New age constraints on the Lower Cretaceous Jiufengshan Formation of Inner Mongolia, China and their implications for the spatiotemporal development of the Jehol Biota

The Jehol Biota comprises significant fossils that help to elucidate the evolution of Early Cretaceous terrestrial ecosystems. In this paper, we provide three new zircon U-Pb age constraints (124.3 & PLUSMN; 1.5 Ma, 124.9 & PLUSMN; 1.6 Ma, and 121.5 & PLUSMN; 1.4 Ma) from the base to the top of the Jiufengshan Formation (Xinganling Group) at the Naketa section in the north Great Xing'an Range of eastern Inner Mongolia, China, within a succession that contains the typical Eosestheria-Ephemeropsis trisetalis-Lycoptera davidi (EEL) assemblage of the Jehol Biota. Combined biostratigraphic and radio-isotopic dating suggests that the Jiufengshan Formation in the Naketa section corresponds to the upper part of the Yixian Formation and the lower part of the Jiufotang Formation, making it Barremian to earliest Aptian in age. Our findings allow us to test a widely accepted hypothesis about the migration and radiation of the Jehol Biota, and show that these organisms preserved within the lower part of the Jiufengshan Formation reached the Naketa area during the second and third evolutionary stages. The preservation of Jehol elements in the Naketa section provides valuable clues regarding the evolutionary history of the Jehol Biota and its spatiotemporal development. Furthermore, our study allows us to explore possible links between evolutionary processes and concurrent tectonism in the North China Craton, as the timing of this Jehol migration occurred when the tectonic setting changed from a compressional to an extensional regime.