Multi-Stage Paleoclimatic Evolution of the Early Cretaceous Jehol Biota

The Early Cretaceous Jehol Biota of northeastern China, a remarkable terrestrial lagerstätte, is renowned for its exceptional fossil preservation of diverse organisms, including plants, insects, dinosaurs, birds, and mammals. The Jehol Biota is commonly divided into three stages: JBS I, II, and III. However, detailed paleoclimatic reconstructions across these stages remain scarce. Here we report the distributions and compound-specific carbon isotopes of alkanes from JBS I samples collected in the Sichakou Basin. We then integrate these findings with previous alkane data from JBS II and JBS III to reconstruct secular climate changes. Our results reveal an overall shift towards relatively dry and cool conditions from JBS I to JBS III, with the most arid interval occurring between late JBS II and early JBS III. Specifically, the results are reflected in our proxies as follows: the average chain length of n-alkanes increased, the aquatic plant n-alkane contribution index decreased, the pristane/phytane ratio increased, and the carbon isotopes of n-alkanes showed a positive shift from JBS I to JBS III, with the most pronounced values observed from late JBS II to early JBS III. Quantitative analysis of n-alkane carbon isotope values suggests an estimated average mean annual precipitation of ~1200 mm/yr across these stages, with the minimum values recorded between late JBS II and early JBS III. We suggest that shrinking atmospheric circulation likely drove the reduced precipitation observed in the Jehol Biota region. This study provides a comprehensive paleoclimatic reconstruction for the Jehol period and suggests that major radiation of the Jehol Biota may have occurred under relatively dry and cool conditions.