Induan

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 252.17 Ma and 251.2 Ma (million years ago). It is preceded by the Changhsingian and is followed by the Olenekian.

The Induan is roughly coeval with the regional Feixianguanian stage of China.

The Induan stage was introduced into scientific literature by Russian stratigraphers in 1956, who divided the Scythian stage that was used by Western stratigraphers into the Induan and Olenekian stages. The Induan stage is named for the Indus region of Pakistan. 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.

The top of the Induan stage (the base of the Olenekian) is at the first appearance of ammonite species Meekoceras gracilitatis.

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