国際標準模式層断面及び地点
The Tremadocian is the lowest stage of Ordovician. Together with the later Floian stage it forms the Lower Ordovician epoch. The Tremadocian lasted from to 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.