The reconstruction of formational process of coastal plains and sea level change of Toyama Bay area

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K03987
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17030:Human geosciences-related
• Research Institution: Niigata University
• Principal Investigator: URABE ATSUSHI 新潟大学, 災害・復興科学研究所, 教授 (20281173)
• Co-Investigator(Kenkyū-buntansha): 片岡 香子 新潟大学, 災害・復興科学研究所, 教授 (00378548) ; 高清水 康博 新潟大学, 人文社会科学系, 准教授 (10446370)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 海水準変動 / 射水平野 / 魚津埋没林 / 縄文海進 / 弥生の海退

Outline of Final Research Achievements

Several borehole investigations were carried out in the Imizu Plain along the Toyama Bay coast to reconstruct the sedimentary facies of the Alluvium, the evolution of the sedimentary environment and paleogeography of the area. The results indicate that a narrow sandbar and a muddy lagoon were established near the present shoreline about 7200 years ago, and that the peak elevation of the Jomon sea level in this area was similar to that of the present sea level. The results of the borehole survey in the Uozu buried forest area, combined with the previous borehole results, indicate that the formation of the buried forest in the Uozu area was not caused by climatic change in sea level, but by relative sea-level change (subsidence).

Free Research Field

地質学，第四紀学

Academic Significance and Societal Importance of the Research Achievements

富山湾沿岸の射水平野における沖積層の形成と堆積環境の復元から，約7200年前の海水準は現在と同様の標高であることが明らかとなった．また，国内において定説化されている弥生の海退に関する有力な根拠が，従来の魚津埋没林の形成から議論されているが，魚津埋没林での検討から，埋没林の形成は弥生の海退以降の海水準の上昇ではなく，ローカルな沈降により形成されたことが明らかとなった．国内各地において漠然と定説化されている弥生の海退現象や縄文海進のピーク標高についても広く再検討の必要が示唆される．