Integrated Geochemical and Morphological Data Provide Insights into the Genesis of Ferromanganese Nodules
Integrated Geochemical and Morphological Data Provide Insights into the Genesis of Ferromanganese Nodules
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DOI：
10.3390/min8110488
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发表时间：
2018-10
期刊：
影响因子：
2.5
通讯作者：
M. Benites;C. Millo;J. Hein;B. Nath;B. Murton;D. Galante;L. Jovane
中科院分区：
文献类型：
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作者：
M. Benites;C. Millo;J. Hein;B. Nath;B. Murton;D. Galante;L. Jovane
铁锰结核是通过海水和/或沉积物孔隙水中的金属沉淀而生长的。不同成因类型的形成取决于水体和上层沉积物的组成和氧化还原条件、水深以及表层沃茨的初级生产力。结核的许多特征已被用来研究其成因。在本文中，我们使用计算机断层扫描，扫描电子显微镜-能量色散X射线光谱和微X射线荧光数据比较不同环境中的结核，以更好地了解地球化学差异如何与不同的形态特征相关联。我们使用纯水成结核和混合型结核与不同比例的水成和成岩生长纹层的代表性样品。我们的研究结果表明，在混合型结核中，高吸光度的块状富锰（Mn/Fe高达40）纹层和低吸光度的树枝状贫锰（Mn/Fe约1）纹层之间存在微量交替，表明了水成氧条件和亚氧成岩输入的韵律交替。这种微韵律交替在纯水成结核中是不存在的，它们在化学和形态上都是同质的。提出了一个概念模型，以解释这些地球化学和形态差异，即氧化-亚氧化锋相对于结核基底的垂直迁移。
Ferromanganese nodules grow by precipitation of metals from seawater and/or sediment pore water. The formation of different genetic types depends on the composition and redox conditions of the water and upper sediment layers, water depth, and primary productivity in surface waters. Many characteristics of nodules have been used to investigate their genesis. In this paper, we compare nodules from different environments using Computed Tomography, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy, and Micro X-ray Fluorescence data to better understand how geochemical differences are linked to different morphological features. We use representative samples of purely hydrogenetic nodules and mixed-type nodules with various proportions of hydrogenetic and diagenetic growth laminae. Our results show a micrometric alternation between high-absorbance massive Mn-enriched (Mn/Fe up to 40) laminae and low-absorbance dendritic Mn-depleted (Mn/Fe about 1) laminae in mixed-type nodules, suggesting the rhythmic alternation of hydrogenetic oxic conditions and suboxic diagenetic input. This micro-rhythmic alternation is absent in purely hydrogenetic nodules, which are homogenous both chemically and morphologically. A conceptual model is proposed to account for these geochemical and morphological differences in terms of the vertical migration of the oxic-suboxic front relative to the base of the nodules.