Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

H (Human Geosciences ) » H-CG Complex & General

[H-CG32] Interdisciplinary approach to earth surface processes related to deposition, erosion and sediment transport

Sun. May 26, 2019 10:45 AM - 12:15 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Koji Seike(Geological Survey of Japan, AIST), Naofumi Yamaguchi(Center for Water Environment Studies, Ibaraki University), Hajime Naruse(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Hideko Takayanagi(Institute of Geology and Paleontology, Graduate School of Science, Tohoku University)

[HCG32-P03] Depositional environment based on grain size of surface sediments around Okinoerabu-jima, Tokuno-shima and Amami-oshima Islands

*Atsuko Amano1 (1.National institute of Advanced Industrial Science and Technology)

Keywords:grain size, seabed photography, sedimentary environment

The spatial variation of grain size around Okinoerabu-jima, Tokuno-shima and Amami-oshima Islands located at Ryukyu Islands was compiled based on surface sediment samples and seabed photographs. Surface sediments around islands above the water depth of 600 m show gravels and very coarser sands characterized by high contents of calcium carbonate deposition mainly originated from coral, shells and briozoans. On the other hand, slope and flat areas below the water depth of 600 m are deposited medium-very fine sands (2-4φ) and shows to become a finer toward increasing in water depth, concave geometry including the Yoron and Okinoerabu basins in silt (4-7φ). These results indicate that hydrodynamics effects to sedimentary process decrease toward the increasing water depth and hemipelagic sediments are deposited in the basin. Ripple marks in the seafloor are observed at 66 sites by the seabed photographs. The water depths of these sites are mostly above 1000 m and the values of grain size 1-3φ. The current directions assumed by the ripple mark show complex changes and indicate that the bottom currents change affected by the microtopography.