183 / 2025-04-14 11:02:51

Cerium isotope evidence for rapid marine oxygen fluctuations in South China during the Late Ordovician mass extinction

Late Ordovician,Mass Extinction,Redox,Cerium,South China

Theme 3: Earth-Life Co-evolution Through Time > Session 3e: Mass extinctions and lesser calamities in the marine realm

The Late Ordovician Mass Extinction (LOME) comprises two major pulses of biodiversity loss linked to rapid changes in climate and marine oxygen availability, but the precise driving mechanisms remain unresolved. Here we present cerium isotope (δ¹⁴²Ce) data, a novel redox sensitive proxy, from a carbonate-dominated uppermost Ordovician profile in South China to track the regional burial of Mn oxide and reconstruct redox dynamics during the LOME within this basin. Two pronounced negative δ¹⁴²Ce excursions that indicate a decrease in the amount of Mn-oxide burial in sediments occur coincidently with the two severe extinction pulses in the late Katian and mid-Hirnantian. These two reducing events are separated by a short-term appearance and proliferation of Hirnantia fauna in the early Hirnantian suggesting more oxic conditions The first negative Ce isotope excursion during the late Katian suggests a reduction in Mn-oxide burial, thus a deoxygenation in South China basin during the first extinction pulse (LOME-1), potentially driven by incursion of anoxic water onto the epicontinental shelf inner sea. Subsequently in the late Hirnantian, the second negative Ce isotope excursion also indicates a rapid re-expansion of anoxic bottom waters lasting ~200 kyrs, based on biostratigraphic controls, in the innermost shelf during the second extinction pulse (LOME-2) in response to the deglaciation and transgression. This study further strengthens the connection between vacillating (de)oxygenation and marine faunal turnover during latest Ordovician. Perhaps more importantly, this pioneering approach highlights the potential of using δ¹⁴²Ce as a promising proxy for tracking local-regional scale marine redox conditions in Earth history and offers new insights into the interplay between climate change, marine oxygen variability, and mass extinction events.