Geochemical investigation on stratigraphy of Cretaceous-Paleogene bounday

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K04054
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: Kuroda Junichiro 東京大学, 大気海洋研究所, 准教授 (10435836)
• Co-Investigator(Kenkyū-buntansha): Tejada Maria・L・G 国立研究開発法人海洋研究開発機構, 海域地震火山部門(火山・地球内部研究センター), 主任研究員 (40598778)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 白金族元素 / オスミウム同位体 / 白亜紀-古第三紀境界 / 天体衝突

Outline of Final Research Achievements

In this study we analyzed platinum group element concentrations and osmium (Os) isotope ratios around the Cretaceous-Paleogene (K-Pg) boundary were measured in sediments recovered from drill hole U1514C in the Mentelle Basin. Thirty-five samples were collected from depths ranging from 390 to 399 m below the seafloor. The data set has a high temporal resolution with an average interval of 70,000 years. A clear decrease in Os isotope ratios and a sharp peak in platinum group element concentrations were observed in the sediment at a depth of 393.52 m below the seafloor. This depth coincides with the K-Pg boundary, as determined by calcareous nannofossil analysis. This clearly indicates that the stratigraphic level of the Late Cretaceous impact event is preserved. The achievement of the fully continuous K-Pg boundary is the major accomplishment of this study.

Free Research Field

地球化学

Academic Significance and Societal Importance of the Research Achievements

本研究では，生物大量絶滅という社会的にも関心の高いテーマについて，南半球高緯度で欠損のない堆積物の完全連続セクションが得られた点が重要な点である．白金族元素やオスミウム同位体組成を用いて，白亜紀末の天体衝突時の古気候記録の連続性が評価できたことは重要な学術的意義である．この研究の結果，白亜紀末の天体衝突直後に石灰質ナノプランクトンの生産停止が，広くオーストラリア周辺海域で起こっていたことが判明した点も重要な発見であった．