Late Pennsylvanian (Gzhelian) Tubiphytes reef in southern Guizhou Province, China: new insights into a peculiar reef-building association and paleoenvironment changes

A Late Pennsylvanian (Gzhelian) Tubiphytes reef from Guizhou Province, southern China, is a new type of triple hybrid carbonate buildup mainly constructed by in situ Tubiphytes, microbes, corals, and abundant marine synsedimentary cement. The Tubiphytes reef indicates the formation of a notable abiotic-microbial-skeletal hybrid carbonate in a high-energy environment on a shallow marine carbonate platform margin with active water circulation during the Late Pennsylvanian. In the studied reef, in situ Tubiphytes skeletons form a complexly anastomosing micro-framework often encrusted by Archaeolithoporella and calcimicrobes. The colonial rugose coral Ivanovia could provide a protected condition for reef to grow due to their abilities of wave resistance. Early marine synsedimentary cement plays an important role in the formation of the reef by strengthening its framework. The opportunistic Tubiphytes has a wide range of environmental adaptations and can build reefs under the high energy conditions in the study area. This study illustrates a novel example of a Tubiphytes-dominated reef that is classified as a triple hybrid carbonate in the eastern Paleo-tethys Ocean. The development of the studied reef may reflect a significant change in the paleoenvironment and may be proposed to derive from the interaction among low atmosphere pCO2, high seawater Mg2+/Ca2+ molar ratio, and the evolution of reef-building communities in the Pennsylvanian.