Paleogeography and Tephras of the Kimotsuki Lowland, Southern Kyushu, Japan, in the Middle to Late Holocene

摘要

This paper discusses the paleogeogra- phy of the Kimotsuki Lowland, southern Kyushu Island, during the middle to late Holocene based on tephrochronology and AMS ~14C dating. As indicated by the Ikeda pumice fall on the berm deposits, the most landward bay- mouth barrier was formed about 5.5 - 5.7 ka, and the entire barrier appears to have been formed within about 100 years. The relative height of sea level at that time is estimated to be about 3-5 m above the present sea level. Five tephra layers occur in the peat de- posits, four of which are identified as the Sakurajima-Takatoge 2 (4.5 ka), the Kiri- shima-Miike (4.2 ka), the Kaimondake-9c (2 ka) and the Kaimondake-12a (A.D. 874). The fifth layer has not yet been correlated. Three AMS ~14C dates obtained from the base of the peat deposits, along with the tephrochronology, indicate that the accu- mulation of the peat began 5.6 ka to 5.0 ka and lasted for at least 4,000 years.