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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.〔See Gradstein ''et al.'' (2004) for a detailed version of the ICS' geologic timescale〕 == 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 rotundatus''. An official reference profile for the base (a GSSP) had in 2009 not yet been appointed. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Coniacian」の詳細全文を読む スポンサード リンク
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