Procesos gravitacionales-fluviales y preservación de vegetación boscosa en un área volcánica: Formación Rancahué (Oligoceno), Andes neuquinos, Argentina

Reconstruction of a fossil forest reveals details of the palaeoecology, palaeoenvironments and climatic conditions in the late Oligocene of South America

“…Similar values are observed in forests located to the NE of Valdivia (Chile) whose main species are coigüe (N. dombeyi), raulí (Nothofagus alpina), mañio (S. conspicua) and tepa (L. philippiana) (Burschel et al, 1976). Therefore, these extant old forests are good analogues to the fossil forest described here, which grew in an Oligocene volcanic setting close to the Aluminé locality (see more detail in Spalletti et al, 2013).…”

“…In this area, detailed sections of the sedimentary succession were measured and described at bed scale (Fig. 3), and cross-sections depicting the distribution and geometry of the sedimentary units constructed (Spalletti et al, 2013).…”

“…In the studied area, the Rancahué Formation is characterised by three facies associations that represent different accumulation conditions in a fluvial/alluvial environment under important volcanic input (Spalletti et al, 2013). Facies association A is characterised by coarsegrained clast-and matrix-supported conglomerates composed of basaltic cobbles and boulders, interpreted as deposited in subaerial talus and foot-talus slopes by debris floods, hyperconcentrated flows, avalanches, landslides and debris flows.…”

“…Facies association C consists of massive and faintly laminated siltstones and mudstones. These are interpreted as accumulated from suspension fallout in subaerial and subaqueous environments, with periodic contribution of ash falls (Spalletti et al, 2013). Paleosols were formed in fine-grained tefra, essentially composed of volcanic glass shards with clay minerals, minute organic debris and amorphous particles.…”

“…The Oligocene Patagonian wood record includes members of the Araucariaceae, Podocarpaceae (Conwentz, 1885;Gothan, 1908;Pujana, 2008), Cupressaceae (Conwentz, 1885), Nothofagaceae (see review of Poole, 2002;Pujana, 2007Pujana, , 2009b, Proteaceae, Atherospermataceae, Myrtaceae, Anacardiaceae, Leguminosae and Rosaceae families (Pujana, 2007(Pujana, , 2008(Pujana, , 2009a. This record of in situ Oligocene petrified forests is exceptional in southern South America and its occurrence has contributed significantly to our understanding of past ecosystems (Brea et al, 2007(Brea et al, , 2009 and palaeoenvironments in the Aluminé Basin (Spalletti et al, 2013).…”