Chronology
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Etymology
Name formality
Formal
Usage information
Celestial body
Regional usage
Global (ICS)
Time scale(s) used
ICS Time Scale
Definition
Chronological unit
Stratigraphic unit
Time span formality
Formal
Lower boundary definition
Lower boundary GSSP
FAD of the Ammonite D. (E.) simplex
39°22′15″N 9°23′07″W / 39.3708°N 9.3853°W / 39.3708; -9.3853
Lower GSSP ratified
2014[2]
Upper boundary definition
FAD of the Ammonites Leioceras opalinum and Leioceras lineatum
Upper boundary GSSP
Fuentelsaz, Spain
41°10′15″N 1°50′00″W / 41.1708°N 1.8333°W / 41.1708; -1.8333
Upper GSSP ratified
2000[3]
The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 184.2 Ma (million years ago) and 174.7 ±0.8 Ma.[4] It follows the Pliensbachian and is followed by the Aalenian.[5]
The Toarcian Age began with the Toarcian Oceanic Anoxic Event, a major anoxic event associated with marine extinctions and increased global temperatures that sets its fossil faunas apart from the previous Pliensbachian 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 of Thouars, just south of Saumur in the Loire ValleyofFrance. The stage was introduced by French palaeontologist Alcide d'Orbigny in 1842, after examining rock strata of this age in a quarry near Thouars.
In Europe this period is represented by the upper part of the Lias.
The base of the Toarcian is defined as the place in the stratigraphic record where the ammonite genus Eodactylites first appears. A global reference profile (aGSSP) for the base is locatedatPeniche, Portugal. The top of the stage is at the first appearance of ammonite genus Leioceras.
In the Tethys domain, the Toarcian contains the following ammonite biozones:
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: CS1 maint: numeric names: authors list (link)
ka = kiloannum (thousands years ago); Ma = megaannum (millions years ago); Ga = gigaannum (billions years ago).
See also: Geologic time scale • Geology portal •
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