A02_P03

Identification of marine reservoir effect in the Holocene sediments from the Nobi Plain, central Japan

Nakanishi T¹, Hori K², Nakashima R³, Hong W⁴

¹Museum of Natural and Environmental History, Shizuoka, Japan, ²Department of Earth Science, Tohoku University, Sendai, Japan, ³Geological Survey of Japan (GSJ), Advanced Industrial Science & Technology (AIST), Tsukuba, Japan, ⁴Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, Republic of Korea

To investigate the relationship between paleoenvironmental changes and marine reservoir effects, the radiocarbon ages of marine shells and terrestrial plants were measured from the same horizons of the Holocene sediments. Two sediment cores, HN1 and OG, were obtained from the western margin of the Nobi Plain, which faces the Kuroshio warm current. This plain is a fluvial–coastal lowland formed mainly by Kiso, Nagara, and Ibi rivers (Hori et al., 2019). These drilling sites are located in subsidence area associated with the Yoro fault (Kuwahara, 1968; Ishiyama et al., 2007). Based on analyses of lithology, molluscan assemblages, and radiocarbon dating, we interpreted five sedimentary units in order of older age: estuary, prodelta, delta front, delta plain, and artificial soil. These paleoenvironmental changes had been mainly associated with the sea-level rise during the deglacial period. Terrestrial accumulation curve was consistent with the Kikai-Akahoya volcanic ash (K-Ah: ca. 7,300 cal BP; Machida and Arai, 2003). The reservoir ages during the period from 9,300 to 2,800 cal BP of 13 pairs obtained from the estuary to delta front facies were evaluated. The average from 140 ± 70 to 900 ± 50 was 350 ± 180 years. The chronological change in the reservoir effect will be compared with the previous results from the other coastal area in Southwest Japan (Nakanishi et al., 2017ab, 2019). Drilling program of the sediment cores were supported by the Grants-in-Aid for Scientific Research, Kakenhi JP17K18526. Radiocarbon dating was funded by the JSPS Kakenhi grant number JP18H01310.