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| Coniacian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 89.8 ± 0.3 – 85.7 ± 0.2Ma | |||||||||
| Chronology | |||||||||
| |||||||||
| Etymology | |||||||||
| Name formality | Formal | ||||||||
| Usage information | |||||||||
| Celestial body | Earth | ||||||||
| Regional usage | Global (ICS) | ||||||||
| Time scale(s) used | ICS Time Scale | ||||||||
| Definition | |||||||||
| Chronological unit | Age | ||||||||
| Stratigraphic unit | Stage | ||||||||
| Time span formality | Formal | ||||||||
| Lower boundary definition | FAD of theInoceramidBivalveCremnoceramus deformis erectus | ||||||||
| Lower boundary GSSP | Salzgitter-Salder quarry,Germany 52°07′27″N10°19′46″E / 52.1243°N 10.3295°E /52.1243; 10.3295 | ||||||||
| Lower GSSP ratified | May 2021 | ||||||||
| Upper boundary definition | FAD of the Inoceramid BivalveCladoceramus undulatoplicatus | ||||||||
| Upper boundary GSSP | Olazagutia,Spain 42°52′00″N2°11′48″W / 42.8668°N 2.1968°W /42.8668; -2.1968 | ||||||||
| Upper GSSP ratified | January 2013[2] | ||||||||
TheConiacian is anage orstage in thegeologic timescale. It is a subdivision of theLate CretaceousEpoch orUpper CretaceousSeries and spans the time between 89.8 ± 0.3Ma and 85.7 ± 0.2 Ma (million years ago). The Coniacian is preceded by theTuronian and followed by theSantonian.[3]
The Coniacian is named after the city ofCognac in theFrench region ofSaintonge. It was first defined by French geologistHenri Coquand in 1857.
The base of the Coniacian Stage is at the first appearance of theinoceramidbivalve speciesCremnoceramus deformis erectus. The official reference profile for the base (aGSSP) 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 inoceramidbivalveCladoceramus undulatoplicatus.
The Coniacian overlaps the regionalEmscherian Stage ofGermany, which is roughly coeval with the Coniacian and Santonian Stages. Inmagnetostratigraphy, the Coniacian is part ofmagnetic chronozone C34, the so-calledCretaceous Magnetic Quiet Zone, a relatively long period with normal polarity.[citation needed]
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 insequence 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 globaltransgressions) on top of the longer first order trend. The followingregression (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, ananoxic event (OAE-3) occurred in theAtlantic Ocean, causing large scale deposition ofblack 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]
The Coniacian is often subdivided into Lower, Middle and Upper Substages. It encompasses threeammonitebiozones in theTethys domain:
In theboreal domain the Coniacian overlaps just one ammonite biozone: that ofForresteria petrocoriensis.[citation needed]
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