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Integrated Geochemical and Morphological Data Provide Insights into the Genesis of Ferromanganese Nodules

1
Instituto Oceanográfico, Universidade de São Paulo, São Paulo 05508-120, Brazil
2
United States Geological Survey, Santa Cruz, CA 95060, USA
3
National Institute of Oceanography, Dona Paula 403004, India
4
National Oceanographic Centre, Southampton SO14 3ZH, UK
5
Brazilian Synchrotron Light Laboratory, Campinas 13083-100, Brazil
*
Author to whom correspondence should be addressed.
Minerals 2018, 8(11), 488; https://doi.org/10.3390/min8110488
Received: 18 September 2018 / Revised: 16 October 2018 / Accepted: 19 October 2018 / Published: 26 October 2018
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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Abstract

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. View Full-Text
Keywords: ferromanganese nodules; growth conditions; diagenesis; CT tomography; µ-XRF ferromanganese nodules; growth conditions; diagenesis; CT tomography; µ-XRF
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Benites, M.; Millo, C.; Hein, J.; Nath, B.N.; Murton, B.; Galante, D.; Jovane, L. Integrated Geochemical and Morphological Data Provide Insights into the Genesis of Ferromanganese Nodules. Minerals 2018, 8, 488.

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