Coniacium

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system series step ≈ age ( mya )
higher higher higher younger
chalk Upper Chalk Maastrichtium 66
⬍
72
Campanium 72
⬍
83.6
Santonium 83.6
⬍
86.3
Coniacium 86.3
⬍
89.7
Turonium 89.7
⬍
93.9
Cenomanium 93.9
⬍
100.5
Lower Cretaceous Albium 100.5
⬍
112.9
Aptium 112.9
⬍
126.3
Barremium 126.3
⬍
130.7
Skin rivium 130.7
⬍
133.9
Valanginium 133.9
⬍
139.3
Berriasium 139.3
⬍
145
deeper deeper deeper older

The Coniacium (in German usage often shortened to Coniac) is a chronostratigraphic level of the Upper Cretaceous in the history of the earth . It can be dated geochronologically to the period from approx. 89.7 to approx. 86.3 million years. The coniac follows the turonium and is replaced by the santonium .

Naming and history

The rock units typical for this stage are located in the historic Saintonge landscape near the city of Cognac ( Charente department , France). Henri Coquand introduced the level and name to scientific literature in 1857.

Definition and GSSP

The lower limit of the level is defined by the first appearance of the Inoceramen species Cremnoceramus rotundatus (identical to Cremnoceramus deformis erectus ), the upper limit by the first appearance of the Inoceramen species Cladoceramus undulatoplicatus . A GSSP (global type locality and type profile of the lower level limit) for the Coniacium has not yet been made binding. The Salzgitter-Salder limestone quarry is a promising candidate .

Breakdown

The coniacium is divided into lower, middle and upper coniacium at the lower level.
The coniacium together with the santonium formed the stratigraphic level of the Emscher .

In Tethysbereich for Coniacian be biostratigraphically three ammonite zones excreted:

In the boreal area, the Forresteria petrocoriensis zone appears at the bottom .

Magnetostratigraphy

The entire coniacium belongs magnetostratigraphically to the C34 anomaly, the so-called "Cretaceous magnetic calm zone" with normal polarity.

Sea level cycles

After reaching the absolute maximum sea level in the Unterturon , a gradual renewed decline in the sea ​​level becomes noticeable in the Coniacium . However, this 1st order cycle is overlaid by a shorter-period sea level rise (2nd order cycle), which leads to transgressions globally and culminates in the central coniacium. This is followed by the regression Co1 (87.0 Ma BP), which separates the middle and upper coniacium from one another. A third order cycle also causes a new transgression in the upper coniacium.

Oceanic anoxic event

From the Central Coniacian onwards, an oceanic anoxic event occurs in the Atlantic area with the formation of black slate sediments , the so-called OAE-3 , which lasts into the Central Cantonium (87.3 - 84.6 Ma BP). It is the longest and last such event during the Cretaceous Period.

Individual evidence

  1. ↑ Meyers, PA, Bernasconi, SM, 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, 1816-1830.

literature

  • Felix Gradstein, Jim Ogg, Jim & Alan Smith: A Geologic timescale. Cambridge University Press 2004 ISBN 978-0-521-78673-7
  • Hans Murawski & Wilhelm Meyer: Geological dictionary . 10., rework. u. exp. Ed., 278 p., Enke Verlag, Stuttgart 1998 ISBN 3-432-84100-0 .

Web links