Coniacian

Coniacian
89.8 ± 0.3 – 86.3 ± 0.5 Ma
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Chronology
Etymology
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitAge
Stratigraphic unitStage
Time span formalityFormal
Lower boundary definitionFAD of the Inoceramid Bivalve Cremnoceramus deformis erectus
Lower boundary GSSPSalzgitter-Salder quarry, Germany
52°07′27″N 10°19′46″E / 52.1243°N 10.3295°E / 52.1243; 10.3295
Lower GSSP ratifiedMay 2021
Upper boundary definitionFAD of the Inoceramid Bivalve Cladoceramus undulatoplicatus
Upper boundary GSSPOlazagutia, Spain
42°52′00″N 2°11′48″W / 42.8668°N 2.1968°W / 42.8668; -2.1968
Upper GSSP ratifiedJanuary 2013[2]

The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 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 inoceramid bivalve species Cremnoceramus deformis erectus. The official reference profile for the base (a 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 bivalve Cladoceramus undulatoplicatus.

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 sequence stratigraphy seen as a first order cycle. During the middle Coniacian a shorter, second order cycle, caused a temporary rise of the sea level (and global 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 anoxic event (OAE-3) occurred in the Atlantic Ocean, causing large scale deposition of 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 ammonite biozones in the Tethys domain:

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

References

Notes

  1. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. September 2023. Retrieved December 16, 2024.
  2. ^ Lamolda, M.; Paul, C.; Peryt, D.; Pons, J. (March 2014). "The Global Boundary Stratotype and Section Point (GSSP) for the base of the Santonian Stage, "Cantera de Margas", Olazagutia, northern Spain". Episodes. 37 (1): 2–13. doi:10.18814/epiiugs/2014/v37i1/001. 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.