FINE-TUNING LATE MAASTRICHTIAN FAUNAL UPHEAVALS, CLIMATIC EVENTS AND MAJOR VOLCANIC EPISODES

Highly diversified planktic foraminiferal assemblages (~65 species) prevailed in the early late Maastrichtian (mid C31n, ~68.8 Ma) at the South Atlantic DSDP Site 525A. A rapid warming (~2°C deep water) at the base CF4/ top C31n is associated with carbonate dissolution and enhanced planktic test-fragmentation indicative of ocean acidification. A subsequent cooling (~1 °C deep water) resulted in a faunal turnover and minor extinction event (base C30n, upper CF4), marked by the disappearance of Archeoglobigerina cretacea, Globotruncana bulloides, G. gandolfi nsp., Contusotruncana fornicata, C. plummerae, and C. plicata. Increased environmental stress in upper zone CF4 is supported by species dwarfing, presence of Guembelitria cretacea in open marine settings and a marked increase in the abundance of low oxygen tolerant species such as Heterohelix navarroensis (~30%) and Pseudoguembelina costulata (~15%).

The dissolution event (base CF4) and high stress environment and extinctions (top CF4) can be traced through the Tethys (Egypt, Israel) to the Indian Ocean (DSDP Site 217 and the Cauvery basin, SE India). In the Tethys (Egypt), correlative high stress conditions in shallow marine settings are recorded by G. cretacea blooms (40-60%) and a decline in the relative abundance of globotruncanids (20%). In the Indian Ocean, the onset of severe faunal stress and intense carbonate dissolution (base CF4) is associated with ongoing Ninetyeast Ridge volcanism. Environmental and faunal changes of the early Late Maastrichtian that have long remained an enigma can now be linked to at least two events – Ninetyeast Ridge volcanism and the onset of Deccan Trap volcanism. Other potentially coeval volcanic episodes yet to be investigated include Eightyeast Ridge, Southern Indian Ocean, and Andean volcanism. Absolute ages (U-Pb) of these volcanic events are vital to confirm this association.