earth science

Rhaetian

Rhaetian is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Rhaetian rather than just read about it. In short: The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age of the Jurassic).

Key takeaways

Rhaetian belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Rhaetian to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rhaetian from memory before moving on to harder problems.

Reference excerpt

The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age of the Jurassic). The base of the Rhaetian lacks a formal GSSP, though candidate sections include Steinbergkogel in Austria (since 2007) and Pignola-Abriola in Italy (since 2016). The end of the Rhaetian (and the base of the overlying Hettangian Stage) is more well defined. According to the current ICS (International Commission on Stratigraphy) system, the Rhaetian ended 201.4 ± 0.2 Ma (million years ago). In 2010, the base of the Rhaetian (i.e. the Norian–Rhaetian boundary) was voted to be defined based on the first appearance of Misikella posthernsteini, a marine conodont. However, there is still much debate over the age of this boundary, as well as the evolution of M. posthernsteini. The most comprehensive source of precise age data for the Late Triassic comes from astrochronologically constrained terrestrial strata of the Newark basin in the eastern United States. Correlating the Newark basin to marine sections encompassing the Norian–Rhaetian boundary is mainly achieved via magnetostratigraphy, though such correlations are subject to debate and revision. Some authors have suggested that the Rhaetian lasted less than 5 million years using magnetostratigraphy from Turkish strata and a presumed gap or unconformity in Newark strata. However, both of these lines of evidence have been met with skepticism. A commonly cited approximation of 208.5 Ma (used by the ICS from 2012 to 2023) is based on a "long-Rhaetian" hypothesis reconstructed from the Steinbergkogel GSSP candidate. Most recently, aspects of the "short-Rhaetian" hypothesis have been revived by radiometric dating of Peruvian bivalve extinctions and magnetostratigraphy at the Pignola-Abriola GSSP candidate. These studies suggest that the base of the Rhaetian was close to 205.5 Ma, and in 2024 the ICS updated the start of the Rhaetian to approximately 205.7 Ma. During the Rhaetian, Pangaea began to break up, though the Atlantic Ocean was not yet formed.

Stratigraphic definitions The Rhaetian is named after the Rhaetian Alps, a mountain chain stretching over parts of eastern Switzerland, northern Italy and western Austria. The stage was introduced in scientific literature by Austrian geologist Eduard Suess and German paleontologist Albert Oppel in 1856.

Index fossils and biotic events In 2010, the Triassic subcommission of the ICS voted that the base of the Rhaetian should be defined by the first appearance of the conodont Misikella posthernsteini. M. posthernsteini's direct ancestor Misikella hernsteini first appears shortly before the boundary. Around the same time is the first occurrence of the more extravagant conodont species Epigondolella mosheri (also called Mockina mosheri), which may be used as a proxy in areas where M. posthernsteini is uncommon or occurs later in time than it does elsewhere. In the Tethyan domain (i.e. the area of the Tethys Ocean), the Sagenites reticulatus and Paracochloceras suessi ammonite biozones begin at the base of the Rhaetian. In the boreal domain (i.e. the area of the Northern ocean), the base of the Cochloceras (Paracochloceras) amoenum biozone is used instead. Extinctions at the beginning of the Rhaetian include the ammonite Metasibirites and almost all species of the large bivalve Monotis, which was abundant throughout the world in the Norian but only persisted into the Rhaetian in the form of a few miniaturized species endemic to the Tethys ocean. The Norian–Rhaetian boundary also experienced an overturn in radiolarian species, with the beginning of the Proparvicingula moniliformis biozone. Maron et al. (2015) provided a chemostratigraphic option for defining the base of the Rhaetian at the Pignola-Abriola section. This sequence records a pronounced negative spike in δ13C just before the first appearance of Misikella posthernsteini (sensu stricto) and the Proparvicingula moniliformis radiolarian zone. Rigo et al. (2020) found this same pattern in the nearby Mt Volturino and Madonna del Sirino sections, as well as the Kastelli section of Greece. They also found it in East Panthalassan sediments (Kennecott Point of British Columbia and New York Canyon of Nevada) and West Panthalassan sediments (Wombat and northern Carnarvon Basins of Australia and the Kiritehere section of New Zealand). It was construed to be related to the same event responsible for the Norian–Rhaetian extinction, which heavily impacted ammonoids, bivalves, conodonts and radiolarians. The Norian–Rhaetian extinction may have been caused by the eruption of the Angayucham large igneous province in Alaska, or the asteroid responsible for the Rochechouart impact structure in France. However, the dating of these geological events and their effects on life are uncertain at best.

GSSP candidates The Rhaetian does not yet have an official GSSP, but two candidates have been formally proposed. Krystyn et al. (2007) proposed the Austrian Steinbergkogel section, a Norian–Rhaetian limestone sequence near Hallstatt. It records many potential Norian–Rhaetian biostratigraphic events, such as the appearance of the conodonts Misikella hernsteini and M. posthernsteini (sensu lato) and the ammonoid Paracochloceras suessi. It also record the extinction of large Monotis bivalves and the disappearance of ammonoids including Metasibirites and some Sagenites forms with lateral nodes. A second formal GSSP candidate was not provided until Rigo et al. (2015) proposed the Pignola-Abriola section of southern Italy. This is a sequence of the Norian–Rhaetian Calcari con Selce ("Cherty limestone") Formation named after two nearby towns. It preserves a diverse array of conodonts (including the Misikella hernsteini–posthernsteini morphocline) as well as pronounced radiolarian zones.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Rhaetian

Start with the simplest possible case. Write down what Rhaetian claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Rhaetian before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Rhaetian ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Rhaetian

In research: Rhaetian appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Rhaetian in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Rhaetian is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geological ages, Late Triassic, Rhaetian, so understanding it makes those chapters shorter.
In everyday life: Look for Rhaetian outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Rhaetian in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rhaetian means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Rhaetian out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rhaetian in simple terms?

Why does Rhaetian matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Rhaetian?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Rhaetian.