Correlation of the Cambrian Evolutionary Radiation: geochronology, evolutionary stasis of earliest Cambrian (Terreneuvian) small shelly fossil (SSF) taxa, and chronostratigraphic significance

Early faunas with Watsonella crosbyi with or without Aldanella spp. have been equated with the Siberian Tommotian Stage (uppermost Terreneuvian) and used to define a proposed Cambrian Stage 2 base. Much earlier Terreneuvian occurrences are now shown by recovery of these micromolluscs below the I' carbon excursion in the Siberian 'Nemakit-Daldynian' Stage and comparable delta C-13 excursions in the middle Meishucunian (China) and middle Chapel Island Formation (Avalonia). This delta C-13 excursion, a reliable Stage 2 marker, lies in a c. 10 Ma interval in the Cambrian Radiation in which long-ranged small shelly fossil taxa provide limited biostratigraphic resolution.