Elucidation of sedimentary process in the inner part of fluvial-coastal plain and quantitative change in sediment production of the drainage basin since the early-middle Holocene

2018 Fiscal Year Final Research Report

• Project/Area Number: 17H07151
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Single-year Grants
• Research Field: Geography
• Research Institution: Hosei University
• Principal Investigator: Hasada Kodai 法政大学, 文学部, 助教 (80804088)
• Project Period (FY): 2017-08-25 – 2019-03-31
• Keywords: 沖積層 / 海水準変動 / 堆積環境 / 氾濫原 / 完新世 / 濃尾平野

Outline of Final Research Achievements

This study investigated the evolution of Latest Pleistocene to Holocene deposits based on the analysis of two borehole core sediments (KG and OZ cores) obtained from the inner part of the Nobi Plain, central Japan. Two cores were taken from the present floodplain of the plain where prodelta deposits have not been distributed. Sedimentary environmental changes have the following features: (1) delta progradation occurred since 8-8.5 cal kyr BP, (2) environment made the transition from marine to fluvial at about 5-5.5 cal kyr BP when the rate of sea-level rise decreased. Sediment accumulation rates were almost equal to the rate of sea-level rise. This suggests that sediment accumulation have been strongly influenced by the postglacial sea-level change.

Free Research Field

地理学

Academic Significance and Societal Importance of the Research Achievements

流域における長期的な土砂生産量の把握は、完新世における環境変化（降水量変化や森林伐採など）やそれらが地形形成に与える影響を議論することにつながるとともに、河川での土砂管理や土砂災害への対策を実施する上でも重要な課題となっている。沖積低地の堆積土砂量に基づいて流域での土砂生産量を推定するには、低地の広範囲における堆積物の特徴や堆積年代を明らかにする必要がある。しかし、完新世前・中期、海水準上昇期の堆積中心である低地内陸域を対象とした研究は少ない。特に、海進から海退に転じる前後の堆積システムの発達過程を詳細に把握するまでには至っておらず、内陸域における研究の蓄積が求められている。