Press Releases

2016.07.11

Bolide impact triggered the Late Triassic extinction event in equatorial Panthalassa:Professor Yasuhiro Kato, Department of Frontier Research Center for Energy and Resources/System Innovation, and other researchers.

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 104–105 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.

 

(a) Late Triassic generic diversities of radiolarians23, conodonts41, and Pacific (North American) ammonoids40, as compared with the Os isotope record9,45 in the Panthalassa Ocean. The abrupt decrease in the 187Os/188Os ratio in the middle Norian is synchronous with the Manicouagan impact event at 214–215 Ma. Stepwise or episodic extinctions in the (1) end-middle Norian, (2) end-Norian, and (3) end-Triassic are possibly linked with a large bolide impact7, an oceanic anoxic event (OAE)4, and the Central Atlantic Magmatic Province (CAMP) volcanic event5,6, respectively. The gradual decrease in radiolarian diversity just prior to the end-middle Norian may have occurred within radiolarian biozone 6B. Gray shaded areas in the radiolarian and conodont generic diversities represent the number of genera; the genera first appear in the upper Norian and Rhaetian. The geological time scale is from refs 46 and 47. Triassic radiolarian fossil zones (FZ) and their age correlations are from refs 7, 20 and 48; the biostratigraphic framework for our age model is shown in Supplementary Fig. S2. (b) Late Triassic palaeogeographic map showing approximate locations of the Manicouagan carter and the inferred depositional area of the bedded chert in the Mino Belt, in low-latitude zones of the Panthalassa Ocean11. The map is created using ACD Systems Canvas Draw software (Version 2.0).

 

Scientific Report URL: http://www.nature.com/articles/srep29609