Japan Geoscience Union Meeting 2016

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS13] Evolution of the Pelagic Realm

Mon. May 23, 2016 9:00 AM - 10:30 AM 203 (2F)

Convener:*Atsushi Matsuoka(Department of Geology, Faculty of Science, Niigata University), Toshiyuki Kurihara(Graduate School of Science and Technology, Niigata University), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Tetsuji Onoue(Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University), Katsunori Kimoto(Japan Agency for Marine-Earth Science and Technology), Tatsuo Nozaki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Hayato Ueda(Department of Geology, Niigata University), Kenta Kobayashi(Department of Geology, Faculty of Science, Niigata University), Takashi Hasegawa(Division of Global Environmental Science and Engineering, Graduate School of Natural Science and Technology, Kanazawa University), Chair:Atsushi Matsuoka(Department of Geology, Faculty of Science, Niigata University), Toshiyuki Kurihara

9:45 AM - 10:00 AM

[MIS13-04] Micrometeorites from Triassic and Jurassic bedded cherts of the Mino and Chichibu belts, Southwest Japan.

*Mitsutaka Miura1, Tetsuji Onoue1 (1.Department of Earth and Environmental Sciences, Faculty of Science, Kumamoto University.)

Keywords:micrometeorite, Middle Triassic, Early Jurassic, Chichibu Belt, Mino Belt, beded chert

Micrometeorites, which are submillimeter-sized extraterrestrial particles that survive atmospheric entry, originate from dust-producing objects such as comets and asteroids. Ancient micrometeorites found in sedimentary rocks are of key interest as a historical record of meteoroid populations in the solar system. We report the recovery of well-preserved micrometeorites, older than 240 Ma, in radiolarian chert from the Chichibu Belt on Ajiro Island (Middle Triassic) and Mino Belt on Inuyama area (Late Triassic to Early Jurassic). These study sections consist of rhythmic alternations of chert and shale beds. Samples were mechanically crushed and passed through 1.0 mm mesh sieve until less than 5 g of the fine fraction was collected. We also used a hydrofluoric acid dissolution method for determining micrometeorite content of chert samples. However, no micrometeorites have been recognized using this method. Magnetic components were separated using the method for liquid-suspended particles with a magnetic field strength of ~500 mT. Micrometeorites were handpicked from the magnetic components. The collection of micrometeorites comprised 72 cosmic spherules, which are particles that totally melted during atmospheric entry. Analysis of the accretion rate for cosmic spherules reveals high accretion rates of small spherules in the Middle Triassic (Anisian) and Early Jurassic (Hettangian). However, the possible link between the enhancements in the accretion rate of cosmic spherules and variations in the flux of extraterrestrial matter to the Earth requires further scrutiny.