Aalenian
First Middle Jurassic age, named for Aalen; introduced for ammonite zones between older Toarcian and Bajocian concepts.
Language and route: International scientific terminology from German town name. German town name place-name Aalen → international scientific stage-name Aalenian (English); older place-name origin not inferred.
Literal gloss: of/from Aalen
The name and its history
Karl Mayer-Eymar · 1864
- What does the word literally mean?
- ‘of/from Aalen’, referring to Aalen in Baden-Württemberg, Germany.
- What did the original author mean?
- Karl Mayer-Eymar proposed Aalenian in 1864 to distinguish beds around the Toarcian–Bajocian transition which had been assigned inconsistently to the stages on either side.
- Why was the name needed?
- Oppel’s fossil subdivisions highlighted an interval that did not fit the inherited two-stage division of Lower and Middle Jurassic comfortably.
- What evidence supported the original concept?
- Ammonite zones, notably the Leioceras opalinum assemblage, helped recognise the separate interval.
- How has geology changed the concept?
- The Aalenian now begins at the globally ratified Fuentelsaz section in Spain. The faunal marker’s presence does not make the stage “of Aalen” in the literal geographic sense.
Further historical context
The name invokes Aalen in Baden-Württemberg, Germany. Karl Mayer-Eymar proposed Aalenian in 1864 to distinguish beds around the Toarcian–Bajocian transition which had been assigned inconsistently to the stages on either side.
Oppel’s fossil subdivisions highlighted an interval that did not fit the inherited two-stage division of Lower and Middle Jurassic comfortably. Ammonite zones, notably the Leioceras opalinum assemblage, helped recognise the separate interval.
The Aalenian now begins at the globally ratified Fuentelsaz section in Spain. The faunal marker’s presence does not make the stage “of Aalen” in the literal geographic sense.
Editorial qualification
Historically the Aalenian was sometimes placed in the Lias/Lower Jurassic; its Middle Jurassic position was internationally standardised later.
Related names
Sources
- ICS International Chronostratigraphic Chart, 2026/06 — Official current ranks and names; ages are subject to revision
- Middle Jurassic of Britain, Geological Conservation Review introduction — Middle Jurassic naming sequences and classification
- P. Fauré, Le Jurassique: divisions et étages, histoire de la géologie — French historiographical account; some first-year claims conflict with other accounts
- ICS Subcommission on Jurassic Stratigraphy, stage working groups — Individual stage boundary status and GSSP locations