A05_P08

Detection of tectonic movement and marine reservoir effect in the Holocene sediments from the Ukishima plain, Shizuoka, central Japan

Nakanishi T¹,  Ishiyama T², Noguchi M³, Hong W⁴

¹Museum of Natural and Environmental History, Shizuoka, Shizuoka, Japan, ²the University of Tokyo, Tokyo, Japan, ³Geoanalysis Network of Tokyo capital region, Tokyo, Japan, ⁴Korea Institute of Geoscience & Mineral Resources, Daejeon, Republic of Korea

To investigate paleoenvironmental changes and tectonic activities, one Holocene sediment core with length of 30 meters was obtained from the Ukishima plain in the inner part of Suruga Bay, which corresponds on the boundary of the Eurasia and Philippine Sea Plates. This drilling site locates in a subsidence area associated with the subduction of the Philippine Sea Plate (Matsuda, 1978, Matsubara, 1984, Fujiwara et al., 2006, 2008, Komatsubara et al., 2007). Based on analyses of lithology, molluscan and diatom assemblages, and radiocarbon dating, we interpreted six sedimentary facies in order of older age: transgressive lag, estuary, estuary front, inner bay, lagoon, and artificial soil. These paleoenvironmental changes had been mainly associated with the sea-level rise during the deglacial period. To determine marine reservoir effects, the radiocarbon ages of marine shells and terrestrial plants were measured from same horizons of estuary to inner bay sediments. Reservoir ages of 6 pairs from these facies were recognized during the period from 7,900 to 6,800 cal BP. The average was 310 ± 120 years within 150 ± 70 to 470 ± 60. The chronological change in the reservoir effect will be correlated with the Holocene sediments from the coastal area in Southwest Japan under the Kuroshio warm current (Nakanishi et al., 2017ab, 2019). This core was obtained by the Headquarters for Earthquake Research Promotion at the Japanese Ministry of Education, Culture, Sports, Science and Technology. Radiocarbon dating was partially funded by the Japan Society for the Promotion of Science KAKENHI grant number JP18H01310.