Upheavals during the Late Maastrichtian: Volcanism, climate and faunal events preceding the end-Cretaceous mass extinction

The late Maastrichtian was a time of major climate, evolution and extinction extremes. Rapid climate warming of 2-3°C in intermediate waters between 69.5 and 68Ma (top C31r to base C30n) accompanied maximum evolutionary diversification (43% increase, zone CF5 to low CF4) in planktic foraminiferal history, followed immediately by a cluster of extinctions. During the last 250ky of the Maastrichtian (C29r, zones CF2-CF1), rapid warming of 4°C in intermediate waters and 8°C on land resulted in high-stress environments ending in the mass extinction. The end-Cretaceous mass extinction is recorded in sediments between massive Deccan lava flows in India and attributed to SO₂ and CO₂ outgassing leading to ocean acidification. The early late Maastrichtian climate and faunal upheavals are not well known.Here we document the faunal similarities of both events from the Indian Ocean through the Tethys and Gulf of Mexico. Results show that both extreme warm events are marked by high-stress environments characterized by decreased abundance and diversity of large specialized species and dwarfing, high abundance of low oxygen tolerant species, and disaster opportunist surface dweller Guembelitria blooms. The similarity in faunal response with the Deccan warming of C29r (CF2-CF1) suggests that volcanism was also responsible for the warming and faunal upheaval of the early late Maastrichtian. Major volcanic activity at this time included the onset of Deccan eruptions and Ninetyeast Ridge volcanism. The role of the Chicxulub impact appears to have been a contributing, rather than causal, factor in the mass extinction.