Paleotemperature estimations for the Río Turbio Formation (Santa Cruz, Argentina): a key for understanding the Eocene climate deterioration

CAROLINA PANTI

Mendoza

Congreso; 4 International Palaeontological Congress; 2014

The Eocene was a time of a great climatic turnover, ranging from the warmest global climates during the Early Eocene to cold temperate climates close to the Eocene/Oligocene boundary. Although the analyses of Eocene climates have received great interest during the last years, Middle/Late Eocene climatic conditions in southern South America are not so well constrained. The study of the fossil angiosperms leaves of the Rio Turbio Formation shows a strong reduction of neotropical elements and diversity from the lower towards the upper levels of the Unit. In order to explain this observation, we estimated climatic conditions for this time interval on the bases of the analysis of leaf assemblages preserved in the Río Turbio Formation. The mean annual temperature (MAT) estimation were performed using univariate (LMA) and multivariate (CLAMP) approaches based in the updated version of the newest climatic-leaf data set knows as CLAMP3 SA. The study was carried out at three levels: (1) MAT estimation for the Río Turbio Formation; (2) MAT estimation for the Lower Member and (3) MAT estimation for the Upper Member. For the Río Turbio Formation univariate models indicate a MAT of 17 (±2.1) ºC value slightly below that the one obtained for the Lower Member (18.5 ±2.1 ºC). On the other side, the MAT calculated for the Upper Member show a decrease of about 5ºC (13 ±2.1 ºC). Canonical correspondence analysis shows similar tendencies to those obtained from univariate model with barely high values being more pronounced for the Upper member (16 ºC). This analysis show a decrease in the TMA values during the deposition of the Río Turbio Formation which can be pointing that the climatic conditions became cooler towards the upper levels allowing the development of the subantarctic paleoflora type in the region. The results obtained are consistent with the strong reduction in diversity (up to 30%) that the leaf assemblage shows towards the Upper Member of this unit which is accompanied by the reduction of the neotropical elements and by the increase in the proportion of austral components, mainly represented by Nothofagus.