Paleoclimatic studies based on fossil wood from the Río Leona Formation (Miocene), Santa Cruz, Argentinean Patagonia.

PUJANA, R. R.; RUIZ, D. P.

Congreso; XIV International Palynological Congress - X International Organisation of Palaeobotany Conference.; 2016

Secondary xylem (wood) is a plant tissue that is greatly influenced by external climatic factors like temperature and water availability. Because of this, there are some anatomical characters of fossil wood that enable to do inferences about the climate condition prevailing in the place where the plant lived. Fossil woods are used to estimate the temperature and humidity during the Miocene of Santa Cruz province, Argentina. The studied material comes from the Río Leona Formation and consists of numerous permineralized wood fragments assigned to two conifers and twelve dicots. Petrographic slides and acetate peels were made. To calculate the mean annual temperature (MAT) and the mean annual precipitation (MAP) the equations proposed by Wiemann et al. (1998 and 1999) and the method of coexistence approach (CA) were used. The 17 equations proposed by Wiemann et al. for MAT estimation gave very different values between -1.63 °C and 28°C, showing that these equation are questionable for this case. The CA seems to be a more reliable method, giving a MAT between 8.7 and 11.6 ºC. Wiemann et al. MAP equation gave an unlikely result (5780 mm), instead the CA method gave a MAP between 824 and 2260 mm. Carlquist´s vulnerability and mesomorphy indexes were also calculated, with values of 0.5 and 246.77 respectively. Mean sensibility index varies between 0.08 and 0.54. Based on these results, it can be concluded that the zone had a temperate humid climate, with enough water availability and a marked seasonality influenced by temperature. The variation in the mean sensibility index results shows that the annual growth was not constant and adverse climatic conditions or other factors could have affected it.