| Toarcian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 184.2 ± 0.3 – 174.7 ± 0.8Ma | |||||||||
 Map of Earth at 180 million years ago; the boundaries of present-day landmasses, countries, and states are superimposed as black outlines | |||||||||
| Chronology | |||||||||
| |||||||||
| Etymology | |||||||||
| Name formality | Formal | ||||||||
| Usage information | |||||||||
| Celestial body | Earth | ||||||||
| Regional usage | Global (ICS) | ||||||||
| Time scale(s) used | ICS Time Scale | ||||||||
| Definition | |||||||||
| Chronological unit | Age | ||||||||
| Stratigraphic unit | Stage | ||||||||
| Time span formality | Formal | ||||||||
| Lower boundary definition | Peniche, Portugal | ||||||||
| Lower boundary GSSP | FAD of theAmmoniteD. (E.) simplex 39°22′15″N9°23′07″W / 39.3708°N 9.3853°W /39.3708; -9.3853 | ||||||||
| Lower GSSP ratified | 2014[2] | ||||||||
| Upper boundary definition | FAD of the AmmonitesLeioceras opalinum andLeioceras lineatum | ||||||||
| Upper boundary GSSP | Fuentelsaz, Spain 41°10′15″N1°50′00″W / 41.1708°N 1.8333°W /41.1708; -1.8333 | ||||||||
| Upper GSSP ratified | 2000[3] | ||||||||
TheToarcian is, in theICS'geologic timescale, anage andstage in theEarly or Lower Jurassic. It spans the time between 184.2Ma (million years ago) and 174.7 ±0.8 Ma.[4] It follows thePliensbachian and is followed by theAalenian.[5]
The Toarcian Age began with theToarcian Oceanic Anoxic Event, a majoranoxic event associated with marine extinctions and increased global temperatures that sets its fossil faunas apart from the previousPliensbachian age. It is believed to have ended with a global cooling event known as the Comptum Cooling Event, although whether it represented a worldwide event is controversial.[6]
The Toarcian takes its name from the city ofThouars, just south ofSaumur in theLoire Valley ofFrance. The stage was introduced by French palaeontologistAlcide d'Orbigny in 1842, after examiningrock strata of this age in aquarry near Thouars.
In Europe this period is represented by the upper part of theLias.
The base of the Toarcian is defined as the place in the stratigraphic record where theammonitegenusEodactylites first appears. A global reference profile (aGSSP) for the base islocated atPeniche, Portugal. The top of the stage is at the first appearance of ammonite genusLeioceras.
In theTethys domain, the Toarcian contains the following ammonitebiozones:
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