Provenance and paleogeography of the Southern Paraná Basin : geochemistry and U\\Pb zircon geochronology of the Carboniferous-Permian transition.

Abstract

The Carboniferous-Permian transition of the intracratonic Paraná Basin (S Brazil) includes important evidence of the climate change, tectonics, and paleogeographic configuration of SW Gondwana. During this period, the Late Paleozoic Ice Age (LPIA) was in its final phase in the Paraná Basin, producing a temperate-tropical climate through the transition to the Permian. UPb laser ablation ICP-MS detrital zircon dates and whole-rock geochemistry of rocks from the upper Itararé Group (Carboniferous) and the lowermost Rio Bonito Formation (Early Permian) in the southern Paraná Basin are determined to characterize the sedimentary-dispersal patterns of the source area and glacial paleoflow. Geochemistry proxies suggest that the studied units experienced different degrees of weathering, with the Itararé Group's units forming in an arid environment. The overlying Rio Bonito Formation's units were deposited under hotter and more humid climate conditions. The Late Carboniferous to Early Permian units showed similar zircon-age distribution patterns, with a Neoproterozoic main peak from the Uruguayan Sul-Riograndese Shield. A lack of Mesoproterozoic sources in the studied samples indicates that this area of the Paraná Basin probably did not receive sediments from the African side during the Late Carboniferous as previously described. This result suggests a more complex system in which ice caps and small ice sheets dominated the glacial environment during the Late Carboniferous in this segment of SW Gondwana.