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

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.

Characterization and Quantification of Magnetofossils Within Abyssal Manganese Nodules From the Western Pacific Ocean and Implications for Nodule Formation

“…Geochemistry, Geophysics, Geosystems (Benites et al, 2018;Yamazaki & Shimono, 2013), the existence of which is supported by magnetic and morphological data that indicate the presence of minor detrital magnetic minerals in the studied nodules (Figures 4b, 4c, and S1). These detrital minerals were likely transported to the open ocean by wind and settled onto the seafloor (Yamazaki & Shimono, 2013).…”

“…Similar elemental compositions between biogenic manganese oxides and bulk nodules are detected in nodules (Figure b). Additional elements in bulk nodules (Figure b) will be due to detrital inputs (Benites et al, ; Yamazaki & Shimono, ), the existence of which is supported by magnetic and morphological data that indicate the presence of minor detrital magnetic minerals in the studied nodules (Figures b, c, and S1). These detrital minerals were likely transported to the open ocean by wind and settled onto the seafloor (Yamazaki & Shimono, ).…”

Presence of biogenic magnetite in ferromanganese nodules

“…One slab was used to prepare a 100 μm thin section for micro‐X‐ray fluorescence (μ‐XRF) and scanning electron microscopy analyses, which are detailed in the study by Benites et al . (). The other slab was kept for rock magnetic studies.…”

Genesis of Pyrite Concretions: Constraints from Mineral and Geochemical Features of Longtan Formation in Anhui Province, Eastern China

“…Mineral concretions in sedimentary rocks, including ferromanganese (Fe-Mn), Co-rich, siderite and phosphorite ones, contain potential important (non)-metallic resources [1][2][3][4][5][6] and record many important diagenetic and paleoenvironmental information [5][6][7][8]. Although increasing studies tend to divide concretions into three main types, that is, syngenetic, diagenetic and epigenetic [9][10][11], all of them record the composition and conditions of the surrounding sediment layers [5,6].…”

“…Mineral concretions in sedimentary rocks, including ferromanganese (Fe-Mn), Co-rich, siderite and phosphorite ones, contain potential important (non)-metallic resources [1][2][3][4][5][6] and record many important diagenetic and paleoenvironmental information [5][6][7][8]. Although increasing studies tend to divide concretions into three main types, that is, syngenetic, diagenetic and epigenetic [9][10][11], all of them record the composition and conditions of the surrounding sediment layers [5,6]. Pyrite concretions record the sedimentary formation processes [7,8], the subsequent metasomatic growth and/or alteration [12,13], microbial sulphate reducing pyrite formation versus later-formed (metasomatic or hydrothermal related) pyrite formation [12,13] and thus determine the mineral and geochemical characteristics of pyrite concretions are highly important [8].…”