Mid Paleogene dinoflagellate distribution in the Southwestern Atlantic Ocean: paleoceanographic implications

GUERSTEIN, G.R., DANERS, G. Y FERREIRA, E.

Foz do Iguassu

Congreso; Eos Trans. AGU - 2010 The Meeting of the Americas.; 2010

The Middle Eocene dinoflagellate cyst organic walled assemblages from subtropicalSW Atlantic basins are characterized by well represented species considered members of the so called “Transantarctic Flora” (TF). This flora, including especies of Enneadocysta, Deflandrea, Vozzhennikovia, Spinidinium and Arachnodinium, has been widely recorded in Middle Eocene sections from Southern Hemisphere high latitudes. Moderate to low representativity of Enneadocysta spp. along with other components of the Southern Ocean endemic dinoflagellate flora have been observed in samples from Colorado Basin (~38°S), Argentina, Punta del Este Basin (~36°S), Uruguay and Sergipe Basin (~11°S), Brazil. Previous research developed in the Tasman area has related the presence of this endemic taxa at mid latitudes to the formation of a strong clockwise subpolar gyre (“cold trap”) favoured by the continental blockage of the Tasmanian Gateway. In this paper we propose that the observed dinoflagellate cystdistribution in the SW Atlantic basins can be explained by a similar dynamical mechanism operating close to the present Weddell Gyre. The blockage of the Tasmanian Gateway and a partially-open Drake Passage both contributed to the formation of a strong western-intensified clockwise gyre that may have transported the endemic flora components, mainly represented by Enneadocysta spp., from the Antarctic continent northward along the SW Atlantic Shelf during the Middle – early Late Eocene. During the Late Eocene, the endemic component became less abundant and is partially replaced by more diverse assemblages with bipolar markers of cooler, typical oceanic species and an increased number of heterotrophic protoperidiniaceans. The opening and deepening of the Tasmanian Gateway and Drake Passage and the subsequent development of the ACC during the Oligocene disrupted the subpolar gyre and promote the extinction of the TF species.