Recovery of high-resolution paleomagnetic intensity records from marine sediments in a reduced condition

2023 Fiscal Year Final Research Report

• Project/Area Number: 19H01997
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: Yamazaki Toshitsugu 東京大学, 大気海洋研究所, 教授 (80344125)
• Co-Investigator(Kenkyū-buntansha): 山本 裕二 高知大学, 教育研究部総合科学系複合領域科学部門, 教授 (00452699) ; 臼井 洋一 金沢大学, 地球社会基盤学系, 准教授 (20609862) ; 中村 教博 東北学院大学, 高等教育開発室, 教授 (80302248)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 古地磁気 / 岩石磁気 / 初期続成 / 赤鉄鉱

Outline of Final Research Achievements

In deep-sea sediments below the Fe-redox boundary, unprotected detrital magnetite and magnetofossil are lost in the process of reduction diagenesis, and their remanent magnetization intensity decreases to 10% or less. Nonetheless, paleomagnetic direction and relative paleointensity are preserved. In such sediments, silicate-hosted magnetic inclusions and hematite survive the dissolution, and the former carries about a half of saturation isothermal remanent magnetization and the letter carries about 30%. From the grain size distribution of the host silicates and the amount of magnetite embedded, it is estimated that the silicate-hosted magnetic inclusions may not be a efficient recorder of detrital remanent magnetization. Hence, hematite may be an important carrier of the natural remanent magnetization.

Free Research Field

古地磁気学、海洋地質学

Academic Significance and Societal Importance of the Research Achievements

赤鉄鉱はその飽和磁化が磁鉄鉱の100分の１程度と極めて小さいことから、海底堆積物の自然残留磁化を担う磁性鉱物としては従来見過ごされることが多かったが、還元続成作用を受けた海底堆積物では重要な担い手となることが本研究で初めて指摘された。磁性鉱物が還元溶解を受けた堆積物でも赤鉄鉱が古地磁気記録を保持できることは、従来磁性鉱物の還元溶解を理由に研究対象とされなかった堆積物を活用することへ道を開く。