Ice-Hothouse Transition and Palynological Evidences in Brazil

The Gondwanan Late Paleozoic ice-hothouse transition is especially well documented in the Brazilian portion of the Paraná Basin through paleontological and geological data. Spore-pollen associations enclosed in its sedimentary deposits represent diverse plant communities developed on distinct terrestrial ecosystems, which were subject to environmental and climate changes throughout the Pennsylvanian and Permian. The spore-pollen succession of this time span is composed of four palynozones, in ascending stratigraphical order: Ahrensisporites cristatus, Crucisaccites monoletus, Vittatina costabilis, and Lueckisporites virkkiae zones. The associations of the two basal zones are more representative of interglacial and periglacial Pre-Glossopteris floras under a general glacial dominant condition during Pennsylvanian times. Their main components are spores and monosaccate pollen grains, which represent Psilopsida, Lycopsida, Sphenopsida, Filicopsida, and Gymnospermopsida (mainly Cordaitales and early confers-like plants) plant groups. The latest Pennsylvanian/earliest Permian Vittatina costabilis Zone represents the terminal and postglacial Glossopteris Flora, recorded from the uppermost terminal glacial lithostratigraphic unit and better documented in coal beds and associated deposits. Gymnosperm taeniate bisaccate and polyplicate pollen grains become progressively plentiful in this zone, representing new plant groups, mainly linked to Glossopteridales and other gymnosperms; spores are particularly abundant within coal beds. A subsequent semiarid to arid climate phase is denoted by the increasing of not taeniate bisaccate, taeniate mono- and bisaccate, as well as polyplicate and praecolpate pollen grains, which characterize the Lueckisporites virkkiae Zone (late Cisuralian to Guadalupian), demonstrating the dominance of gymnosperm groups, more adapted to environments under water scarcity and warming climate conditions. In general, climatic amelioration in the postglacial phase is associated with an increase in the number of spore-pollen genera. Contrastingly, the beginning of the more arid phase is related to a general decrease in diversity.