Early Miocene paleoclimate in southern Patagonia inferred from fossil woods

Abstract

Patagonia has a rich record of fossil woods that are a unique data store of paleoclimatic information. We studied the wood flora recovered from the Río Leona Formation (early Miocene) of southern Patagonia near El Calafate and Río Turbio localities, Santa Cruz Province, Argentina. The fossil wood assemblage was analyzed using various methodologies (anatomy analysis, Vulnerability and Mesomorphic indices, and the Coexistence Approach) to determine paleoclimate variables including mean annual temperature (MAT) and mean annual precipitation (MAP). The anatomy analysis developed by Wiemann et al. (1998, 1999) is based mostly on woods from the Northern Hemisphere. We applied those equations to extant woods from the southernmost region of South America to test their functionality and to compare them with the results obtained from the fossils. These equations gave limited results. Climate signals from fossil woods suggest a microthermal climate for the region with MAT of 8–12 °C and MAP of 80–170 cm/year. In addition, part of the results points towards an environment with water in abundance (i.e., Coexistence Approach and some wood characters influenced by the environment) and other results suggest wood tolerance to hydric stress (i.e., Vulnerability Index, Mesomorphy Index, and wood characters influenced by the environment). These suggest an environment with rainy and dry seasons, which is also supported by the presence of well-marked growth ring boundaries and false rings. These conditions can be found today in central Chile, a region that shares some vegetation elements with the Río Leona Formation and has a Mediterranean climate.