Permian floras fromCarapacha Basin, central Argentina. Description and importance

Abstract

This paper completes the taxonomic description of the recently discovered Permian “ Glossopteris”taphofloras from Carapacha Basin and compares its entire paleofloristic assemblage with other known Permian plant associations from Argentina. Carapacha Basin was a halfgraben located in the southern region of La Pampa province (central Argentina) that received fluvial/lacustrine sediments from Early Permian to Late Permian times. On the basis of their Glossopteris leaves, two paleofloristic associations are recognized. The older Estancia San Roberto (ESR) association contains leaves with scarce and narrow anostomoses, whereas the younger Curacó River (CR) association has glossopterid leaves with distinct and complex anastomoses, plus glossopterid fructifications. In both taphofloras sphenopsid stems, ferns, and petrified gymnosperm wood were also identified. Curacó River association -described in this paper- includes eleven types of glossopterid leaves, as follows: Gangamopteris sp., Glossopteris browniana Brongniart,, 1828, G. damudica Feistmantel,, 1881, G. cf. G. euryneura Maheshwari,, 1965, G. pampeana Melchor & Césari nov. sp., G. argentina Archangelsky,, 1958b, G. wilsonii (Seward) Archangelsky et al. 1981, G. communis Feistmantel,, 1876, G. tortuosa Zeiller,, 1902, G. cf. G. pandurata Pant & Gupta,, 1971, and Glossopteris sp. From the same association we also describe scale leaves, Dictyopteridium sp., Neomariopteris sp., Phyllotheca sp., and Cordaites sp. The composition of both associations allows to relate them to the Gangamopteris biozone (ESR association) and Dizeugotheca superzone (CR association) of early Early Permian and late Early Permian to Late Permian age, respectively. In particular, the last association has strong affinities with the exuberant flora from La Golondrina Basin (Patagonia). The paleoflora recovered from Carapacha Basin is meaningful because it is a new permian record from a geographic area with intermediate position among basins of northwest and west Argentina, Buenos Aires Province, Patagonia and Malvinas/Falkland Islands. The compositional differences among these paleofloras can be accounted for paleoenvironmental, local geographic and taphonomic factors. Furthermore, its presence does not support the hypothesis of allochthony of Patagonia for Permian times.