Periodic oceanic euxinia and terrestrial fluxes linked to astronomical forcing during the Late Devonian Frasnian-Famennian mass extinction
Oceanic anoxia is considered as the immediate cause of the Frasnian-Famennian mass extinction, yet the frequency of anoxia and associated environmental modulators remains unknown. Here, we demonstrate that astronomical forcing paced oceanic anoxic episodes by mediating land-ocean interactions during the Upper Kellwasser (UKW) Event, using an ultra-high-resolution (one centimeter spacing), multi-proxy geochemical profile of a UKW interval from the Upper Devonian Chattanooga Shale of Tennessee, USA. Organic and inorganic geochemical indices for oceanic anoxia/euxinia, marine primary productivity, terrestrial plant/soil inputs, and clastic sediment inputs show synchronous fluctuations that were paced by the Earth's orbital precession. This study provides the first mechanistic evidence linking the periodicity of Late Devonian oceanic euxinia to astronomical forcing and identifies terrestrial-to-marine inorganic and organic fluxes as the driver of this linkage. These results suggest that astronomical forcing modulated the expression of environmental stressors that led to the Frasnian-Famennian mass extinction.