Gymnosperm flora from the Nirihuau formation (late oligocene-early miocene), RFO negro Province, Argentina

摘要

The Cenozoic paleofloras in the area of San Carlos de Bariloche, Argentina are located mainly along the ?irihuau and Pichileufú rivers, and belong to several stratigraphie units. Of these, the flora of Pico Quemado is situated in the most basal part of the ?irihuau Formation and is probably late Oligocene-early Miocene in age. It is described herein, gymnospermous foliar impressions and compressions of Araucaria nathorstii Dusén (section Araucaria) and an ovuliferous scale of Araucariaceae; the latter constitutes the first evidence of reproductive structures belonging to section Araucaria for the Cenozoic of South America. Foliar impressions and compressions of Podocarpaceae are also present. Among them, the presence of podocarps with bilateral leaves related to Dacrycarpus de Laubenfels, previously known from Eocene outcrops of Chile, Argentina and Antarctica, allows extending their record up to the late Oligocene-early Miocene of Patagonia and relating them with the fossil and extant floras from the Australasian region. The morphology of the studied leaves, as well as their affinities with extant forms, together with the sedimentology, palynology, angiospermous megaflora and presence of freshwater bivalvia, allow suggesting a fluvial-shallow lacustrine depositional setting, developed under temperate to warm-temperate and humid climate.