Coniacian

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Coniacian
89.8 ± 0.3 – 86.3 ± 0.5 Ma
Chronology

The Coniacian is an

Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by the Turonian and followed by the Santonian.[3]

Stratigraphic definitions

The Coniacian is named after the city of Cognac in the French region of Saintonge. It was first defined by French geologist Henri Coquand in 1857.

The base of the Coniacian Stage is at the first appearance of the

GSSP
) is located in Salzgitter-Salder, Lower Saxony, Germany.

The top of the Coniacian (the base of the Santonian Stage) is defined by the appearance of the inoceramid

.

The Coniacian overlaps the regional Emscherian Stage of Germany, which is roughly coeval with the Coniacian and Santonian Stages. In magnetostratigraphy, the Coniacian is part of magnetic chronozone C34, the so-called Cretaceous Magnetic Quiet Zone, a relatively long period with normal polarity.[citation needed]

Sequence stratigraphy and geochemistry

After a maximum of the global sea level during the early Turonian, the Coniacian was characterized by a gradual fall of the sea level. This cycle is in

transgressions) on top of the longer first order trend. The following regression (Co1, at 87,0 Ma) separates the Middle from the Upper Coniacian Substage. An even shorter third order cycle caused a new transgression during the Late Coniacian.[citation needed
]

Beginning in the Middle Coniacian, an

black shales in the Atlantic domain. The anoxic event lasted till the Middle Santonian (from 87.3 to 84.6 Ma) and is the longest and last such event during the Cretaceous period.[4]

Subdivision

The Coniacian is often subdivided into Lower, Middle and Upper Substages. It encompasses three

:

In the boreal domain the Coniacian overlaps just one ammonite biozone: that of Forresteria petrocoriensis.[citation needed]

References

Notes

  1. ^ International Commission on Stratigraphy. "ICS - Chart/Time Scale". www.stratigraphy.org.
  2. . Retrieved 24 December 2020.
  3. ^ See Gradstein et al. (2004) for a detailed version of the ICS' geologic timescale
  4. ^ See Meyers et al. (2006)

Literature

  • Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
  • Meyers, P.A.; Bernasconi, S.M. & Forster, A.; 2006: Origins and accumulation of organic matter in expanded Albian to Santonian black shale sequences on the Demerara Rise, South American margin, Organic Geochemistry 37, pp 1816–1830.

External links