Radiometric dating
The GSSP of the Floian is the Diabasbrottet Quarry () which is an outcrop of a shale-dominated stratigraphic succession. The lower boundary of the Floian is defined as the first appearance of "Tetragraptus approximatus" which is above the base of the Tøyen Shale. Radiometric dating has set the Tremadocian-Floian boundary at million years ago.