Faunal distributions across the Ordovician–Silurian boundary, Anticosti Island and Percé, Québec, Canada

Abstract

The disappearances of typical Ordovician taxa are staggered within the strata of member 7 of the Ellis Bay Formation and immediately above on Anticosti Island. The appearances of typical Silurian taxa on Anticosti Island are also staggered, but range from member 7 into the typical Becscie Formation. The Hirnantia brachiopod fauna and the Mucronaspis trilobite fauna of the Percé area are younger than the base of the Gamachian and are of the persculptus Zone. An ordered succession of appearances on Anticosti Island and the Oslo region is demonstrated: the lower boundary of the Oulodus? nathani conodont Zone, then the brachiopods Zygospiraella and Stricklandia, and then the trilobite Acernaspis. The acuminatus Zone within the Anticosti Island and Percé sequences cannot be recognized as such; its lower boundary is, however, drawn on the basis of the first appearance of Acernaspis, in accordance with what is known of the first occurrence of this trilobite in Europe and Asia. The Anticosti Island and Percé area sequences are taken to represent continuous uninterrupted deposition without strong palaeoecological control on the evolving faunas in either place; each taxonomic unit evolved at its own rate.