First age of the Middle Jurassic
The Aalenian () is a subdivision of the Middle Jurassic Epoch/Series of the geologic timescale that extends from about 174.7 ±0.8 Ma to about 170.9 ±0.8 Ma (million years ago). It was preceded by the Toarcian and succeeded by the Bajocian.
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 northeastern end of the Swabian 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. The global reference profile (GSSP) is located 500 meters north of the village of Fuentelsaz in the Spanish province of Guadalajara. 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:
References.
Notes.
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