Paleobiological significance of the James Ross Basin.

The extensive Late Mesozoic–Early Cenozoic sedimentary succession exposed within the James Ross Basin, Antarctica has huge potential to enhance paleobiological investigations into both the marine and terrestrial fossil records. In excess of 7 km in total thickness and spanning the Early Cretaceous (Aptian)–Late Eocene in age, it represents an invaluable high-latitude (~65°S) site for comparison with lower latitude, tropical ones in an essentially greenhouse world. The Early Cretaceous (Aptian–Albian) sequence is deep-water but there are indications of shallowing to inner shelf depths in both the Turonian and Coniacian stages. The first prolific shallow-water marine fauna occurs in the Santonian–Campanian Santa Marta Formation and this is followed by repeated occurrences through the later Campanian, Maastrichtian, Danian and Middle Eocene (Lutetian). In this study an attempt has been made to compare these Antarctic faunas directly with the well-known ones of the same age from the US Gulf Coast. Detailed comparisons made for three time slices, Late Maastrichtian, Danian and Middle Eocene, indicate that the Antarctic is characterised by both low taxonomic diversity and high levels of endemism. The James Ross Basin is providing important evidence to indicate that the highest southern latitudes have always been characterised by a distinctive temperate biota, even on a pre-glacial Earth. The roots of at least some elements of the modern Southern Ocean biota can be traced back to a Late Mesozoic–Early Cenozoic austral realm.