THE SIGNIFICANCE OF CALCAREOUS NANNOPLANKTON “BOOM-BUST” SUCCESSIONS FOLLOWING THE K-PG MASS EXTINCTION EVENT: NEW INSIGHTS FROM EL KEF, TUNISIA

The K-Pg mass extinction event (∼66 Ma) was caused by a meteorite impact off the Yucatán Peninsula in the Gulf of Mexico, which eliminated ~75% of species on Earth. Among the biggest casualties were calcareous nannoplankton, a group of single-celled, photosynthetic algae which produce microscopic calcite plates called coccoliths. Although 93% of nannoplankton species were eradicated at the K-Pg boundary, the severity of the extinction and the pacing of the subsequent recovery was hemispherically asynchronous. In the Southern Hemisphere, extinction rates were lower and recovery assemblages were dominated by previously rare Cretaceous survivors which became regionally incumbent. In contrast, the Northern Hemisphere experienced much higher extinction rates and post-extinction assemblages were dominated by successions of short-lived Paleocene bloom taxa. These high abundance, low diversity “boom-bust” assemblages persisted for at least 400,000 years after the mass extinction event, and are thought to represent ecological experimentation as nannoplankton adapted to a volatile environment. However, the specific environmental and ecological mechanisms which drove switches between dominant bloom taxa are uncertain.

Here, we present calcareous nannoplankton assemblage data in a series of cores from El Kef, Tunisia: the GSSP (Global Boundary Stratotype Section and Point) for the K-Pg boundary. This site samples an outer-shelf/upper slope environment in the paleo-Tethyan Ocean, where sedimentation rates were high. The K-Pg recovery interval at El Kef is therefore expanded, making it possible to examine nannoplankton “boom-bust” successions at incredibly high resolution for at least 2 Myr after the mass extinction event. This multi-proxy study will compare nannoplankton abundance counts to stable isotope (δ¹³C and δ¹⁸O) and biomarker data, and planktic foraminifera, dinoflagellate, and benthic foraminifera abundance counts, in order to determine which ecological and environmental variables were responsible for driving the switches between dominant nannoplankton bloom taxa. Because cyclostratigraphy will be conducted at El Kef, nannoplankton assemblages at this locality will also be correlated to open-ocean sites where environmental and ecological conditions would have been very different.