Extinctions within major pelagic groups (e.g., radiolarians and conodonts) occurred in a stepwise fashion during the last 15 Myr of the Triassic. Although a marked decline in the diversity of pelagic faunas began at the end of the middle Norian, the cause of the middle Norian extinction is uncertain. Here we show a possible link between the end-middle Norian radiolarian extinction and a bolide impact. Two palaeoenvironmental events occurred during the initial phase of the radiolarian extinction interval: (1) a post-impact shutdown of primary and biogenic silica production within a time span of 10 4 -10 5 yr, and (2) a sustained reduction in the sinking flux of radiolarian silica for ∼0.3 Myr after the impact. The catastrophic collapse of the pelagic ecosystem at this time was probably the dominant factor responsible for the end-middle Norian conodont extinction.
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