A New Triassic Timescale

The current Triassic chronostratigraphic scale is a hierarchy of three series divided into seven stages, divided further into 15 substages. Ammonoid and conodont biostratigraphies provide the primary basis for chronostratigraphic definition based on global stratotype sections and points (GSSP). I propose that Triassic chronostratigraphic definition should rely entirely on ammonoid biochronological events and thereby reject conodont biostratigraphy and the GSSP methodology. Here I propose a new Triassic chronostratigraphy that divides the Triassic into four series (Scythian, Dinarian, Carnian and Norian), recognizes a four-stage Scythian (Griesbachian, Dienerian, Smithian and Spathian), elevates the Carnian and Norian substages (Julian, Tuvalian, Lacian, Alaunian and Sevatian) to stage rank, and includes the Rhaetian as a stage in the Norian Series. A sparse but growing database of precise radioisotopic ages supports the following calibrations: base of Triassic ~ 252 Ma, base Smithian ~ 251 Ma, base Anisian ~ 247 Ma, base Ladinian ~ 242 Ma, base Carnian ~ 237 Ma, base Norian ~ 221 Ma, base Rhaetian ~ 205 Ma, base Jurassic ~ 201 Ma. Triassic magnetostratigraphy is a series of multichrons at best, and needs vast improvement to make a substantial contribution to the Triassic timescale. ....a GSSP is intended to be permanent, and thus immune to further changes in the status of its perceived naturalness. —Walsh, Gradstein and Ogg (2004, p. 208) The game of science is, in principle, without end. He who decides one day that scientific statements do not call for any further test, and that they can be regarded as finally verified, retires from the game. —Karl Popper (1959, p. 53)