Figure 3.

Integrated chemo- and biostratigraphic correlation of terminal Proterozoic successions in (A) Spitsbergen, (B) Namibia, and (C) northwestern Canada. Note that data are plotted against stratigraphic thickness, which does not vary linearly with time; in particular, postglacial negative δ¹³C excursions likely took place during relatively brief intervals of time. The bandwidth of δ¹³C variations encompasses the majority of samples and is similar to δ¹³C variations noted in shallow seawater today. The strong difference in Sr isotope compositions of well preserved limestones immediately above the lower and upper Varanger tillites suggests that the two glaciations can be distinguished even though δ¹³C variations are similar. Fossil zonation scheme as explained in Fig. 1.; tillites are represented by double triangles; broad lines above and below the Witvlei Group in the Namibian column indicate stratigraphic breaks; radiometric ages are from Klein and Beukes (14), Hoffman et al. (41), and Grotzinger et al. (44). Stratigraphic abbreviations for northwest Canada as in Fig. 1; other abbreviations: Dr, Dracoisen Fm.; Wi, Wilsonbreen Fm.; El, Elbobreen Fm.; Ak, Akademikerbreen Group; Ns, Schwarzrand Subgroup of the Nama Group; Nk, Kuibis Subgroup of the Nama Group; Wt, Witvlei Group; Ot, Otavi Group.