Definition of Late Cretaceous stage boundaries in Antarctica using strontium isotope stratigraphy

New Sr-87/Sr-86 analyses of macrofossils from 13 key marker horizons on lam es Ross and Vega Islands, Antarctica, allow the integration of the Antarcti c Late Cretaceous succession into the standard biostratigraphic zonation sc hemes of the Northern Hemisphere. The Sr-87/Sr-86 data enable Late Cretaceo us stage boundaries to be physically located with accuracy for the first ti me in a composite Southern Hemisphere reference section and so make the are a one of global importance for documenting Late Cretaceous biotic evolution , particularly radiation and extinction events. The Sr-87/Sr-86 values allo w the stage boundaries of the Turonian/Coniacian, Coniacian/Santonian, Sant onian/Campanian, and Campanian/Maastrichtian, as well as other levels, to b e correlated with both the United Kingdom and United States. These correlat ions show that current stratigraphic ages in Antarctica are too young by as much as a stage. immediate implications of our new ages include the fact t hat Inoceramus madagascariensis, a useful fossil for regional austral corre lation, is shown to he Turonian (probably Late Turonian) in age; the "Mytil oides" africanus species complex is exclusively Late Coniacian in age; both Baculites bailyi and Inoceramus ci. expansus have a Late Coniacian/Early S antonian age range an important heteromorph ammonite assemblage comprising species of Eubostry-choceras, Pseudoxybeloceras, Ainoceras, and Ryugasella is confirmed as ranging from latest Coniacian to very earliest Campanian. A n important new early angiosperm flora is shown to be unequivocally Coniaci an in age. Our strontium isotopic recalibration of ages strengthens the sug gestion that inoceramid bivalves became extinct at southern high latitudes much earlier than they did in the Northern Hemisphere and provides confirma tion that, in Antarctica, belemnites did not persist beyond the: Early Maas trichtian.