Types and biotic successions of Ordovician reefs in China

Ordovician reefs are located in the South China, Tarim, and North China blocks, in low-latitude epicontinental marine regions and mostly consist of large-scale carbonate platforms. During the Paleozoic, faunal radiation reef biota diverged and thrived in diverse paleogeographic settings. Algal reefs of the Early Ordovician, Calathium-lithistid sponge-algal reefs of the late Early Ordovician to early Middle Ordovician, and coral-stromatoporoid-algal reefs of the early Late Ordovician, indicate change from Cambrian to Paleozoic biota. Coral-stromatoporoid-algal reefs were the basic communities after 100 Ma. The macroevolution of biotic structures generally shows increased complexity; the evolution of China’s reef biota parallels that worldwide. Important aspects are: (1) The Calathium-algal reefs from the early Tremadocian Nantzinkuan Formation, Zhangjiajie, western Hunan are the pioneer reefs, and the Darriwillian Yijianfang Formation, Bachu are the relic reefs. (2) The bryozoan-dominated reefs of the late Tremadocian Fenhsiang Formation, Middle Yangtze Platform are unique. (3) The early coral-stromatoporoid-algal reefs are highly restricted in China. (4) The algal reefs from the latest Katian on the western margin of the Yangtze Platform, represent an abnormal reef-building environment during the initial stages of Gondwanan glaciations.