Cyclostratigraphy of the Terrestrial Permian Linxi Formation in Northeast China

The Middle Permian witnessed major environmental crises and global carbon-cycle perturbation, commonly attributed to the Emeishan large igneous province. To investigate the response of the continental carbon cycle, we analyzed organic carbon isotopes, gamma ray (GR), and magnetic susceptibility (MS) records from lacustrine deposits of the Middle Permian Linxi Formation, based on the TD-1 core and the Taohaiyingzi section in Alukhorqin Banner, Northeast China. Cyclostratigraphic analyses reveal Milankovitch cycles, including the 405-kyr long eccentricity, ~100-kyr short eccentricity, ~35-kyr obliquity, and ~22-kyr precession cycles. An astronomical time scale spanning from 267.2 ± 1.2 Ma to 259.2 ± 1.2 Ma is constructed based on astronomical tuning, carbon isotope stratigraphic correlation between the section and the core, and integration with a published U-Pb zircon age from the section. The obliquity power to total power (O/T) and obliquity amplitude modulation (AM) in the GR and MS records further reveal a ~1.2-Myr long-term obliquity cycle. By comparing with other well-dated carbon isotopic records, we identify globally synchronous carbon cycle perturbations in the Linxi Formation. The organic carbon isotope record from the Linxi Formation was paced by ~1.2-Myr long-term cycles, suggesting that long-term obliquity forcing was involved in the carbon cycle besides the volcanism during the Middle Permian.