In the
geologic timescale
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronol ...
, the Kimmeridgian is an
age in the
Late Jurassic Epoch and a
stage in the Upper Jurassic
Series. It spans the time between 154.8 ±0.8
Ma and 149.2 ±0.7 Ma (million years ago). The Kimmeridgian follows the
Oxfordian and precedes the
Tithonian
In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the K ...
.
Stratigraphic definition
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.
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
stratigrapher
Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostrat ...
s as the base of the
Portlandian
The Portland Group (defining the Portlandian) is a Late Jurassic (Tithonian) lithostratigraphic group (a sequence of rock strata) in South East England. The name is derived from the Isle of Portland in Dorset where the strata are exposed ...
(''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
ICS may refer to:
Computing
* Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy
* Industrial control system, computer systems and networks used to control industrial plants and infrastructu ...
.
The base of the Kimmeridgian is at the first appearance of
ammonite
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
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
The Isle of Skye, or simply Skye (; gd, An t-Eilean Sgitheanach or ; sco, Isle o Skye), is the largest and northernmost of the major islands in the Inner Hebrides of Scotland. The island's peninsulas radiate from a mountainous hub dominated ...
,
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
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
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
Notes
Literature
*; 2004: ''A Geologic Time Scale 2004'',
Cambridge University Press.
*; 1832: ''Sur Les Soulèvemens Jurassiques Du Porrentruy: Description Géognostique de la Série Jurassique et Théorie Orographique du Soulèvement'', Mémoires de la Société d'histoire naturelle de Strasbourg 1: pp 1–84, F. G. Levrault, Paris.
External links
GeoWhen Database - KimmeridgianJurassic-Cretaceous timescale
at the website of the subcommission for stratigraphic information of the ICS
Stratigraphic chart of the Upper Jurassic
at the website of Norges Network of offshore records of geology and stratigraphy
{{Geological history, p, m
*02
Geological ages