Chronology of the Holocene Shallow Marine Sediments under the Tokushima and Nobi Plains, Central Japan by Tephras and Radiocarbon Dates(＜Special Section＞Determination of the Construction of an Outcrop Database to Reveal Eruptive History (3))

Abstract

Analysis of volcanic glass and radiocarbon dating were applied to shallow marine sediment of 6 cores obtained from the Tokushima and Nobi plains, central Japan. Six basal horizons of Kikai-Akahoya (K-Ah) ash and two ones of Amagi-Kawagodaira (Kg) ash were identified from these cores based on the contents of volcanic glass, morphology of glass shards and these colors. The known ages of these tephras, K-Ah: 7165-7303 cal BP and Kg: 3137-3160 cal BP, were compared with the radiocarbon ages measured around these horizons. Seven pairs of radiocarbon ages from plants and shells were consistent with the tephra eruption ages. However, other 1 pair was 500-1000 years older than the age of tephra because the age was obtained from organic sediment. Integrated chronology by tephras and radiocarbon dating will enable to determine us high-resolution interpretation of shallow marine sediments.