Preliminary paleoecological analysis from the flora of El Palmar Formation(Late Pleistocene), Entre Rios, Argentina

Acta geológica lilloana 26 (1): 63–74, 2014

Abstract

The characteristics of the secondary xylem andgrowth rings of 18 fossil woods were analyzed. The fossil specimens come from El PalmarFormation (Late Pleistocene) in the southernmost of the Uruguay Basin (Entre Rios, Argenti-na). According to thermoluminescence dating, this formation was deposited in the Last Inter-glacial (IE5), considered to have been the warmest and wet interval of the late Pleistocene.The Vulnerability (V) and Mesomorphy Indexes (M) were calculated, when it was possible, theanatomical structure was correlated to the environmental conditions. The fossil woods havea Mesomorphic behavior was observed from samples with high vulnerability to processes ofobstructions or apoplexy of vessels. All the fossil specimens showed a value of V superior to1 (21% V = ?10 y 79% V = ?10), low density of vessels per mm² and M values above200. Regarding the presence of the growth rings, 7 fossil species showed growth ring de-marcated by axial parenchyma marginal or terminal and only 3, Laurinoxylon artabeae Brea,Schinopsixylon heckiisensu Brea et al. and Menendoxylon areniensis Lutz, demarcated bythickening and compression of fibers. This preliminary analysis suggests that the flora of thisgeological period was exposed to a high humidity environment, where the efficiency of waterconductivity by plants was the prevailing condition throughout. Deepening the study of thegrowth ring characteristics, the influence of intrinsic factors and the response of the environ-ment will allow us a better understanding of the Pleistocene ecosystems of the UruguayBasin