Dinoflagellate cyst zonation for the middle to upper Eocene in the Austral Basin, southwestern Atlantic Ocean: implications for regional and global correlation?

GONZÁLEZ ESTEBENET, M.S.; ., GUERSTEIN, G.R; RODRÍGUEZ RAISING, M.E; PONCE JUAN JOSE

Geological Magazine

Cambridge University

Año: 2017 vol. 154 p. 1022 - 1036

The well-exposed marine Eocene units from southwestern Patagonia, Argentina, containuseful information for reconstructing regional climate and oceanographic patterns in an area adjacentto the Drake Passage. The aim of this paper is to integrate dinoflagellate cyst data from three sectionsof the southwestern Austral Basin (Río Turbio Formation) to propose a zonation scheme, which can beapplied to other southwestern Atlantic Ocean sites. Assemblages of organic walled dinoflagellate cystshave been analysed in different cropping-out sections and cores, showing the high potential of this fossilgroup as biostratigraphicmarkers. Comparison of dinoflagellate cyst events of the uppermember of theRío Turbio Formation with calibrated biostratigraphic ranges in the Palaeogene South Pacific Oceanallowed us to date and correlate these sedimentary sections. The resulting zonation consists of fourdinoflagellate cyst zones labelled RTF 1 to RTF 4, between the middle Lutetian and late Priabonian. Asa final point, we applied dinoflagellate cyst species with importance as palaeoenvironmental markersto assess long-term climatic and oceanographic evolution for the area. This study shows that theendemic?Antarctic dinoflagellate cyst assemblage is dominant during the middle to late Eocene (RTF1 to RTF 3), while a significant replacement of these taxa by cosmopolitan species characterizes theupper part of the upper member of the Río Turbio Formation (RTF 4). This turnover seems to be aconsequence of changes in the ocean circulation patterns forced by deepening of the southern Atlanticgateways (the Drake Passage and the Tasman Gateway).