Descent into the Cryogenian

The Cryogenian Period brackets an interval of profound glaciation, commonly referred to by the evocative epithet ‘Snowball Earth’. According to its recent redefinition, the Cryogenian began before the onset of low-latitude glaciation ca. 717 Ma and ended during its final and catastrophic melting phase ca. 635.5 Ma. Pending future ratification of a Global Stratotype Section and Point or GSSP, the onset of the Cryogenian Period is estimated at about 720 Ma. However, no consensus has yet been reached concerning the best section or criteria for its definition. The articles in this special issue represent the state-of-the-art in Tonian-Cryogenian transition stratigraphy around the world and will contribute to the selection of the future GSSP