New data for palaeoclimatic reconstructions in the upper/middle Uruguay river basin : caesalpinioid Fabaceae woods in the Late Pleistocene

Abstract

The El Palmar Formation is the principal unit deposited during the Late Pleistocene by the Uruguay River in eastern Entre Ríos province, Argentina and north-western Uruguay. The Arroyo Yuquerí fossiliferous locality (c. 31°36′ S, 58°06′ W), part of the El Palmar Formation, is one of the richest sites in fossil woods. This article describes and determines 11 fossil woods, including seven new species closely related to modern Parapiptadenia, Microlobius, Anadenanthera, Pseudopiptadenia (Mimoseae, Fabaceae) and Chloroleucon, Enterolobium and Cedrelinga (Ingeae, Fabaceae). Coexistence approach, nearest living relatives (NLR) methods and mesomorphic and vulnerability indices were used to determine palaeoclimatic conditions. Comparisons of NLR of fossil woods, coupled with other previously identified taxa, suggest that a mature and evergreen woodland was present in the middle Uruguay River Basin during some Pleistocene events (MIS 5a and MIS7, according to absolute datings of the fossiliferous sedimentary unit). This caesalpinoid legume woodland was shaped by an environment with abundant humidity, and the structure of the water conduction system in the studied species was efficient. Finally, the results indicate a more humid and warmer climate than at present in the study area.