| Kimmeridgian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 154.8 ± 0.8 – 149.2 ± 0.7Ma | |||||||||
| Chronology | |||||||||
| |||||||||
| 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 theAmmonitePictonia baylei | ||||||||
| Lower boundary GSSP | Flodigarry,Skye,Scotland,UK 57°39′40″N6°14′44″W / 57.6610°N 6.2455°W /57.6610; -6.2455 | ||||||||
| Lower GSSP ratified | 2021[2] | ||||||||
| Upper boundary definition | Not formally defined | ||||||||
| Upper boundary definition candidates |
| ||||||||
| Upper boundary GSSP candidate section(s) | |||||||||
In thegeologic timescale, theKimmeridgian is anage in theLate JurassicEpoch and astage in the Upper JurassicSeries. It spans the time between 154.8 ±0.8Ma and 149.2 ±0.7 Ma (million years ago). The Kimmeridgian follows theOxfordian and precedes theTithonian.[2]
The Kimmeridgian Stage takes its name from the village ofKimmeridge on theDorset coast,England. The name was introduced into the literature by French geologistAlcide d'Orbigny in 1842,[3] although it seems to have been first suggested byThomas Webster in 1812.[4] TheKimmeridge Clay Formation takes its name from the sametype 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 thepetroleum in theNorth Sea.[citation needed]
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 Britishstratigraphers as the base of thePortlandian (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; As of 2004[update] Tithonian is the uppermost stage of the Jurassic in the timescale of theICS.[5]
The base of the Kimmeridgian is at the first appearance ofammonite speciesPictonia baylei in thestratigraphic column.[6] TheGlobal Boundary Stratotype Section and Point (GSSP) for the base of the Kimmeridgian is the Flodigarry section atStaffin Bay on theIsle of Skye,Scotland,[7] 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.[8] The top of the Kimmeridgian (the base of the Tithonian) is at the first appearance of ammonite speciesHybonoticeras hybonotum. It also coincides with the top ofmagnetic anomaly M22An.[6]
The Kimmeridgian is sometimes[weasel words] subdivided into Upper and Lower substages.[citation needed] In theTethys domain, the Kimmeridgian contains sevenammonitebiozones:[citation needed]
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