Qiaojia Fm

The type section is at Niujiaochang in Qiaojia County, Yunnan. The Qiaojia Fm is derived from the Qiaojia Bed proposed by Guo Wenkuiand Ye Zhizheng during the geological survey on the mineral resources in Ludian and Qiaojia, Yunnan.

In 1965, Southwest Institute of Geology named the Early Ordovician strata in the lower part the “Lower Qiaojia Fm” and the Middle Ordovician strata in the upper part the “Upper Qiaojia Fm” on the basis of the study on fossil assemblages. These two terms were subsequently applied to the strata in southwestern Sichuan and northeastern Yunnan by No.1 Sichuan Team of Regional Geological Survey, and were followed by Lai et al. (1982). Considering the similar lithology of these two formations and the lenticular or variable ferruginous sandstone or limestone which separates these two formations, the present book suggests that the Lower Qiaojia Fm and the Upper Qiaojia Fm had better be merged. As the Lower Qiaojia Fm and Upper Qiaojia Fm have been widely accepted for long time, they are taken here as two lithological members.

Synonym: (巧家组）

The Qiaojia Fm is divided into two members. Lower member, equivalent to the previously defined Lower Qiaojia Fm, is 30-100 m thick, and is represented by a lower part of dark gray thin- to thick-bedded medium- to fine-grained sandstone intercalated with shale and limestone, and an upper part of limestone intercalated with mudstone. Upper member, equivalent to the previously defined Upper Qiaojia Fm, is 10-50 m thick, and is dominated by the medium-bedded argillaceous limestone, with shale in the upper part and ferruginous sandstone or limestone at the base. Sometimes, the basal ferruginous sandstone or limestone occurs as a 0.5-11.4 m thick oolitic hematite bed; but in most areas, it is variable and is lenticular. The Qiaojia Bed had previously been thought to be composed of nodular limestone at the top, green shale in the upper part, white sandstone with a base ferruginous shale in the middle and limestone intercalated with shale in the lower, and to be Middle Ordovician in age.

The lower member yields graptolites Didymograptus murchisoni, D. nanus; trilobite Taihungshania, Megala spides; brachiopods Leptellina sinensis, Sinorthis typica; Cephalopod Armenoceras. The upper member yields corals Calostylis sp., Ningnanophyllum shengi, N. ningnanense, N. minor, Calostylis crassisepta, C. sichuanensis, C. ningnanensis, Proturaea ningnanensis, Yohophyllum kueiyuanensis and ostracod, gastropod, cystoid and cephalopod.