Precise U Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery

Details Precise U Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery Precise U Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008e%26psl.267..266s&link_type=abstract

Earth and Planetary Science Letters, Volume 267, Issue 1-2, p. 266-275.

Mathematics

Logic

16

Scientific paper

New precise zircon U Pb ages are proposed for the Triassic Jurassic (Rhetian Hettangian) and the Hettangian Sinemurian boundaries. The ages were obtained by ID-TIMS dating of single chemical-abraded zircons from volcanic ash layers within the Pucara Group, Aramachay Formation in the Utcubamba valley, northern Peru. Ash layers situated between last and first occurrences of boundary-defining ammonites yielded 206Pb/238U ages of 201.58 ± 0.17/0.28 Ma (95% c.l., uncertainties without/with decay constant errors, respectively) for the Triassic Jurassic and of 199.53 ± 0.19 / 0.29 Ma for the Hettangian Sinemurian boundaries. The former is established on a tuff located 1 m above the last local occurrence of the topmost Triassic genus Choristoceras, and 5 m below the Hettangian genus Psiloceras. The latter sample was obtained from a tuff collected within the Badouxia canadensis beds. Our new ages document total duration of the Hettagian of no more than c. 2 m.y., which has fundamental implications for the interpretation and significance of the ammonite recovery after the topmost Triassic extinction. The U Pb age is about 0.8 ± 0.5% older than 40Ar 39Ar dates determined on flood basalts of the Central Atlantic Magmatic Province (CAMP). Given the widely accepted hypothesis that inaccuracies in the 40K decay constants or physical constants create a similar bias between the two dating methods, our new U Pb zircon age determination for the T/J boundary corroborates the hypothesis that the CAMP was emplaced at the same time and may be responsible for a major climatic turnover and mass extinction. The zircon 206Pb/238U age for the T/J boundary is marginally older than the North Mountain Basalt (Newark Supergroup, Nova Scotia, Canada), which has been dated at 201.27 ± 0.06 Ma [Schoene et al., 2006. Geochim. Cosmochim. Acta 70, 426 445]. It will be important to look for older eruptions of the CAMP and date them precisely by U Pb techniques while addressing all sources of systematic uncertainty to further test the hypothesis of volcanic induced climate change leading to extinction. Such high-precision, high-accuracy data will be instrumental for constraining the contemporaneity of geological events at a 100 kyr level.

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