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

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

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 Negro Province are described. The megafloral assemblage is dominated by angiosperms, having recognized at least 16 foliar morphotypes. They consist of nano- to microphyll leaves mostly with toothed margin. Nothofagaceae is the main component by richness and relative abundance followed by Myrtaceae and a possible Proteaceae. Lineariform leaves with parallelodromous venation, typically of monocots (Typhaceae?) are also numerous. Among the remainder taxa, there are forms comparable to those of extant Berberidaceae and Anacardiaceae. A single fern and conifer branches (Austrocedrus type) have been recognized. A palynological assemblage, from the same megafloral level, is characterized by a relatively low diversity of taxa. They are dominated by Nothofagus ?fusca? beech (ca. 60 %) and podocarps (ca. 15 %). Fern spores are subordinated mainly represented by Lophosoriaceae (Lophosoria quadripinnata C.Chr., 1920), possible Blechnaceae, and Pteridaceae (Pteris type). Herbaceous angiosperms of the Onagraceae, Malvaceae, Asteraceae, and Gunneraceae occur in trace amounts as well as swamp families of the Typhaceae. Woody angiosperms related to Winteraceae (Drymis type), Proteaceae and Myrtaceae are present but in low frequencies (ca. 1 %). Brackish to fresh-water algae (Botryoccocus Kützing, 1849) are also recorded through the section. By their taxonomic composition, with dominance of Nothofagaceae (leaves and pollen) and the physiognomic leaf features, this assemblage can be characterized as a ?Subantarctic paleoflora?. The occurrence of the pollen markers Glencopollis ornatus Pocknall and Mildenhall 1984, Baumannipollis chubutensis Barreda, 1993 and Tubulifloridites antipodica Cookson, 1947, supports the middle Miocene age determined by radiometric data.