HIGH-RESOLUTION CA-TIMS DATING OF THE CARBONIFEROUS—PERMIAN SUCCESSION, PARANá BASIN, BRAZIL

The late Paleozoic Ice Age (LPIA) is Earth’s only record of a CO₂-forced climatic transition from an icehouse to greenhouse state in a vegetated world and in the presence of metazoan life. Despite a refined framework of Gondwanan ice distribution, questions remain about the timing, volume, and synchronicity of high-latitude continental ice and the subsequent deglaciation, ultimately precluding our understanding of linkages between ice volume, sea level, and high- and low-latitude climate. Poor constraints on the timing and synchronicity of glacial and interglacial transitions reflect a lack of accurate high-resolution radioisotopic dates from ice-proximal Carboniferous-Permian successions. In turn, the dearth of dates inhibits robust intra-Gondwana correlations as well as their correlation to lower latitude proxy records. The Rio Bonitio Fm in southern Brazil hosts the oldest non-glaciogenic Carboniferous-Permian deposits of the Paraná Basin, recording the icehouse-to-greenhouse transition. Despite efforts using different geochronological techniques (all U-Pb zircon), over the last two decades, to constrain the timing of these deposits, there are discrepancies in published data sets of the Candiota and Faxinal coals of the Rio Bonito Fm that range from syndeposition of coals to upwards of 30 Ma between deposits. These discrepancies have hindered the correlation of the Candiota and Faxinal sediments and the underlying glacial deposits within the larger Gondwanan framework. Here we present the first U-Pb ages on closed system single crystal zircons using CA-TIMS techniques on Carboniferous-Permian ash deposits of the Paraná Basin. Our results and conclusions are not in agreement with multi-crystal U-Pb TIMS ages as well as SIMS ages that suggest coeval deposition of these coals. In addition preliminary results from a new ash fall ash obtained from core in the North of the Basin are in agreement with the age of the Candiota section in the South and suggest deglaciation was near synchronous across the Paraná Basin, and occurring near the Carboniferous-Permian boundary.