The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), approximately. The Aptian succeeds the Barremian and precedes the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

, all part of the Lower/Early Cretaceous. The Aptian partly overlaps the upper part of the Western European Urgonian Stage. The Selli Event, also known as OAE1a, was one of two oceanic anoxic events in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Period, which occurred around 120 Ma and lasted approximately 1 to 1.3 million years, being marked by enhanced silicate weathering, as well as ocean acidification. The Aptian extinction was a minor

extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occ ...

hypothesized to have occurred around 116 to 117 Ma.

Stratigraphic definitions

The Aptian was named after the small city of Apt in the Provence region of

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 ...

, which is also known for its crystallized fruits. The original type locality is in the vicinity of Apt. The Aptian was 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 1840. The base of the Aptian Stage is laid at

magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

M0r. A global reference profile for the base (a GSSP) had in 2009 not yet been appointed. The top of the Aptian (the base of the Albian) is at the first appearance of

coccolithophore Coccolithophores, or coccolithophorids, are single-celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the kingdom ...

species ''Praediscosphaera columnata'' in the stratigraphic record.

Subdivision

In the Tethys domain, the Aptian contains eight ammonite biozones: * zone of ''Hypacanthoplites jacobi'' * zone of ''Nolaniceras nolani'' * zone of ''Parahoplites melchioris'' * zone of ''Epicheloniceras subnodosocostatum'' * zone of ''Duffrenoyia furcata'' * zone of ''Deshayesites deshayesi'' * zone of ''Deshayesites weissi'' * zone of ''Deshayesites oglanlensis'' Sometimes the Aptian is subdivided in three substages or subages: Bedoulian (early or lower), Gargasian (middle) and Clansayesian (late or upper). In modern formal chronostratigraphy the Aptian is divided into Lower and Upper sub-stages. The Lower Aptian is equivalent to the Bedoulian, and it includes the ''oglanensis'' to ''furcata'' Tethyan ammonite zones. The Upper Aptian is equivalent to the Gargasian and Clansayesian, it includes the ''subnodosocostatum'' to ''jacobi'' Tethyan ammonite zones (Gradstein et al. 2004).

Lithostratigraphic units

Examples of rock units formed during the Aptian are: Antlers Formation, Cedar Mountain Formation, Cloverly Formation, Elrhaz Formation, Jiufotang Formation, Little Atherfield, Mazong Shan, Potomac Formation, Santana Formation, Twin Mountains Formation, Xinminbao Group and Yixian Formation.

Climate

A cold episode occurred at the start of the Aptian, as evidenced by the migration of the dinoflagellates ''Cepadinium variabilis'' and ''Pseudoceratium nohrhansenii'' into lower latitudes. A decline in global ''p''CO₂ occurred from about 1,000 ppm to 800 ppm from the start of the Aptian to the C10 positive carbon isotope excursion. During the late Aptian, ''p''CO₂ was between 515 ± 79 and 1029.8 ± 158 ppm as evidenced by the stomatal density of ''Pseudofrenelopsis capillata''.

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: Terrains crétacés'', vol. ii.

External links

GeoWhen Database - AptianMid-Cretaceous timescale
at the website of the subcommission for stratigraphic information of the ICS *Stratigraphic charts of the Lower Cretaceous

an

at the website of Norges Network of offshore records of geology and stratigraphy {{Geological history, p, m Aptian, *05 Geological ages Cretaceous geochronology