- 国立科学博物館専報 (ISSN:00824755)
- vol.15, pp.37-"48-2", 1982
Deposits of the Oshino basin located in the northeast of Mt. Fuji consits of the Oshino fossil lake sediments and pyroclastic materils of Mt. Fuji. The geological sequence in the Oshino area before and after the appearance of the fossil lake is studied. The results of electric prospecting carried by the Ministry of Agriculture and Forestry indicate that the route of the Katsura River and the configuration of ground before the Oshino lava flow was not greatly different from the present ones. The Oshino lava, a branch of the Saruhashi lava flow, dammed up the valley of the former Katsura River and caused the appearance of the Oshino lake. The deposits of the fossil lake, consisting mainly of clay 1.2-12.0m in thickness, are dated 7,150±140 years B. P. by the ^<14>C method. The assemblage of fossil pollen in the deposits indicates a cold-temperate flora which is scarcely different from the present flora in this area. Most insect and seed fossils are squatic or semiaquatic species and do not suggest a different climatic condition from the present one. The fossil flora of diatom is separately reported in another paper in this volume. The swampy deposits at a depth of 2-3m, located at the central area of the basin, are dated 3,020±65 and 2,450±75 years B. P. on the burried wood identified as a species of Alnus.