The End Triassic Extinction event (ETE; 201.564 ± 0.022 Ma1) is one of the so called “Big Five” mass extinctions during the Phanerozoic era, i.e. the last 541 million years. From an ecological perspective, marine and terrestrial ecosystems were severely affected2,3, with estimated losses of up to 80% of all species3,4. Repeated and widespread magmatic activity in the Central Atlantic Magmatic Province (CAMP), a Large Igneous Province formed during the initial stages of the breakup of the Pangaea supercontinent, is often considered as the causal mechanism behind the biotic crisis5,6,7,8. CAMP is Earth’s largest known igneous province and covered an area larger than 10 million km2 on the Pangaea supercontinent (Fig. 1)9. The original volume of magmatic rocks is estimated to exceed 3 million km3 with eroded remnants of flood basalt and intrusions preserved today across Africa, Europe, North and South America9. The magmatic units of CAMP are mainly composed of low-Ti basaltic lavas or intrusions (sills and dykes) with distinct geochemical compositions that can be correlated across all four continents1,9. U-Pb chronology suggests that a large portion of the magmas were emplaced within a few hundreds of thousands of years that overlapped with the ETE1,5,10,11,12. Emissions of greenhouse gases from CAMP likely were sourced both from volcanic degassing during eruptions and thermogenic degassing from shallow intrusion of magmas into carbon-rich sedimentary basins6,13. Major disturbances of the carbon cycle during ETE and the succeeding Triassic–Jurassic boundary interval (201.36 ± 0.17 Ma11) are demonstrated by multiple negative carbon isotope excursions in δ13C org (CIE) both in marine and continental sediments14,15,16,17,18,19,20. While it was previously thought that the lowermost preserved CAMP lavas postdated the onset of CIE’s, recent U-Pb chronology has shown that some of the intrusions are slightly older than the lavas and thus appear to coincide with or even pre-date the first CIE5,6. The sedimentary and fossil records preserve evidence for increased atmospheric CO 2 interpreted as evidence for global warming21,22,23,24 and sites showing photic zone euxinia25,26 during ETE and thus contemporaneously with CAMP greenhouse gas emissions. Finally, increased concentrations of genotoxic mercury (Hg) in ETE sediments have been explained as being sourced from the CAMP volcanics7,8,27. Moreover, the malformation and mutagenesis of land plants (fern spores) have recently been linked to loading of volcanogenic Hg to the atmosphere8.

Figure 1 Late Triassic paleogeographic map showing the distribution of land (Pangaea supercontinent) and sea c. 200 million years ago. Also shown are: (i) the original extent of c. 201 million year old lava flows and intrusions of the Central Atlantic Magmatic Province (CAMP); (ii) the locations of a marine (Kurusu, Japan) and a continental (Fundy and Newark basins, USA) sedimentary succession of the end-Triassic mass extinction (ETE) with reported iridium (Ir) or full platinum-group element (PGE) concentrations (white stars); (iii) the location of the CAMP volcanics studied for PGEs in Morocco (grey star). The paleogeographic map is modified from ref. 2 with location of CAMP from ref. 9 and the locations of ETE sections with Ir and/or PGE anomalies from refs. 16,28,31,45,49,50. Full size image

Other explanations for the causes of mass extinction associated with the ETE include bolide impact28,29,30, or a combination of bolide impact and volcanism31 that may have caused positive feed-back effects through destabilization of methane-hydrate reservoirs in the oceans and ocean acidification16. Two impact craters (Rochechouart, France30 and Manicouagan, Canada32) have previously been correlated to the end-Triassic but both have been shown to be older than ETE33,34. Soft-sediment deformation structures (seismites) in end-Triassic strata in the UK were originally suggested to have been impact-related29, but have also been mapped elsewhere across NW Europe and attributed to repeated seismicity connected to tectonic activity associated to CAMP emplacement35,36. Although there was an early report of shock-deformed quartz in end-Triassic sediments of Italy32, this has not been confirmed in subsequent studies37,38. Similarly, none of these authors32,37,38, or others, have reported spherules that are expected by a bolide impact into quartz-free oceanic crust. Thus, there remains little field or petrographic support for the impact hypothesis. The geochemical proxies, in particular Ir and the other platinum-group element (PGE) data, therefore remain the only data for which the jury is still out as to whether their origin is terrestrial or not. The impact hypothesis is, for example, convincingly demonstrated for the Cretaceous-Paleogene boundary, the youngest of the five biggest mass extinctions during the Phanerozoic era. The evidence includes not only impact spherules, shocked quartz and chronology39,40,41,42 but also chondritic Ir and other PGE values reported for the well-known impact layer39,43. Here we therefore examine new and published Ir and other PGE data associated with the end-Triassic mass extinction and CAMP volcanism, and evaluate the merits of the volcanic and impact hypotheses as the causal mechanisms of mass extinction.