Yehli Fm

The type section of the Yehli Formation is the Changshangou section at Zhaogezhuan, Guye District, Tangshan City, Hebei (116°01’49” E，39°59’37” N). The section is remeasured by the Second Regional Regional Geological Survey Team of Heibei Province in 1982. Also, the section is very close to the section measured at Yardangshan by the Xinjiang First Regional Geological Survey Team in 1977. In the type section, the formation is 116.90 m thick. The Yehli Formation was named by Grabau (1924). The name is derived from Yeli Village, Kaiping Township, Tangshan City, northeastern Hebei Province. The Yeli Fm is derived from the Yeli Limestone proposed by Sun Yunzhu (Y.C. Sun) and Grabau in 1920. The Yeli Limestone was renamed the Yeli Bed by Xiaopanzhonghong (1940), the Yeli Series by Wang Yu et al. (1954) and the Yeli Fm by Zhang (1962).

Synonym: (冶里组)（寒武系部分）; Yeli Formation (spelling)

The Yehli Formation is principally a carbonate sequence of gray thick-bedded limestone and argillaceous limestone intercalated with edgewise limestone and yellowish green shale. Lower part consists of thick-bedded leopard micritic limestone with pyrite nodules and crystal casts. Middle part consists of grey argillaceous ribbon limestone intercalated with thin-bedded limestone and edgewise conglomerate. Upper part consisting of grey, medium-bedded argillaceous limestone, intercalated with edgewise conglomerate and dark green shale being about 10 to 20 cm in thickness. In the type area, the Yeli Fm is 150 m thick.

An interval of about 50 m at the base of the Yehli Formation yields trilobites Pseudokoldinioidia [=Missisquoia] perpetis (Zhou & Zhang); Yosimuraspis magezhuangensis (Zhou), Y. longa Zhou & Zhang, graptolites Dictyonema ex.gr. flabelliforme Eichward, Callograptus chrysanthemoides Lin, and conodonts Cordylodus intermedius Furnish. In Tangshan area, the Yeli Fm includes graptolite Rhabdinopora flabelliformis zone, Callograptus taitzehoensis zone, Adelograptus-Clonograptus zone; trilobite Yosimuraspis zone, Wanliangtingia zone and Asaphellus trinodosus zone; conodont Cordylodus lindstromi zone, Chosonodina herfurthi-Cordylodus angulatus zone and Glyptoconus quadraplicatus zone, in ascending order (An et al., 1983, 1990), and is roughly equivalent to R. flabelliformis zone to Adelograptus-Clonograptus zone. The graptolite fauna from the Yeli Fm includes R. flabelliformis assemblage, Anisograptus assemblage, Psigraptus assemblage and Adelograptus-Clonograptus assemblage, in ascending order (Lin, 1988; Wang and Erdtmann, 1986; Wang et al., 1992). Sun (1933) and Zhang Wentang(1949) studied and established the graptolite zones. Zhou et al. (1978, 1983) further studied the graptolite zones. An et al. (1983) described the conodonts.

On the detailed study on the Dayangcha section of the Yeli in Huanjiang, Jilin, by Chen et al. (1986, 1988), the boundary between the Yeli Fm and the underlying Cambrian can be considered as one of the best candidates stratotype internationally for the boundary of the Ordovician-Cambrian, and is marked by the first appearance of Cordylodus lindstromi.