The Kimmeridgian Stage takes its name from the village of
Kimmeridge on the
Dorset coast,
England. The name was introduced into the literature by French geologist
Alcide d'Orbigny in 1842, although it seems to have been first suggested by
Thomas Webster in 1812. The
Kimmeridge Clay Formation takes its name from the same
type location (although this formation extends from the Kimmeridgian stage of the Upper Jurassic into the Lower Cretaceous). It is the source for about 95% of the
petroleum in the
North Sea. Historically, the term Kimmeridgian has been used in two different ways. The base of the interval is the same but the top was defined by British
stratigraphers as the base of the
Portlandian (
sensu anglico) whereas in France the top was defined as the base of the Tithonian (
sensu gallico). The differences have not yet been fully resolved; Tithonian is the uppermost stage of the Jurassic in the timescale of the
ICS. The base of the Kimmeridgian is at the first appearance of
ammonite species
Pictonia baylei in the
stratigraphic column. The
Global Boundary Stratotype Section and Point (GSSP) for the base of the Kimmeridgian is the Flodigarry section at
Staffin Bay on the
Isle of Skye,
Scotland, which was ratified in 2021. The boundary is defined by the first appearance of ammonites marking the boreal Bauhini Zone and the subboreal Baylei Zone. The top of the Kimmeridgian (the base of the Tithonian) is at the first appearance of ammonite species
Hybonoticeras hybonotum. It also coincides with the top of
magnetic anomaly M22An.
Subdivision The Kimmeridgian is sometimes subdivided into Upper and Lower substages. In the
Tethys domain, the Kimmeridgian contains seven
ammonite biozones: • zone of
Hybonoticeras beckeri • zone of
Aulacostephanus eudoxus • zone of
Aspidoceras acanthicum • zone of
Crussoliceras divisum • zone of
Ataxioceras hypselocyclum • zone of
Sutneria platynota • zone of
Idoceras planula == References ==