The South China Block: A reef-building focal point in Givetian (Middle Devonian) of eastern Palaeotethys

The Middle Devonian witnessed the expansion of global coral-stromatoporoid reefs, but knowledge of reefs derives mainly from Laurussia and adjacent regions. Although South China Block (SCB) is renowned for reef proliferation in the eastern Palaeotethys, reef growth and their global implications remain under-explored. Using data from 353 references and 6731 thin sections, this study provides a comprehensive summary regarding reef ecosystems of SCB, plus comparison and integration with global records. Two main findings are outlined: (1) Reef growth. Three well-differentiated ecological associations and six high-resolution developing stages are recognised, and the mid-Givetian marked the peak of reef-building. The transition from epicontinental seas to rifting platforms reflects reef expansion from extensive open marine biostromes to barrier reef–lagoon communities. Reef growth was driven primarily by climate, temperature, and sea-level changes/tectonic activities, facilitating carbonate precipitation and extensive shallow-water habitats. (2) Global implications. Compared with major reef regions, the significance of SCB is noted in three aspects, including abundant fossil materials, unusual palaeogeographic location (eastern Palaeotethys), and exceptional reef pattern (broad inland sea to platforms and intra-platform basins). Based on the newly refined reef database, the global spatial distribution of Givetian reefs indicates SCB as a reef-building hotspot in eastern Palaeotethys. Moreover, the new temporal trajectory implies the reef peak occurred earlier in the Middle Devonian, supporting Givetian as an acme of Phanerozoic reef-building. Overall, this study highlights the underestimated role of SCB in understanding global Givetian reef expansion, Phanerozoic reef evolution, and the intricate interplay of local/global factors controlling reef growth.