Middle Devonian stromatoporoid-dominated reefs at Maoying, South China: New insights into age, biotic turnover and palaeogeographical model

Middle Devonian was the time for extensive reefs across South China, but their importance in understanding the development of reef communities was undervalued. This study described the lithostratigraphical and palaeontological features of the Middle Devonian reef deposits at Maoying Town, Guizhou Province, South China. Two different units are recognised based on five road-cut exposures. The lower unit is characterised by argillaceous limestone, yielding a variety of auto- to autoparabiostromes. The biostromes are dominated by morphologically diverse stromatoporoids, including Gerronostromaria, Salairella, Synthetostroma, and Stachyodes, with subordinate roles of tabulate corals, rugose corals, chaetetids, bryozoans, brachiopods, gastropods, bivalves, and tubeworms. The upper unit consists mainly of parabiostromes, characterised by abundant dendroid and bulbous stromatoporoids (Amphipora, Stachyodes, and Actinostroma), along with leperditicopid ostracods, parathuramminid foraminifers, and calcispheres. The environments of these two units are interpreted to be open marine and back-reef to lagoonal environments, respectively. Newly recognised icriodid and bipennatid conodonts from the lower unit and brachiopod Stringocephalus in the upper unit indicate a Givetian age of the entire succession, pushing back the age of the latter from Frasnian of the previous thought. Comparison with nearby two sections possibly reflects a palaeogeographical turnover from ramp to isolated platform. This study sheds light on understanding how reef communities changed in relation to environmental conditions in South China during the global Givetian reef expansion.