Mid-Cenozoic vegetation reconstruction based on palynological data from southeastern Santa Cruz province, Argentina

HEREDIA, M. EVELINA; PAEZ, MARTA M.; GUERSTEIN, G. RAQUEL; PARRAS, ANA

Bariloche

Congreso; VI Southern Conection Congress; 2010

The present work is part of a multidisciplinary project including sedimentological data, facies analysis, marine invertebrates and palynology, comprising pollen, spores and organic walled dinoflagellate cyst as well. Based on the terrestrial palynological data we intend to determine the response of the vegetation to the climate changes occurred during the Late Oligocene – Early Miocene in Santa Cruz Province, Argentina. The aim of this study is to analyze the palynological assemblages recoverd from four sections between 49ºS and 50º 30’S. In two of them crops out the Centinela Fm. (latest Oligocene to Lower Miocene in age) at Estancia 25 de Mayo (50º 30’S, 72º 15’W; dated as 22.5 Ma) and La Escondida sections, southwestern Santa Cruz Province. Gran Bajo (49º 31’S, 68º 14’W; dated between 25.9 and 25.3 Ma) and Meseta Chica (49º 31’S, 68º 15’ W) sections allow to characterize San Julián Fm. on the Atlantic coast. All ages are based on 87Sr/86Sr ratios. In this presentation we show the results from both Gran Bajo and Meseta Chica sections where a minimum of 300 palynomorphs were counted in each sample in order to achieve, frequency diagrams and cluster analysis to determine palynological zones. The information from Gran Bajo section indicates that a large humid temperate forest developed towards the end of the Late Oligocene mainly represented by elements belonging to Nothofagaceae, Podocarpaceae and Araucariaceae, together with an incipient herb – shrub vegetation (Proteaceae, Anacardiaceae, Ephedraceae, Caryophyllaceae, Onagraceae, Chloranthaceae, Restionaceae, Asteraceae, Sparganiaceae, Cyperaceae and Poaceae). Furthermore, there is an important pteridophytic diversity (Cyatheaceae, Dicksoniaceae and Blechnaceae) that might have developed as part of the lower layer of the forest. This information is in agreement with a shallow marine environment close to the coast barely influenced by ocean waters. Upwards, in the Meseta Chica section, the elements representing the forest are still dominant though its composition changed as it is shown by the reduction mainly of Phyllocladidites mawsonii and some other arboreal taxa typical of the lower section.