Floian

EtymologyName formalityFormalUsage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitAgeStratigraphic unitStageTime span formalityFormalLower boundary definitionFAD of the GraptoliteTetragraptus approximatusLower boundary GSSPDiabasbrottet quarry, Västergötland, Sweden
58°21′32″N12°30′09″E / 58.3589°N 12.5024°E / 58.3589; 12.5024Lower GSSP ratified2002Upper boundary definitionFAD of the ConodontBaltoniodus triangularisUpper boundary GSSPHuanghuachang section, Huanghuachang, Yichang, China
30°51′38″N110°22′26″E / 30.8605°N 110.3740°E / 30.8605; 110.3740Upper GSSP ratified2007

The Floian is the second stage of the OrdovicianPeriod. It succeeds the Tremadocian with which it forms the Lower Ordovician series. It precedes the Dapingian Stage of the Middle Ordovician. The Floian extended from 477.1 to 471.3 million years ago. The lower boundary is defined as the first appearance of the graptolite species Tetragraptus approximatus.