Marine ferromanganese nodules (nodules, hereafter) are widely found abyssal concretions with concentric layers of manganese-iron-hydroxides, which typically grow at a speed of about few mm/Myr (e.g., Verlaan & Cronan, 2022;von Stackelberg, 2000). These nodules are considered as a future mineral resource of Cu, Ni, Co, and rare earth elements. While such nodules are also found buried in deeper sediments, many of them are still exposed on the sediment surface despite their geologically old age of tens of millions of years (e.g., Verlaan & Cronan, 2022;von Stackelberg, 2000). The nodules are composed of two phases: diagenetic buserite with metal ions in sediment and hydrogenetic vernadite with colloids in seawater (e.g., Skowronek et al., 2021;Usui & Someya, 1997;Usui et al., 1989;Verlaan & Cronan, 2022). Usui and Ito (1994) demonstrated using Ocean Drilling Program cores that buried nodules are usually found in stratigraphic layers corresponding to hiatuses or slow sedimentations. Graham et al. ( 2004) reported using 10 Be chronology that the surface ages of the buried nodules
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