NO EVIDENCE FOR BIOTIC STRESS OR EXTINCTIONS AMONG PLANKTONIC FORAMINIFERA ACROSS THE LATEST CRETACEOUS DECCAN EVENT

Abrupt mass extinctions of ~75% of plant and animal species, including >90% of planktonic foraminifera species, mark the Cretaceous-Paleogene (K/Pg) boundary 66 million years ago. There is broad consensus that an asteroid impact that created the Chicxulub crater on the Yucatan Peninsula triggered the extinctions. Still, some researchers consider the eruption of the Deccan Traps (west-central India), especially an event starting ~250 kyr before the end of the Cretaceous, as a contributory, if not the primary, cause for the terminal Cretaceous extinctions. Our study investigates the hypothesis that Deccan eruptions were a significant contributor to K/Pg extinctions by analyzing changes in planktonic foraminiferal species distributions, stable isotopic values (δ¹⁸O and δ¹³C), and test size (i.e., the “Lilliput Effect”) during the last 500 k.y. of the Cretaceous from deep-sea sites at high (ODP Holes 689B, 690C, southern South Atlantic; IODP Hole 1579D, Agulhas Plateau, SW Indian Ocean) and low (ODP Hole 1049C, Blake Plateau, western Atlantic) latitudes. Samples from Holes 690C and 1049C record no significant changes in species abundance or diversity across the Deccan Event. Further, no significant change in test size has been observed within the Deccan interval. High latitude sites record poleward expansion followed by equatorward contraction of the geographic range of several thermophilic planktonic species; this migration is attributed to CO₂ outgassing and global warming associated with the Deccan eruptions. Oxygen isotopic analyses also reveal a brief warming coincident with the Deccan Event at three of the four sites studies with a return to pre-event temperatures before the asteroid impact. While the environmental and biological shifts were likely forced by Deccan volcanism are observed, these shifts did not continue through to the K/Pg boundary suggesting the bolide impact was indeed the cause of the K/Pg extinctions.