Maastrichtian stratigraphy of Antarctica

Application of a strontium isotope stratigraphy to the Late Cretaceous sedimentary succession of Antarctica has provided the impetus for a comprehensive stratigraphical revision of the terminal Maastrichtian Stage. Both the base and top of the stage have been defined by strontium isotope dates, and a series of inter-island correlations within the James Ross Island region (north-eastern Antarctic Peninsula) indicates the presence of a 1150-m-thick sequence of fine-grained clastic sedimentary rocks. A prolific ammonite fauna has been used to define four informal biozones, and a provisional Early-Late Maastrichtian boundary established. Two regional unconformities have been identified within the Antarctic Maastrichtian succession, dated at approximately 70 Ma and 68 Ma, respectively. Both these stratigraphical hiatuses may be linked to global sea-level regressions, as could the presence of an extremely shallow-water fauna in the 65.4–65.3 Ma time interval. There is certainly evidence of low shallow-marine palaeotemperatures in the Antarctic Peninsula throughout the Maastrichtian and these three regressions may be glacioeustatic in origin. Antarctic Maastrichtian marine faunas are clearly of comparatively high abundance but low taxonomic diversity. There is evidence of a number of key taxonomic groups being preferentially excluded from the high southern latitudes through the Campanian–Maastrichtian by the dual controls of low temperature and decreasing water depth.