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The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.〔For a detailed geologic timescale see Gradstein ''et al.'' (2004)〕 The Toarcian age began with the Toarcian turnover, the extinction event that sets its fossil faunas apart from the previous Pliensbachian age. ==Stratigraphic definitions== The Toarcian takes its name from the city of Thouars, just south of Saumur in the Loire Valley of France. The stage was introduced by French palaeontologist Alcide d'Orbigny in 1842, after examining rock strata of this age in a quarry near Thouars. In Europe this period is represented by the upper part of the Lias. The base of the Toarcian is defined as the place in the stratigraphic record where the ammonite genus ''Eodactylites'' first appears. A global reference profile (a GSSP) for the base is located at Peniche, Portugal. The top of the stage is at the first appearance of ammonite genus ''Leioceras''. In the Tethys domain, the Toarcian contains the following ammonite biozones: *zone of ''Pleydellia aalensis'' *zone of ''Dumortieria pseudoradiosa'' *zone of ''Phlyseogrammoceras dispansum'' *zone of ''Grammoceras thouarcense'' *zone of ''Haugia variabilis'' *zone of ''Hildoceras bifrons'' *zone of ''Harpoceras serpentinum'' *zone of ''Dactylioceras tenuicostatum'' 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「Toarcian」の詳細全文を読む スポンサード リンク
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