The age of pelagic Panthalassic deep-sea bedded chert has been assigned based on radiolarian biostratigraphy. However, Triassic radiolarian biostratigraphy is in many cases not precisely correlated to the conodont zones and the standard geological timescale. In this study, we investigated the conodont biostratigraphy of two radiolarian-controlled bedded chert sections of Anisian age: the Ajiro Island section in Oita Prefecture and the Kurusu section in Aichi Prefecture. We recognised six conodont biozones in the studied sections: the upper Olenekian Novispathodus brevissimus-Icriospathodus collinsoni and Triassospathodus homeri Zones, the lower Anisian Chiosella timorensis Zone, the middle Anisian Paragondolella bulgarica Zone, the upper Anisian Paragondolella excelsa Zone and the uppermost Anisian to lowermost Ladinian Paragondolella trammeri Zone. These conodont zones were successfully correlated to the standard Triassic radiolarian zonation proposed by Sugiyama (1997, Bull. Mizunami

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The ca 252 Ma Permian-Triassic boundary (PTB) represents the most severe mass extinction event of the Phanerozoic, with the disappearance of~80% of marine invertebrate species. Large-scale eruption of the Siberian Traps is the commonly favored cause, although the link between volcanism and extinction remains debated. Here, we report evidence for an extraterrestrial 3 He influx in the PTB section of deep-sea bedded cherts from Japan. This unusual signal indicates a significant increase in the influx of interplanetary dust particles, likely related to an asteroid shower in the inner solar system. High-resolution stratigraphy indicates that the peak flux of dust particles occurred during the final 500 kyr of the Permian, concurrent with a pre-extinction decline in radiolarian diversity.

The end-Permian mass extinction (EPME) was the most severe mass extinction event of the Phanerozoic, and was associated with the development of global oceanic anoxia. The intensification of ocean anoxia preceded the EPME, but the degree of intensity and timing of oceanic redox changes in the mid-Panthalassa Ocean remain debated. Here we present the results of geochemical and multivariate statistical analyses of a late Guadalupian to Lopingian (middle–late Permian) bedded chert succession from the Iwaidani section, Japan, which preserves pelagic deep-sea facies from the ocean floor to the lower flank of a mid-Panthalassan seamount. The entire section yields a low manganese-enrichment factor (MnEF <1), suggesting that suboxic conditions has appeared in the depositional environment already in the late Guadalupian. Enrichment factors of other redox-sensitive trace-elements (e.g., vanadium and uranium) and principle component analysis (PCA) of major element data show the development of suboxic to weakly anoxic conditions across the Guadalupian/Lopingian boundary. Subsequently, anoxic conditions, as inferred from enrichments in U, Mo, Ni, Cu, Zn, and Tl, were developed during the middle Lopingian. Extremely high concentrations of U and Mo (enrichment factors of ∼6 and ∼5,500, respectively) indicate that H2S-rich euxinic conditions developed during the latest Lopingian and around the time of the EPME. The cause of the shift toward more reducing conditions in the early–middle Lopingian is unknown, but PCA results suggest that the euxinic conditions occurred in association with intensified continental weathering in response to a temperature rise during the ca. 200 kyr before the EPME.

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Superanoxia across the Permian/Triassic boundary, which is a long period of oceanic anoxia from the late Middle Permian to the early Middle Triassic, has been recognized and debated well in the context of the end Permian mass extinction. However, few studies have focused on the Middle Triassic anoxia because of limited application of geochemical proxies. To reconstruct paleoenvironmental changes during the termination stage of Superanoxia, various geochemical proxies were applied to chemical compositions of the Middle Triassic (Anisian) bedded chert sequence in the Mino belt, Japan, which accumulated in a deep seafloor environment in a low‐ to mid‐latitude zone of the Panthalassa Ocean. Three anoxic events were identified by statistically robust geochemical proxies during the middle Anisian. Degrees of calibrated‐chemical weathering intensity show higher values during these anoxic events, suggesting that the intensified continental weathering was a trigger mechanism for the oceanic anoxic events in the middle Anisian. Furthermore, our data indicate that the termination of Superanoxia in the Panthalassa Ocean was associated with a gradual decrease in continental weathering rates during the middle to late Anisian.