MULTI-PROXY APPROACH TO DECODE THE END-CRETACEOUS MASS EXTINCTION

Mass extinctions generally involve a complex array of interrelated causes and are best evaluated by a multi-proxy approach as applied here for the Cretaceous-Tertiary (Paleogene) boundary (KTB or KPB) mass extinction. This study documents and compares the planktic foraminiferal records, carbonate dissolution effects, stable isotopes, and magnetic susceptibility at Bidart (France), Gamsbach (Austria) and Elles (Tunisia) in order to explore the environmental conditions in the 160 ky (Plummerita hantkeninoides zone CF1) leading up to the mass extinction. Results show that planktic foraminiferal assemblages at Bidart and Gamsbach are more diverse than those at Elles primarily due to unusually high abundance (20-30%) and diversity (~15 species) of globotruncanids in the two deep-water sections, but lower abundance (<10%) and diversity (<10 species) at the middle shelf Elles section. Oxygen isotopes in zone CF1 record rapid climate warming and a return to cooler temperatures prior to the mass extinction.

The onset of the biotic crisis is observed in the top 50-60 cm below the KTB at Bidart and Gamsbach and in the top ~4.5 m at Elles where sedimentation is much higher. These intervals record low magnetic susceptibility, low percent CaCO₃, a high foraminiferal fragmentation index (FI) and increased abundance of species with dissolution-resistant morphologies. The correlative interval in India, where the mass extinction was documented in intertrappean sediments between the longest lava flows, records significantly stronger carbonate dissolution effects ending with the mass extinction. Based on current evidence carbonate dissolution appears linked to ocean acidification as a result of massive Deccan volcanism. The estimated 12,000–28,000 Gigatons (Gt) of CO₂ and 5200–13,600 Gt of SO₂ introduced into the atmosphere likely triggered the carbonate crisis in the oceans resulting in severe stress for marine calcifiers leading to the mass extinction.