Revision of the position of the Ordovician-Silurian boundary in southern Ontario: regional chronostratigraphic implications of delta C-13 chemostratigraphy of the Manitoulin Formation and associated strata
delta C-13 values of 142 samples from the Manitoulin Formation and subjacent strata collected from 14 exposures and two drill-cores on Manitoulin Island, Bruce Peninsula, and the region south of Georgian Bay suggest that the Manitoulin Formation is latest Ordovician (Hirnantian) rather than earliest Silurian in age. A delta C-13 excursion identified as the Hirnantian isotope carbon excursion (HICE