BIOGEOGRAPHIC CONSTRAINTS AND PALAEOCEANOGRAPHY OF PLANKTONIC FORAMINIFERA IN THE LATE APTIAN-ALBIAN OF THE NORTHERN SOUTH ATLANTIC

Biogeographic differentiation plays a key-role in constraining the definition of biostratigraphic frameworks, which can be applied to interbasinal and global correlations. Planktonic communities migrate latidudinally following major changes in water masses. In addition, coupled with sea-level changes, local environmental conditions or geogeographic constraints, regional biostratigraphic records are strongly affected, commonly causing the non-representation of the full global range of a biostratigraphically-significant species in every basin.

The asymmetrical distribution of planktonic foraminiferal communities during the Cretaceous reflects, basically, surface to deep-water circulation patterns and paleolatitudinal temperature gradients. As a consequence, the following main patterns are discernible in the characterization of late Aptian-Albian biogeographic pronvinces: · biogeographic patterns were dominated by surface-water latitudinal gradients during the mid-Cretaceous; · the equatorial Tethyan Realm was latitudinally broader during the mid-Cretaceous, with less distinct transitional boundaries between low and high latitudes.

In the late Aptian-Albian northern South Atlantic, the establishment of a narrow epicontinental seaway featuring extensive shallow neritic settings, mesotrophic-eutrophic epipelagic conditions, and a conspicuous oxygen-minimum layer (which expanded periodically across outer shelf areas during the mid-Cretaceous), constrained the widespread development of deep-water dwelling planktonic foraminifera (e.g., Ticinella, Biticinella, Globigerinelloides,and Rotalipora)typical biozonal markers for the Tethyan mid-Cretaceous.