Division and correlation of the Ordovician strata in the Upper Yangtze region (Zhang et al., 2014a). (A) the broad area in the Upper Yangtze region containing the typical black shale of the Wufeng Formation; (B) the area extending from northern Sichuan to southern Shanxi; (C) the area extending from southeastern Sichuan to northeastern Yunnan; (D) the area extending from southwestern Hunan to northeastern Guangxi.