Triassic Timescale

German geologists began to study rocks now recognized as Triassic during the late 1700s. In 1823, one of those German geologists, a very astute mining engineer named Friedrich August von Alberti (1795 – 1878), coined the term ‘Trias formation’ for an c. 1 km thick, tripartite succession of strata in southwestern Germany – the Bunten Sandsteins, Muschelkalk and Keuper of the German miners. Alberti also recognized Triassic rocks outside of Germany, throughout much of Europe and as far away as India and the United States. By the end of the nineteenth century, Triassic rocks had been identified across Europe and Asia, and in North America, South America and Africa. Indeed, in 1895, the Austrian geologist Edmund von Mojsisovics (1839–1907) and his collaborators published a complete subdivision of Triassic time based on ammonoid biostratigraphy and, in so doing, introduced many of the Triassic chronostratigraphic terms still used today. The twentieth century saw the elaboration of an ammonoid-based Triassic timescale, especially due to the work of Canadian palaeontologist E. Timothy Tozer (1928-2010). During the last few decades, work also began on developing a global magnetic polarity timescale for the Triassic, a variety of precise numerical ages tied to reliable Triassic biostratigraphy have been determined, and conodont biostratigraphy has become an important tool in Triassic chronostratigraphic definition and correlations.

The current Triassic chronostratigraphic scale is a hierarchy of three series (Lower, Middle, Upper) divided into seven stages (Lower = Induan, Olenekian; Middle = Anisian, Ladinian; and Upper = Carnian, Norian, & Rhaetian) further divided into 15 substages (Induan = Griesbachian & Dienerian; Olenekian = Smithian & Spathian; Anisian = Aegean, Bithynian, Pelsonian, & Illyrian; Ladinian = Fassanian & Longobardian; Carnian = Julian & Tuvalian; Norian = Lacian, Alaunian, and lower Sevatian; Rhaetian = upper Sevatian). Ammonoid and conodont biostratigraphies provide the primary basis for the chronostratigraphy.

The following figure is reproduced from Ogg, J., C. Huang, & L. Hinnov. 2014. Triassic timescale status: A brief overview. Albertiana, 41, 3-30.