The new discovery of the Mid-Triassic typical platform-marginal reefs and slump limestone in southeastern Yunnan, China

The huge typical platform-marginal oolitic shoal and reefal limestone have been firstly discovered that distributed in the mid-Triassic Guanling Formation, the Dongshan area of the Luxi County, Yunnan Province, during the end of 2012. At the same time, the thin-bedded micritic limestones and slump structures of platform fore-marginal slope are also developed in the Fangbai village, Xiangyang town. There are apparent vertical tripartite frameworks in the platform marginal reefs: the reefal-base subfacies composed of the shoal oolitic and pisolitic limestones; the reefal-core subfacies composed of the boundstone and sponge-hydroid frameworkstone, especially development of bluegreen algae bound-textures and sparry pectinate cement-textures; and the reefal-cap subfacies composed of the dark-gray thin-bedded micrite and muddy limestone of the platform fore-marginal slope. In the horizontal distribution, the reefs model developed three obvious properties: the back-reef subfacies consisted of the platforms limestones; the reefal-core subfacies consisted of the boundstone and sponge-hydroid frameworkstone; the front-reef subfacies consisted of the thin-bedded micrite and shale of platform fore-marginal slope with local development of the slump structure and slump breccias that are composed of the reefal limestone, oolitic and pisolitic grainstones.