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The Gelasian is an age in the international geologic timescale or a stage in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary period/system and Pleistocene epoch/series. It spans the time between 2.588 ± 0.005 Ma (million years ago) and 1.806 ± 0.005 Ma.〔() GeoWhen Database〕 It follows the Piacenzian stage (part of the Pliocene) and is followed by the Calabrian stage. During the Gelasian the Red Crag of Butley and Newbourn and the Norwich and Weybourne Crags, all from East Anglia (England) were deposited. The Gelasian is an equivalent of the Praetiglian and Tiglian stages as defined in the Netherlands, which are commonly used in northwestern Europe. ==Definition== The Gelasian was introduced in the geologic timescale in 1998.〔The Gelasian was first proposed by Rio ''et al.'' (1998)〕 It is named after the Sicilian city of Gela in the south of the island. In 2009 it was moved from the Pliocene to the Pleistocene so that the geologic time scale be more consistent with the key changes in Earth's climate, oceans, and biota that occurred 2.588 million years ago. The base of the Gelasian is defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone (at the Gauss-Matuyama magnetostratigraphic boundary), isotopic stage 103. Above this line notable extinctions of the calcareous nanofossils occur: ''Discoaster pentaradiatus'' and ''Discoaster surculus''.〔〔Gradstein ''et al.'' (2005), p. 28; Rio ''et al.'' (1998)〕 The GSSP for the Gelasian is located at the Monte Sant Nicola near Gela. The top of the Gelasian is defined magnetostratigraphically as the end of the Olduvai (C2n) chronozone, and faunally as the extinction level of the calcareous nanofossil ''Discoaster brouweri'' (base of biozone CN13). Above the Gelasian as the first occurrences of the calcareous nannofossil ''Gephyrocapsa sp.'' and the extinction level of the planktonic foraminifer ''Globigerinoides extremus''.〔〔Gradstein ''et al.'' (2005); Rio ''et al.'' (1998)〕 During the Gelasian the ice sheets in the Northern Hemisphere began to grow, which is seen as the beginning of the Quaternary ice age. 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「Gelasian」の詳細全文を読む スポンサード リンク
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