Candidate GSSPs [and likewise GSSAs] are evaluated by the ICS and its constituent subcommissions and working groups based on a long list of criteria (Hedberg, 1976; Cowie et al., 1986; Salvador, 1994; Remané et al., 1996; Harper et al., 2023). The most important of these is that the boundary at the candidate stratotype is defined at the level in rock coincident with 'a single stratigraphic signal within an interval of multiple, varied stratigraphic signals', that should allow for reliable, high-resolution correlation across the greatest possible palaeogeographical range of palaeoenvironmental settings (Finney, 2013).

Identification and field investigations of candidate stratotype sections and boundary intervals, and drafting of proposals, are carried out by subcommissions of ICS (stratigraphy.org/subcommissions) and usually by smaller boundary-working groups. One or more candidate GSSP proposals [and/or GSSA proposals] may be considered for approval by the voting members (ca. 20; voting member tenured for a maximum of 12 years) of a subcommission, and a single proposal that receives a supermajority vote (>60% of the voting membership) is considered approved. One consequence of this approach is that disagreement can arise, because type sections that are favoured for historical reasons may be abandoned, previously established boundary levels may be greatly changed, and in some instances historical units (and their names) are replaced by new and different ones (retiring old names).

Once accepted by a subcommission, a proposal is then forwarded to the ICS for consideration and approval. The ICS voting members are the executive officers of ICS and the chairs of the 17 ICS subcommissions, each of whom has a single vote. They evaluate and discuss each proposal, then vote. If the proposal is approved by supermajority votes, the proposal is forwarded to the IUGS Executive Committee. Once it is also approved by majority within the IUGS Executive Committee, the proposal is formally ratified and recognised as an international geostandard. The ICS executive updates the International Chronostratigraphic Chart and the GSSP table on stratigraphy.org (typically within days).

A manuscript documenting the ratified GSSP proposal is submitted for publication, generally in the IUGS's journal Episodes (episodes.org). At the GSSP stratotype locality, a physical marker should be placed, that may be officially launched in a public dedication ceremony (typically 1-3 year after ratification). A proposal to change a newly established unit and/or GSSP cannot be made within the first 10 years after its ratification, a clause to ensure the stability of the global chronostratigraphic framework.

Cowie, J.W., Ziegler, W., Boucot, A.J., Bassett, M.G., and Remané, J., 1986, Guidelines and Statutes of the International Commission on Stratigraphy (ICS). Courier Forschungsinstitut Senckenberg, v. 83, pp. 1-14.

Finney, S.C., 2013, The Reality of GSSPs. Ciências da Terra, v. 18, pp. 9-12.

Harper, D.A.T., Bown, P., and Coe, A., 2022, Chronostratigraphy: understanding rocks and time. In: Coe, A.L., ed., Deciphering Earth's History: the Practice of Stratigraphy. Geological Society, London, pp. 227-243.

Hedberg, H.D., ed, 1976, International Stratigraphic Guide - A Guide to Stratigraphic Classification, Terminology, and Procedure. New York, John Wiley & Sons, 200 p.

Remané, J., Bassett, M.G., Cowie, J.W., Gohrbandt, K.H., Lane, H.R., Michelsen, O., and Wang, N., 1996, Revised guidelines for the establishment of global chronostratigraphic standards by the International Commission on Stratigraphy (ICS). Episodes, v. 19, pp. 77-81. https://doi.org/10.18814/epiiugs/1996/v19i3/007

Salvador, A., ed, 1994, International Stratigraphic Guide - A Guide to Stratigraphic Classification, Terminology, and Procedure, Second Edition. Boulder, Colorado, The International Union of Geological Sciences and The Geological Society of America, 214 p.