THE INTERNATIONAL COMMISSION on STRATIGRAPHY AND GSSPs

The mission of the International Commission on Stratigraphy is to establish an International Chronostratigraphic Chart with a single set of global units at the ranks of Stage, Series, and System with the lower boundary of each defined by a Global Standard Boundary-Stratotype Section and Point or GSSP, which are the basis for the geochronologic units of the Geologic Time Scale with the ranks of Age, Epoch and Period. GSSPs mark points in time that define the beginnings of the time units. GSSPs have been selected for 61 of the 101 stages of the Phanerozoic and for the Ediacaran System of the Proterozoic.

Selection of a GSSP is a long-term endeavor. Historical revisions to a chronostratigraphic unit, differing concepts of it among specialists, and different units from different regions must be evaluated, and determination made for the single unit to be used as a global standard. Stratigraphic signals at the preferred stratigraphic level must be evaluated to determine those that offer the greatest potential for reliable correlation of the lower boundary of the unit into as many facies and as worldwide as possible. Successions worldwide must be studied to determine which best meet the criteria for a global stratotype section. These activities are carried out by ICS subcommissions. For a stratigraphic horizon in a single stratigraphic section to be further considered as a GSSP, a formal proposal must be submitted to a vote. Approval requires a supermajority (>60%) of “yes” votes within the appropriate Subcommission. If approved by a Subcommission, the proposal is forwarded to the voting membership of ICS - the executive officers of ICS and chairs of all ICS Subcommissions, where the proposal must again receive a supermajority of “yes” votes. If approved by ICS, a recommendation is forwarded to the IUGS Executive Committee, where a majority vote ratifies the ICS recommendation. Subsequently, the GSSP is marked by a plaque and an article on the GSSP is published in Episodes. Given the length of this process and the many levels of approval, as well as the discussion and deliberation that occurs at each level, the GSSPs and the units they define truly warrant validity, legitimacy, and authority as global standards.