Astronomical time scale and stratigraphic division constrained by the Milankovitch cycles and SPICE event in the Cambrian of the Xuzhou, Jiangsu Province

The lack of high-precision age constraints for the internal age of the Cambrian in North China has always affected the research and comparison of Cambrian strata worldwide. This study, using magnetic susceptibility data from the Cambrian strata of the Xuzhou area, identifies Milankovitch cycles within the sedimentary strata. By utilizing stable carbon isotope excursion curves, the lower Furongian in the study area was discerned to exhibit a Steptoean positive carbon isotope excursion (SPICE) event, lasting ∼1.6–1.8 Myr, with a peak age constrained to 494.6 ± 2.9 Ma. Using in situ RbSr dating from glauconite grains in the base of the Mantou Formation (Stage 4), the stratigraphic age was constrained to about 513 Ma. By anchoring the identified 405-kyr calibration time series to these two ages, a relatively high-resolution astronomical time scale was constructed. The results indicate that the Cambrian Stage 4 to early Stage 10 in the Xuzhou area of North China spans from 512.30 ± 2.9 Ma to 490.03 ± 2.9 Ma, with a duration of 22.27 ± 0.2 Myr. Specifically, the basal ages of the Mantou Formation (Series 2 to Miaolingian Series; Stage 4 to early Drumian stage), Zhangxia Formation (Miaolingian to Furongian Series; early Drumian to middle Paibian stage), and Chaomidian Formation (Furongian Series; middle Paibian to early Stage 10) were determined to be 512.30 ± 2.9 Ma, 504.00 ± 2.9 Ma, and 495.74 ± 2.9 Ma, respectively, with durations of 8.30 ± 0.2 Myr, 8.26 ± 0.2 Myr, and 5.71 ± 0.2 Myr. This series of studies not only standardized the classification of lithostratigraphic units in the Xuzhou area, but also provided precise chronological evidence for exploring the climatic-biota-environmental ecological evolution during the Cambrian period.