The Late Devonian Frasnian-Famennian (F/F) biotic crisis: Insights from δ13Ccarb, δ13Corg and 87Sr / 86Sr isotopic systematics

A severe biotic crisis occurred during the Late Devonian Frasnian-Famennian (F/F) transition (± 367 Myr). Here we present δ13Ccarb, δ13Corg and 87Sr / 86Sr isotopic systematics, from identical samples of two sections across F/F boundary in South China, which directly demonstrate large and frequent climatic fluctuations (∼200 kyr) from warming to cooling during the F/F transition. These climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing, and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land, which would have increased riverine delivery to oceans and primary bioproductivity, and subsequent burial of organic matter, thereby resulting in climate cooling. Such large and frequent climatic fluctuations, together with volcanic-induced increases in nutrient (e.g., biolimiting Fe), toxin (sulfide) and anoxic water supply, and subsequent enhanced riverine fluxes and microbial bloom, were likely responsible for the stepwise faunal demise of F/F biotic crisis.