The Jiwozhai patch reef: A palaeobiodiversity hotspot in middle Givetian (Devonian) of South China

This study is a detailed palaeontological and palaeoecological analysis of a middle Givetian (Middle Devonian) high-diversity patch reef located in a platform interior setting in South China. The location is Jiwozhai, Guizhou Province, in the Dushan Formation. A total of 83 species (including 23 undetermined species) belonging to 44 genera of reef organisms were identified, based on a detailed statistical analysis from 28 quadrats on the vertical section of the patch reef. The main reef builders are laminar and encrusting-behaviour stromatoporoids, laminar tabulate corals, and laminar encrusting chaetetids, forming coverstones to build the reef framework, while abundant massive and branching tabulate corals and solitary rugose corals are also important for the formation of the reef by filling the spaces between the components of the coverstones. Reef dwellers including brachiopods, bryozoans, tubeworms, calcified cyanobacteria and gastropods, are only scarcely distributed in the Jiwozhai patch reef, having little impact on the distribution pattern. Consistent with the densely distributed species at Jiwozhai, complex ecological relationships, including extensive encrustations, spatial competition, and symbiosis have also been found among different organisms. The high biodiversity level of the Jiwozhai patch reef in platform interior emphasizes that understanding of species richness and diversity of functional groups in different habitats is critical for Givetian reef ecosystem reconstruction. Location of the patch reef in a platform interior may be the reason for the high diversity biota. The results from the Jiwozhai patch reef are evidence for a stable reef structure with evenly distributed major reef-frame builders and complex ecological relationships. The high level of species diversity is a common feature in South China, as well localities of many other palaeocontinents during the Givetian Period.