Improving the Upper Triassic numerical time scale from cross-correlation between Tethyan marine sections and the continental Newark basin sequence

Abstract

Magnetostratigraphic cross-correlations between biochronologically well-dated Tethyan marine sections and the astronomically tuned sedimentary sequence from the continental Newark basin (eastern North America) help to improve the Upper Triassic time scale. We show here that the most recent radiometric results constraining the age of the base and top of the Upper Triassic (∼237 and ∼200 Ma, respectively) strengthen the chronostratigraphic calibration of the Newark sedimentary sequence proposed by Krystyn et al. [Earth Planet. Sci. Lett. 203 (2002) 343–351]; these results allow one to reconcile the Milankovitch-based cyclostratigraphy from the Newark sequence, the magnetostratigraphic data from both marine and continental environments, and Upper Triassic biostratigraphy (including data on Tethyan marine faunas and on terrestrial vertebrates). According to this calibration, the successive Upper Triassic stages would have very different durations: ∼10 Myr for the Carnian (237–227 Ma), ∼25 Myr for the Norian (227–202 Ma) and ∼2 Myr for the Rhaetian (202–200 Ma, but only if the entire Rhaetian is recorded in the Newark sequence). We further show that the biozone durations in the Upper Triassic would have been highly variable and, as a whole, would have lasted much longer than in the Lower and Middle Triassic.