Resumen

GUTIERREZ, Pedro Raúl  y  LIMARINO, Carlos Oscar. Sinclinal of Rincón Blanco section (northwest of La Rioja: carboniferous-permian boundary in Northwest argentina. Ameghiniana [online]. 2006, vol.43, n.4, pp.687-703. ISSN 1851-8044.

The finding of palynological associations in the Río del Peñón Formation (Late Carboniferous-Early Permian) is addressed. The fossiliferous section is located in the northern Precordillera, more precisely at the Río Blanco area, situated to the west of Jagüe Town. The Río del Peñón Formation (1,270 m thick) is composed of three members, the lower (729 m thick) bears 21 fossilifeous levels, whereas both the middle (161 m thick) and upper members contain only 2. The lower 16 fossiliferous levels contain palynological associations referred to the Raistrickia densa-Convolutispora muriornata Biozone (DM, C Sub-biozone?). The rest of the palynological levels are here included in the Pakhapites fusus-Vittatina subsaccata Biozone (FS). Moreover, in this paper the stratigraphic relationship among the palynological associations, the megafloristic NBG Biozone and the marine invertebrates assemblages described by previous authors (Tivertonia jachalensis- Streptorhynchus inaequioenatus Biozone) are also identified. The palynological information here presented and previous radiometric ages reported not only by the underlying Punta del Agua Formation (287 and 295 Ma) but also by a riodacitic sill intercalated in the lowermost part of the Río del Peñón Formation (287,8±0,7 Ma) allow to assign the Río del Peñón Formation to the uppermost part of the Upper Carboniferous-Lower Permian. Moreover, the ages of the NBG and DM Biozones are constrained to the beginning of the Permian. Finally the Rincón Blanco section is proposed as a potential stratotype for the boundary between the DM and FS Biozones and thus for the Carboniferous-Permian boundary.

Palabras clave : Argentina; La Rioja; Paleopalynology; Biostratigraphy; Geochronology; Carboniferous-Permian boundary.