Darriwilian
Period
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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... Wikipedia
Epoch: Middle Ordovician
Occurred: 467.3 (+/- 1.1) million years ago - 458.4 (+/- 0.9) million years ago
Lower boundary definition: FAD of the Graptolite Undulograptus austrodentatus
Lower boundary GSSP: Huangnitang Section, Huangnitang Village, Changshan, Zhejiang, China; 28°51′14″N 118°29′23″E / 28.8539°N 118.4897°E
Lower GSSP ratified: 1987
Upper boundary GSSP: Fågelsång section, Sularp Brook, Skåne, Sweden; 55°42′49″N 13°19′32″E / 55.7137°N 13.3255°E
Upper GSSP ratified: 2002
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