Abstract
Dinoflagellate cyst analysis has been carried out on boring core materials in order to reconstruct the coastal paleoceanography around the Tsushima Island during the Holocene time. Submarine samples were collected at -8.5m depth at the inner part of Mine Bay in Kami-Tsushima. The sediments consist of dark grey sandy to clayey silt including many shell fragments. Two 14C ages using these shell fragments are dated; 1, 100±110 yrs BP at -4m horizon and 7, 150±320300yrs BP at -24.5m horizon. Such marine palynomorphs as dinoflagellate cysts, microforaminiferal linings, and acritarchs were found in the sediments. The dinoflagellate cysts consist mainly of Gonyaulacoid group of Spiniferites bulloideus, Spin. cf. bentori, Spin. cf. delicatus, Protoperidinioid group of Brigantedinium spp., Selenopemphix quanta, Votadinium carvum, Vot. spinosum, and Gymnodinioid group of Polykrikos schwartzii. On the basis of the occurrence mode of dinoflagellate cysts and microforaminiferal linings, three assemblages are recognized: A: assemblage from -1m to -4m depth is characterized by a moderate abundance of cysts and high species diversity. B: assemblage recorded from -5m to -1.7m depth features a great abundance of cysts and high species diversity, and C: assemblage obtained from -18m to -25m depth has few cysts and lower species diversity. These assemblages reflect the early transgression, climatic optimum, and late regression oceanographic conditions of the Holocene time in ascending order.
Some archaeological sites of the Early Jomon Period (ca. 6, 000yrs BP) on the northwestern coast of Kami-Tsushima Island are now located at -1m to -2m below the present sea level. Both paleoceanographic and archeological evidence suggests that the sea level at the time of the Holocene climatic optimum was not higher than the present one, and that the western part of this island has been subsiding since the middle Holocene.
