Revision of the position of the Ordovician–Silurian boundary in southern Ontario: regional chronostratigraphic implications of δ13C chemostratigraphy of the Manitoulin Formation and associated strata

A significant revision of the Ordovician–Silurian boundary position is proposed based on δ13C chemostratigraphy from southern Ontario, suggesting the Manitoulin Formation is latest Ordovician (Hirnantian) rather than earliest Silurian. The study identified a Hirnantian isotope carbon excursion (HICE) in the upper Queenston Formation to lower-middle Manitoulin Formation, supporting this conclusion and aligning with biostratigraphic data from conodonts and brachiopods. Notably, the HICE is absent on Manitoulin Island but present in the Bruce Peninsula and adjacent regions, indicating age variations across the area. This challenges the traditional boundary placement at the base of the Manitoulin Formation, instead suggesting it lies near the base of the overlying Cabot Head Formation. These findings have major implications for interpreting the geologic history and marine depositional patterns of the latest Ordovician in North America.

Bergström, S. M., Kleffner, M., Schmitz, B., & Cramer, B. D. (2011). Revision of the position of the Ordovician–Silurian boundary in southern Ontario: regional chronostratigraphic implications of δ¹³C chemostratigraphy of the Manitoulin Formation and associated strata. Canadian Journal of Earth Sciences, 48(11), 1447–1470. https://doi.org/10.1139/e11-039