An Oligocene microthermal forest dominated by Nothofagus in Sierra Baguales, Chilean Patagonia: Response to global cooling and tectonic events

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2019-08, Vol.528, p.1-13
• Main Authors: Gutiérrez, Néstor M., Pino, Juan Pablo, Le Roux, Jacobus P., Pedroza, Viviana, Oyarzun, José Luis, Hinojosa, Luis Felipe
• Format: Article
• Language: English
• Subjects: Andean tectonics; Bartonian-Rupelian cooling; Paleoclimate; Río Leona Formation
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2019.04.006

A large fossil leaf assemblage (>3700 specimens) is reported from the Oligocene Río Leona Formation in the Sierra Baguales of Chilean Patagonia. The association comprises 29 species but is dominated by Nothofagus genera, which constitutes 65% of specimens. The collection can be classified as a Mixed Palaeoflora of the Austral-Antarctic association. Stratigraphic analysis of the assemblage indicates a decrease in species diversity and richness over time, which was accompanied by species turnover. Quantitative studies of foliar morphology (CLAMP, Leaf Margin Analysis) indicates cool-to-cold and dry climatic conditions, with a Mean Annual Temperature of 9.2 °C, a relatively high seasonality in temperature and precipitation, and a Mean Annual Precipitation of 931 mm. Nothofagus only became dominant in southeastern Patagonia during the Rupelian, coinciding with a marked global cooling period linked to the initiation of glaciation in Antarctica about 34 Ma. The decrease in precipitation following this event is attributed to the development of a rain shadow to the east of the rising Southern Patagonian Andes, which must have been of the order of 1000 m or more for topographic climate forcing to take effect. This contrasts with the rain shadow development east of the Andes at lower latitudes, which was mainly manifested after the middle Miocene. •Patagonian fossil plant diversity and climate has been integrated with tectonic and climatic events during Oligocene•Nothofagus genus presence in Patagonia during Oligocene, is the first evidence that this lived under microthermal conditions•Are recorded lowest precipitation, temperature and diversity during Cenozoic in Patagonia•The decline diversity and turnover in Patagonia is resulting from the development of a rain shadow during Cenozoic•Temperature and precipitation drop was conditioned by Drake Passage opening, Patagonian Andes uplift and Oligocene cooling