Guandi Fm

It was named by Ting and Wang in 1937. The type section is located in the areas from Yilong to Guandijian (103°16'E, 25°22'N) and from Canglangpu to hainiushan (103°37'E, 25°27'N) in Malong Xian, eastern Yunnan Province. The reference section is at Yuejiashan Mt., southwest of the Qujing Xian in eastern Yunnan.

Synonym: （关底组） ; Kuanti Fm. The Mientian Fm (Grabau, 1924) is also a synonym of the Guandi Fm and had long ago been abolished by Ding and Wang (1937). The Shangcun Fm (proposed by Bian Zhaoxiang in 1924), resting in between the Tangchi Fm of the Ordovician System and the Devonian System and consisting of violet and green shale intercalated with minor sandstone, is probably also a synonym of the Guandi Fm. The Malung Limestone (Grabau, 1926, p. 10) is equivalent to the dark grey crystalline limestone horizon in the lower part of the Guandi Fm, i.e., the sixth horizon in the Yilung-Guandi section classified by Ding and Wang (1937).

The Guandi Fm is subdivided into two parts. The lower part ("the Yuejiashan Member"), approximately 220 m in thickness, consists of yellow green, grey green shale and muddy siltstone intercalated with thin-bedded marl and sandstone, and occasionally with purple mudstone. The upper part ("the Guandi Member"), about 560 m thick, is composed of purple, yellow, yellow green siltstone, shale and mudstone (Figure).

[Figure The Silurian strata from the western suburb of Qujing, Yunnan Province (Photography from Wang Guangxu et al., 2020). A. the lithology of Guandi Fm at Longwangmiao quarry; B. the lithology near the top of Miaogao Fm at Hongmiao Section; C. the black shale from the base of the Yusongsi Fm at Hongmiao Section]

The fossils can mainly be seen in the lower part, and a few are from the upper part. The formation is rich with brachiopoda Striispirifer yunnanensis, Atrypoidea foxi, Retziella uniplicata, Nikiforovaena sinensis, Morinorhynchus; trilobite Acanthopyge; corals Squameofavosites, Favosites, Parastriatopora, Ketophyllum, Zelophyllum, Cystiphyllum, Mucophyllum, Holmophyllum; nautiloid Heyuncunoceras, Platydiscoceras; bivalves Grammyasioides, Leiopteris; conodont Ozarkodina crispa (collected from the upper part), and gastropod, etc.