Sequential high-density radiocarbon dating to detect invisible event layers in marine sediments

We present a unique application of radiocarbon measurements on hemipelagic sediments that uses continuous radiocarbon dating of total organic carbon ( 14 C TOC age) to recognize event deposits. The 14 C TOC age of sediments is not commonly used for age determination because total organic carbon includes various origins, such as marine, terrestrial, and reworked old fragments. In this study, the 14 C TOC ages of some horizons were found to be older than those of the deeper ones through continuous 14 C TOC measurements at 0.5- to 1.0-cm intervals. The reversal 14 C TOC ages resulted not from the settlement of organic particles from the terrestrial environments, such as floodings, but from the submarine slope failures. Therefore, we can regard the reversal 14 C TOC layers as event layers due to geohazards. After reconstruction of the age model using foraminiferal tests obtained from the sediment core used in this study, depositional ages of event layers were identified. Well correlation with historical natural disasters after the 15 th century suggest validity of the method proposed by the current study.