BIOGEOGRAPHY OF LATE CRETACEOUS PLANKTONIC FORAMINIFERA AT SOUTHERN HIGH PALEOLATITUDES: THE COMPLEX INTERPLAY BETWEEN CLIMATE AND BIOTIC INTERACTIONS (Invited Presentation)

Late Cretaceous paleotemperature estimates reveal a similar trend at low and high latitudes, with a warming phase from the Albian to the Cenomanian followed by a hot greenhouse interval that spans the Turonian to Santonian and then a progressive cooling phase during the Campanian through Maastrichtian. Coincident with the hothouse interval, planktonic foraminifera underwent major changes, marked by species diversification among oligotrophic taxa in the Turonian-Coniacian and by the appearance of oligotrophic and meso-eutrophic taxa in the Coniacian-Santonian, while the hothouse to coldhouse transition in the Santonian–early Campanian is characterized by few extinctions.

We present quantitative assemblage data of Turonian-Maastrichtian planktonic foraminifera from ODP Hole 700B (Northeast Georgia Rise), Hole 762C (Exmouth Plateau), Hole 1138A (Kerguelen Plateau) and Hole 690C (Maud Rise). Sites studied were located between paleolatitude 47° and 65°S in the southern South Atlantic and Indian Ocean where any change in vertical gradients and surface water temperatures of the circum-Antarctic region were registered.

The paleolatitudinal position of the biogeographic boundaries are extrapolated by plotting eco- morphogroup diversity (shallow/deep dwellers, eutrophic/oligotrophic, unkeeled/keeled). Biogeographic distribution patterns reveal that the highest paleotemperatures of the Turonian-Santonian coincide with the broadest expansion of the Tethyan tropical climatic belt. The increase of the low to high latitude temperature gradient correlates to a change in composition of the assemblages in the Santonian, and marks the transition from a dominantly Tethyan influence to a more Transitional affinity throughout the Campanian until the development of the Austral Province in the Maastrichtian. Quantitative assemblage data are used to gain information on the interplay between climate change and biotic interactions through analysis of the degree of endemism and of biotic interchange, and to document sudden abundance increases for individual taxa. Previous recognition of poleward and equatorward migration of species are investigated to evaluate if the suggested diachronism across latitudes is climate-related or is an artifact of the Signor-Lipps effect because of species rarity.