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The Aalenian is a subdivision of the Middle Jurassic epoch/series of the geologic timescale that extends from about 174.1 Ma to about 170.3 Ma (million years ago). It was preceded by the Toarcian and succeeded by the Bajocian.〔See Gradstein ''et al.'' (2004) for a detailed version of the geologic timescale〕 ==Stratigraphic definitions== The Aalenian takes its name from the town of Aalen, some 70 km east of Stuttgart in Germany. The town lies at the southwestern end of the Frankischer Jura. The name Aalenian was introduced in scientific literature by Swiss geologist Karl Mayer-Eymar in 1864. The base of the Aalenian is defined as the place in the stratigraphic column where the ammonite genus ''Leioceras'' first appears. A global reference profile is located 500 meters north from the village of Fuentelsaz in the Spanish province of Guadalajara.〔Cresta ''et al.'' (2001)〕 The top of the Aalenian (the base of the Bajocian) is at the first appearance of ammonite genus ''Hyperlioceras''. In the Tethys domain, the Aalenian contains four ammonite biozones: *zone of ''Graphoceras concavum'' *zone of ''Brasilia bradfordensis'' *zone of ''Ludwigia murchisonae'' *zone of ''Leioceras opalinum'' 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「Aalenian」の詳細全文を読む スポンサード リンク
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