Japan Geoscience Union Meeting 2016

Presentation information


Symbol B (Biogeosciences) » B-PT Paleontology

[B-PT05] Decoding the history of Earth: From Hadean to Modern

Wed. May 25, 2016 3:30 PM - 5:00 PM 105 (1F)

Convener:*Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Chair:Shogo Aoki(Graduate School of arts and science, University of Tokyo)

4:45 PM - 5:00 PM

[BPT05-24] Carbon dioxide emission during OAE 1a from the oil reservoir in Brazilian offshore

*Akihiro Kano1 (1.Graduate School of Social and Cultural Studies, Kyushu University)

Keywords:Cretaceous, OAE, carbon dioxide

Development of a huge oil field has been unveiled in Brazilian offshore during the last decade. It consists of ~150 m thick porous carbonate distributed in an area of half Honshu, which was formed in ~1 million years. Depositional setting was likely a saline lake developed in the onset of continental rifting between South America and Africa. However, laminated texture and rapid depositional rate are supportive alternative view that it was deposited from carbonate spring (travertine). Since this discovery, travertine researchers have been focusing the origin of this carbonate oil reservoir. The Brazilian carbonate rock comprises a huge carbon mass of 1.23 x 1019 mole, when we take the porosity and the carbonate content similarly 50%.
Travertine is a rapid CO2-degassing system as well as a carbonate-depositing system. Our results in Japan and Indonesian travertines indicated the degassing surpassed the carbonate deposition with G/P ratio of 7-18. When we introduce this to the carbon mass of the Brazilian carbonate, the degassed CO2 is calculated 1.2-2.7 x 1015 ton as carbon, which is equivalent to 2-5% of crustal inorganic carbon of Berner (1990). If the degassing had occurred in a period of 1 myr, the average degassing rate corresponds to 14-32% of the modern emission from fossil fuel.
Depositional age of the Brazilian carbonate was 123 Ma during the Ocean Anoxic Event (OAE) 1a. The most likely climatic background was warming due to increase in CO2 concentration, and its potential source might be superplume forming the Pacific oceanic rises or accelerated volcanism in subduction zones. However, an enormous degassing from the Brazilian carbonate calculated here could be more than a candidate trigger of OAE 1a if it was a travertine system.