Precession-driven climate cycles and time scale prior to the Hirnantian glacial maximum

Paleozoic astrochronologies are limited by uncertainties in past astronomical configurations and the availability of complete stratigraphic sections with precise, independent age control. We show it is possible to reconstruct a robust Paleozoic ~104-yr-resolution astrochronology in the well-preserved and thick Upper Ordovician reference record of Anticosti Island (Canada). The clear imprint of astronomical cycles, including ~18 k.y. precession, potential obliquity, and short and long eccentricity, constrains the entire Vauréal Formation (~1 km thick) to only ~3 m.y. in total, representing ~10 times higher accumulation rates than previously suggested. This ~10⁴ yr resolution represents an order of magnitude increase in the current standard temporal resolution for the Katian and even allows for the detection of sub-Milankovitch climate-scale variability. The loss of a clear precession signal in the uppermost Vauréal Formation might be related to contemporaneous global cooling prior to the Hirnantian glacial maximum as indicated by the δ¹⁸O record. Complementary to the study of cyclostratigraphy of longer and often simplified records, it is important to recognize stratigraphic hiatuses and complexities on the ~10⁴ yr scale to achieve robust sub-eccentricity-scale Paleozoic astrochronologies.