Here we describe in detail turbidite and hemipelagic mud layers in deep-sea sediments from a core collected from the area east of Mikura-Jima Island. The 196 cm long core sample comprises mainly quartz, volcanic glass, scoria, radiolaria, and foraminifera in silty clay. The silty clay is interbedded with two scoriaceous sand layers deposited as turbidites. We identified the boundaries between hemipelagic and turbidite muds in the silty clay using a variation of grain components and physical properties, as follows. At the boundary, radiolarian and foraminiferal abundances increase, and scoria particles decrease rapidly upwards in the uppermost turbidite muds, whereas these grains are present in consistent numbers throughout the hemipelagic mud layers. Lowest wet bulk density values also indicate the boundary. In addition, we obtained ~(14)C ages of 1296-1171 cal year AD and 2611-2431 cal year BC from the hemipelagic mud layers at 92.5-96.6 and at 33-37 cm depth, respectively.
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