[SCG65-P02] Origin of deep-sea turbidite by stratigraphic variations of terrigenous organic carbon ratio, examples from the off Kii and Boso peninsulas
Keywords:turbidite, terrigenous organic carbon, stratigraphic variation
Sediment cores were acquired from the off Kii Peninsula (KT-12-34-PC01, 5.2 m long) at about 2,000 m water depth and the off Boso Peninsula (KS-13-T5-PC02, 9.2 m long) at about 2,500 m water depth by using piston corer. The coring sites of KT-12-34-PC01 and KS-13-T5-PC02 were not directly affected by the submarine canyon. These sediments are composed mainly of olive black clayey silt layers, but includes numerous turbidite layers. Nine intervals of turbidite mud and hemipelagic mud were examined by stable organic carbon analyses. Turbidite mud layers were distinguished from hemipelagic mud by visual examination of soft X-radiographs, on which they show weaker X-ray transmission. Continuous sub-samples were collected at one centimeter intervals from turbidite mud and hemipelagic mud. Total organic carbon contents and stable organic carbon isotope ratio were measured by using an elemental analyzer (Flash EA and Flash 2000) and a mass spectrometer (MAT 253) at the National Museum of Nature and Science, Tokyo. The terrigenous and marine fractions of the organic carbon in the sediment were calculated from the measured stable organic carbon isotope ratio.
In sediment core KT-12-34-PC01, the stable organic carbon isotope ratio was between –19.1‰ and –22.6‰, and the estimated terrigenous fraction was between 0% and 40%. Stratigraphic variations of both flood-induced and slope failure sediments are recognized in TerOC ratio. These results indicate that deep-sea turbidite off the Kii Peninsula were deposited by flood or slope failure. In sediment core KS-13-T5-PC02, the stable organic carbon isotope ratio was between –20.4‰ and –21.7‰ and the estimated terrigenous fraction was between 11% and 28%. Stratigraphic variations of slope failure sediments are recognized in TerOC ratio. These results indicate that deep-sea turbidite off the Boso Peninsula were mainly deposited by slope failure.
The stratigraphic variations of TerOC ratio might be important information for paleoseismic studies by using deep-sea turbidites.
Omura, A., Ikehara, K., Katayama, H., Usami, K., Irino, T., Kuwae, M., Shirai, M. and Ashi, J. (2014) Stratigraphic variations of terrigenous organic carbon ratios in flood and slope failure sediments of marine area, examples from the modern natural disasters of Japan. 19th International Sedimentological Congress, Geneva, T2S3-P14.