Survivorship of Planktonic Foraminifera in the Cretaceous-Palaeogene Transition: A Carbonate Demand Perspective

The Cretaceous-Palaeogene (K-Pg) boundary interval is marked by the mass extinction of more than 50% of the larger more specialized Cretaceous planktic foraminifera, followed by the extinction of ~33% generalist species (short-term survivors) (Keller and Abramovich, 2009 Punekar et al., 2014). Adaptation strategies identified in Cretaceous planktic foraminifera assemblages within this biotic-stress interval include changes in the community structure through shifts in abundance of species and diversity decline. Changes on a species level are reported as inter- and intra- specific dwarfing, malformation and test-wall thinning. Guembelitria cretacea is typically small sized triserial species identified as the only long-term survivor of this event. Through this study, we test the ocean acidification hypothesis of the late Maastrichtian planktic stress by understanding the link between species carbonate demand and their survivorship at the K-Pg boundary.

Four-dimensional X-ray microscopy (FDXRM) scans of pristine Cretaceous planktic morphogroups (the globotruncanids, the rugoglobigerinids and the planoheterohelicids) from pristine late Maastrichtian zone CF4 of DSDP 525A (South Atlantic) yield the most accurate estimation of their respective test calcite volume. The average test weights and the FDXRM reference estimates together suggest that the scaling of calcium carbonate for globotruncanids, planoheterohelicids, rugoglobigerinids, w.r.t. the guembelitrids is 10-269ug, 6-28ug and 9-60ug respectively. This scaling is significant in context of the observed survivorship of these morphogroups across the K-Pg boundary interval. The new results establish a preliminary link between the carbonate demand, ocean acidification related carbonate crisis (especially in the late Maastrichtian biozone CF1) and the survivorship of these morphogroups. However, other detrimental environmental factors in this critical stress interval cannot be ignored.