New micro- and megafloral records from the upper section of Ñirihuau Formation (middle Miocene), Río Negro Province, Argentina

BECHIS, F.; BARREDA, V. D.; PASSALÍA, M.G.; CAVIGLIA, N.; PANTI, C.

General Roca

Congreso; 11° Congreso de la Asociación Paleontológica Argentina; 2016

Asociación Paleontológica Argentina

New floral records from the upper Ñirihuau Formation, at Tres Alamos section, Río NegroProvince are described. The megafloral assemblage is dominated by angiosperms, havingrecognized at least 16 foliar morphotypes. They consist of nano- to microphyll leaves mostlywith toothed margin. Nothofagaceae is the main component by richness and relativeabundance followed by Myrtaceae and a possible Proteaceae. Lineariform leaves withparallelodromous venation, typically of monocots (Typhaceae?) are also numerous. Amongthe remainder taxa, there are forms comparable to those of extant Berberidaceae andAnacardiaceae. A single fern and conifer branches (Austrocedrus type) have been recognized.A palynological assemblage, from the same megafloral level, is characterized by a relativelylow diversity of taxa. They are dominated by Nothofagus ?fusca? beech (ca. 60 %) andpodocarps (ca. 15 %). Fern spores are subordinated mainly represented by Lophosoriaceae(Lophosoria quadripinnata C.Chr., 1920), possible Blechnaceae, and Pteridaceae (Pteristype). Herbaceous angiosperms of the Onagraceae, Malvaceae, Asteraceae, and Gunneraceae77occur in trace amounts as well as swamp families of the Typhaceae. Woody angiospermsrelated to Winteraceae (Drymis type), Proteaceae and Myrtaceae are present but in lowfrequencies (ca. 1 %). Brackish to fresh-water algae (Botryoccocus Kützing, 1849) are alsorecorded through the section. By their taxonomic composition, with dominance ofNothofagaceae (leaves and pollen) and the physiognomic leaf features, this assemblage can becharacterized as a ?Subantarctic paleoflora?. The occurrence of the pollen markersGlencopollis ornatus Pocknall and Mildenhall 1984, Baumannipollis chubutensis Barreda,1993 and Tubulifloridites antipodica Cookson, 1947, supports the middle Miocene agedetermined by radiometric data