Late Holocene slackwater deposits on the Nakagawa River, Tochigi Prefecture, Japan

A continuous succession of slackwater deposits was investigated on the Nakagawa River, Karasuyama Town in Tochigi Prefecture, Japan. Forty-one and 32 flood events were estimated from two sedimentary cores. Minimum sedimentation rate is estimated at 4.6 mm/year and the calculated maximum flood recurrence interval is 14 years. The sedimentation rates are high compared to other published data and are thought to be the key reason as to why these deposits were preserved in Japan, previously considered too humid. High sediment accumulation rates are thought to compensate for any bioturbation activity that would disturb and homogenise the slackwater deposits. This study is important because it presents a new arena for palaeoflood analysis, suggesting that there is potential for slackwater preservation in similar humid settings.