Strontium isotope correlation of the basal Maastrichtian Stage in Antarctica to the European and US biostratigraphic schemes

New Sr-87/Sr-86 dating allows the correlation of a marker horizon within th e prolific Late Cretaceous Gunnarites antarcticus faunal assemblage of the Cape Lamb Member, Snow Hill Island Formation, Vega Island, Antarctica with reference sections in Europe and the USA. This horizon is between 81.5 and 96.5 m above the base of the G. antarcticus assemblage. Replicate analysis of six macrofossils from within it yielded a mean value for Sr-87/Sr-86 of 0.707 735 9 +/- 0.000 004 3 (+/- 2 s.e., n=17). This ratio in turn yields a numerical age of 71.0 +/- 0.2 Ma when compared to the standard Sr-87/Sr-86 reference curve for the latest Cretaceous, for which the Campanian-Maastri chtian boundary is placed at 71.3 +/- 0.5 Ma. The value of 0.707 735 9 +/- 0.000 004 3 correlates to a level in the Belemnella lanceolata belemnite Zo ne of the Chalk of northwestern Germany that is 2.5 +/- 5 m beneath the bas e of the overlying B. pseudobtusa Zone land 7.5 m above the Campanian-Maast richtian belemnite boundary, and to an interval within the ammonite zonatio n of the US Western Interior that spans the early Maastrichrian Baculites b aculus and B. eliasi zones, but with a most likely level within the B. elia si Zone. An earliest Maastrichtian age is thereby determined for the Antarc tic horizon, and indeed for the entire G. antarcticus assemblage. Gunnarite s, sensu lato, is an important ammonite marker for the base of the Maastric htian throughout the southern high-latitude regions, and the associated lar ge heteromorph ammonite Diplomoceras may comprise a macrofossil link back t o the Maastrichtian type sections.