Sequence Stratigraphy and δ13C of the Upper Katian Vauréal Formation, Anticosti Island: Insights into Glacio-Eustatic Record of the Upper Katian Sea-Level Changes

Anticosti Island (Québec, Canada) preserves a thick, well-preserved, and fossiliferous Ordovician/Silurian boundary section, making it a critical part of our understanding of the link between the Early Paleozoic Icehouse and the Late Ordovician mass extinction. While much of the work on Anticosti has focused on the Ordovician/Silurian boundary itself, underlying Katian strata remain comparatively understudied. Much like the Ordovician/Silurian boundary, the Katian Stage (453-445.2 Ma) is a dynamic interval marked by significant faunal reorganizations (e.g., the Boda Event), perturbations of the global carbon cycle (e.g., Guttenberg and Kope excursions), and major climate transitions. However, in many basins, the stratigraphic expression, timing, and drivers of these events, as well as their relationship, remain poorly constrained. Here, we develop a sequence model for the upper part Vauréal Formation at the Rivière à l’Huile section. The Vauréal Formation records a range of shallow-marine environments from a gently sloping mixed carbonate-siliciclastic ramp along the eastern margin of Laurentia. Combining sedimentological, and stratigraphic data, based on filed work and pretrographic observation, we identify complex, repeating stacking patterns in the Rivière à l’Huile section. Distinct stratigraphic packages are bounded by major stratigraphic surfaces, marked by erosion and non-deposition. These high-frequency cycles are thus interpreted as reflecting glacio-eustatic fluctuations. Integration of high resolution δ13C data within this sequences model allows us to then: 1) evaluate the relationships between relative sea-level fluctuations and carbon-cycle perturbations, and 2) distinguish local sedimentological controls from regional or global geochemical signals. Furthermore, integrating these results with existing biostratigraphic and cyclostratigraphic frameworks for the Ordovician/Silurian boundary on Anticosti allows us to provide improved temporal constraints on environmental and oceanographic changes leading up to the Late Ordovician mass extinction. By refining the stratigraphic architecture of the upper Katian succession, this study contributes to a better understanding of the links between glacio-eustatic sea-level changes, carbon-cycle perturbations, and faunal turnover during the lead-up to the Late Ordovician mass extinction.