Biodiversity And Community Palaeoecology Of The Givetian (Devonian) Patch Reef In Southern Guizhou

The Middle Devonian Givetian period was in a relatively stable stage of tectonic movement,with relatively weakened continental weathering intensity and less accumulation of terrestrial debris.Moreover,the global carbonate platform rapidly extended due to the warm surface seawater in mid-low latitudes and the ongoing transgression during this interval.Such ideal climatic and environmental conditions greatly stimulated the prosperity of the coral-stromatoporoid reef ecosystem,which reached the highest during the Phanerozoic in terms of scales and range.After nearly 100 years of continuous research,the sedimentary-evolution pattern of the Givetian reefs has been basically clarified.However,in-situ quantitative statistics on the biodiversity,ecology and community composition of Givetian reefs is lacking,which largely limits our further understanding on the evolutionary model of reef ecosystem and coeval palaeobiodiversity change pattern in key geological transitional periods during the Devonian.The relationship between the evolution of reefs and the palaeoenvironmental changes during the Middle Devonian also remains to be elucidated.This study is a detailed palaeontological and palaeoecological analysis of a Givetian high-diversity 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 or 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 distributed in the Jiwozhai patch reef.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 results from the Jiwozhai patch reef are evidence for a stable reef structure with evenly distributed major reef-frame builders.In a word,the high palaeobiodiversity 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.