NBMG exceptions to STA
Abbreviations for ordinal numbers
NBMG prefers the format of “2nd” and “3rd” (with no superscript).
USGS prefers “2d” and “3d” as shown in the citations below (STA, p. 240).
4. Bates, R.L., and Jackson, J.A., eds., 1980, Glossary of geology
(2d ed.): Falls Church, Va., American Geological Institute, 749 p.
5. Billings, M.P., 1972, Structural geology (3d ed.): Englewood
cliffs, N.J., Prentice-Hall, 606 p.
7. Brown, J.A., 1960, Granules, in Gillson, J.L., and others, eds.,
Industrial minerals and rocks * * (3d ed.): New York,
American Institute of Mining, Metallurgical, and
Petroleum Engineers, p. 443-454.
Chicago Manual of Style (9.8) says that both versions are acceptable. The version used by USGS is often preferred for legal documents—that is probably why USGS uses it as a government format (Congressional documents use 2d as well). The “2nd” and “3rd” version is more common.
Either format can be used as long as the author is consistent within the document.