Constraints for the Causes of Mass Extinction at the Triassic–Jurassic Boundary Based on High Precision Platinum Group Element Analyses

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  • FUJISAKI Wataru
    Department of Earth and Planetary Sciences, Tokyo Institute of Technology
  • SAWAKI Yusuke
    Department of Earth and Planetary Sciences, Tokyo Institute of Technology
  • YOKOYAMA Tetsuya
    Department of Earth and Planetary Sciences, Tokyo Institute of Technology
  • YAMAMOTO Shinji
    Department of Earth Science and Astronomy, The University of Tokyo
  • MARUYAMA Shigenori
    Earth Life Science Institute (ELSI), Tokyo Institute of Technology

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Other Title
  • 高精度白金族元素濃度分析を利用したトリアス紀―ジュラ紀境界大量絶滅原因の推定
  • コウセイド ハッキンゾク ゲンソ ノウド ブンセキ オ リヨウ シタ トリアスキ-ジュラキ キョウカイ タイリョウ ゼツメツ ゲンイン ノ スイテイ
  • Constraints for the Causes of Mass Extinction at the Triassic–Jurassic Boundary Based on High Precision Platinum Group Element Analyses

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Abstract

The cause of mass extinctions during the Phanerozoic period has been a long standing problem in geology. The large magmatic activity (CAMP: Central Atlantic Magmatic Province) associated with the breakup of Pangaea or a bolide impact event would have led the mass extinction at the Triassic–Jurassic (T–J) boundary. However, the cause of the mass extinction is still controversial because of insufficient geological evidences. In this study, we conducted detailed geological survey of the Inuyama area where good exposure of deep-sea sediments across the T–J boundary is observed. We collected rock samples bed-by-bed to analyze the abundances of platinum group elements (PGEs) with a high spatial resolution. Twenty-eight samples were powdered and spiked with 99Ru, 105Pd, 190Os, 191Ir, 194Pt. The sample was digested by a 2 : 1 mixture of HNO3 and HCl in a sealed Carious tube at 240°C for 48 hours. After chemical separation using an anion exchange resin, PGEs (except for Os) were measured by a quadrupole type inductively coupled plasma-mass spectrometry (ICP-MS). The PGEs concentrations were determined by the isotope dilution method. After solvent extraction with CCl4 and HBr, micro-distillation method was employed to purify Os. The Os isotopes were determined by Negative-Thermal Ionization Mass Spectrometry (N-TIMS). The relationship between Pd/Pt and Ir/Pt, as well as the PGE patterns, demonstrate that the high PGEs contents in shales can be explained by the incorporation of basaltic rocks supplied from CAMP. In addition, compared with fossil records, the highest PGE abundances (Os and Pd) are discovered from a shale just above the chert including the first appearance of Jurassic type radiolarian. These lines of evidence indicate that the CAMP volcanism would have contributed to the mass extinction at the T–J boundary.

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 64 (5), 341-348, 2015

    The Japan Society for Analytical Chemistry

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