Paper No. 7
Presentation Time: 8:00 AM-6:00 PM
Biostratigraphic Versus Geochronologic Frameworks in the Early Permian from Paraná Basin
The main biostratigraphic problem of the most of Gondwanan Carboniferous-Permian deposits is the absence of significant chrono-correlating marine faunal elements preventing correlations with the Late Carboniferous and Early Permian international stages. Besides, radiometric data are still scarce and conflictive in the Paleozoic sequences of Gondwana, militating against accurate age calibration of the available biostratigraphic schemes found throughout the super-continent. Thus, correlation with international stratigraphic stages can be considered as difficult and speculative in the most part of the cases. For all these reasons, a stronger geochronologic framework is needed throughout Gondwana in order to enable to get more accurate calibration of regional biostratigraphic schemes with the global time-scale. Recent radiometric zircon ages reported from the Rio Bonito Formation, in southern Paraná Basin, show significant discrepancies when compared one another. The data have been obtained from tonstein layers interbedded with coal seams that belong to same stratigraphic interval within this unit. The absolute ages estimated varies from the Carboniferous/Permian boundary to the early Middle Permian (Rodian), according to one of the well-known geological time-scales frequently used. Consequently, different time intervals can be attributed to the same biozone or fossil assemblage depending of the absolute age chosen. Taking into account these controversial ages, a biostratigraphic point of view is emphasized herein and compared with the geochronologic framework published for the Paraná Basin and neighboring basins from southern South America and southern Africa. Consequently, the radiometric calibration of distinct formal and informal biozones recorded in the Paraná Basin are shown and discussed. In conclusion, the biostratigraphic framework is equally as consistent and robust as geochronologic one and permits a relative accurate inter-basinal or intercontinental correlation.