Biotic crisis in the late Ordovician: Insights from δ13Corg and δ13Ccarb isotopic systematics

摘要

New paired carbonate and organic-carbon carbon-isotope analyses from the latest Ordovician to earliest Silurian in the Yangtze Sea on the South China Plate, show a positive δ13C excursion in the latest Ordovician Hirnantian Stage, corresponding in time to large climatic fluctuation and severe biotic crisis. The climatic fluctuation is interpreted to have been induced initially by mountain building, and subsequent enhanced chemical and physical weathering, which would have increased riverine delivery to oceans and primary bioproductivity, and subsequent burial of organic matter, thereby resulting in climate cooling. Such large climatic fluctuation, together with increases in nutrients (e.g., biolimiting Fe), toxins (sulfide) and anoxic water supply,and subsequent enhanced riverine fluxes and microbial bloom, were likely responsible for the stepwise faunal demise of the O-S biotic crisis.