Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Poster

B (Biogeosciences) » B-BG Biogeosciences & Geosphere-Biosphere Interactions

[B-BG02] Interrelation between Life, Water, Mineral, and Atmosphere

Mon. May 21, 2018 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Ken Takai(Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology), Kentaro Nakamura(Department of Systems Innovation, School of Engineering, University of Tokyo), Yuichiro Ueno(東京工業大学大学院地球惑星科学専攻, 共同), Yohey Suzuki(Graduate School of Science, The University of Tokyo)

[BBG02-P01] New evidence and significance of biogenic Mn oxides in 12Ma carbonaceous sedimentary rocks in the Hokuroku district, Akita: constrain from fossil DNA and magnetic field

*Yuya Tsukamoto1, Takeshi Kakegawa1 (1.Graduate School of Science,Tohoku University)

Keywords:biogenic Mn oxides, low temperature hydrothermal activities, DNA extraction, Magnetic field

Mn oxides are commonly found on the modern seafloor or around the terrestrial hot springs. Role of Mn-oxidizing bacteria has been discussed by previous investigators to promote precipitation of Mn oxides. However, it has been challenging to distinguish biogenic Mn oxides from abiogenic Mn oxides, because of their mineralogical similarity. It will become possible to identify biogenic Mn oxides, by accumulating unique characteristics of biogenic Mn oxides and clarifying differences with abiogenic Mn oxides. Such characteristics of biogenic Mn oxides will be used as a tool, i.e., mineral bio-marker, to find the evidence of Mn-oxidizing bacteria in the ancient rocks, in particular from Archean.
Stratified and disseminated Mn ore deposits are present in the Hokuroku district, Akita prefecture. Significant amounts of Mn were mobilized in host rocks by ca. 12 Ma submarine hydrothermal activities and then Mn oxides were precipitated on or beneath the seafloor. One type of ore has a colloform structure, which resembles the stromatolite, with Mn oxides (todorokite) and reduced carbon.
Fossil DNA extraction was successful from this Mn ore, excluding the possibility of later contamination. This is the first success of DNA extraction, specific for Mn-oxidizing bacteria (Acinetobacter and Pseudomonas), in geological samples as old as 12 Ma. As a result, two kinds of Mn-oxidizing bacteria, which are commonly found in the surface of modern ferromanganese crusts, are identified. In addition, magnetic field was detected on Mn oxides in colloform structure by magnetic field microscopy (MFM). Magnetic field is generated when Mn oxide has high cation vacancies and abundance of Mn4+, which are common in biogenic Mn oxides.
The above comprehensive analyses on the same Mn oxides indicate that Mn oxides in colloform structure are biogenic in origin. This study will be utilized in the search for ancient biogenic Mn oxides and give a hint to understand the ancient Mn cycles.