Aalenian
174.7 ± 0.8 – 170.9 ± 0.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
The Aalenian GSSP in Spain
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 2023.[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	FAD of Ammonites Leioceras opalinum and Leioceras lineatum
Lower boundary GSSP	Fuentelsaz, Spain 41°10′15″N 1°50′00″W / 41.1708°N 1.8333°W / 41.1708; -1.8333
Lower GSSP ratified	2000[2]
Upper boundary definition	FAD of the Ammonites Hyperlioceras mundum, Hyperlioceras furcatum, Braunsina aspera, and Braunsina elegantula
Upper boundary GSSP	Cabo Mondego, Portugal 40°11′57″N 8°54′15″W / 40.1992°N 8.9042°W / 40.1992; -8.9042
Upper GSSP ratified	1996[3]

The Aalenian ( /ɑːˈliːniən/) 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.^[4]

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.^[5] 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

• 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. (in French)
• Sepkoski, J.; 2002: A compendium of fossil marine animal genera (entry on cephalopoda), Bulletins of American Paleontology 364, p 560.

• 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