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 geochron ...
, the Bajocian is an
age and
stage in the
Middle Jurassic
The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...
. It lasted from approximately 170.9 ±0.8
Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the
Aalenian Age and precedes the
Bathonian
In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...
Age.
Stratigraphic definitions
The Bajocian Stage takes its name from the
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
name (Bajocae) of the town of
Bayeux, in the region of
Normandy
Normandy (; or ) is a geographical and cultural region in northwestern Europe, roughly coextensive with the historical Duchy of Normandy.
Normandy comprises Normandy (administrative region), mainland Normandy (a part of France) and insular N ...
in
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
. The stage was named and introduced in scientific literature by French palaeontologist
Alcide d'Orbigny
Alcide Charles Victor Marie Dessalines d'Orbigny (6 September 1802 – 30 June 1857) was a French naturalist who made major contributions in many areas, including zoology (including malacology), palaeontology, geology, archaeology and anthropol ...
in 1842.
The base of the Bajocian stage is defined as the place in the stratigraphic column where
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s of the
ammonite
Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''
Hyperlioceras'' first appear. A global reference profile (a
GSSP
A Global Boundary Stratotype Section and Point (GSSP), sometimes referred to as a golden spike, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. ...
) for the base is located at
Murtinheira, close to
Cabo Mondego in
Portugal
Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...
.
[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''
*zone of ''
Sonninia propinquans''
*zone of ''
Witchellia laeviuscula''
*zone of ''
Hyperlioceras discites''
References
Notes
Literature
*; 2004: ''A Geologic Time Scale 2004'',
Cambridge University Press
Cambridge University Press was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessme ...
.
*; 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-Cretaceousan
Lower Jurassictimescales, 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