The Ordovician-Silurian boundary (late Katian-Hirnantian) of western Anticosti Island: revised stratigraphy and benthic megafaunal correlations

A revised stratigraphy of the Ellis Bay Formation on western Anticosti Island reveals critical insights into one of Earth's most significant mass extinction events, marking the transition from the Ordovician to Silurian periods. The study identifies three new members—Fraise, Juncliff, and Parastro—within this formation, which spans approximately 80–90 meters and captures the Hirnantian shelly fauna's onset near its base. This fauna, characterized by brachiopods like Eospirigerina and Hindella, ends abruptly at the top of the reefal Laframboise Member, coinciding with a major extinction event that wiped out Hirnantian brachiopods, stromatoporoids, corals, crinoids, and nautiloids. The recovery in the earliest Silurian (Rhuddanian) is marked by small-shelled brachiopod faunas, including both Ordovician hold-over taxa and new arrivals like Viridita and Koigia. This revision highlights the formation's role as a key record of environmental changes during this pivotal period.

Copper, P., Jin, J., & Desrochers, A. (2013). The Ordovician-Silurian boundary (late Katian-Hirnantian) of western Anticosti Island: revised stratigraphy and benthic megafaunal correlations. Stratigraphy, 10(4), 213–227. https://doi.org/10.29041/strat.10.4.02