| ① | Upper part of Dicellograptus complexus graptolite belt | Carbonaceous shale and siliceous shale interbedded with multiple thin volcanic ash layers, with thickness of 0.15-1.50 m. It is characterized by
obvious increase of clay minerals, peak response of GR, and no obvious relationship between
volcanic ash and TOC. | South Sichuan, East
Sichuan-West Hubei | Qiliao in Shizhu, Mingzhong in Chengkou, Xiema in Baokang |
| ② | Top of Paraorthograptus pacificus graptolite belt | East Sichuan-
West Hubei | Qiliao in Shizhu, Mingzhong in Chengkou, Xiema in Baokang |
| ③ | Bottom of Coronograptus cyphus graptolite belt | South Sichuan,
East Sichuan | Huangcao in Wulong,
Shuanghe in Changning |
| ④ | Middle part of Coronograptus cyphus graptolite belt | East Sichuan,
Western Hunan-Hubei | Qiliao in Shizhu, Bailu in
Wuxi and Guanwu in Hefeng |
| ⑤ | Middle-lower part of Demirastrites triangulatus graptolite belt | A thick layer of bentonite with a thickness of more than 5 cm (5-15 cm, or up to 40 cm). The GR value
is 215-235 cps. There are often mutations in lithofacies above and below the boundary in key areas. | All areas of the middle-
upper Yangtze region | Shuanghe in Changning, Guanyinqiao in Qijiang, Qiliao in Shizhu, Bailu in Wuxi, Mingzhong in Chengkou,
Xiema in Baokang, etc. |
| ⑥ | Upper-top of Lituigrapatus convolutus graptolite belt | East Sichuan,
Northwest Hubei | Qiliao in Shizhu, Mingzhong in Chengkou, Xiema in Baokang, Dengjia’ao in Changyang |
| ⑦ | Bottom of Stimulograptus sedgwickii graptolite belt | Northeast Hubei | Mingzhong in Chengkou |
| ⑧ | Bottom of Spirograptus guerichi graptolite belt | Northeast Hubei,
North Sichuan | Mingzhong in Chengkou,
Yangba in Nanjiang |