Astronomical tuning of the end-Permian extinction and the Early Triassic Epoch of South China and Germany

- Astrochronology of four sections in South China yields an Early Triassic timescale.
- The end-Permian extinction duration was <40 kyr, and δC13 excursion was <6 kyr.
- The Smithian-Spathian boundary event and the δC13 shift lasted 50 kyr.
- The Induan and Olenekian stage durations are 2.0±0.1 myr and 3.1±0.1 myr.
- Duration of the Early Triassic Epoch is 5.1±0.1 myr.

The timing of the end-Permian mass extinction and subsequent prolonged recovery during the Early Triassic Epoch can be established from astronomically controlled climate cycles recorded in continuous marine sedimentary sections. Astronomical-cycle tuning of spectral gamma-ray logs from biostratigraphically-constrained cyclic stratigraphy through marine sections at Meishan, Chaohu, Daxiakou and Guandao in South China yields an integrated time scale for the Early Triassic, which is consistent with scaling of magnetostratigraphy from climatic cycles in continental deposits of the Germanic Basin. The main marine mass extinction interval at Meishan is constrained to less than 40% of a 100-kyr (kilo-year) cycle (i.e., <40 kyr) and the sharp negative excursion in δC13 is estimated to have lasted <6 kyr. The sharp positive shift in δC13 from −2‰ to 4‰ across the Smithian-Spathian boundary at Chaohu was completed in 50 kyr. The earliest marine reptiles in the Mesozoic at Chaohu that are considered to represent a significant recovery of marine ecosystems did not appear until 4.7 myr (million years) after the end-Permian extinction. The durations of the Griesbachian, Dienerian, Smithian and Spathian substages, including the uncertainty in placement of widely used conodont biostratigraphic datums for their boundaries, are 1.4±0.1, 0.6±0.1, 1.7±0.1 and 1.4±0.1 myr, implying a total span for the Early Triassic of 5.1±0.1 myr. Therefore, relative to an assigned 251.902±0.024 Ma for the Permian-Triassic boundary from the Meishan GSSP, the ages for these substage boundaries are 250.5±0.1 Ma for base Dienerian, 249.9±0.1 Ma for base Smithian (base of Olenekian stage), 248.2±0.1 Ma for base Spathian, and 246.8±0.1 Ma for the base of the Anisian Stage. This astronomical-calibrated timescale provides rates for the recurrent carbon isotope excursions and for trends in sedimentation accumulation through the Early Triassic of studied sections in South China.

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