[M-IS16] Paleoclimatology and paleoceanography

[MIS16-P12] Sedimentary characteristics, age and event of a marine core collected from Uranouchi Bay, Kochi, Japan

*Masafumi MURAYAMA^1,3, Wataru Tanikawa², Akira Ijiri², Tatsuhiko Hoshino², Takehiro Hirose², Katsuya Nejigaki³, Kazuno Arai³, Go-Ichiro Uramoto³, Kondo Yasuo⁴, Hiromasa Ozaki⁵, Minoru Yoneda⁵ (1.Faculty of Agriculture and Marine Science, Kochi University, 2. Institute for Extra-cutting-edge Science and Technology Avant-garde Research, Kochi Institute for Core Sample Research, JAMSTEC, 3.Center for Advanced Marine Core Research, Kochi University, 4.Faculty of Science and Technology, Kochi University, 5.The University Museum,The University of Tokyo)

Keywords:Uranouchi Inlet Bay, Marine Core, Event sediment, 14C age

Sediment cores collected from the inner part (10m depth) of Uranouchi Bay, Kochi Prefecture, have been analyzed to investigate the history of changes in the marine environment. Uranouchi Bay that extends in the east-west direction with 12 km is located in the central part of Tosa Bay, Kochi Prefecture facing to the north side of the Yokonami Peninsula. This is well known as a sinking bay caused by subduction-zone earthquakes. Two 4 m sediment cores were collected by vibro coring using the university research vessel "Neptune". These core samples are considered to have recorded detailed environmental changes in the bay having no affecting the surrounding river. These core samples were carried out X-ray CT and visual observation, physical properties, identification and ¹⁴C dating of fossil shells. The lithology of the sediments was olive to gray colored silty clay with a lot of shell fragments. The most upper part of these cores was providing dark colored and had a strong hydrogen sulfide odor. In addition, a well-laminated sedimentary layer with a thickness of 8 cm was observed in the lower part of the core (around 306 m from the core top). This sedimentary layer was confirmed in a similar depth collected at a nearby water depth of 8 M, but no lamination was developed. Radiocarbon dating (AMS 14C age) of shell fragments from the 8 layer of sediment was performed. At the bottom of the core, showing about 3800 years ago, the estimated average deposition rate was 102 cm / kyr. In this presentation, we will introduce these results.