Descrição de novos espécimes de folhas fósseis provenientes da Bacia do Abunã, Quaternário, Rondônia, Brasil

Abstract

The Sedimentary Basin of Abunã is located near the channel of the Madeira River, in the state of Rondônia - Brazil, and is characterized by a flat relief, resulting from accumulation processes of fluvial sediments along the Quaternary. Within this context, there has been an increase in published works in recent years, reporting the paleoenvironmental and paleoclimatic characteristics of this region. The present study aims to describe the leaf morphology and taxonomic recognition of four fossils leaves collected in the outcrop Stake 93 (09 ° 16'25.05 "S; 64 ° 38'16.87" W) at the construction site of the Hydroelectric Power Plant Jirau (UHE). The samples were submitted to a previous curatorial preparation and were numbered and packed with PVC film and placed in paraffin molds. The date for the layer from which the material analyzed here has been presented, has already been presented in previous works, presenting an age of ± 43,500 A.P. The specimens were photographed and the venation patterns redesigned. The taxonomic recognition was made based on the key of identification of angiosperms following the detail proposed by the Manual of Leaf Architecture, being also that were compared with representatives of the current Amazonian flora through consultation the specific bibliography. From the presence of typical elements it was possible to record the occurrence of two families: Chrysobalanaceae, primary vein of pinnate and secondary semicraspedodromous, opposite venation and alternating in the same leaf, determining the registration of a new morphogen and morphospecies, Temporarily referred to as of Morphotype 02; Calophyllaceae, with numerous secondary venations, parallel to each other, filling the entire foliar field, defining the description of a new morphospecies for the genus Calophyllum, here temporarily termed Calophyllum sp1. The presence of these families indicates similarity with the flora currently established in the region, making possible the inference of a paleoclimate very similar to the existing one. Thus, this finding corroborates previous studies that postulate the presence of a typically tropical forest already established since at least ± 43,500 years, corresponding to the Late Pleistocene.