Permian-Triassic mass extinction event recorded in bedded chert sequence in southwest Japan
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文摘
Rock types in southwest Japan change across the Permian-Triassic boundary. Late Permian bedded chert grades upward into latest Permian siliceous claystone, carbonaceous mudstone of unknown age, early Triassic siliceous claystone with carbonaceous mudstone and chert interbeds, and then into middle Triassic to Jurassic bedded chert. These stratigraphic lithologic variation also accompany the decline and recovery of radiolarians in the Changxingian stage and Smithian stage, respectively. The Permian-Triassic boundary is not precisely defined because of poor stratigraphic control, but it is thought to occur at the boundary between the carbonaceous mudstone and the Changxingian siliceous claystone, or somewhere in the carbonaceous mudstone.