Lenhos fósseis do neógeno da Bacia do Acre, Formação Solimões: Contexto paleoambiental

Abstract

This paper discusses the study of fossil wood collected along the banks of Acre, Furnaia, Juruá, Purus and Moa rivers, located in the outcrops of Solimões Formation (Upper Miocene), Acre Basin. The anatomical and morphological description of the cellular structures was accompanied by inferences about the preservation of the woods constituent elements, aiming to bring together taphonomic data and palaeoenvironmental regional parameters. The results indicate silica as the major component of the fossils, also occurring inclusions of iron oxides. The group of anatomical features includes vessels of medium (100 to 200 μm) to large (≥ 200 μm) diameter, with a predominance of solitary vessels, few vessels per square millimeter and simple perforation plates. The presence of these characters enabled to infer a tropical climate in Acre at the late Miocene. The presence of growth rings and vessels trending to semi-porosity suggests a variation in water availability, which indicates a seasonal climate with a dry season. The palynological record found in the literature indicates a palaeovegetation with the presence of freshwater lakes and tropical marshes. Permanent water bodies (wetlands, shallow lakes) were frequent during the deposition of the Solimões Formation, indicating that the Amazon south-western basin acted as a plane basin, similar to the system of the modern Pantanal, but fed by the Andes. The fossil woods have affinity with the recent botanical families Caesalpinioideae (Fabaceae), Lythraceae and Myrtace, which can be related to this palaeoenvironment.