Tremadocian

EtymologyName 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, Canada
49°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, Sweden
58°21′32″N12°30′09″E / 58.3589°N 12.5024°E / 58.3589; 12.5024Upper GSSP ratified2002

The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from 486.85 to 477.1 million years ago. The base of the Tremadocian is defined as the first appearance of the conodont species Iapetognathus fluctivagus at the Global Boundary Stratotype Section and Point (GSSP) section on Newfoundland.