Callovian
Last Middle Jurassic age named after the Kellaways Clay of Wiltshire; once placed in the Upper Jurassic by many British geologists.
Language and route: International scientific terminology from English locality name, Latinised in scientific French. Kellaways / Kelloway (Wiltshire locality) → Latinised Callovian in scientific use.
Literal gloss: of/from Kellaways
The name and its history
Alcide d’Orbigny · c. 1849–1852 (differing historical attributions)
- What does the word literally mean?
- ‘of/from Kellaways’, referring to Kellaways near Chippenham, Wiltshire, England.
- What did the original author mean?
- D’Orbigny adapted a name based on the Kellaways Clay and regional formations to place a recognised upper Middle Jurassic ammonite succession into his European stage framework.
- Why was the name needed?
- Jurassic stages derived from British rock formations did not have comparable lithologies and unit limits across Europe.
- What evidence supported the original concept?
- British Kellaways beds and their ammonites were compared with European marine successions for a usable fossil chronology.
- How has geology changed the concept?
- The modern Callovian is the highest Middle Jurassic stage; its proposed global basal marker remains under study, and it was formerly treated as Upper Jurassic by many British geologists.
Further historical context
The name invokes Kellaways near Chippenham, Wiltshire, England. D’Orbigny adapted a name based on the Kellaways Clay and regional formations to place a recognised upper Middle Jurassic ammonite succession into his European stage framework.
Jurassic stages derived from British rock formations did not have comparable lithologies and unit limits across Europe. British Kellaways beds and their ammonites were compared with European marine successions for a usable fossil chronology.
The modern Callovian is the highest Middle Jurassic stage; its proposed global basal marker remains under study, and it was formerly treated as Upper Jurassic by many British geologists.
Editorial qualification
The route between Kellaways/Kelloway and Latinised Callovian is conventional; no independent etymology of the English placename is claimed.
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
- Oxfordian and Kimmeridgian stratigraphy, Geological Conservation Review — Reassessment of regional stages and Oxfordian/Callovian limits
- ICS Subcommission on Jurassic Stratigraphy, stage working groups — Individual stage boundary status and GSSP locations