Huajiying Formation
The Huajiying Formation is a geological formation in Hebei, People's Republic of China. Known for its fossils including feathered dinosaurs, the age of the formation is uncertain. It may represent an early portion of the Jehol Biota, dating to somewhere in the early Cretaceous or late Jurassic periods. It may correlate with the early Cretaceous Dadianzi Formation and parts of the Yixian Formation, with an age range between 140 and 122 Ma ago. It contains the Qiaotou Member, sometimes treated as a distinct formation. Age and stratigraphy. The Huajiying Formation contains the following members, in order from  youngest to oldest: The age of the formation is uncertain. Ji and colleagues suggested in 2008 that the Qiaotou Member correlates with the Dawangzhangzi bed of the Yixian Formation, dated to ~122 Ma ago by Zhou in 2006. Ji "et al." also suggested that the lower Sichakou Member correlates with the Dadianzi Formation, dated to 140 Ma ago by Tian and colleagues in 2003. Paleobiota. The faunal lists below are based on a survey of the Huajiying Formation by Jin Fan and colleagues in 2008, unless otherwise noted.