2021 Fiscal Year Final Research Report

A new approach to determine age of deposition and paleoenvironment change in annually laminated tufa

Research Project

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Project/Area Number	19K21661
Research Category	Grant-in-Aid for Challenging Research (Exploratory)
Allocation Type	Multi-year Fund
Review Section	Medium-sized Section 4:Geography, cultural anthropology, folklore, and related fields
Research Institution	Gifu University
Principal Investigator	Katsuta Nagayoshi 岐阜大学, 教育学部, 准教授 (70377985)
Co-Investigator(Kenkyū-buntansha)	阿部理名古屋大学, 環境学研究科, 助教 (00293720) 森本真紀岐阜大学, 教育学部, 准教授 (30377999) 中川麻悠子東京工業大学, 地球生命研究所, 特任助教 (20647664)
Project Period (FY)	2019-06-28 – 2022-03-31
Keywords	トゥファ / 安定同位体比 / 火山
Outline of Final Research Achievements	We investigated a new approach to determine age of deposition and paleoclimate changes in annually laminated tufa. Previous studies indicated that the conventional 14C and 234U-230Th methods is difficult for age determination of tufa. To solve this problem, we carried out the high-resolution analyses of stable isotope compositions in annually laminated modern-tufa and paleo-tufa of Nigori River of Asama volcano in central Japan. Modern tufa δ18O from the riverbed reflected the variation in temperature of river water. Based on the results, we investigated pattern matching between the 25-years paleo-tufa δ18O record of summertime-averaged values and the last 2000 years record of tee-ring width. Results indicated statistically significant six ages, which implies that this approach has a difficulty in uniquely determining the depositional age. However, our approach suggests that the tufa occurrence and geochemical results can constrain the estimated ages.
Free Research Field	環境変動解析学
Academic Significance and Societal Importance of the Research Achievements	近年、陸域の古環境を高時間分解能（季節単位）で記録する研究試料として、トゥファが注目されてきた。しかし通常使用される14C法や234U-230Th法を適用することは困難であった。本研究はこの課題を克服するため、トゥファ年輪記録と樹木年輪記録のパターンマッチングをトゥファの産状や安定同位体組成と合わせて解析することで、新しい年代推定法への可能性を示すことができた。これにより、汎世界的に石灰岩地帯に分布するトゥファや、他地域の火山性トゥファ及び段丘崖の年代推定への適用が期待でき、時間的空間的高解像度の陸域古環境の復元や、古文書を利用できない火山活動評価への展開に繋がることが期待できる。