国際標準模式層断面及び地点
The International Commission on Stratigraphy (ICS) originally divided the Upper Ordovician into two stages. After considerable research, however, it was determined that no single faunal zone existed that could accommodate the upper stage of this division. Therefore, in 2003, the ICS voted to add an additional stage to its official international time scale. This was named the Hirnantian after Bancroft's stage. In 2006 the ICS ratified the Wangjiawan section as the official Global Boundary Stratotype Section and Point (GSSP) for the Hirnantian stage.