|
The Induan is, in the geologic timescale, the first age of the Early Triassic epoch or the lowest stage of the Lower Triassic series. It spans the time between Ma and Ma (million years ago).〔According to Gradstein ''et al.'' (2004). Brack ''et al.'' (2005) give 252.6 to 251.0 Ma〕 It is preceded by the Changhsingian and is followed by the Olenekian. The Induan is roughly coeval with the regional Feixianguanian stage of China. ==Stratigraphic definitions== The Induan stage was introduced into scientific literature by Russian stratigraphers in 1956,〔Kiparisova & Popov (1956)〕 who divided the Skythian stage that was used by Western stratigraphers into the Induan and Olenekian stages. The Russian subdivision of the Lower Triassic then slowly replaced the one used in the West. The base of the Induan stage (which is also the base of the Lower Triassic series, the base of the Triassic system and the base of the Mesozoic erathem) is defined as the place in the fossil record where the conodont species ''Hindeodus parvus'' first appears, or at the end of the negative δ18O anomaly after the big extinction event at the Permian-Triassic boundary. The global reference profile of the base of the Induan is situated in Changxing County, China.〔Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi und Wu Shunbao: ''The Global Stratotype Section and Point (GSSP)of the Permian-Triassic Boundary.'' Episodes, 24(2): 102-114, Beijing 2001 .〕 The top of the Induan stage (the base of the Olenekian) is at the first appearance of ammonite species ''Meekoceras gracilitatis''. Though the Induan is an unusually short age at this point in the geologic timescale, it still contains five ammonite biozones in the boreal domain and four ammonite biozones in the Tethyan domain. 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「Induan」の詳細全文を読む スポンサード リンク
|