Dinoflagellate cysts from Punta del Este and Colorado basins - a proposal of ocean circulation patterns during the Middle to Late Eocene

AMENABAR, CECILIA R.; GUERSTEIN, RAQUEL; DANERS, G.; MORALES, E.

General Roca

Congreso; 11º CONGRESO DE LA ASOCIACIÓN PALEONTOLÓGICA; 2016

Asociació Paleontológica Argentina

The analysis of middle Eocene dinoflagellate cystassemblages from Punta del Este (~36°S, Uruguay) and Colorado (~38°S,Argentina) basins allows to interpret ocean circulation patterns on the SouthAmerican Shelf prior to the deepening of the Drake Passage. The assemblagescontain several endemic-Antarctic taxa, being Enneadocysta dictyostila (Menéndez, 1965) Stover and Williams, 1995emend. Fensome et al., 2006 the mostabundant. This species is the unique member of the endemic assemblageapparently tolerant to warm surface waters. The presence of endemic taxa at SouthPacific mid latitudes has been related to a strong clockwise subpolar gyre favoredby the partial continental blockage of the Tasmanian Gateway and the DrakePassage. The distribution of dinoflagellate cyst assemblages along the SouthAtlantic Ocean Shelf can be explained by a similar mechanism induced by acyclonic subpolar gyre on the South Atlantic Ocean. The western boundarycurrent of this gyre, starting on the west Antarctic continental slope, wouldfollow a similar path to the present Malvinas Current on the Patagonian slope,which introduces cold oceanic waters to the shelf and intensifies the northwardshelf transport. Thus, we speculate that during the middle Eocene the westernboundary current of a proto-Weddell Gyre transported the circum-Antarcticwaters and the endemic taxa northward along the Southwestern Atlantic Shelf.The opening and deepening of both passages and the development of an unconstrainedcircumpolar current during the latest Eocene disrupted the subpolar gyres promotingthe extinction of the endemic species.