Stratigraphic Subdivision and GSSPs of the Triassic: Progress, Problems, and New Proposals

The distribution of marine Triassic strata is extremely uneven worldwide. Lower Triassic successions are widely distributed across all continents, whereas marine Upper Triassic strata are largely limited to Europe and only sporadically exposed elsewhere. Consequently, the Upper Triassic has received far less study than the Lower and Middle Triassic. Within the Triassic System, Global Stratotype Sections and Points (GSSPs) have been established for the bases of the Induan, Ladinian, and Carnian stages. However, GSSPs for the bases of the Olenekian, Anisian, Norian, and Rhaetian remain unresolved. In recent years, following a formal working group vote, the Pizzo Mondello section in northern Italy was selected as the GSSP for the base of the Norian. A formal proposal for this GSSP is currently under review for final ratification by the Subcommission on Triassic Stratigraphy. Selection of the GSSP for the base of the Anisian has also progressed significantly and is approaching a working group vote. Two candidate sections: the Desli Caira section in Romania and the Wantou section in China may be finally ratified for this GSSP in 2026. The GSSP for the base of the Olenekian remains debated regarding both the primary marker and candidate sections, despite more than 20 years of discussion. For the base of the Rhaetian, two candidates: the Pignola Abriola section in Italy and the Steinbergkogel section in Austria both use the first occurrence (FO) of the conodont Misikella posthernsteini as a boundary proxy. However, additional stratigraphic work is needed to establish this GSSP. The current stratigraphic subdivision of series and stages is highly uneven. The Late Triassic Epoch (~35.6 Myr) is seven times longer than the Early Triassic Epoch (~5 Myr). In particular, the Norian Stage (21.6 Myr) is substantially longer than the entire Early Triassic Epoch (Induan and Olenekian combined). Triassic biotas exhibit three evolutionary episodes, calibrated to the Induan–Olenekian, Anisian–Julian, and Tuvalian–Rhaetian intervals, suggesting three natural epochs/series. Here, we propose upgrading the Julian and Tuvalian substages to full stage status, and placing the Middle–Upper Triassic series boundary at the Julian–Tuvalian boundary, coinciding with the Carnian Pluvial Event (CPE). Furthermore, because the Late Triassic Epoch is excessively long (233.6–201.4 Ma), we suggest upgrading the Lacian, Alaunian, and Sevatian substages of the Norian Stage to stage level. In contrast, new geochronological data indicate that the Induan (1.24 Myr) is much shorter than the Olenekian (3.65 Myr), and even the Spathian substage (2.257 Myr) is longer than the entire Induan Stage. The Smithian–Spathian boundary also records a major climatic change associated with a significant biotic extinction event. Therefore, we further propose upgrading both the Smithian and Spathian substages to full stage status, resulting in a Lower Triassic comprising three stages: Induan, Smithian, and Spathian. In summary, we propose a new stratigraphic subdivision scheme along with four additional GSSPs to improve stratigraphic resolution and better align with the major evolutionary tempos of biotas and environments during the Triassic.