The Early Silurian Gun River Formation of Anticosti Island, eastern Canada: A key section for the mid-Llandovery of North America

A revised stratigraphic analysis of the Early Silurian Gun River Formation on Anticosti Island, Quebec, reveals a 85–100 m thick carbonate succession deposited in a deepening, tropical carbonate ramp or shelf. The formation is divided into four members (Lachute, Innommee, Sandtop, and Macgilvray), providing critical insights into the mid-Llandovery period following the Late Ordovician mass extinctions. The study demonstrates gradual faunal turnover from low-diversity Rhuddanian communities to more diverse mid-Aeronian assemblages, marked by abundant large pentamerids, indicating sustained deposition without major sedimentary gaps. Deposition occurred at 30–60 m water depths, 40–80 km offshore from the Laurentian craton, with evidence suggesting periodic sub-storm wave base conditions in southern tropical latitudes (20°–25° S). The absence of shallow-water reefs and ooid shoals further supports this interpretation.

Copper, P., Long, D. G. F., & Jin, J. (2012). The Early Silurian Gun River Formation of Anticosti Island, eastern Canada: A key section for the mid-Llandovery of North America. Newsletters on Stratigraphy, 45(3), 263–280. https://doi.org/10.1127/0078-0421/2012/0024