New Early to Middle Triassic U–Pb ages from South China: Calibration with ammonoid biochronozones and implications for the timing of the Triassic biotic recovery

摘要: New zircon U–Pb ages are proposed for late Early and Middle Triassic volcanic ash layers from the Luolou Baifeng formations (northwestern Guangxi, South China). These based on analyses of single, thermally annealed chemically abraded zircons. Calibration with ammonoid indicate a 250.6±0.5 Ma age early Spathian Tirolites/Columbites beds, 248.1±0.4 Neopopanoceras haugi Zone, 246.9±0.4 middle Anisian Acrochordiceras hyatti 244.6±0.5 Balatonites shoshonensis Zone. The new dates previously published duration ca. 3 my Spathian, minimal durations 4.5±0.6 6.6+0.7/−0.9 Anisian. in better agreement 252.6±0.2 than 251.4±0.3 Permian–Triassic boundary. also highlight extremely uneven four substages (Griesbachian, Dienerian, Smithian, Spathian), which exceeds half entire Triassic. simplistic assumption equal subdivisions is no longer tenable reconstruction recovery patterns following end Permian mass extinction.