New age constraints on the early Jehol Biota of Luanping, northeastern China

Abstract The Jehol Biota sensu stricto consists of numerous exceptionally well preserved fossils typically found in the Yixian and Jiufotang formations of northeastern China. These respectively record the middle and late evolutionary stages of the Jehol Biota. The Dabeigou Formation appears in outcrop in Luanping, Chengde, northern Hebei and hosts the early Jehol Biota as documented by the presence of representative Ephemeropsis trisetalis (insect) and Peipiaosteus (fish) fossils. Although biostratigraphic constraints have been established for this formation, uncertainties persist regarding its exact age range and especially its time of inception. The present study describes U-Pb geochronological results which date the Zhangjiakou and Dabeigou formations found in the Yushuxia outcrop of Luanping. Results indicate an upper age constraint of 134.8 Ma for the Zhangjiakou Formation and an overall age range of 134.5–129.3 Ma for the Dabeigou Formation. Integrated analysis of biostratigraphy and geochronology indicate that the Dabeigou Formation and the Sichakou Sedimentary Member of the Huajiying Formation in Fengning, Chengde, northern Hebei, generally correlate with Members 2 and 3 of the Dabeigou Formation in Luanping. Previous studies do not reach in consistent of which formation contains the early evolutionary stages of the Jehol Biota. This study supports that the Dabeigou Formation in Luanping bears the early Jehol Biota.