Aalenian

The Aalenian /ɑːˈliːniən/ is a subdivision of the Middle Jurassic epoch/series of the geologic timescale that extends from about 175.6 Ma to about 171.6 Ma (million years ago). It was preceded by the Toarcian and succeeded by the Bajocian.^[1]

Stratigraphic definitions

The Aalenian takes its name from the town of Aalen, some 70 km east of Stuttgart in Germany. The town lies at the southwestern end of the Frankischer Jura. The name Aalenian was introduced in scientific literature by Swiss geologist Karl Mayer-Eymar in 1864.

The base of the Aalenian is defined as the place in the stratigraphic column where the ammonite genus Leioceras first appears. A global reference profile is located 500 meters north from the village of Fuentelsaz in the Spanish province of Guadalajara.^[2] The top of the Aalenian (the base of the Bajocian) is at the first appearance of ammonite genus Hyperlioceras.

In the Tethys domain, the Aalenian contains four ammonite biozones:

• zone of Graphoceras concavum
• zone of Brasilia bradfordensis
• zone of Ludwigia murchisonae
• zone of Leioceras opalinum

Palaeontology

†Ammonitids

†Ammonitids of the Aalenian
Taxa	Presence	Location	Description	Images
Abbasites Abbasites platystomus	Confirmed.[3]		The only known species in this Alaskan genus. Abbasites is believed to be ancestral to the ammonite family Otoitidae.	Life restorations of two different ammonite genera.
Ancolioceras	Confirmed.[3]
Asthenoceras	Confirmed.[3]
Bradfordia	Confirmed.[3]
Brasilia	Confirmed.[3]
Bredyia	Confirmed.[3]
Canavarella	Confirmed.[3]
Constileioceras	Confirmed.[3]
Cylioceras	Confirmed.[3]
Euaptetoceras	Confirmed.[3]
Eudmetoceras	Confirmed.[3]
Euhoploceras	Confirmed.[3]
Fontannesia	Confirmed.[3]
Graphoceras	Confirmed.[3]
Haplopleuroceras	Confirmed.[3]
Hyperlioceras	Confirmed.[3]
Leioceras	Confirmed.[3]
Ludwigia	Confirmed.[3]		Synonymous with a modern plant genus.
Malladaites	Confirmed.[3]
Padragosiceras	Confirmed.[3]
Parammatoceras	Confirmed.[3]
Planammatoceras	Confirmed.[3]
Praestrigites	Confirmed.[3]
Pseudammatoceras	Confirmed.[3]
Puchenquia	Confirmed.[3]
Reynesella	Confirmed.[3]
Sonninia	Confirmed.[3]
Spinammatoceras	Confirmed.[3]
Staufenia	Confirmed.[3]
Stephanoceras	Confirmed.[3]
Trilobiticeras	Confirmed.[3]
Tugurites	Confirmed.[3]

†Belemnites

Belemnites of the Aalenian
Taxa	Presence	Location	Description	Images
Belemnopsis	Confirmed.[3]			Belemnites.
Holcobelus	Confirmed.[3]
Homaloteuthis	Confirmed.[3]
Megateuthis Megateuthis gigantea	Confirmed.[3]		This Eurasian species was the largest known Belemnite and could grow to lengths of up to 10 feet.
Paramegateuthis	Confirmed.[3]
Rhabdobelus	Confirmed.[3]
Sachsibelus	Confirmed.[3]

†Thalattosuchians

References

Notes

Literature

• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
• Cresta, S.; Goy, A.; Ureta, S.; Arias, C.; Barrón, E.; Bernad, J.; Canales, M.L.; García-Joral, F.; García-Romero, E.; Gialanella, P.R.; Gómez, J.J.; González, J.A.; Herrero, C.; Martínez, G.; Osete, M.L.; Perilli, N. & Villalaín, J.J.; 2001: The Global Boundary Stratotype Section and Point (GSSP) of the Toarcian-Aalenian Boundary (Lower-Middle Jurassic), Episodes 24(3): pp 166–175.
• Mayer-Eymar, K.; 1864: Tableau synchronistique des terrains jurassiques. 1 Tabelle, Zürich. (French)
• Sepkoski, J.; 2002: A compendium of fossil marine animal genera (entry on cephalopoda), Bulletin of American Paleontology 364, p 560.

External links

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