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Tremadocian

Subdivision of the Ordovician according to the ICS, as of 2024.Vertical axis scale: Millions of years agoEtymologyName formalityFormalUsage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitAgeStratigraphic unitStageTime span formalityFormalLower boundary definitionFAD of the ConodontIapetognathus fluctivagus.Lower boundary GSSPGreenpoint section, Green Point, Newfoundland, Canada49°40′58″N57°57′55″W / 49.6829°N 57.9653°W / 49.6829; -57.9653Lower GSSP ratified2000Upper boundary definitionFAD of the GraptoliteTetragraptus approximatusUpper boundary GSSPDiabasbrottet quarry, Västergötland, Sweden58°21′32″N12°30′09″E / 58.3589°N 12.5024°E / 58.3589; 12.5024Upper GSSP ratified2002The Tremadocian is the lowest stage of Ordovician.

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