Integration of Paleozoic-Mesozoic radiolarian biostratigraphy and U-Pb ages: establishment as a geologic timescale and its application

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05690
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Stratigraphy/Paleontology
• Research Institution: Niigata University
• Principal Investigator: Kurihara Toshiyuki 新潟大学, 自然科学系, 准教授 (10447617)
• Co-Investigator(Kenkyū-buntansha): 植田 勇人 新潟大学, 自然科学系, 准教授 (70374197) ; 松岡 篤 新潟大学, 自然科学系, 教授 (00183947)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 放散虫 / 生層序基準面 / ウランー鉛年代 / ジルコン / 年代尺度

Outline of Final Research Achievements

We conducted radiolarian biostratigraphic and geochronologic studies for the integration of Paleozoic-Mesozoic radiolarian zones and zircons U-Pb ages, with the aim of establishing a useful timescale that can arrange geological events on a unified time axis. As a result, we obtained reliable sedimentation ages from U-Pb dating of zircons in several important radiolarian-bearing strata such as the Devonian, Permian, and Cretaceous ages, by using analyses of the texture and shape of zircon crystals and statistical methods (peak separation). In addition, the validity of the sedimentation ages was verified by confirming that the age values measured in the same biohorizons of several areas are converged to a constant value. These findings provided from the integration of radiolarian zones and U-Pb ages make it possible to discuss geologic history based on the direct compilation of the formation ages of fossil-bearing strata and tectonic events such as generation of igneous rocks.

Free Research Field

地質学・微古生物学

Academic Significance and Societal Importance of the Research Achievements

本研究では，中・古生代の放散虫化石帯の一部にジルコンのU-Pb年代を入れることができた．中・古生代では未だに年代値が大きく変更される階境界がある中で，本研究で化石帯に信頼性の高い堆積年代値を入れたことは，現行の年代値を独立した視点から検証することに繋がる．また，デボン紀については，日本と東アジアの堆積岩と火成岩形成の年代を統一的な時間軸上に載せて直接比較し，東アジア規模で形成史を再解釈した．これは，複合的な地質現象においても個々の事象を１つの時系列上に適切に配列させえる尺度があれば，物質科学と古生物学は融合して諸現象の因果関係に新しい解釈を与えることができることを示す本研究の成果である．