The Aalenian () is a subdivision of the
Middle Jurassic Epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided by ...
/
Series
Series may refer to:
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* Caroline Series (born 1951), English mathematician, daughter of George Series
* George Series (1920–1995), English physicist
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* Series, the ordered sets used in ...
of 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 geochr ...
that extends from about 174.1
Ma to about 170.3 Ma (million years ago). It was preceded by the
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.
The Toarcian ...
and succeeded by the
Bajocian
In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. 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.
Stra ...
.
Stratigraphic definitions
The Aalenian takes its name from the town of
Aalen, some 70 km east of
Stuttgart in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. The town lies at the northeastern end of the
Swabian Jura. The name Aalenian was introduced in scientific literature by
Swiss geologist
Karl Mayer-Eymar
Karl David Wilhelm Mayer-Eymar (29 July 1826 – 25 February 1907) was a Franco-Swiss paleontologist and geologist known for his work on classifying the stratigraphy of the Tertiary into 12 stages. He was born Karl Mayer but added the anagram Eymar ...
in 1864.
The base of the Aalenian is defined as the place in the stratigraphic column where the
ammonite genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''
Leioceras'' first appears. The global reference profile (
GSSP
A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted ...
) is located 500 meters north of the village of
Fuentelsaz
Fuentelsaz is a municipality located in the province of Guadalajara, Castile-La Mancha, Spain. According to the 2004 census
A census is the procedure of systematically acquiring, recording and calculating information about the members of a g ...
in the
Spanish
Spanish might refer to:
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**Spaniards are a nation and ethnic group indigenous to Spain
**Spanish language, spoken in Spain and many Latin American countries
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* Spanish, Ontario, Can ...
province of Guadalajara
Guadalajara () is a province of Spain, belonging to the autonomous community of Castilla–La Mancha. As of 2013 it had a population of 257,723 people. The population of the province has grown in the last 10 years. It is located in the centre of ...
.
[Cresta ''et al.'' (2001)] The top of the Aalenian (the base of the Bajocian) is at the first appearance of ammonite genus ''
Hyperlioceras
''Hyperlioceras'' is an extinct genus of cephalopod included in the ammonitid family Graphoceratidae that lived during the Bajocian stage of the Middle Jurassic. The type species is ''Hyperlioceras discites'' (Waagen, 18567)
Morphology
The shel ...
''.
In the
Tethys domain, the Aalenian contains four ammonite
biozone
In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa, as opposed to a lithostratigraphic unit which is defined by the lithological properties ...
s:
*zone of ''
Graphoceras concavum''
*zone of ''
Brasilia bradfordensis''
*zone of ''
Ludwigia murchisonae''
*zone of ''Leioceras opalinum''
References
Notes
Literature
*; 2004: ''A Geologic Time Scale 2004'',
Cambridge University Press
Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by King Henry VIII in 1534, it is the oldest university press in the world. It is also the King's Printer.
Cambridge University Pre ...
.
*; 2001: ''The Global Boundary Stratotype Section and Point (GSSP) of the Toarcian-Aalenian Boundary (Lower-Middle Jurassic)'', Episodes 24(3): pp 166–175.
*; 1864: ''Tableau synchronistique des terrains jurassiques. 1 Tabelle'', Zürich.
*; 2002
''A compendium of fossil marine animal genera (entry on cephalopoda)'' Bulletins of American Paleontology 364, p 560.
External links
Lower Jurassic timescale
at the website of the subcommission for stratigraphic information of the ICS
*Stratigraphic chart o
the Upper
an
Lower
Jurassic, at the website of Norges Network of offshore records of geology and stratigraphy
{{Geological history, p, m
*01
Geological ages