The nature of Ordovician limestone-marl alternations in the Oslo-Asker District (Norway): witnesses of primary glacio-eustasy or diagenetic rhythms?

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

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.

The Middle Ordovician icehouse has been suggested to be sparked by extra-terrestrial dust associated with an asteroid break-up. Here, the authors use an astronomically calibrated timescale to decouple millennia-scale climate and biodiversity change from the meteorite shower 468.4 million years ago.