[MIS17-P02] Genesis of Mn-nodules as deep sea floor bacterial stromatolite
Keywords:Mn-nodules , stromatolite , biogenic genesis, fractal-like morphologiy, bacterial biomineralization, Co-rich Mn crust
In this report, the author summarize these results and compare other biogenetic precipitation of Mn oxides.
Samples of Mn nodules and Co-rich Mn crust in Pacific ocean were used for mineralogical examinations : Morphology, OM, XRD, TEM, SEM, EDS, HRTEM, X-ray CT, mathematical simulation by assuming fractal morphology.
The results (Figs.) showed the followings: morphology is fractal-like nature; the fourth order corresponds to top dome shapes of the columnar stromatolite structure, which will be mentioned later.
Bacterial signature(fossil) was widely found on the surface and inner structure. Manganese and Iron metabolic bacteria may be symbiotically cooperating to form Mn nodules. Mineralogy of the Mn oxide is characterized by 2.5 Å manganate and/or 10 Å phyllomanganate. Thin rhythmic banding is always found as growth layer, essentially similar dome-like stromatolite and sometimes it is interrupted by some event layer. There is a discussion for this thin layer as Milankovitch cycle (Han et al., 2003). Textural similarity to the present hot spring stromatolite (Akai et al.,1995,1997) conaining Mn-stromatolite is very strong. We have found stromatolite structure also at Onneto-Yunotaki Mn deposit (Kanai and Akai,2008). Mn-nodule aggregate is apparently a kind of relic of Precambrian stromatolite bio-community.