A new tonstein occurrence in the eastern Paraná Basin associated with the Figueira coalfield (Paraná, Brazil): Palynostratigraphy and U-Pb radiometric dating integration

Abstract

Tonsteins are layers generated from volcanic ash fall and constitute an important chronostratigraphic marker that allows the correlation between layers in and out of the sedimentary basin, as well as the calibration of biostratigraphic frameworks. In this contribution a new occurrence of tonstein is reported associated with the coal seams in Paraná state, in the Paraná Basin, and it was used as a tie point in local and intra-Gondwanan palynostratigraphy. First, the volcanic origin of the layer was attested by using methods as petrography, SEM and XRD. Then, the layer was dated by U-Pb zircon with LA-ICP-MS method, obtaining an age of 286 ± 3 Ma which corresponds to the Artinskian (middle Cisuralian), thus the layers are correlated with the coal seam from Faxinal coalfield. However, the palynostratigraphic position for the studied interval was at the Protohaploxypinus goraiensis Subzone (lower Vittatina costabilis Zone), due to the presence of Protohaploxypinus goraiensis, Illinites unicus, Vittatina, and Converrucosisporites confluens while palynostratigraphy of Faxinal places it at the Hamiapollenites karooensis Subzone (upper Vittatina costabilis Zone). Therefore, one possible explanation is that the boundary between the subzones of Vittatina costabilis Zone is younger on the studied site than in the rest of the basin.