DECIPHERING AGE DISPERSION IN HIGH-RESOLUTION CA-TIMS U-PB ZIRCON ANALYSIS: EXAMPLES FROM THE CARBONIFEROUS-PERMIAN PARANÁ AND KAROO BASINS

The late Paleozoic is recognized as a highly dynamic period in Earth’s history, one characterized by large-scale fluctuations in sea-level and inferred changes in glacial ice volume related to atmospheric forcing from pCO2. The Paraná and the Karoo Basins of SW-SC Gondwana record one of the highest fidelity glacial records of the LPIA up to 1,300 Km thick, and laterally extensive glacial deposits forming a combined area of 2.3x10⁶ km². Despite numerous studies, current temporal constraints prohibit the regional correlation of the Paraná Basin glacial and postglacial deposits and the correlation of these deposits with the lithological equivalent in the Karoo Basin. Here we present a new high-resolution stratigraphic framework built using single crystal U-Pb zircon CA-TIMS. Our study highlights some of the achievements of the single crystal CA-TIMS approach, though also highlight some of the challenges faced in age interpretation and methods for mitigation. We show that age dispersion at the >5% level associated with recycled zircons can be screened quickly with LA-ICP-MS. A more complex issue involves interpreting dispersion associated with precision at the percent level and less, which in some cases can be mitigated with more aggressive chemical treatments. Additional sources of dispersion may include mixing of minor amount of core, not identified in the surface screening of zircons via LA-ICP-MS. Regardless of the causes for age dispersion, quantitative methods are more robust in extracting depositional ages than subjective data selection, and are currently being developed and refined. Here we will highlight examples that demonstrate advances as well as pitfalls.