Abstract
This paper presents new radiometric dating of zircons (IDTIMS U–Pb) from tonsteins interbedded with coal seams from the Candiota coalfield (Rio Grande do Sul State). The ages obtained, 296.9 ± 1.65 Ma and 296 ± 4.2 Ma, are consistent within error and are quite different from a previously published age of 267.1 ± 3.4 Ma. Calibrations of palynostratigraphic data with numerical ages showed that the Candiota coals from the southern Paraná Basin, related to the Protohaploxypinus goraiensis subzone are constrained to the Asselian. Consequently the basal part of the Gondwana sequence in the southern part of the basin must belong to the Carboniferous–Permian boundary and not to the Sakmarian, as it was previously considered. The new results have far reaching significance for correlations of the Paraná Basin with sequences of the Argentinian Paganzo Basin (302 ± 6 Ma and 288 ± 7 Ma) and also with the Karoo Basin, with the top of the Dwyka tillite (302 ± 3 Ma and 299.2 ± 3.2 Ma) and with the lowermost Ecca Group (288 ± 3 Ma and 289.6 ± 3.8 Ma). This new evidence supports the presence of an active and widespread Upper Carboniferous volcanism in western Gondwana.
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