Lower Triassic sedimentary rocks deposited in pelagic regions of Panthalassa show anomalously clay-rich and silica-poor lithologies compared with the deep marine chert-dominated successions that characterise older and younger strata. The end-Permian mass extinction, which impacted radiolarians, has been proposed as an explanation for this so-called “chert gap” through its inferred impact on biogenic silica production. To test this hypothesis, we evaluated linear sedimentation rates (LSRs) for an upper Olenekian (upper Lower Triassic) siliceous claystone succession in Tsukumi, Oita Prefecture, Southwest Japan. Correlation of conodont biohorizons allows extrapolation of absolute ages obtained by previous studies in South China onto our studied sections. Results show that LSR is higher in the Lower Triassic claystone than in typical Mesozoic radiolarian bedded chert. This implies that increased burial flux of clastic material, not decreased biogenic silica burial flux, drove deposition of clay-rich sediments in pelagic Panthalassa during the late Olenekian.
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