In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age.[4]
| Bajocian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 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 | FAD of the Ammonites Hyperlioceras mundum, Hyperlioceras furcatum, Braunsina aspera, and Braunsina elegantula | ||||||||
| Lower boundary GSSP | Cabo Mondego, Portugal 40°11′57″N 8°54′15″W / 40.1992°N 8.9042°W | ||||||||
| Lower GSSP ratified | 1996[2] | ||||||||
| Upper boundary definition | FAD of the Ammonite Gonolkites convergen | ||||||||
| Upper boundary GSSP | Ravin du Bès, Bas-Auran, Alpes de Haute, France 43°57′38″N 6°18′55″E / 43.9606°N 6.3153°E | ||||||||
| Upper GSSP ratified | July 2008[3] | ||||||||
Stratigraphic definitions
editThe Bajocian Stage takes its name from the Latin name (Bajocae) of the town of Bayeux, in the region of Normandy in France. The stage was named and introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1842.
The base of the Bajocian stage is defined as the place in the stratigraphic column where fossils of the ammonite genus Hyperlioceras first appear. A global reference profile (a GSSP) for the base is located at Murtinheira, close to Cabo Mondego in Portugal.[5] The top of the Bajocian (the base of the Bathonian) is at the first appearance of ammonite species Parkinsonia convergens.
Subdivision
editThe Bajocian is often divided into Lower/Early and Upper/Late subages or substages.
In the Tethys domain, the Bajocian contains seven ammonite biozones:
- zone of Parkinsonia parkinsoni
- zone of Garantiana garantiana
- zone of Strenoceras niortense
- zone of Stephanoceras humphriesianum
- zone of Sonninia propinquans
- zone of Witchellia laeviuscula
- zone of Hyperlioceras discites
References
editNotes
edit- ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
- ^ Pavia, G.; Enay, R. (March 1997). "Definition of the Aalenian-Bajocian Stage boundary". Episodes. 20 (1): 16–22. doi:10.18814/epiiugs/1997/v20i1/004. Retrieved 23 December 2020.
- ^ Fernández-López, Sixto Rafael; Pavia, Giulio; Erba, Elisabetta; Guiomar, Myette; Maria Helena Henriques; Lanza, Roberto; Mangold, Charles; Morton, Nicol; Olivero, Davide; Daniele Tiraboschi (2009). "The Global Boundary Stratotype Section and Point (GSSP) for base of the Bathonian Stage (Middle Jurassic), Ravin du Bès Section, SE France" (PDF). Episodes. 32 (4): 222–248. doi:10.18814/epiiugs/2009/v32i4/001.
- ^ See for a detailed geologic timescale Gradstein et al. (2004)
- ^ The GSSP is described by Pavia & Enay (1997)
Literature
edit- Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
- Alcide d´Orbigny; 1842: Paléontologie française. 1. Terrains oolitiques ou jurassiques, 642 pp., Bertrand, Paris.
- Pavia, G. & Enay, R.; 1997: Definition of the Aalenian-Bajocian Stage boundary, Episodes, 20(1): pp 16–22.
- Sepkoski, J.; 2002: A compendium of fossil marine animal genera (entry on cephalopoda), Bulletins of American Paleontology 364, p 560.
- Rodríguez-de la Rosa, Rubén A.; Velasco-de León, María Patricia; Lozano-Carmona, Diego-Enrique; Arellano-Gil, Javier (2018). "Middle Jurassic ankylosaur tracks from Mexico" (PDF). Boletín de la Sociedad Geológica Mexicana. 70 (2): 379–395. doi:10.18268/BSGM2018v70n2a8. S2CID 187400703.
External links
edit
- GeoWhen Database - Bajocian
- Jurassic-Cretaceous and Lower Jurassic timescales, at the website of the subcommission for stratigraphic information of the ICS
- Stratigraphic chart of the Upper Jurassic, at the website of Norges Network of offshore records of geology and stratigraphy