Toarcium

system	series	step	≈ age ( mya )
higher	higher	higher	younger
law	Upper Jurassic	Tithonium	145 ⬍ 152.1
		Kimmeridgium	152.1 ⬍ 157.3
		Oxfordium	157.3 ⬍ 163.5
	Middle Jurassic	Callovium	163.5 ⬍ 166.1
		Bathonium	166.1 ⬍ 168.3
		Bajocium	168.3 ⬍ 170.3
		Aalenium	170.3 ⬍ 174.1
	Lower Jurassic	Toarcium	174.1 ⬍ 182.7
		Pliensbachium	182.7 ⬍ 190.8
		Sinemurium	190.8 ⬍ 199.3
		Hettangium	199.3 ⬍ 201.3
deeper	deeper	deeper	older

The Toarcium (more rarely Toarc or Toarcien) is a chronostratigraphic stage of the Lower Jurassic in the history of the earth . Geochronologically , this period is roughly dated from 182.7 million to 174.1 million years ago. The beginning of the toarcium (before 182.7  Ma ) is given with an uncertainty of ± 0.7 Ma, the end of the toarcium (before 174.1 Ma) with an uncertainty of ± 1.0 Ma. In the time interval of Toarciums follows Aalenian , the Toarcian even following the Pliensbachian .

Naming and history

The Toarcium was named after the French city of Thouars . Thouars is halfway between Angers and Poitiers . In 1842 Alcide Dessalines d'Orbigny determined this level in a quarry near Thouars.

Definition and GSSP

The stratigraphic determination of the toarcium is based on the group of ammonites. The beginning of the toarcium is defined by the occurrence of the ammonite genus Eodactylites . The end is determined by the appearance of the genus Leioceras . The GSSP ("Global Stratotype Section and Point" corresponds roughly to a type profile) of the Pliensbachium / Toarcium border is now near Peniche in Portugal .

Subdivision of the Toarcium

The toarcium is subdivided into the following ammonite biozones in the tethyl area:

• Aalensis zone after Pleydellia aalensis
• Pseudoradiosa zone according to Dumortieria pseudoradiosa
• Dispansum zone after Phlyseogrammoceras dispansum
• Thouarsense zone according to Grammoceras thouarsense
• Variabilis zone according to Haugia variabilis
• Bifrons zone according to Hildoceras bifrons
• Serpentinum zone according to Harpoceras serpentinum
• Tenuicostatum zone after Dactylioceras tenuicostatum

literature

• Felix Gradstein, Jim Ogg, Jim & Alan Smith: A geologic time scale. Cambridge University Press 2005, ISBN 0-521-78673-8
• Hans Murawski & Wilhelm Meyer: Geological dictionary . 10., rework. u. exp. Ed., 278, Enke Verlag, Stuttgart 1998, ISBN 3-432-84100-0 .
• Alcide d'Orbigny: Paléontologie française. 1. Terrains oolitiques or jurassiques. 642 pp., Bertrand, Paris, 1842

Web links

• German Stratigraphic Commission (Ed.): Stratigraphische Tisch von Deutschland 2002 . Potsdam 2002 ISBN 3-00-010197-7 (PDF; 6.57 MB)
• Commission for the paleontological and stratigraphic research of Austria of the Austrian Academy of Sciences (Ed.): The Stratigraphic Table of Austria (sedimentary layer sequences). Vienna 2004 (PDF; 376 KB)
• International Chronostratigraphic Chart v 2016/04 of the International Commission on Stratigraphy . In: Chart . In: stratigraphy.org of the International Commission on Stratigraphy in the International Union of Geological Sciences (IUGS). Junxuan Fan and Xudong Hou (English; JPEG file).

supporting documents

1. ↑ International Chronostratigraphic Chart v 2016/04 of the International Commission on Stratigraphy . In: Chart . In: stratigraphy.org of the International Commission on Stratigraphy in the International Union of Geological Sciences (IUGS). Junxuan Fan and Xudong Hou, accessed and received on September 21, 2016 (English; JPEG file).