Early Miocene climate estimations in Patagonia: The case of Pico Quemado, Ñirihuau Formation (Lower-Middle Miocene)

Abstract

The climate during the early Neogene in Patagonia is characterized by the increase of the average temperatures until the mid-Miocene Climatic Optimum. However, the terrestrial paleoclimate of southern South America during this period is unclear. Therefore, a physiognomic analysis on the Pico Quemado (Ñirihuau Formation, lower-middle Miocene) megaflora was realized. Three types of analyses were performed: 1) Leaf Margin Analysis (LMA); 2) Leaf Area Analysis (LAA); and 3) a CLAMP analysis (Climate Leaf Analysis Multivariate Program) with two different dataset. The LMA and CLAMP predicted an estimated a Mean Annual Temperature of 10.4 ± 2.1 °C, 8.5 ± 2.1 °C and 7.2 ± 1.4 respectively. The estimations of Mean Annual Precipitation were of 123.7 ± 21.2 cm. Through the CCA, other parameters were estimated, i. e. Cold Mean Month Temperature (−3.3 ± 3.8 °C, 1.6 ± 1.6 °C); Warm Mean Month Temperature (17.4 ± 3.3 °C; 14.1 ± 1.2 °C); Mean Growing Season Precipitation (121.9 ± 42.6 cm; 78.1 ± 42.6 cm); Precipitation of the Three Consecutive Wettest Months (116.2 ± 15.3 cm; 88.5 ± 15.3 cm); and Precipitation of the Three Consecutive Driest Months (40.2 ± 19.8 cm; 54.1 ± 19.8 cm). From these results, the Pico Quemado megaflora can be characterized as having a cool temperate climate, with moderate precipitations and the development of bi-seasonality. The obtained estimations are concordant with previous morphological studies in Pico Quemado, which had proposed the same climate conditions. However, these results are inconsistent compared to other studies of early Neogene Southern Hemisphere that suggest that the climate could be warmer. This difference might be due to the few studies of climatic estimations during the early Neogene in Patagonia, precluding detailed comparisons. In conclusion, Pico Quemado paleoflora exhibits unique climatic conditions, and also floral compositions, as suggested in previous works and here corroborated. The study realized constitutes the first climatic estimations for an Argentinean megaflora developed during the Neogene.