PALEOBIOGEOGRAPHY OF CAMPANIAN-MAASTRICHTIAN FORAMINIFERA IN THE SOUTHERN HIGH-LATITUDES

Distributions of planktonic and benthic foraminifera have revealed Antarctic land-sea distributions, oceanic surface gyre configurations, and changes in the configurations of the Tethyan, Transitional, and Austral realms during Campanian-Maastrichtian time. Poleward changes in the diversity of total and keeled planktonic species of the Southern Hemisphere are compared for the early and late Campanian and early and late Maastrichtian. Latitudinal diversity gradients were weakest during the early Campanian and more pronounced during the late Campanian and Maastrichtian. Shallow marine seaways within West Antarctica are suggested by similarity of Late Cretaceous nearshore benthic and open ocean planktonic assemblages from southern high-latitude land and drill sites, and by the occurrence of recycled Cretaceous marine microfossils from Antarctic interior and continental margin localities. Development of a major water mass boundary between cool surface waters south of about 50-degrees-S paleolatitude and warmer surface waters to the north in the South Atlantic and Indian Ocean may have caused biogeographic isolation of Austral Realm assemblages during late Campanian and early Maastrichtian time. Several planktonic foraminifera show significant diachroneity in their latitudinal distributions. Magnetobiostratigraphic data suggest that Abathomphalus mayaroensis migrated from high to low latitudes, whereas Pseudotextularia elegans, Globigerinelloides subcarinatus, Globotruncanella citae, Globotruncanella petaloidea, Globotruncana bulloides, and Globotruncana subcircumnodifer made time-transgressive poleward migrations. The distribution of A. mayaroensis is in agreement with isotopic evidence for late Maastrichtian climatic cooling, while that of P. elegans correlates with a latest Maastrichtian warming event (about 66.8-66.6 Ma). Delayed first occurrences of the other taxa cannot be explained by paleoclimatic factors alone; variations in global eustatic sea-level and orogeny between southern South America and West Antarctica may have also influenced the taxonomic composition of southern high latitude foraminiferal assemblages.