NO SAFER IN THE SOUTH: A SHALLOW MARINE MOLLUSCAN RECORD OF THE CRETACEOUS-PALEOGENE (K-PG) MASS EXTINCTION EVENT IN ANTARCTICA

The Cretaceous–Paleogene (K–Pg) mass extinction of 66 Ma is a key event in Earth history, with extinction of many previously dominant terrestrial and marine groups. There has been much debate about the nature (and causes) of the extinctions and whether higher latitude biota coped better with the crisis. We have examined the highest southern latitude site K–Pg extinction site on Seymour Island, Antarctica (65°S today, and during the Late Cretaceous). Here, an exceptionally thick and abundantly fossiliferous Maastrichtian – Danian (~70 – 65 Ma) section is preserved within a sequence of marine siltstones and sandstones deposited in a back-arc basin setting to the East of the Antarctic Peninsula. We have produced stratigraphic range data for molluscan macrofossil groups (primarily ammonite, bivalve and gastropod molluscs), based on detailed new sedimentary sections and a comprehensive taxonomic reassessment of the fauna from the shallow marine sediments of the ~1000 m thick López de Bertodano Formation exposed on Seymour Island.

Results show an initial increase and subsequent fluctuations in the diversity and richness of the fauna in the lower portion of the López de Bertodano Formation can be related to a combination of regional (sea level and redox) and global (sea level, temperature and climate) palaeoenvironmental changes, before a single rapid extinction event at the K–Pg boundary, clearly recorded in both benthic and nektonic groups. The early Paleocene is dominated by opportunistic and infaunal molluscan taxa, with initial taxonomic and ecological recovery in the Danian taking ~350 kyrs. These new data do not support claims for either a gradual or double extinction pulse in Antarctica, and suggest both the tempo and the taxonomic severity of the extinction, at least in neritic settings, was the same across all latitudes.