The Jehol Biota is one of the most representative Cretaceous terrestrial biotas, and provides an important window into the evolution of terrestrial ecosystems. Previous paleoenvironmental reconstructions on the Jehol Biota have focused mainly on its core distributionregion in northern Hebei and western Liaoning, while non-core distribution regions remain poorly studied. The organic-rich shales of the Lower Cretaceous Jiufengshan Formation in the northern Great Xing’an Range yield abundant fossils, providing a valuable archive for elucidating the palaeoenvironmental mechanisms that promoted the flourishing and preservation of the Jehol Biota, as well as the evolution of Early Cretaceous lacustrine ecosystems.
Recently, XUE Yan, a PhD candidate at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), working under the supervision of Professors ZHENG Daran and LI Gang and collaborating with Professor JING Zhenhua from the Chengdu University of Technology, conducted a multi-proxy geochemical investigation on the Jiufengshan Formation at the Shiyoukuangtun section in the Dayangshu Basin, eastern Inner Mongolia. Along with systematic paleontological and comprehensive stratigraphical work, this study integrated stable organic carbon isotope analyses, Rock-Eval pyrolysis, iron speciation, and redox-sensitive trace-element geochemistry to reconstruct the lake ecosystem and bottom-water conditions that prevailed when the Jehol Biota inhabited the basin. It further examined the relationship between organic-matter enrichment and fossil preservation. The results were published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
The Jiufengshan Formation is a classic unit for studying the Jehol Biota, containing the characteristic Eosestheria-Ephemeropsis trisetalis-Lycoptera davidi (“EEL”) assemblage. This study first reports the clam shrimp genus Diestheria in this formation, and assigns the clam shrimp to the Eosestheria-Diestheria assemblage. Together with isotopic age constraints, the paleontological evidence supports the correlation of the Jiufengshan Formation with the Yixian and lower Jiufotang formations in western Liaoning. This indicates that the Dayangshu Basin hosted a lacustrine ecosystem rich in the Jehol Biota, comparable to the basins in the core area.
The Jehol Biota in the Jiufengshan Formation is concentrated mainly in the organic-rich shales, which have an average total organic carbon (TOC) content of approximately 7.75% and thus exhibit good hydrocarbon-generating potential. Rock-Eval results show that the organic matter in these shales is dominated by hydrogen-rich Type I kerogen, indicating that lacustrine algae were an important source. This interpretation is consistent with the C/N ratios and relatively negative δ13Corg values. Iron speciation data and redox-sensitive trace elements further reveal distinctive bottom-water chemistry during intervals of organic-matter enrichment: bottom waters were predominantly anoxic and ferruginous during organic-shale deposition, but oxic to suboxic during mudstone deposition.
On this basis, the research team proposed a “productivity-preservation coupling” model for the Jehol Biota in the Jiufengshan Formation of the Dayangshu Basin. High algal primary productivity sustained thriving lacustrine communities of fishes, insects, and clam shrimps, while delivering large amounts of organic matter to the lake floor and creating favorable conditions for organic-shale generation. Continued microbial degradation of organic matter consumed dissolved oxygen in the bottom waters and promoted the development of anoxia. With limited sulfide availability, ferruginous bottom waters were characterized by the accumulation of Fe2+. This oxygen-depleted setting inhibited aerobic degradation of organic matter and benthic bioturbation, while reactive iron may have further enhanced preservation through organic-matter stabilization and early mineralization.
The above study proposes that high algal productivity supplies organic matter for the ecosystem, whereas ferruginous-anoxic bottom waters promote fossil preservation. Together, these processes generated the organic-rich, fossil-rich lacustrine deposits of the Jiufengshan Formation. This study provides a new geochemical perspective on the expansion, ecological evolution, and exceptional preservation of the Jehol Biota during the Early Cretaceous.
This research was supported by the National Natural Science Foundation of China and the Strategic Priority Research Program of the Chinese Academy of Sciences (Category B).
Reference: Xue, Y., Jing, Z.H.*, Teng, X., Zhang, X., Liu, P.H., Song, S.Y., Fang, R., Li, G., Zheng, D.R.*, 2026. Biodiversity and paleoenvironmental reconstruction of the Jehol Biota in the Jiufengshan Formation of eastern Inner Mongolia, northeastern China. Palaeogeography, Palaeoclimatology, Palaeoecology, 700, 114111.https://doi.org/10.1016/j.palaeo.2026.114111.
Fig.1 Conceptual model for flourishing and preservation of Jehol Biota in Jiufengshan Formation of Shiyoukuangtun section.
Fig.2 Fossil clam shrimp from Jiufengshan Formation of Shiyoukuangtun section.
Fig.3 Changes in water-column redox conditions recorded in Jiufengshan Formation of Shiyoukuangtun section.
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