Holocene relative sea-level change and rate of sea-level rise from coastal deposits in the Toyooka Basin, western Japan

This study presents relative sea-level (RSL) change from 11,200 to 500 cal. BP in the Toyooka Basin, western Japan. Diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment cores obtained from thick Holocene fluvial and marine deposits. An age model was constructed based on tephrochronology and 31 radiocarbon ages from elevations of -46.85 to +1.51 m in 19 cores. The RSLs in the Toyooka Basin are -31.05 m in elevation at 10,000 cal BP, above -4.00 m at 7900 cal. BP, -0.47 m at 6700 cal. BP and +0.15 m at 3300 cal. BP. A rapid sea-level rise, at a rate of about 23 mm/yr, is observed during the period from 10,600 to 10,300 cal. BP. Relative sea-level rose at a rate of about 12 mm/yr between 10,000 and 7900 cal. BP. The rate of sea-level rise decelerated at 7900 cal. BP, from about 12 mm/yr (10,000-7900 cal. BP) to 3 mm/yr (7900-6700 cal. BP). The mid-Holocene sea-level highstand probably occurred between 7000 and 6000 cal. BP, but it remains difficult to constrain its elevation. These RSL features described here may provide a typical example of Holocene sea-level changes resulting from both eustatic and hydro-isostatic components for the Japanese islands.