An asteroid impact in the Late Triassic triggered mid-Norian radiolarian faunal turnover in the Panthalassa Ocean

Anomalously high platinum group element (PGE) concentrations in Upper Triassic (middle-upper Norian) pelagic bedded chert succession in Japan, have been attributed to an extraterrestrial source and impact event that formed the 90-km-diameter Manicouagan crater in Canada. Previous geochemical studies have revealed that the anomalously high PGE abundances resulted from a large chondritic impactor (3.3-7.8 km in diameter). Here we report evidence that the Late Triassic impact triggered the remarkable faunal turnover of siliceous plankton (radiolaria) in the Panthalassa Ocean. Radiolarian species data indicate that this faunal turnover records the largest extinction and origination rates within the 30 Myr interval in the Late Triassic to earliest Jurassic. Our high-resolution biostratigraphic, sedimentological and geochemical data revealed that there are two paleoenvironmental events in the initial phase of the radiolarian faunal turnover interval: (1) the post-impact shutdown of primary productivity within the timespan of 104 years, and (2) significant and sustained reduction in the sinking flux of radiolarian silica for 0.4-0.6 Myr after the impact. A sharp reduction in marine primary and secondary productivity, triggered by a large impact, may have also played an important role in the extinction of Norian marine faunas (ammonoids, monotid bivalves, and conodonts) in the Panthalassa Ocean.