The end-Triassic marks one of the five biggest mass extinctions, and was followed by a well-known second-order extinction event in the Early Jurassic. Previously published geological time scales were inadequate for correlation of extinctions with other global events and to unravel their dynamics. Here we present a revised time scale based on high-precision U-Pb ages integrated with ammonoid biochronology resolved to the zone level. This compilation suggests that the end of the Triassic Period (ca. 200 Ma) coincided with peak volcanism in the Central Atlantic magmatic province and that terrestrial floral and faunal extinctions may have slightly preceded the marine biotic crisis. The 87Sr/86Sr and δ13C stratigraphic records are compatible with volcanically induced global environmental change that could be the proximal cause of extinction. The revised Early Jurassic time scale suggests that peak extinction in the early Toarcian occurred at 183 Ma. Recent isotopic dating of flood basalts from the southern Gondwanan Karoo and Ferrar provinces documents a synchronous culmination in volcanic activity at 183 ± 2 Ma. The onset of volcanism is correlative with the start of a rapid rise in seawater 87Sr/86Sr ratios. A recently recognized negative δ13C anomaly, tentatively ascribed to a massive release of methane hydrate, and the subsequent widespread oceanic anoxia suggest that the environmental perturbations thought to trigger the extinction also seriously disrupted the global carbon cycle. The interval between these two extinctions is 18 m.y., significantly shorter than the hypothetical 26 m.y. periodicity of extinctions.
|Number of pages||10|
|Journal||Special Paper of the Geological Society of America|
|Publication status||Published - Jan 1 2002|
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