The Stratigraphic Code

By design, the Stratigraphic Code is meant to be an evolving document, one that requires change as the field of earth science evolves. The principles embodied by any code, however, reflect the state of knowledge at the time of its preparation.

The Codes of Stratigraphic Nomenclature prepared by the Committee on Stratigraphic Nomenclature (1933), the American Commission on Stratigraphic Nomenclature (ACSN 1961, 1970), and the North American Commission on Stratigraphic Nomenclature (NACSN 1983, 2005, 2021) have been used widely as a basis for stratigraphic terminology. Their formulation was a response to needs recognized during the past century by government surveys (both national and local), professional societies, academia, and private industry for uniform standards and common procedures in defining and classifying formal rock bodies, their fossils, and the time spans represented by them.

The Codes have served the profession admirably and have been drawn upon heavily for codes and guides prepared in other parts of the world (International Subcommission on Stratigraphic Classification, International Stratigraphic Guides 1976, p. 104–106; 1994, p. 143–147).

New Code (in prep.)

This revision, to be entitled “Stratigraphic Code of the Americas”, will succeed the North American Stratigraphic Code (2021). The changes adopted in this new version of the Code of the Commission were separately published in the Stratigraphy journal between 2023 and 2026. These changes include:

  • (1) Addition of Chemostratigraphic Units (Articles 61 and 62) and the subsequent renumbering of Articles 61–97 as Articles 63–99. Tables 1 and 2 and Text-Figure 1 are revised (Report 15 – Scott et al., 2023);
  • (2) Revision of Articles 2 and 20 to address culturally offensive or inappropriate unit names and to encourage the use of Indigenous place names (Report 16 – MacNaughton et al., 2024); and
  • (3) As noted elsewhere in the Website, the Commission has been renamed the “Commission on Stratigraphic Nomenclature of the Americas”, and the Code renamed the “Stratigraphic Code of the Americas”. In recent years, membership of the Commission has extended beyond North America to include organizations from countries in Central and South America and the Caribbean. During the 80th Annual Meeting (2025), the Commission voted to change its name and the name of the Code to emphasize this. This was reflected in the updated Bylaws (Report 17 – Dafoe et al., 2026).
  • Draft version (November 2026) of the New Code will become available here.

Suggestions for future modifications or additions to the Code are always welcome. Suggestions may be made to representatives of your organization who are current commissioners, or to the Commission Chair and Vice Chair. Suggested and adopted modifications are announced to the profession by serial Notes and Reports published in the Stratigraphy journal.

Previous Codes
Spanish and French translations of the North American Stratigraphic Code (NACSN, 2021)

Special Volumes and Journal Articles

  • Set in Stone: The work of the North American Commission on Stratigraphic Nomenclature (R.C. Orndorff, ed., 2009) is a special issue of the Stratigraphy journal that offers a comprehensive view of the Commission. Chapters include a full history of the Commission and the successive stages in development of the Code, advice on its use, discussions of the theoretical and practical issues of time and rock units that are addressed in the Code, and the articles of procedure.

  • Wheeler, H.E., Scott, W.F., Bayne, G.W., Steele, G., and Mason, J.W. 1950. STRATIGRAPHIC COMMISSION Stratigraphic Classification. AAPG Bulletin, Vol. 34, No. 12, pp. 2361–2365.

  • AAPG Committee on geologic names and correlations, J.G. Bartram, Chair. 1939. Classification and nomenclature of rock units. AAPG Bulletin, Vol. 23, No. 7, pp. 1068–1088. Re-issue of Committee on Stratigraphic Nomenclature (Ashley et al., 1933) with slight modifications to Articles 9 and 17.