A NEW HIGH RESOLUTION SULFUR ISOTOPE RECORD ACROSS THE CRETACEOUS–PALEOGENE (K–PG) MASS EXTINCTION EVENT IN ANTARCTICA

The ‘Big Five’ Phanerozoic mass extinctions are often linked to instability in major elemental cycles such as carbon and sulfur, with important implications for understanding geochemical and biotic changes to the Earth system during such events. The Cretaceous–Paleogene (K–Pg) extinction of 66 Ma is the most recent of the ‘Big Five’, but geochemical changes associated with the event and their causes are poorly documented. Several of the hypothesised events around the K–Pg interval such as bolide impact, flood basalt volcanism, anoxia, and increased weathering all have implications for the global sulfur cycle.

To investigate further, we have extracted carbonate-associated-sulfate (CAS: a proxy for marine sulfate isotope composition) from well-preserved molluscan shell material, derived from the abundantly fossiliferous 1000m-thick López de Bertodano Formation of Seymour Island, Antarctica. With a high palaeolatitude of 65°S (identical to the present day), this is one of the most important sites for studying the cause and effects of the K–Pg extinction. Our new CAS isotope data, together with pyrite sulfide isotope data taken from bulk sediment samples, represent the first record of seawater sulphate and sulfur cycle changes across the K–Pg transition.

We show several negative spikes in CAS-δ³⁴S in the Maastrichtian (probably a local palaeoenvironmental signal or an artefact of diagenesis), a gradual increase in seawater δ³⁴S from +15 to +19‰ during the final 1 myr of the Cretaceous, and an enigmatic massive positive sulfur isotope excursion up to ~50‰ in the earliest Paleocene. These intriguing new data which exhibit high rates of variability, could indicate the presence of a smaller global seawater sulphate reservoir during the latest Cretaceous – early Paleocene with important implications for seawater chemistry and geochemical cycling before, during, and after this major mass extinction event.