Isotope curves delineating d13Ccarb and d16O variations across the Cambrian–Ordovician boundary at Green Point, western Newfoundland (Canada) are presented. The d13Ccarb profile of the section reveals a composite (three peaks) negative shift of *6.0 % and starts immediately at the base of bed 23 of the Broom Point Member. The 13Ccarb profile ties to conodont and graptolite zones and indicates that the lowest occurrence of planktic graptolites in Bed 25 largely coincides with the C. lindstr