Reconstruction of Holocene environmental changes based on magnetic properties of lacustrine and inner-bay sediments

2017 Fiscal Year Final Research Report

• Project/Area Number: 15K05321
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Doshisha University
• Principal Investigator: Hayashida Akira 同志社大学, 理工学部, 教授 (30164974)
• Co-Investigator(Renkei-kenkyūsha): FUKUMA Koji 同志社大学, 理工学部, 准教授 (80315291)
• Research Collaborator: ANRAKU Kazuhiro 同志社大学, 大学院・理工学研究科, 大学院生 ; TAKANASHI Yutaro 同志社大学, 大学院・理工学研究科, 大学院生
• Project Period (FY): 2015-04-01 – 2018-03-31
• Keywords: 古地磁気永年変化 / 環境磁気学 / 磁性鉱物 / 初期続成作用 / 土壌流出

Outline of Final Research Achievements

Intending to contribute high-resolution chronology and environment study, we investigated magnetic properties of the Holocene lacustrine and inner-bay sediments, including remanent magnetization, variation of magnetic concentration, coercivity distribution and thermomagnetic properties. Although the sediments from brackish-water basins, Lake Ogawara and Lake Abashiri, had suffered loss of magnetic minerals possibly due to reductive diagenesis, high-coercivity magnetic minerals, hematite and goethite, were enhanced in the topmost sediment from the Haneji Inner-Bay and the Shioya Bay on Okinawa Island, suggesting significant runoff of red soils from the watershed. On the other hand, sediments from Ichi-no-megata, Beppu Bay and a fresh-water interval of Lake kushu are characterized by stable remanent magnetization. These results are correlative to the standard record from Lake Biwa, representing regional records of Holocene paleomagnetic secular variation of the Japanese Islands.

Free Research Field

古地磁気学