Toarcian

Toarcian
182.7 ± 0.7 – 174.1 ± 1.0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Chronology
−200 — – −195 — – −190 — – −185 — – −180 — – −175 — – −170 — – −165 — – −160 — – −155 — – −150 — – −145 — – Mesozoic T Jurassic K LT Early Middle Late EK Rhaetian Hettangian Sinemurian Pliensbachian Toarcian Aalenian Bajocian Bathonian Callovian Oxfordian Kimmeridgian Tithonian Berriasian       ← Triassic–Jurassic extinction event Subdivision of the Jurassic according to the ICS, as of 2021.[1] Vertical axis scale: millions of years ago.
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 the Ammonite D. (E.) simplex 39°22′15″N 9°23′07″W / 39.3708°N 9.3853°W / 39.3708; -9.3853
GSSP ratified	2014[2]
Upper boundary definition	FAD of the Ammonites and
Upper boundary GSSP	Fuentelsaz, Spain 41°10′15″N 1°50′00″W / 41.1708°N 1.8333°W / 41.1708; -1.8333
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 182.7 Ma (million years ago) and 174.1 Ma.^[4] It follows the Pliensbachian and is followed by the Aalenian.^[5]

The Toarcian Age began with the Toarcian turnover, the extinction event that sets its fossil faunas apart from the previous Pliensbachian age.

Stratigraphic definitions[]

The Toarcian takes its name from the city of Thouars, just south of Saumur in the Loire Valley of France. 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 first appears. A global reference profile (a GSSP) for the base is located at Peniche, Portugal. The top of the stage is at the first appearance of ammonite genus .

In the Tethys domain, the Toarcian contains the following ammonite biozones:

• zone of
• zone of Dumortieria pseudoradiosa
• zone of
• zone of Grammoceras thouarcense
• zone of
• zone of Hildoceras bifrons
• zone of Harpoceras serpentinum
• zone of Dactylioceras tenuicostatum

References[]

Sources[]

• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
• d´Orbigny, A.C.V.M.D.; 1842: Paléontologie française. 1. Terrains oolitiques ou jurassiques, Bertrand, Paris. (in French)
• Elmi, S., Rulleau, L., Gabilly, J. & Mouterde, R. 1997: Toarcien. In: Cariou, E. & Hantzpergue, P. (eds): Biostratigraphie du Jurassique ouest-européen et méditerranéen. Bulletin du Centre des Recherches, Elf Explor. Prod. Mém., 17.

External links[]

• GeoWhen Database - Toarcian
• Lower Jurassic timescale, at the website of the subcommission for stratigraphic information of the ICS
• Stratigraphic chart of the Lower Jurassic, at the website of Norges Network of offshore records of geology and stratigraphy