Tentative Correlation Between Floral Succession In the Brazilian Paraná Basin and Global Climatic Changes during the Permian Times

The floral succession from Permian strata of the Paraná Basin suggest a reasonable correlation between global climatic changes based on paleo-pCO2 and relative sea-level curves and floristic and environmental changes occurred in this basin. Recent radiometric zircon ages obtained from two different stratigraphic intervals through the Lower Permian sequence permitted a better correlation with international stages of the geological column. As a result, three distinct floristic changes can be delineated from humid to seasonal arid conditions. The first floral stage or “Peat-forming Stage” overlies stratigraphically few deglaciation cycles containing marine invertebrates associated to Australian “Eurydesma Fauna” dated as Asselian/Early Sakmarian. This stage is characterized by the first appearance of glossopterids which are dominant elements; also Phyllotheca-type sphenopsids, lycopsids, pecopterid ferns and cordaitaleans are locally abundant. They correspond to vegetation that lived under wet conditions in coastal lowlands after Early Permian glacial phase and are directly associated to peat-forming environments recorded in upper Itararé Group and Rio Bonito Formation. The time interval assumed is Middle to Late Sakmarian based on radiometric U-Pb dating. The second floral stage or “Mediterranean Stage” corresponds basically to assemblages recovered from the Irati Formation considered as Late Artinskian by U-Pb ages. Differently from under- and overlying floras, this stage is mainly composed of petrified wood with glossopterid, cordaitalean and conifer alliances. They represent transported logs derived from near-shoreline vegetation which lived under a warmer wet-dry seasonal climate. The last stage or “Sub-tropical Stage” includes assemblages from Teresina and Rio do Rasto formations assigned to Rodian/Wordian-Wuchiapingian interval based on the biostratigraphic correlation with African sequences. These assemblages are dominated by glossopterids, Sphenophyllum and Schizoneura-type sphenopsids and pecopterid ferns; in the younger deposits, lycopsids are locally abundant. They correspond to vegetation that lived in coastal settings and mixed lacustrine, deltaic and fluvial environments under warm preferentially dry conditions.