Refining chitinozoan biostratigraphy through the early and late Aeronian biogeochemical events on Anticosti Island, Quebec, eastern Canada

The Silurian is marked by a series of biogeochemical events that are expressed in the rock record as positive δ13C excursions and that drove turnovers in marine biodiversity. Exploring these events provides a unique window into the functioning of the ancient Earth system. The anomalies in the carbon isotope record provide an excellent stratigraphic tool for global correlations in the Paleozoic. Anticosti Island has an exceptionally well-preserved stratigraphic record of the Ordovician–Silurian boundary interval, allowing for the study of the early and late Aeronian events and their impact on chitinozoan communities. This study fills a historic gap in the chitinozoan biostratigraphic record of Anticosti Island and provides a refined biostratigraphic framework for global Llandovery correlations. A total of 42 samples from the Merrimack, Gun River, Menier, and Jupiter formations near the mouth of the Jupiter River and from two cores (La Loutre and Martin La Mer) in the south-central part of the island are examined. We redefine the Ancyrochitina ramosaspina Local Biozone and document a total of 27 chitinozoan species. Five new species are described: Bursachitina praedolioliformis n. sp., Cyathochitina triangula n. sp., Plectochitina triplesiensis n. sp., Plectochitina anulata n. sp., and Anthochitina admirabilis n. sp. We formalise B. praedolioliformis as a smooth-walled precursor of Eisenackitina dolioliformis. We recognise a distinct faunal turnover at the onset of the late Aeronian event, notably represented by the appearance and radiation of diverse, highly ornamented species. This contrasts with the extinction of marine life we expected to see, based on the documented diversity loss at the onset of other Silurian events.