日本海および東シナ海沿岸の主な海岸砂丘地帯の形成期と固定期について

Abstract

This paper consists of the history of the formation of the sand dune region and some conditions of the sand dune forming periods and the sand fixing periods in five sand dune regions, the Fukiagehama region (in Kagoshima Prefecture), the Genkai region (in Fukuoka Prefecture), the Yahata region (in Niigata Prefecture), the Shonai region (in Yamagata Prefecture) and the Akita region (in Akita Prefecture). The following results were obtained;1) Many of the sand dune regions are thought to have been formed after the formation of the sand bar caused by a rise of the sea level during the Jomon transgression (7, 000-5, 000y.B.P.).2) Some buried humic sand beds are intercalated in the aeolian sand layer, and they indicates the time under the sand fixing condition. The buried humic sand beds are colored brown-dark brown-blackish brown-black, and are called the Kurosuna bed.3) In Fukiagehama region, one Kurosuna bed and one black humic ash bed are observed.In the Genkai region, five Kurosuna beds are intercalated. They suggests that the time of the early Jomon culture period (about 5, 300C-14y.B.P.), the middle-later Jomon period (about 3, 400C-14y.B.P.), the Yayoi-Heian period (about 2, 000-1, 000y.B.P.), the Muromachi period (about 500y.B.P.) and after 500y.B.P.In the Yahata region, one Kurosuna bed is observed, and the upper aeolian sand bed covering the Kurosuna bed was supplied with the little transgression about 1, 000y.B.P.Three Kurosuna beds are intercalated in the Shonai sand dunes. After the Kohun period (about 1, 400-1, 300y.B.P.), much volume of the sand was supplied from the seacoast.The Akita region is composed of many parallel sand ridges. Between the ridges are belts of marshes or shallow lakes, which are parallel to the shoreline. These many sand ridges are grouped into three. The inner and the middle ridges were formed from the early Jomon to the late Jomon. The outer one were formed after the late Jomon, and are the largest in scale.4) The stable period from the middle Jomon to the Kohun period was common to these regions, but in details these ages are different due to the local conditions.5) After the Kohun period, the supply of the sand was increased through these regions.