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 Bajocian is an
age and
stage in the
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
. It lasted from approximately 170.3
Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the
Aalenian Age and precedes the
Bathonian Age.
Stratigraphic definitions
The Bajocian Stage takes its name from the
Latin name (Bajocae) of the town of
Bayeux
Bayeux () is a Communes of France, commune in the Calvados (department), Calvados Departments of France, department in Normandy (administrative region), Normandy in northwestern France.
Bayeux is the home of the Bayeux Tapestry, which depicts ...
, in the region of
Normandy in
France. The stage was named and introduced in scientific literature by French palaeontologist
Alcide d'Orbigny in 1842.
The base of the Bajocian stage is defined as the place in the stratigraphic column where
fossils of the
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) ...
genus ''
Hyperlioceras'' first appear. A global reference profile (a
GSSP) for the base is located at
Murtinheira, close to
Cabo Mondego in
Portugal.
[The GSSP is described by Pavia & Enay (1997)] The top of the Bajocian (the base of the Bathonian) is at the first appearance of ammonite species ''Parkinsonia convergens''.
Subdivision
The Bajocian is often divided into Lower/Early and Upper/Late subages or substages.
In the
Tethys domain, the Bajocian contains seven ammonite
biozones:
*zone of ''Parkinsonia parkinsoni''
*zone of ''
Garantiana garantiana''
*zone of ''
Strenoceras niortense''
*zone of ''
Stephanoceras humphriesianum
''Stephanoceras'' (meaning ''crown horn'') is an extinct genus of Stephanoceratoid ammonite which lived during the Bajocian (Middle Jurassic). It is the type genus of the family Stephanoceratidae.
Type species
''Ammonites humphriesianum'' J. ...
''
*zone of ''
Sonninia propinquans''
*zone of ''
Witchellia laeviuscula''
*zone of ''
Hyperlioceras discites''
References
Notes
Literature
*; 2004: ''A Geologic Time Scale 2004'',
Cambridge University Press.
*; 1842: ''Paléontologie française. 1. Terrains oolitiques ou jurassiques'', 642 pp., Bertrand, Paris.
*; 1997: ''Definition of the Aalenian-Bajocian Stage boundary'', Episodes, 20(1): pp 16–22.
*; 2002
''A compendium of fossil marine animal genera (entry on cephalopoda)'' Bulletins of American Paleontology 364, p 560.
*
External links
Jurassic-Cretaceous
an
Lower Jurassic
timescales, 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