Some potential Proterozoic GSSPs

Formal adoption of a Precambrian chronostratigraphic timescale will require placements of Global Stratotype Sections and Points (GSSPs) at well chosen locations in the geological record (Bleeker, 2004a, b; Robb et al., 2004). Formalization of GSSPs in a chronostratigraphic framework does not require complete abandonment of chronometric scales; for example, the geon scale (Hofmann, 1990, 1999) may be used in parallel with any stratigraphically based scheme according to the convenience of scientific communication. Given wide usage of prior chronometric subdivisions in Precambrian time, GSSP selection should be guided by these subdivisions, at least at the levels of eons and eras (see Robb et al., 2004). Thus an Archean-Proterozoic boundary should be placed in a rock succession at approximately 2500 Ma age, and eras within the Proterozoic Eon should conform broadly to a three-part subdivision of Paleo-, Meso-, and Neo-, that correspond approximately with their current chronometric boundaries at 1600 and 1000 Ma (Plumb, 1991). The names of these eons and eras need not change, for we have ample precedent of consistent terminology usage both before and after GSSP formalization. The symbolic meanings of three Proterozoic eras can remain unchanged as long as our present chronostratigraphic definitions adhere to the features of Earth history that governed selection of the currently formalized chronometric tripartite subdivision (most thoroughly described by Plumb and James, 1986). If the presen