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

M Sinnesael,P.I Mclaughlin,A Desrochers,P Claeys,T.R.A Vandenbroucke,J De Weirdt,A Mauviel

doi:10.1130/g49083.1

Abstract

AbstractPaleozoic 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.

Highlights

The theory of astronomical climate forcing has revolutionized our understanding of Cenozoic climate systems and is the basis for unprecedented continuous time scales with precision down to ∼104 yr (Zachos et al, 2001)
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)
Paleozoic astrochronologies are typically based on identification of the stable 405 k.y. eccentricity cycle instead of shorter astronomical cycles, which have the potential to provide an orderof-magnitude increase in temporal resolution

Summary

INTRODUCTION

The theory of astronomical climate forcing has revolutionized our understanding of Cenozoic climate systems and is the basis for unprecedented continuous time scales (astrochronologies) with precision down to ∼104 yr (Zachos et al, 2001). Several researchers have interpreted the record of eccentricity (∼100 and ∼405 k.y.) and long obliquity (∼1.2 m.y.) cycles in the Upper Ordovician reference outcrop sections of Anticosti Island, Québec, Canada (Fig. 1; Long, 2007; Elrick et al, 2013; Ghienne et al, 2014; Mauviel et al, 2020). Extrapolating these interpreted accumulation rates for the relatively homogeneous upper Katian subsurface lithology results in total time spans of tens of millions of years, which is inconsistent with integrated stratigraphic constraints indicating an estimated duration of only 4–5 m.y. Updated biostratigraphy together with new chemostratigraphy indicate that the Vauréal Formation belongs to Ka4, a stage slice estimated at a total duration of 4–5 m.y. (Fig. 1D; see the Supplemental Material; McLaughlin et al, 2016)

METHODS

CONCLUSIONS