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The Yanliao Biota is notable for producing rare and well-preserved Jurassic vertebrate fossils. Many discoveries in the Bawanggou section, northern Hebei Province have greatly enhanced our knowledge of important vertebrate fossils from the Yanliao Biota, including an arboreal euharamiyidan mammal, maniraptoran theropods, salamanders and pterosaurs. However, lacking of precise dating for the sediments bearing these fossils in the Bawanggou section hampered further understanding of the evolution of this biota. Here we report a chronology based on secondary ion mass spectrometry (SIMS) U-Pb zircon analyses from the Tiaojishan Formation bearing the Yanliao Biota in the Bawanggou section. Three bentonite layers dated to 159.0 ± 1.1 Ma, 159.5 ± 0.8 Ma, and 159.8 ± 0.8 Ma, respectively, were found to be interstratified with the fossil-bearing layer in this area. These data place the Yanliao Biota from Qinglong in the Oxfordian Stage of the Upper Jurassic and provide stringent constraints on vertebrates discovered in the Bawanggou section. Previous biostratigraphic studies and our geochronology show that fossil assemblage in the Bawanggou section is coeval with the Linglongta Biota (late Yanliao Biota) preserved in the Daxishan section (western Liaoning Province). [ABSTRACT FROM AUTHOR]

The Valanginian and Hauterivian stages of the Early Cretaceous are an important time interval for the co-evolution of key vertebrate taxa and flowering angiosperm, as well as for the diversification of dinosaurs and early birds on continents. Among these, the Early Cretaceous Jehol Biota in northern China provides the most valuable fossil evidence. Lower Cretaceous terrestrial strata in the Luanping Basin, northern China, is notable for its continuous sedimentary sequence and preservation of the early Jehol Biota, thus providing crucial evidence for probing into terrestrial ecosystem and paleoclimatic change. In this study, we present a chronology for the Lower Cretaceous Dabeigou and Dadianzi formations based on SIMS U–Pb zircon analyses and previous biostratigraphy and lithostratigraphy from the Zhangjiagou section in the Luanping Basin, northern China. The lowest Dabeigou Formation yields age of 134.1 ± 1.0 Ma, and the upper Dadianzi Formation is constrained to 127.8 Ma, respectively. Previous geochronologic, biostratigraphic studies, and our new geochronology show that the Dabeigou and Dadianzi formations in the Luanping Basin are coeval with the Huajiying Formation in the Sichakou basins, representing the early Jehol Biota evolution, and thus are undoubtedly deposited earlier than the Yixian Formation in western Liaoning. Our findings, combining with the fossil evidence and geochemistry data show that the early evolution of the early stage of the Jehol Biota is constrained to ~132 Ma, characterized by a positive carbon isotope excursion (CIE) and increased biodiversity. The cooler temperature than the underlying sediments attribute to the primary productivity and thus helps the Jehol Biota to thrive. • We report a new chronology for the Lower Cretaceous in the Luanping Basin. • It's consistent with the early Jehol Biota preserves in the Senjitu-Sichakou basins. • Our findings show an age gap between the early–middle Jehol Biota. • Our data allow reconstructing chrono-stratigraphic columns around the Jehol area. • Testing the link between paleoclimatic change and the development of the Jehol Biota. [ABSTRACT FROM AUTHOR]