九州東岸、延岡平野北部における完新世中期の相対的海水準に関する資料 : 貝類・珪藻化石群集分析とAMS14C年代測定の結果

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The author discussed the relative sea-level (RSL) and paleoenvironment in the middle Holocene in the northern part of the Nobeoka Plain (the Inabazaki Lowland) , east coast of Kyushu Island. Hand-drilling surveys were performed in order to observe Holocene sediments and to obtain core samples for AMS radiocarbon dating and fossil assemblage analysis of molluscan shells and diatoms. The Holocene sediments of the lowland are mainly composed of sandy mud with abundant molluscan shells. Calibrated ages of inter-tidal shells and wood fragment from the core samples range from 6,498 - 6,300 cal BP(Beta-150426)to 6,249- 5,984 cal BP(Beta-150425) . The fossil molluscan assemblages of the middle Holocene sediments consist of inner-bay muddy bottom association ,inner-bay sandy bottom association and tidal flat association. The fossil diatom assemblages imply that the sedimentary environments of the Holocene sediments were tidal flat condition and that the upper limit of marine sediments is 1.6m above present sea-level. They show that the culmination of the Jomon transgression had reached the lowland at about 6,500 cal BP and the tidal flat had formed. These results indicate that the RSL at about 6,500 to 6,OOO cal BP in the Nobeoka Plain had risen and had reached O.5 to 1.O m above present sea-level.
宮崎大学の論文
2005-03-30