Radioisotopic Calibration of the Guadalupian (Middle Permian) Series: Review and Updates

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Four high-precision U-Pb CA-IDTIMS dates for the Roadian (lower Guadalupian) of 274.0 ± 0.12 and 273.1 ± 0.1 Ma and for the Wuchiapingian (lower Lopingian) of 260.16 ± 0.39 and 258.14 ± 0.20 Ma were obtained from Permian tuff beds in the periphery of the Okhotsk Massif, N-E Russia. The beds are well constrained within the local lithostratigraphic and regional biostratigraphic framework. Besides regional bivalves and brachiopod faunas, the ammonoid Sverdrupites harkeri occurs close to the recovered Roadian tuffs. This ammonoid provides direct correlation of the tuffs with the Kazanian Stage on the Russian Platform and the Roadian Stage in the Canadian Arctic, where the conodont index species of the Roadian Stage Jinogondolella nankingensis gracilis and Sverdrupites harkeri and other Roadian ammonoids are documented from the Assistant Formation. Our review of the Kungurian-Roadian-Wordian successions in the main well-studied regions suggests that the base of the Roadian Stage should be extended down to approximately 277 Ma and the Roadian-Wordian boundary should be placed at approximately 271 Ma. The new calibration of the Roadian Stage reduces the duration of the enormously long Kungurian Stage from about 10 Myr approximately to 6.0–6.5 Myr. If the proposed calibration is correct, the duration of Guadalupian Series would be almost twice as great as in the previous estimates. Our results also suggest a possible correlation of the P3 alpine glacial event in the Eastern Australia with the Wordian and possible uppermost Roadian Stages. This P3 event corresponds with the disappearance of ammonoids and conodonts in the upper Roadian and Wordian in high-latitudes regions, i.e. N-E Russia, Russian and Canadian Arctic and Australia, perhaps due to extreme cooling of these areas. The new radioisotopic ages in the Okhotsk Massif and surrounding regions improve the numerical calibration of the palynological zonation in the Eastern Australia and provide a direct correlation of the regional biostratigraphic brachiopod and bivalve zonation of N-E Russia with the International Geologic Time Scale. This zonation becomes a solid and reliable regional correlation tool within the vast territory from Taymyr and East Siberia to entire N-E Russia and Transbaikalia.