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The Tortonian is in the geologic timescale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tortonian roughly overlaps with the regional Pannonian stage of the Paratethys timescale of Central Europe. It also overlaps the upper Astaracian, Vallesian and lower Turolian European Land Mammal Mega Zones, the upper Clarendonian and lower Hemphillian North American Land Mammal Ages and the upper Chasicoan and lower Huayquerian South American Land Mammal Ages. ==Definition== The Tortonian was introduced by Swiss stratigrapher Karl Mayer-Eymar in 1858. It was named after the Italian city of Tortona in the region Piemont. The base of the Tortonian stage is at the last common appearance of calcareous nannoplankton ''Discoaster kugleri'' and planktonic foram ''Globigerinoides subquadratus''. It is also associated with the short normal polarized magnetic chronozone C5r.2n. A GSSP for the Tortonian has been established in the Monte dei Corvi section near Ancona (Italy).〔By Hilgen ''et al.'' (2005)〕 The top of the Tortonian (the base of the Messinian) is at the first appearance of the planktonic foram species ''Globorotalia conomiozea'' and is stratigraphically in the middle of magnetic chronozone C3Br.1r. 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「Tortonian」の詳細全文を読む スポンサード リンク
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