https://doi.org/10.1130/G49083.1 Manuscript received 19 October 2020 Revised manuscript received 23 March 2021 Manuscript accepted 12 May 2021 © 2021 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Precession-driven climate cycles and time scale prior to the Hirnantian glacial maximum M. Sinnesael1,2,3, P.I. McLaughlin4, A. Desrochers5, A. Mauviel5, J. De Weirdt2, P. Claeys1 and T.R.A. Vandenbroucke2 1 Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium 2 Department of Geology, Ghent University, Krijgslaan 281/S9, 9000 Ghent, Belgium 3 Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK 4 Indiana Geological and Water Survey, Indiana University, Bloomington, Indiana 47405, USA 5 Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada ABSTRACT costi Island and explores several astrochronolog- Paleozoic astrochronologies are limited by uncertainties in past astronomical configurations ical scenarios within the available stratigraphic and the availability of complete stratigraphic sections with precise, independent age control. constraints. Pre-Hirnantian glacial buildup is We show it is possible to reconstruct a robust Paleozoic ∼104-yr-resolution astrochronology in well established (Vandenbroucke et al., 2010; the well-preserved and thick Upper Ordovician reference record of Anticosti Island (Canada). Pohl et al., 2016), and correctly documenting The clear imprint of astronomical cycles, including ∼18 k.y. precession, potential obliquity, Late Ordovician astronomical cycles is crucial and short and long eccentricity, constrains the entire Vauréal Formation (∼1 km thick) to only for constructing high-resolution time scales and ∼3 m.y. in total, representing ∼10 times higher accumulation rates than previously suggested. studying dynamic changes in climate and bio- This ∼104 yr resolution represents an order of magnitude increase in the current standard diversity (Saupe et al., 2020). In general, reli- temporal resolution for the Katian and even allows for the detection of sub-Milankovitch able identification of high-frequency Paleozoic climate-scale variability. The loss of a clear precession signal in the uppermost Vauréal astronomical cycles can pave the way toward Formation might be related to contemporaneous global cooling prior to the Hirnantian glacial a greatly enhanced understanding of the inter- maximum as indicated by the δ18O record. Complementary to the study of cyclostratigraphy play between biotic evolution and environmental of longer and often simplified records, it is important to recognize stratigraphic hiatuses change. and complexities on the ∼104 yr scale to achieve robust sub-eccentricity-scale Paleozoic astrochronologies. GEOLOGICAL SETTING AND STRATIGRAPHY INTRODUCTION explain because most of the insolation power The lower Paleozoic mixed siliciclastic-car- The theory of astronomical climate forcing lies in the obliquity and precession bands—not bonate succession of Anticosti Island contains has revolutionized our understanding of Ceno- in the eccentricity. some of the thickest, most fossiliferous, well- zoic climate systems and is the basis for unprec- Several researchers have interpreted the exposed, and little-altered Upper Ordovician edented continuous time scales (astrochronolo- record of eccentricity (∼100 and ∼405 k.y.) sections preserved on Earth (Fig. 1; Desrochers gies) with precision down to ∼104 yr (Zachos and long obliquity (∼1.2 m.y.) cycles in the et al., 2010; Finnegan et al., 2011). The succes- et al., 2001). Pre-Cenozoic astrochronologies Upper Ordovician reference outcrop sections of sion was deposited within a structural embay- face several challenges relating to (1) uncer- Anticosti Island, Québec, Canada (Fig. 1; Long, ment along the eastern margin of Laurentia on tainties in the deep-time astronomical solu- 2007; Elrick et al., 2013; Ghienne et al., 2014; the distal portion of a Taconic-Acadian foreland tions and parameters (Berger and Loutre, Mauviel et al., 2020). However, extrapolating located in the paleo(sub-)tropics (10°S–25°S; 1994; Waltham, 2015); (2) less-complete and these interpreted accumulation rates for the Fig. 1B; Blakey, 2013). Our study focuses on the less-well-preserved strata; and (3) the sparsity relatively homogeneous upper Katian subsur- subsurface part of the upper Katian Vauréal For- of geochronologic anchor points. Consequently, face lithology results in total time spans of tens mation, consisting of predominantly gray, inter- Paleozoic astrochronologies are typically based of millions of years, which is inconsistent with bedded micrite, calcarenite, and marl deposited on identification of the stable 405 k.y. eccentric- integrated stratigraphic constraints indicating an in a mid- to outer-shelf environment (Fig. S1 ity cycle instead of shorter astronomical cycles, estimated duration of only 4–5 m.y. (Cooper and in the Supplemental Material1; Long, 2007). which have the potential to provide an order- Sadler, 2012; McLaughlin et al., 2016). While The lithological variations of interest in this of-magnitude increase in temporal resolution. acknowledging challenges to pre-Cenozoic study are multimeter bed bundles, and not the However, the prevalence of eccentricity-based astrochronologies, our study makes use of new centimeter- to decimeter-thick limestone-marl astrochronologies is mechanistically difficult to subsurface records from recent drilling on Anti- couplets that are potentially early diagenetic 1Supplemental Material. Time-series analyses scripts and data. Please visit https://doi .org/10.1130/GEOL.S.14810550 to access the supplemental material, and contact [email protected] with any questions. CITATION: Sinnesael, M., et al., 2021, Precession-driven climate cycles and time scale prior to the Hirnantian glacial maximum: Geology, v. 49, p. XXX–XXX, https://doi.org/10.1130/G49083.1 Geological Society of America | GEOLOGY | Volume XX | Number XX | www.gsapubs.org 1 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G49083.1/5361418/g49083.pdf by guest on 25 September 2021 A D B C Figure 1. (A) Map of the bedrock geology of Anticosti Island, Québec, Canada (after Mauviel et al., 2020). (B) Map of the Late Ordovician paleogeographic reconstruction for southern Laurentia (modified from Blakey, 2013). (C) Photo of differential weathering profile between more carbonate versus shale intervals of the upper Vauréal Formation in Vauréal Canyon representing precession (P) cycles bundled in short eccentricity (SE) cycles (person next to red bar for scale). (D) Stratigraphic column of carbonate-dominated Anticosti Island subsurface (modified from McLaughlin et al., 2016). in origin (Fig. 1C; Nohl et al., 2019). Previ- Paper (NACP) core (49°37′20′′N, 63°26′18′′W; the record (see the Supplemental Material). The ous outcrop studies suggested that eccentric- Fig. 1A; McLaughlin et al., 2016). The two LL1 potassium (40K perent) record as measured ity is the dominant astronomical signal in the cores were correlated using the informal lith- by natural gamma-ray (NGR) logging was used Vauréal Formation (Long, 2007; Elrick et al., ological units V2–V5 defined by McLaughlin as proxy for time-series analyses. This proxy 2013; Mauviel et al., 2020). Updated biostra- et al. (2016) (see also Figs. 1A and 2; Fig. S2; reflects the multimeter cycles of carbonate ver- tigraphy together with new chemostratigraphy see the Supplemental Material). The greater sus clay lithology of interest and is continuously indicate that the Vauréal Formation belongs to thickness of lithological units in the LLI core recorded with the highest available resolution Ka4, a stage slice estimated at a total duration of is attributed to separation by ~10 km along the (10 cm). Evolutive harmonic analysis (EHA) 4–5 m.y. (Fig. 1D; see the Supplemental Mate- south-directed depositional dip of the Anti- (Thomson, 1982) and TimeOpt, eTimeOpt, rial; McLaughlin et al., 2016). costi Basin. The NACP core and the western and timeOptTemplate (Meyers, 2015, 2019) outcrop sections were correlated based on analyses were done with “Astrochron” (https:// 13 METHODS their bulk δ Ccarb (carb—carbonate) records cran.r-project.org/web/packages/astrochron/ The La Loutre #1 core (LL1; 49°35′18′′N, (Figs. 1A and 2; Mauviel and Desrochers, index.html; Meyers, 2014) in R (R Core Team, 63°38′14′′W) was drilled by Consortium 2016; McLaughlin et al., 2016). Additionally, 2017). TimeOpt is a statistical optimization Hydrocarbures Anticosti ∼10 km southwest of 472 new NACP samples were measured for bulk method that can simultaneously consider power 13 18 the well-studied New Associated Consolidated δ Ccarb and δ Ocarb to increase the resolution of spectra distributions and amplitude modulation 2 www.gsapubs.org | Volume XX | Number XX | GEOLOGY | Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/doi/10.1130/G49083.1/5361418/g49083.pdf by guest on 25 September 2021 Figure 2. Compiled stratigraphy and proxy data for the Upper Ordovician section of Anticosti Island, Québec, Canada. Dashed lines repre- sent boundaries between informal lithological units as defined by McLaughlin et al. (2016). The V4–V5 boundary is mainly characterized by a decrease in clay content with more pure limestones in unit V5 (thinner dashed line). Red rectangle (880–403 m) indicates the interval selected