Algal-sponge reefs have been discovered recently in the upper part of the Lower Ordovician Fengxiang Formation

and their age corresponds to Late Tremedocian. The reefs consist mainly grainstone

mudstone

boundstone and bafflestone. The depositional sequence of the algal-sponge reefs suggests a evolution series starting from shallow to deep. The reefs grew on relief bases

and then enhanced the initial forms of the bases as they grew. Bounding and baffling were the main factors in the formation of Calathium-algal and algal-PulchrilaminaArchaeoscyphia communities.