Xiguayuan Fm

N. Hebei. The Xiguayuan Formation was erected by the 2^nd Geological Survey Team of Hebei Province in 1975. The type section locates in 3 km to the Luanping County of northern Hebei.

Synonym: In its evolution, it used to refer to the “Jiufotang Fm” (Pang Qiqing, 1984), “Huajiying Fm” (Wang Si’en, 1990).

[Figure: Type section of Xiguayuan Formation between Liying and Xigayuan, Luanping County of Hebei Province]

[Figure: Measured section of Xiguayuan Formation]

The Huajiying Fm (= Xiguayuan Fm in this Lexicon) mainly comprises fluvio-lacustrine and lacustrine siltstones interbedded with numerous layers of tuffs and tuffaceous clastic rocks. Key specimens of the Early Jehol Biota were preserved in great fidelity in the lacustrine shales of the Huajiying Formation.

"Huajiying Fm (= Xiguayuan Fm), the lowest Jehol fossil-bearing deposits in northern China, … Huajiying Formation of the Sichakou Basin in northern Hebei Province, northern China contains key vertebrate taxa of the early Jehol Biota, e.g., Protopteryx fengningensis, Archaeornithura meemannae, Peipiaosteus fengningensis, and Eoconfuciusornis zhengi. This formation arguably documents the second-oldest bird-bearing horizon, producing the oldest fossil records of the two major Mesozoic avian groups Enantiornithes and Ornithuromorpha." (Saihong Yang et al., 2020, "The appearance and duration of the Jehol Biota: Constraint from SIMS U-Pb zircon dating for the Huajiying Formation in northern China", Proc. Nat. Acad. Sci. USA, 117: 14299-14305).