Authigenic Lepidocrocite and Greigite Particles inAquatic Environments off the Yangtze River Estuary
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摘要: 以2010年11月“长江口及东海海洋综合考察”的基金委公共航次期间采集的长江口外不同站位的水体悬浮体颗粒为对象，使用扫描电镜和能谱仪相结合的方法对其进行了系统观察和研究，发现了铁氧化物和铁硫化物两种自生矿物集合体.铁氧化物集合体由纤铁矿微晶构成，形态不规则；铁硫化物集合体由大小均一的胶黄铁矿微晶构成，呈莓球状.纤铁矿的形成与周围水体的物理化学条件相关，而胶黄铁矿的形成则与有机质包裹的局部微环境有关.水体中所形成的两类自生铁矿物沉降到海底后，会受到底质物理化学条件的制约.本研究表明陆架泥质沉积体中的一部分莓球状铁硫化物属于水体沉积成因，当利用沉积物中黄铁矿莓球体进行环境分析时，需要充分考虑该部分自生铁硫化物的影响.Abstract: A scanning electron micrometer with energy-dispersive X-ray analytical system is used to investigate the suspended particles collected in 2010 in aquatic environments off the Yangtze River estuary in this study. The results show that iron oxide and iron sulfide co-exist in the same environment. Iron oxide is lepidocrocite, which accumulates in porously irregular aggregates. Iron sulfide is greigite and aggregates into organized framboids. The greigite framboids are enclosed by organic films. Lepidocrocite is in agreement with the environmental conditions. Meanwhile, greigite only exists at a local patch covered with organic films. Both lepidocrocite and greigite particles settle down easily, but their preservation depends on the early diagenesis conditions. It is suggested that at least a minor part of the iron sulfide framboids commonly found in the sedimentary sequences perhaps originates from their upward aquatic environment.
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Key words:
- the Yangtze River estuary /
- suspended particle matter /
- authigenic mineral /
- lepidocrocite /
- greigite /
- sedimentology /
- geochemistry
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图 2 悬浮颗粒中的铁氧化物集合体SEM图像和能谱图
a.铁氧化物集合体SEM图像.集合体形态不规则、结合松散、微晶可以辨认.十字符号为能谱分析位置，下同；b.铁氧化物能谱图.构成元素为Fe和O，图中的Au为镀金产生的，C为滤膜产生的
Fig. 2. SEM image of oxide aggregation and its EDX pattern
图 3 悬浮颗粒中的铁硫化物莓球状集合体及其能谱图
a, b, c.发育良好的莓球状集合体及其能谱图，硫化物微晶清晰、数量多、呈半有序排列, 能谱图中元素组成以Fe、S为主, 见于DH3-4站底层; d, e, f.莓球状集合体及其能谱图，硫化物微晶较多、呈无序排列, 能谱图中元素组成以Fe、S为主, 见于DH3-6站中层; g, h, i.莓球状集合体及其能谱图，硫化物微晶数量较多、呈无序排列, 能谱图出现了Fe、S等元素, 见于DH3-5站表层; j, k, l.莓球状集合体及其能谱图，硫化物微晶数量少、形态清晰、呈无序排列, 能谱图出现了Fe、S等元素, 见于DH3-3站表层
Fig. 3. SEM images of the iron sulfide framboids ang their energy dispersive X-ray patterns
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