Early Ordovician (late Tremadocian to early Floian) reefs on the Yangtze Platform margin of the Hunghuayuan Formation at Zhangzhai section in southeastern Guizhou  South China show three types of reefs in two broad categories: microbial-dominated (stromatolite and lithistid sponge-Calathium-calcimicrobial) reefs and metazoan-dominated (lithistid sponge-Calathium) reefs