sediments has shown that the dominant domain state in all sediments is superparamagnetic. Remarkably uniform superparamagnetic grain sizes of between 80 and 95 Å were found for all 128 sediments. © 1999 John Wiley & Sons, Inc. 相似文献
5.
Marcos A. E. Chaparro G. Suresh Mauro A. E. Chaparro V. Ramasamy Ana M. Sinito 《Environmental Earth Sciences》2013,70(1):201-213
The Ponnaiyar River is one of the largest rivers of the Tamil Nadu state (India), flowing a distance of 430 km from its point of origin to the sea. This work contributes with new data of magnetic and elemental composition of river sediments, and improves the knowledge obtained by preliminary and previous studies of rivers from Southeastern India. Magnetic susceptibility, anhysteretic and isothermal remanent magnetization and chemical determinations (major and trace metals) were measured. Magnetic results reveal the predominance of magnetite-like mineral with magnetic grain size variations along the river and in depth. Most of the uppermost samples have the major presence of trace metals and higher values of magnetic concentration. Magnetic and chemical variables were also analysed as potential pollution indicators using multivariate statistical techniques: canonical correlation and fuzzy c-means clustering analyses, which confirmed the existence of relationships, but not in a simple way, between magnetic and chemical variables. Furthermore, fuzzy analysis allows classifying the data in different well-differentiated groups regarding the trace metal load, concentration and feature-dependent parameters. The most polluted samples show high concentration of trace elements and magnetic carriers, softer and coarser magnetic minerals; on the contrary, the unpolluted samples (from the deepest sediments) have the opposite characteristics. 相似文献
6.
Greigite has been identified in the sediments of Loch Lomond using X-ray diffraction. Greigite is the dominant magnetic mineral in the oldest sediments recovered, while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies. A layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations, probably as a consequence of magnetite dissolution associated with sulphide rich pore-waters produced at the time of a marine incursion. The greigite largely oxidises once the sediment is exposed to air, but if freeze dried the greigite becomes surprisingly stable. Following freeze drying the greigite can be heated to 280°C in air before it alters and loses its strong ferrimagnetic properties. 相似文献
7.
围绕覆盖区矿产综合预测的基本思路和关键方法问题,讨论了非线性矿产预测理论和方法如何在覆盖区矿产综合预测中发挥作用,重点介绍了成矿奇异性理论与非线性矿产预测方法在覆盖区矿产预测“弱信息”提取、“复合叠加信息”分解、“缺失和不完整信息”融合等关键问题中的应用.结合正在实施的中国地质调查局“覆盖区矿产综合预测”计划项目,介绍了三方面的研究进展:(1)覆盖层中地球化学元素迁移机理与覆盖层对地表地球化学异常的屏蔽和衰减作用;(2)如何识别由于覆盖层影响而造成的“弱”且“复杂”的地球化学异常;(3)如何综合具有缺失或不完整的多元勘查信息以达到提高覆盖区矿产综合预测精度、降低预测不确定性的目的.以东天山戈壁沙漠覆盖区海相火山岩型铁矿、大兴安岭南部草原覆盖区铁多金属矿、武夷山层控矽卡岩型铁矿等矿床预测为例,介绍了综合预测方法的应用过程和应用效果.研究结果表明,奇异性理论和分析方法可以有效地用于提取水系沉积物地球化学和地球物理(重、磁)弱异常,合理分解复合叠加异常,在此基础上,采用地球化学和地球物理异常的数据融合技术,分别建立了推断铁镁质火山岩、中酸性侵入岩、矽卡岩和热液蚀变等成矿或控矿地质要素的综合信息模型,以及基于综合预测要素建立的覆盖区矿产预测后验概率证据权模型和模糊逻辑模型.应用结果显示,介绍的预测方法不仅可以在出露区圈定成矿远景区,而且在戈壁沙漠覆盖区及第三、第四系松散沉积物覆盖区等均可圈出具有重要资源潜力的远景区,这些远景区往往会被传统的预测方法所遗漏. 相似文献
8.
大同盆地高砷地下水系统沉积物环境磁学特征 总被引：1，自引：0，他引：1
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. 相似文献
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Sand and silt grains: Predetermination of their formation and properties by microfractures in quartz
Examination of quartz from plutonic source rocks, sediments and soils, using both optical and scanning electron microscopes, reveals that the mineral is, almost always, cut by sets of partially healed, subplanar, subparallel microfractures dividing it into sheets typically one to a few micrometres thick. The structure, which originates in source rocks, is not due to crystal cleavage although it does show weak crystallo‐graphic influence in its directions. One to several sets of microfractures, intersecting at varying angles, can be present in any one quartz crystal. The microfractures vary in quality like cleavages; separation takes place readily along some, less so along others. In superficial environments, the ease with which microfractures can be reopened largely controls the durability of quartz and the degree to which comminution can proceed. However, this type of breakage must cease when grains are one sheet thick (about 2–20 Mm in diameter). Hence quartz suddenly changes from being the dominant mineral in silt fractions to a normally minor constituent of clay fractions. The shape of grains depends largely on the number of (and angles between) microfrac‐ture sets present in the parent quartz. Most quartz grain surfaces represent fractures whose details characterize the pre‐emergent history of the quartz rather than sedimentary environments. 相似文献
10.
通过多参数磁性测量,分析探讨了长江中下游干流3种不同粒级(<2mm,<0.28mm和<0.125mm)河底沉积物中磁性矿物的类型、含量、颗粒变化及空间分布特征。3种粒级中,磁性矿物主要富集在<0.125mm的细质沉积物中。对细质沉积物的分析表明,长江中下游干流河底沉积物的磁性矿物含量较长江口高近10倍,类型以亚铁磁性矿物磁铁矿为主,颗粒以假单畴-多畴为主,超顺磁性颗粒含量较低。从中游到下游,磁性矿物含量呈下降趋势,颗粒呈变细趋势。干流磁性矿物含量远高于支流,颗粒远粗于支流,支流泥沙的汇入不断影响干流沉积物的磁性特征。 相似文献
11.
Yu. N. Markova A. V. Oshchepkova M. I. Kuzmin E. P. Solotchina P. A. Solotchin V. A. Bychinskii K. V. Chudnenko 《Stratigraphy and Geological Correlation》2018,26(3):344-353
The study of bottom sediments of Lake Baikal recovered by submarine drilling at the Selenga–Buguldeika saddle (core VER93-2 st. 24GC) allowed us to reconstruct the climatic events in the Baikal region in the last 20–25 k.y. On the basis of the data on distribution of chemical elements in the core section, the mineral composition of sediments was calculated by the physicochemical modeling method. A study of how ratios of clay minerals changed in the section allowed us to identify the Pleistocene–Holocene boundary, Bølling–Allerød postglacial warming, and Late Dryas cooling. The calculated data on mineral composition of bottom sediments from the core VER93-2 demonstrate a good fit to the X-ray diffraction analysis results. The proposed approach can be used in calculation of mineral compositions of other sedimentary sequences with known chemical composition. 相似文献
12.
杭州湾北岸芦潮港潮滩沉积物磁性特征的年际变化及其粒度控制 总被引：1，自引：1，他引：0
对杭州湾北岸芦潮港潮滩2007-2010年固定点沉积物进行了逐月的磁性测量和粒度分析,探讨了磁性特征的月际、年际变化及其与粒度的关系。结果显示,2007-2009年,芦潮港潮滩沉积物的磁性特征呈现出相似的季节性变化特征,磁性参数χ、χARM、SIRM以及比值χARM/SIRM总体上在12月次年7至月表现为高值,8-11月为低值,S-300变化趋势与之相反。粒度分析显示,每年12月至次年7月沉积物粒度总体较细,8-11月较粗,这说明潮滩较细沉积物中含有较多的亚铁磁性矿物,与已报道的2004-2005年研究结果相似。相比前三年,2010年1-7月及12月沉积物磁性矿物含量相对下降,8-11月份磁性矿物含量相对上升,导致2010年磁性参数月际变化幅度减小。同时,2010年沉积物粒度月际变化特征也发生了改变,即1-7月及12月沉积物粒度变粗,8-11月沉积物变细。相关分析表明,磁性参数与粒度之间的关系在2007-2010年中没有发生明显的变化,说明2010年沉积物粒度月际变化模式的改变是磁性特征月际变化改变的主导因素。尽管如此,长江流域来沙下降对河口潮滩沉积物物源的可能影响,仍需予以长期关注。 相似文献
13.
The influence of hydrodynamics on the chemical composition of sediments is based on the uneven distribution of element abundances in different size fractions. In this study, 72 size‐fractional sediments from the Huanghe (Yellow River) and Changjiang (Yangtze River) riverbeds were measured with XRD, SEM, ICP‐AES and ICP‐MS. The analysis results show that the mineral and chemical characteristics change with grain size in the Huanghe and Changjiang sediments. According to the principal components analysis, three independent geochemical factors were found. The first factor elements, Zr, Hf, Th, U, Y, La and TiO2 are influenced by the existence of heavy minerals. The second factor elements, Al2O3, alkalis, alkaline earth (excluding Ca and Sr) and most of the transitional metals are dominated by clay minerals. The third factor group includes Ca and Sr, which were controlled by calcium‐bearing mineral contents and chemical weathering intensities. The various grain size distributions greatly affect the mineralogical and chemical compositions of bulk sediments. Compared to other size fractions, the 5–6PHI size fractions of the Huanghe and Changjiang sediments have special mineralogical and chemical compositions, and intermediate volume percentages. Weight or volume percentage of each size fraction may be more suitable than mean grain‐size of the bulk sediment to elucidate the grain size effects. Chemical Index of Alteration (CIA) values increase steeply with decreasing grain size, while Weathering Index of Parker (WIP) values are relatively stable. Because of the big influence of the abundance of clay minerals on CIA values, it is questionable to use CIA as a proxy of weathering intensity. Considering the clay mineral effects, stability in values and heterogeneous material properties, WIP has the potential to indicate the chemical weathering intensity of sediments. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
14.
Herein we document and interpret an absolute chronological dating attempt using geomagnetic paleointensity data from a post-glacial sediment drape on the western Antarctic Peninsula continental shelf. Our results demonstrate that absolute dating can be established in Holocene Antarctic shelf sediments that lack suitable material for radiocarbon dating. Two jumbo piston cores of 10-m length were collected in the Western Bransfield Basin. The cores preserve a strong, stable remanent magnetization and meet the magnetic mineral assemblage criteria recommended for reliable paleointensity analyses. The relative paleomagnetic intensity records were tuned to published absolute and relative paleomagnetic stacks, which yielded a record of the last ∼8500 years for the post-glacial drape. Four tephra layers associated with documented eruptions of nearby Deception Island have been dated at 3.31, 3.73, 4.44, and 6.86 ± 0.07 ka using the geomagnetic paleointensity method. This study establishes the dual role of geomagnetic paleointensity and tephrochronology in marine sediments across both sides of the northern Antarctic Peninsula. 相似文献
15.
Y. R. Kulkarni S. J. Sangode D. C. Meshram S. K. Patil Yatindra Dutt 《Journal of the Geological Society of India》2014,83(4):376-384
Mineral magnetic analysis including thermo-magnetic studies and clay mineralogy on bed load and floodplain sediments from the Godavari river indicate distinct mineral assemblages. The floodplain sediments up to the delta region are characterised by unimodal ferrimagnetic mineralogy marked by the presence of maghemite and single domain magnetites derived from Deccan basalts. On the other hand the bed loads show varied magnetic mineral assemblages depicting greater local mixing from the non-basaltic bedrock province. The temperature dependent magnetic susceptibility and clay mineralogy of the floodplain samples show titanomagnetites (Fe3O4-Fe2TiO4), maghemite (χ LF-Fe2O3) and smectite that are characteristic of the Deccan Volcanic Province (DVP). Presence of this ferrimagnetically dominant unimodal assemblage up to the delta region and probably into the Bay of Bengal off the Godavari river is attributed to extensive chemical weathering of the basalt. The quantitative approach of mineral magnetism, therefore, can be used to study the paleomonsoon variability and its relation to Deccan basalt weathering from the Godavari-Bengal fan system. 相似文献
16.
R. Thompson T. D. J. Cameron C. Schwarz K. A. Jensen V. Van Maenhaut Lemberge L. P. Sha 《第四纪科学杂志》1992,7(4):319-334
Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex. 相似文献
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ROY THOMPSON KEVIN J. EDWARDS 《Boreas: An International Journal of Quaternary Research》1982,11(4):335-349
Magnetic analyses have been carried out on sediments collected from Lough Catherine. Northern Ireland, as part of a wider environmental study. The sediments span the whole of the Holocene. Radiocarbon and pollen dating of the palaeomagnetic signature locked in the sediments form the basis of an Irish Holocene geomagnetic master curve. The mineral magnetic characteristics of the sediments correspond with environmental changes, such as eighteenth century landscaping and the elm decline as revealed by pollen analyses. Both marginal and central sediments have been analysed. The sediments can be correlated by using either magnetic, pollen, or 14 C measurements. These three independent core correlation methods all agree extremely well with each other. A mathematical method is described which can be used to calculate continuous accumulation rates and influxes. 相似文献
20.
本文扼要介绍了中国第四纪古地磁学研究的进展,其主要结论为：中国黄土－古土壤的主要磁性矿物是磁铁矿、赤铁矿和磁赤铁矿,特征剩磁载体为磁铁矿;Ｌ８和Ｌ３３分别记录了Ｍ／Ｂ和Ｇ／Ｍ地磁极性转换过程;Ｊａｒａｍｉｌｌｏ极性亚带的顶、底分别位于Ｌ１０和Ｌ１２;六盘山以东的黄土剖面,由于土壤化作用强烈,成土过程产生的次生剩余磁性已将持续时间只有５０００ａ左右的Ｂｌａｋｅ极性亚时的原始磁信息掩盖,无法分离出来;只有六盘山以西的黄土剖面才有可能记录Ｂｌａｋｅ极性亚时。黄土的剩余磁性受“Ｓｍｏｏｔｈｉｎｇ”和“Ｌｏｏｋ－ｉｎ”效应的影响很小,因此是研究极性转换期间地球磁场形态学和古风向的合适物质。 相似文献