CONICET | Buscador de Institutos y Recursos Humanos

THE Cerro Piche Graben appears as a notorious depression in the terrain, with an Eastern-Western orientation and a maximum width of 5 km, at the central region of Río Negro province, North Patagonia, Argentina. It extends for 40 km and is limited to the West by the Queupuniyeo ranges and towards the East by the Bajos Hondos Plateau. The stratigraphic relationships between the sedimentary sequence included in the graben and the surrounding units are still reason for discussion and have led to very different interpretations.The first observations in this area were made by Corbella (1973), who recognized a tectonic depression bounded by two subparallel faults that generate a block gravitational structure which he denominated Cerro Piche Graben. This author described a sedimentary sequence circumscribed to the depression composed of conglomerates, sandstones, tuffaceous sandstones, tuffs and claystones with plant remains, that overlays Los Menucos Group (Labudia and Bjerg, 2001) in erosive discordance. Corbella (1973) also mentioned that these outcrops would be correlated with those described near to Los Menucos town, where the Triassic flora is well known (Miranda, 1966; Stipanicic, et al. 1968; Artabe 1985a, b). At the western area of the graben Labudia et al. (1992) described a 100 m thick sedimentary succession composed of eight fining-upward sequences of fanglomerates, conglomerates, greywackes and mudstones. In these rocks, they found a single specimen of the lycophyte Pleuromeia sp., and as a consequence they assigned a Middle-Late Triassic age to these strata, indicating that they coincide to the initial stages of the volcano-sedimentary sequence of Los Menucos Group (Labudia and Bjerg, 2001). New interpretations carried out by Falco et al. (2017) would indicate that these deposits correspond to a sedimentation stage later than Los Menucos Group.The work of Labudia et al. (1992) constitutes so far the only contribution about the Cerro Piche paleofloras. Other materials were found by these authors and assigned with doubts to Pleuromeria sp., but were not published. The purposes of the present paper are: 1. to describe for the first time conifer permineralized woods from sedimentary rocks from Cerro Piche Graben, 2. to revise the plant fossils previously studied by other authors, and 3. to provide new information to resolve disagreements about the age of Cerro Piche sedimentary succession.