DELAYED CALCAREOUS NANNOPLANKTON RECOVERY IN THE K/PG IMPACT CRATER: PRELIMINARY RESULTS FROM IODP-ICDP EXPEDITION 364

New cores recovered from the Chicxulub Impact Crater (Expedition 364, Site M0077) offer an exciting opportunity to examine the recovery of life at “ground zero”. Calcareous nannoplankton, a group of marine autotrophs, were decimated during the mass extinction event. Because these organisms lie near the base of the marine food web, examining their response to this event provides clues as to which ecological and environmental variables were important in facilitating full ecosystem recovery.

The Danian at Site M0077 is represented by indurated limestones with 1-5 mm thick wispy styolites. These sediments reveal that nannoplankton assemblages are dominated by calcareous dinoflagellate cysts and Braarudosphaera. Although these taxa are commonly observed in K/Pg sections during the earliest recovery, the abundance of Braarudosphaera at Site M0077 is unusual. This taxon is often cited as an environmental stress indicator with an ecological preference for cold water and high nutrients. Coastal ocean sites such as Forada and Agost feature similar Braarudosphaera abundances, suggesting this is a shallow water signal.

Cretaceous survivors are rare in the early Danian, and new Paleocene species do not appear consistently until several meters above the boundary. This, coupled with the persistence of Braarudosphaera into the latest Paleocene, indicates stressed environmental conditions for millions of years following the event. Paleocene bloom taxa including Neobiscutum and Prinsius that are typical of Northern Hemisphere recovery assemblages are also observed higher up in the section. With age control, we can therefore determine how delayed nannoplankton recovery was at “ground zero” compared to more distal sites.

In comparison to nannoplankton, earliest Danian assemblages of planktic foraminifera (which occupy a higher trophic level) are relatively normal, suggesting faster recovery rates. This disconnect between ecological strategy and recovery rate indicates the conditions that hindered nannoplankton recovery were specific to this group. These observations suggest that environmental and/or ecological variables such as niche space, temperature, nutrients, and light availability were critical in fully restoring the marine ecosystem.