国際標準模式層断面及び地点
The base of the Thanetian stage is laid at the base of magnetic chronozone C26n. The references profile (Global Boundary Stratotype Section and Point) is in the Zumaia section (43° 18'N, 2° 16'W) at the beach of Itzurun, Pais Vasco, northern Spain. Fossils of the unicellular planktonic marine coccolithophore "Areoligeria gippingensis" make their first appearance at the base of the Thanetian, and help define its lowest stratigraphic boundary.