[M-IS09] Gas hydrates in environmental-resource sciences

[MIS09-P07] Isotopic compositions of Carbon, Oxygen, and Strontium in authigenic carbonates from Umitaka Spur, off-Joetsu, southeast of Japan Sea

*Yoshihiro Kakizaki¹, Tsuyoshi Ishikawa², Tatsuya Kawai³, Akihiro Hiruta¹, Ryo Matsumoto¹ (1.Gas Hydrate Research Laboratory, Organization for Strategic Coordination, Meiji University, 2.Kochi Institute for Core Sample Research, JAMSTEC, 3.Department of Marine & Earth Sciences, Marine Works Japan Ltd.)

Keywords:authigenic carbonates, shallow gas hydrate, Japan Sea

We present isotopic compositions of Carbon (δ¹³C), Oxygen (δ¹⁸O), and Strontium (⁸⁷Sr/⁸⁶Sr) in authigenic carbonates from Umitaka Spur, off-Joetsu, southeast of Japan Sea.
The carbon isotopic values in authigenic carbonate from Umitaka Spur are higher than those of Joetsu Knoll and west off-Tobishima Island. This range corresponds to the δ¹³C values of thermogenic methane (Bernard et al., 1978). Range of the δ¹⁸O values of authigenic carbonates from Umitaka Spur is mostly equal to those of Joetsu Knoll and west off-Tobishima Island.
The ⁸⁷Sr/⁸⁶Sr ratios in authigenic carbonates from shallow depth of Umitaka Spur is equal to those of modern surface seawater in off-Joetsu. The Sr-isotopic ratios in authigenic carbonate from deeper depth are lower ratios. This Sr-isotopic trend can be correlated to the global Sr-isotopic trend in seawater from late Pleistocene to present. It indicates that Sr-isotopic ratio of authigenic carbonate reflects the Sr-isotopic ratio of seawater at the time of deposition. The Sr-isotopic ratios in pore water are parallel lower than those of authigenic carbonate. It indicates that pore water includes light Sr by diagenetic procedure.
Acknowledgments: This study was conducted as a part of the shallow methane hydrate exploration project of METI. Isotopic measurement of Strontium was performed in Kochi Core Center, by visiting scientist program of JAMSTEC.