Darriwilian
The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the Dapingian and succeeded by the Upper Ordovician Sandbian stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species Undulograptus austrodentatus around 467.3 million years ago. It lasted for about 8.9 million years until the beginning of the Sandbian around 458.4 million years ago.
The name Darriwilian is derived from Darriwil, a parish in County of Grant, Victoria (Australia). The name was proposed in 1899 by Thomas Sergeant Hall.
The GSSP of the Darriwilian is the Huangnitang Section (28°51′14″N 118°29′23″E / 28.8539°N 118.4897°E) near the village Huangnitang, 3.5 km southwest of Changshan County Town (Zhejiang, China). It is an outcrop of the Ningkuo Formation, consisting of mainly black shale. The lower boundary of the Darriwilian is defined as the first appearance datum of the graptolite species Undulograptus austrodentatus in that section.
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