Coniacian
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Coniacian | |||||||||||||
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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 definitionsThe 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 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 geochemistryAfter 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]
SubdivisionThe 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] ReferencesNotes
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