Middle Ordovician astrochronology decouples asteroid breakup from glacially-induced biotic radiations

Abstract

Meso-Cenozoic evidence suggests links between changes in the expression of orbital changes and millennia-scale climatic- and biotic variations, but proof for such shifts in orbital cyclicity farther back in geological time is lacking. Here, we report a 469-million-year-old Palaeozoic energy transfer from precession to 405 kyr eccentricity cycles that coincides with the start of the Great Ordovician Biodiversification Event (GOBE). Based on an early Middle Ordovician astronomically calibrated cyclostratigraphic framework we find this orbital change to succeed the onset of icehouse conditions by 200,000 years, suggesting a climatic origin. Recently, this icehouse was postulated to be facilitated by extra-terrestrial dust associated with an asteroid breakup. Our timescale, however, shows the meteor bombardment to post-date the icehouse by 800,000 years, instead pausing the GOBE 600,000 years after its initiation. Resolving Milankovitch cyclicity in deep time thus suggests universal orbital control in modulating climate, and maybe even biodiversity accumulation, through geological time.

A Baltic Perspective on the Early to Early Late Ordovician δ13C and δ18O Records and Its Paleoenvironmental Significance

“…A. Rasmussen et al, 2021) further supporting the notion that they are glacio-eustatically controlled. This interval precisely correlates to the interval where the current Baltic δ 18 O record shows the strongest positive trend, in accordance with the inferred lower Middle Ordovician sea-level drop (Figure 14).…”

“…The millennial‐scale of the sea‐level changes on Baltica was recently confirmed by a geochronologically calibrated astrochronology through the Dapingian−early Darriwilian (J. A. Rasmussen et al., 2021) further supporting the notion that they are glacio‐eustatically controlled. This interval precisely correlates to the interval where the current Baltic δ 18 O record shows the strongest positive trend, in accordance with the inferred lower Middle Ordovician sea‐level drop (Figure 14).…”

“…A. Rasmussen et al (2021) used a marginal succession on Baltica to show a shift in the expression of orbital cycles that postdates by just 200,000 years the brachiopod 18 O-inferred onset of colder climate in the upper B. norrlandicus zone. This orbital shift was suggested to be associated with the build-up of icecaps in Gondwana.…”

Orbital and Millennial‐Scale Cycles Through the Hirnantian (Late Ordovician) in Southern China

“…However, the resolution of our sampling, coupled with enhanced noise due to variations in SR and chaotic geological processes, posed challenges in precisely constraining these millennial‐scale cycles within various climate proxy records. It is noteworthy that millennial‐scale variations have been recognized in diverse proxies and geological settings during the Late Ordovician glacial period (Elrick & Hinnov, 2007; Williams, 1991), as well as throughout the Phanerozoic era (Franco et al., 2012; Kochhann et al., 2020; Pope & Read, 1998; Rasmussen et al., 2021). These cycles have predominantly been identified in rhythmite depositions (Kochhann et al., 2020; Rodríguez‐Tovar & Pardo‐Iguízquiza, 2003; Walters et al., 2020) and carbonate‐clay (light‐dark) laminae formations (Ma et al., 2021).…”

Stable ocean redox during the main phase of the Great Ordovician Biodiversification Event

“…Thus, an increase in oxygenation could not have triggered the earliest Darriwilian inception phase of the GOBE as previously suggested 24 . Both global and regional biotic richness data shows that the peak of this main phase occurred during the late Dw1 1 , 9 , 10 , 53 . Therefore, we find that a relatively stable global oxygenation state of the oceans prevailed during the period leading up to the maximum increase of biodiversity of the GOBE (Interval I, Fig.…”