Response of calcareous nannoplankton to paleoenvironmental changes across the Aptian-Albian transition of the southern South Atlantic (Falkland Plateau, DSDP Site 511)

The late Aptian-early late Albian transition has been characterized by changes in surface water temperature and fertility recognized in several successions at low- and mid-latitudes. Less is known about paleoenvironmental conditions at higher latitudes. In this work we focused on the southern South Atlantic which is a key region to explore the Early Cretaceous oceanography and climate. We studied calcareous nannofossils in the Deep Sea Drilling Project (DSDP) Site 511, drilled on the Falkland Plateau, which yields one of the few sedimentary sequences at southern high-latitudes that records a relatively continuous upper Aptian–Albian sequence. Calcareous nannofossils were investigated to refine the biostratigraphy, reconstruct size variations of Watznaueria barnesiae and Biscutum constans and obtain relative abundances.

The data collected indicate that responded to temperature and fertility fluctuations throughout the studied interval. Specifically, the temperature and nutrient index are suggestive of multiple variations in surface water conditions related either to global perturbations and local changes in the paleoceanography. Relatively lower temperature and fertility characterized the late Aptian. A brief warming phase is associated with the Aptian/Albian boundary followed by a moderate change in the assemblage composition in the early and early late Albian, with abundant cold-water species Repagulum parvidentatum and more abundant surface-water fertility species. Morphometric analyses indicate changes in W. barnesiae and B. constans average size which mostly follow the size patterns identified in the Tethys across the same stratigraphic interval suggestive to reflect a global response to paleoenvironmental changes occurred during this peculiar phase. W. barnesiae size variations are of less amplitude compared to B. constans and occur at different stratigraphic levels. Both species show smaller specimens in the late Aptian compared to the middle-late Aptian. Largest B. constansare identified in the early late Albian. A difference in the total average size of both species is also identified, with average larger specimens occurring in the Falkland compared to the Tethys.