[S-CG48] Ocean Floor Geoscience

[SCG48-P07] Characteristics of Deposits in the Southern Okinawa Trough: Preliminary Report of Cruise KH-23-11

Daisuke Kuwano¹, *Seiya Fujishima¹, Minoru Ikehara², Stephen Obrochta³, Makoto Otsubo⁴, Masataka Kinoshita⁵, KH-23-11 Shipboard Scientists (1.Kyoto University, 2.Marine Core Research Institute, Kochi University, 3.Akita University, 4.Geological Survey of Japan, Research Institute of Earthquake and Volcano Geology, 5.Earthquake Research Institute, University of Tokyo)

Keywords:Okinawa trough, Back-arc basin, Turbidity current, Turbidite

The Okinawa Trough is currently an active back-arc basin, representing an early stage of continental crustal thinning characterized by intermittent rifting since approximately 2 million years ago. However, the mechanisms driving crustal thinning at this stage remain unclear. In order to elucidate these processes, comprehensive marine geoscientific observations were conducted during cruise KH-23-11 of the R/V Hakuho-maru from December 2023 to January 2024. This study focuses on the lithology and accumulation rate of sediments that infilled the axial portion of the back-arc basin during the early stages of development. During the cruise, heat flow piston coring and long-piston coring were conducted at eight sites. Several cores were split on board and then imaged using the Namahage core image scanner prior to color and thermal conductivity measurements. Finally, the archive halves of the split cores were and visually described and the working halves were samples. On shore, the cores were imaged by the CT scanner at the Marine Core Research Institute, Kochi University. Sediments primarily consist of homogenous clay to silt and well-sorted clay interspersed with very fine to medium sand, suggesting that sediment transport to the southern Okinawa Trough is predominated by turbidity currents originating from Taiwan, as well as hemipelagic sediment deposition. Future research will aim to estimate sedimentation rates, which is expected to elucidate the relationship between heat flow, interstitial water composition, and sedimentary systems.