Biozona de Intervalo

BALARINO, M.L. Y GUTIÉRREZ, P.R.

Léxico Estratigráfico de la Argentina. Volumen VI. Carbonífero

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2008; p. 77 - 78

We suggest the use of this new zone for a plant assemblage found in several localities, showing intermediate aspects between zones NBG (véase) and Gangampteris. Originally, it was defined as a floral age (or stage) TRAMPEADERSENSE -véase- (Archangelsky & Arrondo in Archangelsky 1971). Later, it was considered a possible ecofacies within the NBG zone (Archangelsky & Azcuy 1985). Recent work by different authors suggests that a gradual change of assemblages took place during the latest Carboniferous (possibly Stephanian) in Paganzo and Calingasta-Uspallata basins, underscoring a transitional nature of plant evolution as recorded in several sedimentary sequences. (This gradual change coincides with the controvertial C-P boundary). The Interval zone contains exclusive taxa, like Cornucarpus patagonicus and Krauselcladus argentinus; other characteristic species, exclusive to the zone but known elsewhere in a different stratigraphic position are Asterotheca piatnitzkyi and Alloiopteris sp. Severalspecies become extinct in this unit: Bergiopteris insignis, Botrychiopsis weissiana, Ginkgophyllum diazii, Malanzania nana and Cordaites riojanus, while others have their first record, i.e. Botryochiopsis plantiana, Paranocladus? fallax, Samaropsis spp. and Pecopteris sp. The first record of new plant groups (conifers) and incomers from more temperature to warm climates (pecopterids) characterize the Interval zone.