ANALYSIS OF LOW AND HIGH LATITUDE PLANKTONIC FORAMINIFERAL DISTRIBUTIONS ACROSS THE LATE MAASTRICHTIAN DECCAN VOLCANISM EVENT

The biotic turnover at the Cretaceous-Paleogene (K-Pg) boundary has long been recognized as one of the most devastating events in the history of life. Despite overwhelming evidence that the asteroid impact caused the terminal Cretaceous extinctions, some workers still argue that volcanism during an eruption of the Deccan flood basalts (west central India) ~250 kyr before the K-Pg boundary was also a cause of major biotic extinctions. If true, there should be evidence of volcanic-induced biotic stress in the ocean, which should include a globally consistent record of corresponding extinctions and a test size reduction, also known as a “Lilliput effect”, among environmentally sensitive species. Our study examines changes in stratigraphic distributions, species diversity and test size changes of planktonic foraminiferal assemblages during the last 500 kyr of the Cretaceous. Sites selected to identify evidence of such biotic stress are from two deep-sea boreholes, ODP Holes 1049C (low latitude; Blake Plateau, North Atlantic) and 690C (high latitude; Maud Rise, southern South Atlantic). Both sites are stratigraphically complete across the K-Pg interval and have excellent age control and stable isotope data with the late Maastrichtian Deccan Event fully represented.

From our size distribution study, multiple species that lived in mixed layer and thermocline habitats were measured for their test areas (trochospiral taxa) and maximum test length (serial taxa)). To avoid methodological biases, samples were microsplit and a random number generator was used to randomly select specimens for measurement from a gridded tray until a minimum of 20 specimens per species were measured. Distribution data do not show an increased extinction rate that is correlative to the Deccan Event. Instead, nearly all species present 250 kyr before the Deccan Event are still present up to the K-Pg boundary. Moreover, test measurement data obtained so far reveal no changes in test size that correlate to the Deccan Event. The only notable effect of the Deccan Event on planktonic foraminiferal assemblages is the poleward migration of two thermophilic planktonic foraminiferal species, Pseudotextularia elegans and Constusotruncana contusa, at the same time as a warming event that has been well documented by various paleotemperature proxies.