Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

B (Biogeosciences ) » B-BC Biogeochemistry

[B-BC03] Interrelation between Life, Water, Mineral, and Atmosphere

Tue. May 28, 2019 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Takeshi Kakegawa(Graduate School of Science, Tohoku University), Tadashi Yokoyama(Graduate School of Integrated Arts and Sciences, Hiroshima University), Keisuke Fukushi(Institute of Nature & Environmental Technology, Kanazawa University), Fumito Shiraishi(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University)

[BBC03-P06] Organic matter around Miocene Kuroko ore deposits: Implications to Archean submarine hydrothermal microbial community

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

Keywords:Kuroko, Chemoautotroph, stable isotope

Kuroko ore deposits were products of black smoker activities at 15 Ma paleo-Japan Sea. Kuroko is often covered by organic-rich sedimentary rocks, but details of these organic matter have not been unclear. Here I report analytical results of stable isotopes, Raman spectroscopy and bitumen compositions of organic matter around Miocene Kuroko deposits.

In general, all geochemical characteristics of organic matter were uniform in the same horizon of Kuroko deposits. On the other hand, H/C ratios and Raman spectroscopic data suggest that organic matter were extensively graphitized by thermal degradation only around Kuroko. More 12C- and 14N-enriched features are found in Kuroko-associated kerogen and bitumen. Such stable isotope data suggest the presence of chemoautotrophs, which utilized hydrothermal CH4and NH3. However, geochemical and geological characteristics of the examined samples suggest that hydrothermal CH4and NH3were produced by thermal degradation of sedimentary organic matter, which are mainly derived from photoautotrophs. This further suggests that chemoautotrophs at Kuroko were not independent and had strong connection to surface photoautotrophs.
Organic matter enriched in 12C and 14N are ubiquitous around many middle-Archean Kuroko ore deposits. Such stable isotope compositions also imply the presence of submarine hydrothermal microbial communities. However, 12C- and 14N-depleted organic matter, which most likely represent photoautotrophs, are also common around Archean Kuroko deposits. Such contrast stable isotope characteristics suggest that deep submarine chemoautotrophs already had linkages to surface photoautotrophs since Archean age.