The Triassic taphoflora of the Paraná Basin, southern Brazil: a biostratigraphical approach

Abstract

A Triassic taphoflora identified in the Central Region of the State of Rio Grande do Sul, southern Brazil, represents an important biostratigraphical stage in the palæofloristic succession of the Paraná Basin. A megafloristic association composed of compressed leaves, fronds and seeds of a ‘ Dicroidium Flora’ shows a predominance of the Dicroidium genus, with several species and other important taxa like Neocalamites sp., Cladophlebis sp., Tetraptilon aff. heteromerum, Ginkgoites antarctica, Sphenobaiera sp., Podozamites sp., Nilssonia sp., Pteruchus sp. and Carpolithus sp. Taking into account the stratigraphical distribution of different species of the Dicroidium genus, a biostratigraphical framework was established. Considering that the recognition of this ‘ Dicroidium Flora’ was based on limited outcrops belonging to one lithostratiphical level (Santa Maria Formation — Passo das Tropas Facies), it was impossible to established a formal biostratigraphical zonation. Instead, at the present time, an informal floristic interval, named the ‘ Dicroidium odontopteroides Flora’, is proposed (Late Anisian to Late Ladinian, Middle Triassic). An ‘ Araucarioxylon Flora’ composed of secondary woods of the Araucarioxylon type and stems of Rhexoxylon brasiliensis was also identified several km apart. The compressed fossils of the ‘ Dicroidium Flora’ and the petrified stems of the ‘ Araucarioxylon Flora’ could represent different but contemporaneous communities corresponding to fluvial-lacustrine environments.