Acritarchs (Group Acritarcha Evitt 1963): general concepts, applications and importance in the biostratigraphic analysis of the Pennsilvanian and Permian interval of the Paraná Basin

Abstract

Despite their uncertain biological affinity, the palynomorphs known as acritarchs are commonly used for biostratigraphic and paleoenvironmental interpretation, particularly of Cambrian to Devonian deposits. This paper presents an updated review of the morphology, classification and stratigraphic distribution of organic- walled microfossils included in this group, as well as their application in Geosciences. Brazilian records from Paleozoic intracratonic basins, especially from Pennsylvanian and Permian deposits of the Paraná Basin, are discussed. The main results of the analysis of this interval in the basin are (i) many of the taxa identified as acritarchs are related to species of prasinophyceae and zygnemataceae algae, and (ii) the record of intervals with abundant association of specimens assigned to the genera Micrhystridium and Veryhachium, which corroborates previous interpretations of a Permian stratigraphic marker of marine nature at the top of the Palermo Formation and base of the Irati Formation. The taxonomic review supports the idea of a worldwide decrease in diversity of these taxa during the Pennsylvanian and Permian interval (phytoplankton blackout), especially considering richness at the generic level, which was much lower than that observed in pre-Carboniferous deposits in Brazil and in other parts of the world.